Effect of austenitization temperature (875-975 ℃) on the microstructure and mechanical properties of the novel Cr-Mn-Si series high strength medium carbon low alloy 40CrMnSi2Mo steel under air cooling condition was studied by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and laser scanning confocal microscope (LSCM). The results show that when austenitized at 875 ℃ and 900 ℃, the microstructure is dominated by martensite with a small amount of the undissolved precipitates (NbC). The prior austenite grains are fine and stable. The tensile strength is 1997 MPa and 2003 MPa, the elongation is 11.0% and 12.0%, and the fracture toughness is 70.3 MPa·m^1/2 and 73.6 MPa·m^1/2, respectively. When austenitized at 975 ℃, the solubility of NbC increases and the pinning effect decreases. The growth of austenite grain size decreases the thermal stability so that the coarse bainite/martensite multiphase is obtained under air cooling. The tensile strength is 1980 MPa, the elongation is 10.5%, and the fracture toughness is only 77.6 MPa·m^1/2. The effect of the austenite grain refinement on the strength and toughness of the 40CrMnSi2Mo steel is not obvious. The fine bainite/martensite multiphase can be obtained after austenitizing at 950 ℃. The mechanical properties achieve an excellent combination, with the tensile strength of 2040 MPa, the elongation of 12% and the fracture toughness of 86.6 MPa·m^1/2.

Selective laser melting (SLM) technology was used to prepare WC-12Co cemented carbide specimens, and the optimal SLM process parameters were obtained through the analysis of orthogonal test results, and the specimen formed by the optimal process was subjected to microwave heat treatment, and the effect of microwave heat treatment on the microstructure and properties of the SLM-formed WC-12Co cemented carbide was investigated. The results show that the optimal SLM process parameters is laser power of 100 W, scanning speed of 390 mm/s, scanning spacing of 0.06 mm. When the laser energy density is 97 J/mm³, the specimen has the least microscopic defects on the horizontal surface, the highest relative density and Vickers hardness, which are 87.33% and 1421 HV3. The number of microscopic defects on the SLM formed specimen after microwave heat treatment is greatly reduced compared with that before heat treatment, and the mechanical properties of the material are significantly improved, but the average grain size of WC increases. When the microwave heat treatment temperature is 1300 ℃, the holding time is 20 min, and the temperature increase rate is 15 ℃/min, the SLM formed specimen has the best comprehensive mechanical properties, and the Vickers hardness and flexural strength reach the maximum value of 1586 HV3 and 834 MPa, respectively, and the relative density is 97.4%.

Effect of tempering temperature on microstructure and strength-toughness of high-strength wear-resistant steel was studied in the tempering temperature range of 200-700 ℃. The results show that the martensite lath degenerates after tempering at 500-700 ℃, resulting in a significant decrease in tensile strength, yield strength, and hardness. The impact absorbed energys of V-notch and U-notch are both less than 12 J. After tempering at 200-400 ℃, the impact properties of the specimens are significantly improved. The tempering temperatures corresponding to the impact absorbed energy peak of V-notch and U-notch are 250 ℃ and 300 ℃, respectively. The yield strength and tensile strength are maintained at more than 1340 MPa and 1660 MPa, respectively, and the elongation exceeds 10%. The tested steel achieves the best comprehensive mechanical properties after tempering at 250 ℃, with V-notch and U-notch impact absorbed energy of 40 J and 59 J, respectively, the yield strength of 1374 MPa, the yield ratio of 0.80 and the strength-toughness product of 92 269 MPa·J·cm^-2. Based on the hindering effect of Si on the precipitation of cementite, the higher Si content in the steel increases the temper brittleness range. The tempering temperature brittleness range of the tested steel is 450-700 ℃.

ZL208 alloy was subjected to solid solution treatment at different temperatures (550-580 ℃) for 8 h and aging at 220 ℃ for 16 h, and the effect of solid solution temperature on its microstructure and properties was studied. The results show that after solid solution and aging treatment, the microstructure of ZL208 alloy partially transforms from dendrites to equiaxed crystals. With the increase of solid solution temperature, the size of the second phase particles at the grain boundary decreases firstly and then increases. The tensile strength, hardness and elongation after fracture of the alloy show a trend of first increasing and then decreasing. This is because the increase in solid solution temperature increases the solubility of Cu and Ni atoms in the α-Al matrix, improving the ability of matrix to resist plastic deformation. At the same time, the second phase at the grain boundary can also restrict grain growth, thereby improving the strength and hardness of the alloy. However, when the solid solution temperature is 580 ℃, overburning occurs, which is detrimental to the properties of the alloy. Therefore, the optimal solid solution and aging process for the ZL208 alloy is 570 ℃×8 h+220 ℃×16 h. After this process, its tensile strength is 336.87 MPa, yield strength is 210.45 MPa, hardness is 97.48 HV0.1, elongation after fracture is 8.56%, and the fracture mode is brittle fracture.

Effect of heat treatment process on the properties and roughness of the W3Mo4Cr5V6 steel after abrasive wear was studied by means of MLD10 abrasive wear tester and VL2000DX-SVF17SP laser confocal microscope. The wear mass loss rate, surface wear morphology and roughness changes under different heat treatment conditions were compared and analyzed. The results show that the wear resistance of the W3Mo4Cr5V6 steel after different heat treatments is significantly improved compared with that of the as-cast steel. Under the same test condition, the wear mass loss after heat treatment is 17-24.9 mg less than that of the as-cast. After quenching at 1100 ℃ for 1 h and tempering at 550 ℃ for 2 h, the wear mass loss of the specimen is less, the hardness uniformity is better and the wear resistance is excellent. With the increase of wear time, the surface roughness of different specimens decreases gradually. Among them, that of the specimen quenched at 1100 ℃ for 1 h and tempered at 550 ℃ for 2 h decreases from Ra=9.30 μm to Ra=7.60 μm, and the roughness value between different fields of view is stable. The mass loss of the specimens during the wear process is mainly caused by abrasive ploughing, brittle fracture and fatigue shedding.

TA10 titanium alloy was heated at 860 ℃(in the two-phase region) and at 900 ℃(in the single-phase region), respectively, and then water cooled, air cooled and furnace cooled. The effect of different cooling methods on the microstructure and impact property of the TA10 titanium alloy was studied by means of optical microscope, scanning electron microscope, XRD and impact test. The results show that when the heating temperature is in the two-phase region, the alloy forms a bimodal structure after water and air cooling, and an equiaxed structure after furnace cooling. After heating at different temperatures, under different cooling methods, the impact property of the alloy after furnace cooling is the best, followed by air cooling, and that after water cooling is the worst. When the heating temperature is 860 ℃ in the two-phase region, the impact absorbed energy of the alloy after furnace cooling is the best and the maximum impact absorbed energy is 88 J. The fracture under three cooling methods is dimple morphology when the alloy is heated at 860 ℃. The size of dimples in the fracture under furnace cooling condition is the largest. When the heating temperature is 900 ℃ in the single-phase region, the alloy forms a fine lamellar β transformed microstructure after water cooling and air cooling, and coarse β grains appear. After furnace cooling, coarse lamellar β transformed microstructure is formed, and the α phase on grain boundary is obviously coarsened. The fracture under three cooling methods is rock-like morphology, and dimples with shallow depth and small size are distributed on the surface.

Rockwell hardness tester, optical microscope, scanning electron microscope and transmission electron microscope were used to study the effects of tempering cooling method on the hardness, microstructure and -20 ℃ low-temperature impact toughness of 80 mm thick Q690D steel. The results show that the tempering cooling method has little effect on the hardness distribution in the thickness direction of the quenched and tempered steel, compared with the quenched state hardness, the maximum hardness difference decreases from 13 HRC to 6 HRC. After tempering at 620 ℃ followed by air cooling, carbides precipitate along austenite grain boundary and lath boundary, the impact absorbed energy of the steel at -20 ℃ is 65 J, and the impact fracture morphology is quasi cleavage. After tempering followed by water cooling (5-8 ℃/s), the precipitation of carbide at grain boundary and strip boundary is restrained, the impact absorbed energy of the steel at -20 ℃ is increased to 210 J, and the fracture morphology is mainly dimples. After tempering followed by water cooling, the impact absorbed energy at -20 ℃ of industrial produced steel is 174-252 J, which is increased by 105% to 397% compared with air cooling.

Effects of the soaking temperature and over-aging temperature during continuous annealing on microstructure and mechanical properties of C-Si-Mn-Al steel DH780 were investigated by using the Gleeble-3500 thermal simulator, and the microstructure and mechanical properties under different processes were compared and analyzed. The results show that when the soaking temperature is 750 ℃, the martensite content in the microstructure after cooling is about 32%, and there is still obvious banded structure. As the soaking temperature increases, the carbon content of austenite in the two-phase region gradually decreases, and the morphology and proportion of the ferrite and martensite formed by cooling also change. When the soaking temperature is 820 ℃, the microstructure after cooling is composed of about 40% martensite and a small amount of retained austenite and bainite, and ultimately, the tensile strength shows a downward trend, while the yield strength shows an upward trend. As the over-aging temperature increases, the carbon atoms in the martensite diffuse to the grain boundaries, the degree of over-saturation decreases, the high-density dislocations decrease, the retained austenite and part of the martensite decompose, and when the over-aging temperature is higher than 310 ℃, it leads to a downward trend in the final tensile strength and the change of the yield strength is not significant. When the soaking temperature is 800 ℃ and the over-aging temperature is 320 ℃, the tensile strength is 847 MPa and the yield strength is 328 MPa, which can obtain dispersed martensite and basically eliminate the banded structure. The C-Si-Mn-Al steel DH780 can obtain relatively good comprehensive properties.

To investigate the effect of annealing treatment on the microstructure and magnetic properties of NdFeB magnets, powder sintered NdFeB magnets were annealed at 500-600 ℃. XRD, SEM and magnetic performance measuring instruments were used to analyze and characterize the NdFeB magnets. The results show that the annealing treatment has little effect on the structure of the main phase Nd₂Fe₁₄B of the NdFeB magnets, but mainly affects the distribution and composition of the rich-Nd phase. After annealing treatment, the coercivity of the NdFeB magnets is improved to varying degrees. After annealing at 550 ℃, the rich Nd phase is continuous and uniformly distributed along the grain boundaries of the Nd₂Fe₁₄B main phase, and the content of Nd in the rich-Nd phase increases while the content of Fe decreases, and the coercivity of the magnets has the best improvement effect, increasing from 1135 kA/m to 1434 kA/m, correspondingly increased by 26.3%. After annealing treatment, the residual magnetism of the magnets doesn't change significantly, but the maximum magnetic energy product decreases to varying degrees.

The 022Cr18Ni8N metastable austenitic stainless steel with a 90% cold-rolling deformation was chosen as the research object. Stress-relief annealing treatments were conducted within the temperature range of 100-700 ℃ for 30 min. Subsequently, room temperature tensile tests were carried out on both the cold-rolled specimens and those annealed at different temperatures. Additionally, the microstructural variations of the specimens were investigated by utilizing x-ray diffraction (XRD), transmission electron microscopy (TEM), and nano-indentation techniques. The results show that the reverse transformation temperature of deformation-induced martensite in the steel is within the range of 500-600 ℃. During the annealing process at 100-400 ℃, the tensile and yield strengths of the specimens are enhanced compared to the cold-rolled state. This improvement can be ascribed to the obstruction of dislocation motion caused by the diffusion of solute atoms during annealing, along with an increase in martensite content, which effectively offsets the negative effect of the decreased dislocation density. When annealed at 500 ℃, although the martensite content is higher than that in the cold-rolled state and the annealed states within 100-400 ℃, the significant reduction in dislocation density predominantly governs the strength variation, resulting in a lower strength compared to the former two conditions. When annealed within the temperature range of 600-700 ℃, the reverse transformation of deformation-induced martensite leads to a substantial decrease in martensite content, simultaneously causing a remarkable reduction in strength.

The 20MnCr5H steel for precision formed gears was subjected to subcritical spheroidizing annealing (710 ℃×8.5 h) and spheroidizing annealing in dual-phase region (750 ℃×1.5 h+680 ℃×7 h, 750 ℃×4 h+710 ℃×4 h, 770 ℃×4 h+720 ℃×4 h), and the spheroidizing effects under different processes were investigated. The results show that under the spheroidizing annealing in dual-phase region, higher austenite zone temperature will make it difficult for lamellar pearlite to spheroidize in a short time, while shorter austenite zone holding time will help to improve the spheroidization efficiency. Good spheroidization effect is achieved under 750 ℃×1.5 h + 680 ℃×7 h process. Compared with the spheroidizing annealing in dual-phase region, the spheroidization effect of the 20MnCr5H steel is the best under 710 ℃×8.5 h subcritical spheroidizing annealing, and the spheroidization rate reaches 98%. This is due to the fact that after the process treatment, more dislocations and small-angle grain boundaries in the microstructure can promote the dissolution and spheroidization of flaky cementite more quickly. It is a reasonable spheroidizing annealing process for precision forming gears.

55vol%SiC_p/6061Al composite was prepared by using hot isostatic pressing method. The effect of aging treatment at 170, 180, and 190 ℃ on the mechanical properties of the composite was investigated. The results show that the hardness and bending strength of the as-prepared composite are 182.4 HBW and 440 MPa, respectively. The composite exhibits typical double-peak aging behavior and dynamic acceleration phenomenon. As the aging temperature increases from 170 ℃ to 190 ℃, the time corresponding to the first peak aging decreases from 2.5 h to 0.3 h. The aging treatment can significantly improve the mechanical properties of the composite and the optimal aging temperature is 180 ℃. Correspondingly, the hardness of the composite aged for 1 h is the highest, which is 236.3 HBW, with an increment of 29.6%, while the bending strength of the composite aged for 4.5 h is the highest, which is 612 MPa, with an increment of 39.1%.

Pulsed electromagnetic treatment was added on basis of the conventional heat treatment of 42CrMo steel, and two processes of magnetization followed by tempering and tempering followed by magnetization were used to study the effects of different processes on the wear resistance, hardness, impact properties and tensile properties of the 42CrMo steel. The results show that compared with the conventional heat treatment, the wear resistance and hardness of the 42CrMo steel by pulsed electromagnetic treatment are improved in different degrees, in which the optimal group of magnetization followed by tempering, the wear mass loss is reduced by 0.0031 g and the hardness is improved by 1.8 HRC compared with the conventional heat treatment; and in the optimal group of tempering followed by magnetization, the wear mass loss is reduced by 0.0027 g and hardness is improved by 2.5 HRC. Their impact properties are significantly reduced, and the tensile strength and elongation don't change significantly. Among them, the specimens with magnetization followed by tempering have better abrasion resistance with a maximum increase of 64.5%, and the specimens with tempering followed by magnetization have better hardness with a maximum increase of 6.6%.

Based on the phase transition points of a new designed 4140 steel determined using a dilatometer, the Gleeble-3800 thermal simulator was used to conduct different spheroidizing annealing simulations, including subcritical spheroidizing annealing, step cooling spheroidizing annealing, and isothermal spheroidizing annealing. The results show that during subcritical spheroidizing annealing, even after a long holding time, the original martensitic region is spheroidized, while the original bainitic region just begins to spheroidize. In the step cooling spheroidizing annealing test, the spheroidization rate is increased to 75%, and as the heating temperature increases, the amount of lamellar cementite also increases. For the isothermal spheroidizing annealing process, heating at 760 ℃ followed by isothermal holding at 720 ℃ results in a spheroidization rate of 82%, with hardness meeting the user's requirement of ≤185 HBW. However, localized carbide aggregation is observed. Therefore, based on Thermo-Calc calculations of the isothermal transformation curve for the 4140 steel, a preheating stage at 700 ℃ is added before the isothermal spheroidizing annealing. With the optimized preheating+isothermal spheroidizing annealing process, the continuous heat treatment furnace in the production line successfully produces 4140 round steel that meets the design specifications, achieving spheroidization rate of ≥90%, Brinell hardness of ≤175 HBW, with uniformly distributed microstructure.

Effect of pre-aging at 120-180 ℃ for 5 min before baking at 180 ℃ for 30 min on the bake hardening response of AA7075 high-strength aluminum alloy was studied using high-resolution transmission electron microscopy, microhardness tester, and tensile testing machine. The results indicate that when the pre-strain before pre-aging is 3%-30%, an increase in the pre-strain will also promote a more significant bake hardening effect. When the pre-strain is 5%, with the increase of pre-aging temperature (120-180 ℃), the η′ strengthening phase amount of the AA7075 alloy gradually increases, and the strength and hardness increase from 405 MPa and 142 HV5 to 478 MPa and 160 HV5, respectively. At the same time, when pre-aged at 180 ℃ for 5 min, there is a certain amount of η′ phase and a small amount of η phase in the matrix. Adding pre-aging process before baking enables to promote the formation of GP zone significantly, and the bake hardening response is the best.

The gas hydrogen permeation process of Zr-Sn-Nb alloy sheet was studied, and the effects of hydrogen permeation time and annealing time on hydrogen content and its distribution were investigated. The results show that with the increase of hydrogen infiltration time, hydride content increases and the hydrides appear to aggregate, form a winding and growing strip structure, and finally gradually present a fine network distribution. During the annealing process, the hydrogen atoms spread from the outer surface to the center of the wall, and the two ends spread to the middle. The higher the hydride content, the longer the annealing time, the more fully the hydride diffusion, the strip hydrides decompose into several fine hydrides and dispersed evenly in the zirconium matrix. The exponential function was used to fit the law of hydrogen content-hydrogen infiltration time, and the corresponding relationship between the quantitative hydrogen infiltration process and hydrogen content of Zr-Sn-Nb alloy was obtained.

In view of the problems such as surface soft spots and warping deformation in the process of carburizing and quenching heat treatment of a type of thrust disc ball (tapered) bearing with large diameter resulted in product repair or scrapping, the causes of soft spots and excessive warpage deformation on the surface of the thrust disc workpiece are analyzed, measures such as reasonably increasing the surface carbon concentration, increasing the temperature of the second quenching, adding cold treatment, and improving the heat treatment fixture were proposed. After the process improvement, the surface troostite of the thrust disc workpiece is qualified, the hardness is controlled between 58 and 63 HRC, and the warping deformation is controlled within 0.8 mm, which solves the problem of surface soft spots, controls the warping deformation, and improves the first-time acceptance rate of this type of product, meeting the production needs.

By forging 70% deformation of the Ti1023 titanium alloy in the two-phase region and heating at 785-885 ℃ for 30-300 min, the recovery and recrystallization law of the deformed microstructure under different heating temperatures and holding time were observed and analyzed. The results show that after the deformation of the Ti1023 titanium alloy in the two-phase region, the deformed microstructure is dominated by recovery when the heating temperature below 800 ℃, supplemented by recrystallization, the microstructure retains the deformed morphology, and the recrystallized grains don't grow. When heated at 800-885 ℃, the deformed microstructure is dominated by recrystallization, supplemented by recovery. When the heating temperature is constant and the holding time is prolonged, the recrystallized grains grow. When the holding time is constant, the higher the heating temperature, the shorter the time required to complete recrystallization, and the more obvious the trend of grain growth. The recrystallized grain growth is not conducive to the refinement of the deformed microstructure.

Tests of quenching at 900 ℃ with different cooling rates were carried out for a high carbon low alloy wear-resistant steel by using L78 dilatometer. The microstructure of the quenched steel was observed by metallographic microscope, and the hardness was measured by 450SVD digital Vickers hardness tester. The results show that when the cooling rate is less than 0.4 ℃/s, the microstructure of the tested steel is pearlite plus a small amount of ferrite, and the hardness value is 254-313 HV5. When the cooling rate is 0.4 ℃/s, the microstructure is full pearlite and the hardness value is 317 HV5. When the cooling rate is 0.5-1 ℃/s, the microstructure is composed of pearlite, bainite, martensite and retained austenite, and the hardness value is 435-726 HV5. When the cooling rate is 2-3 ℃/s, the microstructure is bainite, martensite and retained austenite, and the hardness value is 726-753 HV5. When the cooling rate reaches 4 ℃/s, the microstructure is martensite and retained austenite, and the hardness is 784 HV5. When the cooling rate further increases to 150 ℃/s, the microstructure has no obvious change, and the hardness value changes little, which is 810-825 HV5. When the cooling rate reaches 180 ℃/s, the hardness value drops to 785 HV5, while the microstructure is still martensite and retained austenite, but the amount of the retained austenite is increased.

Current research status of vacuum low-pressure carburizing technology was systematically discussed. The development trend of vacuum low-pressure carburizing technology was analyzed from the prospectives of process, theory, equipment and application, which provides ideas for breaking the bottleneck of single strengthening performance technology and promoting the application of vacuum low-pressure carburizing technology in new materials and fields. At the same time, the development of vacuum low-pressure carburizing equipment at home and abroad was compared, providing reference and inspiration for equipment manufacturing enterprises.

Effects of adding different contents high-purity rare earth Ce element on the inclusions, as-cast microstructure and hardness of high-purity S355NL low alloy steel were investigated. The types, sizes and shapes of inclusions, as well as the as-cast microstructure and hardness were analyzed and evaluated by using scanning electron microscopy, optical microscopy, and Vickers hardness testing. The results indicate that with the Ce addition ranging from 0.0011% to 0.0049%, the irregularly shaped large Al₂O₃ and MnS inclusions in the S355NL low alloy steel are modified into fine spherical rare earth inclusions. When Ce is added at levels between 0.0011% and 0.0049%, it initially reacts with O and S to form small spherical rare earth oxysulfides. However, with the increase of Ce content, excess Ce can react with As and P, leading to larger irregular rare earth inclusions. Additionally, the incorporation of Ce refines the dendritic structure of the S355NL low alloy steel and enhances its hardness. Considering both the inclusion modification and hardness optimization, the optimal range for Ce addition in the S355NL low alloy steel is determined to be 0.0011% to 0.0049%.

Hot compression experiments were carried out on Fe-13Mn-4.4Al-0.64C-0.1Ti low density steel at deformation temperature of 900-1100 ℃ and strain rate of 0.01-0.1 s^-1 by Gleeble-3500 thermal simulation testing machine. The strain-compensated constitutive equation was established on the basis of the traditional constitutive model. The hot deformation behavior of the experimental steel was studied by verification and analysis. The influence of deformation conditions on hot deformation behavior and microstructure evolution was studied by electron backscattering diffraction. The results show that the deformation behavior of the Fe-13Mn-4.4Al-0.64C-0.1Ti low density steel is dynamic recrystallization type at the temperature of 900-1100 ℃ and strain rate of 0.01-0.1 s^-1. The flow stress decreases with the increase of deformation temperature or the decrease of strain rate. The migration of small angle boundary to large angle boundary promotes dynamic recrystallization. The hot deformation activation energy of the material is 396.44 kJ/mol. The relative absolute error of the strain-compensated constitutive equation is 5.4%, and the linear fitting correlation coefficient is 0.987, which indicates that the constructed strain-compensated constitutive equation can accurately predict the flow stress behavior of the low density steel under different deformation conditions.

DIL 805A type fully automatic phase transformer was used to determine the expansion curve of LC3 cryogenic cast steel under different cooling rates between 0.05-150 ℃/s, and the tangent method was used to determine the phase transformation point Ac₁ of 700 ℃ and Ac₃ of 849 ℃. Combined with microstructure analysis and microhardness to determine the actual transformation products, and the CCT curve was plotted using Origin software. The results show that the microstructure is ferrite + pearlite when the cooling rate is 0.05-2 ℃/s, ferrite + pearlite +bainite when it is 5-20 ℃/s, bainite + martensite when it is 30-50 ℃/s, martensite + retained austenite when it is 80 ℃/s, and martensite when it is 100-150 ℃/s. Hardness of the LC3 cryogenic cast steel gradually increases from 168 HV10 to 453 HV10 with the increasing of cooling rate. Martensite critical cooling rate is about 80 ℃/s.

Thermal expansion curves of a medium carbon Cr-Mn-Si low alloy steel under different cooling rates were determined by using Formast-FⅡ dilatometer, and the continuous cooling transformation (CCT) curve of the undercooled austenite of the tested steel was plotted in combination with the observation of the metallographic microstructure. The effect of cooling rate on the microhardness and the onset temperature of the undercooled austenite phase transformation of the tested steel was investigated, and the microstructure and properties of the medium carbon Cr-Mn-Si low alloy steel large forgings at different positions after heat treatment were analyzed. The results show that Ac₃=855 ℃, Ac₁=770 ℃, Ms=375 ℃ and Mf=200 ℃ for the medium carbon Cr-Mn-Si low alloy steel. When the cooling rate is less than or equal to 0.28 ℃/s, the ferrite and pearlite transformation mainly occurs in the high temperature zone, and the bainite transformation occurs in the middle temperature zone. When the cooling rate is 0.28-0.83 ℃/s, the bainite transformation mainly occurs in the middle temperature zone, and the martensite transformation occurs in the low temperature zone. When the cooling rate is greater than or equal to 1.66 ℃/s, only the martensite transformation occurs. With the increase of cooling rate, the microhardness of the tested steel firstly rises linearly and then increases slowly, and the phase transformation start temperature firstly decreases sharply and then basically remains stable. The edge of heat-treated medium carbon Cr-Mb-Si low alloy steel large forgings microstracture is martensite and bainite complex, the positions at R/2 and the core microstracture are bainite, the tensile strength (1467.0 MPa) and hardness (475 HV5) values at the edge position are the highest, indicating that appropriate amount of martensite can significantly improve the strength of bainite structure while maintaining good plasticity.

Variation of equilibrium phases with temperature of Nimonic 80A alloy with different element contents was calculated by Thermo-Calc thermodynamic simulation software, and the effects of main elements on the types of precipitates, precipitation temperature and precipitation content were analyzed. In order to verify the reliability of thermodynamic calculation, the microstructure characteristics, qualitative and quantitative analysis of aged alloy samples were carried out by means of SEM, TEM, XRD and so on. The results show that the equilibrium precipitates of Nimonic 80A alloy are γ, γ', M₂₃C₆, MX and M₇C₃ phases. Decreasing C content cannot only increase the precipitation temperature of M₇C₃ phase, but also promote the precipitation amount of γ'phase; increasing the content of Al and Ti increases the precipitation temperature of M₇C₃, γ' and M₂₃C₆ phases, and promotes the precipitation of γ'and M₂₃C₆ phase, in which the effect of single Al element is higher than that of Ti element; increasing the total content of Ti+Al increases the precipitation temperatures of M₂₃C₆ and γ' phases, and the precipitation content of γ' phase increases significantly. With the increase of Ti/Al ratio, the precipitation content of γ' phase decreases gradually. Under 1060 ℃×8 h air cooling, 845 ℃×24 h air cooling and 700 ℃×16 h air cooling double aging process, a large number of M₇C₃, M₂₃C₆ and γ' phases are precipitated. The γ' phases of different sizes strengthened the precipitation strengthening of the alloy, and the carbides strengthened the grain boundary strengthening of the alloy. Within the prescribed range of alloy composition, the lower limit of C content(0.05%-0.075%), the middle limit of Al content(1.3%-1.6%) and the upper limit of Ti content(2.3%-2.7%) were selected. The upper limit of the total amount of Ti+Al(3.65%-4.46%) and the middle limit of the specific content of Ti/Al(1.76) can obtain a good distribution ratio of precipitated phase.

Phase transition points of three ultra-low carbon bainitic steels with Mn contents of 1.5%, 1.8%, and 2.1%, respectively, were determined using a thermal expansion meter, and the continuous cooling transformation(CCT) curves of the three tested steels were plotted in conjunction with optical microscopy(OM) and scanning electron microscopy(SEM) observation and Vickers hardness measurements. The effects of Mn content on phase transformation points, CCT curves, microstructure and hardness were analyzed. The results show that the change of Mn equivalent caused by the increase of Mn content affects the bainite transformation temperature. In addition, the increase of Mn content makes the Ac₃ of the tested steel show a downward trend, and the hardness is also improved.

Types of equilibrium precipitated phases in 445 ultra-purified ferritic stainless steel with different Mo content (0.68%, 1.79% and 2.37%) were analyzed by Thermo-Calc thermodynamic software. The specimens were annealed at 1020 ℃ for 10 min and aged at 700 ℃/870 ℃ for 1 h. The SEM and TEM methods were used to study the precipitation of second phases in the 445 stainless steel after annealing and aging. The results show that the types of equilibrium precipitates calculated by Thermo-Calc are basically consistent with the experimental results of microstructure observation and phase analysis. The second phases with different morphologies are precipitated in the aged 445 stainless steel, including Laves phase Fe₂(Nb, Mo) with strip-like shape distributing inside the grain and (Nb, Ti)C carbides with irregular granular shape presenting inside the grain and at the grain boundaries. There is remarkable difference in sensitivity of precipitated phases for the 445 ultra-purified ferritic stainless steel with different Mo contents. As the Mo content increases, the precipitation temperature of second phase rises and the amount of second phase precipitation also increases at the same aging temperature.

Effect of C and N contents on microstructure and mechanical properties of 12%Cr ferritic heat-resistant steel was studied by observing the microstructure and tensile tests at room temperature and high temperature of three groups of 12%Cr ferritic heat resistant steel with different C and N contents. The results show that when the C content increases from 0.14% to 0.20%, the size of martensite laths decreases, δ-ferrite disappears, and the effect of martensite lath refinement improves the strength of the steel. When the N content increases from 0.004% to 0.02%, the prior austenite grain size and martensite lath width decrease, and the number of MX precipitates in the laths increases. The solution strengthening and the second phase strengthening enhance the strength of the steel, while the δ-ferrite reduces the strength, and the change of C and N contents has little effect on the plasticity. According to production practice, when the C content is reduced to 0.14% and the N content is controlled at 0.02%, the tensile properties of the tested steel is optimal. The yield strength, tensile strength and elongation at room temperature are 573.5 MPa, 763.0 MPa, and 24%, respectively. When the tensile test temperature is 550 ℃, the yield strength, tensile strength, and elongation are 344.5 MPa, 414.0 MPa, and 34%, respectively.

Critical point and the continuous cooling transformation test of the third generation aviation bearing steel CSS-42L at cooling rate of 0.02-40 ℃/s were carried out by DIL805A quenching dilatometer with dilatometric method. The static CCT curve was drawn, and the microstructure and Vickers hardness at room temperature were analyzed. The results show that the critical points Ac₁ and Ac₃ of the CSS-42L steel are 655 ℃ and 738 ℃, respectively. In the process of continuous cooling, only martensitic transformation occurs at different cooling rates, and the starting temperature of martensitic transformation decreases with the decrease of cooling rate. The tested CSS-42L steel has a maximum microhardness of 330 HV50 at the cooling rate of 1.6 ℃/s.

Effects of modification with different amounts of Ce on microstructure and hardness of the as-cast ADC12 aluminum alloy were studied by using OM, hardness testing, conductivity testing and other methods, as well as the changes in microstructure, hardness, and conductivity after annealing at different temperatures. The results show that within the range of 0% to 0.6%Ce, with the increase of Ce addition, the size of the α-Al phase and that of eutectic Si phase in the tested ADC12 aluminum alloy continuously decrease, and the hardness increases to 67.8 HBS, indicating a better modification effect. When the Ce addition continues to increase to 0.8%, the modification effect for the tested ADC12 aluminum alloy deteriorates, and the optimal Ce addition amount is 0.6%. Annealing treatment of the 0.6% Ce modified ADC12 aluminum alloy at 450, 480, 510, and 540 ℃ can refine the eutectic Si phase in the as-cast ADC12 aluminum alloy, enhance the hardness and conductivity of the alloy. When the annealing temperature is 510 ℃, the hardness and conductivity of the ADC12 aluminum alloy reach their optimal values of 84.5 HBS and 22.61 MS/m, respectively.

Precipitates, homogenization temperature and homogenization time of GH6783 superalloy were calculated by JMatPro software. Microstructure of the as-cast and homogenized alloy and the segregation behavior of elements were analyzed and characterized by means of optical microscope, scanning electron microscope and energy dispersive spectrometer, in order to analyze evolution law of microstructure and segregation coefficient during the homogenization process of the GH6783 superalloy. The results show that major precipitates of the GH6783 superalloy include low-melting brittle phase(Laves phase), NiAl phase, et al. Nb element is the most serious segregation element of the as-cast GH6783 superalloy, with segregation coefficient up to 2.205, and Ti element is secondly serious. Nb and Ti elements are positive segregation element, and Cr, Fe and Co are negative segregation. Two stage homogenization treatment at 1130 ℃ for 4 h and 1190 ℃ for 32 h can dissolve Laves phase and make element diffusion uniformly of the as-cast GH6783 superalloy. After homogenization, segregation coefficient of Nb element decreases to 1.048.

In order to study the segregation behavior of elements in the banded structure of cold-rolled duplex steel DP780 and its effect on mechanical properties, OM, SEM, EMPA, EBSD and other methods were used to characterize and analyze the morphology and element distribution characteristics of the banded structure, tensile properties and microstructure change during the tensile process, fracture mechanism, and so on. The research results show that the macroscopic segregation formed by redistribution of C, Mn, Al and Si solute elements during the solidification process leads to the formation of banded structure, which is mostly distributed parallel to the rolling direction at 1/2 and 1/4 of the plate thickness, the grain size distribution is obviously nonuniform, and the small angle grain boundary density of the banded structure is significantly higher than that of the equiaxed structure. Meanwhile, the properties and microstructure change in tensile process indicate that after 10% tensile pre-deformation, the fibrosis is more obvious in the banded structure specimen, increasing the resistance of dislocation movement during the deformation process and improving the strength. The banded structure can also cause dislocation pile-up and lattice distortion, deteriorating the ability to deform. The banded structure reduces the coordinated deformation ability of the matrix structure, resulting in prominent anisotropy. Further, the observation of fracture morphology shows that the initial crack initiation occurs at the M/F phase interface, and a tear ridge is formed at the M/F interface during fracture, while the location and size of the tear ridge are consistent with that of the banded structure. There is a martensite band region with poor plastic deformation ability between the tear ridges, and the ferrite side of the M/F interface has significant plastic deformation; the specimen with equiaxed structure exhibits uniform axial deformation and better fracture plasticity.

Liquefied natural gas is an important new clean energy, and the construction of 200 000 cubic meters of LNG storage tanks is currently leading the development of LNG storage tanks. Meanwhile, 9Ni steel has gradually become the mainstream product of LNG storage tank construction by virtue of its excellent comprehensive mechanical properties. The effect of microstructure on the mechanical properties of the tested steel was investigated by means of X-ray diffraction, electron probe and transmission electron microscopy to unravel the underlying mechanisms behind the ‘high strength and low yield ratio’ reinforcement exhibited by the tested steel. The tested results show that the grain size of tempered sorbite and the volume fraction of reversed austenite are crucial microstructural parameters influencing the yield ratio of the tested steel. Following treatment with QLT process, compared with the QT process, the grain size of tempered martensite in the tested steel is coarsened from 8.1 μm to 13.1 μm, while the volume fraction of reverse transformation austenite is increased from 5% to 10.2%. Consequently, its yield strength is improved to 622 MPa, while maintaining a stable tensile strength and reducing the yield ratio to 0.87. These changes primarily stem from localized enrichment of nickel elements within the tested steel, leading to variations in parameters associated with multi-scale levels of tempered sorbite and reversed austenite. As a result, these alterations indirectly effect its mechanical properties.

Thermo-mechanical fatigue behavior of 4Cr5Mo2V hot work die steel was studied by changing the cycle lower limit temperature in different temperature ranges (100-600, 160-600, 200-600 and 300-600 ℃) using MTS thermo-mechanical fatigue hydraulic servo machine. The macro morphology and microstructure of the TMF specimens were analyzed by ultra depth of field microscope, optical microscope (OM) and scanning electron microscope (SEM). The results show that the thermo-mechanical fatigue lag loop of the tested steel has obvious asymmetry. The lower the lower limit temperature, the larger the area enclosed by the hysteresis loop, and the shorter its fatigue life. The larger the temperature range, the larger the width of the main crack, the more tortuous the propagation path and the more serious the damage. With the increase of lower limit temperature, the coarsening degree of martensite and carbide in the tested steel increases. When the temperature range is 300-600 ℃, the continuous action time of temperature cycle and mechanical cycle is longer, and the coarsening phenomenon of martensite laths and carbide precipitation is more serious.

Microstructure, forming property, mechanical properties and Luders band evolution of the 5182-O aluminum alloy materials were characterized by SEM, topometer and universal tensile testing machine. The results show that after intermediate annealing treatment, the content of the second phase in the sheet decreases, the grain size increases from 19 μm to 34 μm, the material strength slightly decreases (R_m=273 MPa, R_p0.2=121 MPa), the elongation slightly increases (A₅₀=27.8%), the yield point elongation (YPE) is eliminated, and the Luders band on the surface of the punched parts is significantly improved. The intermediate annealing process can effectively improve the Luders band while ensuring the mechanical properties and formability of the 5182-O aluminum alloy used for automotive panel coverings. The significant improvement in the Luders band is mainly attributed to a more matched grain size and less bulk Al₆(FeMn) second phases, which weakens the PLC effect during plastic deformation. At present, the board prepared by this process has been applied to the production of automotive interior panel in some domestic OEMs.

In order to investigate the effect of holding temperature on the properties of sherardized layer, sherardized layer containing Mg was prepared on the surface of Q345R steel by using powder sherardizing at three holding temperatures (410, 430 and 450 ℃). The thickness, elemental distribution, wear resistance and corrosion resistance of the sherardized layer were characterized by using analytical methods such as scanning electron microscope, wear tester and electrochemical workstation. The results show that a continuous sherardized layer can be formed when the holding temperature is between 410-450 ℃. The sherardized layer becomes thicker as the holding temperature increases and reaches the maximum thickness of 110 μm at 450 ℃. The wear resistance of the sherardized layer decreases with the increase of holding temperature, and the main wear mechanisms of the sherardized layer are abrasive, adhesive and oxidative wear. The corrosion resistance of the sherardized layer increases first and then decreases with the increase of holding time, and the sherardized layer has the best corrosion resistance when held at 430 ℃.

Laserline-LDF3000 fiber-coupled semiconductor lase was used to harden the surface of nodular cast iron and gray cast iron. Effect of laser processing parameters on microstructure, depth and hardness of hardened layer was studied, and the hardening ability of the two types of cast irons was compared. The results show that at the same energy density, the hardened layer depth of the nodular cast iron is higher than that of the gray cast iron, and the depth of the hardened layer of the two types of cast irons with only slight melting on the surface is basically the same, around 0.8 mm. The main factors affecting the hardened layer depth of the tested cast irons are process parameters and material thermal conductivity. The hardened layer depth of the nodular cast iron has an approximate linear correlation with the energy density, but no linear relationship exists between them for gray cast iron because of its higher thermal conductivity. The surface hardness of the nodular cast iron (55-60 HRC) is higher than that of the gray cast iron (45-50 HRC) after laser hardening, and the influence of process parameters on the surface hardness is relatively small. The laser hardening ability of the nodular cast iron is higher than that of the gray cast iron.

Shot peening and shot peening-polishing treatments were applied to the 55Si2MnMoV spring steel. The surface roughness, hardness, and residual stress were characterized by using laser confocal microscopy, microhardness tester and X-ray residual stress analyzer. Fatigue tests were conducted to plot S-N curves and observe fatigue fracture morphology, thereby investigating the fatigue property of the 55Si2MnMoV spring steel subjected to shot peening. The results indicate that shot peening improves the fatigue property of the spring steel specimens. Compared to the untreated specimen, the fatigue strength of the both shot peened and shot peened-polished specimens is increased by 16.7%. Although the surface roughness of the shot peened-polished specimens is lower than that of the shot peened specimens, their fatigue strength remain the same. Shot peening treatments do not change the fatigue fracture mechanism, as all the specimens exhibit a fracture mode initiated by surface cracks. The residual compressive stress in the hardened layer of the shot peened specimens is the primary factor contributing to the enhanced fatigue strength.

Ultrasonic shot peening was first applied to strengthen the plow surface of 65Mn steel, followed by laser processing to create bionic clam shell micro-texture for reducing adhesion and drag. A shot-peening/bionic clam shell micro-texture composite modified layers with texture ratios of 19%, 23% and 37% were formed, and tribological properties tests were conducted under lubrication with artificially prepared earthworm fluid by using the HSR-2M reciprocating friction and wear tester. The hardness and surface roughness of the specimens were measured by using HV-1000D Vickers hardness tester and TR200 roughness tester, respectively. Surface structure and wear scar morphology were observed by using M330BD-HK830 metallurgical microscope and S-4800FE scanning electron microscope. The results show that ultrasonic shot peening alone increases the surface roughness of the 65Mn steel plow, which leads to an increase in the friction coefficient, while the improved hardness enhances wear resistance. The single bionic clam shell micro-texture with a texture ratio of 23%, without shot peening, provides limited improvement in the friction-reducing and wear-resistance of the 65Mn steel plow, reducing the friction coefficient and wear rate by 4.83% and 29.18%, respectively, compared to the unpeened and untextured specimen. Both shot peening and bionic clam shell micro-texture improve the friction-reducing and wear-resistant properties of the 65Mn steel plow to varying degrees. The specimen with texture ratio of 37% exhibits the best friction-reducing and wear-resistant properties, with maximum reductions in the friction coefficient and wear rate of 23.45% and 86.77%, respectively, compared to the unpeened and untextured specimen.

Surface modification of the 25Cr2Ni4WA steel specimens with thickness of 2 mm was carried out with programable ion permeation (PIP) technology. The main processes were nitriding temperature of 530 ℃, cyanate concentration of 32%, nitriding time of 20, 40, 60 and 90 min, respectively, and after nitriding, oxygenation treatment was carried out, with oxygenation temperature of 450 ℃ and oxygenation time of 15 min. The microstructure, surface hardness, cross section hardness, tensile properties and fracture morphologies of the specimens treated by different PIP processes were analyzed. The results show that the structure of the permeation layer is composed of oxide film, loose layer, bright white layer and diffusion layer. The thickness of permeation layer increases with the extension of nitriding time, but the growth rate of infiltration layer decreases. PIP treatment can significantly improve the hardness of the specimens, in which the hardness of the specimens with nitriding time of 60 min is the highest and 2.3 times of the substrate one. After PIP treatment, the tensile properties of the specimens decrease, and the deeper the penetration layer, the more the decrease, and the specimens as a whole show ductile-brittle mixed fracture.

A coupled electric-magnetic-thermal multi-physical field model for cutter ring was established based on finite element software, and induction tempering simulation was performed on cutter ring with gradient hardness. The results show that during the induction tempering process of the cutter ring, the induced current density and magnetic induction intensity gradually decrease along the radial direction of the ring, with the maximum value occurring at the center of the ring closest to the coil. From the center to the edge direction, the temperature of the ring gradually decreases. As the coil current increases, the induced current density, magnetic induction intensity, core temperature and edge temperature of the ring also increase. As the frequency of the coil current increases, the induced current density, core temperature and edge temperature of the ring also increase, but the magnetic induction intensity decreases. The maximum relative error of the radial temperature of the cutter ring obtained from the experiment and simulation is 8.1%, which verifies the accuracy of the simulation.

To solve the problem of insufficient plasticity and toughness in low alloy wear-resistant steel, the quenching-tempering(Q-T) process of the ZG30CrMnSiMoVTi steel was optimized and improved by means of JmatPro and ANSYS softwares. The microstructure and comprehensive properties of the tested steel under two heat treatment processes were studied by using metallographic observation, hardness, impact and tensile tests. The results show that the water-air alternating cycle controlled cooling+tempering process with water quenching time of 10 s, air quenching time of 8 s, and cycling for 3 times can be used as the optimized heat treatment process obtained from the simulation and analysis of the steel piece of 60 mm×250 mm. For the average hardness from heart to surface, there is not much difference between 49.75 HRC after Q-T treatment and 46 HRC after 3 cycles, but the hardness at different positions after 3 cycles and tempering is more uniform. Compared with the specimen treated with Q-T, the tensile strength of the specimen after 3 cycles and tempering increases from 1246.3 MPa to 1551.7 MPa, the yield strength increases from 1038.6 MPa to 1293.1 MPa, the elongation after fracture increases from 10.5% to 12.6%, and the impact absorbed energy increases from 17.7 J to 29.1 J. Compared with the Q-T treated one, the specimen with water quenching time of 10 s, air quenching time of 8 s, and three cycles + tempering has a more uniform microstructure, and its hardness distribution is more uniform, the tensile strength, yield strength and impact absorbed energy are all improved to a certain extent.

By conducting thermodynamic calculations on the changes in the content of main elements in a novel nickel-based heat-resistant alloy C-HRA-3, the possible characteristics of the second phase that might precipitate at various temperatures were analyzed. The results show that the main precipitated phases in C-HRA-3 alloy are γ' and M₂₃C₆, with a precipitation amount of approximately 3.7wt% for γ' phase and 1.11wt% for M₂₃C₆ phase at 700 ℃. The C element has a significant impact on the precipitation amount, redissolution temperature and melting point of M₂₃C₆ phase in the alloy. The effect of Co element on the precipitation phase and melting point is relatively small. The Mo element plays a decisive role in the precipitation behavior of M₆C phase. The increase in Al and Ti content will significantly increase the precipitation amount and redissolution temperature of the γ'-phase. The Nb element has no effect on the precipitation amount of γ'-phase, but has a significant impact on the proportion of Nb in the composition elements of the γ'-phase.

Due to the shape differences between the large and small ends of bevel gears, uneven distribution of hardening layer was caused by uneven quenching temperature distribution on the surface of bevel gears during traditional single-frequency electromagnetic heating. To solve the problem, two induction heating coil structures (hood coil and profile coil) were designed, an asynchronous dual-frequency segmented iterative cyclic induction heating method for bevel gears based on profiled coil was proposed, a physical model of electric-magnetic-thermal multi-parameter coupling was constructed and verified by induction heating test. The results show that the hood coil can heat the tooth bottom of the bevel gear well, and the profile coil can profiling heat the top and surface of the gear tooth. On this basis, the simulation results of electric-magnetic-thermal multi-field coupling for asynchronous dual-frequency induction heating show that the cycle state of asynchronous dual-frequency induction heating has a large influence on the uniformity of the temperature distribution of the tooth surface of the bevel gear. When the total time of asynchronous dual-frequency induction heating is certain, with the increase of the number of iterations, it helps to avoid excessive local temperatures, and improve the uniformity of the temperature in the direction of the imitation tooth profile and tooth width, and when the iteration cycle is up to 4 times, the temperature difference in the direction of the tooth width and the tooth profile is no longer changed significantly. As the ratio of medium and high frequency induction heating time increases, the uniformity of temperature distribution on the tooth surface of the bevel gear decreases. The asynchronous dual-frequency induction heating test on the bevel gear verifies the correctness of the constructed temperature field model.

Stabilizing treatment fixture for titanium alloy designed by conventional methods is thick and heavy, and the verification cycle is long. By studying the high temperature tensile and creep behavior of the TA15 titanium alloy, a finite element model of the high temperature rupture lifetime of titanium alloy was established to simulate the deformation of the fixture under high temperature loading conditions and optimize the fixture structure. The results indicate that based on the creep test results and the Allometric1 function in the data analysis software, the creep constitutive equation of the TA15 titanium alloy is ε·=7.411×10^-8σ^2.759. The ABAQUS quasi-static analysis module and the creep constitutive equation of the TA15 titanium alloy can be used for the verification of stabilizing treatment fixture, providing a basis for its optimization design.

Static and dynamic microstructure evolution and fracture behavior of the 06Cr25Ni20 austenitic heat-resistant steel at different high temperature tensile temperatures were analyzed by means of optical microscope, scanning electron microscope, transmission electron microscope and high temperature laser confocal microscope. The results show that the yield strength of the tested steel decreases from 180 MPa to 40 MPa, the tensile strength decreases from 450 MPa to 50 MPa, and the elongation after fracture increases from 44% to 56% with the increase of tensile test temperature in the rang of 600-1000 ℃.The fracture is ductile. The number of dimples gradually decreases with the increase of temperature, and the size and depth gradually increase. The recrystallization phenomenon occurs in the microstructure, and the secondary phase black carbide and intragranular substructure decrease or even disappear with the temperature increasing. The formation of cracks and fracture are mainly generated at the interface between austenite and ferrite and high energy grain boundaries when the tested steel is stretched at high temperature.

In order to solve the problem of color difference caused by sulfuric acid anodizing of the 7075 aluminum alloy thick plate, optical microscope, scanning electron microscope, room temperature tensile testing and other methods were used to study the microstructure and properties of different color parts. The results show that the cooling rate is the main reason for the color difference of the sulfuric acid anodized film layer of the 7075 aluminum alloy thick plate. In the parts that can not reach the required cooling rate during solution treatment, a large number of micron-sized η phases are generated, and the film layer is formed unevenly during the sulfuric acid anodizing, resulting in a gray-black appearance. In the parts that can reach the required cooling rate during solution treatment, the microstructure is dominated by nano-scale η′ metastable precipitated phase, and the film layer is uniform during sulfuric acid anodizing, and the color is normally gray white. The gray-black part after sulfuric acid anodizing is re-heat-treated to regulate the microstructure, ant then the color of the film layer is returned to normal gray white.

During the reliability validation process of a specific natural gas engine, a fracture of the exhaust valve occurred. The fracture cause was analyzed by using methods such as morphology observation, chemical composition analysis and hardness testing, and improvement measures were proposed. The results indicate that the chemical composition and hardness of the exhaust valve material meet the requirements of GB/T 12773-2021. The hardness test shows that the maximum actual working temperature of the exhaust valve is 725-735 ℃. The oxide layer generated on the valve stem under high temperature extends to the substrate and forms microcracks on the surface of the valve stem. High temperature causes layered precipitates to precipitate along the grain boundary, further accelerating the propagation of microcracks along the grain boundary, and gradually developing into deeper cracks, ultimately leading to fatigue fracture of the valve stem. It is recommended that reducing the operating temperature of the exhaust valve through optimizing the combustion system parameters, or alternatively, selecting NCF 3015 or Inconel 751 materials with superior temperature resistance can ensure the exhaust valve meets the operational requirements.

A high-temperature fastening bolt (20Cr1Mo1VTiB steel) for the high-stress main steam valve of a steam turbine unit cracked after serving for 1.29×10⁵ h. The cracking failure cause of the high-temperature fastening bolt was analyzed by means of chemical composition examination, SEM and TEM microstructure observation, XRD detection, and mechanical property testing. The results show that the fracture of the bolt is primarily due to creep damage from long-term high-temperature and high-stress conditions of serving. Additionally, the accumulation of creep damage is mainly due to two types of creep voids forming in microcrack zones near coarse inclusions sharp corners and along the interface of Laves phase. With the increase of running time, the number of creep voids in the 20Cr1Mo1VTiB steel bolt matrix continuously rises and aggregates, eventually forming crack sources that lead to fatigue rupture.

Failure analysis of the fractured front stabilizer bar of a certain vehicle in strength endurance road test was carried out by using direct reading spectrometer, hardness tester, scanning electron microscope and metallographic microscope. The results show that chemical composition and Rockwell hardness of the front stabilizer bar can meet the requirement of material standard and part drawing. The fracture failure mode is fatigue fracture. Connection zone between the stabilizer bar and the stop ring, hard and brittle secondary quenching martensite and low hardness secondary tempered troostite exist in the crack source because of the heat input of the welding process in installation of the stop ring. Fatigue fracture occurs in the area of the test and extends till instantaneous overload fracture occurs. Failure phenomenon reproduced through rapid fatigue bench test. Such kind fracture failure can be avoided by controlling the welding parameters of the stop ring to make the microstructure of the stabilizer bar not be influenced.

According to the characteristics of heat treatment processing and service enterprise, the national standard GB/T 32151.19—2024 Requirements of the greenhouse gas emissions accounting and reporting—Part 19: Heat treatment enterprise puts forward the boundary and reporting scope of greenhouse gas emissions accounting, and clearly stipulates the calculation method of carbon emission of fixed combustion source and process emission and the acquisition method of related emission factors. The release and implementation of the standard provides a basis for enterprises to establish and improve the quality management of carbon emission data.