Effect of austenitization temperature on microstructure and mechanical properties of 40CrMnSi2Mo steel under air cooling

doi:10.13251/j.issn.0254-6051.2024.12.001

Abstract

Abstract: 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.

Key words: 2 GPa grade 40CrMnSi2Mo steel, bainite/martensite duplex microstructure, tensile strength, fracture toughness

CLC Number:

TG142.1

Yu Linran, Liu Geng, Yang Zhuoyue, Su Jie, Ning Jing, Ding Yali. Effect of austenitization temperature on microstructure and mechanical properties of 40CrMnSi2Mo steel under air cooling[J]. Heat Treatment of Metals, 2024, 49(12): 1-8.

References

[1]范长刚, 董瀚, 时捷, 等. 2200 MPa级超高强度低合金钢的组织和力学性能[J]. 兵器材料科学与工程, 2006(2): 31-35.
Fan Changgang, Dong Han, Shi Jie, et al. Microstructure and mechanical properties of 2200 MPa grade ultra-high strength low alloy steels[J]. Ordnance Material Science and Engineering, 2006(2): 31-35.
[2]Li J, Zhan D, Jiang Z, et al. Progress on improving strength-toughness of ultra-high strength martensitic steels for aerospace applications: A review[J]. Journal of Materials Research and Technology, 2023, 23: 172-190.
[3]Kim Y K, Kim K S, Song Y B, et al. 2.47 GPa grade ultra-strong 15Co-12Ni secondary hardening steel with superior ductility and fracture toughness[J]. Journal of Materials Science and Technology, 2021, 66: 36-45.
[4]Caballero F G, Bhadeshia H K D H. Very strong bainite[J]. Current Opinion in Solid State and Materials Science, 2004, 8(3/4): 251-257.
[5]Tomita Y, Okabayashi K. Improvement in lower temperature mechanical properties of 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel with the second phase lower bainite[J]. Metallurgical Transactions A, 1983, 14(2): 485-492.
[6]Tomita Y, Okabayashi K. Mechanical properties of 0.40 pct C-Ni-Cr-Mo high strength steel having a mixed structure of martensite and bainite[J]. Metallurgical Transactions A, 1985, 16(1): 73-82.
[7]Tomita Y, Okawa T. Effect of modified heat treatment on mechanical properties of 300M steel[J]. Materials Science and Technology, 1995, 11(3): 245-251.
[8]方鸿生, 刘东雨, 常开地, 等. 1500 MPa级经济型贝氏体/马氏体复相钢的组织与性能[J]. 钢铁研究学报, 2001(3): 31-36.
Fang Hongsheng, Liu Dongyu, Chang Kaidi, et al. Microstructure and properties of 1500 MPa economical bainite/martensite duplex phase steel[J]. Journal Iron and Steel Research, 2001(3): 31-36.
[9]方鸿生, 冯春, 郑燕康, 等. 新型Mn系空冷贝氏体钢的创制与发展[J]. 热处理, 2008, 23(3): 2-19.
Fang Hongsheng, Feng Chun, Zheng Yankang, et al. Creation and development of novel Mn series air cooled bainitic steels[J]. Heat Treatment, 2008, 23(3): 2-19.
[10]Fang H S, Zheng Y K, Chen X Y, et al. Novel air-colled bainitic steels[J]. Journal of Metals, 1988, 40(3): 51.
[11]高古辉, 桂晓露, 谭谆礼, 等. Mn-Si-Cr系无碳化物贝氏体/马氏体复相高强钢的研究进展[J]. 材料导报, 2017, 31(11): 74-81.
Gao Guhui, Gui Xiaolu, Tan Zhunli, et al. Carbide-free bainite/martensite multiphase high strength steels: A review[J]. Materials Review, 2017, 31(11): 74-81.
[12]熊金生, 宁静, 苏杰, 等. 固溶温度对G33超高强度钢微观组织和力学性能的影响[J]. 金属热处理, 2021, 46(7): 160-164.
Xiong Jinsheng, Ning Jing, Su Jie, et al. Effect of solution temperature on microstructure and mechanical properties of ultra-high strength steel G33[J]. Heat Treatment of Metals, 2021, 46(7): 160-164.
[13]Liu Z B, Tu X, Wang X H, et al. Carbide dissolution and austenite grain growth behavior of a new ultrahigh-strength stainless steel[J]. Journal of Iron and Steel Research International, 2020, 27(6): 732-741.
[14]Lü L F, Fu L M, Sun Y L, et al. Microstructure and mechanical behaviour of ultra-high strength of fine-grained AISI 4140 steel[J]. Materials Research Innovations, 2015, 19(S4): 64-67.
[15]Furuhara T, Kikumoto K, Saito H, et al. Phase transformation from fine-grained austenite[J]. ISIJ International, 2008, 48(8): 1038-1045.
[16]Jr J W M. Comments on the microstructure and properties of ultrafine grained steel[J]. ISIJ International, 2008, 48(8): 1063-1070.
[17]Wang C F, Wang M Q, Shi J, et al. Effect of microstructural refinement on the toughness of low carbon martensitic steel[J]. Scripta Materialia, 2008, 58(6): 492-495.
[18]Hartshorne M I, McCormick C, Schmidt M, et al. Analysis of a new high-toughness ultra-high-strength martensitic steel by transmission electron microscopy and atom probe tomography[J]. Metallurgical and Materials Transactions A, 2016, 47(4): 1517-1528.
[19]宁静, 杨卓越, 苏杰, 等. 固溶温度对30Cr4Si2NiMoWNb超高强度钢力学性能的影响[J]. 钢铁研究学报, 2017, 29(12): 1030-1034.
Ning Jing, Yang Zhuoyue, Su Jie, et al. Influence of solution treatment temperature on mechanical properties of 30Cr4Si2NiMoWNb steel[J]. Journal of Iron and Steel Research, 2017, 29(12): 1030-1034.
[20]方萍, 苏杰, 赵晓丽, 等. 奥氏体化温度对30Cr4Si2NiMoNb超高强度钢强韧性的影响[J]. 金属热处理, 2013, 38(5): 88-91.
Fang Ping, Su Jie, Zhao Xiaoli, et al. Effect of austenitizing temperature on strength-toughness of 30Cr4Si2NiMoNb ultrahigh strength steel[J]. Heat Treatment of Metals, 2013, 38(5): 88-91.
[21]Lee S J, Park J S, Lee Y K. Effect of austenite grain size on the transformation kinetics of upper and lower bainite in a low-alloy steel[J]. Scripta Materialia, 2008, 59(1): 87-90.
[22]Lan L Y, Qiu C L, Zhao D W, et al. Effect of austenite grain size on isothermal bainite transformation in low carbon microalloyed steel[J]. Materials Science and Technology, 2011, 27(11): 1657-1663.
[23]Garcia-Mateo C, Caballero F G, Bhadeshia H K D H. Development of hard bainite[J]. ISIJ International, 2003, 43(8): 1238-1243.
[24]Xu G, Liu F, Wang L, et al. A new approach to quantitative analysis of bainitic transformation in a super bainite steel[J]. Scripta Materialia, 2013, 68(11): 833-836.
[25]Toji Y, Matsuda H, Raabe D. Effect of Si on the acceleration of bainite transformation by pre-existing martensite[J]. Acta Materialia, 2016, 116: 250-262.
[26]Gui X L, Gao G H, Guo H, et al. Effect of bainitic transformation during BQ&P process on the mechanical properties in an ultrahigh strength Mn-Si-Cr-C steel[J]. Materials Science and Engineering A, 2017, 684: 598-605.
[27]Wang K, Tan Z, Gao G, et al. Microstructure-property relationship in bainitic steel: The effect of austempering[J]. Materials Science and Engineering A, 2016, 675: 120-127.
[28]Yu Y S, Wang Z Q, Wu B B, et al. Tailoring variant pairing to enhance impact toughness in high-strength low-alloy steels via trace carbon addition[J]. Acta Metallurgica Sinica, 2021, 34: 755-764.
[29]Stormvinter A, Miyamoto G, Furuhara T, et al. Effect of carbon content on variant pairing of martensite in Fe-C alloys[J]. Acta Materialia, 2012, 60(20): 7265-7274.