Effect of tempering temperature on microstructure and mechanical properties of 40CrNiMo steel for flexible gear

doi:10.13251/j.issn.0254-6051.2021.08.019

Abstract

Abstract: Through pre-treatment (solid solution), austenitizing and tempering at different temperatures, effect of austenitizing temperature on growth rate of austenitic grain and the hardness of the 40CrNiMo steel was studied by means of optical microscope, scanning electron microscope, Rockwell hardness tester, tensile testing machine and impact testing machine, and the effect of tempering temperature on microstructure and mechanical properties of bainite/martensite multiphase steel was explored. The results show that the austenitic grains grow slowly first and then rapidly with the increase of austenitizing temperature during the pre-treatment, but the hardness value of the steel remains about 56 HRC. A large number of fine carbides precipitate and microstructure remains the original plate strip shape at the temperature range from 250 ℃ to 500 ℃, and the strength and hardness of the tested steel decrease, while the plasticity and toughness decrease first and then increase with the increase of tempering temperature. When tempered at 400 ℃, the lowest elongation and the lowest impact absorbed energy are obtained, which indicates that tempering brittleness occurs when tempered at 400 ℃. When the tempering temperature rises to 600 ℃, the matrix structure transforms into tempering sorbite, and the strength and hardness of the tested steel are the lowest but the impact absorbed energy is up to 147 J.

Key words: 40CrNiMo steel, austenitizing temperature, tempering temperature, mechanical properties

CLC Number:

Liu Xiaoxiao, Zhang Zheng, Zhang Jie, Yang Ran, Yu Chengshuang, Han Lina, Qiao Junwei. Effect of tempering temperature on microstructure and mechanical properties of 40CrNiMo steel for flexible gear[J]. Heat Treatment of Metals, 2021, 46(8): 99-104.

References

[1]王敬忠, 李科元, 刘阿娇, 等. 40CrNiMo钢国内外研究现状[J]. 钢铁, 2018, 53(5): 1-10.
Wang Jingzhong, Li Keyuan, Liu Ajiao, et al. Research status of 40CrNiMo steel at home and abroad[J]. Iron and Steel, 2018, 53(5): 1-10.
[2]冯海生, 王黎钦, 郑德志, 等. 柔性齿轮-柔性转子-滑动轴承系统动特性分析[J]. 哈尔滨工程大学学报, 2015, 36(3): 384-388, 403.
Feng Haisheng, Wang Liqin, Zheng Dezhi, et al. Analysis of the dynamic characteristics of flexible gear-flexible rotor-journal bearing system[J]. Journal of Harbin Engineering University, 2015, 36(3): 384-388, 403
[3]Ebrahimian A, Ghasemi Banadkouki S S. Mutual mechanical effects of ferrite and martensite in a low alloy ferrite-martensite dual phase steel[J]. Journal of Alloys and Compounds, 2017, 708: 43-54.
[4]Bakhtiari R, Ekrami A. The effect of bainite morphology on the mechanical properties of a high bainite dual phase (HBDP) steel[J]. Materials Science and Engineering A, 2009, 525(1/2): 159-165.
[5]Akbarpour M R, Nematzadeh F, Amiri S E H, et al. Effect of long duration intercritical heat treatment on the mechanical properties of AISI 4340 steel[J]. Materials Science-Poland, 2010, 28(2): 401.
[6]Lepera F S. Improved etching technique to emphasize martensite and bainite in high-strength dual-phase steel[J]. JOM, 1980, 32(3): 38-39.
[7]Ravi A M, Navarro-López A, Sietsma J, et al. Influence of martensite/austenite interfaces on bainite formation in low-alloy steels below Ms[J]. Acta Materialia, 2020, 188: 394-405.
[8]Feng J, Frankenbach T, Wettlaufer M. Strengthening 42CrMo4 steel by isothermal transformation below martensite start temperature[J]. Materials Science and Engineering A, 2017, 683: 110-115.
[9]Bohemen van S M C, Santofimia M J, Sietsma J. Experimental evidence for bainite formation below Ms in Fe-0.66C[J]. Scripta Materialia, 2008, 58(6): 488-491.
[10]Navarro-López A, Hidalgo J, Sietsma J, et al. Unravelling the mechanical behaviour of advanced multiphase steels isothermally obtained below Ms[J]. Materials and Design, 2020, 188: 108484.
[11]饶静, 郭永谦, 陈冬至, 等. 回火对低碳贝氏体钢冲击性能的影响[J]. 冶金丛刊, 2015(6): 10-13.
Rao Jing, Guo Yongqian, Chen Dongzhi, et al. Influence on impact property of tempering process in low-carbon bainitic steel[J]. Metallurgical Collections, 2015(6): 10-13.
[12]王立军, 余伟, 武会宾, 等. Si对超高强钢残留奥氏体回火稳定性与力学性能的影响[J]. 材料热处理学报, 2010, 31(10): 30-36.
Wang Lijun, Yu Wei, Wu Huibin, et al. Effects of Si on tempering stability of retained austenite and mechanical properties of ultra-high strength steels[J]. Transactions of Materials and Heat Treatment, 2010, 31(10): 30-36.
[13]吴会亮, 周平, 霍孝新, 等. 热处理对35CrMo预硬型塑料模具钢组织与硬度的影响[J]. 金属热处理, 2013, 38(12): 54-57.
Wu Huiliang, Zhou Ping, Huo Xiaoxin, et al. Effects of heat treatment process on microstructure and hardness of 35CrMo pre-hardened plastic die steel[J]. Heat Treatment of Metals, 2013, 38(12): 54-57.
[14]Wang Xuming, Xu Lixin, Liu Hongyi, et al. Analysis on low temperature impact toughness and fracture appearance of Q420 angle steel[C]//2017 International Conference on Smart City and Systems Engineering (ICSCSE). IEEE Computer Society, 2017: 223-226.
[15]李璞, 魏世忠, 张程, 等. 回火温度对3Cr3Mo2NiW钢力学性能和断口形貌的影响[J]. 金属热处理, 2020, 45(6): 22-27.
Li Pu, Wei Shizhong, Zhang Cheng, et al. Effect of tempering temperature on mechanical properties and fracture morphology of 3Cr3Mo2NiW steel[J]. Heat Treatment of Metals, 2020, 45(6): 22-27.