回火温度对柔性齿轮钢40CrNiMo组织及力学性能的影响

通过预处理(固溶处理)、等温淬火以及不同温度回火等处理方法,利用光学显微镜、扫描电镜、洛氏硬度计、拉伸试验机、冲击试验机等设备研究了奥氏体化温度对40CrNiMo钢奥氏体晶粒长大速度以及硬度的影响,探索了回火温度对贝氏体/马氏体多相钢微观组织和力学性能的影响。结果显示,预处理期间,奥氏体晶粒随奥氏体化温度的升高首先缓慢增长然后快速长大,然而硬度保持在56 HRC左右。250~500 ℃回火时,大量细小的碳化物析出,微观组织仍然保持原来的板条状,试验钢的强度、硬度降低,塑韧性呈现先降低后升高的趋势;400 ℃回火试样伸长率最低,冲击吸收能量最小,表明400 ℃回火时出现回火脆性;回火温度升高到600 ℃,基体组织发生再结晶,转变为回火索氏体,此时强、硬度最低,冲击吸收能量高达147 J。

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

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.