回火温度对新一代传动齿轮钢C61组织及性能的影响

采用扫描电镜、透射电镜、X射线衍射仪、显微硬度计、拉伸试验机和冲击试验机等分析手段对C61齿轮钢试样经1000 ℃淬火+回火处理后组织和碳化物的析出行为及力学性能进行了研究。结果表明,试验钢在淬火和深冷状态下,一次碳化物基本溶解,基体为板条马氏体组织,此时固溶强化作用提供了较好的强韧化基础。当回火温度为420 ℃时,析出的M₃C渗碳体为其提供了较高的强度,但这种析出相的存在对冲击性能具有较大的损伤;M₃C渗碳体会在482 ℃回火时溶解,10~20 nm尺寸的棒状M₂C碳化物在板条马氏体内的弥散析出,提供了较高强度的同时改善了冲击性能。随着回火温度的继续升高,大量逆转变奥氏体生成,不仅有效提高冲击性能,同时强度下降也更为明显;且M₂C碳化物粗化长大,第二相的强化作用降低。综合得出,试验钢在482 ℃的回火条件下能达到较好的强韧化匹配,抗拉强度和屈服强度分别为1781 MPa和1546 MPa,冲击吸收能量为97 J,硬度峰值为52 HRC。

Effect of tempering temperature on microstructure and properties of a new generation transmission gear steel C61

Microstructure, carbide precipitation behavior and mechanical properties of C61 gear steel specimens after quenching at 1000 ℃ and tempering were studied by using SEM, TEM, XRD, microhardness tester, tensile testing machine and impact testing machine, etc. The results show that under the quenched and cryogenic conditions, the primary carbides in the tested steel are basically dissolved and the matrix is lath martensite. In this condition, the solid solution strengthening can provide a better basis for strengthening and toughening. When the tempering temperature is 420 ℃, the precipitated M₃C cementite provides higher strength, but the presence of which has greater damage to the impact property. The M₃C cementite will dissolve when tempered at 482 ℃, and the rod-shaped M₂C carbides with a size of 10-20 nm are dispersed and precipitated in the lath martensite, which not only provides higher strength but also improves the impact property. With the increase of tempering temperature, a large amount of reverse-transformed austenite is formed which not only effectively improves the impact property but also makes the strength decrease more obviously, meanuhile, the M₂C carbides become coarser and the strengthening effect of the second phase decreases. It can be concluded that the tested steel can achieve better matching of strength and toughness under the tempering condition of 482 ℃, at which the tensile strength is 1781 MPa, yield strength is 1546 MPa, impact absorbed energy is 97 J, and peak value hardness is 52 HRC.