渗碳层厚度对18Cr2Ni4WA钢齿轮淬火畸变影响的模拟研究

Simulated research on influence of carburized layer thickness on quenching distortion of 18Cr2Ni4WA steel gear

采用有限元模拟软件,对热处理气淬过程中渗碳层对18Cr2Ni4WA钢弧形齿轮温度场、应力场、应变场的影响进行了分析,并结合第一性原理方法对其作用机制进行了探索。结果表明:渗碳层厚度对18Cr2Ni4WA钢弧形齿轮温度场的影响较小,但是应力场结果显示当渗碳层厚度小于0.5 mm时,齿顶表面应力波动明显,齿顶表面的应力由渗碳层厚度0.1 mm的86.7 MPa增加至2.0 mm的278.6 MPa。应变场结果表明在渗碳层厚度为2.0 mm时,齿顶表面等效应变初始值达到2%。第一性原理计算结果显示随着碳浓度的增加,Fe-Fe原子之间的成键强度消弱,新形成的Fe-C键和Cr-C键明显增强,而且Fe与C原子之间电子密度呈明显的方向性。Fe-Fe键的消弱导致18Cr2Ni4WA钢的膨胀系数会随碳浓度增大而增大,因此齿轮因渗碳层过厚而产生的升温畸变在气淬降温阶段并不能恢复,从而加大齿轮尺寸跳动。

Influence of carburized layer on the temperature field, stress field and strain field of the 18 Cr2 Ni4 WA steel arc-gear during gas quenching process was analyzed by means of finite element simulation software, and the action mechanism was explored further in combination with the first-principles method. The results show that the influence of depth of carburized layer on the temperature field of 18 Cr2 Ni4 WA arc gear is small. But the stress field of surface layer in gear fluctuates is obvious when the depth of carburized layer is smaller than 0.5 mm, which increases from 86.7 MPa at the thickness 0.1 mm of the carburized layer to 278.6 MPa at 2.0 mm. The results of the strain field show that when the thickness of the carburized layer is 2.0 mm, the initial value of the equivalent strain on the surface of tooth top reaches 2%. The first-principles calculation results show that with the increase of carbon concentration, the bond strength between Fe-Fe atoms weakens. However, the newly formed Fe-C bond and Cr-C bond are obviously strengthened, and the electron density between Fe and C atoms shows obvious directionality. Therefore, the weakness of the Fe-Fe bond causes expansion coefficient of the 18 Cr2 Ni4 WA steel to increase with the addition of carbon concentration. Then it will cause the heating-up distortion of the gear be not capable of recovering during the gas quenching and cooling process for its excessively thick carburized layer. As a result, the fluctuation of gear geometric dimension will be aggravated obviously.