碳含量对4Cr5Mo2V型热作模具钢冷热疲劳性能的影响

采用自约束热疲劳试验法,结合SEM、EDS以及Jmat-pro热力学计算软件等研究了碳含量(0.35%和0.71%)变化对4Cr5Mo2V型热作模具钢冷热疲劳性能的影响。结果表明:提高含碳量后,钢中析出大量细小弥散的MC型碳化物,从而使0.71%C钢的抗回火软化性能和热稳定性能均强于0.35%C钢;冷热疲劳循环1000次后,提高碳含量推迟了疲劳裂纹的萌生,当循环次数增加到2000次后,虽然0.71%C钢表面和基体的软化程度均弱于0.35%C钢,但该钢存在较多尺寸较大且呈聚集状态分布的未溶碳化物,这些碳化物在应力的作用下与基体脱离,脱离处成为裂纹扩展的通道,从而促进了疲劳裂纹萌生和扩展。

Effect of carbon content on thermal fatigue properties of 4Cr5Mo2V hot work die steel

With self-constrained thermal fatigue test method, the effect of carbon content(0.35% and 0.71%) on the thermal fatigue properties of 4Cr5Mo2V hot work die steel was studied by SEM, EDS and Jmat-pro thermodynamic calculation software. The results show that with the increase of carbon content, a large amount of finely dispersed MC-type carbides are precipitated in the steel, so that the temper softening resistance and thermal stability of the 0.71%C steel are better than those of the 0.35%C steel. After 1000 cycles of thermal fatigue, increasing the carbon content delays the initiation of thermal fatigue cracks. When the number of cycles increases to 2000, although the softening of the surface and matrix of 0.71%C steel is weaker than that of 0.35%C steel, but there are many undissolved carbides with large size and obvious aggregation distribution in the 0.71%C steel. These carbides are detached from the matrix under the effect of stress, and the detached places become channels for crack propagation, thereby promoting the initiation and propagation of fatigue cracks.