固溶温度对Cr-Co-Mo马氏体钢碳化物演变及力学性能的影响

利用SEM和TEM研究了固溶温度对Cr-Co-Mo马氏体钢碳化物演变行为及力学性能的影响。结果表明,随着固溶温度的升高,基体中M₆C碳化物回溶,屈服强度下降而室温冲击吸收能量递增;原始奥氏体晶粒由于缺乏晶界上球形M₆C碳化物的钉扎作用迅速长大,细晶强化效果减弱,但晶界处裂纹源减少使得韧性提高。在1120 ℃固溶后晶粒尺寸最大,而马氏体基内析出与基体共格的纳米棒状M₂C碳化物平均粒径最小、单位面积百分数最高和颗粒间距最短,因此即使损失了细晶强化效果,但析出强化增补了强度,使得屈服强度在晶粒长大后不发生大幅下降;同时,由于共格析出提高了基体的变形协调性,韧性也未发生降低。

Effect of solid solution temperature on carbide evolution and mechanical properties of Cr-Co-Mo martensitic steel

Effect of solution treatment temperature on the carbide evolution behavior and mechanical properties of a Cr-Co-Mo martensitic steel were investigated by SEM and TEM methods. The results show that as the solution treatment temperature increases, the M₆C carbides re-dissolve into the matrix, the yield strength decreases, while the impact absorbed energy at room temperature increases; concurrently, the prior austenite grains grow rapidly due to the lack of pinning by spherical M₆C carbides on the grain boundaries, which weakens the grain refinement strengthening effect, but improves the toughness by reducing the crack origins at the grain boundaries. When solution treated at 1120 ℃, the grain size is the largest, but the yield strength does not decrease significantly after grain growth, and the toughness is not reduced. The reasons for this is that the average particle size and the area fraction of nanoscale M₂C carbide are the smallest and the highest respectively, and the particle spacing is the shortest, so that the precipitation strengthening effect effectively makes up for the loss of the grain refinement strengthening effect; and simultaneously, the coherent precipitation of nano scale rod-like M₂C carbide with the matrix results in that both the deformation compatibility of the matrix and the toughness are improved.