亚临界热处理对高铬铸铁组织及性能的影响

Effect of subcritical heat treatment on microstructure and properties of high chromium cast irons

针对高铬铸铁常规淬火-回火过程能耗高的问题,对3种合金成分的高铬铸铁进行亚临界热处理试验,并研究了该工艺对其组织、硬度和表面耐磨性的影响。结果表明,经500~650℃保温1~14h亚临界热处理后,高铬铸铁组织主要是残留奥氏体、M_(7)C_(3)碳化物、(Fe,Cr)_(23)C_(6)。碳化物、Mo_(2)C碳化物和珠光体;3种高铬铸铁硬度在550~600℃保温6~12h内均有峰值,峰值硬度最高为57.4HRC,Mo元素对硬度的影响最大。高铬铸铁在保温过程中析出二次碳化物促使奥氏体发生珠光体相变,珠光体的相变强化和二次碳化物析出强化作用在长时间保温过程中逐渐降低;碳含量相对最高的共晶高铬铸铁经600℃保温8h后耐磨性能最佳。由此可知,提升高铬铸铁耐磨性首先应提高共晶碳化物数量,其次添加Mo等元素提升析出强化效果。

Aiming at the problem of high energy consumption in conventional quenching and tempering process of high chromium cast irons,the subcritical heat treatment tests of three kinds of high chromium cast irons were carried out.Moreover,the effect of the process on the microstructure,hardness and surface wear resistance was studied.The results show that the microstructure of high chromium cast irons is primarily composed of retained austeniteM_(7)C_(3)carbide(Fe,Cr)_(23)C_(6)carbide,Mo_(2)Ccarbide and pearlite when subjected to holding temperatures ranging from 500℃C to 650℃for 1 h to 14 h.A peak value in hardness is observed for the three high chromium cast irons when holding at 550℃C to 600℃for 6 h to 12 h,with the highest peak hardness being 57.4 HRC.The hardness is most significantly influenced by the Mo element.During the insulation process,the pearlite phase transformation of austenite is promoted by the precipitation of secondary carbides in high chromium cast irons.The effects of pearlite transformation strengthening and precipitation strengthening of secondary carbides gradually decrease with prolonged holding time.The eutectic high chromium cast iron with the highest carbon content exhibits the best wear resistance when holding at 600 for 8 h.It can be seen that the first step to improve the wear resistance of high chromium cast irons is to increase the amount of eutectic carbides,and then to add elements such as Mo to enhance the precipitation strengthening effect.