回火对高Ni-Cr铸铁残余奥氏体量和硬度的影响

Influence of Tempering Treatment on Retained Austenite Content and Hardness of High Ni-Cr Cast Iron

研究了回火温度和回火时间对金属型铸造高Ni-Cr铸铁铸态组织中残余奥氏体转变和硬度的影响。结果表明:(1)用75Si Fe孕育和用REMg变质处理的高Ni-Cr铸铁中均存在大量的残余奥氏体。350℃回火时,残余奥氏体仍能稳定存在,随着回火温度升高和回火时间延长,残余奥氏体数量逐渐降低,转变为贝氏体。(2)用75Si Fe孕育的高Ni-Cr铸铁回火后,其硬度随回火温度的上升和回火时间的延长而小幅下降;用REMg变质的高Ni-Cr铸铁在400℃回火20 h时出现二次硬化,其硬度峰值为62.3 HRC。(3)当回火温度达到500℃时,残余奥氏体转变为回火索氏体,试样的回火硬度下降。

The influence of tempering temperature and tempering time on retained austenite transformation in as-cast structure and hardness of permanent mold-cast high Ni-Cr cast iron was investigated. The result showed：（1）There was big amount of retained austenite existing in the as-cast structure of both the 75 Si Fe-inoculated and REMg-modified high Ni-Cr cast irons.When tempering at 350 ℃,the retained austenite still stably existed,however,the retained austenite content gradually reduced and transformed into bainite with tempering temperature elevating and holding time prolonging.（2）After tempering,the hardness of the 75 Si Fe-inoculated high Ni-Cr cast iron decreased by small steps with the tempering temperature elevating and tempering time prolonging;After tempering at 350 ℃ for 20 h,the secondary hardening occurred with the REMg-modified high Ni-Cr cast iron, and its peak hardness value was of 62.3 HRC.（3）When the tempering temperature reached 500 ℃,the retained austenite transformed into tempered sorbite and the tempered hardness of the specimen dcreased.