马氏体气阀钢粗晶问题探讨与实践

本文结合抚钢生产的小尺寸冷拔材—马氏体气阀钢粗晶、脆断问题现状，着重对气阀钢的成分、相变点、热加工制度等因素进行分析探讨，并进行了工艺标定试验。结果表明：终轧温度对粗晶影响较大，终轧温度≥850℃可保证获得细晶达8 ~10级；严格进行电炉冶炼操作，将钢中Si含量控制在中下线较为有利；避免在临界变形量为7－14％范围内成型，基本上成功解决了气阀钢断口粗晶问题。此外，640~720℃?h，500℃出炉空冷退火处理对原本细化的钢材不会产生粗晶问题。

Discussion and Practice on Martensitic Valve Steel Coarse grain problem

Combined with the coarse grain,brittle fracture problems of small size cold-drawn steel of martensitic valve steel,the composition,phase change,thermal processing system and other factors were analyzed and the process calibration was tested on the air valve steel.The results show that the finishing rolling temperature can effect on coarse grain serious than the others,final rolling temperature of not less than 850 ℃can ensure to obtain fine crystal 8~ 10 degree.Strict electric furnace smelting,Si content was controlled below the middle line was more favorable.Avoiding the critical deformation for 7%~14% range forming basically solved the coarse grain problem of valve steel fracture.In addition,640 ~ 720 ℃×2 h,500 ℃ air cooling annealing treatment on original fine grain steel will not produce coarse grain problem.