热处理工艺对微Nb高Mo型H13钢组织与性能的影响

Effect of heat treatment process on microstructure and properties of niobium microalloyed steel H13 with high molybdenum

采用OM、SEM、TEM和力学性能测试等手段,研究了不同淬回火工艺对微Nb高Mo型H13钢的组织及性能的影响。结果表明:微量Nb的加入能改善钢的室温冲击性能。试验钢经淬、回火处理后的组织均为回火马氏体和少量残留奥氏体及未溶碳化物。试验钢在1030~1060℃淬火并在600~630℃的较高温度回火后,有优良的强韧性配合,此时含微量Nb的NM2钢综合力学性能最好,当淬火温度超过1090℃时试验钢的硬度急剧提高,从而恶化钢的综合力学性能。试验钢在550~570℃范围内回火时出现了明显的二次硬化,主要是由于在该温度范围内渗碳体溶解加速,同时钢中的特殊碳化物M23)C6、M6C和MC等析出量增加,所以选择回火温度时尽量避开此温度范围。

The influence of quenching and tempering processes on microstructure and properties of niobium microalloyed steel H13 with high molybdenum was studied by means of OM,SEM,TEM and mechanical properties tests.The results show that,with the addition of Nb content,the impact property of the tested steels are improved obviously at room temperature,however,no remarkable improvements of other mechanical properties are found.After quenching and tempering,the main microstructure is tempered martensite,besides,a little amount of retained austenite and undissolved carbides can be found.Excellent comprehensive properties of strength and toughness are achieved when the test steel is quenched at 1030-1060℃and tempered at 600-630℃.In addition,the NM2 exhibits optimum comprehensive mechanical properties after heat treatment,the comprehensive mechanical properties deterioration is caused by high hardness when the test steel are quenched over 1090℃.Secondary hardening phenomenon appeared when the steel is tempered in temperature ranging from 550 to 570℃,which is due to accelerated dissolution of cementite and the increasing precipitation quantity of M23C6,M6C and MC.Therefore,the above temperature range should be avoided in the tempering process.