非调质NM400复相耐磨钢的相变行为

为进一步优化非调质NM400复相耐磨钢不同组织配比,利用Gleeble-3800热模拟试验机探究了试验钢在连续冷却条件下的组织转变规律,并结合金相法和硬度法,绘制出试验钢的动态连续冷却转变(CCT)曲线。结果表明,当冷速低于1 ℃/s时,试验钢组织为铁素体+粒状贝氏体+珠光体,部分粗大的原奥氏体晶粒转变为粒状贝氏体和珠光体。在冷却速率为5~40 ℃/s时,试验钢不再发生珠光体转变,显微组织均为铁素体+贝氏体+马氏体。并随着冷速的增加,马氏体含量不断增加,硬度升高;此外,不同分段冷却方案下,较低的中冷温度以及较长的空冷时间均有利于铁素体和贝氏体的转变。同时,残留奥氏体含量则随铁素体含量的增大而增大;由于试验钢的Ms点较高,马氏体板条较宽,并且有自回火现象发生。

Phase transformation behavior of non-quenched and tempered NM400 multiphase wear-resistant steel

In order to further optimize the different microstructure ratios of non-quenched and tempered NM400 multiphase wear-resistant steel, the Gleeble-3800 thermal simulation testing machine was used to explore the microstructure transformation law of the tested steel under continuous cooling conditions, and the metallographic method and the hardness method were combined to draw the dynamic continuous cooling transformation (CCT) curves. The results show that when the cooling rate is lower than 1 ℃/s, the microstructure of the steel is composed of ferrite+granular bainite+pearlite, there are some coarse austenite grains transform into granular bainite and pearlite either. When the cooling rate is 5-40 ℃/s, the pearlite transformation no longer occurs, and the microstructure is composed of ferrite+bainite+martensite. With the increase of cooling rate, the martensite content increases and the hardness increases. In addition, under different step cooling schemes, the lower middle cooling temperature and longer air cooling time are beneficial to the transformation of ferrite and bainite, and the retained austenite content increases with the increase of ferrite content. Due to higher Ms point, the martensite lath of the steel is wide, and self-tempering phenomenon occurs in the steel.