4Cr5Mo2V热作模具钢的CCT曲线及碳化物沿晶析出温度测定

Measurement of CCT curves and carbide intergranular precipitation temperature of 4Cr5Mo2V hot-working die steel

通过热膨胀仪、电阻仪和硬度计,结合扫描电镜和能谱仪,对不同冷速下4Cr5Mo2V钢的组织和硬度进行表征,绘制CCT曲线,并对钢中碳化物沿晶析出温度进行了测定。结果表明,随着冷却速度的降低,硬度降低,组织依次转变为马氏体、贝氏体和珠光体,珠光体和贝氏体转变临界冷却速度分别为0.015℃/s和0.25℃/s;冷却速度不大于0.25℃/s时,钢中有碳化物沿晶析出,且随冷却速度降低,碳化物沿晶析出温度升高,0.01℃/s冷却速度下,析出温度最高为1022℃。

Microstructure and hardness of 4Cr5Mo2V steel at different cooling rates were observed and measured by using thermal expansion meter,resistance meter and hardness tester,combined with scanning electron microscope and energy dispersive spectroscopy.CCT curves of the tested steel were plotted,and the temperature of carbide intergranular precipitation in the steel was determined.The results show that as the cooling rate decreases,the hardness decreases and the microstructure transforms into martensite,bainite and pearlite in sequence.The critical cooling rates for pearlite and bainite transformation are 0.015 C/s and 0.25℃/s,respectively.When the cooling rate is not greater than 0.25 C/s,carbides precipitate along the grain in the steel,and as the cooling rate decreases,the temperature of carbide precipitation along the grain increases.At a cooling rate of 0.01℃/s,the highest precipitation temperature is 1022℃.