等温冷却时间对Ti-V-Mo复合微合金钢组织转变及硬度的影响

Effect of isothermal cooling time on microstructure transformation and hardness of a Ti-V-Mo microalloyed steel

通过OM、SEM、TEM和维氏硬度计等手段研究了不同等温冷却时间对Ti-V-Mo复合微合金钢组织转变、析出行为及硬度的影响,探讨了影响硬度变化的因素。结果表明,Ti-V-Mo复合微合金钢奥氏体化后在630 ℃等温冷却0~3 h,随着等温时间的延长,基体中的铁素体比例不断增加而马氏体和贝氏体比例逐渐降低,硬度呈现先升高再趋于平稳,再升高至其最大值,最后略有下降。60~1200 s时,硬度出现平台是因为纳米级(Ti,V,Mo)C粒子的沉淀强化效果能够弥补相变导致基体软化造成的硬度损失;3600 s时,硬度达到最大值为457 HV,此时纳米级(Ti,V,Mo)C粒子产生的沉淀强化效果最佳。

Effect of isothermal cooling time on microstructure transformation,precipitation behavior and hardness of a Ti-V-Mo microalloyed steel was investigated by means of OM,SEM,TEM and Vickers hardness tester,and the factors influencing the hardness change were discussed.The results reveal that when the Ti-V-Mo microalloyed steel after austenitization is isothermally cooled at 630 ℃ from 0 to 3 h,with the increase of isothermal time,the proportion of ferrite in the matrix increases while the proportion of martensite and bainite decreases.In addition,the hardness increases firstly and then becomes stable,then re-increases and finally declines slightly.At the isothermal time ranging from 60 s to 1200 s,the hardness plateau occurs because the precipitation strengthening effect of(Ti,V,Mo)C nano-particles can compensate for the hardness loss caused by matrix softening due to phase transformation.When the isothermal time is 3600 s,the maximum hardness is 457 HV,and the precipitation strengthening effect of(Ti,V,Mo)C nano-particles is the best.