卷取温度对Ti-V-Mo复合微合金化超高强度钢组织及力学性能的影响

EFFECT OF COILING TEMPERATURE ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ti-V-Mo COMPLEX MICROALLOYED ULTRA-HIGH STRENGTH STEEL

利用OM,EBSD,TEM,XRD及物理化学相分析法,对不同卷取温度下Ti-V-Mo复合微合金化热轧高强钢的强化增量进行了估算和分析,分别讨论了卷取温度对屈服强度和MC相粒子对均匀塑性的影响规律.结果表明,在600℃卷取时具有最佳的综合力学性能：抗拉强度为1134 MPa,屈服强度为1080 MPa,延伸率为13.2%,均匀延伸率为6.8%,其析出强化增量sp在444～487 MPa范围内,甚至更高,主要是由质量分数高达72.6%的10 nm以下的（Ti,V,Mo）C粒子提供的.析出强化和细晶强化是主要的强化方式,sp的改变是导致不同卷取温度下屈服强度变化的主要因素.随着卷取温度由500℃升高至600℃,抗拉强度和屈服强度均不断增加,均匀延伸率不但没有降低,反而呈线性缓慢增加.其主要原因是sp对屈服强度的贡献量不断提高,在提高强度的同时改善了均匀塑性.

Among various hardening factors of steels, precipitation hardening has the least embrittlement vector value except grain refinement hardening. Giving full play to the precipitation hardening of microalloyed carbonitrides is an important aspect in the development of microalloyed high strength steels. Recently, the research on behaviors of precipitation and development of microalloyed high strength steels is mainly focused on these relatively simple microalloyed steels including single V, single Ti, Ti-V and Ti-Mo microalloyed steels, while paid less attention on complex microalloyed steels such as Ti-V-Mo steels. Therefore, it is expected to provide a theoretical basis and a practical significance for the development of Ti-V-Mo microalloyed high strength steel. Various hardening increments at different coiling temperatures were calculated. Meanwhile, the effect of coiling temperatures on yield strength and the influence of MC particles on uniform elongation were discussed by means of OM, EBSD,TEM, XRD and physical- chemical phase analysis. The results show that Ti- V- Mo steel has the best mechanical properties with ultimate tensile strength of 1134 MPa, yield strength of 1080 MPa, elongation of 13.2% and uniform elongation of 6.8% at coiling temperature of 600 ℃. The precipitation hardening increment was high to about444～487 MPa due to the mass fraction of about 72.6% of total precipitates with a size of ？10 nm. In addition, precipitation hardening and grain refinement hardening are the main mechanisms to improve the strength of Ti-V-Mo steel, while the variation in precipitation hardening increment causes a significent difference in yield strength. With the coiling temperature increases from 500 ℃ to 600 ℃, the ultimate tensile strength and yield strength increase continuously, but the uniform elongation increases slowly instead of decreasing, which is mainly attributed to an increase of precipitation hardening increment.