冷却速率对Ti-V-Mo复合微合金钢组织转变及力学性能的影响

Effect of Cooling Rate on Microstructure Evolution and Mechanical Properties of Ti-V-Mo Complex Microalloyed Steel

利用OM、EBSD、HRTEM和Vickers硬度计等手段研究了冷却速率对Ti-V-Mo复合微合金钢组织转变、析出相及硬度的影响,阐明了(Ti,V,Mo)C在不同冷却速率下的析出规律及其对显微组织和硬度的作用机理。结果表明,当冷却速率低于20℃/s时,随着冷却速率的增加,析出相平均尺寸由13.2 nm逐渐减小至6.9 nm,铁素体平均晶粒尺寸由5.06 mm逐渐细化至2.97 mm,硬度呈先快速增大而后缓慢增大的趋势,铁素体的细晶强化和(Ti,V,Mo)C的沉淀强化是硬度升高的主要因素;冷却速率为20~30℃/s,其对晶粒细化和沉淀强化的影响效果已趋于饱和,硬度基本保持不变,此时Ti-V-Mo复合微合金钢的硬度具有最大值410 HV,屈服强度高达1090 MPa。Ti-V-Mo复合微合金钢的硬度y与冷却速率x符合指数衰减关系:y=-229exp(-x/5)+412。

Nanoscale co-precipitation strengthening in steels has attracted increasing attention in re- cent years and has become a new cornerstone for the development of advanced high performance steels with superior combination of strength and ductility. Rolling process, finishing temperature, cooling rate and coiling temperature are the main factors which affect the mechanical properties of microalloyedsteels by changing the volume fraction and particle size of precipitates. Nevertheless, the influence of cooling rate on microstructure evolution, precipitates and mechanical properties of complex microalloyed ferritic Ti-V-Mo steel has been rarely reported. In this work, the precipitation law of （Ti, V, Mo）C carbides at different cooling rates and its effect on microstructue evolution and mechanical properties of Ti-V-Mo complex miroalloyed steel were studied by OM, EBSD, HRTEM and Vickers-hardness test. The results in- dicated that the hardness first increased quickly and then increased slowly as the cooling rate increased （lower than 20 ℃/s）; the mean size of （Ti, V, Mo）C particles decreased from 13.2 nm to 6.9 nm and the average size of ferrite grain reduced from 5.06 μm to 2.97 μm; the hardness of Ti-V-Mo steel was im- proved by the means of grain refinement hardening and precipitation hardening. However, when the cool- ing rate increased from 20 ℃/s to 30 ℃/s, its effects on grain refinement hardening and precipitation hard- ening has become saturated, so the hardness was kept flat and achieved a maximum vlaue of 410 HV, and the yield strength reached as high as 1090 MPa. The hardness y of Ti-V-Mo microalloyed steel and cooling rates x accord with a exponential decay relationship： y=-229exp（-x/5）＋412.