再结晶区变形后冷却速率对Nb-V-Ti-N微合金钢组织演变及力学性能的影响

Effect of cooling rate after recrystallization deformation on microstructural evolution and mechanical properties of Nb-V-Ti-N microalloyed steel

利用Gleeble-3800热/力模拟机研究了Nb-V-Ti-N微合金钢的动态连续冷却转变规律,并探讨了再结晶区变形后冷速对其组织及性能的影响。结果表明:当冷速由0.1℃/s增大至30℃/s时,实验钢发生铁素体、珠光体、贝氏体和马氏体相变,冷速区间分别为0.1~30℃/s、0.1~8℃/s、3~30℃/s和15~30℃/s;随着冷速的增大,铁素体、珠光体和贝氏体相变温度分别由785、682和498℃降低到625、553和415℃,而马氏体相变温度则由342℃升高为365℃。当冷速由3℃/s增大至8、20和30℃/s时,钢中大角度晶界占比由0.734不断减少到0.509;平均有效晶粒尺寸先由10.62μm减小到7.46μm后增大到9.61μm,最小值在20℃/s获得;平均KAM值先由0.419°略降低到0.407°后升高到0.691°,最小值在8℃/s获得。此外,当冷速由0.1℃/s增大至30℃/s,实验钢的显微硬度由(197±23.3)HV0.1逐渐增加到(316±11.8)HV0.1,屈服强度由(475±67.1)MPa增加到(818±33.9)MPa。分析可知,为了获得良好的强度-韧性配合,实验钢再结晶区变形后适宜的冷速为8℃/s。

The dynamic continuous cooling transformation curves of Nb-V-Ti-N microalloyed steel were studied by using Gleeble-3800 thermal-mechanical simulator,and the effect of cooling rate after recrystallization deformation on its microstructure and properties was investigated.The results show that when the cooling rate increases from 0.1℃/s to 30℃/s,the phase transformation of ferrite,pearlite,bainite and martensite occurs in the experimental steel,and the corresponding cooling rate range is 0.1-30℃/s,0.1-8℃/s,3-30℃/s and 15-30℃/s,respectively.With the increase of cooling rate,the transformation temperatures of ferrite,pearlite and bainite decrease from 785,682 and 498℃to 625,553 and 415℃,respectively,while the transformation temperature of martensite increases from 342℃to 365℃.When the cooling rate increases from 3℃/s to 8,20 and 30℃/s,the proportion of large angle grain boundaries in the steel decreases from 0.734 to 0.509,the average effective grain size first decreases from 10.62μm to 7.46μm and then increase to 9.61μm,and the minimum value is obtained at 20℃/s.The average KAM value first decreases slightly from 0.419°to 0.407°and then increases to 0.691°,and the minimum value is obtained at 8℃/s.In addition,when the cooling rate increases from 0.1℃/s to 30℃/s,the microhardness of the experimental steel gradually increases from(197±23.3)HV0.1 to(316±11.8)HV0.1,and the yield strength increases from(475±67.1)MPa to(818±33.9)MPa.The analysis shows that in order to obtain a good strength-toughness match,the appropriate cooling rate of the experimental steel after recrystallization deformation is 8℃/s.