Nb对高Ti耐候钢连续冷却后显微组织及硬度的影响

采用Gleeble热模拟试验机研究了微合金元素Nb对高Ti耐候钢奥氏体连续冷却转变行为的影响,通过光学显微镜(OM)、透射电镜(TEM)以及硬度测试等手段比较了0.050%Nb和无Nb试验钢连续冷却转变后显微组织和硬度的变化。结果表明,Nb能抑制铁素体相变,促进贝氏体相变。冷却速度由5 ℃/s提高到10 ℃/s,两种试验钢的晶粒细化效果均最显著,无Nb钢和0.050%Nb钢硬度分别增加了22 HV0.2和25 HV0.2。冷却速度为40 ℃/s时,无Nb试验钢中析出物主要为6～13 nm球形Ti(C, N)复合析出物;含Nb试验钢中主要为5～12 nm球形(Ti, Nb)(C, N)和10～15 nm方形(Ti, Nb)(C, N)复合析出物,含Nb试验钢析出物较多,因此析出强化作用更强。在高Ti耐候钢中,Nb产生的晶粒细化作用并不显著。在相同冷速下,0.050%Nb试验钢的硬度略高于无Nb试验钢,最大差值仅为11 HV0.2。

Effect of Nb on microstructure and hardness of high Ti weathering steel after continuous cooling

Effect of Nb on continuous cooling transformation behavior of the high Ti weathering steel was studied by Gleeble thermal simulation testing machine. Microstructure and hardness of the tested steel without Nb addition and that added 0.050% Nb after continuous cooling transformation were observed and analyzed by optical microscope (OM), transmission electron microscope (TEM) and hardness test. The results show that Nb can inhibit ferrite transformation and promote bainite transformation. When the cooling rate increases from 5 ℃/s to 10 ℃/s, the grain refinement effect of the two tested steels is the most significant, and the hardness of the steels without and with Nb addition increases by 22 HV0.2 and 25 HV0.2, respectively. When the cooling rate is 40 ℃/s, the precipitate in the steel without Nb is mainly 6-13 nm spherical Ti(C,N), while the precipitates in the 0.050% Nb-microalloyed steel are mainly 5-12 nm spherical (Ti,Nb) (C,N) and 10-15 nm square (Ti,Nb) (C,N). The amount of precipitates in 0.050% Nb-microalloyed steel is more, so the precipitation strengthening effect is more significant. The effect of Nb on grain refinement is not significant in the high Ti weathering steel. The hardness of 0.050%Nb-microalloyed steel is only slightly higher than that of the steel without Nb at the same cooling rate, the maximum difference is only 11 HV0.2.