加热温度对钒微合金中碳钢组织及性能的影响

采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、电子背散射(EBSD)、拉伸试验及断裂韧性试验等研究了奥氏体化加热温度对钒微合金中碳钢珠光体等温转变组织特征及强韧性的影响。结果表明:随加热温度的提高,实验钢的强度先大幅提高,在930℃时达到最大后略降。890℃时原奥氏体晶粒尺寸(AGS)细小且均匀,当加热温度为930℃及以上时,AGS显著增大且不均匀,珠光体团尺寸(PCS)的变化趋势与AGS一致。PCS对断裂韧性KQ值的影响可用式KQ=196.578-16.876PCS来表达。断口分析表明,珠光体团界对解理滑移带起约束作用,减小珠光体团尺寸对韧性优化有利。合理选取加热温度,控制含钒沉淀相的溶解比例,是获取较理想的组织参量及强韧性匹配的关键。

Effect of heating temperature on microstructure and properties of vanadium microalloyed medium carbon steel

Effects of austenitizing heating temperature on microstructure characteristics and strength and toughness of vanadium microalloyed medium carbon steel were studied by means of optical microscope(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM), electron backscatter diffraction(EBSD) technique, tensile test and fracture toughness test. The results show that the strength of the experimental steel increases greatly with the increase of heating temperature, and reaches the maximum at 930 ℃ and then decreases slightly. The prior austenite grain size(AGS) is fine and uniform at 890 ℃, and when the heating temperature is 930 ℃ or above, the prior austenite grain size increases significantly and is uneven. The change trend of pearlite colony size(PCS) is consistent with that of AGS. The effect of pearlite colony size on fracture toughness(KQ) value can be expressed by KQ=196.578-16.876PCS. The fracture analysis shows that the pearlite colony boundary restricts the cleavage slip band and the reduction of pearlite colony size is beneficial to the optimization of toughness. Reasonable selection of heating temperature and control of dissolution ratio of vanadium precipitated phase are the key to obtaining ideal microstructure parameters and strength and toughness matching.