钛微合金化高强钢的连续冷却相变规律

Phase transformation law of a Ti-microalloyed high-strength steel during continuous cooling

为了研究钛微合金化高强钢在连续冷却条件下的相变规律,通过热膨胀法及金相分析研究了低碳钢(C-Mn钢)和钛微合金钢(Ti钢)在连续冷却过程中的组织变化及过冷奥氏体的相变规律,分析了钛元素和变形对试验钢相变规律的影响,并讨论了连续冷却转变(CCT)与等温转变(TTT)曲线的关系。结果表明:随着冷速的增加,试验钢的主要相变组织由铁素体向贝氏体转变。在C-Mn钢中加入钛元素提高了过冷奥氏体的稳定性,抑制了铁素体和珠光体转变,促进了贝氏体转变;在奥氏体未再结晶区进行变形使试验钢的CCT曲线整体向左上方移动,提高了相变开始温度;变形提高了铁素体的形核率,促进了铁素体相变,铁素体组织得到细化;变形促进了贝氏体相变,使板条贝氏体变短,细化贝氏体组织。

In order to study the phase transformation law of Ti-microalloyed high-strength steel under continuous cooling conditions,the microstructure changes and the undercooled austenite phase transformation law of low carbon steel(C-Mn steel)and Ti-microalloyed steel(Ti steel)during continuous cooling were studied through thermal expansion method and metallographic analysis.The influence of titanium element and deformation on the phase transformation law of the experimental steels was analyzed,and the relationship between continuous cooling transformation(CCT)and isothermal transformation(TTT)curves was discussed.The results show that with the increase of cooling rate,the main phase transformation microstructure of the experimental steels changes from ferrite to bainite.Adding titanium to the C-Mn steel improves the stability of undercooled austenite,inhibits the transformation of ferrite and pearlite,and promotes the transformation of bainite.The deformation in the unrecrystallized austenite zone causes the overall CCT curves of the experimental steel to shift to the upper left,increasing the starting temperature of phase transformation.Deformation increases the nucleation rate of ferrite,promotes ferrite phase transformation,and refines the ferrite structure.Deformation promotes bainite transformation,shortens lath bainite and refines bainite structure.