珠光体钢轨钢连续冷却转变曲线测定及组织分析

Determination of continuous cooling transition curves and microstructure analysis of pearlitic rail steel

利用L78淬火膨胀仪绘制了珠光体钢轨钢过冷奥氏体的连续冷却转变曲线。结合显微组织分析与硬度试验结果,研究了珠光体钢轨钢在连续冷却过程中的显微组织和力学性能变化。结果表明,试验钢的临界温度是:Ac_(1)=735.3℃,Ac_(cm)=812.2℃,Ar_(1)=697.9℃,Ar_(cm)=773.8℃。将试验钢以10℃/s升温至860℃保温10 min完成奥氏体化后冷却,当冷速在3℃/s及以下时,组织为珠光体与局部铁素体;当冷速在4~8℃/s时,组织为珠光体与少许马氏体;当冷速在11℃/s及以上时,组织为马氏体与残留奥氏体。且没有发生贝氏体转变。综合分析该钢轨钢的组织转变及硬度变化,应选择4~8℃/s之间的冷却速率,以形成细化的珠光体组织及少量马氏体组织。

Continuous cooling transition curves of the supercooled austenite of the pearlitic rail steel was plotted by using the L78 quenching dilatometer.Combined with the metallographic structure analysis and hardness test results,the microstructure and mechanical properties of the pearlitic rail steel during continuous cooling were studied.The results show that the critical phase transition temperature of the test steel is as follows:Ac_(1)=735.3℃,Ac_(cm)=812.2℃,Ar_(1)=697.9℃,Ar_(cm)=773.8℃.The tested steel was heated to 860℃at 10℃/s for 10 min to complete austenitization and then cooled.When the cooling rate is 3℃/s or below,the microstructure is pearlite and local ferrite.When the cooling rate is 4-8℃/s,the microstructure is pearlite and a little martensite.When the cooling rate is above 11℃/s,the microstructure is martensite and retained austenite.There is no bainite transition.To comprehensively analyze the microstructure and hardness of the rail steel,in order to form the refined pearlite microstructure and a small amount of martensitic microstructure,the cooling rate between 4-8℃/s should be selected.