Abstract: The phase transformation characteristics of high strength steel SCr440 ( 0.40% C, 1.00% Cr) for automotive fasteners are studied by thermal simulation. From 850 °C by cooling rate ≤ 1℃ /s continuous cooling, the transformed structure is ferrite and pearlite, and bainite and martensite occur in structure with cooling rate reached 2 ℃/s, by cooling rate ≥7 °C/s the main structure in steel is martensite and bainite. The pearlitic transformation temperature is 550 ~700 °C during isothermal conditions, and bainitic transformation occurs when the transformation temperature decreased below 550 °C. Based on thermal simulation results, the Φ 18 mm SCr440 steel rod has been successfully rolled, and can be used to manufacture 10.9 grade automobile flange bolts by cold drawing to Φ 17 mm rod, then spheroidizing annealing at 700 ~ 760 °C and cold drawing to Φ15.7 mm rod.

摘要： 通过热模拟试验研究了高强度汽车紧固件用钢SCr440（0.40%C,1.00%Cr）的组织转变行为。从850℃连续冷却时,当冷速≤1℃/s时,转变后的组织为铁素体和珠光体;当冷速达到2℃/s时,组织中开始出现贝氏体和马氏体;当冷速≥7℃/s时,组织主要以马氏体和贝氏体为主。等温转变时,珠光体转变的温度为550～700℃;当转变温度降低到550℃以下,组织中出现贝氏体。依据热模拟试验结果,进行工业轧制Φ18 mm SCr440钢盘条,冷拔至Φ17 mm,再经球化退火700～760℃及冷拔成Φ15.7 mm线材,可用于制造10.9级汽车用法兰面螺栓。