Abstract: According to the phenomenon of occurring bainite and martensite in structure of Ф6.5~12mm coil of steel SCM435 rolling in winter season led to higher cracking rate of wire and rod, the analysis on continuous cooling transformation curves of austenite measured by Gleeble-1500 hot simulator and morphology of structure according with cooling rale 0.5~30°C/s has been carried out to get the cooling rate for forming structure of ferrite + pearlite being ≤0.5°C/s；by measuring the cooling rate of Ф6.5~12mm coil of steel SCM435 and observing the corresponding structure, it is found that the temperature of coil leaving insulation cover is ≥600°C with cooling rate 0.8〜4℃/s led to the structure of steel being ferrite + pearlite and partial bainite and martensite. With adjusting loop laying temperature and Stelmor Z1〜Z3 cooling roller speed in wind cooling line for Ф6.5~12mm coil of steel SCM435, the temperature of coil leaving insulation cover is ≤550℃ and the austenite structure of steel is transformed completely into ferrite + pearlite, as a result the cold-heading cracking rate of coil decreases from original 20% to less than 3%.

Key words: Steel SCM435, Coil, Cold-Heading Cracking, CCT Curves, Cooling Speed, Ferrite+Pearlite, Bainite, Martensite

摘要： 针对Ф6.5~12mm SCM435钢盘条冬季热轧时,出现贝氏体和马氏体而导致冷镦开裂率高的现象,通过Gleeble-1500热模拟试验机测定的奥氏体连续冷却转变曲线和冷却速度0.5~30℃/s对应的组织形貌的分析,得出形成铁素体+珠光体组织的冷却速度≤0.5℃/s;通过Ф6.5~12mm SCM435钢盘条的冷却速度和对应的组织发现散卷出保温取的温度≥600℃,冷却速度为0.8~4℃/s,其组织除铁索体+珠光体外形成部分贝氏体和马氏体。通过调整Ф6.5~12mm SCM435钢盘条轧制时的吐丝温度和斯太尔摩风冷线Z1~Z13段辊道速度,使其出保温罩时温度≤550℃,钢的奥氏体组织完全转变为铁素体+珠光体,冷镦开裂率由20%降至3%以下。

关键词: SCM435钢, 盘条, 冷锹开裂, CCT曲线, 冷却速度, 铁素体+珠光体, 贝氏体, 马氏体