Abstract: According to specification of SCM435 steel hot rolled wire rod, the austenite grain size is ≥7 grade and the reduction of area is N≥ 35%. The test results show that in the original process the mixed grain size structure of 中12 mm SCM435 steel wire is distributed along the surface of the wire rod with depth 0. 5 mm, and the austenite grain size rating is 4(25% )+7. 5(75% ) ； the rating of austenite grain size at the rest of the core area is 7. 5. There is more martensite in the microstructure, and the reduction of area of steel is lower. Through analysis on the causes of mixed grain structure, and decreasing finishing rolling temperature from 935 Y to 850 °C , and outgoing temperature decreasing from 900 °C to 850 °C the rating of austenite grain size of 4)12 mm SCM435 steel hot rolled wire rod increases from 7. 5 to 8. 5 and the mixed grain structure on surface of wire rod disappeared, the proportion of martensite in the microstructure decreases, and the average reduction of area increases from 35% to 40% .<br />

Key words: Material Index SCM435 Steel, Mixed Grain Size, Reduction of Area, Process Improvement, Finisliing Rolling Temperature<, br />

摘要： 协议要求SCM435钢热轧盘条奥氏体晶粒度≥7级以及断面收缩率≥35%。试验结果表明,原始工艺条件下,Φ12 mm SCM435钢盘条混晶组织沿着线材的表层分布,从表面到深度0.5mm区域为混晶区,奥氏体晶粒度为4级（25%）+7.5级（75%）;其余心部区域晶粒度7.5级。显微组织中马氏体（M）比例高,断面收缩率低。通过混晶组织产生原因的分析,采取将精轧温度由935℃降至850℃、吐丝温度由900℃降至850℃等措施,使Φ12 mm SCM435钢热轧盘条晶粒度由7.5级升至8.5级,盘条表层混晶组织消失;同时降低了显微组织中M比例,断面收缩率均值由35%提升到40%。