Abstract: Owing to less rolling passes and non-control cooling rate device after finishing rolling, the two kinds of structure-pearlite + ferrite and bainite + martensite in Φ70 ~ 80 mm round bar of steel 40CrMo (/% : 0. 40 ~0. 41C, 0. 97 〜1.05Cr, 0. 17Mo) produced by continuous rolling mill strain easily occur. By using Gleeble-2000 thermal simulation machine the continuous cooling transformation (CCT) curves of two kinds of original structure specimens of heat batch Nol and No2 are measured, and the structure and micro-region analysis of finished products by heating at 1 150 ℃ for 5 min then cooling with 10 °C/s to 900 丁 for 10 s and deforming 30% with strain rate 20 s^-1 and cooling with 0. 2 ~ 10 ℃/s to 200 °C are studied. Results show that the martensite structure occurs as the finished products is cooling with large cooling rate after rolling ； with cooling speed 0. 1 ~ 1 ℃ /s for round bar after rolling the steel 40CrMo can get normal structure i. e. bainite and/or pearlite structure.

Key words: Steel 40CrMo, Round Bar, Hot Rolling, Cooling Rate, Structure

摘要： 连续式棒材轧机生产Φ70～80 mm 40CrMo系圆钢(/%:0.40～0.41C、0.97～1.05Cr、0.17Mo)时,由于轧制道次少,终轧后无控制冷却装置,易出现珠光体+铁素体和贝氏体+马氏体两种类型组织。通过Gleeble-2000热模拟试验机测试炉批No1和炉批No2这两类原始组织试样的连续冷却转变(CCT)曲线和研究了该钢1150℃保温5 min后以10℃/s冷至900℃停留10 s,以变形速率20 s^-1变形30%再以0.2～10℃/s冷却至200℃的组织和微区成分。结果表明,轧后冷却速度大则产生马氏体组织,40CrMo系圆钢在0.1～1℃/s冷却速度下可获得正常的贝氏体组织和珠光体组织。

关键词: 40CrMo钢, 圆棒材, 热轧, 冷却速度, 组织