Abstract: The mechanical properties of steel SAE8640 280mm x 325mm casting bloom (/% : 0.41C, 0.20Si, 0.80Mn, 0.005S, 0.014P, 0.46Cr, 0.43Ni, 0.21Mo, 0.043All, 0.0011O, 0.0054N) at 550~1200℃ has been measured by using Gleeble 1500 thermal simulation machine, and the morphology of fracture of tensile specimen is observed by scanning electron microscope. Results show that the steel SAE8640 has obvious 3-brittle zone： I brittle zone ＞1200℃ , II brittle zone 950~1000°C and Ⅲ brittle zone 650~750℃；the reduction of area of steel at 950〜1000°C is 60% and the morphology of tensile fracture is mainly river pattern type fracture, it should be avoid rolling at this temperature range； and the reduction of area of steel at 650~750 °C is ≥65% , the tensile fracture is tough fracture to meet the requirement on plasticity of casting bloom in straightening process.

摘要： 采用Gleeble 1500热模拟试验机对SAE8640钢280mm×325mm连铸坯（/% : 0.41C，0.20Si，0.80Mn，0.005S，0.014P，0.46Cr，0.43Ni，0.21Mo，0.043Alt，0.0011O，0.0054N）的550~1200℃力学性能进行了测定,并应用扫描电镜观察了拉力试样的断口形貌。结果表明,SAE8640钢有明显的3个脆性区:Ⅰ脆性区＞1200℃,Ⅱ脆性区950~1000℃,Ⅲ脆性区650~750℃;该钢950~1000℃的断面收缩率为60%,拉伸断口为脆性河流状花样,应避免在该温度范围进行轧制,该钢650~750℃的断面收缩率≥65%,拉伸断口为韧性断裂,可满足连铸坯矫直时塑性的要求。

关键词: SAE8640合金钢, 280mm x 325mm连铸坯, 高温, 断面收缩率, 脆性区, 断口