微合金钢第Ⅲ脆性区的形成机理

为研究微合金钢第Ⅲ脆性区形成机理及其影响因素,控制连铸坯的表面裂纹,采用Gleeble热力模拟机测定了S355微合金钢在不同温度下的抗拉强度及断面收缩率。使用扫描电镜对拉伸断口进行观察分析,同时采用透射电镜对析出物进行观察分析。在此基础上对拉伸试样进行金相实验,对第二相析出进行热力学计算,分析了组织状态及第二相析出规律对脆性区的影响。结果表明,在第Ⅲ脆性区(660~850℃)内,拉伸断口呈冰糖状,韧窝较浅,形貌表现为沿晶脆性断裂。铁素体网膜沿奥氏体晶界优先析出、第二相沿晶界析出是第Ⅲ脆性区形成的主要原因。

Formation mechanism of brittle zone III of microalloyed steel

In order to study formation mechanism of brittle zone III and control the surface cracks of continuous casting slab,the tensile strength and reduction area of S3 5 5 microalloyed steel at different deformation tempera-tures were studied by Gleeble thermal simulation machine.Tensile fracture was observed by scanning electron mi-croscopy,and transmission electron microscopy was used to analyze the precipitates distribution.The influence of microstructure shape and precipitation behavior on the brittle zone III have been studied by metallographic experi-ment and second-phase thermodynamic calculation.The results show that brittle zone III of tested steel is about 660-850℃.In the brittle zone,the hot tensile fracture shows small sugar surface and shallow dimple,which is typical intergranular embrittlement fracture.Proeutectoid film-like ferrite formed along the austenite grain bounda-ry,second-phase precipitated along the grain boundary are the two main reasons for formation of brittle zone III.