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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。
In order to study the formation mechanism of the third brittle zone of microalloyed steel and its influencing factors, the surface cracks of the slab were controlled. The tensile strength and the reduction of area of S355 microalloyed steel at different temperatures were measured by Gleeble thermal simulator. Scanning electron microscopy (SEM) was used to observe and analyze the tensile fracture, and the precipitates were observed and analyzed by transmission electron microscope. On this basis, the tensile specimens were metallurgically tested and the second phase precipitation was calculated thermodynamically. The influence of the microstructure and the second phase precipitation on the brittle zone was analyzed. The results show that in the third brittle zone (660 ~ 850 ℃), the tensile fracture has the shape of rock candy, the dimple is shallower and the morphology is brittle fracture. The ferrite reticulate preferentially precipitates along the austenite grain boundaries and the second phase precipitates along the grain boundaries, which is the main reason for the formation of the third brittle zone.