通过热模拟试验、光学显微镜、扫描电镜、电子探针等分析测试手段对热轧过程中28Cr2Mo铸坯的断裂行为进行了系统的研究。结果表明：在铸坯断口表面出现了明显的过烧现象，断口附近存在明显的脱碳区域；同时在断口附近的柱状晶横截面内还观察到了Cr、Mn的氧化物夹杂以及沿晶界存在断续的内部裂纹，而且这些裂纹内壁发生了严重氧化；在铸坯的心部区域观察到了很多尺寸不均、内壁光滑的不连续的孤立孔洞。分析表明铸坯中的裂纹是气孔缺陷在加热过程中不断氧化、宽化并且在热应力作用下不断扩展而形成的。也就是说铸坯中的内部缺陷是导致热轧过程中断裂的内在因素，而加热过程中的加热速度过快以及加热温度不均匀则是断坯现象发生的外在诱因。
The fracture behaviors of 28Cr2Mo slabs during hotrolling process were studied systemically by thermal simulation tensile test, OM and SEM. The results show that the overheat phenomenon is observed on the surface of slab fracture. An obvious decarburization region exists near the fracture surface. From the transversal section of columnar grains, it can be seen that impurities composed by oxide of Cr and Mn are observed in grain boundaries in this region. Besides those phenomena, some discontinuous internalcracks with seriously inner oxidation are observed lying on grain boundaries; Lots of isolated voids are distributed in the center region of slab. The inner wall of isolated voids is smooth and no oxide layer is observed. During the heating process, the faults are oxided by hot air, and then widened and spreaded under the internal stress. When the faults interact each other, the cracks are formed. That is to say, the internal faults in slab are the main factor and the quickly heat velocity and high temperature during preheat process make those fault develop and form the crack.
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