中厚板延伸率不合格试样断裂机理研究

Fracture Mechanism Research for Fault Elongation of Sample for Heavy and Medium Plate

中厚板拉伸试样出现了延伸率不合问题,并且拉伸试样断口出现了层状撕裂现象。通过对试样断口形貌、试样变形区和未变形区金相组织的研究,认为:中厚板中心区域珠光体比例高是层状撕裂试样厚度中心呈现脆性的原因,这种脆性区导致在拉伸过程中最先萌生裂纹,并最终导致拉伸试样延伸率不合;出现层状撕裂的试样在拉伸之前并不存在结构上的分层和断口分层,在断口上出现的平行于轧制方向的裂纹是在拉伸过程中形成的;当珠光体带的宽度超过25μm时,试样在拉伸过程中在珠光体带中易出现裂纹并导致断口出现层状撕裂。

Sometimes fault elongation appeared in the heavy and medium plate. The laminar tearing always appeared in the fracture of the tensile sample. By means of the fractography and the micrography both of the deformed and undeformed area some conclusions can be obtained： First, the higher proportion of pearlite in the center area of the thickness direction is the reason for the rock-candy structure appeared at the center of the tensile sample which caused crack and finally caused the fault elongation, Second, before tensile test there is neither lamellar crack at the center of the thickness direction and nor lamination at the point of structure, and laminar tearing of the fracture and cracks parallelling to the rolling direction are formed in the tensile test. Third, during the tensile test, cracks are more likely happened in the pearlite band which is more than 25 μm in width and lead to laminar tearing.