钢板内部缺陷失效分析

Failure Analysis of Defects in Steel Plate

采用120mm厚的45^#钢轧制板材经粗加工后进行调质处理,热处理后超声探伤发现钢板厚度方向中部存在缺陷。通过失效分析认为,钢板内部的缺陷为沿变形方向分布的带状组织,部分带状组织中存在沿晶裂纹。形成带状组织及裂纹的机理是原材料钢锭浇铸过程中心部形成枝晶偏析,轧制过程中偏析区被拉长因而形成偏析条带,条带区因富含Mn、S、P等元素形成硬度较高的马氏体组织,调质热处理过程中在组织应力及热应力作用下马氏体条带组织区域发生沿晶脆性开裂。

The 45 steel rolled plate with 120 mm thickness was roughly-treated and tempered. After heat treatment, the defects in the middle part of the thickness direction of the steel plate were found by ultrasonic inspection. The results of failure analysis show that the defects in the steel plate are banded structure and distributed along the deformation direction,and some of the banded structures have intergranular cracks. The mechanism of appearance of banded structure and crack is as follows:the central part of the ingot casting process appear dendritic segregation,and the segregation zone is lengthened during the rolling process to form the segregation zone. Because of the high hardness of martensite structure forms in the strip zone,the microstructure of martensite strip is cracked along the intergranular brittleness under the action of microstructural stress and thermal stress during the tempering treatment.