对不同厚度规格中厚钢板用超声波探伤观察到的缺陷统计和分析表明：中厚钢板内部缺陷为钢板厚度中心区域珠光体带中的微裂纹。位于偏析区内宽度超过25 μm珠光体带中；裂纹源为珠光体带中MnS类型的塑性夹杂与钢基体的界面；裂纹的形成温度低于700 ℃，形成于轧后冷却或矫直阶段。铸坯中心线偏析是产生裂纹的内部条件，轧后冷却或矫直过程中的张应力是外部条件。
Flaws in the heavy and medium plate of different thickness detected by ultrasonic detector were studied. Conclusions are: firstly, flaws are caused by microcracks in the pearlite band at the center area of the plate; secondly, microcracks mostly appear in the pearlite band wider than 25 μm located in the centerline segregation area; thirdly, the interface between MnS type plastic inclusions and the matrix is the source of cracks; fourthly, microcracks form after the hot rolling and at the temperature lower than 700 ℃. The internal condition for cracking is the centerline segregation of slab and the external is the tensile stress of slab formed during cooling or straightening.
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