针对低合金中厚板超声波探伤合格率低的问题，采用低倍、金相、扫描电镜检验和断口形貌分析对探伤不合格的中厚板进行研究，得出结论：引起超声波探伤不合格的主要原因是钢中的氢含量偏高和板坯中心偏析严重，条状MnS夹杂物集聚氢导致氢致裂纹，板材中心部位因偏析产生的少量马氏体、贝氏体组织导致轧后应力集中，在冷却速度较快的条件下产生微裂纹，最终造成探伤缺陷。通过计算得知MnS夹杂物前端的氢陷阱中氢的浓度远高于陷阱中氢的最大饱和浓度，过剩的氢造成裂纹。采用铸坯及板材轧后缓冷等措施，使板材探伤合格率大幅度提高。
By analyzing the low qualified percent of low alloy steel medium plate by ultrasonic detection, the research on macrostructure, microstructure, SEM and fracture are carried out. The results showed that the defects in steel plate were mainly caused by higher content of [H] and serious centerline segregation in plate. Aggregation of hydrogen near the stripy MnS inclusion led to the hydrogen induced crack，and the martensite and bainite produced due to the central segregation in plate led to the increase of the stress concentration which induced the crack under the condition of rapid cooling after rolling. It was learned from the calculation that the hydrogen concentration in the hydrogen trap at the front of stripy MnS inclusion was higher than the maximum saturated concentration in the hydrogen trap, so that cracks were created. The percent qualified by ultrasonic test were greatly increased by slow cooling both of slab and medium plate after rolling.
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