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采用超声波探伤,低倍、宏观断口、金相和扫描电镜检验方法,对低碳低合金钢板中白点缺陷进行了探讨。分析了钢板中白点缺陷的宏观特征和微观形貌。钢板在垂直板面方向轧制力的作用下,使处于钢板中心位置的白点缺陷平面平行于板面方向分布,混杂在疏松和偏析区中,以致造成在低倍酸浸试片上不易辨认。钢板中白点缺陷发生在珠光体条带粒状贝氏体区,钢板中白点裂纹使z向拉伸强度稍微降低,使z向塑性指标和冲击韧性值明显下降。超声波探伤配合水平断口观察是鉴定钢板白点缺陷的有效方法。加强冶炼中合金料烘烤,注意合成渣和喷粉料的干燥,以及确保钢坯缓冷,是消除白点的有效措施。
Ultrasonic flaw detection, low magnification, macroscopic fracture, metallographic and scanning electron microscopy methods were used to investigate the white point defects in low carbon low alloy steel. The macro features and microscopic morphology of white point defects in steel sheets were analyzed. Under the action of rolling force in the direction of vertical plate, the white flaw plane at the center of the steel plate is distributed parallel to the plate surface and mixed in the loose and segregation zone, so that it is not easy to identify on the low acid leaching test plate. White point defects in the steel plate occurred in the granular bainite zone of the pearlite bands. The white point cracks in the steel plate slightly decreased the tensile strength in the z direction, resulting in a marked decrease in the z-direction plasticity index and the impact toughness value. Ultrasonic flaw detection combined with the level of fracture observation is an effective method to identify white spot defects. Strengthen the smelting alloy material baking, pay attention to the synthesis of slag and powder spray drying, and to ensure slow billet, is an effective measure to eliminate white spots.