针对某钢厂生产的38B3汽车用钢，探伤时发现棒材表面有纵向裂纹的现象，采用金相显微镜和扫描电镜对裂纹试样进行观察和分析，结果表明，38B3汽车用钢棒材表面纵裂纹的产生，主要是由于Al、Si、Na等氧化物夹渣分布于连铸坯的表层下面，在轧制过程中由于应力作用沿Al、Si、Na等氧化物夹渣集中处产生裂纹。通过采取相应的措施改善工艺以获得高质量的铸坯。

The phenomenon of the longitudinal crack was detected by ultrasonic test on the bar surface of 38B3 auto-motive steel. Metallographic microscope and scanning electron microscope were used to observe and analyze the crack sample. The oxide inclusions of Al, Si, Na were found to form mainly under the surface of the continuous casting billet. The crack was produced along the place where the oxide inclusions were concentrated by the stress during rolling. Some measures were carried out to improve the technique so that the casting billet with high quality could be obtained continuously.