用扫描电子显微镜（SEM）对微观结构进行了表征，试样分别取自平板的亚表面、t/4和t/2位置。采用机械研磨、抛光、4% nital溶液腐蚀的制备SEM纵向横截面试样，使用Zeiss Ultra-55扫描电子显微镜金相显微镜进行显微组织观察。

The microstructure was characterized by scanning electron microscope. Samples were taken from the subsurface, T/4 and T/2 positions of the plate respectively. The SEM longitudinal cross section samples were prepared by mechanical grinding, polishing and etching with 4% nital solution, and the microstructure was observed by Zeiss Ultra-55 scanning electron microscope and metallographic microscope.