某一材料未知的液压扳手驱动板在与活塞杆接触的部位发生断裂，通过理化检验对该驱动板的断裂原因进行了分析，并提出了改进措施。结果表明：该驱动板材料为X2NiCoMo18-8-5马氏体时效钢；驱动板发生了疲劳断裂，驱动板与活塞杆接触部位产生擦痕，形成应力集中，在受到活塞杆作用时，擦痕处进一步扩大形成裂纹源，使用中裂纹不断扩展最终导致断裂；建议加大液压扳手驱动板与活塞杆接触部位棱角的弧度，保证接触部位光滑并正确装配活塞杆，以避免产生擦痕。

A hydraulic wrench driving plate of unknown material fractured at the contact part with the piston rod. By the physical and chemical analysis, the fracture cause of the driving plate was analyzed and the improvement measures were proposed. The results show that the material of the driving plate was X2NiCoMo18-8-5 maraging steel. A fatigue fracture of the driving plate occurred. The scratches were produced at the contact part of the driving plate with the piston rod, resulting in the stress concentration, and the crack source was further formed at the scratches under the force of piston rod. And then the cracks propagated continuously, finally leading to the fracture. It was suggested to increase the edge radian of the contact part between the hydraulic wrench driving plate and the piston rod, make the surface of the contact part smooth and assemble the piston pod correctly to avoid the scratches.