Mandrel bar plays a crucial role in producing large diameter seamless pipes in modern industries. In production line, it have to bear strong and complicate stretch, compressing touching stress and high temperature cold-hot yield stress under high speed cycling. Under these circumstance, chemical components, mechanical propertied, no-metallic inclusion, grain size, microstructure, ultrasonic test, size precision, surface finish, all these factories of steel are required very strictly. Mandrel bar is made from H13(4Cr5MoSiV1).