Mandrel is one of the most important tools to produce large-diameter seamless steel pipe in modern tech.Because of the poor circumstance of the rolling process of seamless steel pipe,mandrel in the rolling process has to withstand large and complex stretching, high temperature thermal fatigue stress, so the requirements of the chemical composition, mechanical properties, non-metallic inclusions, grain size, microstructure, ultrasonic testing, dimensional accuracy, roughness etc is crucial. We mainly use H13 (4Cr5MoSiV1) material,mandrel quality and service life have reached the international advanced level of similar products, with an annual capacity of 15,000 tons .