Development Of High - Performance H13 Mandrel For Speed - Regulating Mandrel Bar Rolling Mill

Mandrel is an important tool for thermal deformation of the seamless steel tube rolling unit. It requires high heat resistance and toughness due to its application in the harsh environment. H13steel is commonly used as mandrel materials with excellent comprehensive performance.It has been reported that the addition of Nb in H13can successfully increase heat resistance and optimizing H13compositions can improve the impact toughness. The purpose of the work is to contrast analyze the difference between H13-Nb (addition of Nb), H13, and H13-L (optimization of composition). The different segregation, primary carbides, structure between large size H13-Nb, H13and H13-L mandrel were investigated by employing methods of OM, SEM, EDS, EBSD, TEM, and the mechanical properties including the hardness, impact toughness and tensile test were measured at room temperature. The results show that:(1)Mandrel of H13-Nb, H13, and H13-L was deal with the same smelting condition, high temperature diffusion forging production and annealing process. The segregation of H13basically eliminated. Addition of0.06%Nb aggravates segregation compared with H13. Nb increases the precipitation temperature of MC-primary carbides, and changes the type of MC-primary carbides from mainly VC to mainly (Nb, V)C which easily induces gravitational segregation of H13-Nb. Lower Si prompted network connecting band segregation and optimization the composition decrease the primary carbide of H13-L(2)Combining the experimental curve rule of quenching temperature-hardness, quenching temperature-grain size, tempering temperature-hardness and performance requirements actually used, optimum treatment process of mandrel of H13-Nb, H13, and H13-L was at1030℃quenching,640℃tempering twice.(3)The severe segregation leads to unfavorable structure of the large and nonhomogeneous effective grain size(EGS) of annealed H13-Nb, and the primary carbides do not decrease or change significantly after quenching and tempering, resulting in low toughness and plasticity. The banded segregation of H13-L improved after quenching and tempering, organization was relatively homogeneous. Due to less liquid chromatography carbide, toughness and plasticity improved greatly.