Microstructure Regulation And Performance Optimization Of New Hot Working Die Steel

The hot work die steel is mainly used to manufacture hot forging dies,hot extrusion dies,die-casting dies and hot upsetting dies that need to bear high loading,thermal shocks and thermal wear during service.These dies are widely used in aerospace,new energy vehicles,rail transit and other industries.With the rapid development of modern industry,the most widely used H13 steel cannot match the existing service conditions due to the poor thermal strength above 600°C.Therefore,a new type of hot work mold steels with the high temperature performance of the mold for prolonging the service life of the mold is urgently needed in the mold industry.Based on the composition of H13 steel,a new HBJ3 steel was designed by alloy optimization,that is,reducing the Cr content,increasing Mo content,and adding W.The mechanical properties,high temperature strength and wear properties of H13 steel were characterized at room temperature,and the relationship model between microstructure and service performance was established.The main conclusions are as follows:（1）It can be seen from thermodynamic calculation that in HBJ3 steel,the dissolution temperature of M₂₃C₆ carbide decreases,and the dissolution temperature of MC increases,together with the increase of precipitation of M₆C type equilibrium carbides.Compared with H13 steel,the volume fraction of stable MC and M₆C alloy carbide increases,leading to an appropriate increase in quenching and tempering temperature in HBJ3 steel.（2）The hardness of HBJ3 steel increases with the increase of quenching temperature.Compared with the maximum hardness of H13 steel at 1100℃,the hardness of HBJ3 steel at1160℃has not reached the maximum value.At the same quenching temperature,the original austenite grain sizs of HBJ3 are finer.（3）The tempering softening resistance of HBJ3 steel is obviously better than that of H13 steel.The hardness of HBJ3 steel tempered at 600℃and 650℃is 52 HRC and 45 HRC respectively,which is 10 HRC and 18 HRC higher than that of H13 steel.With the prolongation of holding time at 600℃,the carbide growth rate of HBJ3 steel is slow,and the fine carbide precipitates and disperses in the matrix,which makes HBJ3 steel maintain a high hardness of 45 HRC after holding at 600℃for 48 h.（4）When the service temperature exceeds 600℃,the high temperature strength of HBJ3steel is obviously better than that of H13 steel.The undissolved carbides in HBJ3 steel can prevent the germination and propagation of cracks,thus improving the high temperature tensile strength and dimensional stability.At 650℃,the tensile strength of HBJ3 steel is 735 MPa,which is increased by 52%.At 700℃,the tensile strength of HBJ3 steel is 400 MPa,which is more than twice that of H13 steel.（5）The wear resistance of HBJ3 steel is better than that of H13 steel.The higher oxidizability of HBJ3 steel is beneficial to the formation and growth of oxide layer at high temperature.Compared with H13 steel,the transformation of HBJ3 steel from mild oxidation wear to severe oxidation wear is delayed.