Design,Manufacture,Microstructure And Properties Of A New Type Of Nitrogen Bearing Hot Work Die Steel

Hot work die steel is mainly used in making mold for pressing solid metal that were heated above recrystallization temperature or high temperature liquid metal.Due to the lack of strength and toughness of steel,molds could notsuffer from high temperature when used,thus lead to local collapse and fracture and results in failure.Therefore,a higher standard for strength and toughness of hot work die steel is necessary.Comparing to foreign products,domestic hot work die steel has lower cleanliness and high temperature strength,a shorter service life and less steel grades,which calls for developing new hot work die steel with excellent performances.There are two methods in developing new hot work die steel,optimizing the component of steel or improving its production engineering process.This study calculates the effect of different content of C,Cr and N on equilibrium phase of new nitrogenous hot work die steel ZX007(3Cr7Mo2NiSiVN),thus providing support for composition optimization design and improvement of heat treatment engineering.In this study,the ZX007 steel was melted by "VIM+ESR",and the continuing cooling transformation curve(CCT curve)of new ZX007 steel was measured.It is discovered that new ZX007 steel is low-carbon lath martensitic steel with excellent hardenability.It can be seen from the CCT curve that ZX007’s ACt is 863℃,Ac3 is 954℃,Ms is 310℃,Mr is 160℃.Under different cooling velocity,with the final microstructure of only uniform Martensite,it is a Martensite hot work die steel.The microstructure and properties of hot work die steel are largely determined by heat treatment system.It is discovered in this study that after ZX007 steel went through fire quenching of 1080℃ and double tempering heat treating of 500～600℃×2 h,the quenching martensite decomposed,in the meantime,ZX007 steel has an excellent comprehensive mechanical properties.Comparing to H13 and ASSAB8407,ZX007 steel has better impact and tensile properties.It has a good application prospect in hot work die steel field.