Study On The Heat Treatment Of Substrate Materials Of Composite Cold-work Die Steel

Early failure of high alloyed steel such as tipping, rupture etc. due to the segregation of carbides was successfully overcome with the development of composite cold-work die steel (CCWMS) in recent year, the service life of the dies was therefore prolonged.At present, the blade of CCWMS is usually made of widely used high alloyed cold-work die steel namely high chrome steel and high speed steel, which are usually carbides segregation free.There are three basic requirements for the substrate materials of CCWMS, i.e. 1) it should has sufficient strength and hardness to support the faceplate after heat treatment together with the faceplate; 2) it should has enough hardenability; 3) it should be relatively cheap.Among all the existing steels, structural alloy steel has favourable strength and ductility, high hardenability and low price. For the reason of which, the purpose of this paper is to study whether structural alloy steel can be used as the substrate materials of CCWMS.In this paper, 4 kinds of structural alloy steels 42CrMo, 5CrMnMo, 60Si2Mn and 50CrMnV which are commonly used in industry were selected as objects.The mechanical properties and microstructure of these 4 kinds of steels after high temperature quenching followed tempering were investigated through tensile test, bending test, impact test, hardenability examination, metallographic analysis, fractography and transmission electron microscopy.The results show that high temperature quenching has no significant influence on the mechanical properties of structural alloy steel. The tensile strength of all above mentioned steels decreases slightly with the elevating of quenching temperature, but the value of which keeps higher than 1000 MPa all the while. These steels demonstrate high hardness after low temperature tempering which is up to about 50HRC, in case of high temperature tempering, the hardness of all the steels is 40HRC or so. Therefore, the strength and hardness all can meet the requirement of substrate of CCWMS. After high temperature quenching, the plasticity and ductility are much higher than the blade materials, and the reduction of area after high temperature tempering are all above 20%, so the plasticity and ductility can meet the the requirement of substrate of CCWMS as well.The microstructure coarsens with the elevating of quenching temperature which results in the worsening of mechanical properties, but the amount of lath martensite increases and the primary substructures changed to high density dislocations, thus, the ductility of these structural alloy steels is not influenced significantly after high temperature quenching.