Effect Of Titanium Content On Microstructure And Properties Of New Hot Working Die Steel 4Cr5Mo SiV1Ti

The rapid development of mold industry and the demand for high efficiency and high precision production put forward higher requirements for the comprehensive performance of mold materials.As a typical hot work die steel,4Cr5MoSiV1 steel has excellent performance and wide application,however,with the improvement of the requirements of the parts and the more severe service conditions,the failure forms such as plastic deformation,cracking and thermal wear will appear in the service process of the material.Titanium microalloying technology can effectively improve the comprehensive mechanical properties of steel materials,and its application in the development of new steel materials is becoming more and more extensive,but the research in hot work die steel lacks relevant literature reports.In this paper,based on the composition of 4Cr5MoSiV1 steel,titanium microalloying technology is selected,and the composition of 4Cr5MoSiV1Ti steel is designed through JMatPro software,according to the calculation results,titanium microalloying hot working die steel is prepared by smelting.Through optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffractometer（XRD）to explore the effect of titanium content on the microstructure and carbides of4Cr5MoSiV1Ti steel,and explore the effect of titanium content on the mechanical properties and tempering stability of 4Cr5MoSiV1Ti.The optimal addition amount of Ti element in 4Cr5MoSiV1 steel is selected,then the 4Cr5MoSiV1Ti steel with the preferred composition was subjected to a high temperature hot compression experiment with a deformation temperature of 950～1150℃and a strain rate of0.01～10 s^-1 to analyze the deformation mechanism,high temperature deformation structure and instability characteristics,the constitutive equation and hot working diagram of 4cr5mosiv1Ti steel at high temperature are established.The conclusion of the study is as follows:1.JMatPro software simulation calculation results show that:4Cr5MoSiV1 steel and 4Cr5MoSiV1Ti steel tempering process exist in M₂₃C₆,M₂（C,N）,M（C,N）,M₆C and other precipitation phases,among them,M₂₃C₆ and M₂（C,N）carbides have the largest volume fraction,which is the main precipitation phase,and the remaining phases are all below 0.100%;the suitable range of adding Ti element mass fraction is 0%to 0.600%,in this range,the carbide precipitated after quenching and tempering is small,which has a positive effect on improving the strength and hardness of4cr5mosiv1Ti steel.2.After the heat treatment process of 4Cr5MoSiV1Ti steel quenched at 1040℃+600℃′2 h+580℃′2 h tempered,its hardness and plasticity increased first and then decreased with the increase of Ti content.The reduction of area and elongation after fracture of 4cr5mosiv1Ti steel are higher than those of 4Cr5MoSiV1 steel.When the Ti mass fraction in the experimental range is 0.127%,the mechanical properties of4Cr5MoSiV1Ti steel are the best.When the Ti mass fraction is 0.127%,the tensile strength of 4Cr5MoSiV1Ti steel at room temperature reaches 1788 MPa,which is 264MPa higher than that of 4Cr5MoSiV1 steel;the hardness reaches 51.5 HRC,which is3.7 HRC higher than that of 4Cr5MoSiV1 steel;the shrinkage rate of section is increased by 35.0%of 4Cr5MoSiV1 steel to 47.0%.3.When the Ti mass fraction is 0.127%,the microstructure of 4Cr5MoSiV1Ti steel is a mixed structure of tempered troostite and tempered sorbite.The tempered martensite lath bundle is smaller than that of 4Cr5MoSiV1 steel without titanium,and the alloying element Ti has the effect of refining tempered martensite.The precipitated carbides in the structure are mainly Cr-rich M₂₃C₆ and M₇C₃,V₂C hard carbides,Mo-rich MC,M₂C,M₃C₂ carbides,there are many kinds of hard carbides in the structure.4.The trace element Ti improves the tempering stability of 4Cr5MoSiV1 steel below 640℃when the mass fraction is 0.044%and 0.127%,and after tempering at high temperature（700℃）,the addition of Ti element increases the high temperature tempering of 4Cr5MoSiV1 steel hardness.5.4Cr5MoSiV1Ti（0.127%）steel is a temperature and strain rate sensitive material,there is a multi-peak rheological curve when the strain rate is 10 s^-1.The thermal deformation activation energy of 4Cr5MoSiV1Ti steel is 560.49 KJ/mol,and the safe area for stable hot processing is:deformation temperature 1080～1150℃,strain rate 0.01～1 s^-1.