Study On The Microstructure And Mechanical Properties Of 7Cr4Mo3W2V1 Hot Work Die Steel

The hot working die steel mainly works under high temperature conditions,which is subjected to the effect of quick heating and cooling and repeated mechanical load.If the mechanical properties of high temperature strength,wear resistance and thermal stability of hot working die steel are not enough,deformation and cracking can on the die,which affect accuracy of die and even scrap the die.It is difficult to meet the demands of die when the temperature is above 600 ? for the current hot working die steel,such as H13,5CrNiMo and 5CrMnMo.Therefore,we urgently need to develop a new type of hot working die steel to improve the high temperature performance and the service life of the die.In this paper,7Cr4Mo3W2V1 hot working die steel was developed.The effects of different heat treatment processes on the microstructure,hardness,impact properties,thermal stability,high temperature strength of hot working die steel were studied.Compared with the widely used H13 steel,we can draw the following conclusions:1.The quenching hardness of tested steel reachs peak walue of 61.9HRC at 1150? and is 3.3HRC higher than that of H13 steel.The Undissolved carbides is not dissolved completely even at 1120? and plays the role of pinning grain boundary.The average grain size of the tested steel after quenching at 1120? is 9.4?m which is 35.5?m smaller than that of H13 steel.2.The tempering hardness of tested steel increases with the increasing of quenching temperature at same tempering temperature.The hardness of the tested steel tempered at 620? reaches 51.3HRC,while the hardness of H13 steel is only 39.6HRC.3.The impact energy of the tested steel firstly declines and then upward with the increase of tempering temperature,and the lowest value of impact energy appears at tempering temperature for 510?.This is mainly due to the secondary hardening and Tempering softening.4.The thermal stability of tested steel improves with the increasing of quenching temperature.After temperature of 650? for 24 h,the hardness of the tested steel quenched at 1120? can still reach 34.1HRC,which is 4.5HRC higher than that of the tested steel quenched at 1030? and is 8.7HRC higher than that of H13 steel.5.Increasing quenching temperature can improve the high temperature tensile strength of tested steel.When the tensile temperature is 650?,the tensile strength and yield strength of the tested steel quenched at 1120? reach 912 MPa and 630 MPa,which are 169 MPa and 138 MPa higher than that of tested steel quenched at 1030? respectively.6.The best thermal stability,high temperature strength and comprehensive mechanical properties of 7Cr4Mo3W2V1 can be obtained at 1120?+620? heat treatment process in the paper.