Research On Mechanical Properties And Thermal Fatigue Properties Of New H13 Steel

As a high-end hot work die steel,H13 steel has excellent resistance to thermoplastic deformation,thermal fatigue resistance and ablation resistance,It is widely used in the manufacture of hot extrusion dies,hot forging dies,die-casting dies for aluminum,copper and their alloys,But there is also the problem of insufficient thermal strength at high temperatures,which also leads to its limitations.This paper compares the microstructure and thermal fatigue properties of ultra-fine H13 steel and new H13-1 steel after different heat treatment processes,Get the following conclusions:(1)Through the analysis of the structure and mechanical properties of the two experimental steels with different quenching temperatures and different tempering temperatures,The determined heat treatment process is: 1040?×40 min,oil quenching,600?×1h,air cooling and secondary tempering.After this process,the grain size of H13-1 experimental steel is smaller than H13 steel,And the grain shape is uniform,Its average grain size is 80?m.The hardness of the H13 and H13-1experimental steels at room temperature are 44.3HRC and 45.8HRC respectively;The tensile strength and elongation after breaking are 1631.7MPa and 1837.5MPa;4.6% and 12% respectively;The impact absorption energy is 8.9J and 13.5J respectively;The high temperature tensile strength at 600? are 642.1MPa and748 MPa respectively.(2)In the thermal fatigue test,with the increase of the upper limit temperature,the crack initiation period shortens and the growth rate increases,and the cracks generally initiate preferentially at the V-shaped notch;Under the same experimental conditions,the thermal fatigue properties of H13-1 are better than those of H13 steel.The crack initiation time of H13 experimental steel is shorter than that of H13-1 experimental steel,and its growth rate mainly shows a trend of fast first and then slow,The crack growth rate of H13-1 experimental steel is slow,especially after 3500 cycles at 630?,the crack growth rate is very slow.The crack propagation of the two experimental steels was mainly transgranular in the early stage,and intergranular in the later stage.(3)After the same number of cycles,the number and size of carbides in the H13-1 experimental steel are significantly smaller than those in the H13 experimental steel.After many cycles,large-size(Cr,Fe,Mo)7C3 composite carbides were produced at the grain boundaries of the experimental steel,At the same time,the surface of the experimental steel will also form oxide Cr2O3,These carbides and oxides will fall off the surface of the experimental steel during the cycle,forming pits and accelerating the initiation of cracks.In different stages of thermal fatigue crack growth,strength and plasticity play different roles,The higher the strength,the better the ability to resist crack initiation;the better the toughness,the better the ability to resist crack propagation.