Effect Of Mechanical Properties On Repetitive Impact Wear Behavior Of Mold Steels

The surface of molds will be subjected to frequent dynamic load impacts during service,which will alter the surface dimensional accuracy of the molds and reduce the surface quality of machine parts,failing the production requirements.The dynamic load impact wear has become one of the important reasons for the mold failure.Therefore,mold steel is not only required to have good toughness and high fatigue resistance,but also to have good impact wear resistance.Different heat treatment processes have an important influence on the anti-wear performance of metallic material.In order to study the influence of hardness and toughness on the impact wear resistance of mold steel,25Cr3Mo2 Ni WV new mold steel was taken as the research object in this paper.The samples with different mechanical properties were obtained by tempered at different temperatures.Then the microstructure and fracture morphology were observed with the changes of tempering temperature.The impact wear experiments were carried out by the MLD-10 wear testing machine.Analytical balance,optical microscope,electron microscope and micro-hardness tester analyzed the weight loss,wear surface morphology,cross-section crack morphology and work hardening phenomenon of 25Cr3Mo2 Ni WV steel after wear test.The wear behaviors and failure modes of 25Cr3Mo2 Ni WV steel treated with different tempering temperatures under dynamic impact were systematically studied.The effect of hardness and toughness on the impact wear performance and mechanism of25Cr3Mo2 Ni WV steel was analyzed.In order to study the impact and wear performance comparison of several materials with the same hardness,30 Si Mn2Mo V steel and H13 steel were tempered at specific temperatures,followed by the comparative impact experiment at the same wear conditions.The results are shown below.1.Within the tempering temperature range set in this experiment,as the tempering temperature increased,the hardness of the test steels decreased and the toughness increased;the 25Cr3Mo2 Ni WV steel showed the secondary hardening phenomenon at 550?,and the hardness was the highest.2.The microstructure and fracture morphology of the test steels changed with the tempering temperature.The microstructure of 25Cr3Mo2 Ni WV steel was tempered martensite at 300?,tempered troostite at 500?600?,and tempered sorbite at 680?,the secondary carbides of 25Cr3Mo2 Ni WV steel tend to grow up during hightemperature tempering,and the fracture mode at room temperature changed from quasi cleavage fracture to ductile fracture.3.In the process of impact wear,the weight loss of test steel increased continuously with the increased of wear time,the dominant wear mechanisms of all tempered steels varied from the slight plastic deformation to micro-cutting and adhesive wear,finally to micro fatigue peeling wear.4.Hardness and toughness have an important influence on the impact wear resistance of the test steels.The better the combination of hardness and toughness,the smoother the impact wear surface,the less obvious the fatigue peeling phenomenon,and the better the impact wear resistance.The impact wear resistance of25Cr3Mo2 Ni WV steel tempered in the temperature range of 500??600? was the best.5.After the impact wear test,the different degrees of plastic deformation and work hardening occurred on the impact surface of test steels and the work hardening of the H13 steel was the most obvious after impact,and the surface metal with higher hardness played a certain role of wear resistance.High strain concentration band appeared in local area of H13 steel surface.6.Three types of cross-section damage states occurred in the test steels after impact wear: Brittle fatigue cracks appeared in the impact section of the specimen with higher hardness and lower toughness.Ductile fatigue crack occured in the impact section of the specimen with lower hardness and higher toughness.After the impact test,the surface metal of the high temperature tempered specimens of25Cr3Mo2 Ni WV and 30 Si Mn2Mo V steel collapsed and extruded along the crack,resulted in the great wear loss.The coarse carbides in 30 Si Mn2Mo V steel promoted the initiation of microcracks and deteriorated the impact wear resistance of materials.