| The lightweight of automobiles has become a trend of automobile development.High-strength steel sheets are widely used to manufacture structural parts of automobile bodies,and hot stamping dies are also widely used in automobile industry production.The service life of the die is the decisive factor of the processing cost.Generally speaking,wear is a key factor affecting the life of hot stamping dies,so it is of great significance to study the friction and wear behavior of high-strength steel hot stamping dies.This paper studies the high-temperature friction and wear properties of high thermal conductivity die steels SDCM and H13 steel,reveals their potential wear mechanism,builds an Archard wear prediction model,and uses a numerical method to study the temperature evolution of the die during the automotive A-pillar cyclic hot stamping process Regularity and wear behavior,and predict the wear life of SDCM,H13 and HTCS-130 three hot stamping die steels;in order to further improve the high temperature wear resistance of the die and prolong the service life,the effect of plasma nitriding surface heat treatment on die wear is discussed.It is expected to provide a reference for the selection,design and optimization of the die in the automotive A-pillar cyclic hot stamping process.The main conclusions are as follows:(1)Under the service conditions of 200?300?,high thermal conductivity die material SDCM steel mainly suffers from adhesive wear and oxidative wear,while H13 steel suffers from oxidative wear,adhesive wear and severe abrasive wear.SDCM steel has a lower friction coefficient and Wear rate,and because of its lower Cr content,it shows lower oxidation resistance at high temperature,so it has more excellent high temperature wear resistance;(2)In the automotive A-pillar cyclic hot stamping process,when the die temperature is 25°C and the stamping speed is 200 mm/s,after 15 times stamping,the maximum wear depth of SDCM,H13 and HTCS-130 steel dies reaches 5.90×10-5 mm,20.8×10-5 mm and 24.8×10-5 mm,the predicted life is 168849,70009 and 53847pieces respectively.When the die material is SDCM steel,the predicted life is about twice and three times than H13 and HTCS-130 steels,the die can reach thermal equilibrium faster and keep at a lower temperature,which shows that SDCM die steel has better wear resistance and thermal conductivity,which can significantly extend the service life improve production efficiency;(3)After plasma nitriding,a continuous dense nitride layer composed of?-Fe2-3N and?'-Fe4N is formed on the surface of SDCM steel.The thickness of the nitriding layer is about 250?m,and its surface hardness reaches 70 HRC,which is higher than that of SDCM steel without nitriding.The hardness is increased by 132%;compared with the SDCM steel without nitriding treatment,the friction coefficient and wear rate of the SDCM steel after plasma nitriding are significantly reduced,and the high temperature wear resistance of the SDCM steel by plasma nitriding has a significant improvement effect;(4)The maximum wear depth of the SDCM steel die after plasma nitriding is significantly reduced.The predicted life is 336394 pieces.Compared with the predicted life of the SDCM steel die without plasma nitriding,the predicted life of68849 pieces,the service life is increased by about 50%.Plasma nitriding can further improve the high temperature wear resistance and service life of SDCM steel die. |
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