Study On Microstructure And Properties Of Hot Stamping Die Steel After Surface Treatment

The hot stamping process of high-strength steel has attracted widespread attention.However,the hot stamping parts of high-strength steel are subject to abrasion during the punching process,the life of the blanking die is often less than 10,000 pieces,and the die will be scrapped due to wear.At present,the hot stamping parts of high-strength steel are mainly cut by laser.However,laser cutting consumes large energy,and the cost of laser cutting can account for about 50% of the production cost of the part,which greatly improves the high-strength steel.In order to improve the service life of blanking dies,this article chooses the advanced die steels 1.2343,1.2344,EX1,EX6,EX7 which were commonly used in the market.After soft-nitriding and soft-nitriding + PVD TiAlN of these five die steels,they were subjected to microstructure observation and performance testing to select punching die steels for the hot stamping parts of high-strength steel with better performance.This test is aimed at the problem that the life of blanking dies is generally short.After the surface treatment such as soft nitriding and soft nitriding + PVD TiAlN is performed on the die steels such as 1.2343,1.2344,EX1,EX6,EX7.The XRD,SEM,hardness,and abrasion tests were used to analyze the microstructure,hardness and friction and wear properties of the test die steel.At the same time,DEFORM-3D software was used to simulate the analysis of the quality of the die section and the wear of the die during the die punching process in order to find a way to obtain a high-quality punched section and increase the life of the die.The research shows that the surface hardness and wear resistance of the sample after soft nitridation have been greatly improved compared to the substrate.The maximum hardness of 3-2 sample is HV1405,the distribution gradient of microhardness is very poor,and the wear amount is the largest,being 0.0007 g;The minimum hardness of 5-2 sample is HV1006,the distribution gradient of microhardness is the best,and the wear amount is the smallest,being 0.0002 g.The brittleness grade of 1-2,4-2,and 5-2 mold steel samples is brittleness grade 1,the brittleness grade of 2-2 samples is grade 2,and the brittleness grade of 3-2 sample is grade 3.After soft nitriding+PVD TiAlN,the surface hardness and wear resistance of the sample have been greatly improved compared to the substrate.The maximum wear of 1-3 sample is 0.0004 g,and the minimum wear of 5-3 sample is 0.0001 g.According to the indentation test method performed on the Rockwell hardness tester,it can be known that the film-base bonding force of the 3-3 sample is HF4,The film-base bonding force of 1-3,2-3 and 4-3 sample is HF3.The film-base bonding force of 5-3 sample is HF1.This paper also uses the DEFORM-3D software to carry out an orthogonal test simulation analysis of the punching process.The cross-section quality of the punched parts and the wear of the die steel were studied under different conditions like the blanking clearance,the radius of the punch cutting edge and the initial hardness of the punch.According to the situation,it is concluded that the influence of three factors is as follows: die hardness>die clearance>die radius.By comparison,the optimal scheme is: the gap of the convex die is 0.14 mm,the radius of the fillet of the die is 4 mm,and the hardness of the mold is 89 HRC.The distribution map of the wear depth of the die shows that the most severely worn areas are concentrated at the corners of the die,and as the hardness of the die increases,the wear depth of the die decreases,so by soft nitriding the surface of the die steel + PVD TiAlN treatment can greatly improve the surface hardness of mold steel and prolong the service life of mold steel in actual use.