Research On Hot Stamping Process Parameters And Cooling System

The applications of ultra-high strength steel for automotive, not only lightened the carbody and reduced the fuel emissions, but also improved the bending rigidity and torsionalrigidity to ensure the safety of the whole vehicle. So that, ultra-high strength steel was usedmore widely in automobile manufacturing field. But it is hard to use traditional coldstamping process to form this type of steel, due to the high strength and its bad stampingproperty. Hot stamping is a new technology, especially used for forming ultra-high strenghsteel. The principle of hot stamping is that the boron alloy steel plate which tensile strengthis500MPa-600MPa at room temperature is heated to austenitizing temperature for a fewminutes, making sure that the microstructure is austenitized compeletly. And then send theplate into hot stamping tools with cooling channels inside, which can form the plate, at thesame time, the steel plate is quenched by the surface of the die. The high temperatureaustenite changed into lath martensite, which caused the strength greatly enhanced. Thestrength can reach to1500MPa or so.First of all, ultra high strength steel22MnB5with the thickness of2mm adopted forautomobile was selected for this study with the aid of metallographic microscope, Laserconfocal scanning microscope, SEM, tensile test enginery and microhardness tester, whichare aiming for analyzing the effect of the heating parameters of austenization on the materialgrain size, microstructures, average microhardness and tensile strength of ultra high strengthsteel. The tested results exhibited that the optimal heating parameters of austenization for22MnB5steel with the thickness of2mm were the temperature between900℃and950℃and the heating time of5min.Through finite element modeling and experimental research, we used the cooling system of the hot stamping tools for this study and studied the effect of the parameters of thecooling pipes on the workpiece’s cooling effect. The results concluded that when we couldsatisfy the requirements such as the die strength, manufacturing costs and processingfeasibility, the using of the cooling channel geometry parameters of the large diameter, smallsidewall spacing and small distance between the cooling pipe and the workpiece could makethe flow rate of cooling water in the pipe more uniform, cooling efficiency higher andcooling effect better. When we used the larger diameter pipe, smaller sidewall spacing andsmaller distance between the cooling pipe and the workpiece, the martensitic transformationwas more complete, the martensite lath was much smaller, and the mechanical propertiessuch as micro hardness and tensile strength were much better.