The Feasibility Study Of Hot Stamping Process For TRIP780 High Strength Steel

The development of the hot stamping technology has satisfied the people's increasing requirements of the weight reduction and safety.At present,the boron steel has been widely used in automotive safety parts as a hot-stamping-steel,however,the boron steel has transformed into the full martensitic structure which brings the problem of low elongation.In order to solve this problem,other high strength steels have been studied for the hot stamping with high strength and high plasticity.The existing TRIP steel is usually deformed via the cold forming technology,and the strength of final products is close to raw materials.Although the TRIP steel has entered the rank of high strength steels,the strength of the TRIP steel is usually about 1/3 to 2/3 of the boron steel after hot stamping process,moreover,the springback is hard to be controlled during the cold forming process.In this paper,the high strength steel TRIP780 was studied for the feasibility of applying to the hot stamping process.The heat treatment process of different quenching rates was carried out by the thermal simulation testing machine.The results after macro mechanical property tests were analyzed by combining with the microstructure observations qualitatively and quantitatively.Meanwhile,in order to study the comprehensive mechanical performance of TRIP steel for hot stamping products under different quenching rates,the Charpy impact experiments and three point bending tests were carried out after the fast quenching process and the slow quenching process,where the hot stamping steel B1500 HS was also introduced to compare.Since experimental conditions are hard to be controlled precisely during the actual process of hot stamping experiments,and those parameters of the hot stamping process are usually not fully met the thermal simulation experiment conditions.For this reason,actual hot stamping experiments for the U-shaped product were carried out for studying the processing suitability and the forming uniformity.Furthermore,the TRIP780 steel was applied into the quenching and partitioning process in order to get higher elongation,so as to verify the applicability of TRIP steel with high silicon content to the quenching and partitioning hot stamping process.And the thermal simulation experiment,three point bending tests,impact tests and the microstructure observation qualitatively and quantitatively were carried out to further study the hot stamping process of TRIP steel.Results obtained are as follows:1.The strength and elongation of TRIP steel are excellent for the full martensite transformation,where the strength is close to B1500 HS steel with the elongation and the product of strength and plasticity increasing by 87.57% and 80.16% respectively.2.With results of the Charpy impact tests and three point bending tests,the TRIP steel has the highest impact toughness and the smallest folding angle under the quenching rate of 40 ?/s,which represents the plastic is excellent.3.In the actual U-shaped hot stamping experiment,the TRIP steel has better hot stamping applicability and more uniform mechanical properties for different positions of U-shape parts than B1500 HS.4.Compared with the traditional hot stamping process,the TRIP steel after Q&P hot stamping process has a higher plasticity and toughness.Moreover,compared with B1500 HS,TRIP780 with higher silicon content is more suitable for quenching and partitioning hot stamping process.