Study On The Process Of Partitioning-Hot Stamping Of The Steel With The High Product Of The Strength And Ductility Applied To Automobile

Developing the new high-strength steel is an effective way to lighten automobile’sweight and it is also a primary method to deal with the problems of safety, society andenvironment. In this study, based on a new kind of steel which applied to automobile,Hot Stamping-online Partitioning (HS-OP) and Hot Stamping-Dynamic Partitioning(HP-DP) process were presented to simplify the hot-stamping process. Heat treatmentexperiment was carried out in the salt bath furnaces instead of quenching andpartitioning process in dies. For HS-OP process, this paper focused on researching theeffects of different parameters of quenching and partitioning (Q&P) process (such asquenching temperature, partitioning temperature and partitioning time) on mechanicalproperties and microstructure of the steel, and got the optimal parameters. At the sametime, the effects of different parameters of Q&P process on dynamic mechanicalproperties, microstructure and energy absorption characteristic of the steel were alsostudied. For HP-DP process, this study investigated the effects of quenching mediumand cooling rate on mechanical properties and microstructure of the steel. Mainconclusions are drawn as follows:Q&P process has great influences on mechanical properties and microstructure ofthe hot-stamping steel. The results showed that good performance of the steel can beobtained and the product of strength and ductility can reach20088MPa%after beingquenched at240℃and partitioned at360℃with60s. The lath martensite, bulkmartensite and retained austenite were obtained through the Q&P process. The energyabsorption characteristic and mechanical properties under dynamic loading weredifferent from these under static loading. The optimum energy absorption characteristicof the steel was got by quenched at240℃and partitioned at330℃with60s, underdynamic loading, and grains of martensite were stretched. But the type and structurewere the same as before. The phenomenon of dynamic partitioning was took place whenthe steel quenched in the appropriate quenching medium and the elongation and theproduct of strength and ductility of the steel were obviously increased. And cooling ratebetween Msand Mfwas the key factor to affect the mechanical properties andmicrostructure of the steel. The microstructure of the steel via dynamic partitioning wasthe same as the microstructure via the Q&P process. The conclusions above prove thatHS-OP and HP-DP process have the application prospects in industrial manufacturing.