Study On Air-Cooled Q&P Process Of Ultra-High Strength Hot Formed Steel Sheet

In the automobile lightweight background,replace traditional automotive steel with third generation advanced high strength steel(AHSS)in automobile structure,make the weight of automobile reduced 20 percent.But structure safety recommends the new generation of automobile steel exist excellent mechanical performance,good energy absorption characteristics in collision,and the product of strength and elongation(PSE),which indicator of mechanical performance,need reach to 20.0GPa·% and above.these recommends the material have the high strength performance and maintain well plasticity and tenacity.The Q&P heat treatment process,based on the transformation induced plasticity effect of austenite and martensite-austenite duplex theory,could make the well balance of strength and plasticity exist in traditional high strength steel using in hot forming.This paper combined the new quenching technology of air cooling and Q&P heat treatment process,with self-designed accuracy-controlled air-cooled quenching platform,researched the air-cooled Q&P heat treatment process.The purpose of new process reaching is improve PSE in traditional automobile high strength steel to reach the mechanical performance requirement of the third generation AHSS and provide the theoretical foundation and the solution project for the industry.This paper takes 22MnB5,the automobile ultra-high strength steel,as research object,calculated the beat quenching temperature in Q&P process with CCE model and empirical calculating formula.The microstructure and the rule of mechanical performance in different partitioning temperature and time is researched with accuracy-controlled air-cooled quenching platform.Research The stability of retained austenite after air-cooled quenching and partitioning process.Review the next result:According to the theoretical quenching temperature model,designed the air-cooled quenching and partitioning process experiment project,based on the one step quenching and partitioning process,and research the microstructure after quenching and partitioning process.the result shows that,the microstructure of hot forming in room temperature,after air cooled quenching and partitioning process,is lath martensite with filmy,blocky,and granular retained austenite,which mechanical performance improved a lot when compared with normal quenching hot forming steel.In the partitioning temperature is 270? and the partitioning time is 90 s condition,the tensile strength is 1359 MPa,the elongation is 15.9% and the PSE reach 21.76GPa·%.in the partitioning temperature is 300? and the partitioning time is 30 s condition,the tensile strength is 1410 MPa,the elongation is 15.7% and the PSE reach 22.14GPa·% which have best mechanical performance and the PSE is much higher than the normal quenching 10.79GPa·%.the microstructure,after air-cooled Q&P process,is martensite and retained austenite,the max content of retained austenite is 7.1wt.% and the min is 2.8wt.%,the average carbon content in retained austenite is 1.1wt.%.when the specimen was broken by stretch,and the average carbon content is 1.49 wt.%,it can prove that with the method of Q&P process combined with air cooled quenching could improve the stability of retained austenite and the PSE.The above experiment result shows that,the combined air-cooled Q&P heat treatment process,experiment in self-designed accuracy-controlled air-cooled quenching platform,as a new method of Q&P process for hot forming steel,could improve the PSE of automobile high strength steel effectively.The new process have the advantages of accuracy controlled cooling process,easily to operate,wildly used,which have excellent huge potential and application in prospect in automobile steel plate production industry.