Effect of Silicon on Retained Austenite Stabilization in Intercritically Annealed Steels

1. Effect of Silicon on Retained Austenite Stabilization in Intercritically Annealed Steels Erin E. Perry1,2, R. James Johnson1 and Emmanuel De Moor1 1Dept. of Metallurgy & Materials Science, Colorado School Of Mines, Golden, CO USA 2Dept. of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, MA USA Results: Tensile Properties Experimental Procedure Motivation Material Advanced high strength steels (AHSS) are attractive because of their strength and ductility, making them ideal for the automotive industry in order to improve fuel economy. www.cambodiavietnamholidays.com/Vietnam-Cars/ • Heat Treating • Calculated Fractions • Intercritical annealing temperatures were calculated using Thermo-CalcTM • Optimum quench temperature calculations were conducted using the Koistinen-Marburger equation and assuming “full” partitioning in the absence of carbide formation Conclusions One variety of AHSS is quenched and partitioned (Q&P) steels. Q&P steel processing involves reheating in the intercritical region or above the A3 temperature, followed by cooling to a carefully selected quench temperature that results in partial transformation of austenite to martensite. The steel is then isothermally partitioned at the quench temperature in order to allow carbon to diffuse from martensite to austenite, thus stabilizing it. Speer et al., 2003 The addition of silicon is believed crucial to retard cementite formation albeit the partitioning temperature range requiring Si alloying has not been detailed. Austenite stabilization via one-step Q&P is investigated here at three Si levels. • . Austenite was successfully stabilized in the Low Si alloy via one-step Q&P. • Intercritical ferrite fractions have a pronounced effect on the tensile properties: tensile strengths of 625-690 MPaand total elongation between 10 and 17% were obtained for the 50% intercritical ferrite microstructures whereas tensile strengths of 946to 1190 MPa and total elongations not exceeding 7% were obtained for the 25% intercritical ferrite containing microstructures. Results: Austenite Fractions Low Medium High 50% aint References Speer, J.; Streicher, A.; Matlock, D.; Rizzo, F. & Krauss, G.Damm, E., ed.,  (2003), Austenite Formation and Decomposition, Merwin, M., chapter Quenching and partitioning: a funamentally new process to create high strength TRIP sheet microstructures, pp. 505-522. Clarke, A. (2006). Carbon partitioning into austenite from martensite in a silicon containing high strength sheet steel. (Doctoral dissertation, Colorado School of Mines). Thomas, G. (2009). Simulation of hot-rolled advanced high strength sheet steel production using a gleeble system. (Master's thesis, Colorado School of Mines). 25% aint Acknowledgements This material is based upon work supported by the National Science Foundation and the Air Force Office of Scientific Research under Grant No. DMR-1062797 The input of the sponsors of the Advanced Steel Processing and Products Research Center, an NSF industry/university cooperative research center at the Colorado School of Mines is gratefully acknowledged. . Pt : 120s Data and Calculated Fractions