Abstract
The microstructure of steels treated by Q&P (quenching and partitioning) process was characterized, a method of controlling retained austenite fraction based on inhomogeneous martensitic transformation was proposed, and the mechanical properties of steels treated by Q&P process were measured. The results show that the microstructure of the studied steels is mainly composed of initial martensite, fresh martensite and retained austenite. The initial marteniste formed at the first quenching step is easily etched; the fresh martensite formed at the final quenching step looks like ‘blocky’ type phase, and the retained austenite is mainly located on the packet boundary and initial austenite grain boundary. The inhomogeneous microstructure causes the experimental optimum quenching temperature corresponding to maximum retained austenite fraction to be higher than the calculation based on CPE (constrained paraequilibrium) model. The product of tensile strength and total tensile elongation is 47. 5 GPa%, and tensile strength of 1760 MPa was obtained for the steel with carbon content of 0.51 wt%. The TRIP (transformation induced plasticity) effects of the large fractioned metastable austenite make a main contribution to the high ductility improvement, and the martensitic matrix provides high strength.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Heimbuch R. Overview: Auto/Steel partnership, www.a-sp.org
Wang C Y. Investigation on 30 GPa% grade ultrahigh-strength martensitic-austenitic steels. Degree of doctor dissertation. Beijing: Central Iron & Steel Research Institute, 2010
Wang C Y, Shi J, Cao W Q, et al. Investigation on 30 GPa% grade ultrahigh-strength martensitic-austenitic steels. Proceedings of International Conference on Advanced Steels, 2010, Guilin
Matlock D K, Bräutigam V E, Speer J G, et al. Application of the quenching and partitioning (Q&P) process to a medium-carbon high Si microalloyed bar steel. Mater Sci Forum, 2003, 426–432: 1089–1094
Edmonds D V, He K, Rizzo F C, et al. Quenching and partitioning martensite a novel steel heat treatment. Mater Sci Eng A, 2006, 438–440: 25–34
Speer J G, Streicher A M, Matloch D K, et al. Quenching and Partitioning: A Fundamentally New Process to Creat High Strength Trip Sheet Microstructure, Austenite Deformation and Decomposition. Damm E B, Merwin M, eds. Warrendale, PA: ISS/TMS, 2003. 502–522
Wang C Y, Shi J, Cao W Q, et al. Study on the martensite in low carbon CrNi3Si2MoV steel treated by Q&P process. Acta Metall Sin, 2011, 47(6): 720–726
Chen S, Yu H. Investigation on martensitic steel using a quenching-partitioning-tempering process via electron backscatter diffraction analysis. Sci China Tech Sci, 2011, 55(3): 646–651
Hsu T Y. Martensitic Transformation and Martensite. 2nd ed. Beijing: Science Press, 1999. 23
van der Zwaag S, Zhao L, Suzelotte O. et al. Thermal and mechanical stability of retained austenite in aluminum-containing multiphase TRIP steels. ISIJ Int, 2002, 42(12): 1565–1570
Sugimoto K, Noboru U, Mitsuyuki K. Effects of volume fraction and stability of retained austenite on ductility of TRIP-aided dual-phase steels. ISIJ Int, 1992, 32(12): 1311–1318
Wang C Y, Shi J, Cao W Q, et al. Characterization of microstructure obtained by quenching and partitioning process in low alloy martenstic steel Mater Sci Eng A, 2010, 527: 3442–3449
Wells C, Mehl R F. Rate of diffusion of carbon in austenite in plain carbon, in nickel and in manganese steels. Trans AIME, 1940, 140: 279–306
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Wang, C., Zhang, Y., Cao, W. et al. Austenite/martensite structure and corresponding ultrahigh strength and high ductility of steels processed by Q&P techniques. Sci. China Technol. Sci. 55, 1844–1851 (2012). https://doi.org/10.1007/s11431-012-4875-9
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11431-012-4875-9