Influence of original microstructure on the transformation behavior and mechanical properties of ultra-high-strength TRIP-aided steel

Abstract

The transformation behavior and tensile properties of an ultra-high-strength transformation-induced plasticity (TRIP) steel (0.2C-2.0Si-1.8Mn) were investigated by different heat treatments for automobile applications. The results show that F-TRIP steel, a traditional TRIP steel containing as-cold-rolled ferrite and pearlite as the original microstructure, consists of equiaxed grains of intercritical ferrite surrounded by discrete particles of M/RA and B. In contrast, M-TRIP steel, a modified TRIP-aided steel with martensite as the original microstructure, containing full martensite as the original microstructure is comprised of lath-shaped grains of ferrite separated by lath-shaped martensite/retained austenite and bainite. Most of the austenite in F-TRIP steel is granular, while the austenite in M-TRIP steel is lath-shaped. The volume fraction of the retained austenite as well as its carbon content is lower in F-TRIP steel than in M-TRIP steel, and austenite grains in M-TRIP steel are much finer than those in F-TRIP steel. Therefore, M-TRIP steel was concluded to have a higher austenite stability, resulting in a lower transformation rate and consequently contributing to a higher elongation compared to F-TRIP steel. Work hardening behavior is also discussed for both types of steel.

Keywords

high strength steels / transformation-induced plasticity / phase transformations / mechanical properties / original microstructure / work hardening

References

[1] Zackay VF, Parker ER, Fahr D, Busch R. The enhancement of ductility on high-strength steels. Trans. ASM, 1967, 60(2): 252.

[2] Pereloma EV, Timokhina IB, Hodgson PD. Microstructure and mechanical properties of thermomechanically processed C-Si-Mn steels. Ironmaking Steelmaking, 2001, 28(2): 198.

[3] Ryu HB, Speer JG, Wise JP. Effect of thermomechanical processing on the retained austenite content in a Si-Mn transformation-induced-plasticity steel. Metall. Mater. Trans. A, 2002, 33(9): 2811.

[4] Jimenez-Melero E, van Dijk NH, Zhao L, Sietsma J, Offerman SE, Wright JP, van der Zwaag S. Characterization of individual retained austenite grains and their stability in low-alloyed TRIP steels. Acta Mater., 2007, 55(20): 6713.

[5] Zhu R, Li S, Karaman I, Arroyave R, Niendorf T, Maier HJ. Multi-phase microstructure design of a low-alloy TRIP-assisted steel through a combined computational and experimental methodology. Acta Mater., 2012, 60(6–7): 3022.

[6] Seong BS, Shin EJ, Lee YS Han CH, Kima YJ, Kim SJ. Effect of retained austenite and solute carbon on the mechanical properties in TRIP steels. Phys. B, 2004, 350(1–3): E467.

[7] Wang XD, Huang BX, Rong YH, Wang L. Microstructures and stability of retained austenite in TRIP steels. Mater. Sci. Eng. A, 2006, 438–440, 300.

[8] Blondé R, Jimenez-Melero E, Zhao L, Schell N, Brück E, Zwaag S v d, van Dijk NH. The mechanical stability of retained austenite in low-alloyed TRIP steel under shear loading. Mater. Sci. Eng. A, 2014, 594, 125.

[9] Zrník J, Muránsky O, Lukáš P, Nový Z, Sittner P, Horňak P. Retained austenite stability investigation in TRIP steel using neutron diffraction. Mater. Sci. Eng. A, 2006, 437(1): 114.

[10] Blondé R, Jimenez-Melero E, Zhao L, Wright JP, Brück E, van der Zwaag S, van Dijk NH. High-energy X-ray diffraction study on the temperature-dependent mechanical stability of retained austenite in low-alloyed TRIP steels. Acta Mater., 2012, 60(2): 565.

[11] Chiang J, Lawrence B, Boyd JD, Pilkey AK. Effect of microstructure on retained austenite stability and work hardening of TRIP steels. Mater. Sci. Eng. A, 2011, 528(13–14): 4516.

[12] Shen YF, Liu YD, Sun X, Wang YD, Zuo L, Misra RDK. Improved ductility of a transformation-induced-plasticity steel by nanoscale austenite lamellae. Mater. Sci. Eng. A, 2013, 583, 1.

[13] Zhang S, Findley KO. Quantitative assessment of the effects of microstructure on the stability of retained austenite in TRIP steels. Acta Mater., 2013, 61(6): 1895.

[14] Sugimoto K, Fiji D, Yoshikawa N. Fatigue strength of newly developed high-strength low alloy TRIP-aided steels with good hardenability. Procedia Eng., 2010, 2(1): 359.

[15] Sugimoto K, Kanda A, Kikuchi R, Hashimoto S, Kashima T, Ikeda S. Ductility and formability of newly developed high strength low alloy TRIP-aided sheet steels with annealed martensite matrix. ISIJ Int., 2002, 42(8): 910.

[16] Caballero FG, Allain S, Cornide J, Puerta Velásquez JD, Garcia-Mateo C, Miller MK. Design of cold rolled and continuous annealed carbide-free bainitic steels. Mater. Des., 2013, 49, 667.

[17] Maruyama H. X-ray measurement of retained austenite volume fraction. J. Jpn. Soc. Heat Treat., 1977 198.

[18] Dyson DJ, Holmes B. Effect of alloying additions on the lattice parameter of austenite. J. Iron Steel Inst., 1970, 208, 469.

[19] J. Univ. Sci. Technol. Beijing, 1995, 2(1)