Effects of pre-strain and baking parameters on the microstructure and bake-hardening behavior of dual-phase steel

Abstract

In a typical process, C-Mn steel was annealed at 800°C for 180 s, and then cooled rapidly to obtain the ferrite-martensite microstructure. After pre-straining, the specimens were baked and the corresponding bake-hardening (BH) values were determined as a function of pre-strain, baking temperature, and baking time. The influences of pre-strain, baking temperature and baking time on the microstructure evolution and bake-hardening behavior of the dual-phase steel were investigated systematically. It was found that the BH value apparently increased with an increase in pre-strain in the range from 0 to 1%; however, increasing pre-strain from 1% to 8% led to a decrease in the BH value. Furthermore, an increase in baking temperature favored a gradual improvement in the BH value because of the formation of Cottrell atmosphere and the precipitation of carbides in both the ferrite and martensite phases. The BH value reached a maximum of 110 MPa at a baking temperature of 300°C. Moreover, the BH value enhanced significantly with increasing baking time from 10 to 100 min.

Keywords

dual-phase steel / pre-strain / baking treatment / microstructure / hardening

References

[1] Kang YL. Theory and Technology of Processing and Forming for Advanced Automobile Steel Sheets, 2009, Beijing, Metallurgical Industry Press, 230

[2] Dong HF, Li J, Zhang Y, Park JK, Yang QX. Numerical simulation on the microstress and microstrain of low Si-Mn-Nb dual-phase steel. Int. J. Miner. Metall. Mater., 2010, 17(2): 173.

[3] Cai YH, Wang C, Zhang JS. Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy. Int. J. Miner. Metall. Mater., 2013, 20(7): 659.

[4] Waterschoot T, De AK, Vandeputte S, Cooman BC D. Static strain aging phenomena in cold-rolled dual-phase steels. Metall. Mater. Trans. A, 2003, 34(3): 781.

[5] Timokhina IB, Pereloma EV, Ringer SP, Zheng RK, Hodgson PD. Characterization of the bake-hardening behavior of transformation induced plasticity and dual-phase steels using advanced analytical techniques. ISIJ Int., 2010, 50(4): 577.

[6] Chang PH. Temper-aging of continuously annealed low carbon dual phase steel. Metall. Trans. A, 1984, 15(1): 73.

[7] Xie LL. The Bake Hardening and Formability Research of Advanced High Strength Steel, 2012, Beijing, University of Science and Technology Beijing, 20

[8] Cottrell AH, Bilby BA. Dislocation theory of yielding and strain ageing of iron. Proc. Phys. Soc. A, 1949, 62, 49.

[9] Zhao JZ, De AK, De Cooman BC. Formation of the Cottrell atmosphere during strain aging of bake-hardenable steels. Metall. Mater. Trans. A, 2001, 32(2): 417.

[10] De AK, De Blauwe K, Vandeputte S, De Cooman BC. Effect of dislocation density on the low temperature aging behavior of an ultra low carbon bake hardening steel. J. Alloys Compd., 2000, 310(1–2): 405.

[11] Tang ZG, Ding H, Ding H, Cai MH, Du LX. Effect of prestrain on microstructures and properties of Si-Al-Mn TRIP steel sheet with niobium. J. Iron Steel Res. Int., 2010, 17(4): 59.

[12] Zhang JC, Fu RY, Zhang M, Liu RD, Wei XC, Li L. Bake hardening behavior of TRIP and DP steels. J. Univ. Sci. Technol. Beijing, 2008, 15(2): 132.

[13] Shi LY, Liu YM, Huang JH, Zhang SQ, Zhao XK. Growth kinetics of cubic carbide free layers in graded cemented carbides. Int. J. Miner. Metall. Mater., 2012, 19(1): 68

[14] Tang ZY, Ding H, Ding H, Cai MH, Du LX. Effect of baking process on microstructures and mechanical properties of low silicon TRIP steel sheet with niobium. J. Iron Steel Res. Int., 2010, 17(7): 68.

[15] Anazadeh Sayed A, Kheirandish S. Affect of the tempering temperature on the microstructure and mechanical properties of dual phase steels. Mater. Sci. Eng. A, 2012, 532, 21.

[16] Wang ZG, Zhao AM, Zhao ZZ, Ye JY, Tang D, Zhu GS. Microstructures and mechanical properties of C-Mn-Cr-Nb and C-Mn-Si-Nb ultra-high strength dual-phase steels. Int. J. Miner. Metall. Mater., 2012, 19(10): 915.

[17] Baker LJ, Parker JD, Daniel SR. Mechanism of bake hardening in ultralow carbon steel containing niobium and titanium additions. Mater. Sci. Technol., 2002, 18(5): 541.