Anisotropic Increase in Yield Strength by Straining and Baking of Bake-Hardenable Steel

Abstract:

The yield strength was investigated in a prestrained and baked bake-hardenable sheet steel, which can increase the dent-resistance of exterior automotive body panels. Instead of a standard bake-hardenability test in which the final tensile test is in the same direction as prestrain, the strain-path effect in denting of stamped and paint-baked panels was examined by changing the direction of final tensile tests in uniaxially prestrained and baked samples. The prestrained samples showed the maximum of 0.2% proof stress at 45° to the prestrain axis and the minimum at 90°. Baking raised the minimums at 0° and 90° so that the anisotropy decreases. Furthermore, the strain path changes were characterized by a scalar product of previous and current strain-rate mode tensors. By regarding this parameter as the degree of reactivation of slip systems, the anisotropy observed after prestraining and baking was microscopically explained from the viewpoints of residual stress, crystal plasticity, and dislocation pinning.

• Periodical: Materials Science Forum (Volumes 495-497)
• Pages: 1485-1492
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.495-497.1485
• Online since: September 2005
• Authors: Shunji Hiwatashi, Shigeru Yonemura
• Keywords: Anisotropy, Bake Hardening, Dislocation Pinning, Residual Stress, Slip System, Strain-Path Changes

References

[1] F.D. Bailey, R.P. Foley and D.K. Matlock: Proceedings of Symposium on High Strength Sheet Steels for the Automotive Industry, edited by R. Pradhan, Iron and Steel Society, Warrendale, PA (1994), p.119.

[2] A. Okamoto, K. Takeuchi and M. Takagi: The Sumitomo Search, September 1989, p.183.

[3] K. -M. Radlmayr, H. Ponschab and M. Blaimschein: in Recent Developments in Sheet Metal Forming Technology, (Proceedings of the IDDRG'94 Open Sessions 18th Biennial Congress), edited by M.J.M. Barata Marques, INETI, Lumiar, Lisboa, Portugal (1994).

[4] T.N. Seel: SAE Technical Paper Series 910291, SAE, Warrendale, PA (1991).

[5] Y. Omiya, K. Kase, I. Tsukatani and Y. Okano: in Sheet Metal Forming Beyond 2000, (Proceedings of the IDDRG 20th Biennial Congress, June 17-19, 1998, Genval, Brussels, Belgium), p.415.

[6] H. Takechi: in Hot- and Cold-Rolled Sheet Steels, edited by R. Pradham and G. Ludkovsky, TMS-AIME, Warrendale, PA (1988), p.117.

[7] W.C. Jeong: Metall. and Mater. Trans. A, Vol. 29A (1998), p.463.

[8] W.T. Roberts and D.V. Wilson: in Recent Developments in Sheet Metal Forming Technology, (Proceedings of the IDDRG'94 Open Sessions 18th Biennial Congress), edited by M.J.M. Barata Marques, INETI, Lumiar, Lisboa, Portugal (1994), p.67.

[9] H. Ishigaki: in Mechanics of Sheet Metal Forming, Material Behavior and Deformation Analysis, Edited by D.P. Koistinen and N. -M. Wang, Plenum Press, New York (1978), p.315.

[10] G. Jun and W.F. Hosford: Metall. Trans. A, Vol. 17A (1986), p.1573.

[11] R. Pradhan: SAE Technical Paper Series 910290, SAE, Warrendale, PA (1991).

[12] B.B. Hundy: J. Iron Steel Inst., October 1954, p.127.

[13] M. Blaimschein, K.M. Radlmayr, A. Pichler, E. Till and P. Stiaszny: in Advanced Sheet Metal Forming, (Proceedings of the 19th Biennial IDDRG Congress, June 10-14, 1996, Eger, Hungary), Edited by M. Tisza, The University of Miskolc (1996), p.445.

[14] K.H. Kim and J.J. Yin: J. Mec. Phys. Solids, Vol. 45 (1997) p.841.

[15] E. Aernoudt, J. Gil Sevillano and P. Van Houtte: in Constitutive Relations and Their Physical Basis, (Proceedings of 8th Risø International Symposium on Metallurgy and Materials Science), edited by S.I. Andersen et al., Risø National Laboratory, Roskilde (1987).

[16] C. Teodosiu: in Modelling of Plastic Deformation and Its Engineering Applications, (Proceedings of 13th Risø International Symposium on Metallurgy and Materials Science), edited by S.I. Andersen et al., Risø National Laboratory, Roskilde (1992).

[17] E.F. Rauch and J. -H. Schmitt: Mat. Sci. and Eng., Vol. A113 (1989), p.441.

[18] J.L. Raphanel, J. -H. Schmitt and B. Baudelet: Int. J. Plasticity, Vol. 2 (1986), p.371.

[19] J.H. Schmitt, E. Aernoudt and B. Baudelet: Mat. Sci. and Eng., Vol. 75 (1984), p.13.