Variation of solute distributions during deformation and bake hardening process and their effect on bake hardening phenomenon in ultra-low carbon bake hardening steels
- 259 Downloads
Three-dimensional atom probe was used to investigate solute carbon and other elements distributions during bake hardening process after pre-deformation and also to analyze their effect on bake hardening phenomenon of the steels. Two different kinds of bake hardening steels were prepared and annealed by water quenching. The as-received samples were pre-deformed at different levels (from 0 to 10%), and baked at 170 °C for 20 min. Distributions and concentrations of solute elements in the steels were characterized with three-dimensional atom probe. Bake hardening values of the steels were examined by tensile experiments. Three dimensional atom probe detection results indicate that C distribution changes little with the increase of pre-deformation in BH-Mn steel. In BH-P steel, however, with the increase of pre-deformation, more C clusters form in the matrix and C concentration decreases. Distribution patterns and the maximum separation distance method results prove that the C cluster is just C segregation or C together with P segregation rather than vanadium carbides precipitate. Moreover, bake hardening experiment results indicate that BH values are similar in the two BH steels and the BH values change only a little as the pre-deformation increases from 2 to 10%. The 4% pre-deformation induces the highest BH values in the two BH steels, and is considered to be the critical pre-deformation in making the balance of Cottrell atmosphere in the two BH steels.
KeywordsSolute Distribution Vanadium Carbide Steel Matrix Interstitial Free Tensile Experiment
The authors are thankful to VANITEC, National Nature Science foundation of China program under Grant No. 50934011, and National Basic Research Program of China (973) under Grant No. 2010CB630802 for the project funding.
- 1.Tanioku T, Hoboh Y, Okamoto A, Mizui N (1991) Development of a new bake-hardenable galvannealed sheet steel for automotive exposed panels. In: SAE Technical Paper 910293, Warrendale, pp 303–308Google Scholar
- 2.Taylor KA, Speer JG (1997) Development of vanadium-alloyed, bake-hardenable sheet steels for hot-dip coated applications. In: 39th MWSP conference proceedings, ISS, vol XXXV, Indianapolis, pp 49–61Google Scholar
- 4.Waterschoot T, Vandeputte S, De Cooman BC, Houbaert Y (1999) The Influence of P, Si and Mn on the mechanical properties and bake-hardening of Ti-ULC Steels. In: 41st MWSP conference proceedings, ISS, vol XXXVII, Indianapolis, pp 425–433Google Scholar
- 7.Wen Y, Su Q, Wuttig M (1998) Interstitial analysis of ultra low carbon and interstitial free steels. In: 39th MWSP conference proceedings, ISS, vol XXXV, pp 271–280Google Scholar
- 10.Al-Shalfan W, Speer JG, Findley K, Matlock DK (2006) Metall Mater Trans A 37A:206Google Scholar
- 25.Liu QD, Liu WQ, Wang ZM, Zhou BX (2008) Acta Metall Sin 44:786 (in Chinese)Google Scholar
- 26.Wang H, Shi W, He YL, Fu RY, Li L (2011) Acta Metall Sin 3:263 (in Chinese)Google Scholar