Influence of Cooling Rate on Free Interstitial Concentration in Type 430 Ferritic Stainless Steel

Abstract:

In ferritic steels, the amount of free C and N should be as low as possible to avoid the formation of Cottrell atmospheres and their associated discontinuous yielding and Lüders bands during forming. During the post-annealing cooling of ferritic stainless steel, carbides and nitrides of the type MX and M₂₃C₆ precipitate. The volume fraction of the precipitates is determined by chemical composition, microstructure and the cooling path. In some cases, precipitation might not be sufficient to remove all free interstitials from the matrix, in which case, the process parameters or composition of the steel should be reconsidered. Here, thermodynamic and kinetic calculations using Thermo-calc and TC Prisma software have been made to investigate the precipitation of C and N as a function of total interstitial content and cooling rate. According to the calculations, decreasing the cooling rate would result in a more efficient precipitation and hence, less free C and N in the matrix, but the amount is not sufficient to remove the upper yield point. Furthermore, changing the C and N content of the steel was found to have insignificant influence. However, the free C and N could possible be bound through a more complex cooling.

• Periodical: Key Engineering Materials (Volumes 611-612)
• Pages: 111-116
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.611-612.111
• Online since: May 2014
• Authors: Timo J. Juuti*, Timo Manninen, David A. Porter
• Keywords: Cooling Rate Simulation, Ferritic Stainless Steel, Precipitation

References

[1] International Stainless Steel Forum, The Ferritic Solution, Belgium, (2007).

[2] F. Garofalo, G.V. Smith, D.C. Marsden, ASM. 49 (1957) 373-408.

[3] V.T.L. Buono, B.M. Gonzalez, M.S. Andrade, Scripta Mater. 38 (1998) 185-190.

[4] P.C. Pistorius, M. Coetzee, J. South. Afr. Inst. Min. Metall. (1996) 119-125.

[5] A.A. De Sotomayor, E.J. Herrera, J. Mater. Sci. 29 (1994) 5833-5838.

[6] T. Juuti, L.P. Karjalainen, E. -P. Heikkinen, Adv. Mater. Res. 409 (2012) 690-695.

[7] T. Juuti, T. Manninen, L.P. Karjalainen, D. Porter: Submitted to Thermec 2013 (2013).

[8] R.E. Hook, J.A. Elias, Met. Trans. 3(1972) 2171-2180.

[9] A.H. Cottrell, B.A. Bilby, Proc. Phys. Soc. A. 62(1949) 49-62.

[10] F. Yoshida, Y. Kaneda, S. Yamamoto, Int. J. Plast., 24 (2008) 1792-1818.

[11] K. Takeda, N. Nakada, T. Tsuchiyama, S. Takaki, ISIJ Intern. 48 (2008) 1122-1125.