Investigation of Possible Mechanisms for Developing Long Steel Products with Ultrafine Grained Microstructure

Abstract:

The obtainment of ultrafine grain microstructures, by the application of process parameters which are potentially feasible under industrial conditions, is attractive to develop a new generation of low alloy steel (Ultrafine Grain Steel, UFG) characterized by high strength and toughness, good cold/warm formability, environmentally-friendly process. The ferrite grain size refinement beyond existing levels by means of hot rolling mills, without requiring drastic plant changes, can be achieved by lowering the rolling temperature down to the range A_e3 - A_r3 in the finishing stands. In this temperature range different metallurgical mechanisms may take place. Austenite recrystallization is slower and there is a greater chance of obtaining non-recrystallized deformed austenite (pancake), which after phase transformation will give finer ferrite (Heavy Gamma Deformation). Or, in alternative, Deformation Induced Ferrite Transformation can occur especially in C-Mn steels, promoting the formation of ultrafine ferrite grains (DIFT). Most of the existing studies on UFG steel focus on flat products. In this paper the mechanisms to be exploited for producing UFG long products are identified and examined on different low and medium carbon non-alloyed steels, as the common grades used for fastener applications. In particular, Heavy Gamma Deformation and DIFT are investigated through laboratory tests aimed at determining the process parameters affecting the two mechanisms in different ranges of chemical composition. On the basis of the results found, some basic concepts for industrialization on modern hot rolling mills will be given.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 744-749
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.744
• Online since: May 2014
• Authors: Claudio Guarnaschelli*, Ilaria Salvatori, Tommaso Coppola
• Keywords: Austenite Recrystallization, Deformation Induced Ferrite Transformation (DIFT), Ferrite Grain Refinement , Heavy Austenite Deformation, Ultrafine Grain Steel (UFG)

References

[1] Valiev RZ. Mater Sci and Eng A 234 (1997) 59.

[2] Segal VM. Mater Sci. and Eng. A 271 (1999) 322.

[3] Saito Y, Utsunomiya H, Tsuji N, Sakai T. Acta Mater. 47 (1999) 579.

[4] Tsuji N, Ueji R, Minamino Y. Scripta Mater. 47 (2002) 69.

[5] Inoue T, Torizuka S, Nagai K. International Symposium on Ultrafine grained Steels (ISUGS 2001), The Iron and Steel Institute of Japan, Fukuoka, Japan (2001) 88–91.

[6] A. P. Zhilyaev, G. V. Nurislamova, B. K. Kim, M. D. Baro, J. A. Szpunar and T. G. Langdon, Acta. Mater. 51 (2003) 753.

[7] Y. Ivanisenko, W. Lojkowski, R. Z. Valiev and H. J. Fecht, Acta. Mater. Vol. 51 (2003) 5555.

[8] Y. Ivanisenko, R. K. Wunderlich, R. Z. Valiev and H. J. Fecht, Scr. Mater. 49 (2003) 947.

[9] Q. Cui and K. Ohori, Mater. Sci. Tech. 16 (2000) 1095.

[10] T. Inoue, S. Torizuka and K. Nagai, Mater. Sci. Tech. 18 (2002) 1007.

[11] I. Chikushi, M. Kozaki, R. Kurahashi, M. Takahashi, A. Adachi and S. Takaoka, AISE Steel Technology, June (2002) 42.

[12] T. Morimoto, I. Chikushi, R. Kurahashi and J. Yanagimoto, Steel Res. Int. 76 (2005) 514.

[13] M. R. Hickson, P. J. Hurley, R. K. Gibbs, G. L. Kelly and P. D. Hodgson, Metall. Mater. Trans. A 33 (2002) 1019.

[14] Z. Yang and R. Wang, ISIJ Int. 43 (2003) 761.

[15] S. C. Hong, S. H. Lim, K. J. Lee, D. H. Shin and K. S. Lee, ISIJ Int. 43 (2003) 394.

[16] J. K. Choi, D. H. Seo, J. S. Lee, K. K. Um and W. Y. Choo, ISIJ Int. 43 (2003) 746.

[17] H. Beladi, A. Zarei- Hanzaki, G. L. Kelly and P. D. Hodgson, Mater. Sci. Tech. 20 (2004) 213.

[18] Maki, T.: Formation of Ultrafine-grained Structure by Heavy Deformation in Steels, Proc. of 7th ICTP (2002), Yokohama, 1-10.

[19] K. Miyata, M. Wakita, S. Fukushima, M. Eto, T. Sasaki and T. Tomida, Materials Science Forum 539-543 (2007) 4698-4703.

DOI: 10.4028/www.scientific.net/msf.539-543.4698

[20] L. Longfei, Y. Wangyue and S. Zuqing, Metall. Mater. Trans. A 37A (2006) 609.

[21] Y. D. Huang, W. Y. Yang and Z. Q. Sun, J. Mater. Proc. Tech. 134 (2003) 19.

[22] G. Azevedo, R. Barbosa, E. V. Pereloma and D. B. Santos, Mater. Sci. Eng. A 402 (2005) 98.