Physical metallurgy of high strength low alloy strip steel production using compact strip processing

Abstract

The physical metallurgy of high strength low alloy (HSLA) steel production by compact strip processing or direct slab casting is reviewed. Specimens were extracted from 50 mm thickness cast Nb + Ti(+ V)HSLA slabs and quenched to room temperature, before and after the slab was heat treated in a tunnel furnace at 1150°C. These specimens were analysed to track changes in composition and microstructure during processing, in particular the formation of complex (Nb,Ti)(C,N) precipitates during solidification and subsequent heat treatment. It is shown that partial dissolution of the precipitates takes place during thermal equilibration, increasing the solute content of niobium and titanium before hot rolling. Tailoring of the industrial thermomechanical processing route, to improve the Charpy toughness and hardness of thin slab cast niobium HSLA linepipe and other grades, is also described.

References

‘Metals statistics 2002’, 94th edn; 2002, New York, American Metal Market LLC.

Marraccini

: Private communication, Nucor Steel Berkeley, SC, USA, 2002.

DeArdo

: Unpublished research, University of Pittsburgh, PA, USA, 2002.

Garcia

C. I.

: Proc. Int. Symp. on ‘Thin slab casting and rolling’: (TSCR’ 2002 ), Guangzhou, December 2002, Chinese Society for Metals.

Flemming

et al.: Metall. Plant Technol., 1988, 11, 16–35.

Pottore

N. S.

: ‘The evolution of microstructure during the solidification and subsequent cooling of low-alloy steels’, PhD thesis, University of Pittsburgh, PA, 1986.

Kaspar

Zentara

Herman

J. C.

: Steel Res., 1994, 65, 279.

Crowther

D. N.

Mitchell

P. S.

Baker

T. N.

: Proc. ‘Materials solutions’ Conf., Columbus, OH, USA, October 2002, ASM International, 5–15.

Lee

S. W.

Garcia

C. I.

DeArdo

A. J.

: ‘Study of the distribution of precipitates and its effect on the austenite grain growth behavior of Ti-bearing steels’, Basic Metals Processing Research Institute report, University of Pittsburgh, PA, USA, 1999.

10.

Zhou

Priestner

: ISIJ Int., 1996, 36, 1397–1405.

11.

Luo

Karjalainen

L. P.

Porter

D. A.

Limatainen

H.-M.

Zhang

: ISIJ Int., 2002, 42, 273–282.

12.

‘Continuous caster roundup – 2001’, Iron Steelmaker, 2001, 28, 36–46.

13.

Garcia

C. I.

: Proc. Int. Symp. on ‘Thin slab casting and rolling’: (TSCR’ 2002 ), Guangzhou, December 2002, Chinese Society for Metals.