Recrystallization Controlled Rolling of Steels


Abstract:

The aims of recrystallization controlled rolling especially followed by accelerated cooling (RCR + ACC) are to produce hot rolled steel products having high strength, high toughness and good weldability. The concept of RCR+ACC is attractive in that it is a relatively uncomplicated and high productivity process and can be applied on conventional mills. The means of RCR is to make use of the grain refinement by repeated recrystallization of austenite with an intelligent design of deformation/temperature schedules with the help of computer models to calculate microstructure evolution and, above all, to retain the fine austenite microstructure during inter-pass delays and during cooling down to Ar3 by a suitable dispersion of second phase particles. The fine austenite structure together with suitably fast cooling leads subsequently to a minimization of the ferrite grain size after transformation. Microalloying with Ti and V together with nitrogen can help to produce HSLA products with very favourable combinations of yield strength and toughness. The effects of the RCR + ACC process parameters are discussed in relation to the microstructure development, final ferrite grain size and mechanical properties of Ti-V-(Nb)-N steels. A comparison of the results of full scale industrial plate processing using RCR practice with and without application of ACC with the results obtained at low finish rolling temperature CR practice is also made.

Keywords:

vanadium microalloyed steel, recrystallization controlled rolling, static recrystallization, hot rolled steel, accelerated cooling, austenite grain size, ferrite grain size, grain refinement, niobium, titanium and nitrogen, V(C,N).


Author:

T. Siwecki (1) and G. Engberg (2)

Affiiation

  1. Swedish Institute fO,r Metals Research, Stockholm, Sweden
  2. SSAB Tunnplat Borlange, Sweden


Source:

Thermo-Mechanical Processing in Theory, Modelling & Practice, Stockholm, Sweden, 4-6 Sept. 1996, pp.121-144