Microstructure and microtexture of ultrafine ferrite formed in 0 center dot 1%C steel using new strip rolling process

A new hot strip rolling process is discussed which is capable of producing ultrafine, equiaxed ferrite grains (i.e. less than 2 mum) in the surface re gion of steel strip. Both microstructural and texture analysis of low carbo n steel strip that has been rolled using this method are used to show that the ferrite forms by strain induced transformation. Analysis by electron ba ckscatter diffraction (EBSD) indicates that a strong ferrite microtexture e xists within the individual austenite grains in which the ferrite nucleates . The results from bulk X-ray texture analysis confirm that the ferrite for ms as a result of transformation from austenite that has undergone heavy sh earing during rolling, with nucleation occurring on the austenite substruct ure. In the centre region of the strip, a bainitic microstructure forms aft er rolling during air cooling. In the transition region between the surface and the centre of the strip, ferrite is shown to nucleate to form closely spaced parallel 'rafts' of ferrite grains traversing individual austenite g rains. Again, EBSD is used to show that the ferrite located within these ra fts is strongly textured, which, in combination with microstructural eviden ce, suggests that this ferrite nucleates along intragranular shear bands th at form in the austenite in this region of the strip during rolling. MST/47 93.