Effect of the heterogeneity in solidification microstructure on the hot-rolling behaviour of stainless steels : final report

The production of high-alloyed steel plates and sheets involves several problems of shape control during and after hot rolling (width control) or even after cold rolling (waves, roping) . These shape defects result from the behaviour of the prior solidification microstructure during the first steps of hot rolling. Clearly, different solidified zones appear in the slabs such as columnar and equiaxed grains. Their distribution depends stroogly on the solidification conditions. Moreover, chemical segregation is also dependent on these conditions. All these phenomena lead to an anisotropy of the material at least during the first rolling passes, before recrystallisation. The problem is particulary important for the materials where the solidification microstructure is retained until the first rolling passes. So, the practical aims of this project are: -to control the dimensions of flat products, by making savings on metal, energy, time and processing costs (better know-how of anisotropic behaviour and determination of the more consistent thermo-mechanical cycles during hot rolling), - to increase the service properties of the delivered products (improvement of the homogeneityof structure). The project has been focused on different stainless steels produced in various conditions (chemical composition, casting conditions) leading to various solidification structures (particulary different percentage of equiaxed grains): two ferritic stainless steels (X6Cr17 and X2Cr12) cast with and without modifying the chemical composition, one austenitic-ferritic steel (X2CrNi MoCuN25.6.3) and one super-austenitic steel (X1 CrNi MoCu24.22.6.3).