The effect of reheating conditions and chemical composition on delta ferrite content in austenitic stainless steel slabs

The specimens, selected from different locations of as-cast 304 stainless s teel slab, were annealed according to the temperature profiles, which simul ated the industrial re-heating process before hot rolling. Annealing, follo wing thermal cycles with maximum temperatures between 1230 and 1270 degrees C for a total time of 1 h, reduced the delta ferrite content, increased th e size of the individual ferrite island and changed its shape to a more sph erical one. An increase of annealing time to 1.5 h caused a drastic reducti on in delta ferrite content and its further spheroidization. Moreover, the size of the individual ferrite islands was decreased. While after 1 h of an nealing, the delta ferrite content depended on a particular thermal cycle a nd its maximum temperature; after a longer annealing time of 1.5 h, the del ta ferrite content was very similar for all the thermal cycles applied. A s tatistical analysis of over 2200 industrial data, describing the slab chemi cal compositions and edge quality of the hot rolled plates was conducted. G enerally, the alloying elements suppressing the delta ferrite formation imp roved the plate edge quality. In particular, carbon and nitrogen exerted th e strongest influence, and the higher sum of both elements led to a lower p robability of the edge cracking. (C) 2000 Kluwer Academic Publishers.