The influence of large boride particles on microstructural evolution in AISI 304 steel

Microstructural evolution in AISI 304 stainless steel and in a similar steel containing 1 % boron during hot torsion was studied by means of quantitative optical microscopy and transmission electron microscopy. Particular attention was focused on the influence of the large volume fraction of hard boride particles on the dynamic recrystallization parameters and the characteristics of the dislocation substructure. Dynamic recrystallization in the austenitic matrix was accelerated significantly in the presence of boride particles. This was accounted for by the superposition of both local strain accumulations around the curved particle interfaces and higher overall strain energy stored in the austenite. Hot workability, however, remained extremely poor probably because of the high strain rate used in this study. Changes of the dislocation substructure in the austenitic matrix during hot deformation were found to be similar in both steels and were interpreted according to a model that has been so far used predominantly for cold deformation. The study of the substructure of the boride particles showed that they remained almost undeformed during the deformation process.