連続鋳造・直送圧延再現試験による低合金鋼の割れ発生条件とその機構

抄録

Surface cracking during direct rolling of continuously cast low alloy steel slabs has been investigated by means of hot tensile tests simulating the above process. The hot ductility of directly cooled specimens is not reduced by high strain rate deformation corresponding to that in rolling. While, in the specimens predeformed at temperatures ranging from γ/α duplex phase to lower temperature γ region at slow strain rate corresponding to that in bending and/or straightening processes of CC slabs, ductile intergranular fracture of austenite is easily induced by the subsequent deformation even at high strain rate, resulting in poor ductility. This ductility loss can be explained in terms of dynamic precipitation of carbonitrides such as AlN and/or NbC within the matrix as well as on the grain boundaries during the prior slow strain rate deformation. Although the embrittlement mechanism is essentially the same as in CC slabs, the ductility is also influenced by the final deformation conditions because of the morphological change of carbonitride precipitates in the process.