1988 年 28 巻 12 号 p. 1021-1027
Surface cracking during direct rolling of continuously cast low alloy steel slabs has been investigated by means of hot tensile tests simulating the 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 low temperature γ region at slow strain rate corresponding to that in bending and/or straightening operations 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 carbide, nitride, or carbonitride such as AlN and/or NbC (or NbC(N)) within the matrix as well as on the γ grain boundaries during the prior slow strain rate deformation. The ductility is also influenced by the final deformation conditions because of the morphology change of the precipitates in the process, although the embrittlement mechanism is essentially the same as in the CC process.