高炭素鋼の高温延性に及ぼすバナジウムの影響

抄録

Effects of V on hot ductility of a high C steel have been investigated by means of hot tensile testing in relation to hot cracking on the continuously cast slab surface. The ductility of the specimens initially solution-treated at high temperatures is largely reduced in slow strain rate deformation at temperatures ranging from γ/α duplex to low temperature γ region. The ductility trough with the minimum value at temperatures just below the Ae₃ points, which are significantly lower than those in low C steels, is deepened and widened into high temperature region of 950°C by small amount of V addition. The embrittlement in γ region can be explained in terms of V(C, N) precipitation during the slow strain rate deformation ; strain concentration within soft precipitation-free zones along γ grain boundaries induces microvoids by decohesion of densely line-uped precipitates at the boundaries from the matrix, and leads to the final fracture by their coalescence. The intergranular ductile fracture in γ/α duplex phase region can be caused by the strain concentration in soft ferrite layers along γ grain boundaries in addition to the effect of the dynamic precipitation of V(C, N). Ductility improvement with an increase in the strain rate can be explained from V(C, N) precipitation and/or ferrite formation during deformation.