1987 Volume 73 Issue 9 Pages 1162-1169
For the purpose of improving the ductility and toughness of pearlitic eutectoid steel, such as rail steel, controlled-rolling was carried out. In this paper, controlled-rolling means the rolling in low temperature austenite ( γ ) region. The effects of rolling conditions and alloy additions on the microstructure and mechanical properties were investigated.
The results are summarized as follows:
(1) γ grains of the eutectoid steels controlled-rolled are refined or elongated, consequently, pearlite colonys become refined.
(2) Also in eutectoid steel, the addition of Nb and V has a retardation effect on recrystallization. Cr addition also has the effect a little. Si addition does not show any such effects.
(3) The nucleation rate of γ→ pearlite transformation in the unrecrystallized γ grain boundaries is higher than that in the recrystallized ones.
(4) As for eutectoid steel, in general, the ductility and the toughness increase accompanying with decrease in yield strength accordingly as the controlled-rolling intensifies more. Only the steel to which Nb was added shows an improvement in ductility and toughness without a decrease in strength.
(5) Si addition improves the fracture toughness markedly.
(6) The combination of the complex addition of Nb, Si and the intensified controlled-rolling is effective for the improvement of ductility and toughness of rail steels.
