The Influence of Reduction-Ratio in the Hot-Rolling on the Strength and Toughness of Quenched and Tempered Steel

Abstract

The influence of reduction-ratio in the hot-rolling on the microstructure and mechanical properties of quenched and tempered low C, 3.5%Ni steel was investigated and the following conclusions were obtained;
The average γ grain size became finer with increasing reduction-ratio but, the grains were more elongated in their shape in the rolling-direction. With increasing reduction-ratio, the unit crack path (U. C. P.) observed in the fractured surface of longitudinal Charpy V-notch specimen became finer, while U. C. P. in the transverse specimen changed less evidently. The fracture appearance transition temperature in the longitudinal specimen behaved similarly to that of U.C.P. with increasing reductionratio.
The difference in the unit crack path and shape of non-metallic inclusions between longitudinal and transverse direction brought about the directional difference in Charpy transition temperature.
The upper and lower yield point in the stress-strain curve separated more appreciably with increasing reduction-ratio from 1 to 8. This is due to the fact that the inhomogeneity in the cast structure such as micro-segregation was leveled out and consequently the difference of tensile strength at various locations disappeared.
Both columnar and equiaxed zones in the cast structure responded similarly to the reduction-ratio, but the quantity of non-metallic inclusion was larger in equiaxed zone with the consequence of some what inferior ductility in the latter. The orientation of reduction with respect to the columnar axis in the cast structure had no appreciable influence on the various properties.