Effect of warm working on structure and properties of low-carbon steels

Two laboratory-prepared low-carbon steels were hot rolled to bar stock. This material was then preheated at 650°C and rolled in single-pass reductions which varied from εR=0·25 to 0·96. The longitudinal tensile and impact properties of the warm-rolled products were measured and compared with those of the original stock. The structure of the materials was studied by using conventional optical and electron microscopy and X-ray techniques. Warm deformation increased the strength and decreased the ductility and upper-shelf(Cv)_max values of both steels. The impact transition temperature increased initially with strain and then decreased, so that at the highest strain it was lower than that of the as-hot-rolled condition. The strength increase is associated with the reduction in effective grain size and the introduction of a recovered substructure. The improvements in transition temperature at the higher strains are the result of cleavage separations induced by crystallographic texture.