High-Strength Low-Alloy Steel

Abstract

Growth kinetics of Widmanstätten austenite in ferrite in high-strength low-alloy steel is based on a model that describes diffusion controlled growth of precipitates with shapes approximating to needles or plates, where all the factors that may influence the precipitate growth, i.e. diffusion, interface kinetics and capillarity, are accounted for within one equation. The ratio between calculated and experimental values of the radius of the advancing tip is inversely proportional to the degree of supersaturation. Following this theoretical work, the tensile behaviour of high-strength low-alloy steel after tempering is discussed, and well explained in view of the interactions of mobile dislocations and dissolved carbon and nitrogen atoms and their effects on the strain hardening exponent. In the final section, splitting during fracture of tensile and impact loading is examined. Delamination does not occur in the as-rolled condition, but is severe in steel tempered in the temperature range of 500–650 °C. Steel that has been triple quench-and-tempered to produce a fine equiaxed grain-size also does not exhibit splitting. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating are responsible for the delamination.