Effect of heat treatment on mechanical properties of microstructure of four different heats of ASTM A710 steel

Abstract

Abstract : A710 is an high strength low alloy steel whose strength is a result of both a fine grained microstructure and a dispersion of copper precipitates. For these reasons, the tensile and impact properties of an A710 plate depend as much on the thermo-mechanical history of each plate as on the chemistry of each heat. Since plates shipped from steel suppliers are frequently heat treated under different conditions, it is difficult to attribute property differences to chemistry variations rather than to heat treatment variations or vice versa. Heat to heat property differences must be determined for a specific, known heat treatment. This report describes the variability in the mechanical properties of four plates (representing four heats of steel) that have received known, and carefully controlled, heat treatments at the National Bureau of Standards. The sensitivity of these properties to heat treatment variations within each heat of steel is also reported here. Optical and electron metallographic techniques were used to determine as-received and heat treated microstructures. Scanning electron fractography was used to ascertain the fracture mechanism in the tensile and impact tests. This report also contains two appendices in which splitting fracture and microchemistry observations in A710 are discussed. Keywords: Grain size; Age hardening; Ultra fine niobium carbon nitride; Tables(data); Charts; Photographs; Microchemistry. (Author)