Split heat mechanical property comparison of ESR and VAR 4340 steel

Abstract

This report addresses a mechanical property characterization of a split argon-oxygen decarburized (AOD) heat of 4340 steel which was further processed by vacuum arc remelting (VAR) and electroslag remelting (ESR) into 12.7 cm (5 inch) square forgings. Properties examined were hardness, tensile, Charpy V-notch impact, and fracture toughness as a function of tempering temperature over the range of 163 °C (325 °F) to 649 °C (1200 °F)for both the longitudinal and transverse orientations. Microstructural aspects are also addressed. Results indicate nearly identical tensile properties for the ESR and VAR processed material. Ductility measurements were anisotropic for both remelting techniques. Charpy impact values were consistently higher for VAR material, especially at tempering temperatures exceeding 260 °C (500 °F). A significant amount of scatter in impact data was observed at tempers from 163 °C (325 °F)to 204 °C (400 ° F ). Fracture toughness, K_q, was higher for VAR material in both the LT and TL orientations for tempering temperatures up to 427 °C (800 °F). It is believed that the lower fracture toughness of the ESR material is associated with the presence of calcium aluminate inclusions, and possibly the material’s higher gas content.