A study of simulated weld heat affected zone structures and properties of HY-80 low alloy stee

Abstract

Single and double cycle simulation techniques have been employed to investigate the structure and properties of the heat affected zone in HY-80 steel due to a single submerged arc weld run and to the deposition of a tempering bead on a pre-existing edge bead heat affected zone. The thermal cycles used for simulation had peak temperatures of 1275°C, 930°C, 7650C and 6500C and corresponded to those experienced in the parent material during the submerged arc welding of 1.5 in. thick plate using a nominal heat input of 54kJ. in and a preheat temperature of 120°C. Double cycling utilized specific combinations of these thermal cycles. Half the total number of simulated specimens received post cycle heat treatment at 650°C. Charpy V-notch impact transition curves and tensile and hardness data have been obtained for each condition studied and structural examination has employed the carbon extraction replica technique in the electron microscope. The results indicate that the properties of the weld heat affected zone in HY-80 steel are superior to those obtained for QT-35 steel but inferior to those of the HY-80 parent material. The tempering bead technique has been shown to have, at best, only a limited tempering effect on the grain coarsened region of an edge bead heat affected zone and can also cause an increase in the susceptibility of this region to brittle fracture. Post weld heat treatment at 6500C is recommended, wherever possible, for HY-80 weldments. The calculation of weld heat affected zone thermal cycles, which correlate well with the practical situation, has been made possible by the development of a series of computer programs. These programs include functions to account for the release of latent heat from the solidifying weld pool and the variation of thermal conductivity with temperature.