AbstractThe grain coarsened tensile properties in the heat affected zone (HAZ) of medium strength (Rp0·2⋍330–470 MN m−2) low carbon microalloyed, C–Mn, and 2·25Cr–1Mo steels have been examined using the weld simulation technique. Very high values of yield and tensile strength (Rp0·2>900 MN m−2; Rm>1100 MN m−2) can be obtained for low heat input welding (E<1 MJ m−1;∆t8/510 s), however, a substantial reduction in the values of Rp0·2and Rmoccurs, with the exception of the 2·25Cr–IMo steel. Based on the empirical equations developed, and the Suzuki BL70 hardness formula, it is shown that the grain coarsened HAZ yield and tensile strength can be calculated to an accuracy of±50 MN m−2, while elongation at fracture and reduction in area can be predicted to an accuracy of±3% and±7%, respectively.MST/I077