Influence of Heat Treatment Conditions on Microstructure and Properties of HFW Seam of X60 Steel

On-line heat treatment process of X60 steel weld seam welded by high-frequency welding (HFW) technology was simulated by means of a muffle furnace in the lab, and the effects of normalizing temperature on microstructure and properties were studied. The results show that the microstructure of HFW seam was composed of acicular ferrite, polygonal ferrite, bainite and pearlite. With the increase of normalizing temperature, the amount of bainite gradually decreased, until vanished away, and the grain sizes of welded seam, heat affected zone and base material increased gradually. The tensile strength of HFW seam gradually decreased, and the impact absorbing energy first increased and then decreased with the increase of normalizing temperature. After normalizing at 920 ℃, the tensile strength of HFW seam was 532 MPa and the impact absorbing energy was up to maximum of 139 J. Comparing with the grain size of the welded seam after on-line heat treatment at 920 ℃, the grain size after simulation heat treatment at the same normalizing temperature in the lab was a little bigger, but the tensile strength and toughness of them were almost the same.