Some Studies on Heat-Affected Zone (HAZ) Toughness Behavior of API 5L X52 Steel

Abstract

Heat Affected Zone (HAZ) simulation by Gleeble is a useful method for evaluating welding process parameters to improve the toughness of weld HAZ by optimizing process parameters. The HAZ Toughness in low alloy steels is strongly influenced by the welding parameters (as HAZ microstructure is influenced by the heat input and cooling rate). In the present work different regions of weld HAZ of API 5L X52 steel have been simulated by using Gleeble @ 3800 Thermal- Mechanical Simulator. Two cooling rates (t_8/5) 10 s to simulate low heat input (LHI) welding conditions without preheating, (t_8/5) 40s to simulate high heat input (HHI) welding were used. Charpy V-notch impact tests were conducted on the simulated as well as on the base material at room temperature (25° C) and at -40° C. Results showed that HHI simulated coarse grain HAZ (CGHAZ) region attributed highest Impact energy of 300 J in comparison to 199 J of base material at 25° C. In HAZ regions, lowest room temperature toughness was observed in sub critical HAZ (SCHAZ) for both HHI and LHI conditions. Lowest impact energy at -40° C was observed in fine grained HAZ (FGHAZ) for both HHI and LHI conditions. Hardness test showed that LHI samples exhibited slightly higher hardness than HHI condition and the hardness profile for HAZ regions was similar for both HHI and LHI conditions.