Influence of Chemical Composition and Post Welding Heat Treatment on the Microstructure and Mechanical Properties of High Strength Steel Weld Metals

摘要

The present work is part of a research program for the development of welding procedures for chains and accessories for application in mooring systems of oil platforms. In the specific case of the work in subject, the development of different covered electrodes formulations is discussed for obtaining high mechanical strength and impact toughness, of the order of 860 MPa and 50 joules at -20°C, respectively. Welded joints using the developed electrodes were prepared for evaluation of the mechanical properties, using a preheat of 200°C, direct current, flat position and heat input of 1.5 kJ/mm. After welding, tensile, impact Charpy-V and hardness tests were performed in specimens removed integrally from the weld metal, both in as welded and heat treated conditions. The post weld heat treatment (PWHT) was conducted at 600°C for 1, 2 and 3 hours. The results shows that the obtained weld metals have mechanical properties higher than the minimum required for the welding of a IACS W22 R4 Grade steel, and particularly good impact properties, which indicates that the correct control of the chemical composition, particularly, of Mn-Ni balance, makes possible to achieve an adequate strength/toughness relationship for high strength steel weld metals, where the PWHT is mandatory. In addition, it was verified that the increase in the time of PWHT did not promote substantial impairment on mechanical properties.