Influence of Chemical Composition on the Mechanical and Microstructural Properties of High Strength Steel Weld Metals Submitted to PWHT

Abstract

The development of new filler metals for offshore industry is challenging because high strength and toughness levels are required after post-welding heat treatment (PWHT) is applied to reduce residual stresses. The higher chromium contents added to the chemical composition of welding consumables to attain the required ultimate tensile strength are usually associated with reduced toughness. This work presents a comparative analysis of the behavior of two high strength steel weld metals with different Cr–Mo and Mn–Ni additions that were submitted to PWHT. Weld metals obtained by shielded metal arc welding process were evaluated using mechanical tests (Charpy-V notch and Vickers microhardness) and microstructural analysis (scanning electron microscopy and electron backscattered diffraction) conducted in samples removed from the center line of weld deposits, both in the as-welded and heat-treated (600 °C for 1 h) conditions. Although similar results were obtained in the as-welded condition, different behaviors were observed after PWHT. While impact toughness for Cr–Mo additions was reduced by carbide precipitation, as predicted by thermo-calc simulation, weld metal based on Ni–Mn addition exhibited improvements after PWHT because the predominantly martensite microstructure was tempered. This makes the latter more appropriate for weldments submitted to PWHT.