Hydrogen-Induced Cracking in GMA Welds of Vanadium–Titanium Microalloyed High Strength Steel

Abstract

High strength low alloy (HSLA) steels are developed to provide better strength, toughness, and improved weldability. These steels are often used as better alternatives for quenched and tempered steels due to the excellent combination of these properties. The beneficial properties in these steels are achieved by careful control of composition and by adopting suitably controlled thermomechanical processing (TMCP). Improved weldability is achieved by maintaining carbon at lower level. To compensate the effect of carbon, small amounts of alloying elements, such as niobium, vanadium, titanium, aluminium, and nitrogen are added. Though these steels have good weldability, they suffer from hydrogen induced cracking especially at high strength levels. In the present study, hydrogen induced cracking susceptibility of a newly developed indigenous vanadium-titanium microalloyed high strength steel was evaluated by means of implant cracking test. Welding was carried out using the GMAW process at different heat input levels. It was found that the coarse-grained heat affected zone (CGHAZ) of the steel is prone for hydrogen induced cracking at lower heat inputs. The implant test results indicated that the critical stress level increases with increasing heat inputs. The results were correlated with the microstructural modifications that occur in the CGHAZ at different welding conditions. The microhardness variations in that region were in good agreement with the observed results.

Evaluation of Cracking Susceptibility of Weldment Container for Nuclear Power Plant

“…It is known [14] that cold cracks occurred in pressure vessel weldment, especially at the HAZ, due to a low ductility, which is not sufficient to relax the developed stresses. The presence of V in the WSTE-51 steel promotes fine carbide precipitation in the grain boundaries and favors the nucleation of cracks to accommodate the thermal stresses [2,15]. The weld overpass technique reproduced in the VINCKIER test dissipates the thermal stresses by renormalizing the whole weldment including the HAZ.…”