EFFECT OF AGING TREATMENT ON THE MICROSTRUCTURES AND PROPERTIES OF T-250 LASER WELDS

Abstract

The mechanical and fatigue crack growth properties of T-250 laser welds aged at various temperatures have been evaluated. The results show that there are austenitic pools dispersed along the interdendritic boundaries. Their sizes and amounts increase with increasing ageing temperature. After 593-degrees-C ageing, an extensive formation of lamellar reverted austenite was observed throughout the weld metal. The 482-degrees-C aged welds had the highest strength and lowest ductility among the welds. Impact toughness increases with increasing ageing temperature. The crack growth rate, in general, decreases with increasing ageing temperature. The base metal, the HAZ, and the weld metal show a similar crack growth characteristics for the weld aged at 482-degrees-C and 538-degrees-C. However, for the welds aged at 593-degrees-C, the weld metal displays a lower crack growth rate compared to that of the base metal and HAZ. The results also indicate that a crack might change its growth direction become arrested if impinged on by an austenite pool. It is obvious that austenite pools reduced the weld strength, but they could improve the resistance to fatigue crack propagation. The 426-degrees-C aged welds exhibit an unstable crack growth at the weld metal in the employed DELTAK range.