Fractographic and Microstructural Analysis of SCC Specimens of HY-100, HY-130, and HY-180 Steel Weldments

摘要

This report summarizes an investigation of the microstructures and fracture morphologies of selected double-V weldments of HY-100, HY-130, and HY-180 steels fractured under stress in an aqueous environment. The specimens, which were prepared using substantially different welding practices and filler materials, displayed similar K sub Iscc values. Optical examination of the microstructures showed that repeated thermal cycling, which occurs during fabrication of GTA (gas-tungsten-arc) fine-bead as-welded specimens, resulted in a uniform, fine-grained, tempered microstructure that offered the greatest resistance to stress-corrosion (SCC). Microvoid coalescence (MVC) was the dominant fracture mode. Coarse-bead, as-welded, GMA (gas-metal-arc) specimens contained substantial amounts of high-temperature-transformation products which fractured by cleavage. Heat treating these specimens, to a lower yield strength, refined the microstructure and improved the SCC resistance. The dominant fracture mode of the heat-treated specimens was MVC. Microbranching of the advancing crack front occurred in the cross-bead, as-welded specimens and may be responsible for the relatively high K sub Iscc values reported.