S. D. Kiser, B. A. Baker, Special Metals Company, Newton, NC
Nickel-Chromium-Iron alloys and welding products have been used throughout the life of the nuclear welding industry. From the beginning, Welding Electrode 182 and Filler Metal 82 were used to weld alloy 600 until they were found to be susceptible to primary water stress-corrosion-cracking (PWSCC). This brought about the need for a 30% Cr-containing alloy 690 along with Welding Electrode 152 and Filler Metal 52. These materials were resistant to PWSCC, but the welding products are susceptible to DDC.Because DDC is a solid state cracking phenomenon that may occur in highly restrained austenitic welds, most of the existing tests were ineffectual for measuring DDC. The Ohio State University welding group introduced the Strain-to-Fracture (STF) test to measure the tendency for DDC. A number of nuclear welding materials have been subjected to STF testing and a new nickel alloy material with 30% chromium has shown substantially improved DDC cracking resistance when measured with the STF test. This paper discusses the development of the welding material.
Summary: This nickel alloy welding material has shown a factor of 3x improvement in critical strain rate over existing nuclear welding products in the OSU Strain-to-Fracture test. This significant improvement is effected by the encouragement of optimally deployed MC-type carbides which pin migrating grain boundaries to form interlocking serpentine boundaries which resist DDC.
