HP9-4-.30 weld properties and microstructure

HP9-4-.30, ultra high strength steel, the case material for the Advanced Solid Rocket Motor (ASRM), must exhibit acceptable strength, ductility, toughness, and stress corrosion cracking (SCC) resistance after welding and a local post weld heat treatment (PWHT). Testing, to date, shows that the base metal (BM) properties are more than adequate for the anticipated launch loads. Tensile tests of test specimens taken transverse to the weld show that the weld metal overmatches the BM even in the PWHT condition. However, that is still some question about the toughness and SCC resistance of the weld metal in the as welded and post weld heat treated condition. To help clarify the as welded and post weld heat treated mechanical behavior of the alloy, subsize tensile specimens from the BM, the fusion zone (FZ) with and without PWHT, and the heat affected zone (HAZ) with and without PWHT were tested to failure and the fracture surfaces subsequently examined with a scanning electron microscope. Results are given and briefly discussed.