![]() The test program involved five alloys and seven test media. In addition, tests were conducted to evaluate the effects of overloads and metallurgical factors on corrosion fatigue crack growth. This experimental program was undertaken to obtain information on stress corrosion cracking and corrosion fatigue crack growth in high-strength metal alloys suitable for airframe components. The weld procedure was found to be tolerant to rather wide parameter variations. Variations in land thickness, plasma gas flow rate, current, travel speed, and arc length were characterized by measuring weld bead shape geometry. This PWHT produced the best combination of strength, toughness, and acceptable residual stresses. more » The test technique systematically varied the essential plasma arc parameters: current, travel speed, plasma gas or wire feed speed while maintaining constant arc length and torch set-up conditions. Therefore, a comprehensive development plan was performed to fully characterize plasma arc welding HP 9Ni-4Co-0.30 steel. The minimum mechanical property requirements of the weldment are 190 ksi yield, 205 ksi ultimate, 8% elongation, 25% reduction in area and 90 ksi/in. The HP 9Ni-4Co-0.30C steel was chosen for the ASRM application because the material has excellent strength, toughness, and weldability. Plasma arc welding (PAW) was chosen because this process assures a full penetration root pass with the keyhole mode. The plasma arc welding process is used to fabricate the advanced solid rocket motor (ASRM) casing for the Space Shuttle. ![]() This susceptibility to SCC was reduced by stress relieving. Under the conditions of these tests, the straight polarity plasma arc welded HP 9Ni4Co-0.30C steel plate was found highly susceptible to SCC in the nonstress-relieved condition. The stress relief also had a positive effect on the mechanical properties of more » the welds (the most important being an increase of 21 percent on the YS). No failures occurred at 50 percent of YS in the stress-relieved specimens which indicates a beneficial effect of the stress relief on the SCC resistance of these welds. Stress-relieved specimens (exposed to alternate immersion) failed at 75 and 90 percent of YS. All the nonstress-relieved specimens exposed to salt spray and alternate immersion failed. The stress levels were 50, 75, and 90 percent of the corresponding 0.2-percent yield strength (YS). Specimens obtained from stress-relieved material were tested in alternate immersion. Round tensile specimens obtained from nonstress-relieved material were tested in 100-percent relative humidity at 38 C (100 F), in 3.5-percent NaCl alternate immersion, and in 5-percent salt spray at 35 C (95 F). After welding, only part of the material was stress relieved at 510 C (950 F) for 3 h. Prior to the welding, the material was double tempered at 538 C (1,000 F). A stress corrosion cracking (SCC) investigation was conducted on HP 9Ni-4Co-0.30C steel plate welds (welded by using straight polarity plasma arc and HP 9Ni-4Co-0.20C weld wire) since this material is being considered for use in the Advanced Solid Rocket Motor (ASRM) program.
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