Interest in the welding of ultra-high strength steel sheet has been generated within the last several years by the requirement of the rocket motor case industry for a very high strength-to-weight material. For this reason virtually all recent activity in learning to weld these steels has been closely associated with the missile industry; this report is largely a summary of missile industry welding experience with these steels.
The candidate base metal alloys for this classification (nominal yield strength greater than 200,000 psi) are discussed, and the reasons for the preference for the low alloy martensitic class are reviewed. The requirement for fracture toughness and resistance to multiaxial loading is important in this selection. A recently developed type, the high nickel maraging steels, shows promise in preliminary analysis of better meeting these requirements, and is discussed.
The procedures for tungsten arc welding these steels are reviewed in some detail. At these high strength levels the fracture toughness is, at best, limited and every effort must be made to minimize the flaw size. Since the weld metal, without benefit of rolling, is a likely zone for flaws to occur, attention to weld process details cannot be too strongly encouraged. The thermal cycles required (preheat and post heat) for these steels are unusual, compared to those procedures used for lower strength steels, and are discussed.
The mechanical behavior of these steels in a motor case loading system has proved difficult to predict by the conventional weld joint tensile tests. For this reason the motor case requirement has touched off a wave of testing developments. Fracture toughness has become an important consideration and tests have been developed to measure this property. Biaxial bulge tests and subsized cylinder tests are also discussed. Base metal and weldment capabilities are presented in terms of these tests.
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| Number of Pages : | 23 |
| Published : | 1962 |
