Report On The Fourth Maraging Steel Project Review

This report resulted from a survey of users and manufacturers of maraging steels, Government agencies, research institutions, and published literature. It presents the technical status of the 18-percent nickel maraging steels in detail and brings together a large body of knowledge with regard to the metallurgical and engineering aspects of maraging steels. Since such steels were first announced in 1959, they have become highly important in aerospace, defense, and industrial work. The requirements of the National Aeronautics and Space Administration have given impetus to their development, and research now underway is expected to result in further improvements and applicability. The NASA Office of Technology Utilization sponsored this report as part of its program to disseminate information on technological developments which appear to be useful for general industrial applications.

Recent studies of the developments in welding steels with yield strengths greater than 150 ksi have included low-alloy martensitic steels, medium-alloy martensitic steels, nickel maraging steels, and bainitic steels. Only weldments from medium-alloy martensitic steels and nickel maraging steels have mechanical properties approaching those of the base plate without a complete postweld heat treatment. The most serious problem with the other steel is low toughness in the weld fusion zone. Adequate weld metal toughness under conditions of elastic strain can be obtarined over the entire 150 to 225 ksi yield-strength range only if the tungsten-arc welding process is used. Processes with higher deposition rates can produce comparable weld deposits only in the lower portion of the range. Above a yield strength of 200 ksi, 18Ni maraging steel weldments have the best combination of strength and toughness. Below 200 ksi, the HP 9-4-25 medium-alloy martensitic steel and 12Ni maraging steel weldments have nearly equal properties.

The report summarizes the advancements made in the development and welding of steels possessing yield strengths greater than 150,000 psi. Steels discussed include the medium carbon, low-alloy martensitic steels; low carbon alloy martensites; and nickel maraging steels. Almost all programs which have the objective of developing high-strength steels have an equally important phase concerned with filler metal development. Filler metals are also discussed. The new welding processes discussed are Narrow-Gap welding, electron-beam welding, plasma-arc welding, high-frequency resistance welding, electroslag welding, laser welding, and interrupted-arc (dip trasfer) MIG welding. (Author).

The Memorandum discusses the current situation on the inclusion of fracture-toughness testing requirements in specifications for high-strength steels used for military applications. The Memorandum was prepared at the request of The Technical Cooperation Program (TTCP), and contains information from Canadian and British members of that program, as well as U.S. information. Military applications discussed include missile motor cases, aircraft landing gear, gun tubes, armor plate, and hydrofoils. (Author).