Commercial and military aircraft landing gears are often produced using low alloy steel, 300M, with cadmium plating for corrosion resistance. Within a few years, cadmium plating will not be possible because of environmental concerns. A possible alternative is the use of a stainless steel that has strength levels comparable to 300M and does not require cadmium coatings. The development of such a steel has been of great interest to airplane manufacturers, landing gear producers, and speciality steel companies. Despite several years of work, an ultra-high strength stainless steel with sufficient toughness for landing gear applications has not been developed. This research explores the development of an ultra-high strength, precipitation-strengthened martensitic stainless steel that has both high strength and toughness, and is strengthened by the precipitation of particles of R-phase. These steels contain approximately 12 wt. % chromium, 5 wt. % molybdenum, 12 wt. % cobalt, and up to 6 wt. % nickel. Variations of these in the steel are expected to result in yield strength and ultimate tensile strength of 1475MPa and 1650MPa, respectively, and also would have excellent toughness. With this award, the effects of cobalt, molybdenum and carbon are to be examined on the strength and toughness of these alloys. To have good toughness, the alloying content of the steels will be controlled, primarily through the nickel content, so that the steels contain 6 to 8 volume % retained austenite in the as-quenched condition.
Successful development of an ultra-high strength stainless steel for landing gear applications will answer a major industrial need. Educational benefits include experience for a female graduate student to assist in the research. Students will be trained to use the scanning electron microscope to examine fracture surfaces and X-ray diffraction to measure retained austenite content. Students learn how to use such equipment and analysis methods when they are working on research projects that provides these types of experiences.
