High Strength Corrosion Resistant Steel Alloy for Aerospace Industry
Aircraft landing gears and structures have stringent performance requirements. They are subjected to severe loads, corrosion, and adverse environmental conditions, and have complex shapes which vary in thickness. 300M steel is widely used for high stress aircraft landing gears and structures. This steel is not corrosion-resistant and requires protective coatings. Plating of 300M steel involves using cadmium for corrosion resistance on external surfaces and chrome for wear resistance on internal surfaces. New restrictions have listed cadmium and chrome coatings as substances of concern due to the environmental and health risks associated with the manufacturing of cadmium and chrome coatings. Recently, a new alternative non-toxic zinc-nickel coating is being developed, however, the zinc-nickel coating does not solve the corrosion problem if it cracks. Ultimately, the use of stainless steel provides a more robust solution, reducing maintenance time and cost of repairs caused by corrosion.
New cobalt-free, quenched and tempered high strength corrosion resistant steel (“HSCR steel”) provides the same strength, ductility, and toughness as the 300M steel and while it possesses corrosion resistance in salt spray test. HSCR steel is protected by the U.S. Patent No 8,361,247.
Table 1 shows a comparison of room temperature mechanical properties of the HSCR steel and 300M steel after solution annealing, oil quenching, and tempering.
HSCR steel has showed no rust after the salt spray test in 5% NaCl solution at 95°F for more than 200 hrs.
Aerospace applications of the wrought HSCR steel include landing gear components, rotatable shafts, actuators, flap tracks, slat tracks, fasteners, and others.
Modification of the HSCR steel is applicable for casting, including investment casting, sand casting and other commonly used casting techniques. The casted HSCR steel possesses higher strength than the casted 17-4 PH stainless steel at the same ductility and toughness. Corrosion resistance of the casted HSCR steel is lower than casted 17-4 PH stainless steel and it is comparable with the corrosion resistance of the casted 420 martensitic stainless steel.
Table 2 shows a comparison of mechanical properties of the casted HSCR steel and 17-4 PH stainless steel after annealing and hardening
Aerospace applications of the investment casted HSCR steel include hydraulic fluid system components, motion control and actuation systems, cargo system, bearing cages, flight critical and safety components.