Aircraft Quality 4340 Steel Helps the Rubber Meet the Runway
December 31, 2012 -
Made from a pitch-perfect mixture of nickel, chromium, molybdenum and other elements, AISI 4340 alloy steel is known as "aircraft quality" steel for a good reason: It is a crucial ingredient in many of the most durable parts of commercial and military aircraft. Thanks to certain properties that set it apart from other alloys, 4340 steel is especially important as a component of the landing gear and undercarriage parts that enable high-capacity jets to take off and land safely.
A plane is useless without reliable landing gear. During its functional lifespan, a given plane may execute tens of thousands of takeoffs and landings. Every year, millions of such maneuvers are performed around the world. The fact that landing gear failures are exceedingly rare is a testament to the durability and strength of modern aeronautical equipment. The resilient 4340 steel bars, sheets and tubes that hold together most commercial planes' landing gear complexes are the principal reason for this incredible safety record.
Every time a commercial plane touches down, the force of its meeting with the ground places a tremendous amount of weight and pressure on its two rear landing gear clusters. The tubes and plates that hold these units together must be able to withstand both the initial impact as well as the multi-dimensional movements that buffet a rapidly-decelerating aircraft.
Fortunately, aircraft quality 4340 steel is durable enough to absorb these forces and bend slightly without losing its strength or integrity. Unlike some other grades of steel, 4340 steel is particularly receptive to "case-hardening." This process involves adding additional carbon to the surface of the parts during heat treatment which produces a super-hard "shell" that reduces its susceptibility to denting and fracturing. Case-hardened landing gear holds up better against the flying bits of gravel, asphalt and other debris that get kicked up during the landing process.
Thanks to its unique blend of carbon, chromium, nickel and molybdenum, aircraft quality 4340 steel is also unusually ductile without being overly malleable. In addition to case-hardening, it also responds well to certain heat treatments that confer extra strength and durability.
Landing gear steel can be heated rapidly and then allowed to cool slowly in a process known as "annealing." This allows it to be shaped with greater precision at cold temperatures and reduces its susceptibility to heat. Both properties are essential in the high-impact, high-temperature environment to which landing gear is regularly exposed.
Since 4340 grade steel is lighter than has a strength to weight ratio better than other alloys, it's well-suited for inclusion in dense landing gear. Landing gear made from aircraft quality 4340 tubes and plates may weigh dozens of pounds less than similar equipment made from other alloys. In an industry that values fuel efficiency, this can have a significant effect on fuel mileage and may save airlines thousands of dollars per year. Whether it's contributing to the airline industry's solid safety record or saving thousands of gallons of fuel every year, landing gear made from aircraft quality 4340 steel does plenty to earn its excellent reputation.