This is the "king" of the hardening grades of constructional alloy steels. Because of richer alloy content, 4340 possesses much deeper hardenability than the 4100 series. This advantage is realized principally where high strength is required in heavy sections. In addition, unusually high hardenability insures maximum toughness and ductility at the desired strength level. The fatigue-tensile ratio makes this grade ideal for highly stressed parts. It maintains its strength, ductility, and toughness at relatively high temperatures. It has remarkable non-distorting properties for an alloy steel. Thus, for high strength in heavy sections, or for highly stressed parts operating under the most severe conditions, or where the greatest margin of safety is desired, this is the steel to use.

Nickel-Chromium-Molybdenum Steel

UNS G43400