Maraging steels (from martensitic and aging) are steels (iron alloys) which are known for possessing superior strength and toughness without losing malleability, although they cannot hold a good cutting edge. Aging refers to the extended heat-treatment process. These steels are a special class of low- carbon ultra- high-strength steels which derive their strength not from carbon, but from precipitation of inter-metallic compounds. The principal alloying element is 15 to 25% nickel. Secondary alloying elements are added to produce intermetallic precipitates, which include cobalt, molybdenum, and titanium. Original development was carried out on 20 and 25% Ni steels to which small additions of Al, Ti, and Nb were made.
The common, non-stainless grades contain 17-19% nickel, 8-12% cobalt,3-5% molybdenum, 0.2-1.6% titanium. Addition of chromium and produces stainless grades resistant to corrosion. This also indirectly increases hardenability as they require less nickel: high-chromium, high-nickel steels are generally austenitic and unable to transform to martensite when heat treated, while lower-nickel steels can transform to martensite.
Properties
Due to the low carbon content maraging steels have good machinability. Prior t o aging, they may also be cold rolled to as much as 80- 90% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the properties of heat affected zone. When heat-treated the alloy has very little dimensional change, so it is often machined to its final dimensions. Due to the high alloy content maraging steels have a high hardenability. Since ductile FeNi martensites are formed upon cooling, cracks are non-existent or negligible. The steels can be nitrided to increase case hardness, and polished to a fine surface finish.
Non-stainless varieties of maraging steel are moderately corrosion- resistant, and resist stress corrosion and hydrogen embrittlement. Corrosion- resistance can be increased by cadmium plating or phosphating.
