|
Maraging steels (a portmanteau of "martensitic" and "aging") are steels (iron alloys) that 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 that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt.% nickel. Secondary alloying elements, which include cobalt, molybdenum, and titanium, are added to produce intermetallic precipitates,.〔 Original development (by Bieber of Inco in the late 1950s) was carried out on 20 and 25 wt.% Ni steels to which small additions of Al, Ti, and Nb were made; a rise in the price of cobalt in the late 1970s led to the development of cobalt-free maraging steels 〔.〕 The common, non-stainless grades contain 17–19 wt.% nickel, 8–12 wt.% cobalt, 3–5 wt.% molybdenum, and 0.2–1.6 wt.% titanium. Addition of chromium 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. Alternative variants of Ni-reduced maraging steels are based on alloys of Fe and Mn plus minor additions of Al, Ni, and Ti where compositions between Fe-9wt.% Mn to Fe-15wt.% Mn have been used.〔.〕 The Mn has a similar effect as Ni, i.e. it stabilizes the austenite phase. Hence, depending on their Mn content, Fe-Mn maraging steels can be fully martensitic after quenching them from the high temperature austenite phase or they can contain retained austenite. The latter effect enables the design of maraging-TRIP steels where TRIP stands for Transformation-Induced-Plasticity. ==Properties== Due to the low carbon content maraging steels have good machinability. Prior to aging, they may also be cold rolled to as much as 90% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the original properties to the 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Maraging steel」の詳細全文を読む スポンサード リンク
|