The Full Wiki

Maraging steel: Wikis

Advertisements
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Encyclopedia

From Wikipedia, the free encyclopedia

Maraging steels (a portmanteau of martensitic and aging) are iron alloys which are known for possessing superior strength and toughness without losing malleability, although they can not hold a good cutting edge. 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.[1] Secondary alloying elements are added to produce intermetallic precipitates, which include cobalt, molybdenum, and titanium.[1] 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, and 0.2–1.6% 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.

Contents

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 80–90% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the properties of heat affected zone.[1]

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 the alloys have a high hardenability. Since ductile FeNi martensites are formed upon cooling, cracks are non-existent or negligible. They can also be nitrided to increase case hardness. They can be polished to a fine surface finish.

Non-stainless varieties of maraging steels are moderately corrosion-resistant, and resist stress corrosion and hydrogen embrittlement. More corrosion protection can be gained by cadmium plating or phosphating.

Heat treatment cycle

The steel is first annealed at approximately 820 °C (1,510 °F) for 15–30 minutes for thin sections and for 1 hour per 25 mm thickness for heavy sections, to ensure formation of a fully austenitized structure. This is followed by air cooling to room temperature to form a soft, heavily-dislocated iron-nickel lath (untwinned) martensite. Subsequent aging (precipitation hardening) of the more common alloys for approximately 3 hours at a temperature of 480 to 500 °C produces a fine dispersion of Ni3(X,Y) intermetallic phases along dislocations left by martensitic transformation, where X and Y are solute elements added for such precipitation. Overaging leads to a reduction in stability of the primary, metastable, coherent precipitates, leading to their dissolution and replacement with semi-coherent Laves phases such as Fe2Ni/Fe2Mo. Further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite.

Newer compositions of maraging steels have revealed other intermetallic stoichiometries and crystallographic relationships with the parent martensite, including rhombohedral and massive complex Ni50(X,Y,Z)50, or Ni50M50 in simplified notation.

Uses

Maraging steel's strength and malleability in the pre-aged stage allows it to be formed into thinner rocket and missile skins than other steels, reducing weight for a given strength. Maraging steels have very stable properties, and, even after overaging due to excessive temperature, only soften slightly. These alloys retain their properties at mildly elevated operating temperatures and have maximum service temperatures of over 400 °C (752 °F).[citation needed] They are suitable for engine components, such as crankshafts and gears, and the firing pins of automatic weapons that cycle from hot to cool repeatedly while under substantial load. Their uniform expansion and easy machinability before aging make maraging steel useful in high-wear components of assembly lines and dies. Other ultra-high-strength steels, such as Aermet alloys, are not as machinable because of their carbide content.

In the sport of fencing, blades used in competitions run under the auspices of the Fédération Internationale d'Escrime are often made with maraging steel. Maraging blades are required in foil and épée because crack propagation in maraging steel is 10 times slower than in carbon steel, resulting in less blade breakage and fewer injuries. The notion that such blades break flat is a fencing urban legend: testing has shown that the blade-breakage patterns in carbon steel and maraging steel blades are identical[citation needed]. Stainless maraging steel is used in bicycle frames and golf club heads. It is also used in surgical components and hypodermic syringes, but is not suitable for scalpel blades because the lack of carbon prevents it from holding a good cutting edge.

Maraging steel production, import, and export by certain states, such as the United States,[2] is closely monitored by international authorities because it is particularly suited for use in gas centrifuges for uranium enrichment; lack of maraging steel significantly hampers this process.

Physical properties

References

  1. ^ a b c Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, p. 119, ISBN 0-471-65653-4 .
  2. ^ PART 110--EXPORT AND IMPORT OF NUCLEAR EQUIPMENT AND MATERIAL, http://www.nrc.gov/reading-rm/doc-collections/cfr/part110/full-text.html, retrieved 2009-11-11. 
  3. ^ ASM Materials Information Online
  4. ^ Yuji Ohue, Koji Matsumoto, "Sliding–rolling contact fatigue and wear of maraging steel roller with ion-nitriding and fine particle shot-peening", volume 263, issues 1–6, 10 September 2007, pages 782–789, 16th International Conference on Wear of Materials

External links

Advertisements

Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message