Tweezers made of martensitic stainless steel JIS SUS410

Martensitic stainless steels are a family of

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

s having body-centered tetragonal (BCT)

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

and a predominately

martensite Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. Properties Mar ...

structure. They are characterized by being magnetic and having the ability to be hardened through heat treatment. Martensitic stainless steels are designated as part of the 400-series of stainless steels in the

SAE steel grades The SAE steel grades system is a standard alloy numbering system (SAE J1086 – Numbering Metals and Alloys) for steel grades maintained by SAE International. In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were both ...

numbering system.

History

In 1912, Harry Brearley of the Brown-Firth research laboratory in

Sheffield, England Sheffield is a city in South Yorkshire, England, situated south of Leeds and east of Manchester. The city is the administrative centre of the City of Sheffield. It is historically part of the West Riding of Yorkshire and some of its southe ...

, while seeking a corrosion-resistant alloy for gun barrels, discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in ''

The New York Times ''The New York Times'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of ...

''. Brearly applied for a U.S. patent during 1915. This was later marketed under the "''Staybrite''" brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in 1929 in

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

. The characteristic body-centered tetragonal martensite microstructure was first observed by German microscopist Adolf Martens around 1890. In 1912, Elwood Haynes applied for a U.S. patent on a martensitic stainless steel alloy. This patent was not granted until 1919.

Overview

Martensitic stainless steels can be high- or low-carbon steels built around the composition of iron, 12% up to 17% chromium, carbon from 0.10% (Type 410) up to 1.2% (Type 440C): The chromium and carbon contents are balanced to have a martensitic structure. They may contain some nickel which allows a higher chromium or molybdenum content, thereby improving corrosion resistance and as the carbon content is also lower, the

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.creep resistance.

Common grades

* Type 410 is a general purpose grade containing 0.15% maximum carbon. * Type 420 increases the carbon content to 0.15% mininum for improved strength * Type 431 has added nickel content for improved corrosion resistance * Types 440A, 440B and 440C increases the carbon content . Type 440C contains 0.95-1.20% carbon for highest hardness. Types 440B and 440A decreases the carbon content relative to Type 440C for improved toughness.

Properties

Corrosion resistance

Martensitic stainless steels are generally resistant to corrosion only in relatively mild environments and have lower corrosion resistance compared to austenitic stainless steels.

Strength

Martensitic stainless alloys are hardenable by heat treatment, specifically by quenching and stress relieving, or by quenching and tempering (referred to as QT).Budynas, Richard G. and Nisbett, J. Keith (2008). Shigley's Mechanical Engineering Design, Eight Edition. New York, NY: McGraw-Hill Higher Education. . The alloy composition, and the high cooling rate of quenching enable the formation of martensite. Untempered martensite is low in toughness and therefore brittle.Tempered martensite gives steel good hardness and high toughness as can be seen below, and is largely used for medical surgical instruments, such as scalpels, razors, and internal clamps.

Physical properties

Martensitic stainless steels are ferromagnetic due to their BCT crystal structure.

Processing

When formability, softness, etc. are required in fabrication, steel having 0.12% maximum carbon is often used in soft condition. With increasing carbon, it is possible by hardening and tempering to obtain tensile strength in the range of , combined with reasonable toughness and ductility. In this condition, these steels find many useful general applications where mild corrosion resistance is required. Also, with the higher carbon range in the hardened and lightly tempered condition, tensile strength of about may be developed with lowered ductility. Martensitic stainless steel can be nondestructively tested using the

magnetic particle inspection file:Wet magnetic particle testing on a pipeline.jpg, A technician performs MPI on a pipeline transport, pipeline to check for stress corrosion cracking using what is known as the "black on white" method. No indications of cracking appear in this ...

method, unlike austenitic stainless steel.

Applications

Martensitic stainless steels, depending upon their carbon content and are often used for their corrosion resistance and high strength. They are also used for their wear resistance. * Up to about 0.4% C they are used mostly for their mechanical properties in applications such as pumps, valves, and shafts. * Above 0.4% C they are used mostly for their wear resistance, such as in cutlery, surgical blades, plastic injection molds, and nozzles. Grade EN 1.4313 (CA6NM) is used for nearly all the hydroelectric turbines in the world, including those of the huge "Three Gorges" dam in China.

References

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