Ferritic stainless steel

Last updated

Ferritic stainless steel (SUS445J2) is used for the roof exterior of the Kyocera Dome Osaka, Japan. Kyocera Dome and Osaka Loop Line 2016-07-02.jpg
Ferritic stainless steel (SUS445J2) is used for the roof exterior of the Kyocera Dome Osaka, Japan.

Ferritic stainless steel [2] [3] forms one of the five stainless steel families, the other four being austenitic, martensitic, duplex stainless steels, and precipitation hardened . [4] For example, many of AISI 400-series of stainless steels are ferritic steels. By comparison with austenitic types, these are less hardenable by cold working, less weldable, and should not be used at cryogenic temperatures. Some types, like the 430, have excellent corrosion resistance and are very heat tolerant. [5]

Contents

History

Canadian-born engineer Frederick Mark Becket (1875-1942) at Union Carbide industrialised ferritic stainless steel around 1912, on the basis of "using silicon instead of carbon as a reducing agent in metal production, thus making low-carbon ferroalloys and certain steels practical". [6] He discovered a ferrous alloy with 25-27% Chromium that "was the first of the high-chromium alloys that became known as heat-resisting stainless steel." [7]

Ferritic stainless steels were discovered early but it was only in the 1980s that the conditions were met for their growth:

Metallurgy

Fe - Cr Phase diagram Diagramme phase Fe Cr.svg
Fe – Cr Phase diagram

To qualify as stainless steel, Fe-base alloys must contain at least 10.5%Cr.

The iron-chromium phase diagram shows that up to about 13%Cr, the steel undergoes successive transformations upon cooling from the liquid phase from ferritic α phase to austenitic γ phase and back to α. When some carbon is present, and if cooling occurs quickly, some of the austenite will transform into martensite. Tempering/annealing will transform the martensitic structure into ferrite and carbides.

Above about 17%Cr the steel will have a ferritic structure at all temperatures.

Above 25%Cr the sigma phase may appear for relatively long times at temperature and induce room temperature embrittlement.

Chemical composition

Chemical composition of a few grades of stainless steel.
Main alloying elements only: chromium (Cr) along with:
Ni, Mo, Nb, Ti, and C, N; Balance: Fe
AISI / ASTMENWeight %
CrOther elementsMelts at
4051.400012.0 – 14.0—
409L1.451210.5 – 12.56(C+N)<Ti<0.65
410L1.400310.5 – 12.50.3<Ni<1.0
4301.401616.0 – 18.0—1510 [10]
4391.451016.0 – 18.00.15+4(C+N)<Ti<0.8
430Ti1.451116.0 – 18.0Ti: 0.6
4411.450917.5 – 18.50.1<Ti<0.6

0.3+3C<Nb<1.0

4341.411316.0 – 18.00.9<Mo<1.4
4361.451316.0 – 18.00.9<Mo<1.4

0.3<Ti<0.6

4441.452117.0 – 20.01.8<Mo<2.5

0.15+4(C+N)<Ti+Nb<0.8

4471.459228 – 30.03.5<Mo<4.5

0.15+4(C+N)<Ti<0.8

Corrosion resistance

The pitting corrosion resistance of stainless steels is estimated by the pitting resistance equivalent number (PREN).

PREN = %Cr + 3.3%Mo + 16%N

Where the Cr, Mo, and N, terms correspond to the contents by weight % of chromium, molybdenum and nitrogen respectively in the steel.

Nickel (Ni) has no role in the pitting corrosion resistance, so ferritic stainless steels can be as resistant to this form of corrosion as austenitic grades.

In addition, ferritic grades are very resistant to stress corrosion cracking (SCC).

Physical properties

Ferritic stainless steels are magnetic. Some of their important physical, electrical, thermal and mechanical properties are given in the table here below.

Physical properties of the most common ferritic stainless steels
AISI / ASTMDensity
(g/cm3)		Electrical
resistance
(μΩ·m)		Thermal
conductivity
at 20 °C
(W/(m·K))		Specific
heat
0...100 °C
(J/(kg·K))		Thermal
expansion
0...600 °C
(10−6/K)		Young's
modulus
(GPa)
409 / 4107.70.582546012220
4307.70.602546011.5220
430Ti / 439 / 4417.70.602546011.5220
434 / 436 / 4447.70.602346011.5220
4477.70.621746011220

Compared to austenitic stainless steels, they offer a better thermal conductivity, a plus for applications such as heat exchangers. The thermal expansion coefficient, close to that of carbon steel, facilitates the welding to carbon steels.

Mechanical properties

Mechanical properties (cold rolled)
ASTM A240EN 10088-2
—UTS

(MPa, min)

0.2% yield stress

(MPa, min)

Elongation

(%, min)

—UTS

(MPa)

0.2% yield stress

(MPa, min)

Elongation

(%, min)

409390170201.4512380 – 56022025
410415205201.4003450 – 65032020
430450205221.4016450 – 60028018
439415205221.4510420 – 60024023
441415205221.4509430 – 63025018
434450240221.4113450 – 63028018
436450240221.4526480 – 56030025
444415275201.4521420 – 64032020

Applications

Related Research Articles

<span class="mw-page-title-main">Stainless steel</span> Steel alloy resistant to corrosion

Stainless steel, also known as inox, corrosion-resistant steel (CRES), and rustless steel, is an alloy of iron that is resistant to rusting and corrosion. It contains iron with chromium and other elements such as molybdenum, carbon, nickel and nitrogen depending on its specific use and cost. Stainless steel's resistance to corrosion results from the 10.5%, or more, chromium content which forms a passive film that can protect the material and self-heal in the presence of oxygen.

<span class="mw-page-title-main">Austenite</span> Metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element

Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727 °C); other alloys of steel have different eutectoid temperatures. The austenite allotrope is named after Sir William Chandler Roberts-Austen (1843–1902). It exists at room temperature in some stainless steels due to the presence of nickel stabilizing the austenite at lower temperatures.

Surgical stainless steel is a grade of stainless steel used in biomedical applications. The most common "surgical steels" are austenitic SAE 316 stainless and martensitic SAE 440, SAE 420, and 17-4 stainless steels. There is no formal definition on what constitutes a "surgical stainless steel", so product manufacturers and distributors often apply the term to refer to any grade of corrosion resistant steel.

<span class="mw-page-title-main">Martensitic stainless steel</span> One of the 5 crystalline structures of stainless steel

Martensitic stainless steel is a type of stainless steel alloy that has a martensite crystal structure. It can be hardened and tempered through aging and heat treatment. The other main types of stainless steel are austenitic, ferritic, duplex, and precipitation hardened.

<span class="mw-page-title-main">Carbon steel</span> Steel in which the main interstitial alloying constituent is carbon

Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Cryogenic hardening is a cryogenic treatment process where the material is cooled to approximately −185 °C (−301 °F), usually using liquid nitrogen. It can have a profound effect on the mechanical properties of certain steels, provided their composition and prior heat treatment are such that they retain some austenite at room temperature. It is designed to increase the amount of martensite in the steel's crystal structure, increasing its strength and hardness, sometimes at the cost of toughness. Presently this treatment is being used on tool steels, high-carbon, high-chromium steels and in some cases to cemented carbide to obtain excellent wear resistance. Recent research shows that there is precipitation of fine carbides in the matrix during this treatment which imparts very high wear resistance to the steels.

<span class="mw-page-title-main">Superalloy</span> Alloy with higher durability than normal metals

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.

The weldability, also known as joinability, of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others. A material's weldability is used to determine the welding process and to compare the final weld quality to other materials.

<span class="mw-page-title-main">Orthodontic archwire</span> Wire used in dental braces

An archwire in orthodontics is a wire conforming to the alveolar or dental arch that can be used with dental braces as a source of force in correcting irregularities in the position of the teeth. An archwire can also be used to maintain existing dental positions; in this case it has a retentive purpose.

<span class="mw-page-title-main">Chromium(II) carbide</span> Chemical compound

Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr3C2, Cr7C3, and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.

<span class="mw-page-title-main">Intergranular corrosion</span> When crystallite boundaries are more corrosive than their interiors

In materials science, intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides.

<span class="mw-page-title-main">Austenitic stainless steel</span> One of the 5 crystalline structures of stainless steel

Austenitic stainless steel is one of the five classes of stainless steel by crystalline structure. Its primary crystalline structure is austenite and it prevents steels from being hardenable by heat treatment and makes them essentially non-magnetic. This structure is achieved by adding enough austenite-stabilizing elements such as nickel, manganese and nitrogen. The Incoloy family of alloys belong to the category of super austenitic stainless steels.

<span class="mw-page-title-main">SAE steel grades</span> Standard alloy numbering system for steel grades

The SAE steel grades system is a standard alloy numbering system for steel grades maintained by SAE International.

<span class="mw-page-title-main">Alloy steel</span> Steel alloyed with a variety of elements

Alloy steel is steel that is alloyed with a variety of elements in amounts between 1.0% and 50% by weight, typically to improve its mechanical properties.

Zeron 100 is a super duplex stainless steel developed by Rolled Alloys. The alloy has excellent corrosion resistance combined with high strength. It typically contains 25% chromium and 7% nickel and 3.6% molybdenum along with copper and tungsten additions. Zeron 100 has a 50–50 austenitic–ferritic structure. It also has greater resistance to chloride pitting, crevice corrosion and stress corrosion cracking than exhibited by the standard 300 series stainless steels.

<span class="mw-page-title-main">Duplex stainless steel</span> Stainless steel that has both austenitic and ferritic phases

Duplex stainless steels are a family of stainless steels. These are called duplex grades because their metallurgical structure consists of two phases, austenite and ferrite in roughly equal proportions. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as type A2/304 or A4/316. The main differences in composition, when compared with an austenitic stainless steel is that the duplex steels have a higher chromium content, 20–28%; higher molybdenum, up to 5%; lower nickel, up to 9% and 0.05–0.50% nitrogen. Both the low nickel content and the high strength give significant cost benefits. They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc. and in the petrochemical industry in the form of pipelines and pressure vessels. In addition to the improved corrosion resistance compared with the 300 series duplex stainless steels also have higher strength. For example, a Type 304 stainless steel has a 0.2% proof strength in the region of 280 MPa (41 ksi), a 22%Cr duplex stainless steel a minimum 0.2% proof strength of some 450 MPa (65 ksi) and a superduplex grade a minimum of 550 MPa (80 ksi).

<span class="mw-page-title-main">SAE 304 stainless steel</span> Most common stainless steel

SAE 304 stainless steel is the most common stainless steel. It is an alloy of iron, carbon, chromium and nickel. It is an austenitic stainless steel, and is therefore not magnetic. It is less electrically and thermally conductive than carbon steel. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.

Havar, or UNS R30004, is an alloy of cobalt, possessing a very high mechanical strength. It can be heat-treated. It is highly resistant to corrosion and is non-magnetic. It is biocompatible. It has high fatigue resistance. It is a precipitation hardening superalloy.

<span class="mw-page-title-main">475 °C embrittlement</span> Loss of plasticity in ferritic stainless steel

Duplex stainless steels are a family of alloys with a two-phase microstructure consisting of both austenitic and ferritic phases. They offer excellent mechanical properties, corrosion resistance, and toughness compared to other types of stainless steel. However, duplex stainless steel can be susceptible to a phenomenon known as 475 °C (887 °F) embrittlement or duplex stainless steel age hardening, which is a type of aging process that causes loss of plasticity in duplex stainless steel when it is heated in the range of 250 to 550 °C. At this temperature range, spontaneous phase separation of the ferrite phase into iron-rich and chromium-rich nanophases occurs, with no change in the mechanical properties of the austenite phase. This type of embrittlement is due to precipitation hardening, which makes the material become brittle and prone to cracking.

References

  1. ↑ "屋根:大阪ドーム" (in Japanese). Japan Stainless Steel Association. Retrieved 12 October 2023.
  2. ↑ Lacombe, P.; Baroux, B.; Beranger, G., eds. (1990). Les Aciers Inoxydables. Les éditions de Physique. pp. Chapters 14 and 15. ISBN   2-86883-142-7.
  3. ↑ The ferritic solution. 2007. ISBN   978-2-930069-51-7. Archived from the original on 21 December 2019. Retrieved 14 July 2019.
  4. ↑ The International Nickel Company (1974). "Standard Wrought Austenitic Stainless Steels". Nickel Institute. Archived from the original on 9 January 2018. Retrieved 9 January 2018.
  5. ↑ "304 vs 430 stainless steel". Reliance Foundry Co. Ltd. Retrieved 28 May 2022.
  6. ↑ "Frederick Mark Becket American metallurgist". Encyclopaedia Britannica. 7 January 2021.
  7. ↑ Cobb, Harold M. (2012). Dictionary of Metals. ASM International. p. 307. ISBN   9781615039920.
  8. ↑ Charles, J.; Mithieux, J.D.; Santacreu, P.; Peguet, L. (2009). "The ferritic family: The appropriate answer to nickel volatility?". Revue de Métallurgie. 106: 124–139. doi:10.1051/metal/2009024.
  9. ↑ Ronchi, Gaetano (2012). "Stainless Steel for House-ware". Metal Bulletin.
  10. ↑ "Stainless steel melting points". Thyssenkrupp Materials (UK) Ltd. Retrieved 28 May 2022.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.