A Guide to Stainless Steel Grades

STAINLESS STEEL GRADES

A GUIDE BY INTAMET

304 / 304L Generally regarded as 18/8 stainless steel due to nominal Chrome (18%) and Nickel Content (8%), this grade is associated with typical applications where environment corrosion is not a key factor. This alloy has good welding characteristics and machining properties. The lower the carbon content the more resistant material is to carbide precipitation at higher temperature. Typical applications include internal architectural, heat exchanger and food processing.

304H In alloy terms similar to 304, with a carbon content range of 0.040% minimum, to 0.080%. The higher carbon level increases strength when using in higher temperature applications such as pressure containing lines and vessels and often associated with Petrochemical. This grade is normally certified with a grain size of No. 7 or courser. The grain size should be considered when the material is being formed to extremes.

321/321H This alloy is a stabilized grade of in essence 304 with the addition of Titanium (Ti) at 5 x Carbon content minimum. It prevents carbide precipitation during welding and improves elevated temperature properties. Excellent resistance to oxidation and good creep strength. Corrosion resistance good. "H" grade is same alloy with a higher carbon range of 0.040% to 0.080%. Typical applications include refinery equipment, automotive exhaust headers, welded pressure vessels and generally applications with higher temperature service.

316/316L - 316H - 316TI Often referred as marine grade, 316 austenitic stainless steel materials with their inclusion of Molybdenum (Mo) offer excellent corrosion resistance. Superior to 304 in corrosion resistance this grade also offers a high resistance to pitting and crevice corrosion, in chloride environments. This alloy offers excellent welding characteristics and good forming properties. Low carbon grades "316L" and stabilized grades "316Ti" are very good for welding, whilst 316H and 316Ti with higher carbon content are good at higher strength elevated temperature application. Apart from marine, petrochemical, power generation and external architectural applications, 316 is regularly used in process control.

347/347H 347/347H stainless steel is similar to 321 albeit this stabilised grade by the addition of Columbium and Tantalum. This offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range 427-816 Degrees C. This grade is advantageous for high temperature service because of its good mechanical properties with higher creep and stress rupture. This alloy is often used in high heat applications in power generation and petrochemical environment.

310 / 310S / 1.4841 / 1.4845 Often referred as 25-20. With a typical chemical range of the main elements 25% Chrome / 20% Nickel. These alloys are associated with heat resistant applications as retain high strength at elevated temperatures with minimal oxidisation. Often used in industrial boiler manufacture, burner nozzles and refractory components.

904L This is a low carbon, high alloy austenitic stainless steel including an element of copper. With high elements of Nickel (23-28%) and Molybdenum (4 -5%) this alloy offers superior resistance to aggressive media such as sulphuric acid and is highly resistant to chloride attack and crevice corrosion. In cost terms, many attributes of this alloy can be achieved by consideration of Duplex UNS S31803.

DUPLEX 2205 / UNS S31803 / F51 Duplex grades sit between an Austenitic (300 Series) and Ferritic (400 Series) stainless steel. Duplex UNS S31803 analysis provides higher Chrome and Molybdenum together with a lower Nickel content over that of 316 austenitic grade, for which it often substitutes. This presents a very good combination of corrosion resistance with superior strength with higher yield and tensile properties. This grade also features improved and more uniform resistance to stress corrosion cracking, pitting and crevice corrosion. Typically used in pressure vessel and chemical conveying systems.

SUPER DUPLEX UNS S32750 / UNS 32760 / F53 / F55 Super Duplex is modified chemical form over "standard" duplex, providing even higher strength and very high uniform corrosion pitting resistance characteristics.

These grades are often used in offshore petrochemical applications in a marine environment where significant high strength and corrosion resistance is required.

6 MOLY - UNS S31254

Also referred as 254 SMO, this grade was developed with Seawater applications in mind. With an excellent resistance to pitting and corrosion, good weldability and typically 50% higher strength than most austenitic 300 grades, applications regularly include seawater handling equipment, heat exchangers and desalination equipment.

NICKEL ALLOY GRADES ALLOY 200 /201 99.6% commercially pure nickel grade. Highly resistant to various aggressive chemicals and caustic alkalies. The alloy has a low hardness, good ductility, formability and conductivity. Mostly used in chemical processing applications and synthetic fibres production where purity is one of prime criteria. Other examples include electrical components.

Alloy 201 is a low carbon version of 200. It is preferred for cold forming and machining and generally used in higher temperature applications exceeding 315 Degrees C.

ALLOY 400 A 63-70% Nickel based alloy. This alloy is very versatile with excellent corrosion resistance in varying applications over a wide range of temperatures and conditions. Typically used in petrochemical refining and marine environments. In the annealed condition "normal", it is relatively low in strength due partly to the other main element of copper in the region of 32%, but is therefore excellent at resistance to stress corrosion cracking and offers good weldability.

ALLOY 600 / 601 Alloy 600 is a Nickel - Chrome alloy with in the region of 14-17% Chrome and 72% minimum Nickel. The grade is associated with wide temperature range corrosion applications from cryogenic through to high elevated temperature up to 1093 Degrees C. It is tough from an impact perspective offering high mechanical strength, non-magnetic with good welding properties often used in nuclear reactors.

601 holds lower range of Nickel and Carbon over that of 600. The key strength is its resistance to high temperature oxidisation. Often used in furnaces, and for burners, combustor components and power generation super heater supports.

ALLOY 625 This alloy offers high strength, formability and outstanding corrosion resistance.

With 58% minimum Nickel, Chrome of 20-23% and the addition of Molybdenum of 8-10%, the Molybdenum integrates with the Nickel to provide great strength and superior corrosion resistance in a wide range of temperature. Widely used in petrochemical fields and where weight is a factor. A key advantage over other alloys is the ability to consider thickness reduction whilst maintaining strength.

800 / 800H / 800HT These "iron based" Nickel alloys with 30-35% Nickel. 39.5% minimum Iron and 1923% Chrome, are normally associated with use in high temperature applications requiring optimum creep and rupture properties. The chromium in the alloy imparts resistance to oxidation and corrosion. The high percentage of nickel maintains an austenitic structure so that the alloy is ductile. The nickel content

also contributes resistance to scaling, general corrosion, and stress-corrosion cracking. The iron content provides resistance to internal oxidation. Applications include heat exchangers, petroleum processing.

825 825 is a Nickel-Iron-Chrome alloy with 38-46% Nickel, 22% minimum Iron, 19.523.5% Chrome. It also has additions of Molybdenum, Copper and Titanium that assist provide exceptional resistance to corrosive environments. The inclusion of titanium aims to stabilise the alloy against sensitization to inter-granular corrosion.

Applications include chemical processing, oil and gas recovery, acid production, nuclear fuel reprocessing.

Disclaimer The data provided in this section is provided in good faith based on primarily secondary published data in order to provide a brief understanding and introduction to various alloys. Intamet limited shall not be held responsible for any such reliance on accuracy or content.

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