Types of Stainless

Austenitic Stainless Steel

These are chromium and nickel containing stainless steels with very low carbon content. They are non-magnetic, but can become slightly magnetic when cold worked. Cold working also enhances their strength. Austenitic Stainless Steels have excellent corrosion resistance; good formability; good weldability, and excellent mechanical properties over a wide range of temperatures. In addition, these steel are easy to clean, which enhances their use in applications in hygienic and sterile environments.

Typical application for the various grades include:

304/304L Tanks, storage vessels and pipe work for corrosive liquids. Process equipment in the mining, chemical, cryogenic, food, beverage and pharmaceutical industries. These stainless steels are also used for manufacturing holloware, cutlery, architectural products and sinks.

309/310 These grades have a higher chrome and nickel content that the 304 grade. As a result of their high oxidation resistance, these steels are used for high temperature applications such as furnace, kiln and catalytic converter components.

318/316L Tanks, pressure vessels, pipe work and components for more aggressive conditions and specialised applications, such as the manufacture of tank containers for bulk transportation of chemicals and corrosive liquids. The molydenum content enhances the corrosion resistance.

321/316Ti These are the "stabilised" grades. They are resistant to sensitisation and thus the possibility of Intergranular Corrosion. In addition they are used in components, which require elevated temperature strength and corrosion resistance, such as afterburners, super heaters, compensators and expansion bellows.

Ferritic Stainless Steels

Ferritic Stainless Steel are plain chromium stainless steels, usually with a low carbon content. They are magnetic and have good ductility and resistance to corrosion and oxidation. They are generally resistant to stress corrosion cracking. However, there are weldability limitations which restrict their use to thinner gauges. 3CR12 is a special grade, developed and patented by Columbus Stainless which largely overcome this problem.

Conventional Ferritic Grades:

Typical grades and applications for the conventional different grades include :

Automotive exhaust tubing and catalytic convertor casings

Kitchen sinks, washtroughs, cutlery, kitchen and catering equipment and utensils.

This grade is specially produced by Columbus Stainless for used in automotive components. Its superior mechanical strength at elevated temperatures (up to 850 deg C) makes it the ideal material for the front end (close to the engine) of an exhaust system. It can also be used for fabrication of heat exchanger tubes.

AISI 444
AISI Grade 444 has a very similar PRE (Pitting Resistance Equivalent) to Grade 316, meaning that its corrosion resistance is similar in aggressive outdoor environments, e.g. at the coast. Grade 444 tubing can be polished, bent and welded by conventional methods and tubing will be marked clearly on the inside of the tube. PRE is defined as %Cr + (3.3%Mo) + (16%N) which gives an indication of the steels resistance to pitting corrosion.

Utility Grade:

This is a price competitive, corrosion resisting, weldable, utility ferritic stainless steel with particular advantages in wet abrasive applications. Unlike other ferritic stainless steels it can be welded in thicknesses of up to 30mm. It is extremely used in the mining, materials handling and sugar industries due to its resistance to atmospheric corrosion and wet abrasive corrosion.

Martensitic Stainless Steels

These were the first stainless steels industrially developed and used for knife blades. They are plain chromium stainless steels that can be hardened and strengthened by heat treatment. Common grades include 410, 420, 431, 440. They are usually supplied in the annealed state.

Duplex Stainless Steels

These stainless steels contain insufficient Ni to develop a fully austenitic crystal structure and therefore consist of a mixed ferritic-austenitic (i.e. duplex) crystal structure. These grades were originally developed to address the susceptibility of the austenitic stainless steels to stress corrosion cracking in thicker gauge welded structures made of austenitic materials.

Lean Duplex Grades:

These grades contain no Mo and as example there are grades 2001 and 2101

Conventional Duplex Grades:

These grades contain higher levels of Ni, Cr and Mo than austenitic grades. Examples are grades 2205 and 2304.

Super Duplex Grades:

These contain very high levels of both Mo and N for increased corrosion resistance, and increased Ni to maintain the ferrite/ austenite balance. Grade 2507 is an example.

For more information please contact us at General Enquiries