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Austenitic Grades

Austenitic grades are alloys commonly used for stainless applications. The austenitic grades have no magnetic. There are two subgroups of austenitic stainless steel, 300 series and 200 series, 300 series are the most common austenitic alloys.

Straight Grades

The straight grades of austenitic stainless steel contain a maximum of .08% carbon. There is a misconception that straight grades contain a minimum of .03% carbon, but the spec does not require this. As long as the material meets the physical requirements of straight grade, there is no minimum carbon requirement.

Low Carbon Grades

Low carbon grades are used to provide extra corrosion resistance after welding. The letter “L” signifies low carbon, like 304L, 316L. Since the carbon content is reduced, there is no chromium carbide or intergranular corrosion. ”L” grade therefore is resistant to most hostile chemical compounds and is used when there needs the maximum levels of resistance to corrosion and contamination.

You may wonder why don’t all stainless steels have “L” grades. This is because "L" grades are more expensive and carbon at high temperatures imparts great physical strength. Normally the factory will buy the raw material in “L” grades but specify the physical properties of the straight grade to retain straight grade strength.

High Carbon Grades

High Carbon Grades contain carbon between 0.04% and 0.10%. You will see the letter “H” follows after the alloy like 316H. “H“ grades are often applied when the materials are at extreme temperatures because the high carbon content can help the material retain strength. “L” grades are used where annealing after welding is impractical, such as in the field where pipe and fittings are being welded.

Type304：The most prevalent Austenitic grade, comprising around 18% chromium and 8% nickel. Chemical processing equipment, food, dairy, beverage industries, heat exchangers, and milder chemicals.

Type316：It has a chromium content of 16％ to 18％ and a nickel content of 11％ to 14％. Molybdenum has been added to the nickel and chrome of the 304. Molybdenum is used to prevent pit-type attacks. Chemical processing, the pulp and paper industries, food and beverage processing and dispensing, and more corrosive environments all employ Type 316. The molybdenum content must be at least 2%.

Type317：Contains a higher percentage of molybdenum than 316 for highly corrosive environments. It must include a minimum of 3% "moly." It's frequently used in stacks with scrubbers.

Type317L：Restricts maximum carbon content to 0.030% max. and silicon to 0.75% max. for extra corrosion resistance.

Type317LM：Requires molybdenum content of 4.00% min.

Type317LMN：Requires molybdenum content of 4.00% min. and nitrogen of .15% min.

Type321/Type347：These types have been developed for corrosive resistance for repeated intermittent exposure to temperature above 800 degrees F. SS321 is made by the addition of titanium and SS347 is made by the addition of tantalum/columbium. These grades are primarily used in the aircraft industry.

Type 430	The basic ferritic grade, with a little less corrosion resistance than Type 304. This type combines high resistance to such corrosives as nitric acid, sulfur gases, and many organic and food acids.
Type 405	Has lower chromium and added aluminum to prevent hardening when cooled from high temperatures. Typical applications include heat exchangers.
Type 409	Contains the lowest chromium content of all stainless steels and is also the least expensive. Originally designed for muffler stock and also used for exterior parts in non-critical corrosive environments.
Type 434	Has molybdenum added for improved corrosion resistance. Typical applications include automotive trim and fasteners.
Type 436	Type 436 has columbium added for corrosion and heat resistance. Typical applications include deep-drawn parts.
Type 442	Has increased chromium to improve scaling resistance. Typical applications include furnace and heater parts.
Type 446	Contains even more chromium added to further improve corrosion and scaling resistance at high temperatures. Especially good for oxidation resistance in sulfuric atmospheres.

Duplex Grades

It is the newest grade of stainless steel. It is the combination of austenitic and ferritic material. Material of this grade has higher strength and superior resistance to stress corrosion cracking. Stainless steel 2205 is a typical example.

Precipitation Hardening Grades

Precipitation hardening grades offer a combination of fabricability, strength, ease of heat treatment, and corrosion resistance. These grades include 17Cr-4Ni (17-4PH) and 15Cr-5Ni (15-5PH). This material is intended for use in the manufacture of bars, rods, wire, forgings, and other similar products. Martensitic precipitation-hardenable alloys are beginning to find more use in the flat rolled form. While the semi-austenitic precipitation-hardenable stainless steels were originally intended for sheet and strip applications, they have found numerous other uses. Many of these steels, which were originally developed for aerospace uses, are now gaining commercial recognition as really cost-effective materials in a variety of applications.

Super Alloy Grades

Superalloys are used when 316 or 317 are unable to withstand attack. They contain very large amounts of nickel, chrome and molybdenum. Price of these grades usually are higher.

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