February 23, 2019
400 Series Martensitic - Typical grade: 410
Straight chromium (12-18%), magnetic and can be hardened by heat treatment. Typical use: Fasteners, pump shafts
400 Series Ferritic - Typical grade: 430
Straight chromium (12-18%), "low" carbon, magnetic, but not heat treatable. Typical use: Appliance trim, cooking utensils.
200/300 Series Austenitic - Typical grade: 304
Chromium (17-25%)/Nickel (8-25%), non-magnetic, not heat treatable. Can develop high strength by cold work. Additions of molybdenum (up to 7%) can increase the corrosion resistance. Typical use: Food equipment, chemical equipment, architectural applications
Austenitic Stainless Steels
This family of stainless steels is made up of two groups of materials: Chromium-Manganese-Nickel types, or 200 Series, and the Chromium-Nickel types, or 300 Series.
The 200 Series alloys possess mechanical and corrosion resisting properties similar to their corresponding 300 Series materials. They also exhibit higher hardness and yield strength as well as excellent ductility and superior creep properties at elevated temperatures and are usually non-magnetic. These alloys were originally developed to conserve nickel as compared to the 300 Series by replacing nickel with manganese at a ratio of 2% manganese for each percent of nickel replaced.
300 Series stainless steels are the most widely used products produced by Allegheny Ludlum Corporation. They are classified as austenitic, and are hardenable only by cold working methods. These grades of stainless have chromium (approx. 18 to 30%) and nickel (approx. 6 to 20%) as their major alloying additions. Type 304 (also known as 18-8) is the most widely used alloy of all stainless steels.
Ferritic Stainless Steels, 400 Series Straight Chromium, Non-Hardenable
These grades of stainless have 11 to 30% chromium as the major alloy addition and are low carbon. Ductility and formability are less than that of the austenitic grades. The corrosion resistance competes with the austenitic grades for certain applications. Thermal conductivity is about half that of carbon steels. Ferritic stainless steels are magnetic, and resistance to high-temperature corrosion is better than that of martensitic types. They generally have good ductility and can be welded or fabricated without difficulty. These grades can be processed to develop an aesthetically pleasing, bright finish and, hence, are often used for automotive trim and appliance molding. They also find use in functional applications where cost is a major factor, e.g., automotive exhaust systems, catalytic converters, radiator caps, and chimney liners. These grades can also be hardened by cold rolling, but cannot be hardened as much as the austenitic alloys.
Martensitic Stainless Steels, 400 Series, Straight Chromium, Hardenable
These grades of stainless steel have chromium in the range of 11 to 17% as the major alloying addition, but the carbon levels are in amounts from .10 to .65%. This radically changes the behavior of the martensitic alloys relative to the ferritic 400 Series alloys. The high carbon enables the material to be hardened by heating to a high temperature, followed by rapid cooling (quenching). Martensitic types offer the ideal combination of corrosion resistance and superior mechanical properties, as produced by heat treatment to develop maximum hardness, strength and resistance to abrasion and erosion. The 400 Series martensitic grades that Allegheny Ludlum makes are AL 403, AL 410, AL 410HC, AL 420, 420HC, AL 425 Modified, and AL 440A. (Note: HC stands for high carbon.) The martensitic grades are usually sold in the soft state. This allows the customers to cut or form the parts before they are thermally hardened. End uses include cutlery, scissors, surgical instruments, wear plates, garbage disposal shredder lugs, and industrial knives. The AL 403 alloy is used to make vanes for steam turbines.
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