Why is it important to use the correct type of Stainless Steel ?
|VARIOUS TYPES OF STAINLESS STEEL
18-8: 300 series stainless steel having approximately (not exactly) 18% chromium and 8% nickel. The term “18-8” is used interchangeably to characterize fittings made of 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the “18-8” types, but slight differences in chemical composition do make certain grades more resistant than others do against particular chemicals or atmospheres. “18-8” has superior corrosion resistance to 400 series stainless, is generally nonmagnetic.
304: Type 304 is an austenitic steel possessing a minimum of 18% chromium and 8% nickel, combined with a maximum of 0.08% carbon. It is a non-magnetic steel which cannot be hardened by heat treatment, but instead must be cold worked to obtain higher tensile strengths.
The 18% minimum chromium content provides corrosion and oxidation resistance. The alloy’s metallurgical characteristics are established primarily by the nickel content (8% mm.), which also extends resistance to corrosion caused by reducing chemicals. Carbon, a necessity of mixed benefit, is held at a level (0.08% max.) that is satisfactory for most service applications.
The stainless alloy resists most oxidizing acids and can withstand all ordinary rusting. HOWEVER, IT WILL TARNISH. It is immune to foodstuffs, sterilizing solutions, most of the organic chemicals and dyestuffs, and a wide variety of inorganic chemicals. Type 304, or one of its modifications, is the material specified more than 50% of the time whenever a stainless steel is used.
Type 304 is especially suited for all types of dairy equipment – milking machines, containers, homogenizers, sterilizers, and storage and hauling tanks, including piping, valves, milk trucks and railroad cars. This 18-8 alloy is equally serviceable in the brewing industry where it is used in pipelines, yeast pans, fermentation vats, storage and railway cars, etc. The citrus and fruit juice industry also uses Type 304 for all their handling, crushing, preparation, storage and hauling equipment.
In those food processing applications such as in mills, bakeries, and slaughter and packing houses, all metal equipment exposed to animal and vegetable oils, fats, and acids is manufactured from Type 304.
316: For severe environments. There are many industrial processes that require a higher level of resistance to corrosion than Type 304 can offer. For these applications, Type 316 is the answer.
Type 301 contains less chromium and nickel than 302 for more work hardening.
Type 302 is the basic type of the 300 series, 18% chromium— 8% nickel group. It is the renowned 188
Stainless and is the most widely used of the chromium nickel stainless and heat resisting steels.
Type 303 contains added phosphorus and sulfur for better machining characteristics. Corrosion resistance is slightly less than 302/304.
Type 303Se contains Se and P added to improve machinability.
Type 305 has increased nickel to lower work hardening properties.
Type 309/309S have added chromium and nickel for more corrosion resistance and high temperature scaling resistance. 309S contains less carbon to minimize carbide precipitation.
Type 310/310S have higher nickel content than 3093/09S to further increase scaling resistance. 310S contains less carbon than 310 to minimize carbide precipitation.
Type 321 contains titanium to tie up the carbon and avoid chromium carbide precipitation in welding.
Type 330 ultra-high nickel content provides best corrosion resistance to most furnace atmospheres. This grade has low coefficient of expansion, excellent ductility and high strength.
Type 347 – 348 have columbium tantalum added to tie up the carbon and avoid chromium carbide precipitation in welding. Use for temperatures from 800 to 1650 degrees F.
Type 405 contains 12% chromium with aluminum added to prevent hardening.
Type 430 is the basic type in the ferritic group, possessing good ductility and excellent resistance to atmospheric corrosion. Its scaling resistance is higher than 302 in intermittent service, somewhat lower in continuous use.
Type 430F/430Se have sulfur and selenium (respectively) added for increased machinability.
Type 442 has added chromium for improved resistance to scaling.
Type 446 has still higher chromium content (27%) for added scaling resistance and is highest of the standard straight chromium types. Alloys with over 30% chromium become too brittle to process.
Type 410 is the basic Martensitic type. It is the general purpose corrosion and heat resisting chromium stainless steel. It can be hardened by thermal treatment to a wide range of mechanical properties. It can be annealed soft for cold drawing and forming. This grade is always magnetic.
Type 403 is a special, high quality steel made for blades and buckets for steam turbine and jetengine compressors. This grade is eminently suited for very highly stressed parts. This material is magnetic in all conditions.
are modifications of Type 410, being the free machining, nonseizing, nongalling alloys. These properties are obtained by the addition of sulfur or selenium to Type 410. This is a heat treatable grade with corrosion resistance and other characteristics closely approaching those of Type 410.
Type 420 is a chromium stainless steel capable of heat treatment to a maximum hardness of approximately 500 Brinell. It has a maximum corrosion resistance only in the fully hardened condition. Type 420 is magnetic in all conditions.
Type 431 is a nickel bearing (1.252.00%) chromium stainless steel which may be heat treated to high mechanical properties. It is magnetic in all conditions of use. It has superior corrosion resistance to Types 410, 416, 420, 430 and 440 stainless steels.
Type 440C is the stainless steel that can be heat treated to the highest level.