At Metal Supplies Ltd we have the different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. In metallurgy stainless steel is defined as a steel alloy with a minimum of 11.5% chromium content by mass. Stainless steel does not stain, corrode or rust as easily as ordinary steel (it's "stains less"), but it is not stain-proof. Stainless steel’s resistance to corrosion and staining, low maintenance, relative in expense, and familiar luster make it an ideal base material for a host of commercial applications. As an incite into the wide ranging possibilities of stainless steel, we have compiled some basic information on a selection of our most popular grades and surface finishes, which are available in various forms such as: Rounds, Flats, Tubes, Box Sections, Sheets, Plates, Floor Plates, Angles, Channels, Squares, Hexagons, Tees, Mesh, Fittings & Clamps. For more information please Contact us.

Common Grades.

Type 304: The most common grade; the classic 18/8 stainless steel. Its the most versatile and most widely used stainless steel, available in a wider range of products, forms and finishes than any other, its balanced austenitic structure enables it to be severely deep drawn without intermediate annealing. Grade 304 has good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304 is excellent in a wide range of atmospheric environments and many corrosive media, although subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. It has excellent forming and welding characteristics by all standard fusion methods, both with and without filler metals, although heavy welded sections in Grade 304 may require post-weld annealing for maximum corrosion resistance, post-weld annealing is not required when welding thin sections. Its excellent overall toughness and low temperature properties respond well to hardening by cold working. It also benefits from ease of fabrication, ease of cleaning and the beauty of its appearance.

Type 316: The second most common grade (after 304) amongst the austenitic stainless steels, its austenitic structure also gives the Grade 316 excellent toughness, even down to cryogenic temperatures. Grade 316 is the standard molybdenum-bearing grade, alloy addition of molybdenum gives Grade 316 excellent overall corrosion resistant properties in a range of atmospheric environments and many corrosive media and a particularly higher resistance to pitting and crevice corrosion than that of Grade 304. Grade 316 however is subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. It has excellent forming and welding characteristics by all standard fusion methods, both with and without filler metals. Heavy welded sections in Grade 316 will require post-weld annealing for maximum corrosion resistance however post-weld annealing is not required when welding thin sections. Grade 316 also has good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 316 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 316 steel is used in the handling of certain food and pharmaceutical products where it is often required in order to minimize metallic contamination. Its also known as marine grade stainless steel due to its increased resistance to chloride corrosion and its increased ability to resist saltwater corrosion compared to Grade 304, however it is not resistant to warm sea water. In many marine environments Grade 316 exhibits surface corrosion, usually visible as brown staining.

Type 303: The free machining version of Grade 304; Grade 303 represents the optimum in machinability among the austenitic stainless steels, it is primarily used when production involves extensive machining. The addition of sulfur and phosphorus which is responsible for the improved machining and galling characteristics of Grade 303 lowers its corrosion resistance, it still has good resistance to mildly corrosive atmospheres however its significantly less than that of Grade 304. As well as reducing the corrosion resistance, the sulphur additions in Grade 303 also result in poor weldability (welds must be annealed for maximum corrosion resistance) and reduced formability compared to Grade 304, therefor sharp bends should not be attempted. Grade 303 has good oxidation resistance in intermittent service to 760°C and in continuous service to 870°C. Continuous use in 425-860°C range are not usually recommended due to carbide precipitation, Grade 303 usually does not have a low carbon content so is susceptible to sensitisation. Grade 303 should not be exposed to marine or other similar environments, as these will result in rapid pitting corrosion, because the sulphide inclusions in Grade 303 are primarily aligned along the rolling direction the corrosion resistance is particularly reduced in cross-sections. The structure of Grade 303 has excellent toughness, although the sulphur in Grade 303 does reduce this slightly and like other common austenitic stainless steels, it is subject to stress corrosion cracking in chloride containing environments above 60°C.

Type 310: Combining excellent high temperature properties with good ductility and weldability characteristics suited to all standard methods, Grade 310 is designed for high temperature service and is generally used at temperatures starting from about 800 or 900°C. Grade 310 has good resistance to oxidation in intermittent service in air at temperatures up to 1040°C and 1150°C in continuous service, provided reducing sulphur gases are not present and good resistance to thermal fatigue and cyclic heating. Widely used where sulphur dioxide gas is encountered at elevated temperatures. Continuous use in 425-860°C range is not recommended due to carbide precipitation, if subsequent aqueous corrosion resistance is needed, but often performs well in temperatures fluctuating above and below this range. The high chromium content - intended to increase high temperature properties - also gives this grade excellent corrosion resistance at normal temperatures, and when in high temperature service exhibits good resistance to oxidizing and carburising atmospheres. It has seawater resistance similar to that of Grade 316 and resists fuming nitric acid at room temperature and fused nitrates up to 425°C. Grade 310 is subject to stress corrosion cracking but more resistant than Grades 304 or 316.

Type 321: Similar to Grade 304 but a lower risk of weld decay due to the addition of titanium. Grade 321 is used because it is not sensitive to inter granular corrosion after heating within the carbide precipitation range of 425-850°C. Grade 321 is the grade of choice for applications in the temperature range of up to about 900°C, combining high strength, resistance to scaling and phase stability particularly where subsequent aqueous corrosive conditions are present. Corrosion resistance is equivalent to Grade 304 in the annealed condition, and superior if a weldment in these grades has not been post-weld annealed or if the application involves service in the 425-900°C range. Grade 321 has excellent forming and welding characteristics, by all standard fusion methods, both with and without filler metals, post-weld annealing is not required. It also has excellent toughness, even down to cryogenic temperatures. Grade 321 has good oxidation resistance in intermittent service to 900°C and in continuous service to 925°C. This grade performs well in the 425-900°C range but is subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Grade 321 does not polish well, so is not recommended for decorative applications.

Type 431: This heat treatable, nickel-bearing grade resists scaling in intermittent service to 925°C and in continuous service to 870°C, but is generally not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. It has excellent resistance to a wide variety of corrosive media and reasonable resistance to salt water in cold southern waters but less resistant than Grade 316 in tropical waters. Overall the corrosion resistance of Grade 431 is approximately the same as or slightly below that of Grade 304. Performance is best with a smooth surface finish, in the hardened and tempered condition. It has excellent tensile and torque strength, and good toughness, making it ideally suited to shafting and bolt applications. In the annealed condition this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult, however it can be hardened to approximately 40HRC. Because of its high yield strength, this grade is not readily cold worked and is therefore not recommended for use in operations such as cold heading, bending, deep drawing or spinning. Fabrication must be by methods that allow for poor weldability due to cracking, a pre-heat of 200-300°C is recommended prior to welding and usually also allow for a final harden and temper heat treatment.

Common Finishes.

Standard mill finishes can be applied to flat rolled stainless steel directly by the rollers and by mechanical abrasives. Steel is first rolled to size and thickness and then annealed to change the properties of the final material. Any oxidation on the surface (scale) is removed by pickling, and the passivation layer is created on the surface. A final finish can then be applied to achieve the desired aesthetic appearance. Also after rolling many of our tubes, flats and round bars are then pre-polished to various finishes and are available for immediate dispatch.

Hot rolled (HR). Annealed (for thicker plates).

Hot rolled (HR). Annealed and passivated.

Cold rolled (CR). Annealed, pickled and passivated with an additional pass-through highly polished rollers.

Bright annealed (BA). Pickled and passivated with an additional pass-through highly polished rollers then Bright Annealed under Oxygen-free atmospheric conditions.

Brushed finished.

Satin finished.

Mirror polished.

Bead blast finished.

Plastic coated (PC1). This is generally used to protect the finish on sheets, where in a thin protective plastic film coating is bonded over one of the surfaces of the steel, between rollers.

Plastic coated (PC2). This is generally used to protect the finish on sheets, where in a thin protective plastic film coating is bonded over both of the surfaces of the steel, between rollers.