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316- THE FIRST STEP
Courtesy of Australian Stainless Steel Development
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This Benefit Added On: May 1, 2001
If a job requires greater corrosion than grade 304 can provide, grade 316 in the 'next step up'. Grade 316 has virtually the same mechanical, physical, and fabrication charactersitics as 304 with better corrosion resistance, particularly to pitting corrosion in chloride environments.
Grade 316(UNS S31600) is the second most popular grade in the stainless steel family. It accounts for about 20% of all stainless stee produced.
Corrosion resistance
Grade 316 has excellent corrosion resisitance in a wide range of media. Its main advantage over grade 304 is its increased ability to resist pitting and crevice corrosion in warm chloride environments. It resists ordinary rusting in virtually all architectural applications, and is often chosen for more aggressive environments such as sea-front buildings and fittings on wharves and piers. It is also restistant to most food processing environments, can be readily cleaned, and resists organic chemicals, dye stuffs and a wide variety in inorganic chemicals.
In hot chloride environments, grade 316 is subject to pitting and crevice corrosion and to stress corrosion cracking when subjected to tensile stresses beyond about 50 C. In these severe invironments duplex grades such as 2205(UNS S31803) or higher alloy austenitic grades including 6% molybdenum(UNS S31254) grades are more appropriate choices.
The corrosion resistance of the low carbon version of 316(316L) is the same as standard 316. It is mostly chosen to give better resistance to sensitation in welding(316L).
Heat resistance
Like grade 304, 316 has good oxidation resistance in intermittent service to 870 C and in continuous service to 925C. Continuous use of 316 in the 425-860 C range is not recommended if subsequent exposure to room temperature aqueous environments is anticipated, but it often performs well in temperatures fluctuating above and below this range.
Like other austentic stainless steels 316 has excellent toughness down to temperatures of liquefied gases and has application at these temperatures, although lower cost grades such as 304 are more usually selected for cryogenic vessels.
Like other austentic grades, 316 in the annelaed condition is virtually non-magnetic(ie. very low magnetic permeability). While 304 can become significantly attracted to a magnet after being cold worked, grade 316 is almost always virtually totally non-responsive. This may be a reason for selecting grade 316 in some applications.
Another characteristic that 316 has in common with austentic steels is that it can only be hardened by cold working. An ultimate tensile strength in excess of 1,000MPa can be achieved and, depending on quanity and product form required, it may possible to order to a specific worked strength(see ASTM A666 or EN10088-2).
Annealing (also referred to as solution treating) is tha main heat treatment carried out on grade 316. This is done by heating to 1,010-1,120 C and rapidly cooling-usually by water quenching.
Fabricability
Like other austenitic stainless steels, grade 316 has excellent forming characteristics. It can be deep drawn without intermediate heat softening enabling it to be used in the manufacture of drawn stainless parts,such as sinks and saucepans. However, for normal domestic artticles the extra corrosion resistance of grade 316 is not necessay. 316 is readily brake or rolled formed into a variety of other parts for application in the industrial and architectural fields.
Grade 316 has an outstanding weldability and all standard welding techniques can be used (although oxyacetylene is not normally used.) Although post-weld annealing is often not required to restore 316's corrosion resistance, making it suitable for heavy gauge fabrication, appropriate post-weld clean-up is recommended.
Machinabilty of 316 is lower than most carbon steels. The standard austentic grades like 316 can be readily machined if slower speeds and heavy feeds are used, tools are rigid and sharp, and cutting fluids are used. An 'improved machinability' version of 316 also exists.
Forms available
Grade 316 is available in virtually all stainless product forms including coil, sheet, plate, strip, tube, pipe, fittings, bars, angles, wire, fasteners and castings. 316L is also widely available, particularly in heavier products such as plate, pipe and bar. Most stainless steel surface finishes, from standard to special finishes, are available.
Applications
Typical applications for 316 include boat fittings and structural mambers;architectural components paricularly in marine, polluted or industrial environments;food and beverage processing equipment;hot water systems;and plant for chemical, petrochemical, mineral processigng, photographic and other industries.
Although 316 is often described as the 'marine grade' it is also seen as the first step up from the basic 304 grade.
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