316 Stainless Steel

  • Introduction
  • Chemical Composition
  • Mechanical Properties
  • Other Designations (equivalent materials)
  • Principal Design Features
  • Applications
  • Machinability
  • Forming
  • Welding
  • Welding 316 Stainless to Low Carbon Steel
  • Shielding gasses for MIG
  • Heat Treatment
  • Forging
  • Hot Working
  • Cold Working
  • Annealing
  • Aging
  • Tempering
  • Hardening
  • Other Comments
  • Disclaimer

Introduction [i]

316 is a chromium-nickel-molybdenum austenitic stainless steel with good strength and excellent corrosion resistance, as supplied in the annealed condition with a typical brinell hardness of 175.Characterised by high corrosion resistance in marine and industrial atmospheres, it exhibits excellent resistance to chloride attack and against complex suphur compounds employed in the pulp and paper processing industries. The addition of 2% to 3% of molybdenum increases its resistance to pitting corrosion and improves its creep resistance at elevated temperatures. Also it displays good oxidation resistance at elevated temperatures and has excellent weldability.

316 cannot be hardened by thermal treatment, but strength and hardness can be increased substantially by cold working, with susequent reduction in ductility.

It is now available with improved machinability (by calcium injection treatment), which has little effect on corrosion resistance and weldability while greatly increasing feeds and/or speeds, plus extending tool life.

It is used extensively by the Marine, Chemical, Petrochemical, Pulp and Paper, Textile, Transport, Manufacturing and allied industries.

Chemical Composition
Min. % Max %
Carbon 0 0.08
Silicon 0 1.00
Manganese 0 2.00
Nickel 10.00 14.00
Chromium 16.00 18.00
Molybdenum 2.00 3.00
Nitrogen 0 0.10
Phosphorous 0 0.045
Sulphur 0 0.03
Mechanical Property Requirements – Annealed to ASTM A276-98b 316
Finish Hot Finish Cold Finish
Dia or Thickness mm All Up to 12.7 Over 12.7
Temsile Strength Mpa Min. 515 620 515
Yield Strength Mpa Min. 205 310 205
Elongation in 50mm % Min. 40 30 30
Typical Mechanical Properties At Room Temperature – Annealed
Finish Cold Drawn Other
Tensile Strength Mpa 680 590
Yield Strength Mpa 500 280
Elongation in 50mm % 42 55
Impact Charpy V J 190 180
Hardness HB 195 155
Rc 13

Material Characteristics [ii]

Corrosion Resistance

Excellent in a range of atmospheric environments and many corrosive media – generally more resistant than 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 1000mg/L chlorides at ambient temperatures, reducing to about 500mg/L at 60°C.

316 is usually regarded as the standard “marine grade stainless steel”, but it is not resistant to warm sea water. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.

Heat Resistance

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 316L is more resistant to carbide precipitation and can be used in the above temperature range. Grade 316H has higher strength at elevated temperatures and is sometimes used for structural and pressure-containing applications at temperatures above about 500°C.

Heat Treatment

Solution Treatment (Annealing) – Heat to 1010-1120°C and cool rapidly. These grades cannot be hardened by thermal treatment.

Welding

Excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 316 with Grade 316 and 316L with Grade 316L rods or electrodes (or their high silicon equivalents). Heavy welded sections in Grade 316 require post-weld annealing for maximum corrosion resistance. This is not required for 316L. Grade 316Ti may also be used as an alternative to 316 for heavy section welding.

Welding 316 Stainless to Mild Steel [iii]

316L (including ER316LSi) filler metal should be used with 316L and 316 base metals. CF-8M and CF-3M are the cast equivalents of 316 and 316L, respectively.

Use 309L (including ER309LSi) when joining mild steel or low alloy steel to stainless steels, for joining dissimilar stainless steels such as 409 to itself or to 304L stainless, as well as for joining 309 base metal. CG-12 is the cast equivalent of 309. Some 308L applications may be substituted with 309L filler metal, but 316L or 316 applications generally require molybdenum and 309L contains no molybdenum.

[iv]The usual choice for the filler when welding stainless to mild is 309L. 309 is over alloyed stainless steel (19/10) so when diluted by the mild steel gives a deposit approximately like 308L / 304L.

There are other fillers that give a crack free weld, 312, 308MoL, 307 and 310 will all work but these are less widely available than 309L.

Shielding gasses for MIG  [v]

The best gas for MIG welding stainless is 97.5% Argon +2.5% CO2. Previously an Argon/Oxygen mix was widely used, but this doesn’t give as smooth a finish as the Argon/CO2 mix.

For mild steel welding 80% Argon plus 20% CO2 is common, with 95% Argon plus 5% CO2 often used for thin sections, but even 5% CO2 is too oxidising for stainless and will leave the weld looking black. 

Machining

A “Ugima” improved machinability version of grade 316 is available in round and hollow bar products. This machines significantly better than standard 316 or 316L, giving higher machining rates and lower tool wear in many operations.

Dual Certification

It is common for 316 and 316L to be stocked in “Dual Certified” form – mainly in plate and pipe. These items have chemical and mechanical properties complying with both 316 and 316L specifications. Such dual certified product does not meet 316H specification and may be unacceptable for high temperature applications.

Citations / Credits 

[i] Interlloy Pty Ltd

[ii] AZO Materials

[iii] Lincoln Electric

[iv] Mig Welding.co.uk

[v] Mig Welding.co.uk

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