Stainless Steel - Grade 316L - Properties, Fabrication and Applications (UNS S31603) Background

Grade 316 is the standard molybdenum-bearing grade, second in importance to 304 amongst the austenitic stainless steels. The molybdenum gives 316 better overall corrosion resistant properties than Grade 304, particularly higher resistance to pitting and crevice corrosion in chloride environments.

Grade 316L, the low carbon version of 316 and is immune from sensitization (grain boundary carbide precipitation). Thus it is extensively used in heavy gauge welded components (over about 6mm). There is commonly no appreciable price difference between 316 and 316L stainless steel.

The austenitic structure also gives these grades excellent toughness, even down to cryogenic temperatures.

Compared to chromium-nickel austenitic stainless steels, 316L stainless steel offers higher creep, stress to rupture and tensile strength at elevated temperatures.

Key Properties

These properties are specified for flat rolled product (plate, sheet and coil) in ASTM A240/A240M. Similar but not necessarily identical properties are specified for other products such as pipe and bar in their respective specifications.

Composition

Table 1. Composition ranges for 316L stainless steels.

Mechanical Properties

Table 2. Mechanical properties of 316L stainless steels.

Physical Properties

Table 3. Typical physical properties for 316 grade stainless steels.

Grade Specification Comparison

Table 4. Grade specifications for 316L stainless steels.

Note: These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.

Possible Alternative Grades

Table 5. Possible alternative grades to 316 stainless steel.

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 weld ability by all standard fusion and resistance methods, both with and without filler metals. Heavy welded sections in Grade 316 require post-weld annealing for maximum corrosion resistance. This is not required for 316L.

316L stainless steel is not generally weldable using oxyacetylene welding methods.

Machining

316L stainless steel tends to work harden if machined too quickly. For this reason low speeds and constant feed rates are recommended.

316L stainless steel is also easier to machine compared to 316 stainless steel due its lower carbon content.

Hot and Cold Working

316L stainless steel can be hot worked using most common hot working techniques. Optimal hot working temperatures should be in the range 1150-1260°C, and certainly should not be less than 930°C. Post work annealing should be carried out to induce maximum corrosion resistance.

Most common cold working operations such as shearing, drawing and stamping can be performed on 316L stainless steel. Post work annealing should be carried out to remove internal stresses.

Hardening and Work Hardening

316L stainless steel does not harden in response to heat treatments. It can be hardened by cold working, which can also result in increased strength.

Applications

Typical applications include:

• Food preparation equipment particularly in chloride environments.

• Pharmaceuticals

• Marine applications

• Architectural applications

• Medical implants, including pins, screws and orthopaedic implants like total hip and knee replacements

• Fasteners