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Stainless Steel - Grade 316 – Properties, Fabrication and Applications

Chemical Formula

Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S

Topics Covered

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. It has excellent forming and welding characteristics. It is readily brake or roll formed into a variety of parts for applications in the industrial, architectural, and transportation fields. Grade 316 also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections. Grade 316L, the low carbon version of 316 and is immune from sensitisation (grain boundary carbide precipitation). Thus it is extensively used in heavy gauge welded components (over about 6mm). Grade 316H, with its higher carbon content has application at elevated temperatures, as does stabilised grade 316Ti. The austenitic structure also gives these grades excellent toughness, even down to cryogenic 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 316 grade of stainless steels. Grade C Mn Si P S Cr Mo Ni N 316 Min - - - 0 - 16.0 2.00 10.0 - Max 0.08 2.0 0.75 0.045 0.03 18.0 3.00 14.0 0.10 316L Min - - - - - 16.0 2.00 10.0 - Max 0.03 2.0 0.75 0.045 0.03 18.0 3.00 14.0 0.10 316H Min 0.04 0.04 0 - - 16.0 2.00 10.0 - max 0.10 0.10 0.75 0.045 0.03 18.0 3.00 14.0 - Mechanical Properties Table 2. Mechanical properties of 316 grade stainless steels. Grade Tensile Str (MPa) min Yield Str 0.2% Proof (MPa) min Elong (% in 50mm) min Hardness Rockwell B (HR B) max Brinell (HB) max 316 515 205 40 95 217 316L 485 170 40 95 217 316H 515 205 40 95 217 Note: 316H also has a requirement for a grain size of ASTM no. 7 or coarser. Physical Properties Table 3. Typical physical properties for 316 grade stainless steels. Grade Density (kg/m3) Elastic Modulus (GPa) Mean Co-eff of Thermal Expansion (µm/m/°C) Thermal Conductivity (W/m.K) Specific Heat 0-100°C (J/kg.K) Elec Resistivity (nΩ.m) 0-100°C 0-315°C 0-538°C At 100°C At 500°C 316/L/H 8000 193 15.9 16.2 17.5 16.3 21.5 500 740 Grade Specification Comparison Table 4. Grade specifications for 316 grade stainless steels. Grade UNS No Old British Euronorm Swedish SS Japanese JIS BS En No Name 316 S31600 316S31 58H, 58J 1.4401 X5CrNiMo17-12-2 2347 SUS 316 316L S31603 316S11 - 1.4404 X2CrNiMo17-12-2 2348 SUS 316L 316H S31609 316S51 - - - - - 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. Grade Why it might be chosen instead of 316? 316Ti Better resistance to temperatures of around 600-900°C is needed. 316N Higher strength than standard 316. 317L Higher resistance to chlorides than 316L, but with similar resistance to stress corrosion cracking. 904L Much higher resistance to chlorides at elevated temperatures, with good formability 2205 Much higher resistance to chlorides at elevated temperatures, and higher strength than 316 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. 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.

Stainless Steel - Grade 304

Chemical Formula

Fe, <0.08% C, 17.5-20% Cr, 8-11% Ni, <2% Mn, <1% Si, <0.045% P, <0.03% S

Background

Stainless steel types1.4301 and 1.4307 are also known as grades 304 and 304L respectively. Type 304 is the most versatile and widely used stainless steel. It is still sometimes referred to by its old name 18/8 which is derived from the nominal composition of type 304 being 18% chromium and 8% nickel. 304 Stainless Steel Type 304 stainless steel is an austenitic grade that can be severely deep drawn. This property has resulted in 304 being the dominant grade used in applications like sinks and saucepans. 304L Stainless Steel Type 304L is the low carbon version of 304. It is used in heavy gauge components for improved weldability. Some products such as plate and pipe may be available as “dual certified” material that meets the criteria for both 304 and 304L. 304H Stainless Steel 304H, a high carbon content variant, is also available for use at high temperatures. Property data given in this document is typical for flat rolled products covered by ASTM A240/A240M. ASTM, EN or other standards may cover products sold by Aalco. It is reasonable to expect specifications in these standards to be similar but not necessarily identical to those given in this datasheet.

Chemical Composition

Table 1. Typical chemical composition for 304 stainless steel alloys % 304 304L 304H C 0.08 max 0.03 max 0.10 max Mn 2.0 2.0 2.0 Si 0.75 0.75 0.75 P 0.045 0.045 0.045 S 0.03 0.03 0.03 Cr 18-20 18-20 18-20 Ni 10.5 12 10.5 N 0.1 0.1 -

Properties

Mechanical Properties Table 2. Typical mechanical properties for 304 stainless steel alloys Grade 304 304L 304H Tensile Strength (MPa) 520 500 520 Compression Strength (MPa) 210 210 210 Proof Stress 0.2% (MPa) 210 200 210 Elongation A5 (%) 45 45 45 Hardness Rockwell B 92 92 92 Physical Properties Table 3. Typical mechanical properties for 304 stainless steel alloys Property Value Density 8.00 g/cm3 Melting Point 1400-1450°C Modulus of Elasticity 193 GPa Electrical Resistivity 0.072x10-6 Ω.m Thermal Conductivity 16.2 W/m.K at 100°C Thermal Expansion 17.2x10-6 /K at 100°C Alloy Designations Stainless steel 304 also corresponds to the following standard designations and specifications: Euronorm UNS BS En Grade 1.4301 S30400 304S15 304S16 304S31 58E 304 1.4306 S30403 304S11 - 304L 1.4307 - 304S11 - 304L 1.4311 - 304S11 - 304L 1.4948 S30409 304S51 - 304H Corrosion Resistance 304 has excellent corrosion resistance in a wide variety of environments and when in contact with different corrosive media. Pitting and crevice corrosion can occur in environments containing chlorides. Stress corrosion cracking can occur at temperatures over 60°C. Heat Resistance 304 has good resistance to oxidation in intermittent service up to 870°C and in continuous service to 925°C. However, continuous use at 425-860°C is not recommended if corrosion resistance in water is required. In this instance 304L is recommended due to its resistance to carbide precipitation. Where high strength is required at temperatures above 500°C and up to 800°C, grade 304H is recommended. This material will retain aqueous corrosion resistance. Fabrication Fabrication of all stainless steels should be done only with tools dedicated to stainless steel materials. Tooling and work surfaces must be thoroughly cleaned before use. These precautions are necessary to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product. Cold Working 304 stainless steel readily work hardens. Fabrication methods involving cold working may require an intermediate annealing stage to alleviate work hardening and avoid tearing or cracking. At the completion of fabrication a full annealing operation should be employed to reduce internal stresses and optimise corrosion resistance. Hot Working Fabrication methods, like forging, that involve hot working should occur after uniform heating to 1149-1260°C. The fabricated components should then be rapidly cooled to ensure maximum corrosion resistance. Heat Treatment 304 stainless steel cannot be hardened by heat treatment. Solution treatment or annealing can be done by rapid cooling after heating to 1010-1120°C. Machinability 304 has good machinability. Machining can be enhanced by using the following rules:          Cutting edges must be kept sharp. Dull edges cause excess work hardening.          Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.          Chip breakers should be employed to assist in ensuring swarf remains clear of the work          Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities. Welding Fusion welding performance for type 304 stainless steel is excellent both with and without fillers. Recommended filler rods and electrodes for stainless steel 304 is grade 308 stainless steel. For 304L the recommended filler is 308L. Heavy welded sections may require post-weld annealing. This step is not required for 304L. Grade 321 may be used if post-weld heat treatment is not possible.