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316 Same Grades: UNS S31600, SS316, 316SS, AISI 316, DIN 1.4401, DIN 1.4408, DIN X5CrNiMo17122, TGL 39672 X5CrNiMo1911, TGL 7143X5CrNiMo1811, ISO 2604-1 F62, ISO 2604-2 TS60, ISO 2604-2 TS61, ISO 2604-4 P60, ISO 2604-4 P61, ISO 4954 X5CrNiMo17122E, ISO 683/13 20, ISO 683/13 20a, ISO 6931
Stainless Steel 316 is a stainless steel containing Chromium-Nickel-Molybdenum. Grade 316 Stainless Steel is the second most commonly used stainless steel, behind 304 stainless steel. It is an austenitic, corrosion-resistant steel with excellent strength, toughness, fabrication characteristics and weldability. These two are chemically similar, containing comparable levels of nickel (Ni) and chromium (Cr). Nickel enhances the low-temperature performance of stainless alloys, generally imparting good ductility to avoid brittleness in cryogenic conditions. Chromium, meanwhile, is the main element responsible for the corrosion-resistant properties of stainless steels.
316 is a member of the 18/8 chromium nickel family of austenitic stainless steels, with an addition of 2% molybdenum for improved corrosion resistance, particularly to localised corrosion in chloride containing environments. The very tough and ductile austenitic structure gives grade 316 excellent formability and fabrication characteristics.
AISI 316 Chemical Composition
| Composition | Value |
Iron (Fe) | 68.5% |
Chromium (Cr) | 16.25% |
Nickel (Ni) | 11.5% |
Molybdenum (Mo) | 2.5% |
Manganese (Mn) | 1% |
Silicon (Si) | 0.5% |
Nitrogen (N) | 0.05% |
Carbon (C) | 0.04% |
Phosphorus (P) | 0.023% |
Sulfur (S) | 0.015% |
AISI 316 Physical Properties
Material Density | 8000 kg/m3 |
Elastic Modulus | 193 GPascal |
Mean Thermal Expansion Coefficient | 16.5 μm/m/oC |
Mean Thermal Conductivity | 18.9 W/m*K |
Specific Heat Capacity | 500 J/kg*K |
Electrical Resistivity | 740 (nΩ*m) |
Melting Onset | 1380 oC / 2510 oF |
Melting Completion | 1400 oC / 2550 oF |
Embodied Energy | 53 MJ/kg |
Calomel Potential | -50 mV |
Max Tensile Strength | 580 MPa |
Yield Tensile Strength | 290 MPa |
Elongation | 40% (50 mm) |
Elongation at break | 50% (50 mm) |
Rockwell Hardness | 95 HB |
Brinell Hardness | 219 |
Toughness/Hardness
Austenitic stainless steels are inherently tough and 316 stainless steel is no different, maintaining the ductile fracture mode and high absorbed energy in impact tests to cryogenic temperatures (-200°C).
Pressure Vessels
AS1210, Pressure Vessels, allows the use of grade 316 up to a temperature of 800°C. The standard allows the use of higher design stresses for 316H at all temperatures.
Cold Fabrication
Grade 316 is readily workable, by the standard methods of sheet metal working, with the exception that it cannot be oxygen cut. Plasma cutting is normal. The deep drawing capability of grade 316 is outstanding, because of its high austenite stability.
High Temperature Corrosion
The generally accepted maximum service temperatures for grade 316 (and grade 304) in air are 870°C for intermittent service and 925°C for continuous service.
Corrosion Resistance
When exposed to a variety of hostile conditions and media, stainless steel 316 possesses good corrosion resistance. Although it is often referred to as "marine grade," it is not resistant to warm sea water. Pitting and crevice corrosion may occur in warm chloride conditions. Above 60°C, Grade 316 is susceptible to stress corrosion cracking.
Heat Resistance
In intermittent service to 870°C and continuous service to 925°C, stainless steel 316 offers strong oxidation resistance. If corrosion resistance in water is necessary, however, prolonged usage at 425-860°C is not suggested. Because of its resistance to carbide precipitation, 316L is preferred in this case. Grade 316H is indicated when strong strength is needed at temperatures over 500°C.
Machinability
The machinability of stainless steel 316 is exceptional. The following guidelines may help you improve your machining: The cutting edges must remain razor-sharp. Excessive work hardening is caused by dull edges. Light cuts should be made, but they should be deep enough to avoid work hardening by riding on the material's surface. Chip breakers should be used to help keep swarf out of the way of the job. Heat concentrates at the cutting edges due to austenitic metals' low thermal conductivity. Coolants and lubricants are thus required and must be used in huge amounts.
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.
Benches and equipment for the laboratories: Being very easy to clean and multipurpose, this alloy is very suitable for the laboratory equipment and benches.
Household Equipment: stainless steel 316 is suitable for making household utensils such as knives and cutleries. They are suitable based on their mechanical properties, durability, heat resistance, and aesthetic appeal.
Food and Beverage industry: The intrinsic property of stainless steel 316 to be resistant to corrosion makes its way to the food and beverage industry. From storage to transportation and from easy cleaning to sterilisation, this type is very beneficial to the industry.
Aerospace Industry: Stainless steel 316 is a material of huge favor in making parts used in the aerospace industry, for example, it can be used to manufacture CNC machining aerospace parts. This comes as a result of its lightweight, tensile strength, corrosion resistance, and extreme durability. SS 316 is suitable for making aerospace parts such as actuators, fasteners, landing gear components, etc., as they possess these properties.
Heat exchangers: Being resistant to corrosion and having high durability, Grade 316/316L is a highly reliable choice for being used in heat exchangers.
Textile industry: This type of stainless steel endures deterioration with its inherent properties of strength and high-resistance, making it the most suitable for the textile industry.
Petrol industry: Stainless steel 316 is known for the formation of oxide layers that inhibit the process of oxidation. This property is useful for the petrol industry. Moreover, the high heat resistance of the alloy makes it very suitable for the petrol industry.
Nuclear reactors: Grade 316 is known to be of big use to the nuclear industry. The nuclear reactors have to be made out of the best material to ensure safe chemical reactions.
This alloy is very resistant to corrosion, can handle extreme temperatures, is durable and holds immense strength, making it a safe choice for nuclear reactors. The high mechanical formability is very advantageous to nuclear power plants.
Within the austenitic stainless steels, AISI 304 and AISI 316 represent the most widely used grades for industrial piping systems. While both offer excellent general corrosion resistance, weldability, and formability compared to carbon steels, critical differences in their composition and performance dictate their suitability for specific service environments. Selecting the best grade requires a thorough understanding of these distinctions.
AISI 304 is an 18% chromium, 8% nickel austenitic stainless steel, often referred to as "18-8" stainless. AISI 316 builds upon the 304 composition by adding molybdenum, typically in the range of 2-3%. This addition is the primary differentiator, significantly enhancing resistance to specific corrosive agents, particularly chlorides. The "L" variants 304L and 316L feature a controlled maximum carbon content to minimize susceptibility to sensitization during welding, which can lead to intergranular corrosion in the heat-affected zone. 304L and 316L grades are strongly preferred for welded fabrications, especially in corrosive environments.
While both grades primarily comprise iron (Fe), chromium (Cr) for passive oxide layer formation, nickel (Ni) for austenitic structure stability and ductility, and controlled levels of carbon (C), manganese (Mn), silicon (Si), phosphorus (P), and sulfur (S), the presence of 2.00-3.00% molybdenum in 316 is Different. Molybdenum dramatically enhances the stability and protective quality of the passive chromium oxide film, particularly in the presence of chlorides, weak acids, and reducing conditions. The table below summarizes key compositional ranges per ASTM A240/A240M and ASTM A312/A312M:
| Element | AISI 304 (%) | AISI 304L (%) | AISI 316 (%) | AISI 316L (%) |
|---|---|---|---|---|
| Chromium (Cr) | 18.00 - 20.00 | 18.00 - 20.00 | 16.00 - 18.00 | 16.00 - 18.00 |
| Nickel (Ni) | 8.00 - 10.50 | 8.00 - 12.00 | 10.00 - 14.00 | 10.00 - 14.00 |
| Molybdenum (Mo) | ≤ 0.75 | ≤ 0.75 | 2.00 - 3.00 | 2.00 - 3.00 |
| Carbon (C) | ≤ 0.08 | ≤ 0.030 | ≤ 0.08 | ≤ 0.030 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| Silicon (Si) | ≤ 0.75 | ≤ 1.00 | ≤ 0.75 | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Nitrogen (N) | ≤ 0.10 | ≤ 0.10 | ≤ 0.10 | ≤ 0.10 |
Both 304/304L and 316/316L have similar mechanical properties. Typical minimum requirements for annealed condition per ASTM A312/A312M (Seamless Pipe) are comparable:
Tensile Strength: 515 MPa (75 ksi) min.
Yield Strength (0.2% offset): 205 MPa (30 ksi) min.
Elongation: 35% min.
In practice, 316/316L has slightly higher tensile and yield strength than 304/304L at room temperature due to the molybdenum addition. However, both grades possess excellent toughness and ductility down to cryogenic temperatures. The primary mechanical selections are usually met by both, shifting the focus decisively towards corrosion performance.
Both grades offer excellent resistance to a wide range of oxidizing environments and atmospheric corrosion. 316/316L may show better performance in some sulfuric acid concentrations and reducing acids like phosphoric acid.
Pitting and Crevice Corrosion: This is the paramount difference. Molybdenum drastically improves resistance to localized corrosion initiated by chlorides and other halides. In environments containing brackish water, seawater, salt-laden atmospheres, bleach, or chloride-containing process streams, 316/316L is superior. The Pitting Resistance Equivalent Number (PREN), calculated as %Cr + 3.3x%Mo + 16x%N, provides a comparative index: 304L is ~18-20, and 316L is ~23-26. Higher PREN indicates better pitting resistance. For piping exposed to chlorides above ambient temperature, 304/304L is often inadequate, leading to premature failure via pitting or crevice corrosion under gaskets or deposits. So, choose 316/316L stainless steel.
Intergranular Corrosion: The low-carbon "L" grades 304L and 316L are essential for welded components to prevent sensitization in the heat-affected zone (HAZ) during welding. Standard 304/316 can be sensitized if cooled slowly through the critical temperature range (425-860°C), making them susceptible to intergranular attack in corrosive environments. Post-weld solution annealing is impractical for most piping systems, solidifying the preference for L grades.
Both grades exhibit good oxidation resistance in intermittent service up to 870°C and continuous service up to 925°C in dry air. However, 316/316L generally performs with superior strength at elevated temperatures due to the molybdenum content. More critically, 316/316L offers better resistance to sulfidation and corrosion by hot organic acids and fatty acids encountered in processes like food production or chemical synthesis.
Both 304/304L and 316/316L possess excellent cold-forming characteristics typical of austenitic stainless steels, including bending, drawing, and spinning. However, 316/316L exhibits a slightly higher rate of work hardening during cold forming operations compared to 304/304L. For most standard pipe bending and fabrication, both grades are readily workable.
Both 304/304L and 316/316L are readily weldable by all common fusion welding techniques (GTAW/TIG, GMAW/MIG, SMAW, SAW). The critical factor is matching or over-alloyed filler metals (like ER308L for 304L and ER316L for 316L). Post-weld heat treatment is generally not required for these grades.
The addition of molybdenum and higher nickel content makes AISI 316/316L more expensive than 304/304L. The premium typically ranges from 20% to 40% or more, depending on market conditions, product form, size, and quantity. Using 316/316L where 304/304L is sufficient represents unnecessary expenditure.
Choose AISI 304/304L When:
The environment is mild, primarily atmospheric or freshwater.
Handling concentrated nitric acid or organic acids at moderate temperatures.
Applications involve food, beverage, dairy, pharmaceutical, high-purity water, or certain chemical processes with no chlorides or reducing acids.
Cost sensitivity is high, and the absence of significant chloride exposure can be guaranteed.
Always specify 304L for welded systems.
Choose AISI 316/316L When:
Chlorides are present in any significant concentration (> 50-100 ppm), especially at elevated temperatures or in stagnant/crevice conditions, such as coastal/marine atmospheres, seawater cooling, bleach handling, saltwater aquariums, chemical processing with chlorides, pulp and paper mill liquors.
Exposure to dilute sulfuric acid, phosphoric acid, sulfite liquors, acetic acid, or other reducing acids.
Enhanced resistance to pitting and crevice corrosion is a critical design requirement.
Superior performance in high-temperature applications involving sulfur compounds or organic acids is needed.
Always specify 316L for welded systems exposed to corrosive media.
