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Alloys often are added to steel to increase desired properties. Marine-grade stainless steel, called type 316, is resistant to certain types of corrosive environments.
There is a variety of different types of 316 stainless steel. Some common types are the L, F, N, and H variants. Each is slightly different, and each is used for different purposes. The “L” designation means 316L steel has less carbon than 316.
Qualities Shared By 316 and 316L
While similar to Type 304, which is common in the food industry, both type 316 and 316L exhibit better corrosion resistance and are stronger at elevated temperatures. They also are both non-hardenable by heat treatment and can be readily formed and drawn (pulled or pushed through a die or smaller hole).
Annealing (a treatment to reduce hardness and increase ductility, or the ability to accept plastic deformation) 316 and 316L stainless steels require heat treatment of between 1,900 and 2,100 degrees Fahrenheit (1,038 to 1,149 degrees Celsius) before rapidly quenching.
Differences Between 316 and 316L
316 stainless steel has more carbon in it than 316L. This is easy to remember, as the L stands for “low.” But even though it has less carbon, 316L is very similar to 316 in almost every way. Cost is very similar, and both are durable, corrosion-resistant, and a good choice for high-stress situations.
316L, however, is a better choice for a project that requires a lot of welding because 316 is more susceptible to weld decay than 316L (corrosion within the weld). However, 316 can be annealed to resist weld decay. 316L also is a great stainless steel for high-temperature, high-corrosion uses, which is why it’s so popular for use in construction and marine projects.
Qualities of Type 316 Steel
Type 316 steel is an austenitic chromium-nickel stainless steel that contains between two and 3% molybdenum. The molybdenum content increases corrosion resistance, improves resistance to pitting in chloride ion solutions, and increases strength at high temperatures.
Type 316 grade stainless steel is particularly effective in acidic environments. This grade of steel is effective in protecting against corrosion caused by sulfuric, hydrochloric, acetic, formic, and tartaric acids, as well as acid sulfates and alkaline chlorides.
How Type 316 Steel Is Used
Common uses for type 316 stainless steel include in the construction of exhaust manifolds, furnace parts, heat exchangers, jet engine parts, pharmaceutical and photographic equipment, valve and pump parts, chemical processing equipment, tanks, and evaporators. It also is used in pulp, paper, and textile processing equipment and for any parts exposed to marine environments.
Qualities of Type 316L Steel
The lower carbon content in 316L minimizes deleterious carbide precipitation (carbon is drawn out of the metal and reacts with chromium due to heat, weakening the corrosion resistance) as a result of welding. Consequently, 316L is used when welding is required to ensure maximum corrosion resistance.
Properties and Composition of 316 and 316L Steels
Physical Properties of type 316 and 316L steels:
- Density: 0.799g/cubic centimeter
- Electrical resistivity: 74 microhm-centimeters (20 degrees Celsius)
- Specific Heat: 0.50 kiloJoules/kilogram-Kelvin (0–100 degrees Celsius)
- Thermal conductivity: 16.2 Watts/meter-Kelvin (100 degrees Celsius)
- Modulus of Elasticity (MPa): 193 x 103 in tension
- Melting Range: 2,500–2,550 degrees Fahrenheit (1,371–1,399 degrees Celsius)
Here is a breakdown of the percentages of various elements used to create type 316 and 316L steels:
|Element||Type 316 (%)||Type 316L (%)|
|Carbon||0.08 max.||0.03 max.|
|Manganese||2.00 max.||2.00 max.|
|Phosphorus||0.045 max.||0.045 max.|
|Sulfur||0.03 max.||0.03 max.|
|Silicon||0.75 max.||0.75 max.|
|Nitrogen||0.10 max.||0.10 max.|