Frequently-Asked Questions about 304 and 316 Stainless Steel

Type 304 stainless steel is the most versatile and widely used of the austenitic stainless steels. It contains chromium-nickel and low carbon: 18 percent chromium and 8 percent nickel austenitic alloy.

Type 304 is ideal for automotive applications, kitchen equipment, hose clamps, springs, truck bodies, exhaust manifolds, stainless flatware, storage tanks, pressure vessels, piping, and stainless steel return grilles. The alloy provides good resistance to moderately acidic or caustic solutions. However, it is less ideal for welding; the low carbon version (304L) is recommended for welding, as it provides increased resistance to intergranular corrosion.

Type 304 is easy to fabricate and clean, and helps to prevent product contamination. It comes in a variety of finishes and appearances to blend seamlessly into any project.

The typical analysis is represented by ASTM-A240 and ASME-SA240. The following is the element percentage by weight.

C=0.08
Mn=2.00
P=0.045
S=0.030
Si=1.00
Cr=18.00
Ni=8.00-12.00
N=0.10

Type 316 stainless steel is an austenitic chromium-nickel stainless- and heat-resisting steel with superior corrosion resistance compared to other chromium-nickel steels, even when exposed to chemical corrodents like sea water and brine solutions.

Like Type 304, Type 316 is employed in a variety of applications, but is even more resistant to chemical attack.

Type 316 stainless steel is durable and easy to fabricate, clean, weld, and finish. In the manufacture of pharmaceuticals, stainless steel containing molybdenum – like Type 316, which contains 2 percent – are required to avoid excessive metallic contamination. It is considerably more resistant to solutions of sulfuric acid, chlorides, bromides, iodides and fatty acids at high temperatures.

The typical analysis is represented by ASTM-A240 and ASME-SA240. The following is the element percentage by weight.

C=0.08
Mn=2.00
P=0.04
S=0.03
Si=1.00
Cr=16.00-18.00
Ni=10.00-14.00
Mo=2.00-3.00

Stainless steel is non-corrosive because of the chromium within the alloy. Oxygen combines with chrome to form chrome oxide, commonly called ceramic.

Stainless steel forms a protective coating on its surface, which resists oxidation or rusting. The formation of this film is instantaneous in an oxidizing atmosphere, like air, water, or other fluids containing oxygen. When the layer has formed, the metal has become passivated, and the oxidation rate slows to less than 0.002 inches (or 0.05 mm) per year).

When the passive surface film is removed, the base metal is exposed and can form rust. This is why it’s important to never expose stainless steel to chlorine, which combines with chromium and removes the protective layer.

Epoxy powder coating is a thermoset polymer coating that adds further chemical resistance to stainless steel. It is tough and durable. Our clear protective coating protects stainless steel from corrosion, salt air pitting, fingerprints, and smudges. The finish makes our products much easier to keep clean.

Stainless steel is easy to clean with simple products.

• However, you should never use any chemicals that contain chlorine. This includes any cleaners, acids that clean tile or brick, and certain detergents. Even the vapors can attack stainless steel. Always read product labels before using cleaners near or on stainless steel.
• You also should never use steel wool to clean stainless steel. Particles of the steel wool get trapped in the grain of the stainless, and these particles will rust.
• Never use cleaners containing halogen salts around stainless steel, especially chlorides. Halogens are easy to recognize because they end in the letters “ine,” like fluorine, chlorine, bromine, iodine, and astatine.

Chlorides cause pitting, crevice corrosion, and stress corrosion cracking on stainless steels. Temperatures higher than ambient and those that cycle between hot and cold can worsen corrosion, because it causes chlorides to concentrate due to evaporation.

Low levels of chlorine are typically safe for use around stainless steels, but no higher than 200 parts per million (ppm) for 304 stainless steel and 1,000 ppm for 316 stainless steel. Low chlorine levels in tap water systems will not negatively affect austenitic stainless steels, however, chlorine concentrations as little as 25 ppm can have a detrimental effect and is dependent on concentration, temperature, pH, and more.

Typical mechanical properties required for annealed material are covered by ASTM-A240.

Yield Strength .2% Offset=30,000
Ultimate Tensile Strength=80,000
Elongation=50%
Hardness R=90 max