Stainless Steel Type 304 and 304L: UNS S30400 and S30403

What Is Type 304/304L

Type 304 and 304L stainless steel is the modern version of 18-8 stainless steel, containing approximately 18 percent chromium and 8 percent nickel, and is the most commonly specified stainless steel used throughout the world. It is a versatile, general-purpose austenitic grade with good resistance to atmospheric corrosion and to many chemicals, foods, and beverages.

Chemical Composition

For Type 304 the limits are carbon 0.07 percent maximum, chromium 17.5 to 19.5 percent, nickel 8.0 to 10.5 percent, manganese 2.0 percent, silicon 0.75 percent, nitrogen 0.10 percent, phosphorus 0.045 percent, and sulfur 0.030 percent. Type 304L limits carbon to 0.03 percent maximum with nickel extended to 8.0 to 12.0 percent.

Mechanical Properties

Minimum values for 304 are yield strength 205 MPa, tensile strength 515 MPa, and elongation 40 percent. For 304L the minimums are 170 MPa yield and 485 MPa tensile with 40 percent elongation. Maximum hardness is 92 HRB for both. The grades can be specified in the annealed condition with very good formability.

Dual Certification

Type 304L can be dual certified as 304 when the composition meets the lower carbon limit of 304L and the higher strength levels of 304. This simplifies procurement because one material satisfies both specifications.

Magnetic and Physical Behavior

304/304L is non-magnetic in the annealed condition but may become slightly magnetic as a result of cold working. Physical properties include density 0.285 lb per cubic inch, elastic modulus 28 million psi, thermal conductivity 9.4 BTU per foot hour degree F, and electrical resistivity 28.3 microhm-inch.

Applications and Standards

304 is used for food processing equipment, kitchenware, chemical containers, architectural trim, and general fabrication, while 304L is specified for welded applications where the low carbon eliminates chromium carbide precipitation and enhances as-welded corrosion resistance. Typical specifications include ASTM A240, A666, and ASME SA240.

Frequently Asked Questions

Q: What is the chromium content of 304?

A: 17.5 to 19.5 percent with 8.0 to 10.5 percent nickel.

Q: What is the difference between 304 and 304L?

A: 304L limits carbon to 0.03 percent for welded service.

Q: Can 304L be dual certified as 304?

A: Yes, when composition and strength meet both requirements.

Q: Is 304 magnetic?

A: No, unless cold worked.

Q: What is the tensile strength of 304?

A: 515 MPa minimum.

Q: What applications use 304L?

A: Welded vessels, tanks, and piping in corrosive service.

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