What Is the Difference Between 304 and 904L Stainless Steel?

304 and 904L at a Glance

304 stainless steel, UNS S30400 and EN 1.4301, is the most widely used austenitic grade: an 18-8 chromium-nickel alloy intended for general corrosion service, food equipment and architectural applications. 904L, UNS N08904 and EN 1.4539, is a high-alloy austenitic stainless steel containing about 20% chromium, 25% nickel, 4-5% molybdenum and 1-2% copper. The additional nickel, molybdenum and copper give 904L markedly better resistance to reducing acids and to chloride pitting and crevice corrosion, at a significantly higher material cost.

The table below compares the standard limits for 304 per ASTM A240 (UNS S30400) and for 904L per ASTM B625 (UNS N08904). Values are maximum percentages unless a range is shown.

	304 (S30400)	904L (N08904)
C	0.08	0.020
	2.00	2.00
P	0.045	0.045
S	0.030	0.035
	0.75	1.00
	17.5-19.5	19.0-23.0
	8.0-10.5	23.0-28.0
		4.0-5.0
		1.0-2.0
N	0.10	0.10

Molybdenum: raises resistance to pitting and crevice corrosion in chloride environments such as seawater, brine and bleaching chemicals.

Nickel: 904L contains roughly three times the nickel of 304, which stabilises the austenitic structure and improves resistance to stress corrosion cracking in several media.

Copper: improves resistance to sulfuric and phosphoric acid, which is why 904L is specified for acid production and handling equipment.

Per ASTM A240, 304 sheet has minimum tensile strength 515 MPa and minimum yield strength 205 MPa with 40% elongation. 904L plate per ASTM B625 has minimum tensile strength 490 MPa, minimum yield strength 215 MPa and 35% elongation. Both grades are fully austenitic and essentially non-magnetic in the annealed condition. Because 904L contains roughly 25% nickel plus 4-5% molybdenum and copper, its price is substantially higher than 304; the exact premium follows nickel and molybdenum market prices.

	304	904L
	515 MPa	490 MPa
	205 MPa	215 MPa
	40%	35%

904L is the material of choice for chemical equipment such as reactors, piping and heat exchangers handling sulfuric or phosphoric acid, for seawater desalination units, and for marine and offshore components exposed to chloride-rich media. 304 covers the conventional fields: food processing equipment, kitchen counters and sinks, storage tanks, building decoration, household appliances and general industrial plant where the medium is only mildly corrosive.

If the environment is mildly corrosive, chloride-free and cost-sensitive, 304 is normally sufficient and is the economical option. Choose 904L when the process stream contains chlorides, reducing acids, seawater or other aggressive media, or when the equipment must meet a long guaranteed service life in chemical or marine duty. The decision should be based on the actual corrosion load, not on a general preference for a higher alloy grade.

Q1: Is 904L stronger than 316L?

A1: 904L offers better corrosion resistance than 316L in chlorides and reducing acids, with comparable strength. It is preferred for aggressive chemical and seawater service where 316L would pit or suffer crevice attack.

Q2: Why is 904L so expensive?

A2: The grade contains roughly 25% nickel, 4-5% molybdenum and 1-2% copper. These alloying elements, especially nickel and molybdenum, dominate the raw material cost and make 904L substantially more expensive than 304.

Q3: Can 904L replace 304 in general applications?

A3: Technically yes, but it is unnecessary and uneconomic. In mildly corrosive, chloride-free environments 304 performs the same function at a fraction of the cost.

Q4: Is 904L magnetic?

A4: No. 904L is fully austenitic in the annealed condition and is essentially non-magnetic, like 304.

Q5: Which standards cover 904L?

A5: 904L is covered by ASTM B625 and B673 for plate and pipe, and by EN 10088-2 as material number 1.4539 for plate and sheet.

Q6: Is 904L weldable?

A6: Yes. The low carbon content avoids sensitisation, and standard austenitic welding practice with matching or slightly over-alloyed filler metal is used.