904L vs 316L Stainless Steel: Creep Resistance and High-Temperature Limits

Creep Resistance in Austenitic Stainless Steels

Creep is the time-dependent deformation of a material under constant stress at elevated temperature. For steels, creep becomes a design factor when the operating temperature is high enough relative to the melting point, typically above about 0.4 of the absolute melting temperature. For austenitic stainless steels this means creep considerations begin around 425-500 deg C, depending on stress level and required life. Creep resistance matters in chemical processing, power generation, pressure vessel fabrication and heat exchanger design. However, the two grades compared here, 316L and 904L, are alloyed primarily for corrosion resistance; neither is intended for sustained load-bearing service in the creep range, and this distinction is central to correct material selection.

904L and 316L: Grade Overview

316L (UNS S31603, EN 1.4404, JIS SUS316L) is a low-carbon molybdenum-bearing austenitic grade widely used for general corrosive service, especially in chloride and mildly acidic environments. Its carbon is limited to 0.03% maximum to prevent sensitization during welding. 904L (UNS N08904, EN 1.4539) is a higher-alloy austenitic grade with 23-28% nickel, 19-23% chromium, 4-5% molybdenum and 1-2% copper. It was developed for resistance to sulfuric and phosphoric acids, chloride pitting and crevice corrosion, and it is classified as a fully austenitic high-alloy steel rather than a heat-resistant grade.

Chemical Composition Comparison

Element	316L (UNS S31603)	904L (UNS N08904)
Carbon, max %	0.030	0.020
Chromium %	16.0 - 18.0	19.0 - 23.0
Nickel %	10.0 - 14.0	23.0 - 28.0
Molybdenum %	2.0 - 3.0	4.0 - 5.0
Copper %	-	1.0 - 2.0
Silicon, max %	0.75	1.00
Manganese, max %	2.00	2.00

Composition limits follow ASTM A240 for both grades.

Mechanical Properties Comparison (Annealed)

Property	316L	904L
Tensile strength, min MPa	485	490
Yield strength (0.2%), min MPa	170	220
Elongation, min %	40	35
Density, g/cm3	7.93	8.00

At room temperature, 904L shows a higher minimum yield strength than 316L because of its higher alloy content, while elongation is slightly lower. Neither difference is significant for high-temperature design.

High-Temperature and Creep Performance: What the Standards Say

The elevated-temperature capability of both grades is limited. EN 10028-7, the European standard for flat products of steels for pressure purposes, provides elevated-temperature proof strength values for both 1.4404 (316L) and 1.4539 (904L) only up to 400 deg C; above this temperature, sustained-load design would require creep data that is not standardized for these grades. In practice, both materials are used at temperatures up to about 400-450 deg C for lightly loaded or non-pressure components, and 904L does not provide a meaningful creep advantage over 316L in this range. For equipment that must carry stress above about 500 deg C, the correct choice is a grade designed for the creep range: the H-grade 316H for moderate chloride-bearing service, 321H for higher temperatures, or the heat-resistant grades 309S and 310S for oxidation-dominated service. In short, the design driver for selecting 904L over 316L is corrosion resistance in sulfuric acid, phosphoric acid or chloride-rich media, not high-temperature strength. Where corrosion and moderate heat act together up to about 400 deg C, 904L is the more resistant choice; where genuine creep duty is involved, neither 316L nor 904L is appropriate.

Frequently Asked Questions

Which has better creep resistance, 904L or 316L?

Neither grade is approved for sustained load-bearing service in the creep range. Above about 400-500 deg C, both lose strength rapidly, and 904L offers no meaningful creep advantage over 316L. For creep duty, specify H-grades or heat-resistant grades instead.

Can 904L be used at 500 deg C?

Only for lightly loaded or non-pressure components, and with caution. Standards such as EN 10028-7 provide design data for 904L only up to 400 deg C, and the alloy is not classified as a heat-resistant grade.

Why choose 904L over 316L?

Choose 904L when the corrosion environment demands it: hot sulfuric or phosphoric acid, aggressive chlorides, or severe pitting and crevice corrosion service such as seawater heat exchangers. The higher nickel, molybdenum and copper content gives clearly superior corrosion resistance.

Is 904L more expensive than 316L?

Yes. The high nickel and molybdenum content of 904L makes it substantially more expensive than 316L on a weight basis. The extra cost is justified only when the corrosion performance of 316L is insufficient.

What grades should be selected for creep service above 500 deg C?

For sustained loads above about 500 deg C, select 316H (carbon 0.04-0.10%) where chloride corrosion is also present, 321H for higher-temperature oxidizing service, or 309S and 310S for severe oxidation duty. Design allowable stresses must follow the applicable code.

Can 904L and 316L be welded without post-weld heat treatment?

Both are low-carbon grades, so they can normally be used in the as-welded condition without solution annealing in corrosive service. Matching or over-alloyed filler metal is recommended, and 904L joints should use high-alloy fillers to maintain corrosion performance.