ASTM A240 904L Stainless Steel Plate

1. Standard: ASTM A240 / ASME SA240
2. Thickness: 0.3~100mm or as required
3. Width: 1000~2500mm or as required
4. Length: 0~12m or as required

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Product Introduction

ASTM A240 904L Stainless Steel Plate is the grade buyers reach for when 316L fails but a nickel alloy is overkill. It is a low-carbon superaustenitic stainless steel (UNS N08904, EN 1.4539) with roughly 25% nickel, 20% chromium, 4.5% molybdenum and 1.5% copper - a chemistry that sits between standard austenitic stainless steels and the true nickel alloys. That middle position is exactly why it exists: it resists reducing acids and chloride pitting well enough for most chemical and flue-gas duties, at a fraction of the price of Hastelloy.

Product Forms

Bar & Rod

Plate & Sheet

Coil & Strip

Pipe & Tube

Fitting: Flange, Tee, Elbow, Reducer etc.

Forging: Ring, Shaft, Circle, Block etc.

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Chemical Composition of 904L (UNS N08904, ASTM A240)

The composition below is the official ASTM A240 range for plate, sheet and strip. The low carbon (0.020% max) is deliberate: it keeps the steel weldable without carbide precipitation, which is why the L in 904L matters.

Element	Content, %	Role in the alloy
Chromium (Cr)	19.0 - 23.0	Passive film and general corrosion resistance
Nickel (Ni)	23.0 - 28.0	Austenite stability; resistance to reducing acids
Molybdenum (Mo)	4.0 - 5.0	Pitting and crevice corrosion resistance
Copper (Cu)	1.0 - 2.0	Boosts resistance to sulfuric and phosphoric acid
Carbon (C)	0.020 max	Low carbon for welded service
Manganese (Mn)	2.0 max	Residual deoxidizer
Silicon (Si)	1.0 max	Residual
Nitrogen (N)	0.10 max	Minor strength contribution

Mechanical Properties per ASTM A240

Like most superaustenitic grades, 904L is supplied in the solution-annealed condition. It is not a high-strength alloy - you buy it for corrosion performance, and the numbers below are the minimums the mill certificate must meet.

Property	Minimum requirement
Tensile strength	490 MPa (71 ksi)
Yield strength (0.2% offset)	216 MPa (31 ksi)
Elongation in 50 mm	35%
Hardness	Typically below 200 HB

Physical Properties

The density of 904L is about 7.95 to 8.0 g/cm3, essentially the same as 316L, so weight estimates for a steel structure carry over without adjustment. The melting range is roughly 1300 to 1390 C. The pitting resistance equivalent number (PREN), calculated as Cr + 3.3xMo + 16xN, lands around 34 - comfortably above 316L (about 24) and close to the lower super-duplex range, which is why it handles chloride environments that pit 316L.

Where 904L Earns Its Place

The alloy is chosen for a fairly narrow list of services. It handles dilute to medium-concentration sulfuric acid better than any standard austenitic grade, thanks to the copper addition. It resists phosphoric acid in wet-process fertilizer equipment. It performs well in chloride-containing process streams where 316L pits, and it is the classic material for flue-gas desulfurization (FGD) scrubbers, seawater-cooled heat exchangers and the sulfuric acid cooling coils you find in refinery and acid plant service.

Where it does not belong: strongly oxidizing acids (nitric acid at concentration), temperatures above about 400 C, and chloride environments severe enough that 6% Mo superaustenitic (254SMO) or super-duplex is the next step up. The rule of thumb is simple: start at 316L, move to 904L when 316L fails in reducing acid or chloride pitting, and move to a 6% Mo grade or nickel alloy when 904L fails.

Sizes, Finishes and Supply

Plate is the standard delivery form for the alloy, following ASTM A240 in thicknesses from about 3 mm up to 50 mm or more, cut to width and length or sheared to order. Surface finishes follow the stainless plate range - 2B pickled and blasted is the default for fabrication; polished finishes are available but usually unnecessary for pressure equipment. Because the material is more expensive than standard austenitic grades, buyers commonly order cut blanks rather than full plates, which reduces waste. Ends are supplied plain, and welding is typically done with matching 904L (ER385) filler wire.