{"id":6261,"date":"2026-09-25T21:11:19","date_gmt":"2026-09-25T18:11:19","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/2026\/09\/25\/aisi-f55-aisi-f53-difference\/"},"modified":"2026-09-30T10:44:43","modified_gmt":"2026-09-30T07:44:43","slug":"aisi-f55-aisi-f53-difference","status":"publish","type":"post","link":"https:\/\/www.defencemetal.com\/index.php\/2026\/09\/25\/aisi-f55-aisi-f53-difference\/","title":{"rendered":"What Is the Difference Between AISI F55 and AISI F53?"},"content":{"rendered":"

AISI F55<\/strong> and AISI F53<\/strong> are the two most common members of the super duplex family. Their chromium and nickel bands are the same. The difference lies in F55’s copper and tungsten<\/strong> additions and — far more importantly — in the fact that ASTM gives the two grades different elongation minima.<\/strong><\/p>\n

The difference in composition<\/h3>\n

F53 (UNS S32750) is a pure chromium-nickel-molybdenum-nitrogen duplex: neither copper nor tungsten is present as an alloying element.<\/strong> The 0.50 % maximum given for copper is an impurity ceiling, not an addition.<\/p>\n

F55 (UNS S32760) contains both 0.50–1.00 % copper and 0.50–1.00 % tungsten. F53 forgoes both and raises the nitrogen instead.<\/p>\n

Compared in figures<\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
PROPERTY<\/th>\nAISI F55 (S32760)<\/th>\nAISI F53 (S32750)<\/th>\n<\/tr>\n<\/thead>\n
EN \/ W.Nr<\/td>\n1.4501<\/td>\n1.4410<\/td>\n<\/tr>\n
Carbon (C)<\/td>\n0.030 % max<\/td>\n0.030 % max<\/td>\n<\/tr>\n
Chromium (Cr)<\/td>\n24.00 – 26.00 %<\/td>\n24.0 – 26.0 %<\/td>\n<\/tr>\n
Nickel (Ni)<\/td>\n6.00 – 8.00 %<\/td>\n6.0 – 8.0 %<\/td>\n<\/tr>\n
Molybdenum (Mo)<\/td>\n3.00 – 4.00 %<\/td>\n— (see note)<\/td>\n<\/tr>\n
Copper (Cu)<\/strong><\/td>\n0.50 – 1.00 % (addition)<\/strong><\/td>\n0.50 % max (impurity)<\/strong><\/td>\n<\/tr>\n
Tungsten (W)<\/strong><\/td>\n0.50 – 1.00 %<\/strong><\/td>\nnot specified<\/strong><\/td>\n<\/tr>\n
Nitrogen (N)<\/td>\n0.20 – 0.30 %<\/td>\n— (see note)<\/td>\n<\/tr>\n
Manganese (Mn)<\/td>\n1.00 % max<\/td>\n1.20 % max<\/td>\n<\/tr>\n
Silicon (Si)<\/td>\n—<\/td>\n0.80 % max<\/td>\n<\/tr>\n
Proof strength (Rp0.2)<\/td>\n\u2265 550 MPa<\/td>\n\u2265 550 MPa<\/td>\n<\/tr>\n
Tensile strength (Rm)<\/strong><\/td>\n\u2265 750 MPa<\/strong><\/td>\n\u2265 795 – 800 MPa<\/strong><\/td>\n<\/tr>\n
Elongation (ASTM A240)<\/strong><\/td>\n\u2265 25 %<\/strong><\/td>\n\u2265 15 %<\/strong><\/td>\n<\/tr>\n
Elongation (EN \/ NORSOK)<\/td>\n\u2265 25 %<\/td>\n\u2265 25 %<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Note on molybdenum and nitrogen:<\/em> for S32750 the ASTM and EN ranges do not overlap. ASTM gives Mo 3.0–5.0 % and N 0.24–0.32 %, while EN 10088-3 (1.4410) gives Mo 3.0–4.5 % and N 0.24–0.35 %. Because the four independent organisations we require could not be reached, we have left these two rows blank. Dual certification of a heat made to ASTM against EN is not automatic.<\/strong><\/p>\n

The most critical row: elongation<\/h3>\n
\n

Under ASTM A240 the elongation minimum is 15 % for F53 and 25 % for F55.<\/p>\n

Against that, F53’s tensile strength minimum is the higher of the two (795–800 MPa against 750 MPa). In other words these two grades are not direct equivalents<\/strong>, and the difference is given incorrectly on most distributor sites. If a drawing calls for 25 % minimum elongation, F53 does not meet it under ASTM A240.<\/p>\n<\/div>\n

The claim that “F55 is superior”<\/h3>\n

It is often said in the market that F55’s tungsten makes it superior to F53. The data do not support that.<\/p>\n

First: tungsten does not count in most specifications’ PREN calculation.<\/strong> Ten organisations including NORSOK M-630 use the tungsten-free formula (PREN = %Cr + 3.3×%Mo + 16×%N); only Rolled Alloys and IMOA use the tungsten-bearing one.<\/p>\n

Second, and more striking: Rolled Alloys’ own comparison<\/strong> — and Rolled Alloys owns the F55 brand — puts F53 ahead even when the tungsten-bearing formula is used (41.9 for 2507 against 41.5 for ZERON 100).<\/p>\n

The difference between them therefore cannot be defended on PREN. It should be sought in F55’s copper for acid service, and in weld metal performance.<\/p>\n

Shared properties<\/h3>\n

Both grades are suitable for sour service under NACE MR0175 \/ ISO 15156<\/strong> in the solution annealed condition with a hardness limit of 28 HRC maximum<\/strong>, and both appear in the NORSOK M-630 material data sheets.<\/p>\n

The upper service temperature is the same as well: approximately 270 to 316 \u00b0C<\/strong>. The limit is metallurgical rather than mechanical — alpha-prime precipitation in the ferrite phase, and sigma phase above it.<\/p>\n

What to watch when ordering<\/h3>\n
\n

Three points<\/p>\n

1.<\/strong> State whether the elongation requirement is to be taken from ASTM or from EN\/NORSOK — for F53 the difference is between 15 % and 25 %.<\/p>\n

2.<\/strong> CPT (critical pitting temperature) values measured to different test standards cannot be compared. Even the same producer may publish a different test standard for the same grade. Ask which test standard was used when comparing quotations.<\/p>\n

3.<\/strong> NORSOK MDS numbers belong to the product form, not the grade; the same MDS list is given for both F53 and F55. An MDS number alone does not identify the grade.<\/p>\n<\/div>\n

Where are they used?<\/h3>\n

Both are used in offshore oil and gas, seawater cooling, desalination, flue gas desulphurisation, pulp and paper, and chemical process equipment. F55’s copper comes into its own in acid environments, while F53’s higher nitrogen shows in strength and post-weld performance.<\/p>\n

Designations, standards and AMS equivalents<\/h3>\n

The same steel is called different things depending on which system you are speaking in. Most ordering and certification confusion starts here, so a short summary:<\/p>\n