Which stainless steel to choose: 17 grades compared on the data

At a glance: physical properties (strength depends on condition, see the sections)

Which stainless steel is the strongest, and which is the weakest?

Hardened 440C and aged 17-4 PH are the strongest stainless steels in our data, and annealed austenitic plate is among the weakest. Hardened and tempered 440C reaches 1,896 MPa yield and 1,965 MPa tensile at only 2 % elongation, all at the 600 °F temper. 17-4 PH depends on aging: H900 is 1170 MPa minimum and 1262 MPa typical yield, H1025 is 1000 and 1117 MPa, and H1150 is 725 and 869 MPa (bar).

Annealed austenitic plate sits at the bottom. On ASTM A240 plate minimums 304 is 205 MPa yield (EN 1.4301 plate: 210 MPa), while 304L and 316L are 170 MPa, and 409 sheet is also 170 MPa. General engineering knowledge, not in our data: mills often certify one heat to both grades. Duplex grades sit in the middle: 2205 plate is 450 MPa, 2304 is 400 MPa, and 2507 is 550 MPa as seamless tube and 530 MPa as forgings.

Condition moves some grades a lot. 301 runs from 205 MPa minimum yield annealed to 965 MPa full hard, with tensile rising from 515 to 1276 MPa. 410 is 205 to 290 MPa typical yield annealed and 1089 MPa after a 1010 °C oil quench and a 260 °C temper.

How do 304, 304L, 316, 316L, 301 and 303 differ?

The austenitic grades differ mainly in carbon, molybdenum and sulfur. 304 is the common 18 percent chromium, 8 to 11 percent nickel grade. The 304L datasheets cap carbon at 0.030 percent against 0.08 percent for 304, which limits chromium carbide at grain boundaries after welding; the cost is a lower plate minimum, 485 MPa tensile for 304L against 515 MPa for 304. Plain 304 suits unwelded parts, and 304L suits welded ones.

Adding 2 to 3 percent molybdenum gives 316, with better pitting and crevice resistance than 304 and the same plate minimums. In a NIST study of annealed plate, yield was 193 to 213 MPa at 295 K and 656 to 663 MPa at 4 K. 316L adds the low-carbon welding benefit. Our data gives no chloride limit for 316 or 316L, and crevice corrosion is not quantified for any grade.

301 is the cold-work grade: its elongation minimum falls from 40 percent annealed to 9 percent full hard. The price is corrosion: Outokumpu prints a critical pitting temperature below 10 °C, and carbide precipitation after welding restricts it. 303 is the free-machining grade with at least 0.15 percent sulfur. That sulfur gives pitting starting points, so it resists less than 304 and pits in chloride above 60 °C; its weldability is poor and it is not readily cold worked.

When does a ferritic stainless steel (409, 430, 444) beat an austenitic grade?

A ferritic grade wins when you need heat conduction, low thermal expansion or resistance to chloride cracking, and the part is not thick-welded or used below freezing. ATI's 20 to 100 °C means give 430 23.86 W/(m·K) against 16.3 for 301, and the 20 to 500 °C means are 25.96 against 21.4. The martensitic 410, 440C and S41500 conduct about as well, but EN 1.4418 (EN 1.4418) prints only 15 W/(m·K).

409 is the low-chromium, titanium-stabilised exhaust-system grade, with 10.5 to 11.75 percent chromium. Outokumpu prints a critical pitting temperature below 10 °C for 409, 430 and 304 alike, so that test does not separate them.

430 has 16 to 18 percent chromium, is magnetic and cannot be hardened by heat. Its weak points are welds, where martensite and coarse grain cost ductility and corrosion resistance, and low temperatures: Macsteel says it may suffer brittle fracture at sub-zero temperatures and should not be used cryogenically.

444 adds about 2 percent molybdenum. In ATI's 1000-hour boiling-salt U-bend tests it did not crack where 304 and 316 cracked, and its pitting potential in 1000 ppm chloride is 0.58 V vs SCE, against 0.35 V for 304 and 0.56 V for 316. Toughness is low near its transition temperature.

Which stainless steel resists chloride pitting and stress corrosion cracking best?

Duplex grades and ferritic 444 both show chloride cracking resistance in our sources, and the profiles do not rank them. By PREN minimum, super duplex 2507 is highest for pitting; 2304 prints 25 to 26, 2205 prints 34 to 35.8 and 2507 at least 41 to 42.5, against 24 for 316L and 18 for 304L. 2507 passes ASTM G48 method A at 50 °C, a pass level and not a measured value, while 2205 has a separate Rolled Alloys value of 35 °C against 10 °C for 316 and 316L.

2304 is a different case: ATI and Alleima both call its general corrosion and critical pitting resistance comparable to 316L, so its gain is cracking resistance. The 125 °C limit applies to dilute chloride, and above it with more than about 10 ppm chloride Alleima recommends 2205, 2507 or Sanicro 28.

The 304 profile, quoting Wikipedia, gives a rule of thumb of about 400 mg/L chloride at ambient temperature and about 150 mg/L at 60 °C. 444 has a Ugitech PREN of 24.5, about equal to 316L at 24. 17-4 PH goes the other way: peak-aged material is more prone to stress corrosion cracking, and Carpenter says good resistance comes from aging at 1025 °F (552 °C) or higher. Seawater is left out here.

How hot and how cold can each stainless steel be used?

In oxidizing air the printed limits are 871 °C continuous for 304L (ATI), 840 °C for 301, 850 °C for 444 (600 °C with water or sulphur compounds), 760 °C intermittent for 303 (Aalco does not recommend continuous service at 870 °C, because of carbide precipitation), and 790 to 815 °C continuous and 870 °C intermittent for 430 (Macsteel prints 730 °C continuous). Oxidation limits for 304, 316 and 316L are not in our data, and 316's printed service range of 750 to 925 °C has no stated basis.

Duplex and 17-4 PH are limited by embrittlement, not scaling. ATI says to avoid 343 to 530 °C for 2205, so its practical ceiling is 316 °C (ASME) or 280 °C (other pressure-vessel rules). 2304 is printed at 280 to 315 °C depending on the code, 2507 loses impact strength in prolonged service above 250 °C (its 232 °C figure is a sour-service limit), and 17-4 PH keeps its strength to about 316 °C.

Martensitic grades are limited by tempering. 410 is listed to 649 °C for scaling, but tempering at 482 to 538 °C drops Charpy impact to 38 J and 33 J, against 76 J at 260 °C. 440C has a NASA use limit of about 400 °C.

For cold service the best-documented grades are austenitic. Annealed 301 at -196 °C shows typical values of 1896 MPa tensile, 517 MPa yield and 30 percent elongation (ATI). The soft martensitic UNS S41500 is printed down to -60 °C and EN 1.4418 from -30 °C.

What do the martensitic and precipitation-hardening grades give up for strength?

They give up corrosion resistance, weldability or toughness, and the trade changes with the heat treatment. 410 has about 12 percent chromium. Annealed it is 450 to 510 MPa tensile and easy to form; hardened from 1010 °C and tempered at 260 °C it reaches 1331 MPa tensile at 17 percent elongation. Welding without a 350 to 400 °F preheat and an immediate full anneal makes it air harden and crack (Rolled Alloys).

440C has 0.95 to 1.20 percent carbon and 16 to 18 percent chromium. It reaches 60 HRC after a 1900 °F oil quench and a 300 °F temper,.

The soft martensitic grades EN 1.4418 (EN 1.4418) and UNS S41500 (UNS S41500) trade carbon for nickel to keep toughness. EN 1.4418 is quenched and tempered to QT760 (550 MPa yield, 760 to 960 MPa tensile, 90 J Charpy) or QT900 (700 MPa yield, 900 to 1100 MPa tensile, 80 J). S41500 runs from 520 MPa yield at QT700 to 800 MPa at QT900. In saturated sodium chloride at 20 °C, DEW's laboratory table lists a risk of pitting for 1.4418 and slight attack with a risk of pitting for S41500. S41500 is capped at 23 HRC for sour gas. DEW rates its weldability poor and asks for about 150 °C preheat and a post-weld temper, which is the normal practice for this type.

17-4 PH is the balanced choice when strength must come with moderate corrosion resistance. Jacquet calls its corrosion resistance comparable to 304 in most media. Minimum Charpy values are 20 J for H1025 and 41 J for H1150.

Terms used

Austenitic

chromium-nickel stainless that stays tough and non-magnetic when annealed. Examples: 304, 316, 301, 303. Only cold work hardens it.

Ferritic

chromium stainless with little or no nickel. Magnetic, not heat-hardenable, and a better heat conductor than austenitic grades. Examples: 409, 430, 444.

Martensitic

stainless hardened by quenching and softened by tempering. Examples: 410, 440C, and soft low-carbon nickel grades. QT760 means quenched and tempered to 760 MPa minimum tensile.

Precipitation hardening

strengthening by one aging step that grows fine particles in the metal. 17-4 PH is the example. H900 means aged at 900 °F (about 480 °C), H1025 at 1025 °F; a higher number gives lower strength and more toughness.

Duplex

about half ferrite, half austenite: stronger than austenitic grades and better against chloride cracking. Examples: 2304, 2205, 2507. An overmatched filler is weld metal with more nickel than the base.

PREN and critical pitting temperature

PREN is a score from chromium, molybdenum and nitrogen; higher means better pitting resistance, but it ranks alloys and is not a design limit. Critical pitting temperature is where pits start in a test solution; only values from the same test compare.

Sensitization and sigma phase

chromium carbide at grain boundaries after heat in roughly the 450 to 900 °C range, as in a weld, makes the boundary corrode; L grades limit it. Sigma phase is a brittle phase from long holds near 650 °C. 475 °C embrittlement is toughness lost in duplex and ferritic grades after long holds between roughly 343 and 530 °C.

Chloride stress corrosion cracking

cracking of a stressed part in chloride, usually when warm. Austenitic grades are prone to it; ferritic and duplex grades resist it. It has its own temperature limits, separate from pitting.

HRC and Charpy

HRC is Rockwell C hardness. Charpy energy, in joules, is impact toughness.

What to check before you order

1. Send the grade, the product form and the condition you need: annealed, cold-worked temper (301), quenched and tempered (QT760, QT900), aged (H900 to H1150) or solution annealed (duplex). Ask for a mill certificate that prints the condition, because datasheet values often do not.
2. For welded austenitic parts, ask for the carbon limit on the certificate (0.030 percent maximum for L grades) and the welding procedure. Duplex needs an overmatched or matching filler, rapid cooling after any solution anneal, and a heat input of 0.5 to 2.5 kJ/mm for 2205 and 2304 or 0.2 to 1.5 kJ/mm for 2507, interpass under 150 °C, no preheat; 410 and S41500 need preheat and a post-weld temper.
3. State the chloride level, the temperature and the tensile stress, and ask the supplier for a crevice-corrosion limit; do not rely on the 304 rule of thumb from Wikipedia. Move to a duplex for warm, stressed service.
4. For 17-4 PH, name the aging condition and ask for a certificate that proves it. Where chloride cracking is possible, ask for aging at 552 °C or higher and state the yield you need, since higher aging lowers strength (H1025 1000 MPa, H1150 725 MPa minimum); do not accept annealed material for service.
5. For hot service, set the real temperature range, including start-up, against the limits: 280 to 316 °C practical ceiling and the 343 to 530 °C band to avoid for 2205, above 250 °C for 2507, 425 to 540 °C for 430.
6. If the part sits in seawater or other salt-water service, read the separate seawater article on this site, because this article leaves seawater out.

What do we not know yet?

• No profile holds a price or a lead time for any grade, so this article cannot say which choice is cheapest; cost has to come from a quote.
• Corrosion data are not on one scale. Only the 409, 2205 and 2507 profiles carry a critical pitting temperature as a value, each from a different test; 301 prints below 10 °C from Outokumpu in text, the 10 °C for 316 and 316L comes from the 2205 profile, and the 304, 316, 316L and 430 profiles carry none of their own.
• No chloride limit for 316 or 316L is in the data, crevice corrosion is not quantified for any grade, and hydrogen embrittlement and galling are not covered. Stabilised austenitic, super-austenitic, high-nickel and lean duplex grades below 2304 are also missing.
• Low-temperature and fatigue data are thin: cryogenic strength only for 316 and 301, fatigue only for 316, 301 and 2205 by different methods, fracture toughness only for 440C.
• Maximum service temperature mixes oxidation, pressure-code, embrittlement and sour-service limits, and no like-for-like creep comparison or duplex sigma-phase data is in the profiles.

Questions people ask