# UNS S31603 Forgings (316L)

**Supplier:** Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory
**Address:** No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China
**Telephone:** +86 189 2135 9659
**Email:** sales@steelforgepieces.com
**Page:** https://www.steelforgepieces.com/Stainless-Steel/UNS-S31603.html
**Last reviewed:** 2026-10-05

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UNS S31603 is the UNS number for 316L stainless steel, a low-carbon austenitic grade carrying 2.00 to 3.00 % molybdenum. The molybdenum is what the grade is bought for: it holds the passive film together against chloride pitting and crevice attack at conditions where 304L gives up. Carbon capped at 0.030 % keeps chromium carbides out of the grain boundaries when the part is welded. Jiangyin Jiangnan Metal Co., Ltd. forges S31603 to customer drawing as seamless rolled rings, flanges, bars, hollow bars, discs, blocks, sleeves, tube sheets and shafts.

## UNS S31603 at a glance

- **Designation:** S31603 is the UNS number. The common name is 316L and the forging grade symbol in ASTM A182 is F316L.
- **Chemistry:** 0.030 % C max, 16.0 to 18.0 % Cr, 10.0 to 15.0 % Ni, 2.00 to 3.00 % Mo, 2.00 % Mn max, 1.00 % Si max, 0.10 % N max, balance Fe.
- **Forging minima, ASTM A182 F316L:** 70 ksi [485 MPa] tensile, 25 ksi [170 MPa] yield, 30 % elongation, 50 % reduction of area.
- **Plate minima, ASTM A240:** 70 ksi [485 MPa] tensile, 25 ksi [170 MPa] yield, 40 % elongation, 217 HBW or 95 HRB maximum.
- **Heat treatment:** solution treat and quench, 1900 F [1040 C] minimum under A182.
- **Equivalents:** 316L, EN 1.4404, X2CrNiMo17-12-2, SUS316L, 316S11.
- **Minimum order:** one piece, forged to drawing.
- **Certificate:** EN 10204 3.1 as standard, 3.2 with third-party inspection on request.

## What UNS S31603 is

S31603 and 316L are the same steel under two naming systems. UNS gives it a number, AISI gives it a name, and ASTM A182 writes it into a forging specification as grade symbol F316L. A drawing calling for S31603 is asking for the chemistry. A drawing calling for F316L is asking for a forging certified to the testing, heat treatment and marking rules of A182 as well.

Two numbers define the grade against its neighbours. Carbon at 0.030 % maximum, against 0.08 % for standard 316, starves the reaction that throws chromium carbides onto the grain boundaries while a weld cools through roughly 450 to 850 C. That is the whole reason the L grade exists. The cost is strength, which is why some designers move to F316LN and buy the yield back with nitrogen. Molybdenum at 2.00 to 3.00 % is the second number, and it is the one that separates 316 from 304.

## UNS S31603 chemical composition

Weight percent, balance iron. Single figures are maxima.

| Element | Symbol | ASTM A182 F316L | ASTM A240 / A276 | EN 1.4404 |
|---|---|---|---|---|
| Carbon | C | 0.030 | 0.030 | 0.030 |
| Manganese | Mn | 2.00 | 2.00 | 2.00 |
| Silicon | Si | 1.00 | 0.75 | 1.00 |
| Phosphorus | P | 0.045 | 0.045 | 0.045 |
| Sulphur | S | 0.030 | 0.030 | 0.030 |
| Chromium | Cr | 16.0 to 18.0 | 16.0 to 18.0 | 16.5 to 18.5 |
| Nickel | Ni | 10.0 to 15.0 | 10.0 to 14.0 | 10.0 to 13.0 |
| Molybdenum | Mo | 2.00 to 3.00 | 2.00 to 3.00 | 2.00 to 2.50 |
| Nitrogen | N | 0.10 | 0.10 | 0.110 |

Nickel runs wider at the top in A182, 10.0 to 15.0 % against 10.0 to 14.0 % in A240, because extra nickel helps hold austenite stable at the lower carbon level. EN caps molybdenum at 2.50 % where ASTM allows 3.00 %, so 1.4404 and A182 F316L are not automatically interchangeable where the specification is tight. Product analysis on a finished forging may deviate within the tolerances of the standard. Every heat ships with its own certificate of analysis.

PREN, taken as %Cr + 3.3 x %Mo + 16 x %N, puts a typical heat in the mid-20s: above 304L, below the 6 % molybdenum and duplex grades. PREN is a comparison index, not an acceptance requirement.

## UNS S31603 mechanical properties

Acceptance minima differ by product form, and quoting plate figures on a forging drawing is a common source of argument at inspection.

| Property | ASTM A182 F316L, forgings | ASTM A240 316L, plate |
|---|---|---|
| Tensile strength, min | 70 ksi [485 MPa] | 70 ksi [485 MPa] |
| Tensile, sections over 5 in. [130 mm] | 65 ksi [450 MPa] | not applicable |
| Yield strength, 0.2 % offset, min | 25 ksi [170 MPa] | 25 ksi [170 MPa] |
| Elongation in 2 in. [50 mm] or 4D, min | 30 % | 40 % |
| Reduction of area, min | 50 % | not specified |
| Hardness, max | not specified for austenitic grades | 217 HBW or 95 HRB |

These are acceptance minima, not typical test results. A182 sets no Brinell band for the austenitic grades, so hardness on a forging is reported as measured unless your specification states a limit. The structure is austenitic and cannot be hardened by heat treatment.

Austenitic steels keep their ductility going down, and S31603 is used at cryogenic temperatures without an impact problem. Going up, yield strength falls steadily, so code work at 300 C and above runs from much lower allowables than the room-temperature figure suggests. Sustained service above roughly 425 C brings carbide precipitation and sigma phase into play, and a stabilised or H grade such as 321H or 347H is usually the better buy.

## UNS S31603 physical properties

| Property | Value at 20 C |
|---|---|
| Density | 7.98 g/cm3 |
| Modulus of elasticity | 193 GPa |
| Thermal conductivity | 16.3 W/m.K |
| Coefficient of thermal expansion | 15.9 micron/m.C |
| Electrical resistivity | 7.4 micro-ohm.cm |
| Magnetic response | essentially non-magnetic annealed, permeability rises with cold work |

## Heat treatment and forging practice

| Operation | Condition | Purpose |
|---|---|---|
| Start forging | 1150 to 1200 C | Breakdown and shaping |
| Finish forging | not below 950 C | Avoid residual strain and cracking |
| Forging ratio | 3:1 minimum, higher on request | Close porosity, refine structure |
| Solution treat | 1900 F [1040 C] minimum | Take carbides into solution |
| Quench | water or forced air by section | Clear the sensitising range before carbides reform |
| Delivery condition | solution annealed as standard | ASTM delivery condition |

What decides the result is the cooling, not the soak. The quench has to carry the forging through roughly 450 to 850 C fast enough that carbides get no chance to reform at the grain boundaries, which on heavy sections means a real water quench started without delay. A piece that sat too long in transfer can pass its tensile test and still fail an ASTM A262 Practice E test. There is no conventional stress-relief window of the sort a carbon steel has, because extended time in the sensitising range undoes the solution anneal.

Austenitic stainless stays stiff at temperature and work-hardens quickly, so the press does more work for the same reduction and the low end of the window is narrower. Finishing too cold risks cracking. Finishing too hot leaves a coarse grain that shows up later as poor ultrasonic response. Ring geometries are pierced and then rolled radially and axially, which runs the grain flow around the circumference instead of cutting across it.

## What is UNS S31603 equivalent to?

Indicative comparison, not a certified substitution.

| System | Designation | How close |
|---|---|---|
| UNS | S31603 | The grade itself |
| AISI / SAE | 316L | Same steel, general grade designation |
| ASTM forgings | A182 F316L, A965, A988 | Same steel in forging specifications |
| ASTM other forms | A240, A276, A479, A312 TP316L, A403 WP316L | Same steel, other product forms |
| EN material number | 1.4404 | European counterpart, tighter on Cr, Ni and Mo |
| EN name | X2CrNiMo17-12-2 | 1.4404 in name form |
| EN neighbour | 1.4435 | Richer in nickel and molybdenum |
| JIS, Japan | SUS316L | Japanese counterpart |
| BS, UK | 316S11 | British counterpart |
| NF, France | Z3CND17-11-02 | French counterpart |
| GOST, Russia | 03Ch17N13M2 | Nearest Russian grade |

Mechanical acceptance, permitted residuals, product-form scope and pressure-equipment approval all differ between ASTM and EN. A 1.4404 certificate does not by itself satisfy a drawing calling for A182 F316L.

### Choosing between the neighbouring grades

| Grade | UNS | Molybdenum | When it is the right choice |
|---|---|---|---|
| 304L | S30403 | none | Clean water, steam, mild chemistry. Same job for less money where chlorides are absent |
| 316 | S31600 | 2.00 to 3.00 % | Higher strength at 515 and 205 MPa, where welding is controlled |
| 316L | S31603 | 2.00 to 3.00 % | Chloride or acid service on a welded assembly that cannot be re-annealed |
| 316LN | S31653 | 2.00 to 3.00 % | Code calculation fails on the low yield of 316L but low carbon has to stay |
| F51 duplex | S31803 | higher | Roughly double the yield, plus chloride SCC resistance |
| 904L | N08904 | around 4 % | Chloride or sulphuric duty past the point where 316L pits |

## Corrosion behaviour and where the grade stops

S31603 handles general corrosion across a wide span of process chemistry, and its recognised strength is resistance to intergranular attack in the as-welded condition. Published data shows it performing in phosphoric, nitric, citric, lactic and acetic acids, in hydroxides, in nitrate, chloride, acetate and sulphate salts, and in marine atmospheres.

The limits matter as much as the range. Chloride stress corrosion cracking is the classic failure mode for every standard austenitic and becomes a live risk above roughly 60 C in chloride solutions under tensile stress. Crevice geometry under gaskets and deposits will start attack at conditions the open surface tolerates. Strong reducing acids, hydrochloric in particular, are outside the grade. Where any of that describes the service, a duplex, super duplex or nickel alloy is the right answer.

## UNS S31603 forged products

Forged to drawing or specification. Not held as catalogue stock. Minimum order one piece.

| Product form | Also called | Size range | Single-piece weight |
|---|---|---|---|
| Forged bar | Round, square, flat, rectangular, hex bar | 80 to 1200 mm dia. or across flats, up to 8000 mm long | 20 to 20,000 kg |
| Hollow forgings | Hollow bar, sleeve, bush, bushing, cylinder, barrel, casing, shell, hub, housing | 150 to 2500 mm OD, 50 to 2000 mm ID | up to 20,000 kg |
| Seamless rolled rings | Radial-axial rolled rings | 200 to 3000 mm OD, height up to 1000 mm | up to 15,000 kg |
| Forged rings | Mandrel-forged and punched rings | 200 to 3000 mm OD | up to 20,000 kg |
| Discs, blocks and plates | Forged disc, disk, block, slab, tube sheet | 200 to 2500 mm dia., or to drawing | up to 20,000 kg |
| Shafts | Gear shaft, pinion shaft, spindle, stepped shaft, eccentric shaft | up to 8000 mm long | up to 20,000 kg |
| Forged flanges | Weld-neck, slip-on, blind, custom profile | 100 to 3000 mm OD | up to 10,000 kg |
| Valve components | Bodies, bonnets, seat rings, stems, plugs, blocks | to drawing | to drawing |

## Where S31603 forgings go

Chemical and petrochemical pressure vessels, heat exchangers and piping. Pulp and paper digesters, liquor tanks and paper machine parts. Food, dairy and brewing equipment where weld-line corrosion cannot be tolerated. Pharmaceutical and fine-chemical plant. Offshore and subsea production hardware. Compressor and nitrogen generator components. Valves, pumps and fittings across all of them.

## Testing, inspection and certification

Ultrasonic examination of austenitic stainless forgings is carried out to EN 10228-4, the part written for austenitic and austenitic-ferritic steels, or to ASTM A388 where a US specification governs. EN 10228-3 covers ferritic and martensitic forgings and is the wrong reference for this grade.

Available on request: liquid penetrant to ASTM E165 or EN ISO 3452, intergranular corrosion testing to ASTM A262 Practice E, ferrite measurement, positive material identification by XRF or OES, impact testing including sub-zero, and grain size determination. Material ships with an EN 10204 type 3.1 works certificate as standard, or type 3.2 endorsed by a nominated inspection body when the order calls for it.

## Questions we get asked

**Is UNS S31603 the same as 316L?**
Yes. S31603 is the UNS number for 316L. The same steel is EN 1.4404, JIS SUS316L, BS 316S11, and in forged form ASTM A182 grade F316L. UNS S31600 is standard 316, which permits higher carbon.

**How much molybdenum does UNS S31603 contain?**
2.00 to 3.00 % under ASTM A182 and A240, and 2.00 to 2.50 % under EN 1.4404. Molybdenum separates the 316 family from 304 and is the reason the grade resists chloride pitting and crevice attack. A datasheet for this grade with no molybdenum in the composition table is wrong.

**What is the difference between 316 and 316L?**
Carbon, and what follows from it. 316L is capped at 0.030 % C against 0.08 % for 316, which keeps chromium carbides off the grain boundaries during welding. The trade is strength: A182 requires 485 MPa tensile and 170 MPa yield for F316L against 515 and 205 MPa for F316.

**Why do some sources give 30 % elongation and others 40 %?**
They are quoting different specifications. ASTM A182 requires 30 % elongation and 50 % reduction of area for forged F316L. ASTM A240 requires 40 % for plate, with a 217 HBW or 95 HRB ceiling that A182 does not impose on austenitic grades. Both are correct for their own product form.

**What heat treatment do S31603 forgings get?**
Solution treat and quench, 1900 F [1040 C] minimum under A182, then a rapid quench in water or forced air by section. The cooling rate through roughly 450 to 850 C is what preserves the corrosion resistance.

**Can S31603 be welded without post-weld heat treatment?**
In most cases yes, which is the main reason to specify the L grade. Normally welded without preheat or post-weld heat treatment using matching 316L or 316LSi filler. Thick-section, heavily restrained or severe-service fabrications should be checked against the governing code.

**Are forged rings better than rings cut from plate?**
For pressure-retaining and rotating parts, generally yes. Ring rolling runs the grain flow around the circumference, helping fatigue and toughness in the hoop direction, while a ring flame-cut from plate inherits the plate's directionality. Several pressure codes and OEM specifications require forged rings for that reason.

**What do you need to quote?**
A drawing or the main dimensions, grade and governing specification, quantity, supply condition black or machined, NDT and certification requirements, and the delivery port. If the grade is not fixed, give us the medium, temperature and pressure instead.

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## Contact

Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China
Telephone: +86 189 2135 9659
Email: sales@steelforgepieces.com
Web: https://www.steelforgepieces.com/

Composition and property limits quoted from ASTM A182, ASTM A240 and EN 10088 as published. Figures are for guidance; the governing documents are the purchase order specification and the material certificate issued with the forging.