317LN / UNS S31753 Forgings - Nitrogen Alloyed 3% Mo Austenitic

Where 317LN Sits

Think of the 317 family as 316L with more molybdenum. 317LN then adds nitrogen on top of that. The result is a grade that holds its strength at temperature better than 317L and resists chloride pitting further, while the low carbon keeps grain-boundary carbide precipitation out of the picture during welding and thermal processing.

It is corrosion resistant in dilute sulphuric solutions at moderate temperature, very dilute hydrochloric acid at moderate temperature, industrial phosphoric acid up to 100 °C, sulphurous acid and solutions of sulphites and bisulphites at high temperature, and hot organic acids including acetic, formic and citric. Published isocorrosion data puts 317LN above 304L, 317L and 316L in sulphuric acid across most of the concentration range.

The microstructure is austenitic with roughly 1 to 2 % residual ferrite after solution annealing. It is non-magnetic in the solution treated condition and very slightly ferromagnetic after cold work.

On specifications, read this before you order. The standard that lists UNS S31753 is ASTM A240 / ASME SA-240, which covers plate, sheet and strip for pressure vessels. We did not find S31753 in ASTM A182, A479, A965 or A336, and there is no A182 grade symbol such as "F317LN" in circulation. Forgings in this grade are therefore supplied to S31753 chemistry with the mechanical acceptance criteria, heat treatment condition and test scope written into the purchase order. If your project needs a forging standard named on the certificate, tell us at enquiry stage and we will tell you honestly what can and cannot be certified.

What We Forge in 317LN

Rings and circular work

Seamless rolled rings, closure rings, wear rings and retaining rings. Rolled from an upset and pierced blank so the grain follows the circumference rather than being cut across it.

Flanges and body forgings

Weld neck, slip-on, blind and long weld neck blanks to ASME B16.5 and B16.47 dimensions, plus valve bodies, bonnets and nozzle forgings.

Tube sheets and plate-form parts

Forged and machined tube sheets, covers and closures for exchangers and columns in chemical and petrochemical duty.

Shafts and long work

Pump shafts, agitator shafts, spindles and stepped shafts, drawn out with intermediate upsetting to keep the reduction ratio honest along the full length.

Hollows, sleeves, bushings

Forged and bored hollow sections, which saves significant machining against solid bar on thin-wall parts and cuts the swarf you pay for twice.

Forged bar and billet

Round, square and flat forged bar for re-machining, where the print calls for forged rather than rolled product.

Chemical Composition

Table 1. Limits per ASTM A240 / ASME SA-240 for UNS S31753. Single values are maxima. Typical analyses combine a published mill datasheet with a general grade datasheet; the two differ slightly on nickel and molybdenum, which is normal between producers working inside the same range.
Element	ASTM A240 limit, %	Typical mill analysis, %
Carbon	0.030 max	0.02
Silicon	0.75 max	–
Manganese	2.00 max	–
Phosphorus	0.045 max	–
Sulfur	0.030 max	–
Chromium	18.0 – 20.0	18.2
Nickel	11.0 – 15.0	13 – 14
Molybdenum	3.0 – 4.0	3.0 – 4.2
Nitrogen	0.10 – 0.22	0.15
Iron	balance	63 – 64

Pitting resistance equivalent calculates at 32, using %Cr + 3.3×%Mo + 16×%N. Nitrogen is weighted sixteen times in that formula, which is why a nominal 0.15 % addition moves the number as much as it does.

Mechanical Properties

There are two published minimum sets for this grade and they are not the same. Which one applies to your order depends on which standard you buy against, so both are given here rather than averaged into a single misleading figure.

Table 2. The A240 column applies to plate, sheet and strip. The EN 10088 column is the guaranteed minimum for hot rolled plate from 5 to 75 mm thickness as published by a European producer. A general grade datasheet also quotes tensile 590 MPa min and yield 285 MPa min, consistent with the EN set.
Property at 20 °C	ASTM A240 minimum	EN 10088 minimum
Tensile strength	550 MPa	590 MPa [86 ksi]
Yield strength, 0.2 % offset	240 MPa	290 MPa [43 ksi]
Yield strength, 1.0 % offset	not stated	315 MPa [46 ksi]
Elongation	40 %	40 %
Hardness	217 HBW max	not stated

Elevated temperature tensile data

Austenitic grades lose a large share of their room temperature yield strength in the first 200 °C. Design against the figures at service temperature, not the room temperature number on the certificate.

Table 3. Minimum guaranteed values to EN 10088 for hot rolled plate 5 to 75 mm, after solution annealing. Values for forgings are agreed on the order.
Temperature	0.2 % yield, MPa	1.0 % yield, MPa	Tensile, MPa	Elongation, %
20 °C / 68 °F	290	315	590	40
100 °C / 212 °F	225	255	525	40
200 °C / 392 °F	185	210	490	40
300 °C / 572 °F	165	190	460	35
400 °C / 752 °F	150	175	450	30
500 °C / 932 °F	135	160	440	25

Elastic properties

Young's modulus 200 GPa [29 000 ksi] and shear modulus 77 GPa [11 200 ksi] at room temperature, with Poisson's ratio 0.299. Both moduli fall steadily with temperature, reaching 165 GPa and 62 GPa respectively at 500 °C. A general grade datasheet also reports elongation at break of 45 % and Brinell hardness around 190 for wrought product.

Physical and Thermal Data

Table 4. Density 7900 kg/m³. Expansion figures are mean coefficients over the interval from 20 °C to the stated temperature.
Temperature	Resistivity, µΩ·cm	Thermal conductivity, W/m·K	Specific heat, J/kg·K	Mean expansion from 20 °C, ×10^-6/K
20 °C	80	14	500	–
100 °C	87	15	500	16.0
200 °C	94	16.5	520	16.5
300 °C	100	18	530	17.0
400 °C	105	19.5	540	17.5
500 °C	110	21	540	18.0

Thermal conductivity of 14 W/m·K at room temperature is low, around a quarter of plain carbon steel. That matters in two practical ways: soak times in the furnace run roughly 50 % longer than for carbon steel of the same section, and heat does not escape the cutting zone during machining, so it goes into the tool.

Hot Working and Heat Treatment

Hot forming, 900 to 1150 °C (1652 to 2102 °F)Keep the surface clean and avoid oil contamination. A neutral or slightly oxidising furnace atmosphere is required. Allow the longer soak the low conductivity demands.
If forming finishes below 950 °C (1742 °F), solution annealing is necessaryPublished practice for that case is 1080 to 1180 °C (1976 to 2156 °F). This is not optional housekeeping; it restores the structure the grade depends on.
Solution anneal at 1100 to 1150 °C (2012 to 2102 °F)Then water quench. The purpose is to avoid intermetallic phase precipitation, which cuts both ductility and corrosion resistance. A second published source gives 1080 to 1175 °C followed by rapid water quenching, which overlaps the same window.
Quench fastSlow cooling through the precipitation range in a molybdenum-bearing, nitrogen-bearing austenitic grade defeats the whole heat treatment. Section thickness governs how fast is achievable, so discuss heavy sections before ordering.

317LN is not hardenable. There is no quench-and-temper cycle and no ageing cycle for this steel. Any strength above the solution annealed level comes from cold work, at the cost of ductility and with a slight ferromagnetic response appearing. If a supplier quotes you a hardened or aged condition in 317LN, they have the wrong grade.

Fabrication

Welding

Weldable by GTAW, GMAW, MMAW, SAW and other current processes, with good resistance to hot cracking. Care is needed with autogenous processes, high energy processes and fully austenitic fillers. No preheat and no post weld heat treatment are required. Maximum interpass temperature 120 °C (248 °F). Post weld pickling and passivation are necessary.

Filler metals

Covered electrode E317L-15 or E317L-16 to ASME Section II Part C SFA 5.4; bare wire ER317L to SFA 5.9. An 18-16-5L filler with higher molybdenum is preferred where the weld metal must match the parent corrosion resistance. Overalloyed 904L or other Cr-Ni-Mo fillers are also used.

Cold forming

Ductility is excellent and the grade cold forms without trouble, but the high nitrogen content and the work hardening rate mean it takes noticeably more power than structural steel or a standard austenitic grade. Size the press accordingly.

Machining

Less machinable than a 13 % Cr martensitic stainless because of the work hardening. Published turning parameters with carbide tooling, dry or with cutting oil: 6 mm depth at 0.5 mm/rev and 70 to 80 m/min; 3 mm at 0.4 mm/rev and 85 to 95 m/min; 1 mm at 0.2 mm/rev and 100 to 110 m/min. With high speed steel and cutting oil the same depths run at 11 to 16, 18 to 23 and 25 to 30 m/min.

Pickling

Standard solutions of 10 to 20 % nitric acid with 1.5 to 5 % hydrofluoric acid at 20 to 60 °C, or 10 to 20 % sulphuric acid with 1.5 to 5 % hydrofluoric acid. Raising the temperature shortens the time. Rinse thoroughly afterwards.

Cutting

Thermal cutting by plasma or thermal sawing, and mechanical cutting by shearing, stamping or cold sawing. After thermal cutting, pickle or grind to remove the oxide layer before the part goes into service.

Corrosion Test Results

Table 5. Standardised corrosion test results published by a European producer of the grade. Results on our material are confirmed by test on request and are not assumed from this table.
Test	Attack type	Published result
ASTM A262 practice A	Intergranular	Step or dual structure
ASTM A262 practice B (Streicher)	Intergranular	Under 1 mm per year
ASTM A262 practice C (Huey)	Intergranular	Under 1.5 mm per year
ASTM A262 practice E (Strauss)	Intergranular	No cracking after bending
ASTM G48 method A	Pitting	Critical pitting temperature 20 °C (68 °F) or above
ASTM G48 method B and ASTM G78	Crevice	Critical crevice temperature 10 °C (50 °F) or above

Typical Applications

Published applications for the grade are chemical tankers, the petrochemical industry, chemical and pharmaceutical processing, oil and gas, food and beverage, and pollution control equipment. Forged parts we are commonly asked for in these sectors include pump and agitator shafts, valve bodies and bonnets, flange and nozzle forgings, exchanger tube sheets, closure and wear rings, and bored sleeves for vessel internals.

Testing and Certification

Every heat ships with a mill certificate to EN 10204 3.1. Third party inspection to 3.2 is arranged where the purchase order names the inspection body. The standard scope covers ladle and product chemical analysis including nitrogen, room temperature tensile and elongation, hardness, the solution annealing record with temperature and quench medium, and a dimensional report. Available on request: intergranular corrosion testing to ASTM A262 at the practice you specify, pitting or crevice testing to ASTM G48, ultrasonic examination, liquid penetrant examination, ferrite measurement, grain size, elevated temperature tensile testing, and positive material identification. Say which of these you need in the enquiry, because several of them have to be planned before the material is melted rather than after the part is machined.

Questions We Get Asked

What is the difference between 317L and 317LN?

Nitrogen. 317LN specifies 0.10 to 0.22 % nitrogen, which raises both yield and tensile strength above 317L, stabilises the austenite and contributes strongly to pitting resistance through the 16×%N term in the PREN formula. Carbon stays low in both, so both resist sensitisation during welding. Choose 317LN when you need the extra strength at the same corrosion performance, or the extra pitting margin at the same section.

Is 317LN covered by ASTM A182?

We found no evidence that it is. The specification that lists UNS S31753 is ASTM A240 / ASME SA-240 for plate, sheet and strip. There is no established A182 grade symbol for 317LN. Forgings are supplied to S31753 chemistry with mechanical and test requirements agreed on the order. If your piping specification demands an A182 grade, the nearest listed molybdenum-bearing options are F317L or F316L, and that is a decision for your design authority rather than for us.

What is the European equivalent of 317LN?

EN 1.4434, X2CrNiMoN18-12-4. Be careful here: some data sources list 1.4439 (X2CrNiMoN17-13-5) against S31753, but 1.4439 is separately identified as 317LMN / UNS S31726, a higher molybdenum grade. Two independent sources, including a European producer's own 317LN datasheet, give 1.4434 for S31753. Order against the UNS number to remove the ambiguity.

Can 317LN be hardened by heat treatment?

No. It is a fully austenitic grade with no hardening response. Supply condition is solution annealed and water quenched. Additional strength is only available through cold work.

What is the PREN of 317LN?

32, calculated as %Cr + 3.3×%Mo + 16×%N on a typical analysis. For comparison the grade shows a critical pitting temperature of 20 °C or above in ASTM G48 method A and a critical crevice temperature of 10 °C or above in method B.

What filler metal should be used?

E317L-15 or E317L-16 covered electrodes, or ER317L wire. Where the weld metal must match the parent metal for corrosion, use an 18-16-5L filler with higher molybdenum, or an overalloyed 904L or Cr-Ni-Mo filler. No preheat or post weld heat treatment, maximum interpass 120 °C, and pickle and passivate afterwards.

Does 317LN need annealing after forging?

Yes in practice. Hot forming runs from 900 to 1150 °C, and if the final forming temperature falls below 950 °C a solution anneal at 1080 to 1180 °C is required. Our standard route is to solution anneal at 1100 to 1150 °C and water quench, which avoids the intermetallic precipitation that would otherwise cost ductility and corrosion resistance.

What sizes and forms can you supply?

Seamless rolled rings, flanges and body forgings, shafts and spindles, discs, tube sheets, sleeves, bushings, bored hollows and forged bar. Send a drawing, or give the grade with outside diameter, inside diameter, length or thickness, quantity and the test scope you need.

Data sources. Composition limits and plate mechanical minima for UNS S31753 per ASTM A240 / ASME SA-240 grade tables. Typical analysis, room temperature mechanical values, heat treatment range of 1080 to 1175 °C, non-hardenable behaviour and application list per AZoM, "Stainless Steel Grade 317LN (UNS S31753)". Elevated temperature tensile data to EN 10088, physical and thermal tables, PREN of 32, ferrite content, hot and cold forming practice, welding and filler metal guidance, pickling, cutting, machining parameters and ASTM A262 and G48 corrosion results per the Industeel UR 317LN producer datasheet, which also gives EN 1.4434 as the Euronorm designation. Cross-system designations SUS 317LN, STS 317LN and 022Cr19Ni13Mo4N from a published comparison table. Elongation at break of 45 % and Brinell hardness near 190 from a materials property database. Figures on this page are for reference; the governing document is the edition of the standard named on your purchase order. Reviewed 1 October 2026.

317LN (UNS S31753) Forgings

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