316L Mod forgings, EN 1.4435 and UNS S31603 modified
Low-silicon, high-molybdenum urea-grade 316L. Melted, forged, solution annealed, machined and tested in one works.
316L Mod is a modified 316L austenitic stainless steel with extra-low silicon and a raised molybdenum content, developed for urea and ammonium carbamate service. It carries the designations EN 1.4435 (X2CrNiMo18-14-3) and, under ASTM practice, 316L Modified or UNS S31603 modified. Typical chemistry is below 0.03 per cent carbon, about 18 per cent chromium, 13.5 per cent nickel, 2.6 per cent molybdenum and below 0.5 per cent silicon, with manganese between 1 and 2 per cent. Low carbon, low silicon and a nickel content close to 14 per cent together keep the alloy fully austenitic and free of intermetallic precipitation, with ferrite held below 0.5 per cent in the solution annealed and water quenched condition. The same material is traded as 316L UG, meaning urea grade, and under mill trade names such as UREA 316L.
316L Mod at a glance
- EN number
- 1.4435 (X2CrNiMo18-14-3)
- UNS
- S31603 modified
- Also called
- 316L Modified, 316L UG, urea grade 316L
- Key limits
- Si below 0.5 per cent, Mo about 2.6 per cent, ferrite below 0.5 per cent
- Solution anneal
- 1120 to 1180 C, water quench
- Designed for
- Urea and carbamate environments
- Not designed for
- Nitric acid service
Why silicon and ferrite decide the grade
Ordinary 316L to EN 1.4404 or ASTM A182 F316L allows silicon up to 1.00 per cent and sits at the lower end of the nickel and molybdenum bands. In a high pressure urea synthesis loop that chemistry suffers selective and intergranular attack. The urea grade variant works on three fronts. Silicon is cut to below 0.5 per cent. Molybdenum is pushed toward the top of the 316L range at around 2.6 per cent. Nickel is lifted close to 14 per cent so the structure solidifies fully austenitic instead of carrying delta ferrite stringers that corrode first.
The ferrite limit of 0.5 per cent is an acceptance criterion rather than a target. It is reached only when the correct solution anneal is applied, that is heating to 1120 to 1180 C followed by a water quench. Hot work performed between 1200 C and 950 C has to be followed by that full final anneal. Skip it and the microstructure the grade was bought for is not present in the finished part.
Chemical composition
| Element | ASTM A182 F316L (S31603) | 316L Mod, typical | Reason for the limit |
|---|---|---|---|
| C | 0.030 max | below 0.03 | Limits carbide precipitation and sensitisation |
| Si | 1.00 max | below 0.5, often ordered at 0.40 max | The defining urea grade restriction. High silicon promotes selective attack |
| Mn | 2.00 max | 1.0 to 2.0 | Deoxidation and hot cracking control |
| P | 0.045 max | 0.045 max | Grain boundary embrittlement |
| S | 0.030 max | 0.030 max, frequently tighter | Sulphide inclusions act as pit initiation sites |
| Cr | 16.0 to 18.0 | about 18, ordered 16.0 to 19.0 | Passive film stability |
| Ni | 10.0 to 15.0 | about 13.5, ordered 12.5 to 15.0 | Holds a fully austenitic structure at ferrite below 0.5 per cent |
| Mo | 2.00 to 3.00 | about 2.6, ordered 2.2 to 3.0 | Resistance to carbamate and chloride attack |
| N | 0.10 max | By agreement | Some urea specifications add nitrogen |
| Fe | Balance | ||
Base specification from the ASTM A182 chemical requirements table. Urea grade typical values from the Industeel UREA 316L datasheet, edition 03/2020.
Mechanical properties
Figures below apply to the solution annealed and water quenched condition. Guaranteed minima and typical results are separated, since the two are often confused in circulated datasheets.
| Property | Typical at 20 C | Guaranteed minimum, t below 20 mm |
|---|---|---|
| 0.2 per cent proof stress | 250 MPa, 36 ksi | 190 MPa, 27 ksi |
| 1 per cent proof stress | 280 MPa, 41 ksi | not specified |
| Tensile strength | 530 MPa, 77 ksi | 490 MPa, 71 ksi |
| Elongation | 55 per cent | not specified |
| Impact, KCV at room temperature | 120 J/cm2 or above | not specified |
| Temperature | 0.2 per cent PS | 1 per cent PS | Tensile strength | Elongation |
|---|---|---|---|---|
| 20 C, 68 F | 250 MPa | 280 MPa | 530 MPa | 55 per cent |
| 100 C, 212 F | 190 MPa | 210 MPa | 490 MPa | 55 per cent |
| 200 C, 392 F | 160 MPa | 180 MPa | 460 MPa | 55 per cent |
| 300 C, 572 F | 135 MPa | 155 MPa | 420 MPa | 55 per cent |
| 400 C, 752 F | 125 MPa | 140 MPa | 390 MPa | 55 per cent |
Source: Industeel UREA 316L datasheet, edition 03/2020.
Physical properties
| Temperature | Mean expansion, 10-6 per K | Resistivity, micro ohm cm | Conductivity, W/m K | Specific heat, J/kg K | E, GPa | G, GPa |
|---|---|---|---|---|---|---|
| 20 C, range 20 to 100 C | 16.0 | 74 | 15 | 500 | 200 | 75 |
| 200 C, range 20 to 300 C | 16.5 | 90 | 17 | 550 | 185 | 70 |
| 400 C, range 20 to 500 C | 17.5 | 100 | 20 | 590 | 170 | 64 |
Corrosion performance and the Huey test
Urea grade material is normally released against the Huey test, ASTM A262 Practice C, run over five periods of 48 hours. Specification limits in common use are a weight loss below 130 mg/dm2 per 24 hours, with maximum intergranular penetration of 200 micrometres longitudinal and 70 micrometres transverse. Industeel reports production results inside those limits across a two-year sample of heats.
We do not run A262 in our own laboratory. The test is placed with an accredited third-party laboratory and the report is issued alongside the mill certificate. State the practice and the acceptance limits at enquiry stage so the test is scheduled into the programme rather than added at the end of the job.
Fabrication
Hot and cold forming
Hot forming runs from 1200 C down to 950 C after uniform through heating, followed by a solution anneal at 1120 to 1180 C and a water quench. The fully austenitic structure cold forms without difficulty, though the raised molybdenum and the work hardening rate call for heavier equipment than 304 of the same section.
Welding
TIG, plasma, MIG, manual metal arc, submerged arc and flux cored arc welding are all usable. A fully austenitic structure is sensitive to hot cracking, so welds are made with a high manganese, nitrogen alloyed filler, nominally 20 chromium, 16 nickel, 3 molybdenum, 6.5 manganese and 0.2 nitrogen. Use basic coated electrodes or basic fluxes, hold heat input at 1.5 kJ/mm or below and keep interpass temperature under 150 C. Weld metal has to stay extra low in ferrite and silicon with no carbide, nitride or intermetallic precipitation.
Pickling and passivation
The grade goes into service pickled and passivated. A nitric and hydrofluoric bath of 10 to 20 per cent HNO3 with 1.5 to 5 per cent HF is used at room temperature for a few hours, or for about 20 minutes at 60 C. A bath of 10 to 20 per cent H2SO4 with 1.5 to 5 per cent HF is an alternative.
Handling
Urea grade surfaces are kept away from carbon steel throughout to avoid iron contamination. Parts are marked for traceability to the heat number and shipped on lined pallets.
316L Mod against neighbouring grades
| Grade | Designations | Position | Page |
|---|---|---|---|
| 316L | EN 1.4404, UNS S31603, A182 F316L | General purpose low carbon 316. Silicon up to 1.00 per cent. Not a urea grade. | A182-F316L |
| 316L Mod | EN 1.4435, S31603 modified, 316L UG | Low silicon, molybdenum about 2.6 per cent, ferrite below 0.5 per cent. The standard 316 variant for urea plants. | This page |
| 310MoLN | EN 1.4466, UNS S31050, UREA 25.22.2 | A modified 310L with much higher chromium, nickel and nitrogen for more severe carbamate duty. Not interchangeable with 316L Mod. | UNS S31050 |
| 6 per cent molybdenum austenitic | A182 F44, UNS S31254 | Super austenitic for chloride and seawater service. | A182-F44 |
| Sanicro 28 | UNS N08028 | High chromium, nickel, molybdenum and copper for phosphoric and sulphuric acid duty. | Sanicro 28 |
| 904L | UNS N08904 | High alloy austenitic with copper for reducing acids. | 904L |
316L Mod product forms
Each item below is forged from a single piece of steel melted on site. No welded fabrication and no purchased billet of unknown origin.
| Product form | Typical duty |
|---|---|
| Seamless rolled rings | Vessel and reactor rings, flange blanks |
| Forged rings | Heavy sections outside the ring mill envelope, seat rings |
| Forged flanges | Weld neck, blind, slip on, orifice and long weld neck to ASME B16.5, B16.47 and API 6A |
| Tube sheets, discs and covers | Carbamate condensers, strippers, heat exchangers |
| Shafts and spindles | Pump and agitator shafts |
| Bars, blocks and billets | Round, flat and square feedstock for machined bodies |
| Hollow cylinders, sleeves and bushings | Heavy wall pipe sections and liners |
| Valve and pump components | Bodies, bonnets, stems, seat rings and nozzles for ball, gate, globe, check and plug valves |
Forging is carried out on a 6300 tonne hydraulic press with ring rolling to 6 m diameter, backed by 14 heat treatment furnaces and an in-house machine shop. Send the drawing and we confirm the size envelope for your specific part.
Melting route and traceability
Most forging suppliers in China buy billet. This works starts one step earlier, at the furnace. 316L Mod is melted in the electric arc furnace, refined in the ladle furnace and decarburised under vacuum, which is the route that delivers the very low carbon and the tight silicon control the grade depends on. Clean and superalloy grades run through vacuum induction melting, vacuum arc remelting and protective atmosphere electroslag remelting. Maximum heat size is 60 tonnes. Steel then moves through the press or the ring mill, the heat treatment furnaces and the machine shop without leaving the site, so the certificate traces the finished part back to its melt number instead of stopping at a purchased billet.
The works has operated in Zhouzhuang Town, Jiangyin City since 1997 and employs 460 people, including 9 senior engineers, 32 intermediate engineers and 140 technicians. It holds CCS, BV, DNV, LR and NK approvals and exports to North America, Europe, the Middle East and Asia Pacific.
Testing and certification
| Item | Detail |
|---|---|
| Chemical analysis | Optical emission spectrometry to ASTM E415, infrared carbon and sulphur analysis to ASTM E1019, positive material identification on request |
| Mechanical testing | Tensile testing to ASTM A370 and ISO 6892, Charpy V-notch to minus 60 C |
| Ultrasonic examination | ASTM A388, EN 10228-3, SEP 1921 on request |
| Surface examination | Dye penetrant for austenitic material, magnetic particle to ASTM E709 where applicable |
| Metallography | Grain size to ASTM E112, ferrite assessment |
| Corrosion testing | ASTM A262, including Practice C Huey, and ASTM G28, placed with an accredited third-party laboratory |
| Certification | EN 10204 3.1 as standard, EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector on request |
| Approvals held | CCS, BV, DNV, LR, NK |
Frequently asked questions
What is 316L Mod stainless steel?
A modified 316L austenitic stainless steel with extra-low silicon and raised molybdenum, designated EN 1.4435 or X2CrNiMo18-14-3 and UNS S31603 modified. Typical chemistry is below 0.03 per cent carbon, about 18 per cent chromium, 13.5 per cent nickel, 2.6 per cent molybdenum and below 0.5 per cent silicon. The balance keeps the alloy fully austenitic with ferrite below 0.5 per cent after solution annealing and water quenching, which is what gives the improved corrosion resistance in urea and carbamate environments.
Are 316L Mod, 316L UG and 1.4435 the same material?
In commercial practice they are. All three describe the low silicon, high molybdenum, low ferrite urea variant of 316L. Trade names such as UREA 316L belong to individual mills. Plain 316L to EN 1.4404 or ASTM A182 F316L is not an equivalent, since it allows silicon up to 1.00 per cent and carries no ferrite ceiling.
How does 316L Mod differ from 310MoLN and UNS S31050?
They are separate urea plant grades. 316L Mod is a modified 316L at roughly 18 chromium, 13.5 nickel and 2.6 molybdenum. 310MoLN, also called UREA 25.22.2 or EN 1.4466 under UNS S31050, is a modified 310L with much higher chromium, nickel and nitrogen for heavier carbamate duty. Order each under its own designation.
What heat treatment does 316L Mod require?
Solution anneal at 1120 to 1180 C, then water quench. That dissolves carbides and holds ferrite below 0.5 per cent. Hot forming runs from 1200 C down to 950 C and has to be followed by the full final anneal.
Can 316L Mod be used in nitric acid?
No. The grade was developed for urea and ammonium carbamate, and the Industeel datasheet states it is not designed for nitric acid application. Huey testing to ASTM A262 Practice C is a quality check on the steel rather than a nitric service qualification.
Do you melt the steel or buy billet?
We melt it. Carbon, alloy, stainless and duplex grades run through the electric arc furnace, ladle furnace and vacuum oxygen decarburisation. Clean and superalloy grades take the vacuum induction, vacuum arc and protective atmosphere electroslag route. Maximum heat size is 60 tonnes.
Request a quotation for 316L Mod forgings
Send the six items below and a price normally comes back within two working days. The material grade or specification, for example EN 1.4435 or your own urea grade specification. The dimensions or a drawing in PDF, DWG, DXF or STEP. The quantity and any expected repeat volume. The delivery condition, whether as forged, proof machined or finish machined. The heat treatment and testing requirements. The certification level and destination port.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
+86 189 2135 9659 and sales@steelforgepieces.com
Reviewed 28 September 2026 by the technical sales team at Jiangyin Jiangnan Metal Co., Ltd. Alloy data compiled from the ASTM A182 chemical requirements table and the Industeel UREA 316L datasheet, edition 03/2020. Typical values are indicative and do not replace the acceptance limits agreed at order.