AISI 310MoLN (UNS S31050) Forged Forging Steel Parts

Key Advantages Over Other Stainless Steels

• Great resistance to urea carbamate corrosion (specifically designed for urea plants)
• Excellent high-temperature oxidation resistance up to 1100°C (2010°F)
• Good resistance to stress corrosion cracking and intergranular corrosion
• Higher strength and hardness compared to standard 304 and 316 stainless steels
• Excellent toughness and ductility at both room and cryogenic temperatures
• Good weldability and formability for custom part fabrication

In addition to AISI 310MoLN, we also manufacture forgings from a wide range of other stainless steel grades, nickel alloys, and carbon and alloy steels to meet different application requirements.

Chemical Composition (Weight %)

Mechanical Properties (Delivery Condition)

Material Comparison Table

Comprehensive Testing Capabilities

• Mechanical testing: Tensile testing, Charpy impact testing (−320°F to +350°F) and hardness testing
• Non-destructive testing (NDT): Ultrasonic testing (UT), liquid penetrant inspection (LPI) and magnetic particle inspection (MPI)
• Chemical analysis: Spectrometric analysis to verify chemical composition
• Metallurgical testing: Macro-etching, microstructure analysis and grain size evaluation
• Dimensional inspection: Precision metrology using CMM and advanced measuring equipment

All non-destructive testing is carried out by our qualified in-house NDT personnel, following documented procedures under our ISO 9001:2015 quality management system. For projects requiring third-party witnessed NDT, we coordinate with customer-nominated inspection agencies, who may independently verify the results. Third-party NDT certification to ASNT, PCN, or equivalent schemes can be arranged through the customer’s appointed inspection body.

Mill Test Certificate (MTC) — EN 10204 3.1 & 3.2

EN 10204 3.1 certificates are issued as standard with every order. A 3.1 MTC is prepared and signed by our own authorised quality representative and contains full traceability of test results to the specific product supplied.

EN 10204 3.2 certificates are available when the customer arranges a nominated inspection agency (such as SGS, Bureau Veritas, TÜV, Intertek or their equivalents). These certificates need an independent, accredited third-party inspection body to witness, verify and co-sign the test results. We welcome and accommodate the presence of third-party inspectors at all agreed hold points in our Jiangyin facility.

Both certificate types include:

• Heat number and melting type with full traceability
• Detailed dimension test results
• Complete heat treatment cycle parameters
• Full chemical analysis results including tramp elements
• Individual mechanical test results and hardness values
• Ultrasonic test and surface crack examination results
• Visual and verification inspection confirmations
• Results of any additional tests specified in drawings or orders

Pitting Resistance Equivalent Number (PREN)

The PREN is a widely accepted single-number index that ranks stainless steels by their resistance to chloride pitting. It is calculated from the alloy's actual certified chemistry using the formula:

Using the minimum guaranteed composition of AISI 310MoLN (Cr 24%, Mo 1.6%, N 0.09%), the minimum PREN is:

At the nominal / mid-range composition (Cr 25%, Mo 2.1%, N 0.12%), the typical PREN is approximately 34–36, placing 310MoLN firmly above the super-austenitic threshold of 32 and well ahead of standard 316L (PREN ≈ 24) and 317L (PREN ≈ 28).

Urea Carbamate Corrosion — Why 310MoLN Was Specifically Designed for This

Standard austenitic stainless steels experience severe corrosion in urea synthesis loops. The process fluid, ammonium carbamate, is one of the most aggressive corrosive media in the chemical industry.Combined with high temperatures (170–200°C), high pressures (14–25 MPa), and a strongly oxidizing, highly concentrated carbamate solution, this environment breaks down the chromium oxide passive layer on conventional stainless steels at unacceptable rates.

AISI 310MoLN addresses this through a three-pronged metallurgical strategy:

• Very low carbon (≤0.02 wt%): Prevents chromium carbide precipitation at grain boundaries during welding and service exposure, deleting the sensitized zones that are prime sites for intergranular attack (IGA) in urea carbamate environments.
• Elevated chromium (24–26%) + molybdenum (1.6–2.6%): Greatly increases the stability and self-repair speed of the passive oxide layer even under strongly reducing attack from carbamate ions at elevated temperatures. Molybdenum enriches the passive film at the metal-oxide interface, acting as a "corrosion buffer."
• Nitrogen (0.09–0.15%): Stabilizes the austenite phase against sensitization and sigma-phase formation at elevated temperatures, while also increasing pitting resistance by preferentially concentrating at passive film defect sites.

The result is a material that passes the stringent ASTM G28 Method A (boiling 50% H₂SO₄ + Fe₂(SO₄)₃) and ASTM G28 Method B (42% MgCl₂ stress corrosion cracking) qualification tests — both mandatory for urea plant approval by major licensors including Stamicarbon, Saipem (formerly Snamprogetti) and Toyo Engineering.

High-Temperature Oxidation & Hot Corrosion Resistance

Above 600°C, corrosion is dominated by oxidation rather than aqueous corrosion mechanisms. With 24–26% chromium content, 310MoLN forms a dense, adherent, self‑healing Cr₂O₃ protective layer that resists breakaway oxidation in air up to around 1100°C — the same maximum temperature as standard AISI 310S. This makes 310MoLN is the best choice material for cyclic thermal applications, where its molybdenum and nitrogen additions deliver improved creep resistance at intermediate temperatures (600–800°C) compared to standard 310S. In sulphidizing atmospheres (refinery and petrochemical environments containing H₂S), 310MoLN outperforms 316L grades. The higher chromium‑to‑iron ratio in its oxide scale reduces the formation of iron sulphide pathways that lead to rapid corrosion. However, in severely sulphidizing conditions above 700°C, nickel‑base alloys still remain the preferred choice. Our engineering team can recommend the most suitable material for your specific operating conditions.

Weldability of AISI 310MoLN

310MoLN has good overall weldability, though several characteristics differentiate it from standard 304/316 grades and must be respected:

Pre-weld Preparation

• No preheating needed for base metal temperatures above 10°C. Unlike carbon steels, austenitic stainless steels do not need preheating — in fact, preheating is counterproductive as it slows cooling and increases sensitization risk.
• All surfaces to be welded must be cleaned to bright metal finish within 25 mm of the weld zone. Contamination from carbon steel, chlorides, grease or paint will cause weld defects or promote subsequent corrosion.
• For urea plant service, the joint preparation must get a surface finish of Ra ≤ 1.6 μm to minimize crevice corrosion initiation sites.

Recommended Welding Consumables

Interpass Temperature & Heat Input Control

• Maximum interpass temperature: 150°C — This is the single most critical parameter. Exceeding 150°C may cause sensitization — chromium carbide precipitation at grain boundaries — which severely reduces corrosion resistance in urea and sour gas service. Use temperature-indicating crayons or contact thermometers to monitor and verify interpass temperature throughout welding.
• Heat input limit: 1.5 kJ/mm maximum per pass — Lower heat input reduces the time the heat-affected zone (HAZ) spends in the sensitization temperature range (600–900°C). Stringer beads are strongly preferred over wide weave beads for the same reason.
• In thick-section welding (wall thickness >50 mm), use a back-step welding sequence to distribute heat more evenly and prevent thermal bowing of the workpiece.

Post-Weld Heat Treatment (PWHT)

 For 310MoLN used in general corrosion service, PWHT is normally not required or recommended.Where service conditions are extremely demanding — such as high-pressure urea synthesis loops — a full solution anneal (1080–1150°C followed by water quenching) after welding will fully restore corrosion resistance, although this is only practical for smaller weldments.For large fabricated assemblies, the preferred method is strict control of heat input and interpass temperature during welding.

Machining of AISI 310MoLN Forged Components

310MoLN is more difficult to machine than standard 304/316 stainless steels, mainly due to its higher work‑hardening rate — caused by its nitrogen content — and its tendency to create built‑up edge (BUE) on cutting tools. The following recommendations are based on our CNC machining experience with 310MoLN forgings at our Jiangyin production facility.

• Tooling: Use sharp, positive-rake carbide inserts (grade ISO P25–P35 for roughing, P10–P20 for finishing). Coated carbide (TiAlN or AlTiN PVD coating) significantly extends tool life in nitrogen-strengthened austenitic grades. Avoid high-speed steel (HSS) tooling except for drilling small holes.
• Cutting speeds: Reduce surface speed by 25–35% compared to 316L (typical starting point: 80–120 m/min for turning; 50–80 m/min for milling). Excessive speed leads to rapid work-hardening of the cut surface and premature tool wear.
• Feed rate: Use higher feed rates than instinctively expected — light cuts allow the tool to "rub" rather than cut, accelerating work hardening. A minimum depth of cut of 0.3 mm for finishing and 2–4 mm for roughing prevents the tool from skating on the hardened surface layer.
• Coolant: Flood coolant is mandatory for all operations. Minimum 8% soluble oil concentration. Coolant also prevents localized heating that can cause distortion in thin-section machined parts.
• Workholding: Avoid over-clamping thin-wall rings and shells — the material's lower yield strength (≥250 MPa) means distortion under excessive chuck pressure can lead to out-of-round finished dimensions. We recommend purpose-built soft-jaw fixtures for finish-machining ring forgings.
• Grinding and finishing: For sealing faces and bores, use aluminium oxide (Al₂O₃) grinding wheels. Silicon carbide wheels can contaminate the surface with free carbon, which creates galvanic corrosion cells in aggressive service environments.

Available Delivery Conditions & Surface Finish Options

Our AISI 310MoLN (UNS S31050) forgings are available in different delivery conditions to minimise your downstream fabrication effort. The appropriate condition depends on your application, service environment, and dimensional requirements:

Typical Lead Times

Lead times for AISI 310MoLN forgings depend on client's drawings, weight, needed testing and current order schedule at our Jiangyin facility. The following is a general guide based on our average production turnaround:

How to Request a Quote — Step-by-Step

Our RFQ (Request for Quotation) process is designed to be fast and transparent. Here is exactly what happens when you contact us:

1. Submit your RFQ — Send us your drawing (PDF, DXF or STEP), purchase spec,  quantity and any specific testing requirements to sales@jnmtforgedparts.com or via the contact form. The more detail you provide, the faster and more accurate our quotation will be.
2. Technical Review (within 24 hours) — Our engineering team reviews your drawing for feasibility, identifies any manufacturability concerns, and selects the optimal forging route (open die, ring rolling, or combination). We will contact you immediately if we have clarifications.
3. Formal Quotation (within 48–72 hours) — You receive a detailed quotation including unit price, tooling cost (if any), lead time, applicable standards, and a list of inspection and test documents that will be provided. No hidden charges.
4. Order Confirmation & Production Planning — Once you confirm the order, a detailed production plan is created. You receive a purchase order acknowledgement with scheduled milestones: material receipt, forging date, heat treatment, testing, and shipping.
5. Production with Milestone Updates — Our project coordinator sends you milestone updates with photographic evidence at key stages (forging, heat treatment, dimensional inspection). Third-party inspectors are welcome at our Jiangyin factory at agreed inspection hold points.
6. Final Inspection & Documentation — Before shipment, you receive a complete documentation package: EN 10204 3.1 or 3.2 MTC, dimensional inspection report, UT/LPI/MPI reports, heat treatment records, and commercial documents (packing list, certificate of origin).
7. Shipping & Delivery — Parts are individually tagged, wrapped in VCI film, and packed in export-grade wooden crates. We offer EXW, FOB Shanghai/Ningbo, CIF or DAP Incoterms. Standard sea freight or air freight available.

Minimum Order Quantities (MOQ) & Packaging

• Minimum order weight: 30 kg per line item for custom forgings; no minimum for stock bar material.
• No maximum order weight: We can produce single pieces up to 30,000 kg and handle blanket orders of more than 500 tonnes per year.
• Packaging: All forgings are individually tagged with heat number, part number and weight. VCI anti-rust paper and film wrapping. Export wooden crates that meet ISPM 15 phytosanitary treatment are used for all export markets.
• Payment terms: Standard is T/T (Telegraphic Transfer). We will accept a Letter of Credit (L/C) at sight for orders over $50,000.The payment schedule depends on how big the order is and how long the two parties have been doing business together