Nickel alloy · Werkstoff 2.4600 · UNS N10629

2.4600 Forgings: NiMo28 / Alloy B-4 / UNS N10629 Nickel-Molybdenum Alloy

• W.-Nr. 2.4600
• NiMo28
• UNS N10629
• Alloy B-4
• NiMo29Cr / N10675 (alloy B-3)
• DIN 17744
• VdTÜV 512

Published 11 April 2019 · Last updated 8 August 2026 · Reviewed by the Jiangyin Jiangnan Metal Co., Ltd. engineering department

What is 2.4600 (NiMo28 / alloy B-4 / UNS N10629)?

2.4600 is a nickel-molybdenum alloy strengthened by solid solution. It contains 26 to 30 % molybdenum in a nickel matrix with a minimum of 65 % nickel. The molybdenum content is what gives the alloy its resistance to hydrochloric acid and other reducing acids across the full concentration range and up to boiling temperature.

The chromium content is 0.5 to 1.5 %. That is too little to form the chromium oxide passive film that protects stainless steels and Ni-Cr-Mo alloys such as C-276 and alloy 59. As a result the alloy performs very well in reducing conditions and corrodes rapidly in oxidizing conditions. 2.4600 is therefore selected for a defined environment rather than as a general upgrade over stainless steel.

The alloy is not age hardenable. Strength comes from molybdenum held in solid solution, so there is no aged condition and no H-number. Forgings are solution annealed, quenched rapidly and delivered in that condition.

Two alloys share the material number 2.4600 in European practice. Alloy B-4 (NiMo28, UNS N10629) has the composition limits tabulated below. Alloy B-3 (NiMo29Cr, UNS N10675) has a wider iron range and permits tungsten and niobium. Both were introduced to improve on the thermal stability of the earlier alloy B-2. Since the material number alone does not distinguish them, the UNS number should be stated on the purchase order.

2.4600 equivalent designations and cross-references

This alloy appears under several designations depending on the specifying body. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written under any of them.

Cross-references are given for procurement convenience. The controlling document on any order is the specification named on the purchase order, and that specification is what appears on the material test certificate.

2.4600 chemical composition to DIN 17744

Three limits in the table below carry most of the engineering meaning. Molybdenum provides the reducing acid resistance. Iron and chromium are held to narrow windows because both reduce stability if they drift high. Carbon at 0.01 % maximum keeps chromium and molybdenum carbides out of the grain boundaries, which is what allows the alloy to be welded without knife line attack.

Composition per the published alloy B-4 limits (Krupp VDM) under material number 2.4600 and DIN 17744. Alloy B-3 (NiMo29Cr / N10675) differs: Cr 0.3 to 3.0 %, Mo 26.0 to 32.0 %, Fe 1.0 to 6.0 %, with W up to 3.0 % and Nb+Ta up to 0.4 % permitted. The heat analysis for your order is reported on the EN 10204 certificate.

Alloy B-2, alloy B-3 and alloy B-4 compared

All three are Ni-28Mo alloys with similar corrosion resistance in clean hydrochloric acid. They differ mainly in thermal stability, that is, how the alloy behaves during the time it spends in the intermediate temperature range while being welded, stress relieved or slow cooled.

Where a component is being replaced in existing alloy B-2 plant and will not be welded into the assembly, alloy B-2 remains valid. Where the component will be welded or will see repeated thermal cycles, specify alloy B-3 or B-4, since the composition control that separates them from B-2 exists to keep intermetallic phases out of the heat affected zone. For forged components ordered against European documentation, 2.4600 / UNS N10629 is the usual choice.

2.4600 mechanical properties

2.4600 is a solid solution alloy, so its strength is set by molybdenum content and grain size rather than by heat treatment. There is one property set to consider, the solution annealed condition, and it does not change after the part leaves the quench tank.

Values are typical for solution annealed material of 3.2 mm (0.125 in.) section and are given for design orientation. Heavy forged sections normally show somewhat lower strength with similar ductility. Guaranteed minima are those of the specification named on the purchase order and are reported per heat on the EN 10204 certificate.

2.4600 physical properties

Density, precipitation band and filler designation per published 2.4600 datasheet data. Modulus is a typical value for Ni-28Mo alloys and is indicative. Where a physical property enters a code calculation, use the value from the governing design code rather than a supplier datasheet.

Corrosion behaviour of 2.4600

The behaviour of this alloy depends on whether the environment is reducing or oxidizing. In reducing conditions it outperforms Ni-Cr-Mo grades. In oxidizing conditions it corrodes rapidly, faster than carbon steel in some cases.

Media where 2.4600 performs well

• Hydrochloric acid across the full concentration range and up to boiling point. This is the main application for the alloy.
• Sulfuric acid over a wide concentration band in the non-aerated, non-oxidizing state.
• Phosphoric acid, acetic acid, formic acid and other organic acids.
• Hydrogen chloride gas, including at elevated temperature.
• Chloride stress corrosion cracking resistance. The high nickel matrix is effectively immune, which is a second reason for selecting the grade.

Media that attack 2.4600

• Nitric acid and other oxidizing acids.
• Ferric (Fe3+) and cupric (Cu2+) ions in an otherwise suitable acid. Corrosion of upstream carbon steel dissolves iron into the process stream, and ferric ions convert a safe environment into an aggressive one.
• Dissolved oxygen or aeration. An acid that is safe when deaerated may not be when air ingress occurs.
• Chlorine, hypochlorite, peroxides and persulfates.
• Wet chlorine and oxidizing salts.

This table is a screening aid and not a corrosion rate prediction. Service behaviour depends on concentration, temperature, velocity, aeration, trace contaminants and crevice geometry acting together. Corrosion allowance and final material selection are the responsibility of the plant designer or a qualified corrosion engineer and should be verified by coupon or loop testing in the actual medium.

Thermal stability and why 2.4600 is always quenched

Nickel-molybdenum alloys of this composition are metastable at room temperature. Held between about 500 and 820 °C, the alloy precipitates ordered nickel-molybdenum intermetallic phases, principally beta phase Ni4Mo, at the grain boundaries. Two effects follow. Impact toughness falls, and the molybdenum depleted zones next to the precipitates corrode preferentially, producing intergranular attack in service.

This is the reason for the following production and fabrication rules:

• Forgings are water quenched from solution annealing rather than air cooled, so that the part passes through the precipitation band in minutes rather than hours.
• Heavy sections need particular attention because the core cools more slowly than the surface. Section thickness is a metallurgical constraint on this alloy, not only a handling one.
• Interpass temperature during welding is controlled and low, typically not more than about 100 °C, to limit the cumulative time in the band.
• Conventional post weld stress relief cycles are not applied. Where post weld heat treatment is required, it is a full re-solution anneal and quench rather than a subcritical hold.
• Alloy B-3 and alloy B-4 were developed with closer composition control to slow this precipitation. That is the main reason to select them over alloy B-2.

2.4600 forged product forms

Jiangyin Jiangnan Metal Co., Ltd. produces 2.4600 / NiMo28 / UNS N10629 by open-die forging and seamless ring rolling, working to customer drawing. Because the alloy is costly per kilogram and dense at 9.2 g/cm3, a near-net forged shape is normally recommended, and for bored components a trepanned or hollow forged blank. Both reduce input weight and shorten machining time.

Production capability

The equipment listed below is our general open-die and ring rolling capability. Nickel-molybdenum alloys are worked in a narrower temperature range than steel and are supplied from a smaller ingot base, so the practical maximum for a 2.4600 part is confirmed case by case at enquiry stage against ingot availability and part geometry.

• Forging hammers

  1 t, 3 t, 5 t and 9 t open-die forging hammers for bars, shafts and blocks.

• Hydraulic press

  Open-die press for heavy sections, cogging and upsetting.

• Ring rolling

  3 m and 6 m seamless ring rolling mills for rectangular, contoured and profiled sections.

• Heat treatment

  Furnaces with calibrated chart recording and quench facilities sized for rapid transfer.

• Machining

  Rough and finish machining to drawing, including deep boring, trepanning and tube sheet drilling.

• Test laboratory

  Universal testing machine, impact tester, hardness testers, metallographic microscope and magnetic particle equipment.

Forging and heat treatment of 2.4600

1. Raw materialIngot or billet to DIN 17744. Heat number recorded, chemistry verified on receipt.
2. HeatingSlow uniform soak in a clean, low sulfur furnace atmosphere.
3. ForgingNarrow hot working range. Multi-step reduction with frequent reheats.
4. Ring rollingRadial-axial rolling to profile where the geometry is a ring.
5. Solution annealApprox. 1050 to 1100 C, soaked to section thickness.
6. Rapid quenchWater quench with fast transfer through the 500 to 820 C band.
7. MachiningRough or finish machined to drawing. Descale and pickle as required.
8. Test and certifyChemistry, mechanicals and NDE, then EN 10204 3.1 or 3.2.

Hot working

2.4600 has a narrow hot working range and a high flow stress, roughly twice that of austenitic stainless steel at the same temperature. Presses and hammers are sized accordingly and reductions are taken in more steps than an equivalent steel forging requires. Typical practice is a start temperature of about 1150 to 1200 °C with the finishing temperature held above about 900 °C. Below that the alloy work hardens sharply and cracking risk increases. Sulfur bearing lubricants and sulfur containing furnace atmospheres must be avoided, since nickel alloys are embrittled by sulfur pick-up at forging temperature.

Solution annealing

The finished forging is solution annealed in the region of 1050 to 1100 °C, soaked until the heaviest section reaches temperature, then quenched rapidly in water. This dissolves any intermetallic phase formed during forging and cooling, and moves the part through the precipitation band fast enough that none re-forms. Transfer time from furnace to quench is part of the procedure. On heavy forgings it is the parameter that determines whether the core passes the intergranular corrosion test.

Temperatures given are typical industry practice for the 2.4600 family and are indicative. The parameters applied to a given order are set against the governing specification and recorded on the heat treatment chart supplied with the certificate.

Welding and machining 2.4600

Welding

2.4600 can be welded by GTAW (TIG), GMAW (MIG), SMAW and plasma processes using a matching Ni-Mo filler, W.-Nr. 2.4695 for TIG rod. The procedure rules that matter are those that keep the joint out of the precipitation band.

• Weld in the solution annealed condition, on clean, degreased, oxide free surfaces. Residues containing sulfur, lead, zinc or phosphorus cause hot cracking. This includes marker pen, cutting fluid and adhesive tape residue.
• No preheat.
• Keep interpass temperature low, typically at or below 100 °C. Allow the joint to cool between passes rather than running continuously.
• Use low heat input, stringer beads and minimal weaving.
• Do not apply conventional post weld stress relief. Where PWHT is required by the code or the process licensor, it must be a full re-solution anneal and quench.
• Use tools and grinding media reserved for nickel alloys to avoid iron contamination of the surface.

Machining

2.4600 work hardens rapidly, has low thermal conductivity so heat stays in the cutting zone, and produces a tough continuous chip. Recommended practice: rigid setup with short tool overhang, sharp positive rake carbide tooling, low cutting speed with heavy positive feed, and continuous flood coolant. The tool must not dwell or rub, because the work hardened layer left behind is harder than the parent material and the next pass has to cut through it. Use a depth of cut sufficient to get below any previously hardened layer, and change tools on a set schedule rather than on failure.

Testing, inspection and certification

Every 2.4600 forging is supplied with an EN 10204 3.1 material test certificate as standard, issued by our own independent inspection department. EN 10204 3.2 certificates witnessed by a third party such as TÜV, DNV, BV, Lloyd's Register or ABS are available on request and are scheduled into the production plan when the order is placed.

Applications of 2.4600 forgings

Most applications of this alloy come from the same requirement: a reducing acid that lower cost materials will not survive. The industries below account for the majority of 2.4600 orders.

Applications are taken from published guidance for the 2.4600 alloy family together with our own order history. All of them assume the environment remains free of oxidizing contaminants. See the selection warning above.

How to specify a 2.4600 forging order

The seven steps below remove most of the ambiguity that otherwise appears later as a certificate query or a rejected part.

1. State the designation2.4600 / NiMo28 / UNS N10629 to DIN 17744. The UNS number resolves the B-3 or B-4 question.
2. Describe the mediumAcid, concentration, temperature and all contaminants, particularly oxidizers.
3. Send the drawingFinished dimensions, tolerances, surface finish and machining allowance.
4. Delivery conditionSolution annealed and rapidly quenched. Do not specify ageing.
5. Define NDEUT standard and class, PT if required, ASTM G28 method A where the anneal must be proven.
6. Certificate levelEN 10204 3.1 or 3.2. For 3.2, name the inspection body.
7. Commercial dataQuantity, delivery date, destination port and Incoterms.

Suggested drawing callout

Specification errors on 2.4600 orders

• 1. Writing 2.4600 with no UNS number

  The material number covers both alloy B-3 and alloy B-4. Adding the UNS number, N10629 or N10675, removes the ambiguity from the purchase order, the mill order and the certificate.

• 2. Not declaring oxidizing contaminants

  The most common cause of premature Ni-Mo failure. Trace ferric or cupric ions from upstream steel or brass will damage a correctly manufactured part. Supply the full stream analysis with the enquiry.

• 3. Specifying an ageing or stress relief cycle

  Usually carried over from a stainless steel specification. On 2.4600 it precipitates embrittling intermetallics. Solution anneal and quench is the correct condition.

• 4. Allowing a slow cool after annealing

  Air cooling a heavy section leaves the core in the precipitation band too long. Rapid water quench with controlled transfer time is part of the specification.

• 5. Specifying magnetic particle inspection

  The alloy is non-magnetic, so MT will not detect anything. Specify dye penetrant testing for surface examination.

• 6. Calculating weight at steel density

  At 9.2 g/cm3 against 7.85, the part is about 17 % heavier than a steel density estimate. Use the weight calculator.

• 7. Ordering solid bar for a bored part

  Machining out the centre of an expensive, hard to cut alloy wastes both material and cutting time. Request a trepanned or hollow forged blank.

• 8. Using shop tooling shared with carbon steel

  Iron embedded in the surface from grinding wheels, wire brushes or fixtures becomes a corrosion initiation site. Nickel alloys require dedicated tools and a clean handling area.

Glossary

2.4600

EN/DIN material number for a nickel-molybdenum alloy with 65 % minimum nickel and 26 to 30 % molybdenum. Covers alloy B-4 (UNS N10629) and alloy B-3 (UNS N10675).

NiMo28

EN short name for the alloy B-4 chemistry under material number 2.4600.

UNS N10629

Unified Numbering System designation for alloy B-4. The unambiguous way to name this material on a purchase order.

DIN 17744

German standard covering the chemical composition of wrought nickel alloys containing molybdenum and chromium.

VdTÜV 512 and 517

German pressure vessel material approval sheets for alloy B-4 and alloy B-3 respectively.

Reducing environment

An environment in which the cathodic reaction is hydrogen evolution rather than reduction of an oxidizer. Hydrochloric, dilute sulfuric, phosphoric and organic acids are typical. The environment 2.4600 is designed for.

Oxidizing environment

An environment containing an oxidizing agent such as nitric acid, dissolved oxygen, ferric or cupric ions, chlorine or peroxide. Not suitable for 2.4600.

Beta phase Ni4Mo

An ordered nickel-molybdenum intermetallic that precipitates on slow cooling or prolonged intermediate temperature exposure, embrittling the alloy and creating an intergranular corrosion path.

Knife line attack

A narrow band of intergranular corrosion beside a weld fusion line. The weakness of alloy B-2 that alloys B-3 and B-4 were developed to address.

Solution annealing

Heating to dissolve secondary phases, then quenching rapidly to retain the single phase structure at room temperature. The delivery heat treatment for 2.4600.

Seamless rolled ring

A ring produced by piercing a forged billet and rolling it out on a ring mill, giving circumferential grain flow with no weld seam.

Trepanned blank

A forged bar with the centre removed by trepanning rather than drilling, saving material and machining time on bored components.

EN 10204 3.1

A test certificate issued by the manufacturer's own independent inspection department based on tests on the delivered material. Type 3.2 is the same document countersigned by a third party inspector.

ASTM G28 method A

A boiling ferric sulfate and sulfuric acid test used to detect intergranular attack. Used to verify that a solution anneal reached the core of a heavy forging.

Frequently asked questions about 2.4600

Technical references

1. DIN 17744, Wrought nickel alloys with molybdenum and chromium, chemical composition, Deutsches Institut für Normung.
2. VdTÜV Werkstoffblatt 512 (alloy B-4) and 517 (alloy B-3), Verband der Technischen Überwachungsvereine, Germany.
3. Published material data sheet for material number 2.4600 (alloy B-3 and alloy B-4, UNS N10675 and N10629), M. Woite GmbH, Erkrath, Germany, for composition, density and welding filler designation.
4. EN 10204:2004, Metallic products, types of inspection documents, CEN, Brussels.
5. EN 10228-3, Non-destructive testing of steel forgings, part 3: ultrasonic testing, CEN.
6. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt, Verein Deutscher Eisenhüttenleute.
7. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
8. ASTM G28, Standard Test Methods for Detecting Susceptibility to Intergranular Attack in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
9. ASM Handbook, Volume 13B: Corrosion: Materials, ASM International, sections on nickel and nickel alloys.
10. ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, J.R. Davis (ed.), ASM International.
11. ISO 15156 and NACE MR0175, Materials for use in H2S-containing environments in oil and gas production, ISO, where sour service qualification applies.

Standards are cited at the revision current at the time of the last page review. For procurement, always reference the revision in force at the contract date. Property values on this page are given for engineering orientation. Contractual values are those stated on the purchase order and reported on the material test certificate.

Related grades and forged products

Nickel alloys we forge

• Hastelloy B-2
• Hastelloy B-3
• Hastelloy B-4
• Hastelloy B
• Hastelloy C-276
• Hastelloy C-22
• Hastelloy C-4
• Hastelloy C-2000
• Hastelloy G-3
• Hastelloy X
• Alloy 59
• Alloy 602
• Inconel 625
• Inconel 718
• Incoloy 825
• Incoloy 925

2.4600 by forged form

• 2.4600 forging rings
• 2.4600 forged rings
• 2.4600 forged tubes
• 2.4600 forged sleeves
• 2.4600 forged discs
• 2.4600 forged cylinders
• 2.4600 forging products
• 2.4600 forging pieces

Trade mark notice. Hastelloy® is a registered trade mark of Haynes International, Inc. Nicrofer® is a registered trade mark of its respective owner. Inconel® and Incoloy® are registered trade marks of Special Metals Corporation. Material made by those companies and sold under those brand names is theirs. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is described as 2.4600 / NiMo28 / UNS N10629 to DIN 17744, the same generic chemistry, manufactured independently. We are not affiliated with, sponsored by or endorsed by any of the trade mark holders named. All other product names, brand names and trade marks are the property of their respective owners.

Disclaimer. The technical information on this page is provided for general engineering guidance. Corrosion behaviour depends on the complete service environment and cannot be predicted from a single datasheet. Material selection, corrosion allowance and design calculations remain the responsibility of the plant designer or a qualified corrosion engineer and should be verified by testing in the actual medium. Contractual properties are those stated on the purchase order and reported on the material test certificate.