2.4675 / UNS N06200 / NiCr23Mo16Cu Forgings Nickel-chromium-molybdenum alloy with a copper addition. Forged rings, flanges, bars, discs, shafts and tube sheets to ASTM B564, ASTM B462 and DIN 17744.

DefinitionWhat is material 2.4675?

2.4675 is a nickel-chromium-molybdenum corrosion-resistant alloy with a copper addition, designated NiCr23Mo16Cu under EN chemical notation and UNS N06200 under the American system. It belongs to the group of Ni-Cr-Mo alloys that also includes C-276, C-22 and Alloy 59. It is the only member of that group in which copper is added deliberately.

The alloy is intended for process streams that are neither consistently oxidising nor consistently reducing. Molybdenum at 16 % provides resistance under reducing conditions such as hydrochloric acid and dilute sulfuric acid. Chromium at 23 % provides resistance under oxidising conditions and in streams contaminated with ferric ions or dissolved oxygen. Copper at about 1.6 % improves performance in sulfuric acid across the full concentration range, which is the area where the older Ni-Cr-Mo grades are weakest. The result is one alloy that covers process upsets and mixed-acid duty.

Three points matter when 2.4675 is bought as a forging rather than as plate or tube:

• The alloy is solid-solution strengthened, not precipitation hardened. There is no ageing cycle and no H-condition. Every forging is delivered solution annealed and water quenched.
• The hot working window is narrow. The alloy is more sensitive to strain and strain rate than austenitic stainless steel, so forging is carried out in moderate reductions with frequent reheating rather than in a few heavy blows.
• Corrosion performance depends on the final anneal. Hot work leaves carbides and intermetallic phases at grain boundaries. Only a correct re-anneal and rapid quench dissolves them. A 2.4675 forging that was slow-cooled from forging temperature can still meet every mechanical requirement on the certificate.

Jiangyin Jiangnan Metal Co., Ltd. supplies 2.4675 as an open-die forged and ring-rolled product. These routes suit pressure-containing shapes in an expensive alloy, where machining a solid billet down to size would not be economic. Common enquiries are seamless rolled rings for reactor and column flanges, forged tube sheets for shell-and-tube heat exchangers in sulfuric acid service, agitator and pump shafts, and valve bodies and seat rings for aggressive media.

Cross-referenceWhat are the equivalent designations for 2.4675?

This material appears under at least six names depending on which standards body wrote the drawing. All of the designations below describe the same chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written against any of them.

If the drawing carries a trade name rather than a generic designation, write it on the purchase order as "UNS N06200 / W.Nr. 2.4675 / NiCr23Mo16Cu". That wording is unambiguous, is correct for independently produced material, and is what appears on our mill test certificate.

ChemistryWhat is the chemical composition of 2.4675?

The composition limits below follow DIN 17744 and ASTM B574 for UNS N06200. Two figures are worth checking on any mill certificate: silicon capped at 0.08 % and carbon capped at 0.010 %. Both limits are much tighter than a typical stainless steel and both exist to suppress grain-boundary precipitation during cooling. A heat that runs high on either element will still pass a tensile test but will be less resistant to intergranular attack.

There is no tungsten in this alloy. C-276 carries 3 to 4.5 % W, while 2.4675 reaches comparable pitting performance through higher chromium. PREN (Cr + 3.3 Mo) is about 76.

Melting practice

Jiangyin Jiangnan Metal Co., Ltd. sources 2.4675 billet melted by EAF plus AOD or VOD, followed by electroslag remelting (ESR). VIM plus ESR is used where the customer specification calls for a cleaner product. ESR is relevant for this grade because it reduces macro-segregation of molybdenum. In a heavy forged section, segregation can leave a molybdenum-lean band running through the wall of a rolled ring.

MechanicalWhat are the mechanical properties of 2.4675?

In the solution annealed condition, 2.4675 / UNS N06200 has a specified minimum tensile strength of 690 MPa (100 ksi), a minimum 0.2 % proof strength of 310 MPa (45 ksi) and a minimum elongation of 45 %. Typical measured values run above the minima. Impact toughness is high, with Charpy V-notch energies near 500 J at room temperature and around 570 J at minus 196 °C, so the alloy is used for cryogenic as well as ambient service.

Typical values for mill-annealed bar as published for UNS N06200. Certified values are established on test coupons from each heat and heat-treatment lot. Note that 427 °C is the ASME Section VIII Division 1 limit for this alloy, so the higher-temperature row is given for information only.

Impact energy rises at cryogenic temperature. Face-centred-cubic nickel alloys have no ductile-to-brittle transition, so 2.4675 is a candidate for LNG and cryogenic chemical service as well as for hot acid duty.

PhysicalWhat are the physical properties of 2.4675?

The density of 2.4675 / UNS N06200 is 8.50 g/cm³ (0.307 lb/in³). This figure drives every weight calculation on an RFQ. A 2.4675 ring is about 9 % heavier than the same geometry in carbon steel, which matters when the material is priced by weight.

Two points follow for design work. Thermal conductivity is roughly one fifth that of carbon steel, so heat exchanger thermal design must use 9.1 W/m·K rather than a stainless value. Thermal expansion is close to austenitic stainless steel, so 2.4675 tube sheets and clad joints mate well with 300-series internals without excessive differential expansion.

CorrosionHow corrosion-resistant is 2.4675?

2.4675 / UNS N06200 is one of the broadest-range corrosion-resistant alloys available in forged form. Its main advantage is in sulfuric acid, where the copper addition extends the usable envelope across the concentration range. Published comparisons show it performing better than C-22, C-276, Alloy 625, 254 SMO and 316L in sulfuric acid up to about 80 %, and in hydrochloric acid up to about 10 %.

Pitting and crevice resistance

Critical pitting temperature (CPT) and critical crevice temperature (CCT) are measured in acidified 6 % ferric chloride to ASTM G48. They give the lowest temperature at which attack appears within 72 hours, so a higher figure means more margin. 2.4675 has a higher critical crevice temperature than C-276, which is the usual reason it is selected for gasketed flange faces and tube-sheet-to-tube joints.

Source: published laboratory data for UNS N06200 and the comparison alloys. In the more aggressive Green Death mixed-acid solution, the lowest temperature at which pitting has been observed in this alloy is 100 °C. In Yellow Death, no pitting was recorded up to the 150 °C maximum test temperature, with a crevice temperature of 95 °C.

Stress-corrosion cracking and seawater

Where a different alloy is the better choice

Specify another material in the following cases:

• Hot concentrated hydrochloric acid above roughly 5 to 10 % near boiling. Rates climb steeply. A Ni-Mo alloy such as B-3 (N10675), which carries no chromium, performs better in strictly reducing HCl, but it fails quickly if oxidising contaminants appear.
• Hot concentrated nitric acid. High-molybdenum alloys are not the best choice. A low-Mo, high-Cr alloy such as Alloy 690, or stainless 310, is normally used for pure nitric duty.
• Structural service above 427 °C. That is the ASME Section VIII Division 1 ceiling for this grade. 2.4675 is a wet-corrosion alloy, not a heat-resistant alloy.
• Hydrofluoric acid. Nickel alloys can suffer internal as well as external attack in HF, so published external-loss rates understate the risk. Field trials are necessary.
• Chloride-free duty where 316L is adequate. 2.4675 costs several times more per kilogram, so it should not be specified where it gives no benefit.

Selection2.4675 compared with C-276, C-22, Alloy 59, 625, 825 and 316L

The Ni-Cr-Mo group is crowded and the differences between grades are real but narrow. The table below places 2.4675 among the alloys it is most often compared against.

PREN calculated as Cr + 3.3 Mo, plus 1.65 W where tungsten is present and 16 N for nitrogen-alloyed stainless. PREN ranks pitting resistance only. It says nothing about acid resistance, and the crevice temperature in Table 5 usually governs a flanged or gasketed design.

Heat treatmentHow is 2.4675 heat treated?

2.4675 has one heat treatment: solution annealing at 1149 °C (2100 °F) followed by water quenching. Hold time is 10 to 30 minutes depending on section thickness, with heavier sections requiring the full 30 minutes. Sections under about 10 mm can be rapid air cooled. Forgings are water quenched.

Why the quench rate controls the corrosion result

Between roughly 600 °C and 1000 °C, molybdenum-rich intermetallic phases and carbides nucleate at grain boundaries in this alloy family. They consume molybdenum and chromium from the surrounding matrix and leave a depleted band on either side of each boundary, and that band is where intergranular attack starts. Water quenching takes the part through the sensitive range fast enough that the phases do not form. A slow-cooled 2.4675 forging looks the same, passes tensile and hardness testing, and then corrodes intergranularly in service.

For this reason, ASTM G28 Method A intergranular corrosion testing should appear on the purchase order for any wetted 2.4675 forging. It is the practical check that the anneal and quench were carried out correctly, and it costs a small fraction of a replacement set of reactor internals.

• Step 1ForgeStart 1232 C
  Finish 954 C
• Step 2Rough machineRemove scale
  Leave test prolongations
• Step 3Solution anneal1149 C
  10 to 30 min soak
• Step 4Water quenchRapid through
  600 to 1000 C
• Step 5TestTensile, hardness
  ASTM G28 A
• Step 6NDT and certifyUT, PT
  EN 10204 3.1 / 3.2

FabricationHow is 2.4675 forged, welded and machined?

Forging

The hot forging window for UNS N06200 runs from a start temperature of 1232 °C (2250 °F) down to a finish temperature of 954 °C (1750 °F). That is a narrow band by forging standards, and the alloy is more sensitive to strain and strain rate than austenitic stainless steel. Three rules follow:

• Use moderate reductions with frequent reheats. Heavy single blows generate local heating and shear bands. Small repeated reductions with returns to the furnace give a more uniform recrystallised structure.
• Do not continue below 954 °C. The alloy work-hardens quickly and cracking risk rises sharply. Returning the piece to the furnace costs less than scrapping a ring.
• Finish with light passes. Ending on light reductions at the upper part of the range promotes fine, uniform grain rather than a mixed structure that scatters ultrasonic testing.

Forging reduction ratio is set at a minimum of 4:1 for bars, shafts and blocks, and 3:1 for seamless rolled rings, measured from the as-cast ESR ingot. Every hot-formed 2.4675 part is re-annealed and water quenched afterwards.

Welding

2.4675 welds readily by GTAW (TIG), GMAW (MIG) and SMAW (stick). Matching consumables are ERNiCrMo-17 solid wire to AWS A5.14 (DIN 2.4698, SG-NiCr23Mo16Cu) and ENiCrMo-17 covered electrodes to AWS A5.11 (DIN 2.4699). Practical points:

• Use low heat input and low interpass temperature, typically below 100 °C, to limit time in the precipitation range.
• No preheat is required beyond removing moisture. Preheating adds time at temperature without benefit.
• Clean thoroughly before welding. Sulfur, grease, marking paint and copper contamination all cause hot cracking in nickel alloys.
• Where full base-metal corrosion performance is required in the weld zone, re-anneal and quench after welding. Weld metal is less resistant than wrought material because of its as-cast, segregated microstructure.

Machining

2.4675 machines like other solution-annealed nickel alloys. It work-hardens rapidly and does not tolerate dwell. Use rigid setups, sharp positive-rake carbide tooling, slow speeds with heavy positive feed, and generous flood coolant, and keep the tool cutting at all times. A tool that stops cutting glazes the surface, and the next pass then has to cut through a work-hardened layer. Allow generous machining stock on forgings, since a scrapped near-net part costs more than the extra material.

Cold work

The alloy is stiffer than austenitic stainless steel and work-hardens more, so cold forming often needs several stages with intermediate anneals. Any cold forming that produces 7 % or more outer-fibre elongation must be followed by a full re-anneal. Cold work does not usually affect general, pitting or crevice resistance, but it does affect stress-corrosion cracking behaviour, which is frequently the property the alloy was selected for.

Product formsWhat 2.4675 forgings can we produce?

Jiangyin Jiangnan Metal Co., Ltd. produces 2.4675 / UNS N06200 components by open-die forging, seamless ring rolling and upset forging, all to customer drawing. The forms below are the ones we quote most often. Items not listed can usually be made from a forged block or a rolled ring blank.

• 2.4675 forged rings
• 2.4675 rolled rings
• 2.4675 forged flanges
• 2.4675 round bars
• 2.4675 forged discs
• 2.4675 forged shafts
• 2.4675 tube sheets
• 2.4675 sleeves
• 2.4675 bushings
• 2.4675 forged pipes
• 2.4675 forged tubes
• 2.4675 valve parts
• 2.4675 forged gears
• 2.4675 forged blocks

CapabilityProduction capability for 2.4675 forgings

Nickel alloy envelopes are smaller than our carbon and stainless steel limits, because the narrow forging window and higher flow stress of 2.4675 restrict how much material can be moved per heat. The figures below are our working limits for this grade.

Typical lead time

Standard 2.4675 forgings quote at 8 to 12 weeks from order confirmation to ex-works dispatch, driven mainly by ESR billet procurement rather than shop time. Orders requiring EN 10204 3.2 third-party witness or additional corrosion testing typically run 12 to 16 weeks. Where a suitable billet is already in stock, shorter deliveries are sometimes possible, so ask when you enquire.

StandardsWhich standards and codes cover 2.4675?

For forgings the governing specifications are ASTM B564 / ASME SB-564 and ASTM B462 / ASME SB-462. The full family of product standards for UNS N06200, together with the applicable design code temperature limits, is set out below.

Code limits change between editions. Reference the code edition in force at the contract date and confirm allowable stresses with your Authorised Inspector or Notified Body. Jiangyin Jiangnan Metal Co., Ltd. supplies material and certification. Design responsibility remains with the purchaser.

Certification we supply

• EN 10204 3.1 mill test certificate as standard, listing heat number, full chemistry, mechanical results and heat treatment record.
• EN 10204 3.2 with third-party witness through a client-nominated inspection body such as TÜV, DNV, BV, Lloyd's, ABS or SGS, on request.
• Multi-designation certification listing 2.4675, N06200, NiCr23Mo16Cu and the applicable ASTM specification on one document, which prevents customs and receiving inspection disputes.
• ASTM G28 Method A intergranular corrosion test report where specified.
• NACE MR0175 / ISO 15156 compliance statement for sour service.
• Ultrasonic and penetrant reports to the acceptance class stated on the order.

ApplicationsWhere are 2.4675 forgings used?

2.4675 is specified where a failure costs considerably more than the material, and most often where the process stream is not chemically stable enough for a cheaper alloy.

ProcurementHow to specify a 2.4675 forging order

Seven items to include on the purchase order. Each one changes what is delivered.

Drawing callout

MATERIAL:      UNS N06200 / W.Nr. 2.4675 / NiCr23Mo16Cu
               per ASTM B564 (forgings) or ASTM B462 (flanges/fittings)
               Melt practice: EAF + AOD/VOD + ESR

CONDITION:     Solution annealed 1149 C (2100 F), soak 10-30 min
               per section thickness, WATER QUENCH.
               No ageing or precipitation treatment. Not applicable.

FORGING:       Start 1232 C max, finish 954 C min.
               Minimum reduction ratio 4:1 (3:1 for rolled rings).
               Re-anneal and quench after all hot forming.

MECHANICAL:    Rm min 690 MPa, Rp0.2 min 310 MPa, A min 45 %
               Hardness for reference only. No age hardening possible.

CORROSION:     ASTM G28 Method A. Report result on MTC.
               ASTM G48 Method C CCT where chlorides present.

NDE:           UT per ASTM A388 or EN 10228-3, class as noted
               PT per ASTM E165 / EN ISO 3452 on machined and wetted faces
               MT not applicable. Material is non-magnetic.

CERTIFICATION: EN 10204 3.1 mill certificate
               (3.2 third-party witness where stated)
               State all equivalents: 2.4675 / N06200 / NiCr23Mo16Cu

MARKING:       Heat no., specification, condition, drawing no.
               Low-stress stamp or vibro-etch on non-wetted surface only

OrderingEight specification errors seen on 2.4675 enquiries

Taken from our quotation and receiving inspection records for this grade.

Tools2.4675 forging weight calculator

ToolsBuild a 2.4675 RFQ

ReferenceGlossary

2.4675

EN / Werkstoff number for the nickel-chromium-molybdenum-copper alloy also designated NiCr23Mo16Cu and UNS N06200.

UNS N06200

Unified Numbering System designation for the same 59 Ni, 23 Cr, 16 Mo, 1.6 Cu chemistry, used throughout ASTM and ASME specifications.

NiCr23Mo16Cu

EN chemical designation: nickel base, 23 % chromium, 16 % molybdenum, with copper.

Solution annealing

Heating to 1149 °C (2100 °F) and water quenching to dissolve carbides and intermetallic phases and restore corrosion resistance after hot or cold forming. The only heat treatment that applies to this alloy.

Solid-solution strengthening

Strengthening produced by dissolved alloying elements distorting the crystal lattice rather than by precipitates. It cannot be adjusted by heat treatment, which is why 2.4675 has no H-conditions.

Mu-phase and P-phase

Molybdenum-rich intermetallic compounds that precipitate at grain boundaries if the alloy is held or cooled slowly through roughly 600 to 1000 °C. They embrittle the material and deplete the surrounding matrix of Mo and Cr, causing intergranular attack.

PREN

Pitting Resistance Equivalent Number. For nickel alloys, Cr + 3.3 Mo, approximately 76 for 2.4675. It ranks chloride pitting resistance only, not acid resistance.

CPT and CCT

Critical Pitting Temperature and Critical Crevice Temperature: the lowest temperatures at which pitting or crevice attack occurs in acidified 6 % ferric chloride per ASTM G48. For 2.4675, 145 °C and 80 °C respectively.

ASTM G28 Method A

Intergranular corrosion test in boiling ferric sulfate and sulfuric acid. The routine check that a solution anneal and quench were performed correctly on a nickel alloy forging.

ASTM G36

Stress-corrosion cracking test using stressed U-bends in boiling 45 % magnesium chloride. 2.4675 showed no cracking in 1,008 hours.

ESR

Electroslag Remelting. A secondary melting route that improves cleanliness and reduces macro-segregation of molybdenum, which matters in heavy forged sections of this alloy.

EN 10204 3.1 and 3.2

Inspection document types. 3.1 is a mill certificate issued by the manufacturer's independent inspection function. 3.2 is countersigned by an independent third party or the purchaser's representative.

P-No. 43

ASME base metal grouping for welding procedure qualification that includes UNS N06200. F-No. 43 is the matching filler metal grouping.

Trepanned billet

A billet with the core removed as a solid slug rather than machined away as swarf, reducing raw material input on hollow components by 40 to 60 %.

FAQFrequently asked questions about 2.4675

SourcesTechnical references

Chemistry, mechanical, physical and corrosion data on this page are drawn from published standards and manufacturer technical literature. Values certified on our mill test certificates are independently measured on calibrated equipment traceable to national standards.

1. ASTM B564, Standard Specification for Nickel Alloy Forgings, ASTM International.
2. ASTM B462, Standard Specification for Forged or Rolled Alloy Pipe Flanges, Forged Fittings, and Valves and Parts for Corrosive High-Temperature Service, ASTM International.
3. ASTM B574, Standard Specification for Low-Carbon Nickel-Chromium-Molybdenum Alloy Rod, Bar, and Wire, ASTM International.
4. ASTM B575, Standard Specification for Low-Carbon Nickel-Chromium-Molybdenum Alloy Plate, Sheet, and Strip, ASTM International.
5. ASTM B622, Standard Specification for Seamless Nickel and Nickel-Cobalt Alloy Pipe and Tube, ASTM International.
6. ASTM B472, Standard Specification for Nickel Alloy Billets and Bars for Reforging, ASTM International.
7. ASTM G28, Standard Test Methods for Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys, ASTM International.
8. ASTM G36, Standard Practice for Evaluating Stress-Corrosion-Cracking Resistance of Metals and Alloys in a Boiling Magnesium Chloride Solution, ASTM International.
9. ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution, ASTM International.
10. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
11. DIN 17744, Wrought nickel alloys with molybdenum and chromium, chemical composition, material number 2.4675 NiCr23Mo16Cu.
12. VdTÜV Werkstoffblatt 539, with Kennblatt 9677, 9678 and 9679.
13. ASME Boiler and Pressure Vessel Code, Section II Part D and Section VIII Division 1, and ASME B16.5, B16.34 and B31.3, latest editions.
14. NACE MR0175 / ISO 15156, Petroleum and natural gas industries, materials for use in H2S-containing environments in oil and gas production.
15. AWS A5.14 (ERNiCrMo-17) and AWS A5.11 (ENiCrMo-17), American Welding Society.
16. Haynes International, Inc., published technical data and corrosion laboratory results for HASTELLOY® C-2000® alloy (UNS N06200): physical properties, tensile and impact data, iso-corrosion tables, CPT and CCT results and seawater crevice results.
17. D. M. Aylor et al., Paper No. 329, CORROSION 99, NACE International, 1999, seawater crevice corrosion study conducted at LaQue Laboratories.
18. EN 10204, Metallic products, types of inspection documents, CEN.
19. EN 10228-3, Non-destructive testing of steel forgings, ultrasonic testing, CEN.

Standards are cited by designation without a revision year because revisions change. For procurement, reference the edition in force at the contract date. All trademarks are the property of their respective owners.

Related gradesOther nickel alloys we forge

• C-276 / N10276 forgings
• C-22 / N06022 forgings
• C-2000 / N06200 forgings
• C-4 / N06455 forgings
• Alloy 59 / N06059 forgings
• B-3 / N10675 forgings
• B-2 / N10665 forgings
• G-3 / N06985 forgings
• Hastelloy X forgings
• Alloy 625 / N06625 forgings
• Alloy 600 / N06600 forgings
• Alloy 601 / N06601 forgings
• Alloy 690 / N06690 forgings
• Alloy 825 / N08825 forgings
• Alloy 800H forgings
• Alloy 602 / N06025 forgings
• All nickel alloy grades