NiCr23Mo16Al at a glance
- Designation
- NiCr23Mo16Al · 2.4605 · UNS N06059
- Alloy family
- Nickel chromium molybdenum, low carbon
- Common trade name
- Alloy 59 / Nicrofer® 5923 hMo
- Composition standard
- DIN 17744, VdTÜV 505
- Forging standard
- ASTM B564 / ASME SB-564
- Flanges and fittings
- ASTM B462
- Forging temperature
- 950–1180 °C (1740–2155 °F)
- Heat treatment
- Solution anneal 1100–1180 °C, quench. Not aged.
- Density (typical)
- ≈ 8.6 g/cm³
- PREN (Cr + 3.3 Mo)
- ≈ 76
- Sour service
- NACE MR0175 / ISO 15156
- Matching filler
- ERNiCrMo-13 / SNi 6059 / 2.4607
- Forms produced
- Rolled rings, flanges, discs, shafts, bars, sleeves, bushings, tube sheets
- Non-destructive testing
- EN 10228-3, SEP 1921, ASTM A388
- Certification
- EN 10204 3.1 / 3.2
- Manufacturer
- Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China
01 DEFINITIONWhat is NiCr23Mo16Al?
NiCr23Mo16Al is the DIN designation for a wrought nickel base corrosion resistant alloy. It contains 22.0 to 24.0 % chromium, 15.0 to 16.5 % molybdenum and 0.10 to 0.40 % aluminium, with nickel as the balance. Iron is limited to 1.5 % maximum. The material number is 2.4605 and the UNS number is N06059. The same composition is sold as Alloy 59, and by its originator as Nicrofer® 5923 hMo.
Chromium at 23 % gives passivity in oxidising media such as nitric acid. Molybdenum at 16 % gives resistance to pitting and crevice attack in chloride solutions, and to reducing acids such as hydrochloric and dilute sulphuric. Aluminium acts as a deoxidiser, improving melt cleanliness and hot workability without forming a hardening phase. Carbon is limited to 0.010 % and silicon to 0.10 %. Both limits sit an order of magnitude below those of the older Ni-Cr-Mo grades, which reduces carbide and intermetallic precipitation at grain boundaries during hot working and welding.
The alloy contains no tungsten, copper, titanium or tantalum, and iron is capped at 1.5 % against the 5 to 7 % allowed in Alloy 22 and Hastelloy® C-276. It is therefore the most chemically simple and the most phase stable member of the Ni-Cr-Mo group, and is used for long-life equipment in mixed and contaminated acid duty.
NiCr23Mo16Al and NiCr23Mo16Cu (Alloy 2000)
The two designations differ by one element symbol and are often confused on enquiries. NiCr23Mo16Al (2.4605 / N06059) is the aluminium deoxidised Alloy 59. NiCr23Mo16Cu (2.4675 / N06200) is Alloy 2000, which carries about 1.6 % copper for sulphuric acid duty and allows a higher iron content. The two are not interchangeable and their mill certificates are not equivalent. Order against the grade stated on the drawing. Both are forged at this plant.
02 CHEMISTRYChemical composition of NiCr23Mo16Al
The chemical composition of NiCr23Mo16Al (2.4605 / UNS N06059) is given below in weight percent, with nickel as the balance. Every heat is analysed and the actual values are reported on the EN 10204 3.1 mill certificate supplied with the forgings.
| Element | Symbol | Min. % | Max. % | Function |
|---|---|---|---|---|
| Nickel | Ni | Balance (≈ 59 % typical) | Austenitic matrix, resistance to stress corrosion cracking | |
| Chromium | Cr | 22.00 | 24.00 | Passivity in oxidising acids, highest of the C-family |
| Molybdenum | Mo | 15.00 | 16.50 | Pitting, crevice and reducing acid resistance |
| Aluminium | Al | 0.10 | 0.40 | Deoxidiser, melt cleanliness and hot workability |
| Iron | Fe | - | 1.50 | Capped low for phase stability |
| Copper | Cu | - | 0.50 | Residual |
| Manganese | Mn | - | 0.50 | Deoxidiser, sulphur control |
| Cobalt | Co | - | 0.30 | Residual, limit applies to nuclear service |
| Silicon | Si | - | 0.10 | Held low to suppress intermetallic phases |
| Carbon | C | - | 0.010 | Ultra low, prevents grain boundary carbides |
| Phosphorus | P | - | 0.015 | Impurity limit |
| Sulphur | S | - | 0.010 | Impurity limit, hot workability |
Limits per DIN 17744 and VdTÜV material data sheet 505, equivalent to ASTM B574 and B564 for UNS N06059. Where the purchase order cites a different edition or a tighter customer specification, that document governs.
Pitting resistance equivalent number
PREN is calculated as %Cr + 3.3 × %Mo. At the mid range of the specification, 23.0 % chromium and 15.75 % molybdenum, the result is about 75, rising to about 78 at the upper limits. This is above Alloy 22 and Hastelloy® C-276, and well above the 6 % molybdenum super austenitic stainless steels. PREN is used for ranking alloys and does not replace corrosion testing in the actual process medium.
03 PROPERTIESMechanical and physical properties
The values below apply to NiCr23Mo16Al in the solution annealed condition, with mechanical minima taken from VdTÜV material data sheet 505. They are indicative for design screening. Certified values are established by tensile testing of each heat treatment lot and reported on the mill certificate.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, Rm | ≥ 690 MPa | ≥ 100 ksi |
| Proof strength, Rp0.2 | ≥ 310 MPa | ≥ 45 ksi |
| Proof strength, Rp1.0 | Agreed at enquiry | |
| Elongation A5 | ≥ 45 % | ≥ 45 % |
| Impact toughness, KV | Agreed at order. The alloy remains tough to cryogenic temperature. | |
| Hardness | ≤ 100 HRB typical | ≤ 100 HRB typical |
| Property | Value |
|---|---|
| Density | ≈ 8.6 g/cm³ (0.311 lb/in³) |
| Melting range | ≈ 1310–1360 °C (2390–2480 °F) |
| Modulus of elasticity | ≈ 210 GPa |
| Thermal conductivity | ≈ 10.5 W/(m·K) |
| Mean thermal expansion, 20–100 °C | ≈ 12.4 × 10⁻⁶ /K |
| Specific heat capacity | ≈ 420 J/(kg·K) |
| Electrical resistivity | ≈ 1.28 µΩ·m |
| Hot working range | 950–1180 °C (1740–2155 °F) |
| Solution annealing | 1100–1180 °C, rapid quench |
| Magnetic response | Non-magnetic, relative permeability ≈ 1.001 |
Typical published values for UNS N06059. Confirm design allowables against the governing code and the certified test report for the heat supplied.
Corrosion behaviour
- Sulphuric acid. Resistant across a wide concentration and temperature window. In boiling dilute sulphuric acid the corrosion rate is markedly lower than that of conventional Ni-Cr-Mo grades.
- Hydrochloric acid. Resistant across the full concentration range at moderate temperature, which also covers organic processes that generate HCl in situ.
- Nitric and phosphoric acid. The 23 % chromium level carries oxidising and mixed acid service, including contaminated mineral acids.
- Chloride pitting and crevice corrosion. PREN of about 76 suits seawater, brine and halide bearing process streams.
- Stress corrosion cracking. The high nickel content resists chloride induced SCC. The grade is listed in NACE MR0175 / ISO 15156 for sour service.
- Wet flue gas. A reference material for FGD absorbers, ducts and quench zones handling condensing halide acids.
04 PRODUCT FORMSNiCr23Mo16Al forgings we manufacture
The following NiCr23Mo16Al open-die forgings are produced to customer drawing. Ring, bar and disc sizes are quoted against the drawing, and single piece weight is confirmed with the quotation.
| Forged form | Typical service |
|---|---|
| Seamless rolled rings | Absorber and reactor shell courses, flange blanks, seal and bearing housings |
| Forged flanges | Weld neck, blind and slip-on blanks to ASTM B462, ASME B16.5, B16.47 and EN 1092-1 |
| Discs and blanks | Valve discs, blind covers, tube sheet blanks, closure plates |
| Shafts and spindles | Agitator and chemical pump shafts, plunger pump rods, valve stems |
| Round bars and billets | Machining stock for fittings, fasteners and valve internals |
| Sleeves and bushings | Wear sleeves, shaft protection sleeves, compressor and subsea bushings |
| Tube sheets | Shell and tube heat exchangers in acid and halide duty |
| Forged pipe, hollows and nozzles | Heavy wall vessel nozzles, set-on and set-through blanks, thick wall acid lines |
| Valve bodies, seat rings, blocks | Ball, gate, globe, check and plug valve components |
| Custom near net shapes | Forged to drawing with machining allowance to specification |
05 PROCESSHow we forge NiCr23Mo16Al
NiCr23Mo16Al is a solid solution nickel alloy with high hot strength and a narrow working window, so the forging sequence matters as much as the chemistry. This is the route used at the plant.
- MeltingEAF with AOD or VOD refining to reach the low carbon, silicon and sulphur levels the grade requires, followed by ESR remelting to tighten chemistry and improve ingot soundness.
- Heating and upsettingIngot soaked and worked within 950 to 1180 °C (1740 to 2155 °F). Working below the lower limit risks cracking because hot strength is high. Exceeding the upper limit risks grain coarsening and incipient melting, since the alloy begins to melt near 1310 °C.
- Open-die forgingMulti-heat upsetting and drawing on hydraulic open-die presses, to break down the cast structure and develop a continuous grain flow that follows the part geometry.
- Ring rollingSeamless rings radial-axial rolled to size for absorber courses, flange blanks and housings, giving circumferential grain flow rather than a machined from solid structure.
- Solution annealing1100 to 1180 °C, commonly near 1120 °C, followed by water quench or forced air cooling. Cooling faster than about 150 °C per minute down to 500 °C preserves corrosion resistance. No ageing treatment is applied.
- MachiningRough or finish machining on CNC lathes and boring mills to the drawing, with agreed allowance for final machining by the customer.
- Testing and certificationChemistry, mechanical testing, PMI and ultrasonic examination, released with an EN 10204 3.1 or 3.2 certificate.
Heat treatment
The alloy is solid solution strengthened and has no precipitation hardening response. The specified treatment is solution annealing followed by rapid cooling. An ageing cycle would form intermetallic phases at the grain boundaries and reduce the corrosion resistance the grade is bought for. Where a drawing or specification calls for ageing on N06059, raise a query before the order is released.
- Solution annealing. 1100 to 1180 °C (2010 to 2155 °F), commonly 1120 °C.
- Cooling. Water quench or forced air, faster than about 150 °C per minute down to 500 °C for best corrosion performance. Heavy sections must be quenched.
- Cold working. Carry out on solution annealed material. Deformation beyond about 15 % requires a final solution anneal.
- Cleanliness. Surfaces must be free of sulphur, lead, zinc and other low melting contaminants before heating, and the furnace atmosphere must be low in sulphur.
06 QUALITYTesting and certification
NiCr23Mo16Al forgings are ultrasonically examined to EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class stated on the purchase order. An EN 10204 3.1 certificate is issued as standard. An EN 10204 3.2 certificate countersigned by a third party inspection body such as TÜV, SGS, BV, Lloyd's or DNV, or by the customer's own inspector, is issued where the order requires it.
Tests available on NiCr23Mo16Al forgings
- Chemical analysis. Spectrometric analysis of the heat, reported against DIN 17744, VdTÜV 505 and ASTM B564 limits.
- Tensile test. Rm, Rp0.2 and elongation at room temperature. Elevated temperature testing on request.
- Impact test. Charpy V-notch at ambient, low or cryogenic temperature.
- Hardness. Brinell or Rockwell survey. Required for NACE MR0175 orders.
- Ultrasonic testing. EN 10228-3, SEP 1921 or ASTM A388.
- Liquid penetrant testing. ASTM E165 for surface indications.
- Intergranular corrosion test. ASTM G28 method A, the standard acceptance test for wrought nickel rich alloys.
- Pitting and crevice corrosion test. ASTM G48 on request.
- Grain size and microstructure. ASTM E112 with photomicrographs.
- Positive material identification. On-piece PMI before despatch, which is worth specifying on a grade easily confused with N06022 and N06200.
- Dimensional report. Measured against the drawing.
Traceability is maintained from heat number through forging, heat treatment charge and test report. Each piece is hard stamped or vibro-etched with the heat number, grade and order number.
07 APPLICATIONSWhere NiCr23Mo16Al forgings are used
NiCr23Mo16Al is specified where the duty is too aggressive for 6 % molybdenum stainless steels, and where the process alternates between oxidising and reducing conditions. These are the industries that order the grade most often.
| Industry | Typical NiCr23Mo16Al components |
|---|---|
| Flue gas desulphurisation | Absorber internals and support rings, quench nozzles, ducting flanges |
| Chemical process plant | Reactor and column nozzles, agitator shafts, forged flanges, tube sheets |
| Sulphuric and hydrochloric acid | Pump shafts and sleeves, valve bodies and stems, piping flanges |
| Oil, gas and petrochemical | Wellhead and Christmas tree parts, subsea connectors, sour service valve components |
| Pulp and paper | Bleach plant components, digester hardware, chlorine dioxide service parts |
| Waste incineration | Scrubber components, wet electrostatic precipitator hardware, gas cooling internals |
| Fertilizer and acid plants | Urea, LDPE and mixed acid plant components with alternating oxidising and reducing duty |
| Pharmaceutical and fine chemicals | Reactor shafts, seal housings, forged nozzles for corrosive batch processes |
Alloy selection depends on acid concentration, temperature, contaminants and velocity. Send the service conditions with the enquiry and we will say where a different grade, such as Alloy 22, Alloy 686, Hastelloy® C-276 or Alloy 625, may serve better or cost less.
08 SELECTIONNiCr23Mo16Al compared with similar alloys
NiCr23Mo16Al is one of several nickel alloys used in aggressive acid and chloride service. The comparison below shows nominal chemistry and what each grade is usually chosen for.
| Grade | UNS | W.-Nr. | Cr | Mo | W | Fe max | PREN | Chosen for |
|---|---|---|---|---|---|---|---|---|
| NiCr23Mo16Al (Alloy 59) | N06059 | 2.4605 | 23 | 16 | - | 1.5 | ≈76 | Highest Cr and Mo with no tungsten and almost no iron, oxidising and reducing acid |
| NiCr23Mo16Cu (Alloy 2000) | N06200 | 2.4675 | 23 | 16 | - | 3.0 | ≈76 | Copper addition for sulphuric acid duty |
| Alloy 22 (NiCr21Mo14W) | N06022 | 2.4602 | 21 | 13.5 | 3.0 | 6 | ≈70 | General purpose Ni-Cr-Mo grade, widely stocked |
| Alloy 686 | N06686 | 2.4606 | 21 | 16 | 3.8 | 5 | ≈80 | Highest Mo and W for seawater and severe halide service |
| Hastelloy® C-276 | N10276 | 2.4819 | 16 | 16 | 4.0 | 7 | ≈75 | Long established reducing acid grade, weaker in oxidising media |
| Alloy 625 | N06625 | 2.4856 | 21.5 | 9.0 | - | 5 | ≈51 | Higher strength, seawater and elevated temperature service |
PREN calculated as Cr + 3.3 × Mo + 1.65 × W from nominal mid range chemistry, for ranking only. Order and inspect against the limits in the governing standard, not against this table.
09 FAQNiCr23Mo16Al questions we are asked
What is NiCr23Mo16Al?
NiCr23Mo16Al is a wrought low carbon nickel chromium molybdenum alloy standardised in DIN 17744 as material number 2.4605 and equivalent to UNS N06059. It contains nominally 23 % chromium, 16 % molybdenum and 0.1 to 0.4 % aluminium with nickel as the balance, and resists oxidising acids, reducing acids and chloride pitting.
What are the equivalents of NiCr23Mo16Al?
NiCr23Mo16Al corresponds to W.-Nr. 2.4605, UNS N06059 and the trade designations Alloy 59, Nicrofer® 5923 hMo, Haynes® 59, ATI 59 and BÖHLER L059. The nearest Chinese designation is NS3311. It is not the same as NiCr23Mo16Cu, 2.4675, N06200, Alloy 2000, which carries a copper addition.
What standards cover NiCr23Mo16Al forgings?
Chemistry is defined in DIN 17744 and VdTÜV material data sheet 505. UNS N06059 forgings are covered by ASTM B564 and ASME SB-564, forged or rolled flanges and fittings by ASTM B462, rod and bar by ASTM B574, ASME SB-574 and DIN 17752, and plate, sheet and strip by ASTM B575, ASME SB-575 and DIN 17750. Jiangyin Jiangnan Metal supplies forgings to ASTM B564 or to the customer's own specification.
What is the forging temperature of NiCr23Mo16Al?
NiCr23Mo16Al is forged between 950 °C and 1180 °C, that is 1740 to 2155 °F. Working below that range risks cracking because the hot strength of the alloy is high. Exceeding the upper limit risks grain coarsening and incipient melting, since the alloy begins to melt near 1310 °C. The forging must be solution annealed after hot working.
What heat treatment is applied to NiCr23Mo16Al forgings?
Solution annealing only. NiCr23Mo16Al forgings are solution annealed at 1100 to 1180 °C and rapidly cooled by water quench or forced air. The alloy is solid solution strengthened and has no precipitation hardening response, so it is not aged. An ageing cycle would precipitate intermetallic phases and reduce the corrosion resistance. Rapid cooling through the critical range is what preserves that resistance.
Is NiCr23Mo16Al weldable?
Yes. NiCr23Mo16Al is welded by GTAW, GMAW and SMAW using the matching filler ERNiCrMo-13, also designated SNi 6059 and W.-Nr. 2.4607. Because carbon is limited to 0.010 % and silicon to 0.10 %, the alloy shows little tendency to grain boundary precipitation in the heat affected zone, which is one reason it is chosen over older Ni-Cr-Mo grades for heavily welded equipment.
What is the PREN of NiCr23Mo16Al?
Using PREN = %Cr + 3.3 × %Mo with the nominal composition of 23 % chromium and 16 % molybdenum, the pitting resistance equivalent number is about 76. That is higher than Alloy 22 and Hastelloy® C-276, and well above the 6 % molybdenum super austenitic stainless steels.
Is NiCr23Mo16Al suitable for sour service?
Yes. UNS N06059 is listed in NACE MR0175 / ISO 15156 for sour oil and gas service, subject to the hardness and processing limits stated in that standard, and is also covered by API 6ACRA. Confirm the environmental limits and hardness cap on the enquiry so the correct test scope is quoted.
What is the difference between NiCr23Mo16Al and Hastelloy® C-276?
NiCr23Mo16Al carries about 23 % chromium against roughly 16 % in C-276, which makes it substantially better in oxidising media such as nitric acid. It also contains no tungsten and holds iron below 1.5 %, giving better phase stability, whereas C-276 relies on tungsten and allows up to about 7 % iron.
Which NiCr23Mo16Al forged shapes can you supply?
Jiangyin Jiangnan Metal Co., Ltd. open-die forges NiCr23Mo16Al into seamless rolled rings, flanges, discs, blanks, shafts, spindles, round bars, sleeves, bushings, tube sheets, forged pipe, nozzles, valve bodies, seat rings and custom near net shapes to drawing.
How are NiCr23Mo16Al forgings tested before shipment?
Every NiCr23Mo16Al forging is chemically analysed and tensile tested, then ultrasonically examined to EN 10228-3, SEP 1921 or ASTM A388. ASTM G28 method A intergranular corrosion testing, ASTM G48 pitting testing, Charpy impact, hardness, liquid penetrant, PMI and dimensional reporting are added on request. Results are released on an EN 10204 3.1 or 3.2 certificate.
Where can I buy NiCr23Mo16Al open-die forgings?
NiCr23Mo16Al forgings are manufactured by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Send drawings or dimensions to sales@steelforgepieces.com or call +86 189 2135 9659. The company forges to customer drawing and exports worldwide.
What do I need to send to get a NiCr23Mo16Al quotation?
Send the grade, that is NiCr23Mo16Al, 2.4605 or N06059, the drawing or finished dimensions, the quantity, the governing specification, whether the piece is wanted rough machined or as forged, whether NACE MR0175 applies, the NDT class and the certificate type. With that, Jiangyin Jiangnan Metal Co., Ltd. quotes within one working day.
Do you supply NiCr23Mo16Al in small quantities?
Yes. Single piece and prototype orders in NiCr23Mo16Al are accepted alongside production quantities, because the plant is an open-die forge working to drawing rather than a die forging line requiring tooling investment.
10 MANUFACTURERAbout Jiangyin Jiangnan Metal Co., Ltd.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin City, Jiangsu Province, China. The company forges carbon steel, alloy steel, tool steel, stainless steel and nickel base alloys, including NiCr23Mo16Al (2.4605 / UNS N06059), into seamless rolled rings, flanges, shafts, discs, bars, sleeves, bushings, tube sheets and custom shapes made to customer drawing.
The plant runs hydraulic open-die presses and a ring rolling mill, supported by in-house heat treatment, CNC machining and a testing laboratory. Forgings are released with EN 10204 3.1 or 3.2 certification and exported to chemical process, oil and gas, power generation, marine and heavy machinery customers worldwide. Lead time is confirmed with the quotation.
Open-die forging factory
Zhouzhuang Town, Jiangyin City
Jiangsu Province, China
11 REQUEST A QUOTATIONGet a price for your NiCr23Mo16Al forging
Send a drawing, a sketch or plain dimensions. Include as much of the following as is available.
- Grade, that is NiCr23Mo16Al, 2.4605, UNS N06059, or the trade name on the drawing
- Drawing or finished dimensions, plus machining allowance if the part will be finished in your own shop
- Quantity, and whether this is a prototype, a spare or a production run
- Governing specification, such as ASTM B564, ASTM B462, DIN 17744 or your own document
- Whether NACE MR0175 / ISO 15156 applies
- NDT class and acceptance standard
- Certificate type, EN 10204 3.1 or 3.2, and the inspection body if 3.2
- Destination port and required delivery date
13 REFERENCESStandards cited on this page
- DIN 17744. Wrought nickel alloys with molybdenum and chromium, chemical composition.
- DIN 17750. Nickel and nickel alloy plate, sheet and strip.
- DIN 17752. Nickel and nickel alloy rod and bar.
- VdTÜV Werkstoffblatt 505. NiCr23Mo16Al (2.4605) pressure vessel material data sheet.
- ASTM B564 / ASME SB-564. Nickel alloy forgings.
- ASTM B462. Forged or rolled UNS N06059 and other alloy pipe flanges, forged fittings, valves and parts.
- ASTM B574 / ASME SB-574. Low carbon nickel chromium molybdenum alloy rod.
- ASTM B575 / ASME SB-575. Low carbon nickel chromium molybdenum alloy plate, sheet and strip.
- ASTM B622 / ASME SB-622. Seamless nickel and nickel cobalt alloy pipe and tube.
- NACE MR0175 / ISO 15156. Materials for use in H2S containing environments in oil and gas production.
- API 6ACRA. Age hardened and corrosion resistant alloys for oilfield equipment.
- EN 10204. Metallic products, types of inspection documents, 3.1 and 3.2.
- EN 10228-3. Non-destructive testing of steel forgings, ultrasonic testing.
- SEP 1921. Ultrasonic testing of forgings, acceptance classes.
- ASTM A388. Ultrasonic examination of steel forgings.
- ASTM G28. Detecting susceptibility to intergranular corrosion in wrought nickel rich alloys.
- ASTM G48. Pitting and crevice corrosion resistance by ferric chloride solution.
- ASTM E112. Determining average grain size.
- AWS A5.14. ERNiCrMo-13, SNi 6059, W.-Nr. 2.4607 matching filler metal.
Document JJM-N06059-EN. Last revised . Hastelloy® and Haynes® are registered trademarks of Haynes International, Inc. Nicrofer® is a registered trademark of VDM Metals GmbH. Inconel® and Incoloy® are registered trademarks of Special Metals Corporation. Trade names appear on this page for grade identification only. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with, endorsed by or a licensee of those companies, and supplies material to the equivalent standardised chemistries named alongside each trade name.