What UNS N07252 is
UNS N07252 is a wrought, age-hardenable nickel superalloy used for parts that carry load in hot gas and hot process streams. Its strength comes from a fine dispersion of Ni3(Al,Ti) gamma-prime particles that form during a controlled ageing treatment after solution treating.
Key points of the composition:
- Molybdenum at about 10 % provides solid-solution strengthening of the nickel matrix.
- Cobalt at about 10 % lowers the stacking fault energy and raises the gamma-prime solvus, so the strengthening phase stays stable at higher service temperatures than in iron-bearing alloys such as Inconel 718.
- Carbon at 0.10–0.20 % and boron at 0.003–0.010 % form and strengthen grain-boundary carbides, which improves creep life.
UNS N07252 work hardens quickly and has a narrow hot-working window. It is a difficult alloy to forge and to machine, and is normally bought as a finished or near-finished forging rather than as stock for the customer to cut down.
Designations and equivalents
UNS N07252, M-252 and Alloy 252 are three names for the same material. Older editions of ASTM B637 listed it as Grade 689. Order using the UNS number together with the governing specification, since the trade name alone is ambiguous across suppliers.
| System | Designation | Applies to |
|---|---|---|
| UNS | N07252 | All product forms |
| Common / trade name | M-252, Alloy 252 | All product forms |
| Former ASTM grade | Grade 689 | Superseded designation in earlier B637 editions |
| ASTM | B637 | Bars, forgings and forging stock |
| ASME | SB-637 | Boiler and pressure vessel code applications |
| Frequent misspelling | UNS NO7252 | Letter O typed for the digit zero, same alloy |
Note on the zero. Buyers and drawings often write UNS NO7252 with a capital letter O. The correct designation uses a digit zero, N07252. Enquiries written either way are quoted the same.
Chemical composition
UNS N07252 contains 18.00–20.00 % chromium, 9.00–11.00 % cobalt, 9.00–10.50 % molybdenum, 2.25–2.75 % titanium, 0.75–1.25 % aluminium and 0.10–0.20 % carbon, with nickel as the remainder.
| Element | Limits, wt % | Role in the alloy |
|---|---|---|
| Ni Nickel | Remainder | Matrix |
| Cr Chromium | 18.00–20.00 | Oxidation and hot-corrosion resistance |
| Co Cobalt | 9.00–11.00 | Raises the γ′ solvus, high-temperature strength |
| Mo Molybdenum | 9.00–10.50 | Solid-solution strengthening |
| Ti Titanium | 2.25–2.75 | Forms Ni3(Al,Ti) γ′ |
| Al Aluminium | 0.75–1.25 | Forms Ni3(Al,Ti) γ′ |
| C Carbon | 0.10–0.20 | Grain-boundary carbides |
| B Boron | 0.003–0.010 | Grain-boundary strengthening, creep life |
| Fe Iron | 5.00 max | Residual |
| Mn Manganese | 0.50 max | Residual |
| Si Silicon | 0.50 max | Residual |
| P Phosphorus | 0.015 max | Impurity |
| S Sulfur | 0.015 max | Impurity, controlled for hot ductility |
Heat analysis is reported on every mill certificate. Product (check) analysis of the finished forging is available when the purchase order calls for it.
Mechanical properties
In the solution treated and precipitation hardened condition, ASTM B637 requires a minimum tensile strength of 160,000 psi (1100 MPa), a minimum 0.2 % offset yield strength of 90,000 psi (620 MPa), 20 % minimum elongation, 18 % minimum reduction of area and 310 HBW minimum Brinell hardness.
| Property | Imperial | Metric |
|---|---|---|
| Tensile strength, min | 160,000 psi | 1100 MPa |
| Yield strength (0.2 % offset), min | 90,000 psi | 620 MPa |
| Elongation in 2 in. / 50 mm (or 4D), min | 20 % | 20 % |
| Reduction of area, min | 18 % | 18 % |
| Brinell hardness, min | 310 HBW | 310 HBW |
Stress-rupture requirement
ASTM B637 also sets a stress-rupture acceptance test for UNS N07252. For hot service this is usually the governing property rather than room-temperature strength.
| Test temperature | Applied stress | Minimum life | Min. elongation |
|---|---|---|---|
| 1500 °F (816 °C) | 30,000 psi (205 MPa) | 100 h | 10 % |
The values above are specification minima. Production forgings normally test above them. Where a design depends on a particular property, state the required value on the purchase order and it will be tested and reported on the certificate. Confirm all limits against the current edition of ASTM B637, which is revised periodically.
Heat treatment
UNS N07252 is supplied in the solution treated and precipitation hardened condition unless the order specifies otherwise. A typical two-stage cycle is:
| Stage | Temperature | Hold | Cooling |
|---|---|---|---|
| Solution treatment | 1975–2050 °F (1079–1121 °C) | 1–2 h | Air cool |
| Precipitation hardening (ageing) | 1300 ± 25 °F (704 ± 14 °C) | 20 h | Air cool or furnace cool |
Solution treatment returns the gamma-prime and the carbides to solution and sets the grain size. The ageing hold then re-precipitates gamma-prime as a fine, uniform dispersion. Soak times are set per part rather than per grade, because a heavy ring cools more slowly through the solution treatment than a thin flange.
Sequence machining around the heat treatment. Remove the bulk of the stock in the solution treated condition, then age, then finish. Heavy cutting after ageing is slow and hard on tooling. Confirm the exact cycle against your governing specification or approved procedure before release.
UNS N07252 forgings we produce
Jiangyin Jiangnan Metal Co., Ltd. produces UNS N07252 as seamless rolled rings, forged rings, flanges, round bars, disks, sleeves, bushings, hollow bars, shafts, tube sheets and near-net shaped parts, all made to customer drawings by open-die forging.
Seamless rolled rings
Pierced and radial-axial rolled, giving continuous circumferential grain flow and better tangential properties than a ring cut from plate.
Forged rings and sleeves
Upset and mandrel-forged rings, bushings and sleeves for applications where a rolled ring is not practical.
Flanges
Weld-neck, blind, slip-on and special-profile flanges, forged to dimension or to a machining allowance.
Round bars and billets
Forged round bar and forging stock, peeled or black, cut to length for onward machining.
Disks and blanks
Upset disks, discs and pancake blanks for rotating parts, valve seats and cover plates.
Shafts and spindles
Drawn shafts, stepped shafts, spindles and eccentric shafts for pumps, compressors and drive trains.
Hollow bars and tubes
Trepanned or mandrel-forged hollows and tube blanks that save machining time on bored components.
Tube sheets and nozzles
Forged tube sheets, nozzles and body blanks for heat exchangers and pressure equipment.
Weights run from a few kilograms up to multi-tonne single pieces. Dimensional capability depends on the geometry and on the ratio of finished size to forged size, so send the drawing and we will confirm the achievable envelope with the quotation.
Melting and process route
UNS N07252 supplied by our works follows this route:
- Melting. Electric arc furnace melting, then vacuum oxygen decarburisation to remove carbon, gases and volatile impurities, then electroslag remelting to refine the solidification structure and reduce segregation and non-metallic inclusions.
- Ingot conditioning. Surface inspection and grinding of the remelted ingot before heating.
- Open-die forging or ring rolling. Multiple heats within a controlled hot-working window, with the reduction sequence planned to close porosity and orient grain flow to the loaded direction of the part.
- Heat treatment. Solution treatment and precipitation hardening in furnaces with calibrated, recorded temperature control.
- Machining. Rough or finish machining to drawing, as ordered.
- Testing, marking and release. Mechanical testing, non-destructive testing, dimensional inspection, hard stamping and certification.
Forging orients grain flow along the shape of the part. In a rolled ring the flow runs continuously around the circumference, which raises tangential strength and fatigue life in the direction that a pressure-containing or rotating ring is loaded.
The works employs 460 staff, including 9 senior engineers, 32 intermediate engineers and 140 technicians.
Testing, inspection and certification
UNS N07252 forgings are ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388 as specified on the order, and certified to EN 10204 3.1. Third-party EN 10204 3.2 certification is available on request.
Included as standard
- Heat chemical analysis, reported on the certificate
- Room-temperature tensile test: tensile strength, 0.2 % yield, elongation, reduction of area
- Brinell hardness
- Dimensional inspection against the approved drawing
- Heat number and order traceability, hard stamped on the part
- EN 10204 3.1 certificate
Available on request
- Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, to a stated acceptance class
- Liquid penetrant or magnetic particle examination
- Stress-rupture testing per ASTM B637
- Elevated-temperature tensile testing at a stated temperature
- Grain size, macro-etch and microstructure examination
- Third-party inspection and EN 10204 3.2 certification (SGS, BV, TÜV, Lloyd's or a nominated inspector)
- Positive material identification (PMI) at final release
Applications
UNS N07252 is specified where a component has to keep its strength in a hot, loaded and often corrosive environment. Typical uses of forgings in this grade:
| Sector | Components |
|---|---|
| Gas turbines and turbochargers | Rotor and wheel blanks, combustor and casing rings, spacers, seal rings, fasteners |
| Valves | Bodies, bonnets, seat rings, stems, plugs and blocks for high-temperature ball, gate, globe, check and plug valves |
| Pumps and compressors | Shafts, impeller blanks, sleeves, wear rings and casing parts for chemical and plunger pumps and industrial air compressors |
| Oil, gas and subsea | Wellhead and Christmas tree components, subsea and deepwater production hardware, connectors |
| Pressure equipment | Tube sheets, nozzles, forged flanges and body blanks for shell-and-tube heat exchangers, columns, towers and air receivers |
| Power transmission | Gear blanks, spindles, couplings and drive shafts in gearboxes and turbine drive trains |
| Process and heavy industry | Rolls, wheels, manifolds and crystalliser parts in chemical, pharmaceutical, pulp and paper and cement plant |
Below roughly 650 °C, Inconel 718 is usually the more economical choice and is easier to weld. UNS N07252 is specified above that range.
UNS N07252 compared with other nickel superalloys
UNS N07252 holds strength to a higher temperature than Inconel 718 and is harder to weld and machine. It sits in the same gamma-prime family as Waspaloy and René 41, with more molybdenum than Waspaloy and lower titanium and aluminium than René 41.
| Alloy | Strengthened by | Cr / Co / Mo, % | Practical strength limit | Weld and machine |
|---|---|---|---|---|
| UNS N07252 (M-252) | γ′ Ni3(Al,Ti) | 19 / 10 / 10 | High | Difficult |
| Inconel 718 | γ″ Ni3Nb | 19 / – / 3 | Moderate, about 650 °C | Good, the easiest of this group |
| Waspaloy | γ′ Ni3(Al,Ti) | 19 / 13 / 4 | High | Difficult |
| René 41 | γ′ Ni3(Al,Ti) | 19 / 11 / 10 | Very high | Very difficult, strain-age cracking risk |
| Inconel 625 | Solid solution | 21 / – / 9 | Lower, corrosion grade | Good |
Nominal chemistry is rounded for comparison. The binding limits for UNS N07252 are in the composition table above.
Machining and fabrication
UNS N07252 work hardens rapidly and is harder to machine than austenitic stainless steel, Inconel 625 or Monel 400. It also reaches higher strength than those alloys.
Machining practice
- Rigid machines, short tool overhang and heavy workholding. Deflection causes rubbing, and rubbing work hardens the surface ahead of the next pass.
- Positive rake, sharp edges and a generous nose radius. Change inserts on a set schedule rather than at failure.
- Low surface speed with a heavy, constant feed. Do not dwell in the cut.
- Depth of cut below the previous hardened layer, so each pass cuts fresh metal.
- High-pressure coolant delivered to the cutting edge.
- Rough machine in the solution treated condition, age, then finish.
Welding
Gamma-prime strengthened alloys of this type are prone to strain-age cracking in the heat-affected zone. Where welding cannot be avoided, weld in the solution treated condition, control heat input, and apply a full post-weld solution and ageing treatment. Qualify the procedure on representative material and section thickness before running production parts.
Questions and answers
What is UNS N07252?
UNS N07252 is a precipitation-hardenable nickel-cobalt-molybdenum superalloy sold under the trade name M-252 or Alloy 252. It contains about 19 % chromium, 10 % cobalt and 10 % molybdenum, with titanium and aluminium additions that form a gamma-prime strengthening phase during ageing. ASTM B637 covers it as bars, forgings and forging stock for moderate and high temperature service. Older editions of that standard listed it as Grade 689.
Is UNS N07252 the same as M-252?
Yes. M-252 is the trade name and UNS N07252 is the Unified Numbering System designation for the same alloy. It also appears as Alloy 252, and as Grade 689 in older editions of ASTM B637. Order using the UNS number together with the governing specification, since the trade name alone is ambiguous across suppliers.
Which specification covers UNS N07252 forgings?
ASTM B637, Standard Specification for Precipitation-Hardening and Cold Worked Nickel Alloy Bars, Forgings, and Forging Stock for Moderate or High Temperature Service. The ASME equivalent is SB-637. Jiangyin Jiangnan Metal Co., Ltd. supplies UNS N07252 forgings to ASTM B637 with EN 10204 3.1 certification as standard.
What are the mechanical properties of UNS N07252?
In the solution treated and precipitation hardened condition, ASTM B637 requires a minimum tensile strength of 160,000 psi (1100 MPa), a minimum 0.2 % offset yield strength of 90,000 psi (620 MPa), minimum elongation of 20 %, minimum reduction of area of 18 % and minimum Brinell hardness of 310 HBW. The stress-rupture requirement is 100 hours minimum life at 1500 °F (816 °C) under 30,000 psi (205 MPa) with 10 % minimum elongation.
What is the difference between UNS N07252 and Inconel 718?
The two alloys strengthen by different mechanisms and suit different temperatures. UNS N07252 is a cobalt and molybdenum bearing gamma-prime alloy that holds strength above roughly 700 °C. Inconel 718 is niobium strengthened by gamma double-prime, contains around 18 % iron, welds and machines far more easily, and is normally limited to about 650 °C.
Inconel 718 is the usual choice where weldability, cost and machinability govern the selection. UNS N07252 is used when the service temperature is too high for 718.
Can UNS N07252 be made into seamless rolled rings?
Yes. UNS N07252 is supplied as seamless rolled rings produced by piercing and radial-axial ring rolling. This gives continuous circumferential grain flow and better tangential properties than a ring cut from plate or bar. Jiangyin Jiangnan Metal Co., Ltd. produces UNS N07252 seamless rolled rings, forged rings, flanges and disks to customer drawings.
Is UNS N07252 difficult to machine?
Yes. UNS N07252 work hardens rapidly and is harder to machine than austenitic stainless steel, Inconel 625 or Monel 400. Machining requires rigid setups, positive and uninterrupted cuts, low surface speeds with heavy feeds, sharp carbide or ceramic tooling and generous coolant. Most heavy stock removal is done in the solution treated condition before precipitation hardening.
Who supplies UNS N07252 forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China that supplies UNS N07252 (M-252) forgings worldwide, including seamless rolled rings, forged flanges, round bars, disks, sleeves, bushings, shafts and tube sheets. Material is melted by EAF plus VOD plus ESR, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and certified to EN 10204 3.1 or 3.2.
Contact sales@steelforgepieces.com or +86-189-2135-9659.
What information is needed to quote a UNS N07252 forging?
Send the drawing or the finished dimensions with machining allowance, the quantity, the governing specification and heat treatment condition, the certificate type required (EN 10204 3.1 or 3.2), any non-destructive testing acceptance class, and the destination port. A firm price and lead time is normally returned within one working day.
What is UNS N07252 used for?
UNS N07252 is used for components that must keep high strength and creep resistance at elevated temperature. Typical applications include gas turbine and turbocharger rotating parts, combustor and casing rings, valve bodies, seats and stems for high temperature service, pump and compressor shafts, gearbox and power transmission parts, wellhead and subsea equipment, and heat exchanger tube sheets and nozzles in chemical and petrochemical plant.
Request a quote for UNS N07252 forgings
Send a drawing or the dimensions and a firm price and lead time will normally come back within one working day. Include as much of the following as you have:
- Drawing, or finished dimensions with the machining allowance you want left on
- Quantity, and whether this is a one-off, a prototype or a repeat order
- Specification and condition, for example ASTM B637, solution treated and precipitation hardened
- Certificate type, EN 10204 3.1 or 3.2 with a named third-party inspector
- Non-destructive testing standard and acceptance class, if required
- Destination port and required delivery date
Zhouzhuang Town, Jiangyin City
Jiangsu Province, China
Enquiries are answered in English or Chinese. Drawings are treated as confidential and are not shared outside the quotation process.