2.4693 Forging Parts: Ni-Fe-Co Controlled Expansion Superalloy

What is 2.4693?

2.4693 is a nickel-iron-cobalt superalloy hardened by precipitation of niobium and titanium bearing phases. Nickel runs 35.0 to 40.0 %, cobalt 12.0 to 16.0 %, niobium 4.3 to 5.2 % and titanium 1.3 to 1.8 %, with iron as the balance.

The chemistry contains almost no chromium. Chromium raises thermal expansion in conventional nickel alloys, so leaving it out produces a low and nearly constant coefficient of thermal expansion from room temperature up to an inflection point, together with a high and stable modulus of elasticity. This behaviour is used where running clearances must stay tight through a thermal cycle. Gas turbine seals, spacers and casing rings are typical applications, as are components that must hold dimensional stability beyond what stainless or low alloy steel can give.

The absence of chromium also limits oxidation resistance. There is no protective chromia scale, so extended service in an oxidising atmosphere at high temperature normally requires a protective coating or a controlled atmosphere. Where oxidation or aqueous corrosion resistance is the governing requirement, a chromium bearing grade is the correct selection. See when to choose another grade below.

In the solution treated and aged condition the alloy reaches about 1350 MPa tensile and 1100 MPa yield at room temperature, higher than most Inconel and Incoloy grades. It also work hardens rapidly, which makes machining slow and makes the forging and heat treatment route a significant part of the finished part cost.

Jiangyin Jiangnan Metal Co., Ltd. forges 2.4693 to customer drawings at its plant in Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, using open-die hammers of 1, 3, 5 and 9 tonnes, a hydraulic press up to 5,000 tonnes, and 3 m and 6 m seamless ring rolling mills. Melting is by EAF + VOD + ESR, or VIM + ESR + VAR where a cleaner ingot is required.

What forged products are available in 2.4693?

Product form is selected by geometry rather than by grade. The routes below are all available in 2.4693, allowing for the narrower hot working window and higher press loads compared with carbon or stainless steel.

• Rolled rings
• Gear ring blanks
• Shafts and spindles
• Eccentric shafts
• Discs and disc blanks
• Tube sheets
• Flanges and nozzles
• Forged pipe and tube
• Sleeves and bushings
• Blocks and bars
• Valve trim
• Near net shape forgings

2.4693 designation cross-reference

2.4693 is a material number of the German Werkstoffnummer system, and it is the designation most often used on European drawings for this nickel-iron-cobalt chemistry. Buyers sourcing the same chemistry under other numbering systems commonly cross-reference the designations below.

What is the chemical composition of 2.4693?

The principal elements below are the limits Jiangyin Jiangnan Metal supplies to as standard. Nickel, cobalt and iron form the matrix. Niobium and titanium are the hardening additions that produce the strength after ageing.

Carbon, manganese, chromium, phosphorus and sulphur are residual elements held to the limits of the governing purchase specification. State those limits on the order if the application controls them. Values are reported on every certificate we issue.

What are the mechanical properties of 2.4693?

The values below are room temperature properties in the solution treated and precipitation hardened condition, which is how most finished forgings are supplied. Both metric and imperial units are given because drawings for this grade arrive in both.

Values are typical for the aged condition and are given for enquiry purposes, not as a guaranteed acceptance criterion. Guaranteed minima depend on the governing specification, section size and test location, and are agreed at order stage. Heavy sections may test below thin section values. Where this matters, specify the test coupon location and orientation on the drawing.

Physical properties and thermal expansion

Thermal expansion is the property this alloy is normally selected for. Below the inflection temperature the coefficient of expansion stays low and nearly flat. Above it the coefficient rises toward values typical of conventional alloys and the design benefit is lost. Component service temperature therefore has to be checked against the inflection point as well as against a strength limit.

Physical property values are typical published figures for this alloy chemistry, given for design orientation. They are not acceptance values and are not certified. Where a physical property governs the design, request measured data on the specific heat at order stage.

What heat treatment is applied to 2.4693 forgings?

2.4693 develops its strength in two stages. Both are carried out in house on the same order, so the forging stays inside our traceability chain between them.

Solution treatment dissolves the niobium and titanium bearing phases back into the matrix and sets the grain size. Ageing then precipitates them in a controlled, fine distribution, which produces the tensile strength of about 1350 MPa. The ageing step is a two stage cycle with a controlled furnace cool between the holds. This controlled cool sets the precipitate size distribution. A single hold followed by air cooling will not reach the specified properties.

Typical cycle, given for orientation. The governing specification, section thickness and required property combination determine the cycle actually used. The cycle is fixed at order stage and recorded on the heat treatment chart supplied with the certificate.

Forging practice for 2.4693

2.4693 forges in a narrower window than steel and loads the press harder. Three points govern the result.

Temperature window

Hot working is carried out at about 1010 to 1120 °C, with the finishing temperature kept above roughly 955 °C. Below that the alloy work hardens quickly and the risk of forging bursts and surface laps rises. Reheating between operations is normal on heavy sections. Each reheat is logged.

Reduction and grain flow

A forging ratio of at least 4:1 is used to break down the as-cast structure. Reduction is taken in several controlled steps rather than in a few heavy blows, because the flow stress leaves little margin for a heavy pass. Where grain flow direction matters, for example on rotating rings and high stress shafts, state the required orientation on the drawing and we will macroetch to verify it.

Cooling after forging

Slow cooling after the final operation, then solution treatment. Quenching from forging temperature is not used on this grade. It leaves residual stress that causes distortion during later machining.

Machining and welding

Machining behaviour is similar to other nickel base superalloys, with rapid work hardening as the main difficulty, and the alloy is stronger in the aged condition than most Inconel and Incoloy grades. Practical points:

• Rough machine in the solution treated condition wherever the drawing allows it. Leave finishing until after ageing.
• Use a rigid setup with minimum tool overhang. Deflection causes rubbing, which work hardens the surface and increases the load on the following pass.
• Use sharp positive rake carbide, moderate cutting speed and heavy positive feed. Maintain continuous contact and do not let the tool dwell in the cut.
• Use flood coolant throughout. Use a peck cycle for deep drilling to clear chips.
• Allow for machining time in the schedule. It is a significant part of finished part cost on this grade, which is why near net shape forging often reduces total cost on complex profiles.

For welding, treat any joint as requiring a full post-weld solution treatment and re-age to restore properties in and around the fusion and heat affected zones. For many geometries a one piece near net shape forging costs less than a welded assembly and avoids the post-weld heat treatment. Discuss welded fabrication at enquiry stage.

Where are 2.4693 forgings used?

The alloy is specified where dimensional stability through a thermal cycle, high strength, or both, justify the cost and the machining difficulty. The table below covers the service areas our 2.4693 forgings are supplied into.

Production capability for 2.4693

2.4693 is produced on the same equipment as the rest of our nickel alloy programme. The figures below are plant maxima. The practical limit for a given part depends on geometry, section change and the reduction required.

Ring OD range

80-6000mm rolled ring

Max forged length

12000mm

Single piece weight

10-15000kg

Hydraulic press

5000tonnes

Open-die hammers

1/3/5/9tonnes

Ring mills

3 m, 6 mradial axial

Equipment used on this grade

Jiangyin Jiangnan Metal Co., Ltd. employs about 460 people including 9 senior engineers and 32 intermediate engineers, and has exported open-die forgings and seamless rolled rings since 2008.

2.4693 production process flow

Every 2.4693 order passes the eight stages below. Each stage is logged and traceable on the final certificate.

1. Raw materialEAF+VOD+ESR
   or VIM+ESR+VAR
   heat number traced
2. Forging1010-1120 °C
   finish above 955 °C
   ratio 4:1 min
3. Slow coolcontrolled cool
   no quench from
   forging heat
4. Solution treat980-1010 °C
   1 h per 25 mm
   rapid cool
5. Rough machinemachining stock
   to drawing
   easier before age
6. Two stage age720 °C 8 h
   FC 55 °C/h
   620 °C 8 h
7. Test and NDEUT EN 10228-3
   tensile, hardness
   MT / PT surface
8. Certify and shipEN 10204 3.1
   or 3.2 witnessed
   marked and packed

Standards, testing and certification

What is tested, and to which acceptance class, is agreed before production starts. No charge applies to the items listed below except the third party inspection body fee on a 3.2 certificate.

Witness and hold points

Customers may witness any production stage, including chemistry, forging, heat treatment, mechanical testing and final non-destructive examination. Hold points added to the order at enquiry stage carry no charge. Only the inspection body fee applies on a 3.2 certificate. Documentation is retained for ten years.

How to specify a 2.4693 forging order

State the following seven items on the enquiry or purchase order.

1. Material designationState 2.4693. If the drawing carries another designation for the same chemistry, list it as well so the certificate can be cross referenced.
2. Delivery conditionSolution treated only, or solution treated and aged to final properties.
3. Drawing2D drawing or 3D model with tolerances, machining allowance and any grain flow requirement.
4. Melting routeEAF+VOD+ESR as standard, or VIM+ESR+VAR where a cleaner ingot is required.
5. ExaminationUltrasonic standard and acceptance class. Any surface examination by MT or PT.
6. CertificationEN 10204 3.1, or 3.2 naming the inspection body that will witness.
7. CommercialQuantity, target date, destination port and incoterm.

Specification errors to avoid with 2.4693

Six common errors on this grade.

1. Assuming the alloy is corrosion resistant because it is a nickel alloy

The alloy contains almost no chromium. Oxidation and aqueous corrosion resistance are limited. If the environment is the governing requirement, select a chromium bearing grade.

2. Specifying it for service above the inflection temperature

Above roughly 415 °C the expansion coefficient rises and the design advantage is lost. Check the service temperature before selecting the grade for expansion control.

3. Leaving the delivery condition unstated

An order line reading only "2.4693 forged ring, OD 900" does not say whether the part should arrive solution treated for the buyer to machine and age, or fully aged and ready to install. This is a common cause of shipment delay.

4. Finish machining before ageing

Ageing produces a small dimensional change. On a tight tolerance bore the change can exceed the tolerance band. Rough machine before ageing, finish after.

5. Treating the two stage age as a single hold

The controlled furnace cool between the two ageing holds sets the precipitate size distribution. A single hold followed by air cooling will not meet the property table.

6. Omitting the ultrasonic acceptance class

Naming the standard without the class leaves acceptance undefined. State both, for example EN 10228-3 with the required quality class, so acceptance is defined before production starts.

When another grade is the better choice

If the governing requirement in your application appears in the left column below rather than low thermal expansion, another grade may suit better. All of the grades listed are forged in the same plant.

Glossary

Frequently asked questions about 2.4693

Standards referenced on this page

1. EN 10204:2004, Metallic products, types of inspection documents, CEN, Brussels.
2. EN 10228-3, Non-destructive testing of steel forgings, Part 3, ultrasonic testing of ferritic or martensitic steel forgings, CEN.
3. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Pruefblatt, Verein Deutscher Eisenhuettenleute.
4. ASTM A388/A388M, Standard practice for ultrasonic examination of steel forgings, ASTM International, West Conshohocken, PA.
5. ISO 9001:2015, Quality management systems, requirements, International Organization for Standardization.
6. ASM Handbook, Volume 1, Properties and selection: irons, steels and high-performance alloys, ASM International, Materials Park, OH. Sections on iron-nickel and nickel base superalloys.
7. ASM Handbook, Volume 14A, Metalworking: bulk forming, ASM International. Sections on forging of heat resistant alloys.

Standards are cited at the revision known at the date of last review. For procurement, always reference the revision in force at the contract date. Chemistry and mechanical values on this page describe material as supplied by Jiangyin Jiangnan Metal Co., Ltd. Physical property values are typical published figures for this alloy chemistry, given for design orientation and not certified.

Related grades we forge

• Nimonic 901
• NI-SPAN-C Alloy 902
• Nimonic 80A
• Nimonic 75
• Nimonic 81
• Nimonic 86
• Udimet 520
• Multimet N155
• Incoloy 926
• Hastelloy C-2000
• Hastelloy B
• A286 / S66286
• 17-4PH / S17400