CoCr26Ni9Mo5W Forgings

Grade

What is CoCr26Ni9Mo5W used for?

CoCr26Ni9Mo5W is specified where a part must resist wear and corrosion at the same time. Typical duties are pump and valve internals in chloride-bearing or slurry service, mixer and agitator components, extruder and screw conveyor parts, rolls, nozzles and glass-contact tooling.

Two properties account for most specifications. The first is resistance to galling. Cobalt-base alloys do not cold-weld to a mating surface in the way austenitic stainless steels do, which is why valve seats and stems are made from them. The second is resistance to cavitation and slurry erosion, where the alloy performs better than the common Ni-Cr-Mo corrosion alloys in comparative erosion testing.

High-carbon cobalt hardfacing alloys have limited ductility. CoCr26Ni9Mo5W retains high ductility and impact toughness, so it can be forged into load-bearing shapes rather than applied only as a weld overlay.

Cross-reference

CoCr26Ni9Mo5W equivalents and specifications

The designations below all describe the same cobalt-base alloy. If your drawing calls out any one of them, we can quote it.

DIN designation

CoCr26Ni9Mo5W

Werkstoff number

2.4681

UNS number

R31233

Rod

ASTM B815

Plate, sheet, strip

ASTM B818

Pressure vessel code

ASME Section VIII Div. 1, Code Case 2121

Sour service

NACE MR0175

Trade name

ULTIMET^®

ULTIMET^® is a registered trademark of Haynes International, Inc. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with, endorsed by or licensed by Haynes International. The name appears here only to identify the equivalent alloy designation.

Chemistry

Chemical composition of CoCr26Ni9Mo5W

Nominal composition in weight percent, with cobalt as the balance element.

* Cobalt is the balance. Figures are nominal. The heat analysis on the EN 10204 certificate issued with your order governs. Send your specification if a tightened range is required on any element.

Mechanical

Mechanical properties of CoCr26Ni9Mo5W

Typical tensile data in the solution annealed condition, in both imperial and SI units.

Typical values for solution annealed material, published for guidance. They are not guaranteed minima and do not replace the tensile results on the mill certificate. Section size, reduction ratio and test orientation all affect results on a heavy forging. State your acceptance criteria and test position at enquiry stage and we will confirm what can be met before the order is placed.

Hardness and work hardening

In the annealed condition the alloy is not particularly hard, but its work-hardening rate is high. Even light cold deformation raises surface hardness appreciably. This is the reason for its performance against galling and cavitation in service, and also the reason it requires a specific approach in the machine shop. See machining and welding.

Process

Production route for a CoCr26Ni9Mo5W forging

The sequence matters. CoCr26Ni9Mo5W loses corrosion resistance if it is left in the hot-worked condition, so a solution anneal follows forging in every case.

1. Melting. EAF followed by VOD refining, with ESR remelt available where the specification or the section size requires it.
2. Heating and open-die forging. The billet is upset and drawn on the press to break down the cast structure and work the full cross-section. Rings are punched and expanded on the ring rolling mill to give continuous circumferential grain flow.
3. Re-annealing. Solution anneal at 1177 °C (2150 °F), hold 10 to 30 minutes by thickness, water quench. This step restores the corrosion resistance and ductility after hot forming.
4. Machining. Scale removal and stock allowance turned to drawing, or finish machining on request.
5. Non-destructive testing. Ultrasonic testing to the nominated acceptance class, plus PT or MT where specified.
6. Documentation and despatch. EN 10204 3.1 or 3.2 certificate, heat number traceability, marking, preservation and export packing.

Product forms

CoCr26Ni9Mo5W forged shapes and sizes

All items are made to drawing or to a size list. Open-die forging is a single-piece process, so there is no fixed catalogue.

• Rings & rolled rings Seamless rolled rings, retaining rings, wear rings, seat rings.
• Bars, shafts & spindles Round, square and flat bar, stepped shafts, eccentric shafts, pump spindles.
• Discs & blanks Solid discs, gear blanks, valve disc blanks, cover plates.
• Flanges & tube sheets Weld-neck and blind flange forgings, tube sheets, baffle plates.
• Sleeves & hollow bar Bushings, liners, cylinders, bored and trepanned hollows.
• Valve components Bodies, bonnets, seat rings, stems, plugs, gates and balls.

Forging size range

Ranges are indicative for the open-die process. Cobalt-base alloys are ordered in small quantities more often than in tonnage lots, and single-piece and prototype orders are accepted.

Quality

Testing, certificates and traceability

Specify the level required with the enquiry and it is quoted with the part.

Material certificates

• EN 10204 3.1, issued by our own quality department, independent of production.
• EN 10204 3.2, witnessed and countersigned by a third party such as TUV, SGS, BV, DNV or Lloyd's Register, or by your own inspector.

Non-destructive testing

• Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. State the quality class and acceptance level with the enquiry.
• Liquid penetrant (PT) and magnetic particle (MT) where the drawing calls for surface examination. CoCr26Ni9Mo5W is non-magnetic in the annealed condition, so PT rather than MT is normally the correct choice.

Documentation package

• Heat number and melt-to-part traceability
• Chemical analysis, ladle and on request product analysis
• Tensile and impact results at the specified test position
• Heat treatment charts for the solution anneal
• Dimensional inspection report
• NDT reports, marking record and packing list

Applications

Where CoCr26Ni9Mo5W forgings are used

Grouped by industry, with the parts most often requested.

• ValvesBodies, bonnets, seat rings, stems, plugs, gates, balls and blocks for ball, gate, globe, check and plug valves, where galling of the seat and stem is the failure mode.
• PumpsShafts, sleeves, wear rings, impeller components and plunger parts for chemical, slurry and plunger pumps handling abrasive or chloride-bearing fluids.
• Oil & gasSubsea and deepwater production hardware, wellhead and Christmas tree components, manifold parts, supported by NACE MR0175 listing for sour service.
• Chemical processingAgitator and mixer parts, extruder and screw conveyor components, nozzles, column and tower internals, tank and silo fittings.
• Pressure equipmentShell and tube heat exchanger tube sheets, flanges, forged pipe and tube, pressure vessel and air receiver components, preheaters.
• Power & rotating equipmentRings, spindles, gears and bars for turbines, gas compressors, gearboxes and power transmission assemblies.
• Pulp, paper & mineralsRolls, forged wheels and components for paper and pulp plant, cement, sugar and concrete mills and mixers, where slurry erosion governs service life.
• Pharmaceutical & biochemicalProcess equipment components requiring both surface finish and resistance to chloride pitting.

Downstream

Machining and welding CoCr26Ni9Mo5W

Machining

CoCr26Ni9Mo5W work-hardens rapidly, and this governs how it is cut. The tool must engage below the hardened layer rather than rub on top of it.

• Rigid machine and short tool overhang. Vibration glazes the surface.
• Sharp positive-rake tooling, replaced on schedule rather than at visible wear.
• Heavier depth of cut than for stainless steel, so the edge engages virgin material.
• Low to moderate surface speed with generous, constant feed. The tool should not dwell in the cut.
• Flood coolant, well directed.

We can supply the forgings rough machined or fully finish machined to drawing, which is how most cobalt-alloy parts are ordered.

Welding

The alloy is weldable by GTAW (TIG), GMAW (MIG), SMAW (stick) and SAW with matching filler. Ductility and resistance to weld cracking are better than in high-carbon cobalt hardfacing alloys, and the same chemistry is widely applied as a weld overlay. Re-anneal after welding where optimum corrosion performance is required.

Questions

CoCr26Ni9Mo5W: frequently asked questions