Refractaloy 26 Forgings: AISI 690, Z6NKCDT38, AMS 5760

The property that matters in service is slow relaxation. A bolt made from this alloy holds preload for long periods and still tolerates the strain imposed on it without cracking. The matrix is austenitic, so the coefficient of thermal expansion is comparatively high. Where the bolt works against a ferritic casing, differential expansion between the joint members has to be allowed for in the joint design. Thermal conductivity is low compared with carbon steel, so heating and cooling rates are controlled throughout our forging and heat treatment cycle.

Where the alloy is used

• Steam turbine bolting: casing studs, double end studs, nuts and washers working under sustained preload at temperature.
• Gas and steam turbine blades and vanes, including blade preforms, nozzle parts and diaphragm components.
• Valve internals: main steam, governing, control and reheat valve spindles, stems, seats, sleeves and bonnets.
• Rotating and static hardware such as turbine wheels, discs, spacers, sealing rings and gland seal rings.
• Fasteners for power plant and petrochemical service where stress relaxation resistance governs the design.

We forge both. For the nickel-chromium alloy see our Inconel 690 forgings page.

The table below gives the specified range for Refractaloy 26 to AMS 5760. Each heat we forge is checked by spectrometric analysis, and both ladle and product analysis are reported on the mill test certificate.

Ranges are as specified for AMS 5760. Where a customer specification is narrower than the table above, we buy or melt to the customer range and state it on the certificate.

Data note. Tables 3 and 4 give typical values for solution treated and double aged material, intended for enquiry and preliminary design. Certified values for your order, covering chemistry, tensile, hardness and any elevated temperature or stress rupture testing you specify, are reported per heat and per heat treatment lot on the EN 10204 3.1 certificate issued with the forgings.

Refractaloy 26 develops its properties by solution treatment followed by a two stage age. The first age precipitates and coarsens carbides at the grain boundaries. The second, at lower temperature, develops the fine gamma prime that carries the strength.

Soak times are set by section thickness and by the customer specification or the AMS 5760 revision in force. Where an OEM procedure is supplied we heat treat to that procedure and issue the furnace charts with the certificate.

Welding and machining

Refractaloy 26 can be welded, but welding after final heat treatment over-ages the heat affected zone. Where weld repair or fabrication cannot be avoided, plan a full re-solution treatment and the complete double age afterwards to restore properties. Nickel base fillers such as ERNiCr-3 or ERNiCrMo-3 are the usual choice. Most OEM specifications restrict or prohibit weld repair on load bearing turbine hardware, so read the drawing note first.

For machining, treat the alloy as a difficult to cut superalloy. It work hardens quickly, generates high cutting forces and abrades tooling. Use rigid fixturing, sharp positive rake PVD coated carbide, reduced surface speed with adequate feed per revolution, and high pressure through tool coolant. Do not let an insert dwell or rub without cutting, because a work hardened skin forms at once and ruins the following pass.

Every shape listed below is forged to customer drawing in Refractaloy 26 / AISI 690 / Z6NKCDT38 / AMS 5760. We forge open die, so there is no die cost and no minimum volume driven by tooling. Single replacement parts and small maintenance batches run alongside series work.

The equipment and size figures cover our full forging range across all grades. Refractaloy 26 parts normally sit well inside that envelope. If a part falls outside it, send the drawing and we will say whether it is within our press capacity.

Quality control runs across the whole route: ingot melting, forging, heat treatment, machining and final inspection before release. The following applies to Refractaloy 26 forgings.

Most enquiries for this grade arrive from one of four other materials. The table shows where each of them sits.

We forge all of the alloys above. See Inconel 718, Nimonic 80A, Waspaloy and Incoloy 901. If a legacy drawing is unclear about which grade it calls for, send it over with the operating temperature and we will help you work it out.

Send a drawing in PDF, DWG or STEP format to sales@steelforgepieces.com. These details let us quote without a second round of questions:

1. Grade and specification revision, for example Refractaloy 26 to AMS 5760, or the OEM material specification number.
2. Finished dimensions and tolerances, and whether you want as forged, rough machined or finish machined.
3. Quantity, and whether this is a one off replacement or a repeating order.
4. Heat treatment condition required at delivery, or the OEM heat treatment procedure to follow.
5. Testing and certification: UT class, PT, elevated temperature tensile, stress rupture, EN 10204 3.1 or 3.2.
6. Delivery port and required date.

Quotations are normally returned within 24 hours on working days. Technical questions are answered by our forging and heat treatment staff.

• Inconel 718
• Inconel 706
• Inconel 690
• Inconel X-750
• Inconel 617
• Incoloy 901
• Incoloy 925
• Nimonic 80A
• Nimonic 90
• Nimonic 263
• Nimonic 901
• Waspaloy
• Rene 41
• Udimet 520
• Udimet 720
• Haynes 188
• Haynes 230
• Multimet N155
• MP35N
• 17-4PH
• PH13-8Mo

Reference for this page

This datasheet may be quoted with attribution: