UNS N06626 forgings in Inconel 625LCF

Alloy description

Alloy 625 is a solid-solution-strengthened nickel-chromium-molybdenum alloy stiffened by niobium. It is one of the most corrosion-resistant structural alloys in general industrial use and holds its strength from cryogenic temperature into the high-temperature range. Standard alloy 625 is not optimised for repeated strain, and components such as bellows, flexible couplings and expansion joints normally fail by low-cycle fatigue rather than by corrosion.

UNS N06626, alloy 625LCF, was developed for that service. Three things are changed relative to UNS N06625:

• Restricted interstitials. Maximum carbon is reduced to 0.030 %, silicon to 0.020 % and nitrogen to 0.020 %, which suppresses the carbide and nitride particles that act as crack initiation sites under cyclic strain.
• Controlled melting. Vacuum induction melting, usually followed by remelting, is the route normally specified to hold those interstitial limits reliably.
• Controlled grain size. The material is processed to a fine, uniform grain structure, ASTM No. 5 or finer in the sheet product for which the grade was written. This is the main source of its fatigue advantage.

Because the chemistry stays inside the alloy 625 envelope, material certified to N06626 also satisfies the requirements of N06625. Corrosion behaviour is the same as alloy 625: effectively unattacked by fresh water, seawater, neutral salts and alkaline media; resistant to oxidising chemicals through the nickel-chromium matrix and to reducing conditions through the high nickel and molybdenum content; and in thin sections close to immune to chloride stress-corrosion cracking.

Alloy 625LCF was written as a sheet and strip specification (AMS 5879), because bellows are formed from thin gauge. When Jiangyin Jiangnan Metal Co., Ltd. supplies forgings in this grade, chemistry is held to the N06626 limits and the forging is produced, heat treated and tested to ASTM B564 / ASME SB-564 for UNS N06625, with grain size controlled on request. State on the enquiry if the part is fatigue-critical, so that the grain-size requirement is written into the order.

Chemical composition of UNS N06626

Weight percent. Single values are maxima unless a range is shown. Nickel is the balance.

The three restricted elements define the grade. All other limits are the same as standard alloy 625. Material certified with 0.05 % C or 0.35 % Si is alloy 625, not alloy 625LCF.

Mechanical properties

Typical room-temperature properties, annealed

Typical values for annealed material, given for design guidance. They are not purchase requirements. Acceptance minima are listed in Table 3.

Acceptance minima for forgings, ASTM B564 / ASME SB-564

Grade 1 is the normal supply condition for service up to 593 °C (1100 °F). Grade 2 is specified above that temperature, where creep and rupture resistance governs, and where maximum intergranular corrosion resistance after welding is required. Confirm all figures against the edition of the standard named in the purchase order.

Physical properties

Standards and equivalents

Werkstoff 2.4856 is shared with alloy 625 and does not by itself cover the restricted C, Si and N of the LCF variant. Where the fatigue property is the reason for the material choice, specify UNS N06626 on the order rather than 2.4856 alone.

UNS N06626 compared with UNS N06625

Where the governing failure mode is cracking after many load cycles, N06626 is the correct selection. Where the governing requirement is corrosion, oxidation or static strength, standard N06625 meets the same duty at lower cost and shorter lead time. Jiangyin Jiangnan Metal Co., Ltd. forges both grades and will confirm which one the drawing requires before quoting.

UNS N06626 forged product range

All parts are made to the customer drawing or size list.

Open-die forging is not tooling-bound, so sizes and geometry outside the ranges above can often still be produced. Send the drawing for confirmation.

Manufacturing process

Each stage is recorded against the heat number and reported on the certificate.

1. Melting and billet supply

   Vacuum induction melting, normally with a remelt stage, is the route specified where the restricted carbon, silicon and nitrogen limits of N06626 must be met reliably. Billet melted by EAF + VOD + ESR is available where the purchaser specification permits it. The melting route is agreed before order confirmation.

2. Heating and open-die forging

   Billet is heated in a controlled-atmosphere furnace and forged below 1180 °C, with reheating as often as the reduction requires. Upsetting and drawing are planned to work the centre of the section so that grain flow follows the finished contour instead of being cut through during machining.

3. Ring rolling

   Where the shape suits it, rings are pierced and rolled seamless rather than cut from plate. This produces continuous circumferential grain flow.

4. Heat treatment

   Solution treatment and, where the order requires it, ageing are carried out in calibrated furnaces with chart recording. Grade 1 is annealed at 871 °C minimum. Grade 2 is solution annealed at 1093 °C minimum and rapidly cooled.

5. Machining

   Parts are supplied as forged, rough machined to an agreed allowance, or finish machined to drawing tolerance. Nickel alloys work-harden ahead of the tool, so cutting is planned at low speed with rigid tooling and positive feed.

6. Non-destructive examination and release

   Ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388, with dye penetrant where specified, followed by dimensional inspection, marking against the heat number and issue of the certificate.

Testing, inspection and certification

Applications for UNS N06626 forgings

The grade is selected where a component sees repeated thermal or mechanical strain in a corrosive environment. Typical service includes:

Related forged shapes from the same plant: forged sleeves, forged nozzles, and the full open-die forging product range.

Ordering information

Include the following nine items in the enquiry to receive a firm price and lead time on the first reply.

1. Drawing or rough forging dimensions. PDF, STEP or DWG preferred, dimensioned sketch accepted.
2. Grade. UNS N06626, and whether N06625 is also acceptable, since this affects the price.
3. Quantity, and whether repeat orders are expected.
4. Delivery condition. As forged, rough machined with allowance, or finish machined.
5. Heat treatment condition. Annealed, Grade 1, or solution annealed, Grade 2, plus ageing if required.
6. Governing specification and its edition, for example ASTM B564-19.
7. NDT requirement and acceptance class, for example UT to EN 10228-3 Class 3.
8. Certificate type. EN 10204 3.1, or 3.2 with the named inspection body.
9. Destination port and required delivery date.

Send the enquiry to sales@steelforgepieces.com or call +86-189-2135-9659. Quotations are normally returned within one working day.

Frequently asked questions about UNS N06626

Source and citation

This page is maintained by the technical sales department of Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China. Data is compiled from the published alloy literature for INCONEL alloy 625LCF and from ASTM B564, ASTM B443, AMS 5879 and ASME SB-564. Verify all figures against the current edition of the governing standard before use in design.