UNS S15500 Forgings

Designations and equivalents

One alloy, five names. Buyers reach it through whichever system their drawing uses, which is why the same steel turns up on enquiries as S15500, as XM-12 and as 1.4545.

S17400, 1.4542, X5CrNiCuNb16-4, AISI 630 and SUS 630 are not equivalents. Those designate 17-4PH, a separate alloy with higher chromium and a different melt practice.

Specifications by product form

For a forging, the governing document is A705. A564 is frequently quoted instead, because buyers work from bar practice, and the chemistry is the same in both, but the testing and sampling clauses differ. State which one applies on the order.

ASTM B564 covers nickel alloy forgings. It is sometimes quoted for S15500 in error and does not apply to this steel.

Chemical composition

AMS 5659 is the tighter of the two documents on residuals, holding sulphur to 0.015 % against 0.030 % in the ASTM grades, and it caps molybdenum where ASTM does not list the element at all. Where a part is bought to A705 but destined for fatigue-critical service, it is worth writing the AMS sulphur limit into the order.

Heat treatment

Solution annealing and ageing are both carried out here, so parts leave the works in the condition stated on the order rather than needing treatment elsewhere. Ageing temperatures sit between 482 and 621 °C, low enough that scale and distortion during hardening stay small, which is why many customers rough machine first and age afterwards.

H1000 and H1050 are not recognised conditions for this alloy and appear on enquiries from time to time through confusion with other PH grades. If a drawing calls for one of them, the intended condition is usually H925 or H1075 and we will ask before proceeding. Annealing after hot work is at 1038 °C for one hour with rapid cooling, so that the material responds correctly to ageing.

Mechanical properties

The figures below are specification minimums, not typical results. Hardness bands are from AMS 5659.

H1150M is supplied against properties agreed at enquiry, since the double-overaged values are not listed uniformly across the ASTM and AMS documents. Transverse properties are lower than longitudinal and cannot be determined where the section measures under about 76 mm in the test direction; rounds, squares and hexagons have no short-transverse direction. In heavy forgings the result depends on section size and test position, so the ruling section and the sampling location are fixed at enquiry stage and testing is carried out on prolongations taken from the forging itself.

Charpy requirements, where the order carries them, are agreed as a separate line rather than taken from the grade tables. Impact testing down to minus 60 °C runs in the works laboratory on a JBN-300 pendulum with a DWC-60 bath; below that temperature the test is placed with an accredited laboratory.

Physical properties

Expansion and conductivity figures vary a little between published datasheets according to the temperature interval used, so take them as design guidance rather than acceptance values.

Melting and forging route

The steel for an S15500 forging is melted on site rather than bought as billet. Carbon, alloy and stainless heats run through a 25 t electric arc furnace, are refined in 25 t and 50 t ladle furnaces, and go through vacuum oxygen decarburisation in 30 t or 60 t units where carbon and nitrogen need holding down. Maximum heat size is 60 tonnes.

Because S15500 is a remelted grade by definition, the second stage matters. Protective-atmosphere electroslag remelting in 3 t and 6 t furnaces satisfies AMS 5659 Type 2. Where Type 1 vacuum melt is called for, the route is 3 t vacuum induction melting followed by 6 t vacuum arc remelting. Having both in house is the reason this grade does not need subcontracting out, which is the usual bottleneck for Chinese forging shops working to AMS documents.

From ingot the part is cogged or upset on 6300 t, 4000 t or 2000 t hydraulic presses, or ring rolled on radial-axial mills at 6 m, 3 m and 1 m. Five hammers between 750 kg and 5 t cover drawing out and smaller batch work. Heat treatment follows in one of 14 furnaces, including two 15 m well-type furnaces that let long shafts hang vertically through quench instead of distorting on a hearth. Machining, inspection and certification close out the route, all under the same roof, so the certificate traces back to a melt number rather than stopping at a purchased billet.

Forged forms and size limits

Everything below is forged from a single piece of steel melted here. No welding, no casting, no bought-in billet of unknown origin.

Machining, welding and forming

S15500 cuts in every condition it can be supplied in, and H1150M gives the longest tool life. The sequence most machine shops settle on is to rough out in Condition A or an overaged condition, age to the required H condition, then finish. Fully aged H900 material at 388 to 444 HB is hard going for turning, drilling and milling, and it is worth asking whether the design genuinely needs that strength before specifying it.

Welding is by shielded fusion or resistance methods with AWS E/ER630 filler. A weldment should be re-solution treated and aged afterwards, or at minimum re-aged, otherwise the heat-affected zone will not match the parent properties. The alloy is not suited to cold working and tolerates only mild forming, best attempted in the overaged condition. Nitriding can be arranged through qualified treaters; case hardness and depth depend on the process and the ageing condition and are confirmed against the treater's qualified procedure rather than quoted here.

Applications

The combination that drives selection is high strength with moderate corrosion resistance to roughly 316 °C, in a grade that behaves predictably through thickness.

• Chemical and plunger pump shafts, impeller and casing parts, compressor components.
• Valve stems, seat rings, bodies and blocks for ball, check, globe, gate and plug valves.
• Flanges, tube sheets, nozzles and covers for pressure vessels and shell-and-tube heat exchangers.
• Subsea and wellhead hardware, including Christmas tree and BOP components.
• Gear blanks, spindles and turbine parts where transverse loading rules out an air-melted grade.
• Aircraft components, pressure transducer bodies and nuclear parts bought to AMS 5659.
• Forged rolls, wheels, manifolds and crankshafts in paper, sugar and cement plant.

S15500 against S17400

These two come up side by side on almost every enquiry, so it is worth being plain about where the difference is real and where it is not.

Published data does not agree on whether S15500 holds a real corrosion advantage over S17400. Both sit above 410 and below 304 and 316 in general corrosion resistance, so corrosion alone is a weak reason to choose between them. The defensible reasons are section thickness, loading direction and whether the specification demands a remelted product.

Related grade pages: 17-4PH and PH13-8Mo.

Inspection and certification

Because the steel is melted here, chemistry is verified at the furnace rather than copied from a supplier's certificate. Release against an order runs melt analysis, mechanical testing on a representative prolongation, non-destructive examination, dimensional check, then certification.

Corrosion testing to ASTM A262, G28 or G48 is placed with an accredited laboratory and the report is issued alongside the mill certificate. Flag it on the enquiry so it is scheduled before shipment rather than added to the delivery date afterwards.

Ordering

Six items in the first email usually remove a round trip: grade or specification, dimensions or drawing, quantity and expected repeat volume, delivery condition, heat treatment and testing requirements, then certification and destination port.

Data sources

Composition limits, heat-treatment cycles and minimum mechanical properties on this page are compiled from AMS 5659, ASTM A705/A705M, ASTM A564/A564M and published alloy datasheets, including the ARMCO 15-5 PH product data bulletin and the Rolled Alloys 15-5 datasheet. Where documents differ, the difference is noted in the text. Figures are given for guidance and carry no warranty; the purchase order and the governing specification revision take precedence, and nothing here replaces an engineering assessment of a particular application.

A plain-text version of this page is available at UNS-S15500.md.

Other stainless grades

• 17-4PH
• PH13-8Mo
• A286
• All stainless grades

Other material families

• Carbon steel
• Alloy steel
• Tool steel
• Nickel alloy