1.4840 Forgings in Heat-Resisting 25Cr-20Ni Stainless Steel (AISI 310 / UNS S31000)

Designations and cross-references

ASTM A473 covers austenitic, austenitic-ferritic, ferritic and martensitic stainless steel forgings, and is the specification usually invoked for 310 and 310S forged parts alongside A182.

Chemical composition

For 310S and 1.4845 the only change is carbon at 0.08 % max. For 1.4841 silicon rises to 1.5 to 2.5 %. Chemistry is checked on site by optical emission spectrometry to ASTM E415 and by infrared carbon and sulphur analysis to ASTM E1019. Handheld positive material identification on the finished part is available on request.

Mechanical properties

Specified minimum values, annealed

Typical values against temperature

These are typical figures for the grade and not acceptance criteria. Tensile and impact tests on forgings are run in house to ASTM A370 and ISO 6892 on 600 kN and 300 kN machines. Charpy V-notch testing is available down to minus 60 C. Below minus 60 C the work is placed with an accredited third party laboratory.

Physical properties

High thermal expansion and low conductivity are normal for austenitic grades. In heavy 1.4840 sections they are the reason the forging and annealing schedule has to be controlled, and both steps are run here rather than subcontracted.

Forging and heat treatment

1.4840 is solution annealed between 1040 C and 1150 C and cooled rapidly, which returns the carbides to solution and restores ductility. The grade is austenitic and cannot be hardened by heat treatment. Strength comes from composition and section size. Where a part runs above about 650 C, repeating the anneal after roughly 1,000 service hours keeps the material soft.

Fourteen furnaces are in use on site. Eleven car bottom furnaces take work to 8,000 by 2,000 by 2,000 mm. Three high temperature car bottom furnaces cover the upper solution annealing range. Two 15 m well type furnaces allow long shafts to be quenched vertically, which limits distortion. Charts are issued with the certificate.

Where 1.4840 is the wrong grade

Specifying 310 outside its envelope is a common and expensive mistake, so the limits are set out here as well as the strengths.

• Continuous service from 425 C to 860 C. Carbides precipitate through this band. If the duty cycle sits there, use the low carbon 1.4845 or 310S instead.
• Chloride and sour service. This is a heat-resisting grade. Published data rates its stress corrosion behaviour above 304 and 316, but cracking remains possible and 310 is not a seawater or brine material. For those duties we quote duplex and super duplex (F51, F53, F55), 904L, F44, or a nickel alloy such as Incoloy 825.
• Design by oxidation limit alone. Supplier data for 310 gives about 1150 C continuous and about 1040 C intermittent. EN 10095 table B.2, as summarised by the British Stainless Steel Association, gives 1050 C for 1.4845 under intermittent or cyclic oxidation. Both sets of figures are guidance, and strength at the service temperature has to be checked as well.
• Above roughly 1100 C, or in strongly carburising atmospheres. A cast heat-resistant grade or a higher nickel alloy such as AISI 330, Incoloy 800H and 800HT or Inconel 601 will normally last longer than 1.4840.

Typical applications

Published application data for 310 type steel sits in furnace and combustion hardware: furnace construction and furnace parts, steam boilers, oil and gas burner parts, carburising and heat treatment boxes, baskets and jigs, heater hangers, annealing and melting pots, heat exchangers, thermocouple parts, petroleum plant internals, and apparatus loaded mechanically at temperature. Welding consumable literature gives pyrolysis furnace tube joints as a typical 310 type application, with service to 1050 C.

Against what is produced here:

• Seamless rolled rings and forged rings for furnace retaining rings, burner rings, kiln and support rings and radiant tube flanged rings.
• Forged flanges to ASME B16.5 and B16.47 in ASTM A182 F310, weld neck, blind, slip-on and long weld neck, for hot gas and flue duct connections.
• Forged tube sheets and discs for heat exchangers, supplied proof machined so they can be ultrasonically examined.
• Forged shafts for furnace rollers, fans, dampers and heater hangers, quenched vertically in the well furnaces where length requires it.
• Forged bars and blocks as stock for machined furnace fittings, thermowells and burner parts.
• Forged cylinders, sleeves and bushings for carburising retorts, muffle sections and heavy wall hot gas spools, bored from solid forged blanks.
• Forged valve parts including bodies, bonnets, seat rings and stems for high temperature gas and flue duty.

Manufacturing route and size limits

Most forging suppliers in China buy billet. This works starts a step earlier, at the furnace. Stainless grades such as 1.4840 are melted in a 25 t electric arc furnace, refined in 25 t or 50 t ladle furnaces, and treated in 30 t or 60 t vacuum oxygen decarburisation units where low carbon or controlled nitrogen is called for. That last route is what makes the 310S and 1.4845 variant a mill order here rather than a stockist purchase. Maximum heat size is 60 tonnes.

Melting, forging, heat treatment, machining and testing all happen on one site, so traceability runs from the melt number to the shipped part instead of stopping at a bought-in billet certificate.

Testing and certification

Ultrasonic testing of 1.4840 forgings is carried out to ASTM A388, EN 10228-3 or SEP 1921 as specified, on a PXUT-3300 digital flaw detector with USM35XS and CTS-22 units. Magnetic particle inspection does not apply to this austenitic grade. Surface examination is by liquid penetrant or visual method, with an industrial endoscope for bores. Grain size is rated to ASTM E112 in the metallography room.

EN 10204 3.1 mill certificates are standard. EN 10204 3.2 certificates witnessed by BV, DNV, LR, SGS, TUV or your own inspector are available on request. The works holds CCS, BV, DNV, LR and NK approvals. Intergranular corrosion testing to ASTM A262 or G28, which is worth adding if your 310 order needs a sensitisation check, is placed with an accredited third party laboratory and reported with the mill certificate. State it on the enquiry so it is scheduled before shipment.

Questions we are asked about 1.4840

What is 1.4840 steel?

It is the Werkstoff number quoted for X15CrNi25-20, a heat-resisting austenitic stainless steel with 24 to 26 % chromium, 19 to 22 % nickel and up to 0.25 % carbon. It is cross-referenced to AISI 310, UNS S31000 and SUS 310, and is chosen for oxidation resistance and strength at high temperature.

Is 1.4840 the same as 310 or 310S?

1.4840 is normally cross-referenced to 310. 310S is the low carbon version at 0.08 % C max and carries the number 1.4845, X8CrNi25-21, with better resistance to scaling and sensitisation, which is why it is usually chosen for welded work. 1.4841 is a third variant with 1.5 to 2.5 % silicon added, cross-referenced to AISI 310 and 314 and to UNS S31400. EN 10095 covers 1.4845 but not 1.4840, and some welding data sheets use 1.4840 for the cast grade GX15CrNi25-20, so check the number against your drawing.

Can 1.4840 be welded?

Yes. The usual processes all apply, and 310 or 310S type filler wire and electrodes are the normal match. Consumable literature for 310 type welds gives service to 1050 C in pyrolysis furnace tube work. We do not weld-fabricate forgings. Every part shipped here is forged from one piece of steel melted on site, and weld preparations are machined to your detail.

What temperature will 1.4840 take?

Supplier data for 310 gives about 1150 C continuous and about 1040 C intermittent. EN 10095 table B.2, as summarised by the British Stainless Steel Association, gives 1050 C for 1.4845 under cyclic oxidation. Treat both as guidance and check design strength at temperature. Avoid long exposure between 425 C and 860 C.

Do you keep 1.4840 in stock?

Forgings are made to order from steel melted here, not cut from stock bar. That is what allows a 10 kg minimum with no minimum piece count, and also one-off rings to 6,000 mm outside diameter. Send the drawing and the required condition and the forging, heat treatment and testing are quoted as one price.

What paperwork comes with the forging?

EN 10204 3.1 as standard, and EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector on request. Heat treatment charts, ultrasonic reports to ASTM A388 or EN 10228-3, dimensional reports and positive material identification records are included as applicable. The works holds CCS, BV, DNV, LR and NK approvals.