1.4912 / X7CrNiNb18-10 (347H) Open-Die Forgings
Niobium-stabilised austenitic creep-resisting stainless steel, forged to drawing in Jiangyin, Jiangsu.
- EN number
- 1.4912
- EN name
- X7CrNiNb18-10
- Equivalents
- 347H / S34709
- Condition
- +AT solution annealed
- Rp0.2 min
- 205 MPa
- Rm
- 510 to 710 MPa
Jiangyin Jiangnan Metal Co., Ltd. forges 1.4912 on its own open-die press: rolled rings, flanges, shafts, discs, round bars, sleeves, bushings, tube sheets and forged pipe. Prices are quoted per drawing, since forged weight, tolerance class and test scope all move the number.
What is material 1.4912?
EN 1.4912 is the material number for X7CrNiNb18-10, a niobium-stabilised austenitic creep-resisting stainless steel. It is the high-carbon member of the 18/10 niobium-stabilised family, and its closest international equivalents are AISI 347H, UNS S34709 and JIS SUS347H. The grade appears in EN 10222-5 (steel forgings for pressure purposes), EN 10216-5 (seamless tubes for pressure purposes) and EN 10088-1 (list of stainless steels).
Carbon is held at 0.04 to 0.10 percent so that creep strength can be calculated for design, and niobium at 0.40 to 1.20 percent ties that carbon up as niobium carbide instead of chromium carbide.
| EN material number | 1.4912 |
|---|---|
| EN name | X7CrNiNb18-10 |
| Type | Austenitic creep-resisting stainless steel |
| Density | 7.9 g/cm3 |
| Delivery condition | +AT, solution annealed |
| Standards | EN 10222-5:2017, EN 10216-5:2014, EN 10088-1 |
| Forged forms | Rings, flanges, shafts, discs, bars, sleeves, bushings, tube sheets, pipe, valve parts |
1.4912 chemical composition
| Limit | C | Si | Mn | P | S | Cr | Ni | N | Nb |
|---|---|---|---|---|---|---|---|---|---|
| Min | 0.04 | - | - | - | - | 17.0 | 9.0 | - | 0.40 |
| Max | 0.10 | 1.00 | 2.00 | 0.040 | 0.015 | 19.0 | 12.0 | 0.10 | 1.20 |
The stabilisation rule for the grade is 10 x C < Nb < 1.2 percent. The American grades that people treat as equivalent run slightly wider bands, so if a drawing quotes both an EN number and an ASTM grade, tell us which one governs the order. We then melt to whichever window is tighter rather than guess.
Mechanical properties, solution annealed
| Property | Longitudinal | Transverse |
|---|---|---|
| Tensile strength Rm | 510 to 710 MPa | |
| Proof strength Rp0.2 | 205 MPa min | |
| Elongation A | 40 percent min | 30 percent min |
| Impact energy KV at +20 C | 100 J min | 60 J min |
| Impact energy KV at -196 C | - | 40 J min |
Published values for the same condition, useful for design work but not acceptance criteria: hardness around 180 HB, Young's modulus 200 GPa, shear modulus 77 GPa, Poisson's ratio 0.28, thermal conductivity 16 W/m.K, thermal expansion 16 micrometre/m.K, specific heat 480 J/kg.K, melting range 1390 to 1430 C, PREN around 18. One published source puts the maximum mechanical service temperature near 940 C and the maximum corrosion service temperature near 520 C. Allowable stress always comes from the design code that governs the vessel, not from a supplier page.
1.4912 equivalent grades
| System | Designation |
|---|---|
| EN | X7CrNiNb18-10, 1.4912 |
| AISI / ASTM | 347H |
| UNS | S34709 |
| JIS | SUS347H |
Cross-references are a starting point for enquiry, not a substitute for the purchase order standard. If your specification names an ASTM forging grade, quote it in full and we confirm in writing before melting whether one heat can satisfy both documents.
1.4912 is not 1.4550. 1.4550 (X6CrNiNb18-10, AISI 347) is the lower carbon general purpose grade. 1.4912 carries a guaranteed carbon minimum, and that is what makes creep design possible.
Quote on 1.4912 forgings
Send the drawing, the governing standard and its edition, the quantity and the delivery condition. You get forged weight, lead time and price.
Heat treatment
1.4912 is austenitic. It cannot be quenched and tempered, and it cannot be age hardened. The normal delivery condition is +AT, solution annealed and cooled fast enough to keep carbon in solution. EN 10222-5 also recognises a stabilising anneal below the usual solution temperature for the niobium and titanium bearing grades.
Every piece we forge is re-annealed after forging, with soak time and quench set from the governing section thickness. Furnace charts are recorded and can go out with the certificate if you ask for them on the order.
If a supplier offers you solution treatment plus ageing on this grade, they have confused it with a precipitation hardening steel such as A286.
Corrosion behaviour and what to put on the order
Niobium holds carbon more strongly than chromium does, so carbon precipitates as niobium carbide rather than as chromium carbide at the grain boundaries. That is the whole point of stabilisation. Even so, the European data record for 1.4912 under EN 10216-5 does not list resistance to intergranular corrosion as a guaranteed property of the grade.
Where the service needs proven intergranular corrosion resistance, name the test on the purchase order, for example ASTM A262 Practice E or EN ISO 3651-2. We run it and report the result on the certificate. Leaving it as an assumption is how disputes start at inspection.
Machining and welding notes
1.4912 work hardens quickly, which is the main practical complaint from machine shops. Rigid setups, positive rake tooling, a real depth of cut, reduced surface speed and continuous flood coolant all help. Dwelling is what kills tools, because the glazed surface left behind is harder than the cut that made it.
For welding, a niobium-stabilised filler matching the base metal is normal practice. Tell us the filler and the procedure you plan to qualify and we keep the forging chemistry consistent with it.
1.4912 forgings we manufacture
Everything is made to drawing or specification: seamless rolled rings, forged flanges, shafts and spindles, discs, round bars, sleeves and bushings, tube sheets, forged tube and pipe, valve bodies, valve seat rings, valve stems, blocks, nozzles, gears, forging rolls, crankshafts and eccentric shafts, manifolds and forged wheels.
Where the grade is used
Because 1.4912 is rated for creep, it goes into pressure equipment and hot service: pressure vessels, shell and tube heat exchangers, columns and towers, preheaters, superheater and reheater components, refinery units including fluid catalytic cracking, chemical and pharmaceutical process plant, waste heat recovery and recuperators, turbine and power transmission parts, gas compressors, and offshore and subsea production equipment.
Melting, testing and certification
Melting routes for 1.4912 are EAF plus VOD, with ESR remelting where cleanliness or segregation control justifies the cost. Ultrasonic examination follows whichever standard you nominate: EN 10228-3, SEP 1921 or ASTM A388. Certificates are issued as EN 10204 type 3.1, or type 3.2 with third party endorsement where the project requires it.
To quote we need the drawing or rough dimensions with tolerance, the governing standard and its edition, the quantity, and the delivery condition. With that we come back with forged weight, lead time and price.
Common questions about 1.4912
Is 1.4912 the same as 347H?
They are treated as equivalent in practice. 1.4912 / X7CrNiNb18-10 is the European designation and 347H / UNS S34709 is the American one. The composition windows are close but not identical, so state which standard governs your order.
What is the difference between 1.4912 and 1.4550?
Carbon. 1.4550 (X6CrNiNb18-10, AISI 347) is the lower carbon standard grade. 1.4912 holds carbon at 0.04 to 0.10 percent, and that guaranteed minimum is what supports elevated temperature creep design.
Can 1.4912 be hardened by heat treatment?
No. It is austenitic and is supplied solution annealed. Strength can only be raised by cold work, which does not apply to heavy forgings.
What is the chemical composition of 1.4912?
To EN 10216-5:2014: C 0.04 to 0.10, Si max 1.00, Mn max 2.00, P max 0.040, S max 0.015, Cr 17.0 to 19.0, Ni 9.0 to 12.0, N max 0.10, Nb 0.40 to 1.20 percent, iron balance, with 10 x C < Nb < 1.2.
What sizes can you forge?
We are an open-die shop, so the limit is set by your drawing rather than by a stock list. Send dimensions and we confirm feasibility and forged weight the same working day.
Who supplies 1.4912 forgings from China?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures 1.4912 rings, flanges, shafts, discs and bars to customer drawings. Tel +86 189 2135 9659, email sales@steelforgepieces.com.
Composition and mechanical values on this page are taken from the EN 10216-5, EN 10222-5 and EN 10088-1 records for 1.4912 and are given for guidance. The standard named on the purchase order governs. Page reviewed .