Z6CNNb18-10 Forgings: EN 1.4550 / X6CrNiNb18-10 / AISI 347
Niobium-stabilised austenitic stainless steel. Forged rings, seamless rolled rings, flanges, bars, shafts, discs, sleeves and tube sheets.
Z6CNNb18-10 is the French AFNOR designation for a niobium-stabilised chromium-nickel austenitic stainless steel containing 17.00 to 19.00 % Cr, 9.00 to 11.00 % Ni, max 0.06 % C and max 1.00 % Nb. It corresponds to EN X6CrNiNb18-10 (material number 1.4550), AISI 347 / TP347 and UNS S34700.
The niobium addition ties up carbon as stable niobium carbide, so the grade resists chromium-carbide precipitation and intergranular corrosion both in the solution-annealed state and after a sensitising heat exposure. For that reason it is specified for welded pressure equipment operating in the 425 to 850 C range.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu, China, producing Z6CNNb18-10 forgings to customer drawings. Enquiries: 0086-189-2135-9659, sales@steelforgepieces.com.
Z6CNNb18-10 equivalent grades
Z6CNNb18-10 appears under different designations depending on the standard body. The table below lists the recognised cross-references. The chemistry windows differ slightly between standards, the AFNOR window being the tightest on carbon and nickel, so the governing standard should be stated on the purchase order.
| Standard / Country | Designation |
|---|---|
| AFNOR (France) | Z 6 CNNb 18-10, Z6CNNb18-10 |
| EN / DIN (Europe) | X6CrNiNb18-10, 1.4550 (related: X5CrNiNb18-10 / 1.4546, X10CrNiNb18-10) |
| AISI / ASTM (USA) | AISI 347, TP347 (high-carbon variant 347H) |
| UNS (USA) | S34700 |
| SAE (USA) | 30347 |
| JIS (Japan) | SUS 347 |
| GB/T (China) | 06Cr18Ni11Nb, S34778 |
| GOST (Russia) | 08Kh18N10B |
| PN (Poland) | 0H18N12Nb |
| Trade shorthand | 18-10 Nb, 18/8 Nb |
Chemical composition
Two windows are shown because this material is ordered against either the French or the European standard. Where a drawing states "Z6CNNb18-10 or equivalent", we confirm in writing which window the heat will be certified to before melting.
| Element | AFNOR Z6CNNb18-10 | EN X6CrNiNb18-10 (1.4550) | UNS S34700 / AISI 347 |
|---|---|---|---|
| Carbon (C) | max 0.06 | max 0.08 | max 0.08 |
| Silicon (Si) | max 0.75 | max 1.00 | max 1.00 |
| Manganese (Mn) | max 2.00 | max 2.00 | max 2.00 |
| Phosphorus (P) | max 0.040 | max 0.045 | max 0.045 |
| Sulphur (S) | max 0.015 | max 0.015 | max 0.030 |
| Chromium (Cr) | 17.00 to 19.00 | 17.00 to 19.00 | 17.00 to 20.00 |
| Nickel (Ni) | 9.00 to 11.00 | 9.00 to 12.00 | 9.00 to 13.00 |
| Niobium (Nb) | max 1.00 | max 1.00 | max 1.10 |
| Iron (Fe) | Balance | ||
Mechanical and physical properties
Values apply to the solution-annealed condition. Forged sections are tested after final heat treatment. Acceptance values for heavy sections are agreed per order, since properties in open-die forgings vary with section thickness and test-piece location.
| Property | Symbol | Value |
|---|---|---|
| Tensile strength | Rm | 510 to 740 MPa |
| 0.2 % proof stress | Rp0.2 | min 205 MPa |
| Elongation | A | min 40 % |
| Hardness | HB | max 230 |
| Modulus of elasticity | E | 200 GPa |
| Density | rho | 7.90 g/cm3 |
| Specific heat capacity at 20 C | cp | 500 J/(kg·K) |
| Thermal conductivity | lambda | 15 W/(m·K) |
| Magnetic response | Non-magnetic, austenitic |
| Temperature | 100 C | 200 C | 300 C | 400 C | 500 C |
|---|---|---|---|---|---|
| Yield point Re, MPa | 175 | 155 | 136 | 125 | 119 |
| Modulus E, GPa | 194 | 186 | 179 | 172 | 165 |
| Linear expansion, 10-6/K | 16.0 | 16.5 | 17.0 | 17.5 | 18.0 |
Impact toughness remains above 70 J/cm2 down to minus 253 C, so the grade is also used in cryogenic service.
Heat treatment of Z6CNNb18-10 forgings
- Forging: heated and worked in the hot-working range, with a controlled finishing temperature to avoid grain coarsening. Start and finish temperatures are set per part geometry in our forging procedure.
- Solution annealing: 1020 to 1100 C followed by rapid cooling in water or forced air according to section size. This dissolves carbides and restores the fully austenitic structure.
- Stabilising or stress-relief: a sub-critical stabilising cycle is occasionally specified for severe service. Practice varies between standards and end users, so this is run only when stated on the order or drawing.
- Post-weld heat treatment: normally not required, which is the main reason this grade is selected for fabricated assemblies.
Corrosion behaviour
Published data for the equivalent grade 1.4550 reports resistance to intergranular corrosion in the heat-treated state and after sensitising treatment, higher oxidation resistance than the titanium-stabilised equivalent, and resistance to nitric acid and nitrates at concentrations up to approximately 55 % and temperatures to approximately 80 C. It performs well in rural and non-industrial urban atmospheres and in less aggressive marine atmospheres.
Like all 18-10 austenitic grades, it has limits. Service in hot concentrated halide environments, strong reducing acids, or any condition where chloride stress-corrosion cracking is credible should be reviewed against a duplex or higher-alloy option. We also forge A182 F51, F53, F55, 904L and Inconel 625. Send the service medium and temperature with your enquiry and we will confirm whether this grade suits the duty.
Z6CNNb18-10 forged products
All items are made to customer drawing or specification. As an open-die shop we accept one-off and small-batch work.
| Product group | Items | Typical end use |
|---|---|---|
| Rings | Seamless rolled rings, forged rings, retaining rings, valve seat rings | Pressure vessels, heat exchangers, turbine and compressor casings |
| Flanges | Weld-neck, blind, slip-on, long weld-neck, special-bore forged flanges | Pipelines, reactors, absorption towers |
| Bars and shafts | Forged round bars, shafts, spindles, eccentric shafts, crankshafts | Power transmission, pumps, gearboxes, agitators |
| Discs and blocks | Forged discs, tube sheets, blocks, bodies, gear blanks | Heat exchangers, valve bodies, separators |
| Hollow sections | Forged tubes, pipes, sleeves, bushings, nozzles | Autoclaves, transport tanks, coolers, reactors |
| Valve components | Valve stems, seats, bonnets and body forgings for ball, gate, globe, check and plug valves | Chemical, refinery and oil and gas valve manufacture |
Typical industries
Documented applications for this grade include chemical plant producing nitric acid and its derivatives, salts and fertilisers; cryogenic equipment; pharmaceutical and food processing plant including dairies, sugar refineries and breweries; and refinery and petrochemical service. Associated equipment types are pipelines, autoclaves, transport tanks, heat exchangers, absorption towers, pumps, coolers and reactors.
Manufacturing and quality route
- Melting: EAF plus VOD, with ESR available where the specification or the end user requires remelted material.
- Forming: open-die forging and ring rolling, with forging ratio and final heat treatment recorded on the certificate.
- NDT: ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388 as specified. PT and other methods on request.
- Certification: EN 10204 3.1 as standard, EN 10204 3.2 with third-party witness on request.
- Standards commonly invoked for this grade: NF A 36-607, NF A 35-573, EN 10222-5, EN 10250-4, EN 10272, ASTM A182 F347.
Frequently asked questions
What is Z6CNNb18-10 steel?
Z6CNNb18-10 is the French AFNOR designation for a niobium-stabilised Cr-Ni austenitic stainless steel with 17.00 to 19.00 % chromium, 9.00 to 11.00 % nickel, max 0.06 % carbon and max 1.00 % niobium. In the European system it is X6CrNiNb18-10, material number 1.4550. In the American system it is AISI 347 / UNS S34700.
What is the difference between Z6CNNb18-10 (347) and 321 stainless steel?
Both are stabilised austenitic grades that resist intergranular attack after exposure to sensitising temperatures. Type 321 is stabilised with titanium. Z6CNNb18-10 / 347 is stabilised with niobium, sometimes with tantalum. Published comparison notes that this grade serves the same purpose as the titanium-stabilised equivalent but offers higher oxidation resistance. Niobium also survives arc transfer better than titanium, so 347 filler and base metal are common in welded construction. We forge AISI 321H and A182 F321 for comparison.
Is Z6CNNb18-10 magnetic?
No. In the solution-annealed condition the structure is fully austenitic and the material is non-magnetic. Heavy cold work can induce a slight magnetic response, which is relevant if the part is machined from a forged blank with significant cold finishing.
Can Z6CNNb18-10 be welded?
Yes. Published data for 1.4550 states the grade is fully weldable and does not require additional heat treatment after welding. Match the filler to the base grade and follow the applicable WPS.
What is the minimum order quantity?
Open-die forging suits single pieces and small batches, so there is no fixed piece-count minimum. Practical limits come from melt and billet size. Send the drawing and we will confirm feasibility and the most economical starting size.
How do I request a quotation?
Email the drawing or the dimensions, quantity, governing standard, required NDT and certificate type to sales@steelforgepieces.com, or call 0086-189-2135-9659. Without a drawing, the rough OD x ID x height, or OD x length, plus the service conditions, is enough for an indicative price.
Request a quotation for Z6CNNb18-10 forgings
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone 0086-189-2135-9659
Email sales@steelforgepieces.com
Email your drawing for a quotation
Last updated . Property and equivalence data is compiled from published grade datasheets for Z6CNNb18-10 / X6CrNiNb18-10 / 1.4550 and is given for guidance. The governing specification on the order takes precedence.