Materials & grades
347 / 347H stainless steel: equivalents 1.4550 (X6CrNiNb18-10), SUS347 and 347S31
347 is a niobium-stabilised 18-10 austenitic stainless steel, the same family as 304 and 321. Niobium ties up carbon, so welds resist intergranular corrosion and the steel holds up at 425–815 °C; the counterparts are 1.4550 (X6CrNiNb18-10) in Europe and SUS347 in Japan.
Names by standard
What it is called in each region
| Region | System | Designation | Norma | Match |
|---|---|---|---|---|
| USA | AISI/ASTM | 347 | ASTM A240 (plate, sheet, strip); A276 / A479 (bar) | Same material |
| UNS | S34700 | — | Same material | |
| AISI/ASTM | 347HHigh-carbon version (C 0.04–0.10 %, niobium 8×C minimum) for high-temperature strength. Covered in this entry as a variant. | ASTM A240 | Closest equivalent | |
| UNS | S34709UNS number of 347H. | — | Closest equivalent | |
| UK | BS (withdrawn) | 347S31Withdrawn British name listed against 1.4550 and S34700 by Outokumpu and Atlas. New orders use EN 10088. | — | Equivalent |
| BS 970 (1955 EN series) | EN58GOld EN series name listed by Atlas Steels for 347. | — | Closest equivalent | |
| EU | EN 10027-1 name | X6CrNiNb18-10Nickel 9.00–12.00 % against 9.0–13.0 % in ASTM A240. | EN 10088-2; EN 10088-3 | Equivalent |
| EN 10027-2 number | 1.4550Material number of X6CrNiNb18-10. | EN 10088-2; EN 10088-3 | Equivalent | |
| India | IS 1570 (Part 5) | X04Cr18Ni10NbSilicon up to 1.0 % against 0.75 % in ASTM A240. | IS 1570 (Part 5):1985 | Equivalent |
| Japan | JIS G 4303 / G 4304 / G 4305 | SUS347Silicon up to 1.00 % against 0.75 % in ASTM A240. | JIS G 4303 (bar); JIS G 4304 / G 4305 (plate, sheet, strip) | Equivalent |
| JIS (tube grades) | SUS347HListed by Nippon Steel against 347H (S34709), for boiler and heater tube. | — | Closest equivalent |
On equivalence
- 347 versus 321: both stabilise an 18-10 base, 321 with titanium (5×(C+N) to 0.70 %) and 347 with niobium (10×C to 1.00 %). ASTM A240 gives them the same minimum strength. See the 321 entry.
- 1.4550 (X6CrNiNb18-10) caps nickel at 12.00 %, against 13.0 % in ASTM A240, and sets sulphur at 0.015 %, against 0.030 %. Both use a niobium range of 10×C to 1.00 %.
- Nippon Steel's tube table lists chromium 17.0–20.0 % and niobium 10×C to 1.10 % for SUS347; the Nose JIS reference sheet gives 17.00–19.00 % and a niobium floor only. Check the product standard on the order.
- 347S31 is the old British name and is withdrawn; use EN 10088 for new orders. Sources also list EN58G from the 1955 BS 970 EN series.
- 347H is a separate UNS (S34709) with 0.04–0.10 % carbon. Do not substitute 347 for 347H where high-temperature strength is specified.
Chemical composition
Composition limits, mass %
| Element | 347 (S34700)USA · ASTM A240 | 347H (S34709)USA · ASTM A240 | X6CrNiNb18-10 (1.4550)EU · EN 10088-2 (cast analysis) | X04Cr18Ni10NbIndia · IS 1570 (Part 5):1985 | SUS347Japan · JIS G 4303 (bar), as tabulated in the Nose reference sheet |
|---|---|---|---|---|---|
| C | ≤0.08 | 0.04–0.10 | ≤0.08 | ≤0.08 | ≤0.08 |
| Si | ≤0.75 | ≤0.75 | ≤1.00 | ≤1.0 | ≤1.00 |
| Mn | ≤2.00 | ≤2.00 | ≤2.00 | ≤2.0 | ≤2.00 |
| P | ≤0.045 | ≤0.045 | ≤0.045 | ≤0.045 | ≤0.045 |
| S | ≤0.030 | ≤0.030 | ≤0.015 | ≤0.030 | ≤0.030 |
| Cr | 17.0–19.0 | 17.0–19.0 | 17.00–19.00 | 17.0–19.0 | 17.00–19.00 |
| Ni | 9.0–13.0 | 9.0–13.0 | 9.00–12.00 | 9.0–12.0 | 9.00–13.00 |
| Nb | 10×C–1.00 | 8×C–1.00 | 10×C–1.00 | 10×C–1.0 | ≥10×C |
Mechanical properties
Strength and hardness
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| AnnealedSpecified minimums, plate, sheet and strip (ASTM A240); hardness is a maximumASTM A240, via ATI and Atlas Steels Section 9 | ≥515 MPa≥75 ksi | ≥205 MPa≥30 ksi | ≥40 % | ≤201 HB (≤92 HRB) |
| AnnealedTypical values for plate, sheet and strip, not a specificationATI datasheet for 347, via Combined Metals | 640 MPa93 ksi | 250 MPa36 ksi | 45 % | 84 HRB |
| 347H annealedSpecified minimums, plate, sheet and strip (ASTM A240); hardness is a maximumASTM A240 S34709, via Euro Inox tables and ICAST | ≥515 MPa≥75 ksi | ≥205 MPa≥30 ksi | ≥40 % | ≤201 HB (≤92 HRB) |
| Solution annealed (+AT)Specified, hot rolled plate up to 75 mm, transverse testEN 10088-2, via Euro Inox tables | 500–700 MPa73–102 ksi | ≥200 MPa≥29 ksi | ≥40 % | — |
| Solution treatedSpecified, JIS table in the Nose reference sheet (it gives reduction of area, so it is the bar standard JIS G 4303; plate limits in JIS G 4304 / G 4305 were not read); hardness is a maximumJIS, via Nose Stainless reference sheet (reduction of area ≥50 %) | ≥520 MPa≥75 ksi | ≥205 MPa≥30 ksi | ≥40 % | ≤187 HBW (≤90 HRBW) |
| Annealed plate, sheet and strip (X04Cr18Ni10Nb)Specified minimums; hardness is a maximumIS 1570 (Part 5):1985, Table 2 | ≥515 MPa≥75 ksi | ≥205 MPa≥30 ksi | ≥40 % | ≤183 HB (≤88 HRB) |
| Annealed bars and flats (X04Cr18Ni10Nb)Specified minimums (reduction of area ≥50 %)IS 1570 (Part 5):1985, Table 3 | ≥517 MPa≥75 ksi | ≥207 MPa≥30 ksi | ≥40 % | — |
| Hot rolled plate, 10–20 mmOutokumpu typical values for 4550, transverse, not a specificationOutokumpu Steel Grades, Properties and Global Standards, Table 6 | 595 MPa86 ksi | 260 MPa38 ksi | 45 % | — |
In practice
Behaviour, heat treatment and uses
Characteristics
- Niobium is added at 10 times the carbon content or more. It forms niobium carbide in preference to chromium carbide, so the steel resists intergranular corrosion after welding or exposure to 425–815 °C (ATI, Combined Metals).
- Nose notes that titanium-stabilised 321 is not recommended for decorative parts; its sheet has no such note for 347.
- Good resistance to polythionic-acid stress corrosion cracking, which makes it a standard choice around refinery reactors (Smiths Metal).
- Austenitic, non-magnetic when annealed and hardenable only by cold work (Smiths Metal).
- 347H raises carbon to 0.04–0.10 % for high-temperature strength in heater and boiler tube (Nippon Steel).
- Density about 7.9–8.0 g/cm³, modulus of elasticity 193–200 GPa and thermal conductivity 15–16 W/m·K at 20 °C (Outokumpu, ATI).
Heat treatment
- Solution annealing: 980–1150 °C (1795–2100 °F) followed by rapid cooling (JIS guidance, Nose).
- Austenitic and not hardenable by heat treatment; strength rises only with cold work (Smiths Metal).
- Avoid long holds in the 425–815 °C (800–1500 °F) range; this is the chromium carbide precipitation range that niobium is added to protect against (Combined Metals).
Usos habituales
- Refinery and petrochemical plant: fired-heater tubes, FCC units, thermowells and reactor components
- Boiler and reheater tube in 347H
- Chemical processing and nuclear-industry equipment
- Welded vessels and pipework exposed to the sensitising range in service
Stainless steels
Similar grades compared
| Grado | C % | Mn % | Cr % | Ni % | Tensile, first listed condition |
|---|---|---|---|---|---|
| 347 / 1.4550 | ≤0.08 | ≤2.00 | 17.0–19.0 | 9.0–13.0 | ≥515 MPa |
| 201 / 1.4372 | ≤0.15 | 5.50–7.50 | 16.0–18.0 | 3.5–5.5 | ≥515 MPa |
| 301 / 1.4310 | ≤0.15 | ≤2.00 | 16.0–18.0 | 6.0–8.0 | ≥515 MPa |
| 303 / 1.4305 | ≤0.15 | ≤2.0 | 17.0–19.0 | 8.0–10.0 | 650 MPa |
| 304 / 1.4301 | ≤0.08 | ≤2.00 | 18.0–20.0 | 8.0–10.5 | ≥515 MPa |
| 304L / 1.4307 | ≤0.030 | ≤2.00 | 18.0–20.0 | 8.0–12.0 | ≥485 MPa |
| 309 / 309S | ≤0.08 | ≤2.00 | 22.0–24.0 | 12.0–15.0 | ≥515 MPa |
| 310 / 310S | ≤0.08 | ≤2.00 | 24.0–26.0 | 19.0–22.0 | ≥515 MPa |
| 316 / 1.4401 | ≤0.08 | ≤2.00 | 16.0–18.0 | 10.0–14.0 | ≥515 MPa |
| 316L | ≤0.030 | ≤2.00 | 16.0–18.0 | 10.0–14.0 | ≥485 MPa |
Composition from the US standard where one exists, otherwise the first standard listed on each grade's page. Strength conditions differ between grades; open a grade for its full table.
Preguntas resueltas
Common questions
What is the equivalent of 347 stainless steel?
1.4550 (X6CrNiNb18-10) in Europe, SUS347 in Japan, X04Cr18Ni10Nb in India and 347S31 in old British standards. The EN grade caps nickel at 12 % against 13 % for ASTM 347.
What is the difference between 321 and 347?
Both resist intergranular corrosion after welding and share the same ASTM A240 minimum strength. 321 uses titanium to bind carbon; 347 uses niobium. They are not interchangeable without approval, so use the grade the drawing or specification names.
What is the difference between 347 and 347H?
Carbon. 347 allows 0.08 % at most; 347H requires 0.04–0.10 % and a niobium minimum of 8×C. The extra carbon gives 347H better creep strength for heater and boiler tubes. Mechanical minimums in ASTM A240 are the same.
Is 347 stainless steel weldable?
Yes. Smiths Metal list it as weldable by common fusion and resistance techniques, and niobium stabilisation gives resistance to intergranular corrosion after exposure to the 425–815 °C precipitation range (Combined Metals).
Is 1.4550 the same as 347?
They are close equivalents but not identical. 1.4550 allows 9–12 % nickel and 17–19 % chromium; ASTM A240 347 allows 9–13 % nickel and 17–19 % chromium. Both require niobium of 10×C to 1.00 %.
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Related references
References
Sources
- Outokumpu: Steel Grades, Properties and Global Standards — Cross-reference of EN, ASTM, UNS and JIS names with the superseded British, DIN and French names; EN and ASTM minimum properties for plate; Outokumpu typical values.
- Atlas Steels, Product Reference Manual Section 9: stainless steel properties and equivalent grades — UNS, old British BS, Euronorm and JIS cross-reference, with ASTM A240 composition and specified mechanical properties. States that cross-references are approximate.
- ATI 347 Austenitic Stainless Steel (UNS S34700) — ASTM A240 / ASME SA-240 composition and minimum tensile, yield, elongation and hardness.
- Combined Metals: Alloy 347 stainless steel data sheet (ATI source, 2024) — Niobium stabilisation, sensitising range, applicable specifications and ATI typical annealed properties.
- Euro Inox: Stainless Steel: Tables of Technical Properties (2nd edition, 2007; Cedinox copy) — EN 10088 cast-analysis limits and minimum mechanical properties by product form for the EN grade, with the matching AISI/ASTM name.
- Bureau of Indian Standards, IS 1570 (Part 5):1985 Schedules for wrought steels, stainless and heat-resisting steels (Public.Resource.Org copy) — Table 1 composition, Table 2 plate, sheet and strip mechanical requirements, Table 3 bar and flat requirements. Figures read from page images of the scan.
- Nose Stainless: steel types, composition and mechanical properties (JIS reference sheet) — JIS composition, solution-treatment range, 0.2 % proof stress, tensile strength, elongation, reduction of area and hardness for the stainless plate grades, including SUS316Ti, SUS347 and SUS890L.
- Nippon Steel: stainless steel pipe and tube grade list (catalog P007) — Names 316Ti, 347, 347H and 904L against UNS, EN and JIS (SUS316Ti, SUS347, SUS347H, SUS890L) with tube composition and minimum strength.
- ICAST: ASTM A240 UNS S34709 — Second source for 347H composition and minimum properties.
- Smiths Metal Centres: 347 stainless technical datasheet (2023) — Applications, polythionic-acid cracking resistance and general description.
- Zhejiang Guanyu Stainless Steel Tube Co.: 347 vs 347H vs 347HFG (ASTM A213 tube) — Cb+Ta 10×C–1.0 for 347 and 8×C–1.0 for 347H, nickel 9.0–13.0, tube chromium 17.0–20.0.
- Total Materia: JIS SUS347 (JIS G 4303:2021 stainless steel bars) — Governing standard shown as JIS G 4303 (bars); solution treatment 980–1150 °C; British 347S31 listed.
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.