Stainless Steel 347
AISI/SAE 347 · UNS S34700 · ASTM A240 TP347 · EN 1.4550, X6CrNiNb18-10 · JIS SUS347
347 is a niobium-stabilized austenitic stainless (S34700, 1.4550, X6CrNiNb18-10, SUS347, A240 TP347) in which Nb ties up carbon as NbC, preventing chromium carbide precipitation and intergranular corrosion in welded and elevated-temperature service.
Values for the Solution Annealed condition
347 tempers and conditions
347 is supplied in 10 conditions, soft to hard. Solution Annealed is the default FabDigit quotes; the values on this page are for it.
- Annealed
- Hot Finished
- 347H
- Solution Annealed
- Stabilize Annealed
- As Welded
- Cold Drawn
- 1/4 Hard
- 1/2 Hard
- Full Hard
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
softened condition (sheet/strip/wire, equivalent to solution annealed) | Soft sheet, strip and wire for forming, spinning and cold heading. | 240 | 600 | 48 | 155 HB | 2.4 % IACS |
Hot Finished / Hot Rolled Annealed bar (ASTM A276) | Economical large-section bar and plate for machined weldments and hot-service piping supports. | 240 | 600 | 42 | 165 HB | 2.4 % IACS |
High-carbon (0.04–0.10 % C) variant, solution annealed ≥1050 °C | Pick for ASME code creep service above 540 °C — higher allowable stresses and better rupture life than plain 347. | 240 | 620 | 45 | 165 HB | 2.4 % IACS |
Solution AnnealedDefault 1010–1120 °C, rapid cool (ASTM A240/A276 standard delivery) | Default stock condition for plate, sheet, bar, pipe and tube — maximum ductility and corrosion resistance. | 245 | 620 | 45 | 160 HB | — |
870–900 °C hold after solution anneal | Extra Nb-carbide precipitation treatment for parts exposed to severe intergranular-corrosion service (nitric acid, long hot holds). | 255 | 615 | 43 | 165 HB | 2.4 % IACS |
ER347 / E347 weld metal deposit | Matching filler deposit condition; used for as-welded design values in stabilized 18-8 joints. | 400 | 600 | 35 | 180 HB | 2.4 % IACS |
Cold Drawn / Cold Finished bar (ASTM A484, ~10–20 % reduction) | Higher strength, tighter tolerance and better surface for screw-machine parts and fasteners. | 550 | 760 | 25 | 23 HRC | 2.4 % IACS |
Quarter hard | Light temper rolling where extra stiffness is needed but some bending is still required. | 550 | 900 | 12 | 25 HRC | 2.4 % IACS |
Half hard | Springy strip for clamps, shims and gasket/bellows plies that see little forming. | 790 | 1,035 | 9 | 32 HRC | 2.3 % IACS |
heavily cold rolled strip (≈ 965 MPa min yield) | Maximum strength flat product for flat springs and diaphragms; essentially no forming capability. | 1,000 | 1,275 | 6 | 38 HRC | 2.3 % IACS |
What is 347?
347 is a niobium-stabilized austenitic stainless (S34700, 1.4550, X6CrNiNb18-10, SUS347, A240 TP347) in which Nb ties up carbon as NbC, preventing chromium carbide precipitation and intergranular corrosion in welded and elevated-temperature service. Annealed material runs about 245 MPa yield, 620 MPa tensile, 45 % elongation and 160 HB, with service to 870 °C, and is stocked as plate, sheet, hot-finished and cold-drawn bar, tube and quarter to full hard strip. General corrosion resistance is comparable to 304 rather than 316, and NbC makes it abrasive to machine; 321 is the usual titanium-stabilized alternative. 347 has a density of 7.96 g/cm³ (0.288 lb/in³), heavier than 83% of stainless steel grades. It melts at 1,400°C (2,552 °F). 347 has a yield strength of 245 MPa (35.5 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 94% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 193 GPa (28 Msi).
What is 347 used for?
- Boiler and superheater piping
- Refinery and petrochemical process piping
- Exhaust systems and expansion bellows
- Welded pressure vessels for hot service
- Heat exchanger tubes and tubesheets
- Aircraft collector rings and ducting
- Furnace parts and radiant tube supports
Advantages
- Readily welded — 90/100, better than 95% of stainless steel grades
- Forms and bends easily — 80/100, better than 93% of stainless steel grades
- Polishes to a fine finish — 80/100, better than 89% of stainless steel grades
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- High service temperature — 870°C (1,598 °F), better than 83% of stainless steel grades
Limitations
- Low strength — 245 MPa (35.5 ksi), worse than 94% of stainless steel grades
- High embodied carbon — 5.5 kg CO₂/kg, worse than 77% of stainless steel grades
347 properties
Typical room-temperature values for 347-Solution Annealed; bars are the position among stainless steel grades.
Physical3
347 has a density of 7.96 g/cm³ (0.288 lb/in³), heavier than 83% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
347 has a yield strength of 245 MPa (35.5 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 94% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
347 is rated for continuous service to 870°C (1,598 °F). It conducts heat at 16 W/m·K (9.24 BTU/hr·ft·°F), better than 58% of stainless steel grades. Thermal expansion is 16.6 µm/m·K (9.22 µin/in·°F).
Electrical3
347 conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (66/100), better than 59% of stainless steel grades.
Sustainability4
Producing a kilogram of 347 takes about 57 MJ of energy and emits 5.5 kg of CO₂ — more than 62% of stainless steel grades. Typical recycled content is 60%.
Manufacturability7
347's machinability is fair (38/100, better than 63% of stainless steel grades); weldability excellent (90/100); formability very good (80/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 347 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 347
Is 347 easy to machine?
Gummy and work-hardening with abrasive NbC particles — use rigid setups, positive-rake coated carbide, heavy constant feed, no dwelling, and flood coolant; ~40 % of 1212 speeds.
Can 347 be welded?
Excellent by GTAW/GMAW/SMAW with ER347/E347 filler; the Nb stabilization means no post-weld solution anneal is needed, but keep heat input low and interpass < 150 °C to limit distortion and hot-cracking risk.
Can 347 be formed, bent or molded?
Cold forms and deep draws well but work-hardens faster than 304 — allow extra power, generous radii and intermediate anneals at 1010–1120 °C followed by rapid cooling.
Manufacturability
The process limits FabDigit applies to 347. Every 347 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair38 / 100 |
|---|---|
| ISO material group | M.1 |
| Cutting speed (rough / finish) | 150 / 180 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better80 / 100 |
|---|---|
| Weldability | Excellent90 / 100 |
| Bendable | Yes |
347 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C347H: 0.04–0.10 | ≤ 0.08 | 0.05 |
| Mn | ≤ 2 | 1.5 |
| Si | ≤ 0.75 | 0.5 |
| P | ≤ 0.05 | |
| S | ≤ 0.03 | |
| Cr | 17 – 19 | 18 |
| Ni | 9 – 13 | 11 |
| NbNb(+Ta) ≥ 10×C; EN 1.4550 requires Nb ≥ 10×C, max 1.00 | ≤ 1 | 0.6 |
| Talimited only in nuclear/Co-controlled orders | ≤ 0.1 | |
| NEN 1.4550 limit | ≤ 0.1 | 0.04 |
| Fe | balance |
What surface finishes work on 347?
Passivate per ASTM A967 or electropolish after machining; not anodizable — bead blast, No.4 brush or mirror polish are the usual finishes, and pickling paste removes weld heat tint.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 347 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S34700
- ASTM
- A240 TP347
- EN / DIN / Werkstoff-Nr.
- 1.4550X6CrNiNb18-101.4912
- GB (China)
- 06Cr18Ni11Nb
- JIS
- SUS347
How much does 347 cost?
347 is a premium-cost stainless steel ($$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
347 — frequently asked
What is 347 used for?
347 is typically used for boiler and superheater piping, refinery and petrochemical process piping, exhaust systems and expansion bellows, welded pressure vessels for hot service, heat exchanger tubes and tubesheets and aircraft collector rings and ducting. In short: niobium-stabilized austenitic stainless.
What is the yield strength of 347?
347 has a typical yield strength of 245 MPa (35.5 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 94% of stainless steel grades. Strength varies by condition: see the 10 listed tempers.
Is 347 easy to machine?
Not especially — machinability is rated fair (38/100, better than 63% of stainless steel grades). Gummy and work-hardening with abrasive NbC particles — use rigid setups, positive-rake coated carbide, heavy constant feed, no dwelling, and flood coolant; ~40 % of 1212 speeds.
Can 347 be welded?
Yes — weldability is rated excellent (90/100). Excellent by GTAW/GMAW/SMAW with ER347/E347 filler; the Nb stabilization means no post-weld solution anneal is needed, but keep heat input low and interpass < 150 °C to limit distortion and hot-cracking risk.
What surface finishes work on 347?
Passivate per ASTM A967 or electropolish after machining; not anodizable — bead blast, No.4 brush or mirror polish are the usual finishes, and pickling paste removes weld heat tint.
Can 347 be formed, bent or molded?
Cold forms and deep draws well but work-hardens faster than 304 — allow extra power, generous radii and intermediate anneals at 1010–1120 °C followed by rapid cooling.
What is the maximum service temperature of 347?
347 is rated for continuous use to about 870°C (1,598 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 347 Solution Annealed and 347H?
Solution Annealed is the default condition — default stock condition for plate, sheet, bar, pipe and tube — maximum ductility and corrosion resistance. 347H: pick for ASME code creep service above 540 °C — higher allowable stresses and better rupture life than plain 347. Yield strength is 245 MPa in Solution Annealed versus 240 MPa in 347H.
How much does 347 cost?
347 is a premium-cost stainless steel ($$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 347?
Yes — 347 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A240/A240M — Cr and Cr-Ni Stainless Plate, Sheet and Strip — ASTM International (2023)
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM International (2023)
- EN 10088-2 — Stainless steels, technical delivery conditions for sheet/plate (1.4550) — CEN (2014)
- GB/T 1220 / GB/T 4237 (0Cr18Ni11Nb) — SAC (2015)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- 347/347H Stainless Steel Product Data Sheet — AK Steel / Cleveland-Cliffs (2021)
- Outokumpu Steel Grade 4550 datasheet — Outokumpu (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.