Stainless Steel 347H
AISI/SAE 347H · UNS S34709 · ASTM A240 TP347H
347H is the high-carbon, creep-rated version of niobium-stabilized 347 (S34709, A240 TP347H), where the raised carbon content improves elevated-temperature creep and rupture strength while Nb stabilization keeps welded joints resistant to intergranular attack.
Values for the Solution Annealed condition
347H tempers and conditions
347H is supplied in 5 conditions, soft to hard. Solution Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hot Finished (hot rolled, annealed and descaled) bar / seamless pipe | Economical large-section bar and seamless pipe; slightly coarser surface and marginally lower strength than cold-worked product. | 250 | 585 | 45 | 170 HB | 2.4 % IACS |
mill-annealed bar/forging condition | Bar, forgings and fittings delivered fully annealed when softness and machining/forming ease matter more than strength. | 255 | 600 | 50 | 150 HB | 2.4 % IACS |
Solution AnnealedDefault 1040–1120 °C, rapid cool (ASTM A240/A213 delivery condition) | Standard as-supplied condition for plate, tube and pipe; maximum ductility and corrosion resistance, ASME-code creep properties. | 275 | 620 | 45 | 160 HB | — |
885–950 °C hold after solution anneal or welding | Specify when maximum immunity to intergranular / polythionic-acid attack and knife-line attack is required in refinery service. | 280 | 615 | 43 | 165 HB | 2.4 % IACS |
Cold Drawn / cold finished bar (ASTM A484 condition B) | Choose for close-tolerance small-diameter bar, higher yield strength and better surface for machined fittings and studs. | 520 | 790 | 28 | 225 HB | — |
What is 347H?
347H is the high-carbon, creep-rated version of niobium-stabilized 347 (S34709, A240 TP347H), where the raised carbon content improves elevated-temperature creep and rupture strength while Nb stabilization keeps welded joints resistant to intergranular attack. Annealed material gives about 275 MPa yield, 620 MPa tensile, 45 % elongation and 160 HB, with service to 815 °C, in plate, sheet, hot-finished and cold-drawn bar and stabilize-annealed product. It is abrasive and slow to cut (machinability 35) and formability is limited (68); 321H is the titanium-stabilized alternative where NbC tool wear or lead time is a problem. 347H 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). 347H has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 77% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 195 GPa (28.3 Msi).
What is 347H used for?
- Boiler and superheater tubing
- Refinery heater and reformer piping
- Power plant steam headers
- High-temperature pressure vessels
- Petrochemical reactor internals
- Expansion joints and bellows
- Furnace hangers and tube supports
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- High service temperature — 815°C (1,499 °F), better than 77% of stainless steel grades
- Ductile — tolerates forming and impact — 45%, better than 76% of stainless steel grades
- Forms and bends easily — 68/100, better than 75% of stainless steel grades
Limitations
- Low strength — 275 MPa (39.9 ksi), worse than 77% of stainless steel grades
347H properties
Typical room-temperature values for 347H-Solution Annealed; bars are the position among stainless steel grades.
Physical3
347H 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).
Mechanical15
347H has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 77% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
347H is rated for continuous service to 815°C (1,499 °F). It conducts heat at 16.1 W/m·K (9.3 BTU/hr·ft·°F), better than 61% of stainless steel grades. Thermal expansion is 16.6 µm/m·K (9.22 µin/in·°F).
Electrical3
347H conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (57/100), worse than 66% of stainless steel grades.
Sustainability4
Producing a kilogram of 347H takes about 60 MJ of energy and emits 5.3 kg of CO₂ — more than 70% of stainless steel grades. Typical recycled content is 60%.
Manufacturability8
347H's machinability is fair (35/100, better than 51% of stainless steel grades); weldability very good (78/100); formability good (68/100).
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. 347H is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 347H
Is 347H easy to machine?
Machine like 321/304 but expect abrasive NbC: rigid setup, sharp coated carbide, 25–60 m/min, heavy positive feed to cut through the work-hardened skin, flood coolant, no dwelling.
Can 347H be welded?
Readily welded by GTAW/GMAW/SMAW with ER347/E347 filler (ER16-8-2 for thick multipass creep service); low heat input, no preheat, keep interpass low to limit hot cracking, and add a 900 °C stabilizing anneal where knife-line attack or polythionic SCC is a risk.
Can 347H be formed, bent or molded?
Cold forms well but work-hardens fast — allow ~50 % more press force than mild steel, generous bend radii, and interstage annealing; hot work at 1150–1200 °C and always solution anneal afterwards.
Manufacturability
The process limits FabDigit applies to 347H. Every 347H part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair35 / 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 | Better68 / 100 |
|---|---|
| Weldability | Excellent78 / 100 |
| Bendable | Yes |
347H 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 |
|---|---|---|
| Cdeliberately high for creep strength (H grade) | 0.04 – 0.1 | 0.06 |
| Si1.00 max in some product standards | ≤ 0.75 | 0.5 |
| Mn | ≤ 2 | 1.5 |
| P | ≤ 0.05 | 0.03 |
| S | ≤ 0.03 | 0.01 |
| Cr | 17 – 19 | 18 |
| Ni | 9 – 13 | 11 |
| NbNb(+Ta) ≥ 8 × C per ASTM A240/A213; min shown for C = 0.04 | 0.32 – 1 | 0.6 |
| Fe | balance |
What surface finishes work on 347H?
Pickle and passivate (ASTM A380/A967) or electropolish after fabrication to restore the chromium oxide film; takes a good mechanical or mirror polish, never anodized, and can be Ni-brazed in vacuum or dry hydrogen.
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 347H in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S34709
- ASTM
- A240 TP347H
How much does 347H cost?
347H 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.
347H — frequently asked
What is 347H used for?
347H is typically used for boiler and superheater tubing, refinery heater and reformer piping, power plant steam headers, high-temperature pressure vessels, petrochemical reactor internals and expansion joints and bellows. In short: high-temp niobium-stabilized stainless.
What is the yield strength of 347H?
347H has a typical yield strength of 275 MPa (39.9 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 77% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is 347H easy to machine?
Not especially — machinability is rated fair (35/100, better than 51% of stainless steel grades). Machine like 321/304 but expect abrasive NbC: rigid setup, sharp coated carbide, 25–60 m/min, heavy positive feed to cut through the work-hardened skin, flood coolant, no dwelling.
Can 347H be welded?
Yes — weldability is rated very good (78/100). Readily welded by GTAW/GMAW/SMAW with ER347/E347 filler (ER16-8-2 for thick multipass creep service); low heat input, no preheat, keep interpass low to limit hot cracking, and add a 900 °C stabilizing anneal where knife-line attack or polythionic SCC is a risk.
What surface finishes work on 347H?
Pickle and passivate (ASTM A380/A967) or electropolish after fabrication to restore the chromium oxide film; takes a good mechanical or mirror polish, never anodized, and can be Ni-brazed in vacuum or dry hydrogen.
Can 347H be formed, bent or molded?
Cold forms well but work-hardens fast — allow ~50 % more press force than mild steel, generous bend radii, and interstage annealing; hot work at 1150–1200 °C and always solution anneal afterwards.
What is the maximum service temperature of 347H?
347H is rated for continuous use to about 815°C (1,499 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 347H cost?
347H 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 347H?
Yes — 347H 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 — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip — ASTM International (2023)
- ASTM A213/A213M — Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — ASTM International (2022)
- ASTM A312/A312M and A479/A484 (S34709 pipe and bar) — ASTM International (2022)
- ASME BPVC Section II Part D — allowable stresses for SA-213 TP347H — ASME (2023)
- GB/T 1220 / GB/T 24593 (0Cr18Ni11Nb, 07Cr18Ni11Nb) — SAC (2018)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Sandvik / Alleima 347H and Outokumpu 4550 datasheets — Alleima, Outokumpu (2023)
- (SMM / Mysteel / 1688 ) (2025)
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.