Stainless Steel 348H
AISI/SAE 348H · UNS S34809 · ASTM A240 TP348H
348H is the higher-carbon version of the niobium/tantalum-stabilised 348 austenitic stainless (S34809, ASTM A240 TP348H), with carbon held high to raise creep strength at elevated temperature.
Reference datasheet — 348H is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed condition
348H tempers and conditions
348H is supplied in 6 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hot finished / hot rolled and annealed bar and plate | Economical heavy plate and large-section bar for pressure vessel and header parts where surface finish is not critical. | 260 | 600 | 48 | 165 HB | 2.4 % IACS |
~900 °C hold after solution anneal | Choose when maximum immunity to intergranular and knife-line attack is needed after welding or for severe nitric-acid/high-temperature service. | 270 | 610 | 48 | 163 HB | 2.4 % IACS |
AnnealedDefault solution annealed (ASTM A240/A213/A479 condition A) | Standard supply condition for plate, sheet, pipe and tube used in high-temperature and nuclear pressure service. | 275 | 620 | 50 | 160 HB | — |
Cold drawn / cold finished bar and tube (lightly cold worked) | Pick for close tolerances, better surface finish and higher yield strength in small-diameter bar, tube and fasteners. | 480 | 725 | 25 | 18 HRC | 2.4 % IACS |
Quarter hard | Use for stiffer springs, clips and formed strip parts where some cold formability must remain. | 515 | 860 | 12 | 25 HRC | 2.4 % IACS |
Half hard | Highest strength normally stocked in strip form; only mild bending is possible. | 760 | 1,035 | 8 | 32 HRC | 2.4 % IACS |
What is 348H?
348H is the higher-carbon version of the niobium/tantalum-stabilised 348 austenitic stainless (S34809, ASTM A240 TP348H), with carbon held high to raise creep strength at elevated temperature. It is specified for nuclear reactor piping and high-temperature nuclear components, and is available as plate, pipe, bar and forgings in Annealed, Stabilize-Annealed, Hot Finished, Cold Drawn, 1/4 Hard and 1/2 Hard conditions. Annealed material gives 275 MPa yield, 620 MPa tensile, 50 % elongation and 160 HB (82 HRB), with maximum service temperature 815 °C. Nb/Ta carbides make it abrasive to machine and nuclear-grade sourcing limits availability and raises cost; 347H is the nearest alternative. 348H 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). 348H 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 50% and the elastic modulus is 195 GPa (28.3 Msi).
What is 348H used for?
- Nuclear reactor piping
- High-temperature nuclear components
- Reactor internal support structures
- Superheater and reheater tubing
- High-temperature steam headers and spools
- Forged valve and fitting bodies for hot service
- Pressure-retaining plate for nuclear equipment
Advantages
- Ductile — tolerates forming and impact — 50%, better than 90% of stainless steel grades
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- Readily welded — 80/100, better than 80% of stainless steel grades
- Forms and bends easily — 70/100, better than 79% of stainless steel grades
- High service temperature — 815°C (1,499 °F), better than 77% of stainless steel grades
Limitations
- Low strength — 275 MPa (39.9 ksi), worse than 77% of stainless steel grades
348H properties
Typical room-temperature values for 348H-Annealed; bars are the position among stainless steel grades.
Physical3
348H 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
348H 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 50% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
348H is rated for continuous service to 815°C (1,499 °F). It conducts heat at 16.3 W/m·K (9.42 BTU/hr·ft·°F), better than 68% of stainless steel grades. Thermal expansion is 16.6 µm/m·K (9.22 µin/in·°F).
Electrical3
348H conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (55/100), worse than 71% of stainless steel grades.
Sustainability4
Producing a kilogram of 348H takes about 78 MJ of energy and emits 5 kg of CO₂ — more than 87% of stainless steel grades. Typical recycled content is 55%.
Manufacturability7
348H's machinability is fair (38/100, better than 63% of stainless steel grades); weldability very good (80/100); formability very good (70/100).
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. 348H is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 348H
Is 348H easy to machine?
Gummy and work-hardening with abrasive Nb/Ta carbides — use rigid setups, sharp positive-rake carbide, ~30–60 m/min, heavy positive feed and flood coolant; avoid dwelling to prevent glazing.
Can 348H be welded?
Readily welded by GTAW/GMAW/SMAW with ER347/E347 filler; no post-weld anneal is normally required, but minimise heat input and consider a ~900 °C stabilising anneal where knife-line attack or hot nitric service is a concern.
Can 348H be formed, bent or molded?
Cold forms well in the annealed condition though springback and work hardening exceed 304; hot work at 1150–1200 °C and always solution anneal at 1040–1100 °C followed by rapid cooling.
348H 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 |
|---|---|---|
| Craised carbon for creep strength (the 'H' grade) | 0.04 – 0.1 | 0.07 |
| Cr | 17 – 19 | 18 |
| Ni | 9 – 13 | 11 |
| NbNb (+Ta) ≥ 8 × C; Nb+Ta reported together | 0.56 – 1 | 0.75 |
| Tarestricted for nuclear (low neutron capture) | ≤ 0.1 | 0.05 |
| Corestricted for nuclear service | ≤ 0.2 | 0.1 |
| Mn | ≤ 2 | 1.5 |
| Si1.00 max in some product specs | ≤ 0.75 | 0.5 |
| P | ≤ 0.05 | 0.03 |
| S | ≤ 0.03 | 0.01 |
| Fe | balance |
What surface finishes work on 348H?
Cannot be anodised — pickle and passivate per ASTM A380/A967, electropolish for nuclear cleanliness; takes a good mechanical polish, with carbide stringers occasionally showing as faint comet tails.
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).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 348H in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S34809
- ASTM
- A240 TP348H
How much does 348H cost?
348H is a high-cost stainless steel ($$$$), pricier than about 78% 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.
348H — frequently asked
What is 348H used for?
348H is typically used for nuclear reactor piping, high-temperature nuclear components, reactor internal support structures, superheater and reheater tubing, high-temperature steam headers and spools and forged valve and fitting bodies for hot service. In short: creep-resistant 348 variant; nuclear-service stabilised grade; 815 °C service limit.
What is the yield strength of 348H?
348H 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 6 listed tempers.
Is 348H easy to machine?
Not especially — machinability is rated fair (38/100, better than 63% of stainless steel grades). Gummy and work-hardening with abrasive Nb/Ta carbides — use rigid setups, sharp positive-rake carbide, ~30–60 m/min, heavy positive feed and flood coolant; avoid dwelling to prevent glazing.
Can 348H be welded?
Yes — weldability is rated very good (80/100). Readily welded by GTAW/GMAW/SMAW with ER347/E347 filler; no post-weld anneal is normally required, but minimise heat input and consider a ~900 °C stabilising anneal where knife-line attack or hot nitric service is a concern.
What surface finishes work on 348H?
Cannot be anodised — pickle and passivate per ASTM A380/A967, electropolish for nuclear cleanliness; takes a good mechanical polish, with carbide stringers occasionally showing as faint comet tails.
Can 348H be formed, bent or molded?
Cold forms well in the annealed condition though springback and work hardening exceed 304; hot work at 1150–1200 °C and always solution anneal at 1040–1100 °C followed by rapid cooling.
What is the maximum service temperature of 348H?
348H 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 348H cost?
348H is a high-cost stainless steel ($$$$), pricier than about 78% 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.
Sources
- ASTM A240/A240M — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip (TP348H, S34809) — ASTM International (2023)
- ASTM A213/A213M — Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater and Heat-Exchanger Tubes — ASTM International (2022)
- ASTM A479/A479M — Stainless Steel Bars and Shapes for Boilers and Other Pressure Vessels — ASTM International (2021)
- ASME BPVC Section II Part D — Properties (Metric), austenitic stainless allowable stresses — ASME (2023)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ATI 347 / ATI 348 Technical Data Sheet — ATI Specialty Materials (2020)
- Machinery's Handbook — machinability ratings for stainless steels — Industrial Press (2020)
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.