Stainless Steel 347LN-3/4 Hard
Supply condition
AISI/SAE 347LN · UNS S34751
3/4 Hard = three-quarter hard
High-strength strip for flat springs and shims with only simple bends.
Values for the 3/4 Hard condition
Other 347LN tempers and conditions
347LN is listed in 8 conditions; see the grade overview at 347LN.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault solution annealed 1040–1120 °C, rapid quenched | Standard supply condition for plate, pipe, tube, bar and forgings; maximum corrosion resistance and ductility for nuclear/pressure service. | 290 | 620 | 50 | 160 HB | — |
880–930 °C hold after solution anneal | Chosen for severe hot nitric-acid or long high-temperature service where all residual carbon must be tied up as NbC. | 300 | 610 | 45 | 165 HB | 2.4 % IACS |
As-welded deposit (ER347 / E347 type filler, no PWHT) | Design basis for weld metal and HAZ in nuclear/piping joints welded without post-weld solution anneal. | 400 | 600 | 35 | 180 HB | 2.3 % IACS |
Cold drawn / cold finished bar (annealed + drawn) | Bar and tube where tighter tolerance, better surface and higher yield strength are needed than annealed. | 500 | 720 | 30 | 16 HRC | 2.4 % IACS |
Quarter hard | Light cold-rolled temper for springy sheet parts still needing appreciable forming ability. | 545 | 880 | 12 | 25 HRC | 2.4 % IACS |
Half hard | Structural sheet, clamps and springs where strength outweighs formability. | 790 | 1,060 | 10 | 32 HRC | 2.4 % IACS |
3/4 HardThis page Three-quarter hard | High-strength strip for flat springs and shims with only simple bends. | 960 | 1,230 | 7 | 37 HRC | 2.4 % IACS |
heavily cold rolled strip per ASTM A666 | Maximum strength thin strip; essentially no forming beyond flat blanking. | 1,000 | 1,300 | 4 | 40 HRC | 2.4 % IACS |
What is 347LN-3/4 Hard?
347LN-3/4 Hard is 347LN supplied in the 3/4 Hard condition — high-strength strip for flat springs and shims with only simple bends. 347LN-3/4 Hard has a yield strength of 960 MPa (139 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 7% and the elastic modulus is 193 GPa (28 Msi). 347LN-3/4 Hard has a density of 7.95 g/cm³ (0.287 lb/in³), heavier than 81% of stainless steel grades. It melts at 1,400°C (2,552 °F). Annealed is the default condition FabDigit quotes; 3/4 Hard is available on request or by drawing note.
Advantages
- High strength — 960 MPa (139 ksi), better than 98% of stainless steel grades
Limitations
- Limited ductility — 7%, worse than 99% of stainless steel grades
- Limited service temperature — 300°C (572 °F), worse than 90% of stainless steel grades
- Limited formability — 20/100, worse than 86% of stainless steel grades
- Low fracture toughness — 90 MPa·√m (81.9 ksi·√in), worse than 75% of stainless steel grades
347LN-3/4 Hard properties
Typical room-temperature values for 347LN-3/4 Hard; 23 are specific to this condition. Other listed values are 347LN reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
347LN-3/4 Hard has a density of 7.95 g/cm³ (0.287 lb/in³), heavier than 81% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
347LN-3/4 Hard has a yield strength of 960 MPa (139 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 7% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
347LN-3/4 Hard is rated for continuous service to 300°C (572 °F). It conducts heat at 16.2 W/m·K (9.36 BTU/hr·ft·°F), better than 64% of stainless steel grades. Thermal expansion is 16.5 µm/m·K (9.17 µin/in·°F).
Electrical3
347LN-3/4 Hard 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 347LN-3/4 Hard takes about 53 MJ of energy and emits 5.2 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 60%.
Manufacturability8
347LN-3/4 Hard's machinability is poor (32/100, worse than 62% of stainless steel grades); weldability very good (70/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 347LN-3/4 Hard
Is 347LN easy to machine?
Cut like 347/321 — rigid setups, sharp positive-rake carbide, heavy flood coolant, 20–30 % lower speed than 304 because NbC particles are abrasive and chips are stringy.
Can 347LN be welded?
Excellent: GTAW/GMAW/SMAW with ER347/E347 (or Nb-free 316L only where allowed); low heat input, interpass ≤150 °C, no post-weld anneal needed thanks to ultra-low C plus Nb.
Can 347LN be formed, bent or molded?
Very ductile hot (1150–1250 °C) and cold, but work-hardens fast — allow for springback, use interstage anneals for deep draws and avoid stopping hot work below ~900 °C.
What surface finishes work on 347LN?
Pickle (HNO₃/HF) or electropolish after fabrication and passivate per ASTM A967; polishes to a mirror finish; never anodised, and avoid iron contamination from carbon-steel tooling.
347LN 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 |
|---|---|---|
| Cultra-low carbon, controlled range | 0.01 – 0.02 | 0.01 |
| Nnitrogen-strengthened | 0.06 – 0.1 | 0.08 |
| Cr | 17 – 19 | 18 |
| Ni | 9 – 13 | 10.5 |
| Nbstabiliser; standard requires ≥15×C (Nb+Ta basis in some specs) | 0.2 – 1 | 0.4 |
| Mn | ≤ 2 | 1.5 |
| Si | ≤ 1 | 0.5 |
| P | ≤ 0.05 | — |
| Snuclear orders often restrict S ≤0.015 and Co ≤0.05 | ≤ 0.03 | — |
| Fe | balance | — |
347LN-3/4 Hard — frequently asked
What is 347LN-3/4 Hard used for?
347LN-3/4 Hard is typically used for nuclear primary and secondary piping, high-pressure welded piping systems, superheater and reheater tubing, pressure vessel shells and nozzles, steam headers and manifolds and welded expansion joints and bellows. In short: stabilized, sensitization-resistant 347; nitrogen-boosted weld strength; nuclear-grade piping choice.
What is the yield strength of 347LN-3/4 Hard?
347LN-3/4 Hard has a typical yield strength of 960 MPa (139 ksi) and a tensile strength of 1,230 MPa (178 ksi) — stronger than 98% of stainless steel grades. Strength varies by condition: see the 8 listed tempers.
Is 347LN-3/4 Hard easy to machine?
Not especially — machinability is rated poor (32/100, worse than 62% of stainless steel grades). Cut like 347/321 — rigid setups, sharp positive-rake carbide, heavy flood coolant, 20–30 % lower speed than 304 because NbC particles are abrasive and chips are stringy.
Can 347LN-3/4 Hard be welded?
Yes — weldability is rated very good (70/100). Excellent: GTAW/GMAW/SMAW with ER347/E347 (or Nb-free 316L only where allowed); low heat input, interpass ≤150 °C, no post-weld anneal needed thanks to ultra-low C plus Nb.
What surface finishes work on 347LN-3/4 Hard?
Pickle (HNO₃/HF) or electropolish after fabrication and passivate per ASTM A967; polishes to a mirror finish; never anodised, and avoid iron contamination from carbon-steel tooling.
Can 347LN-3/4 Hard be formed, bent or molded?
Very ductile hot (1150–1250 °C) and cold, but work-hardens fast — allow for springback, use interstage anneals for deep draws and avoid stopping hot work below ~900 °C.
What is the maximum service temperature of 347LN-3/4 Hard?
347LN-3/4 Hard is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM A240/A240M — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet and Strip (UNS S34751) — ASTM International (2023)
- ASTM A312/A312M — Seamless and Welded Austenitic Stainless Steel Pipes — ASTM International (2022)
- ASTM A666 — Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate and Flat Bar — ASTM International (2015)
- ASME BPVC Section II Part D — Material Properties (physical/allowable stress tables for 347 group) — ASME (2023)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- EN 10088-2 / 1.4550 (X6CrNiNb18-10) stabilised austenitic stainless — CEN (2014)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.