Tungsten Alloy Class 2 Tungsten-SR (Stress relieved)
Heat-treated state · default condition
ASTM B760 Class 2
Default stocked condition for doped tungsten rod and wire: fibrous worked structure with residual stress removed, best balance of strength and handleability before service recrystallization.
Values for the SR condition
Other Class 2 Tungsten tempers and conditions
Class 2 Tungsten is listed in 6 conditions; see the grade overview at Class 2 Tungsten.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Sintered | Semi-finished doped tungsten billet as it leaves the sintering furnace; used only as feedstock for swaging, rolling or drawing. | — | 180 | 0 | 28 HRC | 25 % IACS |
Recrystallized | Condition after >2200 °C exposure or deliberate anneal — the AKS bubbles produce long interlocking grains giving the best creep/sag resistance, at the cost of near-zero RT ductility. | 450 | 600 | 0.5 | 37 HRC | 172 W/m·K |
Rolled sheet/plate/foil, stress relieved | Cross-rolled doped tungsten sheet, plate and foil supplied stress relieved for furnace shielding, boats and high-temperature structural parts. | 700 | 850 | 4 | 40 HRC | 30 % IACS |
SRDefaultThis page Stress relieved | Default stocked condition for doped tungsten rod and wire: fibrous worked structure with residual stress removed, best balance of strength and handleability before service recrystallization. | 800 | 1,050 | 3 | 42 HRC | 163 W/m·K |
As-swaged / as-drawn | Maximum-strength worked condition; choose where the highest room-temperature tensile strength of rod or coarse wire is needed and residual stress is acceptable. | 1,450 | 1,700 | 2 | 50 HRC | 29 % IACS |
Fine drawn wire | Heavily drawn AKS filament wire; pick for lamp/heater coils and cutting wire where ultra-high as-drawn tensile strength is required. | 2,600 | 3,000 | 2 | 55 HRC | 31 % IACS |
What is Class 2 Tungsten-SR?
Class 2 Tungsten-SR is Class 2 Tungsten heat treated to SR — default stocked condition for doped tungsten rod and wire: fibrous worked structure with residual stress removed, best balance of strength and handleability before service recrystallization. Class 2 Tungsten-SR has a yield strength of 800 MPa (116 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 56% of tungsten alloy grades. Elongation at break is 3% and the elastic modulus is 405 GPa (58.7 Msi). Class 2 Tungsten-SR has a density of 19.25 g/cm³ (0.695 lb/in³), heavier than 76% of tungsten alloy grades. It melts at 3,422°C (6,192 °F).
Advantages
- High service temperature — 2,500°C (4,532 °F), better than 95% of tungsten alloy grades
Limitations
- Low fracture toughness — 10 MPa·√m (9.1 ksi·√in), worse than 83% of tungsten alloy grades
- Hard to polish — 60/100, worse than 83% of tungsten alloy grades
Class 2 Tungsten-SR properties
Typical room-temperature values for Class 2 Tungsten-SR; 11 are specific to this condition. Other listed values are Class 2 Tungsten reference data and may not represent this condition. Bars are the position among tungsten alloy grades.
Physical3
Class 2 Tungsten-SR has a density of 19.25 g/cm³ (0.695 lb/in³), heavier than 76% of tungsten alloy grades. It melts at 3,422°C (6,192 °F).
Mechanical14
Class 2 Tungsten-SR has a yield strength of 800 MPa (116 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 56% of tungsten alloy grades. Elongation at break is 3% and the elastic modulus is 405 GPa (58.7 Msi).
Thermal5
Class 2 Tungsten-SR is rated for continuous service to 2,500°C (4,532 °F). It conducts heat at 163 W/m·K (94.2 BTU/hr·ft·°F), better than 62% of tungsten alloy grades. Thermal expansion is 4.5 µm/m·K (2.5 µin/in·°F).
Electrical3
Class 2 Tungsten-SR conducts electricity at 30 % IACS, better than 64% of tungsten alloy grades.
Chemical & Environmental3
Corrosion resistance is good (68/100), better than 79% of tungsten alloy grades.
Sustainability4
Producing a kilogram of Class 2 Tungsten-SR takes about 400 MJ of energy and emits 27 kg of CO₂ — more than 74% of tungsten alloy grades. Typical recycled content is 30%.
Manufacturability8
Class 2 Tungsten-SR's machinability is not recommended (10/100, better than 52% of tungsten alloy grades); weldability not recommended (12/100); formability not recommended (8/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Class 2 Tungsten-SR
Is Class 2 Tungsten easy to machine?
Treat as a grinding/EDM material — diamond or CBN grinding, wire EDM and laser cutting dominate; if turning, use rigid setups, negative-rake carbide at low speed and preheat to 200–400 °C to avoid chipping.
Can Class 2 Tungsten be welded?
Only electron-beam or laser welding in high vacuum gives usable joints, and the fusion zone recrystallizes to brittle coarse grains; vacuum brazing with Ni, Cu-Ag or Zr-based fillers is the preferred joining route.
Can Class 2 Tungsten be formed, bent or molded?
Cold forming is not feasible; bend, coil and draw warm (400–1200 °C depending on section) above the ductile-brittle transition, and avoid any post-recrystallization deformation.
What surface finishes work on Class 2 Tungsten?
Chemically etch (alkaline ferricyanide or HF/HNO₃) or electropolish to remove drawing lubricant and surface defects; no anodizing — apply CVD/PVD or silicide coatings if oxidation protection above 500 °C is needed.
Class 2 Tungsten 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 |
|---|---|---|
| Kresidual potassium from AKS doping (55–95 ppm) — the sag-resisting bubble former | 0.01 | 0.01 |
| Siresidual from silicate dopant | 0 – 0.01 | 0 |
| Alresidual from aluminate dopant | 5×10⁻⁴ – 0 | 0 |
| Fe | ≤ 0 | 0 |
| Mo | ≤ 0.01 | 0 |
| C | ≤ 0 | 0 |
| O | ≤ 0.01 | 0 |
| N | ≤ 0 | 5×10⁻⁴ |
| Ni | ≤ 0 | 0 |
| W99.95 % min excluding dopant residues | balance | — |
Class 2 Tungsten-SR — frequently asked
What is Class 2 Tungsten-SR used for?
Class 2 Tungsten-SR is typically used for incandescent lamp filaments, halogen lamp coils, high-temperature heating elements and vacuum furnace hardware. In short: sag-resistant doped tungsten; 2500 °C service in vacuum; standard lamp filament grade.
What is the yield strength of Class 2 Tungsten-SR?
Class 2 Tungsten-SR has a typical yield strength of 800 MPa (116 ksi) and a tensile strength of 1,050 MPa (152 ksi) — stronger than 56% of tungsten alloy grades. Strength varies by condition: see the 6 listed tempers.
Is Class 2 Tungsten-SR easy to machine?
Not especially — machinability is rated not recommended (10/100, better than 52% of tungsten alloy grades). Treat as a grinding/EDM material — diamond or CBN grinding, wire EDM and laser cutting dominate; if turning, use rigid setups, negative-rake carbide at low speed and preheat to 200–400 °C to avoid chipping.
Can Class 2 Tungsten-SR be welded?
Not readily — weldability is rated not recommended (12/100). Only electron-beam or laser welding in high vacuum gives usable joints, and the fusion zone recrystallizes to brittle coarse grains; vacuum brazing with Ni, Cu-Ag or Zr-based fillers is the preferred joining route.
What surface finishes work on Class 2 Tungsten-SR?
Chemically etch (alkaline ferricyanide or HF/HNO₃) or electropolish to remove drawing lubricant and surface defects; no anodizing — apply CVD/PVD or silicide coatings if oxidation protection above 500 °C is needed.
Can Class 2 Tungsten-SR be formed, bent or molded?
Cold forming is not feasible; bend, coil and draw warm (400–1200 °C depending on section) above the ductile-brittle transition, and avoid any post-recrystallization deformation.
What is the maximum service temperature of Class 2 Tungsten-SR?
Class 2 Tungsten-SR is rated for continuous use to about 2,500°C (4,532 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Class 2 Tungsten-SR and Class 2 Tungsten-FW?
SR is the default condition — default stocked condition for doped tungsten rod and wire: fibrous worked structure with residual stress removed, best balance of strength and handleability before service recrystallization. FW: heavily drawn AKS filament wire; pick for lamp/heater coils and cutting wire where ultra-high as-drawn tensile strength is required. Yield strength is 800 MPa in SR versus 2,600 MPa in FW.
Sources
- ASTM B760 — Tungsten Plate, Sheet, and Foil — ASTM International (2017)
- ASTM F288 — Tungsten Wire for Electron Devices and Lamps — ASTM International (2018)
- GB/T 3875 / GB/T 4181 (2017)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (Refractory Metals) — ASM International (1990)
- Tungsten — material properties and product forms — Plansee SE (2023)
- Thermophysical properties of tungsten — CRC Handbook of Chemistry and Physics (2020)
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.