Tungsten Alloy Class 3 Tungsten-SR (Stress relieved)
Heat-treated state · default condition
ASTM B760 Class 3
The standard stocked condition: 0.5–6.4 mm ground TIG electrodes and instrument rod, worked fibre structure retained by a low-temperature stress relief.
Values for the SR condition
Other Class 3 Tungsten tempers and conditions
Class 3 Tungsten is listed in 5 conditions; see the grade overview at Class 3 Tungsten.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Sintered | Pick for large-section blanks, crucibles and stock destined for further hot working; brittle and only 92–97 % dense. | 250 | 300 | 0 | 30 HRC | 26 % IACS |
Recrystallized / annealed | The condition reached in service near the arc tip or after high-temperature annealing: lowest strength, essentially zero RT ductility, but best dimensional stability at temperature. | 400 | 500 | 0.5 | 36 HRC | 31 % IACS |
Swaged / hot-worked rod | Pick for larger-diameter rod and electrode blanks where full density and moderate strength are enough before finish drawing. | 700 | 900 | 2 | 43 HRC | 29 % IACS |
Sheet / plate, rolled and stress-relieved | Pick for X-ray targets, shielding, heat shields and sputter targets supplied per ASTM B760 flat product. | 700 | 850 | 3 | 43 HRC | 29 % IACS |
SRDefaultThis page Stress relieved | The standard stocked condition: 0.5–6.4 mm ground TIG electrodes and instrument rod, worked fibre structure retained by a low-temperature stress relief. | 900 | 1,100 | 2 | 46 HRC | 150 W/m·K |
What is Class 3 Tungsten-SR?
Class 3 Tungsten-SR is Class 3 Tungsten heat treated to SR — the standard stocked condition: 0.5–6.4 mm ground TIG electrodes and instrument rod, worked fibre structure retained by a low-temperature stress relief. Class 3 Tungsten-SR has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 69% of tungsten alloy grades. Elongation at break is 2% and the elastic modulus is 400 GPa (58 Msi). Class 3 Tungsten-SR has a density of 19 g/cm³ (0.686 lb/in³), lighter than 57% of tungsten alloy grades. It melts at 3,410°C (6,170 °F).
Advantages
- Good corrosion resistance — 70/100, better than 88% of tungsten alloy grades
Limitations
- Low fracture toughness — 10 MPa·√m (9.1 ksi·√in), worse than 83% of tungsten alloy grades
Class 3 Tungsten-SR properties
Typical room-temperature values for Class 3 Tungsten-SR; 11 are specific to this condition. Other listed values are Class 3 Tungsten reference data and may not represent this condition. Bars are the position among tungsten alloy grades.
Physical3
Class 3 Tungsten-SR has a density of 19 g/cm³ (0.686 lb/in³), lighter than 57% of tungsten alloy grades. It melts at 3,410°C (6,170 °F).
Mechanical14
Class 3 Tungsten-SR has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 69% of tungsten alloy grades. Elongation at break is 2% and the elastic modulus is 400 GPa (58 Msi).
Thermal6
Class 3 Tungsten-SR is rated for continuous service to 500°C (932 °F). It conducts heat at 150 W/m·K (86.7 BTU/hr·ft·°F), worse than 52% of tungsten alloy grades. Thermal expansion is 4.5 µm/m·K (2.5 µin/in·°F).
Electrical3
Class 3 Tungsten-SR conducts electricity at 30 % IACS, better than 64% of tungsten alloy grades.
Chemical & Environmental3
Corrosion resistance is very good (70/100), better than 88% of tungsten alloy grades.
Sustainability4
Producing a kilogram of Class 3 Tungsten-SR takes about 400 MJ of energy and emits 28 kg of CO₂ — more than 74% of tungsten alloy grades. Typical recycled content is 25%.
Manufacturability7
Class 3 Tungsten-SR's machinability is not recommended (10/100, better than 52% of tungsten alloy grades); weldability not recommended (10/100); formability not recommended (5/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Class 3 Tungsten-SR
Is Class 3 Tungsten easy to machine?
Treat as a brittle refractory: diamond/CVD grinding, EDM or wire EDM preferred; if turning, use carbide/CBN with heavy rigid setups and preheat 200–400 °C — and always wet-grind with local extraction and dust control because the swarf is mildly radioactive.
Can Class 3 Tungsten be welded?
Not a structural weld metal — fusion welds recrystallize and become glass-brittle; join by vacuum brazing (Ni, Cu-Ag, Pd-Ni) or electron-beam welding with preheat, or mechanically clamp/shrink-fit.
Can Class 3 Tungsten be formed, bent or molded?
Made by press-and-sinter of doped W/ThO₂ powder then hot swaging, rolling or drawing above ~1200 °C, with all bending/straightening done hot (>300–500 °C); cold forming cracks the material.
What surface finishes work on Class 3 Tungsten?
Supplied chemically cleaned or centerless-ground; electropolishing in NaOH gives smooth emitter tips, and CVD/PVD or plated Ni/Cu layers are used where oxidation above 500 °C must be blocked — no anodizing.
Class 3 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 |
|---|---|---|
| ThO22 % class (EWTh-2 / WT20); 1 % class EWTh-1 / WT10 runs 0.8–1.2 % | 1.7 – 2.2 | 2 |
| Fetypical impurity limit | ≤ 0.01 | 0 |
| Mo | ≤ 0.01 | 0.01 |
| C | ≤ 0.01 | 0 |
| Oexcluding the ThO₂ dispersoid | ≤ 0.01 | 0 |
| other impurities, total | ≤ 0.05 | 0.02 |
| W≥97.3 % W balance | balance | — |
Class 3 Tungsten-SR — frequently asked
What is Class 3 Tungsten-SR used for?
Class 3 Tungsten-SR is typically used for TIG welding electrodes, electron emitters, vacuum tube cathodes and high-current arc components. In short: low work function emitter; classic thoriated TIG electrode; mildly radioactive swarf.
What is the yield strength of Class 3 Tungsten-SR?
Class 3 Tungsten-SR has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 69% of tungsten alloy grades. Strength varies by condition: see the 5 listed tempers.
Is Class 3 Tungsten-SR easy to machine?
Not especially — machinability is rated not recommended (10/100, better than 52% of tungsten alloy grades). Treat as a brittle refractory: diamond/CVD grinding, EDM or wire EDM preferred; if turning, use carbide/CBN with heavy rigid setups and preheat 200–400 °C — and always wet-grind with local extraction and dust control because the swarf is mildly radioactive.
Can Class 3 Tungsten-SR be welded?
Not readily — weldability is rated not recommended (10/100). Not a structural weld metal — fusion welds recrystallize and become glass-brittle; join by vacuum brazing (Ni, Cu-Ag, Pd-Ni) or electron-beam welding with preheat, or mechanically clamp/shrink-fit.
What surface finishes work on Class 3 Tungsten-SR?
Supplied chemically cleaned or centerless-ground; electropolishing in NaOH gives smooth emitter tips, and CVD/PVD or plated Ni/Cu layers are used where oxidation above 500 °C must be blocked — no anodizing.
Can Class 3 Tungsten-SR be formed, bent or molded?
Made by press-and-sinter of doped W/ThO₂ powder then hot swaging, rolling or drawing above ~1200 °C, with all bending/straightening done hot (>300–500 °C); cold forming cracks the material.
What is the maximum service temperature of Class 3 Tungsten-SR?
Class 3 Tungsten-SR is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Class 3 Tungsten-SR and Class 3 Tungsten SINT?
SR is the default condition — the standard stocked condition: 0.5–6.4 mm ground TIG electrodes and instrument rod, worked fibre structure retained by a low-temperature stress relief. SINT: pick for large-section blanks, crucibles and stock destined for further hot working; brittle and only 92–97 % dense. Yield strength is 900 MPa in SR versus 250 MPa in SINT.
Sources
- AWS A5.12/A5.12M — Tungsten and Tungsten-Alloy Electrodes for Arc Welding and Cutting (EWTh-2) — AWS (2009)
- ASTM B760 — Tungsten Plate, Sheet, and Foil — ASTM International (2017)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (Refractory Metals) — ASM International (1990)
- Tungsten materials and electrode datasheets — Plansee SE / / Midwest Tungsten (2023)
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.