Precious Metal B540-SR (Stress relieved)
Heat-treated state
GB B540
Pick when formed contact springs and rivets need dimensional stability and reduced springback distortion without losing all cold-work strength.
Values for the SR condition
Other B540 tempers and conditions
B540 is listed in 4 conditions; see the grade overview at B540.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SADefault Solution annealed | Standard stocked soft temper for stamping, drawing and cladding of contact strip and wire; maximum ductility and lowest contact resistance. | 55 | 195 | 35 | 44 HB | 16 % IACS |
SRThis page Stress relieved | Pick when formed contact springs and rivets need dimensional stability and reduced springback distortion without losing all cold-work strength. | 170 | 260 | 22 | 68 HB | 15.5 % IACS |
Ductile hardened | Choose for sliding contacts, brushes and formed springs needing higher hardness and wear life while still permitting bending and riveting. | 280 | 330 | 10 | 100 HB | 14.8 % IACS |
Age (order) hardened Pd-Cu / Pd-Ag-Cu alloy grade | Use for high-wear, low-force sliding contacts, slip rings and probe tips where maximum hardness and erosion resistance are needed; applies to the ordering Pd-Cu/Pd-Ag-Cu alloy grades, not to pure palladium. | 550 | 750 | 8 | 22 HRC | 6 % IACS |
What is B540-SR?
B540-SR is B540 heat treated to SR — pick when formed contact springs and rivets need dimensional stability and reduced springback distortion without losing all cold-work strength. B540-SR has a yield strength of 170 MPa (24.7 ksi) and a tensile strength of 260 MPa (37.7 ksi) — weaker than 64% of precious metal grades. Elongation at break is 22% and the elastic modulus is 121 GPa (17.5 Msi). B540-SR has a density of 12.02 g/cm³ (0.434 lb/in³), heavier than 67% of precious metal grades. It melts at 1,554°C (2,829 °F). SA is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Readily welded — 80/100, better than 87% of precious metal grades
- Good corrosion resistance — 95/100, better than 82% of precious metal grades
- Stiff — 121 GPa (17.5 Msi), better than 80% of precious metal grades
B540-SR properties
Typical room-temperature values for B540-SR; 13 are specific to this condition. Other listed values are B540 reference data and may not represent this condition. Bars are the position among precious metal grades.
Physical3
B540-SR has a density of 12.02 g/cm³ (0.434 lb/in³), heavier than 67% of precious metal grades. It melts at 1,554°C (2,829 °F).
Mechanical12
B540-SR has a yield strength of 170 MPa (24.7 ksi) and a tensile strength of 260 MPa (37.7 ksi) — weaker than 64% of precious metal grades. Elongation at break is 22% and the elastic modulus is 121 GPa (17.5 Msi).
Thermal6
B540-SR is rated for continuous service to 350°C (662 °F). It conducts heat at 71.8 W/m·K (41.5 BTU/hr·ft·°F), worse than 60% of precious metal grades. Thermal expansion is 11.8 µm/m·K (6.56 µin/in·°F).
Electrical3
B540-SR conducts electricity at 15.5 % IACS, worse than 62% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is excellent (95/100), better than 82% of precious metal grades.
Sustainability4
Producing a kilogram of B540-SR takes about 55,000 MJ of energy and emits 3,900 kg of CO₂ — more than 62% of precious metal grades. Typical recycled content is 60%.
Manufacturability8
B540-SR's machinability is fair (38/100, worse than 66% of precious metal grades); weldability very good (80/100); formability very good (75/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with B540-SR
Is B540 easy to machine?
Soft and gummy — use sharp positive-rake carbide/diamond tools, high speed, light feed and copious lubrication; collect all chips for refining.
Can B540 be welded?
Resistance, laser and micro-TIG welding of contacts to Cu/CuNi carriers is routine; avoid hydrogen-rich flames to prevent H absorption and embrittlement.
Can B540 be formed, bent or molded?
Excellent cold formability in the annealed temper (stamping, deep drawing, cladding to Ag/Cu strip); interanneal at 700–900 °C in clean inert or slightly oxidizing atmosphere.
What surface finishes work on B540?
No anodizing; finish by polishing, electropolishing or thin Au/Rh flash plating to suppress organic 'brown powder' formation in dry-circuit switching.
B540 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.
| Element | Spec limit (wt %) |
|---|---|
| Ptimpurity limit, pure grade | ≤ 0.02 |
| Rhimpurity limit | ≤ 0.02 |
| Ir+Ruimpurity limit | ≤ 0.02 |
| Feimpurity limit | ≤ 0.01 |
| Cuimpurity limit, pure grade | ≤ 0.01 |
| Pbimpurity limit | ≤ 0 |
| Other elements, totalsum of impurities | ≤ 0.05 |
| PdPure palladium contact grade of ASTM B540; alloy grades of the same specification substitute Ag (up to ~40 %), Cu (up to ~40 %) or Ru (up to ~10 %) for part of the Pd | ≥ 99.95 (balance) |
B540-SR — frequently asked
What is B540-SR used for?
B540-SR is typically used for telecom relays, low-power switches and dry-circuit contacts. In short: tarnish-resistant palladium contact; softest, most formable grade here; dry-circuit relay standard.
What is the yield strength of B540-SR?
B540-SR has a typical yield strength of 170 MPa (24.7 ksi) and a tensile strength of 260 MPa (37.7 ksi) — weaker than 64% of precious metal grades. Strength varies by condition: see the 4 listed tempers.
Is B540-SR easy to machine?
Not especially — machinability is rated fair (38/100, worse than 66% of precious metal grades). Soft and gummy — use sharp positive-rake carbide/diamond tools, high speed, light feed and copious lubrication; collect all chips for refining.
Can B540-SR be welded?
Yes — weldability is rated very good (80/100). Resistance, laser and micro-TIG welding of contacts to Cu/CuNi carriers is routine; avoid hydrogen-rich flames to prevent H absorption and embrittlement.
What surface finishes work on B540-SR?
No anodizing; finish by polishing, electropolishing or thin Au/Rh flash plating to suppress organic 'brown powder' formation in dry-circuit switching.
Can B540-SR be formed, bent or molded?
Excellent cold formability in the annealed temper (stamping, deep drawing, cladding to Ag/Cu strip); interanneal at 700–900 °C in clean inert or slightly oxidizing atmosphere.
What is the maximum service temperature of B540-SR?
B540-SR is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between B540-SA and B540-AH?
SA is the default condition — standard stocked soft temper for stamping, drawing and cladding of contact strip and wire; maximum ductility and lowest contact resistance. AH: use for high-wear, low-force sliding contacts, slip rings and probe tips where maximum hardness and erosion resistance are needed; applies to the ordering Pd-Cu/Pd-Ag-Cu alloy grades, not to pure palladium. Yield strength is 55 MPa in SA versus 550 MPa in AH.
Sources
- ASTM B540 — Standard Specification for Palladium Electrical Contact Material — ASTM International (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (Precious Metals & Electrical Contact Materials) — ASM International (1990)
- Precious Metal Contact Materials — Palladium and Palladium Alloys — Johnson Matthey (2020)
- CRC Handbook of Chemistry and Physics — Physical Properties of the Elements (Pd) — CRC Press (2022)
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.