Steel SK5 · finish state
Steel SK5-BT
Properties of the BT condition, compared with the other SK5 tempers.
Ready-to-use spring/shim strip: high elastic limit with enough toughness to bend and coil without re-heat-treating.
What is SK5-BT?
SK5-BT is SK5 supplied in the BT condition — ready-to-use spring/shim strip: high elastic limit with enough toughness to bend and coil without re-heat-treating. SK5-BT has a yield strength of 1,350 MPa (196 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 95% of steel grades. Elongation at break is 4% and the elastic modulus is 205 GPa (29.7 Msi). SK5-BT has a density of 7.82 g/cm³ (0.283 lb/in³), lighter than 82% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; BT is available on request or by drawing note.
Advantages
- High strength — 1,350 MPa (196 ksi), better than 95% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- Conducts heat well — 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades
Limitations
- Difficult to machine — 14/100, worse than 99% of steel grades
- Limited ductility — 4%, worse than 98% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 90% of steel grades
- Difficult to weld — 18/100, worse than 87% of steel grades
SK5-BT properties
Typical room-temperature values for SK5-BT — 11 properties are specific to this condition; the rest are grade-level values shared by every SK5 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
SK5-BT has a density of 7.82 g/cm³ (0.283 lb/in³), lighter than 82% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
SK5-BT has a yield strength of 1,350 MPa (196 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 95% of steel grades. Elongation at break is 4% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SK5-BT is rated for continuous service to 200°C (392 °F). It conducts heat at 48 W/m·K (27.7 BTU/hr·ft·°F), better than 79% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
SK5-BT conducts electricity at 9.5 % IACS, better than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 87% of steel grades.
Sustainability4
Producing a kilogram of SK5-BT takes about 27 MJ of energy and emits 2.1 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 30%.
Manufacturability8
SK5-BT's machinability is not recommended (14/100, worse than 99% of steel grades); weldability poor (18/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other SK5 tempers and conditions
SK5 is also supplied in 5 other conditions. The full side-by-side table is on the SK5 overview.
- HRDefaultCheapest starting stock for parts that will be re-annealed, machined or hardened afterwards.400 MPa yield · 200 HB
- Q&TWorking condition for cutting edges, saw teeth, scrapers and wear plates where maximum hardness matters more than toughness.1,650 MPa yield · 60 HRC
- BTReady-to-use spring/shim strip: high elastic limit with enough toughness to bend and coil without re-heat-treating.1,350 MPa yield · 47 HRC
- NormalizedUse to refine grain and homogenize forgings/hot-rolled stock before hardening, or where medium strength without quenching is enough.525 MPa yield · 31 HRC
- CRPick for blanking, stamping and forming operations followed by hardening; good gauge tolerance and surface.430 MPa yield · 210 HB
- AnnealedSoftest, most machinable and most formable condition; the standard delivery state for tool-steel bar prior to hardening.380 MPa yield · 185 HB
Working with SK5-BT
Is SK5 easy to machine?
Machine only in the annealed condition (≈45% of 1212) with sharp carbide or coated HSS tooling; once hardened above ~50 HRC, switch to grinding, EDM or hard turning with CBN.
Can SK5 be welded?
Poor weldability at 0.85% C — expect martensite and quench cracks; if unavoidable, preheat 250–350 °C, use low-hydrogen/austenitic filler and post-weld temper immediately.
Can SK5 be formed, bent or molded?
Blank, bend and coil in the soft/annealed temper with generous radii (≥2t) and well-lubricated tooling; blue-tempered strip forms only to spring-type radii, then stress-relieve at 200–260 °C.
What surface finishes work on SK5?
Not anodizable — protect with oil, phosphate/black oxide, electroless nickel, zinc or hard chrome; polish easily to a bright edge but keep humidity off unprotected surfaces.
SK5 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 |
|---|---|---|
| CJIS G 4401 SK5 / SK85 | 0.8 – 0.9 | 0.85 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.1 – 0.5 | 0.35 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Curesidual max | ≤ 0.25 | — |
| Niresidual max; Ni+Cr ≤ 0.35 | ≤ 0.25 | — |
| Crresidual max | ≤ 0.3 | — |
| Fe | balance | — |
SK5-BT — frequently asked
What is SK5-BT used for?
SK5-BT is typically used for hand tools, cold cutting knives, saw blades, doctor and scraper blades, spring clips and retainers and shims and feeler strip. In short: spring carbon steel sheet.
What is the yield strength of SK5-BT?
SK5-BT has a typical yield strength of 1,350 MPa (196 ksi) and a tensile strength of 1,550 MPa (225 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SK5-BT easy to machine?
Not especially — machinability is rated not recommended (14/100, worse than 99% of steel grades). Machine only in the annealed condition (≈45% of 1212) with sharp carbide or coated HSS tooling; once hardened above ~50 HRC, switch to grinding, EDM or hard turning with CBN.
Can SK5-BT be welded?
Not readily — weldability is rated poor (18/100). Poor weldability at 0.85% C — expect martensite and quench cracks; if unavoidable, preheat 250–350 °C, use low-hydrogen/austenitic filler and post-weld temper immediately.
What surface finishes work on SK5-BT?
Not anodizable — protect with oil, phosphate/black oxide, electroless nickel, zinc or hard chrome; polish easily to a bright edge but keep humidity off unprotected surfaces.
Can SK5-BT be formed, bent or molded?
Blank, bend and coil in the soft/annealed temper with generous radii (≥2t) and well-lubricated tooling; blue-tempered strip forms only to spring-type radii, then stress-relieve at 200–260 °C.
What is the maximum service temperature of SK5-BT?
SK5-BT is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SK5-HR and SK5-BT?
HR is the default condition — cheapest starting stock for parts that will be re-annealed, machined or hardened afterwards. BT: ready-to-use spring/shim strip: high elastic limit with enough toughness to bend and coil without re-heat-treating. Yield strength is 400 MPa in HR versus 1,350 MPa in BT.
Can FabDigit make parts in SK5-BT?
Yes — SK5-BT is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- JIS G 4401 Carbon tool steels (SK85/SK5) — JISC (2009)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (AISI 1080 data) — ASM International (1990)
- ASM Specialty Handbook — Tool Materials — ASM International (1995)
- GB/T 1298 (T8A/T9A comparison) — SAC (2008)
- Hardened & tempered / blue-tempered carbon spring strip datasheets — strip mill producers (e.g. Sandvik, Nippon Steel strip) (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.