Steel SK5 · supply condition · default condition
Steel SK5-HR
Properties of the HR condition, compared with the other SK5 tempers.
Cheapest starting stock for parts that will be re-annealed, machined or hardened afterwards.
What is SK5-HR?
SK5-HR is SK5 supplied in the HR condition — cheapest starting stock for parts that will be re-annealed, machined or hardened afterwards. SK5-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). SK5-HR 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).
Advantages
- 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
- 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
- Limited ductility — 12%, worse than 84% of steel grades
- Difficult to machine — 36/100, worse than 81% of steel grades
SK5-HR properties
Typical room-temperature values for SK5-HR — 13 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-HR 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-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SK5-HR is rated for continuous service to 350°C (662 °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-HR 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-HR 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-HR's machinability is fair (36/100, worse than 81% of steel grades); weldability poor (18/100); formability poor (30/100).
Common Calculations5
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-HR
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-HR — frequently asked
What is SK5-HR used for?
SK5-HR 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-HR?
SK5-HR has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SK5-HR easy to machine?
Not especially — machinability is rated fair (36/100, worse than 81% 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-HR 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-HR?
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-HR 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-HR?
SK5-HR 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 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-HR?
Yes — SK5-HR 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.