Steel SK5
JIS SK5
SK5 is a Japanese carbon tool steel at roughly 0.8–0.9 % C (JIS SK family; cross-referenced to T8A and comparable to the T7–T9 AISI carbon tool steels), stocked hot rolled, cold rolled, annealed, normalized, quenched and tempered, or blue-tempered.
Values for the HR condition
SK5 tempers and conditions
SK5 is supplied in 6 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
spheroidize/full annealed (≤ 217 HB) | Softest, most machinable and most formable condition; the standard delivery state for tool-steel bar prior to hardening. | 380 | 640 | 20 | 185 HB | — |
HRDefault Hot rolled | Cheapest starting stock for parts that will be re-annealed, machined or hardened afterwards. | 400 | 710 | 12 | 200 HB | — |
Cold rolled | Pick for blanking, stamping and forming operations followed by hardening; good gauge tolerance and surface. | 430 | 720 | 10 | 210 HB | — |
austenitized ~900 °C, air cooled (fine pearlite) | Use to refine grain and homogenize forgings/hot-rolled stock before hardening, or where medium strength without quenching is enough. | 525 | 1,010 | 11 | 31 HRC | — |
Blue-tempered / hardened-and-tempered spring strip, 44–50 HRC | Ready-to-use spring/shim strip: high elastic limit with enough toughness to bend and coil without re-heat-treating. | 1,350 | 1,550 | 4 | 47 HRC | — |
Quenched and tempered | Working condition for cutting edges, saw teeth, scrapers and wear plates where maximum hardness matters more than toughness. | 1,650 | 2,000 | 2 | 60 HRC | — |
What is SK5?
SK5 is a Japanese carbon tool steel at roughly 0.8–0.9 % C (JIS SK family; cross-referenced to T8A and comparable to the T7–T9 AISI carbon tool steels), stocked hot rolled, cold rolled, annealed, normalized, quenched and tempered, or blue-tempered. Engineers use it for edge holding and spring behaviour in thin sections at low cost, mainly as strip and sheet. Annealed values are about 400 MPa yield, 710 MPa tensile, 12 % elongation and 200 HB, with service limited to about 350 °C. It has no corrosion resistance and poor weldability at this carbon level; 1090 or 1095 strip is the nearest alternative. SK5 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). SK5 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).
What is SK5 used for?
- Hand tools
- Cold cutting knives
- Saw blades
- Doctor and scraper blades
- Spring clips and retainers
- Shims and feeler strip
- Punch and die blanks
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
- High electrical conductivity — 9.5 % IACS, better than 75% 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 properties
Typical room-temperature values for SK5-HR; bars are the position among steel grades.
Physical3
SK5 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 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 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 conducts electricity at 9.5 % IACS, better than 75% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of SK5 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'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.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SK5 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SK5
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.
Manufacturability
The process limits FabDigit applies to SK5. Every SK5 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair36 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair30 / 100 |
|---|---|
| Weldability | Poor18 / 100 |
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SK5 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- JIS
- G 4401 SK5
- Similar grades
- T8A
How much does SK5 cost?
SK5 is a standard-cost steel ($$), cheaper than about 80% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SK5 — frequently asked
What is SK5 used for?
SK5 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?
SK5 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 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 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?
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 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?
SK5 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.
How much does SK5 cost?
SK5 is a standard-cost steel ($$), cheaper than about 80% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in SK5?
Yes — SK5 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.