Steel SK4-N (Normalized)
Heat-treated state
JIS SK4
Air-cooled from ~800–850 °C to break up network carbide and refine grain before hardening.
Values for the N condition
Other SK4 tempers and conditions
SK4 is listed in 10 conditions; see the grade overview at SK4.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stocked condition for bar and strip: softest state for machining, blanking and forming before hardening. | 400 | 670 | 18 | 190 HB | — |
Hot rolled | As-rolled bar and flats, usually re-annealed before machining; cheapest input form. | 450 | 780 | 12 | 22 HRC | 9.5 % IACS |
NThis page Normalized | Air-cooled from ~800–850 °C to break up network carbide and refine grain before hardening. | 500 | 850 | 10 | 25 HRC | 9.5 % IACS |
Cold drawn | Cold-drawn round or flat bar with tight size and clean surface for pin, punch and shaft blanks. | 620 | 800 | 9 | 22 HRC | 9.5 % IACS |
CR ½H | Partially cold-rolled strip for parts that still need moderate bending before hardening. | 750 | 900 | 6 | 30 HRC | 9.3 % IACS |
Cold rolled strip, full hard (spring temper) | Fully work-hardened strip supplied ready-to-use for flat springs, clips and shim blades without heat treatment. | 1,100 | 1,250 | 2 | 43 HRC | 9.2 % IACS |
Q&T 44–48 HRC | Toughest heat-treated condition, used for coil and leaf springs and shock-loaded tooling. | 1,320 | 1,500 | 6 | 46 HRC | 9.2 % IACS |
Q&T 50–55 HRC | Impact-tolerant tool condition for cold chisels, striking punches and shear blades. | 1,500 | 1,750 | 3 | 52 HRC | 9 % IACS |
Q&T 56–60 HRC | Slightly tougher edge condition for punches, chisels and woodworking blades that see impact. | 1,650 | 1,950 | 1 | 58 HRC | 8.5 % IACS |
Q&T 60–63 HRC | Maximum-hardness condition for knife edges, razors, files, scrapers and wear inserts in thin sections. | 1,800 | 2,100 | 1 | 61 HRC | — |
What is SK4-N?
SK4-N is SK4 heat treated to N — air-cooled from ~800–850 °C to break up network carbide and refine grain before hardening. SK4-N has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 63% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi). SK4-N has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F). A is the default condition FabDigit quotes; N is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High electrical conductivity — 9.5 % IACS, better than 75% of steel grades
Limitations
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
- Difficult to machine — 33/100, worse than 86% of steel grades
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
- Limited formability — 22/100, worse than 76% of steel grades
SK4-N properties
Typical room-temperature values for SK4-N; 23 are specific to this condition. Other listed values are SK4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SK4-N has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
SK4-N has a yield strength of 500 MPa (72.5 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 63% of steel grades. Elongation at break is 10% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SK4-N is rated for continuous service to 250°C (482 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
SK4-N 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 SK4-N takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability8
SK4-N's machinability is poor (33/100, worse than 86% of steel grades); weldability not recommended (12/100); formability poor (22/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SK4-N
Is SK4 easy to machine?
Machine only in the spheroidize-annealed state (~45 % of AISI 1212) with sharp carbide or HSS tooling and good coolant; after hardening, only grinding and EDM are practical.
Can SK4 be welded?
Effectively non-weldable for structural joints — high carbon gives hard, crack-prone martensite; if unavoidable, preheat 250–350 °C, use low-hydrogen filler and post-weld temper immediately.
Can SK4 be formed, bent or molded?
Anneal before blanking or bending; cold-rolled strip work-hardens rapidly, so use generous bend radii, and hot-forge at 1050–850 °C followed by slow cooling and spheroidize annealing.
What surface finishes work on SK4?
Grinds and laps to a fine, high-polish edge; protect with oil, black oxide, phosphate or thin plating (bake after plating to avoid hydrogen embrittlement) since bare surfaces rust quickly.
SK4 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 SK95 (old SK4) | 0.9 – 1 | 0.95 |
| Si | 0.1 – 0.35 | 0.22 |
| Mn | 0.1 – 0.5 | 0.35 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Curesidual | ≤ 0.25 | — |
| Niresidual | ≤ 0.25 | — |
| Crresidual | ≤ 0.3 | — |
| Fe | balance | — |
SK4-N — frequently asked
What is SK4-N used for?
SK4-N is typically used for springs, blades, saws and hand tools. In short: tougher than SK3; spring and blade tool steel; hard strip supplied ready to form.
What is the yield strength of SK4-N?
SK4-N has a typical yield strength of 500 MPa (72.5 ksi) and a tensile strength of 850 MPa (123 ksi) — stronger than 63% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is SK4-N easy to machine?
Not especially — machinability is rated poor (33/100, worse than 86% of steel grades). Machine only in the spheroidize-annealed state (~45 % of AISI 1212) with sharp carbide or HSS tooling and good coolant; after hardening, only grinding and EDM are practical.
Can SK4-N be welded?
Not readily — weldability is rated not recommended (12/100). Effectively non-weldable for structural joints — high carbon gives hard, crack-prone martensite; if unavoidable, preheat 250–350 °C, use low-hydrogen filler and post-weld temper immediately.
What surface finishes work on SK4-N?
Grinds and laps to a fine, high-polish edge; protect with oil, black oxide, phosphate or thin plating (bake after plating to avoid hydrogen embrittlement) since bare surfaces rust quickly.
Can SK4-N be formed, bent or molded?
Anneal before blanking or bending; cold-rolled strip work-hardens rapidly, so use generous bend radii, and hot-forge at 1050–850 °C followed by slow cooling and spheroidize annealing.
What is the maximum service temperature of SK4-N?
SK4-N is rated for continuous use to about 250°C (482 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SK4-A and SK4 QT60-63?
A is the default condition — standard stocked condition for bar and strip: softest state for machining, blanking and forming before hardening. QT60-63: maximum-hardness condition for knife edges, razors, files, scrapers and wear inserts in thin sections. Yield strength is 400 MPa in A versus 1,800 MPa in QT60-63.
Sources
- JIS G 4401 — Carbon tool steels (SK95, formerly SK4) — JSA (2009)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4 — Heat Treating (carbon tool steels W-series) — ASM International (1991)
- ASM Handbook Vol. 16 — Machining (machinability ratings) — ASM International (1989)
- GB/T 1298 — Carbon tool steels (T9A/T10A comparison) — SAC (2008)
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.