The workhorse high-carbon tool steel — SK5 per JIS G4401, equivalent to GB T8Mn and AISI W1A-8. C 0.80–0.90%, Si ≤0.35%, Mn ≤0.50%. Quenched to 58–62 HRC with wear resistance for cutting tools, blades, woodworking tools and tape measures.
SKD11 (JIS, equivalent to D2 / 1.2379) is high-carbon, high-chromium cold-work tool steel with 12% Cr — deep hardening, excellent wear resistance, good dimensional stability, but 3–5x the material cost and requires more complex heat treatment. SK5 for simple, thin cutting tools where cost matters and the tool doesn't see heavy abrasive wear or high forming loads.
SK5 for simple, thin, cost-sensitive blades; SKD11 for heavy-duty, high-wear dies.440C is martensitic stainless tool steel (C ~1.0%, Cr ~17%) for cutting tools in corrosive environments — food processing, marine, surgical instruments. Reaches 56–60 HRC but is more expensive and harder to machine. SK5 for standard industrial and consumer cutting tools where corrosion is handled by plating, coating or the application environment.
SK5 for standard cutting tools; 440C for corrosive or hygienic environments.SK4 (C 0.90–1.00%) has higher carbon for slightly higher hardness and edge retention but lower toughness and more quench-cracking risk. SK85 is the newer JIS designation for essentially the same steel as SK5 (C 0.80–0.90%). SK5 is the balanced middle ground — sufficient hardness for most cutting applications with better toughness and quench safety than SK4. Standard for thin blades and tape measures.
SK5 for balanced hardness and toughness; SK4 for maximum edge retention.| Element | SK5 (JIS G4401) % | T8Mn (GB/T 1298) % | W1A-8 (AISI) % | Role |
|---|---|---|---|---|
| Carbon (C) | 0.80 – 0.90 | 0.80 – 0.90 | 0.80 – 0.90 | Provides hardness and wear resistance after quenching |
| Silicon (Si) | ≤ 0.35 | ≤ 0.35 | ≤ 0.30 | Deoxidizer; residual |
| Manganese (Mn) | ≤ 0.50 | 0.40 – 0.60 | ≤ 0.30 | Hardenability; T8Mn has slightly higher Mn |
| Phosphorus (P) | ≤ 0.030 | ≤ 0.030 | ≤ 0.025 | Residual; controlled for toughness |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 | ≤ 0.025 | Residual; controlled for edge quality |
Reference: JIS G4401; GB/T 1298; ASTM A680 (W1A-8). Values typical per standard, actual confirmed on MTC. Plain carbon tool steel — no intentional Cr, Mo or V.
| Condition | Hardness (typ.) | Tensile (typ.) | Typical use |
|---|---|---|---|
| Spheroidized annealed (as-supplied) | ≤ 192 HB | ~650 – 800 MPa | Blanking, forming, machining — part quenched afterwards |
| Pre-hardened (Q&T, as-supplied) | 45 – 55 HRC | ~1,400 – 1,800 MPa | Thin blades, tape measures, scrapers — blank and form, no further heat treat |
| Fully quenched (780–820°C) + tempered (150–200°C) | 58 – 62 HRC | ~2,000 – 2,300 MPa | Finished cutting tools, knives, woodworking blades — service condition |
Values typical per JIS G4401; actual confirmed on MTC. Shallow-hardening — through-hardens in ≤5 mm (water) or ≤2 mm (oil). Strip 0.10–2.0 mm through-hardens readily. Decarburization risk — use controlled atmosphere or allow grinding stock.
| Standard | Grade | C (%) | Mn (%) | Notes |
|---|---|---|---|---|
| JIS G4401 (Japan) | SK5 (also SK85) | 0.80 – 0.90 | ≤ 0.50 | Base reference; SK85 = newer designation |
| GB/T 1298 (China) | T8Mn | 0.80 – 0.90 | 0.40 – 0.60 | Slightly higher Mn for hardenability |
| ASTM A680 / AISI (USA) | W1A-8 / W2-8 | 0.80 – 0.90 | ≤ 0.30 | Water-hardening tool steel |
| DIN / EN (Germany/Europe) | C80W1 (1.1525) | 0.75 – 0.85 | ≤ 0.30 | German carbon tool steel |
Equivalents approximate. For safety-critical cutting tools, confirm full chemistry against your governing spec and the MTC.
0.40–1.20 mm strip, blanked in spheroidized state, quenched (800°C water) and tempered (180°C) to 58–62 HRC, ground. High C gives a hard, sharp edge with good wear resistance for cardboard, plastic, leather and soft metals. Shallow-hardening leaves a tougher core in thicker blades. See saw blade guide.
0.10–0.25 mm strip, supplied pre-hardened (Q&T to 45–52 HRC), blanked to length, printed with graduations, curved (concave) for stiffness. Pre-hardened means the manufacturer only blanks, prints and forms — no heat treatment. SK5's hardness (wear resistance of printed scale and hook) plus toughness (repeated flexing without breaking) makes it the standard tape measure material.
0.60–2.0 mm strip, blanked into planer blades, chisel blades, scraper blades and saw teeth, quenched and tempered to 58–62 HRC, ground. Holds a sharp edge for soft and medium hardwoods. Planer blades supplied as precision-ground flat stock with ±0.005 mm thickness tolerance so multiple blades mount without shimming.
0.30–1.50 mm strip, formed or blanked into cabinet scrapers, gasket scrapers, file blanks and chisel edges, quenched and tempered to 56–60 HRC. Good wear resistance and ability to take a keen edge suit hand tools that are resharpened repeatedly. For files, strip is serrated before hardening — high C ensures teeth harden to file-hard condition that cuts metal without dulling quickly.
Exact parameters confirmed for your section size and target hardness.
Before blanking/forming, spheroidize at 740–760°C then slow cool, producing globular cementite in ferrite. Gives soft, machinable condition (≤192 HB) for blanking, forming and machining. Ensures uniform quench response.
After forming, austenitize at 780–820°C (typically 800°C), hold 5–15 min per 25 mm. Too low = incomplete hardening; too high = grain growth and retained austenite, reducing toughness and edge stability. Controlled-atmosphere or salt-bath furnaces prevent decarburization.
Water quench standard for simple shapes — rapid cooling needed because SK5 is shallow-hardening (no alloying). Oil quench for complex shapes to reduce cracking/distortion, but only through-hardens in thinner sections (≤2 mm). For strip (0.10–2.0 mm), both give through-hardening. As-quenched: 62–65 HRC.
Temper 150–200°C for 1–2 hours to relieve quench stresses and reduce hardness to service range 58–62 HRC. Low-temp temper preserves max hardness and wear resistance while reducing brittleness. For pre-hardened strip (45–55 HRC), higher temper (300–400°C) achieves lower hardness needed for formability in tape measures and thin blades.
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