SKD12 Tool Steel
SKD12 is a Japanese standard cold work tool steel, classified under JIS (Japanese Industrial Standards) G4404. It belongs to the chromium-molybdenum-vanadium alloy system and is primarily valued for its high hardness, wear resistance, and dimensional stability after heat treatment. Designed for cold working applications where tools endure high mechanical stress and abrasion, SKD12 is widely used in mold and die manufacturing. Below is a detailed overview:
Chemical Composition
The typical chemical composition of SKD12 tool steel is as follows:
Element Content Range Role
Carbon (C) 0.95–1.05% Forms carbides with alloying elements to enhance hardness and wear resistance; moderate content balances toughness and hardness.
Chromium (Cr) 4.75–5.50% Improves hardenability, wear resistance, and corrosion resistance; promotes the formation of chromium carbides to enhance abrasion resistance.
Molybdenum (Mo) 0.90–1.40% Significantly enhances hardenability and tempering stability, reduces overheating tendency, and improves strength retention at high temperatures.
Vanadium (V) 0.40–0.60% Refines grain structure, inhibits austenite grain growth, and enhances wear resistance and impact resistance.
Manganese (Mn) 0.40–0.60% Assists in improving hardenability and reduces the critical cooling rate of the steel.
Silicon (Si) 0.20–0.40% Improves oxidation resistance and mechanical properties of the steel, aiding in deoxidation.
Phosphorus (P) ≤0.030% Minimized to avoid embrittlement and machining defects.
Sulfur (S) ≤0.030% Low sulfur content ensures steel purity and toughness.
Key Properties
SKD12 tool steel is engineered to excel in cold working applications, with properties optimized for durability and precision:
1. High Hardness and Wear Resistance
After heat treatment, SKD12 achieves a high hardness of 58–62 HRC, thanks to its high carbon and chromium content. This, combined with the formation of hard chromium carbides, provides exceptional resistance to abrasion and wear—critical for tools in cold stamping, blanking, or forming operations.
2. Good Dimensional Stability
Exhibits minimal distortion during heat treatment, ensuring tight tolerances in finished tools and molds. This stability is essential for precision components like dies or punches where dimensional accuracy directly impacts part quality.
3. Moderate Toughness
While prioritizing hardness and wear resistance, SKD12 retains sufficient toughness to resist chipping or cracking under moderate impact loads, making it suitable for non-severe cold working applications.
4. Corrosion Resistance
The high chromium content (11–13%) grants SKD12 basic corrosion resistance, protecting against rust and mild chemical exposure during storage or light-duty use.
5. Machinability in Annealed State
In its annealed form (hardness ≤255 HBW), SKD12 can be machined (milled, ground, or drilled) with relative ease, allowing for precise fabrication of complex tool geometries before final heat treatment.
Physical Properties
Density: ~7.85 g/cm³
Melting Point: ~1430–1470°C
Thermal Expansion Coefficient: ~10.5×10⁻⁶/K (at 20–200°C)
Thermal Conductivity: ~25 W/(m·K) (at room temperature)
Mechanical Properties (After Heat Treatment)
Property Typical Value
Hardness 58–62 HRC (quenched and tempered)
Tensile Strength (Rm) ~2000–2400 MPa
Yield Strength (Rp0.2) ~1800–2200 MPa
Impact Toughness (Charpy V-notch) ~8–12 J/cm² (at room temperature)
Heat Treatment Process
Proper heat treatment is critical to maximize SKD12’s hardness, wear resistance, and dimensional stability:
1. Annealing
Purpose: Soften the steel for machining and reduce internal stress.
Process: Heat to 800–850°C, hold for 2–4 hours, then furnace cool slowly (≤50°C/hour) to below 500°C before air cooling.
Result: Hardness ≤255 HBW, improving machinability.
2. Quenching
Purpose: Harden the steel by transforming austenite to martensite, forming hard carbides.
Preheating: Heat to 600–700°C to avoid thermal shock, then raise to 850–900°C for uniform heating.
Austenitizing: Heat to 950–1000°C, hold for 20–40 minutes (depending on section thickness) to dissolve carbides evenly.
Cooling: Quench in oil or air (oil quenching for deeper hardness; air quenching for minimal distortion in small parts).
3. Tempering
Purpose: Relieve quenching stress, reduce brittleness, and stabilize hardness.
Process: Temper at 150–200°C for 1–2 hours per 25mm thickness, then air cool. For enhanced toughness (with slight hardness reduction), temper at 250–300°C.
Result: Hardness of 58–62 HRC with optimal wear resistance and minimal distortion.
Application Fields
SKD12 tool steel is widely used in cold working applications requiring high wear resistance and precision:
Cold Stamping Dies: Ideal for blanking dies, piercing dies, and bending dies used in metal sheet forming (e.g., automotive parts, electronic components).
Cold Forging Tools: Suitable for punches, dies, and mandrels in cold forging operations, where resistance to abrasion and deformation is critical.
Cutting Tools: Used for low-speed cutting tools like knives, shears, and slitting blades for metal or non-metallic materials.
Precision Molds: Applied in molds for cold extrusion, drawing, or thread rolling, leveraging its dimensional stability and wear resistance.
Measuring Tools: Utilized in gauges and fixtures requiring high hardness and dimensional accuracy.
Comparison with Similar Steels
Feature SKD62 Tool Steel D2 Tool Steel (Cr12Mo1V1) O1 Tool Steel (Oil-Hardening Carbon Steel)
Carbon Content 0.95–1.05% 1.40–1.60% 0.85–0.95%
Chromium Content 4.75–5.50% 11.50–13.00% 0.40–0.60%
Hardness (HRC) 57–60 58–62 55–58
Toughness High Low Moderate
Hardenability High (air-quenchable) High Low (requires oil quenching)
Wear Resistance Good Excellent Moderate
Best For Cold working molds needing toughness High-wear, low-impact scenarios Simple cold work tools, cost-sensitive needs
SKD12 tool steel is a reliable choice for cold working applications, offering a strong balance of high hardness, wear resistance, and dimensional stability. Its suitability for precision machining in the annealed state and minimal heat treatment distortion make it a practical material for manufacturing cold stamping dies, forging tools, and cutting implements. While toughness is moderate, SKD12 excels in scenarios where wear resistance and precision are prioritized, ensuring long tool life in demanding cold working environments.