SKD61 vs SKD11 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SKD61 and SKD11 are two widely used JIS tool-steel designations that present a common selection dilemma for engineers, procurement managers, and manufacturing planners: choose an alloy optimized for elevated-temperature service and thermal fatigue resistance, or choose one optimized for maximum abrasive wear resistance and dimensional stability in cold working. Decisions typically hinge on operating temperature, expected wear mode, required toughness, weldability, and total life-cycle cost.
SKD61 (JIS) corresponds broadly to AISI H13 (hot-work tool steel) and prioritizes hot-hardness, thermal fatigue resistance, and toughness. SKD11 (JIS) corresponds to AISI D2 (high-carbon, high-chromium cold-work tool steel) and prioritizes high hardness and wear resistance through a high carbide fraction. These functional differences explain why they are often compared in die design, tooling, and component selection.
1. Standards and Designations
- JIS: SKD61 (hot-work tool steel), SKD11 (cold-work tool steel)
- AISI/ASTM equivalents: SKD61 ≈ H13; SKD11 ≈ D2
- EN: H13 equivalents exist under EN X40CrMoV5-1 family; D2 corresponds to EN X153CrMoV12.
- GB (China): SKD61 ~ Cr5MoV; SKD11 ~ Cr12MoV.
Classification:
- SKD61: alloy tool steel (hot-work)
- SKD11: high-carbon, high-chromium cold-work tool steel (alloy/tool)
2. Chemical Composition and Alloying Strategy
| Element | Typical SKD61 (H13) wt% | Typical SKD11 (D2) wt% |
|---|---|---|
| C | 0.32 – 0.45 | 1.40 – 1.60 |
| Mn | 0.20 – 0.50 | 0.30 – 0.60 |
| Si | 0.80 – 1.20 | 0.20 – 0.50 |
| P | ≤ 0.030 | ≤ 0.035 |
| S | ≤ 0.030 | ≤ 0.035 |
| Cr | 4.75 – 5.50 | 11.0 – 13.0 |
| Ni | ≤ 0.30 | ≤ 0.30 |
| Mo | 1.10 – 1.75 | 0.70 – 1.50 |
| V | 0.80 – 1.20 | 0.90 – 1.20 |
| Nb, Ti, B, N | typically trace | typically trace |
How alloying affects performance: - Carbon: drives hardness and carbide volume. SKD11’s high C produces abundant carbides for wear resistance; SKD61’s moderate C balances hardenability and toughness for hot work. - Chromium: increases hardenability and provides corrosion resistance and carbide-forming capacity. SKD11’s high Cr forms large carbide networks for abrasion resistance; SKD61’s moderate Cr contributes to oxidation and high-temperature strength. - Molybdenum and Vanadium: form fine, hard carbides that improve secondary hardening, creep resistance, and wear behavior. SKD61 uses Mo and V for hot-strength and temper resistance; SKD11 uses them to stabilize carbides for wear resistance. - Silicon and Manganese: deoxidation and hardenability modifiers; Si in SKD61 helps high-temperature strength.
Overall, SKD61’s composition targets tempering resistance and thermal-fatigue performance; SKD11’s composition targets high carbide volume and wear resistance for cold-forming applications.
3. Microstructure and Heat Treatment Response
Microstructures: - SKD61 (H13): tempered martensite matrix with dispersed alloy carbides (Mo-rich and V-rich carbides). After appropriate austenitizing and tempering, the matrix retains good toughness and high-temperature strength; carbides are relatively fine and well-distributed. - SKD11 (D2): martensitic matrix with a high volume fraction of hard chromium-rich carbides (M7C3/M23C6/VC), often in a semi-continuous network depending on heat treatment. Carbides confer high wear resistance but reduce ductility and impact toughness.
Typical heat-treatment behavior: - SKD61: austenitize in the range commonly near 1000–1030 °C, quench (usually oil) and perform multi-stage tempering at 500–600 °C. SKD61 responds well to tempering cycles that produce secondary hardening, improving hot strength and toughness. It tolerates thermal cycling better than SKD11. - SKD11: typically air- or oil-hardening after austenitizing near 1000–1030 °C and requires double tempering (often around 500–550 °C). D2/SKD11 often benefits from cryogenic treatment to reduce retained austenite and stabilize hardness. SKD11 microstructure is less tolerant of rapid thermal cycling; tempering must be managed to retain hardness while reducing brittleness.
Processing routes such as normalizing, controlled forging, or thermo-mechanical treatments improve grain refinement and toughness in both grades, but SKD61 gains relatively more toughness benefit from such conditioning.
4. Mechanical Properties
| Property | SKD61 (typical, heat-treated) | SKD11 (typical, heat-treated) |
|---|---|---|
| Hardness (HRC) | 44 – 52 HRC (typical service range) | 56 – 62 HRC (common for cold-work tooling) |
| Tensile strength (MPa) | ~1000 – 1400 MPa (varies widely with temper) | ~1300 – 1800 MPa (higher when fully hardened) |
| Yield strength (MPa) | ~800 – 1100 MPa | ~1000 – 1500 MPa |
| Elongation (%) | 6 – 15% (depends on temper and section) | 3 – 8% (lower due to carbides) |
| Impact toughness (J, qualitative) | Relatively high (good toughness) | Low to moderate (brittle tendency) |
Interpretation: - Strength: SKD11 can achieve higher peak hardness and static strength due to higher carbon and carbide content. - Toughness/Ductility: SKD61 is significantly tougher and more ductile, especially at elevated temperatures and under thermal cycling. - Wear resistance: SKD11 typically exhibits superior abrasive wear resistance; SKD61 offers good wear resistance balanced with thermal fatigue resistance.
5. Weldability
Weldability considerations hinge on carbon equivalent and hardenability. Two useful empirical indices:
-
International Institute of Welding carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
-
Dearden–O’Neill (Pcm) parameter: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - SKD11 (high C, high Cr) produces a high $CE_{IIW}$ and $P_{cm}$, indicating poor weldability and high tendency for hard, brittle martensite and cracking in the heat-affected zone. Preheat, controlled interpass temperatures, and post-weld heat treatment (PWHT) are normally required; even then, welding should be minimized. - SKD61 has a lower carbon equivalence and is more weldable than SKD11, but still requires preheat and PWHT for large cross-sections or critical tooling. The presence of Mo and V increases hardenability somewhat, so weld procedure controls are necessary to avoid HAZ cracking.
Practical advice: For both grades, welding consumables matched to tool-steel families and qualified welding procedures are essential. When possible, design for mechanical joining or use removable inserts to avoid welding.
6. Corrosion and Surface Protection
- Neither SKD61 nor SKD11 are stainless steels; both are susceptible to corrosion and surface oxidation in humid or corrosive environments.
- Typical protection strategies: painting, phosphating, oiling, plating (e.g., nickel or hard chrome), or local surface coatings (PVD/CVD, nitriding) depending on wear/corrosion demands.
- PREN (pitting resistance equivalent number) is used for stainless selection: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index is not applicable to SKD61 or SKD11 because they are not stainless alloys; chromium in SKD11 contributes to carbide formation and wear resistance, not to stainless behavior.
For elevated-temperature oxidation (hot work), SKD61’s alloying (Cr, Mo) provides better scale resistance than SKD11, making SKD61 preferable for hot dies exposed to cyclic oxidizing atmospheres.
7. Fabrication, Machinability, and Formability
- Machinability: SKD61 (lower carbon, fewer carbides) machines better than SKD11. Cutting tools, feeds, and speeds must be adjusted for hardened states; SKD11 is abrasive and accelerates tool wear.
- Formability/bendability: SKD61 is more formable in annealed condition and can be forged/normalized more readily prior to final heat treatment. SKD11 has poor plastic formability in hardened condition and is typically shaped in annealed condition with careful control to avoid carbide fracture.
- Surface finishing: SKD11 requires more aggressive grinding and polishing effort due to hard carbides; EDM is commonly used for intricate features in both grades but electrode wear rates will be higher for SKD11.
- Secondary treatments: Both accept nitriding, but responses differ—SKD61 benefits from nitriding for wear and surface hardness without drastic brittleness; SKD11’s high chromium can complicate nitriding diffusion and adhesion.
8. Typical Applications
| SKD61 (H13) – Typical Uses | SKD11 (D2) – Typical Uses |
|---|---|
| Hot forging dies, extrusion dies, die-casting cores, hot shear blades, hot stamping dies | Cold punches and dies, blanking dies, shear blades, forming dies, gauge components |
| Hot work tooling exposed to thermal cycling and high temperatures | Long-run cold-work tooling where abrasive wear and dimensional stability are dominant |
| Injection molding inserts with thermal load | Wear components in stamping or blanking lines |
Selection rationale: - Choose SKD61 when tooling faces high temperatures, thermal shock, or needs good toughness and temper resistance. - Choose SKD11 when the primary failure mode is abrasive wear at lower temperatures and the tooling benefits from very high hardness and dimensional stability.
9. Cost and Availability
- Cost: SKD11 is often more expensive per kilogram in finished tool form due to higher alloy content and additional machining/grinding time required; SKD61 is generally more economical for larger hot-work tooling volumes.
- Availability: Both grades are commonly stocked as bar, plate, and forgings. SKD61 is especially ubiquitous in hot-work forms; SKD11 is widely available for cold-work tooling but may require longer lead times for large or special-machined parts due to hardenability and machining challenges.
- Supply forms: SKD61 often supplied as forged blocks, air-melted bars, and normalized billets tailored for large dies; SKD11 commonly supplied in pre-hardened plates and bars designed for precision tooling.
10. Summary and Recommendation
| Attribute | SKD61 (H13) | SKD11 (D2) |
|---|---|---|
| Weldability | Fair (requires controls) | Poor (difficult; requires strict PWHT) |
| Strength–Toughness balance | Good (high toughness, good hot strength) | High hardness but low toughness |
| Cost (relative) | Lower-to-moderate | Moderate-to-higher |
Choose SKD61 if:
- The application exposes the tool or component to elevated temperatures, thermal cycling, or shock (hot forging, die casting, hot trimming).
- You need a good balance of toughness, temper resistance, and reparability (weldability) for maintenance.
- You prioritize resistance to thermal fatigue and the ability to be reworked without excessive carbide-related brittleness.
Choose SKD11 if:
- The primary failure mode is abrasive or adhesive wear at ambient or moderately elevated temperatures (cold blanking, fine piercing, long-run stamping).
- You require very high surface hardness and dimensional stability under cold-working loads.
- You accept more challenging machining, grinding, and welding procedures in return for extended wear life.
Final note: Material selection should always consider the full service envelope—load, temperature, cycle frequency, repair strategy, and cost-of-ownership. Where possible, validate the choice with trial runs, targeted heat-treatment optimization, and failure-mode analysis to confirm whether SKD61’s toughness or SKD11’s wear resistance yields the best lifecycle outcome.