H13 vs SKD61 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
H13 and SKD61 are two of the most widely specified hot-work tool steels used for dies, molds, and tooling components exposed to high temperatures, thermal cycling, and abrasive wear. Engineers, procurement managers, and manufacturing planners commonly face the decision between these grades when specifying material for hot forging dies, die casting tooling, extrusion dies, and hot shear equipment. The decision often balances hardenability, temper resistance and thermal fatigue performance against availability, cost, and local naming conventions.
The principal distinction is primarily nomenclature and standards origin: H13 is the AISI/ASTM-style designation commonly used in North America and Europe, while SKD61 is the JIS (Japanese Industrial Standard) designation. Metallurgically they are functionally equivalent hot-work chromium-molybdenum-vanadium tool steels with closely matching chemistries and properties, but selection can be influenced by minor permitted composition windows, local heat-treatment practices, and supply-chain availability.
1. Standards and Designations
- AISI/SAE / ASTM: H13 — common Western designation for hot-work tool steel.
- JIS: SKD61 — Japanese designation for the H13 equivalent.
- DIN / EN: listed under hot-work tool steels (chromium–molybdenum–vanadium types); commonly referenced in European specifications and standards for tool steels.
- GB (China): available under Chinese national standards for hot-work tool steel with equivalent chemical ranges.
- ISO: referenced in international tool-steel classifications as hot-work Cr-Mo-V grade.
Classification: both H13 and SKD61 are tool steels (hot-work tool steel). They are alloy steels with intentional additions of Cr, Mo, and V to provide hardenability, temper resistance, and wear resistance for elevated-temperature service.
2. Chemical Composition and Alloying Strategy
The two grades are essentially equivalent in alloying concept: medium carbon with moderate Cr, Mo and V additions to enhance hardenability, temper resistance, and secondary hardening. The table below shows typical composition ranges commonly found in standards and supplier datasheets.
| Element | Typical H13 (wt%) | Typical SKD61 (wt%) |
|---|---|---|
| C | 0.32 – 0.45 | 0.32 – 0.45 |
| Mn | 0.20 – 0.50 | 0.20 – 0.50 |
| Si | 0.80 – 1.20 | 0.80 – 1.20 |
| P | ≤ 0.030 | ≤ 0.030 |
| S | ≤ 0.030 | ≤ 0.030 |
| Cr | 4.75 – 5.50 | 4.75 – 5.50 |
| Ni | ≤ 0.30 | ≤ 0.30 |
| Mo | 1.10 – 1.75 | 1.10 – 1.75 |
| V | 0.80 – 1.20 | 0.80 – 1.20 |
| Nb/Ti/B/N | trace / typically controlled | trace / typically controlled |
How alloying affects performance: - Carbon: controls hardenability and peak hardness; higher C increases hardness and wear resistance but reduces toughness and weldability. - Chromium: increases hardenability, wear resistance and oxidation resistance at elevated temperatures. - Molybdenum: improves hardenability and high-temperature strength (tempering resistance). - Vanadium: refines carbides and grain size, improving wear resistance and toughness. - Silicon and manganese: deoxidation and strength modifiers; excessive Mn can form brittle phases if uncontrolled.
Minor microalloying and trace elements (Nb, Ti, B) may be present in modern melts to control grain size and improve through-hardening; these are usually tightly controlled by each standard and mill.
3. Microstructure and Heat Treatment Response
Typical microstructures: - As-rolled/normalized: tempered martensitic matrix with dispersed alloy carbides and possible retained austenite depending on processing. - After quench & temper: tempered martensite with uniformly distributed alloy carbides (Cr, Mo, V carbides). Secondary hardening from carbide precipitation during tempering is a key trait for high-temperature temper resistance.
Heat-treatment routes and effects: - Normalizing: refines prior austenite grain size and reduces segregation; typical for large forgings and to produce uniform starting structure prior to hardening. - Quenching (oil or vacuum): austenitize (typical 1000–1050 °C, depending on section size and standard), then quench to achieve martensitic transformation. Both H13 and SKD61 respond similarly; adequate preheating and controlled cooling minimize distortion and cracking. - Tempering: multiple temper cycles (commonly 2–3) at elevated tempering temperatures (e.g., 500–600 °C) to develop required hardness and toughness. Both grades exhibit secondary hardening; selection of temper temperature balances hardness vs. toughness and thermal fatigue resistance. - Thermo-mechanical processing: hot forging followed by controlled normalization improves impact toughness and reduces segregation; final T&T optimizes properties.
Because chemistries are very similar, microstructure evolution and response to heat treatment are effectively interchangeable, though individual supplier heat-treat practices and heat size effects can produce measurable differences in final properties.
4. Mechanical Properties
Typical mechanical property ranges are shown for quenched and tempered conditions commonly used in tooling (values are indicative; specify exact heat-treatment and test standard when procuring material).
| Property | Typical H13 (quenched & tempered) | Typical SKD61 (quenched & tempered) |
|---|---|---|
| Tensile strength (Rm) | 1100 – 1600 MPa | 1100 – 1600 MPa |
| Yield strength (Rp0.2) | 900 – 1400 MPa | 900 – 1400 MPa |
| Elongation (A%) | 6 – 12% | 6 – 12% |
| Impact toughness (Charpy V-notch) | 10 – 40 J (depends on hardness/heat-treat) | 10 – 40 J (depends on hardness/heat-treat) |
| Hardness (HRC) | 40 – 55 HRC (typical production range) | 40 – 55 HRC (typical production range) |
Which is stronger, tougher, or more ductile? - There is no intrinsic strength advantage to either grade; both are engineered for elevated-temperature hardness and temper resistance. Final strength and toughness are highly dependent on exact carbon content, heat-treatment temperature, tempering regime, and section size. - Toughness generally decreases with increasing hardness (higher tempering temperature lowers hardness but increases toughness). Both grades follow the same trade-off. - In practice, differences in toughness or ductility between H13 and SKD61 are typically within process and heat-to-heat variability rather than inherent to a particular designation.
5. Weldability
Weldability of hot-work tool steels is limited by carbon content and hardenability. Key considerations: - Carbon equivalent: higher C, Cr, Mo, V raise hardenability and susceptibility to cracking in the HAZ. - Use preheat, interpass temperature control, and post-weld tempering to minimize cracking and hydrogen-induced cold cracking.
Common weldability indices: - IIW carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (Boehler) index: $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Interpretation (qualitative): - Both H13 and SKD61 exhibit similar $CE_{IIW}$ and $P_{cm}$ values because of near-identical chemistries; both are regarded as moderate-to-difficult to weld without special procedure. - Recommended practice: controlled preheat (often 150–300 °C depending on thickness), low hydrogen consumables, controlled interpass temperature, peening if necessary, and stress-relief/post-weld tempering to restore temper and relieve residual stresses. - Welding is typically used for minor repairs; for critical tooling it's often preferable to weld only on sections that will be reheat-treated and tempered after welding to restore properties.
6. Corrosion and Surface Protection
- H13 and SKD61 are not stainless steels; their corrosion resistance is limited. Selection should consider surface protection and environment.
- Surface protection strategies:
- Protective coatings (PVD/CVD) for wear reduction, not corrosion alone.
- Galvanizing is not typically applicable for tool-steel tooling due to temperature and adhesion concerns.
- Painting, oiling, or chromate-type conversions for storage protection.
- Localized nitriding or surface hardening can enhance surface wear and corrosion resistance where appropriate; note nitriding changes surface chemistry and may affect fatigue behavior.
- PREN (Pitting Resistance Equivalent Number) applies to stainless grades: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This is not applicable for H13/SKD61 because they are non-stainless tool steels and do not rely on Cr content for passive corrosion film formation in the same way stainless alloys do.
7. Fabrication, Machinability, and Formability
- Machinability: in annealed/softened condition these steels are machinable with carbide tooling; cutting speeds and feeds should be conservative compared with low-alloy steels. Hardened H13/SKD61 requires high-performance carbide or ceramic tooling.
- Grinding and EDM: both grades respond well to tool-room grinding and EDM; EDM is commonly used for complex cavity generation and modifications.
- Forming/bending: limited when hardened; in softened condition standard hot and cold forming processes are possible, but springback and work-hardening must be considered.
- Surface finishing: because of alloy carbides, fine polishing to mirror finishes is achievable but may require specialized abrasives and longer cycle times.
8. Typical Applications
| H13 (AISI) — Typical Uses | SKD61 (JIS) — Typical Uses |
|---|---|
| Hot-work die-casting dies (aluminum, zinc) | Hot-work die-casting dies |
| Forging dies (drop forging, upset forging) | Forging dies and hot extrusion tooling |
| Extrusion dies for high-temperature alloys | Extrusion tooling and hot shear blades |
| Hot stamping dies | Hot stamping and hot forming dies |
| Plastic injection molds for high-temperature polymers (selected uses) | Molds for engineering plastics and composite processing |
Selection rationale: - Choose these grades when tooling must resist plastic deformation, maintain hardness at elevated temperatures, and resist thermal fatigue. Choice between H13 and SKD61 is typically driven by regional specification or supplier availability rather than material performance differences.
9. Cost and Availability
- Relative cost: H13 and SKD61 have comparable raw-material costs; market price varies by region, mill, and supply form (round bar, plate, forged block, pre-hardened plate). SKD61 may be more readily stocked in Asia; H13 designation may be more common in North America and Europe.
- Availability: both grades are widely produced and available from multiple mills in forms including bars, plates, forgings, and pre-hardened blanks. Lead times depend on size and heat-treatment state.
- Economies of scale: buying standard bar sizes or pre-hardened plates typically reduces cost compared with custom forgings or small-batch quenched-and-tempered blocks.
10. Summary and Recommendation
Summary table — qualitative comparison
| Attribute | H13 | SKD61 |
|---|---|---|
| Weldability | Moderate–difficult (requires procedure) | Moderate–difficult (requires procedure) |
| Strength–Toughness balance | High strength with good temper resistance; trade-off with toughness at higher hardness | Equivalent: high strength and temper resistance, similar trade-offs |
| Cost & Availability | Widely available in Americas/Europe; common specification name | Widely available in Asia; common JIS specification name |
Conclusions and practical recommendations: - Choose H13 if you are specifying to AISI/ASTM nomenclature, sourcing from suppliers or mills that quote material as H13, or if tooling will be manufactured and maintained in regions where H13 is the standard term. - Choose SKD61 if you are working with JIS-based specifications, sourcing from Asian suppliers, or your purchase orders and quality documentation reference SKD61 as the contract grade. - For critical tooling decisions focus on: exact composition tolerances, specific heat-treatment instructions (austenitizing and temper schedules), required hardness and toughness targets, and clear non-destructive or mechanical acceptance criteria. Because H13 and SKD61 are metallurgically equivalent, ensure procurement emphasizes the heat-treatment condition, traceability, and mill certifications rather than only the grade name.
If you need a sample specification clause or a procurement checklist to ensure equivalent performance when substituting names (H13 ↔ SKD61) across suppliers, I can provide a concise, ready-to-use template.