H13 vs H11 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
H13 and H11 are two of the most widely used hot-work tool steels in industry. Engineers, procurement managers, and manufacturing planners commonly weigh H11 and H13 when specifying dies, hot forging tools, extrusion tooling, or injection-molding hardware that must resist high temperature, cyclic thermal shock, and abrasive wear. The selection dilemma typically revolves around trading off elevated-temperature strength and hot-hardness versus fracture toughness and resistance to impact/chipping under severe mechanical shock.
The principal practical distinction between these grades lies in their balance of high-temperature strength and toughness: H13 is generally specified where hot hardness, tempering resistance and thermal fatigue resistance are primary (e.g., die casting, extrusion), while H11 is often chosen where improved bulk toughness under shock and intermittent high-stress loading is more important. Both are hot-work tool steels with similar base chemistries, but modest differences in molybdenum and processing lead to different mechanical behavior in service.
1. Standards and Designations
- Common standards and designations:
- ASTM/ASME: A681 (specifies AISI/UNS tool steels including H-series)
- EN: EN X40CrMoV5-1 (H13 equivalent) and similar EN numbers for H11 variants
- JIS: SKD61 (approximate equivalent to H13) and SKD5/ SKD9 variants sometimes compared to H11
- GB (China): Comparable designations are often used (e.g., H13/H11 direct designations are common)
- Classification:
- Both H13 and H11 are classified as hot-work tool steels (alloyed tool steels). They are not stainless steels or HSLA; they are carbon-alloy tool steels intended for elevated-temperature tooling.
2. Chemical Composition and Alloying Strategy
Typical composition ranges (wt%) for commercially specified H13 and H11 (representative ranges from common datasheets and standards; exact values depend on the standard and supplier):
| Element | H13 (typical wt%) | H11 (typical 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 | ≤ 0.03 | ≤ 0.03 |
| S | ≤ 0.03 | ≤ 0.03 |
| Cr | 4.75 – 5.50 | 4.75 – 5.50 |
| Ni | ≤ 0.30 (trace) | ≤ 0.30 (trace) |
| Mo | 1.10 – 1.75 | 0.80 – 1.20 |
| V | 0.80 – 1.20 | 0.60 – 1.20 |
| Nb (Cb) | trace | trace |
| Ti | trace | trace |
| B | trace | trace |
| N | trace | trace |
How the alloying affects properties: - Carbon and chromium primarily establish hardenability, martensitic hardening capacity, and tempering response. - Molybdenum increases hardenability, tempering resistance (red hardness), and contributes to elevated-temperature strength — a key reason H13 (higher Mo) exhibits superior hot hardness and thermal fatigue resistance. - Vanadium promotes precipitation strengthening (VC), contributes to secondary hardening and wear resistance. - Silicon improves strength and oxidation resistance at high temperature. - Low levels of Mn, P, S, and trace microalloying elements control toughness and cleanliness.
3. Microstructure and Heat Treatment Response
Typical microstructures: - In the annealed or normalized condition, both grades present a tempered martensite/ferrite matrix with fine alloy carbides (Cr- and V-containing carbides). The carbide distribution and volume fraction are influenced by C, Mo, and V. - After quenching from a sufficiently high austenitizing temperature (commonly 1000–1050 °C for these grades) and subsequent tempering, the microstructure is tempered martensite with alloy carbides and possible retained austenite if over-tempered or slow-cooled.
How common thermal processes affect them: - Normalizing: Refines grain structure; carried out prior to final hardening to homogenize the microstructure and remove segregation. - Quenching & tempering: Both respond well to conventional quench-and-temper cycles. H13’s higher Mo increases hardenability and raises the tempering resistance (retained hardness at higher tempering temps). H11 with slightly lower Mo tends to reach comparable hardness but can show slightly greater retained toughness after optimized tempering. - Thermo-mechanical processing: Forging and controlled rolling prior to normalization can improve toughness by breaking up coarse carbides and refining prior austenite grain size. This is frequently used for large die forgings or heavy tooling to maximize fracture resistance.
Effect on performance: - H13’s microstructure with more Mo supports higher red hardness and resistance to softening at elevated service temperatures. - H11’s microstructure can be tuned (through tempering and thermo-mechanical processing) to maximize bulk toughness and resistance to crack propagation.
4. Mechanical Properties
Typical quenched-and-tempered property ranges (values vary by tempering level and supplier; cited ranges are representative of common H.T. conditions):
| Property | H13 (typical range) | H11 (typical range) |
|---|---|---|
| Tensile strength (MPa) | 1,000 – 1,900 | 900 – 1,700 |
| Yield strength (MPa) | 800 – 1,500 | 700 – 1,300 |
| Elongation (%) | 6 – 12 | 6 – 14 |
| Impact toughness (Charpy V-notch, J) | 15 – 45 | 20 – 60 |
| Hardness (HRC, quenched & tempered) | 40 – 54 | 40 – 52 |
Interpretation: - Strength: Both grades can achieve similar high strengths after proper heat treatment, but H13 is commonly selected when higher retained strength at elevated temperature is required. - Toughness: H11 typically demonstrates somewhat higher bulk toughness and impact resistance in comparable hardness conditions. The difference is magnified when tools are designed for heavy shock loading or repeated mechanical impacts. - Ductility: Comparable; H11 can show a modest advantage in elongation at fracture depending on tempering and processing.
5. Weldability
Weldability is dictated by carbon equivalent and alloying contributions to hardenability and susceptibility to cold cracking.
Useful empirical formulas: - Carbon equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (more sensitive to cracking tendency): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - Both H13 and H11 have moderate carbon and significant alloying (Cr, Mo, V) that raise hardenability; therefore both are considered moderately difficult to weld in the untempered condition. Preheat, interpass temperature control, and post-weld heat treatment (PWHT) are typically required to avoid cracking. - H13’s higher Mo and often slightly higher CE tends to make it marginally more susceptible to hardening and cracking in the heat-affected zone (HAZ), so welding practice must be more conservative (higher preheat, controlled cooling, PWHT). - H11, with slightly lower Mo content, is marginally easier to weld but still requires standard precautions for tool steels (preheat, low heat input, PWHT) and the use of matched or specialized filler metals.
6. Corrosion and Surface Protection
- Neither H13 nor H11 is stainless; both are subject to corrosion in humid or corrosive environments. Typical protection methods include:
- Painting or polymer coatings
- Chemical passivation (limited effectiveness on these alloy steels)
- Localized galvanizing is uncommon for tooling because coatings may affect tolerances and performance.
- Surface engineering (nitriding, PVD coatings, ceramic or DLC coatings) is commonly used to improve surface wear and corrosion resistance.
- PREN (pitting resistance equivalent number) is only meaningful for stainless alloys; for example: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index does not apply to H11/H13 because they are non-stainless tool steels.
7. Fabrication, Machinability, and Formability
- Machinability:
- In the annealed state, both grades are machinable with standard high-speed steel or carbide tooling. H13, with slightly higher Mo and more secondary carbides, can be marginally more abrasive to tooling and may reduce tool life compared to H11 in equivalent conditions.
- When hardened, both are challenging to machine; EDM, grinding, and abrasive machining are typical finishing methods.
- Formability:
- Hot forming (forging) is standard practice for large dies. Both respond well to hot working when appropriate temperatures and strain rates are used.
- Cold forming is limited due to carbon content and risk of cracking.
- Finishing:
- Both accept surface hardening treatments (nitriding, induction hardening for selective areas) and PVD/CVD coatings. H13’s better tempering resistance makes it a slightly better platform for coatings used at elevated temperatures.
8. Typical Applications
| H13 – Typical Uses | H11 – Typical Uses |
|---|---|
| Hot forging dies (press forging, die forging) where thermal fatigue and hot hardness are critical | Heavy drop-forging dies and tooling where bulk fracture toughness and resistance to mechanical shock are prioritized |
| Die-casting tooling and core inserts (high thermal fatigue, red hardness) | Large, thick-section dies for forging where chipping and crack propagation risk is high |
| Extrusion dies and shear blades exposed to elevated temperatures | Liners and tooling for impact-prone operations; applications where tool repairability and toughness matter |
| Hot-work molds for plastic and rubber under high thermal cycling | Applications requiring greater resistance to catastrophic brittle failure |
Selection rationale: - Choose H13 when repeated high-temperature exposure, thermal cycling, and resistance to softening (tempering resistance) are the dominant concerns. - Choose H11 when service includes heavy mechanical impact, large cross-sections prone to internal stresses, or where maximizing bulk fracture toughness is the priority.
9. Cost and Availability
- Cost: H13 is widely produced and stocked globally; its higher molybdenum content can make it slightly more expensive than H11 on a per-kg basis, but pricing is supplier- and market-dependent. H11 may be marginally less costly where inventory and local supply favor it.
- Availability by product form:
- Bars, blocks, plates, forgings, and pre-hardened plate are commonly available for both grades. H13 is perhaps the most commonly stocked hot-work grade worldwide, so lead times and variety of forms are often better for H13.
- For large custom forgings, supply lead times depend more on heat-treatment and forging houses than base material grade.
10. Summary and Recommendation
| Criterion | H13 | H11 |
|---|---|---|
| Weldability (relative) | Moderate–difficult (requires preheat, PWHT) | Moderate (slightly easier than H13, but still requires care) |
| Strength – Hot hardness | High (better red hardness, tempering resistance) | Good (slightly lower elevated-temp strength) |
| Toughness – Resistance to shock/chipping | Good | Better (generally higher bulk fracture toughness) |
| Cost | Moderate–higher (due to Mo content) | Moderate–lower (often slightly cheaper) |
Recommendations: - Choose H13 if: - Your tooling operates at elevated temperatures for extended cycles and needs good red hardness and resistance to thermal softening (e.g., die-casting, extrusion, hot shear). - Thermal fatigue and resistance to softening under cyclic heating are primary failure modes. - Choose H11 if: - The tool or die is subjected to heavy mechanical shock, impact, or where preventing brittle fracture and chipping is the prime concern (large forging dies, shock-prone tooling). - You prioritize fracture toughness and ease of repairability over the maximum high-temperature retention of hardness.
Final note: The practical performance of either grade depends heavily on supply quality, cleanliness, prior thermo-mechanical processing, and the exact heat-treatment schedule. For critical tooling, specify required toughness, acceptable hardness range, and any post-weld heat treatment practice in procurement documents and consult with steel suppliers to obtain mill certifications and recommended thermal cycles tailored to the application.