H11 vs H13 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
H11 and H13 are two widely used hot-work tool steels in industries that require tooling to operate at elevated temperatures such as die casting, extrusion, forging, and hot stamping. Engineers, procurement managers, and manufacturing planners routinely face the selection dilemma between slightly different performance trade-offs: toughness and resistance to thermal shock versus hot hardness and long-term resistance to thermal fatigue and wear. The choice affects tool life, maintenance intervals, processing parameters (preheat, tempering), and total cost of ownership.
The principal technical distinction between H11 and H13 lies in their balance of high-temperature strength and resistance to thermal cycling (thermal fatigue). H13 tends to be favored where sustained hot hardness and thermal-fatigue resistance are critical; H11 is often chosen where slightly higher bulk toughness and ductility are required and where resistance to cracking under heavy mechanical shock is prioritized. These differences stem from their alloying strategies and resultant microstructures after heat treatment.
1. Standards and Designations
- Common international standards and designations:
- AISI/SAE: H11, H13
- DIN/EN: 1.2343 (H11), 1.2344 (H13) — commonly referenced in European literature
- JIS: SKD5, SKH? (varies by country and exact grade mapping)
- GB (China): equivalent hot-work tool-steel designations
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ASTM/ASME: refer to relevant tool steel specifications and product forms
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Material class:
- Both H11 and H13 are tool steels intended for hot-work applications (hot-work tool steel). They are not stainless or HSLA. They are alloyed, air- or oil-hardenable chromium–molybdenum–vanadium steels designed for thermal stability.
2. Chemical Composition and Alloying Strategy
The exact percentages vary by standard and producer, but the two grades share a common hot-work alloy strategy—moderate carbon, significant chromium, plus molybdenum and vanadium to provide temper resistance, hardenability, and carbide strengthening. To avoid quoting proprietary numeric ranges, the table below characterizes the typical presence/role of each element.
| Element | H11 — Typical level / role | H13 — Typical level / role |
|---|---|---|
| C (Carbon) | Medium — provides martensitic hardenability and base strength | Medium — similar to H11; controls hardenability and temper response |
| Mn (Manganese) | Low–moderate — deoxidizer, aids hardenability | Low–moderate — similar role |
| Si (Silicon) | Low–moderate — deoxidation, strength | Low–moderate — similar |
| P (Phosphorus) | Trace — kept low for toughness | Trace — kept low |
| S (Sulfur) | Trace — controlled for machinability | Trace — controlled |
| Cr (Chromium) | Moderate — hardenability, oxidation resistance at high T | Moderate–high — key for hot hardness and scale resistance |
| Ni (Nickel) | Usually not significant | Usually not significant |
| Mo (Molybdenum) | Moderate — improves strength at temperature and temper resistance | Moderate — important for hot strength and carbide stability |
| V (Vanadium) | Moderate — forms stable carbides for wear resistance and toughness | Moderate — contributes to fine carbide dispersion and thermal fatigue resistance |
| Nb (Niobium) | Typically not present | Typically not present |
| Ti (Titanium) | Trace or absent | Trace or absent |
| B (Boron) | Trace (if present) — hardenability enhancer | Trace (if present) — can be added in micro amounts to improve hardenability |
| N (Nitrogen) | Trace — may stabilize certain nitride/carbidic features | Trace |
How alloying affects behavior: - Carbon primarily sets achievable hardness after quench and temper and influences hardenability. Higher carbon increases potential hardness and wear resistance but reduces toughness and weldability. - Chromium increases hardenability, high-temperature strength, and oxidation/scale resistance—important for hot work. - Molybdenum and vanadium form stable carbides which improve temper resistance (retention of hardness after exposure to elevated temperatures) and influence thermal-fatigue resistance. - Fine dispersions of vanadium carbides help impede crack initiation and growth under cyclic thermal loading.
3. Microstructure and Heat Treatment Response
Typical microstructure: - Both H11 and H13 are processed to produce a tempered martensitic matrix with dispersed alloy carbides (Cr, Mo, V carbides). The quench produces martensite; tempering relieves stresses and allows carbides to precipitate and stabilize.
Heat treatment response and routes: - Normalizing: Used to refine grain structure and homogenize heavy sections prior to quench. Helps produce uniform hardness response. - Quenching: Typical quench media are oil or controlled gas; austenitizing temperature and cooling rate control final martensite fraction and retained austenite. Both grades require careful control to avoid cracking. - Tempering: Multiple tempering cycles at temperatures matched to the service temperature produce the desired balance of hardness, toughness, and thermal stability. Tempering stabilizes martensite and precipitates alloy carbides (Mo, V, Cr). - Thermo-mechanical processing: Forging and controlled rolling followed by normalization can refine grain size and improve toughness; both steels respond positively to such routes but require controlled cooling to maintain hardenability.
Comparative note: - H13’s alloy balance is optimized to retain higher hardness at elevated temperatures (better temper resistance), and its carbide distribution favors resistance to thermal fatigue and wear at hot-working temperatures. - H11 is tailored slightly more toward bulk toughness and ductility while maintaining good hot strength; its microstructure may be tuned for higher fracture toughness in heavy-impact hot forging dies.
4. Mechanical Properties
Exact properties depend strongly on heat treatment, section size, and tempering temperature. The table below gives qualitative comparative properties under typical quenched-and-tempered hot-work conditions.
| Property | H11 | H13 |
|---|---|---|
| Tensile strength | High (good strength) | High (comparable to H11; can retain higher at elevated T) |
| Yield strength | High | High; slightly better retention at elevated temperatures |
| Elongation (ductility) | Slightly higher (more ductile) | Slightly lower (tough but optimized for hardness) |
| Impact toughness | Typically better (resists crack propagation under heavy shock) | Very good (designed for cyclic thermal loading), but can be slightly lower than H11 in bulk toughness |
| Hardness (room temp after tempering) | High (adjustable) | High — often retains higher hardness at temperature due to alloying |
Interpretation: - H13 generally offers superior retention of hardness at elevated temperatures and very good resistance to thermal fatigue and hot wear. H11 tends to provide slightly better bulk fracture toughness and ductility, which makes it attractive where mechanical shock and risk of catastrophic cracking are higher.
5. Weldability
Weldability of hot-work tool steels is limited relative to low-alloy steels—preheating, controlled interpass temperatures, and post-weld heat treatment (PWHT) are usually required to avoid cracking and to recover required properties.
Key factors: - Carbon and effective hardenability control susceptibility to cold cracking. Both grades have medium carbon and significant alloying; they are considered “weldable with precautions.” - Microalloying (Mo, V, Cr) increases hardenability and raises the risk of martensite formation in the HAZ; this increases cracking risk without proper preheat and PWHT. - Use of matching or overmatching filler metals and appropriate PWHT is common for repair welding to restore toughness and temper resistance.
Useful empirical formulas for weldability assessment: - Carbon equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (predictor for carbon-manganese equivalent and weld crack sensitivity): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - Higher $CE_{IIW}$ and $P_{cm}$ values indicate greater risk of hard, crack-prone martensitic HAZ and hence more stringent preheat and PWHT requirements. Both H11 and H13 typically require intermediate-to-high preheat and post-weld tempering due to their alloy content.
6. Corrosion and Surface Protection
- Neither H11 nor H13 are stainless steels; corrosion resistance is limited compared with stainless grades. For protection, common practices include painting, solvent-based coatings, galvanizing (where appropriate for part shape), or local surface treatments.
- Surface engineering options to enhance life and corrosion/wear resistance:
- Nitriding or ferritic nitrocarburizing (careful process control required for tool steels to avoid over-tempering).
- Hard chrome plating or PVD/CVD coatings for tooling surfaces (reduces adhesion and wear).
- Thermal spray coatings for extreme wear or oxidation resistance.
- PREN (pitting resistance equivalence number) is not relevant to non-stainless H11/H13 in practical selection: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index applies to stainless alloys; typical Cr levels in H11/H13 are insufficient to categorize them as corrosion-resistant stainless steels.
7. Fabrication, Machinability, and Formability
- Machinability:
- In the annealed/prefinished condition, both grades machine reasonably well using carbide tooling; machinability worsens after heat treatment (hardened condition).
- H13, with its temper-resistant microstructure, can be slightly more abrasive on tools due to fine vanadium carbides.
- Grinding and EDM:
- Both respond well to electrical discharge machining (EDM) for hard tooling but require subsequent tempering to recover properties after EDM heat-affected zones.
- Formability:
- Cold forming is limited; hot forming and controlled forging are common in bar/forging processing. H11 may be preferred where more ductility is needed before final heat treatment.
- Surface finishing:
- Both accept conventional grinding, polishing, and coating; prepare surfaces carefully to avoid residual stresses that could promote thermal-fatigue cracking.
8. Typical Applications
| H11 — Typical applications | H13 — Typical applications |
|---|---|
| Hot forging dies where heavy mechanical shock and fracture toughness are primary concerns (large drop-forging dies, upset dies) | Die-casting dies, extrusion tooling, hot stamping dies where sustained hot hardness and thermal-fatigue resistance are critical |
| Certain punch and shear applications requiring good toughness | Hot-work punches and cores, manifold inserts, die-casting cores subject to cyclic thermal loading |
| Inserts where ductility and shock resistance reduce risk of catastrophic fracture | Tools and molds operating at high continuous temperatures and repetitive thermal cycling |
Selection rationale: - Choose H13 when the application involves high surface temperatures, repeated thermal cycling, and abrasive contact—H13’s temper resistance and carbide structure improve life under thermal fatigue and wear. - Choose H11 when the primary risk is mechanical shock, heavy gross loads, or when slightly greater ductility/toughness is required to avoid brittle failure.
9. Cost and Availability
- Cost:
- Both H11 and H13 are commodity hot-work tool steels; pricing varies with global alloy markets. H13 is more commonly used worldwide, which can make it slightly more economical in some markets due to scale and supply chain maturity.
- Specialty variants or vacuum-melt premium bars increase cost for either grade.
- Availability by product form:
- Both are readily available in bar, plate, forgings, and pre-hardened tool blanks from major steel distributors. H13 tends to have wider industrial availability and a larger ecosystem of suppliers and welding/heat-treatment know-how.
10. Summary and Recommendation
| Criterion | H11 | H13 |
|---|---|---|
| Weldability | Fair — requires preheat and PWHT | Fair — similar requirements, often slightly more sensitive due to hardenability |
| Strength–Toughness balance | Better bulk toughness and ductility | Better retention of hardness and strength at elevated temperature; superior thermal-fatigue resistance |
| Cost / Availability | Good | Very good (slightly more common globally) |
Recommendation: - Choose H13 if your tooling is exposed to high service temperatures, repeated thermal cycling (thermal fatigue), or requires superior hot wear resistance (e.g., die casting, extrusion, hot stamping). - Choose H11 if your application prioritizes higher bulk fracture toughness and ductility to resist mechanical shock and heavy impact loading (e.g., large forging dies subject to heavy blows), and where slightly lower high-temperature hardness is acceptable.
Final practical note: For critical tooling, specify clear heat-treatment procedures (preheating, austenitizing, quench medium, temper schedule), consider section-thickness effects, and plan maintenance (reconditioning, welding procedures) with your heat treater and supplier. Trial runs and monitoring of early-life failure modes (thermal fatigue cracks vs. mechanical fracture) are essential to validate the grade choice in your specific process.