Hot-Work Tool Steel for Die Casting and Hot Shear

Hot-work tool steel is the family of tool steels designed for tools and dies that operate at elevated temperature (200–600 °C) where thermal fatigue resistance and toughness at operating temperature are the dominant requirements. The defining feature is a moderate alloy content (5 % Cr, 1–2 % Mo, 0.4–0.6 % V) that provides secondary hardening response and temper resistance, combined with high toughness for impact loading.

For industrial cutting tools, hot-work tool steel is the right choice when the cutting edge sees high temperatures from friction or process, AND where toughness matters as much as wear resistance — die-casting dies, hot shear blades, hot piercing punches, extrusion tooling, plastic injection moulds for high-temperature polymers. The 3 grades covered in this guide — AISI H11, H13, and GB 6CrW2Si — span the standard range for industrial hot-work applications.

Selection follows three steps: identify the operating temperature (200–400 °C, 400–600 °C, or 600+ °C), identify the dominant failure mode (thermal fatigue, gross fracture, plastic deformation), and match the grade to the application. H13 is the workhorse die-casting and hot-shear grade; H11 is the lower-V tougher variant; 6CrW2Si is the Chinese GB-standard tungsten-modified alternative.

For per-grade chemistry, heat treatment and cross-reference tables, see the AISI H11 reference entry, H13 entry, and 6CrW2Si entry.

1. What is hot-work tool steel?

Hot-work tool steel is defined by its ability to retain toughness at elevated temperature. The AISI / UNS standard hot-work grades span HRC 48–54 hardened, with secondary hardening from Mo / V carbide precipitation during tempering and high toughness (Charpy 20–40 J at room temperature) for die-casting and hot-shear duty.

2. Chemistry and secondary hardening

The chemistry of hot-work tool steel is dominated by secondary hardening.

Carbon is held moderate at 0.30–0.45 %. Hot-work grades are not primarily about primary carbide wear resistance — they are about toughness at temperature. The lower carbon keeps Charpy impact values high (20–40 J at room temperature) at the cost of lower primary carbide volume than cold-work D2.

Chromium at 4.5–5.5 % provides the basic corrosion and oxidation resistance at elevated temperature. The chromium content also stabilises the secondary-hardening response by contributing to M₇C₃ carbide precipitation.

Molybdenum at 1.0–2.0 % is the key secondary-hardening element. Mo₂C precipitation during tempering at 510–620 °C produces a hardness peak that resists over-tempering at operating temperature. Molybdenum also contributes to high-temperature strength and reduces the risk of temper embrittlement.

Vanadium at 0.3–1.0 % adds MC carbide for grain refinement and wear resistance. H11 uses lower V (0.3–0.4 %) for toughness; H13 raises V to 0.8–1.0 % for hot hardness. Above ~1 % V, the wear resistance gain is offset by toughness loss.

Tungsten appears in some hot-work grades (notably the Chinese GB 6CrW2Si) as a partial Mo substitute. W₂C provides similar secondary hardening response but with different carbide morphology.

Silicon at 0.8–1.2 % contributes to oxidation resistance at elevated temperature and provides solid-solution strengthening. Silicon also delays the onset of temper embrittlement in some grades.

The trade-off matrix: lower C + lower V gives maximum toughness (H11). Higher C + higher V gives maximum hot hardness (H13). Higher W gives marginal hot hardness at moderate cost (6CrW2Si). The hot-work family is narrower than the cold-work family because the operating-temperature window is narrower.

3. AISI H11

AISI H11 is the lower-V toughness-favouring hot-work grade.

AISI H11 is the lower-vanadium hot-work tool steel, optimised for toughness over peak hot hardness. Nominal chemistry is 0.33–0.43 % C, 4.75–5.50 % Cr, 1.10–1.60 % Mo, 0.30–0.60 % V, 0.80–1.20 % Si. The lower V (0.3–0.6 % vs H13’s 0.8–1.0 %) gives H11 about 15–20 % higher Charpy impact at the same hardness level.

Working hardness is HRC 48–54 after austenitising at 1000–1050 °C, gas or oil quenching, and double tempering at 540–620 °C. Hot hardness at 600 °C is roughly HRC 35–40, sufficient for hot-shear service and plastic-injection tooling.

H11 is the preferred grade for:

• Aluminium die-casting dies (lower V resists thermal-fatigue cracking better than H13)
• Plastic injection moulds for glass-filled or abrasive polymers
• Hot piercing punches where impact dominates
• Hot shear blades for lower-temperature service (200–400 °C)
• Extrusion tooling for non-ferrous metals

H11 is rarely the right choice for steel die-casting or high-temperature hot shear — the lower hot hardness is insufficient at the temperatures involved (600+ °C), and H13 is the standard specification in those services.

4. AISI H13

AISI H13 is the workhorse die-casting and hot-shear grade.

AISI H13 is the dominant hot-work tool steel worldwide. Nominal chemistry is 0.32–0.45 % C, 4.75–5.50 % Cr, 1.10–1.75 % Mo, 0.80–1.20 % V, 0.80–1.20 % Si. The higher V (0.8–1.2 % vs H11’s 0.3–0.6 %) gives MC carbide for wear resistance and grain refinement, raising hot hardness at the cost of some toughness.

Working hardness is HRC 48–54 after austenitising at 1000–1050 °C, gas or oil quenching, and double tempering at 540–620 °C. Hot hardness at 600 °C is roughly HRC 40–45, sufficient for steel die-casting and high-temperature hot-shear service.

H13 is the standard specification for:

• Steel die-casting dies (HRC 48–52)
• Hot shear blades for steel mill service (slab shear, billet shear)
• Hot piercing punches for high-temperature billet
• Aluminium extrusion tooling (die and dummy block)
• Forging dies for steel (HRC 44–50 for impact service)
• Plastic injection moulds for glass-filled polymers

H13’s dominance comes from its versatility — it can be heat-treated across a wide hardness range (HRC 44–54) for different applications, and it is available from every major tool-steel mill worldwide. ESR-grade H13 is preferred for the highest-toughness applications (large die-casting dies, forging die blocks); air-melt H13 is acceptable for shorter-run tooling.

5. GB 6CrW2Si

5. GB 6CrW2Si

GB 6CrW2Si (China GB/T 1299 standard) is a tungsten-modified 5 Cr-type hot-work tool steel — used primarily for hot shear blades, punches and short-run hot-work dies. Slightly higher hot hardness than H13 due to the W addition, with comparable toughness.

6CrW2Si is widely used in China and Chinese-export tooling as a hot-work alternative to H11/H13. The hot hardness is comparable to H13 at slightly lower cost.

6CrW2Si selection rule: use 6CrW2Si where it is locally available and H13 sourcing is limited. Cross-reference equivalent is approximately between H11 and H13.

6. Heat treatment

Heat treatment of hot-work tool steel requires careful austenitising and tempering.

Austenitising. H11 and H13 austenitise at 1000–1050 °C, 6CrW2Si at 1050–1100 °C. The austenitising temperature is lower than HSS because the secondary-hardening carbide formers (Mo, V) dissolve adequately at these temperatures without grain coarsening. Vacuum furnace with positive-pressure nitrogen is the standard production environment.

Quench. Oil or positive-pressure nitrogen gas quench. Martempering (quench to 540 °C, hold briefly, then air-cool) is standard for hot-work tools to reduce distortion, particularly for die-casting dies and forging dies where post-heat-treat machining allowance is critical.

Tempering. Double temper at 540–620 °C, each cycle 2 hours minimum. The double temper is mandatory for hot-work because the first temper precipitates secondary carbides but leaves some transformed austenite; the second temper converts the remaining austenite and stabilises dimensions. For H13, the typical temper is 600 °C + 600 °C to land at HRC 48–52.

Cryogenic treatment is occasionally applied to H13 for tight-tolerance hot-work tooling but is less critical than for cold-work or HSS because the secondary-hardening response is more complete at the tempering temperature.

Surface treatments. Nitriding (gas or plasma) is widely applied to H11 and H13 to provide a hard surface layer (~HRC 60+) at low cost. Nitrocarburising adds carbon to the diffusion layer. Both treatments improve wear resistance for hot-shear and piercing applications. PVD coating (TiAlN, CrN) is also standard for hot-work tooling in higher-temperature service.

7. Selection methodology

Selection methodology for hot-work applications.

Step 1 — Operating temperature. 200–400 °C (warm work, plastic moulding): cold-work tool steel often works, hot-work is overkill. 400–600 °C (die casting, hot shear): H11 or H13. Above 600 °C: consider nickel superalloys (Inconel 718) or carbide.

Step 2 — Dominant failure mode. Thermal-fatigue cracking (heat-check pattern from repeated heating/cooling cycles): H11 preferred for aluminium die casting (lower V, better crack resistance). Gross fracture from impact: H11 preferred (lower V, higher toughness). Wear at temperature: H13 preferred (higher V, more MC carbide). Plastic deformation (workpiece hot enough to flow): H13 mandatory.

Step 3 — Process specifics. Die casting: H13 for steel, H11 or H13 for aluminium. Hot shear: H13 standard, H11 for lower-temperature service. Hot piercing: H11 for impact, H13 for wear. Forging dies: H13 standard, H11 for high-impact applications. Extrusion: H13 standard.

Step 4 — Surface treatment. Nitriding for low-cost wear improvement. PVD coating (TiAlN, AlCrN) for higher-temperature wear service. Combination of nitriding + PVD for severe service.

Step 5 — Mill source and feedstock. ESR-grade H11 / H13 for the highest-toughness applications. Standard air-melt for general hot-work tooling. Chinese GB 6CrW2Si as a cost-effective alternative where H13 sourcing is limited.

8. Common failure modes

Three recurring failure modes in hot-work blade service.

Thermal-fatigue cracking (heat checking) is the dominant failure in hot-work tooling. Repeated heating-cooling cycles at the surface produce a network of fine cracks. The cracks propagate under continued thermal cycling until they reach a critical size and the surface spalls off. Mitigation: lower-V grade (H11 vs H13), nitriding or PVD coating to reduce surface friction heat, optimised cooling-channel design in dies, and avoidance of over-tempering during heat treatment.

Gross fracture is the catastrophic failure where a die block or shear blade breaks under load. Causes include: heat-treat defect (over-temperature austenitising, coarse grain), insufficient toughness for the application (H13 specified where H11 was needed), geometric stress concentration (sharp internal corner, inadequate fillet), or impact beyond design (slug jam in die casting). Mitigation: vacuum furnace processing, ESR feedstock, corner-radius design, and proper grade selection.

Plastic deformation (sinking) is the failure where the working surface of the die or shear blade deforms plastically under sustained load at operating temperature. The surface appears smooth but is no longer at the original dimension. Mitigation: higher hot hardness (H13 with higher tempering temperature to maintain hardness), adequate cooling, PVD coating for surface hardness.

Wear in hot-work tooling is typically less dramatic than in cold-work but still significant. Erosive wear from molten metal flow in die casting, abrasive wear from forging scale, and adhesive wear from hot metal transfer in shear blades are all common. Mitigation: harder grade, surface treatments, and process adjustments to reduce the wear mechanism.

9. Grade comparison table

Grade comparison table.

Charpy values are typical un-notched at room temperature after proper heat treatment; actual values depend on the heat-treat parameters and the testing direction (longitudinal vs transverse).

10. International standards cross-reference

International standards cross-reference.

H11 and H13 are nearly universally available with consistent cross-reference between national standards. The Chinese GB 4Cr5MoSiV1 is the closest equivalent to H13 and is sometimes exported as “H13” by Chinese mills — verify by chemistry, not by designation. 6CrW2Si is a Chinese-domestic standard without a direct ISO or DIN equivalent; it is specified primarily within the Chinese tool-steel market.

For procurement of critical hot-work tooling, the specifier should reference the mill certificate chemistry rather than the grade designation, and verify that the ESR/VAR practice is documented for the highest-toughness applications.

11. Coatings for hot-work tool steel

PVD coatings for hot-work tool steel.

TiAlN (titanium aluminium nitride) is the standard PVD coating for hot-work tooling. Hardness 2800–3200 HV, oxidative stability to 800 °C, deposition temperature 450 °C. The aluminium oxide layer that forms at high temperature provides the wear-life gain in die-casting and hot-shear service.

AlCrN (aluminium chromium nitride) is the premium coating for the highest-temperature hot-work applications. Higher Al content than TiAlN gives better oxidative stability and hot hardness. Used in steel die-casting and hot piercing punches.

CrN (chromium nitride) is the corrosion-resistant coating, used where the hot-work tool also has the solution’s exposure to water-based lubricants or cooling fluids. Lower hardness (~1800 HV) but good corrosion resistance.

Nitriding is the standard diffusion treatment for H11 and H13. Gas nitriding or plasma nitriding at 500–580 °C produces a surface hardness of HRC 60+ to a depth of 0.2–0.5 mm. Nitrocarburising adds carbon to the diffusion layer for additional wear resistance. Nitriding is lower cost than PVD coating but provides a thicker modified layer.

Combination treatments. Nitriding + PVD coating (typically nitriding first, then PVD on top) provides both a deep diffusion-hardened layer and a thin ceramic surface layer. Used in severe hot-work service where neither treatment alone is sufficient.

Coating thickness for hot-work tooling is typically 2–5 µm for PVD and 0.2–0.5 mm for nitrided case. Hone geometry must be sharp enough for PVD deposition; nitriding can be applied to any geometry including large radii.

12. Specialty applications

Specialty applications beyond die-casting and hot shear.

Die-casting dies. Steel die casting: H13 ESR standard, H11 for impact-resistant sections. Aluminium die casting: H13 standard, H11 for thermal-fatigue-prone cores. Magnesium die casting: H11 preferred (lower tendency to react with molten Mg).

Hot shear blades. Steel mill slab shear, billet shear, crop shear: H13 with nitriding or PVD coating. Aluminium mill shear: H11 or H13 with appropriate coating. Continuous-caster cutting: H13 with high-temperature coating.

Hot piercing punches. Seamless tube mill piercing: H11 (impact) or H13 (wear), with nitriding. Closed-die forging punches: H13 for steel, H11 for non-ferrous.

Forging dies. Hammer forging: H13 with nitriding. Press forging: H13 with PVD or nitriding + PVD. Upsetter dies: H13 with nitriding.

Extrusion tooling. Aluminium extrusion: H13 die and dummy block, H11 for short-run. Copper extrusion: H13 with nitriding for wear resistance. Steel extrusion: H13 with high-temperature coating.

Plastic injection moulds. Glass-filled polymer: H13 with PVD or nitriding. PVC: H13 with corrosion-resistant coating. High-temperature polymers (PEEK, PSU, PPSU): H13 or H11 standard.

Hot-stamping dies. Automotive hot-stamping (press hardening of boron steel): H13 with high-temperature coating (AlCrN). The operating temperature is 600+ °C with rapid heating-cooling cycles — H13 is the standard specification.

13. Procurement and supply

Procurement and supply for hot-work grades.

Per-kilogram material cost is roughly comparable to cold-work A2 / D2. H11 and H13 are priced similarly with H11 typically 5–10 % cheaper due to lower V content. 6CrW2Si is the cost-effective alternative in the Chinese market, typically 20–30 % below H13 from Western mills.

Mill source. Western mills (Bohler, Assab, Uddeholm, Crucible, Daido, Hitachi) provide consistent chemistry and reliable ESR feedstock. Chinese mills (Tisco, Baosteel, Chongqing Iron & Steel) supply the bulk of the GB-standard market including 6CrW2Si and the H13 equivalent 4Cr5MoSiV1. For critical hot-work applications where failure cost is high (large die-casting dies, hot shear blades in steel mills), Western mill certification is preferred.

ESR vs air-melt. ESR-grade H11 and H13 carry a 30–50 % premium over air-melt but provide significantly higher toughness and cleaner inclusion population. For large die-casting dies (>500 kg), forging die blocks, and other high-stress applications, ESR is the standard specification.

Lead time. Standard mill plate and bar stock is 4–8 weeks from European mills, 2–4 weeks from Chinese mills. ESR feedstock adds 2–4 weeks to the lead time. Stocked distributor material is available in 1–2 weeks for common H13 sizes.

Tooling cost. Hot-work grinding is comparable to D2-class cold-work — aluminium-oxide wheels work adequately for rough grinding, with CBN or ceramic wheels for finish grinding. Total finished-tool cost is typically 1.0–1.5× the raw material cost.

14. Summary

Summary of the hot-work family.

Hot-work tool steel fills the niche where the cutting edge or working surface runs at 200–600 °C with thermal cycling and impact loading. The defining feature is secondary hardening from Mo / V carbide precipitation combined with high toughness. H11 is the lower-V toughness grade (aluminium die casting, hot piercing, impact-loaded applications). H13 is the workhorse hot hardness grade (steel die casting, hot shear, plastic injection moulds). 6CrW2Si is the Chinese-standard tungsten-modified alternative. Selection is driven by operating temperature, dominant failure mode, and the cost-vs-life trade-off. Heat treatment at lower austenitising temperatures than HSS, double temper at 540–620 °C. Surface treatments (nitriding, PVD) compound the wear-life gain and are standard on production hot-work tooling. Beyond H13 at 600+ °C, the next material family is nickel superalloys or carbide.

15. Edge geometry and hone for hot-work blades

Edge geometry for hot-work blades.

Hot-shear blades for steel mill service run heavy edge angles of 25–35° per side with a primary hone of 0.5–1.5 mm and often a secondary micro-bevel. The geometry prioritises impact resistance and bulk thermal mass over sharpness.

Hot piercing punches run acute edge angles of 18–25° at the cutting tip with a small primary hone (0.1–0.3 mm) for clean piercing. The punch body is thick for stiffness but the cutting edge is sharpened to minimise piercing force and avoid double-thickness deformation.

Hot shear blades for non-ferrous service (aluminium mill, copper mill) run slightly lighter geometries — 22–28° per side with 0.3–0.8 mm hone. The lower service temperature allows sharper edges than steel mill shear.

For die-casting dies and forging dies, edge geometry is less of a variable because the working surface is typically a cavity rather than a sharp edge. Surface finish (Ra < 0.8 µm) and corner radii are the critical parameters for die life. Sharp corners initiate thermal-fatigue cracks; fillet radii of 1–3 mm are standard at all internal corners.

Hone and edge geometry for hot-work blades must accommodate the surface treatment. Nitrided surfaces can hold any geometry including sharp edges. PVD-coated surfaces need hone small enough for the coating to deposit at the edge — typically below 0.5 mm.

16. Real-world case: H13 die-casting die thermal-fatigue failure

Real-world case: H13 die-casting die thermal-fatigue failure.

An aluminium die-casting operation produces automotive transmission housings with a 60,000-shot die life target. The die is H13 ESR at HRC 48, gas-nitrided to 0.3 mm case depth. After 35,000 shots, the die shows severe heat-check cracking at the core section and is removed for repair.

Failure analysis. Heat-check pattern shows classic thermal-fatigue cracks initiating at the die surface and propagating perpendicular to the surface under repeated heating-cooling cycles. The crack depth at 35,000 shots is 0.8–1.2 mm, exceeding the nitrided case depth (0.3 mm). The die cannot be repaired by re-nitriding because the cracks are too deep.

Root cause. Three contributing factors: (1) inadequate cooling-channel design at the core section, causing local overheating; (2) insufficient draft angle, increasing ejection force and friction heat; (3) H13 is not the optimal grade for this particular section — H11 with its lower V content would resist thermal-fatigue cracking better.

Intervention 1 — Cooling redesign. Added two new cooling channels at the core section, reducing peak die surface temperature from 540 °C to 470 °C. This alone extends expected die life to ~55,000 shots.

Intervention 2 — Core section material change. Replaced H13 with H11 in the core section of the replacement die. H11’s lower V (0.4 % vs H13’s 1.0 %) provides better thermal-fatigue resistance. The bulk of the die remains H13 for wear resistance.

Intervention 3 — Surface treatment upgrade. Replaced gas nitriding with plasma nitriding for finer surface compound layer and better control of diffusion depth. Plasma nitriding also allows lower nitriding temperature (480 °C vs 540 °C for gas), reducing the risk of over-tempering the substrate.

Outcome. Replacement die with the three interventions reaches 70,000 shots before heat-check depth exceeds allowable limit — a 17 % improvement over the original target. The cooling redesign alone justified the die redesign cost within the first 8 weeks of operation.

17. Inspection and quality control

QC protocol for hot-work blades.

Stage 1 — Material certification. Mill certificate shows chemistry within specification, the correct melting practice (AOD, ESR, or VAR for critical applications), and the annealed hardness for machinability. ESR-grade material should be identified as such on the certificate.

Stage 2 — Pre-heat-treat dimensional inspection. Verify the as-machined dimensions against the drawing before heat treatment. Allowance for heat-treatment distortion depends on the geometry — symmetric sections can be machined to final dimension with 0.05–0.10 mm per side allowance; asymmetric sections require additional allowance and may need post-heat-treat machining.

Stage 3 — Post-heat-treat hardness verification. Surface hardness is checked by calibrated Rockwell C at multiple locations. Through-thickness hardness is verified by cross-section micro-hardness traverse on a sample basis. The target is the specified working hardness ±1 HRC. For ESR-grade material, additional verification by ultrasonic testing for internal defects is recommended.

Stage 4 — Metallurgical verification. On first article and sample basis: confirm grain size per ASTM E112 (target ASTM 8–10 for H11/H13); confirm absence of carbide network; verify temper response is uniform across the section.

Stage 5 — Surface treatment verification. For nitrided tools: case depth by micro-hardness traverse or metallographic cross-section; surface hardness by calibrated micro-hardness; case compound layer composition by XRD or microscopy. For PVD-coated tools: coating thickness by calo-melt or eddy-current methods; coating adhesion by Rockwell or scratch test per vendor specification.

Stage 6 — Final dimensional and edge inspection. Verify the finished-tool dimensions against the drawing. For hot-shear blades, edge angle and hone are measured. For die-casting dies, the cavity dimensions are checked against the model with a coordinate measuring machine (CMM).

18. Troubleshooting decision tree

Troubleshooting decision tree for hot-work failures.

Symptom: heat-check cracking on die surface. Cause: thermal fatigue from repeated heating-cooling cycles. Action: redesign cooling channels; lower-V grade (H11) for thermal-fatigue-prone sections; nitriding or PVD coating to reduce friction heat; verify draft angles are adequate. If cracking is shallow (<0.3 mm), re-nitriding can repair; deeper cracks require weld repair or section replacement.

Symptom: gross fracture of die block or shear blade. Cause: heat-treat defect (over-temperature austenitising), insufficient toughness for the application, geometric stress concentration, or impact overload. Action: replace tool; send failed sample for metallurgical analysis; review heat-treatment records and mill certificate. Preventive: vacuum furnace processing; ESR feedstock; verify corner radii per drawing.

Symptom: plastic deformation (sinking) at the working surface. Cause: operating temperature exceeded the alloy’s hot hardness limit. Action: replace tool; reduce operating temperature (better cooling); upgrade to higher-hot-hardness grade (H13, or consider carbide for very high temperatures); PVD coating for surface hardness.

Symptom: excessive wear at the cutting edge or working surface. Cause: insufficient surface hardness for the workpiece abrasion; over-tempering during heat treatment reducing hardness below target. Action: verify surface hardness; PVD coating or re-nitriding if appropriate; review heat-treatment records to confirm tempering temperature was correct.

Symptom: gross cracking during the first few shifts. Cause: hydrogen embrittlement from improper heat-treatment atmosphere, or residual stress from grinding. Action: send failed sample for analysis; verify heat-treatment atmosphere control; verify grinding protocol (coolant flood, no dry grinding).

Symptom: corrosion pitting on a hot-work tool. Cause: cooling water chemistry, exposure to corrosive process fluids. Action: CrN coating; verify water treatment; consider HSS or stainless upgrade for combined wear and corrosion service.

19. Worked example: H11 vs H13 selection for hot shear

Worked example: H11 vs H13 selection for hot shear.

A steel mill is replacing crop-shear blades for billet cutting. The billets are 150 × 150 mm mild steel at 950 °C. Blade geometry is 350 mm wide, 50 mm thick, with an edge angle of 30° per side and a 1.0 mm primary hone. Current blade material is H13 at HRC 50 with nitriding; blade life is 800 shifts before edge rounding and chipping forces replacement.

Step 1 — Operating temperature. The cutting edge runs at 600+ °C during the cut, dropping to 200 °C between cuts. Operating temperature is in the H11 / H13 range. HSS M2 or M42 would also work but at significantly higher cost.

Step 2 — Dominant failure mode. Current failure is edge rounding and chipping after extended service — combination of abrasive wear (oxide scale on billet) and thermal fatigue (repeated heating-cooling). Net shape loss is the issue, not gross fracture.

Step 3 — Grade comparison. H13 at HRC 50 has hot hardness HRC 42 at 600 °C. H11 at HRC 50 has hot hardness HRC 38 at 600 °C. H13 gives 10 % better wear life. H11 gives 15–20 % better thermal-fatigue resistance (lower V content). For this application, wear life and thermal-fatigue life are both important, but H13 has been the standard because the wear-life gain is more measurable.

Step 4 — Try H11 first. Switch to H11 ESR at HRC 50 with plasma nitriding (0.4 mm case depth). H11’s better thermal-fatigue resistance may extend blade life by 10–15 % despite slightly lower hot hardness.

Step 5 — If H11 fails prematurely on wear, return to H13. If the H11 trial does not deliver the expected life improvement, return to H13. The cost of the trial is limited to one blade’s worth of H11 ESR material.

Step 6 — PVD coating upgrade. Independent of the grade choice, apply TiAlN coating to the cutting edge. TiAlN at this hot-work service temperature extends edge life 30–50 % regardless of substrate grade. Combined with the H11 + nitriding, this is expected to deliver 1200–1400 shifts of blade life (50–75 % improvement over the H13 baseline).

Expected outcome. The trial validates whether the application is wear-limited or thermal-fatigue-limited. Either result improves the mill’s understanding of its hot-shear tooling and informs future blade selection across the mill’s hot-shear fleet.

20. Die-casting die design considerations

Die-casting die design considerations.

Cooling-channel design is the single most important factor for die life in aluminium and steel die casting. The channels should be placed as close as possible to the working surface (typically 1–2× the channel diameter from the surface), with adequate diameter (typically 8–12 mm for aluminium dies, 10–15 mm for steel dies), and connected in series or parallel with flow rates that ensure turbulent flow (Reynolds > 10,000). Insufficient cooling is the root cause of most premature die failures.

Draft angles of 1–3° per side are standard for aluminium die casting, 0.5–1.5° for steel die casting. Insufficient draft increases ejection force and friction heat, accelerating die wear and heat-checking. Excessive draft creates dimensional problems in the cast part.

Fillet radii at all internal corners are mandatory. Sharp corners initiate thermal-fatigue cracks. Standard minimum fillet is 1 mm for non-critical corners, 3 mm for highly stressed corners, 6+ mm for the most thermal-fatigue-prone sections.

Gating and overflow design affects both casting quality and die life. Sharp transitions in the melt flow path cause local overheating and erosion. Radiused runners and gates with adequate cross-section reduce these effects.

Ejector pin placement must avoid the highly stressed die sections and provide uniform ejection force. Asymmetric ejection causes bending loads that accelerate die failure.

Material selection by die section. The bulk of the die uses H13 ESR. Highly stressed sections (cores, slides) may upgrade to H13 ESR + plasma nitriding. Thermal-fatigue-prone sections (gates, runner systems) may use H11 for better crack resistance. Sliding wear sections (slides, ejector sleeves) may use H13 + PVD coating.

21. Surface treatments beyond PVD

Surface treatments beyond PVD.

Nitriding (gas or plasma) is the standard diffusion treatment for H11 and H13. Process: 500–580 °C for 10–60 hours in ammonia atmosphere (gas) or nitrogen-hydrogen plasma (plasma). Result: surface hardness HRC 60+ to a depth of 0.2–0.5 mm, with a thin compound layer (white layer) of iron nitrides at the surface. Plasma nitriding gives finer control of the compound layer and lower process temperature.

Nitrocarburising adds carbon to the nitriding atmosphere, typically by adding CO₂ or methane. The carbon diffuses alongside nitrogen and produces a harder compound layer with better wear resistance. Standard process: 570 °C for 2–6 hours. Nitrocarburising is widely used for hot-work tooling where the compound layer needs to support the load.

Boriding (boronising) produces an extremely hard surface layer (FeB + Fe₂B, HRC 70+) by diffusion of boron at 800–950 °C. Used for severe wear applications but with risk of brittleness in the compound layer. Not standard for hot-work tooling but occasionally used for severe abrasive wear at elevated temperature.

Oxidation treatment (steam treatment) produces a thin Fe₃O₄ layer on the surface, typically 3–5 µm thick. Provides modest wear resistance and corrosion resistance, with low cost. Used as a final surface passivation after nitriding on some forging dies.

Weld repair is common for hot-work tools in service. Laser cladding or GTA welding with matching filler material rebuilds worn or cracked surfaces. The weld region must be heat-treated after welding to restore the substrate properties. Multiple weld repairs degrade the substrate due to repeated thermal cycles; tools are typically limited to 2–3 weld repairs before retirement.

Combination treatments are increasingly common. Plasma nitriding followed by PVD coating combines the deep diffusion-hardened layer with the thin ceramic surface layer. Weld repair followed by re-nitriding restores both surface and bulk properties. The combination approach is standard practice for high-value hot-work tooling.

22. Heat treatment quality control

Heat treatment quality control.

Furnace qualification. Vacuum furnaces used for hot-work tool steel heat treatment must be qualified to the applicable aerospace or automotive standard (e.g., CQI-9 for automotive, AMS 2750 for aerospace). Qualification includes temperature uniformity surveys, furnace calibration, and process control documentation.

Process records. Every heat-treatment lot must have a chart record of the austenitising cycle (time at temperature, ramp rate), the quench cycle (medium, agitation, time), and each temper cycle (temperature, time). Records are retained per the procurement specification — typically 7 years for industrial tooling, longer for aerospace.

Sample testing. First article and sample-basis testing includes: hardness per ASTM E18 (Rockwell) or ASTM E384 (Vickers/Knoop micro-hardness); metallographic examination for grain size, decarburisation, and carbide network; Charpy impact on sample basis for critical applications; dimensional check against drawing.

Common defects to catch: Over-temperature austenitising produces coarse grain (ASTM 6 or coarser) and reduced toughness. Insufficient austenitising produces incomplete carbide dissolution and reduced hardness. Improper quench (too slow) produces bainite or pearlite instead of martensite. Insufficient tempering leaves retained austenite that transforms in service and causes dimensional drift. Surface decarburisation (from furnace atmosphere failure) produces a soft skin that has to be removed before nitriding.

First article qualification. Before full production, the first article from each heat-treatment lot should be fully tested (hardness, metallography, dimensions, surface condition) to confirm the process has run correctly. Subsequent lots are tested on a sample basis.

Traceability. Every tool must be traceable to its heat-treatment lot and to the mill heat number. The combination of mill certificate, heat-treatment records, and dimensional inspection provides the documentation chain that supports failure analysis and warranty claims.

23. Industry-specific applications

Industry-specific applications.

Automotive. Hot-stamping dies for press-hardened boron-steel body components use H13 ESR with AlCrN coating. Operating temperatures reach 600+ °C with rapid heating-cooling cycles; H13 is the only commercially viable substrate. Aluminium die-casting for transmission housings, engine blocks, structural components: H13 ESR with plasma nitriding.

Steel mill. Continuous caster cutting torches and crop-shear blades use H13 with high-temperature PVD coating. Slab shear blades for plate mill: H13 with nitriding or PVD. Billet shear: H13 with TiAlN coating.

Forging. Hammer forging dies: H13 with nitriding. Press forging dies: H13 with PVD or nitriding + PVD. Ring-rolling: H13 with PVD. Upsetter dies: H13 ESR with nitriding.

Aluminium extrusion. Extrusion dies and dummy blocks: H13 ESR with PVD or nitriding. Die bearings and liners: H13 with nitriding. Die sets for complex profiles: H13 ESR with multiple weld repairs and re-nitriding cycles.

Glass container manufacturing. Glass-mould blanks and baffles: H13 with nitriding. The combination of glass-contact temperature (~550 °C) and abrasive glass-particle environment drives the H13 specification with regular re-nitriding.

Plastics manufacturing. Injection moulds for glass-filled polymers: H13 with PVD (TiAlN, DLC) or nitriding. High-temperature polymers (PEEK, PSU, PPSU): H13 with nitriding or PVD. PVC processing: H13 with CrN coating for corrosion resistance.

Cement and mining. Crusher hammers and wear liners: H13 is too expensive for these applications — manganese steel or high-chromium cast iron is the standard. Hot-work tool steel does not find significant application in cement and mining outside of crusher wear parts.

24. Real-world case: H11 vs H13 for hot piercing punches

Real-world case: H11 vs H13 for hot piercing punches.

A seamless tube mill operates two piercing presses for 150 mm carbon-steel billets at 1200 °C. Piercing punches fail in two modes: gross fracture (catastrophic, punches last 800–1200 billets) and tip deformation / rounding (gradual, punches last 2500–3500 billets). Current punch material is H13 at HRC 50 with gas nitriding.

Failure analysis. Tip deformation is the dominant failure mode at ~3000 billets. The tip rounds plastically at the operating temperature because the hot hardness of H13 (HRC 42 at 600 °C) is at the lower limit for this service. Gross fractures are rare but expensive — each failure destroys a billet and stops the press for 30 minutes.

Intervention 1 — H13 tip with PVD coating. Apply AlCrN PVD coating to the piercing tip. The coating lifts surface hot hardness to HRC 60+ and reduces friction heat at the tip. Tip deformation mode is delayed but not eliminated. Punch life extends from 3000 to 4500 billets.

Intervention 2 — H11 punch body with H13 tip insert. Replace the monolithic H13 punch with a bimetallic design: H11 body for toughness and thermal-fatigue resistance, H13 tip insert for wear and hot hardness. Brazed or welded joint. H11 body reduces the gross-fracture risk while H13 tip maintains the wear resistance. Combined with PVD coating on the tip, expected punch life extends to 5000–6000 billets.

Intervention 3 — H11 monolithic punch with AlCrN coating. Try a simpler design — H11 monolithic punch with AlCrN PVD coating. H11’s lower V (0.4 % vs 1.0 %) gives slightly less hot hardness but better thermal-fatigue resistance. The AlCrN coating carries the surface hot hardness regardless of substrate. If the trial succeeds, this is the simplest and lowest-cost solution.

Outcome. Trial 3 was adopted as the production specification. H11 + AlCrN delivers 5000+ billets of tip life with zero gross-fracture failures over the 6-month trial period. The H11 substrate cost is 5 % lower than H13, and the AlCrN coating cost is comparable to other PVD options. Net result: 67 % improvement in punch life with no cost penalty and a small reduction in gross-fracture risk.

25. Cost-per-cycle and total cost of ownership

Cost-per-cycle and total cost of ownership.

Hot-work tooling is typically a high-value tool with significant cost per failure event. The cost-per-cycle analysis is the standard procurement methodology for hot-work tooling — particularly for forging and die-casting dies where the tool may represent $10,000–$500,000 in initial cost plus maintenance costs over its life.

Cost components. Raw material (steel cost + ESR premium if applicable), machining (often substantial for large dies), heat treatment, surface treatment (nitriding, PVD), weld repair and re-machining over tool life, and end-of-tool retirement. The proportion varies by tool type: forging die blocks are material-dominant (50–70 % material cost); small die-casting cores are machining-dominant; large die-casting dies are evenly split.

Cycle cost calculation. For a forging die block with 10,000-cycle target life: divide total tool cost by 10,000 cycles. For a die-casting die with 100,000-shot target life: divide total tool cost by 100,000 shots. Compare to the cost per part produced by the tool — the tool cost should be 5–15 % of the part cost for a healthy forging or die-casting operation.

Hidden costs to include:

• Downtime for tool change (often $5,000–$50,000 per change depending on the press size and product value)
• Weld repair cycles (typically 1–3 per die life)
• Scrap parts produced while tool is failing
• Warranty claims for parts produced by worn tools

A premium hot-work tool (H13 ESR + PVD + plasma nitriding) typically has 2× the material cost and 3–5× the cycle life of an entry-level tool (H13 air-melt + gas nitriding). The premium is justified by the cycle-cost reduction in most production-volume applications.

26. Summary

Summary of the hot-work family.

Hot-work tool steel fills the niche where the working surface or cutting edge operates at 200–600 °C under thermal cycling and impact loading. The defining feature is secondary hardening from Mo / V carbide precipitation combined with high toughness. H11 is the lower-V toughness grade (aluminium die casting, hot piercing, impact-loaded applications). H13 is the workhorse hot hardness grade (steel die casting, hot shear, plastic injection moulds). 6CrW2Si is the Chinese-standard tungsten-modified alternative. Selection is driven by operating temperature, dominant failure mode, and the cost-vs-life trade-off. Heat treatment at 1000–1050 °C austenitising and double temper at 540–620 °C is standard. Surface treatments (nitriding, PVD) compound the wear-life gain and are standard on production hot-work tooling. ESR-grade material is preferred for high-stress applications. Beyond H13 at 600+ °C, the next material family is nickel superalloys (Inconel 718) or cemented carbide. Hot-work tool steel sits between cold-work tool steel and the higher-temperature nickel-base and ceramic materials in the industrial tool-material hierarchy.

27. Quick reference card

Quick reference card for the hot-work family.

By operating temperature:

• 200–400 °C: cold-work tool steel (D2, A2) or H11
• 400–600 °C: H11 (impact) or H13 (wear)
• 600+ °C: H13 with PVD coating, or nickel-base superalloy, or carbide

By application:

• Aluminium die casting: H11 (cores) + H13 (bulk), ESR grade, plasma nitriding
• Steel die casting: H13 ESR + AlCrN coating
• Hot shear (steel mill): H13 + TiAlN coating, nitriding
• Hot piercing punches: H11 + AlCrN coating
• Forging dies: H13 ESR + nitriding
• Aluminium extrusion: H13 ESR + nitriding or PVD
• Glass container moulds: H13 + nitriding
• Hot stamping (auto): H13 ESR + AlCrN

By failure mode:

• Heat-check cracking: H11 + improved cooling + lower nitriding temperature
• Tip deformation (sinking): H13 + PVD coating + better cooling
• Gross fracture: ESR feedstock + verified corner radii + lower hardness target
• Wear: H13 + PVD + nitriding + harder substrate

By surface treatment:

• General hot work: plasma nitriding (0.3–0.4 mm case depth)
• Higher-temperature wear: nitriding + AlCrN PVD coating
• Severe thermal cycling: nitriding only (PVD can delaminate under thermal cycling)
• Severe wear at lower temperature: PVD coating only (TiAlN, CrN)

28. Author notes & source confidence

Author notes & source confidence for the hot-work pillar.

This pillar is compiled from publicly available standards (AISI, UNS, WNr/DIN, JIS, GB/T 1299, ISO 4957), major tool-steel manufacturer datasheets (Bohler, Assab/Voestalpine, Uddeholm, Crucible, Daido, Hitachi Metals, Tisco, Baosteel), and standard industrial references on hot-work tool steel heat treatment and surface engineering. The chemistry ranges, heat-treatment parameters, and property ratings are within the published tolerance bands of the cited references.

Confidence levels by claim category:

• Chemistry ranges: high confidence (standardised across multiple sources)
• Heat-treatment parameters (austenitising, tempering temperatures): high confidence (industry standard practice)
• Hot hardness values: medium confidence (depend on heat-treat parameters and test method; values are typical, not guaranteed)
• Charpy impact values: medium confidence (depend on specimen orientation, ESR grade, and heat-treat parameters)
• Cost comparisons: low-medium confidence (market prices vary significantly by region, lot size, and specification)
• Application guidance: medium confidence (based on common industry practice but specific applications may warrant deviation)
• Real-world case results: illustrative not definitive (specific outcomes depend on local conditions)

Known limitations. Specific PVD coating vendors (Oerlikon Balzers, IonBond, Phygen, etc.) have proprietary process variations that produce meaningfully different coating performance even at the same nominal chemistry. The PVD coating discussion in this pillar uses industry-typical values and should be supplemented with vendor-specific datasheets for procurement specifications.

Update cadence. Hot-work tool steel chemistry and heat-treatment specifications are stable across decades — the basic H11, H13, H21 grades have not changed since their introduction in the 1930s–40s. The newer additions are premium PM hot-work grades (similar to the PM HSS evolution) and improved surface treatments. This pillar should be reviewed against current manufacturer datasheets every 2–3 years; significant chemistry changes are rare.