AISI H13 Hot Work Tool Steel — Die Casting, Extrusion & Forging Die Properties
ASTM A681 (UNS T20813) · Published: 2026-06-14 · Updated: July 2026
AISI H13 is the dominant hot-work tool steel globally — if you've ever held a die-cast aluminum part (engine block, laptop case, bicycle frame), you've held something made in an H13 die. Its chromium-molybdenum-vanadium composition provides the...
AISI H13 is the dominant hot-work tool steel globally — if you've ever held a die-cast aluminum part (engine block, laptop case, bicycle frame), you've held something made in an H13 die. Its chromium-molybdenum-vanadium composition provides the unique combination of hot strength (maintaining hardness above HRC 40 at 600°C), thermal fatigue resistance (surviving thousands of heating-cooling cycles without cracking), and toughness (resisting brittle fracture under impact loading).
The key metallurgical feature of H13 is its secondary hardening response. Unlike plain carbon steels that continuously soften as tempering temperature increases, H13 exhibits a hardness peak at approximately 500-550°C due to the precipitation of fine alloy carbides (primarily VC and Mo2C). This secondary hardening peak is what allows H13 dies to maintain their hardness at the elevated temperatures encountered during aluminum die casting (molten aluminum injected at 650-700°C).
Die life optimization for H13 centers on: (1) proper austenitizing temperature — overshooting by even 25°C coarsens the grain and reduces toughness by 30-40%; (2) double or triple tempering — retained austenite from the first temper transforms to fresh martensite on cooling and must be tempered again; (3) surface treatment — nitriding or PVD coatings can extend die life 2-5x in aluminum casting applications.
Quick Facts
| Category | Tool Steel |
| Standard | ASTM A681 (UNS T20813) |
| Density | 7800 |
| Yield Strength | 1,200-1,500 MPa (hardened and tempered, HRC 44-52) |
| Tensile Strength | 1,400-1,800 MPa |
Physical Properties
| Melting Point | 1427°C |
| Thermal Conductivity | 24.3 W/m·K at 20°C |
| Density | 7.80 g/cm³ |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 1.2344 | Compare |
| X40CrMoV5-1 | Compare |
| JIS SKD61 | Compare |
| GB 4Cr5MoSiV1 | Compare |
Heat Treatment & Processing
| Austenitizing | 1000-1040°C, soak 20-30min per 25mm |
| Quenching | Air or oil (air preferred for complex shapes) |
| Tempering | 540-650°C, double temper recommended |
| Annealing | 840-870°C, furnace cool at 10-20°C/h |
Welding & Fabrication
| Preheat | 300-500°C, maintain throughout welding |
| Filler Metal | H13 filler or E312 stainless for repair |
| Pwht | Anneal immediately after welding, re-harden |
| Weldability Rating | Poor — welding is for repair only |
Related Materials
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Frequently Asked Questions
H13 vs H11 — which should I spec for die casting?
H13 (5% Cr) offers better hot hardness and thermal fatigue resistance than H11 (5% Cr but lower carbon and vanadium). For aluminum die casting — spec H13. For forging dies where toughness is more critical than hot hardness — H11 may be a better choice. The practical difference is approximately 10-15% longer die life for H13 in die casting applications.
What causes heat checking in H13 dies?
Heat checking is the network of fine surface cracks caused by thermal fatigue — the die surface expands when it contacts molten metal, then contracts when cooled by the release agent spray. Each cycle produces a small strain. After thousands of cycles, the accumulated plastic strain exceeds the material's ductility at the surface and cracks initiate. Prevention: reduce die surface temperature swing with conformal cooling channels, use a release agent that provides more uniform cooling, and ensure the die is preheated to 200-250°C before the first shot.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu