Technical guide · 2026-08-14
Hot-Work Tool Steel
Hot-work tool steels are selected for dies and inserts repeatedly exposed to hot metal, combining temper resistance, hot strength and toughness with resistance to thermal fatigue and heat checking.
01
Definition and boundary
This category is driven by cyclic thermal and mechanical loading in forging, extrusion and die casting; cold-work wear rankings alone do not predict hot-tool life.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Chromium-molybdenum-vanadium systems retain tempered hardness at temperature.
Clean microstructure and toughness delay heat-check initiation.
Cooling-channel design and surface temperature gradients govern thermal fatigue.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| H13 | Widely used chromium hot-work grade for die casting and extrusion. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| H11 | Tougher chromium hot-work option for impact and thermal cycling. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| H21 | Tungsten hot-work system for stronger hot-hardness emphasis. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
04
Properties and trade-offs
Hot hardness and temper resistance
Thermal-fatigue resistance
Elevated-temperature toughness
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Aluminum die-casting dies
- Hot-extrusion tooling
- Forging dies and hot shear blades
Properties and trade-offs
- Model peak surface temperature and cycle severity.
- Prioritize premium cleanliness for large die-casting blocks.
- Coordinate cooling layout, working hardness and toughness target.
07
Fabrication, durability and inspection
Use slow uniform preheating through transformation ranges.
Control quench rate to balance properties against cracking risk.
Apply multiple tempers and verify the die core reaches temperature.
08
Procurement checklist
- Specify premium or remelted quality when fatigue life requires it.
- State block orientation, center soundness and inclusion acceptance.
- Provide heat-treatment, hardness-uniformity and microstructure criteria.
09
Standards, sources and review
Standards and designation context
- ASTM A681 alloy tool-steel scope
- ASTM A600 where high-speed grades apply
- Buyer drawing and heat-treatment specification