Die casting exposes moulds to intense thermal cycles, high injection pressures, and severe wear. Selecting the right mould steel is crucial for tool longevity, casting quality, and cost-efficiency. National standards differ, as do preferred grades, because of local supply chains, performance priorities, and manufacturing experience. This comprehensive guide examines the working conditions of die casting mould steel, the necessary steel properties, the fundamentals of iron and steel, and the effects of various alloying elements. It also offers detailed insights into commonly used die-casting mould steels, such as H13, SKD61, 1.2344, and others, with a particular focus on 4Cr5MoSiV steel
1. Key Performance Requirements
A first‑class die casting mould steel should provide:
- Thermal‑fatigue resistance – endures continuous heating–cooling cycles without heat‑checking or micro‑cracking.
- Hot strength and hardness – maintains dimensional integrity and resists abrasive wear at cavity‑skin temperatures up to 700 °C.
- Toughness under high pressure – withstands injection pressures of 150–500 MPa and resists gross cracking at sharp radii or thin ribs.
- Dimensional stability after heat treatment – retains precise cavity geometry following quench, temper and subsequent surface hardening.
- Moderate thermal conductivity – dissipates heat quickly enough for short cycle times while preserving core strength.
- Wear and erosion resistance – resists high‑velocity metal flow (70–150 m s⁻¹) at gates and runners, minimising wash‑out.
- Low affinity to molten metal – prevents soldering/sticking with aluminium, magnesium or zinc alloys, protecting surface finish.
- Surface‑treatability – accepts nitriding, PVD or duplex coatings without cracking or spalling, extending service life.
- Good machinability and polishability – allows cost‑efficient cavity machining, EDM, and mirror‑grade finishing where cosmetic quality is critical.
- Temper‑back and oxidation resistance – maintains hardness and surface integrity during long production runs at elevated temperatures.
Common Grades by Standard
| Region / Standard | Typical Grades | Trademark Notes |
|---|---|---|
| United States (AISI) | H13 – industry workhorse. H11 – higher toughness. AISI 8407 – Uddeholm upgrade to H13. H21 – excels at very high temperatures. | |
| Germany (DIN) | 1.2344 – German H13.1.2367 – superior thermal‑fatigue life. 1.2714 – high‑impact hot work.1.2888 – for extreme heat. | |
| Japan (JIS) | SKD61 – Japanese H13. DAC / DAC10 – Daido grades with excellent crack resistance. HPM1 / HPM38 – high polishability. | |
| China (GB) | 4Cr5MoSiV1 – Chinese H13.3Cr2W8V – traditional hot‑work steel.LD – similar to 1.2367. |
4Cr5MoSiV Steel
| Aspect | Details |
|---|---|
| Standard / Designation | GB/T 1299‑2020 “Alloy Tool Steels” – grade 4Cr5MoSiV |
| International Equivalents | AISI H13, DIN 1.2344, JIS SKD61 |
| Typical Chemistry (wt %) | C 0.32–0.45 · Cr 4.75–5.50 · Mo 1.10–1.75 · Si 0.80–1.20 · V 0.80–1.20 · Mn ≤ 0.40 |
| Heat Treatment | Austenitise 1020–1050 °C → oil/air/vacuum quench → double temper 540–600 °C |
| Hardness after HT | 44–52 HRC (Al die‑casting moulds usually 44–48 HRC) |
| Key Properties | • Excellent hot strength and toughness• High thermal‑fatigue resistance• Good machinability and polishability• Accepts nitriding / PVD coatings |
| Primary Applications | • Aluminium and zinc die‑casting moulds• Aluminium extrusion dies• Hot‑forging dies, cores and inserts• Plastic moulds requiring high wear/heat resistance |
3. Performance at a Glance
- Heat crack resistance: Dievar > 8407 > H13 ≈ SKD61
- Toughness / impact: DAC10 > SKD61 > H13
- Thermal conductivity: FDAC > SKD61 ≈ H13
- Heat treatment stability: 8407 > 1.2344 ≈ SKD61
4. Application Based Selection
| Scenario | Recommended Steels |
|---|---|
| Very long tool life | 1.2367, DAC, QRO 90 Supreme |
| Standard aluminium die casting | H13, SKD61, 1.2344 |
| High impact components | H11, 1.2714 |
| Extreme casting temperatures | H21, 1.2888, LD |
| Mirror finish surfaces | FDAC, HPM38 |
Tip: The best steel is not necessarily the most expensive but the one that matches your alloy, shot temperature, cycle time and maintenance regime.
4Cr5MoSiV/H13 Steel: Properties and Characteristics
4Cr5MoSiV, or China H13 steel, is an air-hardening hot-work tool steel that offers excellent properties for die-casting applications. It features outstanding toughness at medium temperatures, suitable hot strength, excellent thermal fatigue performance, and adequate wear resistance. When austenitised at relatively low temperatures and air-quenched, it exhibits minimal distortion from heat treatment. The steel has a low tendency to form oxide scales during air quenching and can withstand erosion from molten aluminium, making it particularly suitable for aluminium die-casting moulds.
Chemical Composition
The standardised chemical composition of 4Cr5MoSiV (according to GB/T 1299-2000) includes:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.33–0.43 |
| Silicon (Si) | 0.80–1.20 |
| Manganese (Mn) | 0.20–0.50 |
| Chromium (Cr) | 4.75–5.50 |
| Molybdenum (Mo) | 1.10–1.60 |
| Vanadium (V) | 0.30–0.60 |
| Phosphorus (P) | ≤0.03 |
| Sulphur (S) | ≤0.03 |
Physical Properties
4Cr5MoSiV has critical temperatures, including Ac1 (853°C), Ac3 (912°C), Ar1 (720°C), and Ar3 (773°C), with Ms at 310°C and Mf at 103°C. Its thermal expansion coefficient ranges from 10.9×10^-6 at 20-100°C to 13.6×10^-6 at 20-700°C. Thermal conductivity varies from 25.9 W/(m·K) at 100°C to 25.9 W/(m·K) at 700°C. The elastic modulus decreases with temperature, from 227,000 MPa at 20°C to 192,000 MPa at 500°C.
Heat Treatment Recommendations
For optimal performance, 4Cr5MoSiV requires careful heat treatment. Hot working temperatures range from 1120 to 1150°C for initial heating, 1070 to 1100°C for forging start, and 900 to 850°C for finish forging, followed by sand or pit cooling. Quenching should be performed with preheating at 650-700°C and 850-900°C, followed by austenitising at 1020-1060°C (optimally 1040°C) and air cooling to achieve a maximum hardness of 52-54 HRC. Tempering at 540-600°C results in a working hardness of 44-48 HRC, ideal for aluminium die-casting applications.
Influence of Alloying Elements in Mould Steel
| Element | Effect on Steel |
|---|---|
| Carbon (C) | Increases hardness and strength, but reduces flexibility. |
| Sulphur (S) & Phosphorus (P) | Impurities; cause brittleness, but aid machinability in small amounts. |
| Manganese (Mn) | Strengthens steel, offsets sulphur effects, and improves hardenability. |
| Silicon (Si) | Boosts hardness and magnetic properties; reduces toughness. |
| Tungsten (W) | Enhances high-temp strength and wear resistance. |
| Chromium (Cr) | Improves hardenability, wear, and corrosion resistance. |
| Vanadium (V) | Refines grain, boosting strength, toughness, and wear resistance. |
| Molybdenum (Mo) | Raises high-temp strength and fatigue resistance; prevents embrittlement. |
Why It Is Popular in China
4Cr5MoSiV (China H13) is the workhorse hot‑work tool steel for Chinese die‑casting shops for the following reasons:
- Local supply chain: Wide availability from domestic steel mills keeps costs and lead times low.
- Balanced performance: Offers a proven mix of hot hardness, toughness, and heat-checking resistance suitable for most aluminium die-casting duties.
- Process familiarity: Heat treatment windows and machining parameters are well established, reducing risks for mould makers.
In Short
H13 and its equivalents remain the global benchmark; however, modern alloys such as 1.2367, DAC, and QRO 90 Supreme provide notably better crack resistance and toughness for high-pressure, long-cycle production. Pairing the right steel with robust mould design, effective cooling, and vigilant maintenance is the surest path to consistent, high-quality castings.
However, material alone is not the entire story—mould design is equally important. A well-designed mould ensures efficient metal flow, improved cooling, extended tool life, and superior casting quality. This is why selecting the right mould partner is crucial.
DSW Industry designs and manufactures die casting moulds in-house and has produced over 3,500 tools worldwide. Our engineering team assists clients in specifying optimal mould steel, delivers turnkey tooling, and provides services ranging from die casting to CNC machining and surface finishing.
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