DH31-EX Material Detailed Information
DH31-EX is a high-performance hot work tool steel developed by Daido Steel. It is an enhanced version of H13 (SKD61, 1.2344), offering superior toughness, heat resistance, and wear resistance. This makes it ideal for high-stress applications such as aluminum die casting molds, hot forging dies, and extrusion dies, where tools experience severe thermal cycling and mechanical loads.
DH31-EX is specifically designed to provide longer tool life, higher resistance to heat checking, and improved toughness compared to conventional hot work steels.
Key Features
- Superior Heat Resistance: Withstands high operating temperatures up to 600°C, reducing tool deformation.
- Excellent Thermal Fatigue Resistance: Ideal for high-cycle die casting and extrusion dies, preventing heat checking and cracking.
- High Toughness & Impact Resistance: Ensures longer tool life, especially in high-stress forging and extrusion applications.
- Good Machinability: Easier to machine compared to other high-hardness tool steels.
Chemical Composition
| Element | Composition (%) |
| Carbon (C) | 0.30 – 0.50 |
| Silicon (Si) | 0.80 – 1.20 |
| Manganese (Mn) | 0.25 – 0.50 |
| Chromium (Cr) | 4.50 – 5.50 |
| Molybdenum (Mo) | 2.00 – 2.80 |
| Vanadium (V) | 0.30 – 0.70 |
| Nickel (Ni) | 0.80 – 1.20 |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.020 |
Key Features in Composition:
- Higher Molybdenum (Mo) Content: Improves heat resistance and strength retention at high temperatures.
- Nickel (Ni) Addition: Enhances toughness and uniform hardness distribution.
- Optimized Carbon (C) and Chromium (Cr) Levels: Ensures a balance between hardness, toughness, and wear resistance.
Mechanical Properties
| Property | Value |
| Hardness (Annealed) | ≤ 229 HB |
| Hardness (Hardened & Tempered) | 46 – 52 HRC |
| Tensile Strength | ~1,800 MPa |
| Yield Strength | ~1,500 MPa |
| Elongation | ~8 – 12% |
| Impact Toughness | Very High |
| Thermal Fatigue Resistance | Superior to H13 / SKD61 |
- Superior thermal fatigue resistance → Reduces cracking in high-temperature die casting molds
- Higher toughness than conventional H13 (SKD61) → Reduces risk of breakage under mechanical stress
- Good wear resistance → Extends tool life in high-pressure environments
- Excellent hardness retention at high temperatures
DH31-EX vs. Other Hot Work Tool Steels
| Property | DH31-EX | SKD61 (H13) | 1.2344 | DHA1 |
| Hardness (HRC) | 46-52 | 45-50 | 45-50 | 45-52 |
| Thermal Fatigue Resistance | Superior | Moderate | Moderate | High |
| Wear Resistance | High | Moderate | Moderate | High |
| Toughness | Very High | High | Moderate | High |
| Heat Resistance | Superior | Moderate | Moderate | High |
| Applications | Die casting, forging, extrusion, plastic molds | General hot work applications | General hot work applications | High-temperature tooling |
Why Choose DH31-EX?
- Better heat resistance and toughness than SKD61 (H13).
- Higher resistance to cracking and fatigue in cyclic heating/cooling applications.
- Longer tool life in high-pressure aluminum/magnesium die casting and hot extrusion applications.
Applications
DH31-EX is widely used in high-temperature tooling applications requiring high toughness, wear resistance, and heat resistance.
Die Casting Molds & Cores
- Aluminum, magnesium, and zinc die casting molds
- Shot sleeves, plungers, and core inserts
Hot Forging Dies
- Forging dies for steel and non-ferrous metals
- Punches and hot forming tools
Plastic Molding Applications
- High-temperature plastic injection molds
- Blow molding dies for engineering plastics
Extrusion Dies & Hot Shear Blades
- Aluminum and copper extrusion dies
- Hot cutting tools and blades
Other High-Temperature Tooling Applications
- Hot stamping dies
- Steel tube and pipe extrusion tooling
Heat Treatment Process
Annealing (Softening for Machining, if Required)
- Heat to 820–860°C, then slowly cool in a furnace.
Hardening
- Preheat at 600–700°C, then heat to 1,020–1,080°C, followed by oil or air quenching.
Tempering
- Temper at 550–650°C to achieve a working hardness of 46-52 HRC, balancing strength and toughness.
Surface Treatments (Optional, for Enhanced Performance)
- Nitriding: Increases surface hardness and wear resistance.
- PVD or CVD Coating: Reduces friction and oxidation for longer mold life.
Alternative Materials
- SKD61 (JIS) / H13 (AISI) / 1.2344 (DIN): Standard hot work tool steel with good overall performance but lower toughness and thermal fatigue resistance than DH31-EX.
- 1.2367 (DIN): Offers higher heat resistance than H13/DH31-EX, but is harder to machine.
- DAC (Daido Steel): Another high-performance hot work steel, but DH31-EX has better toughness and heat resistance.
- DHA1 (Daido Steel): Similar to DH31-EX but with slightly lower toughness.
Conclusion
DH31-EX is a high-performance hot work tool steel that offers superior thermal fatigue resistance, high toughness, and excellent wear resistance, making it ideal for die casting, hot forging, extrusion dies, and high-temperature plastic molding applications.
Best Choice for: High-temperature die casting, forging, and hot extrusion applications
Why Choose DH31-EX? Better heat resistance, higher toughness, and longer tool life than conventional H13 (SKD61)
