HPM38 Material Detailed Information
HPM38 is a premium-grade corrosion-resistant plastic mold steel developed by Hitachi Metals. It is a modified version of AISI 420 (1.2083) stainless steel, offering higher toughness, improved machinability, and enhanced polishability.
HPM38 is particularly well-suited for plastic molding applications requiring high precision, mirror finishing, and resistance to corrosion and wear, making it an ideal choice for optical lenses, medical components, and high-end plastic molds.
Key Features
- Outstanding Corrosion Resistance: HPM38 maintains its properties in humid environments, water-cooled molding applications, and aggressive plastics.
- Superior Polishing Ability: Achieves mirror-like surface finishes, making it perfect for optical lens and precision mold applications.
- Improved Machinability: Easier to cut, mill, and grind compared to conventional stainless mold steels.
- Higher Toughness: Reduces the risk of cracking and chipping under high stress compared to 1.2083 and 420 stainless steel.
- Good Wear Resistance: Suitable for high-volume plastic injection molding and extrusion dies.
Chemical Composition
| Element | Composition (%) |
| Carbon (C) | 0.38 – 0.45 |
| Silicon (Si) | 0.50 – 0.90 |
| Manganese (Mn) | 0.40 – 0.80 |
| Chromium (Cr) | 12.50 – 14.50 |
| Molybdenum (Mo) | 0.90 – 1.30 |
| Nickel (Ni) | 0.50 – 1.00 |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 |
Key Features in Composition:
- High Chromium (Cr) Content (12.5-14.5%): Provides excellent corrosion resistance, making it ideal for humid and corrosive environments.
- Nickel (Ni) & Molybdenum (Mo) Addition: Enhances toughness, wear resistance, and hardness uniformity.
- Optimized Carbon (C) Content: Maintains high strength and excellent polishability.
Mechanical Properties
| Property | Value |
| Hardness (Annealed) | ≤ 229 HB |
| Hardness (Hardened & Tempered) | 48 – 52 HRC |
| Tensile Strength | ~1,700 MPa |
| Yield Strength | ~1,500 MPa |
| Elongation | ~10% |
| Impact Toughness | Superior to 1.2083 (AISI 420) |
- Excellent corrosion and wear resistance
- High toughness and impact strength
- Superior mirror polishing ability
- Better machinability compared to standard stainless mold steels
HPM38 vs. Other Mold Steels
| Property | HPM38 | 1.2083 (AISI 420) | 1.2316 | S136 |
| Hardness (HRC) | 48-52 | 48-52 | 46-50 | 48-52 |
| Wear Resistance | Excellent | Good | Moderate | Excellent |
| Corrosion Resistance | Superior | Good | Excellent | Excellent |
| Toughness | Higher than 1.2083 | Moderate | High | High |
| Machinability | Better than 1.2083 | Moderate | Good | Moderate |
| Polishability | Excellent | Good | Good | Excellent |
| Applications | High-end plastic molds, optical lens molds | General mold steel | Water-cooled molds | High-end mirror-finish molds |
Why Choose HPM38?
- Better toughness and machinability than 1.2083 (AISI 420).
- Higher corrosion resistance than standard tool steels.
- Ideal for ultra-high-precision plastic molding applications requiring superior polishability.
Applications
HPM38 is widely used in plastic molding and high-precision tooling applications, particularly where corrosion resistance, high polishability, and toughness are required.
Plastic Injection Molds
- High-quality plastic parts production
- Optical lens molding (camera lenses, LED lenses, medical lenses)
- Medical plastic molding (syringes, IV components)
Extrusion & Blow Molding Dies
- Blow molding dies for clear plastic bottles
- Extrusion dies for PVC, PET, and medical-grade plastics
Precision Components & Wear-Resistant Parts
- High-precision mechanical parts
- Mold inserts and cavities requiring ultra-high polishing
Other Corrosion-Resistant Applications
- Water-cooled molds used in humid environments
- Molds for chemically aggressive plastics
Heat Treatment Process
Annealing
- Heat to 780–820°C, then slowly cool in a furnace.
Hardening
- Preheat at 600–700°C, then heat to 1,000–1,050°C, followed by oil or air cooling.
Tempering
- Temper at 180–250°C to achieve 48-52 HRC.
Surface Treatment
- Nitriding to improve wear resistance.
- PVD or CVD Coating for additional abrasion protection.
Alternative Materials
- YXR7 (Hitachi Metals): A lower cobalt version of YXR33 with slightly lower heat resistance but similar toughness.
- ASP23 (Powder Metallurgy Steel): A high-performance powder metallurgy (PM) steel with better wear resistance but lower toughness than YXR33.
- HAP40 (Powder Metallurgy Steel): Offers superior hardness and wear resistance, but less toughness than YXR33.
- SKH51 (AISI M2): A general-purpose high-speed steel, but not as tough or heat-resistant as YXR33.
- SKH55 (AISI M35): A cobalt-added high-speed steel, but lower impact strength than YXR33.
Conclusion
HPM38 is a high-quality corrosion-resistant stainless tool steel with excellent toughness, wear resistance, and polishability, making it ideal for high-precision plastic molding applications such as optical lenses, medical components, and clear plastic products.
Best Choice for: High-end plastic injection molds, optical molds, and precision tooling
Why Choose HPM38? Superior corrosion resistance, high toughness, excellent polishability, and improved machinability over conventional stainless mold steels
