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Plastic Mold Steel
BRAND: PROMISTEEL GRADES: P20, 718H, 1.2311, 1.2738, 1.2083, S136, NAK80
SHAPES: Heavy Plate, Forged Block, Flat Bar
DELIVERY CONDITION: Pre-hardened (28-36 HRC), EAF+LF+VD, Annealed
SURFACE: Black, Milled, Grinded FEATURES: High Polishability, Good Photo-etching
APPLICATION: Car Bumpers, TV Housings, Plastic Bottles, Medical Devices
MOQ: 25 Tons
Plastic Mold Steel is the foundation of the modern injection molding industry. Unlike cold or hot work steels, plastic mold steels prioritize polishability, photo-etching capabilities, and corrosion resistance.
We offer a diverse portfolio ranging from standard Pre-hardened Steels (like P20/1.2311) which allow for immediate machining without further heat treatment, to high-performance Stainless Plastic Mold Steels (like S136/1.2083) designed for molding corrosive plastics (PVC) or optical-grade transparent parts. Our steels are produced with high purity to ensure a mirror-finish surface free from pinholes or inclusions.
Product Specifications & Grade Equivalents
Our inventory covers the most widely used global standards for mold bases and core inserts.
Table-1
Select the right grade based on mold size and surface requirements.
International Grade Comparison |
||||
| GB (China) | ASTM / AISI (USA) | DIN (Germany) | JIS (Japan) | Type/Feature |
| 3Cr2Mo | P20 | 1.2311 | - |
Standard Pre-hardened |
| 3Cr2NiMo | P20+Ni | 1.2738 | - |
High Hardenability (Large Molds) |
| 718 / 718H | P20+Ni | 1.2738 | - |
Improved Polishability |
| 4Cr13 | 420 | 1.2083 | SUS420J2 |
Stainless / Corrosion Resistant |
| - | - | - | S136 |
High Mirror Polish Stainless |
| - | P21 | - | NAK80 |
Age Hardening / Super Mirror |
Table-2
Optimized alloy content for uniform hardness and polishability.
Chemical Composition (Mass Fraction %) |
||||||
| Grade | C | Si | Mn | Cr | Ni | Mo |
| P20 / 1.2311 | 0.35~0.45 | 0.20~0.40 | 1.30~1.60 | 1.80~2.10 | - | 0.15~0.25 |
| 718 / 1.2738 | 0.35~0.45 | 0.20~0.40 | 1.30~1.60 | 1.80~2.10 | 0.90~1.20 | 0.15~0.25 |
| S136 / 1.2083 | 0.36~0.45 | ≤0.60 | ≤0.80 | 12.0~14.0 | - | - |
Table-3
Large blocks are available for automotive bumper and dashboard molds.
Supply Range & Size Specifications |
||||
| Product Form | Thickness (mm) | Width (mm) | Length (mm) |
Delivery Condition |
| Forged Block | 200 - 1000 | 300 - 1500 | 1000 - 4000 |
Pre-hardened / Annealed |
| Heavy Plate | 20 - 200 | 1000 - 2300 | 2000 - 5800 |
Pre-hardened (28-34 HRC) |
| Flat Bar | 20 - 300 | 205 - 810 | 2000 - 6000 |
Machined / Black |
| Round Bar | Φ 20 - 600 | - | 3000 - 6000 | Black / Peeled |
Key Features and Advantages
- Pre-hardened Condition: Most P20 and 718 grades are supplied at 28-36 HRC. This allows mold makers to machine the steel directly to the final shape without the risk of distortion caused by subsequent heat treatment.
- Excellent Polishability: High purity (ESR optional) allows the steel to achieve a high-gloss or mirror finish, essential for clear plastic parts (lenses, bottles).
- Corrosion Resistance: Stainless grades like 1.2083 (S136) resist corrosion from acidic plastics (like PVC) and humid working environments, reducing mold maintenance.
- Uniform Hardness: Grades with Nickel (like 1.2738) ensure consistent hardness from the surface to the core, even in blocks up to 400 mm thick.
- Photo-etching Ability: Uniform microstructure ensures clear, consistent texturing patterns.
Typical Applications
Plastic Mold Steel is versatile, supporting industries from consumer goods to automotive:
Automotive Interiors & Exteriors
Large molds for bumpers, dashboards, and door panels (typically uses 1.2738 / 718H).
Home Appliances
Casings for TVs, washing machines, and air conditioners.
Medical & Optical
Syringes, lenses, and transparent containers requiring a mirror finish (uses S136 / NAK80).
Packaging
PET bottle preform molds and bottle caps.
PVC Pipe Fittings
Requires corrosion-resistant steel like 1.2083.
FAQ
Q1: What is the difference between P20 and 718 Steel?
A1: P20 (1.2311) is the standard plastic mold steel. 718 (1.2738) is an upgraded version containing ~1% Nickel. This Nickel addition improves the "hardenability," ensuring that large blocks have uniform hardness at the core. 718 also offers slightly better polishability.
Q2: What does "Pre-hardened" mean?
A2: It means the steel is supplied already heat-treated to a working hardness (usually 28-36 HRC). The benefit is that the customer can machine the mold and use it immediately without sending it out for heat treatment, saving time and eliminating the risk of warping.
Q3: When should I use S136 (Stainless Mold Steel)?
A3: You should use S136 or 1.2083 when:
Molding corrosive plastics (like PVC or Acetates) which release acids.
The mold operates in a humid environment.
A high-grade optical mirror finish is required (e.g., for glasses or clear bottles).
Q4: Can you provide ESR quality for plastic molds?
A4: Yes. For applications requiring a Super Mirror Finish (e.g., optical lenses), we recommend ESR (Electroslag Remelting) grade S136 or 718, as it removes impurities that could cause pitting during polishing.
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