In plastic injection molding, the quality of the mold directly determines the quality of the produced parts, their consistency, appearance, and cost. The reliability and performance of the mold largely depend on the choice of steel used. Depending on the application, production volumes, or the type of plastic injected, several types of steel are available, each with its own advantages.
Most Common Steels and Their Uses:
| Steel | Type | Main Characteristics | Advantages | Disadvantages | Typical Applications |
| 1.2311 (P20) | Pre-hardened steel | Versatile steel already hardened (~30–35 HRC), easy to machine and polish. A good compromise for medium production runs. | Easy to machine, good cost/performance ratio | Less wear-resistant than harder steels | Aesthetic parts, molds for ABS, PP, PE |
| 1.2738 (Modified P20) | Pre-hardened steel with added nickel | More homogeneous than 1.2311, better conductivity and polish ability. Suitable for large molds. | Excellent polish ability, better thermal resistance | More expensive than 1.2311 | Molds for technical parts or large housings |
| 1.2343 / 1.2344 (H11 / H13) | Hot work steel | Excellent resistance to heat and abrasion, used for filled plastics or fast cycles. | Very good heat and wear resistance | Harder to machine, more expensive | Molds for filled plastics (glass, fiber), inserts exposed to high temperatures |
| 1.2083 | Stainless steel | Corrosion-resistant, very good for aggressive materials or humid environments. | Corrosion-resistant, easy maintenance | Lower mechanical strength, expensive | Molds for PVC, transparent parts, or cleanroom use |
| 1.2316 | Enhanced stainless steel | More anti-corrosion alloys than 1.2083, excellent for polishing. | High corrosion resistance, excellent polish ability | More expensive, harder to machine | Optical parts, molds in corrosive environments |
| 1.2767 | High strength hardening steel | Very good hardness (~52 HRC), pressure and wear resistance, good polish ability. | Very high hardness and wear resistance | High cost, more complex machining | Inserts, high-precision cavities |
| Maraging steel (e.g. 1.2709) | High-performance steel | High hardness, very good dimensional stability, suitable for metal 3D printing. | Excellent mechanical strength and stability | Very expensive, requires specific heat treatments | Prototype tooling, complex molds |
Special Cases:
It is common to combine several steels in the same mold, depending on constraints:
– Insert in H13 steel for areas subject to abrasion (filled materials).
– Cavity in stainless steel if the material is corrosive.
– P20 plates for non-critical areas.
Notes on Treatments:
Some steels are pre-treated (delivered with optimized hardness), which helps reduce machining time. Others can be hardened, nitride, or coated to increase wear or corrosion resistance.