The chemical composition of plastic mould steel grades varies significantly depending on the desired properties, such as hardness, toughness, polishability, and corrosion resistance. These are typically alloy steels, with key elements like chromium, molybdenum, manganese, nickel, and carbon determining their performance.
Pre-Hardened Steels (P-Type)
Pre-hardened steels, such as the P20 series, are a common choice for plastic molds. They are often based on a combination of Chromium (Cr), Manganese (Mn), and Molybdenum (Mo).
The chemical composition of three widely used grades in this category is detailed below:
| Grade | C (%) | Si (%) | Mn (%) | P (%) | S (%) | Cr (%) | Mo (%) | Ni (%) |
|---|---|---|---|---|---|---|---|---|
| 1.2311 (P20) | 0.35–0.45 | 0.20–0.40 | 1.30–1.60 | ≤0.030 | ≤0.030 | 1.80–2.10 | 0.15–0.25 | – |
| 1.2312 (P20+S) | 0.35–0.45 | 0.30–0.50 | 1.40–1.60 | ≤0.030 | 0.05–0.10 | 1.80–2.00 | 0.15–0.25 | – |
| 1.2738 (P20+Ni) | 0.35–0.45 | 0.20–0.40 | 1.30–1.60 | ≤0.030 | ≤0.030 | 1.80–2.10 | 0.15–0.25 | 0.90–1.20 |
- 1.2311 (P20) is a general-purpose mould steel with good machinability and polishability.
- 1.2312 (P20+S) has a higher sulfur (S) content, which significantly improves its machinability, making it suitable for molds with complex shapes.
- 1.2738 (P20+Ni) includes nickel (Ni) to improve its through-hardenability and toughness, making it ideal for large, high-load molds.
Corrosion-Resistant Steels
For molds that process chemically aggressive plastics, corrosion-resistant steels are used. These are typically martensitic steels with a high chromium content, often around 13%.
The table below shows the composition of some common and newer corrosion-resistant grades:
| Grade | C (%) | Si (%) | Mn (%) | Cr (%) | Mo (%) | Other |
|---|---|---|---|---|---|---|
| 1.2083 | 0.38–0.45 | max 1.0 | max 1.0 | 12.5–13.5 | – | – |
| 1.4028 | 0.28–0.35 | max 1.0 | max 1.0 | 12.5–14.0 | – | – |
| M333 ISOPLAST | 0.20 | 0.30 | 0.30 | 13.5 | – | +N |
Some modern grades replace a portion of the carbon (C) with nitrogen (N) to enhance both corrosion resistance and toughness. Another example is 2316 steel, which is a premium mould steel containing 16% chromium and 1% molybdenum.
Other Common Steel Grades
Other tool steels are also frequently used for plastic molds:
- H13 A versatile chromium hot-work steel that offers excellent resistance to thermal fatigue from repeated heating and cooling cycles. It is often used for moderate to long production runs.
- S7 An air-hardening tool steel with high carbon and high chromium content, providing a good combination of wear resistance and toughness for large molds and long production cycles.
The chemical compositions of DIN 1.2311, DIN 1.2312, DIN 1.2738, DIN 1.2085, DIN 1.2316S, DIN 1.2316, DIN 1.2083, and AISI 420S steels vary depending on their intended applications. For precise chemical compositions, consult the manufacturer's manual
The chemical compositions of DIN 1.2311 Steel, DIN 1.2312 Steel, DIN 1.2738 Steel, DIN 1.2085 Steel, DIN 1.2316S Steel, DIN 1.2316 Steel, DIN 1.2083 Steel, and AISI 420S steels are tailored to their specific applications, such as plastic molding, die casting, or corrosion-resistant tools. Each steel grade contains distinct percentages of elements like carbon, chromium, molybdenum, and others, influencing properties like hardness, toughness, and corrosion resistance. For example, DIN 1.2316 and AISI 420S often have higher chromium for enhanced corrosion resistance. For precise chemical compositions and detailed specifications, refer to the manufacturer's manual or technical data sheets.