What is 1.2378 mold steel?

1.2378 mold steel is a high-performance tool steel widely used in the mold-making industry, particularly for plastic injection molds. Known for its excellent wear resistance, toughness, and corrosion resistance, this steel grade is ideal for producing high-precision molds that require durability and a high-quality surface finish.

Product Characteristics

1.2378 mold steel is a pre-hardened, high-chromium martensitic stainless steel designed for plastic molding applications. Its key characteristics include:

High Corrosion Resistance: The high chromium content (approximately 13.6%) provides excellent resistance to corrosion, making it suitable for molds operating in humid or chemically aggressive environments. This reduces maintenance costs and extends mold lifespan.
Superior Wear Resistance: The steel’s composition and heat treatment ensure excellent resistance to wear, even under high-temperature conditions, making it ideal for long-term use in injection molding.
Excellent Polishability: 1.2378 offers outstanding surface finish capabilities, making it perfect for molds requiring mirror-like surfaces, such as those used for optical or transparent plastic products.
Good Toughness and Plasticity: Despite its high hardness, the steel maintains good toughness and plasticity, allowing it to withstand complex mold geometries and high-pressure conditions.
Mirror Rust-Proof Properties: The steel’s ability to resist rust and maintain a smooth surface makes it suitable for precision molds, including those used for producing CDs, optical instruments, and medical components.
Ease of Machining: 1.2378 can be machined effectively, especially when processed using advanced techniques like selective laser melting (SLM), which allows for the creation of complex mold structures.

These characteristics make 1.2378 a preferred choice for manufacturing high-quality plastic injection molds, particularly for applications requiring precision, durability, and corrosion resistance.

Chemical Composition

The chemical composition of 1.2378 mold steel is carefully balanced to achieve its desirable properties. Below is a table summarizing its typical chemical composition:

Element	Content (%)
Carbon (C)	0.35–0.45
Silicon (Si)	0.20–0.80
Manganese (Mn)	0.30–0.60
Chromium (Cr)	12.50–14.50
Molybdenum (Mo)	0.10–0.50
Phosphorus (P)	≤0.03
Sulfur (S)	≤0.03

Note: The exact composition may vary slightly depending on the manufacturer and specific production processes.

Mechanical Properties

The mechanical properties of 1.2378 mold steel are optimized through heat treatment processes such as quenching and tempering. The following table outlines its typical mechanical properties:

Property	Value
Hardness (HRC)	48–52 (pre-hardened)
Tensile Strength (MPa)	1500–1800
Yield Strength (MPa)	1200–1400
Elongation (%)	≥10
Impact Toughness (J/cm²)	≥20
Density (g/cm³)	7.75

Note: These values are approximate and depend on heat treatment and processing conditions.

The combination of high hardness, tensile strength, and toughness makes 1.2378 suitable for demanding mold applications, while its good elongation ensures resistance to cracking under stress.

Steel Type

1.2378 is classified as a martensitic stainless tool steel under the DIN EN ISO 4957 standard. It is specifically designed for plastic mold applications and is often delivered in a pre-hardened condition, typically at a hardness of 48–52 HRC. This pre-hardened state eliminates the need for additional heat treatment, reducing the risk of deformation or cracking during mold fabrication. Its martensitic structure, enhanced by high chromium content, contributes to its corrosion resistance and wear resistance, making it a specialized mold steel.

Standard Dimensions

1.2378 mold steel is available in various forms to suit different manufacturing needs. Common forms and dimensions include:

Round Bars: Diameters ranging from 20 mm to 300 mm.
Flat Bars: Thickness from 20 mm to 100 mm, width from 100 mm to 600 mm.
Plates: Thickness from 10 mm to 200 mm, width up to 1000 mm, and length up to 2000 mm.
Blocks: Custom sizes available for specific mold requirements.

These dimensions can be customized based on the application, and the steel can be supplied with black, rough-machined, or turned surfaces to meet specific tolerances.

Equivalent Materials

1.2378 mold steel is equivalent to several other steel grades used in different regions. Below is a list of comparable standards and grades:

AISI/SAE: 420 (modified)
JIS: SUS420J2 (modified)
China (GB/T): 4Cr13
Böhler: M333 ISOPLAST (with enhanced nitrogen alloying for improved properties)

Applications

1.2378 mold steel is widely used in the following applications:

Plastic Injection Molds: Suitable for producing high-precision molds for plastic products, including automotive components, consumer electronics, and packaging.
Optical and Transparent Molds: Ideal for molds used in producing CDs, optical lenses, and other transparent plastic products due to its excellent polishability.
Medical and Food-Grade Molds: Its corrosion resistance makes it suitable for molds used in medical devices and food-grade plastic production.
Complex Geometries: The steel’s machinability and compatibility with selective laser melting (SLM) make it suitable for intricate mold designs.

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