Meaning
High carbon high chromium alloy steel provides the wear resistance needed for abrasive polymer moulding applications. D2 tool steel governs the dimensional stability of injection moulds by maintaining sharp parting lines and resisting abrasive wear from mineral filled thermoplastics. The material specification defines chemical composition limits containing twelve percent chromium and one and a half percent carbon, whereas a part specification details surface finish tolerances and hardness values for an individual moulded component.
Virgin resin processing exerts predictable friction against cavity walls, but abrasive regrind introductions accelerate abrasive wear on core pins and gate inserts. Datasheet values report annealed hardness under twenty five HRC before machining, while vacuum hardening processes achieve final working hardness reaching sixty two HRC after thermal treatment.
Thermal Treatment
Achieving optimal wear performance requires controlled austenitising and subsequent cryogenic cooling. Vacuum furnaces heat the alloy to one thousand degrees Celsius before air quenching to minimise dimensional distortion across complex cavity blocks. Moulders adjust tempering cycles to relieve internal stresses while retaining sufficient carbide volume for high pressure compression moulding tasks.
Insufficient soaking time during hardening leaves retained austenite, which transforms under thermal cycling during long production runs and causes premature edge chipping along thin gate configurations.
Surface Wear
Uncoated cavity surfaces suffer abrasion during glass filled polycarbonate processing. Titanium nitride coatings reduce friction coefficients and prevent adhesive galling between sliding shut off faces. Moulders monitor micro pitting near gate lands because abrasive wear alters melt velocity and creates flashing defects on finished parts.
Proper polishing eliminates microscopic peaks where stress concentrations initiate premature cracking under cyclic clamping loads.
Corrosion Resistance
Chromium carbides provide substantial wear longevity, but free chromium depletion during carbide precipitation lowers resistance to acidic degradation from halogenated flame retardants. Condensation inside chilled water channels pits the internal cooling lines, which restricts fluid velocity and induces localized thermal hotspots across the parting plane. Protective electroless nickel plating prevents chemical attack from reactive decomposition gases during extended downtime periods.
