KWO (Nitriding + Oxidation)

Advanced Oxidation Technology for Anti-Soldering & Corrosion Resistance

KWO Surface Treatment

The Dual-Layer Advantage

KWO is a composite treatment that applies a specialized oxidation process after nitriding.

  • Oxide Layer: The dark outer layer seen in the microstructure acts as a protective shield.

  • Function: This layer prevents direct metal-to-metal contact between the mold and molten aluminum, significantly reducing soldering (sticking) and erosion.

Formation of Protective Oxide (Fe₃O₄)

X-Ray Diffraction (XRD) analysis confirms the chemical stability of the KWO surface.

  • Magnetite (Fe₃O₄): The process generates a dense layer of Fe₃O₄ (Black Rust), which is chemically stable and highly corrosion-resistant.

  • No Red Rust: Unlike harmful rust (Fe₂O₃), this controlled oxide layer enhances the mold’s lifespan under high-temperature conditions.

    * Treatment Condition: 350°C x 1Hr + 520°C (Oxidation) 3.

Hardness Distribution Profile

Comparison of hardness profiles for various hot work steels (H11, H13, 2367) after KWO treatment.

  • Optimization: While the extreme surface hardness is slightly adjusted to accommodate the oxide layer, the sub-surface maintains high hardness to support the structure.

  • Result: A perfect balance between surface lubricity (from oxidation) and structural strength (from nitriding).

Superior Erosion Resistance

Molten Aluminum Erosion Test Results The chart compares the amount of dissolution (material loss) in molten aluminum.

  • Significant Improvement: The KWO treated samples (Right group) show drastically lower material loss compared to Non-KW and standard KW samples.

  • Benefit: This translates to a significantly longer mold life in LPDC and HPDC applications where aluminum erosion is a major failure mode.