1. Hardness Range
Ordinary chrome-plated rods: The surface coating hardness typically ranges from 400-1200 HV (Vickers hardness), with the specific value affected by factors such as the plating bath composition and current density.
Hard chrome rods (hard chrome plating): The hardness is significantly higher, reaching 800-900 HV (Vickers hardness) or 90-100 HRC (Rockwell hardness), making them suitable for high-wear applications.
2. Factors Affecting Hardness
Coating Thickness: Hard chrome plating is typically ≥20μm thick, while ordinary chrome plating is only 0.25-0.5μm. Increasing thickness increases hardness.
Process Parameters:
Low chromic anhydride concentration results in higher hardness, but poor bath stability.
Optimal hardness is achieved when the ratio of sulfuric acid to chromic anhydride is 100:1. Excessive sulfuric acid can actually reduce hardness.
Increasing current density increases hardness, but it stabilizes after exceeding a threshold.
3. Comparison with Other Materials
Chrome-Plated Rods vs. Hard Chrome Rods:
Chrome-plated rods are made of steel with a chrome-plated surface and have a lower hardness (60-80 HRC).
Hard chrome rods are made of a chromium-based alloy and have a higher hardness (90-100 HRC) and better wear resistance.
Chrome Plating vs. Decorative Chrome: Hard chrome emphasizes functionality (wear resistance and high temperature resistance), while decorative chrome emphasizes aesthetics (rust resistance and gloss).
4. Application Scenarios
High hardness requirements: For applications such as hydraulic rods, molds, and piston rods, choose hard chrome rods (≥800 HV).
General wear resistance requirements: For drive shafts and guide components, standard chrome-plated rods (400-700 HV) can meet these requirements. 5. Testing Standards
Hardness testing must comply with standards such as GB/T 9790 (Vickers hardness) or ASTM B456 (Specification for Hard Chrome Coatings) to ensure coating quality.
