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The adhesion strength of hard chrome plating on nickel-chromium steel can be ensured by controlling the following steps:
Surface Preparation
Thoroughly clean the steel surface to remove oil, grease, and contaminants.
Mechanical polishing or grit blasting may be used to slightly roughen the surface, enhancing mechanical interlocking.
Acid Etching / Pickling
Treat the steel surface with an acid solution (typically dilute sulfuric or hydrochloric acid) to remove the oxide layer.
This ensures chemical bonding between the substrate and the chromium layer.
Strike or Underlayer Plating
Apply a thin nickel or nickel-cobalt strike layer before hard chrome plating.
The underlayer improves adhesion and reduces the risk of peeling.
Electroplating Process Control
Temperature: Maintain plating bath at 50–60 °C.
Current Density: 40–60 A/dm² for hard chrome; uniform current ensures even deposition.
Bath Composition: Use high-purity chromium trioxide and sulfuric acid, control impurities.
Agitation: Ensure uniform solution movement to avoid weak spots.
Post-Treatment / Hydrogen Removal
Bake the plated part at 150–200 °C for 1–2 hours to remove hydrogen absorbed during plating.
Hydrogen removal is crucial to prevent hydrogen embrittlement, which can reduce adhesion and cause cracks.
Inspection
Perform adhesion tests such as tape tests, bend tests, or micro-scratch tests to verify bonding strength.
Hard Chrome Plating | Precision Metal Surface Treatment Services
