The chromium plating layer and the base metal are like shoes that are the wrong size-when the temperature rises to 210℃, the difference in expansion between the chromium layer (coefficient of thermal expansion approximately 6.2 × 10⁻⁶/℃) and the steel substrate (11 × 10⁻⁶/℃) generates internal stress. Experimental data shows that for every 100℃ increase, the length difference between the two can reach 0.5 mm/m. This "hard shell encasing a soft core" structure is extremely prone to forming a network of microcracks under rapid heating.
80-120℃: The surface of the chromium plating layer begins to oxidize, forming a brittle oxide film.
150-180℃: The yield strength of the base metal decreases by 30%.
Above 200℃: A peak shear stress is generated at the interface between the chromium layer and the substrate.
Like an ice surface suddenly bearing weight, when the local temperature fluctuation exceeds 15℃/min, cracks will inevitably propagate preferentially along the grain boundaries.
Heating rate <= 8℃/min (optimal measured rate 5℃/min)
Holding time=(roll diameter mm/25) minutes
Grinding pressure is inversely proportional to temperature (<= 0.15MPa at 210℃)
