Blueing

1) A blue oxide film produced on steel by low-temperature heating. 2) Heat treatment of steel springs to relieve strains caused by cold work. 3) Baking in a drying oven until the bright-cleaned wire turns blue under the lime coat. Blueing, produced by heating to temperatures around 300°C (570°F), does not provide corrosion protection, but it is often used as the finish for heat-treated springs.