Letter 29081

Phosphating of tool steel  

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We use a casting of CH13 (hot worked tool steel investment casting)for our component making. This casting undergoes heat treatment (spherodising, machining, gas carburising, hardening and tempering, Hardness = 60 HRC) followed by sand blasting for surface cleaning.

While performing manganize phosphating, we find white patches. We are looking for a unifirm black colour. Can some one help to avoid white patches. Phosphating is followed by tectyl 272 oiling. Corrosion test (as per ASTM B-117 [link is to spec at TechStreet]) on the component with white patches show a good corrosion resistance.

G R Patel
Manufacturer, Power Equipments - Vadodara, Gujarat, India

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