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Yellowish color on stainless steel

Currently our company have running a product like scissors using stainless steel SUS 420 material but each time after heat treatment process a yellowish color will come out, after completed heat treatment process it will proceed to grinding process. The problem is the yellowish color will remain at the cutter blade side and we not sure if this will cause rustiness or not? although we have done washing process before heat treatment and also after grinding process. May I know of any solution can be used to solve this kind problem? passivation is an alternative way or not? thank you.

You need an inert atmosphere in the furnace and clean parts.

10% HCl will do the trick

Passivation should definitely help.

Dear Malcom,

Passivation can definitely help. And lately there has been scientifically proven products available in the market. During grinding, because of the heat generated, the ratio of Cr, S and Fe ratio on the ground surface get imbalanced and more Fe surfaces. This will form rust and that the yellow coulor. I have read about a company known as CST Surtec International, who have mastered in passivation of SS of different varieties of SS200 onwards to 400+.
Regards

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