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What happens to stainless steel when heated red-hot over a gas flame

Customer Question

When I heated a stainless steel knive over a stove-top flame, it blackened. After a day, there appeared to be rust spots on part of the blackened surface. does science know of a way to restore the blackened/rusted part of the knive to it's original appearence? What is involved, and what has happened to the steel such that it turns black?
Submitted: 7 years ago.
Category: Homework
Expert:  DrTutor replied 7 years ago.

Stainless steel is make of iron/chromium alloy. The chromium content is usually 10%.

When you heat the knife, iron reacts with oxygen in the air to give iron oxide which shows up as rust spot. The chromium reacts with oxygen in the air to give chromium oxide which appears to be black.

There are no ordinary way to restore the knife, because iron oxide and chromium oxide can not be converted easily to iron and chromium in its original alloy form.

One possible solution can be to carry out an electrochemical process where the iron oxide and chromium oxide can be reduced back to iron and chromium (but not necessarily in its original alloy form).

DrTutor, Ph.D.
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Customer: replied 7 years ago.
Reply to DrTutor's Post: What does this electrochemical process involve?
And you say that
"iron oxide and chromium oxide can not be converted easily to iron and chromium in its original alloy form." I take this to me that it is in fact possible, just difficult. could you expatiate on this more difficult process?
Expert:  DrTutor replied 7 years ago.

One possible solution can be to carry out an electrochemical process where the iron oxide and chromium oxide can be reduced back to iron and chromium (but not necessarily in its original alloy form).

Customer: replied 7 years ago.
Reply to DrTutor's Post: So about this "eloctrochemical process": Would you make the peice of steel (a knive in this case)complete an electrical circuit, or what?
And what about the more difficult process that would actually cause the iron oxide and chromium oxide to become an alloy? would you have to melt them down, or something?
Expert:  DrTutor replied 7 years ago.

Yes you make the peice of steel (a knive in this case)complete an electrical circuit.

The electrons (from the electricity) will reduce the iron oxide and chromium oxide back to iron and chromium.

Customer: replied 7 years ago.
Reply to DrTutor's Post: And what about the more difficult process that would actually cause the iron oxide and chromium oxide to become an alloy? would you have to melt them down, or something?
Be assured, when I'm satisfied, I'll pay.
Thanks.

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