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Archie Zietman

Why exactly does carbon make steel harden?

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Wullo,

What is it about carbon presence in the steel which makes it harden upon quenching? I'm curious as to exactly why chemically and physics-ally.

 

be merry!

Archie

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The short answer is to many atoms of iron and carbon ( and possibly other elements ) in to small a space - but it's also how they are forced together.

 

If you want the long answer, head over to Google books, and look up a book called " The manufacture of iron in all its various branches ", by a man named ' Fredrrick Overman', in it ( towards the back ) is a section called

THE MANUFACTURE OF STEEL, which has allot of the info you are looking for.

Edited by Greg H.

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Carbon causes steel to be hard when the steel is quenched from an elevated temperature to a cold temperature. It does this by getting into the interstitial spaces between the iron atoms in the face centered cube of austenite. Then when it is quenched, the cube tries to collapse, trapping the carbon atoms inside what is now a highly stressed tetragon, which is hard. A bit over simplified perhaps, but that is how it works.

 

I suggest any entry level intro to physical metallurgy book for a deeper explanation of why this is so. Then "Principles of Heat Treatment", by M.A. Grossman, and "Alloying Elements in Steel" by E.C. Bain for further understanding. It is good to start with John Verhoeven's book published by ASM International titled "Steel Metallurgy for the Non-Metallurgist"

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I second the suggestion of "Steel Metallurgy for the Non-Metallurgist". It's sort of, at least in my limited view, a "Cliff Notes" on steel melallurgy. It deals with so much of what we do in knife making that I'd almost consider the knowledge in this book essential. The book is set out in a pretty logical order and has a good quick summery at the end of each chapter.

 

Doug Lester

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