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<p>carbon to diffuse into the surface of the steel. The depth of this high carbon layer depends on the exposure time, but 0.5mm is a typical case depth. Once this has been done the steel must be heated and quenched to harden this higher carbon 'skin'. Below this skin, the steel core will remain soft due to its low carbon content.</p>

<p><big> History </big></p>
<p>Early <a href="page.php?w=iron">iron</a> <a href="page.php?w=smelting">smelting</a> made use of <a href="page.php?w=bloomery">bloomeries</a> which converted iron ore into metallic iron by heating</p><p>
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