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Recently, I visited industry where they produce steel coils (rebar + plain coils). At the end of the production process, I discover that rebar coils are getting sprayed by water:

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Whereas plain coils are not getting sprayed by water. What's the purpose of spraying water on rebar coils but not on plain coils?

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  • $\begingroup$ The process on the rebar coils is called quenching and tempering, which resulting in higher strength and toughness than hot-rolled bars. A metallurgist can provide better explanation. $\endgroup$
    – r13
    Mar 25, 2021 at 21:25

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The rebar may be getting some hardening depending on temperature and chemical composition. If they are hot enough to show any color ( roughly 1200 F) it is definitely some hardening. Because the transformation from high temperature austenite takes some time ( depending on chemistry ) ; some hardening could develop at lower temperatures. The rebar coils would only need to be straightened and have the anchor pattern rolled into them to be finished. The other coils are likely to have significant further processing such as wire drawing or cold heading so they need to be less hard = more ductile so are cooled slowly.

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