Cold Roll Coil Steel Hardness

I am cold rolling bi-metal steel coils (Copper Alloy on steelback). My challenge is correlating the finished steel hardness with the percent reduction. I need this to choose the proper steel size to begin with to ultimately achieve the proper final hardness and size.

I'm an engineer and not an experienced metalurgist. I assume there curves or formulas available to determine the steel hardness vs % reduction? Does anybody know where I can find these and what other factors I should be considering in this process?

Reply to
Josh
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Josh,

Bascially your final as-rolled hardness is a fuction of the orginal input hardness transformed by the metal flow model base on the amount of strain (%reduction).

Some stress verses strain curves are published ASM International in a book (check the web site). Unfortunately these will be next to useless fo you. Standard hardness verses % reduction curves (really plots) from steel companies (if you can find them!!) are only applicable to their machinary due to redundant deformation.

What you really need is a metal flow model. Generally for steels hardness follows the tensile strength (other will say yield strength but they don't realize that it only applies to the annealed state - they are ignorant of the process of work hardnening).

The metal flow model for you case must use tensile strength (not hardness - hardness is not a ratio scale - has no zero!) can convert to hardness (using tables from per ASTM A360 or SAE J417)

For % reduction e (measured in true strain only!!!)

OCRT=3DICRT* exp (e) for en

Where:

ICRT =3D Input Cold Rolled Tensile Strength (from input hardness) OCRT =3D Output Cold Rolled Tensile strength (can convert to hardness)

e =3D natural or true strain from rolling =3D ln (input thickness/output thickness) + Redundent strain

n =3D necking strain - strain at tensile load.

A =3D intercept factor (specific to steel) - in ksi or N/mm=B2 units B =3D post necking strain hardening factor (specific to steel) ksi/strain or N/mm=B2/strain

Actually it would be easier IMHO to plot these surves from your product using the flow model above rather than search for data.

Good Luck

Ed Vojcak PE

Reply to
Ed

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