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Question:

What is the Rockwell (HRC) Indentation Hardness of Steel?

The hard industrial steels. If there's a bunch, what's a rough average? Also, what is is measured in?

Answer:

There is no average, it depends on the type of steel (hundreds) and the (heat/surface) treatment (infinite possibilities). The Rockwell hardness range covers a large scale so for any given range there is a suffix (C is used for most steel) to denote the selected range. The number is a dimensionless constant that correlates to the strength of the material. Materials can also be surface (case) hardened and then the bulk material will be soft and the surface will be hard, this is typical for items like gears and cams that have rolling wear but are not very heavily stressed to require bulk hardness. Most steel that is hardened is first machined to size and then hardened. If more accuracy is required, they are machined to just over net size, hardened and then ground to the final size as the heat treatment can change the size and shape a little as stresses are released. Some examples: Very hard steel (e.g. a higher quality knife blade): HRC 55–66 Axes, chisels, etc.: HRC 40–45 4140 Cr Mb Steel HRC 28 - 36 , bulk hardened to HRC 54, Nitride case hardened to HRC 60 P20 tool steel can be bulk hardened to over HRC 55 and then tempered down from HRC 51 to 28
Hrc Steel
The general purpose default steel for hard tooling applications is A2 It's cheap, readily available and comes in many different shapes and sizes. It's easy to machine soft. It's easy to harden, you can do it yourself. It is very dimensionally stable during hardening. All the steels mentioned above are specialty steels - expensive to buy, hard to work with, expensive to heat treat and dimensionally unstable during heat treat.

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