The hot rolled surface magnified in the first illustration (left) is an artist’s representation of the scale formed on steel during the hot rolling process. This black or gray scale is acceptable for some structural requirements but it must be removed by machining for most tooling mold applications.
The second illustration (right) depicts the grain structure of hot rolled steel during the rolling process. Hot rolling breaks down coarse grains and reforms them into finer, stronger grained steel. Hot rolled steels are rolled oversized. This allows for scale removal and allows the stock to be machined to a normal size. The oversize will vary from .005″ for very small steel stock to 1/4 inch on larger pieces and alloy steels.
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