If you put your steel parts into a Cress Draw Furnace and set the temperature for 600oF because you want to draw down the hardness a few points to make the part a little tougher, you may get a surprise you don’t expect.
Few people even realize there is a range of dangerous tempering temperatures that exist. All mill sources publish tempering charts that show hardness levels that can be obtained from ‘as quenched’ temperatures to as high as 12000 F. What they don’t tell you, is you should avoid using temperatures between 5000 and 7000 F. This zone of tempering can cause a weakness in the finished part from what is called ‘Blue Brittleness’ or ‘Temper Enbrittlement’. It is most severe when Chromium is present in steel and these temperatures should always be considered ‘off limits’ to any of these steels.
In fact, every heat treated metal has an optimum operating range. If you are lowering the hardness level to induce properties the steel isn’t made for, you are most likely using the wrong grade of metal. All of the tool steels developed by the mills were originally developed to accomplish certain attributes. Look at every application for what it demands and then select the best metal to do the job.
COPYRIGHT © April 2007, by Advisor In Metals
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