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Old 07-09-2018, 09:43 AM
timothale timothale is offline
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Join Date: Feb 2013
Location: near yellowstone
Posts: 80
Default metalurgy 101

Almost 60 years ago my college metalurgy professor demonstrated how steel behaves when heated and cooled. He had a steel wire stretched across the clasroom between 2 insulators and wired in series with a light bulb, he fliped the switch and the wire started heating up and expanded and started to sag, then as it heated and got to a dull glow the wire started to contract and pull back up. The professor explaned at a certain temperature the steel, carbon, and, othe elements rearrange the molecular structure , get dense and were non magnetic. When the metal is rapidly cooled the molecular structure stays locked in. This is the process to harden tool steal then reheating to temper and change some of the structure to get the degree of hardness you want. I have never seen a study to show how much shrinkage in weld cooling is molecular crittical temperature rearrangement VS simple expansion and contraction below the critical rearrangement temperature. I don't know if slowly reheating a cooled weld and slowly cooling would work with out over headin the metal around the weld and making it "dead".,.
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