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  #31  
Old 07-26-2011, 02:31 PM
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87hdrush 87hdrush is offline
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You know Chris you are probably right but my calculator was getting dusty
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  #32  
Old 07-26-2011, 03:00 PM
CARS CARS is offline
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You know Chris you are probably right but my calculator was getting dusty
Don't get me wrong, this is interesting. But I can never seem to get the same gap/no gap or HAZ every time. Anyway, learning is good!
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Old 07-26-2011, 05:13 PM
cameron cameron is offline
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I haven't been around much lately, returned to college in Jan. majoring in Mechanical Engineering. took a break from my studies to see whats new on the site and found this post. I'm taking my ferrous metallurgy final this week so maby I can shed some light on this debate Simply put the changes in low carbon steel (1040 in this case) are dependant on the temperature you heat it to. under 300 degrees there is little change in the granular structure of the steel and it will return to it's original state. To cause shrinkage or distortion the metal must be heated above it's lower transformation temprature (about 1200 degrees) a weld puddle will get you above that temp. The distortion or shrinkage is a result of localized heat increase. Warming the area around the weld will help(but not too hot) If cooled slowly the metal will have little physical change. If the metal is quenched, the rapid cooling will cause a smaller grain structure thus the metal "shrinks". Low carbon steel doesn't harden well this is the reason it is used for bodywork. We have a Rockwell tester in our lab. mabe I could test some weld samples to see just how much the area is effected
I'll take your word that's true for an unrestrained piece of metal. It doesn't mean that you can't shrink sheet metal at much less than 1200 degrees. What is required for shrinkage is that compression stresses in the plane of the sheet exceed the yield strength. This applies whatever the temperature and however the compression stesses are obtained , and whether heating and cooling are involved or not.

Yield strength is affected by the temperature, which is only one of the reasons why shrinking sometimes involves heating.

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