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