If carbon steel bars are heated above the Al transformation point and cooled, their dimensions at room temperature change. The dimensional changes in the case of air cooling are similar with that in the case of furnace cooling. The carbon content of steel bars has effect on the percentage and the direction of dimensional changes.Such dimensional changes are enlarged by the repetition of heating above transformation point and cooling, while they become smaller in some measure with the increase of the holding time at a temperature above the transformation point.