Why Do Steel Bars Bend?
Bars bend due to stresses in the bar either thermal or residual stresses.
Thermal stresses are induced during the cooling process whereas residual stresses are due to the forces exerted on the bar in the rolling process.
Stresses are also induced into the bar by the cold finisher when they straighten the hot rolled bar when pre-straightening and during the peeling process.
It is easier to straighten a medium carbon steel 1045 bar than it is a highter alloy 4140 quench and tempered bar. That is becuase of the greater thermal stresses in the 4140 QT bars which are quenched. The thermal stresses induced in a quenching process make it more difficult to straighten a QT bar.
At Quality Bar our objective is to straighten 1045 bars after peeling to less than thirty thousandths (.030) over the length of a twenty-four foot bar where as with a 4140 QT bar Quality Bar's objective is to do better than fifty thousandths (.050).
Of course there are times when Quality Bar can do better than fifty thousandths and those times are when the mill will ship to do a better job of heat treating.