"CQ, DQ & IF Steels � From �Bumper Component Welding State-of "
CQ, DQ & IF Steels – From “Bumper Component Welding State-of-the-Art Survey” by D.W. Dickinson AISI Bumper Project Group,Dec31, 2000 The commercial quality (CQ) Mild Steel sheet is the least expensive low carbon and low strength commercial product. It has reasonable formability but low strength. Often there is a need for improved formability. Melt processing to improve cleanliness and to exert some measure of particle shape control by melt conditioning with calcium or rare earth or by other means results in a more formable drawing quality (DQ) steel. The figure below Increased C & Mn Lowers Formability shows this measure of formability improvement1 between CQ and DQ product. Because of the cleanliness and particle shape control, these steels also usually exhibit improvements in some areas of welding. The presence of low carbon levels and clean steels results in the elimination of many forms of weld cracking, and the hardness and strength across the heat-affected zone of weldments is most often quite uniform. When even more improved formability is required, vacuum degassing and other melt practices which remove carbon to very low levels (<0.02%C) produce a grade of steel know as Interstitial Free (IF) steels. The extra deep drawing quality and super EDDQ steels on the diagram represent this type of steel sheet. The improved formability and weldability of these steels results in increased cost and decreased strength. Re-addition of Carbon and Manganese to gain back some of the lost strength results in reduced ductility as illustrated in the other figure. The effects are quite complex with reductions do to manganese, further reductions as a result of interactions between the Mn and Carbon, and finally formability reductions because of the effect of forming carbides as the carbon level is continually increased. 1 Takechi, H, “Advances in interstitial-free and bake-hardening steel sheets for automotive applications”, Microallying’95 Conf Proc. 1995