Mild steels have an essentially ferritic microstructure. Drawing Quality (DQ) and Aluminium Killed (AKDQ) steels are examples and often serve as a reference base because of their widespread application and production volume.
Interstitial-free (IF) steels (Low strength and high strength)
IF steels have ultra-low carbon levels designed for low yield strengths and high work hardening exponents. These steels are designed to have more stretchability than Mild steels. Some grades of IF steels are strengthened by a combination of elements for solid solution, precipitation of carbides and/or nitrides, and grain refinement. Another common element added to increase strength is phosphorous (a solid solution strengthener). The higher strength grades of IF steel type are widely used for both structural and closure applications.
Bake hardenable (BH) steels
BH steels have a basic ferritic microstructure and are strengthened primarily by solid solution strengthening. A unique feature of these steels is the chemistry and processing designed to keep carbon in solution during steelmaking and then allowing this carbon to come out of solution during paint baking. This increases the yield strength of the formed part.
Isotropic (IS) steels
IS steels have a basic ferritic type of microstructure. The key aspect of these steels is the delta r value equal to zero, resulting in minimized earing tendencies.
Carbon-manganese (CM) steels
Higher strength CM steels are primarily strengthened by solid solution strengthening.
High-strength low-alloy (HSLA) steels
This group of steels are strengthened primarily by micro-alloying elements contributing to fine carbide precipitation and grain-size refinement.