The graph shows how alpha-prime formation reduces toughness in ferritic stainless steels. The worst toughness-inhibiting effects come from interstitial elements in grain boundaries: oxygen, carbon, and nitrogen. Stabilizing removes the interstitial carbon and nitrogen, along with oxygen and sulfur, from solution. This does not produce a major softening, however, because the precipitate itself has a hardening effect.
Because stabilized alloys are ferritic at all temperatures, there is no automatic grain-refining transformation as exists in carbon steel. If grains grow large from annealing at high temperatures or welding, then the transition temperature increases. Section size also has an effect. Stabilized ferritic stainless steels are seldom used in thicknesses of over several millimeters because of decreasing toughness.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Ferritic Stainless Steels ⇒ Properties
