Automotive panels are assembled by welding after press forming. Press forming subjects some parts to very severe deformation, depending on the design, which can result in cracks and wrinkles if the material does not possess sufficient formability. Materials with good formability are those which can withstand large strain during plastic deformation, and those with a high value of elongation in a tensile test. High strength materials generally cannot withstand much plastic deformation, and there is a general tendency, as shown in the figure, that strength and formability are inversely related. For parts needing good formability, such as the inner and outer panels of a car body, only low strength sheets of low-carbon steel and ultra-low carbon steel can be used. For parts not requiring high formability, high tensile steel that offers higher strength can be used. Therefore, the development of materials involves improving the combination of strength and formability. The development of materials that have both high strength and formability has contributed substantially to the reductions in car body weight that have recently become possible. Development in this direction involves (i) improving formability without reducing the strength of cold-rolled steel sheets for general purposes, and (ii) further increasing strength while maintaining the formability of various high strength steel sheets. The terms "low strength materials" and "high strength materials" used in this context are classified not according to values common to all steel materials but by the strength usually adopted for each application. Since high formability is required for automotive panels, high tensile steel sheets for automotive use have a lower value of strength than structural plates used for buildings and bridges, as shown in the figure.