Metallurgical Factors Affecting the Formability of Cold-rolled High Strength Steel Sheets

Abstract

The metallurgical factors affecting the press formability of cold rolled high strength steels are discussed and the properties of the following 40 kgf/mm² class tensile strength steels are examined: dual phase steel consisting of a ferrite-martensite structure, produced by rapid cooling in a continuous annealing line, which has a very low yield to tensile strength ratio and high n-value; rephosphorized steel, which is a batch-annealed aluminum-killed steel hardened with phosphorus and manganese, having a high r-value and a relatively low yield strength; and a recently developed steel of extra deep drawing quality and high strength which is characterized by its extremely high r-value, over 2.0, and low yield strength. This can be produced by continuous annealing of niobium-stabilized, extra low carbon, phosphorus-bearing steel. The formability and brittleness of the steels are also examined.