Development of Low Carbon-Niobium Steel with Ultra-deep Drawability

Abstract

A study has been made to develop deep-drawing sheet steel which can be produced by continuous annealing as well as box annealing, giving clean surface free from inclusions and orange peel-free surface in deeply drawn condition. To develop this type of steel, the following matters have been taken into consideration : (i) To obtain high ductility as well as favorable texture, ultra low carbon steel is adopted. (ii) Carbide-forming elements are added to fix interstitial carbon and nitrogen and whereby to obtain nonageing properties. (iii) To achieve clean sheet surface and avoid hardening the amount of alloying element is reduced as small as possible. (iv) Not all interstitial C and N do not precipitate by the addition of carbide-forming element. N is fixed as AIN by adding Al, which, in turn, together with carbides provide for the nucleation sites for the precipitation of remained free C. Ultra low carbon, niobium steel with Nb to C ratio of 1 in atomic weight is found to possess excellent properties. It shows high Lankford value, low yield, but relatively high tensile strength. The excellent properties are obtained in continuously annealed condition as well as box-annealed one.