Effect of micro-alloying elements on the stretch-flangeability of dual phase steel

The present paper investigates the effect of micro-alloying elements on the stretch-flangeability of a conventional dual phase steel by means of microstructural analysis and hole expansion tests. The addition of micro-alloying elements suppressed the formation of new ferrite from the intercritical austenite and induced a finer grain size which increased the strength of the steel. The increased amount of intercritical ferrite formed at higher annealing temperature resulted in an improved stretch-flangeability by simultaneously increasing the elongation and decreasing the strength. The addition of 200 ppm Nb was beneficial for the hole expansion performance whereas a detrimental effect on hole expandability was found after the addition of 400 ppm Nb to the dual phase steel.