Lambda value calculation for DP600 and FV 607

Advanced High Strength Steels (AHSS) were developed for use in the automotive industry due to increasing pressure to reduce vehicle emissions and improve vehicle safety. The AHSS DP600 (commercial name) was the main subject of this study. Dual Phase (DP) steel global formability is comparable to conventional HSS but local formability is poor. Automotive component manufacturing processes require excellent material formability. Uniaxial tensile tests and FLCs are insufficient in evaluating total formability. The Hole Expansion Test (HET) was developed to overcome this issue, it evaluates material stretch flangeability.

By varying the punching speed it was discovered that an optimum speed
exists between 1 and 1.6mm/s and the use of the flat die was also beneficial at these
speeds. In terms of average HER, the FV 607 outperformed the DP600 at 2mm/s. At
1mm/s there was no significant difference in measured HER values. An optimum flange
height also exists between 1 and 1.6mm/s. This is understandable since a positive
correlation was observed between HER and flange height. For all speeds tested, the
bulge die produced the highest flanges and it was suggested that this is due to it allowing
more material flow. In terms of thinning, the bulge die produced more thinning at speeds
above 1mm/s and more thinning was exhibited by the specimens which were tested using
the bulge die. Again this is understandable, larger HER values require more excessive
thinning to account for the deformation. Under all conditions the FV 607 exhibited more
thinning compared to DP600. This could be due to the differences in their inherent
material metallurgical structure or even the variations in their edge surface microstructure
response to AWJ machining.