Hardening Effect of the Interstitial Free Steel Due to Cold Rolling

In this research, hardening effect of a 1.6 mm thickness commercial interstitial free (IF) steel has been investigated by tensile test and micro-hardness measurement. Microstructural characterization using optical microscopy revealed the single ferrite phase in all the steels. As-received steel had a homogeneous microstructure with grains size of about 40 µm, whereas the cold-rolled steel shown two different microstructures which included finer grains near the deformed surface and the same with as-received steel in the midsection. The tensile tested results show that the strength and micro-hardness have increased with increasing the deformed reduction, but decreased strongly in the annealed steel. It was found that increase of the YS was mainly contributed by dislocation density of the steels after each cold-rolling passes. Dislocation densities of the steels were calculated as 4.67 × 10¹³ m⁻² for as-received steel and achieved maximum as 8.95 × 10¹⁴ m⁻² for the rolled steel. The IF steel can be strongly hardened by cold rolling in case the application requires the strength instead of the ductility.