Effect of strain ageing on the mechanical properties of interstitial-free steels under as-received, heat-treated, and spot-welded conditions for automotive applications

In this study, the artificial ageing behaviour of interstitial-free steels is investigated under as-received, heat-treated, and spot-welded conditions. All the test specimens except those in the as-received condition were austenitized at 950 degrees C for 15 min followed by water cooling. Both as-received test pieces and heat-treated test pieces were prestrained by 8 per cent in tension, and then aged at 170 degrees C for 10 min, 20 min, 40 min, 60 min, 80 min, and 120 min. The experimental work revealed that strain ageing takes place in as-received, heat-treated, and spot-welded test pieces. However, strain ageing is more pronounced in heat-treated test pieces and spot-welded heat-treated test pieces, compared with the as-received test pieces and spot-welded as-received test pieces. This is due to the nature of heat treatment and spot welding.