Effect of Hot Forging and Boron Content on the Mechanical Properties of Dual Phase Steel

Abstract

Carbon steel is widely used in different applications such as automotive industry. Boron is used as micro-alloying element to enhance the mechanical properties of carbon steel. The objective of the present work is to study the effect of boron on mechanical properties of dual phase steels. Dual phase (DP) steel is used in the underbody suspension for automotives.The material used in the present study was a carbon alloy steel (0.29 Cwt %) with different boron contents 0.0003 and 0.007wt %. The steels were cast using an open air induction furnace. The molten steel had the shape of Y-blocks. The parts of Y-blocks of alloys 0.0003B and 0.007B steels were heated up to 1200oC and then hot forged producing bars. After hot forging, the bars were subjected to air cooling. In the hardening process, the different alloys (0.0003B, 0.007B) were heated up to the intercritical annealing temperatures (between Ac1 and Ac3) for 15 minutes and then water quenched. The resultant microstructures after quenching process were observed as ferrite plus islands of martensite. After that, tempering was done at 300°C, 400°C and 500°C for different interval times. The experimental results revealed the mechanical properties of the selective alloys were significantly changed by boron content and tempering treatment. By increasing the boron content, hardness gradually increased with small effect on ductility of alloys. By increasing the tempering time and temperature, hardness was gradually decreased while ductility was improved. Compression testing was carried out to determine the compression strength and work-hardening coefficient. The studied steel presented typical manifestations related to dynamic strain aging: serrated flow (the Portevin-Le Chatelier effect).