Mechanical and microstructural evaluation of dual phase steel, quenched in bitumen and water at an intercritical temperature: effect of holding time

Low carbon steel was heat-treated at an annealing temperature of 800 °C for a different holding time of 30, 40, 50 and 60 min, to investigate the microstructure evolution and the mechanical properties of Dual Phase (DP) steel. The samples were subjected to different quenching medium (bitumen and water) and the result obtained was analyzed. Optical microscope characterization of the DP steel shows the extensive distribution of martensite phase within the ferrite matrix. The DP steel exhibit improved ultimate tensile strength, yield strength, and hardness when compared with the as-received samples. At the holding time of 50 and 60 min, DP steel quenched in water shows better strength and hardness as compared to bitumen quenched samples. The hardness value of water to bitumen quenched at 50 and 60 min is 169.32 HV as against 167.72 HV and 172.46 HV as against 169.67 HV respectively. Likewise, for ultimate tensile strength, the values showed 600.09 MPa as against 594.42 MPa and 611.22 MPa as against 601.33 MPa respectively, and that of yield strength as 304.14 MPa as against 301.27 MPa and 309.78 MPa as against 304.77 MPa respectively. Despite the slight difference in strength and hardness, both quenching medium (water and bitumen) can be exploited for the production of Dual Phases steel. (paper)