Effect of Heat Treatment on Microstructure, Magnetic and Mechanical Properties of HSLA-100

In this study, the effects of various heat treatments on microstructure, mechanical and magnetic properties of HSLA-100 steel were evaluated. The heat treatments consisted of austenitizing at 900°C for 60 minutes, then quenching by different cooling rates via furnace, air, oil and water; and quenched specimens were aged at 600°C for one hour. Optical and field emission scanning electron microscopes were used for the characterization of the microstructure. A vibrating sample magnetometer, an inductance meter and a susceptometer were used for the characterization of the magnetic properties. Mechanical properties of the specimens were also studied using hardness, tensile strength and impact toughness methods. The fracture surfaces of charpy specimens were examined using scanning electron microscope. The results showed that martensite phase was spread in the all of the cooling rate. The results of magnetic coercivity force indicated that coarse Cu precipitates and martensite-austenite (MA) constituents hinder the domain wall motion and behavior in effective magnetic susceptibility. Moreover, the non-magnetic copper precipitates reduced magnetic permeability. The hardness value of the aged specimens is the same as that of the quenched steels (approximately 300 VHN30). In addition, yield strength as high as 900 MPa was achieved in aged specimens. The highest impact toughness value at -84℃ (approximately 200 J) was obtained in as-received and aged specimens.