Investigation on microstructural, mechanical, and electrochemical properties of water, brine quenched and tempered low carbon steel

We report the microstructural, mechanical and electrochemical response of low carbon steel under water and brine quenching, tempering processes to open a new window for the steel manufacturing industry. Light optical and scanning electron microscopes reveal that microstructure of water quenched steel mainly comprised of packets and blocks of supersaturated lath martensite ( ′) with allotriomorphic ( al) and idiomorphic ( id) ferrites. Due to the higher cooling rate, brine quenching produced lath martensite with Widmanstätten ferrite ( w) and idiomorphic ferrite ( id). Energy dispersive spectroscopy validated the presence of these phases by their elemental composition. Water quenching provided 41% improved while brine quenching 47% improved tensile strengths. They also produced much higher Rockwell hardness, lower elongations, and lower impact toughness compared to the non-heat treated sample. On the other hand, water and brine quenching, tempering processes caused lattice relaxation of ′ by diffusing the excess carbon to phases. This microstructural transformation significantly enhanced the elongation and impact toughness values at little expense of tensile strengths and Rockwell hardness. Electrochemical properties of water, brine quenched and tempered low carbon steel were evaluated in both mild (3% NaCl) and intense (1% HCl) environments. In 3% NaCl solution, the highest corrosion resistance was achieved after water quenching process, while the lowest after water quenching with tempering processes compared to other heat treated samples. On the other hand, the highest corrosion resistance was offered by brine quenched sample and the lowest by brine quenched and tempered sample in an intense 1% HCl solution compared to other heat treated samples.