Thermomechanical treatments of a 1050 pearlite steel

A study of the microstructures and mechanical properties of thermomechanically treated 1050 steel has been carried out. The materials were first transformed to fine and coarse lamellar pearlite structures. These samples were reduced 75 pct in thickness by cold rolling, then heat treated at 780 °C (up-quenching) or 650 °C (annealing) for different periods of time, followed by air-cooling. The mechanical properties were found to be vastly improved by suitable thermomechanical treatments. A significant improvement in yield strength was accompanied by moderate increase in ultimate tensile strength, and the elongations were maintained above 15 pct in 3 cm gage length. The optimal mechanical properties were developed between 30 and 120 seconds during 780 °C up-quenching for coarse pearlite samples and 100 to 400 seconds for both annealed coarse and fine pearlite specimens. In these instances the relatively long duration of heat treatment time shall facilitate the industrial processing of the steel. The improvement in mechanical properties was correlated with distinct microstructures in pearlite regions, which were fine subgrains (or grains) less than 1 μm in size and dispersed globular carbide particles along the subgrain (or grain) boundaries. Formerly with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan.