Effect of tempering temperature on the microstructure and mechanical properties in mooring chain steel

The tensile behavior of a mooring chain steel was investigated after tempering at 560 °C, 600 °C, 640 °C temperatures. With increasing tempering temperature, the steel displayed not only a decrease in strength, but also a slight increase in strain-hardening ability between the proof and ultimate stress. In the meantime, an upper yield point appeared at 640 °C tempered samples. The susceptibility to hydrogen-induced embrittlement reduced on the same precharging hydrogen condition as tempering temperature elevated. These changes of tensile behavior were elucidated from their microstructure variation observed by transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD).