Effect of tempering temperature on the mechanical properties and microstructure of an copper-bearing low carbon bainitic steel

The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copper-bearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the microstructure was mainly the laths of bainite in the as-quenched steel. The bainitic laths were restored and combined after the steel tempered at various temperatures. There were martensite/austenite (M/A) islands and numerous dislocations within and between the bainitic laths, while very fine precipitates of ɛ-Cu were also observed within the laths. With increasing the tempered temperature from 400 to 600°C, the yield strength (YS) increased from 877 to 957 MPa, whereas the ultimate tensile strength (UTS) decreased from 1020 to 985 MPa. The Charpy V-notch (CVN) varied from 68.5 to 42 J, and the value was minimal for the steel tempered at 500°C.