An ultra - high strength steel Q960E,produced by either thermomechanical control process with accelerated cooling plus tempering ( TMCP + AcC + T) or quenching plus tempering ( QT),was investigated with an emphasis on the effect of tempering.The result shows that with the increase of tempering temperature,the yield strength and tensile strength decrease,but the total elongation increases for both the QT and TMCP + AcC + T treated plates.A different response,however,for the impact toughness with regard to tempering was observed.With the increase of tempering temperature,the impact toughness decreases first and then increases,with the lowest values occurring roughly at 400 and 300℃ for the QT and TMCP + AcC + T processes,respectively.The reason for this behavior may be due to the segregation of trace elements to grain boundaries.