Abstract: Medium carbon low alloy wear resistant cast steel was heated to 880,910,930,960 ℃ for 2 h and following by oil quenching,and then tempering progresses were performed at 210,240,260 ℃ for 2 h.At last,second tempering at 240 ℃ for 2 h was performed after determining the best heat treatment accoding to the impact toughness.The properties and martensite substrate of the tested steel after double tempering were studied.The result show that,after double tempering,the tensile strength of the tested steel up to 1 820 MPa,the hardness was 54 HRC and the impact energy was 35 J,the tested steel exhibited a good match with high strength,high toughness and good wear resistance.For the reasons of recovery and disappearance of twins in martensite after second tempering,the martensite substrate was high density of dislocations and small amounts of twins,large numbers of dislocations hindered the crack extension and improved the strength-toughness of the tested steel.