Abstract: To improve the service life of W4Mo3Cr4VSiN(F205) low alloy high speed steel tap,F205 steel was quenched at 1 160℃ and tempered at different temperatures,and the tap tempered at an optimum temperature was then treated with ion plating.The peak of hardness of F205 low alloy high speed steel was gained at 560 ℃.By ion plating,the surface of taps got an about 2.5 μm thick,golden yellow TiN layer.The hardness of the layer reached 1 921 HV50 and the adhesion of the layer was up to 35 N.After ion plating treatment,the service life of taps increased 2 times than that without surface treatment.