Abstract: Microstructure, static and dynamic mechanical properties of three different high-fragmentation steel were studied by means of SEM, Hopkinson pressure bar and tensile testing machine and other instruments. Three Johnson-Cook dynamic constitutive models for three 1000 MPa high-fragmentation steels were fitted. The results show that the three experimental steels have obvious strain hardening properties. When the strain rate is increased from 0.001 s^-1 to 8000 s^-1, the yield strength of No.1 experimental steel is increased by 546 MPa; the yield strength of No.2 experimental steel is increased by 434 MPa; the yield strength of No.3 experimental steel is increased by 667 MPa. The three experimental steels also have obvious temperature effects. The residual carbides in the microstructure of No.1 steel increase the Peirls-Nabarro stress and hinder the dislocation slip. At 500 ℃, the yield strength of the No.1 experimental steel is 450 MPa, which is significantly higher than that of the No.2 and No.3 steels, 330 MPa and 310 MPa.The Johnson-Cook equations of the three experimental high-fragmentation steels are:σe=(1008+1309.04(εp)^{0.679 97})(1+0.1498lnε·^*)(1-T^{*1.188 53});σe=(1000+1214.321(εp)^0.6112)(1+0.480 15lnε·^*)(1-T^{*1.263 05});σe=(1008+1334.871(εp)^{0.610 88})(1+0.116 18lnε·^*)(1-T^{*0.992 47}).

Key words: Johnson-Cook model, dynamic mechanical properties, high-fragmentation steel, yield strength