Study On Crack Propagation Rate Of 600mpa High Strength Steel For Mn-Ti And Nb-V System

The microstructure of 600MPa Mn-Ti and Nb-V steels for cold stamping axle housing was investigated by means of optical microscope. On the low-frequency fatigue tester MTS-810 with frequency of 10 Hz, the crack propagation rate of two chemical components of the tested steels was tested by three-point bending method. The relationship between the propagation rate da/dN and the amplitude of stress intensity factor triangle K was given. The results showed that the microstructure all of two tested steels were ferrite and pearlite, the grain size of Mn-Ti steel and Nb-V steel was 5.8 mu m and 3.3 mu m, respectively. The coefficient C and m in Paris equation of Mn-Ti steel and Nb-Vsteel were determined as m=2.6298, C=4.13x10(-12)mm/cycle and m=2.6799, C=1.30x10(-12) mm/cycle respectively, and the threshold value of crack propagation triangle K-th was 46.50 MPa.m(1/2) and 66.58 MPa.m(1/2), respectively.