Study of high-cycle rotating bending fatigue performance and fracture
behavior in a pearlite-ferrite dual-phase steel
Abstract
To clarify the effects of ferrite morphologies and contents on
high-cycle rotating bending fatigue property of pearlite-ferrite
dual-phase (DP) steel used for fabrication of commercial vehicle
crankshafts, two types of DP steels with different ferrite grain sizes
(S10: 13.1μm and S30: 21.4μm) and ferrite contents (S10:
~9.5vol.% and S30: ~30.4vol.%) were
prepared. Stress-number of high cycles to failure (S-N) fatigue of the
two DP steels were evaluated. Experimental results showed a fatigue
strength of 510 MPa and 400 MPa for S10 and S30 steels, respectively, at
107 cycles. Fatigue cracks in S10 steel extended preferentially along
the grain boundary, but it was easy for crack propagation to extend
within a pearlite colony to form a zigzag crack morphology. Crack
roughness was enhanced and high stress was introduced to the crack
surface due to this kind of crack propagation behavior, which has
positive effects on slowing down crack propagation. However, the crack
propagation in S30 steel mainly occurred inside the soft equiaxed coarse
ferrite grain. Analysis revealed that little stress was introduced to
the crack surface. These results show that it is possible to improve
high cycle rotating bending fatigue strength of pearlite-ferrite DP
steel by appropriately manipulating the volume fraction and
microstructure morphology of ferrite phase.