Fatigue Crack Growth Behavior Of Hadfield High Manganese Steel For Crossing

Cast high manganese steel crossing suffers from repeated cyclic or impact loadingwhen it is in service, resulting in easily severe plastic deformation in the crossing and thusrolling contact fatigue failure. With the rapid development of the Chinese railway of highspeed and heavy load, higher demands have been asked for the service lifetime of highmanganese steel crossing. Previous research on the fatigue behavior of high manganesesteel crossing focuses mainly on the crack initiation, while the investigation into the crackgrowth behavior of the steel is still lacking.The fatigue crack growth (FCG) behavior of the Hadfield high manganese steel forcrossing was investigated under two cyclic stress ratios (R). It is demonstrated that thethreshold stress intensity factor range (ΔKth) decreases with increasing R, and in the nearthreshold region, the Mn13steel exhibits a higher fatigue crack growth resistancecompared with TWIP steel. Further analysis shows that the reasons for this phenomenonare plasticity-induced and roughness-induced crack closure effects, especially the coarseaustenite grain can promote the crack closure.Then the crack3D propagation in the Hadfield high manganese steel wasinvestigated using high-resolution synchrotron radiation X-ray microtomography. In thispaper, a procedure for analyzing a series of tomography images is proposed for measuringlocal crack length (L), defection angle (θ) and crack tip opening displacement (CTOD).The variations in the local L、θ and CTOD at different section with an increase of loadwere analyzed combining with the crack three-dimensional morphology observation. Theresults show that the crack front is very tortuous, there are a lot of concaves and protrudes.Furthermore, for most sections, the protruded crack has no apparent extension, fatiguecrack propagation preferentially at the concave locations. The effects of voids on crackpropagation are different due to random distribution and different shapes.In the end, the image-based finite element model was established using ansyssoftware, which took into account three-dimensional irregular shapes of crack and voids.The results show that the strain distribution of the crack tip at different section is different.The void which locates in front of the crack makes the crack tip strain field enhancement. The overlapping part of two crack segments decreases the crack tip strain concentration, itindicates that the shielding effect between crack segments. Strain concentration is morelikely to occur at the concave region than at the convex. The finite element simulationresults with CT experimental results can validate each other.