Microscopic Deformation Behavior Observation of Lamellar Pearlite during Plastic Deformation

The fatigue ratio of lamellar pearlite steel used for railroad rails is lower than the ratio of general steels.The reason for this has not yet been clarified.It is reported that the direction of the lamellar microstructure in the lamellar pearlite steel affects the fatigue characteristics.In order to clarify the microscopic deformation behavior of the lamellar microstructure considered to affect the fatigue characteristics, static tensile tests of the lamellar pearlite steel were conducted.Using the plastic replica technique, the microscopic deformation behavior i.e. the initiation and propagation of microcracks was observed.Based on the experimental results, transgranular cracks and intergranular cracks were observed.The obtained main results are as follows.(1) The transgranular crack originated in the discontinuous area in the lamellar pearlite microstructure.The transgranular crack initiates in a 45 degree direction to the axis of tension.The transgranular crack does not break through the grain boundary.(2) The intergranular crack does not propagate, but opens.(3) The difference in the material characteristics affected by heat treatment is the total strain of the crack initiation.