Abstract
Fatigue experiments were conducted to elucidate the influence of inclusions on fatigue crack growth behavior of high manganese steel at low stress amplitude near the threshold region and in the region II for the temperature range of 297K to 113K. Two series of steel with different inclusion contents were used. Compact tension specimens were prepared in SL or ST orientation with respect to the rolling direction.The results showed that the fatigue crack growth rate da/dN of SL specimen was higher than that of ST specimen for both series at low stress levels near the threshold region. On their fracture surfaces, slightly larger roughness was measured in the case of ST specimen compared with the SL specimen and the roughness increased slightly with an increase of the content of sulphide inclusion regardless of experimental temperature. Based on these results, it is considered that da/dN in this region is affected by the crack closure due to the surface roughness which depends on the inclusion content and on the orientation. In the region II, the influence of orientation on da/dN was more pronounced than that of content at both 297K and 113K. However, ST specimen with a high inclusion content showed the lower fatigue crack growth rate than the base material at 113K. In order to make clear this reason, fracture surface were observed by a SEM. It is pointed out that microcracks produced in elongated MnS inclusions increase da/dN for SL specimen but reduce da/dN for ST specimen.
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