Effects of deformation on the microstructures and mechanical properties of carbide-free bainitic steel for railway crossing and its hydrogen embrittlement characteristics

The effects of deformation on the microstructures and mechanical properties of carbide-free bainitic steel for railway crossing were studied in detail, with an aim of analyzing the hydrogen embrittlement characteristics of the deformed bainitic steel. A small deformation could cause a notable increase in the strength and a slash decrease in uniform plasticity. High density of dislocations accumulated during the deformation and the newly formed high strength martensite should be responsible for the changes of mechanical properties. Results from the slow strain rate tests reveal that the hydrogen embrittlement sensitivity is higher for the deformed bainitic steel as compared with the undeformed steel, which also increase with increasing reduction. It should be attributed to the newly formed martensite phase, the accumulated dislocations and the heterogeneous residual stress in the deformed specimens. Fractography observations reveal a changed fracture mode from ductile to brittle with increasing hydrogen charging time.