Study On The Service Performance Of Bainitic Rail Steel And The Effect Of Hydrogen

Bainitic rail steel has been favored due to its excellent comprehensive performance.However,challenges like corrosion,environmental fatigue,and wear encountered during its service life require urgent resolution.In the actual production of bainitic rail steel,the abnormal structure also greatly affects its environmental service performances to a certain extent.Therefore,bainitic rail steel is focused on as the research object,the salt bath and oil quenching treatments are employed,and the advanced microscopic analysis techniques are carried out to investigate the influence of factors such as microstructure and rolling deformation on corrosion and wear behavior.Moreover,the penetration of environmental hydrogen and its underlying mechanisms on rolling contact fatigue and wear of bainitic rail steel are thoroughly discussed.The primary research objectives of this study contains:After undergoing salt bath and oil quenching treatments,bainitic rail steel was obtained with microstructures comprising of carbide-free bainite with different lath thickness and martensite,respectively.Microstructural and mechanical property analyses revealed that with an increase in salt bath temperature from 320℃to 395℃,the twin density and dislocation density in bainitic rial steel increased,while the impact toughness and fracture toughness decreased,and fatigue crack growth threshold displayed a diminishing trend.After the oil quenching treatment,the bainitic rail steel exhibited the maximum twin width,twin density,and dislocation density,along with the highest strength,poorest ductility,and relatively lower fatigue crack growth threshold.After a salt bath treatment at 320℃,the bainitic ferrite laths in bainitic rail steels became finer,with lower retained austenite content,which led to a significant reduction in corrosion current and weight gain of salt spray corrosion.After a salt bath treatment at 395℃,the salt spray corrosion weight was the highest,accompanied by larger and deeper corrosion pits.Compared to H₂SO₄ and Na OH solutions,bainitic rail steel exhibited the highest corrosion current density,wear weight loss,and friction coefficient in Na Cl solution.Furthermore,after undergoing rolling deformation,the corrosion current decreased,indicating that the rolling deformation effectively improved its corrosion performance.At a contact stress of 1.7 GPa,the bainitic rail steel exhibits rolling contact fatigue（RCF）median life of approximately 8.1×10⁶ cycles and safety life of approximately 4.6×10⁶ cycles.During the RCF process,the surface undergoes severe plastic deformation,forming a plastic deformation layer and a nanostructured layer.The RCF failure mode of the rail-grade bainitic steel is characterized by shallow spalling,following a cyclic process of"formation-peeling-formation"within the nanostructured layer.The formation mechanism of the nanostructured layer is attributed to dynamic strain-induced low-temperature recovery and recrystallization.After rolling contact fatigue,the hardness of the bainitic rail steel significantly increases,while the friction coefficient and elastic modulus decrease.With the increase of salt bath temperature from 320℃to 395℃,the effective hydrogen diffusion coefficient gradually decreases.After oil quenching,the bainitic rail steel exhibits the highest effective hydrogen diffusion coefficient of 5.55×10^-5 cm²/s.With the increase of deformation amount,the number of hydrogen traps in the bainitic rail steel treated with a 320℃salt bath significantly increases,and the effective hydrogen diffusion coefficient decreases from 4.16×10^-5 cm²/s to 1.06×10^-5 cm²/s.The rolling contact fatigue life test of bainitic rail steel with H charged was carried out.At a contact stress of 1.7 GPa,the bainitic rail steel with H charged exhibits a RCF median life of approximately 2.4×10⁶ cycles and safety life of approximately 0.3×10⁶ cycles.During the rolling contact fatigue process,hydrogen reduces the dislocation density on the surface of the rail-grade bainitic steel,inhibiting low-temperature dynamic recovery and recrystallization.This leads to fragmentation of bainitic plate structures on the surface,hindering the formation of surface nanocrystalline layers and accelerating the formation of surface fatigue cracks,thereby deteriorating the rolling contact fatigue performance.However,hydrogen promotes the transformation of residual austenite on the surface to martensite,increasing hardness and wear resistance.