Developing Bearing Steels Combining Hydrogen Resistance and Improved Hardness
Thermodynamic and kinetic computational modelling are combined to conceive a hydrogen resistant bearing steel. Existing hydrogen resistant steels are not appropriate for bearings due to their low hardness. The proposed microstructure combines a martensitic matrix in which fine cementite precipitates impart strength, and V4C3 nano-scaled particles acting as hydrogen traps. It is demonstrated that the conflicting objectives of ultra-hardness and hydrogen resistance can be concealed by: (1) Adding 0.5 wt.% V to 100Cr6, which allows to preserve existing steel production technology. (2) Following a novel heat treatment procedure consisting of austenitisation (and a subsequent temperature spike to dissolve coarse V4C3), followed by tempering at 600 °C where V4C3 particles form (and a subsequent temperature spike to dissolve coarse cementite), followed by quench and tempering at 215 °C, where fine cementite strengthening particles form. The enhanced trapping capacity of the new steel is demonstrated via thermal desorption; the presence of the desired microstructure after heat treatment is proved via transmission electron microscopy. Concomitant with the trapping ability, a significant hardness increase was observed; this was ascribed to the controlled V4C3 precipitation.
Hydrogen embrittlement; Precipitation; Steel; Nanostructured materials
B.A. Szost, R.H. Vegter and P.E.J. Rivera-Díaz-del-Castillo
KF University Technology Centre, Department of Materials Science and Metallurgy, Pembroke Street, CB2 3QZ Cambridge, United Kingdom
Materials & Design, Vol. 43, January 2013, Pages 499–506