| The effect of surface deformation on resulting properties occurring during the ausform-finishing of carburized 9310 steel gears was studied by carrying out separate uniaxial compression tests on bulk carburized specimens. Each compression specimen comprised a stack of disks that were individually carburized prior to assembly and testing. Using this method, the work hardening response of metastable austenite was determined for 1% carburized 9310 steel in the low temperature ausforming regime. Further, the relationship of the key process variables, namely, ausforming strain, ausforming temperature and isothermal holding time prior to deformation, to the measured properties was determined. The measured properties constituted flow behavior at the deformation temperature, room-temperature microstructure, retained austenite and resulting material hardness.;The effect of increasing strain during ausforming was to increase the degree of deformation induced precipitation of either martensite or bainite or both. The deformation induced precipitation of these phases during deformation cause an accentuation of the work hardening rates (work hardening exponent n = 0.55-0.72) leading to an abnormal positive curvature in the flow curves. Evidence of oriented martensite after low reductions (20%) and dark etching bainite after high reductions (50%) supported the apparent secondary hard-phase hardening. Hardness after ausforming was directly proportional to strain, the highest hardness (750-900 HV-300gm) being achieved at the strains of 50%. High retained austenite contents (;Ausforming carried out below the M;Isothermal holding into the bainite nose followed by deformation (isoforming) proved marginally beneficial with respect to hardness, though promising in reducing the amount of retained austenite. No clear dependence was observed between holding time and resulting hardness at the low reductions of 20%. |
