Corrosion Resistance of Co-containing Maraging Stainless Steel

Corrosion resistance behavior of Co-containing maraging stainless steels was investigated. Neutral salt spray and polarization test showed that maraging stainless steel with high Co content showed poor corrosion behavior. Microstructure observation proved that segregation of Cr in the matrix deteriorated its corrosion resistance. The surface morphology of the aged maraging stainless steel with high Co content indicated that during passivation process, the newly formed passive film with sinusoidal distribution readily destroyed by the corrosive medium, hence, causing poor corrosion resistance. Moreover, through first-principles calculation it was proved that Co increased Fe–Fe ferromagnetic interaction which facilitated the formation Cr-rich clusters.

Torsional deformation-induced gradient hierarchical structure in a 304 stainless steel

After applying torsion to cylindrical 304 stainless steel samples,a gradient structure along the radial direction was obtained.It was found that the volume fraction of a0-martensite increased gradually from the center to the surface of samples.The possibility of deformation-induced martensitic transformation was analyzed theoretically,whose conclusions were consistent with the experimental results.It was found that torsional deformation could produce abundant deformation twin and deformation-induced martensite,which could affect the tensile property of steel distinctly.The existence of deformation and martensite during torsion could increase the strength but deteriorate the ductility dramatically during the tensile test,which should be attributed to the weakening of work hardening ability.As a result of severe deformation,both strain-induced and stress-induced martensite have been observed.Also,two types of martensitic transformation mechanisms during torsional deformation were discussed.

Microstructure characteristics of segregation zone in 17-4PH stainless steel piston rod

The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment.Further investigation showed that the segregation zone was composed of three layers,namely the fine grain martensitic layer,the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface.Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution,microstructure and mechanical properties.The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation.Based on the microstructure and mechanical properties results,an intensive understanding of the cracking in the segregation zone was therefore reached.