Showing papers by "Kazutoshi Nishimoto published in 1987"

Desensitization of Stainless Steels by Laser Surface Heat-Treatment

Abstract: Laser heating was applied for the desensitization heat-treatment of the surface layer in the sensitized HAZ of Type 304 stainless steel. The degree of sensitization was examined by EPR technique and the 10% oxalic acid electrolytic etch test. The CO2 laser with maximum power of 1.5kW was used for heat-treatment. Time-Temperature-Desensitization diagram (TTDS diagram) for sensitized Type 304 stainless steels were developed by calculation assuming the chromium diffusion control for desensitization which might occur when the chromium depleted zone was healed up due to dissolution of chromium carbide and chromium diffusion from the matrix being heated at the solution annealing temperatures. TTDS diagrams calculated agree fairly well with ones determined by corrosion tests. Laser irradiation conditions (e.g., Laser power, beam diameter and traveling velocity )required for desensitization of sensitized Type 304 stainless steels were calculated using additivity rule from the TTDS diagram calculated and theoretical thermal curve of laser heating derived from the heat conduction theory. After laser beam irradiated under an optimum condition predicted by calculation, the sensitized HAZ of Type 304 stainless steel restored complete resistance to intergranular corrosion.

The role of elements in an insert metal for bonding of Si3N4 to refractory metals using Cu-Co-Cr-Ni-W alloy as an insert metal.

Abstract: The roles of elements in the insert metal of 80%copper-20%Haynes No. 188 for bonding of Si3N4 to tungsten and molybdenum have been investigated. EDX analysis of the interlayer of joints revealed that chromium was concentrated in the region adjacent to Si3N4 and copper was concentrated in the center region of the insert layer.CrSi2, Cr2N and CrN were found in the region adjacent to Si3N4. As the results of bonding of Si3N4 to tungsten using insert metals of copper base ternary and binary alloys containing iron, nickel, chromium or cobalt, good strength of joints were obtained only when chromium was contained in the insert metal. These results suggest that chromium is the main element to contribute to bonding of the insert metal to Si3N4 by forming chromium silicide or nitride at the interface and copper which enriched in the center region had the function to relieve the thermal stress by forming buffer layer in the insert layer.