Cr系不銹鋼板の熔接性(第3報)

Abstract

Corrosion test against boiling 65% nitric acid and saturated salt solution have been made on the parent metal and welded specimen of three grades of 18Cr steel plates, one grade of 13Cr and two grades of 18-8 Cr-Ni. Microscopic observations of the corrosion of heat-affected zones in them have been carried out with the following conclusions:1) Corrosion in 18Cr steel welds occur in the coarsened crystal grain area of heat-affected zone in the vicinity of beads. Boiling 65% nitric acid and saturated salt solution present considerably differing conditions. of corrosion.2) In the case of nitric acid, the heat-affected zone is found less susceptible to corrosion when there is coexistence of martensite and ferrite than when there is ferrite alone. In the case of salt solution, intergranular corrosion at martensite-ferrite boundary is conspicuous.3) For both cases, addition of Ti to 18Cr steel aggravates corrosion in the heat-affected zone; liberal addition of Mo besides Ti tends to make it mild.4) General corrosion of 13 Cr steel is worse than those of other grades, but no intergranular corrosion appears in both cases.5) The varying degrees of corrosion in the heat-affected zone between 18 Cr and 13 Cr steel may be reasonably ascribed to different extents of carbide precipitation at intergranular boundary.