Purpose of this study is to develop covered arc-welding electrodes for high strength stainless steel, 18Cr-8Ni-0.2N-0.1Nb (SUS 304N2) and pitting corrosion resistant stainless steel, 25Cr-13Ni-0.8Mo-0.35N.
0.2% proof stress and tensile strength of 20Cr-9Ni-3Mn weld metal increase in proportion to increase of N content. Columnar structure of weld metal tends to become fine-grained by addition of small amount of Nb and Ti. The same also brings about extreme increase of 0.2% proof stress and tensile strength. Addition of 0.2% N, 0.05% Nb and 0.05% Ti results in 0.2% proof stress more than 35 kgf/mm
2 and tensile strength more than 70 kgf/mm
2 (specification values of SUS 304N2). Decrease of elongation, vEo°C and crack resistant property of weld metal associated with addition of above elements is found to be small and neglisible.
Weight loss by pitting corrosion test (5%FeCl
3+1/20 N HCl, 50°C, 48h) of 25Cr-14Ni-0.8Mo-0.30N weld metal (0.11.5g/m
2·h) is slightly greater than that of base metal (less than 1 g/m
2·h). Pitting potential V'
c100 of weld metal (0.96 Vvc SCE) is almost same as that of base metal. It is concluded that initiation of pitting corrosion is almost same as that of base metal, while dissolution rate of pitting corrosion is slightly higher than that of base metal. In spite of increase of Mo and N contents up to 1.8% and 0.34 % respectively, there is no decrease of weight loss by pitting corrosion test. Crack ratio of weld metal decreases as ferrite content increases, while pitting corrosion resistant does not decrease by increase of ferrite content up to 5%.
Various characteristics of welded joint of above two kinds of stainless steel are also described in this article.
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