不銹鋼の応力腐食割れに及ぼす加工の影響

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An experiment was made to examine the effect of cold and hot-working on stress corrosion cracking behavior of 18-8 Cr-Ni stainless steel. After drawing, a wire specimen of 1 mm in diameter was heated at 1050℃ and then cooled in water. The heat treated wire was cold-worked from 10% to 35% in elongation at room temperature, using the Amsler universal machine, and hot-workings were also done at 400℃, 650℃ and 750℃ for the heat treated specimen. To investigate the effect of carbide precipitation upon the stress corrosion cracking, cold worked specimens were heated for 50 hr at 400℃, 650℃ and 750℃. A hot concentrated aqueous magnesium chloride solution (42 wt % MgCl_2) was employed as a corrosive medium, and tensile stresses were imposed on the specimen by a direct weight. The time of fracture was measured, making clock stop by a falling weight when the specimen fractured. For all the specimens, with or without working, the increase of applied stress caused a decrease in time to fracture, t_f. When the log t_f was plotted as a function of the stress imposed on the specimen, a linear relationship was obtained. This straight line had a knee at which the slope of log t_f-stress curve changed. It seems that the two parts of this curve corresponded approximately to crackings initiated before and after film breakdown. The location of the knee was almost unchanged by cold or hot-working and also by carbide precipitation, even through the mechanical properties of specimen changed significantly. Resistance against the stress corrosion cracking of the specimen decreased by cold-working when the applied stress was higher than the stress corresponding to the knee. It was true as well with the hot-worked specimens. It appears that carbide precipitation did not reveal any appreciable effect on the stress corrosion cracking behaviour of the specimen. Microscopic examinations confirmed that the cracks propagate across the individual grain and not interranulare crackings.
社団法人日本材料学会の論文
1960-09-15

不銹鋼の応力腐食割れに及ぼす加工の影響

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