析出硬化型 17-4PH 鋼の溶接部における変態と析出について(第 3 報) : 析出相と溶接熱影響部の組織について

概要

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In the weld heat-affected zone of 17-4PH stainless steel, the softened region is formed. And the authors supposed in the previous report that the cause of the formation of this region is overaging and retained austenite. Therefore, in the present study, the weld heat-affected zone of 17-4PH was examined directly by transmission electron microscopy at first. Next, the behaviors of precipitation and reverse transformation were examined. And lastly the mechanism of formation of retained austenite in this material was confirmed. Main results obtained are as follows. (1) In the softened region of weld heat-affected zone, overaging was confirmed by transmission electron microscopy. (2) The main constituting element of precipitate of 17-4PH is copper and nickel has not remarkable effect on the formation of precipitate. (3) Precipitate is present in delta-ferrite at fairly high temperature in rod-like shape. (4) Aged at relatively high temperature, precipitate changes into spherical in reversed austenite. And orientation relationship between this spherical precipitate and matrix martensite satisfies the relationship by Kurdjumov-Sachs. (5) Reverse transformation from martensite to austenite of 17-4PH is controlled by diffusion process. (6) Retained austenite in 17-4PH is caused by nickel-rich austenite formed by decomposition of martensite heated between A_s and A_f.
1972-01-25