オーステナイト系耐熱合金の管溶接継手部の経年劣化割れの支配因子

概要

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Cracking may occur in the weld Heat Affected Zone (HAZ) of Alloy 800H, one of the austenitic heatresistant alloys during long-term service in the temperature range of 600∿700℃. The authors have conducted a series of restraint cracking tests to consider the mechanism of this crack formation and method of ameliorating the cracking. The following results were obtained. (1) This HAZ cracking can be reproduced by a cylindrical type restraint cracking test. (2) Intergranular oxidation and cracking were detected at the bottom of notched HAZ area of as-welded specimens in the temperature range of 600∿650℃. The area of cracking coincided with the area of γ′phase precipitation. (3) The intergranular cracking occurs when weld tensile residual stress acts upon grain boundaries whose cohesive forces are severely reduced by the intergranular oxidation and precipitation of γ′phases in matrix. (4) A solution treatment which reduces initial weld residual stress, plating of Ni-1%B for preventing oxidation, and the reduction of Ti and/or Al contents which prevents the precipitation of γ′phases are all effective to reduce this type of cracking.
社団法人日本鉄鋼協会の論文
1991-05-01