１９Ｃｒフェライト系ステンレス鋼溶接部の機械的，や金的挙動

Abstract

A study has been carried out into the mechanical and metallurgical properties of welds of the so called super-ferritics with carbon and nitrogen impurities of less than 200 ppm. The tests were carried out on three kinds of materials, one commercial grade and two kinds of 19Cr alloy with carbon and nitrogen impurities of around and less than 30ppm respectively.Tensile test specimens were so designed as to possess a TIG weld bead at the center of the gage sections. They were aged at various temperatures in order to induce 475°C embrittlement, σ-phase embrittlement, high temperature embrittlement, and an embrittlement due to fine carbide and nitride precipitation at grain boundaries. Tensile properties were obtained using an Instron-type machine at room temperature. As a result, it was found that there exist at least four kinds of embrittlement for the present weld joints: a. 475°C embrittlement b. embrittlement due to fine carbide and nitride precipitations at grain boundaries c. high temperature embrittlement d. grain boundary embrittlement due to phosphorous segregation at grain boundaries by 1350°C aging and the following water-quenching. 475°C embrittlement is not induced by welding process only. However once the embrittlement is realized by aging heat treatment, it is most severe at weld section.TIG arc-strike weld cracking test was conducted to investigate the cracking behaviour of weld nugget, especially the locations and the temperature range, the latter being monitored by use of acoustic emission technique. The cracking occurs at sub-grain boundaries at equiaxed zone of the weld nugget in the temperature range of 400-1000°C during cooling after welding. The cracking increases with the increase of heat input. The mechanism of the cracking is of the combination of matrix hardening due to high temperature embrittlement and carbon (nitrogen) segregation at sub-grain boundaries.