Improvement of Toughness in the Weld Metal of High Purity 30Cr-2Mo Steel by Addition of REM : Study on Welding Metallurgy in High Purity Ferritic Stainless Steels (Report 2)

Effect of REM addition on the toughness in the weld metal of high purity 30Cr-2Mo steel was investigated. Welding was carried out by TIG method using deliberately contaminated argon with various ratio of nitrogen or air as shielding gas in order to vary the toughness of weld metals. The toughness of weld metals was evaluatedd using sub-size Charpy V-notch specimens with thickness of 3 mm. The main results obtained in this study are as follows;1) The toughness of the weld metal is significantly improved by addition of REM. Effective content of REM ranges from about 50 ppm to 200 ppm when nitrogen content in shielding gas being less than 1%.2) The quantity of absorbed nitrogen decreases in the REM bearing weld metal, which yields the improvement of toughness in it.3) It was deduced that the decrease of nitrogen in the REM bearing weld metal was attributed to the decrease of its absorption rate due to the formation of REM oxide film or absorbed layer of REM on the surface of the molten pool.