微細TiNによる溶接ボンド部靱性の改善と大入熱溶接用鋼の開発
1975 年 61 巻 11 号 p. 2589-2603
詳細
1975 年 61 巻 11 号 p. 2589-2603
The improvement of toughness of weld fusion zone has been made by converting the microstructure from coarse intermediate stage structure to fine ferrite-pearlite in large heat input welding processes such as one side submerged arc welding, electro gas welding and consumable nozzle electroslag welding.
Following results have been obtained from intensive investigation on effects of TiN upon austenite grain size, transformation behavior and toughness at weld fusion zone:
(1) Fine TiN particles prevent the coarsening of austenite grains. Austenite grain diameter dr at 1400°C can be expressed by the equation, dr = K (r/f) where r=mean particle diameter of undissolved TiN at 1400°C, f=volume fraction of undissolved TiN smaller than 0.05 μ in diameter at 1400°C. The increase of the amount of TiN particle smaller than 0.05 μ undissolved at 1400°C gives rise to the decrease of austenite grain size.
(2) Aggregation of fine TiN particle accelerates the formation of ferrite during cooling. The transformation products are thus further refined.
(3) As a result unit facet diameter of brittle fracture which closely coincides with {100} plane becomes small. Thus the thoughness of fusion zone in large heat input welding is greatly improved.
(4) The fusion zone of commercial 60 kg/mm2 grade steel has proved to be improved by utilization of fine precipitates of TiN both in large and small heat input welding.
