Condition of Generation of Coarse Ferrite Grains in the Weldding Deposit of Low C-2 1/4 Cr-1Mo Steel on Annealing, and Their Effect on the Mechanical Properties

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  • 低炭素2 1/4 Cr-1Mo鋼溶着金属の焼鈍中に生ずる粗粒フェライトの生成条件とその機械的性質に及ぼす影響
  • テイタンソ 21 4Cr-1Mo コウ ヨウチャク キンゾク ノ ショウドン チュウ ニ ショウズル ソリュウ フェライト ノ セイセイ ジョウケン ト ソノ キカイテキ セイシツ ニ オヨボス エイキョウ

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During stress-relief annealing after welding 2 1/4 Cr-1Mo steel pipes with the low hydrogen electrode having the same composition as that of the pipes, ferrite in the welded deposit is sometimes abnormally coarsened. Therefore, we investigated the annealing and welding conditions that develop coarse ferrite and the effect of coarse ferrite upon the mechanical properties, especially creep-rupture strength, of the deposit. The results obtained were as follows: (1) The growth of ferrite starts from the zone where the deposit metal is heat-affected by the next deposit layer, and when the annealing time is long, coarse ferrite grains appear also in the non-heat-affected zone. (2) The higher the annealing temperature in the range which does not exceed Ac1 transformation point, and the quicker the cooling velocity after welding, the more easily grow the ferrite grains. (3) The thermal strain produced by welding promotes the growth of ferrite, but is not the main cause of it. (4) When ferrite in deposit grows, the high-temperature tensile strength and the impact value at room temperature decreases a little. (5) During the creep-rupture test made at the temperature of 550°C, the strength of deposit is reduced due to the growth of ferrite.

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