2 1/4 Cr-1 Mo鋼溶接継手のクリープラプチャ強さにおよぼす熱処理の影響

Abstract

The influence of heat treatment on the creep rupture strength at 550°C of weld joint of 2 1/4 Cr-1 Mo steel, 57 mm thick, were investigated. The used steel was worked with bending, reverse bending and straightening at 950-960°C, which assumed in the manufactured process of a welded seamy tube for heavy thickness steel. After the hot working processes, comparative specimens of base metal, weld metal and weld joint were made in the following three different conditions of heat treatment ; (A) normalizing and tempering (950°C×2.5 h air cooling and 720°C×3.5 h furnace cooling)→submarged arc welding→stress relief (720°C×3.5 h furnace cooling), (B) submarged arc welding→normalizing and tempering (950°C×2.5 h air cooling and 720°C×3.5 h furnace cooling) and (C) submerged arc welding→stress relief (720°C×3.5 h furnace cooling).The results are as follows ;(1) The creep rupture strength of weld metal was inferior to that of base metal for the three different conditions of heat treatment.(2) The creep rupture strength of conventional small size specimens, cut off from the weld joint, were generally superior to that of large size specimens, having the shape as welded but no reinforcement.(3) The heat treatment of normalizing and tempering after welding reduced the creep rupture strength in comparison with that of stress relief after welding. Generally, the creep rupture strength of columnar stracture in weld metal seem to be superior to that of ferrite emerged with the recrystallization by normalizing.