Abstract
It was already reported that quenchings from a temperature under A1 point improved the fatigue strength of steel welded joints, and the reasons of this fatigue strength improvement was attributed to quench aging effect and compressive residual stress in surface layer.On the other hand, aging of steel has a liklihood to make a embrittlement of steel. This experiment was carried out to clarify the effect of this fatigue strength improving heat treatment (low temperature quenching) on the toughness of welded joint.Each welded joint of rimmed steel, 50 kg/mm2 and 60 kg/mm2 steel was heated by hot dip galvanizing, at 500°C and 700°C in furnace, followed by quenching into about 20°C water. Toughness of toe of welded joint was investigated by i) Standard V notch Charpy Impact Test ii) COD Test and iii) ESSO Test.The following results were obtained, 1) The results of Charpy impact test and COD test showed that toughness of SS41, SM50 and HT60 steel welded joints did not decreased remarkably compared with as welded joint by a low temperature quenching.2) The ESSO test result showed that crack arrest temperature of SM50 steel welded joint slightly increased by low temperature quenching, but crack arrest temperature of SS41 and HT60 steel welded joints were nearly same compared with as welded joints.
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