Effect of Interstitially Disolved Atoms on Fatigue Strength Improvement of Steel Welded Joint

Abstract

Authors have already reported that fatigue strength of structural steel welded joint was improved by rapid cooling from below A₁ temperature, and that this improvement depended mainly on quench aging of interstitially disolved atoms. But the amount of them may be decreased by such heat-treatment when as-received steel has more disolved atoms than solid solution limit at heat-treatment temperature.
Therefore, in this study, the effect of interstitially disolved atoms on fatigue strength improvement of welded joint by such heat-treatment for some steels and the amount of interstitially disolved atoms in as-received SS-41 steel were investigated by fatigue test and internal friction measurement.
Results obtained were as follows;
1) Fatigue strength of welded joint of SS-41, SM-41, and SM-50 steels were remarkably improved by rapid cooling from 700°C.
2) By succeeding aging at 50°C, fatigue strength of SS-41 steel welded joint had much disolved atoms were improved, but that of SM-50 steel welded joint had fewer disolved atoms were not improved.
3) The amount of interstitially disolved atoms in as-received SS-41 steel was almost equivalent to solid solution limit at room temperature.