SUS 316L 溶接金属の低温じん性に及ぼす再熱の影響

オーステナイトステンレス鋼溶接金属の低温じん性(第3報)

抄録

Type 316L weld metals contained various delta ferrites ranging from 0% to 9.5%, which were deposited by one pass submerged arc welding, were heat treated at 923 K to 1523 K for 2 s to 86.4 Ks (24 h). From the results of absorbed energy at 77 K and analysis of precipitates by electron and X-ray diffraction, the influence of reheating on low temperature toughness was investigated.
In the weld metal of eutectic delta ferrite (delta=2.7%) which had minimum absorbed energy, the heat treatment for 2 s at the temperature above 1123 K enhanced its absorbed energy considerably as compared to as-welded specimen and in particular the tendency was remarkable at the temperatures of 1423 K and 1523 K.
The absorbed energies of weld metals which contained some delta ferrites decreased with the increase in the heat treating time and this decreasing rate was pronounced at more delta ferrite content and high heat treating temperature. However, in the case for short heat treating time within 120 s, the absorbed energy had a tendency to increase, compared with as-welded one, while in the fully austenitic weld metal, the decrease in absorbed energy could be scarcely detected independent of the heat treating time.
Retained delta ferrite contents after the heat treatment decreased faster at eutectic delta ferrite than at primary delta ferrite. This was considered to be due to the precipitation of M₂₃C₆ and sigma phase facilitated in the case of eutectic delta ferrite because of poor coherency of delta/gamma interface.