ＳＵＳ３１６Ｌオーステナイトステンレス鋼溶接金属の低温じん性に及ぼすδフェライトの影響 オーステナイトステンレス鋼溶接金属の低温じん性 １

Abstract

The influence of δ-ferrite content on notch toughness and elastic-plastic fracture toughness of Type 316L austenitic stainless steel weld metal was investigated. The weld metals were prepared by deposition of single pass weld using submerged arc welding. The amount of δ-ferrite was changed in the range of 0.3 to 11.1 % by addition of nickel and chromium.In notch toughness test of as-welded specimens at 77 and 103 K, there was no simple correlation between the notch toughness and δ-ferrite content, differing from the results of other previous studies relative to this research. In more than about 3%δ-ferrite, the notch toughness increases with δ-ferrite content and reaches a maximum values at about 7%δ-ferrite.The solidification structure indicated that in the 3%δ-ferrite specimen of minimum notch toughness, an eutectic δ-ferrite appeared and furthermore with increasing δ-ferrite content, the morphology alters to vermicular and then lathy ferrite. From these results, it was evident that the δ-ferrite morphology considerably influenced to the notch toughness.On the other hand, the measurement of elastic-plastic fracture toughness Jrc, critical J and dJ/da revealed that these values related reasonably to the notch toughness.In heat treating the specimens at 923 K for 100 h, the absorbed energy decreased dramatically with increasing prior δ-ferrite content. This was considered because δ-ferrite changed to σ phase and carbide by heat treating.