Fatigue behavior of Laves-phase-precipitated Nb-containing ferritic stainless steel JFE429EX in laboratory air and in 3%NaCl solution

Abstract

Effect of Laves phase precipitation on the fatigue behavior in JFE 429EX ferritic stainless steel was investigated. When this material is exposed to the temperature range of 700-900°C, the precipitation of Laves phase (Fe₂Nb) occurs, resulting in the embrittlement of material known as Laves phase embrittlement. Axial loading fatigue tests have been conducted in laboratory air and in 3%NaCl solution using a niobium-containing ferritic stainless steel, JFE 429EX, aged at 700, 800 or 900°C. In laboratory air, the fatigue strengths of 700°C-aged specimen were improved by the fine Laves phase precipitation into α-phase. Whereas the fatigue strengths of 800 and 900°C-aged specimens decreased, which was attributed to the coarsening of Laves phase precipitates. On the other hand, in 3%NaCl solution, the fatigue strengths of all aged specimens were lower than those in laboratory air. That was because sensitization took place during aging, that is, the chromium-depleted zones were formed along grain boundaries.