Aging at 400–600°C of submerged arc welds of 22Cr–3Mo–8Ni duplex stainless steel and its effect on toughness and microstructure

Abstract

Submerged arc welds of a 22Cr–3Mo–8Ni (wt-%) duplex stainless steel were aged in the temperature range 400–600°C to simulate stress relieving conditions of mild steel. Particular attention was paid to the relationship between toughness and microstructure. It was concluded that sufficient toughness could be obtained on aging in the range 500–550°C provided that the aging time did not exceed 10 h. At temperatures >550°C, rather rapid embrittlement occurred as a result of the precipitation of essentially R phase and to some extent π phase. At ~≤500°C, spinodal decomposition of ferrite caused embrittlement, albeit more slowly than the precipitate induced embrittlement. Precipitation of the Mo rich phases Rand π was found to cause depletion of Mo in solid solution in ferrite. This offers a possible explanation for the decrease in pitting corrosion resistance observed in previous work.MST/1426