Tailoring the brittle phase precipitation and mechanical properties in developing ultra-super ferritic stainless steels by Al modification

Abstract

An isothermal ageing experiment was carried out to investigate the influence of Al modification on the brittle phase precipitation behaviour, grain coarsening and mechanical properties of newly designed ultra-super ferritic stainless steel. Experimental results demonstrated that the modification of Al significantly inhibited the formation rate of the sigma phase, retarded the induction period of the chi phase, and promoted the growth process of the Laves phase. Meanwhile, the calculated grain growth kinetics of the surface layer and core layer were compared with the measured values. It was found that the Al modification enhanced the effect of Laves phase precipitation pinning and solid solution drag, which slowed the grain coarsening rate. With the modification of Al, the values of ultimate tensile strength, yield strength (0.2% proof stress) and total elongation increased compared to those of the Al-free alloys. The plasticity of the Al-modified alloys was improved with the retardation of sigma and chi phases at the grain boundary. This study provided valuable insights for the development of Al-modified ultra-super ferritic stainless steels with low precipitation brittleness tendency.

Keywords

• Ultra-super ferritic stainless steel
• Al-modified
• Ageing treatment
• Precipitation
• Embrittlement