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Keywords:

  • cold deformation;
  • high-nitrogen austenitic stainless steel;
  • isothermal aging;
  • mechanical property;
  • precipitation

Abstract

Effects of different treatments (solid solution + cold deformation + aging condition) on the microstructure of Fe–18Cr–18Mn–0.63N high-nitrogen austenitic stainless steel and consequently on its mechanical properties were investigated by microscopic observations and mechanical characterizations. For un-cold-deformed and 20% cold-deformed steels, the results show that, all precipitates are Cr2N phase and the granular precipitates transform into cellular precipitates with increasing aging time. However, in 50% cold-deformed steel only the granular and massive Cr2N precipitates. On the other hand, no cellular Cr2N precipitates are observed, but the precipitation of σ phase is induced. In un-cold-deformed steel, all tensile properties including the ultimate tensile strength, yield strength, and the elongation decrease with increasing aging time, resulting from the precipitation of the second phase. In the cold-deformed steels, the tensile and yield strengths decrease while the elongations firstly increase and then decrease with aging time. Actually, in the cold-deformed steels, the strain recovery or recrystallization mainly causes the decreases in tensile and yield strength in addition to increase in elongation after aged for 1 h. In contrast, the cellular Cr2N precipitation or granular precipitation mainly results in the continually slow decreases in tensile and yield strengths and the relevant decrease in elongation with aging.