Effects of Cold Deformation and Aging Process on Precipitation Behavior and Mechanical Properties of Fe–18Cr–18Mn–0.63N High‐Nitrogen Austenitic Stainless Steel

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.

Secondary Hardening of a High-N Ni-Free Stainless Steel

“…The present study was carried out to explain the increase in hardness observed when annealing is applied to a cold-worked high-N stainless steel. This increase is opposite to what was previously observed on austenitic high N stainless steels, as reported before [ 23 , 24 ]. Using complementary techniques, such as chemical analyses, EBSD mapping and MET examination, allows explaining how and why hardness increases with annealing.…”

“…After annealing for 24h between 500 °C to 1050 °C, it was observed that the strengths decrease with the increase in temperature. For a Fe–18Cr–18Mn–0.63N–0.06C steel, cold-worked up to 50%, and then aged at 850 °C, a decrease in room temperature tensile yield and ultimate strengths when ageing time increased is also recorded by Feng et al [ 24 ]. On Fe–18Cr–19Mn–0.9N–0.06C, Vanderschaeve et al [ 25 ] also extensively studied the effect of annealing on a non-cold worked sample for temperatures between 400 °C to 900 °C.…”

“…Moon et al [ 21 ] observed in a Fe–17.5/20Cr–17.5/20Mn–0.59N alloy that, during hot working at 800 °C, some small intergranular Cr 2 N particles are created, promoting cracks. Feng et al [ 24 ] studied the effect of cold deformation prior to ageing at 850 °C on Cr 2 N precipitation in a Fe–18Cr–18Mn–0.63N alloy. They observed for high deformation that no cellular precipitation exists even for an 8 h or longer ageing, but Cr 2 N precipitates as granular and massive particles inside grains.…”

Microstructure and Mechanical Properties of Metal Injection Molding HK30 Stainless Steel Sintered in N2 and Ar Atmosphere

“…During the sintering, some of the N atoms dissolve into the austenite matrix, while the others combine with chromium to be precipitated at grain boundaries. [22,23]. Thus, the strength of the samples sintered in N 2 is much higher.…”