Precipitation of Si and its Influence on Mechanical Properties of Type 441 Stainless Steel

Abstract

In this study the precipitation of silicon in Type 441 steel (18%Cr-0.4%Nb-0.5%Si) was investigated and its influence on strength properties were determined. To simulate high-temperature service conditions, heat treatments with various ageing times up to 120 hours and temperatures up to 800 °C were performed. Following the aging treatments, micro-and macro-hardness and tensile properties were measured. Microstructure and precipitation were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. Predictions for equilibrium pericipitation were calculated using the Factsage software. According to observations, coarse titanium nitrides (TiN) and niobium carbides (NbC, Fe3Nb3C) were present in all specimens including non-aged ones. These precipitates did not coarsen during ageing, which implies that their growth already occurred in the sheet production process. However, silicon started to precipitate in the course of prolonged annealing. Si contributed to the formation of a secondary phase resembling the Laves-phase (FeNbSi) on grain boundaries. Hardness and yield strength were found to decrease with prolonged ageing at high temperatures. Factors affecting the silicon precipitation are discussed.

On the Impact of the Intermetallic Fe2Nb Laves Phase on the Mechanical Properties of Fe-6 Al-1.25 Nb-X W/Mo Fully Ferritic Light-Weight Steels

“…As claimed by Tokizane et al [73] and Nabiran et al [45], Laves phase coarsening by Ostwald ripening takes place afterwards. The decrease in hardness-increasing elements was detected by EDS (Table 3), which leads in combination with the Laves phase coarsening to a drop in hardness, which is in good comparison to the results of Juuti et al [74] and Guo et al [75].…”

Microstructural and Texture Development during Multi-Pass Hot Deformation of a Stabilized High-Chromium Ferritic Stainless Steel

“…The formation temperature for these phases is generally considered to be below 1 123 K, 23) however with the absence of Mo, as in the current steel, the precipitation would take several hours at 923 K. 24) Therefore, the temperature -time window of the current study is too narrow for most of the intermetallic phases to precipitate.…”

11–23% Cr steels for solid oxide fuel cell interconnect applications at 800 °C – How the coating determines oxidation kinetics

“…The presence of Nb in 441 and 444 leads to the formation of laves phases, a Fe 2 Nb based intermetallic phase with a C14 hexagonal crystal structure [31]. The precipitation of laves phases is also enhanced by Ti in 441 [31] and Mo in 444 [66]. The volume of laves phase precipitates is higher for 444 than for 441.…”