In 316L austenitic stainless steel, the presence of ferrite phase severely affects the non-magnetic properties. 316L austenitic stainless steel with low-alloy type (L-316L) and high-alloy type (H-316L) has been studied. The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy (HT-CLSM). There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions. In L-316L steel, ferrite morphology appears as the short rods with a ferrite content of 6.98%, forming a dualphase microstructure consisting of austenite and ferrite. Conversely, in H-316L steel, the ferrite appears as discontinuous network structures with a content of 4.41%, forming a microstructure composed of austenite and sigma (σ) phase. The alloying elements in H-316L steel exhibit a complex distribution, with Ni and Mo enriching at the austenite grain boundaries. HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes: L-316L steel solidifies in an FA mode, whereas H-316L steel solidifies in an AF mode. These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases, respectively. The solidification mode observed by experiments is similar to the thermodynamic calculation results. The L-316L steel solidified in the FA mode and showed minimal element segregation, which lead to a direct transformation of ferrite to austenite phase (δ → λ) during phase transformation after solidification. Besides, the H-316L steel solidified in the AF mode and showed severe element segregation, which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction (δ → σ + λ).
Abstract
In 316L austenitic stainless steel, the presence of ferrite phase severely affects the non-magnetic properties. 316L austenitic stainless steel with low-alloy type (L-316L) and high-alloy type (H-316L) has been studied. The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy (HT-CLSM). There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions. In L-316L steel, ferrite morphology appears as the short rods with a ferrite content of 6.98%, forming a dualphase microstructure consisting of austenite and ferrite. Conversely, in H-316L steel, the ferrite appears as discontinuous network structures with a content of 4.41%, forming a microstructure composed of austenite and sigma (σ) phase. The alloying elements in H-316L steel exhibit a complex distribution, with Ni and Mo enriching at the austenite grain boundaries. HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes: L-316L steel solidifies in an FA mode, whereas H-316L steel solidifies in an AF mode. These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases, respectively. The solidification mode observed by experiments is similar to the thermodynamic calculation results. The L-316L steel solidified in the FA mode and showed minimal element segregation, which lead to a direct transformation of ferrite to austenite phase (δ → λ) during phase transformation after solidification. Besides, the H-316L steel solidified in the AF mode and showed severe element segregation, which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction (δ → σ + λ).
关键词
316L austenitic stainless steel /
As-cast microstructure /
High-temperature confocal laser scanning microscopy /
Solidification mode /
Ferrite /
Characterization
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Key words
316L austenitic stainless steel /
As-cast microstructure /
High-temperature confocal laser scanning microscopy /
Solidification mode /
Ferrite /
Characterization
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