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通过采用激光共聚焦扫描显微镜对AISI304奥氏体不锈钢的凝固过程进行了原位动态观察研究.发现当冷却速率为0.05℃.s-1时,奥氏体不锈钢以胞状晶方式凝固,其凝固模式为FA模式,即δ铁素体相先从液相中形核并长大,γ相在1 448.9℃时通过与液相发生包晶反应(L+δ→γ)在δ铁素体相界形成,当温度降到1 431.3℃时液相消失,δ铁素体相通过固态相变转变为γ相,富Cr贫Ni的残留铁素体位于胞状晶之间.当冷却速率为3.0℃.s-1时,奥氏体不锈钢以枝晶方式生长,冷却到1346.4℃时包晶反应在液相与δ铁素体相界之间进行,其残留铁素体位于枝晶干,与冷却速率为0.05℃.s-1时相比,其残留铁素体的数量增多,残留铁素体富Cr贫Ni的程度减轻.
The solidification process of AISI304 austenitic stainless steel was observed by laser scanning confocal microscope and found that when the cooling rate was 0.05 ℃ .s-1, the austenitic stainless steel solidified by cell-like crystal, the solidification mode Is the FA mode, that is, the δ ferrite phase nucleates and grows from the liquid phase first, and the γ phase undergoes a peritectic reaction (L + δ → γ) with the liquid phase at 1 448.9 ° C. in the δ ferrite phase boundary , The liquid phase disappears when the temperature drops to 1343.3 ℃, the δ ferrite phase changes to γ phase through solid phase transformation, and the residual ferrite of Cr-depleted Ni is located between the cellular crystals when the cooling rate is 3.0 ℃. s-1, austenitic stainless steel grows as dendrites. When cooled to 1346.4 ℃, the peritectic reaction takes place between the liquid phase and the δ-ferrite phase boundary. The residual ferrite is located at the dendritic dryness and the cooling rate When the temperature is 0.05 ℃ .s-1, the amount of residual ferrite increases, and the residual ferrite rich in Cr and depleted Ni is lessened.