HP295钢中非金属夹杂物形成的热力学分析

Thermodynamic analysis formed by non-metallic inclusions in welding gas vessel steel HP295

针对HP295钢,采用热力学计算预测了冶炼和凝固过程中夹杂物的组成,同时,用扫描电镜(SEM)及能谱仪(EDS)对夹杂物的形貌和成分进行分析.结果表明:采用硅锰脱氧时,钢液中形成的夹杂物主要为鳞石英(SiO2)、锰铝榴石(3MnO.Al2O3.3SiO2)、莫来石(3Al2O3.2SiO2)和刚玉(Al2O3)等4类,且随[Al]含量提高或[O]含量降低,夹杂物逐渐从鳞石英为主向刚玉为主转变,[Al]<1×10-6时主要为鳞石英,a[O]<3×10-3时则以刚玉为主;凝固过程析出夹杂物的组成与[Al]、[O]含量有关,1550℃时,当a[O]>115.6×10-5及[Al]<4.5×10-6时析出鳞石英,当a[O]<115.6×10-5及[Al]<10.5×10-6时析出莫来石,当[Al]>10.5×10-6时析出刚玉;1510℃时,当a[O]>75.2×10-5及[Al]<3.51×10-6时析出鳞石英,a[O]<75.2×10-5及[Al]<8.18×10-6时析出莫来石,[Al]>8.18×10-6时析出刚玉;另外,当钢中有[Ca]存在时,凝固时可能析出钙斜长石甚至假硅灰石,析出物的成分及数量与钙的活度有关.热力学计算预测结果与扫描电镜分析结果基本一致,表明该热力学计算方法是可行的.

The composition of inclusions in the process of steelmaking and solidification is predicted by the thermodynamic calculations for HP235 steel. The morphology and composition of inclusions are analyzed by SEM and EDS. The results show that the inclusions in the molten steel mainly are tridymite （SiO2）, spessartine （3MnO- Al2O3.3SiO2）, mullite （3Al2O3-2SiO2） and corundum （A1203） by using silicon-manganese deoxidization. The composition of inclusions change gradually from tridymite mainly to corundum with the content of [Al] increased, or [O] reduced. Main inclusions is tridymite when [A1] 〈1×10^-6, and the main is corundum when a [O]〈3×10^-3. The composition of inclusions precipitated have relationship with the contents of [AI] and [O] during solidification. At the temperature of 1550℃, the precipitation is tridymite when a[O]〉115.6×10^-5 and [A1]〈4.5×10^-6, the precipitation is mullite when a[O]〈115.6×10^-5 and [A1]〈10.5×10^-6, and the precipitation is corundum when [A1]〉10.5×10^-6. At the temperature of 1510℃, the precipitation is tridymite when a[O]〉75.2×10^-5 and [AI] 〈3.51×10^-6, the precipitation is mullite when a[O]〈75.2×10^-5 and [Al] 〈8.18×10^-6, the precipitation is corundum when [Al]〉8.18×10^-6. In addition, when [Ca] exists in the steel, freezing precipitation of calcium may even leave wollastonite plagioclase. The composition and quantity of precipitates have relationship with the activity of the calcium in the steel. The predicted results by thermodynamic calculations are mainly consistent with the results by SEM and EDS. So, the thermodynamic calculation method is suitable for predicting composition of inclusions in the steel.