超超临界汽轮机转子FB2钢电渣重熔熔渣析晶行为研究

Study on Crystallization Behavior of Electroslag Remelting Slag of FB2 Steel for Ultra-supercritical Steam Turbine Rotor

采用了热力学软件Factsage计算、熔渣差热分析(DSC)及高温水淬渣XRD、SEM-EDS分析相结合的方法,对超超临界汽轮机转子FB2钢电渣重熔用熔渣的析晶动力学及析晶行为进行了研究,预测了电渣重熔过程中渣皮成分,为后续超百吨级电渣锭电渣重熔过程中修正渣皮形成对熔渣成分影响,实现全重熔周期稳定化冶炼技术攻关奠定了基础。研究结果表明:在10℃min的冷却速率下,熔渣至少有3种晶相析出;CaF_(2)作为初晶相,在熔渣中质量占比最大,而Ca_(12) Al_(14) F_(2)O_(32)、MgO则作为针状、孤岛状分布在CaF_(2)基体中;Ca_(3)B_(2)O_(6)析晶温度偏低(1000℃附近),此时熔渣处于半凝固状态,组元迁移速率较低,Ca_(3)B_(2)O_(6)晶相在渣中完全弥散分布,且尺寸较小;CaF_(2)析晶机制为三维生长机制,在冷却过程中均匀形核,并随温度降低快速长大,占据熔渣大部分空间体积;渣皮理论上晶相中大部分是CaF_(2),CaF_(2)基体中嵌杂少量Al_(2)O_(3)、MgO。

The crystallization kinetics and crystallization behavior of the slag for electroslag remelting of FB2 steel for ultra-supercritical steam turbine rotor have been studied by using the combination of thermodynamic software Factsage calculation,slag differential thermal analysis(DSC),high temperature water quenching slag XRD and SEM-EDS analysis.The composition of slag skin in the process of electroslag remelting has been predicted,which has laid a foundation for correcting the influence of slag skin formation on slag composition in the process of electroslag remelting of ultra-hundred-ton electroslag ingot,and has realized the breakthrough of full remelting cycle stabilization smelting technology.The results show that at a cooling rate of 10°C min,there are at least three crystal phases precipitated in the slag.As the primary crystal phase,CaF_(2) has the largest mass proportion in the slag,while Ca_(12) Al_(14) F_(2)O_(32) and MgO are distributed in the CaF_(2) matrix as the shapes of needles and islands.The crystallization temperature of Ca_(3)B_(2)O_(6) is low(near 1000°C).At this time,the slag is in a semi-solidified state,the component migration rate is low,and the Ca_(3)B_(2)O_(6) crystal phase is completely dispersed in the slag and its size is small.The crystallization mechanism of CaF_(2) is a three-dimensional growth mechanism,which nucleates uniformly during the cooling process and grows rapidly with the decrease of temperature,and occupies most of the space volume of the slag.Theoretically,most of the crystal phase in the slag skin is CaF_(2),and a small amount of Al_(2)O_(3) and MgO are embedded in the CaF_(2) matrix.