采用热模拟的方法研究了FB2钢(一种新型9%Cr马氏体耐热钢)中Laves相在焊接热循环中的演化行为. 首先借助SEM观察到存在于原始供货状态下的FB2钢中尺寸在微米级别的Laves相颗粒; 进一步的分析表明, 这些Laves相的出现是由铸造过程中的枝晶偏析导致的. 焊接热模拟实验结果表明, 在加热过程中, Laves相与基体γ-Fe发生共晶反应导致的组分液化会给FB2钢热影响区带来热裂倾向; 在冷却后的样品中发现了一些网状的共晶组织, 利用SEM/EDS和TEM分别得到了该共晶组织的成分信息和结构信息, 确定该共晶组织的2个组分为χ相和γ-Fe. 在此基础之上, 较为详细地分析了不同峰值温度热模拟后样品中共晶组织的形成过程, 解释了共晶组织不同形貌的产生原因.
Elevating steam parameters is the key to enhance the efficiency of fossil power plants, reducing fuel consumption and noxious emission. Therefore, a lot of new creep resistant martensitic stainless steels have been developed, among which FB2 steel (a new 9%Cr martensitic stainless steel) is the most promising candidate for manufacturing steam turbine rotors operated at temperature range from 600 ℃ to 650 ℃. In the present work, the evolution behavior of Laves phase in the as received FB2 steel was studied by thermal simulation technique. Firstly, some sparse micron-sized particles of Laves phase were observed in as received FB2 steel by SEM. It was concluded that the large Laves phase particles formed in casting due to dendritic segregation. Then constitutional liquation resulting from eutectic reaction between Laves phase and γ-Fe in the heating process of welding thermal simulation was found, suggesting a liquation crack tendency in heat affected zone of FB2 steel. In the specimens experiencing thermal simulation, some eutectic microstructures were observed by SEM. Based on the results of EDS analysis and SAED, the two eutectic constituents were identified as χ phase and γ-Fe. At last, the reason for the difference in morphology of eutectic microstructures between specimens experiencing thermal simulation with different peak temperatures was analyzed.
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