Effect of Microstructure Evolution on Thermal Conductivity of Alloy 690

The effect of microstructure evolution on thermal conductivity of alloy 690 electrode was studied according to the working conditions of electrode materials in Joule furnace. Typical compositions of alloy 690 were smelted using pure metal and samples of 690 in different states were obtained by forging， hot rolling and cold rolling. The grain size， grain boundary type， grain boundary distribution， dislocation density， and precipitated phase species of the 690 samples in different states were tested by means of scanning electron microscope （SEM）， energy dispersive spectrometer （EDS）， electron back scatter diffraction （EBSD）， X-ray diffraction （XRD）， and the measurement of thermal conductivity by flash method. The microstructure evolution of alloy 690 materials for joule furnace electrodes in different processing states and its influence on thermal conductivity were clarified. The results show that， alloy 690 in the hot rolled state has the highest thermal conductivity， followed by the wrought state， while alloy 690 in the cold rolled state has the lowest thermal conductivity. The reasons for this are： （1） The grain size and total grain boundary area of 690 alloy change significantly under different deformation processes， and the cold-rolled state alloy has the smallest grain size and the highest total grain boundary area； （2） The grain boundaries of the forged and cold rolled state 690 alloys are dominated by small-angle grain boundaries， The low ΣCSL grain boundaries of the three states of alloy 690 are dominated by Σ3 grain boundaries；（3）The cold-rolled state 690 alloy has the highest dislocation density.（4）The main reason for the large decrease in thermal conductivity of alloy 690 in the cold rolled state is the high grain boundary total area ratio and the high dislocation density after cold rolling.