Abstract
The microstructure and properties of Super304H weld joints were developed and studied. The Creq and Nieq composition points of the deposited metal were all located in the austenite region. The quantity and size of the Nb-phase in the deposited metal with 0.28wt.% Nb were lower than tnat in the other two deposited metals. The phases were mainly γ and Nb(C, N). The content of Nb(C, N) phases in the deposited metal with the 0.6 wt.% Nb content was approximately 2.2 times of the deposited metal with the 0.28 wt.% Nb content. The Nb-phases in the deposited metal with 0.28 wt.% Nb content were lower in quantity, weaker in the strengthening effect, of lower yield strength and lower in size than that the deposited metal with the 0.6 wt.% Nb content.
Highlights
In order to improve the power efficiency of power plants, reducing CO2 emissions and consuming a hig amount of fuel, the turbine inlet steam parameters of supercritical and ultra-supercritical units with higher temperature (600 °C) and pressure1,2 were developed
The matching welding materials (YT-304H) of Super304H steel were developed by Japanese Sumitomo company
In order to improve the performance of the welding process, especially the weld metal crack resistance and the high temperature performance to be matched with the base metal, the compositions of YT-304H made the major adjustments: content improvement of manganese and nickel and addition of approximately 1 wt.% Mo12,13
Summary
Microstructure of deposited metals Solidification sub-grain boundary and Nb phase. The microstructure and composition of the 1# and 2# deposited metals were similar to the 3#, where both were austenite and precipitated phases, as presented in Figs 6 and 7. To the 3# deposited metal, the composition of each element in the solidified sub grain boundary was higher compared to the austenite grains. The contents of niobium in the solidified sub grain boundary and the austenite grains of the three deposited metals were compared. Different cross sections of sub-grain boundary in 1# deposited metal
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