| Nowadays,thermal power units account for 51%of China's whole carbon emission.Reducing the carbon emission of thermal power units is a key factor to fulfill the all-around strategic target of“trying to accomplish carbon neutralization before 2060”.So far,the most effective and important way to reduce the carbon emission caused by thermal power units is improving the unit efficiency.Nevertheless,raising the high temperature properties of heat resistant steels is a precondition for the improvement of unit efficiency.G115 is the first original martensitic heat resistant steel used in thermal power plants developed in China with fully independent intellectual properties.Its high temperature properties,especially the make-up of heat-affected-zone(HAZ)microstructure and type ? creep cracking sensitivity,are fundamental safeguards of its applying to power plant boiler construction.This study took G115 steel as the research object,using Confocal Laser Scanning Microscope(CLSM),to investigate the make-up of the HAZ microstructure and its regularities and rules of evolvement at various simulated temperatures based on which the type ? creep cracking sensitivity of G115 steel HAZ was assessed.The result of this investigation is instructive for welding specification formulation in boiler fabrication and type ? crack prevention during boiler operation.The main conclusions are listed as follows:(1)The microstructure of G115 HAZ was different from traditional 9-Cr martensitic heat resistant steel,which consisted of equiaxed grain zone(EZ),dual zone(DZ)and over-tempered zone(OZ).(2)Displacive martensite/austenite transformation took place in G115 HAZ when heating temperature reached about Ac3.During continuous heating-up,recrystallization would happen in the displacive-transformed austenite.(3)The M23C6 carbide dissolved into base metal when peak temperature was higher than 920?.After post welding heat treatment(PWHT),the M23C6 carbide precipitated again.(4)There was no obvious sensitivity to type ? creep cracking in G115 HAZ. |
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