Research On Corrosion Behavior Of New Austenite Heat Resistant Alloy For Ultra Supercritical Thermal Power Boiler

Ultra-supercritical thermal power technology has been widely recognized and used in countries around the world for its energy saving,emission reduction and thermal efficiency improvement.In order to develop a higher-parameter ultra-supercritical thermal power unit,the key technical bottleneck is the boiler pipe with better performance.Super304H alloy has excellent creep durability,high temperature oxidation resistance and corrosion resistance as a heat-transfer pipe of the boiler.However,after long-term high temperature service,the grain boundary will form a chromium-depleted zone,and the corrosion resistance of the material will decrease,causing serious corrosion.It can even cause explosions.Therefore,after full consideration of the service environment of the ultra-supercritical thermal power boiler,the research group independently researched and developed a new type of austenite heat-resistant code named CHDG-A on the basis of Super304H alloy through the optimization and improvement of its alloy composition.alloy.The corrosion resistance of Super304H alloy and CHDG-A alloy has been systematically studied in this paper,including passivation film research,intergranular corrosion performance,stress corrosion performance,and high-temperature sulfate corrosion performance.The following conclusions have been drawn:The XPS analysis of the passivated CHDG-A alloy and Super304H alloy sample shows that the sample surface has a very thin passivation film,and the passivation film is mainly composed of metal oxides such as CrO₃,Cr₂O₃,and Fe₂O₃.It plays a role in retarding the metal corrosion;the interior is mainly a metal matrix,which acts as a stable passivation film.After aging treatment of CHDG-A alloy and Super304H alloy at different temperatures,the number and size of precipitated phases in the grain boundary and intragranular phase increase with the increase of the aging temperature,and the grain boundary precipitation of the Super304H alloy is compared with the same ageing temperature.The number of precipitated phases in the grain boundary of the lower CHDG-A alloy is large and the size is large.After 16h of the intergranular corrosion test,corrosion cracking occurred mainly on the grain boundary of the CHDG-A alloy.However,there were not only corrosion cracks at the grain boundary of the Super304H alloy sample,but also local grain shedding.After the bending test of the sample after intergranular corrosion,it was found that there was no obvious crack on the curved surface of the CHDG-A specimen,while the increase of the aging temperature of the Super304H alloy increased the number of cracks and increased the depth.After the stress corrosion of CHDG-A alloy and Super304H alloy,the mechanical properties decreased significantly.Alloys are more sensitive to stress corrosion and increase the time to temperature.After creep treatment of the two alloys,the stress corrosion cracking time of the alloy is continuously shortened with the increase of the creep time.From the fracture morphology of the two alloys,it can be seen that the alloy transitions from ductile fracture to brittle fracture.The initial stage of high-temperature sulphate corrosion of CHDG-A alloy and Super304 alloy is mainly high-temperature oxidation.Later,a volatile corrosion product Na₄?CrO₄??SO₄?is generated,and the surface oxide layer is damaged by sulphate.Corrosive substances such as oxygen and sulfur enter the interior of the corrosion layer,and the corrosion is more severe.