Study On Structure And Property Of The Wear-resistant And Heat-resistant Steel

With the extensive use of Circulating Fluidized Bed Boiler(CFB) in our country,the phenomenon of heavy corrosion and wear of thermocouple-protection tube is more and more obvious and become a urgent problem that need to be solved.For the wear-resistant and heat-resistant parts working at high temperature and abrasive wear,their material not only requires high-temperature strength and certain wear resistance,but also requires good oxidation resistance to meet the demand for their performance.According to the working condition of the wear-resistant and heat-resistant parts for Circulating Fluidized Bed Boiler(CFB),this paper designs 10 groups composition of the wear-resistant and heat-resistant steel by the orthogonal experimental method reasonably.Their C,Cr,Ni,Si,Mn,N,Re,S and P content are almost same,but Ti and W content are different.Alloy microstructures were assessed using modern analysis and testing technologies,such as scanning electron microscopy (SEM),X-ray diffraction (XRD) and transmission electron microscopy (TEM).At last,High temperature resistance,hardness and high temperature erosion resistance were tested.The experimental results are below.The microstructure of the wear-resistant and heat-resistant steel at as-cast is austenite+a small amount of ferrite+carbide.The ferrite in the matrix has disappeared and Cr₇C₃ carbide has transformed into Cr₂₃C₆ carbide after annealing.And the microstructure is obviously thinning and uniform.Cr₂₃C₆ and Cr₇C₃ carbide exist along grain boundary and can hinder the grain boundary slipping effectively.The MC carbide exists dispersedly along the grain boundary and in the grain and improve the strength of the steel.The wear-resistant and heat-resistant steels are totally oxidation resistant at 900℃and oxidation resistant at 1100℃.Their surfaces have formed protective oxidation film and the oxidation film improves the service life of material under high-temperature.1Cr18Ni9 is both weak oxidation resistant at 900℃and 1100℃and it's surface hasn't formed protective oxidation film.So the wear-resistant and heat-resistant steels' oxidation resistance is obviously superior to lCrl8Ni9's.After oxidation at 900℃,the oxidation film of the wear-resistant and heat-resistant steel consists of Cr₂O₃,spinel structure (FeCr₂O₄,NiCr₂O₄) and a small amount of F2₂O₃ and Fe₃O₄.After oxidation at 1100℃,the oxidation film consists of Cr₂O₃,spinel structure (FeCr₂O₄,NiCr₂O₄) and Fe₃O₄.With the content of Ti and W element increasing,the hardness and wear resistance of the wear-resistant and heat-resistant steel increase.It is because Ti and W combine with C to form a quantity of hard particle of TiC and WC.Especially TiC can raise the hardness and wear resistance of the wear-resistant and heat-resistant steel.It is significant to add proper content Ti element in wear-resistant and heat-resistant steel.The prototype castings of CFB thermocouple-protection tube and air-hood with the high temperature erosion resistant alloy acquire good application in JiSan electric power plant Shandong HuaJu energy limited company.