Characterization of precipitates in 9%Cr heat resistant steel |
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Affiliation: | GAO Jiaqiang,HONG Jie,XIAO Xinxing,LIU Junliang and WANG Qijiang Research Institute,Baoshan Iron & Steel Co.,Ltd.,Shanghai 201900,China |
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Abstract: | Precipitation strengthening as well as solution strengthening is key mechanism for heat resistant steels.It is very important to characterize the precipitates in 9%Cr ferrite heat resistant steels,especially to show the nanometer-sized particles.By transmission electronic microscope attached with an energy dispersive spectrometer as well as optical microscope,scanning electronic microscope,the microstructure and chemical composition of precipitates in a 9%Cr heat resistant steel after different heat treatments were investigated.It was found that the microstructure of normalized sample was martensite with fine NbC and Fe3C.The microstructure of tempered sample is tempered martensite,and there mainly were two types of precipitates,M23C6 with the size range of 50 - 300 nm and MX with the size of 10 - 100 nm.Superfine M23C6 precipitated preferably on prior austenitic grain boundaries and martensitic lath boundaries,while nanometer-sized MX precipitates were distributed randomly. After short-term creep,Laves phase formed along grain boundaries of the 9%Cr steel,and M23 C6 and MX precipitates were found to become coarser.More information about precipitates in the 9%Cr steel had been exhibited by atomic force microscopy.Thereby,distribution,size and shape of the precipitates as well as their compositions and structures were revealed. |
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Keywords: | characterisation microstructure nanometer-sized precipitates heat resistant steel atomic force microscopy |
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