| G112steel is a new9-12%Cr heat resistant steel.it is expected to use in boiler with30MPa/610℃/625℃parameters. G112steel has been studied in this paper. With the help of OM, SEM, TEM, XRD and chemical phase analysis, this paper investigated the mechanical properties of this steel at room temperature and high temperature, meanwhile the optimization of heat treatment, the evolution of microstructure in the aging processing, the types of precipitates and the effect of microstructure on mechanical properties has also been studied. This paper also analysis creep strengthen and fracture mechanism of G112steel, coMPared the performance of high temperature steam corrosion of9%Cr and11%Cr martensite heat-resistant steel.The results shown that the best heating treatment was1070℃×1h A.c+750℃-760℃×3h A.c, which ensured better strength and plasticity at high temperature. The strength at room temperature and high temperature of G112was decreased with the increasing of tempering temperature, when tempering from750℃to770℃. With the increasing of austenitizing temperature,the strength of G112was also decreased but plasticity increased.In the0～10h aging process, the precipitates were M23C6and M(C,N),after aging10h The Laves phase begin to precipitate, after aging5000h, the precipitates were Laves,M23C6and M(C,N); As the aging time increases,the amount of Laves phase and M23C6phase increasing, the average size of Laves was about600nm, the average size of M23C6was about800nm.The growth rate and the amount of precipitation of the Laves phase were all better than those of the M23C6,the average size of the Laves was smaller than M23C6and having good strengthening effect.During aging process at630℃, the yield strength at high temperature was decreased. This is due to the grow of precipitates reduced the strengthening effect of precipitation.meanwhile, the recovery of martensite lath reduced the lath martensite strengthening effect.The G112steel appears transcrystalline rupture in high temperature creep process (630℃,150MPa). It is possible that M23C6phase and Laves phase which in the the grain boundary is the crack source.During the steam oxidation process at650℃, the thickness of oxidation layer was increase and oxidation rate was decreased, the oxide layer is mainly composed of Fe3O4and Fe2O3. The high temperature steam corrosion resistance of11%Cr steel is superior than the9%Cr steel. Therefore, incressing the content of Cr had significant effects on improving steam corrosion resistance of martensitic steel. |
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