| With the continuous deterioration of global climate environment,people pay more and more attention to the emission of greenhouse gases.Ferritic heat-resistant stainless steel（FHSS）is a key material used in automotive exhaust system,thermal power generation,solid oxide fuel cell and other fields.Its performance has an important impact on increasing the working temperature of components,improving energy conversion efficiency,and reducing greenhouse gas emissions.At the same time,due to the global shortage of Ni resources and the effect of price fluctuations,it is particularly urgent to replace some austenitic stainless steels with FHSSs.Therefore,it is of great significance to develop high performance FHSS.In this paper,the cold and hot formability,aging precipitation behavior,high-temperature mechanical properties and high-temperature oxidation resistance of FHSS were systematically studied.The effect of Al on the properties of Cu-bearing FHSS and its mechanism were analysed.The specific research contents and results are as follows:（1）The cold and hot formability of FHSS was studied,and the effect of Al on the formability of Cu-bearing FHSS was analysed.The addition of 1 wt.%Al can reduce the earing height and improve the uniform deformation ability of the experimental steel.The activation energy of hot deformation of 0Al steel is 339.998 k J/mol,and the Al addition can increase the activation energy to 342.966 k J/mol.The thermal deformation equation of 0Al steel is（?）=3.4868×1012[sinh（0.0225σ）]3.910exp(-339998/RT).The thermal deformation equation of 1Al steel is（?）=4.3016×1012[sinh（0.0195σ）]3.758eRxTp(-342966/RT).The hot processing map of the experimental steel was established.Both experimental steels are prone to destabilize under the high strain rates,and the Al addition of will increase the destabilization areas.The optimal hot working range of 0Al steel is 0.01 s-1-0.03 s-1,950℃-1042℃ and 0.01 s-1-0.11s-1,1042℃-1150℃.The optimal hot working range of 1Al steel is 0.01 s-1-0.04 s-1,950℃-1033℃ and 0.01 s-1-0.20 s-1,1033℃-1150℃.（2）The aging precipitation behavior of 0Al and 1Al steels was studied.The effect of Al on the evolution of precipitates in Cu-bearing FHSS and its mechanism were analysed.Cu-and Nb-rich phases precipitated in 0Al and 1Al steels during aging.The addition of 1 wt.%Al can increase the nucleation rate,the number density and volume fraction of the Cu-rich phase,change the crystal structure of the Cu-rich phase during the coarsening process,and promote the formation of edge dislocations inside the Cu-rich phase.The high-density Al-containing Cu-rich nanoprecipitates can improve the strength and plasticity of the experimental steel at the same time.At the early stage of aging,there is less precipitation of Nb-rich phase in 0Al and 1Al steels.When the aging time is extended to 60 min,the Laves phase began to precipitate in large quantities.Laves phase precipitated in 0Al steel is strip and needle shaped,and has feather like aggregation state.However,the Laves phase in 1Al steel is smaller in size,not easy to agglomerate,and the coarsening rate decreases,showing an irregular blocky morphology with trailing characteristic.（3）The high-temperature mechanical properties of 0Al and 1Al steels were studied.The effect of Al on the high-temperature strength,fracture behavior,softening mechanism and texture evolution of Cu-bearing FHSS was clarified.At high strain rate and low deformation temperature,the addition of Al can increase the tensile strength of the experimental steel,and reduce the fracture elongation.At low strain rate and high deformation temperature,the role of Al is mainly to promote dynamic softening behavior,which can simultaneously improve the high-temperature strength and fracture elongation of the experimental steel.The high temperature fracture mode of 0Al and 1Al steels is ductile fracture.Al can reduce the number of deformation bands in ferrite and improve the coordinated deformation ability of ferrite grains.Under the conditions of low deformation temperature and high strain rate,0Al and 1Al steels mainly have deformed grains,while under the conditions of high deformation temperature and low strain rate,they mainly have recovered grains.Al can promote the dynamic recovery and dynamic recrystallization softening process and strengthen theγfiber texture.（4）The oxidation behavior of 0Al,0.5Al and 1Al steels at 900℃-1100℃ was studied,and the effect of Al on the oxidation resistance of Cu-containing FHSS was analysed.At 900℃,the oxide layer on the surface of 0Al steel appears to upheaval and peel.After adding 0.5wt.%Al,the phenomenon of upheaval and peeling of the oxide layer on the surface of the experimental steel can be obviously improved,and the Al2O3 generated is mainly concentrated in the internal oxide layer.When the addition amount of Al is 1 wt.%,a uniform and dense Al2O3 layer was formed on the surface of the experimental steel.The oxidation rate of the experimental steel can be reduced by one order of magnitude with the addition of0.5 wt.%Al.At 1000℃,the total thicknesses of oxide layer on the surface of 0Al,0.5Al and 1Al steels are 108.09±20.23,90±12.03 and 1.57±0.52μm,respectively.The oxidative weight gain rates of 0Al,0.5Al and 1Al steels are 1.90×10-1,2.70×10-2 and 1.77×10-3mg2·cm-4·h-1,respectively.At 1100℃,the oxidative weight gain rates of 0Al,0.5Al and 1Al steels are 420.31,171.33 and 1.28×10-3 mg2·cm-4·h-1,respectively.The addition of 1 wt.%Al can form the（Al,Cr）2O3 layer with a self-repairable property on the surface of the experimental steel.The oxidative weight gain rate of this oxide layer is 2.7 times lower than that of the pure Al2O3 layer,and the thickness of the oxide layer is 515 times thinner than that of the surface oxide layer of 0Al steel. |
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