In order to improve the high temperature oxidation resistance of HP40Nb steel,experiments of hot-dipped and different diffusion treatments were carried out.The oxidation resistance behavior of the diffusion treatments specimens were studied at 1000℃.The effect of diffusion treatment on hot dip aluminizing steel microstructure and oxidation resistance behavior at high temperature was studied by means of SEM,EDS and XRD.The results showed that the specimens after diffusion at 800℃ for 4h,the coating consisted of inner layer(NiAl+Cr3Si),intermediate layer(Fe2Al5+small amount Ni2Al3) and outer layer(FeAl3).After diffusion at 900℃ for 4h,the coating consisted of inner layer(NiAl+Cr3Si) and outer layer(Fe2Al5+small amount Ni2Al3).After diffusion at 1000℃ for 4h,the coating consisted of inner layer(α+Ni3Al,NiAl+Cr3Si) and outer layer(Fe2Al5+Ni2Al3).After the cyclic oxidation test at 1000℃ for 360h,the coating consisted of outer layer(NiAl+Cr3Si) and inner layer(σ,α+Ni3Al).The oxidation resistance of the specimen which was diffused at 1000℃ for 4h was best,and the rate of mass gain is 13% of the uncoated aluminum layer specimen.It obviously increased the high temperature oxidation resistance behavior owe much to α-Al2O3 scales on the surface of HP40Nb steel during high temperature oxidation process.Moreover,the oxidation resistance of the aluminized coating increased with increasing the diffusion temperature.The presence of σ phase in the coating retarded the inward diffusion of Al in the coating,therefore the coating layer which was gradually consumed due to acting as an aluminum source formed a protective α-Al2O3 at the coating surface after oxidation.The intermetallic compound NiAl and Cr3Si really played an important role of high temperature oxidation resistance except α-Al2O3 scale.
Key words
HP40Nb /
hot dipped aluminizing /
oxidation resistance at high temperature /
α-Al2O3
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