目的 以Super304H钢为基体制备铝扩散涂层，提高其抗蒸汽氧化性能。方法 通过料浆渗铝的方法在Super304H表面制备铝扩散涂层，采用不连续称重法对渗铝Super304H在650 ℃纯水蒸气中的氧化动力学进行研究，并使用X射线衍射仪、扫描电子显微镜和透射电子显微镜对铝扩散涂层以及氧化膜的物相组成和微观组织结构进行表征和分析。结果 渗铝过程中，料浆层中的Al向Super304H基体内扩散，而基体中的Fe向外扩散，形成接近化学平衡配比的FeAl外层和贫Al的FeAl中间层。Al不断通过FeAl层向奥氏体（γ）基体中扩散，使得基体中Al的浓度升高，当Al的浓度增加至临界值时，导致局部区域析出NiAl，后者的形核和长大进一步加剧其周围基体中Ni的贫化。随着γ基体中Ni元素含量的持续降低及Al含量持续升高，γ基体将变得不稳定，并逐步转变为铁素体（α-Fe），最终形成由α-Fe和弥散分布其中的NiAl相组成的互扩散层。在FeAl中Cr元素和水蒸气分子的共同作用下，铝扩散涂层在650 ℃纯水蒸气中形成连续致密且与基体结合紧密的α-Al2O3膜，显著地降低了Super304H的氧化速率。结论 采用料浆渗铝法，可在Super304H钢表面制备出三层结构的铝扩散涂层，由外到内依次为FeAl外层、贫Al的FeAl中间层、由α-Fe和弥散分布其中的NiAl组成的互扩散层。这种结构的铝扩散涂层在650 ℃纯水蒸气中可形成α-Al2O3膜，降低Super304H的氧化速率，提高其抗蒸汽氧化性能。

The work aims to improve the steam oxidation resistance of Super304H by preparing an aluminum diffusion coating on it. The aluminum diffusion coating was deposited onto the Super304H steel through a conventional slurry aluminizing method. Its oxidation kinetics at 650 ℃ in pure steam was studied by discontinuous weighing method. The phase composition and microstructure of the aluminum diffusion coating and the oxide scale were characterized and analyzed by means of X-ray diffraction, scanning electron microscope and transmission electron microscope. During aluminizing, Al in the slurry was diffused into the substrate steel while Fe in the steel diffused outwards, forming an outer layer of FeAl close to the stoichiometric ratio followed by an intermediate layer of Al-depleted FeAl. Through the FeAl layers, Al was constantly diffused into the austenitic (γ) substrate, which induced the increased concentration of Al in the substrate. When the concentration of Al increased to a critical one, NiAl precipitate occurred locally. The nucleation and growth of NiAl precipitate further enhanced the depletion of Ni in its surrounding substrates. With both the depletion of Ni and the enrichment of Al intensifying in the γ substrate, the γ substrate became unstable and then gradually transformed into ferrite (α-Fe). Finally, an interdiffusion layer consisting of α-Fe dispersed with NiAl precipitates developed. Because of the combined action of the dissolved Cr in FeAl as well as the water steam molecule, a continuous and compact oxide scale of α-Al2O3 closely bonded to the substrate was formed on the aluminum diffusion coating in pure steam at 650 ℃, significantly slowing down the oxidation rate of the Super304H steel. Triple-layered aluminum diffusion coating on Super304H steel can be prepared by slurry aluminizing method, composed of a FeAl layer, an Al-depleted FeAl layer, and an interdiffusion layer of α-Fe dispersed with NiAl precipitates from outer to inner. The aluminum diffusion coating of such structure can decrease the oxidation rate of Super304H steel and therefore increase the steam oxidation resistance of the steel by forming the α-Al2O3 scale in the pure steam at 650 ℃.