Effect of Al Hot-Dipping on High-Temperature Corrosion of Carbon Steel in N2/0.1% H2S Gas

Abstract

High-temperature corrosion of carbon steel in N 2 /0.1% H 2 S mixed gas at 600-800˝C for 50-100 h was studied after hot-dipping in the aluminum molten bath. Hot-dipping resulted in the formation of the Al topcoat and the Al-Fe alloy layer firmly adhered on the substrate. The Al-Fe alloy layer consisted primarily of a wide, tongue-like Al 5 Fe 2 layer and narrow Al 3 Fe layer. When corroded at 800˝C for 100 h, the Al topcoat partially oxidized to the protective but non-adherent α-Al 2 O 3 layer, and the interdiffusion converted the Al-Fe alloy layer to an (Al 13 Fe 4 , AlFe 3 )-mixed layer. The interdiffusion also lowered the microhardness of the hot-dipped steel. The α-Al 2 O 3 layer formed on the hot-dipped steel protected the carbon steel against corrosion. Without the Al hot-dipping, the carbon steel failed by forming a thick, fragile, and non-protective FeS scale.

Microstructural Changes of Al Hot-Dipped P91 Steel during High-Temperature Oxidation

“…Hence, the α-Al 2 O 3 peak was weak in Figure 3a. Unequal mass flow and volume change due to the transformation of the topcoat and the alloy layer to Al 13 Fe 4 and Al 5 Fe 2 generated cracks and numerous voids in the coating [5][6][7]9,14,15] ( Figure 3c). The loosely adherent α-Al 2 O 3 scale was partially broken (see the Al map of Figure 3d).…”

“…Hence, the high-temperature oxidation resistance of 9Cr-1Mo steels needs to be improved through surface modification techniques. Aluminum hot-dipping is a simple, cost-effective coating technique that could form the compact, slow growing, protective alumina scale in reaction with oxygen at high temperatures [4][5][6][7][8][9][10][11][12][13][14][15]. It also improves the surface hardness by forming Al-Fe intermetallics [5,7,9,13].…”

“…Aluminum hot-dipping is a simple, cost-effective coating technique that could form the compact, slow growing, protective alumina scale in reaction with oxygen at high temperatures [4][5][6][7][8][9][10][11][12][13][14][15]. It also improves the surface hardness by forming Al-Fe intermetallics [5,7,9,13]. Diverse aluminized coatings have been obtained by hot-dipping carbon steels in Al [5,7,12,13] and Al-Si molten baths [5,9], 5Cr-0.5Mo steels in Al [14] and Al-Si molten baths [16], and 9Cr-1Mo steels in Al-Si [17] and Al-Si-Mg molten baths [15].…”

“…Diverse aluminized coatings have been obtained by hot-dipping carbon steels in Al [5,7,12,13] and Al-Si molten baths [5,9], 5Cr-0.5Mo steels in Al [14] and Al-Si molten baths [16], and 9Cr-1Mo steels in Al-Si [17] and Al-Si-Mg molten baths [15]. They significantly enhanced the high-temperature oxidation and corrosion resistance of the underlying steels through forming α-Al 2 O 3 [5,7,9,[12][13][14]17,18], α-Al 2 O 3 + FeAl [6,15], and FeAl [16] layers. However, microstructural changes during high-temperature oxidation and the oxidation resistance of 9Cr-1Mo steels that were hot-dipped in the Al molten bath have not been adequately investigated before.…”

The Role of Al-10%Si Coating in the Manufacture and Use of Aluminized Open-Joint Steel Tubes

“…The primary purpose of adding Ti is to accelerate the alloying of the coating and to prevent the formation of voids, thereby preventing flaking and improving the oxidation resistance of the alloyed coatings. A number of works concern the structure of the coating after heat treatment [32][33][34][35][36][37][38][39][40][41], corrosion resistance [42][43][44][45][46][47], and susceptibility to plastic shaping [48][49][50].…”