Key Takeaways & Executive Findings
- •• Aluminizing combined with laser shock peening (LSP) significantly enhances the high-temperature oxidation resistance of AISI 321 stainless steel at 620 °C. • The optimal oxidation resistance shifts from aluminized steel to LSP-treated steel after 144 hours, due to the formation of a protective α-Al2O3 film. • LSP-induced subgrain boundaries act as short-circuit paths for Al diffusion, promoting rapid nucleation of α-Al2O3 and improving oxidation resistance. • The combination treatment reduces the oxidation parabolic constant by up to 69.18% compared to aluminized steel and 36.36% compared to untreated 321 steel, offering a promising surface treatment for long service life in solar thermal heat exchangers.
Abstract
The high-temperature oxidation resistance of AISI 321 stainless steel used in solar thermal power heat exchangers determines its service life. In this study, aluminizing and subsequent laser shock peening (LSP) treatments were employed to improve the high-temperature oxidation resistance of AISI 321 stainless steel at 620 °C. These two treatments decreased the oxidation rate of AISI 321 steel. Specifically, the optimal oxidation resistance was observed in aluminized steel before oxidation for 144 h owing to the increased entropy of the LSP-treated specimen. After 144 h, LSP-treated steel achieved the best oxidation resistance because of the formation of a protective α-Al2O3 film. Moreover, the large amount of subgrain boundaries formed on the aluminized layer of the LSP-treated samples could act as short-circuit paths for the outward diffusion of Al, facilitating the rapid nucleation of α-Al2O3. Meanwhile, the aluminized layer could isolate the contact between the oxidation environment and matrix, thereby decreasing the oxidation rate. Furthermore, the minimum oxidation parabolic constant was calculated for LSP-treated steel (6.45787 × 10−14), which was 69.18% and 36.36% that of aluminized and 321 steel, respectively, during the entire oxidation process. Therefore, the combination of aluminizing and LSP treatments can improve the high-temperature oxidation resistance of 321 stainless steel, providing a new idea for its surface treatment to achieve a long service life at high temperatures.
1. Introduction
Owing to its excellent oxidation and corrosion resistance and ductility [1, 2], AISI 321 stainless steel (321 steel) is widely used in heat exchangers for concentrating solar thermal power generation, which are exposed to oxidation and corrosive environments at high temperatures. At such high temperatures, the metallic nanonetworks on the oxide scale of 321 steel accelerate the outward diffusion of Cr and Fe from the protective Cr2O3 layer to the outer spinel layer, thereby deteriorating the integrity of the Cr2O3 film [3, 4]. In addition, galvanic, intergranular, and stress corrosion cracking cause severe spallation of the oxide film, directly exposing the matrix to a corrosive environment. Consequently, high-amplitude cyclic stresses are expected to cause catastrophic fractures in 321 steel components [5]. Therefore, increased oxidation resistance of 321 steel at high temperatures is required for the long service life of heat exchangers.
Surface modification is an effective method for improving the oxidation and corrosion resistance of 321 steels [6, 7]. Aluminizing treatments, including hot-dip [8], pack-cementation [9, 10], and reactive-air [11] aluminizing, are often used to inhibit oxidation by forming a thermodynamically stable thin Al2O3 layer. Among these, pack cementation is a cost-effective and promising technique for fabricating diffusion coatings with stable structures. Huttunen–Saarivirta et al. [9] fabricated 9Cr–1Mo steel with an Al-rich coating by pack cementation and demonstrated that the presence of hard AlN precipitates in the coating improved its erosion and oxidation resistance. Prasetya et al. [10] prepared C steel by pack cementation with Al and Cr. They found that the growth of the oxide scale was inhibited by the Al coating but not restricted by the Cr coating. Shen et al. [12] obtained a hierarchical coating consisting of outer Fe–Al and inner Fe–Zn layers on C steel after pack cementation. The porous Fe–Al layer transformed into a denser coating with the consumption of the Fe–Zn layer, resulting in the improved oxidation resistance of the steel.
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Wei Li, Wenyang Qin, Dapeng Jiang, Guowei Bo, Song Ni, Hui Chen, Yilin Zhao, Weiying Huang, Xulong Peng, Jianjun He, Yanjie Ren, Cong Li, Libo Zhou, Shengde Zhang, Jian Chen (2025). Effect of Aluminizing and Laser Shock Peening Treatments on the High-Temperature Oxidation Resistance of AISI 321 Stainless Steel for Solar Thermal Power Heat Exchanger. Chinese Journal of Mechanical Engineering. https://doi.org/10.1186/s10033-025-01217-7
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Frequently Asked Questions
What is the main objective of the study?
The main objective is to improve the high-temperature oxidation resistance of AISI 321 stainless steel used in solar thermal power heat exchangers by applying aluminizing and laser shock peening treatments.
How do aluminizing and laser shock peening improve oxidation resistance?
Aluminizing forms a protective Al2O3 layer, while laser shock peening introduces subgrain boundaries that act as diffusion paths for aluminum, promoting rapid formation of a protective α-Al2O3 film. The combination reduces oxidation rate and enhances long-term resistance.
What were the key findings regarding oxidation resistance?
The optimal oxidation resistance was observed in aluminized steel before 144 hours, but after 144 hours, LSP-treated steel showed the best resistance due to the formation of a protective α-Al2O3 film. The minimum oxidation parabolic constant was achieved with LSP-treated steel.
What is the significance of the oxidation parabolic constant?
The oxidation parabolic constant indicates the oxidation rate; a lower value means better resistance. The LSP-treated steel had a constant 69.18% lower than aluminized steel and 36.36% lower than untreated 321 steel, demonstrating significant improvement.
What are the practical implications of this study?
The combination of aluminizing and laser shock peening offers a promising surface treatment to extend the service life of AISI 321 stainless steel components in high-temperature solar thermal power applications, potentially reducing maintenance costs and improving reliability.
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