Key Takeaways & Executive Findings
- •• Aging precipitation enhances martensite matrix strength via Ni(Fe,Al) precipitates, reducing transgranular cracking. • Volta potential difference between matrix and NbC particles increases from 11.43 to 18.60 mV, accelerating anodic dissolution at HAGBs. • SCC susceptibility increases with aging due to combined mechanical and electrochemical effects, promoting intergranular fracture. • Findings guide optimization of aging treatments to balance strength and SCC resistance in maraging steels.
Abstract
The effect of aging precipitation on the stress corrosion cracking (SCC) mechanism of Ni(Fe,Al)-maraging steel was studied through the comparative characterization and analyses of the microstructures and fracture features of solid–solution and peak-aged steels. Aging precipitation exerts a chain of impacts on the deformative compatibility and electrochemical difference between the matrix and other phases or interfaces. The strength of the martensite matrix is enhanced by abundant and evenly dispersed Ni(Fe,Al) precipitates, thereby reducing the possibility of splitting across martensite laths. Meanwhile, the Volta potential difference (VPD) between the matrix and primary NbC particles increases from 11.43 to 18.60 mV. Given that most of the primary NbC particles tend to be distributed along high-angle grain boundaries (HAGBs), anodic dissolution along HAGBs accelerates. Therefore, mechanical and electrochemical factors triggered by aging precipitation are involved in the variation in SCC behavior and mechanism. The SCC susceptibility of the steel increases along with the increasing tendency for intergranular cracking.
1. Introduction
Ni(Fe,Al)-maraging steel is a new type of 18Ni-maraging steel with the Ni(Fe,Al) phase as the main precipitate strengthening phase. It employs chemical ordering effects to prevent deformation instead of the traditional strength enhancement around particles caused by noncoherent misfit strains. The detrimental effects of coherent nano-precipitates can be effectively prevented through the interaction between dispersed nano-precipitates and high-density residual dislocations, resulting in a steel strength of up to 2.2 GPa and an elongation of approximately 8.2% [1–4]. Ni(Fe,Al)-maraging steel can be applied in extremely critical load-bearing structures or components, such as aircraft landing gears, ultra-high-pressure vessels, rocket and missile engines, and deep-sea vehicle shells [5]. These structures or components are typically operated under the conditions of corrosive environments and high mechanical loads. The combination of environmental corrosion and heavy loads sharply increases the risk that stress corrosion cracking (SCC) poses severe safety hazards to the operation of associated equipment or facilities.
In maraging steel, the precipitates generated during aging processing can affect SCC behavior from mechanical and electrochemical aspects. Precipitated particles can impede dislocation migration [6], improving the strength of the martensite matrix and affecting its SCC mechanism [7–8]. Wang et al. [9] discovered that the interaction between dislocations and microstructural features, such as grain boundaries and passive film rupture, contributes to enhanced SCC susceptibility in alkaline environment. High dislocation density is always indicative of the low mobility and lessened proliferation of dislocations within martensite laths [10]. This situation would directly result in localized plastic deformation within soft phases or interfaces, thereby increasing susceptibility to SCC [11]. However, some researchers reported that large amounts of dislocations generally exist within the martensite matrix, providing the probability of large-scale deformation around crack tips and thereby blunting cracks [12]. The margin for dislocation mobility and proliferation appears to be more important than the dislocation itself to the reduction of susceptibility to SCC. Undoubtedly, this margin would be affected by precipitated particles.
Precipitation during aging treatment usually nucleates and proceeds at defects, such as atom clusters, pile-up dislocations, and boundaries, through consuming the distortion energy of defects, thereby changing dislocation mobility, as well as the electrochemical activity and hydrogen trapping behavior of defects [13–15]. This effect would lead to an increasingly complex variation in SCC behavior. The previous studies [16–17] revealed that the Volta potential difference (VPD) exists between the precipitated intermetallic compounds and matrix, which induces the microgalvanic effect between the two phases.
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Xiaodong Wu, Tianliang Zhao, Tingping Hou, Zhongyu Cui, Yan Li, Kaiming Wu (2025). Effect of aging precipitation on the stress corrosion cracking behavior of Ni(Fe,Al)-maraging steel. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3062-x
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Frequently Asked Questions
What is the effect of aging precipitation on stress corrosion cracking in Ni(Fe,Al)-maraging steel?
Aging precipitation increases the strength of the martensite matrix via Ni(Fe,Al) precipitates, reducing transgranular cracking, but it also increases the Volta potential difference between the matrix and primary NbC particles, accelerating anodic dissolution along high-angle grain boundaries, thereby increasing SCC susceptibility and promoting intergranular cracking.
How does aging affect the electrochemical behavior of Ni(Fe,Al)-maraging steel?
Aging increases the Volta potential difference between the matrix and primary NbC particles from 11.43 to 18.60 mV, which enhances the microgalvanic effect and accelerates anodic dissolution along high-angle grain boundaries, contributing to intergranular stress corrosion cracking.
What are the key microstructural changes due to aging precipitation?
Aging leads to the formation of abundant and evenly dispersed Ni(Fe,Al) precipitates that strengthen the martensite matrix, and it also affects the distribution of primary NbC particles, which tend to be located along high-angle grain boundaries.
Why does SCC susceptibility increase with aging in this steel?
The increase in SCC susceptibility is attributed to a combination of mechanical and electrochemical factors: the strengthened matrix reduces transgranular cracking, but the increased Volta potential difference and anodic dissolution along grain boundaries promote intergranular cracking, leading to higher overall susceptibility.
What is the significance of this study for engineering applications?
The findings provide insights into optimizing aging treatments to balance strength and stress corrosion resistance in Ni(Fe,Al)-maraging steel, which is critical for applications in corrosive and high-load environments such as aerospace and deep-sea structures.
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