Key Takeaways & Executive Findings
- •• Conventional Q&P processing with coarse partitioned austenite increases corrosion susceptibility and mechanical degradation in medium Ni-bearing steel. • QT samples show preferential corrosion around cementite clusters due to selective dissolution. • A slightly higher partitioning temperature (just above Ms) yields finely distributed austenite within bainite, improving corrosion resistance and mechanical stability. • Microstructural optimization via Q&P at high partitioning temperature is a promising strategy for enhancing durability and reliability in neutral aqueous environments.
Abstract
Through quenching and tempering (QT) and quenching and partitioning (Q&P) processes, this study aimed to investigate the effects of microstructural modifications on the corrosion behavior and corrosion-assisted mechanical degradation of medium Ni-bearing steel. The primary objective was the identification of strategies for the enhancement of the long-term lifespan and reliability of these alloys in neutral aqueous environments. Various electrochemical evaluations and microstructural characterizations were conducted to elucidate the relationship between heat treatment processes and corrosion behavior. The findings reveal that the conventional Q&P process formed partitioned austenite with a coarse size within the martensitic matrix, which led to an uneven distribution of Ni and high kernel average misorientation and resulted in an increased susceptibility to corrosion and corrosion-induced mechanical degradation. In addition, the corroded QT sample displayed preferential attacks around cementite clusters due to selective dissolution. By contrast, a slightly higher partitioning temperature, just above the martensite transformation start temperature, provided finely distributed austenite within bainite in the microstructure, which exhibited lower corrosion kinetics and reduced susceptibility to mechanical degradation in the corrosive environment. This study highlights the potential of microstructural optimization through the Q&P process with a high partitioning temperature as an effective technical strategy for achieving the superior durability and reliability of medium Ni-bearing steel alloys in neutral aqueous environments.
1. Introduction
Ni-bearing steels have garnered considerable attention as structural materials owing to their superior mechanical properties, including high strength, ductility, and exceptional toughness at cryogenic temperatures [1–4]. These outstanding characteristics, which ensure a superior load-bearing capacity, are primarily attributed to their microstructural features, including a martensitic matrix structure, the size and distribution of carbides, and the level of reversed austenite [5–6]. Numerous studies have explored the relationship between the microstructural features and mechanical properties of Ni-bearing steels, particularly in alloys typically containing 5.5%–9% Ni [2,7]. Wu et al. [8] examined a heat treatment process composed of quenching, intercritical quenching, and tempering (i.e., the QLT treatment), for 4.5% Ni steel and demonstrated its effectiveness in attaining superior toughness.
Although substantial progress has been achieved in comprehending the mechanical properties of Ni-bearing steels, limited attention has been given to strategies for the improvement of their resistance to corrosion-assisted mechanical degradation and guaranteed long-term service performance. Corrosion behavior in these steels is influenced by several metallurgical factors, including the size and distribution of cementite [9], residual stress in the martensitic matrix [10], and heterogeneous distributions of alloying elements partitioned in retained austenite (RA) [11]. The effect of these factors on localized electrochemical stability and stress distribution suggests that corrosion resistance can be further improved via microstructural optimization through appropriate heat treatments.
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Jin Sung Park, Seung Woo Jin, Seong Jun Yun, Gyu Bin Baek, Jun-Seob Lee, Soon Gi Lee, Sung Jin Kim (2025). Optimizing microstructure of medium Ni-bearing steel to ensure high resistance to corrosion and corrosion-assisted mechanical degradation. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3077-3
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Frequently Asked Questions
What is the main objective of this study?
The main objective is to investigate the effects of microstructural modifications, achieved through quenching and tempering (QT) and quenching and partitioning (Q&P) processes, on the corrosion behavior and corrosion-assisted mechanical degradation of medium Ni-bearing steel, with the aim of enhancing long-term lifespan and reliability in neutral aqueous environments.
What are the key findings regarding conventional Q&P processing?
Conventional Q&P processing forms coarse partitioned austenite within the martensitic matrix, leading to uneven Ni distribution and high kernel average misorientation, which increases susceptibility to corrosion and corrosion-induced mechanical degradation.
How does a higher partitioning temperature affect the microstructure and properties?
A slightly higher partitioning temperature, just above the martensite transformation start temperature, results in finely distributed austenite within bainite, which exhibits lower corrosion kinetics and reduced susceptibility to mechanical degradation in corrosive environments.
What is the significance of this research for industrial applications?
The research highlights that microstructural optimization through the Q&P process with a high partitioning temperature is an effective technical strategy for achieving superior durability and reliability of medium Ni-bearing steel alloys in neutral aqueous environments, which is valuable for structural applications requiring long-term performance.
What methods were used in this study?
The study employed various electrochemical evaluations and microstructural characterizations to elucidate the relationship between heat treatment processes and corrosion behavior.
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