Is Your Stainless Steel Aging Gracefully? How Short-Term Heat Can Cause Pitting Corrosion
"Uncover the hidden risks of short-time aging on lean duplex stainless steel and how it impacts pitting corrosion behavior. Learn practical tips to ensure the longevity of your materials."
Duplex stainless steels are indispensable in various industries, including oil refining, food processing, pulp and paper, and pharmaceuticals, owing to their enhanced strength, superior chloride stress corrosion cracking (SCC) resistance, and improved pitting corrosion resistance compared to austenitic stainless steels. These materials have evolved through two primary development paths. First, high-alloyed duplex stainless steels emerged in the 1980s, designed to meet the rigorous demands of aggressive environments by optimizing chromium and nickel content and incorporating nitrogen.
In contrast, lean duplex stainless steels (LDSSs), characterized by lower chromium and molybdenum additions, were developed to reduce production costs and conserve natural resources. Despite having similar pitting resistance and better SCC resistance, LDSSs offer comparable strength to traditional austenite grades like 304L and 316L. A novel lean duplex stainless steel (LDSS) 2002, comprising 20.53Cr-3.45Mn-2.08Ni-0.31Mo-0.17N, has been developed and has shown approximately 50% elongation compared to the 30% elongation of the typical lean duplex stainless steel grade LDX 2101 by taking advantage of the transformation-induced plasticity (TRIP) effect.
However, lean duplex stainless steels inevitably experience temperatures between 400 and 1000 °C during manufacturing and welding. Such temperature variations can alter the volume fractions of ferrite and austenite phases and give rise to harmful precipitates, including intermetallic phases (σ, χ), carbides (M23C6), nitrides (Cr2N), and secondary austenite (γ2), which can compromise both the mechanical and corrosion properties of the steels. This article explores the effects of short-time aging on the corrosion behavior of LDSS 2002, providing valuable insights for maintaining material integrity.
How Does Short-Time Aging Impact Pitting Corrosion?
To systematically evaluate the effects of short-time aging on corrosion behavior in LDSS 2002, researchers conducted critical pitting temperature (CPT) tests and Charpy impact tests. The goal was to closely examine changes in pitting corrosion resistance and mechanical properties of aged LDSS 2002 specimens. Microstructure evolution and pit morphology were observed through optical microscopy (OM) and scanning electron microscopy (SEM), with the types of major precipitates determined by transmission electron microscopy (TEM).
- Critical Pitting Temperature (CPT) Tests: Assessed the temperature at which pitting corrosion initiates under controlled conditions.
- Charpy Impact Tests: Evaluated the toughness and impact resistance of the aged specimens.
- Microstructural Analysis: Used optical microscopy (OM) and scanning electron microscopy (SEM) to observe microstructure evolution and pit morphology.
- Precipitate Identification: Employed transmission electron microscopy (TEM) to determine the types of major precipitates formed during aging.
Protecting Your Stainless Steel: Key Takeaways
Understanding and mitigating the effects of short-time aging on LDSS 2002 is crucial for maintaining the integrity and performance of these materials in various applications. By controlling aging temperatures and minimizing the precipitation of detrimental secondary phases, it is possible to enhance the corrosion resistance and mechanical properties of stainless steel components, ensuring their longevity and reliability. These practices are key to optimizing the cost-effectiveness and sustainability of duplex stainless steel in demanding industrial environments.