Surreal illustration of pitting corrosion on stainless steel

Is Your Stainless Steel Aging Gracefully? How Short-Term Heat Can Cause Pitting Corrosion

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Samir D’Costa in Tech & Innovation August 2025 • 5 min read.

"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?

Surreal illustration of pitting corrosion on stainless steel

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).

The study involved solution annealing samples at 1000 °C for 30 minutes to achieve optimal mechanical and corrosion-resistant properties. The samples were then aged at various temperatures (400 °C, 500 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, and 1000 °C) for 10 minutes, followed by water quenching. The Charpy impact test, performed using an AHC-3000/2-AT impact test machine, adhered to the Metallic Materials-Charpy Pendulum Impact Test Method (GB/T229-2007) at room temperature.

  • 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.
Electrochemical measurements were conducted using a CHI660D workstation in a three-electrode cell. The setup included a saturated calomel electrode (SCE) as the reference and a thin platinum foil as the counter electrode. The working electrode consisted of a specimen embedded in epoxy resin, exposing a surface area of 1 cm². Before CPT testing, high-purity nitrogen was bubbled through the solution to remove oxygen. The specimens were polarized at 250 mV (SCE) in 1 mol/L NaCl solution, with the temperature increasing at a rate of 1 °C/min.

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.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

1

What makes duplex stainless steels, particularly lean duplex stainless steel (LDSS) 2002, suitable for industries like oil refining and food processing?

Duplex stainless steels, including LDSS 2002, are favored in industries like oil refining, food processing, pulp and paper, and pharmaceuticals because of their enhanced strength, superior chloride stress corrosion cracking (SCC) resistance, and improved pitting corrosion resistance when compared to austenitic stainless steels. LDSS 2002 offers comparable strength to traditional austenite grades like 304L and 316L, with approximately 50% elongation.

2

How does short-time aging between 400 and 1000°C affect the properties of lean duplex stainless steel (LDSS) 2002?

Short-time aging at temperatures between 400 and 1000°C can significantly alter the properties of LDSS 2002. These temperatures can change the volume fractions of ferrite and austenite phases and lead to the formation of detrimental secondary phases such as intermetallic phases (σ, χ), carbides (M23C6), nitrides (Cr2N), and secondary austenite (γ2). This precipitation can compromise both the mechanical and corrosion properties of the steel, particularly its pitting corrosion resistance.

3

What methods are used to assess the impact of short-time aging on the corrosion behavior of LDSS 2002?

To evaluate the effects of short-time aging on the corrosion behavior of LDSS 2002, researchers use several methods, including critical pitting temperature (CPT) tests to assess pitting corrosion resistance, Charpy impact tests to evaluate toughness, optical microscopy (OM) and scanning electron microscopy (SEM) to observe microstructure evolution and pit morphology, and transmission electron microscopy (TEM) to identify the types of major precipitates formed during aging.

4

What is the significance of the Critical Pitting Temperature (CPT) test in evaluating the corrosion resistance of LDSS 2002, and how is it performed?

The Critical Pitting Temperature (CPT) test is crucial for determining the temperature at which pitting corrosion initiates in LDSS 2002 under controlled conditions. In this test, specimens are polarized at 250 mV (SCE) in a 1 mol/L NaCl solution while the temperature is increased at a rate of 1 °C/min. The CPT value indicates the steel's resistance to pitting corrosion, with a higher CPT indicating better resistance. This test helps assess the impact of short-time aging on the steel's ability to withstand corrosive environments.

5

How can the detrimental effects of short-time aging on lean duplex stainless steel (LDSS) 2002 be minimized to ensure the longevity and reliability of components in demanding industrial environments?

To minimize the detrimental effects of short-time aging on LDSS 2002, it's crucial to carefully control aging temperatures and minimize the precipitation of detrimental secondary phases like intermetallic phases (σ, χ), carbides (M23C6), and nitrides (Cr2N). By optimizing these parameters, it's possible to enhance the corrosion resistance and mechanical properties of stainless steel components, ensuring their longevity and reliability in demanding industrial environments. Furthermore, understanding the specific temperature ranges that promote the formation of these phases allows for tailored heat treatment strategies to mitigate their impact.

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