Tribocorrosion of lightweight steel

09.06.2024
Understanding Construction: What is Light Gauge Steel Framing? - Strucsoft Solutions

Introduction

The advancement in industries has resulted in increasing demand of materials resistant to surface degradation. Two major surface degradation models costing billions annually are tribological failure and corrosion. Tribological wear includes abrasive, fatigue, adhesive, and oxidative wear, while corrosion primarily involves electrochemical mechanisms. The synergy between tribology and corrosion, known as tribocorrosion, accelerates metal degradation, reduces service life, and jeopardizes industrial safety. Tribocorrosion is especially prevalent in sectors like chemical processing and marine equipment. In industrial development, lightweight materials are becoming increasingly important. This is achieved through two methods: using high-strength materials to enable smaller structural components and utilizing low-density materials to reduce component weight while maintaining size. Consequently, Fe-Mn-Al-C lightweight steels are gaining prominence due to their combination of high tensile strength and low density. These steels can be categorized into three types: ferrite, duplex, and austenite steels. Among them, austenite steels exhibit superior mechanical properties. Precipitation strengthening is a common mechanism in enhancing the strength of austenite lightweight steel.

Background Information

Recent studies have focused on the tribology and corrosion behavior of Fe-Mn-Al-C lightweight steel, aiming to modify its performance through alloying elements. Researchers observed a decrease in friction coefficients, wear loss, and surface damage with higher Al content due to increased yield strength and hardness. Further they have found that Cr content below 5 wt% improves pitting resistance, while above 5 wt% worsens it. The self-lubricating effect improves tribology properties was demonstrated using graphite-containing Fe-Mn-Ni-Al steel. Surface modification, such as plasma nitriding, enhances corrosion resistance on Fe-Mn-Al-C steel. Aging treatment is essential for enhancing the strength of lightweight steel. To broaden the utility and improve the reliability of lightweight steels in diverse environments, understanding their tribology, corrosion, and tribocorrosion behavior after aging is crucial. Common alloying elements like Cr and Mo are known to enhance steel strength and corrosion resistance. However, there is a lack of research on the tribology, corrosion, and tribocorrosion behavior of aged lightweight steel alloyed with Cr/Mo.

Microstructural Properties

The microstructure of lightweight steels typically consists of austenite with equiaxed shapes. By adding a significant amount of Al, a ferrite-stabilizing element, the density of the steel decreases notably. This often results in the presence of ferrite in the microstructure. Additionally, Cr and Mo, also ferrite-stabilizing elements, further support ferrite formation. Conversely, Mn and C, which are austenite-stabilizing elements, inhibit ferrite formation, enabling a single austenite matrix to form. Apart from phase composition, grain size is another noteworthy microstructure contrast.

Tribological behaviour

The tribological process on lightweight steels leads to the formation of wear tracks, characterized by pile-ups resulting from friction-pair extrusion. The heat generated during tribology facilitates plastic deformation, gradually expanding these areas along both sides of the wear track. The COF undergoes a running-in period before stabilizing during tribology tests. Initially, the surfaces of both the lightweight steel and the friction-pair are rough, leading to a small contact area and a sharp increase in COF. As the test progresses, asperities wear away, increasing the contact area and stabilizing the COF. The worn surfaces of experimental lightweight steels exhibit grooves, wear debris, and delamination. Frictional forces drive wear debris, forming grooves on the worn surface, while delamination is also detected. Despite significant wear, the lightweight steels maintain excellent toughness, preventing serious damage from delamination.

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Figure-1 Tribology properties of the experimental steels: (a) wear track profile; (b) COF curves; (c) mean COF and SWR [1]

Tribocorrosion behaviour

Lightweight steel exhibits a rough surface with numerous cracks and corrosion pits. The worn surface of lightweight steel suggests the formation of an oxide film due to the presence of oxygen. Tribocorrosion mechanisms involve plastic deformation-induced vacancies and dislocations, destruction of the oxide film, and an increase in material surface roughness. In tribocorrosion tests, the rates of oxide film removal and formation reach equilibrium. Plastic deformation leads to a significant amount of defects in the material. The higher affinity of lightweight steels with oxygen enhances the lubricating effect of the oxide film, particularly containing Mo oxide. Mo’s oxyphilicity amplifies this effect, making the lubricating role of oxide films with Mo oxide more pronounced. Consequently, fresh metal is more readily exposed to the solution, facilitating dissolution. The dissolution weakens the strengthening effect of carbide on the matrix. The presence of NaCl solution acts as a weak lubricant, reducing the impact of contact area on wear performance. To enhance the tribocorrosion resistance of aged lightweight steels, two primary strategies are suggested: Decreasing the number density of precipitates through alloying elements to mitigate galvanic corrosion damage. Adding corrosion-resistant alloying elements to facilitate oxide film formation and reduce material loss during friction.

Figure-2 Corrosion mechanism of experimental steel [1]

Reference

[1] Tang, Y., Ji, P., Li, B., Chen, B., Shi, H., Guo, Y., Zhang, S., Zhang, J., Zhang, X. and Liu, R., 2024. Tribology, corrosion, and tribocorrosion performance of aged lightweight steels: Effects of oxide film and carbide. Corrosion Science231, p.111999.

[2] https://strucsoftsolutions.com/blog/understanding-construction-what-is-light-gauge-steel-framing/

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I am currently working as a Postgraduate Researcher at the University of Leeds, where I am actively involved in research activities. Prior to this, I successfully completed my master's degree through the renowned Erasmus Mundus joint program, specializing in Tribology and Bachelor's degree in Mechanical Engineering from VTU in Belgaum, India. Further I handle the social media pages for Tribonet and I have my youtube channel Tribo Geek.

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