Abstract
Mild steel is the most extensively used carbon steel for numerous industrial applications, where it is exposed to various service environments containing acids, bases and salt solutions. From industrial point of view, plastic deformation and heat treatment are among the essential manufacturing steps in mild steel processing and these steps can implicate its corrosion behaviour. This work investigated the effect of cold plastic deformation and subsequent high temperature heat treatment on the microstructure and corrosion behaviour of mild steel in two different concentrations (0.5M and 1.0M) of sulphuric acid (H2SO4), using the weight loss method. Mild steel samples were cold pressed to thickness reduction of 20%, 40% and 50% and subsequently heat treated at 700oC and 900°C and then air-cooled. The test duration lasted for 25 days and the weight loss measurements were taken at intervals of 5 days. It was observed that corrosion rates of the samples were generally higher in the 1.0M than in 0.5M acid solution. The as-received and heat-treated mild steel samples exhibited higher corrosion rates than the cold-pressed and heat-treated samples. The results indicated strongly that cold working accompanied by heat treatment improves corrosion resistance of mild steel in acidic media.
Highlights
The study of corrosion of mild steel is of tremendous theoretical and practical concern due to its wide industrial applications and the need to prolong its life span in various service environments
The samples were code named as follows: as-received mild steel (AR)-700 and AR-900 for the as-received samples heat treated at 700°C and 900°C, respectively; CP20%-700, CP20%C-900, CP40%-700, CP40%-900, CP50%-700, and CP50%-900 for the samples cold pressed to 20%, 40% and 50% reduction, heat treated at 700°C and 900°C, respectively
The corrosion rates of the samples were generally higher in the 1.0M than in 0.5M acid solution because corrosion rates of mild steel increase with the increase in acid concentration
Summary
The study of corrosion of mild steel is of tremendous theoretical and practical concern due to its wide industrial applications and the need to prolong its life span in various service environments. Mild steel in the form of plates and rods have found numerous applications as structural members in buildings, bridges, pipelines, ships, heavy vehicles and storage vessels (Osarolube, 1998; Clark and Varney, 1987) In these areas of application, mild steel is exposed to various service environments containing acids, bases and salt solutions, where it is prone to corrosion of the exposed surface. From manufacturing point of view, plastic deformation and heat treatment or thermomechanical processing are among the inherent and essential steps in fabrication of mild steel structures (Giuseppe, et al, 2009) and these steps further affect its corrosion behaviour in the service environments. Air cooling was chosen because mild steel is usually subjected to high temperatures and allowed to cool in air during construction or fabrication of mild steel structures
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