In Vitro Microstructure, Mechanical Properties and Corrosion Behaviour of Low, Medium and High Carbon Steel Under Different Heat Treatments

Abstract

Corrosion is a serious problem in the oil and gas industry and corrosion of carbon steel contributes to tonnes of material wastage daily. It is believed that corrosion rate of carbon steel is affected by the carbon content and also any heat treatment carried out on the steels. To attest whether this statement is true, an investigation was conducted on carbon steels which were heat treated and contained varying amount of carbon content. This research aims to evaluate the effect of carbon content and heat treatment to the corrosion behaviour of carbon steels. The sample materials were selected from low, medium and high carbon steels. Three types of heat treatment were performed on all the steels, namely, annealing, quenching as well as quench and temper. The corrosion behaviour was determined by conducting immersion test on the non-heat-treated and heat-treated steel samples. The immersion test was done by immersing samples in 3.5% sodium chloride solution for duration of 1, 2, 4, 5 and 6 weeks. Corrosion rates were calculated using weight loss data according to ASTM G31-72 standard. Immersion test results show that steels with high carbon content and heat treated by quenching with martensitic structure display the highest corrosion resistance, while steels with lower carbon content and heat treated by annealing with large ferrite and pearlite structure display the lowest corrosion resistance. The overall results revealed that corrosion behaviour of the carbon steels was directly affected by the carbon content and heat treatment which altered the microstructures of the steels. In other words, corrosion performance of the carbon steels is very much dependent on the final microstructures formed after heat treatment.