PSI - Issue 22

172 L. Sena, R. C. Reis, A. A. Monteiro , C. Oliveira, C. Reis , P. L. Silva, Analysis of iron FC 250 microstructure under the effect of phosphoric acid corrosion ,2019 Peer-review under responsibility of the First International Symposium on Risk and Safety of Complex Structures and Components organizers L. Sena et al. / Procedia Structural Integrity 22 (2019) 171–180

Keywords: Corrosion, Phosphoric Acid, Cast Iron, SEM;

1. Introduction Many metallic materials are used in various human activities and are exposed to different types of corrosion because they are in contact with different environments and corrosive media (YARO, KHADOM, WAEL, 2013). Approximately 5% of an industrialized nation's profit is spent on preventing and maintaining, or replacing, components lost or contaminated by corrosion. Thus, the need arises to study the behavior of metal alloys on the effect of corrosion, trying to reduce or even eliminate it (OGUNDARE, 2012). The term cast iron includes a large family of ferrous alloys. It comprises iron alloys, which contain more than 2,1% carbon and 1% or more silicon (HALEEM, JABAR, MOHAMMED, 2012). These complex materials have stable and metastable phases, with elements in solution that influence the degree of stability and desired properties obtained through other alloys (HALEEM, JABAR, MOHAMMED, 2012; SHERIF, ABDO, ALMAJID, 2015). The popularity of cast iron is due to its ability to obtain complex shapes, at relatively low costs, and to a range of properties that can be controlled both by composition and cooling rate (HALEEM, JABAR, MOHAMMED, 2012). Cast iron, after its manufacture, forms a protective film on the surface that initially becomes more corrosion resistant than wrought iron or mild steel (SHERIF, ABDO, ALMAJID, 2015). This property is also due to the alloying elements, which play an important role in the sensitivity of cast iron, having silicon as an essential factor, which in higher percentages increases the corrosion resistance (HALEEM, JABAR, MOHAMMED, 2012; SHERIF, ABDO, ALMAJID, 2015). Considering the microstructure, most of the carbon in the gray cast iron is in the form of a continuous network of flake graphite platelets, which are dispersed in the metal matrix. The matrix may be ferritic or perlite, depending on the treatment and composition (CALLISTER, 2002). Matrix is the main factor responsible for controlling mechanical properties and also for its relatively fragility and lack of ductility (OLAWALE et al, 2013). The main reasons for the study against corrosion in metals, and especially in cast iron, is that among a range of acids, phosphoric acid stands out for being widely used in industrial processes such as the production of fertilizers and food products (DEEPA). PADMALATHA, SATIVUM, 2013), cleaning and polishing aluminum as well as other ferrous materials, and in delicate pickling where rust should be avoided (DEEPA, PADMALATHA, SATIVUM, 2013; 2014). The literature on corrosion of metallic materials using phosphoric acid is scarce. Deepa and Padmalatha (DEEPA, PADMALATHA, 2014), verified the corrosion rate in aluminum 6063, in phosphoric acid and sodium hydroxide solutions, obtaining corrosion in both media. The raise of the corrosion rate was greater with the increase of the media concentration and at higher temperatures (DEEPA, PADMALATHA, 2014; KRUIZENGA, GILL, 2013). Corrosion on aluminum was more severe with sodium hydroxide than with phosphoric acid (DEEPA,