Abstract
Erosion-corrosion is one of the most challenging material degradation processes that occur in engineering components that handle slurries. Materials that can withstand a combination of corrosive fluid with suspended particles are required to extend the service life of hydraulic equipment. High chromium cast irons are favorable for these applications as the chromium carbides improve the wear resistance and usually, good corrosion resistance is obtained. In this study, two white cast irons (a 37%Cr - austenitic matrix and 27%Cr - martensitic matrix) were evaluated along with an austenitic stainless steel (UNS S31600) and a martensitic stainless steel (UNS S42000). The experiments were carried out using a submerged jet apparatus in a testing medium of 3.5% NaCl containing sand particles with and without cathodic protection. The most notable finding was that the relative performance of the tested materials varied by altering the testing conditions. The role of hardness in the performance of the different materials was also investigated.
Introduction
Erosion-corrosion phenomenon takes place extensively in slurry pumps. Their operational conditions are highly-aggressive, in terms of erosion, as different size and shape of solids are pumped/transported. Apart from the mechanical damage, electrochemical attack occurs, which enhances the material deterioration damage of the pumps. For this reason, over the past years, numerous white cast irons have been developed to counteract such effects by providing erosion-corrosion resistance, along with high toughness properties.
These cast ferrous alloys can vary in composition and microstructure depending on their application. For example, the carbon/chromium/silicon/molybdenum contents can either improve or worsen the material performance under corrosive wear [1,2]. The carbon and chromium content is also important as low carbon white cast irons, often called hypoeutectic cast irons, are not able to form as many chromium carbides as the high carbon white irons, hypereutectic. Addition of Ti into the composition of the white cast irons has also been studied, as the titanium forms higher hardness carbides than does chromium [3,4]. Also, new concepts have been applied to manufacture white irons with so called “high entropy” microstructure which has been demonstrated to improve their wear resistance [5]. The solidification rates of the white cast irons will affect the overall behaviour of cast irons against erosion-corrosion [6]. Rapid cooling of the cast alloy will transform the austenitic structure to martensitic and produce small carbides. As a result, this martensitic alloy would exhibit superior wear resistance but it would lack corrosion resistance in many conditions including acidic environments [7].
