Comparison of wear rates of polyurethane, grade 20 steel, and high-chromium cast iron under slurry erosion conditions

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With the continuous development of high-tech, erosion wear has become a common form of wear in modern industrial production under the action of slurry erosion. Under slurry erosion conditions with different pH values, various wear-resistant materials exhibited different wear resistance levels. To determine which material is more suitable for resisting slurry erosion, we experimentally investigated the effect of slurries with different pH values on the wear rate of materials such as spray-applied polyurethane, grade 20 steel, and high-chromium cast iron. The experimental results show that the spray-on polyurethane coating has a low wear rate in slurries with various pH values, and this rate remains relatively constant. This indicates that the coating material has good resistance to acid and alkali corrosion as well as erosion wear. High-chromium cast iron has a low wear rate in neutral and alkaline slurries, but its wear rate increases rapidly when the pH value is below 5; therefore, it has poor wear resistance in strongly acidic slurries. Steel grade 20 has the highest wear rate among all the materials tested, and its wear rate also increases sharply when the pH value is below 7. Through the analysis of the wear patterns, we found that under erosion by slurries with different pH values, the wear morphology of the spray-applied polyurethane coating materials was similar, with no obvious differences observed. 20 steel and high-chromium cast iron exhibit similar wear patterns in neutral and alkaline slurries; material removal is primarily due to mechanical action, with no significant corrosion occurring, hence the wear is not severe. However, in acidic slurries, as the pH value continues to decrease, the wear rates of grade 20 steel and high-chromium cast iron increase rapidly. For steel grade 20, it is a material that is not resistant to corrosion; as the corrosivity of the slurry increases, its dissolution rate rises, thereby increasing the wear rate. High-chromium cast iron is a material with certain corrosion resistance; when the pH value of the slurry is greater than 5, an effective passivation film can form on the surface of the material, protecting it from corrosion. However, when the pH value is below 5, once the passivation film is damaged by abrasives, a new passivation film cannot form quickly, and as a result the material will suffer from corrosion. Corrosion causes severe surface damage to the material, resulting in a loose structure and a significant reduction in mechanical strength; when subjected to the impact of abrasive particles, the material easily breaks off. Therefore, as the pH value decreases, under the combined effect of corrosion and abrasion, the wear rate of the material increases rapidly. Sprayed polyurethane coatings exhibit good wear resistance under slurry erosion; especially in corrosive slurries such as acidic ones, they are more suitable than metal materials. Therefore, spray-on polyurethane coatings are more suitable for use on machinery such as mud pumps, acid pumps, and turbine blades, and as a material for repairing machinery, they will yield significant economic benefits.