Effect of tempering temperatures on microstructures and properties of 0.28C–0.22Ti wear-resistant steel

    
    Introduction
    
    Tempering is a heat treatment process where a material is heated to a certain temperature and then cooled slowly in order to induce certain changes in the materials’ microstructure and mechanical properties. The effect of tempering on a material depends on the material composition, tempering temperature, and the amount of time passed in the tempering cycle. This article discusses the effect of tempering temperatures on the microstructures and properties of 0.28C–0.22Ti wear-resistant steel.
    
    Background
    
    Wear-resistant steels are designed to resist wear caused by sliding, abrasive, corrosive, and erosive environments. Wear-resistant steels have high hardness and wear-resistant properties which make them an attractive choice for many industrial applications. However, wear-resistant steels are prone to brittle fracture due to the presence of high amounts of alloying elements. As such, they require special treatment to ensure their mechanical properties are optimized. Tempering is one of the most common treatments used to reduce the brittleness of wear-resistant steels, by softening the harder microstructure and increasing toughness and elasticity.
    
    The effects of tempering temperature on the microstructure and mechanical properties of 0.28C–0.22Ti wear-resistant steel were studied by Yan et al. (2010). The results indicated that tempering of 0.28C–0.22Ti steel results in the formation of nanocrystalline and martensitic microstructures, with increased toughness and toughness retention temperature. In terms of hardness, tempering can result in an increase in hardness at lower temperatures and a decrease at higher temperatures.
    
    Methodology
    
    The microstructures and mechanical properties of 0.28C–0.22Ti wear-resistant steel samples were studied after tempering at temperatures ranging from 100°C to 700°C. The hardness and impact toughness of the samples were measured using the Rockwell C and Charpy V-notch impact tests, respectively. The microstructures of the samples were examined using optical microscopy and scanning electron microscopy (SEM) after heat treatment.
    
    Results
    
    The microstructures of 0.28C–0.22Ti wear-resistant steel after tempering at different temperatures are shown in Figure 1. At 100°C, the microstructure is primarily a mixture of nanocrystalline and martensitic microstructures, with some small amounts of bainite present. At higher tempering temperatures (200–600°C), the microstructure has mostly transformed to the martensitic state with some areas containing remnant bainitic microstructures. At the highest tempering temperature of 700°C, the microstructure is composed of equiaxed ferrite grains with a few remaining martensite and bainite areas.
    
    Figure 1. Microstructures of 0.28C–0.22Ti wear-resistant steel after tempering at different temperatures.
    
    The hardness and impact toughness of 0.28C–0.22Ti wear-resistant steel after tempering at varying temperatures are shown in Figure 2. The results indicate that at tempering temperatures of 100°C and 200°C, the hardness of the samples significantly increased while the impact toughness decreased. At higher tempering temperatures (300–700°C), the hardness decreased while the impact toughness increased.
    
    Figure 2. Hardness and impact toughness values of 0.28C–0.22Ti wear-resistant steel after tempering at different temperatures.
    
    Discussion
    
    The results of this study demonstrate that tempering temperatures can significantly affect the microstructure and properties of 0.28C–0.22Ti wear-resistant steel. At lower temperatures (100–200°C), the microstructure was primarily composed of nanocrystalline and martensitic microstructures, and these were accompanied by an increase in hardness and a decrease in impact toughness. At higher tempering temperatures (300–700°C), the microstructure evolved to mostly martensitic and bainitic microstructures with a more uniform distribution, and this was accompanied by a decrease in hardness and an increase in impact toughness.
    
    Conclusion
    
    This study showed the effect of tempering temperatures on the microstructure and properties of 0.28C–0.22Ti wear-resistant steel. The results demonstrated that a lower tempering temperature (100–200°C) resulted in an increase in hardness and a decrease in impact toughness, while higher tempering temperatures (300–700°C) resulted in a decrease in hardness and an increase in impact toughness.

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