Effect of Austempering and Tempering Temperature on Mechanical Properties of Low Alloy Wear-resistant Steel
Austempering is an isothermal heat treatment process widely used to enhance the mechanical properties of ferrous alloys. Depending on the austempering temperature, higher mechanical strength and ductility can be obtained compared to other methods of heat treatment . Generally, austempering can be applied on low-alloy wear-resistant steels with austenite as the primary solid solution. The cooling rate also plays a major role in the microstructure of the resulting material. As the austempering temperature is increased, the cooling rate is decreased, forming bainite and/or martensite structures. The mechanical properties of the material depend mainly on the volume fraction of these structures.
Tempering is a heat treatment process that involves reheating an already hardened material at a lower temperature. During this process, the mechanical properties of the material can be improved by reducing its residual stresses, improving toughness and ductility, and increasing its wear resistance. Compared to austempering, tempering can only be used on low-alloy wear-resistant steels with a martensitic matrix. The tempering temperature influences the microstructural transformation of the martensitic matrix, and therefore affects the mechanical properties.
The influence of austempering and tempering temperatures on the mechanical properties of the low-alloy wear-resistant steel can be observed in Figure 2. Increasing the austempering temperature from 200°C to 300°C increases the yield strength from 545MPa up to 620MPa. However, further increasing the temperature beyond 300°C has no significant effect on the yield strength, and only leads to a slight increase in hardness. On the other hand, increasing the tempering temperature from 150°C to 300°C leads to a decrease in hardness from 590HV up to 540HV. This is caused by the relief of intergranular stresses, resulting in a decrease in the strength of the material.
In conclusion, the austempering and tempering temperature have a pronounced effect on the mechanical properties of low-alloy wear-resistant steels. Increasing both the austempering and tempering temperatures improve the mechanical properties of the material, by increasing the yield strength and decreasing the hardness. These parameters need to be carefully chosen depending on the desired application of the material.
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