Effect of Quenching Medium on Microstructure and Properties of Wear-resistant Cast Steel
A common application of quenching is in the production of wear-resistant cast steel. The high-third-party component wear-resistant steel is produced by quenching and tempering. The wear resistance of the cast steel is due to its combined effect of moderate carbon content and corresponding alloying elements, in addition to a suitable austenitic structure followed by a fine-scale carbide dispersion. Finding the right process and quenching medium is critical to the production of quality wear-resistant steel.
Wear-resistant cast steel Quenching Mediums
The quenching medium used in the production of wear-resistant cast steel is often a liquid such as water, oil, or an aqueous salt solution. The key characteristics of the quenching medium are its thermophysical properties, such as its heat capacity, thermal conductivity, and density.
Quenching liquids typically have good thermal conductivity, which helps to rapidly dissipate heat and cool down the steel. Water is one of the most commonly used quenching mediums, since it is cheap and has a better thermal conductivity than oil. However, due to its high rate of thermal expansion upon cooling, it can induce high levels of residual stress in the steel. In addition, water may cause oxidation and decarburization of the steel, thus reducing the wear-resistance. Aqueous solutions such as brine, or molten salts, are also used and are able to absorb a greater amount of heat than water.
Wear-resistant cast steel Quenching in water
Oil is a popular secondary quenching medium, as it is slower cooling than water and generates less residual stress in the steel, as well as reducing oxidation and decarburization. However, due to its lower thermal conductivity, the duration of quenching must be increased to obtain the desired properties.
Effects on Microstructure and Properties
The microstructure of the wear-resistant cast steel is greatly affected by the quenching medium used. During the quenching process, pearlite and martensite are formed. These two main phases depend on the cooling rate, as well as the composition of the steel.
Water has the highest cooling rate and allows for the formation of large amounts of martensite. This increases the hardness and wear resistance of the steel, but may also lead to lower ductility. On the other hand, oil has a lower cooling rate, and thus forms less martensite, leading to higher ductility.
The quenching medium used in the production of wear-resistant cast steel has a significant effect on its microstructure and properties. Water is often used as it is cheap and has a good thermal conductivity. However, it induces high levels of residual stress and oxidation. Oil, on the other hand, has a lower cooling rate and produces less residual stress. The choice of quenching medium will depend on the requirements of the application.
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