Hardness values are generally used for engineering materials to define the strength of them. But these hardness values are considered for room temperature conditions. Hardness of materials changes with temperature as other material properties. So in this article, we will explain the effect of temperature onf materials’ hardness values and the term ‘hot hardness’ of materials.
Hot hardness of materials is generally expressed as the ability of material that retain the hardness value at elevated temperatures. Different kinds of materials show different characteristics in this manner.
The best material in hot hardness is ceramics. Ceramics are very superior in high temperature applications. For example the external coatings of space shuttles are made by ceramics. Ceramics are commonly used in high temperature turbine applications also. As you can see from the above graph, the hardness of ceramic is superior to others.
Hardness of stells is varying according to their alloying properties. For example Low carbon steels have low hardness values in room temperature. Also worst in high temperature applications in hardness mean. If you increse the carbon content in the stell, hardness also increases. But there is no significant difference in hot hardness values of high carbon and low carbon steels if you look at above graph.
Some of alloying elements can be added to steel to increase the hardness value. Also high-alloy stells show very good performance in some high temperature applications. Machine tools are generally manufactured with high-alloy steels, because in general machining operations, heat produced because of the friction.
The relation of temperature and hardness of materials can be summarized like that. In general, hardness of materials lower with increasing temperature. But the hardness of ceramics also superior in high temperatures.
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