How do Cylinder Head Bolts perform under high temperature conditions?

1. Material properties
Material selection: Cylinder head bolts are usually made of high-strength, high-temperature resistant materials, such as certain alloy steels or special alloys. These materials can still maintain good mechanical properties and stability at high temperatures.
Heat treatment: Through appropriate heat treatment processes, such as quenching and tempering, the hardness and strength of cylinder head bolts can be improved, while enhancing their ability to resist high-temperature oxidation.

2. Mechanical properties
Strength and toughness: Under high temperature conditions, the strength of cylinder head bolts may decrease, but high-quality materials and reasonable heat treatment can slow down this trend. At the same time, the toughness of the bolts will also be affected to a certain extent, but this should be fully considered during design to ensure that sufficient tightening force can be maintained at high temperatures.
Creep resistance: Under high temperature conditions, materials are prone to creep (that is, the phenomenon of slow plastic deformation of materials under long-term constant stress). Cylinder head bolts must have good creep resistance to ensure that they will not loosen or fail under high temperature and long-term working conditions.

3. Sealing performance
Thermal expansion coefficient: The materials of cylinder head bolts and components such as cylinder head and cylinder block may be different, and their thermal expansion coefficients may also be different. At high temperatures, this difference may cause the gap between the bolts and components to increase, thereby affecting the sealing performance. Therefore, this factor needs to be considered during design and corresponding compensation measures should be taken.
Preload retention: High temperature will change the preload of the bolts. In order to ensure the sealing performance, it is necessary to regularly check and adjust the preload of the bolts. At the same time, it is also crucial to select bolt materials and fastening processes with the ability to maintain preload at high temperatures.

4. Comprehensive performance
High temperature oxidation resistance: Under high temperature conditions, the surface of the cylinder head bolts is prone to oxidation reaction and form oxide scale. This will affect the mechanical properties and sealing performance of the bolts. Therefore, it is necessary to select materials with good anti-oxidation properties and perform surface treatment (such as galvanizing, painting, etc.).
Long-term stability: After the cylinder head bolts work at high temperatures for a period of time, their performance may gradually decline. Therefore, they need to be regularly inspected and replaced to ensure the safe and reliable operation of the engine.