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High-temperature bolts are fastening elements of the engine located inside parts where the temperature can reach peaks of even 700°.

This situation is even more extreme in internal combustion engines, such as in high-performance or racing cars.

On the contrary, the electric motor has no particular need for high-temperature bolts inside it, except for the battery temperature during the charging process.

Despite this rise, the temperature peaks that the electric motor can reach are never comparable to those at which the internal combustion engine.

High-temperature bolts use 

There are at least two points where it is necessary to mount high-temperature bolts inside the internal combustion engine, especially for high-performance cars or race cars

They are typically located:

  •  Inside turbochargers, and
  • Near the exhaust manifolds.

These are the hottest points of the engine that, depending on the type of car, can even become incandescent. 

In some cases, high-temperature bolts can be used also inside braking systems, for example in the thermochromic brakes found in some high-performance car classes.
On the other hand, none of the more classic critical bolts requires the attributes of the high-temperature bolts.
Even though the critical bolts of the fastening elements are subjected to considerable thermal variations, particular forces, or critical applications, they are never exposed to such temperatures.
Only the precious mentioned cases require solutions ad hoc for the bolts of turbochargers or exhaust systems.

Characteristics and differences of the high-temperature bolts compared to classic ones

The main characteristic of high-temperature bolts is being able to withstand very high heat.
This particularly depends on the type of steel used.

  1. For the classic bolts that do not have to perform at high temperatures, steels such as carbon steel or boron steel are used, whose mechanical properties can be altered through hardening and tempering.
  2. For bolts not subject to high temperatures – whatever the strength class may be – the most widespread method is cold forging the steel and then picking the heat treatment most appropriate for the fastener’s application.

Depending on the heat treatment employed, raising or lowering the tempering, the bolt can be better or less performing and adjust to the precise characteristics that it must have to play its role inside the engine.
In this case, heat treatment plays a crucial role in the cold deformation process.
The steels used to assemble high-temperature bolts are instead expressly dedicated to applications subjected to exposure to high heat.
These steels have unique features, such as being nonmagneticnon-oxidizing, and resistant to high temperatures.
These traits must be kept intact also in the bolt. This is why the mechanical properties of the high-temperature bolts are influenced by processes other than classic hardening and tempering.
In the case of these fasteners, the hardening process is one of the first steps to provide strength and the desired mechanical characteristics to the final product. The final result mainly leans on plastic deformation.

In addition to the attention paid to the processing, the high-temperature bolts must also have customized coatings and dedicated oiling.
Every high-temperature bolt component must resist the high heat to which it is subjected, such the coal and oil.
Each fastener is coated and oiled with materials and substances suited to the role it has to play and to the critical conditions it must withstand and be well-performing.
High-temperature bolts present many critical difficulties in their production. From the plastic deformation by cold forging to the choice of coating and oiling, the know-how in producing customized bolts becomes essential to achieve a high-performing result.