Why Are Steel Bolts Heated Before Connecting to Something?

Heat treatment can make steel stronger.

Heating a steel bolt in the manufacturing process is done in order to strengthen the steel. Heating just before connecting the bolt to something is done to accomplish shrink fitting, or to straighten a bent bolt.

Shrink Fitting

Shrink fitting is a process used in assembly processes in general, including bolt fastening. This process consists of heating a building component, then fastening it to another component. The two items then cool, creating a solid and tight connection, stronger than it would be otherwise.

Heat Strengthening

Steel, an alloy of iron manganese and carbon, is a stronger metal than iron alone. To increase the strength of this alloy even further heat treatment can be applied. This causes the molecules of the alloy to realign in a stronger structure, increasing both tensile and yield strength.

Considerations

The term "ultimate tensile strength," refers to a material's ultimate ability to bear weight before breaking. Proper heat treatment of steel bolts increases ultimate tensile strength significantly.

References

• Engineers Edge: Heat Treating Terms
• EFD Induction: Bolt Expansion: A Guide to the Benefits of Induction Heating
• Bolt Depot: About Fastner Materials
• Vacaero: Benefits of Heat Treating
• Toolingu: What Is The Definition Of Shrink Fitting?

Resources

• Speed Bolt Heating: Speed Heater Controller Models