Steel Annealing and Thermodynamics

by | Sep 30, 2015 | Metal Heat Treating Service

Steel annealing is an important process in metal working. Without annealing, it would be nearly impossible to form some types of hardened steel into the needed shapes. However, annealing is made possible by a principle known as thermodynamics and understanding this principle can help you better understand the process.

How Thermodynamics Affects Steel Annealing

Thermodynamics is a branch of science which explains the relationship between heat energy and other types. For example, if you have three systems of energy and two of them are the same temperature as the third system, they are in a state of thermal equilibrium.

Thermal equilibrium means heat exchange is no longer occurring between two things. For instance, if you place two metals together and one is much hotter than the other, heat will dissipate from the hottest metal to the cooler metal, until it reaches thermal equilibrium. In fact, it doesn’t matter how many materials you have in proximity, heat will transfer evenly eventually. This is known as the zeroth law of thermodynamics, and there are three other laws which affect steel annealing processes.

First Law

The first thermodynamic law states energy will remain constant within a system, even when this energy is converted. Energy can be in several forms, including:

  • Heat
  • Light
  • Movement
  • Sound
  • Chemical
  • Electrical
  • Gravitational
  • Nuclear

For instance, braking systems take kinetic or motion energy from the user (by stepping on a brake pedal) and turn it into heat or thermal energy to stop a moving vehicle. However, the amount of energy cannot change in the process.

Second Law

When heat is transferred from one object to another, the temperature cannot raise on its own. In other words, you cannot place a 300 degree object with a 250 degree object and end up with more than 300 degrees of heat.

Third Law

When energy is converted, molecular activity tends to cease as temperatures reach 0 degrees Kelvin. This is the point in which atomic activity is its lowest. In other words, as things cool, the activity of molecules and atoms gradually ceases as it cools and approaches a state of absolute zero. Absolute zero (O degrees Kelvin) is a state where no heat exists and this cannot be achieved on earth.

Steel Annealing

Without thermodynamics, the process of metal annealing could not be possible. There are several process used for softening steel and modern industry has created cost effective solutions for annealing many types of metal. In fact, one company is producing innovative methods like PuroBrite, which creates a clean and shiny surface.

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