Quenching vs. Tempering

Steel is one of the hardest, strongest materials around, but when you use heat treatments, it can become even stronger. Two ways to improve your steel’s strength are quenching or tempering heat treatments in Gastonia, NC. Both involve heating the steel, then cooling it to achieve the desired results. Read on to learn more about how these methods can change and improve your steel’s internal structure.

What is quenching?

Quenching heat treatments in Gastonia, NC involve heating steel to very hot temperatures, up to 1600 degrees Fahrenheit. When the metal is heated this high, the grain structure within the steel starts changing. Eventually, it becomes a material called austenite, which is very soft.

Since soft steel isn’t the goal, the next step is to quench it. That involves plunging the steel into a liquid, which will cool it rapidly. Depending on the liquid and the time it takes to cool, the steel’s grain structure will undergo a number of different changes. This can result in pearlite, ferrite, cementite and martensite, among other structures. Here are four different examples of how different quenching liquids work:

  • Water: Fresh water quenching comes with some challenges: the water has to remain at a consistent temperature, and if it gets too hot, the desired grain structure can’t be achieved. This method of quenching requires careful monitoring to get the desired results.
  • Polymer: Polymer quenching uses fresh water and a solution, agitated and kept at a specific temperature. This method can accommodate interrupted quenching—that is, when you take out parts before they’re fully cooled. It’s also less severe than fresh water or brine quenching, and it minimizes distortion in the steel.
  • Brining or saltwater: This quenching method uses saltwater to quench the steel. The saltwater reduces the steam cloud that develops during quenching, but it’s considered a “severe” treatment. However, you can control the quenching through agitation, temperature and the solution content.
  • Oil: This method is slower than the others, which is good for alloyed steels. (Alloyed steels are prone to cracking in severe methods.) It’s much safer than it used to be, since the work area is fully enclosed, and most operations can recover up to 80 percent of the oil used.

What is tempering?

After steel is quenched, it is very hard, and very brittle. That makes it prone to breakage. Tempering heat treatment in Gastonia, NC reduces some (not all) of the hardness, which helps improve ductility. Instead of heating the metal to extreme temperatures and cooling it rapidly, it’s heated to lower temperatures and cooled in the air. This allows the metal to retain its strength while preventing it from cracking or other difficulties.

Depending on your goals, you may use quenching, tempering or both processes to ensure a strong, ductile result. If you’re not sure which processes are right for your product, it’s wise to talk to a metallurgy professional for custom advice.

To learn more about quenching and tempering heat treatments in Gastonia, NC, call J.F. Heat Treating Inc. today.

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