Heat treatments are common and necessary steps to enhance metals. In fact, most industry applications require these methods to produce metals that meet the rigorous demands of their specific use, whether that’s aerospace, defense, or automotive machinery; medical devices; construction materials; or other uses.
Learn how with heat treatment processes, metals are improved and transformed to meet your application’s necessary criteria. Discover the differences between annealing vs. normalizing vs. tempering, how precipitation hardening works, and more.
What Is Heat Treatment, and Why Does It Change a Metal’s Mechanical Properties?
Higher temperatures and strategic cooling and aging methods can alter the physical and mechanical properties of metals, rearranging, diffusing, moving, or precipitating the atoms in the crystal structure or lattice that makes up the material.
Altering the grain structure results in a material different from the one you started with. With heat treatment processes, metals can become stronger, more malleable, more ductile, more corrosion resistant, harder, and so on. This is why choosing the proper heat treatment is crucial for producing a metal that stands up to the requirements of your desired application.
Annealing
Annealing involves heating a metal to a predetermined temperature, keeping it at that temperature for a certain amount of time, then cooling it very slowly within the same furnace so that temperatures are controlled. This process serves to:
- Keep the mechanical properties of the metal stable
- Soften the metal, thereby increasing its machinability (the ease with which the metal can be cut) and ductility (the ability to be reformed without breaking)
- Relieve internal stresses through slow cooling
The annealing process is commonly used for aluminum alloys, stainless steel metals, carbon steel, brass, and copper alloys.
Key Uses for Annealing
- Sheet metal fabrication
- Marine structural components (depending on the type of metal or metal alloy)
- Aerospace and transportation body frames and engine components
- Electrical wiring and industrial tubing
Normalizing
When a metal undergoes normalizing, it’s heated above its critical transformation temperature, where the microstructure transforms. It’s held at this temperature for a set period of time, then cooled slowly in still, room-temperature air. This process is similar to annealing, but with normalizing, the material isn’t cooled in a furnace; rather, it’s cooled in exposed air, which speeds up the cooling process and results in a finer, stronger grain structure.
The goals of normalizing are to:
- Improve the metal’s toughness
- Create a tougher, stronger material
- Make a pretreated, hard material more ductile and machinable
Common metals that undergo normalizing include carbon steel, alloys that feature chromium and molybdenum, and stainless steel.
Key Uses for Normalizing
- Automotive and construction manufacturing components
- Refine the microstructure of forged or welded materialsÂ
- Landing gear and engine components in the aerospace and transportation industries
- Oil and gas industry components
Quenching and Tempering
Here is quench and temper steel explained in simple terms:
- Quenching. The metal is heated above its critical transformation temperature (as with annealing and normalizing), held at that temperature for a certain period of time, then cooled rapidly. The rapid cooling phase often involves plunging the material in a solution of water, oil, or polymer. This forms a martensitic steel, which, at this stage, is exceptionally strong and hard but is brittle and lacks toughness.
- Tempering. To reduce the quenched steel’s internal stress while maintaining its strength, tempering is then applied. The metal is reheated to a temperature below the critical transformation point, held at that temperature, then cooled in a slow, controlled manner.
Steel is the most commonly used metal for quench and temper.
Key Uses for Quenching and Tempering
- High-stress, extreme applications, such as in the aerospace, defense, and automotive industries
- Gears, axels, landing gear, and engine parts
- Tools and machinery
- Structural components in the construction industry
Precipitation Hardening
The precipitation hardening heat treatment is similar to other methods but involves different heat treatment process metals, primarily alloyed aluminum, copper, and titanium (e.g., aircraft alloys). The process involves significant heating of the metal so that the alloying elements dissolve, cooling it rapidly, then heating the material again to a lower temperature.
The purpose of precipitation hardening is to dissolve the alloying elements, which then produce participates within the metal’s crystal structure. This helps to increase the tensile and yield strength of the metal while maintaining an excellent strength-to-weight ratio.
Key Uses for Precipitation Hardening
- Aerospace and defense structural components
- Nuclear industry components, such as high-pressure valves
- Medical devices and industrial machinery
Stress Relieving
Stress relieving differs from other heat treating processes in that it doesn’t alter the mechanical properties of the material. The process involves heating the metal to a lower temperature than its critical transformation point, holding it at that temperature, then cooling it slowly in the furnace. This might sound especially similar to annealing, but the key difference here is that stress relieving doesn’t heat the material above that critical transformation temp.
Stress relieving is primarily used after a material has been welded, cast, or machined and needs stress reduction to perform well.
Trust Fry Steel as Your Heat Treating Service Provider
Fry Steel is your one-stop shop for purchasing certified, traceable, production-ready bar stock that’s heat treated according to your specific application. There’s no secondary processing step to add to your project timeline—everything is done in house. Our engineers understand heat treatment processes for metals, providing unmatched expertise and a practical advantage for customers. Contact one of our reps today to learn more.
