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Heat treatment of steel in the forgin process

Using advanced techniques to get the absolute most out of metals is key to increasing their efficiency and sustainability in use. Enhancing the properties of metals to the fullest involves applying exacting treatments and processes using state-of-the-art equipment. In this article, we will focus on the heat treatment of steel to optimize the forging process.

Heat treatment

What is heat treatment?

First we need to understand what the term means in the metal industry. Heat treatment involves heating or cooling steel to alter its mechanical characteristics. In other words, by modifying the metal’s structure, the properties of a steel can be changed without altering its chemical composition.

Any such treatment on a steel alloy is employed according to a series of distinct procedures that are specific to the type of material being modified. The objective is to increase the hardness, elasticity and/or strength of the steel and, thus, to prolong its useful life as much as possible.

Heat treatment stages

Any heat treatment consists of a process that can be divided into three phases:

  • Heating the part up to the desired temperature.
  • Holding at the target temperature for several minutes in order for the structural change to take place.
  • Controlled cooling according to the type of treatment and the characteristics of the steel.

What types of heat treatment are there?

Not all metals need the same type of heat treatment. You have to employ the appropriate process depending on the objective you want to achieve. Below, we explain the four main types of heat treatment that are commonly applied to steel:

Quenching

This process serves to enhance the hardness and strength of the steel. To do this, it is heated to a temperature above the transformation point of the material (700°C), changing the steel into what is known as austenite.
It must then be cooled very suddenly and quickly, so the austenite acquires a rigid structure (martensite). Water, oils, gases or even salts can be used for cooling. The process can be carried out either in a staged, superficial or standard way, depending on the end result desired.

Normalization

As its name suggests, normalization is the heat treatment that is intended to return steels to their normal state. This process is usually carried out after a previous, flawed heat treatment. The objective is to remove any internal stresses that may remain in the steel.

Annealing

Annealing is the inverse process to tempering, since the aim in this case is to soften the material so that it can be machined more easily later on. To do this, it must be heated to a high temperature for a longer period of time. In this way, the distortion and residual stresses caused in the crystal structure during the cooling process are reduced.

Tempering

This is the heat treatment that usually follows quenching. Its purpose is to reinforce the hardness that is also the objective of quenching. During the quenching process, the steel becomes very fragile, and tempering can reduce this fragility without losing the desired hardness.
In this process, you heat the steel to below the critical point or recrystallization temperature (staying above 150°C), and then cool it in a controlled manner, usually by air.

Benefits of heat treatment of steel

Being able to transform the same material with different results allows you to take full advantage of the potential characteristics of a metal. Heat treatment provides a series of very important advantages for companies in this industry:

  • Increased efficiency and sustainability: Heat treatment allows us to reuse previously treated metals and give them a new life, rather than discarding them.
  • Cost savings: Sometimes we can save buying additional steel, and by transforming what we already have, get equally effective results.
  • Increased durability: Heat treatment serves to extend the useful life of steel.
  • Less wear: The application of these processes greatly reduces wear, and if it occurs, allows it to be corrected.
  • Safety: Steel used to manufacture any object must meet the requirements of the use it is going to be put to, and its conformity to these standards can be adjusted by heat treatment. This ensures that the metal has the hardness, strength and elasticity required.

ULMA Forge: more than 60 years handling steel

As we have seen, treating steel requires exhaustive and specific technical knowledge. At ULMA Forged, this knowledge has been our business for more than 60 years, 60 years of perfecting technique based on experience.

Forging is a fundamental process in Spanish industry and, as such, it is essential to attend carefully to every link in the chain. Among them are steel treatments, essential for manufacturing top-quality forged products. This is especially true when it comes to sectors such as aerospace, shipbuilding or natural gas, among others.

We can’t help you change the world, but we can help you forge a better future by doing what we do best.