Cementation or Carburization Treatment of Metals

Metallic cementation or carburization of metals is a thermal process used to improve the surface characteristics of a metal. The process imparts an improved hardness, wear resistance and corrosion protection, without compromising base ductility. This hardening technique takes advantage of the transfer of carbon atoms onto the surface of metallic materials.

Among the different carburization methods, the most common is gaseous carburization heat treatment. During this process, the metal is exposed to a controlled environment, often an atmosphere containing carbonaceous gases, such as methane or carbon monoxide. High temperatures are used for this procedure, usually between 850°C and 1050°C.  The carbon atoms present in the gas are absorbed by the metal, diffusing into its crystalline structure creating an enriched outer layer known as the “carburized layer” or “cemented diffusion layer“.

To change the depth and hardness of the cemented layer, process parameters such as temperature, hold time and type of carbonaceous atmosphere can be varied. Once the desired results are achieved, the carburizing metal is slowly cooled to minimize internal stresses and improve the mechanical properties.

Metal carburizing is a highly specialized process that involves a number of factors and variables that directly affect the final properties of the treated material.

One of the most popular variants of Carburization treatment is ionic cementation. This method involves immersing the metal in a mixture of carbon-containing molten salts, exposing the metal to elevated temperatures, but lower temperatures than gas-cementing. This process can offer more precise control over the depth of the cemented layer, while also allowing for thinner and more uniform layers.

Other modern techniques, such as plasma cementation and laser cementation, have recently emerged as advanced alternatives to classic cementation treatments. The first technology harnesses plasma energy to introduce carbon atoms into the surface of the metal, while laser carburizing uses the concentrated heat of a laser beam to selectively treat specific areas of the metal.

Steel case-hardening

Metal case-hardening is widely used in various industrial sectors, especially for optimizing the performance of steels. One of the sectors in which it widely used is the tooling sector, in fact it allows significant increases in the durability and efficiency of tools such as dies, molds and cutting tools. Case-hardened steel is also widely used in industries such as mechanical engineering and automotive. For example, gears, bearings, camshafts, and other components that are subjected to mechanical stress and abrasion greatly benefit from carburizing to improve their durability and strength.

Steel case-hardening always aims to improve surface properties through the introduction of carbon into the surface of the metal, making it more resistant to wear, fatigue and corrosion without compromising its toughness.

During steel carburizing, the metal is exposed to high temperatures in a controlled environment containing carbon, so that the concentration of atoms of this element on the surface compared to that in the steel core is increased. The result is an increase in hardness and strength.

Carburizing and hardening

Quenching is a thermal process that involves heating metal to a critical temperature followed by rapid cooling, often through immersion in a liquid, such as oil or water, depending on the material and desired characteristics. The main goal of quenching is to increase the hardness of the metal by making it stronger.

When we talk about carburizing and quenching, we are referring to processes that aim to improve the hardness of metals, while the main difference between the two is the depth of the effected layer. Metal carburizing acts mainly on the surface of the metal, creating a hardened and resistant layer, while hardening heat treatment acts on the entire structure of the material, making the entire machined piece uniformly harder.

For this reason, the combination of carburizing and hardening is commonly used to obtain optimal performance. For example, a metal can be cemented to enrich the surface with carbon and then quenched to achieve uniform hardness throughout the structure. This combination makes it possible to obtain parts with wear-resistant surfaces and a strong and ductile core.

Finally, to complete the entire metal heat treating process, a further heat treatment called tempering (and possibly also a stress relieving treatment) is provided. It is performed after quenching, which makes the metal extremely hard but also brittle, tempering is essential to improve toughness and resilience without excessively compromising the hardness obtained in quenching.

cementazione e tempra

ATP products for protection during metal carburizing

ATP‘s Metseal coatings are an advanced group of efficient and cost-effective metal surface coatings, designed to create a barrier and protect the part of the metal that you do not want to alter during carburizing heat treatments of ferrous metals. Their purpose is to regulate the diffusion of gases, both inside and outside metals, offering excellent protection and ensuring an excellent result. Copper coatings are usually used to preserve the metal parts that do not need to be treated, but they are much more expensive than ATP coatings.

If you need more information about our protective coatings for metal carburizing, do not hesitate to contact us! We are always available to solve your doubts or to provide a quote.