Cementation of steel itself is a process based on chemical-thermal treatment. Its essence is the implementation of diffusion saturation of the surface of the specified material with a sufficient amount of carbon when heated in a certain environment.
Cementing steel. The purpose of this action
The main objective of this process is to enrich the upper layer of machine parts and elements with the necessary amount of carbon, the percentage of which in this case can be 0.8-1.1%. As a result of this operation, after hardening, a high level of hardness of the material is obtained, while its plastic core is retained. These are important properties of this process.
Varieties
According to the degree of core formation strength, it is customary to distinguish three main groups of the processed material:
- With an unstressed core. This group includes such grades of cemented carbon steels as 10, 15, 20. They are used in parts with small dimensions and irresponsible functions. In this case, under the cemented layer during the implementation of quenching, austenite is converted into a ferrite-pearlite mixture.
- With a weakly hardened core. The composition of this group includes low- chromium chromium steels of such grades as 15X, 20X. Here, additional alloying with small additions of vanadium provides finer grains, which leads to improved ductility and viscosity of the material.
- With a highly hardened core. The steels of this group are used in the manufacture of parts that have a large cross section or complex configuration, and also experience the influence of significant shock loads or are exposed to considerable variable stresses. They carry out the introduction of Nickel (12X2H4A, 12XHZA, 20XH). Due to the scarcity of this material, it is sometimes replaced by manganese, while a small amount of vanadium or titanium is used to crush the grain.
Steel cementation is mainly used to form a high percentage of the hardness of the surface of the part, as well as to achieve high wear resistance, which is created through the use of heat treatment after the specified process.
What parts are subjected to this operation
Steel cementing is used for the following products:
- gears ;
- "fingers";
- shafts;
- axes;
- leverage;
- "worms";
- parts of bearings (large rings and rollers), etc.
Cementing methods
If there are several types of this material, then each of them will use its own methodology for this process. As a rule, cemented steel can be created in various conditions and environments, as well as at a mandatory temperature of 850 to 950 degrees Celsius. Therefore, several methods of this action are shared:
1. The carburizing process taking place in a solid carburetor. In this case, it is possible to use organic substances (animal bones, wood, etc.) and inorganic (coke) in combination with various activators. Enrichment with carbon will occur during the chemical reaction of its oxidation. The use of activators in this case contributes to a better and faster course. This method is especially suitable for achieving large depths of carburization. It is effective in the piece production of steel products. However, this process is very laborious, it entails a large expenditure of effort, time and energy.
2. The carburizing process that occurs under the influence of gases. In this method, it is customary to use enriched gases (natural, main, etc.) or the inert category (nitrogen). It all depends on the individual approach. In addition, gas-based cemented steel is created with a small percentage of aliphatic saturated hydrocarbons, propane or alkanes. Most often, this method is used in large-scale production, but is very costly in terms of cash. A similar method is used in thermal production. At the same time, mixtures of high molecular weight organic compounds (for example, turpentine, ethyl alcohol, etc.) are introduced into a hot rotor furnace, which, in turn, have the ability to decompose under the influence of catalysts (nickel).
3. The process of liquid cementation. It is used in cyanide and cyanide-free baths. Each of these environments is characterized by its features, advantages and disadvantages. For example, cyanide baths are not classified as harmless. They are usually classified as dangerous carriers not only for the environment, but also for humans. Therefore, when working with such material, it is necessary to try to comply with all prescribed safety measures in order to avoid adverse effects. But the method based on a cyanide-free bath is not recommended due to the fact that it leads to irreversible environmental pollution and causes great damage to it. These methods, if applied in practice, are only for obtaining small depths of carburization.
Heat treatment of cemented products
This process is also a rather important stage in the processing of parts. Indeed, even after cementation, the product does not have a high percentage of wear resistance and reliability. Therefore, the final step in this case is the work of hardening and tempering. The hardening process is characterized by a number of features and properties. The whole cementation process takes place under the influence of grain growth, and its return over the cross section is uneven and is consumed unevenly. Therefore, several stages of quenching are distinguished in the work, each of which occurs under certain temperature conditions.
Output
After reviewing the above, we can say that the organization of this process in the manufacture of steel products is very important. This action will significantly strengthen the surface layer of the part. With certain skills in this area and the availability of necessary materials and equipment, steel cementing can be carried out at home.