Case Hardening: Benefits, Process, Types & Applications
The metals used for manufacturing components are hardened through various methods. The need for hardening these metals is a requirement of the applications so that the metal parts remain durable and strength-oriented. If you are looking to learn about case hardening, read the guide below.
Overviews of Case Hardening
What is Case Hardening？
Case hardening is a heat treatment method in which the metal object is subjected to hardness on the outer core, whereas the inner core is left soft. It creates a layer of hardness on the surface and makes it resistant to fatigue and wear.
The materials commonly adopted for the case hardening are low-carbon steel or iron. The material used determines the quality required by the final product. There are multiple methods that can be used when it comes to case hardening, and some of these are nitriding, carbonitriding, carburizing, and cyaniding.
Purpose of Case Hardening
Case hardening is a method that processes the material and makes the outer surface of that material hard, while the inner core remains soft. It creates a thin layer of coat on the component and makes it strength-oriented.
Case hardening enhances the fatigue strength of the metal and makes it tough and wear-resistant. The case hardening also makes the component efficient and weldable.
Advantages of Case Hardening
The process of case hardening has some benefits, which are as follows:
- The resistance of the parts increases by adding a layer of hard material, which makes them durable.
- A hard top layer on the component makes it machinable for applications consisting of using heavy-duty parts.
- Case hardening makes the components resistant to fracture and cracking and makes them weldable.
- A prescribed coat is applied on the surface and enhances the resistance against corrosion.
- The appearance of the steel is enhanced by case hardening, which gives it a glossy look.
Disadvantages of Case Hardening
Case hardening, which has advantages, also has disadvantages. Some of the downsides of this process are as follows:
- The process is expensive and requires expertise and special tools.
- The variation of the hardness is featured in the process, which impacts the strength of the metal. The metal may get distorted during the process.
- The margin for cracking and chipping also increases, which impacts the life of the metal.
- The susceptibility of the metal to corrosion increases when the process is done incorrectly.
Process of Case Hardening
The process of case hardening can be done in four steps, and these are as follows:
Activation
The passive oxide layer is eliminated, which prevents the carbon and nitrogen diffusion on the surface of the сталь, and it is activated.
Покрытие
The active surface is then subjected to a layer of carbon or nitrogen, which improves the diffusion.
Diffusion
The component of steel is heated at a temperature higher than 900 degrees Celsius for many hours, and the environment is rich in nitrogen and carbon. A layer of hardened steel is then retained to make the carbon atoms and nitrogen appear on the surface.
Hardening
The part that is case-hardened is subjected to tempering and quenching in order to improve the mechanical characteristics of the component.
Types of Case Hardening Methods
When it comes to case hardening steel, there are various methods that can be opted for, and these are discussed below.
Heating and Quenching
In order to attain certain qualities of material, like hardness, the process of heating and quenching is used. It is a heat treatment method in which the metal is first heated at a high temperature and then cooled in liquid. The metals, as a result of this heating and cooling, harden, and their structural features change.
Carburizing
Low-carbon steel is mostly metal, which is subject to carburizing. The process involves heating metal in an environment with carbon, which helps to create a layer on the surface of the metal. There are different methods of carburization, and they add corrosion resistance, strength, and wear resistance.
Nitriding
Nitriding is a process commonly opted for in low-alloy steel grades. These metals are heated in an environment that has nitrogen; sometimes, nitrogen is infused through electric discharge. There are different processes involved in nitriding, and it enhances friction, hardness, and strength.
Cyaniding
The cyaniding process involves heating iron alloy in cyanide salt, and the surface of the alloy absorbs nitrogen and carbon. The process of cyaniding is then followed by tempering and quenching so that the required toughness is attained.
Карбонитрирование
Carbonitriding is a process in which the metal is heated in the presence of nitrogen and carbon, and these two elements are infused into the surface of the metal. It leads to case hardening. The process of carbonitriding leads to making the component equipped with wear resistance and hardness.
Ferritic Nitrocarburizing
The ferritic nitrocarburizing hardness of different types of iron, alloy steels, and their metals. The components are first cleaned, and the process is carried out in a ferrite phase. It has a temperature of around 570 degrees centigrade, and the layer of carbon and nitrogen is diffused on the surface.
What Types of Metals Can Be Case Hardened?
There are various types of metals that can be case-hardened, and some of these are as follows:
Low Carbon Steel
Low-carbon steel is infused with carbon at a high temperature, and the amount of carbon in it ranges between 0.1 to 0.25%. When the carbon is diffused on the surface of the steel, the carbon content increases and making it harder. The inner core of the low-carbon steel is ductile, and the outer one is hard, offering resistance against wear and corrosion.
Нержавеющая сталь
Stainless steel is hardened by injecting nitrogen and carbon into it at a high temperature. The surface of the stainless steel hardens this way and keeps the corrosion resistance high.
Чугун
Чугун is also hardened using the process of case hardening, in which nitrogen and carbon are injected at a high temperature so that the surface gets hard. The process of case hardening also enhances the wear resistance of the metal.
High Carbon Steel
When case hardening high-carbon steel, there are some precautionary measures that are crucial. The inner core needs to be pre-protected, and these alloys must be heated at high temperatures. After heating, too much carbon should be introduced, which makes the inner layer ductile and the outer one hard.
Инструментальная сталь
Tool steel is hardened by infusing the elements and then quenching them. The carbon used in the process of case hardening impacts the hardness, and then careful quenching is also opted for.
Typical Applications of Case Hardening
The applications that consider case hardening are the following:
- Camshafts
- Machine tools
- Режущие инструменты
- Aerospace parts
- Forging press
- Стержни
- Metal rolling equipment
- Automobile parts
Заключение
Case hardening enhances the mechanical properties of metals in different ways and makes them suitable for different applications. If you are looking to have case hardening for your components, we at DEK can offer this service to you. We offer different methods of case hardening and choose them according to the nature of your material, followed by application requirements.
Вопросы и ответы
What is the case hardening temperature?
The case hardening temperature varies between 871 to 954 degrees Celsius.
How is case hardening in drying?
Case hardening in drying takes place when the outer surface layer of the metal dries quicker than the inner one.
How do you remove the oxide coating from hardened parts?
Blasting is a common process that helps to remove the layer of oxide from the hardened parts.
How is the hardness measured after case hardening?
The hardness is measured through different methods like Knoop, Vickers, Rockwell, and Brinell testing. The method section depends on factors like required accuracy, type of material, and the depth of hardening.
