Steel hardening is essential for various applications to achieve the desired physical and mechanical properties. Several methods for steel hardening are popular in the manufacturing industry, and induction hardening is one of them. In order to meet the properties of steel workpieces, different steel grades are often selected for induction hardening in industry.
However, not all steel grades are suitable for induction hardening. In this article, we will discuss some popular steel grades that are commonly used in induction hardening projects. Let’s get to it!
What are the steel alloys series used in induction hardening?
Steel alloys are commonly divided into different series based on their composition and properties. The grading system used to classify steel alloys typically involves a four-digit number, with the first digit representing the primary alloying element in the steel. Here is a brief overview of some standard steel alloy series and their corresponding first digit:
- 1xxx: Steels with primary carbon (e.g., 1018)
- 2xxx: Nickel steels (e.g., 2330)
- 3xxx: Nickel-chromium steels (e.g., 3140)
- 4xxx: Molybdenum steels (e.g., 4140)
- 5xxx: Chromium steels (e.g., 5120)
- 6xxx: Chromium-vanadium steels (e.g., 6150)
- 7xxx: Tungsten steels (e.g., 7118)
- 8xxx: Nickel-chromium-molybdenum steels (e.g., 8620)
- 9xxx: Silicon-manganese steels (e.g., 9260).
However, the steel series are unsuitable for induction hardening because it has a threshold of carbon content (0.35%) to harden. The following are the standard steel alloy series that can be hardened through induction hardening.
|41xx series||This series includes 4140, 4142, and 4145, often used in the automotive and aerospace industries.|
|86xx series||These steels are known for their high hardenability and toughness and include 8620, 8630, and 8640. These are popular for manufacturing gears, shafts, and other high-stress components.|
|51xx and 52xx series||These steels contain chromium and carbon and have moderate to high hardenability.|
|13xx and 15xx series||These steels contain varying amounts of carbon and manganese and are often used in manufacturing components that require high strength and durability|
|81xx series||These steels contain nickel, chromium, and molybdenum, known for their high hardenability and toughness.|
Bearing steel for induction hardening
As the name suggests, bearing steel is a type of steel alloy commonly used to manufacture bearings and other high-wear components. This type of steel typically contains high levels of carbon, chromium, and other alloying elements to improve its strength, durability, and wear resistance.
Induction hardening is a popular method for hardening bearing steel. It provides a high level of control over the hardness and depth of the hardened layer. The resulting hardened layer of bearing steel could be several millimeters thick and significantly increase the wear resistance and fatigue strength.
Some examples of steel grades used as bearing steel in induction hardening include AISI 52100, AISI 440C, AISI 4140, AISI 4340, AISI 52100H, AISI 416 stainless steel, and AISI M50 high-speed steel.
Low-alloy boron steel for induction hardening
Low-alloy boron steel contains a small amount (0.001 to 0.003%) of boron as an alloying element. The boron content might seem small, but it is enough to alter the properties of steel.
The boron improves steel’s hardenability, which is steel’s ability to be hardened through heat treatment. Therefore, adding boron to low-alloy steel allows it to be hardened more deeply than it would otherwise.
Low-alloy boron steel is an excellent choice for induction hardening. The added boron increases the hardenability and allows it to be hardened to a greater depth than other types of steel. As a result, it can be used in applications where high wear resistance is required, such as gears, axles, and other high-stress components.
How to choose the best steel grade for induction hardening?
It is hard to specify a perfect steel grade for induction hardening. The suitable steel grade for any induction hardening project depends on the required application. Therefore, choosing the best steel grade for induction hardening involves considering many factors.
Here are some of the critical factors to consider while choosing a steel grade for your induction hardening project;
- Carbon content: It is one of the essential factors to consider when selecting a steel grade for induction hardening. Higher carbon content leads to greater hardness after hardening but can also increase the risk of cracking or distortion. Generally, a carbon content between 0.4% and 0.6% is optimal for induction hardening.
- Alloy composition: Alloying elements impact the hardenability of the steel. For example, manganese helps to increase the depth of hardening, while chromium can improve corrosion, and boron can improve hardenability. So, know the composition of steel grade and analyze whether that fits your requirements or not.
- Microstructure: The microstructure of the steel plays a significant role in its suitability for induction hardening. For example, steels with a fine, uniform grain structure are often easier to harden without cracking or distortion.
- Existing properties: It’s also important to consider the existing properties of steel grade. If the properties suggest the possibility of distortion or cracking during hardening, that should be excluded from the selection list.
- Application requirements: Finally, it’s essential to consider the application’s specific needs when selecting a steel grade for induction hardening. Factors such as the required hardness, wear resistance, and dimensional tolerances should all be considered.
How can you harden the steel that is not suitable for induction hardening?
Not all steel grades are suitable for induction hardening. Several steel grades are not eligible for induction hardening. The reasons could be poor hardenability, high risk of cracking or distortion, and poor response to induction heating.
Generally, the carbon content on the steel decides whether the grade is suitable for induction hardening or not. For example, steel grades with less than 0.3% carbon can not be processed with induction hardening.
There are other methods if any steel grade is unsuitable for induction hardening. You can choose depending on the specific characteristics of the steel and the desired results.
- Carburizing: It involves heating the steel in a carbon-rich environment, such as a gas or liquid, to introduce carbon into the surface layer of the steel. The carbon reacts with the iron to form a more rigid surface layer, while the core of the steel remains relatively soft.
- Flame hardening: This hardening process is carried out by heating the steel using a flame or torch and then cooling it with a jet of water or air. It is ideal for the localized hardening of specific areas of a component.
- Quenching and tempering: The process involves heating the steel to a high temperature and cooling it in a quenching medium, such as oil or water. The steel is then tempered by reheating at a lower temperature and holding it there for a specific time. As a result, steel loses its brittleness and gains toughness.
The composition of alloying elements distinguishes the grades and steel hardenability. Different steel grades can be hardened using induction heating, including 1045, 1050, 4140, 4150, and 5150. However, the excellent steel grade for any induction hardening project depends on the intended use and property requirements.