Some Popular Steel Grades for Induction Hardening

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.

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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 , AISI 440C, AISI , AISI , AISI H, 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.

See the benefits of induction hardening mechanical parts.

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.

Conclusion

The composition of alloying elements distinguishes the grades and steel hardenability. Different steel grades can be hardened using induction heating, including , , , , and . However, the excellent steel grade for any induction hardening project depends on the intended use and property requirements.

What is Induction Hardening?

Induction hardening is a method of quickly and selectively hardening the surface of a metal part. A copper coil carrying a significant level of alternating current is placed near (not touching) the part. Heat is generated at, and near the surface by eddy current and hysteresis losses. Quench, usually water-based with an addition such as a polymer, is directed at the part or it is submerged. This transforms the structure to martensite, which is much harder than the prior structure.

A popular, modern type of induction hardening equipment is called a scanner. The part is held between centers, rotated, and passed through a progressive coil which provides both heat and quench. The quench is directed below the coil, so any given area of the part is rapidly cooled immediately following heating. Power level, dwell time, scan (feed) rate and other process variables are precisely controlled by a computer.

Typical Induction Hardening Materials

Typical materials include:

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• ETD150
• Cast Irons

Benefits of Induction Hardening

Increased Wear Resistance

There is a direct correlation between hardness and wear resistance. The wear resistance of a part increases significantly with induction hardening, assuming the initial state of the material was either annealed, or treated to a softer condition.

Increased Strength & Fatigue Life due to the Soft Core & Residual Compressive Stress at the Surface

The compressive stress (usually considered a positive attribute) is a result of the hardened structure near the surface occupying slightly more volume than the core and prior structure.

Parts may be Tempered after Induction Hardening to Adjust Hardness Level, as desired

As with any process producing a martensitic structure, tempering will lower hardness while decreasing brittleness.

Deep Case with Tough Core

Typical case depth is .030&#; - .120&#; which is deeper on average than processes such as carburizing, carbonitriding, and various forms of nitriding performed at sub-critical temperatures. For certain projects such as axels, or parts which are still useful even after much material has worn away, case depth may be up to ½ inch or greater.

Selective Hardening Process with No Masking Required

Areas with post-welding or post-machining stay soft - very few other heat treat processes are able to achieve this.

Relatively Minimal Distortion

Example: a shaft 1&#; Ø x 40&#; long, which has two evenly spaced journals, each 2&#; long requiring support of a load and wear resistance. Induction hardening is performed on just these surfaces, a total of 4&#; length. With a conventional method (or if we induction hardened the entire length for that matter), there would be significantly more warpage.

Allows use of Low Cost Steels such as

The most popular steel utilized for parts to be induction hardened is . It is readily machinable, low cost, and due to a carbon content of 0.45% nominal, it may be induction hardened to 58 HRC +. It also has a relatively low risk of cracking during treatment. Other popular materials for this process are /, , , ETD150, and various cast irons.

Limitations of Induction Hardening

Requires an Induction Coil and Tooling which relates to the Part&#;s Geometry

Since the part-to-coil coupling distance is critical to heating efficiency, the coil&#;s size and contour must be carefully selected. While most treaters have an arsenal of basic coils to heat round shapes such as shafts, pins, rollers etc., some projects may require a custom coil, sometimes costing thousands of dollars. On medium to high volume projects, the benefit of reduced treatment cost per part may easily offset coil cost. In other cases, the engineering benefits of the process may outweigh cost concerns. Otherwise, for low volume projects the coil and tooling cost usually makes the process impractical if a new coil must be built. The part must also be supported in some manner during the treatment. Running between centers is a popular method for shaft type parts, but in many other cases custom tooling must be utilized.

Greater Likelihood of Cracking Compared to most Heat Treatment Processes

This is due to the rapid heating and quenching, also the tendency to create hot spots at features/edges such as: keyways, grooves, cross holes, threads. (Please talk to an AHT representative if you have concerns.) 

Distortion with Induction Hardening

Distortion levels do tend to be greater than processes such as ion or gas nitriding, due to the rapid heat/quench and resultant martensitic transformation. That being said, induction hardening may produce less distortion than conventional heat treat, particularly when it&#;s only applied to a selected area.

Material Limitations with Induction Hardening

Since the induction hardening process does not normally involve diffusion of carbon or other elements, the material must contain enough carbon along with other elements to provide hardenability supporting martensitic transformation to the level of hardness desired. This typically means carbon is in the 0.40%+ range, producing hardness of 56 &#; 65 HRC. Lower carbon materials such as may be used with a resultant reduction in achievable hardness (40-45 HRC in this case). Steels such as , , 12L14, are typically not used due to the limited increase in hardness achievable.

* Blog was updated in July to reflect our Cullman, Alabama location now having induction hardening. 

About the Author

Scot Clay is the Sales Team Manager at Advanced Heat Treat Corp., where he&#;s been an integral part of the Sales and Marketing Team for over 30 years. He&#;s managed numerous induction hardening projects, solving wear and performance issues for customers throughout the United States. Contact him for technical advice on your next project at 319-291- or for more information.

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