Steel hardness: material resistance

Steel hardness is the resistance that the material offers to the penetration of a harder body, called an indenter.

During the test, a controlled force is applied to the surface of the material through a specific indenter.

👉 Depending on the method used, hardness is determined by measuring:

• the size of the indentation left on the material
• or the depth of penetration

The result obtained makes it possible to assess how resistant the material is to surface deformation.

In other words, hardness is a direct indicator of the steel’s ability to withstand localized stresses without deforming easily.

Hardness tests on materials are essential because they make it possible to obtain quick and reliable information on the mechanical characteristics of steel.

👉 They are widely used because:

• they require relatively short execution times
• they do not significantly damage the sample
• they allow materials, semi-finished products or finished components to be checked
• they provide useful indications on the material’s strength
• they make it possible to verify the effect of heat treatments

In may cases, hardness is also linked to the mechanical strength of the material.

✔ Correct hardness control therefore helps to understand whether the steel is suitable for the intended machining process or application.

The principle behind hardness tests is simple: the material is subjected to a controlled force through an indenter.

The indenter leaves an impression on the surface of the steel.

👉 Subsequently, the hardness value is calculated based on:

• type of indenter used
• applied load
• size or depth of the indentation
• chosen measurement scale

There are different test methods, each suited to specific inspection requirements.

Among the most widely used are:

• Brinell
• Vickers
• Rockwell

The Brinell hardness test is one of the most common for relatively soft materials or materials with structures that are not too fine.

It is often used for medium-low alloy steels, light alloys and materials where it is useful to obtain a wide and representative indentation.

👉 The method involves:

applying a steel or carbide ball to the surface of the material
using a predefined load
holding the load for a defined time
measuring the average diameter of the indentation left on the part

An example of Brinell indication may be:

320 HBW 10/3000

Where:

320 is the hardness value
HB indicates Brinell hardness
W indicates the carbide indenter
10 is the diameter of the indenter in millimeters
3000 is the applied load in kg

👉 The Brinell test is particularly useful when a larger surface area of the material needs to be assessed.

The Vickers hardness test uses a square-based pyramidal indenter.

It is a very versatile method, used both for traditional hardness tests and for more precise measurements on small areas.

👉 It is mainly used for:

• small-sized parts
• finished components
• materials subjected to surface treatments
• laboratory measurements
• microhardness checks
• inspections on specific areas of the material

The Vickers test requires accurate surface preparation and precise reading of the indentation, often through optical systems or a microscope.

✔ It is particularly useful when the behavior of a limited area of the material needs to be analyzed precisely.

The Rockwell hardness test differs from the Brinell and Vickers methods because it does not measure the size of the indentation, but the depth of penetration of the indenter.

👉 This makes the Rockwell method:

• fast
• practical
• suitable for repetitive checks
• easy to read directly from the instrument

The hardness value can be obtained directly, without the need for optical measurements of the indentation.

✔ For this reason, the Rockwell method is widely used in industrial inspections where speed and repeatability are required.

However, the accuracy of the test can be influenced by several factors, including surface quality, part thickness and correct sample preparation.

In the Bonomi Acciai laboratory, hardness tests are a fundamental tool for connecting technical data to the real behavior of the material.

In addition to the values reported in the certificate, the laboratory performs internal checks on the material using dedicated hardness measurement instruments.

Brinell and Rockwell tests are performed in the BA laboratory.

Brinell tests can be performed with different loads:

• HBW 10/3000 → 3000 kgf
• HBW 10/1000 → 1000 kgf
• HBW 10/500 → 500 kgf
• HBW 10/250 → 250 kgf
• HBW 10/100 → 100 kgf

The Rockwell tests performed include:

• HRC
• HRA
• HRN 15
• HRN 30
• HRN 45

Hardness tests at BA are performed both using a bench hardness tester and a versatile portable rebound hardness tester, capable of carrying out checks directly on large components and manufactured parts.

The use of the bench hardness tester makes it possible to perform precise tests compliant with the main reference standards, using different measurement scales according to the material and the characteristics of the part.

The portable rebound hardness tester, on the other hand, represents a practical and flexible solution for carrying out checks directly at the customer’s site or on components that, due to their size or geometry, cannot be checked using traditional laboratory instruments.

This possibility allows fast and non-destructive checks to be carried out directly in the field, reducing downtime, handling operations and the need to transport materials, while guaranteeing timely and effective technical support.

Hardness tests are performed at different stages of the process, depending on quality control requirements and the checks requested on the material.

At BA, hardness is checked on a sample basis on incoming materials, in order to verify conformity with the required specifications and the certificates supplied.

Tests are also carried out on parts subjected to heat treatment directly managed by BA, in order to verify the correct achievement of the expected mechanical characteristics.

In the event of non-conformities or issues detected during the customer’s use of the material, hardness control also represents a useful tool for evaluating any alterations in the material properties, for example due to overheating or abnormal operating conditions.

Thanks to the use of both laboratory and portable instruments, BA is able to carry out fast and effective checks also directly at the customer’s site, offering timely technical support in verification and analysis activities.

Thanks to the availability of both a bench hardness tester and a portable rebound hardness tester, BA is able to perform hardness tests in extremely versatile conditions and on a wide range of materials and components.

Checks can be carried out on:

• barsplates
• machined parts
• cut samples
• components subjected to heat treatment
• large manufactured parts
• already installed parts

This dual measurement possibility allows the inspection to be adapted to different application requirements, guaranteeing fast and effective checks both in the laboratory and directly at the customer’s site.

The flexibility of the instruments used therefore makes it possible to check hardness on all the main types of metallic materials handled by BA, even in the presence of complex geometries or components that are difficult to move.

Surface preparation plays a very important role in obtaining reliable results in hardness tests, since the surface finish significantly affects the accuracy of the reading.

When the part already has a mechanically machined surface, generally no further preparation operations are required.

In other cases, however, it is preferable to properly prepare the area intended for inspection through operations such as:

• cleaning
• flattening
• light surface grinding

For Brinell tests performed with the bench hardness tester, it is also possible to work on relatively rough surfaces, as this method is less sensitive to surface finish.

For other types of hardness tests, and in particular for measurements carried out with a portable rebound hardness tester, surface preparation becomes more important and may require more accurate preparation operations in order to guarantee reliable and repeatable results.

The results of hardness tests are compared with the technical references provided for the material or component being inspected.

In the case of checks on incoming materials, the values detected are verified against the certificates issued by the steel mill, in order to confirm the conformity of the declared mechanical characteristics.

For components subjected to heat treatment, on the other hand, the results are compared with the certificates supplied by the heat-treatment provider, verifying the correct achievement of the hardness values required by the treatment performed.

Depending on the applications and customer requirements, the checks may also be compared with:

• technical reference standards
• material technical data sheets
• specific requirements requested during supply

The hardness test is a fundamental tool for guaranteeing the quality, conformity and reliability of the materials and components supplied to customers.

Through this check, it is possible to quickly verify that the material has the mechanical characteristics required by the technical specifications, reference standards or heat treatments performed.

Hardness measurement also makes it possible to identify any anomalies or alterations in the material, supporting quality control activities both during acceptance and during machining or in the event of non-conformities.

Thanks to the availability of both laboratory and portable instruments, BA can carry out fast checks directly on components, including at the customer’s site, reducing intervention times and providing immediate technical support.

For the customer, this translates into greater confidence in the reliability of the material used, better traceability of checks and the certainty of being able to rely on a qualified technical partner focused on the quality of the product supplied.

In the path dedicated to steel quality, hardness represents one of the most concrete and immediate parameters.

After analyzing the chemical composition, hardness makes it possible to assess how the material responds to mechanical stresses.

👉 In the next articles, we will explore other fundamental aspects of the certificate and quality control, such as:

• impact strength
• grain size
• steel cleanliness
• microstructure
• non-destructive testing

Each parameter contributes to building a complete view of steel quality.

Steel hardness is not just a numerical value.

It is a fundamental indicator of the material’s resistance and its behavior during machining, treatment and final use.

👉 Hardness tests make it possible to verify whether the steel has the required characteristics and whether it is suitable for the intended application.

Understanding this parameter means reading an essential aspect of material quality: its ability to resist.