Why is hardness testing important

This includes fasteners used in nuclear settings, to ensure containment of radioactive substances, which are obviously highly safety critical; or bolting used in petrochemical applications ensuring the safe delivery of millions of barrels of oil — failure of which could have severe environmental consequences.

Whichever product we are talking about, it must be compliant and suitable to go to market. Hardness verification plays an important part of that process. Virtually every engineering component that is manufactured requires a hardness test of some form, as well as it being required for each stage of the production process — from the raw material received from suppliers; after industrial treatments as part of the engineering process; as well as at final product testing before shipping to the customer.

If a material or product has undergone any form of heat treatment as part of its processing, then it again needs to be tested and verified. If engineers have carried out any surface treatment or coating processes, such as nitriding — which involves diffusing nitrogen into the surface of a metal to create a case hardened surface to increase its hardness and corrosion resistance — hardness testing is a primary way to assess conformance.

If you perform any action that modifies the properties of the material or surface of products, it is imperative to verify that the right treatment has been carried out. Hardness testing plays a crucial role in this process. It is important to understand the characteristics of a material in terms of its strength, resistance to wear, and toughness, and this can be achieved via various hardness tests.

Hardness testing is a measurement that establishes how hard a material is, in many instances, in a non-destructive way. This method of testing provides data to show how a material resists indentation through a series of tests in controlled conditions with a continuous load being applied by a pointed or rounded indenter.

There are varied options of hardness testing and the key tests conducted by mechanical and metallurgical engineers include:. The key decision factors are what is the type of material?

What are the required standards to be met? And how accurate do the results need to be? Brinell works incredibly well when testing forgings, castings and larger coarse material samples, as well as bulk metal. Rotech is able to use a greater diameter indenter, which helps to eliminate any variability due to localised, structural differences and surface inconsistencies. These inconsistencies and roughness would provide varied readings according to where the test is carried out on the surface material.

Due to the wider indentation over the surface area, Brinell hardness testing gives a more representative measurement. Non-ferrous metals, pre-heat treated steel, forgings, and castings, may benefit from Brinell hardness tests. Brinell hardness testing needs less preparation than more focussed test methods.

It is a relatively straightforward procedure and is mainly used on rough structured materials, such as forged metals or cast irons. Rotech uses a 5mm or 10mm round carbide ball, which makes an indentation and has an especially high load typically kg and 3,kg. We then measure the indentation, which is analysed using a microscope to find an average result via the Brinell hardness number scale. The Rockwell hardness tester has a depth indicating device that measures the vertical movement of the indenter into the test specimen.

Under an initial minor load of only 3kg-f, the indenter is forced into the test material and left there, while the indicating device marks a zero reference point.

A major load of 15, 30 or 45kgf is then added, forcing the penetration to go even deeper and the indicating device notes that position too. The superficial Rockwell number is therefore the difference in depth from zero reference point after the application of the major load. The main idea and process in both Rockwell and Superficial Rockwell methods are the same.

They both use a diamond or metal ball indenter to measure hardness. However, three slight characteristics differentiate the two methods;. Standard Rockwell test uses an initial minor load of 10kgf and a major load of 60, or kgf while superficial Rockwell method uses only 3kgf as its preliminary minor load and 15, 30 or 45 kgf as the major force.

The superficial test method is primarily used to evaluate small or thin components or materials whose hardness value is a little outside the standard Rockwell scale.

For example, it can test coatings, carburized surfaces and thin strips. Superficial hardness testing gives the finest and most accurate results of the thinnest or tiniest materials. This ensures their quality before they are incorporated in a more significant production process. Without hardness testing, it would be challenging to choose materials that go well together in a manufacturing process. More importantly, products would be wearing out in no time because the wrong materials were used.

Superficial Rockwell hardness test is used extensively to measure the hardness of soft and thin materials that need specific detailing of the specimen. Today, there are motorized versions of Rockwell hardness testers, including one that can conduct both standard and superficial tests. Sign in. Forgot your password?

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Direct marketing Case Studies. An enterprising approach to a marketing re launch Case Studies. How can you select the best hardness testing method? What is the best application for hardness testing? And how can you draw conclusions of hardness tests? The following pages answer these questions — and more. To see our range of hardness testing machines and accessories, check out our hardness testing equipment page. See our Hardness Testing Application Note.

See our Hardness Testing Conversion Poster. Rockwell is a fast hardness test method developed for production control, with a direct readout, mainly used for metallic materials. The Rockwell hardness HR is calculated by measuring the depth of an indent after an indenter has been forced into the specimen material at a given load.

Vickers is a hardness test for all solid materials, including metallic materials. The Vickers Hardness HV is calculated by measuring the diagonal lengths of an indent in the sample material left by introducing a diamond pyramid indenter with a given load.

The diagonals of the indent are measured optically in order to determine the hardness, using a table or formula. Used for hardness testing of all solid materials, including metallic materials Suitable for a wide range of applications Includes a sub-group of hardness testing of welds. Knoop HK is an alternative to the Vickers test in the micro hardness testing range. It is mainly used to overcome cracking in brittle materials, as well as to facilitate the hardness testing of thin layers.

The indenter is an asymmetrical pyramidal diamond, and the indent is measured by optically measuring the long diagonal. Used for hard and brittle materials, such as ceramics Suitable for small elongated areas, such as coatings. The Brinell hardness test is used for hardness testing larger samples in materials with a coarse or inhomogeneous grain structure.

The Brinell hardness test HBW indentation leaves a relatively large impression, using a tungsten carbide ball. The size of the indent is read optically. Used for materials with a coarse or inhomogeneous grain structure Used for larger samples Suitable for forgings and castings where the structural elements are large.

During hardness testing, the indentation will deform the surrounding material and alter its properties. In order to avoid misinterpretations of the perceived hardness, the standards prescribe a certain distance between multiple indentations. Examples of indent spacing in the Vickers hardness test for metallic materials For steel, copper, and copper alloys: Spacing between indents must be at least three diagonal widths For lead, zinc, aluminum, and tin: Spacing between indents must be at least six diagonal widths.

It can be difficult to obtain plane-parallel surfaces during preparation for the hardness test. Also, the indenter should be perpendicular to the test surface. For the Vickers hardness test, the measured diagonals should not deviate more than 5. For the Knoop hardness test, the two halves of the long diagonals must not differ by more than Hardness testing is key in most quality control procedures. Check out our range of hardness testing equipment to ensure your equipment is up to the task.

If you would like to know more about the hardness testing methods for metallic and other materials, including a full definition of hardness testing, the different applications of hardness tests and how to prepare for hardness tests, download our resources. You are also welcome to ask us, in general, about how you can optimize your operation.

We are always happy to help with any enquiry, big or small. If you have a question, drop us a line and we will get back to you as soon as possible. What is the definition of hardness testing? Therefore, when drawing conclusions of a hardness test, you should always evaluate the quantitative value in relation to: The given load on the indenter A specific loading time profile and a specific load duration A specific indenter geometry.

How do hardness tests work? A hardness test is typically performed by pressing a specifically dimensioned and loaded object indenter into the surface of the material you are testing. The hardness is determined by measuring the depth of indenter penetration or by measuring the size of the impression left by an indenter.

Hardness tests that measure the depth of indenter penetration include: Rockwell, Instrumented Indentation Testing, and Ball Indentation Hardness Hardness tests that measure the size of the impression left by the indenter include: Vickers, Knoop, and Brinell. In all hardness tests, the material under the indent should be representative of the whole microstructure unless you attempting to ascertain the different constituents in the microstructure.

Therefore, if a microstructure is very coarse and heterogeneous, you need a larger impression than for a homogeneous material. There are four main hardness tests, each with their own set of benefits and requirements.