Using the Rockwell Hardness Test for Metal Applications

A metal’s hardness indicates its resistance to permanent shape changes when a compressive force is applied. Naturally, it is an important characteristic, and measuring hardness enables a manufacturer to choose an appropriate material for an application.

There are various methods (such as Rockwell, Brinell, and Vickers) for measuring metal hardness. Of these, the simplest and most cost effective is the Rockwell hardness test, which involves applying a specific load on the material using an indenter and measuring how far the indenter penetrates.

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Why do manufacturers run hardness tests?

Manufacturers leverage metal hardness tests to determine the material’s tensile strength, elasticity, and plasticity.

These factors indicate its resistance or susceptibility to mechanical wear and tear for different applications.

Metals must often withstand pressure or extreme temperature during its application use, and hardness testing is an ideal way to determine whether the component can perform.

Because of this, hardness testing is often critical during quality control. Knowing a material’s hardness can also help judge whether additional strengthening measures such as heat treatment are required.

Being the most cost-effective method, the Rockwell Hardness test is widely employed for measuring indentation hardness.

How it works

The Rockwell Hardness test uses a conical diamond or a hard steel ball as an indenter. Initially, a minor load is applied on the metal to be tested. This force is to allow the indenter to penetrate the material surface, thus eliminating any errors causes by surface roughness.

An additional major force is then applied for a predetermined period and then reduced to minor load state. The difference in indenter position before and after the application of the major load is measured. This is the permanent deformation caused by the major load.

The Rockwell hardness scale, which combines multiple test loads and indenter types, allow the user to judge the hardness of the material using the permanent deformation readings.

Use cases

Manufacturers can also use hardness testing to eliminate secondary processes.

One example involved ESI’s client, who was encountering a problem with their metal stamped part. Given the soft steel being used, the part needed to be heat treated and plated. Plating the material, however, caused the parts to become entangled during packing and shipping.

ESI employed the Rockwell method to identify a new stainless steel of appropriate hardness where the entire tempering and plating process could be eliminated.

This substitution allowed the client to eliminate the trouble associated with shipping, and simultaneously allowed the manufacturing process to be shortened and streamlined.

ESI provides a conversion table for anyone using the Rockwell, Brinell or Vickers methods for assessing material hardness. This table can save an engineer’s time, and help assess material qualities such as hardness and approximate tensile strength of the material being tested.

Get your free copy of the hardness conversion table by clicking here or on the link below.

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