Hardness and strength – How are they related?

What is this about?

Hardness and strength are key aspects when talking about tool quality. In previous blog posts we already discussed separately about material strength and hardness (see "Related stories" below). The logic next question is: are strength and hardness somehow related? This is the topic of this article.

Why is that interesting?

Why would it be interesting to obtain the hardness of a material when only the strength is known, or vice-versa calculate strength from known hardness?

The reason is that measuring hardness is easy and very fast compared to measuring strengh, which is complex and difficult. Measuring strength always results in the loss of the test sample because it is tested until failure. That is called "destructive testing". Measuring hardness takes less than one minute to perform and only leaves a tiny indent crater on the surface. Apart from this, the test sample remains undamaged and can be fully used after the test. It is therefore called "non-destructive testing".

How are hardness and strength related?

In fact hardness and strength are quite directly related. The harder a metal is, the higher is its strength. Obtaining precise information is unfortunately more difficult. Much information such as look-up tables, smartphone apps, etc. can be found, but all these data are only approximate! There is no generally applicable exact theory in material science, which allows to exactly determine hardness from strength and vice versa. A precise relation between hardness and strength can only be obtained from measurement data for each specific steel grade.

Sources of data

Some steel makers provide look-up tables and there are also several smartphone apps. Here are some links which we think are useful:

Specific steel data (exact)

Below are links to steel data sheets, which contain exact data determined by the manufacturers:

More related stories:

If you are interest to read more, please check out some of the following blog posts: