For Hard materials with hardness greater than 30 HRC or 300 Vickers or 286 HB it is necessary to pre-broach the slot for the Clins and the broaching tool is recommended.

It is also important to understand that there are so many different hardness test methods in common use that it is easy to get confused. 

Example:
-    AL 7075 has 87HRB what corresponds to 172 hardness Vickers, so no broaching tool is required.
-    An extremely hard steel might have a hardness of 64 HRC and the broaching tool is recommended, while a fairly soft steel might have a hardness of 70 HRB and not broaching tool required.

It should be also noted that Hardness is very important for producing rough metal castings, heat treatment and machining process. Rockwell Hardness (HRC and HRB) and Brinell Hardness (HB or BHN) are most commonly used for steel and iron castings.

How can you convert hardness units?

Formula 1 - Convert HRC into HB

Formula 2 - Convert HRB into HB

With the help of the comparisons between hardness :

Table 1 - HRC to HB, HV, Rm

What tests can I use for hardness?

The Rockwell hardness test is the most used hardness test method and is generally easier to perform than other types of hardness testing methods.
The Rockwell test method is used on all metals, except in conditions where the test metal structure or surface conditions would introduce too many variations; where the indentations would be too large for the application; or where the sample size or sample shape prohibits its use. 

The Brinell hardness test method as used to determine Brinell hardness is defined in ASTM E10. Most commonly it is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method