Rockwell Scale for Steel Hardness

 
When determining the "hardness" of any material, it's helpful to have an objective scale to serve as a basis of comparison. For metals, like the steel used in knife and tool making, the Rockwell scale is are typically used. However, though it is a scale used to describe an object's hardness, it really only accounts for its indentation resistance. Even though indentation resistance may not seem like a crucial deciding factor when judging how well two knives compare to each other, the Rockwell test actually serves as a pretty good indicator of how they will wear with use.

To determine where a metal object's component material falls on the Rockwell scale, a sample of the material has to be placed in a Rockwell type hardness tester. A minor load is applied to the object with an indenter, followed by a major load. The tester determines the material's hardness based on the extent of indentation.

Since every material responds differently to the Rockwell test, different indenters (usually either a Brale indenter or a tiny steel sphere) and loads are used. Each of these corresponds to a different rating on a particular scale. A material tested with a steel sphere at 100 kilograms-force (kgf) would be given a rating along with the abbreviation "HRB." This abbreviation tells the reader exactly how the material was tested, and how it did.

When it comes to tactical and outdoor equipment, especially edged steel items like axes, tomahawks, and knives, most materials will probably be given a rating with the abbreviation "HRC." This means that they were tested with a diamond cone at 150 kgf. The further the cone is able to be pressed into the steel, the softer it is. Steel with a higher rating generally holds a sharper edge, but it also has limited flexibility and can be brittle. Steel with a lower rating indents more easily and requires frequent sharpening, but it is more likely to bend than to shatter.

The HRC rating is useful, but not the only predictor of how well a tool will perform. As a means of comparison, look at 420HC stainless steel versus 1095 high-carbon. 420HC stainless steel is an inexpensive, easy to sharpen high-carbon steel with a low wear resistance commonly used for flatware and lower-end knives, and has a rating of 52-58 HRC. 1095 is a high-carbon steel that rates between 45-66 HRC, but even 1095 that rates between 52-58 HRC can have a higher wear resistance than comparably rated 420 steel due to differences in the metal's composition and how it was worked. Factors like carbide content alter steel in ways that the Rockwell test does not account for, further affecting its hardness.

So, what does the HRC mean for buyers of tactical and outdoor equipment? It gives a good overall look at how the metal can be expected to behave in terms of wear and impact resistance. Depending on how the item in question is going to be used, higher numbers aren't always better.

Tactical Tomahawks and Hand Axes by Rockwell Hardness