Knife Making

From KnifeArt: The Rockwell Hardness Scale explained

understanding-rockwell-hardness-in-knives-7

KnifeArt has just published a good primer on the Rockwell Hardness Scale.

KnifeArt.com is an online retailer of cutsom and high-end production knives. Their selection is truly drool-worthy and worth a perusal if you are timewasting.

They also publish a newsletter with original content. Their latest is a great overview of the Rockwell Hardness scale, and what the technical details mean to the end user.

From Understanding Rockwell hardness in Knives:

History of the Rockwell scale

Stanley P. Rockwell was a metallurgist at a ball bearing plant in New England in 1919. He developed his hardness scale in order to measure the hardness of the bearing races in a way that was quick, accurate, and repeatable.

Manufacturers of everything from watch springs to train wheels had long needed such a test and were quick to apply Rockwell’s scale to all kinds of steel, as well as other metal, parts. Eventually the test was adapted to test non-metallic materials – even plastics.

I am not going to block quote the entire thing, you should check it out for yourself. It is nothing earthshattering, and much of it will be review for many of you. That said, there is plenty to be gleaned from this piece, even for the novice metallurgist.

For instance, while I was comfortable with my better than average understanding of the scale, I never actually knew how the test was performed:

How is Rockwell hardness measured?

The Rockwell scale measures the relative hardness of a metal. It’s based on how deep the resulting indentation is when a heavy object impacts it. So, how do they go about testing metal?

First, the metal needs to be heat-treated and perfectly flat. Otherwise, the test results won’t be accurate.

One method is by using a diamond-tipped cone to forcibly impact the metal. Testers then measure how deep the cone penetrated from a given amount of force. Finally, that measurement is converted into a scale that shows the various metals that were tested and how they all relate to each other.

One small drawback for testing a knife blade is that it leaves a small pinpoint indentation on the blade surface, which some might think is a flaw or defect. The rockwell testing mark can be concealed if the test is done in a area that is hidden from view by the handle.

Even if you know most of what is contained in the article, it still provides a comprehensive overview for reference.

Discussion

Leave a Reply

Your email address will not be published. Required fields are marked *