Which rockwell hardness scale

This force is held for a predetermined amount of time dwell time to allow for elastic recovery. This major load is then released, returning to the preliminary load. After holding the preliminary test force for a specified dwell time, the final depth of indentation is measured.

The Rockwell hardness value is derived from the difference in the baseline and final depth measurements. This distance is converted to a hardness number. The preliminary test force is removed and the indenter is removed from the test specimen. Total test forces range from 15kgf to kgf superficial and regular to to kgf macrohardness. There are so many types of steel, it can be difficult to determine what the best steel for kitchen knives is — unless you have a system of precise measurements.

Enter the Rockwell hardness scale. Think of it as a Scoville scale for steel. The Rockwell hardness scale important to your search for the perfect kitchen knives because harder steel holds its sharp cutting edge better than softer steel. But how hard is hard? The Rockwell hardness test was originally created to measure ball bearings. Seven years after Wilber Scoville decided to get serious about the precise measurement of spiciness, a metallurgist working at a New England ball bearing plant invented an accurate and repeatable way to measure hardness.

Stanley P. Rockwell created a way to measure the steel ball bearings his company created, but the test was easy to apply to any type of metal or non-metallic material. The scale that bears his name determines relative hardness of metal by measuring the depth of an indentation after a heavy object impacts a piece of metal.

Diamond is the hardest natural substance known to man. The most commonly used version of the Rockwell test uses a conical diamond to impact the metal. The amount of force and depth of the cone-shaped indentation is then measured.

The test is performed twice. Initially only a minor load of pressure is applied, and the measurement is taken. The second time — in the exact position — the pressure is increased to a major load of about pounds of pressure, and then the indentation is measured again. The difference between the depth of the first and second indentation determines the hardness. The test is performed at least twice on a piece of metal to produce an average. The Rockwell test is not the only way to measure the hardness of a material.

The scale is created by comparing resistance to indentation. The test is most commonly associated with hardened steels, but it can be performed on practically any material — from plastic to concrete.

There are 30 different Rockwell scales , and each uses a unique combination of test forces and types of indentation. What is a good rockwell hardness for a knife? The hardness of a knife is very important as far as its performance and durability. For instance, a harder steel with a RC of will hold an edge better than a softer steel. However, that same harder steel is less durable and more prone to chipping or even breaking.

Some kitchen knives with high hardness require extreme care so that you do not damage the thin edge. The softer steel is more durable, but won't maintain an edge for as long as the harder steel. Most axes and chisels use a softer steel that can withstand the impacts they encounter in their everyday use. Since pocket knives and hunting knives aren't generally used for chopping wood, they benefit from a harder steel that will take, and keep, a good sharp edge for slicing and cutting.

On the same note, a survival knife that you are going to put to extreme, rugged, brutal, near-abuse would benefit from a rockwell hardness of A knife that could chop trough bone, hard woods, dig and pry needs to be durable first and foremost. The knife with a lower hardness might dull more quickly but it is more likely to survive intact. Because hardness varies based upon intended use, there is no one "good" or "best" hardness for all knives.

Getting what you've paid for The Rockwell test helps knifemakers balance the three most important factors that can affect the quality of their finished product: hardness, flexibility, and toughness. Having these three factors in proper balance allows them to produce a knife that will take a sharp edge and then keep that edge under a range of conditions without damage to the knife.

Buy a high quality knife and you'll experience the lasting quality and pleasure of use that comes from a knife with that properly executed balance. No matter how it's written about knife steels, they all refer to the same scale c.

It can get a little confusing, but just know that the ratings themselves are the same - no matter how the knife maker abbreviates the scale! History of the Rockwell scale Stanley P.

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