When it comes to measuring the hardness of a material, there are multiple methods available. The Rockwell scale is one of the standard methods used to measure a material’s hardness. This hardness scale has been developed to analyze the properties of different minerals and metals. The scale has different numbers that represent hardness based on the indent’s depth caused by the test material’s indentation. This method is suitable for measuring materials with irregular surfaces. Let us look at how you can measure and read Rockwell’s hardness value in this article.
I. Why Use the Rockwell Hardness Scale?
The Rockwell hardness scale is an international standard used to inspect and measure metallic parts. Two main standards in the industry define the Rockwell hardness scale. These are:
- International Standards Organization (ISO 6508-1 Metallic Materials) – Rockwell Hardness Test Part 1
- American Standard Test Method (ASTM E 18) – Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials
The Rockwell hardness scale ensures that all products produced under this scale are internationally uniform regardless of where they are produced or manufactured. This is because the Rockwell hardness scale is recognized by everyone in the industry and accepted worldwide.
Related Article: ASTM Rockwell Hardness Standard Test Reference Guide
II. How Rockwell Hardness Gets Measured?
To calculate and read the Rockwell hardness value, you need to understand some basic measurement units in this case. In the Rockwell hardness testing, the indenter applies the first load to the test piece. The indent is then measured, and the value obtained is used for the base calculations. This first load is removed, and another heavier load is applied to the indenter on the test piece. The Rockwell hardness of the test piece is calculated by subtracting the second load from the first and using the Rockwell formula. The resulting value is then translated to the Rockwell C scale of hardness to determine the hardness of the material.
Related Article: How to Perform a Rockwell Hardness Test?
Related Article: How to Perform a Vickers Hardness Test?
III. How do you Read Rockwell Hardness Value?
The Rockwell hardness value is made up of three main parts. These are a numeric number representing hardness, two letters “HR”, abbreviations representing “Rockwell hardness”, and the Rockwell scale designation, which shows the load applied on the test sample and the type of indenter used in the testing process.
IV. Examples of How to Represent and Read Rockwell Hardness Value
Example 1: A regular Rockwell hardness method (HRC)
45 HRC
The number 45 represents the hardness value of the material.
HR is the abbreviation for Rockwell hardness.
C represents a load of 150 kgf and a diamond indenter of 120°
Example 2: Superficial Rockwell method
80 HR30TW
80 represents the hardness value of the material.
HR is the abbreviation for Rockwell hardness.
30 represents the main load of 30 kgf.
TW represents a 1/16-inch tungsten-carbide ball indenter.
V. What Does a High RC Rating Mean?
The higher the Rockwell number, the harder the material is. A high Rockwell number indicates high steel.
Hard materials on the Rockwell C scale are given values between the mid-50s and above. The best steel for a given application may not always have the highest rating on the RC scale. Despite having great quality, the steel might not perform as well as steel with a lower rating. Materials made from high steel are more expensive to work with but more durable because they need a much harder material to break them, such as materials made from diamond or ceramic.
VI. What Does a Low RC Rating Mean?
Low RC scores suggest that the steel composition is weaker. Since soft steels are pliable, they can bend and deflect more easily than hard, brittle steel. Low RC-rated products are suitable for industrial products because they can be shaped easily, although they can get deformed just as easily. They are cheaper, though, compared to the high RC materials.
VII. Is Higher HRC Better?
A higher RC rating does not necessarily mean you get better material for your application since other factors are involved when deciding which material is best suited for a particular application.
Materials with a higher RC are more durable than materials with a lower RC. But the materials may be expensive to replace or maintain because of the skills needed to work with higher RC. On the other hand, materials with a lower RC are cheaper and can be easily maintained because they are soft. No special skill is required in their maintenance.
Conclusion
Rockwell hardness is a very important factor in manufacturing products. You need hard steels to make your products last longer and soft materials for quick workability and flexibility. Different applications require different hardness. Understanding Rockwell hardness is a critical step in understanding the properties of different materials and how you can put them to good use for your applications.