Hardness is a critical property of materials, particularly in industrial and engineering applications. It refers to the measure of a material’s resistance to deformation, especially plastic deformation, when subjected to a force. In simpler terms, hardness indicates the ability of a material to resist penetration, scratching, or wear. This attribute is crucial when evaluating the performance and durability of materials used in various environments.
There are several hardness measurement scales and methods, but commonly used ones include HLD, HRC, HRB, HV, HB, and HSD. Each of these measurements tests different aspects of a material’s resistance to forces or deformation using specific testing techniques and machinery. It is important to understand the various hardness scales as they may provide different results and are best suited for specific types of materials.
HLD, or Leeb Hardness, is a dynamic hardness test that measures the rebound velocity of a small impact body after being struck against the material under test. The higher the rebound velocity, the harder the material. HLD is utilized for in-situ testing of large and cumbersome components.
HRC, HRB, and other Rockwell Hardness scales utilize a small indenter to create an indentation on the surface of the material under a predetermined force. The depth of indentation is measured, giving us an indication of the hardness. The hardness values are represented as 0-100 HRC, 0-100 HRB, and so on. Rockwell Hardness is typically used for assessing metals and harder materials.
HV represents Vickers Hardness and employs a diamond pyramid indenter with a load applied to create a small indentation on the material’s surface. The dimensions of the indentation are then measured, which reveals the material’s hardness value. Vickers Hardness is suitable for materials with varying hardness levels and thicknesses, including ceramics and thin metal coatings.
HB signifies Brinell Hardness and uses a spherical indenter under a specific load pushed into the material. The diameter of the indentation left is measured to determine the material’s hardness. Brinell Hardness is commonly utilized for softer materials such as aluminum, brass, and certain types of steel.
Lastly, HSD is an abbreviation for Hardness Scleroscope— a less common hardness test method that operates on the principle of measuring the rebound height of a diamond-tipped hammer after it impacts the material’s surface.
Selecting the appropriate hardness measurement method is crucial for obtaining accurate results and gauging material performance. It is essential to consider the specific material properties, industry requirements, and application needs to make informed decisions when selecting hardness measurement methods.
Hardness Conversion Chart
Hardness Conversion Formulas
- Shore Hardness (HS) = Brinell Hardness (BHN) / 10 + 12
- Shore Hardness (HS) = Rockwell Hardness (HRC) + 15
- Brinell Hardness (BHN) = Vickers Hardness (HV)
- Rockwell Hardness (HRC) = Brinell Hardness (BHN) / 10 – 3
Comparison, Differences, and Conversion Between Rockwell Hardness (HRC) and Brinell Hardness (HB)
Hardness is a performance indicator that measures the degree of softness or hardness of a material. There are many methods for hardness testing, each with different principles, leading to different hardness values and meanings.
The most common is the static load indentation hardness test, such as Brinell Hardness (HB), Rockwell Hardness (HRA, HRB, HRC), and Vickers Hardness (HV).
These hardness values indicate the ability of a material surface to resist the indentation of a hard object.
The popular Leeb Hardness (HL) and Shore Hardness (HS) belong to rebound hardness tests, representing the size of the elastic deformation work of metal.
Therefore, hardness is not a simple physical quantity, but a comprehensive performance indicator reflecting the elasticity, plasticity, strength, and toughness of a material.
1. Steel Hardness: The symbol for metal hardness (Hardness) is H.
Depending on the testing method used,
● Conventionally, there are Brinell (HB), Rockwell (HRC), Vickers (HV), and Leeb (HL) hardness measurements, among which HB and HRC are most commonly used.
● HB has a wide range of applications, while HRC is suitable for materials with high surface hardness, such as heat treatment hardness. The difference between them lies in the indenter used in the hardness tester; the Brinell hardness tester uses a steel ball, while the Rockwell hardness tester uses a diamond.
● HV is used for microscopic analysis. Vickers Hardness (HV) is determined by pressing a diamond square cone with a load of up to 120kg and a top angle of 136° into the material surface, and then dividing the surface area of the indentation pit by the load value to get the Vickers hardness value (HV).
● The HL portable hardness tester is easy to measure. It calculates hardness by using an impact ball to bounce off the hardness surface, and the formula for Leeb Hardness HL=1000×VB (rebound speed) / VA (impact speed).
● The most commonly used portable Leeb hardness tester can convert Leeb (HL) measurements into Brinell (HB), Rockwell (HRC), Vickers (HV), and Shore (HS) hardness. Or use the Leeb principle to directly measure hardness values with Brinell (HB), Rockwell (HRC), Vickers (HV), Leeb (HL), Shore (HS).
Rockwell Hardness (HRC) is generally used for materials with high hardness, such as those after heat treatment.
2. HB – Brinell Hardness
This is generally used when the material is softer, such as non-ferrous metals, or steel before heat treatment or after annealing. Brinell Hardness (HB) is measured by applying a certain test load to press a hardened steel ball or carbide ball of a certain diameter into the surface of the metal being tested, maintaining it for a specified time, then unloading, and measuring the diameter of the indentation on the tested surface.
The Brinell Hardness value is obtained by dividing the load by the spherical surface area of the indentation.
Typically, a certain load (generally 3000kg) is used to press a hardened steel ball of a certain size (generally 10mm in diameter) into the material surface, maintained for a period of time, and after unloading, the ratio of the load to the indentation area is the Brinell Hardness value (HB), with units in kilogram-force/mm2 (N/mm2).
3. Rockwell hardness uses the depth of indentation plastic deformation to determine the hardness value index.
A unit of hardness is 0.002 millimeters. When HB>450 or the specimen is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement is adopted instead. This involves using a diamond cone with a 120° apex angle or a steel ball with a diameter of 1.59 or 3.18mm, under a certain load, pressed into the material surface, and determining the material’s hardness from the depth of the indentation. According to different hardness of the test material, three different scales are used:
HRA: Uses a 60kg load and a diamond cone indenter to determine hardness, and is used for materials with extremely high hardness (such as hard alloys, etc.).
HRB: Uses a 100kg load and a hardened steel ball with a diameter of 1.58mm to determine hardness, and is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
HRC: Uses a 150kg load and a diamond cone indenter to determine hardness, and is used for materials with very high hardness (such as hardened steel, etc.).
- HRC implies Rockwell hardness C scale.
- HRC and HB are both widely used in production.
- HRC’s applicable range is HRC 20-67, equivalent to HB225-650.
If the hardness exceeds this range, use Rockwell hardness A scale (HRA).
If the hardness is below this range, use Rockwell hardness B scale (HRB).
The upper limit of Brinell hardness is HB650; it cannot exceed this value.
4. The indenter for the Rockwell hardness tester C scale is a diamond cone with a 120-degree apex angle. The test load is a fixed value, and the Chinese standard is 150 kilograms of force. The indenter for the Brinell hardness tester is a hardened steel ball (HBS) or a hard alloy ball (HBW). The test load varies with the ball diameter, ranging from 3000 to 31.25 kilograms of force.
5. The indentation of the Rockwell hardness is very small, and the measurement value is local, so the average value must be calculated by measuring several points. It is suitable for finished products and thin sheets, and is classified as non-destructive testing. The indentation of the Brinell hardness is larger, and the measurement value is accurate, but it is not suitable for finished products and thin sheets. It is generally not classified as non-destructive testing.
6. The hardness value of Rockwell hardness is a dimensionless number, with no unit. (Therefore, it is incorrect to refer to the Rockwell hardness as a degree.) The hardness value of Brinell hardness has a unit and has a certain approximate relationship with tensile strength.
7. Rockwell hardness is directly displayed on the dial and can also be displayed digitally. It is convenient to operate, quick and intuitive, and suitable for mass production. Brinell hardness requires the use of a microscope to measure the diameter of the indentation, and then look up the table or calculate, the operation is relatively cumbersome.
8. Under certain conditions, HB and HRC can be converted by looking up a table. The mental calculation formula can be roughly remembered as: 1HRC≈1/10HB.
Types of Hardness Tests
Hardness tests are important methods to measure the resistance of materials to various types of deformation, including indentation, scratching, and wear. There are several types of hardness tests which are widely used in industries, each with its specific advantages and applications. These tests include: Brinell (HB), Rockwell (HRC, HRA, HRB), Vickers (HV), and Leeb (HLD).
The Brinell hardness test (HB) is an indentation test that uses a 5 or 10mm diameter tungsten carbide ball indenter and a specific load, typically ranging between 250 and 3000 kgf for metals. The hardness value is calculated by dividing the load by the curved surface area of the indentation. It is suitable for testing coarse-grained materials, castings, and other large objects that cannot be tested by other hardness methods.
Rockwell hardness tests (HRC, HRA, HRB) use different types of indenters and loads, depending on the scale being used. There are three main Rockwell scales: A, B, and C. The HRC scale is typically used for hard materials, using a diamond cone indenter and a load of 150 kgf. The HRA scale is used for thin and hard materials, while the HRB scale is used for softer materials like copper alloys or soft steels. These two scales use a 1/16-inch steel ball indenter and varying loads.
The Vickers hardness test (HV) is a microhardness test that uses a 136-degree diamond pyramid indenter and a range of loads, from 1 to 100 kgf. This test is suitable for a wide range of materials and thicknesses, providing results that are independent of the indenter size. The Vickers test allows for more precise hardness measurements in small and thin samples compared to Brinell and Rockwell methods.
Finally, the Leeb hardness test (HLD) is a dynamic non-destructive test that measures the hardness of a material based on the rebound velocity of a hardened steel impact body. The Leeb method is useful for quickly and efficiently testing large or inaccessible objects, as well as assembled components.
Hardness conversion charts are often used to compare and convert between these different hardness scales. However, it’s essential to remember that conversion accuracy may vary depending on methods, materials, and conditions of the test.
Manufacturing and Engineering Considerations
When considering the manufacturing and engineering aspects of hardness conversion, it is vital to understand the various hardness scales and how they can impact the selection and processing of materials. Hardness conversion charts, such as the steel hardness conversion table, are beneficial tools that allow engineers to compare different hardness scales and choose materials accordingly.
An essential standard in hardness conversion is ISO 18265, which provides guidelines for converting hardness test results from one scale to another. This standard establishes correlations between HLD, HRC, HRB, HV, HB, and HSD hardness scales. Utilizing these conversions can help engineers accurately pinpoint material specifications and predict the mechanical properties of materials.
It is crucial to note that hardness conversion is not a linear process. For instance, a direct conversion of Rockwell C hardness (HRC) to Brinell hardness (HB) could result in inaccuracies. Engineers must rely on the appropriate conversion charts and calculation methods to ensure proper conversion between hardness scales.
In manufacturing and engineering processes, determining the hardness of materials is essential for optimizing performance and durability. Hardness measurements can indicate a material’s resistance to wear, deformation, and indentation, which are vital factors when selecting materials for specific applications.
Some common manufacturing applications that require careful consideration of hardness include:
- Machine components, such as gears and bearings
- Cutting tools and dies
- Wear-resistant coatings or layers
- Structural components in bridges and buildings
In conclusion, understanding hardness conversion charts and their implications on material selection and engineering design is a fundamental aspect of successful manufacturing processes. Adhering to standards such as ISO 18265 and utilizing appropriate conversion methods can facilitate better decision-making and improve overall product performance and manufacturability.
In this article, we have explored the various hardness scales, including HLD, HRC, HRB, HV, HB, and HSD. It is crucial to understand these scales as they serve as important metrics for determining the mechanical properties of materials. Each scale has its own unique characteristics and methods of measurement, making them suitable for specific applications.
To make it easier to compare and convert between these scales, the use of hardness conversion charts is highly valuable. These charts provide standardized relationships between different scales and help streamline the process of identifying appropriate materials for engineering projects, quality control, and research purposes.
It is important to note that while the conversion charts provide useful estimates, these conversions may not be accurate for all materials and conditions due to factors such as material composition, grain size, and the presence of residual stresses. Therefore, it is always recommended to perform direct hardness measurements on the specific material in question whenever possible.
In summary, the understanding of hardness scales and the use of conversion charts play a crucial role in the fields of material science and engineering. These tools not only aid in material selection and quality control but also contribute to driving innovation and improvements in material technology.