The Ultimate Guide to Metal Hardness (with Chart)

Are you curious about the hardness of metals and minerals?

Do you want to learn more about the different types of hardness tests and how they are used to measure a material’s resistance to deformation?

Look no further than this comprehensive guide on metal hardness from MachineMfg.

From scratch hardness testing to rebound hardness testing, this article covers all the different methods used to evaluate the hardness of metals and minerals.

You’ll learn about the various types of indentation hardness tests, including Brinell hardness, Rockwell hardness, Vickers hardness, and micro-hardness, and how they differ in terms of the indenter used, the applied load, and the duration of the load.

In addition to detailed explanations of the different hardness tests, this article also includes a handy chart of non-ferrous metal hardness, with information on tensile strength, Rockwell surface, Vickers, Brinell, and more.

Whether you’re a materials scientist, engineer, or just someone with a general interest in the properties of metals and minerals, this article is a must-read.

So dive in and discover everything you need to know about metal hardness!

What Is Metal Hardness?

Hardness is a metric that measures a material’s resistance to local deformations, such as plastic deformation, indentations, or scratches.

It is a crucial factor in determining the hardness of a material.

Types of Metal Hardness

According to the different test methods, there are three types of hardness.

① Scratch hardness

Hardness is primarily utilized to compare the resistance to local deformation of various minerals.

The process involves using a rod with a hard and soft end to test the material by sliding it along the rod.

The material’s softness or hardness is determined based on the length of the scratch it leaves on the rod.

Typically, scratches made by harder materials are longer and those made by softer materials are shorter.

② Indentation hardness

Indentation hardness testing is primarily used to evaluate metal materials. It involves applying a specified indenter to the surface of the material under test with a specific load.

The material’s hardness is determined by comparing the amount of local plastic deformation on the material’s surface.

There are several types of indentation hardness tests, including Brinell hardness, Rockwell hardness, Vickers hardness, and micro-hardness, which differ in terms of the indenter used, the applied load, and the duration of the load.

③ Rebound hardness

Rebound hardness testing is primarily used for metal materials. The method involves using a special small hammer that is dropped from a specific height to impact the material sample being tested.

The material’s hardness is determined by the amount of strain energy stored in and then released from the sample during the impact, which is measured by the rebound height of the hammer.

Metal Hardness Chart

Metals Mohs Hardness Chart

The Mohs hardness is a standard for representing mineral hardness, first proposed in 1822 by German mineralogist Frederich Mohs. It is a standard used in mineralogy or gemology. Mohs hardness is determined by using a diamond pyramid needle to scratch the surface of the tested mineral and measure the depth of the scratch. The depth of this scratch is the Mohs hardness, represented by the symbol HM. It is also used to indicate the hardness of other materials.

The depth of the measured scratch is divided into ten levels to represent hardness (scratch method): talc 1 (smallest hardness), gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase (feldspar) 6, quartz 7, topaz 8, corundum 9, diamond 10. The hardness of the tested mineral is determined by comparing scratches with the standard minerals in the Mohs hardness tester. Although the measurement of this method is rough, it is convenient and practical. It is often used to measure the hardness of natural minerals.

Hardness values are not absolute hardness values, but values represented in order of hardness.

When applying, compare the hardness by scratching. For example, if a mineral can scratch calcite but not fluorite, its Mohs hardness is 3 to 4, and others are inferred. Mohs hardness is only relative hardness, which is rough. The hardness of talc is 1, diamond is 10, and corundum is 9, but the absolute hardness measured by a microhardness tester is 4192 times that of talc for diamond, and 442 times that of talc for corundum. Mohs hardness is convenient to use and is often used in field operations. For example, the hardness of fingernails is about 2.5, copper coins are 3.5-4, steel knives are 5.5, and glass is 6.5.

In addition to the original list of 1 to 10 kinds of minerals, the hardness values of common metals are listed here for reference.

Common Metal Material Hardness Chart

Hardness of Metal Materials Used in Power Stations

Non-ferrous Metal Hardness Table

Ferrous Metal Hardness Table

The following data is mainly applicable to low-carbon steel (mild steel).

Common HV = HB = HRC Hardness Comparison Table

Hardness testing is the simplest and most straightforward method among mechanical property tests. In order to replace certain mechanical property tests with hardness tests, a relatively accurate conversion relationship between hardness and strength is needed in production.

Experience has shown that there is an approximate corresponding relationship between the various hardness values of metal materials, and between hardness values and strength values. This is because the hardness value is determined by the initial plastic deformation resistance and the continued plastic deformation resistance. The higher the strength of the material, the higher the plastic deformation resistance, and thus the higher the hardness value.

Below is a quick calculator created by our site, based on empirical formulas obtained from experiments. It has practical value, but when accurate data is required, testing is still necessary.

Hardness comparison table of common ferrous metals (Approximate conversion of intensity)

Download Ferrous & Non-ferrous Metal Hardness Table

Metal hardness and strength conversion value, strength and hardness comparison table

HRC / HB Approximate Conversion Tips

• When the hardness is higher than 20HRC, 1HRC≈10HB,
• When the hardness is lower than 20HRC, 1HRC≈11.5HB.

Note: When considering cutting processing, a general conversion of 1HRC ≈ 10HB applies (the hardness of the workpiece material may vary slightly).

The most commonly used indentation hardness tests for metal materials are Brinell, Rockwell, and Vickers hardness tests.

The hardness value indicates a material’s ability to resist plastic deformation caused by the intrusion of another object.

When measuring hardness using the rebound method, the hardness value represents the extent of the metal’s elastic deformation function.

Commonly Used Hardness

Brinell Hardness

The Brinell hardness test uses a ball made of hardened steel or a hard alloy with a diameter of D as the indenter.

A specified test force F is applied to the surface of the material being tested, and after a designated hold time, the test force is removed, leaving an indentation with a diameter of d.

The Brinell hardness value is calculated by dividing the test force by the surface area of the indentation. The symbol for the Brinell hardness value is represented as HBS or HBW.

The difference between HBS and HBW lies in the type of indenter used.

HBS indicates the use of a hardened steel ball as the indenter and is used to determine the Brinell hardness of materials with a value less than 450, such as mild steel, gray cast iron, and non-ferrous metals.

HBW, on the other hand, refers to the use of a hard alloy ball as the indenter and is used to measure the Brinell hardness of materials with a value below 650.

Even when the same material and experimental conditions are used, the results of the two tests may vary, with the HBW value typically being higher than the HBS value, and there is no exact quantitative rule to follow.

In 2003, China adopted international standards and discontinued the use of steel ball indenters in favor of hard alloy ball heads.

As a result, HBS was no longer used and all Brinell hardness values are now represented by HBW.

Although HBW is often simply referred to as HB, references to HBS may still be found in literature.

The Brinell hardness measurement method is suitable for testing materials such as cast iron, non-ferrous alloys, and various steels that have undergone annealing or quenching and tempering processes.

However, it is not suitable for testing samples or workpieces that are too hard, too small, too thin, or do not allow for large indentations on the surface.

Rockwell Hardness

The Vickers hardness test uses either a diamond cone with a 120-degree cone apex angle or a hardened steel ball with a diameter of Ø1.588mm or Ø3.176mm as the indenter, along with a specified load.

The sample is subjected to an initial load of 10kgf and a total load of 60, 100, or 150kgf.

After the total load is applied, the hardness is determined by the difference in indentation depth when the main load is removed while retaining the initial load and the indentation depth under the initial load.

The Rockwell hardness test uses three different test forces and three different indenters, resulting in a total of nine possible combinations and corresponding Rockwell hardness scales.

These nine scales are suitable for a wide range of commonly used metal materials.

The three most commonly used Rockwell hardness scales are HRA, HRB, and HRC, with HRC being the most widely utilized.

Table of commonly used Rockwell hardness test specifications

The Rockwell hardness test is appropriate for hardness values ranging from 20-70HRC. If the hardness of the sample is less than 20HRC, it is recommended to use the HRB scale as the sensitivity of the indenter decreases with increased pressure on the conical part.

However, if the hardness of the sample is greater than 67HRC, it is advised to use the HRA scale as the pressure on the tip of the indenter may become too high and result in damage to the diamond and reduced life of the indenter.

The Rockwell hardness test is known for its ease, speed, and minimal indentation, making it ideal for testing the surface of finished products and harder, thinner workpieces.

However, due to the small indentation, the hardness value may fluctuate greatly for materials with uneven structures and hardness, making it less accurate than the Brinell hardness test.

The Rockwell hardness test is commonly used to determine the hardness of materials such as steel, non-ferrous metals, and cemented carbides.

Vickers Hardness

The principle behind the Vickers hardness measurement is similar to that of the Brinell hardness test.

A diamond pyramid-shaped indenter with an angle of 136° is used to apply a specified test force, F, onto the surface of the material being tested.

After a specified holding time, the test force is removed, and the hardness value is calculated as the average pressure on the unit surface area of the regular pyramid-shaped indentation, with the symbol HV.

The Vickers hardness measurement has a wide range, and it can measure materials with a hardness ranging from 10 to 1000 HV. The indentation is small in size.

This measurement method is commonly used to measure thin materials and surface-hardened layers created through carburizing and nitriding.

Leeb Hardness

The Leeb Hardness Test uses a device equipped with a tungsten carbide ball to impact the surface of the test piece, which then rebounds. The speed of the rebound is affected by the hardness of the material being tested.

A permanent magnetic material is installed on the impact device, which produces an electromagnetic signal proportional to the speed of the impact body’s movement. This signal is then converted into a Leeb hardness value by an electronic circuit, represented by the symbol HL.

The Leeb Hardness Tester is a handheld device that does not require a workbench. Its hardness sensor is compact and can be easily operated by hand, making it suitable for testing large, heavy, or complex geometries.

One of the key benefits of the Leeb Hardness Test is that it results in only light surface damage, making it an ideal option for non-destructive testing. It also provides a unique hardness test for all directions, narrow spaces, and special parts.

Hardness Testers

• Micro Vickers hardness testing machine

HM series:

• Vickers hardness testing machine
  HV series:

• Rockwell hardness testing machine
  HR series:

• Portable Leeb hardness tester
  HH series:

FAQs About Metal Hardness

How to measure hardness of metal?

The most commonly used methods to measure the hardness of metal are the Brinell hardness method, the Rockwell hardness method, and the Vickers hardness method.

How to increase metal hardness?

The strength of metal materials can be improved through the following five methods:

1) Conducting a heat treatment process, such as quenching, tempering, normalizing, etc., based on the required performance and structure.

2) Surface shot peening.

3) Grain boundary strengthening.

4) Dislocation strengthening.

5) Precipitation of certain compounds through deformation and aging, which can improve strength.

At what temperature does metal lose hardness?

At temperatures below -200 degrees Celsius, ordinary steel becomes as brittle as glass.

The low temperature reduces the cohesive forces between metal molecules, making the material more rigid and less able to withstand deformation. This increased rigidity causes the metal to become more prone to breaking under external force.

However, it is important to note that the brittleness of the metal is dependent on the specific situation.

For example, materials with a face-centered cubic structure do not undergo a transition from ductile to brittle behavior at low temperatures.

What determines the hardness of a metal?

1）The hardness of a metal is determined by the strength of the bonding between metal atoms.

2）The harder the metal, the stronger the bonding between the metal atoms and the smaller the radius of the metal atoms.

3）The more valence electrons in the metal atoms per unit volume, the stronger the bonding between the metal atoms and the greater the hardness.

4）In general, for main group metals, moving from left to right within the same period, the atomic radius decreases and the number of valence electrons increases, leading to an increase in hardness.

On the other hand, moving from top to bottom within the same main group, the atomic radius increases while the number of valence electrons remains constant, resulting in a decrease in hardness.

5）For transition elements, the atomic radius decreases from left to right, but the number of valence electrons increases first and then decreases, making the trend in hardness less clear-cut than for the main family elements.

However, elements with high hardness are typically found in the middle of the transition elements within the same period.