Material Hardness: Types, Measurement Scales & Machining Tips

The material’s suitability is crucial for a part to work well in its environment. Among the many properties, hardness plays a key role. Hardness determines if a material can resist indentation or abrasion without deforming. Using a wrong material can lead to part failure or costly rework. That is why assessing material hardness before production is essential to ensure success.

Choose harder materials when your project demands resistance to surface damage. But a high-hardness material is not always ideal. Always consult a knowledgeable machining partner to pick the proper material for your part.

What is hardness?

Hardness refers to a material’s ability to resist external forces without deformation, scratching, indentation, or penetration. In simple terms, it is how well a material holds its shape under pressure.

Different materials show different hardness levels: steel is usually harder than tin, while wood or plastics behave more like softer metals in terms of hardness.

Many internal properties influence hardness. Below are some of them:

• Plasticity — how easily a material deforms permanently under stress.

• Elastic Stiffness — the resistance to returning to original shape after deformation.

• Ductility — how much elongation a material can endure before breaking.

• Toughness — resistance to fracture under stress or impact.

• Strain — the deformation a material undergoes when forces act on it.

• Strength — the maximum load a material can bear before failing.

• Viscoelasticity — when a material shows both viscous and elastic behavior under stress.

• Viscosity — resistance to flow (more relevant in polymers or fluids).

These factors combine to determine the overall hardness of a material.

Hardness of Common Materials

The following presents an overview of common metal hardness examples in everyday life. Take the opportunity to investigate different materials, analyze their relative hardness,

Bronze Hardness

With regards to the hardness of metals, the hardness bronze, specifically represented by UNS C95400, is estimated to be around 170 MPa. It is worth noting that the hardness of aluminum bronzes tends to rise proportionally with the inclusion of higher levels of aluminum, along with other alloy components. Additionally, the hardness is influenced by the application of external forces that occur during cold working processes. Shifting our attention to tin bronze, denoted as UNS C90500 or commonly referred to as gun metal, its Brinell hardness is approximately 75 BHN (Brinell Hardness Number). In the case of copper beryllium, identified as UNS C17200, the Rockwell hardness is recorded to be around 82 HRB (Rockwell Hardness Scale B).

Titanium Hardness

The hardness of titanium alloys can exhibit considerable variation depending on factors such as composition and heat treatment. For instance, commercially pure titanium Grade 2 typically demonstrates a Rockwell hardness of approximately 80 HRB. On the other hand, the titanium alloy Ti-6Al-4V, commonly referred to as Grade 5, typically displays a Rockwell hardness of around 41 HRC. These distinct hardness values highlight the impact of alloy composition and heat treatment in determining the hardness characteristics of titanium alloys.

Copper Hardness

When it comes to the hardness of copper, according to Ezoic data, it demonstrates a Brinell hardness of approximately 250 MPa. Furthermore, the Vickers hardness test reveals that copper possesses a Vickers hardness of around 350 MPa. In terms of the widely recognized Mohs scale, which evaluates the relative hardness of minerals, copper falls into the category of about 3 on the hardness scale.

Brass Hardness

The strength and hardness of brass, specifically cartridge brass UNS C26000, can be described in terms of its ultimate tensile strength and Brinell hardness. The ultimate tensile strength of this type of brass is approximately 315 MPa, indicating the maximum amount of tensile stress it can withstand before fracturing. On the other hand, when measuring its resistance to indentation, the hardness brass UNS C26000 is found to be around 100 MPa, showcasing its ability to withstand external forces without easily deforming.

Steel Hardness

The hardness of steel can vary depending on factors such as carbon content. High-carbon steel, which typically contains around 0.60% to 1.00% carbon, is known for its elevated hardness compared to other steel grades. However, as the carbon content increases, the ductility of the steel tends to decrease. The Brinell hardness of high-carbon steel is typically measured to be approximately 200 MPa. This indicates a substantial level of hardness, reflecting the steel’s ability to resist deformation and withstand external forces.

Iron Hardness

Iron exhibits a hardness of around 4.5 on the Mohs scale. The crystal structure of iron is commonly observed to be body-centered cubic (BCC) in nature. In metals, including iron, and many other solid materials, the atoms are arranged in ordered patterns known as crystals.

Different Types of Material Hardness

Materials show different kinds of hardness depending on how they are stressed. The three main types are:

• Scratch hardness
• Rebound hardness
• Indentation hardness

Scratch Hardness

This measures how well a surface resists scratching by a harder object. It is useful when surface wear or friction matters. For example, if a part is subject to sliding contact, a higher scratch hardness is safer to avoid surface damage. Ceramics often require scratch hardness testing.

Rebound Hardness

Also known as dynamic hardness, rebound hardness is about a material’s ability to elastically recover after impact. You drop an indenter and measure how high it rebounds. A higher rebound means harder, more elastic behavior.

Indentation Hardness

This is probably the most used type. You apply a load via an indenter (ball, cone, or diamond tip) to press into the surface, then you measure the indentation. The Rockwell and Brinell tests are standard methods of indentation hardness.

What is the unit of measurement for material hardness?

There are several scales and units for measuring hardness, each tied to different test methods. These scales are not directly comparable but can be converted approximately via tables.

Common hardness units:

• HB — Brinell Hardness Number

• HRA / HRB / HRC — Rockwell scales

• HV — Vickers hardness

• HL / HLD / HLS — Leeb hardness

• SI (N/mm² or MPa) sometimes used to approximate hardness as pressure units

Note: Hardness is not the same as pressure. Hardness relates to resistance to deformation, while pressure is force per area (N/m²). Be cautious when comparing them. Use a proper conversion table for rough equivalence.

Hardness Conversion Table (Excerpt)

4 Test Methods for Determining Material Hardness

After determining the specific loading or environmental conditions that your component will encounter, you can proceed to assess the suitability of different material options using various hardness test methods. If you have access to the required equipment, you can perform these tests to gather valuable data and make informed decisions.

The Brinell Test

You press a hardened steel ball (indenter) into the material under a known load. After loading, you measure the indentation diameter and compute the Brinell Hardness Number (HB) by formula.

• For hard metals like steel, the load might be 3000 kg (or 30,000 N).

• For softer metals like copper or brass, a smaller load like 500 kg (5,000 N) is used.

The formula:

Symbol:

HB = Brinell hardness (kg/mm2)

F = Force (measured in Newton)

D = Indenter diameter (measured in millimeters)

d = indentation diameter (measured in millimeters)

Rockwell Hardness Test

This test uses a minor load first (e.g. 10 kg) to seat the indenter, then a major load. After removing the major load, the depth of indentation is measured. The hardness number is read from the appropriate Rockwell scale (A, B, C, etc.), depending on material and load type.

For example:

• Steel alloys often use a diamond cone with a 140 kg load on C scale (HRC).

• Copper alloys might use a steel ball and 100 kg load on B scale (HRB).

Mohs Hardness Test

This method measures scratch hardness. You scratch the specimen with a reference material of known hardness or vice versa. The Mohs scale runs from 1 (talc) to 10 (diamond). Modern adaptations use diamond indenters for more precision. It’s helpful for minerals, ceramics, or coatings.

Shore Scleroscope Test

Also used for rebound hardness, this method drops a diamond-tipped hammer inside a glass tube onto the surface. The rebound height is measured: a harder material yields a greater rebound. This method is fast and simple, often used in field or quick testing.

Material Hardness Chart

Below is a detailed chart listing various metal alloys, their hardness on Rockwell B scale, yield strength, and ductility degree:

Why Hardness Matters in Machining & Design

Hardness affects wear resistance, fatigue life, surface finish, machining cost, and longevity of parts. If a part is too soft, it may scratch, bend, or deform under load. If it’s too hard, it might crack or be difficult to machine.

For example:

• A gear made from soft metal may wear rapidly under friction.

• A very hard bearing surface may resist wear, but if it is brittle, it could fracture under shock loads.

Thus, understanding hardness, ductility, toughness, and strength together is critical. Always tailor the material hardness to your operating condition.

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Richconn, Best Choice for Machining Services

If you have been in search of a trustworthy company that provides machining services for various materials, your search concludes here with Richconn. We offer a complimentary analysis of your material hardness, making us the ideal choice for all your machining needs.

• High Precision and Tight Tolerances

Through the integration of cutting-edge technology and extensive expertise, our CNC precision machining services offer exceptional results. As a company certified in ISO 13485 and ISO 9001:2008, we emphasize the importance of quality and guarantee that all components meet the required specifications.

• Fast Prototyping and Production

We accelerate your product development, covering prototyping to production. Quick turnarounds transform designs into prototypes, facilitating faster iterations and reducing time-to-market. Our CNC machining is adaptable for any production volume.

• Dedicated Customer Support

Richconn offers skilled engineers to optimize your designs, reduce expenses, and improve quality. Rely on our team for valuable guidance and unparalleled engineering support, guaranteeing exceptional project outcomes.

Conclusion

For effective material selection in your project, conducting a thorough material hardness test is crucial. There are multiple methods available to assess material hardness. Seeking guidance from an expert company is recommended to receive professional advice and expertise on material hardness meaning. With our extensive experience, we are well-prepared to offer technical recommendations tailored to your specific projects.

FAQ

What is the best hardness test for metals?
It depends. For general metal parts, Rockwell or Brinell tests are most common. Use Rockwell for harder metals and Brinell for softer or coarse grain structures.

Can hardness values from different scales be directly compared?
No. You need conversion tables to approximate equivalences, because each scale uses a different test mechanism and load.

Does higher hardness always mean better performance?
Not always. Higher hardness often comes with reduced ductility and increased brittleness. You must balance hardness with toughness and strength.

How do I choose a machining company with hardness expertise?
Look for a company that offers material testing services, engineering support, and certifications (e.g., ISO). Richconn offers these services and more.

Can we test hardness in-house?
Yes, if you have proper equipment (Rockwell tester, Brinell machine, etc.). But for precise results or complex parts, outsourcing to experts is safer.