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Material Hardness: Types, Testing Methods, Units & Complete Chart | SMS Machining
Created on 06.01
Material hardness is one of the most critical mechanical properties for industrial material selection and CNC machining production. For mechanical parts, automotive components, structural fixtures, and precision machinery, hardness directly determines wear resistance, anti-scratch performance, deformation resistance, and overall service life.
Choosing materials with improper hardness will lead to part deformation, surface abrasion, structural failure, or even entire project collapse. Therefore, evaluating material hardness before manufacturing is an essential step for every engineering design and mass production project.
As a professional ISO 9001 certified OEM manufacturer, SMS deeply understands the importance of hardness matching in custom machining. This comprehensive guide covers what material hardness is, three core types of hardness, standard hardness testing methods, common hardness units & scales, and practical industry application tips to help global engineers and procurement teams select materials accurately.
What Is Material Hardness?
Material hardness refers to the ability of a solid material to resist external mechanical forces, including surface scratching, indentation, penetration, abrasion, and plastic deformation. In short, it is the capability of a material to retain its original physical shape and surface integrity under load and friction.
Hardness varies significantly across different industrial materials. High-strength metals such as carbon steel, stainless steel, and alloy steel feature excellent hardness and deformation resistance. In contrast, tin, aluminum, plastic, and wood belong to soft materials with low hardness, suitable for lightweight and low-load application scenarios.
Multiple factors jointly affect material hardness, including plasticity, ductility, elastic stiffness, toughness, strain strength, viscoelasticity, and viscosity. Different material compositions and heat treatment processes will completely change the final hardness performance of finished parts.
3 Main Types of Material Hardness (Industrial Classification)
According to different force application modes and deformation mechanisms, industrial material hardness is divided into three core categories. Each type corresponds to different working conditions and testing scenarios, which is the key basis for industrial material selection:
1. Scratch Hardness
Scratch hardness refers to a material’s ability to resist surface scratches caused by friction or hard object scraping. It is mainly used to evaluate the surface wear resistance and anti-scratch performance of materials.
In industrial scenarios, parts that work in long-term friction environments must have high scratch hardness. Low scratch hardness materials are prone to surface peeling, roughness increase, and performance attenuation, resulting in frequent equipment maintenance and increased production costs. This test is widely applied to brittle materials such as ceramics, coatings, and precision decorative parts.
2. Rebound Hardness (Dynamic Hardness)
Also known as dynamic hardness, rebound hardness belongs to elastic hardness. It tests the elastic recovery capacity of a material after instantaneous impact force. Different from plastic deformation, materials with high rebound hardness can completely restore their original shape after the external force is removed without permanent deformation.
The testing principle is to drop a standard diamond-tipped indenter hammer on the material surface and judge the hardness value according to the rebound height of the hammer. The higher the rebound height, the better the material elasticity and dynamic hardness. It is commonly used for rapid hardness detection of metal plates, forgings, and large structural parts.
3. Indentation Hardness
Indentation hardness is the most widely used hardness type in mechanical engineering and CNC machining. It refers to the ability of a material to resist continuous pressure and indentation deformation. Engineers and metallurgists generally refer to indentation hardness when discussing material hardness data.
The test applies continuous standard load to form a fixed indentation on the material surface and calculates the hardness value according to the indentation size. It supports both macroscopic and microscopic testing, suitable for almost all metal materials, and is the core standard for industrial material hardness inspection.
Material Hardness Units & Standard Measurement Scales
Many customers confuse hardness units with pressure units. The standard SI unit of material hardness is N/mm² (Pascal), while the pressure unit is N/m². Different hardness testing methods correspond to exclusive measurement scales, which cannot be directly compared, but can be converted through standard conversion tables for reference.
The most commonly used industrial hardness units and scales are summarized below:
- Brinell Hardness (HB / HBW)
: Suitable for low and medium hardness metals, castings, and forgings
- Rockwell Hardness (HRA / HRB / HRC)
: The mainstream scale for industrial metal hardness testing, HRC for hard steel, HRB for soft metals
- Vickers Hardness (HV)
: High-precision testing for thin materials, coatings, and micro-parts
- Leeb Hardness (HLD / HLS / HLE)
: Portable rapid detection for large workpieces
- Mohs Hardness
: Professional scale for scratch hardness testing, suitable for non-metallic materials and mineral materials
5 Common Industrial Material Hardness Testing Methods
Different materials and usage scenarios require targeted hardness testing methods.SMSsorts out the detailed principles, operation steps, and applicable scenarios of mainstream testing methods for your engineering reference:
1. Brinell Hardness Test
The Brinell test is the most classic and widely used macroscopic hardness testing method, compliant with ISO 6506 and ASTM E10 standards. It uses a 10mm standard steel ball or tungsten carbide ball indenter, applies 500KG to 3000KG standard load, and keeps the load for 30 seconds to form a stable indentation on the material surface.
After removing the indenter, measure the indentation diameter with a low-power microscope, calculate the average value, and obtain the Brinell hardness number through a professional formula. It is most suitable for coarse-grained metals, cast iron, aluminum alloy, and medium-low hardness steel parts.
2. Rockwell Hardness Test
Rockwell hardness test is the preferred method for industrial batch detection, with 30 optional scales. The most commonly used are HRC (diamond cone indenter for high-hardness steel, stainless steel) and HRB (steel ball indenter for soft alloys).
The test first applies a small preload to eliminate surface irregularities and ensure indenter fitting, then applies major load to form permanent indentation. The hardness value is calculated according to the indentation depth difference before and after loading. It features fast testing speed and high efficiency, suitable for mass production inspection of CNC machined parts.
3. Vickers Hardness Test
Compliant with ISO 6507 and ASTM E92 standards, the Vickers test uses a unified square diamond pyramid indenter, supporting micro-load to conventional load testing. It is the highest-precision hardness testing method, suitable for soft materials, thin plates, surface coatings, and tiny precision parts.
After loading and holding pressure, measure the diagonal length of the square indentation and calculate the HV value through a fixed formula. It solves the problem of inaccurate detection of ultra-thin and ultra-soft materials by other methods.
4. Mohs Hardness Test
Mohs hardness test is the exclusive detection method for scratch hardness. It uses 10 standard reference materials with fixed hardness values (1 for talc, 10 for diamond). The test principle is to scratch the detected material with reference materials of known hardness to judge the material’s scratch resistance level.
Modern Mohs testing adopts Rockwell diamond indenter for standardized loading and scratching, which is widely used for hardness detection of ceramics, plastics, glass, and non-metallic engineering materials.
5. Scleroscope Rebound Hardness Test
This method is dedicated to detecting rebound (dynamic) hardness. A diamond hammer falls vertically through a fixed glass tube and hits the workpiece surface. The hardness is judged by the hammer’s rebound height.
High-hardness materials produce high rebound height, while soft materials have low rebound. It is suitable for rapid non-destructive testing of large steel structures, mold blanks, and mechanical equipment parts without damaging the workpiece surface.
Material Hardness Reference & Conversion Guide
Different hardness scales cannot be completely equivalently converted, but standard industrial conversion data can provide accurate reference for material selection and quality inspection. High-hardness materials such as 630 stainless steel, carbon steel, and alloy steel are mostly tested by HRC and HB scales; soft materials such as tin and aluminum alloy are dominated by HV and HRB scales.
Professional hardness testing and material matching analysis can effectively avoid part failure caused by improper hardness selection, reduce scrap rate, and optimize production costs.
Why Material Hardness Testing Matters for CNC Machining Projects
- Avoid Structural Failure
: Ensure parts resist abrasion, impact, and deformation in the working environment
- Optimize Machining Process
: Different hardness materials require matched cutting tools, speed, and coolant solutions
- Control Product Quality
: Standard hardness inspection guarantees batch product consistency
- Reduce Comprehensive Cost
: Avoid material waste and after-sales maintenance caused by wrong material selection
SMS Professional Hardness Analysis & CNC Machining Service
SMS is a reliable ISO 9001 certified OEM manufacturing supplier, providing one-stop custom machining solutions from prototype design to mass production. We provide free professional material hardness analysis and material selection consultation for all global clients.
Our professional engineering team accurately judges material hardness performance according to project usage scenarios, matches the most suitable steel, aluminum, tin alloy, and stainless steel materials, and optimizes CNC machining and heat treatment processes to ensure parts meet hardness, wear resistance, and structural strength requirements.
We support low-volume prototype trial production and high-volume batch manufacturing, with fast quotation response and strict quality control. Upload your CAD files now to get a customized manufacturing solution and free material hardness evaluation from SMS!
Conclusion
Material hardness is an irreplaceable core index for industrial material selection and mechanical design. Scratch hardness, rebound hardness, and indentation hardness correspond to different working conditions, while Brinell, Rockwell, Vickers, and Mohs tests form a complete set of industrial hardness detection systems.
Only by accurately testing and reasonably matching material hardness can we ensure the stability and durability of machined parts. Cooperating with professional manufacturers like SMS can effectively avoid material selection errors, improve product quality, and reduce project comprehensive costs.
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