When it comes to industrial blades, toughness and hardness are two essential characteristics of the cutting tool material. There are several different tests manufacturers use to determine the hardness and toughness of blade materials, including tensile and impact tests that can indicate a lot about how a blade will perform in real applications.
With hardness and toughness always competing against each other in any material, it’s essential to understand the differences between the two properties and how to strike the ideal balance. This guide to hardness vs. toughness will help you understand how to choose the right blade material and the best type of steel for your cutting applications.
Here, we’ll also explore the unique processes that make York Saw & Knife your top choice in blade manufacturer, including our reverse engineering method for recreating your existing blade from scratch to fit any profile or any piece of machinery.
What Is Hardness?
Hardness is the ability of a material to resist deformation while under load. More specifically, hardness is measured by a material’s ability to resist indentation by a material that is harder than it.
When a material is said to be hard, it means that it has better wear resistance than other materials that might be in the same class. For example, some hard metals, like stainless steel, are said to be harder than non-alloyed iron because when engineers perform the Rockwell test, the indenting material doesn’t penetrate as far into the stainless steel as it does into the non-alloyed iron.
Harder materials offer many advantages over softer materials, but they also experience some drawbacks. Though a material may be hard, it can become brittle and more susceptible to fatigue, resulting in microfractures under high cyclic loads. For this reason, it’s important to consider the application of the material, as this should dictate how much desired hardness, or softness, the material should have for its given purpose.
Harder materials are able to resist deformation better than softer materials. In demanding applications like cutting, sawing, shearing and chopping, harder materials retain their shape better and keep their cutting edge longer. If a material is too hard for a given application, it can experience stress fractures and will fail prematurely due to its inability to absorb the energies associated with the task it was designed for.
How to Measure and Test for Hardness
There are many different tests that engineers use to measure a material’s hardness. Some of the most common methods are:
- Rockwell test
- Brinell test
- Vickers test
- Knoop test
Each of these tests is conducted in roughly the same manner, all involving an indenter being forced into the material for a standard amount of time and then released. After indentation, engineers measure the size of the indentation and calculate the corresponding hardness number for the given test. How the tests differ is in the shape, material and size of the indenter used in any given test.
Rockwell Test
The Rockwell hardness test uses a conical indenter and is the most common test used for testing the hardness of different types of steel. However, the Rockwell test is not ideal for uneven materials with high levels of inconsistency across the surface. Typically, if the surface variations are larger than the diameter of the indenter, engineers will use a more robust testing option such as the Brinell test.
Brinell Test
The Brinell test uses a larger spherical indenter with high testing loads of around 3,000 kilogram-force (kgf). It’s the preferred test for materials with larger inconsistencies across their structure, such as structural lumber. Having larger indenters helps average out the inconsistencies in the material and provides a more accurate representation of its hardness.
Vickers Test
The Vickers hardness test was developed to test the hardness of very light and malleable materials. Ranging in test forces from 10 g to 1 kg, the Vickers test is able to make much smaller and finer penetrations in softer materials compared to other testing methods. The indenter used in the Vickers test is a pyramid square shape with a fairly relaxed slope that prevents it from piercing the material too deeply.
Knoop Test
The Knoop hardness test is the most common testing method used for very soft and thin materials, like gold. The indenter is similar to the pyramid-shaped version used in the Vickers test but is more elongated on one axis, giving it a rectangular shape. The Knoop test indenter shape helps it distribute its load over a larger area. This prevents it from penetrating materials as deeply as finely pointed indenters.
Examples of Hard Materials for Industrial Blades
Hard materials are able to withstand scratching and indentations easier than softer materials. Hardness is a critical property of materials used in applications like cutting or sawing, where the blades must constantly cut, shear or chop into other materials that are much softer.
The very action of cutting or chopping means that the material doing the cutting will need to be able to resist deformation better than the one being cut. In many cases, the cutting material is expected to retain its cutting edge and remain in service for several thousands of cycles before the edge requires maintenance.
Common industrial blade materials, like high-carbon and stainless steels, are measured using the Rockwell C scale. The Rockwell hardness test is commonly used for these types of blade materials because the size, shape and hardness of the indenter, coupled with the applied test forces, provide a highly accurate hardness measurement — especially when compared across different types of alloyed ferrous metals. The effectiveness of the Rockwell C scale is largely due to the relatively consistent surface characteristics and lack of large surface changes seen in many blade materials.
The hardest material on Earth is diamond, which may initially appear to make the best cutting material since nothing else is hard enough to deform it. However, in practical applications, extremely hard materials like diamond or tungsten will crack and fracture quickly after repeated, cyclical cutting operations. The ability to withstand repeated use without cracking is another quality that’s just as important to cutting materials as hardness is. This property is known as toughness.
What Is Toughness?
When it comes to cutting tools and their material properties, the two most important qualities are hardness and toughness. Critical to understanding the concept of hardness vs. toughness is to know that these properties are generally inversely related — as hardness increases, toughness usually decreases, and vice versa.
Having enough toughness is vital for cutting tools, as it allows the knife or blade to perform repeated cuts, often under large loads, all while keeping it intact and undeformed. If the blade material isn’t sufficiently tough, it cannot absorb the forces and impacts associated with the operation — instead, it simply cracks, chips or becomes permanently deformed very quickly.
In an ideal world, the cutting material would have both the hardest and toughest mechanical properties. However, what’s found in nature is that nearly all materials that are very hard are low in toughness, while those that are very tough are generally not very hard.
To get around this, engineers have created hybrid materials such as carbon fiber. As carbon has exceptional strength but is highly brittle, carbon fiber uses strands woven together into a matrix that’s much more flexible and durable than large pieces of carbon alone.
Similarly, when dealing with materials used in cutting operations, material designers commonly coat tougher, softer metals with ceramic or other metallic coatings to harden the blade surface. This process retains the benefit of the softer material underneath, which can absorb the forces associated with cutting and remain unfractured. Because of the super-hard coating, however, the blade still resists scratching while easily cutting into the softer material being cut, chopped or sheared.
How to Measure and Test for Toughness
Material designers and engineers measure materials for toughness in several different ways. The two most popular tests that indicate the toughness of a material are the standard tensile test and impact test.
The tensile test involves stretching a piece of metal, such as any type of steel, until it is pulled apart by the testing machine. After the test, the force used to pull the material apart gets plotted against the amount of strain the material underwent during the test. The impact test involves heating or cooling the metal to different temperatures, then testing how well that material can endure or absorb an impact from the testing apparatus.
Below is a more in-depth comparison between the two toughness tests.
Tensile Test
The tensile test is the most common method for testing strength vs. hardness vs. toughness because the data collected during the test can be used to understand a lot about the material. The test primarily measures how much deformation the material undergoes as more and more force is applied by pulling it apart at both ends. After the test, the measured amount of tensile force gets converted into units of stress and is plotted against the strain or distance the metal deformed under the force.
Afterward, engineers measure the area under the curve, which gives the amount of energy per unit volume that the material is capable of resisting while under tensile load. This energy per unit volume is an excellent indicator of how tough the material will be and how well it will resist fatigue stresses when used in a cutting, sawing or chopping operation.
Impact Test
The impact test incorporates temperature changes into the test, providing critical data used in industrial settings because of the wide range of temperatures in these environments. The impact test places the metal sample in the path of a large swinging ax that’s then released from a pre-set height and allowed to smash into the sample. The ax arm acts as a pendulum — the distance it swings past the metal piece is used to determine how tough or resistant to the collision energy of the impact the material is.
The impact test displays how important temperature is to the toughness of materials. When materials are cooled — especially to below-freezing temperatures — many of them experience a massive reduction in toughness. They become brittle and are easily cracked by the impact test. Generally, the tougher a material is, the more ductile and resistant to impact it will be, even at lower temperatures, compared to its more brittle counterparts.
Examples of Tough Materials for Industrial Blades
The term tough is relative because toughness always has to be coupled with strength in any given application — even when comparing hardness vs. toughness in steel. In sawing, cutting and chopping applications, the range of materials that are considered tough include:
- Medium to high carbon steels
- Stainless steels
- High alloyed steels
With ferrous metals used in machining or cutting applications, the primary consideration is the metal’s ability to resist fatigue cracking after many cutting cycles, but the blade must also keep its cutting edge long enough before service is required.
With ferrous metals, the addition of carbon makes the metal much stronger, harder and more resistant to deformation under load. Adding too much carbon past an ideal point makes the metal too hard and more prone to fracture. Carbon steel with too much carbon can also exhibit the tendency to shatter or explode apart when under stress, rather than deforming slowly over time. This creates some safety concerns when using metals that are too hard or brittle for applications that involve many impacts under cyclical or repeating forces.
The ideal material contains enough carbon and other alloying elements to make it very hard relative to the materials it’s cutting or chopping, but also ductile and tough enough to resist the forces the blade will encounter through common use. Naturally, the blade always needs to be tough enough that it bends and deforms gradually if pushed past its allowable stresses, rather than fracturing apart at once, as this ensures a safe working environment.
Custom Industrial Blades From York Saw & Knife
It’s essential to have the material know-how and manufacturing capabilities to achieve the most optimal combination of hardness vs. toughness in industrial blades. York Saw & Knife uses a wide range of metals in our industrial blade manufacturing process, including:
- High carbon steel
- Stainless steel
- Solid carbide
- Ceramic
- 52100 high carbon chromium alloy steel
- M-2 molybdenum high-speed steel
- D-2 air-hardening high carbon, high chromium tool steel
- CPM 10V high vanadium tool steel
York Saw & Knife shapes, forms, machines and cuts any of the above materials into a variety of blade profiles using different manufacturing processes. The two processes we specialize in are water jet cutting and laser cutting:
- Water jet cutting: Using high-pressure water jets of up to 50,000 psi, water jet cutting is strong enough to slice through hard metals and produce intricate, highly accurate blade profiles designed to any specifications your application needs.
- Laser cutting: Using amplified light, our team makes highly precise cuts through the metal. Laser cutting enables us to create many design features that aren’t available using conventional machining operations alone.
York Saw & Knife can also reverse engineer your existing blade or knife, matching its exact material and design. If your operation has older pieces of equipment with blades that are no longer manufactured or available for purchase, our reverse engineering process can help.
During reverse engineering, our designers conduct an optical analysis to determine the features of the blade. Next, they perform a Rockwell hardness test to accurately determine the type of metal your blade is composed of. Lastly, our team measures your blade and redesigns it until a recreation of the original blade design is produced.
Learn more about our custom blade manufacturing process by contacting York Saw & Knife today.
Choose York Saw & Knife for Your Industrial Blade Needs
Find the ideal balance between hardness and toughness for your industrial machine blades when you choose to work with York Saw & Knife for your custom industrial blade design. Our team of engineers will work with you to select the best material for your cutting application and provide the correct hardness and toughness levels for your needs.
With over 100 years of blade manufacturing experience, York Saw & Knife is your best choice for high-quality, durable and long-lasting machine blades made in the U.S. Contact us today to learn more about our custom blade manufacturing process or request a quote for your blade needs. Call us at 1-800-233-1969 to speak with a York Saw & Knife representative.
