Properties, hardness and structure of diamond

Many people know that diamond is the hardest natural material in the world. Some have heard of or may have come across the concept of diamond coating or diamond heads on cutting tools. But what exactly is the concept of diamond hardness, and what does it relate to?

Diamonds

The concept of hardness and its measurement has long remained a rather controversial issue. For a very long time they could not develop a method by which it would be possible to determine the amount of this parameter. Until Mohs came up with the idea of ​​measuring this parameter by trying to scratch one mineral with other minerals. If one of them was scratched by the others, then it was automatically assigned a lower hardness value. Taking a standard for each unit, he developed his own hardness scale with values ​​from 1 to 10.

The hardness of a diamond was responsible for 10 points; talc became the standard for one hardness point. Another common gemstone is corundum, which is divided into rubies and sapphires and has an index of 9. Thus, this most common scale and corresponding values ​​were fixed.

Why does diamond have such a high hardness rating? As it turns out, the chemical structure of diamond is pure carbon. The same carbon, which in its normalized state is graphite and whose hardness on the Mohs scale is equal to one.

Why then do they have such different properties if they consist of the same atom? This occurs due to chemical bonds and the structure of the crystal lattice. The carbon atoms in these two substances are connected differently to each other, which gives a different structure.

As you know, there is no material in nature that is harder than diamond. But recently, scientists have developed a synthetic substance, which, according to them, has this indicator by 58% more. This substance is called lonsdaleite. Lonsdaleite can withstand pressures that are 55 GPa greater than the hardest diamond can withstand. Its use is almost impossible due to its high cost. There is no particular need to use such material.

Hardness is the main indicator of tool quality

When choosing a tool for work, we are faced with such a characteristic as hardness, which characterizes its quality.

The higher this indicator, the higher its ability to resist plastic deformation and wear when exposed to the material being processed.

It is this indicator that determines whether the saw tooth will bend when sawing workpieces, or what kind of wire the wire cutters can cut through.

Rockwell method

Among all existing methods for determining the hardness of steels and non-ferrous metals, the most common and most accurate is the Rockwell method.

Rockwell method - determination of metal hardness

Carrying out measurements and determining the Rockwell hardness number is regulated by the relevant documents of GOST 9013-59

.

This method is implemented by pressing indenters—a diamond cone or a carbide ball—into the material being tested.

Diamond indenters are used for testing hardened steels and carbide alloys, while carbide balls are used for testing less hard and relatively soft metals. Measurements are carried out using mechanical or electronic hardness testers.

The Rockwell method provides for the possibility of using a number of hardness scales A, B, C, D, E, F, G, H (54 in total), each of which provides the greatest accuracy only in its own relatively narrow measurement range.

To measure high hardness values ​​with a diamond cone, the “A” and “C” scales are most often used. They are used to test samples made of hardened tool steels and other hard steel alloys. And comparatively softer materials, such as aluminum, copper, brass, and annealed steel are tested with ball indenters on the “B” scale.

Example of Rockwell hardness designation: 58 HRC or 42 HRB.

The numbers in front indicate a number or a conventional unit of measurement. The two letters after them are the Rockwell hardness symbol, the third letter is the scale on which the tests were carried out.

(!)

Two identical values ​​from different scales are not the same thing, for example, 58 HRC ≠ 58 HRA. Rockwell numerical values ​​can only be compared if they belong to the same scale.

Rockwell scale ranges according to GOST 8.064-94:

Locksmith tool

Tools for manual metal processing (chopping, cutting, filing, branding, punching, marking) are made from carbon and alloy tool steels. Their working parts are subjected to hardening to a certain hardness, which should be within the following limits:

Installation tool

This includes various wrenches, screwdrivers, and pliers. The hardness standard for their working parts is set by current standards. This is a very important indicator, which determines how wear-resistant the tool is and can resist crushing. Sufficient values ​​for some instruments are given below:

Metal cutting tool

This category includes consumable equipment for metal cutting, used on machine tools or with hand tools. For its manufacture, high-speed steels or hard alloys are used, which retain hardness in cold and overheated states.

Note:

Some milling cutter manufacturers indicate in the marking the hardness not of the cutter itself, but of the material that it can process.

Fasteners

There is a relationship between the strength class of a fastener and its hardness. For high-strength bolts, screws, and nuts, this relationship is reflected in the table:

If for bolts and nuts the main mechanical characteristic is the strength class, then for such fasteners as lock nuts, washers, set screws, hardness is no less important.

The following minimum/maximum Rockwell values ​​are established by the standards:

Relative hardness measurement using files

The cost of stationary and portable hardness testers is quite high, so their purchase is justified only by the need for frequent use. Many craftsmen, if necessary, practice measuring the hardness of metals and alloys relatively, using improvised means.

Measuring hardness using files

Filing a sample with a file is one of the most accessible, but far from the most objective, ways of checking the hardness of steel parts, tools, and equipment.

The file must have a non-blunted double cut of medium size No. 3 or No. 4.

The resistance to filing and the accompanying grinding noise makes it possible, even with little skill, to distinguish unhardened steel from moderately (40 HRC) or hard-hardened (55 HRC).

For testing with greater accuracy, there are sets of calibrated files, also called scratch hardness testers. They are used for testing saw teeth, milling cutters, and gears. Each such file carries a certain value on the Rockwell scale.

Hardness is measured by briefly scratching the metal surface alternately with files from the kit. Then two close ones are selected - a harder one, which left a scratch, and a less hard one, which could not scratch the surface.

The hardness of the metal being tested will be between the hardness values ​​of these two files.

Hardness conversion table

To compare Rockwell, Brinell, Vickers hardness numbers, as well as to convert the indicators of one method to another, there is a reference table:

Note:

The table shows approximate ratios of numbers obtained by different methods. The error in converting HV to HB values ​​is ±20 units, and the error in converting HV to HR (scale C and B) is up to ±3 units.

When choosing a tool, it is advisable to prefer models from well-known manufacturers. This gives confidence that the purchased product is manufactured in compliance with technology, and its hardness meets the declared values.

The relationship between Rockwell and Brinell hardness of various products.

Articles about products 11/19/2020 10:40:56

Dmitriy

Thanks for the article, just what I was looking for) I wanted to make sure that I took normal screwdrivers and not bullshit ones)

Links

This page was last edited on August 27, 2019 at 00:15.

Advantage of the Vickers method

The advantage of the Vickers method is the ability to measure the hardness of samples and small products made of hard alloys, ferrous and non-ferrous metals, thin sheet steels, hardened and non-hardened steels, castings, semi-precious and precious stones, galvanized, chrome-plated and tin-plated surface coatings of various thicknesses. Measuring hardness does not take much time (requires careful preparation of the surface being tested).

How is the Vickers hardness of test samples calculated?

After the test is completed, the lengths of the indentation diagonals are measured and, based on the average length, the hardness of the sample is calculated according to the tables (for more details, see GOST 2999-75).

Rockwell hardness

The hardness of materials is an integrating indicator of their mechanical properties. There is an empirical correspondence between the hardness value and a number of mechanical properties (for example, compressive, tensile or bending strength).

With the development of mechanical engineering, the need arose to have general methods for measuring hardness. At the beginning of the 20th century, Professor Ludwig developed the theoretical part of the method for determining hardness with a diamond cone. In 1919, Hugh and Stanley Rockwell patented a hydromechanical device, which was named the Rockwell hardness tester.

The relevance of this device is caused by the need to use non-destructive methods of hardness control in the bearing industry. The existing Brinell (HB) method is based on measuring the indentation area of ​​a 10 mm diameter ball.

The imprint is formed using a ball of hardened steel or tungsten carbide, which is pressed into the sample with a certain force. The Brinell method is used to determine the hardness of non-ferrous metals or low-alloy steels and is not applicable to hardened steel samples.

This is due to the fact that the working load is 3000 kgf. The ball is deformed, so the Brinell method cannot be considered a non-destructive testing method.

Rockwell hardness test method

Hardness is a characteristic of a material that is opposite to plasticity, the ability of a material to “flow” under load. The Rockwell hardness measurement technique is intended for non-destructive testing of the hardness of the least ductile materials - steels and their alloys.

The versatility of the method lies in the presence of three hardness scales, which are calibrated for measurement under one of three loads (60, 100 and 150 kgf) to work with one of the measuring heads.

A diamond cone with an angle of 120° and an apex radius of 0.2 mm or a hardened ball with a diameter of 1/16“ (1.588 mm) is used as the working body of the measuring head.

The method is based on recording the direct measurement of the depth of penetration of a solid body by a measuring head (indenter) into the sample material. The depth of the indentation characterizes the ability of the material to resist external influences without forming a roll of displaced metal around the indenter.

The Rockwell hardness unit is a dimensionless value, which is expressed in conventional units up to 100. The displacement of the indenter by 0.002 was taken as a unit of hardness.

Metal hardness according to Rockwell: table

The table was created for a visual comparison of the Rockwell and Brinell methods.

(*) — The presented table of correspondence between hardness on the Rockwell HRA, HRC and HRB scales and hardness on the Brinell scale is for reference only and cannot be used for applied solutions. For technical use, one should rely on data according to GOST 8.064-79 for the Rockwell scales HRA, HRC and Super-Rockwell HRN, HRT, the values ​​in which are reduced to the reference value HRCе.

How does the Rockwell hardness scale work?

11 scales have been developed for determining hardness (A...H, K, N, T), which are designed to work in various combinations of “intendent - load”. For example, scales B, F and G are used for measuring a ball Ø 1.588 with a load on scales B, F - 60 kgf and on scale G - 150 kgf. For scales E, H and K, a Ø 3.175 mm ball with different loads is used.

The following scales are common:

• A - with a cone and a total force on the measuring head of 60 kgf (10 kgf - preliminary load plus 50 kgf - main load).
• B - with a ball Ø 1.588 and a total force on the measuring head of 100 kgf.
• C - with a cone and a total force on the measuring head of 150 kgf.

The preload, which allows you to select hardness tester gaps and destroy the oxide film on the sample, is the same for measurements using any scale.

A dial-type device is used as an indicator, which allows recording the movement of the indenter by 0.002 mm, taking into account the movement of the levers. The maximum movement of the measuring head under working load is 0.2 mm. The indicator contains a scale containing 100 divisions for each measurement method (for example, TK 2 or NOVOTEST TS-R).

Measuring ranges for scales (materials):

• HRA - 20...88 units. (corrosion-resistant and heat-resistant steels)
• HRB - 20...100 units. (copper alloys, ductile iron, low-carbon steels)
• HRC - 20...70 units. (high carbon steels after heat treatment)

Scales A and C are combined, scale B is highlighted in color or displayed separately.

Rockwell hardness tester: what is it and how does it work?

The stationary hardness tester is a solid-cast rigid U-shaped structure (laid on its side) and consists of 2 blocks:

• The measuring unit (top) consists of a dial indicator, which is in contact with the load suspension lever. To eliminate the occurrence of shock loads when the indentation mode is turned on, the suspension arm has a hydraulic damper.
• The installation movement block (bottom) consists of a screw pair with a large pitch for manual movement of the table. The screw pair is used to create preload and large movements of the table. This makes it possible to measure hardness on parts with dimensions much larger than the dimensions of a 20 mm thick sample. The hardness of the table surface is not lower than HRC 50.

Hardness testers may have a displacement motor, an electronic measurement system with a display, and other improvements that do not affect the measurement technique.

Measurements are carried out under normal conditions (temperature - 18...23° C, humidity 70...80%).

Sample requirements:

• the sample (part) must lie stable, not spring, not wobble;
• the surface roughness of the sample is not lower than Ra 2.5 according to GOST 2789-73.

A sample is made for a batch of parts, which undergoes heat treatment along with the parts.

Operating procedure:

• the sample is placed on the table;
• using a lead screw, the sample is brought to the intendor and pre-loaded (the indicator is set to 0);
• the lever (button) turns on the mode of pressing the intendor into the sample;
• when the indicator arrow stops (2...8 seconds after loading), the main load is removed and the hardness value is read.

Modern Rockwell hardness testers, equipped with digital measuring systems, have devices for automatic approach, preloading, control of the amount of force and time of the working load. All improvements must ensure compliance with the requirements of GOST 23677-79.

Pros and cons of the method

The main advantage of the Rockwell hardness measurement method is its versatility. Measurements are carried out with three variable parameters, which allows expanding the scope of its application.

Other advantages of the method:

• refers to non-destructive methods (can be used to control finished products);
• allows you to control cylindrical products in a prism with a diameter of 6 mm or more or with surface curvature R3, taking into account amendments (Appendix 3 according to GOST 9013-59 “ISO 6508-86”);
• allows you to control sheet material with a thickness of 0.3...1.0 mm on the HRA scale (super Rockwell);
• short measurement time (no more than 2 minutes with testing on a control sample);
• ease of reading the results.

The disadvantages include lower accuracy and repeatability of measurements compared to the Brinell and Vickers methods. However, the disadvantages are fully compensated by the advantages.

Measurement equipment

At the time of development of the method under consideration for measuring hardness, there was no special equipment. After the importance of this physical and mechanical characteristic was established in mechanical engineering and other areas of industry, special equipment was developed, which is also based on pressing a ball or cone into the test object. Modern equipment allows you to control with high precision the amount of applied force and holding time. A hardness tester measures the hardness of, as a rule, small objects that are samples of the resulting workpiece. This is due to the very compact size of most models of the devices in question.

Rockwell hardness of titanium - Metalist's Handbook

The concept of metal hardness was previously known only to graduates of technical universities, workers of machine-building plants and blacksmiths. This term came into use with the modern knifeman with the adoption of the law on weapons and GOST standards, which provide signs on the basis of which a knife can be classified as a bladed weapon.

One of the mandatory characteristics by which a particular product is classified as a bladed weapon is the hardness of the steel from which the knife blade is made (or, as it is called in GOST, the warhead of a bladed weapon).

And starting from this moment, the nyfomaniacs in Russia began to slowly read reference books that provide the characteristics of different steels, explanations of the differences between powder and laminated steels, and of course the steel hardness indicators, those very noticeable HRC.

If one car enthusiast can ask another about how many “cubes are in the engine,” then an advanced knifomaniac, looking at the characteristics of a field knife that says “57-59 HRC,” can seriously determine that this is a flimsy model for bushcraft and it belongs on kitchen.

This article will tell you in a simple and understandable form what kind of beast this HRC is, where it came from and why it is needed at all.

Interesting fact : On American and European websites, among the parameters indicated by sellers or manufacturers, it is extremely rare to find such a parameter as steel hardness. This issue is not regulated in any way by law, so the average inexperienced buyer does not need this parameter.

So, what do we need to know about the hardness of metals?

Since ancient times, man has encountered the concept of hardness of materials. I also quickly realized that different materials differ from each other in hardness and strength.

If you hit a stone with a stick, the stick will either break or bounce off. If you hit a stick with a stone, the stick will break. If a coconut falls from a tree onto a pebble beach, it will break.

And if you hit a softer stone with flint for a long time and diligently, then you can quite easily make a head for a stone axe.

Gradually, in the process of evolution, our ancestors realized that different materials have different hardness, and depending on this hardness, they do or do not have the desired properties. Thus was born a method for determining the hardness of a material by comparing it with a certain standard.

Thus, a good carpenter can determine the degree of shrinkage of a log by tapping it with a mallet made of a harder type of wood. Using a special hammer, a potter can determine the degree of readiness of pottery. Willingly or unwittingly, each of us at least once in our lives has resorted to a similar method of determining the hardness of an object.

However, until recently, the most common method for determining the hardness of a material was the sclerometric method. Sclerometry is a physical process where the material being tested scratches (or scratches) a reference sample. If the material being tested scratches the standard, it means the material being tested is harder.

If the material being tested cannot leave a mark on the standard and is easily scratched by the standard, then the material being tested has a hardness less than that of the standard.

Now this procedure seems ridiculous to us, but until recently, this was the only way to determine the hardness of a material.

How else could the ancient Sumerians determine that it was possible to write inscriptions with a sharp stick on almost dried clay?

The issue of determining the hardness of materials (especially stones and metals) became acute at the end of the 18th and beginning of the 19th centuries, with the development of geology and the beginning of the flowering of mechanical engineering.

It was at this time that the “Mohs scale”, known to all physicists and archaeologists, appeared. However, the first to propose measuring the hardness of metals by comparing them with a standard was the French naturalist of the mid-18th century, Rene Antoine Reaumur.

Reaumur actively conducted experiments related to the melting and processing of metals and therefore he was faced with the acute question of determining the various characteristics of the alloys that he obtained in the process of his research.

His ideas were picked up and developed by the German naturalist and geologist Karl Friedrich Christian Mohs. In 1811, he came up with a system for standard comparison of minerals, which now bears his name. Until about the middle of the 20th century, this scale was actively used by geological exploration parties around the world.

The Mohs scale is a comparative table in which known minerals of different hardness are indicated and their hardness is measured in the following criteria:

• Scratched with a fingernail;
• Scratched by copper;
• Scratched by glass;
• Scratches glass;
• Processed only with diamond.

The softest reference mineral is talc, and the hardest mineral is diamond. The hardness of talc on the Mohs scale is “1”, the hardness of diamond is “10”.

Between talc and diamond, as hardness increases, there are: gypsum (hardness 2), calcite (hardness 3), fluorite (hardness 4), apatite (hardness 5), orthoclase (hardness 6), quartz (hardness 7), topaz (hardness 8 ), corundum (hardness 9).

This simple method of determining the hardness of minerals turned out to be indispensable in field conditions.

In addition to the Mohs scale, there are other methods for determining the hardness of materials, which were actively developed at the end of the 19th and beginning of the 20th centuries. There are usually four most well-known methods for determining the hardness of metals:

• Brinell method;
• Vickers method;
• Shore method;
• Rockwell method.

Looking ahead , we note: all these methods are similar to each other, since they are based on pressing a reference sample into the surface of the metal. Only the shape of the standard, the pressure force, and the formula for calculating the value differ.

The element that is pressed into the surface of the metal is called an “indenter”. A steel ball (Brinell method), a diamond cone (Rockwell method), or a diamond pyramid (Vickers and Shore methods) can be used as an indenter.

The demand for these methods of measuring metal hardness is explained by their following features:

• all the methods described make it possible to measure each finished sample separately, which undoubtedly improves the quality of serial products;
• there is no destruction of the finished product (for example, a knife) and in the future it can be used for its intended purpose;
• high measurement speed, which means high productivity of the method.

Important : Test results using different methods are not comparable.

Let's consider each method separately, paying special attention to the Rockwell method.

Brinell method

This method was proposed by the Swede Johan August Brinell in the early 20th century. At that time, this was the most accurate way to determine the hardness of metals. Steel balls of various diameters (from 1.2 to 10 millimeters) are used as an indenter. The diameter of the ball is selected depending on the expected hardness of the metal.

Brinell divided metals into several groups, combining them by hardness. The group with minimal hardness included tin, lead and their alloys. The group with the highest hardness included titanium, nickel and steel alloys. For metals with minimal hardness, a ball of the smallest diameter is used; for metals of high hardness, a ball of the largest diameter is used.

Measurements take place according to the following algorithm: the sample being tested is placed on a special table, and an indenter is pressed into the sample from above with a gradually increasing load.

This happens over a short period of time from 2 to 8 seconds. After reaching the maximum level of dynamic load, the load is maintained in a static state for approximately 10 seconds.

After completing the procedure, the diameter of the indentation is measured on the sample being tested.

Hardness is calculated using a formula that takes into account the applied load, the diameter of the indenter and the diameter of the indentation. Hardness is indicated in the format kgf/mm2, display format HBW.

Vickers method

When measuring hardness using the Vickers method, a pyramid-shaped tip is used as an indenter, the edges of which converge at an angle of 136 degrees. To ensure the accuracy of the test, it is important to observe several points:

• the load must be placed strictly in the center of the diamond tip;
• the load application vector must be strictly perpendicular to the surface of the test sample.

Measurements take place according to the following algorithm: the sample being tested is placed on a special table, and the indenter is pressed into the sample from above immediately with the required load level (the maximum possible value is up to 100 kgf). Next, the indenter is held under load for 10-15 seconds. After removing the indenter, the indentation depth and indentation diagonal are measured.

Next, a calculation takes place according to the form, which takes into account the ratio of the applied load to the diagonal of the indentation and the time during which the test took place. Hardness is indicated in kgf/mm2 format, display format HV. The Vickers method, due to the use of a diamond tip, allows for more accurate measurements than the Brinell method.

Shore method

This method is a continuation of the well-known “tapping” method, when by tapping a part or workpiece, the master tries to determine its hardness. The method was proposed by the American engineer Albert Shore at the beginning of the 20th century. The essence of the method is that the hardness of the metal is determined by the height of the indenter's rebound.

The device for measuring hardness consists of a hollow tube, on which a cut is made along its entire length with marked divisions. The tube is installed on the surface of the sample being measured and a striker with a diamond tip is dropped into it. The hardness of the metal is determined visually by the rebound height of the striker. Essentially, this device is a “sclerometer”.

Shore hardness display format HSD (or HSC, depending on the scale used).

Rockwell method

Recently, this method has become widespread due to its simplicity and versatility. The Rockwell method does not require additional calculations and the measurement value is immediately displayed on the instrument scale.

This method was invented by two namesakes who shared the same surname Rockwell. Their names were Hugh and Stanley.

Both of them worked in a metallurgical holding in Connecticut, where at that time the issue of operational measurement of the hardness of bearing elements arose.

The existing Brinell method did not allow for high-precision measurements, and also did not allow testing on each finished specimen.

Measurement equipment

At the time of development of the method under consideration for measuring hardness, there was no special equipment. After the importance of this physical and mechanical characteristic was established in mechanical engineering and other areas of industry, special equipment was developed, which is also based on pressing a ball or cone into the test object. Modern equipment allows you to control with high precision the amount of applied force and holding time. A hardness tester measures the hardness of, as a rule, small objects that are samples of the resulting workpiece. This is due to the very compact size of most models of the devices in question.

The features of the equipment used include the following points:

1. The test sample is usually placed on a table.
2. The diamond tip is lowered using a weight lever.
3. The important point is that the tip goes down smoothly. This is achieved by using a handle with an oil shock absorber.
4. The holding time of the applicable load depends on the size of the test specimen. As a rule, the indicator is 3-6 seconds. The force of impact is also determined by the size of the workpiece.
5. Important parameters are entered using a special programming console. Due to the fact that the equipment controls the applied force and holding time, the accuracy of the results obtained is quite high.

The equipment in question is produced by a fairly large number of different companies. At the same time, the cost of supply can fluctuate within a fairly wide range.

What is Rockwell Hardness (HRC)?

The HRC rating refers to the Rockwell Hardness Scale, Part C. The Rockwell scale is widely used by metallurgists to determine how hard a piece of steel is: the higher the number, the harder the steel. a particular metal is important to a knife maker because a harder steel will hold an edge better than a softer steel.

There are several different Rockwell scales; each is used for different materials. The C scale is used specifically to grade steel used in knives and tools.

Steel hardness index

The highest HRC is not necessarily the best.

Harder steel tends to hold an edge better than softer steel, but it is also more likely to crack or fail. In fact, if it's really hard, it can break like glass on concrete!

The steel used to make a knife also has a lot to do with how well the knife will hold an edge. Each individual steel alloy has its own optimal range that balances hardness with performance and purpose.

So why does a knife's Rockwell Score matter? What is a good Rockwell hardness for a knife?

The hardness of a knife is very important in terms of its performance and durability. For example, a harder steel with an RC of 58-62 will hold an edge better than a softer steel.

However, this same hard steel is less strong and more prone to cracking or even breaking.

Some kitchen knives with high hardness require special care to avoid damaging the thin cutting edge.

Softer steel is more durable due to its high elasticity. Most axes and chisels use softer steel to withstand the impacts they encounter in everyday work.

Since pocket knives and hunting knives are not typically used for planing and chopping wood, they benefit from using stronger steel that maintains excellent sharpness for cutting soft materials.

However, a survival knife that you're going to put extreme effort into will benefit from a Rockwell hardness of 55-58. A knife that could cut bones and hard wood must first of all be durable. A knife with a lower hardness may become dull faster, but is more likely to survive a large number of impacts and mechanical damage.

Rockwell testing helps knife makers balance the three most important factors that can affect the quality of their finished products: hardness, flexibility and toughness. Having these three factors in the right balance allows them to produce knives for a variety of uses.

There are several different abbreviations that may be used by a knife maker when specifying hardness: HR, HRc, HR C, RC, Rc, Rockwell C, Rockwell Hardness C.

Regardless of how knife steel is written, they all refer to the same C scale.

This can get a little confusing, but just know that the ratings themselves are the same - no matter what designation the manufacturer uses.

Stanley P. Rockwell was a metallurgist at a New England ball bearing plant in 1919. He developed a hardness scale to measure the hardness of bearing balls quickly, accurately and with high repeatability.

Manufacturers of everything from watch springs to train wheels have long needed such testing and quickly adopted the Rockwell scale for all types of steel, as well as other metal parts. Eventually, the test was even adapted to test non-metallic materials—even plastics.

How is hardness measured on the Rockwell scale?

The Rockwell scale measures the relative hardness of a metal. It is based on how deep the dent is when struck by a heavy object. So how do they test metal?

First, the metal must be heat treated and completely flat. Otherwise, the test results will be inaccurate.

One method is to use a diamond-tipped cone to forcefully strike the metal. Testers then measure how deeply the cone penetrates the surface. This measurement is then converted into a scale that shows the different metals that were tested and how they all relate to each other.

One of the small disadvantages of testing a knife blade is that it leaves a small pinhole indentation on the surface, which some may consider a defect. The test mark may be hidden if the test is carried out in an area that is under the handle.

The Rockwell test actually consists of two tests. During the first test, only a small amount of force is applied using a diamond tip, similar to a pencil in a drill press.

This ensures that the test area is completely flat and is the target for the main pressure test. After the first measurement is made, the test is repeated at the same point.

The pressure increases sharply for this second test, with approximately 150 kg. pressures are on this diamond tip.

The difference between the pressure used for the first and second test is the Rockwell hardness number. Two (or more) tests on the same piece of metal will give an average value for that particular piece of steel.

Concept

The hardness of the workpiece is a feature of the material due to which the iron creates resistance upon contact or penetration of a foreign object or body into its layers.
It should not be subject to deformation or destruction under certain loads. This parameter serves the following purposes:

Monitoring the condition of the metal over time.

Extraction of information regarding the minimum and maximum permissible values ​​of the workpiece.

Analysis of the results of processing using high temperatures.

This criterion shows how the part will perform in further use, as well as what its shelf life is. For research, both raw elements and finished parts are used.

Quenching and tempering of high carbon steel

High-carbon steels usually have high hardness as if by themselves. However, the hardening process can make them significantly harder, although it also makes them more brittle. Therefore, hardening is almost always combined with tempering. As a result of tempering, the hardness of the steel decreases and its ductility increases.

After annealing, normalizing or tempering, carbon steel consists of ferrite, free and lamellar, and inclusions of carbides (cementite). Ferrite has low strength and high ductility. Cementite has a very high hardness (about 800 HB) and practically zero ductility. With a small number of cementite inclusions, plastic deformation develops relatively easily and the hardness of the steel is therefore low.

Purpose of the hardness tester

• Quick control of materials and parts, including complex shapes, quality control of heat treatment, determination of the hardness of various parts of mechanisms during their repair.
• The information layer for a dynamic sensor is about 0.8 mm. This indicates the possibility of developing a technique for controlling the depth of the nitrided layer to 0.7 - 0.75 mm for products made of structural steels (for example, grades 38khmyua, 18kh2n4ma, etc.).

Key Features

• Hardness measurement using the most common hardness scales in metalworking, and in particular in mechanical engineering: Brinell (HB), Rockwell (HRC), Leib (HL), etc.
• Hardness measurement using additional (custom) scales (10 scales).
• Changing the sample size.
• Discards the maximum and minimum values ​​when calculating the average.
• Automatic recording of sensor position.
• Automatic accounting of calibration corrections to measurement results to take into account the influence of various factors (geometric and mass-dimensional deviations of the controlled volume).
• The method of calibration corrections allows you to expand the range of controlled products, eliminating the need to grind small parts into a massive plate.
• Recalibration of the entered scales (correction of the calibration dependence).
• Storing in memory settings for various commercially produced products to minimize labor costs and errors when preparing the device for operation.
• Storing measurement results for serially produced products in memory with recording of the batch number and measurement date.
• Three-color (lower - normal - higher) threshold indication of product hardness compliance with the requirements of technological documentation.

Additional features

• Saving measurement results for batches of serially produced products in the device memory and statistical processing of the results.
• Calibration of new (custom) scales.
• Output to the actuator for automatic sorting of controlled products in conveyor production conditions.
• Input for a feedback signal from the actuator to determine the moment the conveyor is ready to measure the next product.
• Setting the calendar and clock.
• Setting the backlight operating time, threshold indication, result display time, auto-off period, change the interface language.
• View measurement statistics.