How to measure metal hardness

Hardness testers for metals. Rockwell and Brinell method

The hardness of metals is understood as their ability to plastically deform under loads that are applied to the part as a result of the introduction into it of an element with a higher hardness - an indenter.

Hardness tests are considered one of the most common, since they determine both the strength of the product and its ability to resist time-varying loads.

At the same time, unlike other control methods, hardness tests are non-destructive, and hardness testers for metals can be quite compact.

The essence of methods for determining the hardness of metals

Tests can be carried out both on reference samples (made from the same metal and subjected to the same heat treatment) and directly on finished parts. In the latter case, it is necessary to take measures to ensure that the tested product does not subsequently suffer external damage.

The choice of hardness testing method depends on:

1. Initial mechanical indicators of strength, elasticity and ductility of the product.
2. Overall dimensions of the part (or the junction of adjacent structural elements, if hardness is established in the area, for example, of a weld).
3. Final result: establish the hardness of the product itself, or the hardness of only its surface (performed for parts that have undergone heat treatment or another type of surface hardening).
4. Requirements for the conditions, time and place of testing. For example, in field conditions, portable hardness testers are more suitable than stationary ones.
5. Stability of measurement results and their reproducibility during repeated testing.

Hardness can be measured by three groups of methods - mechanical (static and dynamic), as well as ultrasonic. In addition, a distinction is made between hardness at room and elevated temperatures (the so-called “hot hardness”). Regardless of this, the physical essence of all methods is the same - a deforming element is introduced into the sample, the movement of which is read on a special scale.

Hardness is considered as the resistance of a metal to irreversible plastic deformation, and therefore differs from other measurements by the presence of special unified instruments - hardness testers for metals.

How to determine the chemical composition of a metal, read the link //proinstrumentinfo.ru/analizator-metallov-i-splavov-tsena/

Brinell hardness testers

The method of determining hardness using the Brinell method is to press a ball of either hardened steel or carbide into the surface of the part. As a result, an imprint in the form of a hemisphere of a certain diameter and depth remains on the metal, which determines the Brinell hardness measure HB.

The method has the following requirements:

1. The indenter must be of strictly defined dimensions. The standard diameters are 10; 5; 2.5; 1.25 and 1 mm. The choice depends on the approximate hardness of the test sample and the load on it:

Ball diameter, mm	Recommended load on the indenter, kN depending on the material of the product
Steels, cast irons, high-strength alloys	Most non-ferrous metals and alloys	Aluminum	Bearing alloys	Lead, tin, babbits
10	29,42	9,8	4,9	2,45	1,225
5	7,335	2,45	1,225	0,613	0,307
2,5	1,84	0,613	0,307	0,153	0,077
1,25	0,459	0,153	0,076	0,038	0,019
1	0,294	0,098	0,049	0,0245	0,013
Recommended range for measuring HB hardness	67450	22315	11158	678	339

1. It is impossible to measure the HB hardness of the same part using different types of Brinell hardness testers.
2. The ratio of the load applied to the product and the area of ​​the print must be constant.
3. When referring to the NV value established during measurements, it is necessary to indicate the conditions under which the result was obtained.
4. The part at the place where hardness is measured must have a smooth and well-polished surface of sufficient thickness (otherwise there may be deformation on the reverse side that impairs the accuracy of the result).
5. It is unacceptable to determine hardness if the test point is located close to the edge of the part.

The Brinell method is unsuitable if the measured hardness exceeds 450 HB: in this case, deformation of the contact surface of the indenter itself occurs.

Hardness testers for metals that implement the Brinell method are divided into devices of the TSh type and the BTB type.

Stationary hardness testers for metals type ТШ, with a mechanical drive from an electric motor, consist of the following components:

• Loading unit, which includes a mandrel with an indenter, a return spring and a housing;
• Drive unit consisting of an electric motor and gear system;
• A lever mechanism that transfers the workload to the ball;
• Desktop;
• Control panels and monitoring of measurement results.
• Counterweights with weights;
• C-shaped bed.

A Brinell hardness tester works like this. The part with the test surface facing up is placed on the table, after which it is raised to the stop located in the indenter body. Next, the electric motor is turned on, which moves the indenter body.

He, overcoming the resistance of the springs, sets in motion the ball, which is pressed into the metal. The final result is read on a scale.

The ratio of the arms of the lever mechanism, as well as the total weight of the loads on the counterweight, is set depending on the expected measurement result (see table above).

Hardness testers for metals of the BTB type have some operational advantages over TS devices: they have an increased size of the working table space, loading modes are changed mechanically, and a more accurate optical system is used to read the result. Work on BTB hardness testers is carried out in the same sequence as on TSh devices, but after testing the sample is scanned by a measuring head, with the result displayed on the screen.

This method is also suitable for determining the hardness of products that are operated at elevated temperatures. To do this, a bath with a liquid heating the sample is placed on the table, and oil is used for temperatures up to 300°C, and molten salt is used for higher temperatures. The sample is placed in a bath on an asbestos board, after which the hardness is measured using the usual method.

Portable hardness testers for metals of the TShP type are affordable and easy to use. The test head of the device is installed on the part at the measurement location and secured with a clamp or special grips. The load is created manually and controlled using an indicator scale. To measure the result, a portable MPB type microscope is used.

The measured print is compared with the values ​​given in the conversion tables.

Hardness testers for metals using the Brinell method have a number of limitations in their use:

• The elastic deformation of the part under load is not taken into account.
• The dynamics of the test (time and speed of indentation of the indenter) very much depend on the initial hardness of the metal.
• The surface at the test site must be strictly perpendicular to the axis of movement of the indenter.
• When repeating hardness measurements, the distance between adjacent prints must be at least 0.20.6 times the diameter of the ball.

Rockwell hardness testers

The Rockwell method of determining the hardness of metals consists of pressing a diamond cone or hardened steel ball into the previously ground surface of the sample. Unlike the previous method, Rockwell hardness involves determining the depth of indentation. The Rockwell method is considered more efficient, and in such hardness testers both the testing process and the subsequent processing of its results are automated.

The essence of the Rockwell method is that a certain reference point is preliminarily selected, and the indenter penetration depth obtained for this coordinate is subtracted from the arbitrarily selected maximum indentation depth.

The Rockwell method has several varieties, each of which is used under certain test conditions (see table):

Method option	A	IN	WITH	F	N	T
Indenter shape	Cone	Ball	Cone	Ball	Cone	Ball
Indenter material	Diamond	Steel	Diamond	Steel	Diamond	Steel
Symbol for hardness	HRA	HRB	H.R.C.	HRF	HRN	HRT
Hardness measuring range	6080	35100	3070	60100	1792	594
Metals	Very high hardness steels	Medium hard steels, non-ferrous alloys	High-hardness steels	Thin sheet metals	For testing thin or small products

Stationary hardness testers for metals that implement the Rockwell method (type TK) are divided into devices with electrical and mechanical drives. Manual hardness tester TK includes:

1. A movable measuring table on which the part is mounted.
2. Lever loading drive.
3. Measuring system (it can be with digital or analogue indication of the result).
4. Working measuring head, with adjustable settings.
5. Oil shock absorber.
6. C-shaped bed.

The sequence of operation of the Rockwell hardness tester is as follows. The sample with the ground surface up is placed on the measuring table, after which it is moved upward until the indenter begins to press into the surface, which is monitored on the hardness tester scale. This is how preliminary loading occurs, the end of which is indicated by the vertical position of the large arrow.

This means that the indenter has penetrated into the surface to a depth at which the elastic deformation of the metal has already turned into plastic. Next, the handle is released, which is returned to the stop by the shock absorber, and the test product is loaded with the main force. In the final position, the load on the part must be at least 510 s, when the desired Rockwell hardness value appears on the indicator.

After this, use the handwheel to return the table to its original position and remove the part from it.

The conventional Rockwell hardness unit corresponds to 2 µm of movement of the working tip of the indenter.

There are also portable varieties of Rockwell instruments. The most popular is the TKP type device, the test head of which is attached to the part being measured. The load from the handle is produced by a three-jaw roller, which transmits force to the spindle in which the indenter is located. The sequence of application of loads - preliminary and main - in TKP-type devices is the same as in stationary hardness testers for metal, where the Rockwell method is used.

Other types of hardness testers for metal are also used - Shore, Vickers, etc. Their price depends on the technical characteristics of the device. For example, the price range for portable dynamic hardness testers is 30,000 to 50,000 rubles, for stationary installations - from 275,000 to 420,000 rubles.

Source: https://proinstrumentinfo.ru/tverdomery-dlya-metallov-statsionarnyj-portativnyj-ultrazvukovoj-tsena/

Standard hardness standards

Standard hardness measures of the first and second categories (hereinafter referred to as measures) are intended to reproduce the hardness of metals according to all standardized hardness scales. Measures are used when checking and calibrating instruments for measuring the hardness of metals (hereinafter referred to as hardness testers).

Description

The measures are made in the form of rectangular or round tiles from carbon or alloy steel in accordance with GOST 9031-75 “Exemplary hardness measures. Technical conditions".

The MET Center has a production license No. 000087-IR, issued by the Federal Agency for Technical Regulation and Metrology.

The measures are manufactured in the modifications MTP-MET, MTSR-MET, MTB-MET, MTV-MET, MTSH-MET and are designed to reproduce the hardness of metals according to the Rockwell, Super-Rockwell, Brinell, Vickers and Shore scales, respectively.

• MTP-MET: Rockwell (HRA, HRB, HRC)
• MTCP-MET: Super-Rockwell (HRN, HRT)
• MTB-MET: Brinell (HB)
• MTV-MET: Vickers (HV)
• MTSH-MET: Shora (HSD)

Marking

According to GOST 9031, the following is applied to the side surface of the standard hardness measure:

1. trademark of the manufacturing company (MET Center);
2. verification month;
3. the serial number of the measure assigned by the body of the state metrological service that carried out the initial verification;
4. the hardness value of the measure with the designation of the hardness scale.

The State verification mark, belonging to the state metrological service body that carried out the verification, is applied to the working surface (in the lower right corner).

Advantages

• minimal scatter of hardness readings over the surface;
• long-term stability;
• custom manufacturing (according to all scales and hardness ranges);
• delivery individually, as well as in sets (GOST 9031).

Compliance with international and national standards

• ISO 6506, ISO 6507, ISO 6508
• ASTM E92, ASTM E384, ASTM E18, ASTM E10

Source: http://www.tverdomer.ru/products/hardness-measures/

Hardness tests

CONTENT

Hardness is the property of a material to resist elastic and plastic deformation or destruction when another, harder body that does not receive residual deformation - an indenter - is introduced into the surface layer of the material.

Methods for determining hardness depending on the temporary nature of the application of load and measuring the resistance to indentation of the indenter are divided into:

• static
• dynamic
• kinetic

The most common are static methods, in which the load is applied to the indenter smoothly and gradually, and the holding time under load is regulated by standards for the corresponding methods.

In dynamic methods for determining hardness, the indenter acts on the sample with a certain kinetic energy expended on elastic recoil and/or the formation of an indent; dynamic hardness is often also called the hardness of the material upon impact. Impact hardness characterizes the resistance to penetration not only on the surface of the sample, but also in a certain volume of the material.

Kinetic methods for determining hardness are based on continuous recording of the process of indentation of the indenter with recording of the diagram “load on the indenter - depth of penetration of the indenter. The peculiarity of this approach is to record the entire kinetics of the process of elastoplastic deformation of the material during indentation of the indenter, and not just the final test result, as with other methods.

Based on the principle of load application, methods for determining hardness can be divided into indentation, rebound, scratching and cutting methods.

Indentation methods are the most common. Hardness in this case is defined as the resistance that the test body provides to the penetration of a harder indenter and primarily reflects the resistance of the surface layers of the material to plastic deformation.

Rebound methods are based on measuring hardness by the height of the rebound of the striker falling onto the test surface. In this case, hardness primarily reflects resistance to elastic deformation. Rebound hardness testing is widely used to control the quality of mill rolls, large products and structures using portable instruments.

Method for measuring hardness by scratching

In scratching and cutting methods, hardness is defined as the material's resistance to scratching or cutting, respectively. The scratching method was developed by Mohs at the beginning of the 19th century; they were given a scale of mineral hardness based on the ability of one to scratch the surface of another. This ten-point scale (from talc No. 1 to diamond No. 10) is used in mineralogy, as well as for assessing the hardness of technical ceramics and single crystals.

When determining hardness by all methods (except microhardness), the integral value of the material’s hardness (averaged for all structural components) is measured.

Hardness values ​​cannot be unambiguously translated into values ​​of other mechanical properties of the material. However, determining hardness is an effective way to compare materials of the same type with each other and control their quality.

Brinell hardness test

The Brinell hardness measurement method is regulated by GOST 9012.

When determining hardness by this method, a steel ball of a certain diameter D is pressed into the test sample under the action of a load P applied perpendicular to the surface of the sample for a certain time. After removing the load, the diameter of the indentation d is measured. The Brinell hardness number is designated by the letters HB and is determined by dividing the load P by the surface area of ​​the spherical imprint F.

For convenience, there are tables of Brinell hardness numbers and dependence on the ball diameter D, indent diameter d and load P.

Polished (Ra 

Source: https://HeatTreatment.ru/ispytaniya-na-tverdost

Methods for determining metal hardness

Hardness is a key characteristic of metals. The quality of alloys, the possibility of using a particular material in a structure, the required type of processing, as well as related properties: strength, wear resistance, etc. depend on its value. Hardness also characterizes other materials: plastic, minerals, composites. For such measurements, a universal hardness tester is used.

The definition of hardness is usually understood as the actual ability of the metal being tested to resist deformation from interaction with a harder material.

Types of Methods

Depending on the method and duration of pressing the identifier into the metal, all methods are divided into the following groups:

They are implemented in the following ways: according to Brinell, according to Rockwell, according to Knoop, according to Vickers.

They are carried out in the following ways: according to Bauman, according to Shore, according to Schwartz, according to Grave, according to Morin. In recent years, indirect methods have also been actively used. Research is carried out using high-precision electronic instruments that record related characteristics, and not the hardness itself.

One of these devices, a portable ultrasonic hardness tester, records the rate of attenuation of vibrations of a rod with an indenter. The method has no requirements for the weight, size or geometry of the object under study.

The only limitation is the coarse-grained structure of the metal product.

Static methods

The most common. Their essence is that the indenter receives a load gradually, and the measurement is carried out in an adjustable period of time (from 10 to 15 s for ferrous metals, from 10 to 180 s for alloys and non-ferrous metals).

Brinell hardness

The characteristics of the metal depend on the size of the imprint left by a metal ball pressed into the surface. The study is carried out on a stationary device - the Brinell press and is regulated by GOST 9012-59.

Brinell hardness is measured by dividing the applied load by the area of ​​the mark and is expressed in HB. Calculations using the formula are not carried out in real conditions; ready-made tables have been developed for this purpose.

Brinnell measurements are suitable for steel no harder than 450 HB and non-ferrous metals no more than 200 HB with a roughness of 1.25 - 2.5 Ra.

Rockwell hardness

The method is suitable for hard, hardened metals. A diamond pyramid or steel ball is used as an identifier. A special press presses the identifier into the metal with an initial load of 10 kg, and then with a full load of 60 or 150 kg. The unit of measurement is HRC. The method is regulated by GOST 9013-59.

Vickers hardness

The standards for conducting the study are contained in GOST 2999-75. Vickers measurements are used for thin metals or top layers of hard metals with a minimum roughness of 0.02 - 0.04 Ra. A diamond tip of a regular tetrahedral pyramid is used as an identifier.

The tip is pressed into the metal being tested for a limited period of time, and then the arithmetic mean of the diagonal of the print is calculated. Using the summary tables and the resulting diagonal, the Vickers number is determined. The unit of measurement is HV.

The main disadvantages of static methods: restrictions on hardness, minimum thickness, metal roughness; low equipment mobility.

Dynamic Methods

They are implemented by measuring the rebound and fall of the striker. The dynamic hardness tester is especially popular. It measures the ratio of the falling speed of the indenter during the fall and rebound. The result from the signals is analyzed by the converter and displayed on the display. The compact portable hardness tester has greater productivity and mobility in contrast to equipment for classical measurement methods.

Shore hardness

The method is regulated by GOST 23273-78. The falling speed of the diamond-tipped striker and the height of its rebound are recorded. The harder the metal, the higher the firing pin bounces. Based on the data obtained, the Shore hardness number is derived. The unit of measurement is HSD. The main area of ​​application of this method is the production and operation of rolling rolls.

Source: https://speranza-ua.com/news/metody-opredeleniya-tverdosti-metalla/

Metal hardness measurement

The ability of a material to resist pressing into its surface layers of another body that does not deform during testing characterizes the hardness of the material.

The pressed body is called an indenter and, depending on the method of measuring hardness and the material itself, can have the shape of a ball, cone or pyramid. The material used for spherical indenters is steel or hard alloy, as well as diamond for conical or pyramidal indenters.

Features of hardness measurement

After pressing the indenter, which occurs with a certain load for 5-15 seconds, an imprint remains on the material, from the area of ​​which the hardness value is calculated.

In this regard, special requirements are imposed on the surface of the test sample: minimal roughness and absence of oxides, plane-parallelism of the measured section and the base of the sample, absence of thermal effects and hardening after sample preparation.

During the process of pressing the indenter, the metal is deformed, creating a zone of increased stress around the point of application of the load, so it is important to maintain the minimum permissible distance between indentations in order to avoid erroneously inflated results. The same applies to hardness measurements at the edge of the sample, but the results in this case may be lower than real ones.

Hardness testing methods

Multiple methods of hardness measurement are based on the same principles, but, depending on the task at hand and the material being studied, they differ in the types of indenters used.

• Brinell. The indenter is a steel ball with a diameter of one to ten millimeters. The method has significant disadvantages - the imprint area is too large, and cannot be used on very hard metals.
• Rockwell. A hard steel ball or a conical diamond with an apex angle of 120 degrees is used as an indenter. The Rockwell method works well on hardened steel samples that cannot be tested using the Brinell method.
• Vickers. The indenter is a diamond pyramid, the angle at the apex of which is 136 degrees. The print has a square shape. The method is optimally suited for analyzing the hardness of hardened steel, high-strength coatings, and weld seams. The Vickers method is used to determine the microhardness of individual structural components at the microscopic level under loads of 10 g.
• Knup. The method is similar to the Vickers method and differs in that the angle at the top of the pyramid is 172.5 degrees, and the imprint is diamond shaped. Used to measure the hardness of narrow parts or surface layers.
• Shora. The indenter is a steel ball, but it is not pressed in, but falls onto the surface of the part. The hardness value is calculated based on the rebound height. The method is used mainly for plastic and rubber products.
• Moosa. An indenter is in the form of a needle, which scratches the surface of a material. Based on the depth of the scratch, hardness is determined.

Applying an indenter imprint on the polished surface of a sample

Hardness measurement as a metallographic research method

Determining the hardness of a material is not only one of the standard mechanical tests of incoming or acceptance inspection of metal, but also a tool for metallographic analysis.

Thus, by changing the microhardness, it is possible to determine the depth of the hardened or decarburized layer, and to evaluate the structural heterogeneity of the thickness of the rolled sheet. In the case of complex dispersed structures after hardening, the hardness value will make it possible to determine whether the material tempering procedure was carried out.

Estimation of layer depth after cementation

Changes in microhardness in the zone of segregation strip of sheet metal

Another important feature of hardness measurement is the direct connection of its values ​​with the strength of the metal. Therefore, this test method is widely used in assessing the strength characteristics of parts and mechanisms in operation (for example, sections of existing pipelines). For this purpose, special portable hardness testers of ultrasonic or dynamic operating principles have been created, requiring minimal surface preparation.

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Source: https://thixomet.ru/izmerenie-tverdosti-metallov/

Methods for measuring the hardness of metals

All methods for measuring the hardness of metals can be divided into two groups: direct and indirect.

 1. Direct methods

These are classical methods for measuring hardness according to Brinell , Rockwell, Vickers, Shore, Super-Rockwell. The hardness of metals is measured or assessed in hardness units .

The principle of measuring hardness by all direct methods follows from the definition of hardness - the ability of a material to resist the penetration of another, harder body.

As a harder body, indenters are used, made, for example, from diamond or tungsten carbide and having a certain shape - ball, cone, pyramid.

Instruments for measuring hardness by direct methods are stationary installations, where a certain load is applied to the indenter, which is embedded in a product or sample. For example, the stationary Rockwell hardness tester NOVOTEST TS-R is equipped with two indenters - a ball with a diameter of 1.5875 mm and a diamond cone pyramid with an angle of 120°, applied test loads of 60,100 and 150 kg.

After applying a load, an imprint remains on the surface of the sample. For each direct method of determining hardness, a dependence is formulated for calculating the hardness value from known values ​​of the applied force and certain geometric parameters of the indentation. For the Rockwell method, for example, the depth of the indentation is recorded.

Among the advantages of direct methods for measuring hardness, it is worth noting the versatility with respect to the material of the test sample. Stationary hardness testers are initially ready to measure the hardness of any metals and alloys without additional calibration. Disadvantages - lack of mobility, limitation in the size of the products being measured, the presence of a fairly large print, slow pace of measurements.

 2. Indirect methods

 There are only two indirect methods - ultrasonic and dynamic. These methods do not directly measure hardness, but only estimate the value of the metal's hardness depending on other physical properties.

2.1. Ultrasonic hardness measurement involves recording the degree of change (damping) in the vibration frequency of a rod with an indenter attached to the end when inserted into the surface of the sample.

The softer the metal, the greater the depth of penetration of the indenter and, accordingly, the area of ​​its contact with the metal, the higher the degree of attenuation of the vibration frequency (in the ultrasonic range).

The method has practically no restrictions on the weight and size of the tested products, leaves a barely noticeable imprint, and is applicable for measuring the hardness of surface-hardened layers and products with a complex structure (gears, bearings, hardware, etc.). Limited use on products with a coarse-grained structure.

2.2. The dynamic method realizes the dependence of the rebound velocity of a rigid body on the hardness on the impact surface.

The softer the metal, the more impact energy is spent on forming an imprint (plastic deformation) and the lower the rebound speed of the striker with a carbide ball.

The dynamic method is applicable for large, massive products with a weight of at least 5 kg and a wall thickness of at least 10 mm. Suitable for measuring hardness, also on cast products. Less sensitive to surface quality than the ultrasonic method.

2.3. Both indirect methods have become widespread in the form of portable, electronic devices. Hardness measurement with a portable hardness tester is based on the correct choice of control method (ultrasound or dynamics) and the use of correct calibration of the device. Typically, portable hardness testers are initially calibrated for steel on steel hardness blocks and have the ability to be custom calibrated on other metals and alloys if samples of known hardness are available.

The advantages of portable NOVOTEST hardness testers are obvious: mobility, portability, autonomy, high speed of measurements. It is also worth noting that electronic instruments have the ability to measure hardness on several scales, archive and statistically process data, and communicate with a computer.

 3. Hardness measures

Used for setting up and testing both portable and stationary hardness testers. They are produced separately for each hardness scale and have unique sizes and ratings in hardness units in accordance with the regulatory and technical documentation. When working with dynamic hardness testers, one should take into account the fact that the mass of any hardness measure is less than 5 kg. In this case, the measures are ground onto a massive plate through a layer of lubricant.

Source: https://novotest.ua/stati/metody-izmereniya-tverdosti-metallov.html

Hardness concept

Hardness is a property of materials that characterizes the ability of one harder body to penetrate another. This characteristic also determines the resistance to plastic deformation or destruction of surface layers when applying strong pressure.

The indicator is measured in a variety of units depending on the method used.

All methods for determining the hardness of materials can be divided into several main groups:

1. Static. Such methods are characterized by the fact that the load gradually increases. The holding time may vary - it all depends on the characteristics of the method used.
2. Dynamic ones are characterized by the fact that the load on the sample is applied with a certain kinetic energy. In this case, the hardness indicator is less accurate, since under dynamic load a certain recoil occurs due to the elasticity of the material. The results of such tests are often referred to as the impact hardness of materials.
3. Kinetic methods are based on continuous recording of indicators during testing, which makes it possible to obtain not only the final, but also an intermediate result. For this, special equipment is used.

Tool hardness measurement

In addition, the classification of methods for determining hardness is carried out according to the principle of applied load. The following methods of testing a sample are distinguished:

1. Indentation is by far the most common way to determine the indicator in question.
2. During rebound, a measurement is made of how high the firing pin flies from the surface of the test sample. In this case, the hardness calculation is carried out based on the resistance to elastic deformation. Methods of this type are quite often used to control the quality of rolling rollers and large-sized products.
3. Methods based on scratching and cutting are used extremely rarely today. They were developed two centuries ago.

Typically, hardness testers have a part that affects the workpiece being tested. Examples include steel balls of various diameters and diamond tips with a pyramid shape. Let's take a closer look at some of the methods used today.

Vickers hardness measurement

There is also the Vickers hardness measurement method, which is regulated by GOST 2999. It has become widespread in determining the hardness of parts and workpieces that have a small thickness. In addition, it can be used to measure the hardness of parts with a surface hard layer.

The features of this method of testing a sample include the following points:

1. The so-called diamond tip is used, which has the shape of a pyramid with four faces and equal sides.
2. A specific holding time is selected.
3. After the load is removed, the dimensions of the diagonals of the resulting print are measured and the arithmetic mean is calculated.
4. The magnitude of the applied load is regulated and can be selected depending on the type of material being tested.
5. The results obtained during the research are designated HV.

Vickers method

In some cases, after the obtained value, the holding time and the magnitude of the applied load are indicated, which makes it possible to determine the hardness value with greater accuracy.

Rockwell hardness test

This method is regulated by GOST 9013. To carry it out, a special device is used for measuring hardness, which allows you to create two successive loads applied to the surface of the sample. Features of such a test include:

1. First, a preload is applied, after which a second load is added.
2. After holding under the total load for 3-5 seconds, the second one is removed, the depth of the indentation is measured, then the preliminary load is removed.
3. The obtained data is measured in conventional units, which are equal to the axial displacement of the indicator by 0.002.
4. The Rockwell hardness number is determined using a special scale of the device.
5. The form of the indicator used may differ significantly. That is why several types of measuring scales have been introduced that correspond to a specific indicator shape.
6. To designate the obtained value, the designations HIRA, HRC, HRB can be used. They correspond to the shape of the indicator and designation scale used.

Rockwell hardness measuring principle

A steel ball and two diamond cones of different sizes can be used as an indicator.

This method of measuring the hardness of hardened parts is carried out only when using a smaller diamond cone, the preliminary applied load is 10 kgf, the main load is 50 kgf.

Preloading eliminates the possibility that the elasticity of the material will cause the values ​​obtained to be less accurate. In addition, preload allows you to measure the hardness of metals and alloys that have undergone preliminary heat treatment.

The Shore hardness method is used to test rolling rollers at the time of manufacture. In addition, checking the indicator under consideration can be carried out during the operation of rollers on rolling machines, since due to the impact, the structure of the metal can change, deteriorating performance. The Shore method is regulated by GOST 23273.

Shore hardness scale

When considering Shore hardness measurement, the following points should be noted:

1. Unlike previous methods, this one is based on the free fall of a diamond indicator onto the test surface from a certain height. For testing, special equipment is used that allows you to accurately record the height of the rebound.
2. The weight of the diamond-tipped striker used is 36 grams. This indicator is important as it is taken into account in the calculations.
3. Hardness is determined by the height of the rebound, the measurement is carried out in conventional units. The sample falls onto the surface with the formation of a small depression, and elasticity leads to rebound. This method is good because it allows testing samples that have undergone preliminary heat treatment. When applied gradually, the resulting load may cause deformation of the tip or ball being used. In this case, the likelihood of their deformation is very small.
4. In this case, 100 units of hardness is considered to be a rebound height of 13.6 mm with the possibility of a slight deviation up or down. This indicator can be obtained by testing carbon steel that has undergone a hardening process. The abbreviation HSD is used as a designation.

Today, this method of measuring hardness is used quite rarely due to the high error and complexity of measuring the height of the bike’s rebound from the test surface.

As previously noted, there are quite a large number of methods for measuring the indicator in question. However, due to the complexity of the tests and the large error, many are no longer used.

In some cases, microhardness testing is carried out. To measure this indicator, a static load is applied to a pyramid-shaped body, and it enters the test sample. The exposure time can vary over a wide range. The indicator is calculated in approximately the same way as with the Vickers method.

Hardness value ratio

When choosing a method for measuring surface hardness, it should be taken into account that there is no relationship between the data obtained. In other words, it is impossible to accurately convert one unit of measurement to another. The dependence tables used do not have a physical meaning, since they are empirical. The lack of dependence can also be attributed to the fact that different loads and different tip shapes are used during testing.

The existing tables should be used with great caution as they only provide approximate results. In some cases, the translation in question may turn out to be very accurate, which is due to the similar physical and mechanical properties of the metals being tested.

In conclusion, we note that the value of hardness is related to many other mechanical properties, for example, strength, elasticity and ductility. Therefore, to determine the basic properties of a metal, hardness is often measured. However, there is no direct relationship between all the mechanical properties of metals and alloys, which should be taken into account when carrying out measurements.

Source: https://stankiexpert.ru/tehnologii/izmerenie-tverdosti.html

The oldest method for measuring hardness

The hardness of materials has long been assessed by their resistance to scratching or cutting. For example, material B scratches material C, but does not scratch material A. And, conversely, material A scratches material B only slightly, but material B very strongly. Thus, the relative hardness of minerals is still assessed using the Mohs mineralogical scale, which was introduced by the German Mohs back in 1811. According to the Mohs scale, diamond has a maximum hardness of 10, and talc has a minimum hardness of 1.

A practical method for measuring hardness

In practice, a similar method of measuring hardness is often used using a special set of files, each of which is thermally hardened to a certain hardness - from low to high. Such a set of six files is shown in the figure below.

Figure – Set of files for measuring the hardness of metals

If the file slides over the material without forming any mark, then this material is considered harder than the file; if the mark remains, it is considered less hard. This relative method of measuring hardness is limited in practical use and does not provide accurate numerical data or scales, especially for modern metals and materials.

What is hardness?

Hardness testing is applied to most materials, especially metals. The very concept of “hardness” has many definitions - from physicists, metallurgists and mechanical engineers. In mineralogy, hardness is the resistance to scratching by another substance, and in metallurgy, it is the ability of a material to resist plastic deformation.

The most commonly used definition of hardness of metals is: “The resistance of a metal to local plastic deformation that occurs when a harder body, such as the tip (indenter) of a testing device, is introduced into it.”

However, hardness can also have other manifestations such as stiffness, resistance to scratching, abrasion or cutting. The hardness of a metal gives it the ability to resist irreversible deformation—bending, breaking, or changing shape.

The greater the hardness of the metal, the greater its resistance to irreversible, for example, plastic deformation. This variety of manifestations of hardness also gives rise to a variety of methods for measuring it.

Hardness measurement using static indentation methods

To measure hardness, the most commonly used methods are static pressing of a ball, diamond cone or diamond pyramid into the material. These methods include:

• Brinell method according to GOST 9012-59) – steel ball;
• Rockwell method according to GOST 9013-59) – diamond cone;
• Super-Rockwell method according to GOST 22975-78 - steel ball or diamond cone;
• Vickers method according to GOST 2999-75 – diamond pyramid;
• microhardness testing method according to GOST 9450-75 - diamond pyramid.

Scratch hardness measurement

This is the oldest method for measuring hardness. This principle is the basis for the Mohs scratch testing of materials, which is used for minerals. In addition, GOST 21318-75 defines a method for measuring the microhardness of a material by scratching it - making a groove - with special diamond pyramids.

Impact imprint method according to GOST 18661-73

It is used for massive parts and structures when other methods cannot be used. Hardness is measured using a special device. A standard block of known hardness is placed in the device. The device is installed on the surface of the part being examined. When a hammer hits the top of the striker, a ball with a diameter of 10 mm is pressed simultaneously into the part and into the standard. By comparing the dimples on the part and the sample, the hardness of the part material is judged.

Method of elastic rebound of the striker (Shor method) according to GOST 23273-78

A special device is used - a scleroscope, inside which a striker with a diamond tip falls freely. Hardness measurement is carried out based on the rebound height of the striker.

Electromagnetic method for measuring steel hardness

This method is based on the dependence of the magnetic characteristics of steel on its structure. Since each steel structure corresponds to a certain hardness, a certain relationship can be established between the magnetic characteristics and hardness. These are less precise than mechanical methods and require a lot of experience to use. They are used for mass testing of the hardness of similar parts.

Ultrasonic method for measuring steel hardness

This method of hardness measurement is called the ultrasonic contact impedance method. The diamond pyramid is pressed against the test sample under constant force and elastic vibrations are excited. The lower the hardness of the sample, the more the indenter presses through its surface. Used to measure hardness in hard-to-reach places.

Source: https://steel-guide.ru/mexanicheskie-svojstva-stali/izmerenie-tverdosti.html

The oldest method for measuring hardness

The hardness of materials has long been assessed by their resistance to scratching or cutting. For example, material B scratches material C, but does not scratch material A. And, conversely, material A scratches material B only slightly, but material B very strongly. Thus, the relative hardness of minerals is still assessed using the Mohs mineralogical scale, which was introduced by the German Mohs back in 1811. According to the Mohs scale, diamond has a maximum hardness of 10, and talc has a minimum hardness of 1.

A practical method for measuring hardness

In practice, a similar method of measuring hardness is often used using a special set of files, each of which is thermally hardened to a certain hardness - from low to high. Such a set of six files is shown in the figure below.

Figure - Set of files for measuring the hardness of metals

If the file slides over the material without forming any mark, then this material is considered harder than the file; if the mark remains, it is considered less hard. This relative method of measuring hardness is limited in practical use and does not provide accurate numerical data or scales, especially for modern metals and materials.

What is hardness?

Hardness testing is applied to most materials, especially metals. The very concept of “hardness” has many definitions - from physicists, metallurgists and mechanical engineers. In mineralogy, hardness is the resistance to scratching by another substance, and in metallurgy, it is the ability of a material to resist plastic deformation.

The most commonly used definition of hardness of metals is: “The resistance of a metal to local plastic deformation that occurs when a harder body, such as the tip (indenter) of a testing device, is introduced into it.”

However, hardness can also have other manifestations such as stiffness, resistance to scratching, abrasion or cutting. The hardness of a metal gives it the ability to resist irreversible deformation—bending, breaking, or changing shape.

The greater the hardness of the metal, the greater its resistance to irreversible, for example, plastic deformation. This variety of manifestations of hardness also gives rise to a variety of methods for measuring it.

Hardness measurement using static indentation methods

To measure hardness, the most commonly used methods are static pressing of a ball, diamond cone or diamond pyramid into the material. These methods include: - Brinell method according to GOST 9012-59) - steel ball; - Rockwell method according to GOST 9013-59) - diamond cone; - Super-Rockwell method according to GOST 22975-78 - steel ball or diamond cone; - method Vickers according to GOST 2999-75 – diamond pyramid;

- microhardness testing method according to GOST 9450-75 - diamond pyramid.

Scratch hardness measurement

This is the oldest method for measuring hardness. This principle is the basis for the Mohs scratch testing of materials, which is used for minerals. In addition, GOST 21318-75 defines a method for measuring the microhardness of a material by scratching it - making a groove - with special diamond pyramids.

Impact imprint method according to GOST 18661-73

It is used for massive parts and structures when other methods cannot be used. Hardness is measured using a special device. A standard block of known hardness is placed in the device. The device is installed on the surface of the part being examined. When a hammer hits the top of the striker, a ball with a diameter of 10 mm is pressed simultaneously into the part and into the standard. By comparing the dimples on the part and the sample, the hardness of the part material is judged.

Method of elastic rebound of the striker (Shor method) according to GOST 23273-78

A special device is used - a scleroscope, inside which a striker with a diamond tip falls freely. Hardness measurement is carried out based on the rebound height of the striker.

Electromagnetic method for measuring steel hardness

This method is based on the dependence of the magnetic characteristics of steel on its structure. Since each steel structure corresponds to a certain hardness, a certain relationship can be established between the magnetic characteristics and hardness. These are less precise than mechanical methods and require a lot of experience to use. They are used for mass testing of the hardness of similar parts.

Ultrasonic method for measuring steel hardness

This method of hardness measurement is called the ultrasonic contact impedance method. The diamond pyramid is pressed against the test sample under constant force and elastic vibrations are excited. The lower the hardness of the sample, the more the indenter presses through its surface. Used to measure hardness in hard-to-reach places.

Source: http://otlivka.info/articles/%D0%B8%D0%B7%D0%BC%D0%B5%D1%80%D0%B5%D0%BD%D0%B8%D0%B5-% D1%82%D0%B2%D0%B5%D1%80%D0%B4%D0%BE%D1%81%D1%82%D0%B8-%D0%BC%D0%B5%D1%82%D0 %B0%D0%BB%D0%BB%D0%BE%D0%B2/