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.
| According to Rockwell | According to Brinell | |||
| HRACone 120° load. 60 kgf | HRCone 120° loaded 150 kgf | HRB Ball Ø 1.58 mm load. 100 kgf | Diameter of printsmm | HBball Ø 10 mmload. 3000 kgf |
| 84,5 | 65 | — | 2,34 | 688 |
| 83,5 | 64 | — | 2,37 | 670 |
| 83 | 63 | — | 2,39 | 659 |
| 82,5 | 62 | — | 2,42 | 643 |
| 82 | 61 | — | 2,45 | 627 |
| 81,5 | 60 | — | 2,47 | 616 |
| 81 | 59 | — | 2,5 | 601 |
| 80,5 | 58 | — | 2,54 | 582 |
| 80 | 57 | — | 2,56 | 573 |
| 79 | 56 | — | 2,6 | 555 |
| 79 | 55 | — | 2,61 | 551 |
| 78,5 | 54 | — | 2,65 | 534 |
| 78 | 53 | — | 2,68 | 522 |
| 77,5 | 52 | — | 2,71 | 510 |
| 76 | 51 | — | 2,75 |
Source: https://www.equipnet.ru/articles/tech/tech_54357.html
Hardness of metals
Mechanical engineering parts and mechanisms, as well as tools intended for their processing, have a set of mechanical characteristics. Hardness plays a significant role among the characteristics. The hardness of metals clearly shows:
- wear resistance of metal;
- possibility of processing by cutting, grinding;
- resistance to local pressure;
- ability to cut other materials and others.
Hardness of metals
In practice, it has been proven that most of the mechanical properties of metals directly depend on their hardness.
Hardness concept
The hardness of a material is its resistance to destruction when a harder material is introduced into the outer layer. In other words, the ability to resist deforming forces (elastic or plastic deformation).
The hardness of metals is determined by introducing a solid body called an indenter into a sample. The role of the indenter is performed by: a metal ball of high hardness; diamond cone or pyramid.
After exposure to the indenter, an imprint remains on the surface of the test sample or part, the size of which determines the hardness. In practice, kinematic, dynamic, and static methods of measuring hardness are used.
The kinematic method is based on the compilation of a diagram based on continuously recorded readings that change as the tool is pressed into the sample. Here the kinematics of the entire process is traced, and not just the final result.
The dynamic method is as follows. The measuring tool acts on the part. The reverse reaction allows you to calculate the expended kinetic energy. This method allows you to test the hardness of not only the surface, but also a certain volume of metal.
Static methods are non-destructive methods that allow you to determine the properties of metals. The methods are based on smooth indentation and subsequent holding for some time. The parameters are regulated by methods and standards.
The applied load can be applied:
- pressing;
- scratching;
- cutting;
- rebound
Machine-building enterprises currently use the Brinell, Rockwell, Vickers methods, as well as the microhardness method, to determine the hardness of materials.
Based on the tests carried out, a table is compiled indicating the materials, the applied loads and the results obtained.
Hardness Units
Each method of measuring the resistance of a metal to plastic deformation has its own methodology, as well as units of measurement.
The hardness of soft metals is measured using the Brinell method. Non-ferrous metals (copper, aluminum, magnesium, lead, tin) and alloys based on them, cast iron (except for white) and annealed steel are subjected to this method.
Brinell hardness is determined by indentation of a hardened, polished ball made of ShKh15 ball bearing steel. The circumference of the ball depends on the material being tested. For hard materials - all types of steel and cast iron - 10 mm, for softer materials - 1 - 2 - 2.5 - 5 mm. Required load applied to the ball:
- iron alloys – 30 kgf/mm2;
- copper and nickel – 10 kgf/mm2;
- aluminum and magnesium – 5 kgf/mm2.
The unit of hardness measurement is a numerical value followed by a numerical index HB. For example, 200 NV.
Rockwell hardness is determined by the difference in applied loads to the part. First, a preliminary load is applied, and then a general load, at which the indenter is introduced into the sample and held.
A pyramid (cone) of diamond or a ball of tungsten carbide (hardened steel) is introduced into the test sample. After removing the load, the depth of the indentation is measured.
The unit of measurement for hardness is conventional units. It is generally accepted that one is the amount of axial displacement of the cone, equal to 2 μm. The hardness designation is marked with three letters HR (A, B, C) and a numerical value. The third letter in the marking indicates the scale.
The technique reflects the type of indenter and the load applied to it.
| Scale type | Tool | Applied load, kgf |
| A | Diamond cone with 120° apex angle | 50-60 |
| IN | 1/16" ball | 90-100 |
| WITH | Diamond cone with 120° apex angle | 140-150 |
Basically, measurement scales A and C are used. For example, the hardness of steel is HRC 2632, HRB 2529, HRA 7075.
Products of small thickness or parts with a thin, hard surface layer are measured by Vickers hardness. The blade used is a regular tetrahedral pyramid with an apex angle of 136°. The display of hardness values is as follows: 220 HV.
Hardness measurement using the Shore method is carried out by measuring the rebound height of a fallen striker. Indicated by numbers and letters, for example, 90 HSD.
Microhardness is determined when it is necessary to obtain the values of small parts, thin coatings, or individual alloy structures. The measurement is made by measuring the imprint of a tip of a certain shape. The value notation looks like this:
Н□ 0.195 = 2800, where
□ — tip shape;
0.196 — tip load, N;
2800 – numerical value of hardness, N/mm2.
Hardness of base metals and alloys
The hardness value is measured on finished parts sent for assembly. Control is carried out for compliance with the drawing and technological process. Tables of hardness values have already been compiled for all basic materials, both in the initial state and after heat treatment.
The Brinell hardness of copper is 35 HB, the values of brass are 42-60 HB units, depending on its brand. For aluminum, the hardness is in the range of 15-20 HB, and for duralumin it is already 70 HB.
Black metals
The Rockwell hardness of cast iron SCH20 HRC 22, which corresponds to 220 HB. Steel: tool – 640-700 HB, stainless steel – 250 HB.
To convert from one measurement system to another, tables are used. The values in them are not true, because they are derived imperially. Not the full volume is presented in the table.
| HB | H.V. | H.R.C. | HRA | HSD |
| 228 | 240 | 20 | 60.7 | 36 |
| 260 | 275 | 24 | 62.5 | 40 |
| 280 | 295 | 29 | 65 | 44 |
| 320 | 340 | 34.5 | 67.5 | 49 |
| 360 | 380 | 39 | 70 | 54 |
| 415 | 440 | 44.5 | 73 | 61 |
| 450 | 480 | 47 | 74.5 | 64 |
| 480 | 520 | 50 | 76 | 68 |
| 500 | 540 | 52 | 77 | 73 |
| 535 | 580 | 54 | 78 | 78 |
Hardness values, even if produced by the same method, depend on the applied load. The lower the load, the higher the readings.
Hardness measurement methods
All methods for determining the hardness of metals use mechanical action on the test sample - indentation of an indenter. But this does not destroy the sample.
The Brinell hardness method was the first to be standardized in materials science. The principle of testing samples is described above. It is subject to GOST 9012. But you can calculate the value using the formula if you accurately measure the imprint on the sample:
HB=2P/(πD*√(D2-d2),
- where P – applied load, kgf;
- D – ball circumference, mm;
- d – circumference of the imprint, mm. The ball is selected relative to the thickness of the sample. The load is pre-calculated from accepted standards for the relevant materials: iron alloys - 30D2; copper and its alloys - 10D2; babbits, lead bronze - 2.5D2.
Symbol of the test principle
Download GOST 9012-59
Schematically, the Rockwell research method is depicted as follows according to GOST 9013.
Rockwell hardness test method
The final applied load is equal to the sum of the initial load and that required for the test. The device indicator shows the difference in penetration depth between the initial load and the test load h –h0.
Download GOST 9013-59
The Vickers method is regulated by GOST 2999. It is schematically depicted as follows.
Vickers method
Mathematical formula for calculation:
HV=0.189*P/d2 MPa
HV=1.854*P/d2 kgf/mm2
The applied load varies from 9.8 N (1 kgf) to 980 N (100 kgf). The values are determined from the tables relative to the measured print d.
Shore method
The method is considered empirical and has a wide range of readings. But the device has a simple design and can be used when measuring large-sized and curved parts.
The Mohs hardness of metals and alloys can be measured by scratching. Mohs at one time proposed making scratches on the surface of an object with a harder mineral. He classified known minerals by hardness into 10 positions. The first is occupied by talc, and the last by diamond.
After measurement using one method, transfer to another system is very conditional. Clear values exist only in the Brinell and Rockwell hardness ratios, since machine-building enterprises widely use them. The dependence can be observed when the diameter of the ball changes.
| d, mm | HB | HRA | H.R.C. | HRB |
| 2,3 | 712 | 85,1 | 66,4 | — |
| 2,5 | 601 | 81,1 | 59,3 | — |
| 3,0 | 415 | 72,6 | 43,8 | — |
| 3,5 | 302 | 66,7 | 32,5 | — |
| 4,0 | 229 | 61,8 | 22 | 98,2 |
| 5,0 | 143 | — | — | 77,4 |
| 5,2 | 131 | — | — | 72,4 |
As can be seen from the table, increasing the diameter of the ball significantly reduces the readings of the device. Therefore, machine-building enterprises prefer to use measuring instruments with the same type of indenter size.
Source: https://stankiexpert.ru/tehnologii/tverdost-metallov.html
Hardness of metals. Metal hardness table
In order for parts and mechanisms to serve for a long time and reliably, the materials from which they are made must meet the necessary operating conditions. That is why it is important to control the permissible values of their main mechanical parameters. Mechanical properties include hardness, strength, impact strength, and ductility. The hardness of metals is a primary structural characteristic.
Concept
The hardness of metals and alloys is the property of a material to create resistance when another body penetrates its surface layers, which does not deform or collapse under accompanying loads (indenter). Determined for the purpose of:
- obtaining information about acceptable design features and operational capabilities;
- state analysis under the influence of time;
- monitoring the results of temperature treatment.
The strength and aging resistance of the surface partly depend on this indicator. Both the source material and finished parts are examined.
Research options
The indicator is a value called the hardness number. There are various methods for measuring the hardness of metals. The most accurate studies involve the use of various types of calculations, indenters and corresponding hardness testers:
- Brinell: the essence of the apparatus is pressing a ball into the metal or alloy being tested, calculating the diameter of the indentation and subsequent mathematical calculation of the mechanical parameter.
- Rockwell: Uses a ball or diamond cone tip. The value is displayed on a scale or determined by calculation.
- Vickers: The most accurate measurement of metal hardness using a diamond pyramid tip.
To determine parametric correspondences between indicators of different measurement methods for the same material, there are special formulas and tables.
Factors that determine the measurement option
In laboratory conditions, if the necessary range of equipment is available, the choice of research method is carried out depending on certain characteristics of the workpiece.
- Approximate value of the mechanical parameter. For structural steels and materials with low hardness up to 450-650 HB, the Brinell method is used; for tool, alloy steels and other alloys - Rockwell; for hard alloys – Vickers.
- Dimensions of the test sample. Particularly small and thin parts are examined using a Vickers hardness tester.
- The thickness of the metal at the measurement location, in particular the cemented or nitrided layer.
All requirements and compliance are documented by GOST.
Features of the Brinell technique
Hardness testing of metals and alloys using a Brinell hardness tester is carried out with the following features:
- Indenter - a ball made of alloy steel or tungsten carbide alloy with a diameter of 1, 2, 2.5, 5 or 10 mm (GOST 3722-81).
- Duration of static indentation: for cast iron and steel - 10-15 s, for non-ferrous alloys - 30, a duration of 60 s is also possible, and in some cases - 120 and 180 s.
- Limit value of the mechanical parameter: 450 HB when measured with a steel ball; 650 HB when using carbide.
- Possible loads. Using the weights included in the kit, the actual deformation force on the test sample is adjusted. Their minimum permissible values: 153.2, 187.5, 250 N; maximum – 9807, 14710, 29420 N (GOST 23677-79).
Using formulas, depending on the diameter of the selected ball and the material being tested, the corresponding permissible indentation force can be calculated.
| Alloy type | Mathematical load calculation |
| Steel, nickel and titanium alloys | 30D2 |
| Cast iron | 10D2, 30D2 |
| Copper and copper alloys | 5D2, 10D2, 30D2 |
| Light metals and alloys | 2.5D2, 5D2, 10D2, 15D2 |
| Lead, tin | 1D2 |
Example notation:
400HB10/1500/20, where 400HB is the Brinell hardness of the metal; 10 – ball diameter, 10 mm; 1500 – static load, 1500 kgf; 20 – period of indentation, 20 s.
To establish accurate figures, it is rational to examine the same sample in several places, and determine the overall result by finding the average value of the obtained ones.
Determination of hardness using the Brinell method
The research process proceeds in the following sequence:
- Checking the part for compliance with the requirements (GOST 9012-59, GOST 2789).
- Checking the health of the device.
- Selecting the required ball, determining the possible force, installing weights for its formation, and the period of indentation.
- Starting the hardness tester and deforming the sample.
- Measuring the diameter of the recess.
- Empirical calculation.
HB=F/A,
where F – load, kgf or N; A – print area, mm2.
НВ=(0.102*F)/(π*D*h),
where D is the diameter of the ball, mm; h – indentation depth, mm.
The hardness of metals measured by this method has an empirical connection with the calculation of strength parameters. The method is accurate, especially for soft alloys. It is fundamental in systems for determining the values of this mechanical property.
Features of the Rockwell technique
This measurement method was invented in the 20s of the 20th century, and is more automated than the previous one. Used for harder materials. Its main characteristics (GOST 9013-59; GOST 23677-79):
- Availability of a primary load of 10 kgf.
- Holding period: 10-60 s.
- Limit values of possible indicators: HRA: 20-88; HRB: 20-100; HRC: 20-70.
- The number is visualized on the dial of the hardness tester and can also be calculated arithmetically.
- Scales and indenters. There are 11 different scales depending on the type of indenter and the maximum permissible static load. The most common in use: A, B and C.
A: diamond cone tip, apex angle 120˚, total permissible static influence force – 60 kgf, HRA; Thin products, mainly rolled products, are being studied.
C: also a diamond cone, designed for a maximum force of 150 kgf, HRC, suitable for hard and hardened materials.
B: 1.588 mm ball, made of hardened steel or hard tungsten carbide, 100 kgf, HRB, used to evaluate the hardness of annealed products.
A ball-shaped tip (1.588 mm) is applicable for Rockwell scales B, F, G. There are also scales E, H, K, for which a ball with a diameter of 3.175 mm is used (GOST 9013-59).
The number of tests performed with a Rockwell hardness tester on one area is limited by the size of the part. A repeat test is allowed at a distance of 3-4 diameters from the previous place of deformation. The thickness of the tested product is also regulated. It should be no less than the tip penetration depth increased by 10 times.
Example notation:
50HRC is the Rockwell hardness of a metal, measured using a diamond tip, its number is 50.
Rockwell Study Design
Measuring metal hardness is more simplified than for the Brinell method.
- Assessment of the dimensions and surface characteristics of the part.
- Checking the health of the device.
- Determination of tip type and permissible load.
- Sample installation.
- Implementation of a primary force on the material of 10 kgf.
- Exercising full appropriate effort.
- Reading the resulting number on the dial scale.
A mathematical calculation is also possible to accurately determine the mechanical parameter.
Provided that a diamond cone is used with a load of 60 or 150 kgf:
HR=100-((Hh)/0.002;
when performing a test with a ball under a force of 100 kgf:
HR=130-((Hh)/0.002,
where h is the penetration depth of the indenter at a primary force of 10 kgf; H – indenter penetration depth at full load; 0.002 is a coefficient that regulates the amount of movement of the tip when the hardness number changes by 1 unit.
Rockwell's method is simple, but not accurate enough. At the same time, it allows the measurement of mechanical properties for hard metals and alloys.
Characteristics of the Vickers technique
Determining the hardness of metals using this method is the simplest and most accurate. The hardness tester works by pressing a diamond pyramidal tip into the sample.
Key Features:
- Indenter: diamond pyramid with apex angle 136°.
- Maximum permissible load: for alloy cast iron and steel - 5-100 kgf; for copper alloys - 2.5-50 kgf; for aluminum and alloys based on it - 1-100 kgf.
- Static load holding period: from 10 to 15 s.
- Test materials: steel and non-ferrous metals with a hardness of more than 450-500 HB, including products after chemical-thermal treatment.
Example notation:
700HV20/15,
where 700HV is the Vickers hardness number; 20 – load, 20 kgf; 15 – period of static force, 15 s.
Vickers study sequence
The procedure is extremely simplified.
- Checking the sample and equipment. Particular attention is paid to the surface of the part.
- Selection of permissible force.
- Installation of the test material.
- Putting the hardness tester into operation.
- Reading the result on the dial.
The mathematical calculation for this method is as follows:
HV=1.8544*(F/d2),
where F – load, kgf; d – average value of the print diagonal lengths, mm.
It allows you to measure high hardness of metals, thin and small parts, while providing highly accurate results.
Ways to switch between scales
Having determined the diameter of the print using special equipment, you can use tables to determine the hardness. The metal hardness table is a proven assistant in calculating this mechanical parameter. Thus, if the Brinell value is known, the corresponding Vickers or Rockwell number can be easily determined.
Example of some match values:
| Print diameter, mm | Research method | ||||
| Brinell | Rockwell | Vickers | |||
| A | C | B | |||
| 3,90 | 241 | 62,8 | 24,0 | 99,8 | 242 |
| 4,09 | 218 | 60,8 | 20,3 | 96,7 | 218 |
| 4,20 | 206 | 59,6 | 17,9 | 94,6 | 206 |
| 4,99 | 143 | 49,8 | — | 77,6 | 143 |
The metal hardness table is compiled on the basis of experimental data and is highly accurate. There are also graphical dependences of Brinell hardness on the carbon content in an iron-carbon alloy. So, in accordance with such dependencies, for steel with an amount of carbon in the composition equal to 0.2%, it is 130 HB.
Sample requirements
In accordance with the requirements of GOSTs, the tested parts must meet the following characteristics:
- The workpiece must be flat, lie firmly on the hardness tester table, its edges must be smooth or carefully processed.
- The surface should have minimal roughness. Must be sanded and cleaned, including using chemical compounds. At the same time, during machining processes, it is important to prevent the formation of work hardening and an increase in the temperature of the treated layer.
- The part must comply with the selected method for determining hardness using parametric properties.
Fulfillment of primary requirements is a prerequisite for measurement accuracy.
The hardness of metals is an important fundamental mechanical property that determines some of their other mechanical and technological features, the results of previous processing processes, the influence of temporary factors, and possible operating conditions. The choice of research methodology depends on the approximate characteristics of the sample, its parameters and chemical composition.
Source: https://FB.ru/article/269317/tverdost-metallov-tablitsa-tverdosti-metallov
What is hardness and how to measure it?
Hardness is the property of a material to resist penetration of an indenter into its surface.
How is hardness measured?
There are two main ways to display the hardness of materials:
- in kilogram-force per square millimeter (kgf/mm2);
- may be designated by the letters HB (HBW), HRB, HRC, HV, HA, HD, HC, HOO, etc.
What methods can be used to measure hardness?
Currently, many methods have been developed for determining the hardness of metals, such as:
- measurement of hardness by indentation under the influence of a static load (according to the Brinell, Rockwell, Super-Rockwell, Vickers, M.S. Drozd, Hertz, Ludvik method, Shore monotron, Brinell press);
- hardness measurement by dynamic indentation (according to the Martel, Poldi method, Nikolaev's vertical impact tester, Schopper and Bauman's spring device, Walzel's pendulum impact tester, Shore's scleroscope, Herbert's pendulum, Kuznetsov's pendulum sclerometer);
- microhardness measurement by static indentation (using the method of Lips, Egorov, Khrushchev, Skvortsov, Alekhin, Ternovsky, Shorshorov, Berkovich, Knoop, Peters, Emerson, Zeiss-Hahnemann microhardness tester, etc.);
- hardness measurement by scratching (Barba file, Mohs, Martens, Hankins device, Bierbaum microcharacterizer, O'Neill sclerometer, Grigorovich, Berkovich).
Among all these methods, the most popular is the method of introducing an indenter under the influence of a static load. The main methods for measuring hardness are: Brinell, Rockwell, Vickers, Shora.
Hardness Testing Requirements
The most common method of measuring hardness has the following requirements:
- the measuring device must be reliable in design, easy to use, universal and applicable to all solids without exception, and the hardness measurement operation itself must be simple and fast;
- regardless of the amount of force applied or energy expended, the hardness value for a homogeneous body at a constant temperature must be a material constant;
- the surface of the sample and the method of its fastening must ensure reliable fixation and do not allow the sample to shift relative to the axis of application of the load;
- hardness must have a completely definite and clear physical meaning, and the correct dimension characterizing the resistance of the material to plastic deformation.
How to calculate the hardness of a material?
The higher the hardness, the higher the load required to determine its hardness. The more accurate the method, the higher the requirements for preparing the test surface of the material. Accordingly, we need to select a method for determining hardness that gives a minimum error with minimal damage to the surface and minimal costs for preparing the surface for testing.
How is the hardness of steel measured?
The most common way to determine the hardness of steel is to introduce an indenter under the influence of a static load using the Brinell, Rockwell, and Vickers methods (see Table 1). And each method has its own hardness measurement scale.
Table 1
Name of the devicePrinciple of operation and tip shapeExample of scale designationFormula for calculating hardnessIndenterScaleDesignation| Brinell device | Indentation of a hardened steel ball with a diameter of 1.25; 2.5; 5 or 10 mm, etc., with loads in the range from 1 to 62.5 kgf or from 62.5 to 3000 kgf into the flat surface of the test body | Carbide spherical indenter ⌀2.5 and force 187.5 kgf | HB(w) | HB(w) 2.5/187.5 | Hardness is calculated along the diagonal of the print as the load divided by the surface area of the print:, kgf/mm2 |
| Rockwell and Super-Rockwell device |
Source: https://metrotest.ru/article/tverdost
In what units is the hardness of a metal measured?
Hardness is the property of a material to resist the penetration of a harder body - an indenter.
Method for determining restored hardness.
Hardness is defined as the ratio of the magnitude of the load to the surface area, projection area or indentation volume. There are surface , projection and volumetric hardness:
- surface hardness - the ratio of the load to the surface area of the print;
- projection hardness - the ratio of the load to the projection area of the print;
- volumetric hardness - the ratio of load to the volume of the indentation.
Hardness is measured in three ranges: macro, micro, nano. The macro range regulates the load on the indenter from 2 N to 30 kN. The microrange (see microhardness) regulates the load on the indenter up to 2 N and the penetration depth of the indenter more than 0.2 microns.
The nanorange regulates only the depth of penetration of the indenter, which should be less than 0.2 μm [1]. Hardness in the nanorange is often called nanohardness.
The value of nanohardness can differ significantly from microhardness for the same material. [2] [3] .
The measured hardness primarily depends on the load applied to the indenter. This dependence is called the size effect , in the English literature - indentation size effect . The nature of the dependence of hardness on load is determined by the shape of the indenter:
- for a spherical indenter - with increasing load, the hardness increases - reverse indentation size effect ;
- for an indenter in the form of a Vickers or Berkovich pyramid - with increasing load, the hardness decreases - direct or simply size effect ( indentation size effect );
- for a spheroconic indenter (type of cone for a Rockwell hardness tester) - with increasing load, the hardness first increases when the spherical part of the indenter is introduced, and then begins to decrease (for the conical part of the indenter).
Methods for measuring hardness [edit | edit code]
Methods for determining hardness based on the method of applying load are divided into: 1) static and 2) dynamic (shock).
There are several scales (measurement methods) for measuring hardness:
- Brinell method - hardness is determined by the diameter of the imprint left by a carbide ball pressed into the surface. Hardness is calculated as the ratio of the force applied to the ball to the area of the imprint (and the area of the imprint is taken as the area of part of a sphere, and not as the area of a circle (Meyer hardness)); dimension of Brinell hardness units MPa (kgf/mm²). The hardness determined by this method is denoted by HBW, where H is hardness Brinell , W is the indenter material, then the indenter diameter, load and holding time are indicated. Steel balls are no longer used as indenters for the Brinell method.
- Rockwell method - hardness is determined by the relative depth of indentation of a steel, carbide ball or diamond cone into the surface of the material being tested. Hardness determined by this method is dimensionless and is designated HRA, HRB, HRC, etc.; hardness is calculated by the formula HR = 100 (130) − h/e , where h is the depth of relative indentation of the tip after removing the main load, and e is a coefficient equal to 0.002 mm for the Rockwell method and 0.001 mm for super Rockwell. Thus, the maximum Rockwell hardness on the A and C scales is 100 units, and on the B scale - 130 units. There are a total of 54 Rockwell hardness scales.
- Vickers method - hardness is determined by the area of the imprint left by a tetrahedral diamond pyramid pressed into the surface. Hardness is calculated as the ratio of the load applied to the pyramid to the surface area of the imprint (with the surface area of the imprint taken as the area of part of a geometrically regular pyramid, and not as the surface area of the actual imprint); dimension of Vickers hardness units kgf/mm² . The hardness determined by this method is designated HV with the obligatory indication of the load and holding time.
- Shore's methods:
- Shore hardness (Indentation method) - hardness is determined by the depth of penetration into the material of a special hardened steel needle (indenter) under the action of a calibrated spring [4]. In this method, the measuring device is called a durometer. Typically, the Shore method is used to determine the hardness of low-modulus materials (polymers). The Shore method, described by ASTM D2240, specifies 12 measurement scales. The most commonly used options are A (for soft materials) or D (for harder materials). The hardness determined by this method is indicated by the letter of the scale used, written after the number with an explicit indication of the method.
- Durometers and Asker scales - the measurement principle corresponds to the indentation method (according to Shore). Branded and national Japanese modification of the method. Used for soft and elastic materials. It differs from the classical Shore method in some parameters of the measuring instrument, brand names of scales and indenters.
- Shore hardness (Rebound method) is a method for determining the hardness of very hard (high-modulus) materials, mainly metals, by the height to which, after an impact, a special striker (the main part of a scleroscope - a measuring device for this method) rebounds, falling from a certain height [5] . Hardness according to this Shore method is assessed in conventional units proportional to the height of the striker’s rebound. The main scales are C and D. Designated HSx , where H is Hardness , S is Shore and x is a Latin letter indicating the type of scale used in the measurement [6][7].
It should be understood that although both of these methods are methods for measuring hardness, proposed by the same author, have the same names and the same scale designations, these are not versions of the same method, but two fundamentally different methods with different scale values, described by different standards.
- Kuznetsov-Herbert-Rehbinder method - hardness is determined by the damping time of the oscillations of a pendulum, the support of which is the metal under study;
- Poldi method (double ball imprint) - hardness is assessed in comparison with the hardness of the standard, the test is carried out by impact pressing a steel ball simultaneously into the sample and the standard (see illustration);
- Mohs Scale - Determined by which of ten standard minerals scratches the material being tested, and which of ten standard minerals scratches the material being tested.
- The Buchholz method is a method for determining hardness using the Buchholz device. Designed for testing the hardness (Buchholz hardness) of polymer paint and varnish coatings when indenting the Buchholz indenter. The method is regulated by ISO 2815, DIN 53153, GOST 22233 standards [8][9].
Source: https://crast.ru/instrumenty/v-kakih-edinicah-izmerjaetsja-tverdost-metalla
How to determine the hardness of metal at home
Mechanical engineering parts and mechanisms, as well as tools intended for their processing, have a set of mechanical characteristics. Hardness plays a significant role among the characteristics. The hardness of metals clearly shows:
- wear resistance of metal;
- possibility of processing by cutting, grinding;
- resistance to local pressure;
- ability to cut other materials and others.
Hardness of metals
In practice, it has been proven that most of the mechanical properties of metals directly depend on their hardness.
Non-ferrous metals
The Brinell hardness of copper is 35 HB, the values of brass are 42-60 HB units, depending on its brand. For aluminum, the hardness is in the range of 15-20 HB, and for duralumin it is already 70 HB.
How is the hardness of a metal measured?
The hardness of a metal is its property of resisting plastic deformation during the contact action of a standard tip body on the surface layers of the material.
Hardness testing is the main method for assessing the quality of heat treatment of a product.
Determination of hardness using the Brinell method . The method is based on inserting a steel ball into a flat surface under load. The hardness number HB is determined by the ratio of the load to the spherical surface of the indentation.
The Rockwell (HR) method is based on statically pressing a tip into the test surface under a certain load. Steel balls are used as tips for materials with hardness up to 450 HR. In this case, the hardness is designated as HRB . When using a diamond cone, hardness is designated as HRA or HRC (depending on load).
Vickers hardness (HV) is determined by statically pressing a diamond tetrahedral pyramid into the test surface. During the test, the indentation is measured with an accuracy of 0.001 mm using a microscope, which is an integral part of the Vickers instrument.
Shor's method . The essence of this method is to determine the hardness of the sample material by the height of the rebound of the striker falling onto the surface of the test body from a certain height. Hardness is assessed in conventional units proportional to the height of the striker's rebound.
HRC hardness numbers for some parts and tools
Parts and toolsHRC hardness number| Hinged bolt heads, hex nuts, clamping handles | 33. 38 |
| Hinge screw heads, setscrew ends and heads, hinge axes, clamping and removable strips, screw heads with internal hex holes, drive chuck pin | 35. 40 |
| Round nut splines | 36. 42 |
| Gears, keys, clamps, crackers for machine grooves | 40. 45 |
| Spring and retaining rings, tension wedges | 45. 50 |
| Self-tapping screws, turning centers, eccentrics, mushroom supports and support plates, mounting pins, collets | 50. 60 |
| Installation nuts, locknuts, blockers for machine grooves, circular eccentrics, eccentric cams, clamps for dividing devices, replaceable jaws for vices and chucks, gear wheels | 56. 60 |
| Working surfaces of gauges - plugs and staples | 56. 64 |
| Copiers, carbon rollers | 58. 63 |
| Jig bushings, rotating bushings for boring bars | 60. 64 |
Table of relationships between hardness numbers according to Brinell, Rockwell, Vickers, Shore
Rockwell, Vickers and Shore hardness values indicated correspond to Brinell hardness values determined using a 10 mm diameter ball.
RockwellBrinellVickers (HV)ShoreHRCHRAHRBPrint diameterHB| 65 | 84,5 | — | 2,34 | 688 | 940 | 96 |
| 64 | 83,5 | — | 2,37 | 670 | 912 | 94 |
| 63 | 83 | — | 2,39 | 659 | 867 | 93 |
| 62 | 82,5 | — | 2,42 | 643 | 846 | 92 |
| 61 | 82 | — | 2,45 | 627 | 818 | 91 |
| 60 | 81,5 | — | 2,47 | 616 | — | — |
| 59 | 81 | — | 2,5 | 601 | 756 | 86 |
| 58 | 80,5 | — | 2,54 | 582 | 704 | 83 |
| 57 | 80 | — | 2,56 | 573 | 693 | — |
| 56 | 79 | — | 2,6 | 555 | 653 | 79,5 |
| 55 | 79 | — | 2,61 | 551 | 644 | — |
| 54 | 78,5 | — | 2,65 | 534 | 618 | 76,5 |
| 53 | 78 | — | 2,68 | 522 | 594 | — |
| 52 | 77,5 | — | 2,71 | 510 | 578 | — |
| 51 | 76 | — | 2,75 |
Source: https://MyTooling.ru/instrumenty/v-chem-izmerjaetsja-tverdost-metalla
Relationships between hardness numbers
The hardness of a metal is its property of resisting plastic deformation during the contact action of a standard tip body on the surface layers of the material.
Hardness testing is the main method for assessing the quality of heat treatment of a product.
Determination of hardness using the Brinell method . The method is based on inserting a steel ball into a flat surface under load. The hardness number HB is determined by the ratio of the load to the spherical surface of the indentation.
The Rockwell (HR) method is based on statically pressing a tip into the test surface under a certain load. Steel balls are used as tips for materials with hardness up to 450 HR. In this case, the hardness is designated as HRB . When using a diamond cone, hardness is designated as HRA or HRC (depending on load).
Vickers hardness (HV) is determined by statically pressing a diamond tetrahedral pyramid into the test surface. During the test, the indentation is measured with an accuracy of 0.001 mm using a microscope, which is an integral part of the Vickers instrument.
Shor's method . The essence of this method is to determine the hardness of the sample material by the height of the rebound of the striker falling onto the surface of the test body from a certain height. Hardness is assessed in conventional units proportional to the height of the striker's rebound.
How to determine the hardness of a metal - Metalworker's Handbook
Mechanical engineering parts and mechanisms, as well as tools intended for their processing, have a set of mechanical characteristics. Hardness plays a significant role among the characteristics. The hardness of metals clearly shows:
- wear resistance of metal;
- possibility of processing by cutting, grinding;
- resistance to local pressure;
- ability to cut other materials and others.
Hardness of metals
In practice, it has been proven that most of the mechanical properties of metals directly depend on their hardness.
How is the hardness of a material measured?
The hardness of a metal is its property of resisting plastic deformation during the contact action of a standard tip body on the surface layers of the material.
Hardness testing is the main method for assessing the quality of heat treatment of a product.
Determination of hardness using the Brinell method . The method is based on inserting a steel ball into a flat surface under load. The hardness number HB is determined by the ratio of the load to the spherical surface of the indentation.
The Rockwell (HR) method is based on statically pressing a tip into the test surface under a certain load. Steel balls are used as tips for materials with hardness up to 450 HR. In this case, the hardness is designated as HRB . When using a diamond cone, hardness is designated as HRA or HRC (depending on load).
Vickers hardness (HV) is determined by statically pressing a diamond tetrahedral pyramid into the test surface. During the test, the indentation is measured with an accuracy of 0.001 mm using a microscope, which is an integral part of the Vickers instrument.
Shor's method . The essence of this method is to determine the hardness of the sample material by the height of the rebound of the striker falling onto the surface of the test body from a certain height. Hardness is assessed in conventional units proportional to the height of the striker's rebound.
