Hardness is a measure of the ability of a metal material to resist being pressed or etched by an external force, and is one of the most important indicators of the mechanical properties of metal materials. Hardness testing is one of the most rapid, economical and simple test methods to evaluate the mechanical properties of metals. Hardness testing can reflect the differences in the properties of metal materials in different chemical compositions, organizational structures and heat treatment process conditions, so it is widely used in the inspection of metal properties, supervision of the quality of heat treatment process and the development of new materials.
Brinell hardness
It is achieved by pressing a Quenching steel ball or carbide ball of diameter D into the surface of the metal material to be measured with a load P of a certain size, holding it for a certain period of time and then removing the load. The ratio of the load P to the surface area of the indentation F is the Brinell hardness value, denoted as HB. Brinell hardness values are generally expressed in kilograms of force/mm² (N/mm²), but in practice they are also commonly used as HBW or HBS.
1 measurement method
Test conditions: the test load and the diameter of the test steel ball need to be determined according to the actual performance of the material. Common test load and steel ball diameter have fixed standards to adapt to the hardness test of different materials.
Measurement process: The material to be tested is firstly placed on the hardness tester, and then indentation test is carried out with the selected load and steel ball. After holding for a certain time, the load is removed and the diameter of the indentation is measured.
Hardness calculation: Based on the diameter of the indentation, the Brinell hardness value can be calculated by means of a formula or by looking up a table.
2 Application
Brinell hardness tester is mainly used for hardness determination of cast iron, steel, non-ferrous metals and soft alloys and other materials.
It is widely used in metallurgy, forging, electric power, petroleum machinery, rail vehicles, automobiles, military equipment, laboratories, colleges and universities and scientific research.
3 the method of expression
Brinell hardness symbol with HBS or HBW. HBS indicates that the indenter is hardened steel ball, used for the determination of Brinell hardness value of 450 below the material; HBW indicates that the indenter is cemented carbide, used for the determination of Brinell hardness value of 650 below the material.
Expression: the number before HBS or HBW is the hardness value, followed by numbers in order to indicate the test conditions, including the diameter of the ball of the indenter, the test load and the test load holding time (10~15s not marked). For example, 170HBS10/1000/30 indicates that the Brinell hardness value of 170 measured with a steel ball of 10mm diameter, held for 30s under a test load of 9807 N (1000 kg.).
Vickers Hardness
Vickers hardness, expressed by the symbol HV, is the British Smith (Robert L. Smith) and Sedland (George E. Sandland) in 1921 in the Vickers company (Vickers Ltd) proposed. It uses a relative surface angle of 136 degrees between the diamond positive prismatic cone indenter, in the provisions of the load F under the action of pressure into the test sample surface, keep a certain period of time after unloading, measure the indentation diagonal length d, and then calculate the surface area of the indentation, and finally out of the indentation of the average pressure on the surface area of the hardness of the metal Vickers value.
1 Measuring method
In the actual measurement, do not need to carry out complex calculations, but according to the measured diagonal length of the indentation d value, directly check the table to get the measured hardness value.
Commonly used Vickers hardness tester load range of 49.03 ~ 980.7N, suitable for larger workpieces and deeper surface layer hardness determination.
For the determination of the hardness of the thinner workpiece, tool surface or plating layer, you can use a small load Vickers hardness, test load of 1.961 ~ 49.03N.
Micro Vickers hardness is suitable for microscopic analysis.
2 Representation
Vickers hardness value of the standard format for reporting xHVy, where x represents the Vickers hardness value, y represents the measurement of the load value used (unit: kg force). For example, 185HV5 hardness value of 185, the measurement of the load value used for 5 kg force.
3 Application range
Vickers hardness tester has a wide range of applications, can measure almost all metal materials used in industry, from very soft materials to very hard materials can be measured. In addition, it can also be used for hardness testing of ceramic materials, plastics and rubber, cardboard materials and so on.
4 Sample requirements
The surface of the specimen should be smooth and flat, no oxide skin, debris and oil.
In general, Vickers hardness specimen surface roughness parameter Ra is not greater than 0.40μm, small load Vickers hardness specimen is not greater than 0.20μm, micro Vickers hardness specimen is not greater than 0.10μm.
Rockwell hardness
Rockwell hardness is an index to determine the hardness value by the depth of indentation plastic deformation. It uses the specified conditions of the indenter (diamond cone, steel ball or tungsten carbide ball) pressed into the surface of the specimen in two steps, and measure the depth of indentation residual depth h to represent the hardness.
1 measurement method indenter and test force
Rockwell hardness test using three kinds of indenter (diamond cone and two diameters of steel ball) and three kinds of test force (60kg, 100kg, 150kg). These combinations correspond to the Rockwell hardness of nine scales, namely, HRA, HRB, HRC, HRD, HRE, HRF, HRG, HRH, HRK. surface Rockwell hardness test uses two indenter and three smaller test force (15kg, 30kg, 45kg), corresponding to six scales.
2 Hardness value calculation
Rockwell hardness value is calculated by the following formula: N-constant (for different scales, N takes 100 or 130); h-residual indentation depth, mm; S-constant (for Rockwell hardness, S = 0.002mm; for surface Rockwell hardness, S = 0.001mm).
3 Characteristics
Advantages: Rockwell hardness test is simple and rapid, the indentation is small, the determination of a wide range, applicable to most metal materials.
Disadvantages: poor representativeness, data repeatability is not good, not applicable to the organisation of uneven material or thin material and surface hardening layer.
4 Application
Rockwell hardness test is commonly used for materials with high hardness, such as Quenching steel, cast iron, etc..
The three commonly used scales are HRA, HRB and HRC, which are suitable for different hardness materials.
Selection of hardness scales
HRA: Used for materials with higher hardness, such as steel sheet, cemented carbide, with 60kg load and diamond cone indenter.
HRB: Used for materials with lower hardness, such as soft steel, non-ferrous metals, annealed steel, etc., with 100kg load and 1.5875mm diameter hardened steel ball.
HRC: For materials with higher hardness, such as Quenching steel, cast iron, etc., using 150kg load and diamond cone indenter.
By selecting the appropriate combination of indenter and test force, Rockwell hardness test can provide accurate hardness values, providing an important basis for material selection and quality control.