HRA 60kg载荷金刚石锥压入器；HRB 100kg载荷1/16"直径钢球压头；HRC 150kg载荷金刚石锥压入器；最常用标尺是HRC、HRB和HRF，其中HRC标尺用于测试淬火钢、回火钢、调质钢和部分不锈钢。这是金属加工行业应用最多的硬度试验方法。HRB标尺用于测试各种退火钢、正火钢、软钢、部分不锈钢及较硬的铜合金。HRF标尺用于测试纯铜、较软的铜合金和硬铝合金。HRA标尺尽管也可用于大多数黑色金属，但是实际应用上一般只限于测试硬质合金和薄硬钢带材料。
Rockwell hardness is an index of hardness value determined by the depth of indentation plastic deformation, with 0.002 mm as a hardness unit. Different head and different test force in rockwell hardness test will produce different combinations, corresponding to different scales of rockwell hardness. There are three scales commonly used, and their application covers almost all commonly used metal materials.
Rockwell hardness (HR) test, when the sample measured is too small or the brinell hardness (HB) is greater than 450, then rockwell hardness measurement is used. The test method is to use a diamond cone with a top Angle of 120 ° or a steel ball with a diameter of 1.5875mm/3.175mm/ 6.35mm/12.7mm to press into the surface of the measured material under a certain load and calculate the hardness of the material from the indentation depth. Laizhou city tester diamond tools factory is A machine tool spindle, rotary plunger, screw, screw, shaft processing, CNC lathe processing, the handle bar, chuck jaw for the company's flagship product, quality guarantee, the most commonly used three kinds of scale as A, B, C, namely, HRA, HRB, HRC, according to the different experimental material hardness, choose different hardness range of scale to indicate:
HRA is the hardness obtained by using 60Kg load and drill cone presser. It is used for materials with higher hardness. For example: steel sheet, hard alloy.
HRB is a hardness obtained from a hardened steel ball with a diameter of 1.5875mm and a load of 100Kg. Examples: mild steel, nonferrous metals, annealed steel, etc.
HRC is the hardness obtained by 150Kg load and drill cone presser. It is used for materials with higher hardness. For example: hardened steel, cast iron and so on.
Rockwell hardness test USES three test forces and three pressure heads. There are nine combinations corresponding to the nine scales of rockwell hardness: HRA, HRB, HRC, HRD, HRE, HRF, HRG, HRH and HRK. The application of these nine scales covers almost all commonly used metal materials.
HRA 60kg load diamond cone presser; HRB 100kg load 1/16" diameter steel ball head; HRC 150kg load diamond cone presser; The most commonly used gauges are HRC, HRB, and HRF. HRC gauges are used to test hardened, tempered, tempered, and partially stainless steels. This is the most widely used hardness test method in the metal processing industry. HRB gauge is used to test all kinds of annealed steel, normalizing steel, mild steel, some stainless steel and hard copper alloy. HRF gauge is used for testing pure copper, softer copper alloys and duralumin. Although HRA gauges can also be used for most ferrous metals, their practical applications are generally limited to testing hard and thin steel strip materials.
The surface rockwell hardness test USES three test forces, two pressure heads, and six combinations corresponding to six scales of surface rockwell hardness. The surface rockwell hardness test is a supplement to the rockwell hardness test. When the rockwell hardness test is used, when the material is thinner, the sample is smaller, the surface hardening layer is shallow or the test surface is coated, the rockwell hardness test should be used instead. A valid hardness test result can be obtained on the sample by using the same head as the rockwell hardness test and a test force that is only a fraction of the size of the rockwell hardness test. The N scale of surface rockwell hardness is applicable to materials tested with HRC, HRA and HRD similar to rockwell hardness. The T scale is suitable for testing materials with HRB, HRF and HRG hardness similar to rockwell hardness.
The scales of rockwell and surface rockwell durometers (i.e. different combination of head and test force) are usually selected according to the type of material, sample thickness and hardness range. The specific selection method is described as follows:
1. Choose according to material type
A scale is mainly used to measure the hardness of tungsten carbide, hard alloy, surface hardened parts and so on.
B scale is mainly used to measure the hardness of non-ferrous metals, alloys, annealed steel and other low-hardness parts.
C scale is mainly used to measure the hardness of carbon steel, tool steel and alloy steel after quenching and tempering.
Selecting by material is not a strict practice. Because each material with its different heat treatment process, its final hardness can not be the same, so adapt to the hardness scale will not be the same.
2. Choose according to the hardness range of the sample:
1) relationship between sample hardness and material composition and heat treatment process: under the same heat treatment process, the higher the carbon content of the material, the higher the hardness of the material. Corresponding to the same material, the hardness caused by the process is: quenching, normalizing, annealing.
2) applicable range of various rockwell hardness scales. Each rockwell hardness scale has a usable range that can be easily determined from the scale on the durometer dial.
3. According to thickness or depth of hardened layer
Rockwell hardness test requires that the thickness of the sample should not be less than 10 times of the residual indentation depth, and there should be no obvious deformation traces on the back side of the sample. The thickness of the sample determines the choice of load. The load must be less than the minimum thickness of the sample. For each hardness test, a minimum measurable thickness exists.
Some scales (such as N, T, W, X, Y) complement the rockwell hardness test and are derived from the surface rockwell hardness test. Because in the use of rockwell hardness test, when the material is thinner, the sample is small, the surface hardening layer is shallow or the test surface coating layer, we should use the surface rockwell hardness test.
The reason why there are so many kinds of rulers is that in the use of rulers, the closer they are to the upper and lower limits, the less accurate they are.
The range of use of HRC ruler is 20~70HRC. When the hardness value is less than 20HRC, the sensitivity decreases because the cone part of the head is pressed too much, then HRB ruler should be used. Diamond tools factory laizhou city testing machine is the machine tool spindle, rotary plunger, screw, screw, shaft processing, CNC lathe processing, the handle bar, chuck jaw for the company's flagship product, although the HRC the upper limit of the scale of 70 HRC, but when the sample hardness greater than 67 HRC, head tip pressure is too large, diamond is easy to damage, head will shorten the service life, so in the measurement of partial HRC hardness scale limit, you should use HRA rod, because the limit range with HRC HRA was, but much smaller test force.
The scope of HRA ruler is 20-88hra, and the following conversion relationship can be obtained from American standard ASTM E140:27HRA≈30HRB; 60 hra material 100 HRB material 20 HRC; 85.6 68 HRC HRA material; It can be seen that, at the same value, the hardness of the corresponding ruler is C, A and B from high to low, but the HRA ruler has A wide test range, basically including HRB and HRC, covering the hardness range from mild steel (HRB) and hard steel (HRC) to hard alloy.
But in fact, the HRA gauge is rarely used to test mild steel. It is mainly used to test thin and hard steel plate, deep carburized carbon steel and hard alloy. In terms of cemented carbide, due to technological progress, the hardness of some materials has reached 93-94hra, and it has become a convention that the hardness of materials exceeds the upper limit of the measurement range of HRA. According to the characteristics of the wide range of HRA scale test, when using rockwell hardness tester to test steel samples, if you do not know whether the samples are soft steel or hard steel, you can use HRA scale to test first. When the hardness value is less than 60HRA, you can use HRB scale; when the hardness value is greater than 60HRA, you can use HRC scale.
The range of use of HRB scale is 20~100HRB. When the hardness value is lower than 20HRB, HRF scale should be used instead because the pressing depth of steel ball is too large, the creep of metal is intensified, the deformation time of sample under the action of test force is prolonged, and the accuracy of test value is decreased. When the hardness value is greater than 100HRB, the sensitivity and accuracy of the steel ball will be reduced due to the shallow pressing depth, so HRC scale should be used instead.
In the use of HRB test steel sample scale, a special note: when don't know in advance sample is soft or hard steel, steel must never use HRB test scale, because with a steel ball head misplaced the hardened steel, steel ball could be out of shape, ball head will be damaged, this is the main reason for the damage of steel ball head. In this case, diamond head should be used first, HRA ruler should be used to test it, and then HRB or HRC should be used.
The HRF ruler can be used from 60 to 100HRF. HRF ruler is one of the most widely used rulers in foreign countries. It is a good method to test pure copper and soft copper alloy materials. But in China, there is also a shortage of standard blocks, and its use is limited.
HRG ruler is suitable for materials with HRB value close to 100. Beryllium bronze, phosphorus bronze and malleable iron whose hardness range is between the high end of HRB ruler and the low end of HRC ruler can greatly improve the sensitivity and accuracy of the test if HRG ruler is used instead.
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