The Rockwell hardness test is one of the three most commonly used hardness tests, as is the Brinell and Vickers hardness test.

The evolution of the Rockwell hardness test national standard, the introduction of the metal Rockwell hardness test GB/T230.1-2004 adopts the International Organization for Standardization ISO 6508-1 - 1999: "The Rockwell hardness test of metal materials Part 1: Test method (A , B, C, D, E, F, G, H, K, N, T scales). This standard replaces GB/T230-1991 "Metal Rockwell Hardness Test Method" and GB/T1818-1994 "Metal Surface Rockwell Hardness Test Method".

First, Rockwell hardness testing method

Principle

The Rockwell hardness test method uses a 120° diamond cone or a cemented carbide ball (with a specified diameter) as the indenter. Under the action of the initial detection force F0, plus the main detection force F1, under the action of the total detection force F, the pressure is applied. The head is pressed into the surface of the sample. After that, the main detection force is removed, and the residual increment h of the indentation depth is measured while retaining the initial test force F0, and the Rockwell hardness is calculated by the formula (3-1) according to the h value and the Changshu N and S (see Table 3-1).

2. Symbols and calculation formulas

The symbols used in Rockwell hardness testing and calculation formulas and their meanings are shown in Table 3-1.

Calculation formula: Rockwell hardness = N-h/s (3 - 1)

According to the definition of Rockwell hardness, a Rockwell hardness (HR) unit is defined as a residual increment of indentation depth of 0.002 mm under specific conditions.

The Rockwell hardness reading is as follows: the diamond indenter (A, C, D scale) formula is Rockwell hardness = l00-h / 0.002; with steel ball or carbide ball indenter (B, E, F, G, H, K scale) is Rockwell hardness = 130-h / 0.002.

It is seen from the formula of HR=N-h/s that the larger the residual increment h of the indentation depth, the lower the Rockwell hardness value; the smaller the h, the higher the hardness value. Where N is a defined constant, with a ball indenter of 130; with a diamond indenter of 100. The so-called ruler is distinguished by a combination of different indenters and total detection force. For example, with a diamond cone indenter, the total detection force is 980.7 N (100 kgf), which is the B scale HRB.

h is the residual indentation depth increment after maintaining the initial detection force F0 after the main detection force is removed. With diamond indenter, under the total detection force of 147lN, after the main detection force is removed, if h is 0.08mm, since each Rockwell hardness unit is 0.002mm, HRC=100-40=60. It can be seen that this value is dimensionless as a conditional unnamed number.

Why are N values ​​defined as 100 and 130? When the indenter is a diamond cone, because HRC (A) is specified for measuring hard materials, such as steel and hard alloy after quenching, the indentation depth is generally 0.2 mm and the hardness value is zero. Case. When the indenter is a ball, it is mostly used to measure medium and low hardness materials, and the hardness value span is large. In order to avoid negative values, the ball's Rockwell scale N value is set to 130. The surface Rockwell N value is defined as 100.

3. Loading method

Weight loading spring loaded hydraulic loading closed loop sensor control

4. Rockwell hardness scale and technical parameters

There are 15 scales in GB/T230.1-2004 standard, including A, B, C, D, E, F, G, H, K9 scales. See Table 3-2 for technical parameters. Surface Rockwell N, T 6 The scale parameters are shown in Table 3-6.

5. Application principle of the ruler

HRA—Applicable to the determination of the hardness of hard or thin hard materials, such as hard alloys, hardened steel after carburizing, thin steel strips after hardening, thin steel sheets, etc. Because the material with HRC>67 still uses 1471N detection force, it is easy to damage the diamond indenter. It is advisable to use a HRA scale with a small detection force and a shallower depth.

HRB—suitable for the determination of medium hardness materials such as annealed medium and low carbon steels, malleable cast iron, various brass and most bronzes, and various hard aluminum alloys after solution treatment aging. The scope of application is 20 to 100 HRB. When the hardness of the sample is less than 20HRB, due to the creep behavior of these metals, the deformation of the sample under the detection force will last for a long time, and the pointer or optical projection scale on the watch will move slowly for a long time, which is difficult to measure accurately. When HRB>100, because the ball penetration depth is too shallow, the sensitivity is lowered, which affects the measurement accuracy.

HRC—The most suitable for the determination of carbon steel, alloy steel and work and die steel after quenching and low temperature tempering. It is also suitable for the determination of chilled cast iron, pearlitic malleable cast iron and titanium alloy. Generally, the material with HRB>100 can be measured by C scale. When HRC<20, because the diamond indenter is pressed too deep, the influence of the indenter cone increases, which causes the sliding phenomenon, which affects the measurement accuracy. It should be replaced by HRB scale.

HRD—a gauge between HRA and HRC that is suitable for pressing a variety of materials between the A and C scales, such as steel specimens after surface heat treatment strengthening, pearlitic malleable cast iron, etc.

HRE—Applicable to the determination of general cast iron, aluminum alloys, magnesium alloys, bearing alloys and other similar soft metals.
HRF—suitable for toughening brass, copper, general aluminum alloy, etc.

HRG—Applies to materials equivalent to HRBs of nearly 100. Because this time is higher than the HRB detection is close to 100.
HRH—Applicable to soft metal alloys such as aluminum, zinc, lead, etc., because the H scale uses a large diameter of the indenter; the detection force is small, and it can be read directly and quickly.
HRK - for bearing alloys and other soft metal materials.

In addition to the three scales of Rockwell A, B, and C, the other six scales, such as Rockwell D, E, F, etc., are added to the revised standard. Because in the ISO standard, these scales have already been applied. After China's accession to the WTO, international trade and technical exchanges will be more frequent. For the reference of various international hardness requirements, the application of these scales is very important.

6. Application range and its characteristics

Rockwell hardness testing is simple, quick, and efficient. Since the detection force is small, the generated indentation is smaller than the indentation of the Brinell hardness detection, and thus there is no significant damage to the surface of the workpiece. Due to the use of a diamond indenter and two diameter balls as the indenter, there are three detection forces, for a total of nine scales (see Table 3-2), which can measure the hardness from softer to harder materials. Wide range of use. Furthermore, there is a pre-detection force, so the slight unevenness of the surface of the test piece has a smaller influence on the hardness value than that of Brinell and Vickers. Therefore, it is suitable for the inspection of machinery, metallurgical thermal processing and semi-finished or finished products in batch production. It is especially suitable for the inspection of finished parts such as cutting tools, molds, measuring tools and tools.

7. Testing and precautions

1) Preparation before testing

(1) The hardness tester and indenter used for Rockwell hardness test shall meet the technical requirements of GB/T230.2-2002 Rockwell hardness tester.
(2) The test is generally carried out at room temperature of 10 to 35 °C. When the accuracy is high, the room temperature should be controlled at (23 ± 5) °C.
(3) When selecting the ruler, according to the material of the sample and its heat treatment state, refer to the application principle of the “5-section” ruler, and select the indenter and the detection force.
(4) If the indenter is removed, the indenter should be installed first. For the side screw to tighten the indenter, the correct device method is: insert the tail of the indenter into the spindle hole, lightly twist the screw cap but do not tighten it, use a sample to add the initial detection force, under the force of the force The step surface is pressed against the lower end surface of the main shaft so that there is no inclination or clearance, and then the fastening screw is tightened.
(5) Select a suitable test bench, the support surface of the test bench should be clean, and the sample should be firmly placed on the test bench to ensure that no displacement or deformation occurs during the test.
(6) Before the inspection, the hardness tester shall be calibrated using a standard Rockwell hardness block similar to the hardness value of the sample, and the test shall be carried out within the allowable error range.

2) Sample

(1) During the preparation of the sample, the surface hardness of the sample shall be affected as much as possible due to heat and cold working.
(2) For tests conducted with a diamond conical indenter, the thickness of the specimen or test layer shall not be less than 10 times the depth of the residual indentation; for tests conducted with a ball indenter, the thickness of the specimen or test layer shall not be less than 15 times the depth of the residual indentation. Figure 3-5 and Figure 3-6 show the minimum thickness of Rockwell hardness.
(3) The test surface of the sample is as flat as possible, and there should be no scale or other dirt or cracks. The surface roughness Ra is generally not more than 0.80 μm.

3) Precautions in the test

(1) Under no circumstances should the indenter be touched with the test bench and the support and sample. There shall be no indentation on the test surface of the specimen, the support and the working surface of the test bench.
(2) When testing, it must be ensured that the direction of the detection force is perpendicular to the detection surface of the sample.
(3) During the detection process, the relevant device should not be subjected to shock and vibration. (4) The detection force should be applied evenly and smoothly, and there should be no impact or vibration.
(5) For low-hardness materials, the retention time can be extended by negotiation and the tolerance is ±2s.
(6) The distance between the centers of two adjacent indentations shall be at least 4 times the diameter of the indentation, but not less than 2 mm.
(7) The distance between the center of any indentation and the edge of the specimen shall be at least 2.5 times the diameter of the indentation, but not less than 1 mm.
(8) The number of detection points on each sample shall be not less than four points (the first point is not recorded). For the detection of large quantities of samples, the number of points can be appropriately reduced.

4) Detection result processing

(1) The Rockwell hardness value given in the test report shall be accurate to 0.5 Rockwell hardness units.
(2) For the Rockwell hardness values ​​measured on the cylindrical surface and the spherical surface, the correction should be made according to Table 3-3 to Table 3-5. The correction values ​​in the table are all positive values.
(3) The written Rockwell hardness is represented by the symbol HR, the hardness value before HR, and the scale used after HR. For example, 50HRC means that the Rockwell hardness value measured by the C scale is 50; 80HRB means that the Rockwell hardness value measured by the B scale is 80; 75HRFW means that the F scale is used, the indenter is a cemented carbide ball, and the hardness value is 75.

Data extracted from the Metal Hardness Test Manual

The most commonly used HR-150A Rockwell hardness tester technical parameters

Main technical specifications:
Measuring range: 20-88HRA, 20-100HRB, 20-70HRC
Test force: 588.4, 980.7, 1471 Newtons (60, 100, 150 kg force)
Maximum allowable height of sample: 170mm
Indenter center to machine wall distance: 135mm
Hardness resolution: 0.5HR
Dimensions: 466 × 238 × 630mm
Weight: about 65kg

main feature:
Manual Rockwell hardness tester, accurate, reliable, durable, and high test efficiency;
Dial direct reading, HRA, HRB, HRC scale;
Optional Rockwell's other rulers;
Precision oil pressure buffer with adjustable loading speed;
Mechanical manual testing process, no electrical control required;
It is widely used in quality control in the production site, and the working environment is adaptable;
Accuracy meets GB/T230.2 ISO6508-2 and American ASTM E18.

Application range:
Determination of Rockwell hardness of ferrous metals, non-ferrous metals, non-metallic materials;

Surface measurement is stable and reliable.
(This article is selected from Laizhou Huayin Hardness Tester)

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