What are the advantages and disadvantages of Brinell hardness testing? What symbols are used?

The ability of a metal material to resist the pressing of other, harder objects into a surface is called hardness, or the resistance of the material to local plastic deformation. Therefore, hardness has a certain relationship with strength. According to the hardness determination method, it can be mainly divided into:

1) Brinell hardness (code HB).

Use a hardened steel ball of a certain diameter d to press into the surface of the specimen under the action of the specified load p, and remove the load after holding it for a period of time, and the indentation with a surface area of f will be left on the surface of the specimen, and the hardness of the specimen is expressed by the size of the load that can be borne by the unit surface area of the specimen: HB=P F. In practice, the diameter of the pit is usually measured directly and the Brinell hardness value is found from the Brinell hardness value table according to the load p and the diameter of the steel ball d (obviously, the larger the pit diameter, the lower the hardness, and the smaller the Brinell hardness value is indicated).

There is a certain relationship between Brinell hardness and the tensile strength of the material: b khb,k is the coefficient, e.g. k for low carbon steel, k for high carbon steel, k ,... for quenched and tempered alloy steelWait a minute.

2) Rockwell hardness (hr).

Use a diamond cone indenter with a certain apex angle (such as 120°) or a hardened steel ball with a certain diameter d to press into the surface of the specimen under a certain load p, hold it for a period of time and then remove the load, and leave an indentation of a certain depth on the surface of the specimen. Composed.

The Rockwell hardness machine automatically measures the pit depth and displays it with a hardness value reading (obviously, the deeper the pit, the lower the hardness and the smaller the Rockwell hardness value is indicated). According to the different indenters and loads, Rockwell hardness is also divided into three types: HRA, HRB and HRC, of which HRC is the most commonly used.

There is a conversion relationship between Rockwell HRC and Brinell HB: HRC.

3) Vickers hardness (HV).

The surface of the material is pressed into the surface of the material with a load of less than 120kg and a diamond square cone press with a top angle of 136°, and the surface area of the material indentation pit is divided.

The load value is the Vickers hardness value (HV).

The Brinell hardness test makes the surface indentation of the material larger, so it is not suitable to test the hardness of the finished product or thin sheet metal. It is commonly used to determine the hardness of blank materials such as non-ferrous metals, low-alloy structural steels, etc. hb

Brinell hardness is expressed in the following numbers: The number before HBS or HBW is the hardness value, and the test conditions are indicated by numbers in order

the diameter of the sphere of the indenter;

test load; The time for the test load to be held (10 to 15 s is not indicated).

Generally speaking, the smaller the Brinell hardness value, the softer the material and the larger its indentation diameter; Conversely, the higher the Brinell hardness value, the harder the material and the smaller the indentation diameter.

The advantages of Brinell hardness measurement are that it has high measurement accuracy, large indentation area, can reflect the average hardness of the material in a large range, and the measured hardness value is also more accurate, and the data is repeatable.

The Brinell hardness range is 8 650 HBW.

For some metal materials, the tensile strength value can be roughly determined based on the Brinell hardness value.

For example: 170HBS10 1000 30 means that a steel ball with a diameter of 10 mm is maintained for 30 seconds under a test load of 9807 N (1000 kgf).

530HBW5 750 means that the Brinell hardness value measured at 10 15s is 530 when a carbide ball with a diameter of 5 mm is maintained under a test load of 7355N (750kgf).

Application: Brinell hardness measurement method is suitable for cast iron, non-ferrous alloys, various annealed and quenched and tempered steels, and it is not suitable to determine samples or workpieces that are too hard, too small, too thin and the surface is not allowed to have large indentations.

The national standard (GB231-84) stipulates that when Brinell hardness test, the commonly used ratio is three, according to the type of metal materials, the hardness range and thickness of the sample, the following table (Brinell hardness test specification) to select the diameter of the test head (steel head) D, the test force F and the holding time.

Brinell hardness: A standard that indicates the hardness of a material.

Brinell hardness characteristics:

Advantages: The measured value is stable, accurate, and can reflect the average hardness of the material more realistically;

Disadvantages: large indentation, slow operation, not suitable for mass production of finished parts and thin parts.

Brinell hardness measurement range: used for hardness measurement of raw materials and semi-finished products, can be used to measure cast iron; Non-ferrous metals (non-ferrous metals), steels with low hardness (e.g. annealed, normalized, quenched and tempered steels).

Brinell hardness: A standard that indicates the hardness of a material.

Brinell hardness: A standard that indicates the hardness of a material.

Brinell (HB) is to press a hardened steel ball or cemented carbide ball of a certain diameter into the surface of the metal to be measured with a certain size of test load, hold it for a specified time, and then unload it to measure the indentation diameter of the measured surface. The cloth hardness value is the quotient of the load divided by the spherical surface area of the indentation. The hardness of cloth type needs to be measured with a microscope to measure the indentation diameter, and then check the table or calculate, which is more cumbersome.

The upper limit of cloth hardness is HB650, which cannot be higher than this value.

The cloth hardness indentation is large, the measurement value is accurate, and it is not suitable for finished products and thin sheets, and it is generally not classified as non-destructive testing.

Brinell hardness. The disadvantages of the test method: the operation time is long, different indenters and test forces are required for different materials, and the indentation measurement is time-consuming; When testing high-hardness materials, the measurement results are inaccurate due to the deformation of the sphere itself.

Because of its large indentation, it is not suitable for measuring finished products and thin parts.

Brinell hardness is mainly suitable for measuring gray cast iron, non-ferrous metals, and various mild steels.

and other materials that are not very hard.

The disadvantage of the Brinell hardness test is that it is generally not suitable for direct inspection on the finished part due to the large indentation diameter. In addition, for materials with different hardnesses, it is necessary to replace the indenter diameter d and load f, and the measurement of the indentation diameter is also troublesome.

Brinell hardness test is most suitable for the hardness of gray cast iron, bearing alloys and other materials.

The disadvantage is that the measurement range is limited, and the indentation diameter is relatively large, which is not suitable for the measurement of finished workpieces. Measurement of low to medium carbon steel, cast iron, non-ferrous metals, etc.

Supplement: The traditional Brinell hardness test has poor wire requirements and requires a certain thickness of the test piece. Now there is a microcomputer with automatic readings.

After the implementation of HBW scale measurement, the measured materials cover a wide range:

all kinds of soft and hard black metals and their alloys;

all kinds of soft and hard non-ferrous metals and their alloys;

all kinds of soft and hard composite materials, etc.;

It is also used for Brinell hardness testing of many non-metallic materials.

Among them, all kinds of cast iron, composite materials, etc. can only be tested with Brinell hardness to obtain ideal results.

Tianyongheng - professional hardness testing instrument.

Brinell hardness: A standard that indicates the hardness of a material.

The commonly used Brinell hardness machine is the quenched steel ball indenter; The Rockwell hardness machine uses a diamond indenter. Therefore, they have different applications when measuring steel materials: Brinell hardness is generally used to determine materials with lower hardness, such as annealed or normalized steel; Whereas, Rockwell hardness is mostly used to determine hardness materials, such as hardened steel.

There is an empirical formula: 1hrc 10hbsTherefore, when the general hardness is above 30HRC, the Rockwell hardness is used, and when it is less than the Brinell hardness, it is expressed by the Brinell hardness.