Hardness is a mechanical property indicator that measures the degree of softness and hardness of a metal material. It represents the ability of the local volume on the metal surface to resist deformation. Hardness is not a simple physical concept, but a comprehensive indicator of mechanical properties such as material elasticity, plasticity, strength, and toughness.

Definition:

Hardness is a performance indicator that measures the degree of softness and hardness of metal materials. Hardness testing is widely used in production practice and scientific research due to its characteristics of simple and fast testing methods, non-destructive testing of parts, and certain relationships with other mechanical properties. It is used to test and evaluate the properties of metal materials. There are many hardness testing methods, which can be basically divided into several types: indentation method (such as Brinell, Rockwell, Vickers hardness, etc.), scratch method (such as Mohs method, etc.), rebound method (such as Shore method), etc.

The physical meaning of hardness values varies with different testing methods. The hardness value of the indentation method represents the ability of the material surface to resist plastic deformation caused by another object's indentation; The hardness value of the scratch method represents the ability of a metal to resist local surface fractures; The hardness of the rebound method represents the magnitude of the elastic deformation work of the metal. Therefore, hardness value is not simply a physical quantity, but a comprehensive performance indicator that characterizes a series of different combinations of physical quantities such as elasticity, plasticity, deformation strengthening, strength, and toughness of materials. It is generally believed that hardness is the ability of a metal to resist deformation or fracture within a small volume on the surface

Category:

The code for metal hardness is H. According to different hardness testing methods, conventional indications include Brinell (HB), Rockwell (HRC), Vickers (HV), and Leeb (HL) hardness, among which HB and HRC are more commonly used.

Measure:

HB has a wide range of applications, while HRC is suitable for materials with high surface hardness, such as heat treatment hardness. The difference between the two lies in the different measuring heads of the hardness tester. The measuring head of the Brinell hardness tester is a steel ball, while the measuring head of the Rockwell hardness tester is a diamond.

HV is suitable for microscopic analysis. The Vickers hardness (HV) is obtained by pressing a diamond square cone indenter with a load of up to 120kg and a top angle of 136 ° into the surface of the material, dividing the surface area of the material indentation by the load value.

HL handheld hardness tester, easy to measure, uses the impact ball head to impact the hardness surface, causing bouncing; Calculate the hardness using the ratio of the rebound velocity and impact velocity of the punch at a distance of 1mm from the surface of the specimen. The formula is: Leeb hardness HL=1000 × VB (rebound velocity)/VA (impact velocity).

The portable Leeb hardness tester can convert Brinell (HB), Rockwell (HRC), Vickers (HV), and Shore (HS) hardness measurements using Leeb (HL). Alternatively, hardness values can be directly measured using Brinell (HB), Rockwell (HRC), Vickers (HV), Leeds (HL), and Shore (HS) principles.

Brinell hardness

Brinell hardness (HB) is generally used when materials are softer, such as non-ferrous metals, steel before heat treatment, or after annealing. Rockwell hardness (HRC) is generally used for materials with higher hardness, such as hardness after heat treatment, and so on.

Cloth hardness (HB) is a test load of a certain size, where a certain diameter of quenched steel ball or hard alloy ball is pressed into the surface of the tested metal, held for a specified time, and then unloaded to measure the diameter of the indentation on the tested surface. The Brinell hardness value is the quotient obtained by dividing the load by the spherical surface area of the indentation. Generally, a hardened steel ball of a certain size (usually 10mm in diameter) is pressed into the surface of the material under a certain load (usually 3000kg), maintained for a period of time, and after unloading, the ratio of the load to the indentation area is the Brinell hardness value (HB), in kilograms per square meter (N/mm2).

Rockwell hardness

Rockwell hardness is the process of pressing a very hard steel ball or diamond cone into the surface of a specimen under a certain load, and determining the hardness of the material based on the depth of indentation [3]. Rockwell hardness is a hardness index determined by the depth of indentation plastic deformation. Use 0.002 millimeters as a hardness unit. When HB>450 or the sample is too small, the Brinell hardness test cannot be used and Rockwell hardness measurement should be used instead. It is a diamond cone with a top angle of 120 ° or a steel ball with a diameter of 1.59 and 3.18mm, pressed into the surface of the tested material under a certain load, and the hardness of the material is calculated from the depth of the indentation. According to the different hardness of the test materials, there are three different scales to represent:

HRA: It is a hardness obtained using a 60kg load and a diamond cone indenter, used for materials with extremely high hardness (such as hard alloys).

HRB: It is the hardness obtained using a 100kg load and a 1.58mm diameter quenched steel ball, used for materials with lower hardness (such as annealed steel, cast iron, etc.).

HRC: It is a hardness obtained using a 150kg load and a diamond cone indenter, used for materials with high hardness (such as quenched steel).

Vickers hardness

The Vickers hardness test for seamless steel pipes is also an indentation test method that can be used to determine the hardness of very thin metal materials and surface layers. It has the main advantages of the Brinell and Rockwell methods and overcomes their basic disadvantages, but it is not as simple as the Rockwell method, and the Vickers method is rarely used in steel pipe standards.