Seamless steel pipes are commonly used to measure the hardness of Brinell, Rockwell, and Vickers.
a. Brinell hardness
Among the seamless steel pipe standards, Brinell hardness is the most widely used, and the hardness of the material is often expressed by the indentation diameter, which is intuitive and convenient. However, it is not suitable for steel pipes with harder or thinner steel.
b. Rockwell hardness
The Rockwell hardness test of seamless steel tubes is the same as the Brinell hardness test, which is an indentation test method. The difference is that it measures the depth of the indentation. Rockwell hardness test is a widely used method at present, in which HRC is second only to Brinell hardness HB in the steel pipe standard. Rockwell hardness can be applied to the determination of metal materials from extremely soft to extremely hard. It makes up for the deficiencies of the Brinell method. It is simpler than the Brinell method, and the hardness value can be read directly from the dial of the hardness machine. However, because of its small indentation, the hardness value is not as accurate as the Brinell method.
c. Vickers hardness
Seamless steel pipe Vickers hardness test is also an indentation test method, which 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 shortcomings, but it is not as simple as the Rockwell method, and the Vickers method is rarely used in steel pipe standards.
2. Hardness testing method of seamless steel pipe
The hardness test of stainless steel should take into account its mechanical properties, which is related to the performance and quality of deformation, stamping, cutting and other processing using stainless steel as a raw material. Therefore, all seamless steel tubes must be tested for mechanical properties. The mechanical property test methods are mainly divided into two categories, one is tensile test and the other is hardness test.
The tensile test is to make a seamless steel tube into a sample, pull the sample to break on a tensile testing machine, and then measure one or several mechanical properties, usually only the tensile strength, yield strength, elongation after break and rate of reduction in area. Tensile test is the most basic mechanical property test method for metal materials. Almost all metal materials, as long as there are requirements for mechanical properties, have specified tensile tests. Especially for materials whose shape is not convenient for hardness testing, tensile testing becomes the only means of testing mechanical properties.
The hardness test is to slowly press a hard indenter into the surface of the sample according to the specified conditions, and then test the depth or size of the indentation to determine the hardness of the material. The hardness test is the simplest, fastest and easiest method to perform in the mechanical properties test of materials. The hardness test is non-destructive, and there is an approximate conversion relationship between the material hardness value and the tensile strength value. The hardness value of the material can be converted into a tensile strength value, which has great practical significance.
Because the tensile test is not easy to test, and it is very convenient to convert from hardness to strength, people are increasingly testing only the hardness of the material and less testing its strength. In particular, due to the continuous advancement and innovation of the hardness tester manufacturing technology, some materials that could not be directly tested for hardness, such as seamless steel tubes, stainless steel plates and stainless steel bands, are now possible to directly test the hardness. Therefore, there is a tendency that the hardness test gradually replaces the tensile test.
Most of the national standards for stainless steel materials specify both tensile test and hardness test. For those materials that are not convenient for hardness testing, such as seamless steel tubes, only tensile tests are specified. In the stainless steel standard, three hardness test methods of Brinell, Rockwell, and Vickers are generally specified to determine the HB, HRB (or HRC) and HV hardness values, and only one of the three hardness values is required. In particular, the company's newly developed portable surface Rockwell hardness tester and pipe Rockwell hardness tester can quickly and accurately test the hardness of stainless steel plates as thin as 0.05mm, stainless steel strips and seamless steel tubes as thin as ￠4.8mm. It has solved problems that were difficult to solve in the past in the country.
3. Seamless steel tube hardness testing tool
Seamless steel pipe with an inner diameter of 6.0mm or more and a wall thickness of 13mm or less can be annealed seamless steel pipe. The W-B75 Vickers hardness tester can be used. It is very fast and simple to test, suitable for rapid and non-destructive seamless steel pipe Conformity inspection. Seamless steel pipes with inner diameter greater than 30mm and wall thickness greater than 1.2mm are tested with Rockwell hardness tester for HRB and HRC hardness. Seamless steel tubes with inner diameter greater than 30mm and wall thickness less than 1.2mm are tested with surface Rockwell hardness tester to test HRT or HRN hardness. For seamless steel pipes with an inner diameter of less than 0mm and greater than 4.8mm, a special Rockwell hardness tester for pipes is used to test the HR15T hardness. When the inner diameter of the seamless steel pipe is greater than 26mm, you can also use the Rockwell or surface Rockwell hardness tester to test the hardness of the inner wall of the pipe.