Introduction of hardness of cs seamless pipe

CS seamless pipe is subject to mechanical properties test. CS seamless pipes are widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames and steel scaffolding used in construction. To save material and processing time, steel pipes have been widely used. There are two main types of mechanical properties testing methods, one is tensile test and the other is hardness test. What we will introduce next is the hardness testing of cs seamless pipes, that is, the ability of metal materials to resist the indentation of the surface of hard objects, which is called hardness.


1) Brinell hardness
In the cs seamless pipe standard, the Brinell hardness is widely used, and the hardness of the material is often expressed by the indentation diameter, which is both intuitive and convenient. However, it is not suitable for steel pipes of harder or thinner steel.

2) Rockwell hardness
The Rockwell hardness test of cs seamless pipe 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, among which HRC is second only to Brinell hardness HB in steel pipe standards. Rockwell hardness can be used to measure metal materials from extremely soft to extremely hard. It makes up for the inadequacy of the Brinell method. It is simpler than the Brinell method and can directly read the hardness value from the dial of the hardness machine. However, due to its small indentation, the hardness value is not as accurate as the Brinell method.

3) Vickers hardness
The Vickers hardness test of cs seamless pipe 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 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.

Detection method

The tensile test is to make a cs seamless pipe 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 fracture and rate of reduction in area. Tensile test is the most basic test method for mechanical properties of metal materials. Almost all metal materials require tensile tests as long as they have requirements for mechanical properties. Especially for those materials whose shape is inconvenient for hardness testing, tensile testing has become the only means of testing mechanical properties.

The hardness test is to slowly press a hard indenter into the surface of the sample with a durometer according to specified conditions, and then test the depth or size of the indentation to determine the hardness of the material. Hardness test is the simplest, fastest and easiest to implement method in material mechanical property test. 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 the tensile strength value, which has great practical significance.

Since the tensile test is inconvenient to test, and the conversion from hardness to strength is convenient, more and more people only test the hardness of the material and less test its strength. Especially due to the continuous progress and innovation of hardness tester manufacturing technology, some materials that could not directly test the hardness, such as cs seamless pipes, stainless steel plates and stainless steel strips, are now possible to directly test the hardness. Therefore, there is a tendency for hardness testing to gradually replace tensile testing.

Detection Tool

The inner diameter of cs seamless pipe is more than 6.0mm and the wall thickness is less than 13mm. For annealed cs seamless pipe, WB type webster hardness tester can be used. It is very fast and easy to test. Qualified inspection. CS seamless pipe with inner diameter greater than 30mm and wall thickness greater than 1.2mm shall use Rockwell hardness tester to test HRB and HRC hardness. The inner diameter of cs seamless pipe is greater than 30mm and the wall thickness is less than 1.2mm. The surface Rockwell hardness tester is used to test the HRT or HRN hardness. For cs seamless pipes with an inner diameter of less than 0mm and greater than 4.8mm, use a Rockwell hardness tester for pipes to test HR15T hardness. When the inner diameter of the cs seamless pipe is greater than 26mm, the hardness of the inner wall of the pipe can also be tested with a Rockwell or surface Rockwell hardness tester.

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