Hardness index of seamless pipe

Posted by zora li on November 25th, 2022

1. Hardness index of seamless pipe

Seamless steel pipes are commonly used to measure Brinell hardness, Rockwell hardness and Vickers hardness.

Brinell hardness

Among the seamless steel pipe standards, the 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. But it is not suitable for steel pipes with harder or thinner steel.

Rockwell hardness

The Rockwell hardness test of seamless steel pipes 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 applied to the determination of metal materials from very soft to very 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, due to the small indentation, the hardness value is not as accurate as the Brinell method.

Vickers hardness

The Vickers hardness test of seamless steel tubes is also an indentation test method that can be used to determine the hardness of very thin metal materials and surfaces. It has the main advantages of the Brinell method and the Rockwell method 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 consider its mechanical properties, which is related to the performance and quality of deformation, stamping, cutting and other processing with stainless steel as raw material. Therefore, all seamless steel pipes must be tested for mechanical properties. The mechanical properties 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 pipe into a sample, break the sample on a tensile testing machine, and then measure one or more mechanical properties, usually only the tensile strength, yield strength, elongation at break and reduction. Volume rates are in regions. Tensile test is the most basic mechanical property test method for metal materials. Almost all metal materials have specified tensile tests as long as mechanical properties are required. Especially for materials whose shape is not convenient 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 according to specified conditions, and then test the depth or size of the indentation to determine the hardness of the material. Hardness testing is the simplest, fastest and easiest way to test the mechanical properties 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 the tensile strength value, which has great practical significance.

Since tensile testing is not easy to test and the conversion from hardness to strength is very convenient, people are increasingly testing materials only for hardness and less for strength. Especially due to the continuous progress and innovation of hardness tester manufacturing technology, some materials that cannot be directly tested for hardness, such as seamless steel pipes, stainless steel plates and stainless steel strips, can now be directly tested for hardness. Therefore, there is a tendency for hardness testing to gradually replace tensile testing.

Tensile tests and hardness tests are specified in most national standards for stainless steel materials. For those materials for which hardness testing is not convenient, such as seamless steel pipes, only tensile testing is specified. In stainless steel standards, three hardness test methods of Brinell, Rockwell and Vickers are generally specified to determine 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 as thin as ￠4.8mm and seamless steel tubes.

Read more : seamless carbon steel pipe