Test method for mechanical properties of seamless steel pipes

Posted by zora li on August 16th, 2022

The mechanical properties of seamless steel pipe are one of the important indexes to ensure the final performance of seamless steel pipe. The mechanical properties of seamless steel pipe mainly depend on the chemical composition of the billet and the heat treatment system of the finished steel pipe.

Its testing methods are mainly divided into two kinds: one is tensile test, the second is hardness test.

The tensile test is made of seamless steel tube samples, which are pulled to fracture on the tensile testing machine, and then one or several mechanical properties are measured. Usually, only tensile strength, yield strength, elongation after fracture and area shrinkage are measured.

A measure of stretching

1, Tensile strength: material in the tensile process, from the beginning to the occurrence of fracture to reach the large stress value, it indicates the steel resistance to fracture capacity.

2, Yield strength: steel or sample in tensile, when the metal material yield phenomenon, during the test to achieve plastic deformation and force does not increase the stress point, should distinguish the upper yield strength and the lower yield strength. In order to measure the yield characteristics of the material, it is stipulated that the stress (generally O. 2% of the original length) when the non-proportional extension is equal to the specified percentage of the extensometer distance is the specified non-proportional extension strength RPO.2.

3, Elongation after fracture: when mechanical properties are tested, the percentage of the ratio between the residual elongation of the post-fracture standard distance and the original standard distance of the material after breaking is called elongation after fracture.

4, Reduction of area: the material by the tensile fracture section, section to reduce the ratio of the area with the original area called reduction of area.

Hardness test  is a hard indenter according to the specified conditions slowly pressed into the sample surface, and then test the indentation depth or size, in order to determine the size of the hardness of the material. Hardness test is a simple, rapid and easy method in mechanical property test of materials. Hardness test is non-destructive and there is an approximate conversion between material hardness and tensile strength. The hardness value of the material can be converted into the tensile strength value, which has great practical significance.

A measure of hardness

1,Brinell hardness

In the seamless steel pipe standard, brinell hardness is widely used, often to indentation diameter to express the hardness of the material, both intuitive and convenient. However, it is not suitable for hard or thin steel pipes.

2, Rockwell hardness

Like Brinell hardness test, rockwell hardness test of seamless steel tube is 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 standard. Rockwell hardness can be applied to determine from very soft to very hard metal materials, it makes up for the Brinell method is not, is simpler than brinell method, can be directly from the hardness machine dial read hardness value. However, due to the small indentation, the hardness value is not as accurate as buchwald method.

3. Vickers Hardness

Seamless steel tube Vickers hardness test is also an indentation test method, can be used to determine the hardness of very thin metal materials and surface layer. It has the main advantages of Brinell and Rockwell methods and overcomes their basic disadvantages, but it is not as simple as Rockwell methods and is seldom used in steel pipe standards.