Tensile testing is to make a seamless steel pipe into a sample, pull the sample to fracture on a tensile testing machine, and then measure one or more mechanical properties, usually only tensile strength, yield strength, elongation after fracture and fracture area. Shrinkage. Tensile testing is the most basic testing method for the mechanical properties of metal materials. Almost all metal materials have specified tensile tests as long as they have requirements for mechanical properties. Especially for materials whose shapes are 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 a seamless pipe sample under 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 most convenient method for testing the mechanical properties of materials. Hardness testing is non-destructive and there is an approximate conversion relationship between material hardness values and tensile strength values. The hardness value of the material can be converted into a tensile strength value, which is of great practical significance.
Since tensile testing is inconvenient and it is convenient to convert from hardness to strength, more and more people only test the hardness of materials and rarely test their strength. Especially due to the continuous improvement and innovation of hardness tester manufacturing technology, the hardness of some materials that could not be directly tested before, such as seamless steel pipes, stainless steel plates and stainless steel strips, can now be directly tested for hardness. . Therefore, there is a trend that hardness testing gradually replaces tensile testing.
Steel pipes generally use three hardness indicators: Brinell, Rockwell, and Vickers to measure their hardness.
1. Brinell hardness
Among seamless steel pipe standards, Brinell hardness is the most widely used, and the indentation diameter is commonly used to express the hardness of the material, which is both intuitive and convenient. But it is not suitable for steel pipes made of harder or thinner steel.
2. Rockwell hardness
The Rockwell hardness test of seamless steel pipes is the same as the Brinell hardness test, both of which are indentation test methods. The difference is that it measures the depth of the indentation. Rockwell hardness test is a widely used method at present. Among them, HRC is second only to Brinell hardness HB in steel pipe standards. Rockwell hardness can be applied to the determination of metallic materials from very soft to very hard. It makes up for the shortcomings of the Brinell method. However, due to its smaller indentation, its hardness value is not as accurate as the Brinell method.
3. Vickers hardness
The seamless steel pipe Vickers hardness test 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 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.
