Hardness test method for stainless steel seamless pipe

When conducting hardness testing on stainless steel, it is essential to consider the mechanical properties of stainless steel seamless pipes, which affect the material's performance during processes like deformation, stamping, and cutting. Therefore, all seamless steel pipes must undergo mechanical performance testing. These tests are typically divided into two categories: tensile tests and hardness tests.

The tensile test involves preparing a sample of the seamless steel pipe, pulling the specimen until it fractures using a tensile tester, and then measuring one or more mechanical properties. The most common properties measured include tensile strength, yield strength, elongation at break, and the rate of reduction in the area.

Tensile testing is one of the fundamental methods for evaluating the mechanical properties of metal materials. It is required for nearly all metal materials where mechanical performance is critical. For materials that are challenging to test for hardness, the tensile test is often the only method used for mechanical performance evaluation.

The hardness test, on the other hand, involves pressing a hard indenter slowly into the surface of the sample under specified conditions. The hardness is determined by measuring the depth or size of the indentation. Hardness testing is the simplest, quickest, and most practical method of assessing mechanical properties, and it is non-destructive. There is a correlation between hardness and tensile strength, which allows the hardness value to be converted into a tensile strength value, offering significant practical benefits.

As tensile testing can be challenging and because strength values can be derived from hardness measurements, hardness testing has become increasingly favored for determining material strength. Advances in hardness testing technology have made it possible to directly test materials, such as seamless steel pipes, stainless steel plates, and stainless steel strips, which were previously difficult to assess. As a result, there is a growing trend toward using hardness testing as an alternative to tensile testing.

Many national standards for stainless steel also specify both tensile and hardness tests. For materials where hardness tests are feasible, such as seamless steel pipes, tensile tests are often the primary requirement. Stainless steel standards generally allow for the use of one of three hardness testing methods: Brinell (HB), Rockwell (HRB or HRC), or Vickers (HV). Only one of these hardness values needs to be measured.

Recent innovations, such as portable Rockwell hardness testers and pipe-specific Rockwell testers, enable fast and accurate hardness testing of stainless steel materials as thin as 0.05 mm and seamless pipes as small as 4.8 mm in diameter. These developments have resolved long-standing challenges in the field.