Stainless steel welded pipe is a basic pipe, so it also has many necessary indicators of hardness, including many aspects. Next, we will talk about the hardness indicators of 16L stainless steel welded pipe. According to different test methods and application ranges, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, shore hardness, microhardness and high temperature hardness. Generally, there are three kinds of hardness commonly used for pipes: Brinell hardness, Rockwell hardness and Vickers hardness.

1. Brinell hardness (HB): a steel ball or cemented carbide ball with a certain diameter is pressed into the surface of the sample with the defined test force (f), and the test force is removed after the defined holding time. The indentation diameter (L) of the sample surface is measured. The Brinell hardness value is the quotient obtained by dividing the test force by the indentation spherical surface area. Expressed in HBS (steel ball), the unit is n / mm2 (MPA), and the calculation formula is as follows: F -- test force pressed into the surface of 316L stainless steel welded pipe sample, N, D -- diameter of steel ball for test, MMD -- uniform diameter of indentation, mm. The measurement of Brinell hardness is correct and reliable, but generally HBS is only suitable for metal materials below 450N / mm2 (MPA), which is not suitable for harder steel or thinner 316L stainless steel welded pipe. Among the dimensions of 316L stainless steel welded pipe, Brinell hardness is the most widely used, and the hardness of the material is often expressed by indentation diameter D, which is intuitive and convenient.

For example, 120hbs10 / 1000130 indicates that the Brinell hardness measured by using a steel ball with a diameter of 10mm under the action of 1000kgf (9.807kn) test force for 30s (seconds) is 120N / mm2 (MPA).

2. Rockwell hardness (HK) Rockwell hardness test, like Brinell hardness test, is an indentation test method. The difference is that it measures the depth of the indentation, that is, under the sequential action of the initial Yong test force (FO) and the total test force (f), the indenter (steel mill cone or steel ball) is pressed into the surface of the sample, and after the holding time is defined, the main test force is removed, and the hardness value is calculated with the measured residual indentation depth increment (E). Its value is an unknown number and is represented by the symbol hr. The scales used include 9 scales such as a, B, C, D, e, F, G, h and K. The scales commonly used for hardness test of 316L stainless steel welded pipe are generally a, B and C, that is, HRA, HRB and HRC. The hardness value is calculated by the following formula: when scale a and C are used for testing, HR = 100-e when scale B is used for testing, HR = 130-e. in the formula, e -- the increment of residual indentation depth, which is shown in the delimited unit of 0.002mm, that is, when the axial displacement of the indenter is one unit (0.002mm), it is equivalent to a number of Rockwell hardness changes.