1. Relevant methods and standards for stainless steel hardness testing
(National Standard, United States, Japan)
Stainless steel products can be classified by delivery format into stainless steel plates, strips, tubes, rods, wires and so on.
If classified according to metallographic structure, they can be divided into the following five types: austenitic stainless steel, ferritic stainless steel, austenitic-ferritic stainless steel, martensitic stainless steel and precipitation hardening stainless steel.
Various stainless steel materials are supplied in different heat treatment states such as annealed, tempered, solution treated, quenched or tempered.
Hardness testing involves slowly pressing a hard indenter into the surface of a sample under specific conditions and then measuring the depth or size of the indentation to determine the hardness of the material.
It is the simplest, fastest and most easily implemented method for testing the mechanical properties of materials.
Hardness testing is non-destructive and there is an approximate conversion relationship between hardness values and tensile strength values.
Due to the inconvenience of tensile testing and the ease of converting hardness to strength, people are increasingly testing material hardness and less frequently testing its strength.
Especially with the continuous progress and innovation in hardness testing technology, some materials that could not be directly tested for hardness in the past, such as stainless steel pipes, stainless steel wires, extremely thin stainless steel plates and steel strips stainless steel, can now be directly tested for hardness.
Therefore, there is a tendency for hardness tests to gradually replace tensile tests.
In stainless steel standards, three hardness testing methods, Brinell, Rockwell and Vickers, are typically stipulated, measuring HB, HRB (or HRC) and HV hardness values respectively.
It is specified that only one of the three hardness values needs to be measured for stainless steel hardness testing.
In American standards for metallic materials, a prominent feature regarding hardness testing is the preference for the Rockwell hardness test, supplemented by the Brinell hardness test, and rarely using the Vickers hardness test.
The American view is that the Vickers hardness test should be used primarily for metal research and testing of small, thin parts.
Chinese and Japanese standards simultaneously use three hardness tests. Users can choose one of these tests based on material thickness and condition, as well as individual circumstances, to test stainless steel materials.
Japanese stainless steel standards relating to tensile testing and hardness testing closely align with corresponding Chinese standards in both methodology and numerical values, indicating that Chinese standards have been influenced by those in Japan.
The Rockwell hardness tester is an exceptionally suitable instrument for stainless steel hardness testing.
Its simplicity and ease of use make it an efficient tool that does not require a professional inspector and can directly read hardness values, making it highly suitable for factory use.
The Rockwell hardness tester is typically used to test the hardness of stainless steel, with standards generally specifying only the HRC and HRB scales.
For annealed stainless steel materials, each type of stainless steel is expected to have a hardness value that does not exceed a certain HRB value, typically in the range of 88-96 HRB.
For quenched and tempered martensitic stainless steel, the hardness value of each grade must not be less than a certain HRC value, typically in the range of 32-46 HRC.
Although only the HRB and HRC scales of the Rockwell hardness tester are specified in stainless steel standards, the Rockwell surface hardness tester can also be used effectively to test stainless steel.
Its principle is identical to that of the Rockwell hardness tester, but it exerts less force. Its hardness values can be conveniently converted to HRB hardness, HRC hardness, Brinell HB hardness or Vickers HV hardness.
Conversion tables can be found on our company's website, coming from the American ASTM Standard or the ISO International Standard.
The surface Rockwell hardness tester is particularly useful for testing thin-walled stainless steel tubes, thin stainless steel plates, thin stainless steel strips and thin stainless steel wires.
Especially, our company's latest development, portable surface Rockwell hardness tester and pipe Rockwell hardness tester, can perform fast and accurate hardness testing on stainless steel plates and strips as thin as 0.05mm and stainless steel tubes as thin as 4.8mm, solving problems that were previously difficult to overcome internally.
2. Hardness test of stainless steel plates and strips
Stainless steel plates include hot-rolled and cold-rolled plates. For stainless steel plates or strips thicker than 1.2mm, Rockwell hardness tester is used to test HRB and HRC hardness.
For plates or strips between 0.2mm and 1.2mm thick, a surface Rockwell hardness tester is used to test HRT or HRN hardness.
For plates or strips thinner than 0.2mm, a surface Rockwell hardness tester paired with a diamond indenter is used to test HR30TM hardness.
For annealed stainless steel plates and strips with a thickness between 0.3 mm and 13 mm, a Vickers hardness tester can also be used.
This instrument is extremely fast and simple, making it very suitable for rapid quality inspection of annealed stainless steel materials.
3. Stainless steel pipe hardness test
Stainless steel pipes include welded stainless steel pipes and cold drawn stainless steel pipes. For those with an inner diameter greater than 30mm and wall thickness greater than 1.2mm, a Rockwell hardness tester is used to test HRB or HRC hardness.
For pipes with an inner diameter greater than 30 mm but a wall thickness less than 1.2 mm, a surface Rockwell hardness tester is used to test HRT or HRN hardness.
For pipes with an inner diameter of less than 30mm but greater than 4.8mm, a specialized Rockwell hardness tester for pipes is used to test HR15T hardness.
When the inner diameter of the pipe exceeds 26 mm, the hardness of the inner wall can also be tested using Rockwell or surface Rockwell hardness testers.
For annealed stainless steel pipes with an inner diameter greater than 6.0mm and a wall thickness less than 13mm, a Webster W-B75 hardness tester can be used.
This tool provides quick and convenient testing and is suitable for rapid, non-destructive qualification testing on stainless steel pipes.
4. Hardness Test of Stainless Steel Rods
For stainless steel rods with a diameter of less than 50mm, a Rockwell hardness tester can be used to test HRB or HRC hardness.
5. Stainless steel wire hardness test
For stainless steel wire with a diameter greater than 2.0mm, a surface Rockwell hardness tester can be used to test HRT or HRN hardness.
