Hardness test method for stainless steel seamless pipe

The significance of hardness test:
Hardness is a performance index to measure the material's ability to resist local plastic deformation. The hardness test of stainless steel seamless pipe (SS smls pipe) is of great significance for evaluating its quality, service life and processing performance. Through hardness test, it can be ensured that the stainless steel seamless pipe meets the design requirements during use and improves the reliability and safety of the product.

Hardness test method for stainless steel seamless pipe:

Hardness test is an important means to measure the hardness of metal materials. There are three main methods commonly used: Brinell hardness, Rockwell hardness and Vickers hardness.

1. Brinell hardness (HB)
The Brinell hardness test uses a steel ball or tungsten carbide ball with a diameter of 10 mm as the indenter. Under the specified test force, it is pressed into the surface of the material for a certain period of time and then the load is removed. The hardness value is calculated by measuring the indentation diameter. This method is suitable for softer metals such as cast iron, steel and non-ferrous metals. The advantage of Brinell hardness is that the indentation area on the specimen is large, which can better reflect the average hardness value of the material, the data is relatively stable and the repeatability is good. However, the test is troublesome, the indentation is large, and the damage to the material surface is also large. It is not suitable for testing finished parts and thin materials.

2. Rockwell hardness (HR)
It is particularly popular in the US metal material standards and takes precedence over the Brinell hardness test. The Rockwell hardness test uses a combination of indenters of different depths and test forces to evaluate the hardness of the material by measuring the difference in depth of the indenter entering and exiting the material. The appropriate scale is selected according to the specific situation, such as HRA, HRB, HRC, etc. The difference in the depth of the indenter entering the material under the initial test force and the total test force is measured. This method is widely used and is suitable for metal materials from very soft to very hard. The advantage of Rockwell hardness is that the measurement is quick and easy, the indentation is small, and it can be used to measure product parts. However, the disadvantage is that due to the small indentation, the measured hardness is not accurate enough and the data repeatability is poor.

3. Vickers hardness (HV)
It is mostly used for soft metals. During the test, the diamond cone on the hardness tester is pressed into the surface of the metal material, the diameter on both sides of the drill mark is measured, and then the Vickers hardness value of the material is calculated. The hardness of the material is characterized by the indentation depth of the indenter. The advantages of Vickers hardness are small test load, shallow indentation, wide application range, and can measure various metal materials from extremely soft to extremely hard. But the disadvantage is that it has high requirements on the surface of the sample, and the diagonal length of the indentation is more troublesome to measure, which is not suitable for large-scale testing. The Vickers hardness test method has high accuracy and reliability.

Other methods: Ultrasonic hardness test method

Ultrasonic hardness test method is a non-contact hardness test method. It transmits ultrasonic signals to stainless steel pipes through ultrasonic sensors, and then receives the reflected signals, and calculates the hardness value according to the propagation speed and attenuation of ultrasonic waves inside the material. Ultrasonic hardness test method has the advantages of fast, simple and non-destructive, and is suitable for hardness testing of large components such as stainless steel pipes.

Specific application of stainless steel seamless pipe hardness test:

For stainless steel pipes of different specifications, the choice of hardness test method is also different. The following are some specific application examples:

Stainless steel pipes with inner diameter greater than Ø30mm and wall thickness greater than 1.2mm: Use Rockwell hardness tester to test HRB and HRC hardness.
Stainless steel pipes with an inner diameter greater than Ø30mm and a wall thickness less than 1.2mm: Use a surface Rockwell hardness tester to test HRT or HRN hardness.
Stainless steel pipes with an inner diameter less than Ø30mm and greater than Ø4.8mm: Use a special Rockwell hardness tester for pipes to test HR15T hardness.
Annealed stainless steel pipes with an inner diameter of more than Ø6.0mm and a wall thickness of less than 6mm: You can use the W-B92 Webster hardness tester, which is very fast and simple to test and is suitable for fast and non-destructive qualified inspection of stainless steel pipes.

Precautions for implementing hardness testing of stainless steel seamless pipes:

1. Choose a suitable test method: Choose a suitable hardness test method according to the specifications, materials and test requirements of stainless steel seamless pipes.
2. Ensure consistent test conditions: When conducting hardness tests, ensure the consistency of test conditions (such as temperature, humidity, shape and size of the indenter, etc.) to improve the accuracy of the test results.
3. Before the hardness test, ensure that the sample surface is flat and clean to avoid interference from other factors in the test results.
4. When testing hardness, the number of test points should be as large as possible to avoid deviation of local hardness values.
5. The test results should be recorded and data should be organized during the test to avoid problems in subsequent tests.

Professional knowledge:
1. Understand the principles of different hardness test methods so that you can choose the appropriate method in actual testing.
2. Hardness is related to the mechanical properties of materials (such as strength, toughness, etc.), but they are not exactly the same. It cannot be simply assumed that the higher the hardness, the stronger the material.
3. The Rockwell hardness test method is usually used for steel hardness testing, while the Brinell hardness test method is often used for non-ferrous metals such as aluminum and copper.

Questions and Answers:

1. Q: Why do we need to test the hardness of metal materials?
A: The hardness test of metal materials can evaluate the material's compressive and deformation resistance, help us select the right material and predict its performance in use.

2. Q: Why do we need to do multiple tests when testing hardness?
A: Multiple tests can reduce random errors and make the test results more reliable and accurate.

3. Q: Can the hardness test represent all the mechanical properties of the material?
A: Hardness is related to the mechanical properties of materials, but they are not exactly the same. The mechanical properties of materials also include strength, toughness, etc., which need to be considered comprehensively.

Conclusion:

The hardness test of stainless steel seamless pipes is an important means to improve product quality. Various hardness test methods and their implementation standards have their own characteristics and advantages and disadvantages. In actual testing, appropriate test methods should be selected according to different use occasions, and tests should be carried out in accordance with the corresponding implementation standards to ensure the accuracy and reliability of the test results.

Read more: Carbon Steel Pipe vs Stainless Steel Pipe or Stainless Steel Seamless Pipe Manufacturing Process