Hardness refers to the ability of a material to resist plastic deformation, scratches, and damage. It is usually measured using a hardness tester. Hardness tests typically include indentation hardness tests, tensile hardness tests for metal materials, Rockwell hardness tests for rocks, and others.
The hardness of a precision steel pipe refers to its ability to resist deformation and quickly return to its original shape under certain test conditions. Generally, higher hardness indicates greater material strength and lower deformation capacity.
Hardness Index Requirements for Precision Steel Pipes
Precision steel pipe hardness is generally categorized into two types: surface hardness and internal hardness.
1. Surface Hardness
Surface hardness refers to the hardness of the material surface after heat treatment and is typically tested using the Rockwell hardness test method.
2. Internal Hardness
Internal hardness refers to the hardness of the steel pipe section or material and is generally tested using the Vickers hardness test method.
Different standards specify varying hardness index requirements for precision steel pipes. For example, the Japanese JIS standard generally sets the hardness index for ordinary precision steel pipes with a thickness of d above 0.5mm to HRC6165. In contrast, the German DIN standard specifies the hardness index for similar precision steel pipes to be between HRC5558. These standards also apply to other pipes, such as carbon steel pipes.
Hardness Range of Precision Steel Pipes
The hardness of precision steel pipes depends on their heat treatment state and the materials used. Below are some common hardness ranges:
After Quenching, Not Tempered
The hardness of 1.45# precision seamless steel pipe after quenching and before tempering is greater than HRC55 and can reach up to HRC62.
Low-Temperature Tempering
The hardness after low-temperature tempering generally falls between HRC58-64, primarily used to maintain high hardness and wear resistance.
Medium-Temperature Tempering
The hardness after medium-temperature tempering generally ranges from HRC35-50, mainly aimed at achieving high yield strength and toughness.
High-Temperature Tempering
The hardness after high-temperature tempering typically falls between HB200-330, providing better overall mechanical properties.
Brinell Hardness
The Brinell hardness of 20# seamless steel pipe is ≤156HBS when it is not heat-treated.
Hardness Testing Methods for Precision Steel Pipes
Hardness testing for precision steel pipes typically involves the Rockwell hardness test, Brinell hardness test, or Vickers hardness test:
Rockwell Hardness Test: Commonly used for precision steel pipes with higher refractoriness.
Vickers Hardness Test: Suitable for testing low-hardness steel.
Brinell Hardness Test: Ideal for smaller product sizes and applications requiring high precision.
Summary
During the production and processing of precision steel pipes, hardness indices should be controlled according to actual needs to ensure the stability and reliability of the steel pipes. It is important to note that these hardness values are based on specific heat treatment conditions, and actual hardness may vary depending on the material, heat treatment process, and specific application requirements.
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