How to improve the hardness of precision stainless steel pipes

Precision stainless steel pipe is a kind of pipe that has extremely high requirements on size, R angle, pipe mouth roundness, verticality, and roughness. For example, the length error needs to be controlled within 0.05mm. This kind of tube is generally used in special industries or precision equipment, and sometimes there are requirements for hardness. So how to improve the hardness of precision stainless steel pipes?

First of all, let’s first understand the two factors that affect the hardness of stainless steel precision pipes: annealing treatment and the carbon content of the steel pipe. One of the factors is that the quality of the annealing treatment of the stainless steel pipe is directly related to the hardness of the pipe. No matter what the material of the pipe is, the country has corresponding standards for its hardness. Another factor is the carbon content. The main role of carbon is to increase the hardness of precision pipes. However, carbon is also an impurity in stainless steel. The higher the content, the harder it is, and the greater the chance of the pipe rusting.

Generally, if you want to improve the hardness of precision stainless steel pipes, without changing the material, you can improve the hardness through the following two processes: annealing and drawing processes.

1. Annealing treatment

Annealing is heating a metal to a specified temperature and then cooling it at a very slow and controlled rate. During cold working, metal can harden. By pre-annealing the steel pipe, cold working can be carried out without any risk of cracking, as annealing releases the mechanical stress generated during machining or grinding, making it easier to draw the stainless steel pipe later. When annealing, you need to be careful not to exceed the annealing time, otherwise, the pipe will be too soft and the hardness may not meet the requirements after drawing.

2. Drawing

The annealed stainless steel pipe is then drawn. Drawing is divided into hot drawing and cold drawing. Cold drawing is forcibly stretched under normal temperature conditions with tensile stress exceeding the yield point strength of the original stainless steel product pipe, causing it to undergo plastic deformation to increase the yield point strength of the pipe and obtain the Required shape and material saving purposes. During the drawing process, the thickness of the stainless steel welded pipe becomes thinner the hardness increases and the cross-section can be ensured to be completely consistent along the entire length; secondly, the shape and size of the steel pipe are precise, and the inner surface roughness can reach Ra≤0.01um.