How to improve the hardness and strength of seamless pipes?

The hardness of seamless pipes (SMLS) is usually determined based on the type of steel used and the heat treatment method. Here are some possible ways to harden seamless steel pipes:

1. Heat treatment
Heat treatment is one of the common methods to improve the hardness and strength of seamless steel pipes. By heating and cooling the steel pipe, its grain structure can be changed, thereby improving its hardness and strength. Specific heat treatment methods include normalizing, quenching, tempering, etc.

Normalizing is to heat the seamless steel pipe to a certain temperature and then cool it to refine its grains and improve its hardness and strength. Quenching is to heat the seamless steel pipe to a critical temperature and quickly cool it to deform its grains and improve its hardness and strength. Tempering is to heat the seamless steel pipe to a certain temperature again and cool it after quenching to make its hardness and strength moderate, while improving its toughness and plasticity.

‌Quenching treatment‌: Tempering treatment is performed immediately after quenching to reduce brittleness and increase hardness‌.
‌Quenching and tempering treatment‌: High temperature tempering after quenching to improve the hardness of the core‌.
‌Surface quenching‌: only improve the surface hardness and maintain the toughness of the core‌.
‌Carburizing‌: make carbides penetrate the surface to improve the surface hardness‌.
‌Carbonitriding‌: improve the surface and core hardness at the same time. ‌

2. Reasonable design process
In the production process of seamless steel pipes, reasonable process design can effectively improve its hardness and strength. Specifically, high temperature rolling, cold drawing, cold drawing and other processes can be used to refine the grains of steel pipes and improve the surface flatness, thereby improving its hardness and strength.

3. Adding alloy elements
The purpose of improving the hardness and strength of seamless steel pipes can be achieved by changing the chemical composition of seamless steel pipes. For example, the carbon content in the steel pipe can be increased, and suitable alloy elements (such as titanium, chromium, nickel) can be added to improve its hardness and strength.

4. Work hardening
The crystal structure of steel can be changed and its hardness can be enhanced through mechanical processing and deformation processing, such as rolling or stretching.

Factors affecting the hardness and strength of seamless steel pipes:
In addition to heat treatment and reasonable design process, there are some other factors that affect the hardness and strength of seamless steel pipes. For example, the composition, grain size, surface state, etc. of the steel pipe will affect its hardness and strength. In addition, the shape and size of the steel pipe will also affect its hardness and strength.

It should be noted that improving the hardness and strength of seamless steel pipes does not mean that their use strength can be increased at will, because strength and toughness affect each other. For example, heat treatment and work hardening may cause the brittleness of seamless steel pipes to increase, and the correct method must be selected. Therefore, while improving the hardness and strength of seamless steel pipes, their toughness and plasticity also need to be considered. It is recommended to consult professionals before any treatment to ensure correct operation.

Conclusion:

This article introduces methods to improve the hardness and strength of seamless steel pipes, including heat treatment, reasonable design process, addition of alloy elements, work hardening, etc. At the same time, factors affecting the hardness and strength of seamless steel pipes are also discussed to help readers better understand and apply these methods. It should be noted that while improving the hardness and strength of seamless steel pipes, their toughness and plasticity also need to be considered to ensure their safe and reliable use.

Read more: Hardness testing method for seamless pipe or Carbon steel tube material and use