Cold-drawn seamless tubes are tubes that are made through a process of drawing a billet or hollow bar over a piercing rod to create the final shape and size. This process involves using a high degree of precision and can result in tubes with a very smooth surface finish and accurate dimensions.
After the cold-forming process, the tubes may be subjected to annealing in order to improve their properties and make them more suitable for certain applications. Annealing is a heat treatment process that involves heating the tubes to a specific temperature and then allowing them to cool at a controlled rate.
There are two main types of annealing processes that may be used on cold-drawn seamless tubes: GBK annealing and NBK annealing.
1. GBK annealing, also known as “soft annealing,” involves heating the tubes to a temperature above their lower transformation point and then allowing them to cool in a controlled atmosphere or under a vacuum. This process is used to reduce the hardness of the tubes and improve their formability.
2. NBK annealing, also known as “full annealing,” involves heating the tubes to a temperature above their upper transformation point and then allowing them to cool in a controlled atmosphere or under vacuum. This process is used to improve the ductility and toughness of the tubes, making them more resistant to cracking and breaking.
Both GBK and NBK annealing processes are used to improve the properties of cold drawn seamless tubes and make them more suitable for certain applications. The specific annealing process that is used depends on the desired properties of the final product and the specific requirements of the application.