Nizhnyi Novgorod State Technical University (Nizhnyi Novgorod, Russia):

G. A. Gevorgyan, Graduate Student, E-mail: borecgor77777@gmail.com
R. A. Vorobiev, Cand. Eng., Associate Prof., E-mail: linuxjuicy@gmail.com
G. V. Pachurin, Dr. Eng., Prof., E-mail: pachuringv@mail.ru
A. N. Kuzmin, Assistant, E-mail: kuznntu@mail.ru

In the manufacture of seamless pipes, the center of a round billet heated to a certain temperature is pierced in a mill and a tube billet is obtained in the form of a hollow shell. The main tool for piercing a hole in a tube stock is the plug mounted on the front of the shaft. The temperature of piercing is approximately 1200 °C. Plugs of the same diameter can be used repeatedly in the piercing mill. During operation, in addition to high temperatures, the plug experiences significant contact pressures, which significantly reduce the service life of the tool. Uninterrupted operation of pipe production can be ensured by maintaining a large stock of plugs. To increase the service life, the surface of the plugs is often subjected to thermal oxidation, which gives it anticorrosive and lubricating properties, which, in turn, prevent, during piercing, welding of the plug surface with the tube cavity. The main consumers of high-strength seamless pipes are the oil and gas industries, and defense industry. Therefore, the issues of increasing the efficiency of piercing production, strength and durability of the tool, ensuring the uninterrupted production of seamless pipes are very relevant. The rationale for the choice of steel grade and the results of development of the optimal technology for the manufacture of plugs for piercing and cross-helical rolling of seamless pipes are presented. Based on the comparison of structural and mechanical characteristics of 4Kh5MF1S, 4Kh5V2FS and 5KhNM steels, the grade of 4Kh5MF1S steel was selected for production of plugs, which provides the optimal quality/price combination. The analysis of the structure and mechanical properties made it possible to recommend the 4Kh5MF1S steel processing mode: quenching from 1070 °C in oil + tempering (holding in oil for 2 hours at a temperature of 600 °C). The 4Kh5MF1S steel treated in this mode can be used for metal products with the increased service life such as the plug with yield strength of σ_0.2 = 1448 MPa and strength σ₀ = 1705 MPa.

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