TMK Research Center, Separate Division, Chelyabinsk, Russia
K. Yu. Yakovleva, Cand. Eng., Head of the Drawing and Pressing Laboratory, e-mail: yakovleva@rosniti.ru
B. V. Barichko, Cand. Eng., Leading Researcher, Drawing and Pressing Laboratory

The study assessed the feasibility of final heat treatment of large thin-walled hexagonal pipes and, accordingly, the possibility of eliminating this operation from the production process. The article presents the results of a study of mechanical properties of EP450-Sh steel depending on the cross-section of tubular products and their actual condition: 1) round pipe blanks with a nominal size of the diameter 50×0.87 mm in the condition after heat treatment; 2) scaled specimens of hexagonal pipes with a nominal size of 45.2×0.87 mm, obtained by profiling in one pass; 3) scaled specimens of hexagonal pipes with a nominal size of 45.2×0.87 mm, obtained by profiling in seven passes. The research has established that profiling with an increase in passes and the degree of deformation up to ~2.2 % insignificantly increases the yield strength of EP450-Sh steel – up to 6–8 %, while ensuring guaranteed compliance with the requirements of regulatory documentation both at room and at elevated temperatures. A different pattern was revealed for relative elongation: profiling with a large number of passes at a deformation degree of ≥ 2.2 % brings the relative elongation of EP450-Sh steel at elevated temperatures closer to the minimum required limit, while profiling with a single pass at a deformation degree of ≥ 1.4 % does not meet the elongation requirements at room temperature. A summary of these results showed that even with minor total deformations accompanying the hexagonal tube profiling process, final heat treatment and, accordingly, the associated subsequent operations of cleaning, straightening, etc., are mandatory and cannot be excluded.

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