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Continuous casting and foundry production
ArticleName Improvement of the casting technology for large ingots for rise of reliability and operating durability of a turbine set rotors manufactured of these ingots
ArticleAuthor N. A. Zyuban, D. V. Rutskii
ArticleAuthorData

Volgograd State Technical University (Volgograd, Russia):

N. A. Zyuban, Dr. Eng., Prof., Head of Chair of Materials Technology
D. V. Rutskii, Cand. Eng., Ass. Prof., Chair of Materials Technology
E-mail (common): tecmat@vstu.ru

Abstract

Production of turbine set rotors from one-piece forgings is an important sector of modern power engineering industry. As a rule, ferritic steel of grade 38ХН3МФА (38KhNMFA) is used to manufacture rotors. A vacuum-cast large forging ingot serves as a part blank for the turbine set rotor; as a result, a comparatively high metallurgical quality of metal is ensured. The paper considers in detail blowing an inert gas through a hollow stopper to evaluate the eff ect of inert gas degassing on the quality of solid forgings manufactured from steel 38ХН3МФА (38KhNMFA). The findings prove that a more vigorous degassing during vacuum casting results in the size reduction of non-metallic inclusions which do not exceed 20 μm. An overall arrangement of non-metallic impurities over the length and cross-section of the forgings produced from a conventional and experimental ingots is identical and coincides with the classical arrangement of inclusions in the ingot. The greater portion of inclusions is located in the forging center line area. The size reduction of non-metallic inclusions due to argon blowing of molten metal stream has a favorable effect on the mechanical properties of the forgings produced power engineering needs. Despite a negligible decrease in strength, ductile properties of experimental forgings increase by 10 to 20 % (particularly in case of impact strength). In addition, ductile-to-brittle transition temperature also falls; it impedes microcrack development and prevents micro-cracks from transforming into macro-cracks thus contributing to product reliability.

keywords Ingot, vacuum casting, solidification, non-metallic inclusions, mechanical properties, forging
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