Volgograd State Technical University, Volgograd, Russia:

S. B. Gamanyuk, Cand. Eng., Associate Professor, Department “Technology of materials”, e-mail: gamanuk@mail.ru
N. A. Zyuban, Dr. Eng., Professor, Head of Department “Technology of materials”, e-mail: tecmat49@vstu.ru
D. V. Rutskii, Cand. Eng., Associate Professor, Department “Technology of materials”, e-mail: rutskiy79@mail.ru
L. V. Palatkina, Cand. Eng., Associate Professor, Department “Technology of materials”, tecmat@vstu.ru

The paper reports findings on the distribution of non-metallic inclusions in the structural zones as well as throughout the mass of a 24.2 ton ingot of 38ХН3МФА steel. It is shown that the distribution of non-metallic inclusions in steel varies throughout the height and cross-section of the ingot. The amount of sulfide and oxysulfide inclusions exceeds that of oxides. It is discovered that the inclusions are presented by compound oxides of manganese, silicon, vanadium, chromium and aluminum; besides, there are sulfide and oxysulfide inclusions as well. The findings prove that there exists a correlation between the contamination index of sulfides and oxysulfides on the one hand, and the ingot height, on the other hand. In the upper part of the ingot, below its hot top, the distribution of the inclusions and their numbers almost fully coincide due to extended heat exposure. In the middle and bottom parts of the ingot in the zone of columnar and large randomly oriented crystals there is a pronounced inverse relation between the distribution of sulfides and oxysulfides. The investigation of inclusions reveals the major role of oxysulfides in the formation of sulfides which are generally located at grain boundaries and reduce metal ductility. This is particularly important for vacuum cast steel since oxygen shortage reduces the amount of oxysulfides and leads to the escape of sulfides and an undesired form.

The reported study was partially supported by RFBR, research project No. 16-38-60007 mol_а_dk.

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