A Study of the Development of Chemical Heterogeneity in Large Forging Ingots: Depending Upon the Configuration and Therm
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er engineering and heavy engineering industries are major consumers of ingots. It is reported that electrical power production by nuclear power stations is constantly growing and has reached 1600 megawatts.[1] The increasing need for the production of extremely large forgings requires the production of large ingots. Over the last years, there has been a tendency to increase the number of products made of 100 to 200 t ingots[2]; the production of unique forgings of steel ingots weighing over 600 tons has also been developing. Unlike traditional manufacturing processes, the manufacture of power engineering and heavy engineering equipment is based on ingenious process decisions, such as the use of electric arc furnace steelmaking (EF) with the furnace capacity of 100–140 tons; use of ladle furnaces (LF) and vacuum ingot casting (VIC) out of several ladles. In particular, such casting methods are used at the Muroran Plant, The Japan Steel Works, Ltd.,[3] the ‘‘Spets Stal’’ Steel Works at Kolpino, Russia,[4] the ‘‘Red October’’ VMC in Volgograd, Russia, etc. Due to the increased weight of ingots, steel quality requirements are becoming stricter since the steel is to be used for the production of large-sized heavy duty parts for power engineering. The quality of large steel ingots for critical components used in power engineering industry has, on the whole, approached the required level as a result of the development of metallurgical processes and the use of NIKOLAI ZYUBAN, Professor, Head, DMITRII RUTSKII and SERGEI GAMANYUK, Associate Professors, and SERGEI KONOVALOV, Graduate Student, are with the Department of ‘‘Technology of Materials’’, Volgograd State Technical University, 28 Lenina Ave, Volgograd 400005, Russia. Contact e-mail: tecmat@ vstu.ru Manuscript submitted December 5, 2013. Article published online September 30, 2014 6200—VOLUME 45A, DECEMBER 2014
modern equipment. Somehow, the fabrication of largesized forgings for power machinery remains a challenging technical task. It is conditioned by an intensive development of ‘‘A’’ segregation, heterogeneous distribution of non-metallic impurities, physical heterogeneity throughout the ingot, and the formation of other defects typical of the solidification of large amounts of metal. Moreover, a larger weight of an ingot results in heavier defects. An uncontrolled formation of inner defects in an ingot, ‘‘A’’ segregation being one of them, can lead to the failure of critical components of power plants during their operation. It can cause technogenic disasters with unpredictable consequences for the environment. Among the worst defects of an ingot are ‘‘A’’ segregation streaks which are increased itchability areas occasionally accompanied by porosity. In an ingot longitudinal section, these areas are presented by streaks enriched with low-melting impurities (Figure 1). The negative influence of this defect on the mechanical properties of products manifests itself in a dramatic decrease of impact strength near the segregation streaks, reduced fatigue strength of metal a
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