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Metal Casting Technologies : March 2010
32 www.metals.rala.com.au TECHNICAL FEATURE The sample was analyzed to check the inclusions. Macro- structure of the ESR ingot was carried out. The longitudinal surface of a section of the steel ingot was faced on the lathe machine followed by polishing with silicon carbide papers from 220 to 1200. The etchant used contained hydrochloric acid (HCl) and water in the ratio 1:1. The etchant was heated to 700C. The polished surface of the ingot was immersed in it for 15 minutes. After etching, the surface was cleaned with cotton in running tap water. The macrostructure was observed. Heat treatment was carried out in a tubular furnace. The furnace was flushed with Nitrogen gas to prevent scaling and decarburization of the steel. Chromel Alumel thermocouples (k type) were used for measuring the temperature. Sample was annealed at 8750C and furnace cooled. An oil bath was kept below one of the end of the furnace. The sample was austenitized at 9500C and quenched in oil. The sample was tempered at 4750C and quenched in oil. Hardness readings were taken on Rockwell C Scale. The sample was polished on different silicon carbide papers followed by velvet cloth polishing with diamond paste. 3% Nital was used to reveal the microstructure. Results The chemical analysis of the ingot is - C% Cr% Mn% S1% S% P% AI.% 0.33 1.5 2 0.32 0.018 0.02 0.05 The desulphurization percentage after ESR was 45.45%. It shows the ESR process is highly effective in removal of sulphur. If mixture of Calcium Fluoride, Calcium Oxide (CaO) and Alumina mixed slag had been used the desulphurization would have been more3. Calcium oxide being hygroscopic absorbs moisture from air. Care has to be taken during ESR of CaO based slags. A sound ingot was produced during the process. There was variation in the voltage and current during the process as compared to the solid electrode ESR process. This was due to the lesser bulk density of the rammed compacted chips, nonuniform compaction & higher feed rate. The ingot surface was not much smooth due to voltage and current variation. Figure 4a shows the ESR ingot. Inclusions in the sample are shown in Figure 4b. It is seen the inclusions are mainly of Rockwell hardness, C scale 38 Rockwell hardness, C scale, annealed 8750C 20 Impact Strength 135 KJ/m2 Ultimate Tensile Strength, annealed, MPa 843 MPa % elongation 10 Ulltimate Tensile Strength, MPa, Quenched and tempered. 1140 MPa % elongation 9 Fig. 4a Fig. 4b Fig. 5 Fig. 6
Media Kit 2010