by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
button in toolbar for more information.
Metal Casting Technologies : March 2007
www.metals.rala.com.au 30 inclusions and the formation of micro porosity and shrinkage holes cannot be avoided and the structure of the ingot shows both dendritic and globular solidification patterns. Paton17 et al. have reported that ESR of boiler steels improved the UTS strength by 25 - 35 percent with an increase in percent elongation by 5 - 33 %. Medovar18 found that the crack formation tendency in the HAZ after welding was reduced in ESR materials. Tensile properties by Gwilym shows as cast properties similar to wrought and retention of isotropic properties after fourfold reduction19. The fracture toughness of steels is improved by 50 - 100 % as inclusions are removed20. The ESR material is less susceptible to corrosion in aggressive media. Resistance to corrosion cracking of ESR 16 TNM steel was superior to that of the open hearth melted steel due to increased grain boundary purity of the ESR steel17. SOME ESR EXPERIMENTAL DETAILS Trials were carried out using mild steel rod electrodes of 40 mm diameter to produce round and square ingots of about 75 mm. Studies were made with CaF2: Al2O3, CaF2 : Al2O3: CaO slags for the purpose of standardization of melting and starting conditions. The starting practice consists bring electrode tip in contact with the starting plate placed on the bottom plate. The slag is kept at 7000C for 2 hours in a different furnace remove any moisture. As soon as the electrode tip touches the starting plate lot of arcing takes place and the slag mixture is added in the mould. With proper control a steady arc is obtained. The slag mixture is added in the gap between electrode and mould wall. The slag mixture melts soon and electrode is dipped in the slag. The whole slag mixture takes some 3 minutes to melt. After the whole slag melts suitable voltage is selected. The electrode feed is adjusted to give the required current and later on the process runs smoothly. To keep constant current electrode feed rate has to be adjusted. Process starting is smooth if prefused crushed slag is used. 0.9 kg slag can be melted in about 5 to 6 minutes in an 80 mm diameter tapered mould using a 40 diameter mm electrode. The slag density is less than the molten steel. The steel drops pass through the slag and collect on the starting plate. Power is reduced at the end of the process so that pipe and central porosity can be removed. For controlling oxidation deoxidizers like aluminium is added to the slag, etc. Foamy slag forms some times during melting of mild steel, presumably due to the evolution of gases from the ingot like carbon monoxide. After the ingot cools or it is red hot, it is stripped from the mould. The tapered shape of mould helps in easy removal of the ingot from. The ingot comes out easily with a small force. The ESR ingots obtained are sound and without a pipe at the top and show columnar grain structure. Figure 7 shows the columnar grains in an ESR ingot. Current used is in the range of 750 Amps with a voltage of 25 V. TECHNICAL FEATURE Figure 6. Figure 7. segregation porosity clouds of non metallic inclusions