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 2011
containing MgFeSi treatment alloy can help to neutralise its harmful effect believed to be by the preferential formation of a Ce-Pb compound. Antimony (Sb) Antimony has a harmful effect similar to that of lead. It is considered that levels of over 0.004% antimony cannot be tolerated in ductile irons without a severe reduction in graphite quality and hence mechanical properties. The effect of antimony is also cooling rate sensitive, tending to segregate to the intercellular regions where it promotes the formation of a mesh-type flake graphite form. Antimony can be introduced to the melt through the steel scrap or by intentional addition where small amounts such as 0.002% is sometimes used to promote a pearlitic matrix, particularly in heavy sections. The subversive effects of antimony can be offset by the addition of cerium. Bismuth (Bi) As little as 0.003% bismuth results in the formation of significant amounts of flake graphite, whilst 0.005% bismuth will almost completely eliminate spheroidal graphite formation. Bismuth is sometimes added to ductile irons in combination with cerium as a means of increasing nodule count. Bismuth and cerium additions can also help to reduce graphite floatation in heavy section ductile iron castings by producing a larger number of smaller nodules, which segregate more slowly towards cope surfaces during solidification. Titanium (Ti) The effect of titanium in ductile iron is to counter the spheroidising action of magnesium and to cause vermicular graphite formation. Indeed, the balanced use of magnesium and titanium is the preferred method for producing compacted graphite cast irons. For general use, titanium levels should be limited to about 0.04%; however, the effect is again section size sensitive. Light section castings can tolerate higher levels, as much as 0.07%, whilst a little as 0.02% can have a subversive effect in heavy section castings. Titanium is typically introduced into the iron through the melting of foundry pig irons, which possibly contain as much as 0.04% titanium, certain structural steels or compacted graphite iron scrap or returns. Where foundries produce both ductile and compacted graphite irons, segregation of scrap and returns is essential. A small addition of cerium is capable of neutralising the subversive effects of titanium. Aluminium (Al) Up to about 0.03% aluminium can be tolerated in ductile irons. Whilst aluminium is not as deleterious as titanium, aluminium tends to promote the formation of vermicular graphite. The presence of aluminium in ductile iron also increases the sensitivity of the iron to hydrogen pinholing. This effect is most pronounced in small green sand moulded castings where as little as 0.01% aluminium can be enough to cause a severe outbreak. Aluminium is introduced into the iron through charge and treatment materials such as steel scrap, ferroalloys and inoculants. Tellurium (Te) Tellurium will react chemically with magnesium to form a telluride thus lowering the effective magnesium level and causing degradation in graphite shape. As little as 0.002% tellurium can cause graphite degradation, higher levels promote carbide formation. ■ METAL Casting Technologies March 2011 45 References Ductile Iron Handbook -- American Foundrymen's Society Inc, 1993 Metallurgy and Production of Grey and Ductile Irons -- BCIRA, Alvechurch, Birmingham, UK Belec Metals Analysers Desktop model, up to 24 element channels, inert gas flushed optics, with Argon stand. Options of ferrous and non-ferrous bases. Portable spectrometer with assortment of probes. Can be used in the field, on-site or at metal auctions for accurate alloy analysis. Laboratory spectrometer, variable configuration, benchtop or free-standing, many optional extras, low Argon and power usage. Multiple bases with spark-stand and probe combination available. G & C Instrument Ser vices Tel: +61 2 4981 7255 Fax: +61 2 4981 7244 Email: info@gciser vice.com.au www.gcinstrument.com.au Lab 3000s Compact Port Vario Lab