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Metal Casting Technologies : March 2009
The use of nickel to produce austenitic irons (Ni resists) Nickel, Manganese and Copper additions can stabilize austenitic matrix structures in flake and ductile irons. The austenitic ductile grades can be used at temperatures up to 1050o C. Typical applications include turbocharger housings, exhaust gas manifolds, hot pressing dies and glass moulds, etc. For applications requiring heat and/or corrosion resistance at least 18% Nickel is needed. Chromium and Silicon additions are also used to improve oxidation and corrosion resistance. Increasing the Nickel level gives improved heat and corrosion resistance combined with greater thermal shock resistance. A 35% Nickel grade is used for minimum expansion and high thermal shock resistance. Increasing the Chromium level of austenitic irons improves oxidation resistance and erosion resistance but produces more intercellular eutectic Chromium rich carbide in the microstructure which limits toughness and machinability. The interdendritic eutectic carbide and the cored nature of the austenite dendrites are shown in Figure 3(b). The higher Si grades containing 4 - 6% Si are referred to as “Nicrosilals”. The heat resisting Ni- Resists and Nicrosilals form part of a large range of austenitic irons  where other grades are designed for: ? Corrosion resistance ? Use at sub-zero temperatures ? Special physical properties such as non-magnetic behaviour or controlled expansion In austenitic irons Nickel can be substituted by Manganese or Copper to give compositions based on 14% Ni plus around 6% Mn or Cu, but these lower Ni alloys are not normally used for heat resistance. As for all graphitic cast irons, in the production of castings it is vital to control Carbon Equivalent where for high Ni irons this is given by: CE = TC% + 0.33Si% + 0.047Ni% - 0.0055Ni% x Si%  High CE values tend to give better founding characteristics (i.e. lowest solidification temperature and highest fluidity) but can cause problems when ductile grades are produced. In the presence of high Ni contents the graphite in Mg treated irons can grow in a degenerate manner instead of forming nodules especially at low cooling rates in thicker sections. This sub-nodular form is referred to as “chunky” graphite. In areas containing such graphite the tensile Protect your moulds permanently with COMP MetCast The innovative release coating for greater productivity Nanocomp MetCast is the world’s first permanent nano-ceramic release coating – perfectly suited for open-mould casting in metal production. The working principal: applied in a thin layer to the mould, it allows long-term production with excellent process stability. Nanocomp MetCast is insensitive to temperature shock, molten metal and cooling water. Even in continuous production, a MetCast coating holds up for several weeks, after which it merely needs to be reapplied on specific areas. Your benefits: ? Effective separating effect and excellent demoulding properties ? Minimal consumption thanks to its extremely long service life and very thin layer application ? Greater productivity and optimal use of casting plant capacity When you choose permanent Nanocomp MetCast coating, you choose unbeatable efficiency for the production process and pass a milestone on the road to achieving an environmentally compatible “white” casthouse. ItN Nanovation AG Untertürkheimer Straße 25 66117 Saarbrücken, Germany ? Improved quality due to consistent process stability ? Convincing savings of time and expenses when compared to single-use products ? Lasting relief for employees, equipment and the environment Tel.: +49 (0) 681 / 50 01 – 561 Fax: +49 (0) 681 / 50 01 – 499 email@example.com www.itn-nanovation.com METAL Casting Technologies March 2009 39 Nanotechnology for ingot casting