Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C37/00—Cast-iron alloys
  • C22C37/10—Cast-iron alloys containing aluminium or silicon

Definitions

• the present invention relates to the industry of construction ferroalloys, particularly to iron-carbon alloys such as cast irons and steels, and more in detail to a high-alloy spheroidal graphite cast iron having an austenitic structure with a chemical composition according to the preamble of claim 1.
• the recent technological developments have led the operating temperature reached by such pieces to increase till reaching values ranging about from 800°C to 1020°C.
• the known alloys used for making these products, in the above operating temperature range, are usually two: high Nickel content cast iron or austenitic stainless Steels.
• the high Nickel content cast iron is available on the market under the name Ni-Resist cast iron and it has an austenitic structure; several compositions of this type of cast iron are known, one that is particularly useful for the application field to which reference is made is that described in the document titled as "Ni-resist type D5S -an improved material for turbocharger housings" published in 1980.
• the IS Steel generally has a yield strength (the temperature being equal) higher than NR cast iron; however it has also a considerably higher cost, about twice that of NR cast iron.
• IS Steel at such temperature value has a quite high yield strength, equal to about 110 Mpa.
• the temperature range is typically that of exhaust manifolds, turbines and turbo manifolds used in the "automotive" field, the problem described above is present.
• the choice of the material with which to make the exhaust manifolds, turbines and turbo manifolds is quite complicated: on one hand, by selecting NR cast iron, cheap castings are obtained but they are easily subjected to damages, on the other hand, by selecting austenitic IS stainless Steel, reliable items are obtained but with a considerable high cost.
• the present invention aims at overcoming the drawbacks of the prior art.
• the present invention aims at providing a material accomplishing the requirements set forth above.
• a first object of the present invention is a high-alloy spheroidal graphite cast iron having an austenitic structure comprising the following ingredients in the following percentages (by weight, on the total amount):
• Chrome (Cr) ranging from 1,6% to 2,0%
• Molybdenum (Mo) ranging from 0,9% to 1,1%
• Niobium (Nb) ranging from 0,3% to 0,5%
• Nickel (Ni) ranging from 34% to 36%
• Silicon (Si) ranging from 6,1% to 6,7%
• Carbon (C) ranging from 1,6% to 2,0%
• Tungsten (W) ranging from 0,5% to 0,7%
• Manganese (Mn) ranging from 0,5% to 0,65%
• the cast iron of the present invention comprises also Phosphorous and Copper in percentages that will be explained below.
• a further object of the present invention is a component, particularly a structural component, made of said cast iron, in particular made by a casting process followed by one or more chip removal machining processes.
• Still another object of the present invention is a turbo manifold for internal combustion engines (Otto or diesel engines) made of said cast iron.
• Figure 1 is the trend of the yield strength as a function of temperature of a known type of cast iron and a Steel, it being known too;
• Figure 2 is the trend of the yield strength of the cast iron according to the present invention.
• Figure 3 is the comparison between yield strengths as a function of temperature of known materials and of the cast iron according to the present invention.
• Figure 4 is the graph of UTS (ultimate tensile strength) of the cast iron according to the present invention.
• the high-alloy spheroidal graphite cast iron having an austenitic structure according to the present invention comprises the following ingredients in the following percentages by weight:
• Chrome (Cr) ranging from 1,6% to 2,0%
• Molybdenum ranging from 0,9% to 1,1 %
• Niobium (Nb) ranging from 0,3% to 0,5%
• Nickel (Ni) ranging from 34% to 36%
• Silicon (Si) ranging from 6,1 % to 6,7%
• Carbon (C) ranging from 1,6% to 2,0%
• Tungsten (W) ranging from 0,5% to 0,7%
• Manganese (Mn) ranging from 0,5% to 0,65%
• the high-alloy spheroidal graphite cast iron having an austenitic structure comprising, among other things, the above ingredients with the mentioned percentages has optimal mechanical properties, which are between those of NR cast iron described above and those of austenitic IS Stainless Steels mentioned above.
• the cast iron according to the present invention has a cost intermediate between that of known NR cast iron and that of austenitic stainless steel, therefore having an interesting cost saving in comparison with austenitic Stainless Steel.
• the cast iron according to the present invention essentially has all the best properties for overcoming the drawbacks mentioned above and for serving the function as a material for making turbo manifolds for internal combustion engines.
• the cast iron according to the present invention has, in a temperature range from about 780°C to 840°C, a yield strength still higher than that of IS Steel, making it even preferable than the latter for specific applications in such temperature range.
• Silicon is a graphitizing element and it moves the eutectic transformation to the left increasing the eutectic temperature; these two combined actions (the graphitizing action and movement of the eutectic curve) reduces the solidification range for a given carbon value.
• Silicon is an Alphagene element and in the value range of the invention (from 6,1 to 6,7%) it moves the solidification of the alloy in the stable system (graphite and ferrite).
• the carbon content of the eutectoid is reduced by the Silicon of about 0,1 % for each
• Tungsten does not affect the formation of the austenitic matrix, since it combines with the graphite segregated by the Silicon and resulting in the formation of further very stable Tungsten carbides.
• Nickel it has to be noted that it has a Gammagene effect and it reduces the critical points and the critical cooling speed, as well as it refines the perlite grain. Nickel, in the shown percentages, guarantees the stability of the cast iron matrix from ambient temperature to 1020°C and it does not generate carbides.
• Chrome it is an Alphagene element and it is a high carbide forming element and it forms very thermally stable carbides.
• the percentages of Chrome shown in the formulation of the cast iron according to the present invention guarantees the graphitization of the eutectic cementite and of perlite to slow down during a normal slow cooling.
• a general improvement of mechanical properties can be obtained by adding from 1,6% to 2% about of Chrome according to the present invention, due to the strong stabilizing effect of perlite, exerted by Chrome, and to the removal of free perlite formed after the slow cooling.
• the cast iron according to the present invention therefore shows an excellent stability at high temperature and a better corrosion resistance preventing scales from being formed helping the formation of the austenitic matrix.
• Molybdenum in the percentages shown above, is the most effective element for improving the resistance of the cast iron according to the present invention and for improving its toughness.
• Molybdenum forms intercrystalline carbides and it easily segregates together with chromes in eutectic phosphides.
• molybdenum added in percentages from 0,9% to 1,1% improves the heat resistance and it provides a good wear resistance.
• Niobium the fact of adding it in percentage from 0,3% to 0,5% into the formulation of the cast iron according to the present invention mainly aims at improving the mechanical properties thereof reducing the size of eutectic cells.
• Tungsten in the percentages shown above, provides the cast iron according to the present invention with an optimal corrosion resistance and most of mineral acids affect it only weakly.
• Tungsten considerably increases the hardness and the high melting temperature makes it a choice very suitable for structural applications subjected to high temperatures, such as those the present invention relates to, such as for instance turbo manifolds, exhaust manifolds for turbines in the "automotive" field or the like. Its high elastic modulus is exploited at low temperatures. Tungsten in percentages from about 0.5% to 0.7% provides a good creep resistance. Surprisingly (even if Tungsten is generally known and not recommended in this field due to its tendency to generate an excessive hardness and a low workability of the material) the applicant has noted that it, inserted in the cast iron according to the present invention, increases the presence of stable intergranular carbides that even more provides dimensional stability and stiffness at high temperatures.
• Manganese in this formulation is also the gammagene element stabilizing pearlite and refining the pearlitic matrix.
• the high-alloy spheroidal graphite cast iron having an austenitic structure according to the present invention further comprises the following ingredients in the following percentages by weight:
• Niobium (Nb) equal to 0,4%
• Molybdenum (Mo) 1
• Nickel (Ni) equal to 36%
• Silicon (Si) equal to 6,4%
• Manganese (Mn) equal to 0,55%
• the yield strength 1 of the cast iron according to the present invention is always higher than that of known NR cast iron.
• the yield strength of the cast iron according to the present invention is even higher than that of the more expensive IS Steel, thus actually making the cast iron according to the present invention not only cheaper than Steel, but also more resistant as regards specific applications.
• the cast iron according to the present invention has a yield strength lower than that of IS Steel, but still sufficient for making turbo manifolds and exhaust manifolds in the automotive field.
• the cast iron according to the present invention is a privileged choice for making such mechanical components.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Supercharger (AREA)
• Exhaust Silencers (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (2)

Family

ID=44554485

Family Applications (1)

Country Status (11)

Cited By (2)

Families Citing this family (2)

Family Cites Families (5)

• 2011
  • 2011-05-17 IT IT000861A patent/ITMI20110861A1/it unknown
• 2012
  • 2012-05-15 WO PCT/IB2012/052429 patent/WO2012156910A2/en not_active Ceased
  • 2012-05-15 CN CN201280023616.XA patent/CN103687972A/zh active Pending
  • 2012-05-15 PT PT127262210T patent/PT2710164E/pt unknown
  • 2012-05-15 EP EP12726221.0A patent/EP2710164B1/en not_active Not-in-force
  • 2012-05-15 BR BR112013029563A patent/BR112013029563A2/pt not_active IP Right Cessation
  • 2012-05-15 SI SI201230379T patent/SI2710164T1/sl unknown
  • 2012-05-15 ES ES12726221.0T patent/ES2555481T3/es active Active
  • 2012-05-15 HU HUE12726221A patent/HUE028165T2/en unknown
  • 2012-05-15 PL PL12726221T patent/PL2710164T3/pl unknown
  • 2012-05-15 RS RS20150813A patent/RS54426B1/sr unknown

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events