EP1652949A1 - Austenitisches wärmebeständiges kugelgraphitgusseisen - Google Patents

Austenitisches wärmebeständiges kugelgraphitgusseisen Download PDF

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Publication number
EP1652949A1
EP1652949A1 EP04770825A EP04770825A EP1652949A1 EP 1652949 A1 EP1652949 A1 EP 1652949A1 EP 04770825 A EP04770825 A EP 04770825A EP 04770825 A EP04770825 A EP 04770825A EP 1652949 A1 EP1652949 A1 EP 1652949A1
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Prior art keywords
cast iron
temperature
heat
spheroidal graphite
resistant
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EP04770825A
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English (en)
French (fr)
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EP1652949A4 (de
Inventor
Kenji Itoh
Keijiro Hayashi
Toru Iwanaga
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Proterial Ltd
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Hitachi Metals Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/04—Cast-iron alloys containing spheroidal graphite
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/06—Cast-iron alloys containing chromium
    • C22C37/08—Cast-iron alloys containing chromium with nickel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/16—Selection of particular materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2530/00—Selection of materials for tubes, chambers or housings
    • F01N2530/02—Corrosion resistive metals

Definitions

  • the present invention relates to a heat-resistant, austenitic spheroidal graphite cast iron suitable for exhaust equipment members, etc. for automobile engines, such as turbocharger housings, exhaust manifolds, catalyst cases, etc.
  • Exhaust equipment members for automobile engines such as turbocharger housings, exhaust manifolds, catalyst cases, exhaust manifolds integrally cast with turbocharger housings, exhaust manifolds integrally cast with catalyst cases, etc. are required to have high heat resistance such as oxidation resistance, high-temperature yield strength, thermal fatigue life (thermal cracking life), etc., because they are used under high-temperature, severe conditions of being repeatedly exposed to a high-temperature exhaust gas passing therethrough, and because they are exposed to sulfur oxides, nitrogen oxides, etc. in the exhaust gas.
  • high heat resistance such as oxidation resistance, high-temperature yield strength, thermal fatigue life (thermal cracking life), etc.
  • the exhaust equipment members for automobile engines have conventionally been formed by heat-resistant cast iron such as austenitic spheroidal graphite cast iron (called "NI-RESIST”) having high heat resistance, ferritic or austenitic cast stainless steel containing large amounts of elements such as Ni, Cr, W, etc. for improved heat resistance, etc.
  • heat-resistant cast iron such as austenitic spheroidal graphite cast iron (called "NI-RESIST) having high heat resistance
  • ferritic or austenitic cast stainless steel containing large amounts of elements such as Ni, Cr, W, etc. for improved heat resistance, etc.
  • a typical austenitic spheroidal graphite cast iron is FCDA-NiSiCr 35 5 2 (JIS G 5510) having a composition comprising, by weight, 2.0% or less of C, 4.0-6.0% of Si, 0.5-1.5% of Mn, 34.0-36.0% of Ni, and 1.5-2.5% of Cr, which has elongation of 10% or more and 0.2-% yield strength of 200 N/mm 2 or more at room temperature.
  • this austenitic spheroidal graphite cast iron has insufficient oxidation resistance and thermal fatigue life, because oxide films, from which cracking occurs, are formed at temperatures of 900°C or higher. Therefore, the austenitic spheroidal graphite cast iron cannot be used for exhaust equipment members exposed to a high-temperature exhaust gas at 900°C or higher.
  • JP59-113160A discloses austenitic spheroidal graphite cast iron having a composition comprising, by weight, 2.5-3.5% of C, 1.5-3% of Si, 0.2-8.0% of Mn, 1-3% of Cr, 18-35% of Ni, 0.05% or less of P, and 0.15% or less of S, the balance being Fe and impurities, which has excellent thermal cracking resistance. It describes in Examples that with a composition comprising 2.9% of C, 2.7% of Si, 1.5% of Mn, 2.0% of Cr and 25.0% of Ni, the balance being Fe and impurities, no cracking occurred at all in a 300-hour durability test at exhaust gas temperatures between 850°C and 200°C.
  • this austenitic spheroidal graphite cast iron is provided with improved thermal cracking resistance by reducing the amounts of harmful precipitates in a microstructure by reducing the amount of Si, it does not have sufficient ductility (room-temperature elongation) to resist tensile stress at room temperature.
  • JP63-114938A discloses a heat-resistant cast iron having a composition comprising, by weight, 2.5-3% of C, 2.6-3.2% of Si, 0.6-1.0% of Mn, 1.8-5.0% of Cr, 16.0-30.0% of Ni, 0.08% or less of P, 0.02% or less of S, 0.03-0.10% of Mg, 0.8-3.3% of Nb, and 0.18-0.7% of Ce and/or La, the balance being Fe and inevitable impurities, which exhibits excellent oxidation resistance particularly in an environment of repeated heating and cooling.
  • the precipitation of inevitable impurities such as P, S, etc.
  • JP06-128682A discloses a high-heat resistance cast iron having a composition comprising 13.0-40.0% by weight of Ni and 3.0-10.0% by weight of Si, the balance being substantially Fe, and at least one element selected from the group consisting of Nb, Mo, V, Ti and Ta being 5-30% by weight of Si, which suffers small weight loss by oxidation. It describes in Example a composition comprising 2.83% by weight of C, 6.17% by weight of Si, 0.85% by weight of Mn, 0.056% by weight of Mg, 20.3% by weight of Ni, 1.99% by weight of Cr, and 1.6% by weight of Mo.
  • This heat-resistant cast iron has improved heat resistance and high-temperature fatigue strength, because it contains as much Si as 3.0-10.0% by weight, Mo being 5-30% by weight of Si.
  • this cast iron has toughness reduced by the addition of a large amount of Si.
  • the mere addition of Mo hinders the spheroidization of graphite and increases the number of carbides, particularly resulting in insufficient ductility at room temperature.
  • JP07-6032B discloses flake graphite cast iron for cylinder heads having a composition comprising, by weight, 3.2-3.7% of C, 2.0-2.4% of Si, 0.2-0.8% of Mn, 0.1 % or less of P, 0.1 % or less of S, 0.1-0.4% of Cr, 0.2-0.6% ofNi, 0.3-0.6% of Mo, and 0.02-0.05% of Sb, the balance being Fe, which has a thermal fatigue resistance particularly improved by Sb.
  • this cast iron has insufficient room-temperature elongation, high-temperature yield strength and thermal fatigue life because of no spheroidization of graphite, particularly insufficient heat resistance when exposed to a high-temperature exhaust gas at 900°C or higher.
  • gasoline is mixed with air in an intake manifold or a collector as an air-intake member and then supplied to a combustion chamber of the engine.
  • the air-intake members are conventionally connected to the engine on the rear side, while exhaust equipment members such as an exhaust manifold and a turbine housing are connected to the engine on the front side.
  • exhaust equipment members such as an exhaust manifold and a turbine housing are connected to the engine on the front side.
  • exhaust equipment members are disposed on the rear side of an engine, so that they are directly connected to an exhaust gas-purifying apparatus to suppress the decrease of an exhaust gas temperature at the time of starting the engine, thereby improving the initial performance of an exhaust gas-purifying catalyst.
  • the exhaust equipment members are disposed on the rear side of the engine, the surface temperatures of the exhaust equipment members are excessively elevated because the exhaust equipment members are less likely to be brought into contact with the wind during the driving of an automobile.
  • the exhaust equipment members for automobile engines are exposed to sulfur oxides, nitrogen oxides, etc. contained in the exhaust gas.
  • the exhaust equipment members for automobile engines are not only required to have high oxidation resistance, but also should withstand severer conditions than conventional ones, such as elevated exhaust gas temperatures, elevated surface temperatures because of rear arrangement, etc.
  • the exhaust equipment members are exposed to as high an exhaust gas as 900°C or higher, particularly around 1000°C, so that they are required to have higher heat resistance.
  • the high or excellent heat resistance means that even when the exhaust equipment members are exposed to a high-temperature exhaust gas containing sulfur oxides, nitrogen oxides, etc., oxide films, from which cracking occurs, are less likely to be formed (excellent oxidation resistance), that the exhaust equipment members are strong enough to resist a compression stress generated when the constrained exhaust equipment members are subjected to high temperatures (high yield strength at high temperatures), and that the exhaust equipment members more desirably withstand many cycles of operation and stop until thermal fatigue fracture occurs by cracking (long thermal fatigue life).
  • the exhaust equipment members are required to have excellent heat resistance and ductility. Vibration and shock are applied to the exhaust equipment members in a production step and an assembling step to an engine, at the time of starting an automobile, during its driving, etc. Thus, the exhaust equipment members are required to have sufficient ductility to resist tensile stress generated by the vibration and shock, so that no cracking occurs. Because metals have low toughness at low temperatures, ductility at room temperature or lower is particularly important. The ductility at room temperature or lower is generally expressed by room-temperature elongation.
  • an object of the present invention is to provide an inexpensively producible, heat-resistant, austenitic spheroidal graphite cast iron, whose heat resistance such as oxidation resistance, high-temperature yield strength, thermal fatigue life, etc. when exposed to an exhaust gas at 900°C or higher is improved without deteriorating room-temperature elongation.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention comprises 1-4.5% by weight of Mo, and 0.001-0.5% by weight of Sn and/or Sb being as (2Sn + Sb).
  • the heat-resistant, austenitic spheroidal graphite cast iron has a composition comprising 1-3.5% of C, 1-6.5% of Si, 3% or less of Cr, 10-40% of Ni, 1-4.5% of Mo, 0.001-0.5% of Sn and/or Sb as (2Sn + Sb), and 0.1% or less of a graphite-spheroidizing element, on a weight basis.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention preferably further comprises 0.3% or less by weight of N.
  • the above heat-resistant, austenitic spheroidal graphite cast iron preferably has room-temperature elongation of 2% or more, weight loss by oxidation of 30 mg/cm 2 or less when kept at 950°C for 200 hours in the air, and 0.2-% yield strength of 55 N/mm 2 or more at 950°C in the air. It also preferably has a thermal fatigue life of 400 cycles or more in a thermal fatigue test of heating and cooling at the highest temperature of 950°C, a temperature amplitude of 800°C and a constraint ratio of 0.5. It further preferably has an average thermal expansion coefficient of 18 x 10 -6 /°C or less in a range from room temperature to 1000°C.
  • composition and properties of the heat-resistant, austenitic spheroidal graphite cast iron of the present invention will be explained in detail below.
  • the percentage is expressed on a weight basis unless otherwise mentioned.
  • C is an element for crystallizing graphite and improving the flowability of a melt.
  • C is less than 1.0%, spheroidal graphite cannot be crystallized, and the melt has too low flowability.
  • C exceeds 3.5%, coarse graphite particles are formed, resulting in spheroidal graphite cast iron with poor room-temperature elongation, and shrinkage cavities are likely to be formed during casting. Accordingly, C is 1-3.5%, preferably 1.5-2.5%.
  • Si is an element contributing to the crystallization of graphite.
  • the inclusion of 1% or more of Si leads to the formation of a passive film of silicon oxide near a surface, resulting in spheroidal graphite cast iron with improved oxidation resistance.
  • Si exceeding 6.5% provides a hard matrix, resulting in remarkable decrease in room-temperature elongation and the deterioration of machinability. Accordingly, Si is 1-6.5%, preferably 4.5-6%.
  • Cr is combined with carbon to precipitate carbides in a cast iron matrix, thereby improving the high-temperature yield strength of the spheroidal graphite cast iron by precipitation strengthening of the matrix. It also forms a dense passive film of chromium oxides near a surface, thereby improving oxidation resistance.
  • Cr exceeding 3% deteriorates workability and adversely affects the spheroidization of graphite. Accordingly, Cr is 3% or less, preferably 1-3%.
  • Ni is an important element to austenitize the matrix structure. When Ni is less than 10%, an austenite is not sufficiently stabilized. On the other hand, when Ni exceeds 40%, an austenitizing effect is saturated, resulting in only increase in a material cost. Accordingly, Ni is 10-40%, preferably 25-40%. The more preferred lower limit of Ni is 30%, and the more preferred upper limit of Ni is 36%.
  • Mo is combined with carbon to precipitate carbides in the cast iron matrix, thereby drastically increasing the yield strength of the matrix by precipitation strengthening in an entire range of temperatures used.
  • Mo is a carbide-forming element, it has little tendency of hindering the spheroidization of graphite.
  • the addition of Mo together with Sn and/or Sb improves the room-temperature elongation without decreasing the number of graphite particles precipitated and a graphite spheroidization ratio.
  • Mo is an element having a small thermal expansion coefficient, it reduces the average thermal expansion coefficient of the cast iron up to around 1000°C, thereby decreasing a thermal strain in a high-temperature range, which is determined by the product of a thermal expansion coefficient and temperature, and thus lowering the resultant thermal stress.
  • the synergistic effect of Mo with Si and Cr provide a dense and strong passive film of silicon oxide, chromium oxide, etc. formed on a surface, and suppresses surface oxidation, thereby improving the oxidation resistance of the cast iron.
  • the synergistic effect of suppressing the thermal stress and improving the oxidation resistance provides the cast iron with a longer thermal fatigue life.
  • Mo exceeding 4.5% decreases room-temperature elongation and machinability due to deteriorated spheroidization of graphite and increased precipitation of carbides.
  • Mo is less than 1%, the matrix of the cast iron is not subjected to sufficient precipitation strengthening by the formation of carbides. Accordingly, Mo is 1-4.5%, preferably 2-4%.
  • Both Sn and Sb increase the number of graphite particles while reducing their segregation, and increase a graphite spheroidization ratio to 75% or more, thereby suppressing Mo from reducing ductility. Even if up to 6.5% of Si tending to reduce the ductility is contained, the addition of Sn and/or Sb provides the cast iron with enough room-temperature elongation without reducing the number and spheroidization ratio of graphite particles. Sn and Sb also prevent the disappearance of graphite by internal oxidation, thereby providing the heat-resistant, austenitic spheroidal graphite cast iron with improved oxidation resistance. Though this mechanism is not necessarily clear, Sn and/or Sb are concentrated in boundaries between graphite particles and a matrix on the matrix side, suppressing C from diffusing from graphite to the matrix, and suppressing oxygen entering into the matrix from reacting with graphite.
  • (2Sn + Sb) is 0.001-0.5%, preferably 0.005-0.5%, more preferably 0.01-0.4%.
  • N stabilizes an austenitic structure and improves the high-temperature yield strength of the matrix.
  • N exceeds 0.3%, the amount of nitrides precipitated increases, and the spheroidization of graphite is hindered, resulting in decreased toughness, and more generation of gas defects such as pinholes, etc. during casting. Accordingly, N is 0.3% or less.
  • N is an element inevitably contained in the austenitic spheroidal graphite cast iron usually in an amount of about 0.002-0.006%, the predetermined amount of N is added when high yield strength is needed at high temperatures.
  • N is preferably 0.01-0.3%, more preferably 0.03-0.2%.
  • lime nitrogen or chromium nitride (Cr 3 N) is added to the melt, or a nitrogen gas is blown into the melt.
  • a graphite-spheroidizing element such as Mg or Ca in pure Mg, Fe-Si-Mg alloys, etc. is added in an amount of 0.1 % or less.
  • the amount of Mg added is preferably 0.02-0.08%.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention may contain Mn and Cu in ranges not deteriorating room-temperature elongation, oxidation resistance, high-temperature yield strength and thermal fatigue life.
  • Mn is an element necessary for stabilizing the austenitic structure, but more than 1.5% of Mn would deteriorate the toughness and heat resistance of the cast iron, be likely to generate gas defects such as blow holes, etc.
  • Cu is, like Ni, dissolved in the matrix to stabilize the austenitic structure, making crystal grains in the matrix structure finer, thereby contributing to the improvement of high-temperature yield strength, and improving oxidation resistance and corrosion resistance.
  • Mn and Cu hinders the spheroidization of graphite, and reduces ductility by the formation of carbide. Accordingly, when Mn and Cu are added, Mn is preferably 1.5% or less, and Cu is preferably 3% or less.
  • P is not only harmful to the spheroidization of graphite, but also precipitated in grain boundaries, deteriorating oxidation resistance and room-temperature elongation. Accordingly, P is preferably 0.08% or less. Because S is also harmful to spheroidization of graphite, S is preferably 0.025% or less.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention is used for exhaust equipment members for automobile engines, which are exposed to an exhaust gas at 900°C or higher, particularly around 1000°C, it should have enough room-temperature elongation, oxidation resistance and high-temperature yield strength. Accordingly, it preferably meets the conditions that its room-temperature elongation is 2% or more, that its weight loss by oxidation is 30 mg/cm 2 or less when it is kept in the air at 950°C for 200 hours, and that its 0.2-% yield strength is 55 N/mm 2 or more in the air at 950°C. To meet such conditions, particularly the high-temperature yield strength should be improved while keeping the room-temperature elongation.
  • the heat-resistant, austenitic spheroidal graphite cast iron preferably has 75% or more of a graphite spheroidization ratio.
  • the austenitic spheroidal graphite cast iron has less than 2.0% of room-temperature elongation, it is likely subjected to cracking by vibration and shock applied during the production of exhaust equipment members, their assembling to engines, at the time of start and during operation of automobile engines, etc.
  • the room-temperature elongation is preferably 2% or more.
  • the heat-resistant, austenitic spheroidal graphite cast iron used for exhaust equipment members for automobile engines is required to have enough room-temperature elongation and heat resistance (oxidation resistance and high-temperature yield strength).
  • the weight loss by oxidation in the air at 950°C and 0.2-% yield strength are indices expressing the level of heat resistance. Smaller weight loss by oxidation and higher high-temperature yield strength lead to better heat resistance.
  • the exhaust equipment members are exposed to sulfur oxides, nitrogen oxides, etc. contained in exhaust gases discharged from engines.
  • Oxidation occurs, oxide films are first formed on a surface, from which microcracks are generated, and the oxidation of microcracks accelerates cracking. By this repetition, cracking propagates deep inside the members.
  • weight loss by oxidation exceed 30 mg/cm 2 when kept in the air at 950°C for 200 hours, lots of oxide films, from which cracking occurs, are formed on a surface, resulting in insufficient oxidation resistance. Accordingly, the weight loss by oxidation is preferably 30 mg/cm 2 or less.
  • the 0.2-% yield strength at 950°C in the air is 55 N/mm 2 or more, preferably 60 N/mm 2 or more.
  • the exhaust equipment members should have a long thermal fatigue life to the repetition of operation (heating) and stop (cooling) of engines. Specifically, in a thermal fatigue test, in which heating and cooling are repeated at the highest temperature of 950°C, a temperature amplitude of 800°C and a constraint ratio of 0.5, the number of cycles (thermal fatigue life) until fracture occurs by cracking is desirably 400 or more.
  • the thermal fatigue life under this condition is an index expressing how high the heat resistance is.
  • exhaust equipment members exposed to an exhaust gas at 900°C or higher, particularly around 1000°C do not have a sufficient thermal fatigue life.
  • the exhaust equipment members are cracked due to a thermal stress generated by the repetition of expansion during heating and shrinkage during cooling.
  • the exhaust equipment members preferably have the above room-temperature elongation, oxidation resistance and high-temperature yield strength, and a small average thermal expansion coefficient between room temperature and a high-temperature region.
  • thermal strain in a high-temperature range which is determined by the product of a thermal expansion coefficient and a temperature, is reduced, resulting in less thermal stress generated, the exhaust equipment members are provided with an improved thermal fatigue life.
  • the average thermal expansion coefficient in a range from room temperature to 1000°C is preferably 18 x 10 -6 /°C or less.
  • Each heat-resistant, austenitic spheroidal graphite cast iron having a chemical composition (% by weight) shown in Table 1 was melted in a 100-kg high-frequency furnace in the air, tapped from the furnace at 1450°C or higher, and poured into a mold at 1300°C or higher to cast a block-shaped sample of 25 mm x 25 mm x 165 mm.
  • the samples of Examples 1-17 are within the range of the present invention, and the samples of Comparative Examples 1-13 are outside the range of the present invention.
  • the samples of Comparative Examples 1-3 contained less than 1% of Mo, the samples of Comparative Examples 4-9 and 11 contained no Sn and Sb at all, the sample of Comparative Example 10 contained more than 4.5% of Mo, the sample of Comparative Example 12 contained more than 0.5% of (2Sn + Sb), and the sample of Comparative Example 13 contained more than 0.3% of N.
  • the sample of Comparative Example 4 corresponds to NI-RESIST DSS (JIS G 5510, JIS-FCDA NiSiCr 35 5 2) containing no Mo, Sn and Sb at all.
  • Example 1 No. Chemical Composition (% by weight) C Si Cr Ni Mo Sn Sb 2Sn+Sb N Mg Example 1 1.97 3.75 1.70 28.5 1.18 - 0.0012 0.0012 0.0065 0.072
  • Example 2 2.01 3.94 1.61 26.9 1.23 0.0007 - - 0.0014 0.0053 0.066
  • Example 3 2.05 4.52 1.78 30.4 2.01 - 0.0052 0.0052 0.0107 0.063
  • Example 4 2.11 4.56 1.65 31.3 2.04 0.0054 - - 0.0108 0.0123 0.071
  • Example 5 1.87 4.85 1.72 32.6 2.21 - 0.0201 0.0201 0.0507 0.069
  • Example 6 1.94 5.13 1.68 31.5 3.05 0.0109 - - 0.0218 0.0713 0.075
  • Example 7 2.04 4.54 1.72 34.1 1.41 0.0067 0.0078 0.0212 0.0042 0.071
  • Example 8 2.03 4.47 1.67 34.1 1.40 0.0005 0.0005 0.00
  • Fig. 1 is a photomicrograph (magnification: 100 times) showing the microstructure of the sample of Example 12
  • Fig. 2 is a photomicrograph (magnification: 100 times) showing the microstructure of the sample of Comparative Example 9.
  • a flanged test piece having a gauge length of 50 mm and a diameter of 10 mm in the gauge length was cut out of each sample, and set in an electric-hydraulic servo, tensile test machine to measure room-temperature elongation (%) at 25°C.
  • Each sample was examined with respect to the relation between a graphite spheroidization ratio and room-temperature elongation.
  • Fig. 3 shows the relation between the graphite spheroidization ratio and the room-temperature elongation.
  • Each sample was further examined with respect to the relation between the amount of Mo and room-temperature elongation.
  • Fig. 4 shows the relation between the amount of Mo and the room-temperature elongation.
  • Example 12 had many graphite particles in a good spheroidal shape.
  • Example 12 had as high a graphite spheroidization ratio as 84% and as high room-temperature elongation as 2.3%.
  • the sample of Comparative Example 9 containing as excessive Mo as 4.87% without Sn and/or Sb had a microstructure containing fewer graphite particles, many of which were not spheroidized.
  • Comparative Example 9 had as low a graphite spheroidization ratio as 64% and as low room-temperature elongation as 0.9%.
  • Fig. 3 indicates that the graphite spheroidization ratio should be 75% or more to obtain a practically sufficient room-temperature elongation (2% or more). If the austenitic spheroidal graphite cast iron had a microstructure having graphite particles deformed from a spheroidal shape to such an extent that the graphite spheroidization ratio becomes less than 75%, it would be close to gray cast iron (flake graphite cast iron) or vermicular cast iron, failing to obtain necessary strength and room-temperature elongation even though its matrix structure were strengthened.
  • the oxidation resistance was evaluated at 950°C in the air. Specifically, a round rod test piece of 10 mm in diameter and 20 mm in length was cut out of each sample, kept at 950°C for 200 hours in the air, and subjected to shot blasting to remove oxide scales, thereby determining weight change (weight loss by oxidation) per a unit area before and after the oxidation test. Smaller weight loss means higher oxidation resistance. The results are shown in Table 2. Also, the relation between the Mo content and the weight loss by oxidation was investigated on each sample. The results are shown in Fig. 5.
  • the weight loss by oxidation is minimum when the Mo content is about 3%, and sufficiently small weight loss by oxidation requires that the Mo content be 1-4.5%.
  • the weight loss by oxidation was 12.3 mg/cm 2 to 25.4 mg/cm 2 , less than 30 mg/cm 2 .
  • the weight loss by oxidation was as much as 32.5-59.0 mg/cm 2 in the samples of Comparative Examples 1-12.
  • Fig. 6 is a photomicrograph (magnification: 400 times) showing the microstructure of the sample of Example 12 after the oxidation test
  • Fig. 7 is a photomicrograph (magnification: 400 times) showing the microstructure of the sample of Comparative Example 4 containing no Mo, Sn and Sb after the oxidation test.
  • Example 12 suffered little surface oxidation and was prevented from the disappearance of graphite by oxidation, while the sample of Comparative Example 4 suffered severe surface oxidation, with oxide films intruding into voids generated by the disappearance of graphite by oxidation, part of internal graphite being disappeared or removed by oxidation.
  • Example 7 The comparison of weight loss by oxidation between the samples of Example 7 and Comparative Example 5 having substantially the same Mo content of about 1.4% with difference in the presence of Sn and Sb revealed that the weight loss by oxidation was 19.2 mg/cm 2 in Example 7, in which (2Sn + Sb) was 0.0212%, while it was 48.6 mg/cm 2 in Comparative Example 5 containing no Sn and Sb, as much as about 2.5 times that of Example 7.
  • Example 12 Likewise, the comparison of the samples of Example 12 and Comparative Example 11 having substantially the same Mo content of about 2.8% revealed that the weight loss by oxidation was 13.5 mg/cm 2 in the sample of Example 12, in which (2Sn + Sb) was 0.0294%, while it was 35.7 mg/cm 2 in the sample of Comparative Example 11 containing no Sn and Sb, as much as about 2.5 times that of Example 12.
  • the Mo content should be 1-4.5%, and (2Sn + Sb) should be 0.001-0.5%.
  • the weight loss by oxidation was less than 15 mg/cm 2 , and to obtain such low weight loss by oxidation, the Mo content is preferably 2-4%.
  • the high-temperature yield strength of each sample was determined by cutting each sample to form a flanged test piece having a gauge length of 50 mm and a diameter of 10 mm in the gauge length, which was set in an electric-hydraulic servo thermal-fatigue-measuring machine to measure 0.2-% yield strength at 950°C in the air.
  • the results are shown in Table 2.
  • Fig. 8 shows the relation between the Mo content and the high-temperature yield strength.
  • Examples 7 and 8 and Comparative Example 5 containing the same amount (about 1.4%) of Mo were compared with respect to high-temperature yield strength, as samples having substantially the same Mo content and different N contents. It was thus found that the samples of Example 7 and Comparative Example 5 containing N in amounts of 0.0042% and 0.0048% (both inevitable levels), respectively, had high-temperature yield strength of about 57 N/mm 2 , while the sample of Example 8 intentionally containing 0.0104% of N had high-temperature yield strength of 64.4N/mm 2 , about 7 N/mm 2 higher.
  • Example 10 and Comparative Example 6, between Example 12 and Comparative Example 7, and between Example 14 and Comparative Example 8, respectively containing substantially the same amount of Mo revealed that the samples of Comparative Examples 6, 7, 8 containing N in inevitable levels had high-temperature yield strength of about 58 N/mm 2 , 62 N/mm 2 and 62 N/mm 2 , respectively, while the samples of Examples 10, 12, 14 intentionally containing 0.01% or more of N had high-temperature yield strength of about 67 N/mm 2 , 71 N/mm 2 and 72 N/mm 2 , respectively, about 9-10 N/mm 2 higher.
  • a cycle of heating and cooling was repeated under the conditions that a ratio of mechanically constraining elongation and shrinkage was 0.5, that the lower limit temperature was 150°C, that the highest temperatures were 750°C, 800°C and 950°C (temperature amplitudes of 600°C, 650°C and 800°C), respectively, and that one cycle was 7 minutes, to cause thermal fatigue fracture by cracking, thereby measuring the number of cycles until fracture occurred to determine the thermal fatigue life.
  • the constraint ratio is expressed by (free thermal elongation - thermal elongation under mechanical constraint) / (free thermal elongation).
  • the constraint ratio of 1.0 means that a test piece is mechanically constrained such that it is not elongated at all when heated, for instance, from 150°C to 950°C.
  • the constraint ratio of 0.5 means that a test piece is mechanically constrained such that it is elongated by 1 mm, for instance, when it is elongated by 2 mm in the case of free thermal elongation.
  • the exhaust equipment members such as turbine housings, exhaust manifolds, catalyst cases, etc.
  • Fig. 9 shows the relation between the Mo content and a thermal fatigue life at a temperature of 950°C and at a constraint ratio of 0.5.
  • Fig. 9 indicates that when the Mo content was about 3%, the thermal fatigue life was longest, and that when the Mo content was within a range of 1-4.5% (Examples 1-17), the thermal fatigue life was 400 cycles or more.
  • any samples of Comparative Examples 1-13 had thermal fatigue lives of less than 400 cycles. Thus, the samples of Examples 1-17 have longer thermal fatigue lives than those of Comparative Examples 1-13.
  • the Mo content should be 1-4.5%, and (2Sn + Sb) should be 0.001-0.5%, to obtain a thermal fatigue life of 400 cycles or more in a thermal fatigue test of heating and cooling at the highest temperature of 950°C, a temperature amplitude of 800°C and a constraint ratio of 0.5.
  • thermomechanical analyzer TAS200 available from Rigaku Corporation
  • TAS200 thermomechanical analyzer
  • Table 3 shows the measured thermal expansion coefficients of Example 12 and Comparative Example 4 in each temperature range.
  • Example 2 No. Graphite Spheroidization Ratio (%) Elongation at Room Temperature (%) Weight Loss by Oxidation (mg/cm 2 ) at High-Temperature Yield Strength (N/mm 2 ) at 950°C 950°C
  • Example 1 88 4.8 25.4 58.4
  • Example 2 86 4.2 23.1 56.2
  • Example 3 84 3.2 14.4 63.7
  • Example 4 82 2.8 13.9 67.5
  • Example 5 82 2.4 12.5 68.6
  • Example 6 79 2.5 12.6 70.7
  • Example 7 90 5.3 19.2 57.2
  • Example 8 85 2.9 22.4 64.4
  • Example 9 86 3.3 16.8 65.3
  • Example 10 84 3.0 12.4 66.5
  • Example 11 83 2.4 12.6 69.8
  • Example 12 84 2.3 13.5 70.6
  • Example 13 81 2.8 12.3 68.6
  • Example 14 80 2.2 12.7 71.6
  • Example 15 79 2.1 16.1 71.3
  • Example 12 Comparative Example 4 RT (1) to 300°C 13.9 15.9 RT to 400°C 14.6 16.6 RT to 500°C 15.3 17.2 RT to 600°C 15.8 17.6 RT to 700°C 16.1 17.7 RT to 800°C 16.4 17.9 RT to 900°C 16.7 18.5 RT to 1000°C 17.4 19.5 Note: (1) Room temperature.
  • Table 2 indicates that as the Mo content increases, the average thermal expansion coefficient decreases in a range from room temperature to 1000°C, and that when the Mo content exceeds 1%, the average thermal expansion coefficient becomes 18 x 10 -6 /°C or less.
  • Table 3 indicates that Example 12 had a smaller thermal expansion coefficient by 1.5-2.1 x 10 -6 /°C than that of Comparative Example 4 containing no Mo, Sn and Sb in every 100°C temperature range from room temperature to 300-1000°C.
  • the heat-resistant, austenitic spheroidal graphite cast iron When used for exhaust equipment members for automobile engines, its average thermal expansion coefficient in a range from room temperature to 1000°C is desirably 18 x 10 -6 /°C or less to suppress cracking due to thermal stress, requiring that the Mo content be 1% or more.
  • Fig. 10 shows exhaust equipment comprising an exhaust manifold 1, a turbocharger housing 2, and a catalyst case 4 as an example of the exhaust equipment members using the heat-resistant, austenitic spheroidal graphite cast iron of the present invention.
  • an exhaust gas (indicated by the arrow A) discharged from an engine (not shown) is gathered in the exhaust manifold 1 to rotate a turbine (not shown) in the turbine housing 2 by the kinetic energy of the exhaust gas, and the air (shown by the arrow B) supplied by driving a compressor coaxially connected to this turbine is compressed to supply the compressed air to the engine as shown by the arrow C, thereby increasing the power of the engine.
  • An exhaust gas discharged from the turbocharger housing 2 is supplied to the catalyst case 4 via a connection 3, and after harmful materials were removed by a catalyst in the catalyst case 4, it was discharged to the air via a muffler 5 as shown by the arrow D.
  • An exhaust gas path passes through the exhaust manifold 1, the turbocharger housing 2, the connection 3 and the catalyst case 4.
  • the exhaust gas path is as thick as 2.0-4.5 mm in the exhaust manifold 1, 2.5-5.5 mm in the turbocharger housing 2, 2.5-3.5 mm in the connection 3, and 2.0-2.5 mm in the catalyst case 4.
  • Fig. 11 exemplifies a turbocharger housing 2
  • Fig. 12 shows its A-A cross section.
  • the turbocharger housing 2 comprises a spiral-shaped scroll portion 2a, whose hollow portion has a complicated shape having a cross section increasing from one end to the other.
  • the turbocharger housing 2 is provided with a waist gate 2b for bypassing an excess exhaust gas for discharge by opening a valve (not shown).
  • the waist gate 2b through which a high-temperature exhaust gas flows, is particularly required to have high oxidation resistance.
  • the heat-resistant, austenitic spheroidal graphite cast iron having the composition of Example 12 was cast to form the exhaust manifold 1 and the turbocharger housing 2, and then machined.
  • the exhaust manifold 1 and the turbocharger housing 2 thus obtained were free from casting defects such as shrinkage cavities, misrun, gas defects, etc., and did not suffer insufficient cutting, etc. when machined.
  • connection 3 and the catalyst case 4 can also be produced by casting the heat-resistant, austenitic spheroidal graphite cast iron of the present invention.
  • the turbocharger housing 2 and the exhaust manifold 1 may be integrally cast, and the catalyst case 4 and the exhaust manifold 1 can integrally be cast when there is not the turbocharger housing 2 therebetween.
  • the exhaust manifold 1 and the turbocharger housing 2 formed by the heat-resistant, austenitic spheroidal graphite cast iron of Example 12 were connected to an exhaust simulator corresponding to high-performance, 2000-cc, straight, four-cylinder gasoline engine for a durability test. As a test condition, one heating-cooling cycle comprising heating for 10 minutes and cooling for 10 minutes were repeated 1000 times.
  • the exhaust gas temperature at a full load was 980°C at an inlet of the turbocharger housing 2. Under this condition, a surface temperature was about 900°C in a convergence portion of the exhaust manifold 1, and about 950°C on a seat 2c of the waist gate 2b of the turbocharger housing 2.
  • Fig. 13 shows the appearance of the turbocharger housing 2 formed by the heat-resistant, austenitic spheroidal graphite cast iron of Example 12 near the waist gate 2b, after the durability test of 1000 cycles.
  • the turbocharger housing 2 had excellent durability and reliability.
  • the exhaust manifold 1 too, no thermal cracking and thermal deformation occurred after the durability test of 1000 cycles.
  • the turbocharger housing 2 formed by the heat-resistant, austenitic spheroidal graphite cast iron of Comparative Example 4 containing no Mo, Sn and Sb, which was connected to the exhaust manifold 1, was subjected to a durability test by an exhaust simulator under the same test conditions as in Examples.
  • Fig. 14 shows the appearance of this turbocharger housing 2 near a waist gate 2b after the durability test. As shown in Fig. 14, rapid oxidation generated large cracks 2d in the waist gate 2b and deformation in the seat 2c by 540 heating-cooling cycles, about half of those in Example 12.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention has sufficient room-temperature elongation and excellent heat resistance (oxidation resistance, high-temperature yield strength and thermal fatigue life).
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention contains expensive Ni, it has a lower melting point and better castability and machinability than those of the cast stainless steel, because it is based on C-rich cast iron.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention can inexpensively produce thin, complicatedly shaped exhaust equipment members for automobile engines, such as exhaust manifolds, turbocharger housings, catalyst cases, etc., which are exposed to an exhaust gas at 900°C or higher, particularly around 1000°C, at a high yield without needing high casting techniques. Even if these exhaust equipment members are disposed in a severe temperature environment in the rear of engines, they exhibit sufficient heat resistance, making it possible to increase the initial performance of exhaust-gas-cleaning catalysts.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention has been explained in cases where they are used for the exhaust equipment members for automobile engines, without intension of restriction, and it is also usable for parts for use in burning such as floors and carriers of incineration furnaces and heat treatment furnaces requiring enough room-temperature elongation and heat resistance, etc.
  • the heat-resistant, austenitic spheroidal graphite cast iron of the present invention not only has enough room-temperature elongation, but also exhibits excellent heat resistance such as oxidation resistance, high-temperature yield strength, thermal fatigue life, etc. when exposed to an exhaust gas at 900°C or higher, particularly near 1000°C, and can be produced inexpensively.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust Silencers (AREA)
EP04770825A 2003-07-18 2004-07-20 Austenitisches wärmebeständiges kugelgraphitgusseisen Withdrawn EP1652949A4 (de)

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JP2003199184 2003-07-18
PCT/JP2004/010314 WO2005007914A1 (ja) 2003-07-18 2004-07-20 オーステナイト系耐熱球状黒鉛鋳鉄

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US7431576B2 (en) 2005-11-30 2008-10-07 Scroll Technologies Ductile cast iron scroll compressor
EP1983194A1 (de) * 2007-04-17 2008-10-22 Scroll Technologies Verformbarer gusseiserner Spiralverdichter
EP2354265A1 (de) * 2010-01-14 2011-08-10 Honeywell International Inc. Austenitisches Gusseisen
US8096793B2 (en) 2006-03-22 2012-01-17 Scroll Technologies Ductile cast iron scroll compressor
EP2573199A4 (de) * 2010-05-21 2016-05-11 Toyota Jidoshokki Kk Austenitisches gusseisen, gussprodukt für ein austenitisches gusseisen sowie verfahren zur herstellung des gussprodukts

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US8333923B2 (en) * 2007-02-28 2012-12-18 Caterpillar Inc. High strength gray cast iron
ES2441598T3 (es) * 2007-08-31 2014-02-05 Kabushiki Kaisha Toyota Jidoshokki Hierro fundido austenítico, proceso para elaborarlo, piezas moldeadas de fundición austenítica y piezas del sistema de descarga de gases
ES2625678T3 (es) * 2008-02-25 2017-07-20 Wescast Industries, Inc. Hierro fundido de grafito nodular Ni-25 resistente al calor para su uso en sistemas de escape
EP2511394B1 (de) * 2011-04-15 2015-05-27 Siemens Aktiengesellschaft Gusseisen mit Niob und Bauteil
ITMI20110861A1 (it) * 2011-05-17 2012-11-18 Fonderia Casati S P A Ghisa a grafite sferoidale ad alto tenore di legante con struttura austenitica, uso di detta ghisa per la fabbricazione di componenti strutturali e componente strutturale realizzato con detta ghisa
CN103290302A (zh) * 2012-02-27 2013-09-11 徐驰 高强度合金球墨铸铁曲轴
US9500097B2 (en) * 2012-04-22 2016-11-22 Precision Turbo & Engine Rebuilders, Inc. Turbocharger containment assembly
CN103014482B (zh) * 2012-12-28 2015-06-10 山东省源通机械股份有限公司 耐热耐腐蚀的奥氏体球墨铸铁生产的金属材料及制法
DE112014002442B4 (de) * 2013-05-14 2019-07-11 Toshiba Kikai Kabushiki Kaisha Gusseisen hoher Stärke und hoher Dämpfungsfähigkeit
CN103469053B (zh) * 2013-08-28 2016-06-22 于佩 一种球墨铸铁基础桩管及其制备工艺
CN105018833A (zh) * 2015-07-09 2015-11-04 王波林 一种等温淬火球铁及其生产推力杆端头的方法
CN105401062A (zh) * 2015-11-17 2016-03-16 益阳紫荆福利铸业有限公司 一种高镍奥氏体耐腐蚀球墨铸铁
CN105603294B (zh) * 2015-12-31 2017-12-19 山东瑞丰达机械股份有限公司 提高球墨铸铁离心式泵壳耐磨性能的方法
CN106048396B (zh) * 2016-07-12 2018-05-22 中国石油集团济柴动力总厂成都压缩机厂 一种耐低温高镍奥氏体球墨铸铁及其制备方法
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JP7109226B2 (ja) * 2018-03-29 2022-07-29 虹技株式会社 球状黒鉛鋳鉄とその製造方法
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Publication number Priority date Publication date Assignee Title
US7431576B2 (en) 2005-11-30 2008-10-07 Scroll Technologies Ductile cast iron scroll compressor
US8096793B2 (en) 2006-03-22 2012-01-17 Scroll Technologies Ductile cast iron scroll compressor
EP1983194A1 (de) * 2007-04-17 2008-10-22 Scroll Technologies Verformbarer gusseiserner Spiralverdichter
EP2354265A1 (de) * 2010-01-14 2011-08-10 Honeywell International Inc. Austenitisches Gusseisen
US8372335B2 (en) 2010-01-14 2013-02-12 Honeywell International Inc. Austenitic ductile cast iron
EP2573199A4 (de) * 2010-05-21 2016-05-11 Toyota Jidoshokki Kk Austenitisches gusseisen, gussprodukt für ein austenitisches gusseisen sowie verfahren zur herstellung des gussprodukts

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CN1826421A (zh) 2006-08-30
EP1652949A4 (de) 2008-06-25

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