WO2008112720A1 - Fontes ferritiques à haute teneur en silicium - Google Patents

Fontes ferritiques à haute teneur en silicium Download PDF

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Publication number
WO2008112720A1
WO2008112720A1 PCT/US2008/056583 US2008056583W WO2008112720A1 WO 2008112720 A1 WO2008112720 A1 WO 2008112720A1 US 2008056583 W US2008056583 W US 2008056583W WO 2008112720 A1 WO2008112720 A1 WO 2008112720A1
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Prior art keywords
nodularity
iron
cast iron
elongation
graphite
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PCT/US2008/056583
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English (en)
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Delin Li
Robert Nelson Logan
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Wescast Industries, Inc.
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Publication of WO2008112720A1 publication Critical patent/WO2008112720A1/fr

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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
    • C22C37/10—Cast-iron alloys containing aluminium or silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D5/00—Heat treatments of cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D5/00—Heat treatments of cast-iron
    • C21D5/04—Heat treatments of cast-iron of white cast-iron
    • C21D5/06—Malleabilising
    • C21D5/14—Graphitising

Definitions

  • the present invention relates to ferritic high-silicon cast irons that exhibit improved microstructure stability, hot oxidation resistance, ductility at both room temperature (RT) and middle temperatures, and elevated-temperature strength, thereby an improved thermal durability. More specifically, the present invention provides a new understanding of the interrelationship among the cast iron chemistry, graphite morphologies, matrix structure, and material properties, which leads to the following disclosed high-silicon cast iron formulae and processes for their production: (1 ) a broad range of graphite nodularity in microstructure, dependent on the casting geometry and service conditions, (2) no greater than 3.00% by mass of the total contents of Groups 5 and 6 transition metals for the desirable balance between the strength and ductility, and (3) controlling the minor elements of magnesium, rare earth metals, and phosphorus for the high elongation at both RT and middle temperatures.
  • Transition metals of Groups 5 and 6 (V, Cr, Nb, Mo, Ta, and W) with body-centered cubic structure in the Periodic Table are added into high-Si cast irons to improve high-temperature strength to a certain extent.
  • SiMo irons are currently used to produce exhaust manifolds, turbocharger housings, turbo housing-integrated exhaust manifolds, turbo outlet pipes, and catalytic converter housings for automobiles.
  • the strengthening effects on ferritic cast irons will be leveled off when the total contents of the alloying elements approach a critical value. Above this critical value, the material ductility will be significantly reduced because of an abrupt increase in the percentage of pearlite and other carbide phases in microstructures.
  • MTB Middle temperature brittleness
  • ETB Elevated or intermediate temperature brittleness
  • ITB elevated or intermediate temperature brittleness
  • ferritic high-Si iron alloys having desirable compositions and microstructures that yield the best balance among the ductility at RT and middle temperatures, elevated-temperature strength, Ad temperature, and oxidation and deformation resistance in order to improve thermal or thermomechanical fatigue durability of such ferritic high-Si iron alloys.
  • the present invention includes a microstructure of ferritic high-Si iron with mixed graphite (MG), namely the graphite nodularity between 30 to 90% (preferably 40 to 80%), or spheroidal graphite (SG), namely the graphite nodularity higher than 90%.
  • MG ferritic high-Si iron with mixed graphite
  • SG spheroidal graphite
  • the CE range is from 4.35 to 4.95 for superior castability and uniform microstructures. This is a base composition for alloying or doping of other elements as described below.
  • One of alloying elements Cr increases Ad temperature, hot oxidation resistance, elevated-temperature strength, with low material cost.
  • a series of Cr-containing formulae has been identified through the new classification diagram of ferritic high-Si irons (Figs. 1 and 2), including the above-described baseline high- Si compositions alloyed with 0.40 to 1.00% Cr. The preferable range 0.4 to 2.0% is used for the multiple element additions.
  • Cr additions significantly increase the amount of lamellar pearlite and carbides in the microstructures. Therefore, annealing heat treatment is often used to reduce the amount of pearlite and carbides and break up them into dispersed structures. It was found in the present invention that the P-doped Cr-containing cast irons exhibit high elongation at the middle temperature even under as-cast conditions. Accordingly, heat treatment may or may not be utilized for the Cr-alloyed high-Si cast irons.
  • the selection principles put forward here include (1 ) controlling the total content of the six metals to no greater than 3.00% by mass (balancing up to 100% of iron and other elements) and (2) controlling the resultant pearlite plus other carbide phases to no greater than 35.0%.
  • the sum of pearlite and carbide phases is directly correlated to the total contents of the carbide former elements such as the six elements mentioned-above.
  • the preferred total amount of the six transition metals is 0.40 to 2.00% and the preferred sum of pearlite and other carbide phases is 4.0 to 25.0%.
  • elements such as Ni, Mn, Cu, Co, and
  • Ni, Mn, Cu, Co tend to reduce Ad and oxidation resistance for ferritic cast irons, and Al may cause casting defects and foundry process issues, and thus intentional inclusion of any of these should be limited.
  • Fig. 1 is a diagram showing new classifications of ferritic high-Si cast irons.
  • the graphite shapes are divided into CG, MG, and SG in terms of the nodularity. However, there should be no distinct demarcation between CG and MG, and between MG and SG structures in this classification.
  • alloying classifications such as MG SiMoCr, SG SiCr P-doped, MG SiCrW, and so on.
  • the way of defining cast irons is novel, by combining the microstructure with the chemistry. Only novel formulae are listed above.
  • Fig. 2 is a tabulated graph illustrating possible chemistry
  • ⁇ r r!(n - r)! stands for the six transition metals of Groups 5 and 6 in the Periodic Table , and r (from 0 to 6) for the number of the six metals taken at a time. There are 64 combinations in total.
  • Fig. 3 is the carbon equivalent (CE) parallelogram diagram showing the ranges of 3.80 to 4.80% Si, 4.35 to 4.95 CE, and the dependent variable Attorney Docket No. : 7349-000014/WO/PO A
  • the inside smaller parallelogram is the preferred compositional zone of which the CE ranges from 4.55 to 4.75 and Si from 4.10 to 4.50% for high-Si castings with the critical thickness of up to 25 mm.
  • the target CE is altered with the casting critical thickness. Generally speaking, the target CE should be decreased with increasing the thickness of castings, because of a decrease in the solidification rates.
  • Fig. 4 is a graph showing the effects of cerium (Ce) additions on graphite nodularity and on tensile elongation at room temperature and 425° C.
  • the baseline compositions are: 4.40% Si, 3.20% C, 0.50% Mo, and 0.018% residual magnesium. Similar to magnesium, cerium additions increased the nodularity and thus elongation at RT, but still showed the MTB trend.
  • Fig. 5 illustrates the effects of phosphorus on the tensile testing results at RT and 425° C for SG cast iron with 3.20% C, 4.40% Si, and 0.50% Mo: (a) elongation and (b) 0.20% offset yield strength. The elongation at 425° C was significantly increased for the P-doped SG SiMo samples.
  • Fig. 6 illustrates the effects of phosphorus (P) on the tensile testing elongation at RT and 425° C for SG SiCr iron (3.20% C, 4.40% Si, and 0.75% Cr, and Mo ⁇ 0.10%).
  • the samples underwent annealing heat treatment prior to tensile testing.
  • the elongation at 425° C was significantly increased for P-doped SG SiCr samples.
  • Fig. 7 is the SEM (Scanning Electron Microscopy) micrographs showing the fracture surface of tensile samples tested at 425° C for SG SiCr iron (4.40% Si and 0.75% Cr): (a) A mixed-mode fracture with some intergranular fracture was observed for regular samples, and (b) no intergranular fracture was observed for P-doped samples.
  • Fig. 8 shows the hot oxidation curves: the weight change rate as a function of the exposure time at the temperature 827° C for four compositions: 4.0%Si SiMo stands for 4.00% Si, 3.40% C, and 0.60% Mo; 4.4%Si SiMo for 4.40% Si, 3.20% C, and 0.45% Mo; 4.4%Si-0.85Cr for 4.40% Si, 0.85% Cr, 3.20% C, and 0.45% Mo; and D5S denotes a grade of Ni-resist cast iron with 35.0% Ni.
  • Fig. 9 is a graph showing the percentage of pearlite plus Mo-rich phases measured by using a light microscopy image analysis method as a function of Mo contents for SiMo iron samples.
  • Fig. 10 shows the 0.20% offset yield strength from tensile testing at 700° C as a function of Cr contents.
  • HT stands for an annealing heat treatment, and As-cast for as-cast condition, prior to tensile testing. As expected, annealing heat treatment reduced the strength of cast irons.
  • Fig. 1 1 is a graph showing tensile elongation at RT as a function of Cr additions.
  • HT stands for an annealing heat treatment, and As-cast for as-cast condition, prior to tensile testing.
  • As-cast for as-cast condition, prior to tensile testing.
  • annealing heat treatment increased the elongation at RT for Cr-alloyed cast irons.
  • Table 1 summarizes the process, main chemistry, microstructures, and tensile elongation at 425 0 C for the three examples.
  • HT * stands for the heat treatment
  • a 1 for annealing at 800° to 960° C and then furnace cooling
  • C 2 for the comparison between heat treatment and as-cast conditions.
  • FeP 3 stands for a mixture of 0.4% Fe-Si (75% Si grade) inoculant out of the total melt charges and 0.10% FeP (25% P) out of the total melt charges, which is used as post inoculation.
  • Table 2 summarizes high temperature oxidation characteristics of ferritic high-Si irons with different graphite shapes (CG, MG and SG).
  • Attorney Docket No. 7349-000014/W0/P0 A
  • Table 3 lists tensile testing results at RT and 425° C of high-Si iron with different graphite nodularity (There were no titanium additions for the samples).
  • the main compositions are 3.20% C, 4.40% Si, and 0.45% Mo.
  • Table 4 compares average CTE (coefficient of thermal expansion) in ⁇ m m '1 C '1 , and Ad temperature of P-doped and baseline SiMo with 4.32% Si: 0.042% P for samples #1 and #2, and 0.016% P for samples #3 and #4.
  • Table 5 contains tensile testing results of SG SiCr irons (3.20%
  • Table 6 illustrates the tensile elongation measured at multiple temperatures in the middle temperature range for SG SiCr iron with 3.20% C, 4.40% Si, 0.75% Cr, 0.030% Mg, and 0.030% P, indicating the elimination of MTB across the middle temperature range instead of a certain temperature for the P-doped samples.
  • the testing temperature exceeds 500° C, the elongation of higher than 10% is typically observed regardless of the sample conditions tested in the invention.
  • Table 7 lists the cycles to failure of SG ferritic high-Si irons with different compositions, measured by using high-frequency induction heating thermal fatigue testing facilities.
  • the test specimen has a cylindrical geometry with approximately 100 mm long, 12 mm outer diameter, and 5 mm inner diameter.
  • the cycling temperatures were from 150° to 820° C.
  • the sample was heated to 820° C Attorney Docket No. : 7349-000014/WO/POA
  • Table 8 summarizes the cycles to failure of EES (engine exhaust simulator) testing by using different exhaust manifold designs and thermal cycling profiles.
  • EGT stands for the exhaust gas temperature and PMT for the peak metal temperature.
  • the testing temperature profiles include 3 to 10 minutes for heating-holding segments and 4 to 10 minutes for cooling segments, dependent on the product programs.
  • Types 1 , 2, and 3 manifolds were made of SiMo irons while type 4 parts contained 0.40% to 1.00% Cr.
  • Type 1 manifold geometry was for turbo charger applications, and types 2, 3, and 4 parts were for natural aspirations. It is seen that (1 ) the cycles to failure of SiMoCr parts were higher than those of SiMo in terms of alloying element effects, and (2) the cycles to failure of the MG parts were higher than those of SG parts in terms of graphite shape effects.
  • the present invention relates to ferritic high-Si cast irons and processes for their production.
  • the iron alloys in accordance with the present invention are particularly suitable for high-temperature use such as automotive exhaust system parts, which will be explained in detail below.
  • a high silicon cast iron composition that exhibits advantageous middle temperature brittleness properties.
  • the composition which in various embodiments also takes the form of cast articles made Attorney Docket No. : 7349-000014/WO/POA
  • the iron composition comprises a carbon equivalent of 4.35 to 4.95, wherein the carbon equivalent is the sum of carbon plus 1/3 silicon; transition metal or metals selected from the group consisting of V, Nb, Ta, Cr, Mo, W, and mixtures thereof at a level of 3% by weight or less; essentially no aluminum; essentially no Mn, Ni, Co, or Cu; magnesium and rare earth metals at levels sufficient to provide the cast iron microstructures upon cooling with 30 to 90% nodularity; and iron.
  • the cast iron compositions are characterized by a microstructure with a nodularity of 30 to 90%.
  • the compositions comprise up to 1.0% or up to 0.8% by weight Mo, up to 0.8% Cr, or up to 1 % Cr.
  • the nodularity is 30 to 80%, 40 to 80%, 30 to 50%, or 30 to 70%.
  • the transition metal or metals are present at a level of 0.4 to 2% by weight and/or the carbon equivalent is from 4.5 to 4.75.
  • a high silicon cast iron composition has a nodularity of 90% or higher and comprises a carbon equivalent of from 4.35 to 4.95; transition metal or metals selected from the group consisting of V, Nb, Ta, Cr, Mo, W, and mixtures thereof at a level of 3% or less by weight; essentially no aluminum; essentially no Mn, Ni, Co, or Cu; 0.012 to 0.050% phosphorous; iron; and magnesium and rare earth metals at sufficient levels to provide a nodularity in the composition upon cooling of greater than 90%.
  • the iron composition comprises up to 0.8% molybdenum, up to 1 % molybdenum, up to 0.8% chromium, or up to 1 % chromium.
  • the composition is characterized by a carbon equivalent is 4.5 to 4.75, and/or comprises 0.4% to 2% by weight of the transition metals.
  • a high-Si cast iron article is characterized by ferrite above 70%, a graphite nodularity of 35% to 85%, and a carbon equivalent of 4.35 to 4.95, preferably 4.55 to 4.75, while the elongation measured at 425 0 C is 4% or higher. In particular embodiments, the elongation is from 5% to 8%.
  • the iron can comprise up to 3% by weight of transition metals selected from V, Nb, Ta, Cr, Mo, W, and combinations thereof, and preferably 0.4% to 2%.
  • a high-silicon cast iron article is characterized by ferrite above 70%, a graphite nodularity of 90% or greater, and an elongation measured at 425 0 C of 10% or greater, and in some embodiments of 12%- 20%.
  • the iron has a phosphorus content of 0.012% to 0.05%, and a carbon equivalent of 4.55 to 4.75.
  • the iron composition of the article comprises up to 3% by weight, and preferably from 0.4% to 2% by weight of transition metals selected from V, Nb, Ta, Cr, Mo, W, and combinations thereof.
  • cast iron compositions and cast articles made from them are provided that have a unique set of physical and material properties. Some embodiments exhibit combinations of nodularity, ferritic structure, and ductility at middle temperatures (as illustrated for example by elongation at 425 0 C).
  • compositions and article have a unique chemical structure as well as material and physical properties.
  • a ferritic cast iron composition consists essentially of Fe, C, Si, Mg, rare earth metal, and Group 5 or 6 transition metals, wherein the carbon equivalent is 4.35 to 4.95 or 4.55 to 4.75 and the elongation measured at 425 0 C is more than 4%.
  • the composition is typically marked by a nodularity in the "mixed graphite" range from 35% to 85%, and the elongation is 5-8%.
  • compositions and articles comprise 0.4-2% by weight of any combination of V, Nb, Ta, Cr, Mo, and W.
  • a ferritic cast iron composition consists essentially of Fe, P, C, Si, Mg, rare earth metal, and Group 5 or 6 transition metals, the carbon equivalent is 4.35 to 4.95 or 4.55 to 4.75 and the elongation measured at 425 0 C is more than 10%.
  • the composition is typically marked by a nodularity in the "spheroidal graphite" range of 90% or more, and the elongation is typically in the range of 12-20% at the middle temperature value of 425 0 C.
  • Fig. 1 shows a classification scheme of ferritic high-Si cast irons.
  • Fig. 2 shows the possible 64 types of combinations by alloying with Groups 5 and 6 elements of body-centered cubic structure.
  • the main elements of cast irons are C, Si and Fe, whose individual effects are well understood.
  • the Si contents are selected according to Ad , oxidation resistance, and ductility requirements.
  • the carbon equivalent, CE relates to C and Si. There will be a higher tendency of shrinkage and forming other casting defects when the CE is either too low or too high.
  • the carbon contents are selected according to the target CE and desired microstructure including graphite shape, dimension, volume percentage and the required distance between graphite inclusions.
  • composition parallelogram consisting of 4.35 to 4.95 CE and 3.80 to 4.80% Si was developed to optimize the solidification path and the resultant microstructures, as shown in Fig. 3.
  • the inside parallelogram zone shows the preferred values of CE from 4.55 to 4.75, Si from 4.10 to 4.50%, and the dependent C content, for castings with the critical thickness of up to 25 mm.
  • target CE is considered as a function of the critical Attorney Docket No. : 7349-000014/WO/PO A
  • the target CE should be decreased with increasing the thickness of castings, because of a decrease in cooling rates.
  • elongation is the percent elongation at break and is measured by standard tensile testing such as ASTM E8 or ASTM E8M. A test specimen is subjected to tension until it fractures from the applied force. Elongation is determined by removing the fractured specimen from the grips, fitting the broken ends together, and measuring the distance between gage marks as L z . The percent elongation at break is calculated by:
  • Elongation at break (%) 100 * (L 2 -L o )/L o , where L 0 is the original gage length
  • the carbon equivalent is from 4.35 to 4.95. This is shown graphically in the parallelogram map of Fig. 3. The carbon equivalent is controlled so as to achieve uniform solidification mode and microstructure of castings.
  • the target CE is altered with the critical thickness of castings.
  • transition metals of Groups 5 and 6 with body-centered cubic structure are carbide formers and ferrite promoters, and increase hot strength to a certain extent.
  • Fig. 2 shows a possible 64 combinations of the six elements.
  • the total content of the six is held to no greater than 3.0%, and illustratively from about 0.4% to about 2%.
  • the pearlite and carbide of the resulting compositions are preferably less than about 35%.
  • Mq and rare earth metals (REM) are preferably less than about 35%.
  • Mg and REM are graphite nodulizers. As inclusion and segregation formers, Mg and REM may contribute to MTB and intergranular fracture. The total residual of Mg and REM is to be varied to achieve a desired nodularity, either mixed graphite or spheroidal microstructures as described herein. In various embodiments, total residual Mg and REM is less than 0.08% Phosphorus
  • phosphorus has been considered a detrimental element in ferritic ductile irons. But it has been found that doping a small amount of P may provide beneficial effects to alleviate the MTB of spheroidal graphite microstructures described herein.
  • the level of phosphorus is controlled from about 0.012% to about 0.050% to balance the ductility at RT and MTB. P-bearing agents and process are developed for P-doping levels.
  • austenite stabilizers they reduce the ferrite stability, Ad and oxidation resistance of ferritic high-Si cast irons. These elements are to be avoided in the ferritic microstructures described herein, except as trace levels or as inevitable impurities.
  • the nodular structure of the irons described herein contributes to their desirable properties.
  • cast irons having a graphite nodularity between 30 and 90% (preferably 40 to 80%) are provided, which can be referred to as a mixed graphite (MG) structure.
  • the microstructure is controlled by the process used for making the cast irons.
  • the microstructure responds most strongly to the amount of magnesium (Mg) and rare earth metal used as spheroidizers adding before the final pour.
  • the level of Mg and REM can be varied along with other process parameters (time of addition, temperature of addition, rate of addition, and so on, all of which tend to vary from furnace to furnace and foundry to foundry) to achieve a desired nodularity.
  • a number of benefits of the MG cast irons have been identified in the present invention: (1 ) better castability by reducing the amounts of spheroidizer and inoculant, elimination of anticompactizing elements such as Ti and Al, (2) modified oxidation resistance characteristics, as seen in Table 2, (3) improvements in MTB, as shown for example in Table 3, and (4) lower manufacturing cost.
  • the MG irons may exhibit a lower CTE (coefficient of thermal expansion) and Young's modulus, thus generating lower thermal stress during thermal cycling.
  • graphite iron has been designed to use the combined effects of a certain level of residual magnesium and moderate graphite nodularity to achieve adequate ductility at both RT and middle temperatures, as shown in Table 3. A new understanding of the interrelationship among the residual magnesium contents, nodularity, and MTB has been provided.
  • ductility at middle temperatures is controlled by two factors; nodularity and magnesium contents. Moreover the nodularity and the magnesium content are related. More specifically, a certain level of nodularity is achieved by adding a certain amount of magnesium. However, too much magnesium causes segregations, thus giving rise to the MTB.
  • Spheroidal graphite tends to be formed by increasing magnesium or/and cerium content. This results in alloys with high elongation and strength at room temperature, but in the middle temperature brittleness range of approximately 300° C to 500° C, a low tensile elongation is often observed. In various embodiments, a small amount of P is added to counter this tendency.
  • two types of SG iron compositions are chosen to reveal the P- doping effects as examples: (1 ) high-Si SG SiMo and (2) SG SiCr.
  • Fig. 5 illustrates the P effects on the tensile testing results of high-Si SiMo iron at RT and 425° C.
  • the elongation at RT was not changed significantly when the P content was increased from 0.016% to 0.048%.
  • the ductility at 425° C was substantially enhanced when doping with 0.025% to 0.048% P.
  • the yield strength at room temperature and at 425° C was also found to slightly increase with increasing P contents.
  • the selective rules determined in present invention are composed of (1 ) controlling the total content no greater than about 3.00% as to form with less than 35.0% of pearlite and other carbide phases, and balance up to 100% of iron and other elements, in contrast to prior art specifying each alloying element content, (2) different strengthening effectiveness of elements, and (3) the cost.
  • amount of the six transition metals is 0.40 to 2.00%, thus maintaining the sum of pearlite and other carbide phases between about 4% and about 25%.
  • SiMoCr such as MG SiMoCr, MG SiVMo, MG SiMo, SG SiCr P-doped, and so on.
  • MG SiMoCr such as MG SiMoCr, MG SiVMo, MG SiMo, SG SiCr P-doped, and so on.
  • MG microstructure a combination of 4.10 to 4.50% Si with 0.30 to 0.60% Mo with MG microstructure was found to yield an optimization of ductility, strength, oxidation and thermal cracking resistance, for SiMo iron.
  • the contents of one alloying element Mo are optimized to be 0.30 to 0.60%.
  • the total amounts are preferably from 0.4 to 2.0%, namely that any combinations are displayed in Fig. 2.
  • SiCr. Cr influences ferritic high-Si iron in these aspects: (1 ) increasing Ad by 30 to 40° C per 1% Cr addition, (2) enhancing hot oxidation resistance, (3) increasing tensile strength, for example, for the yield strength at 700° C as shown in Fig. 10, and (3) decreasing the elongation as shown in Fig. 1 1.
  • Si with a Attorney Docket No. : 7349-000014/WO/POA
  • the Cr-alloyed ferritic high-Si cast irons claimed in the present invention may consist of (1 ) different graphite shapes (MG and SG), (2) with or without P-doping, (3) with (such as SiMoCr, SiWCr) or without (straight SiCr) other alloying elements such as Mo, W 1 V, and Nb, and (4) annealed heat treated and as- cast conditions.
  • the present invention significantly reduces the elements such as Ni 1 Mn, Cu, Co, and Al.
  • first four elements are austenite promoters and reduce Ad of ferritic cast irons while Al causes casting defects and foundry process issues.
  • the inoculant FeP 3 is used, which is a mixture of Fe-Si inoculant and 0.10% FeP (25% P) used as a post inoculation.
  • the mixture inoculant FeP 3 is made as follows.
  • Fe-Si inoculants (75% Si grade and commercially available) were mixed with approximately 0.10% (out of the total melt charges) Ferrous Phosphorus, FeP Attorney Docket No. : 7349-000014/WO/POA
  • HT column of Table 1 Low Cr examples are not heat treated.
  • Heat treatment A 1 indicates the part is annealed at 800° to 96O 0 C and then furnace cooled.
  • C 2 indicates that a comparison is made between a heat treated article and a non-heat treated article, the latter also being referred to as "as-cast.”
  • Table 1 also includes a cross reference to the
  • Heats of irons weighing approximately 100 kg were made using an induction furnace operating at 350 kW and 1 kHz.
  • Different types and addition levels of Fe-Si-Mg based spheroidizers and Fe-Si based inoculants were used, such as 0.50% to 1.20% ReMag ® or Elmag ® supplied by Elkem (ReMag ® and Elmag ® are the registered trademark owned by Elkem AS).
  • Pour temperatures varied from 1385° to 1470° C to cast test Y-blocks and exhaust products. Solidification curves of cast irons were measured using a thermal analysis apparatus. Optical microscopy and digital image analysis software were used in microstructural analysis of the trial samples. A lower amount of spheroidizers and inoculants were added to achieve the mixed graphite structures, as compared to making SG cast irons.
  • Tables 2, 3, 8, and Fig. 4 illustrate the influences of graphite nodularity on oxidation, tensile testing data at RT and 425 C, and EES durability results.
  • the MG iron with 30 to 90% nodularity (without flake graphite) exhibited the combined oxidation features of CG and SG irons.
  • Table 2 briefly summarizes the hot oxidation characteristics of high-Si CG, MG, and SG irons, through a number of tests primarily following ASTM Designation G54-84, performed by the inventors.
  • EES Engine Exhaust Simulator testing was utilized to assess the thermal durability of exhaust manifolds.
  • the thermal cycling profiles in EES testing are characterized by heating/cooling rates, peak/valley temperatures, and holding time at the maximum or minimum temperatures.
  • the cycles to failure determined from EES testing were expressed as the manifold durability, and were in turn influenced by a variety of factors such as manifold geometry, test temperature profiles, constraint ratio, cast iron compositions, and microstructures.
  • the main chemistry elements for manifolds 1 , 2, and 3 were made of SiMo iron, while manifolds 4 contained 0.40 to 1.00% Cr, namely SiMoCr cast irons with different graphite morphologies.
  • Table 8 shows the influences of graphite shapes on the EES performance.
  • the MG cast iron has shown equal or higher EES cycles to failure than CG and SG irons. It also should be pointed out that (1 ) there is a different application scope for CG, MG, and SG irons in terms of product geometries and engine characteristic, and (2) there is a microstructure overlap between CG and MG, and between MG and SG boundaries, respectively.
  • Iron melts are treated with an adequate amount of spheroidizers and inoculants to make SG cast irons with higher graphite nodularity and elongation at RT than MG irons.
  • the total residual content of magnesium and REM is high of up to 0.080% which usually induces the MTB.
  • the preferred P- doped level is 0.025 to 0.040% to attain high elongation at both RT and middle temperatures and to avoid any P-induced shrinkage during solidification, for different ferritic high-Si SG cast irons.
  • Table 4 presents the average CTE from 200° to 800° C, and Ad of regular P content (0.016%) and high P level (0.042%) samples. From the dilatometer tests, no significant difference in CTE and Ad was detected between regular and P-doped samples, even though it has been reported that P additions may increase the Ad temperature.
  • Heats of irons weighing approximately 100 kg were made using an induction furnace operating at 350 kW and 1 kHz.
  • Different types and addition levels of Fe-Si-Mg based spheroidizers and Fe-Si based inoculants were used, such as ReMag® or Elmag® supplied by Elkem (ReMag® and Elmag® are the registered trademark owned by Elkem AS).
  • Pour temperatures varied from 1385° to 1470° C to cast test Y-blocks and exhaust products. Solidification curves of cast irons were measured using a thermal analysis apparatus. Optical microscopy and digital image analysis software were used in microstructural analysis of the trial samples.
  • spheroidizers and inoculants are used for the MG irons than SG irons.
  • a small amount of ferrous-phosphorus was added into ladle with a mixture inoculant for making the SG Cr-alloyed cast irons with P-doped.
  • annealing treatment is employed for the heat treatment of Cr- alloyed cast irons.
  • the holding temperatures ranged from 800° C to 96O 0 C.
  • the dwell time ranged from 2 to 3 hours.
  • the cooling rate ranged from 0.5 to 3.5 C/min.
  • annealing heat treatment was often used.
  • the experimental results of heat treatment were added in the graphs for comparison.
  • annealing decreased the strength and increased elongation at RT. From Table 5, it is seen that there is no or little impact of the heat treatment on the elongation at 425 C. Therefore, there may be a possibility of removing annealing heat treatment for Cr-alloyed cast irons.
  • the cycles to failure of exhaust manifolds from EES testing were observed to increase for Cr-alloyed cast iron, especially for the mixed graphite Cr-alloyed cast iron, as shown in Table 8.
  • the Cr- alloyed high-Si cast irons can consist of (1) different graphite shapes (MG and SG), (2) with or without P-doping, (3) with or without other alloying elements such as Mo, V, W, and Nb, and (4) annealed or as-cast conditions.
  • Articles cast from the compositions and microstructures of the present invention can withstand static and cyclic thermomechanical stresses and chemical attack. Such articles find use in a variety of automotive transportation and industrial applications. Such applications include, but are not limited to, exhaust components such as exhaust manifolds, turbocharger housings, back plates, turbo housing-integrated exhaust manifolds, turbo outlet pipes, hot end components such as catalytic converter housings, and fuel cell components.
  • exhaust components such as exhaust manifolds, turbocharger housings, back plates, turbo housing-integrated exhaust manifolds, turbo outlet pipes, hot end components such as catalytic converter housings, and fuel cell components.

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

Abstract

L'invention concerne des fontes contenant (1) du carbone et du silicium à un équivalent carbone de 4,35 à 4,95; (2) des métaux de transition des groupes 5 et 6 dans le tableau périodique des éléments (Cr, Nb, Mo, Ta, W et V) dont les teneurs totales ne sont pas supérieures à environ 3 %; et (3) des éléments mineurs tels que jusqu'à environ 0,050 % de phosphore (P) et jusqu'à environ 0,080 % de résidu total de magnésium (Mg) et de REM (métaux de terres rares), et (4) le reste en fer (Fe) et en impuretés inévitables. La nodularité du graphite dans les microstructures est constituée d'un graphite mixte, de préférence de 40 à 80 % de nodularité de graphite ou de graphite sphéroïde principalement en fonction de la géométrie de fonte et des conditions de service. Les fontes présentent une stabilité thermique, une résistance à l'oxydation, une ductilité à température moyenne et une résistance à la fatigue thermique supérieures au fer SG ou CG à haute teneur en Si ou au fer SiMo classique.
PCT/US2008/056583 2007-03-12 2008-03-12 Fontes ferritiques à haute teneur en silicium WO2008112720A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110211986A1 (en) * 2008-12-18 2011-09-01 Takashi Arai Ductile iron
US20110297280A1 (en) * 2009-02-27 2011-12-08 Yoshikazu Genma Ferritic spheroidal graphite cast iron
US8999229B2 (en) 2010-11-17 2015-04-07 Alpha Sintered Metals, Inc. Components for exhaust system, methods of manufacture thereof and articles comprising the same
US20170314104A1 (en) * 2016-04-29 2017-11-02 General Electric Company Ductile iron composition and process of forming a ductile iron component
EP3974553A1 (fr) 2020-09-23 2022-03-30 Tupy S.A. Alliage de fonte vermiculaire, bloc et tête de moteur à combustion
CN115125433A (zh) * 2022-06-27 2022-09-30 江苏天奇重工股份有限公司 一种高韧性铁素体球墨铸铁及其制备方法

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US20040091383A1 (en) * 2001-05-16 2004-05-13 Suzuki Motor Corporation Ferrite-based spheroidal graphite cast iron and exhaust system component using the same
WO2006121826A2 (fr) * 2005-05-05 2006-11-16 Wescast Industries Inc. Fonte dotee de proprietes ameliorees a haute temperature

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US4472197A (en) * 1982-03-29 1984-09-18 Elkem Metals Company Alloy and process for producing ductile and compacted graphite cast irons
US20040091383A1 (en) * 2001-05-16 2004-05-13 Suzuki Motor Corporation Ferrite-based spheroidal graphite cast iron and exhaust system component using the same
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GUNDLACH: "Nodularity, Its Measurement, and Its Correlation with the Mechanical Properties of Ductile Iron", DIS RESEARCH PROJECT NO. 37, 18 June 2006 (2006-06-18), Retrieved from the Internet <URL:http://www.ductile.org/member/researchactivity/proj37.pdf> *
WRIGHT ET AL.: "Elevated Temperature Brittleness of Ferritic Ductile Iron", TRANSACTIONS OF THE AMERICAN FOUNDRYMEN'S SOCIETY, vol. 93, 29 April 1985 (1985-04-29) - 3 May 1985 (1985-05-03), pages 853 - 866 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110211986A1 (en) * 2008-12-18 2011-09-01 Takashi Arai Ductile iron
CN102264931A (zh) * 2008-12-18 2011-11-30 三菱重工业株式会社 球墨铸铁
CN102264931B (zh) * 2008-12-18 2014-09-03 三菱重工业株式会社 球墨铸铁
EP2377960A4 (fr) * 2008-12-18 2016-12-14 Mitsubishi Heavy Ind Ltd Fonte à graphite sphéroïdal
EP2377960B1 (fr) 2008-12-18 2018-09-26 Mitsubishi Heavy Industries, Ltd. Fonte à graphite sphéroïdal
US20110297280A1 (en) * 2009-02-27 2011-12-08 Yoshikazu Genma Ferritic spheroidal graphite cast iron
US8540932B2 (en) * 2009-02-27 2013-09-24 Toyota Jidosha Kabushiki Kaisha Ferritic spheroidal graphite cast iron
US8999229B2 (en) 2010-11-17 2015-04-07 Alpha Sintered Metals, Inc. Components for exhaust system, methods of manufacture thereof and articles comprising the same
US20170314104A1 (en) * 2016-04-29 2017-11-02 General Electric Company Ductile iron composition and process of forming a ductile iron component
US10787726B2 (en) * 2016-04-29 2020-09-29 General Electric Company Ductile iron composition and process of forming a ductile iron component
EP3974553A1 (fr) 2020-09-23 2022-03-30 Tupy S.A. Alliage de fonte vermiculaire, bloc et tête de moteur à combustion
CN115125433A (zh) * 2022-06-27 2022-09-30 江苏天奇重工股份有限公司 一种高韧性铁素体球墨铸铁及其制备方法

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