WO2017164382A1 - 球状黒鉛鋳鉄、それからなる鋳造物品及び自動車用構造部品、並びに球状黒鉛鋳鉄からなる鋳造物品の製造方法 - Google Patents
球状黒鉛鋳鉄、それからなる鋳造物品及び自動車用構造部品、並びに球状黒鉛鋳鉄からなる鋳造物品の製造方法 Download PDFInfo
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- WO2017164382A1 WO2017164382A1 PCT/JP2017/012066 JP2017012066W WO2017164382A1 WO 2017164382 A1 WO2017164382 A1 WO 2017164382A1 JP 2017012066 W JP2017012066 W JP 2017012066W WO 2017164382 A1 WO2017164382 A1 WO 2017164382A1
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- graphite
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- spheroidal graphite
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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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
- C22C33/10—Making cast-iron alloys including procedures for adding magnesium
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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
Definitions
- the present invention relates to a spheroidal graphite cast iron, a cast article comprising the same and a structural part for automobiles, and a method for producing a cast article comprising spheroidal graphite cast iron.
- US 5,205,856 when treated with a wire inoculant having powdered ferrosilicon and powdered magnesium silicide, the average particle size of spherical graphite is dramatically reduced and the number of graphite particles is 511 / Disclosed is spheroidal graphite cast iron increased from mm 2 to 1256 pieces / mm 2 (see Fig. 3). In this spheroidal graphite cast iron, the maximum diameter of spheroidal graphite is 32.5 ⁇ m, and spheroidal graphite having a diameter of 12.5 mm or less accounts for 90% or more.
- 5,205,856 is thought to be intended to allow magnesium silicide contained in the wire inoculum to act as crystallization nuclei of graphite, but in order to increase the crystallization nuclei of graphite,
- the metallic silicon derived from the ferrosilicon fed at the same time may remain in the cast article after solidification, and the ductility may be significantly impaired.
- Torjorn Skaland "A new method for chill and shrinkage control in ladle treated ductile iron," Foundry Trade Journal, (UK), 2004, 178 (3620), p.396-p.400 (Hereinafter also referred to as REM) has been reported on the study of spheroidal graphite in a disk-shaped product made of spheroidal graphite cast iron cast treated with a spheroidizing agent containing magnesium ferrosilicon (6% Mg in 45% FeSi, Graphite is formed by spheroidizing treatment using a spheroidizing agent (substantially free of other RE components such as Ce) containing 0.5% La and 1.0% La in 1% Ca and 0.9% Al).
- the present invention relates to spheroidal graphite cast iron having a higher proportion of fine graphite and superior mechanical properties, in particular toughness, to spheroidal graphite cast iron according to the prior art such as the above-mentioned prior art documents, cast articles comprising the same, and for automobiles It aims at providing the manufacturing method of the cast article which consists of a structural component and spheroidal graphite cast iron.
- the spheroidal graphite cast iron of the present invention is a graphite grain observed in an arbitrary cross section (at least in 1 mm 2 ),
- the number of graphite grains with an equivalent circle diameter of 5 ⁇ m or more is N (5-) (pieces / mm 2 )
- the number of graphite grains with an equivalent circle diameter of 5 ⁇ m or more but less than 20 ⁇ m is N (5-20) (pieces / mm 2 )
- a circle is a circle.
- N (2-5) (pieces / mm 2 )
- N (2-5) ⁇ 100 It is preferable to satisfy.
- the spheroidal graphite cast iron of the present invention is N (5-20) / N (5-) ⁇ 0.65 It is preferable to satisfy.
- the cast article of the present invention is made of the above spheroidal graphite cast iron.
- the cast article is preferably an automotive structural part.
- the method of the present invention has the following conditions: N (5-) ⁇ 250, N (5-20) / N (5-) ⁇ 0.6, and N (30-) / N (5-) ⁇ 0.2 [However, N (5-) , N (5-20) and N (30-) are graphite particles observed in any cross section (at least in 1 mm 2 ), each having an equivalent circle diameter of 5 ⁇ m or more.
- the pressure is preferably 10 kPa to 50 kPa.
- the spheroidal graphite cast iron of the present invention has a high proportion of fine graphite, contains graphite particles having a specific particle size distribution, and is excellent in mechanical properties, particularly toughness. Therefore, it is suitable for spheroidal graphite cast iron castings, especially structural parts for automobiles. It is.
- the method of the present invention makes it possible to obtain spheroidal graphite cast iron having excellent mechanical properties, particularly toughness.
- FIG. 1 is a cross-sectional view schematically showing a mold used in Example 1.
- FIG. 3 is a cross-sectional view schematically showing a casting method performed in Example 1.
- FIG. 1 is a schematic cross-sectional view of a spheroidal graphite cast iron casting of Example 1.
- FIG. 2 is an optical micrograph of the microstructure of the spheroidal graphite cast iron casting of Example 1.
- FIG. 2 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 1.
- FIG. 2 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 1.
- FIG. 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 2.
- 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 2.
- 6 is a graph showing the relationship between the cooling curve near the eutectic solidification temperature and the pressing period in Example 1 and Example 2.
- 6 is a schematic diagram showing a cast article (spheroidized graphite cast iron) of Example 3.
- FIG. 3 is an optical micrograph observing the microstructure of a spheroidal graphite cast iron casting of Example 3.
- FIG. 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 3.
- 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 3.
- 2 is an optical micrograph observing the microstructure of a spheroidal graphite cast iron casting of Comparative Example 1.
- 3 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Comparative Example 1.
- FIG. 3 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Comparative Example 1.
- 6 is a schematic diagram showing a cast article (spheroidized graphite cast iron) of Example 4.
- FIG. 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 4.
- 6 is a graph showing the particle size distribution of spheroidal graphite observed in the cross section of the spheroidal graphite cast iron casting of Example 4.
- the composition of the spheroidal graphite cast iron of the present invention is as follows. Any composition may be used as long as it can constitute a graphite-based austenitic cast iron product. For example, a composition containing 2 to 4.5% C, 0.8 to 6% Si, and 0.010 to 0.080% Mg in mass%, with the balance being Fe and inevitable impurity elements, or the composition having desired properties Examples thereof include a composition further containing an appropriate amount of elements, S, P, Mn, Cu, Cr, Ni, Mo, W and the like for obtaining.
- the spheroidal graphite cast iron of the present invention has spheroidal graphite (graphite grains) having a particle size distribution specified as follows. That is, the particle size distribution of the graphite grains, any cross section cut, among the graphite grains observed in at least 1 mm 2, an equivalent circle diameter 5 ⁇ m or more the number of graphite grains N (5-) (pieces / mm 2 ), The number of graphite grains with an equivalent circle diameter of 5 ⁇ m or more and less than 20 ⁇ m is N (5-20) (pieces / mm 2 ), and the number of graphite grains with an equivalent circle diameter of 30 ⁇ m or more is N (30-) (pieces / mm 2 ). ) Satisfies N (5-) ⁇ 250, N (5-20) / N (5-) ⁇ 0.6, and N (30-) / N (5-) ⁇ 0.2.
- the spheroidal graphite cast iron of the present invention has a relatively large number of graphite grains having an equivalent circle diameter of 5 ⁇ m or more (250 pieces / mm 2 or more) and relatively fine graphite grains (graphite grains having an equivalent circle diameter of 20 ⁇ m or less). Spheroidal graphite cast iron with a high ratio and a low ratio of relatively large graphite grains (graphite grains having an equivalent circle diameter of 30 ⁇ m or more). With such a configuration, a spheroidal graphite cast iron having excellent mechanical properties, particularly toughness, can be obtained. In particular, it is possible to further improve toughness by adopting this configuration in a thick cast article having a thickness of 40 mm or more when cast as-is.
- the number N (5-) of graphite grains having an equivalent circle diameter of 5 ⁇ m or more is preferably 300 (pieces / mm 2 ) or more.
- Circle equivalent diameter circle equivalent diameter to 5 ⁇ m or more the number of graphite grains is less than 20 ⁇ m or 5 ⁇ m number of graphite grains ratio N (5-20) / N (5- ) is preferably 0.65 or more, more preferably 0.70 (70% ) Or more, most preferably 0.75 (75%) or more.
- the ratio N (30-) / N (5-) of the number of graphite grains having an equivalent circle diameter of 30 ⁇ m or more to the number of graphite grains having an equivalent circle diameter of 5 ⁇ m or more is preferably 0.15 (15%) or less, more preferably 0.10 ( 10%) or less.
- the spheroidal graphite cast iron of the present invention preferably satisfies N (2-5) ⁇ 100 when the number of graphite grains having an equivalent circle diameter of 2 ⁇ m or more and less than 5 ⁇ m is N (2-5) (pieces / mm 2 ). .
- N (2-5) is more preferably N (2-5) ⁇ 150, most preferably N (2-5) ⁇ 200.
- the spheroidal graphite cast iron of the present invention has D max ⁇ 50.4 ⁇ m, where D max is the equivalent circle diameter of the largest graphite grain among the graphite grains observed in any cut section (at least in 1 mm 2 ). It is preferable to satisfy.
- the spheroidal graphite cast iron of the present invention has N (5-10) (pieces / mm 2 ) number of graphite grains having an equivalent circle diameter of 5 ⁇ m or more and less than 10 ⁇ m, and N (15 -20) (pieces / mm 2 ), it is preferable that ⁇ 0.15 ⁇ (N (5-10) -N (15-20) ) / N (5-10) ⁇ 0.25 is satisfied.
- other preferable features of the spheroidal graphite cast iron of the present invention are the number N (5-10) of graphite grains having an equivalent circle diameter of 5 ⁇ m or more and less than 10 ⁇ m and the graphite grains having an equivalent circle diameter of 15 ⁇ m or more and less than 20 ⁇ m in the cut cross section.
- the quotient of the difference from the number N (15-20) and the number N (5-10) of graphite grains having an equivalent circle diameter of 5 ⁇ m or more and less than 10 ⁇ m is ⁇ 0.15 or more and 0.25 or less.
- the spheroidal graphite cast iron of the present invention is a graphite particle having an equivalent circle diameter of 5 ⁇ m or more.
- the equivalent circle diameter (60% particle diameter) of the graphite grains to be% is d60 ( ⁇ m)
- d60 ⁇ 20 ⁇ m is satisfied.
- the equivalent circle diameters of the graphite grains where the cumulative number of graphite grains is 70%, 80% and 90% of the number of graphite grains having an equivalent circle diameter of 5 ⁇ m or more are d70 ( ⁇ m), d80 ( ⁇ m) and d90 ( ⁇ m), respectively. ), It is preferable that d70 ⁇ 20 ⁇ m, d80 ⁇ 30 ⁇ m, and d90 ⁇ 35 ⁇ m.
- the conditions represented by d60 ⁇ 20 ⁇ m and d80 ⁇ 30 ⁇ m are represented by the aforementioned N (5-20) / N (5-) ⁇ 0.6 and N (30-) / N (5-) ⁇ 0.2, respectively.
- the conditions are substantially the same.
- the spheroidal graphite cast iron of the present invention can be produced by the following method. An example of the manufacturing method of the present invention will be described below for each process.
- Spheroidal graphite cast iron melt Spheroidal graphite cast iron melt
- molten metal Spheroidal graphite cast iron molten metal
- a spheroidizing agent containing Mg or the like in a molten iron alloy (hereinafter referred to as Motoyu) prepared by mixing steel scraps and return scraps and various auxiliary materials as raw materials so as to have a desired component composition, for example, Prepared by adding a predetermined amount of Fe-Si-Mg alloy.
- the spheroidizing agent those containing an appropriate amount of REM and other trace elements as required can be used.
- a sandwich method that is generally performed, a method of supplying a cored wire containing a spheroidizing agent into a ladle containing a hot water, and the like can be used.
- the inoculation method consists of (a) inoculation in the ladle (hereinafter also referred to as primary inoculation) performed in the pouring ladle at the same time as the spheroidization treatment by the sandwich method, and (b) inoculation agent in the molten metal stream line during pouring.
- Known methods such as pouring of pouring so as to be dissolved and (c) inoculation in a mold performed by previously inoculating an inoculum into the cavity of the mold can be used.
- the inoculation methods (b) and (c) are inoculations performed after the primary inoculation, and are sometimes referred to as secondary inoculations.
- a cast article made of spheroidal graphite cast iron of the present invention may be manufactured using a known method such as gravity casting, but the molten metal poured into a gas-permeable mold (hereinafter also referred to as a mold) eutectic solidifies. Before starting, it is preferable to perform a method of pressing the surface of the molten metal with a gas and solidifying the molten metal while allowing the gas to pass through the mold (hereinafter also referred to as an air supply and pressure method).
- the air supply and pressure method By adopting the air supply and pressure method, the ratio of the number of coarse graphite particles is suppressed, and a spheroidal graphite cast iron having a high ratio of the number of fine graphite particles can be easily obtained.
- the air supply and pressure method which is one of the preferred production methods of the present invention, will be described in detail.
- an air sand mold, a shell mold, a self-hardening mold, or other commonly used breathable mold formed using other sand particles can be used.
- a mold formed using ceramic particles, metal particles, or the like can be applied as long as necessary air permeability is ensured.
- a mold using a material having no air permeability, such as a mold can be used as a gas permeable mold when a ventilation hole such as a vent hole is provided to provide air permeability.
- a mold having almost no air permeability such as plaster can be used as a gas permeable mold by mixing a gas permeable material or by providing a part of the gas permeable material with sufficient air permeability.
- air may be used from the viewpoint of cost, and non-oxidizing gas, for example, argon, nitrogen, carbon dioxide may be used from the viewpoint of preventing oxidation of the molten metal.
- non-oxidizing gas for example, argon, nitrogen, carbon dioxide may be used from the viewpoint of preventing oxidation of the molten metal.
- the gas can be pressed against the molten metal by supplying the gas from the gate into the mold.
- the pressure of pressing with gas (hereinafter also referred to as pressing force) is preferably 1 kPa to 100 kPa. If it is less than 1 kPa, the effect of increasing the number of graphite grains is difficult to obtain.
- a more preferable range of the pressing force is 10 kPa to 50 kPa, and more preferably 20 kPa to 40 kPa.
- FIG. 1 is a graph illustrating the relationship between the cooling curve near the eutectic solidification temperature and the pressing period.
- curve C is a cooling curve showing the relationship between the temperature T inside the cast article to be obtained and time t.
- the eutectic solidification period is from the eutectic solidification start time t Es until the temperature T changes substantially constant with respect to the time t to the eutectic solidification end time t Ef (hereinafter also referred to as eutectic solidification time).
- the surface (hereinafter, also referred to as molten metal surface.) In contact with the pressurized gas in the molten metal is poured into the mold temperature of the molten metal of as long a period at the eutectic solidification temperature T E above.
- the melt temperature on the surface of the melt is equal to or lower than the melt temperature inside the cast article to be obtained, and the fluidity of the melt is better when the temperature is higher than the eutectic solidification temperature.
- the value of dt pM is preferably as large as possible.
- the value may be 0 or more, that is, 0 ⁇ dt pE / dt E.
- 0 ⁇ dt pE / dt E ⁇ 1 that is, t pf ⁇ t Ef .
- the tact for applying the air supply pressure method to the subsequent mold in the casting line in mass production can be shortened by ending the pressing at an early stage before completion of eutectic solidification of the entire cast article to be obtained.
- the temperature of eutectic solidification and the start and end times of eutectic solidification may be measured by placing a thermocouple at a predetermined position in the mold and measuring it by a casting experiment or by solidification analysis by a computer. You may ask for. In mass production of the same product, the casting conditions can be regarded as almost the same, so it is not necessary to measure these values related to eutectic solidification each time.
- the air supply gas passes through the inside of the air-permeable mold and is sequentially discharged out of the mold, so that the cooling of the mold is promoted.
- the molten metal surface molten metal surface
- solidification of the molten metal portion in contact with the mold is promoted, so that the solidified shell is quickly brought from the outer edge of the molten metal toward the inside. Easy to form.
- the expansion pressure due to the crystallization of the spherical graphite is not directed to the outside due to the already formed solidified shell, but is directed to the inside, so that the shrinkage of the molten metal accompanying cooling is offset.
- the generation of shrinkage nests is suppressed. This effect makes it easier to obtain a cast article having a high mechanical property, particularly a high impact value.
- the pattern of the pressing force during the pressing period may be arbitrary, but if gas is supplied so that the pressing force increases monotonously from the start of pressing, the effect of suppressing the release of Mg in the molten metal to the outside of the molten metal and the cooling of the mold can be obtained. This is preferable because it is easily formed.
- N (5-20) (pieces / mm 2 ) the number of graphite grains with a diameter of 5 ⁇ m or more and less than 20 ⁇ m
- N (30-) (pieces / mm 2 ) the number of graphite grains with a circle equivalent diameter of 30 ⁇ m or more is N (30-) (pieces / mm 2 )
- N (5-) ⁇ 250, N (5-20) / N (5-) ⁇ 0.6, and N (30-) / N (5-) ⁇ 0.2 can be obtained.
- the cumulative number of graphite grains is calculated when the number of graphite grains is integrated in ascending order of equivalent circle diameter.
- Example 1 As a preferred embodiment of the present invention, an example manufactured by using a gravity casting method in combination with an air pressure method will be described with reference to the drawings. The present invention is not limited to this form.
- FIG. 2 (a) shows the mold used in Example 1
- FIG. 2 (b) shows the casting method of Example 1.
- FIG. The mold 1 has a cavity 2 composed of a sprue part 3, a runner part 4, a feeder part 5 and a product part 6, and a CO 2 cured alkali phenol mold, which is a breathable mold made of silica sand as an aggregate. Using.
- (casting) For casting, a method of carrying out an air feeding and pressurizing method was used in addition to a gravity casting method in which gravity casting was performed in an air atmosphere in which the outside of the mold 1 was at normal temperature and normal pressure. That is, as shown in FIG. 2 (a), from the pouring ladle 7 containing the above-described molten metal M, a volume of molten metal M that fills the product part 6 and the feeder part 5 is poured into the cavity 2 by gravity at 1365 ° C. As shown in FIG. 2 (b), a gas discharge section that discharges gas G generated from an air supply device (not shown) (air in the first embodiment, the same applies to the following embodiments), as shown in FIG.
- FIG. 3 is a schematic cross-sectional view showing a spheroidal graphite cast iron casting 100, in which schematic dimensions are described.
- the pressing force was measured using a pressure sensor (not shown) disposed in the gas flow path of the gas discharge unit 8.
- FIG. 4 shows an optical micrograph of the corroded observation site.
- Base 10 was composed of ferrite 10a and pearlite 10b.
- the spherical graphite 11 contained spherical graphite 11a constituting a so-called bull's eye structure surrounded by the ferrite 10a, and spherical graphite 11b which is not a bull's eye, that is, its periphery is substantially only pearlite. Most of the spherical graphite 11b which is not such a bull's eye was fine with an equivalent circle diameter of 20 ⁇ m or less.
- the obtained photographic data was subjected to image processing, and the number of spherical graphite and the equivalent circle diameter of each spherical graphite were determined. From the obtained results, the number of graphite grains per 1 mm 2 (hereinafter also referred to as the number of grains) (pieces / mm 2 ) was calculated, and the frequency distribution for each equivalent circle diameter range as shown in Table 2 was obtained. .
- the equivalent circle diameter range is less than 2 ⁇ m, 2 ⁇ m or more and less than 5 ⁇ m, 5 ⁇ m or more and less than 10 ⁇ m,..., 45 ⁇ m or more and less than 50 ⁇ m (between 5 and 50 ⁇ m every 5 ⁇ m) and 50 ⁇ m or more.
- measurement was performed using an image analysis apparatus (trade name “A Image-kun” manufactured by Asahi Kasei Engineering Co., Ltd.) (the same applies to other examples and comparative examples described below).
- Table 2 shows the number N of spheroidal graphite contained in the spheroidal graphite cast iron of Example 1, a frequency F of 5 ⁇ m or more, a cumulative degree Cfa of 5 ⁇ m or more, and a reverse cumulative frequency Cfb for each equivalent circle diameter range.
- FIG. 5 is a graph illustrating Table 2.
- the notation indicating the range of the equivalent circle diameter is ⁇ x- '' is not less than x ( ⁇ m), and ⁇ -y '' is y ( ⁇ m).
- xy means x ( ⁇ m) or more and less than y ( ⁇ m).
- N (x-) is the number of grains with an equivalent circle diameter of x ( ⁇ m) or more (pieces / mm 2 ), and N (-y) is the number of grains with an equivalent circle diameter of less than y ( ⁇ m) (pieces / mm 2).
- N (xy) is the circle equivalent diameter of x ([mu] m) or y ([mu] m) than a particle number (number / mm 2).
- Cfa As frequency Cfa, Cfa (5-10) (%), Cfa (5-15) (%), Cfa (5-20) (%), ..., Cfa (5-60) (%) in ascending order It is expressed as Cfa (5-) (%).
- the cumulative frequency in the range of each equivalent circle diameter when adding in descending order from the frequency F (50-) with an equivalent circle diameter of 50 ⁇ m or more is defined as Cfb (60-) (%), Cfb (55 -) (%), Cfb (50-) (%), ..., Cfb (10-) (%), Cfb (5-) (%).
- the number of graphite grains N (5-20) (pieces / mm 2 ) less than 20 ⁇ m and the number of graphite grains N (30-) (pieces / mm 2 ) with an equivalent circle diameter of 30 ⁇ m or more was determined, and from these values, The ratio of the number N (5-20) of particles with an equivalent circle diameter of 5 ⁇ m to less than 20 ⁇ m to the number of particles N (5-) with an equivalent circle diameter of 5 ⁇ m or more: N (5-20) / N (5-) The ratio of the number of grains N (30-) of 30 ⁇ m or more to the number of grains N (5-) of equivalent circle diameter of 5 ⁇ m or more: N (30-) / N (5-) and the equivalent circle diameter of 5 ⁇ m or more but less than 10 ⁇ m The quotient of the difference between the number of graphite grains and the number of graphite grains with an equivalent circle diameter of 15 ⁇ m or more and less than 20 ⁇ m and the number of graphite grains with an equivalent circle diameter of 5
- N (5-20) / N (5-) corresponds to the cumulative frequency from the equivalent circle diameter of 5 ⁇ m to less than 20 ⁇ m: Cfa (5-20) , and N (30-) / N (5- The value of ) corresponds to the reverse cumulative frequency Cfb (30-) up to a circle equivalent diameter of 30 ⁇ m or more.
- Table 4 The results are shown in Table 4.
- the number of equivalent graphite particles (pieces / mm 2 ) is integrated in ascending order of the equivalent circle diameter.
- the cumulative number of graphite grains from 5 ⁇ m to a specific equivalent circle diameter ( ⁇ m) (hereinafter also simply referred to as the cumulative grain number or Nc.
- the unit is the number of pieces / mm 2 ), and the equivalent circle diameter ( ⁇ m) and the cumulative graphite grain number ( Curve / mm 2 ) was obtained.
- the cumulative value Cfa corresponding to each circle equivalent diameter is obtained by setting the maximum value of the number of accumulated graphite particles ( number of graphite particles N (5-) with an equivalent circle diameter of 5 ⁇ m or more) as 100%, and the equivalent circle diameter ( ⁇ m) and The relationship with cumulative frequency (%) was obtained.
- the equivalent circle diameter when the cumulative frequency is n% is represented by dn (hereinafter also referred to as n% particle diameter).
- the 60% particle diameter (d60) is the equivalent circle diameter of graphite grains in which the cumulative number of graphite grains is 60% of the number of graphite grains having an equivalent circle diameter of 5 ⁇ m or more.
- d0 is expressed as the equivalent circle diameter corresponding to the smallest of the observed graphite grains having an equivalent circle diameter of 5 ⁇ m or more (the same applies to the following examples and comparative examples).
- D100 is the maximum equivalent circle diameter D max of the graphite grains.
- FIG. 6 is a graph in which the cumulative number of grains Nc and the cumulative frequency Cfa of 5 ⁇ m or more are plotted against the equivalent circle diameter values in Table 3.
- the equivalent circle diameter on the horizontal axis is expressed in a common logarithmic scale (the same applies to the following examples and comparative examples).
- Cfa is 20 to 50%, that is, the equivalent circle diameter d20 to d50 has a larger n% particle size than (Equation 1), and Cfa is in the range of 50% to 98% (Equation 1).
- the n% particle size was smaller than that, and the Cfa was 99% or more and the n% particle size was larger than that of (Equation 1).
- the particle size distribution of the spherical graphite follows the straight line shown in (Equation 1), that is, when the cumulative frequency Cfa is proportional to the logarithm of the equivalent circle diameter D, the growth of the spherical graphite is a diffusion phenomenon (diffusion-controlled). It is thought to mean that.
- Test test A JIS Z 2241 No. 14A test piece was cut out from area B in Fig. 3, and tensile strength at normal temperature of product 106 in an as-cast condition using a tensile tester (Shimadzu AG-IS250kN) according to JIS Z 2241. Then, 0.2% proof stress and elongation at break were measured. The test results are shown in Table 8.
- Example 2 The result of Example 2 manufactured by only the gravity casting method without using the air supply pressurizing method in combination with the above Example 1 is shown below.
- Example 2 was produced under the same production conditions as Example 1 except that the air feeding and pressurizing method was not used.
- Table 1 the component composition of the molten metal was the same as Example 1.
- Table 5 shows the results of measuring the number N of grains, the frequency F of 5 ⁇ m or more, the cumulative degree Cfa of 5 ⁇ m or more, and the reverse cumulative frequency Cfb of the spheroidal graphite cast iron of Example 2.
- FIG. 7 is a graph illustrating Table 5.
- N (5-20) / N (5-) , N (30-) / N for spheroidal graphite contained in the spheroidal graphite cast iron of Example 2 (5-) and (N (5-10) -N (15-20) ) / N (5-10) were determined. The results are shown in Table 7.
- Example 2 similarly to Example 1, the relationship between the equivalent circle diameter D and the cumulative number of grains Nc in Example 2 and the relationship between the equivalent circle diameter D and the cumulative frequency Cfa were determined. The results are shown in Table 6 and FIG. From Table 6, Table 7 shows the D max (d100) of spheroidal graphite contained in the spheroidal graphite cast iron of Example 2.
- Example 2 When comparing the broken line represented by (Equation 1) shown in FIG. 8 and the relationship between the equivalent circle diameter D and Cfa of Example 2, Example 2 has 10% Cfa, that is, the equivalent circle diameter d10. To the extent, it almost agrees with (Equation 1), Cfa is 10-60%, that is, the range of equivalent circle diameter d10-d60 is n% larger than (Equation 1), Cfa is 60% -98% In the range, the n% particle diameter was smaller than that of (Formula 1), and Cfa was 99% or more, and the n% particle diameter was larger than that of (Formula 1).
- Table 8 shows the results of the tensile test (tensile strength, 0.2% proof stress and elongation at break) and Charpy impact test of Example 2 in the as-cast state.
- Example 2 Comparison of shrinkage nest
- FIG. 9 is a graph showing a relationship between a cooling curve and a pressing period in the vicinity of the eutectic solidification temperature of Example 1 and Example 2 measured at a position in the vicinity of the part A in FIG.
- the cooling curve C1 of Example 1 is indicated by a solid line
- the cooling curve C2 of Example 2 is indicated by a broken line.
- the region where the temperature T is substantially constant in the range of 1140 ° C. to 1160 ° C. with respect to time t is the eutectic solidification interval.
- Example 1 had a eutectic solidification time of 20 s longer than Example 2.
- Example 1 had a eutectic solidification time of 20 s longer than Example 2.
- the reason for this is that in Example 1 in combination with the air supply and pressurization method, the saturation of Mg in the molten metal was increased by pressing with gas (air in Example 1), and the release of Mg out of the molten metal was suppressed. This is probably because more crystallization nuclei of spheroidal graphite such as MgO and MgS were formed.
- the pressing time dt p of Example 1 was 120 s as shown in FIG.
- Example 3 As a preferred embodiment of the present invention, another example manufactured by using a gravity casting method in combination with an air pressure method will be described with reference to the drawings.
- Example 2 (Molten metal) In the same manner as in Example 1, the raw material was melted in a low frequency induction melting furnace to obtain 12000 kg of hot water. Then, in the same manner as in Example 1, in the bottom pocket of the pouring ladle, 1.1% by mass of spheronizing agent with respect to the main hot water, 0.2% by mass of the primary inoculum with respect to the main hot water, and 11 kg of punching Steel scraps were charged in order, 1800 kg of the obtained hot water was poured into the pouring ladle at 1520 ° C., and spheroidization treatment by the sandwich method and primary inoculation were performed simultaneously. The same spheroidizing agent and primary inoculant as those used in Example 1 were used.
- a fresh sand mold which is a breathable mold, having the automobile structural component (support beam) shown in FIG. 10 as a cavity was used.
- Example 2 For casting, the same method as in Example 1 was used, in addition to the gravity casting method in which gravity pouring was performed, and a method in which an air supply and pressure method was carried out.
- Example 3 The microstructure of the cast article (nodular graphite cast iron) of Example 3 was observed in the same manner as in Example 1, and the particle size distribution of the spherical graphite was evaluated in the same manner as in Example 1. The observation position is in the vicinity of the thickness center of the part indicated by E in FIG. 10 (thickness 30 mm). The micrograph is shown in FIG. 11, and the number N of spheroidal graphite, the frequency F of 5 ⁇ m or more, the cumulative degree Cfa of 5 ⁇ m or more, and the reverse cumulative frequency Cfb are shown in Table 6.
- FIG. 12 is a graph illustrating Table 10.
- Example 2 Similarly to Example 1, from the particle size distribution shown in Table 10, N (5-20) / N (5-) , N (30-) / N for spheroidal graphite contained in the spheroidal graphite cast iron of Example 3 (5-) and (N (5-10) -N (15-20) ) / N (5-10) were determined. The results are shown in Table 12.
- the particle size distribution represented by (Formula 2) is a distribution in which the proportion of finer graphite particles is higher than the particle size distribution represented by (Formula 1).
- Example 3 The relationship between the equivalent circle diameter D and Cfa in Example 3 is that of the finer graphite particles compared to (Equation 2) showing a particle size distribution in which the proportion of fine graphite particles is higher than that of (Equation 1) shown by the broken line. The ratio was high. Comparing the alternate long and short dash line shown in (Equation 2) with the relationship between Cfa and D in Example 3, Example 3 is almost equal to (Equation 2) until Cfa is 30%, that is, up to about the equivalent circle diameter d30.
- Cfa is 30 to 98%, that is, the range of equivalent circle diameter d30 to d98 is n% smaller than (Equation 2), Cfa is 99% or more, and n% particle diameter is larger than (Equation 2). It was.
- Table 13 shows the results of the tensile test (tensile strength, 0.2% proof stress and elongation at break) and Charpy impact test of Example 3 in the as-cast state.
- Comparative Example 1 The result of Comparative Example 1 manufactured by only gravity casting without using the air feeding and pressurizing method with respect to Example 3 described above is shown below. Comparative Example 1 was produced under the same production conditions as in Example 3 except that the air supply and pressurization method was not used. As shown in Table 9, the component composition of the molten metal was the same as in Example 3. The method for measuring the number of graphite grains and the particle diameter, the tensile test, and the Charpy impact test are the same as in Example 3.
- Example 3 The microstructure of the cast article of Comparative Example 1 (nodular graphite cast iron) was observed in the same manner as in Example 3, and the particle size distribution of the spherical graphite was evaluated in the same manner as in Example 3. The observation position is the same as in Example 3.
- the micrograph is shown in FIG. 14, and the number N of spheroidal graphite, the frequency F of 5 ⁇ m or more, the cumulative degree Cfa of 5 ⁇ m or more, and the reverse cumulative frequency Cfb are shown in Table 14.
- FIG. 15 is a graph illustrating Table 14.
- Example 3 the relationship between the equivalent circle diameter D and the cumulative number of grains Nc of Comparative Example 1 and the relationship between the equivalent circle diameter D and the cumulative frequency Cfa were determined.
- Table 15 shows the results.
- Table 16 shows the D max (d100) of spheroidal graphite contained in the spheroidal graphite cast iron of Comparative Example 1.
- Comparative Example 1 when comparing the broken line indicated by (Formula 1) and the relationship between the equivalent circle diameter D and Cfa of Comparative Example 1, Comparative Example 1 has a Cfa of 25%, that is, a range of equivalent circle diameters d0 to d25. N% particle size was smaller than (Equation 1), but n% particle size was larger than (Equation 1) in the range of Cfa from 25% to 100%.
- Example 4 As another preferred embodiment of the present invention, another example manufactured by using a gravity casting method in combination with an air pressure method will be described with reference to the drawings.
- Example 4 a mold having a structural part for automobile (steering knuckle) shown in FIG. 17 as a cavity was used, and the mold material, the manufacturing method of the molten metal, the casting method, and the pressing force were the same as in Example 1.
- Table 18 shows the results of measuring the number N of grains, the degree F of 5 ⁇ m or more, the degree of accumulation Cfa of 5 ⁇ m or more, and the inverse degree of accumulation Cfb of the spherical graphite of the cast article (spheroidal graphite cast iron) of Example 4.
- FIG. 18 is a graph illustrating Table 18. The number of grains was measured in the vicinity of the thickness center of the 20 mm thick part indicated by H in FIG.
- N (5-20) / N (5-) , N (30-) / N for spheroidal graphite contained in the spheroidal graphite cast iron of Example 4 (5-) and (N (5-10) -N (15-20) ) / N (5-10) were determined. The results are shown in Table 20.
- Example 4 From FIG. 19, the relationship between equivalent circle diameter D and Cfa in Example 4 was such that the proportion of fine graphite particles was higher than the particle size distribution shown in (Formula 2). That is, when the one-dot chain line shown in (Expression 2) and the relationship between the equivalent circle diameter D and Cfa of Example 4 are compared, Example 4 has a Cfa of 97%, that is, over the range of equivalent circle diameters d0 to d97. The n% particle size was smaller than that of (Formula 2), the Cfa was 98% or more, and the n% particle size was larger than that of (Formula 2).
- the spheroidal graphite cast iron of the present invention can be applied to various structural parts, but is particularly suitable for automobile structural parts because of its excellent toughness.
- it can be applied to steering knuckles, crankshafts, support beams, connecting rods, brake bodies, brake brackets, shackles, spring brackets, turbine housings, carriers, differential cases, engine mount brackets, and the like.
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Abstract
Description
円相当径5μm以上の黒鉛粒数をN(5-)(個/mm2)、円相当径が5μm以上20μm未満の黒鉛粒数をN(5-20)(個/mm2)、及び円相当径が30μm以上の黒鉛粒数をN(30-)(個/mm2)とするとき、
N(5-)≧250、
N(5-20)/N(5-)≧0.6、及び
N(30-)/N(5-)≦0.2
を満たす球状黒鉛鋳鉄である。
N(2-5)≧100
を満たすのが好ましい。
N(5-20)/N(5-)≧0.65
を満たすのが好ましい。
Dmax≧50.4μm
を満たすのが好ましい。
-0.15≦(N(5-10)-N(15-20))/N(5-10)≦0.25
を満たすのが好ましい。
N(5-)≧250、
N(5-20)/N(5-)≧0.6、及び
N(30-)/N(5-)≦0.2
[ただし、N(5-)、N(5-20)及びN(30-)は、それぞれ任意の断面(少なくとも1 mm2中)に観察される黒鉛粒のうち、円相当径が5μm以上の黒鉛粒数(個/mm2)、円相当径が5μm以上20μm未満の黒鉛粒数(個/mm2)、及び円相当径が30μm以上の黒鉛粒数(個/mm2)である。]
を満たす球状黒鉛鋳鉄からなる鋳造物品を製造する方法であって、
通気性鋳型に注湯された溶湯が共晶凝固を開始する前に、前記溶湯の表面を圧力1 kPa~100 kPaでガスにより押圧し、前記鋳型内を前記ガスで通気させつつ前記溶湯を凝固させることを特徴とする。
0≦dtpE/dtE≦1
を満たすのが好ましい。
本発明の球状黒鉛鋳鉄の成分組成は、JIS G 5502に規定の球状黒鉛鋳鉄品(FCD)、JIS G 5503に規定のオーステンパ球状黒鉛鋳鉄品、JIS G 5510に規定の球状黒鉛系のオーステナイト鋳鉄品などを構成可能な成分組成であればよい。例えば、質量%で、2~4.5%のC、0.8~6%のSi及び0.010~0.080%のMgを含み、残部がFe及び不可避的不純物元素からなる組成、又は前記組成に、所望の性質を得るための元素、S、P、Mn、Cu、Cr、Ni、Mo、W等をさらに適量含んだ組成が挙げられる。
本発明の球状黒鉛鋳鉄は以下の方法によって製造することができる。本発明の製造方法の一例を、以下に工程毎に説明する。
球状黒鉛鋳鉄溶湯(以下、溶湯という。)は公知の製造方法で作製できる。すなわち所望の成分組成となるように、原材料として鋼屑や戻り屑、各種副資材を配合して溶製した溶融鉄合金(以下、元湯という。)に、Mg等を含む球状化剤、例えばFe-Si-Mg系合金を所定量添加して作製する。球状化剤としては、特にREM及び必要に応じてその他の微量元素を適量含んだものも使用できる。球状化処理は一般に広く行われているサンドイッチ法、球状化剤を収容したコアードワイヤーを元湯が収容された取鍋内に供給する方法などを用いることができる。
黒鉛粒数を増やす効果があるので、溶湯を鋳型に鋳込む際には接種を併せて行うのが好ましい。接種剤としては一般に使用されているFe-Si系合金を用いることができる。接種方法は、(a)サンドイッチ法による球状化処理と同時に注湯取鍋内で行う取鍋内接種(以下、一次接種ともいう。)、(b)注湯時に溶湯の流線に接種剤を溶け込ませるように添加する注湯流接種、(c)鋳型のキャビティ内に予め接種剤を装入して行う鋳型内接種などの公知の方法を用いることができる。ここで(b)及び(c)の接種方法は、一次接種の後に行う接種であり、二次接種ということがある。
本発明の球状黒鉛鋳鉄からなる鋳造物品は、重力鋳造など公知の方法を用いて製造してもよいが、通気性鋳型(以下、鋳型ともいう。)に注湯された溶湯が共晶凝固を開始する前に、溶湯の表面をガスで押圧し、前記鋳型内を前記ガスで通気させつつ前記溶湯を凝固させる方法(以下、送気加圧法ともいう。)を併せて行うのが好ましい。送気加圧法を採用することにより、粗大な黒鉛の粒数の割合が抑制され、微細な黒鉛の粒数の割合が高い球状黒鉛鋳鉄を容易に得ることができる。以下、本発明の好ましい製造方法の一つである送気加圧法について詳細に述べる。
本発明の好ましい実施形態として重力鋳造法に送気加圧法を併用して製造した一例を、図表を参照しつつ説明する。なお、本発明はこの形態に限定されるものではない。
原材料として、球状黒鉛鋳鉄の戻り屑、鋼屑、黒鉛粉、フェロシリコン、フェロマンガン、リン鉄、純銅及び硫化鉄を所定の配合比で高周波誘導溶解炉に装入して溶解し100 kgの元湯を得た。次いで、底部にポケットを有する注湯取鍋を予熱後、元湯に対し1.05質量%の球状化剤[REMを含有するFe-Si-Mg系合金(東洋電化工業(株)製TDCR-5)]を注湯取鍋のポケットに装入し、その上方に元湯に対して0.1質量%の一次接種剤[Fe-Si系合金(東洋電化工業(株)製 キャスロン75H)]を装入し、さらにその上方に1300 gの打抜き鋼屑をカバー材として装入し、高周波誘導溶解炉から元湯を1510℃で注湯取鍋内に出湯し、サンドイッチ法による球状化処理と一次接種とを同時に行った。次いで、鋳型に鋳込むために用いる注湯柄杓にも、前記柄杓に収容する溶湯に対してSi当量で0.20質量%の二次接種剤[粉末状Fe-Si系合金の接種剤(東洋電化(株)製ストリーム)]を加える二次接種を行った。実施例1の溶湯の成分組成を表1に示す。
図2(a)は実施例1で使用した鋳型を示し、図2(b)は実施例1の鋳造方法を示す。鋳型1は、湯口部3、湯道部4、押湯部5及び製品部6から構成されたキャビティ2を有し、けい砂を骨材とした通気性鋳型であるCO2硬化アルカリフェノール鋳型を用いた。
鋳造は、鋳型1の外部を常温及び常圧とした大気雰囲気中において重力注湯する重力鋳造法に、さらに送気加圧法を実施する方法を用いた。すなわち、図2(a)に示すように、前述の溶湯Mを収容した注湯取鍋7から、製品部6と押湯部5とを満たす体積の溶湯Mをキャビティ2に1365℃で重力注湯し、次いで図2(b)に示すように、不図示の送気装置から発生させるガスG(実施例1では空気、以下に示す実施例についても同様である。)を吐出するガス吐出部8を湯口部3に嵌め合せた後、ガスGを送気してキャビティ2内の溶湯面Sを押圧した。押圧力は25 kPaであり、送気開始から25 kPaに到達するまでの時間は2 s、押圧時間は120 sであった。溶湯Mの凝固後、図3に示すような、押湯105部分と製品106部分とが連結した状態の球状黒鉛鋳鉄鋳物100を鋳型1より取り出した。図3は、球状黒鉛鋳鉄鋳物100を示す模式断面図であり、概略寸法が記載されている。なお、押圧力はガス吐出部8のガス流路内に配置した不図示の圧力センサーを用いて計測した。
鋳放し状態における実施例1の球状黒鉛鋳鉄鋳物100の断面を腐食させ、そのミクロ組織を光学顕微鏡で観察した。観察部位は図3におけるAで示す部位の近傍であり、この部位を通り底面に平行な断面の直径は53.3 mmと算出できるので観察部位の肉厚は53.3 mmである。腐食させた観察部位の光学顕微鏡写真を図4に示す。基地10はフェライト10aとパーライト10bから構成されていた。球状黒鉛11は、フェライト10aで囲繞された、いわゆるブルスアイ組織を構成する球状黒鉛11aと、ブルスアイでない、つまりその周囲がほぼパーライトのみである球状黒鉛11bとを含んでいた。このようなブルスアイでない球状黒鉛11bはそのほとんどが円相当径20μm以下の微細なものであった。
球状黒鉛鋳鉄に含まれる球状黒鉛(黒鉛粒とも言う)の定量測定は、球状黒鉛鋳鉄の断面の組織を光学顕微鏡で観察することによって行った。図3のAで示す部位の近傍を切断することによって得られた任意の断面を光学顕微鏡で100倍の倍率で観察し、合計で1.0 mm2以上の面積となるよう複数の視野の写真を撮影した。実際の測定は、1視野あたり0.37 mm2に相当する画像を5視野分観察して行った(合計面積:0.37 mm2×5=1.85 mm2)。円相当径及び粒数の測定を行うための光学顕微鏡の観察は、基地と黒鉛粒とが明確に識別できるように、観察面を腐食させずに行った。
Cfa=a・log10D+b [ただし、a=0.997、b=-0.697]で表される線である。(式1)で表される破線とCfa=100%との交点の円相当径Dの値は50.4μmである。(式1)で表される破線と、実施例1の円相当径DとCfaとの関係とを比較すると、実施例1は、Cfaが20%、すなわち円相当径d20程度までは(式1)にほぼ一致し、Cfaが20~50%、すなわち円相当径d20~d50の範囲は(式1)よりもn%粒子径が大きく、Cfaが50%~98%の範囲では(式1)よりもn%粒子径が小さく、Cfaが99%以上で(式1)よりもn%粒子径が大きかった。ここで、球状黒鉛の粒径分布が(式1)で示す直線に従う、つまり累積度数Cfaが円相当径Dの対数に比例する関係となる場合は、球状黒鉛の成長が拡散現象(拡散律速)であることを意味すると考えられる。
図3の領域BからJIS Z 2241の14A号試験片を切り出し採取し、JIS Z 2241に従って、引張試験機(島津製作所製AG-IS250kN)を用いて鋳放し状態における製品106の常温での引張強さ、0.2%耐力及び破断伸びを測定した。試験結果を表8に示す。
図3の領域Bから長さ55 mm×高さ10 mm×幅10 mmのシャルピー衝撃試験用の平滑ノッチなし試験片を採取し、衝撃試験機(前川試験機製製作所製シャルピー式300CR)を用いて、JIS Z 2242に従って、鋳放し状態における製品106のシャルピー衝撃値を測定した。試験温度は-30℃とした。試験結果を表8に示す。
上述の実施例1に対し、送気加圧法を併用せずに重力鋳造法のみで作製した実施例2の結果を以下に示す。実施例2は送気加圧法を用いなかった以外は上記実施例1と同様の製造条件で製造したものであり、表1に示すとおり、溶湯の成分組成は実施例1と同じである。ミクロ組織の観察方法、黒鉛粒数及び粒径の測定方法、引張試験及びシャルピー衝撃試験の方法も実施例1と同様である。
表8に実施例2の鋳放し状態における引張試験(引張強さ、0.2%耐力及び破断伸び)及びシャルピー衝撃試験の結果を示す。
ミクロ組織観察において実施例1と実施例2の引け巣の発生程度を比較したところ、実施例1では引け巣はほとんど観察されなかったが、実施例2では若干数の引け巣(ミクロポロシティ)が観察された。
図9は図2の部位A近傍の位置で測定した実施例1と実施例2の共晶凝固温度付近の冷却曲線と押圧期間との関係を示すグラフである。実施例1の冷却曲線C1を実線で示し、実施例2の冷却曲線C2を破線で示す。いずれも、時刻tに対して温度Tが1140℃~1160℃の範囲でほぼ一定に推移している領域が共晶凝固の区間である。図9では、共晶凝固時間の比較のために、冷却曲線C1及び冷却曲線C2の共晶凝固が開始した時刻tEsをt=65 sの時点に揃え、重ねて描画したものである。実施例1及び実施例2の共晶凝固終了の時刻は、いずれも温度T=1135℃に低下した時点とし、それぞれt1Ef及びt2Efとすると、t1Ef=415 s及びt2Ef=395 sであった。これより、実施例1の共晶凝固時間dt1Eは、dt1E=t1Ef-tEs=415 s-65 s=350 sであり、実施例2の共晶凝固時間dt2Eは、dt2E=t2Ef-tEs=395 s-65 s=330 sであった。すなわち、実施例1の方が、実施例2よりも共晶凝固時間が20 s長かった。この理由は、送気加圧法を併用した実施例1では、ガス(実施例1では空気)による押圧によって溶湯中のMgの飽和度が増大し、Mgの溶湯外への放出が抑制されたことによって、MgO、MgSなどの球状黒鉛の晶出核がより多く形成されたことによるものと考えられる。
実施例1の押圧時間dtpは、図9に示したように120 sであった。押圧開始時刻tp0はt=5 sの時点であり、押圧完了時刻tpfはt=125 sの時点であった。共晶凝固開始時刻tEs=65 sを基準とした場合の、共晶凝固開始後の押圧時間dtpEは、dtpE=tpf-tEs=60 sであった。したがって、実施例1の共晶凝固時間dt1Eに対する共晶凝固開始後押圧時間dtpEの割合は、dtpE/dt1E=0.171、すなわち1/5.8であった。
本発明の好ましい実施形態として重力鋳造法に送気加圧法を併用して製造した他の一例を、図表を参照しつつ説明する。
実施例1と同様にして、原材料を低周波誘導溶解炉で溶解して12000 kgの元湯を得た。次いで、実施例1と同様にして、注湯取鍋の底部のポケットに、元湯に対し1.1質量%の球状化剤、元湯に対して0.2質量%の一次接種剤、及び11 kgの打抜き鋼屑を順に装入し、得られた元湯1800 kgを1520℃で前記注湯取鍋内に出湯し、サンドイッチ法による球状化処理と一次接種とを同時に行った。球状化剤及び一次接種剤は実施例1で使用したものと同じものを使用した。次いで鋳型の湯口に向けて鋳込む際に、目標注湯重量に対してSi当量で0.1質量%の二次接種剤[粉末状Fe-Si系合金の接種剤(東洋電化(株)製ストリーム)]を加える二次接種を行った。実施例3の溶湯の成分組成を表9に示す。
鋳型として、図10に示す自動車用構造部品(サポートビーム)をキャビティとして有する、通気性鋳型である生砂型を使用した。
鋳造は、実施例1と同様に、重力注湯する重力鋳造法に、さらに送気加圧法を実施する方法を用いた。重力注湯は1400℃で行い、キャビティ内の溶湯面を押圧する押圧力は35 kPaであった。押圧開始時刻tp0=10 s、押圧完了時刻tpf=190 sであったので、押圧時間dtpは180 sであった。また、共晶凝固開始時刻tEs=35 s、共晶凝固終了時刻tEf=350 sであったので共晶凝固時間dtE=315 sであり、共晶凝固開始後の押圧時間dtpE(=tpf-tEs)=155 sであった。したがって、実施例2の共晶凝固時間dtEに対する共晶凝固開始後の押圧時間dtpEの割合は、dtpE/dtE=0.492、すなわち1/2.0であった。
実施例3の鋳造物品(球状黒鉛鋳鉄)のミクロ組織を実施例1と同様にして観察し、球状黒鉛の粒径分布を実施例1と同様に評価した。観察位置は図10にEで示す部位(肉厚30 mm)の肉厚中心近傍である。その顕微鏡写真を図11に示し、球状黒鉛の粒数N、5μm以上度数F、5μm以上累積度Cfa、及び逆累積度数Cfbを表6に示す。図12は表10を図示したグラフである。
表13に実施例3の鋳放し状態における引張試験(引張強さ、0.2%耐力及び破断伸び)及びシャルピー衝撃試験の結果を示す。
上述の実施例3に対し、送気加圧法を併用せずに重力鋳造のみで作製した比較例1の結果を以下に示す。比較例1は送気加圧法を用いなかった以外は上記実施例3と同様の製造条件で製造したものであり、表9に示すとおり、溶湯の成分組成は実施例3と同じである。黒鉛粒数及び粒径の測定方法、引張試験及びシャルピー衝撃試験の方法も実施例3と同様である。
比較例1の鋳造物品(球状黒鉛鋳鉄)のミクロ組織を実施例3と同様にして観察し、球状黒鉛の粒径分布を実施例3と同様に評価した。観察位置は実施例3と同様である。その顕微鏡写真を図14に示し、球状黒鉛の粒数N、5μm以上度数F、5μm以上累積度Cfa、及び逆累積度数Cfbを表14に示す。図15は表14を図示したグラフである。
表13に比較例1の鋳放し状態における引張試験(引張強さ、0.2%耐力及び破断伸び)及びシャルピー衝撃試験の結果を示す。
本発明の好ましい実施形態として重力鋳造法に送気加圧法を併用して製造した別の他の一例を、図表を参照しつつ説明する。
Claims (10)
- 任意の断面(少なくとも1 mm2中)に観察される黒鉛粒のうち、
円相当径5μm以上の黒鉛粒数をN(5-)(個/mm2)、円相当径が5μm以上20μm未満の黒鉛粒数をN(5-20)(個/mm2)、及び円相当径が30μm以上の黒鉛粒数をN(30-)(個/mm2)とするとき、
N(5-)≧250、
N(5-20)/N(5-)≧0.6、及び
N(30-)/N(5-)≦0.2
を満たすことを特徴とする球状黒鉛鋳鉄。 - 請求項1に記載の球状黒鉛鋳鉄において、
円相当径が2μm以上5μm未満の黒鉛粒数をN(2-5)(個/mm2)とするとき、
N(2-5)≧100
を満たす球状黒鉛鋳鉄。 - 請求項1又は2に記載の球状黒鉛鋳鉄において、
N(5-20)/N(5-)≧0.65
を満たす球状黒鉛鋳鉄。 - 請求項1~3のいずれかに記載の球状黒鉛鋳鉄において、
最大の黒鉛粒の円相当径をDmaxとするとき、
Dmax≧50.4μm
を満たす球状黒鉛鋳鉄。 - 請求項1~4のいずれかに記載の球状黒鉛鋳鉄において、
円相当径が5μm以上10μm未満の黒鉛粒数をN(5-10)(個/mm2)、円相当径が15μm以上20μm未満の黒鉛粒数をN(15-20)(個/mm2)とするとき、
-0.15≦(N(5-10)-N(15-20))/N(5-10)≦0.25
を満たす球状黒鉛鋳鉄。 - 請求項1~5のいずれかに記載の球状黒鉛鋳鉄からなる鋳造物品。
- 前記鋳造物品は自動車用構造部品である請求項7に記載の鋳造物品。
- 以下の条件:
N(5-)≧250、
N(5-20)/N(5-)≧0.6、及び
N(30-)/N(5-)≦0.2
[ただし、N(5-)、N(5-20)及びN(30-)は、それぞれ任意の断面(少なくとも1 mm2中)に観察される黒鉛粒のうち、円相当径が5μm以上の黒鉛粒数(個/mm2)、円相当径が5μm以上20μm未満の黒鉛粒数(個/mm2)、及び円相当径が30μm以上の黒鉛粒数(個/mm2)である。]
を満たす球状黒鉛鋳鉄からなる鋳造物品を製造する方法であって、
通気性鋳型に注湯された溶湯が共晶凝固を開始する前に、前記溶湯の表面を圧力1 kPa~100 kPaでガスにより押圧し、前記鋳型内を前記ガスで通気させつつ前記溶湯を凝固させることを特徴とする鋳造物品の製造方法。 - 請求項8に記載の鋳造物品の製造方法において、
前記圧力が10 kPa~50 kPaであることを特徴とする鋳造物品の製造方法。 - 請求項8又は9に記載の鋳造物品の製造方法において、
前記溶湯が共晶凝固を開始してから共晶凝固を終了するまでの時間をdtE、前記溶湯が共晶凝固を開始してから前記押圧を終了するまでの時間をdtpEとするとき、
0≦dtpE/dtE≦1
を満たすことを特徴とする鋳造物品の製造方法。
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US16/084,333 US20190071756A1 (en) | 2016-03-24 | 2017-03-24 | Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article |
EP17770422.8A EP3434799B1 (en) | 2016-03-24 | 2017-03-24 | Method for manufacturing cast article comprising spherical graphite cast iron |
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US17/726,641 US20220243308A1 (en) | 2016-03-24 | 2022-04-22 | Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article |
US18/235,572 US20230392237A1 (en) | 2016-03-24 | 2023-08-18 | Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article |
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US18/235,572 Division US20230392237A1 (en) | 2016-03-24 | 2023-08-18 | Spheroidal graphite cast iron, cast article and automobile structure part made thereof, and method for producing spheroidal graphite cast iron article |
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EP3434799B1 (en) | 2020-07-08 |
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US20230392237A1 (en) | 2023-12-07 |
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