Flaky graphite cast iron tubular object, corresponding pipe assembly and corresponding manufacturing method

Abstract

< TableDetails number = '0001' > < Title / > < tbl: tgroup cool = '2' > < tbl: colspec cool = 'c001' cool width = '50%' / > < tbl: colspec cool width = 'c002' cool width = '50%' / > < tbl: cool: entry > < tbl: entry = '1' > outer diameter (mm) (tolerance (mm)) < / tbl: entry > < tbl: entry = '1'

Description

[0001] The present invention relates to a flake graphite cast iron tubular object, especially manufactured in a mold.

[0002] The mechanical properties of current flake graphite cast iron pipes must comply with the EN877 standard.

[0003] Ferroalloys are known, for example, from FR3060607A1. However, this alloy is a spheroidal graphite cast iron alloy, not a flake graphite cast iron alloy.

[0004] In addition, inoculants for manufacturing cast iron objects are known. For example, a casting inoculant based on Fe - Si - Bi - La is disclosed in document W00309314, or an inoculant based on Fe - Si+Bi+Ca+Al+rare earths (mainly La) is described in WO2004104252.

[0005] WO9929911 describes an inoculant for flake or spheroidal graphite cast iron, which contains Si+(Ca and / or Sr and / or Ba) and optionally rare earths, namely Ce and / or La, Mg, Al, Mn and / or Ti and / or Zr. However, this inoculant also contains oxygen in the form of metal oxides and sulfur in the form of metal sulfides. Table 6 of the said document describes a commercial inoculant based on FeSi+Ca+Ba [test number P.] and a commercial inoculant based on FeSi+Ca+Bi+rare earths [test number Q].

[0006] Flake graphite cast iron pipes generally should have a tensile strength greater than or equal to 200 MPa, a compressive strength greater than or equal to 350 MPa, and a Brinell hardness HB less than or equal to 260.

[0007] Known flake graphite cast iron pipes have a minimum wall thickness. The thickness depends on the nominal diameter of the pipe. These characteristics ensure the required mechanical properties.

[0008] The nominal diameter of the pipe is usually between 100 and 300 millimeters. The following Table 1 provides examples of the characteristics of known pipes:

[0009] [Table 1]

[0010] Nominal diameter (mm) Outer diameter (mm) Outer diameter tolerance (mm) Nominal wall thickness (mm) Minimum thickness (mm) 100 110 +2 / -1 3.5 3 125 135 +2 / -2 4 3.5 150 160 +2 / -2 4 3.5 200 210 +2.5 / -2.5 5 4 250 274 +2.5 / -2.5 5.5 4.5 300 326 +2.5 / -2.5 6 5

[0011] The aim of the present invention is to be able to propose a tubular object with given dimensions, such as a pipe or a tubular fitting, which is lightweight for the given dimensions and has at least mechanical properties compliant with current standards.

[0012] More specifically, compared with similar objects of the prior art, the tubular object according to the present invention is advantageously 15% to 35% lighter in weight. Therefore, due to its light weight, it is convenient for installation and handling.

[0013] Known flake graphite cast iron pipes have a relatively large wall thickness, and a large amount of raw materials are required to achieve a given compressive strength.

[0014] In particular, the object of the present invention is to provide a tubular object, such as a cast iron pipe, having the same or improved mechanical strength and low raw material consumption. The object of the present invention is also applicable to other flake graphite cast iron tubular objects other than pipes, such as tubular fittings. The present invention aims to reduce the weight while maintaining a given mechanical strength.

[0015] To this end, the present invention relates to a flake graphite cast iron tubular object, especially manufactured in a mold,

[0016] The flake graphite cast iron contains the following elements, in wt%:

[0017] . Carbon (C) is less than or equal to 3.7%,

[0018] . Silicon (Si) is between 2.0% (inclusive) and 3.9% (inclusive),

[0019] . Phosphorus (P) is between 0.05% (inclusive) and 0.2% (inclusive),

[0020] Optional:

[0021] . Sulfur (S) is between 0.10% (inclusive) and 0.14% (inclusive),

[0022] . Manganese (Mn) < 0.7%,

[0023] . Chromium (Cr) < 0.15%,

[0024] . Nickel (Ni) < 0.5%,

[0025] . Molybdenum (Mo) < 0.1%,

[0026] . Vanadium (V) < 0.5%,

[0027] . Copper (Cu) < 0.22%,

[0028] . Titanium (Ti) < 0.065%,

[0029] The balance is iron (Fe), as well as residual elements with a concentration below 0.01% due to cast iron processing and inevitable impurities with a concentration below 0.01%, wherein the tubular object has an outer diameter ( DE ) and a wall thickness ( e ), and the wall thickness has one of the following values according to the outer diameter:

[0030] [Table 2]

[0031] Outer diameter (mm) (tolerance (mm)) Wall thickness (mm) = f(outer diameter) 110(+2.0 / -1.0) From 2.0 to 3.0 135(+2.0 / -2.0) From 2.5 to 3.5 160(+2.0 / -2.0) From 2.5 to 3.5 210(+2.5 / -2.5) From 3.0 to 4.0 274(+2.5 / -2.5) From 3.5 to 4.5 326(+2.5 / -2.5) From 4.0 to 5.0

[0032] According to certain embodiments, an object according to the present invention may include one or more of the following features:

[0033] . The silicon (Si) concentration of the flake graphite cast iron is between 2.8% (inclusive) and 3.9% (inclusive), preferably between 3.1% (inclusive) and 3.9% (inclusive), more particularly between 3.3% (inclusive) and 3.7% (inclusive);

[0034] . The object is obtained by a manufacturing method in which, when pouring liquid cast iron into a mold, there is no temporary heat insulating material or temporary refractory material on the molding surface, or the object is obtained by a manufacturing method in which a temporary refractory material or temporary heat insulating material is deposited on the molding surface before the step of pouring liquid cast iron into the mold;

[0035] . The tensile strength Rm of the flake graphite cast iron is greater than 200 MPa, preferably greater than 340 MPa, especially greater than 380 MPa;

[0036] . The compressive strength Re of the flake graphite cast iron is greater than 350 MPa, preferably greater than 490 MPa, especially greater than 520 MPa;

[0037] . The Brinell hardness HB of the flake graphite cast iron is less than or equal to 260 HB, especially less than or equal to 230 HB;

[0038] . According to the NF A 48 - 730 standard, the impact resistance of the flake graphite cast iron is between 1.30 m (inclusive) and 2.00 m (inclusive);

[0039] . The residual elements include one or more elements selected from the following: calcium (Ca) and aluminum (Al);

[0040] . The residual elements include one or more elements selected from the following: zirconium (Zr), manganese (Mn), and barium (Ba); and

[0041] . The residual elements include one or more elements selected from the following: at least one rare earth, especially cerium (Ce) and bismuth (Bi).

[0042] Another subject of the present invention relates to a pipe component including a matrix, characterized in that the matrix is a tubular object as described above.

[0043] According to certain embodiments, the pipe component according to the present invention is a pipe, especially a pipe including two joint ends or including a joint end and a socket end, or a tubular fitting.

[0044] Another subject of the present invention relates to a manufacturing method for a tubular object as described above or a pipe component as described above, including the following consecutive steps:

[0045] a) Pour liquid cast iron into a mold having a forming surface,

[0046] b) Solidify the liquid cast iron to obtain a blank of the object,

[0047] c) Heat-treat the blank of the object to obtain a cast iron object (16), in particular

[0048] . Graphitization treatment,

[0049] . Ferrite treatment, or

[0050] . Ferrite treatment after graphitization treatment, and

[0051] . Stress relief treatment.

[0052] According to a specific implementation scheme, the manufacturing method may include one or more of the following features:

[0053] - Before and / or during the step of pouring liquid cast iron into the mold, an inoculant is added to the cast iron,

[0054] The amount of silicon added by the inoculant accounts for 0.1% to 0.4% of the mass of the casting, and the silicon content added in the inoculation step is equivalent to the final silicon concentration of the flake graphite cast iron minus the silicon content concentration present in the pouring ladle, and

[0055] The inoculant is an iron alloy, by weight%, which contains a silicon (Si) content of at least 60.0% (inclusive) and at most 80.0% (inclusive), in particular between 62.0% (inclusive) and 69.0% (inclusive) or between 68.0% (inclusive) and 70.0% (inclusive), or between 70.0% (inclusive) and 76.0% (inclusive), and one or more of the following elements:

[0056] . Calcium (Ca) is at least 0.5% (inclusive) and at most 2.1% (inclusive), in particular between 1.2% (inclusive) and 2.1% (inclusive), between 0.6% (inclusive) and 1.9% (inclusive) or between 0.75% (inclusive) and 1.25% (inclusive),

[0057] . Aluminum (Al) is at least 0.5% (inclusive) and at most 1.3% (inclusive), in particular between 0.5% (inclusive) and 1.0% (inclusive), between 0.55% (inclusive) and 1.3% (inclusive) or between 0.75% (inclusive) and 1.25% (inclusive),

[0058] . Zirconium (Zi) ≤ 4.5%, in particular between 2.8% (inclusive) and 4.5% (inclusive),

[0059] . Manganese (Mn) ≤ 3.5%, in particular between 2.5% (inclusive) and 3.5% (inclusive),

[0060] . Barium (Ba) ≤ 5.0%, especially between 3.0% (inclusive) and 5.0% (inclusive),

[0061] . Cerium (Ce) ≤ 2.0%, especially between 1.5% (inclusive) and 2.0% (inclusive),

[0062] . Bismuth (Bi) ≤ 1.3%, especially between 0.8% (inclusive) and 1.3% (inclusive),

[0063] The balance is iron (Fe).

[0064] - The inoculant is an iron alloy, by weight %, having one of the following compositions:

[0065] a) Silicon (Si) is between 68.0% (inclusive) and 70.0% (inclusive), calcium (Ca) is between 1.2% (inclusive) and 2.1% (inclusive), aluminum (Al) is between 0.5% (inclusive) and 1.0% (inclusive), and the balance is iron (Fe);

[0066] b) Silicon (Si) is between 62.0% (inclusive) and 69.0% (inclusive), calcium (Ca) is between 0.6% (inclusive) and 1.9% (inclusive), aluminum (Al) is between 0.55% (inclusive) and 1.3% (inclusive), zirconium (Zr) is between 2.8% (inclusive) and 4.5% (inclusive), manganese (Mn) is between 2.5% (inclusive) and 3.5% (inclusive), barium (Ba) is between 3.0% (inclusive) and 5.0% (inclusive), and the balance is iron (Fe);

[0067] c) Silicon (Si) is between 70.0% (inclusive) and 76.0% (inclusive), calcium (Ca) is between 0.75% (inclusive) and 1.25% (inclusive), aluminum (Al) is between 0.75% (inclusive) and 1.25% (inclusive), cerium (Ce) is between 1.5% (inclusive) and 2.0% (inclusive), bismuth (Bi) is between 0.8% (inclusive) and 1.3% (inclusive),

[0068] The balance is iron (Fe);

[0069] - When pouring liquid cast iron into a mold, the molding surface has no temporary heat insulation or temporary refractory material, and the heat treatment includes:

[0070] . The first step (ED1), heating the blank of the object for 2 to 10 minutes until the graphitization temperature is greater than 800 °C, more specifically, greater than 900 °C but less than 1000 °C. The first step is to release the internal stress initially present in the cast iron,

[0071] . The second step (ED2), graphitization, during which the blank of the flake graphite cast iron is held at the graphitization temperature for 5 to 30 minutes, preferably 15 minutes,

[0072] . The third step (ED3), cooling to a temperature between 880 °C and 750 °C, preferably cooling to 800 °C, with a cooling time of less than 7 minutes, and

[0073] . The fourth step (ED4), ferritization, during which the blank of the object in the cast iron is slowly cooled at a rate of less than 40 °C / minute within a temperature range of 700 °C to 780 °C;

[0074] - Before the step of pouring the liquid cast iron into the mold, depositing a temporary refractory material or a temporary heat-insulating material on the forming surface, and the heat treatment includes:

[0075] . The first step (EW1), ferritization, includes slowly cooling the blank of the object from a furnace inlet temperature of greater than or equal to 800 °C to a ferritization end temperature of less than 740 °C at a cooling rate of less than 40 °C / minute,

[0076] . The second step (EW2), air cooling to a temperature of less than 100 °C, and

[0077] . The third step (EW3), includes heating the blank of the object in the cast iron to a relaxation temperature between 600 °C and 700 °C, and then holding the rough object in the cast iron at this relaxation temperature for 10 minutes to 30 minutes.

[0078] The present invention will be better understood by reading the following description given only by way of example and referring to the accompanying drawings, wherein:

[0079] Figure 1 Figure 1 is a schematic view of a first embodiment of a manufacturing apparatus for a pipe component for forming a tubular object according to the present invention;

[0080] Figure 2 Figure 2 is a time / temperature graph showing different steps of the heat treatment of the blank of the object manufactured by the apparatus shown by Figure 1 for forming a tubular object according to the present invention;

[0081] Figure 3 Figure 3 is a schematic view corresponding to a second embodiment of a manufacturing apparatus for a pipe component for a tubular object according to the present invention;

[0082] Figure 4 Figure 4 is a time / temperature graph showing different steps of the heat treatment of the blank of the object manufactured by the apparatus shown by Figure 3 for forming a tubular object according to the present invention;

[0083] Figure 5 Figure 5 ​​​​​​​​​​is a structural image of the surface of a flake graphite cast iron tubular object of the prior art near the mold side;

[0084] Figure 6 Figure 6 is Figure 5 a structural image of the surface of the flake graphite cast iron tubular object shown on the side opposite to the mold;

[0085] Figure 7 Figure 7 is a structural image of a flake graphite cast iron tubular object according to the present invention, corresponding to the image shown in Figure 5 ; and

[0086] Figure 8 Figure 8 is Figure 7 a structural image of the flake graphite cast iron tubular object shown, corresponding to the image shown in Figure 6 shown.

[0087] Primarily, the term "rare earth" includes one or more of the following elements: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium.

[0088] Figure 1 Shows a manufacturing apparatus for a flake graphite cast iron pipe according to a first embodiment of the present invention, identified by the general reference numeral 2.

[0089] The apparatus 2 includes a supply ladle 4, a pouring device 6, a pouring channel 8, an inoculation device 9, a rotating mold 10, a cooling device 12, and an extraction device 14.

[0090] The apparatus 2 is used to manufacture a pipe component 15, such as a pipe, by centrifugal casting. The pipe component 15 forms a tubular object or a substrate 16 existing as flake graphite cast iron.

[0091] The supply ladle 4 is a refractory crucible containing liquid metal (such as cast iron).

[0092] The pouring device 6, also known as a "basket", has a volume corresponding to the amount of liquid metal required to manufacture one or more substrates 16. The pouring device 6 can be tilted to a pouring position for pouring the liquid metal into the pouring channel 8.

[0093] The pouring channel 8 guides the liquid metal from the pouring device 6 to the mold 10. It also includes an inlet 20 near the pouring device 6 and an outlet 22 extending into the mold 10. The pouring channel 8 is inclined with respect to the horizontal plane such that the position of the outlet 22 is lower than that of the inlet 20, allowing the liquid cast iron to flow under the action of gravity.

[0094] ​​​​​​The rotary die 10, also known as the "shell", has rotational symmetry and is generally cylindrical in the present example. The axis X-X is inclined with respect to the horizontal direction such that the die is parallel to the pouring channel 8. Hereinafter, the terms "axial" and "radial" will be used to refer to the axis X-X. The die 10 has an inner forming surface 24, which is the negative surface of the base 16, and a cylindrical outer surface 26. The inner forming surface 24 has a controllable roughness, called "shot peening", which allows the liquid metal to rotate when poured into the die 10.

[0095] The die 10 includes a flat end 28 facing the inlet 20 and a socket end 30 opposite the inlet 20 and equipped with a core (not shown). The flat end 28 forms the flat end of the base 16, while the socket end 30 forms the socket end of the base 16.

[0096] The die 10 can rotate about the axis X-X. In addition, the die 10 can be translated along the axis X-X between a starting pouring position (where the outlet 22 is opposite the socket end 30) and an ending pouring position (where the outlet 22 is opposite the flat end 28).

[0097] The cooling device 12 includes spraying means adapted to spray a coolant (such as water) onto the outer surface 26 of the die 10. In a variant (not shown), the cooling device can include cooling means other than the means for spraying on the outer surface of the die, such as a water jacket surrounding the outer surface of the die.

[0098] The extraction device 14 is adapted to axially extract the blank of the base 16 obtained at the end of pouring the liquid metal into the die 10 from the die 10.

[0099] The pouring device 6, the cooling device 12 and the extraction device 14, the supply ladle 4 and the pouring channel 8 itself are known and will not be described in detail. The die 10 is made entirely of forged steel, for example.

[0100] The device also includes a heat treatment furnace 40.

[0101] The process of manufacturing the tubular object or the base 16 according to the present invention using the device 2 is as follows.

[0102] The manufacturing method implemented is a method with the so-called "DeLavaud" manufacturing characteristics

[0103] Liquid cast iron is fed into the supply ladle 4. The liquid cast iron in the ladle 4 enables the tubular object or substrate 16 obtained by the manufacturing method according to the present invention to have the chemical composition defined below. The final concentration of silicon in the tubular object or substrate 16 can be determined by adding silicon-containing materials, especially FeSi alloy, before the step of pouring into the mold 10. The possible silicon contribution from the inoculation treatment using a silicon reagent can be considered to determine the amount of silicon added to the liquid metal, so as to obtain a tubular object or substrate 16 with a silicon concentration meeting the requirements of the present invention.

[0104] Therefore, the final concentration of silicon in the tubular object or substrate 16 determined before the step of pouring into the mold 10 can be obtained by adding to the cast iron a silicon concentration equivalent to the concentration of the object minus the concentration provided by the inoculation.

[0105] Before and / or during the step of pouring the liquid cast iron into the mold, an inoculant is added to the cast iron. Advantageously, the so-called "post" inoculation step is implemented by adding the inoculant at least partially into the mold.

[0106] The amount of silicon added by the inoculant accounts for 0.1% to 0.4% of the mass of the casting. The silicon concentration added in the inoculation step corresponds to the final silicon concentration of the flake graphite cast iron minus the silicon concentration of the cast iron present in the pouring ladle or the pouring device 6.

[0107] The increase in the silicon concentration of the flake graphite cast iron according to the present invention should not be obtained by increasing the amount of the silicon inoculant. Therefore, in the case of the DeLavaud method, the silicon concentration in the cast iron of the tubular object provided by the inoculant is between 0.1% and 0.4%.

[0108] The liquid cast iron corresponding to the amount of cast iron required for the substrate 16 is fed from the supply ladle 4 into the pouring device 6.

[0109] The mold 10 is driven to rotate about the axis X-X and is brought to its starting pouring position.

[0110] Then, the liquid cast iron is poured from the pouring device 6 into the pouring channel 8, flows along the pouring channel 8, and is poured into the mold 10 at the socket end 30.

[0111] Next, the mold 10 is brought to its casting end position while gradually pouring liquid cast iron onto the inner mold surface 24 of the mold, and before the liquid cast iron contacts the inner mold surface 24, the inoculation device 9 deposits an inoculant (such as FeSi powder) onto the inner mold surface 24 of the mold 10. Since the inoculant contains silicon, this needs to be taken into account when determining the final concentration of silicon in the molded tubular object or substrate 16. In a variant (not shown), the inoculant can be completely added to the pouring ladle or even to the cast iron flow poured into the pouring channel, but this inoculation method is not preferred.

[0112] Before and during the casting step, except for the inoculant, the inner mold surface 24 of the mold 10 is not covered with other materials, especially without any temporary heat insulation or temporary refractory materials, such as the "wet spray" used in the casting method (see also Figure 3 the device).

[0113] During the entire casting process, the mold 10 is cooled by the cooling device 12.

[0114] The liquid cast iron in the mold 10 is pressed onto the inner mold surface 24 by centrifugation, solidifies and forms a blank 161 of the substrate. A semi-finished product can also be manufactured instead of the blank 161 of the substrate.

[0115] Then, the blank 161 of the substrate is extracted from the mold 10 by the extraction device 14.

[0116] Next, the blank 161 of the substrate is heat-treated, which will be described in more detail below, and at the end of the heat treatment, the substrate 16 is obtained.

[0117] In the context of the present invention, the concentration is expressed in weight % each time. When the concentration is indicated to one decimal place, this indication also corresponds to two decimal places of the same concentration. For example, the indication of the concentration value 3.7% corresponds to the concentration values 3.7% and 3.70%.

[0118] The composition of the flake graphite cast iron for the manufacturing method and the composition of the substrate 16 contain, by weight %, carbon (C) with a concentration less than or equal to 3.7% and silicon (Si) with a concentration between 2.0 (inclusive) and 3.9%.

[0119] The composition of the flake graphite cast iron further contains, by weight %, phosphorus (P) from 0.05% (inclusive) to 0.2% (inclusive).

[0120] The flake graphite cast iron may also contain the following elements, by weight %:

[0121] - sulfur (S) between 0.10% (inclusive) and 0.14% (inclusive),

[0122] - manganese (Mn) < 0.7%,

[0123] - Chromium (Cr) < 0.15,

[0124] - Nickel (Ni) < 0.5%,

[0125] - Molybdenum (Mo) < 0.1%,

[0126] - Vanadium (V) < 0.5%,

[0127] - Copper (Cu) < 0.22%, and / or

[0128] - Titanium (Ti) < 0.065%.

[0129] The remainder of the flake graphite cast iron is iron (Fe), as well as residual elements with a concentration less than 0.01% and inevitable impurities with a concentration less than 0.01% due to the processing of the cast iron.

[0130] In other words, the flake graphite cast iron can be composed of the above elements.

[0131] More specifically, the composition of the flake graphite cast iron does not include aluminum (Al), except possibly aluminum provided by inoculation [see below], so the concentration of Al is less than 0.01%, preferably less than 0.005%. Similarly, the composition of the flake graphite cast iron does not contain magnesium (Mg), so the concentration of Mg is less than 0.01%, preferably less than 0.005%.

[0132] The carbon equivalent C of the flake graphite cast iron EQ = C (%) + 1 / 3 Si (%) + 1 / 3 P (%) can be less than or equal to 4.75%. The % is still expressed in weight %.

[0133] In addition, the carbon equivalent C of the flake graphite cast iron EQ = C (%) + 1 / 3 Si (%) + 1 / 3 P (%) can be less than or equal to 4.7%, preferably between 4.2% (inclusive) and 4.6% (inclusive), especially between 4.2% (inclusive) and 4.5% (inclusive), preferably equal to 4.3%.

[0134] The silicon (Si) content of the flake graphite cast iron is preferably between 2.8% (inclusive) and 3.9% (inclusive), especially between 3.1% (inclusive) and 3.9% (inclusive), particularly between 3.3% (inclusive) and 3.7% (inclusive).

[0135] Figure 2 Shows the time / temperature graph during heat treatment of a blank of the substrate 16 or more generally a blank of a cast iron tubular object manufactured by the device 2 using the "DeLavaud" manufacturing method. Subsequently, the terms "substrate 16" and "cast iron tubular object" will be used synonymously. Figure 1 ​

[0136] The "De Lavaud" manufacturing method includes the steps of pouring liquid cast iron into the mold 10 and solidifying the liquid cast iron to obtain a blank of a flake graphite cast iron tubular object; then heat-treating the cast iron blank. According to the DeLavaud method, the liquid cast iron is poured into the mold 10, and the inner mold surface 24 of the mold 10 has no temporary heat insulation or temporary refractory material deposited thereon.

[0137] After being extracted from the mold, the temperature of the blank of the matrix is generally between 900 °C and 1000 °C, especially equal to about 950 °C. At the entrance of the heat treatment furnace 40, the temperature of the blank of the matrix is generally between 550 °C and 650 °C, especially at a temperature of about 600 °C, forming the starting temperature of the heat treatment in the furnace.

[0138] Figure 2 It is shown that starting from the starting temperature, in the first heat treatment step ED1, the blank of the cast iron tubular object is heated for 2 to 10 minutes until the graphitization temperature is greater than 800 °C, especially greater than 900 °C but less than 1000 °C. The temperature rise in the first step ED1 is used to release the internal stress existing in the cast iron.

[0139] Then, in the second heat treatment step ED2, the blank of the cast iron tubular object is maintained at the graphitization temperature, which is about 950 °C in this example. The time of the second heat treatment step ED2 is between 5 minutes and 30 minutes, and is 15 minutes in this example. In the second step, the cementite dissolves and is transformed into austenite and graphite.

[0140] Then, the third heat treatment step ED3, namely the cooling step, is implemented. In this step, the temperature starts to decrease from the graphitization temperature to the starting temperature of ferrite formation, which is between 880 °C and 750 °C, and is about 800 °C in this example. The temperature decrease during the step ED3 is carried out within a time of less than 7 minutes, for example, between 4 and 7 minutes (excluding), preferably less than or equal to 6 minutes.

[0141] Then, in the fourth heat treatment step ED4, namely the ferrite formation step, the blank of the cast iron tubular object is slowly cooled in the temperature range of 700 °C to 780 °C, that is, the cooling rate is less than 40 °C / minute, preferably 20 °C / minute to 5 °C / minute. In the fourth step, the austenite is transformed into ferrite and graphite.

[0142] Then, in the fifth step ED5, the blank of the cast iron tubular object is cooled from the end temperature of ferrite formation to a temperature below 100 °C, especially cooled to the ambient air temperature of 20 °C.

[0143] Thereby, the tubular object or matrix 16 is obtained.

[0144] The inoculation reagent or inoculant used in the framework of the present invention is ferrosilicon alloy, with the concentration of silicon being at least 60% (inclusive) and at most 80% (inclusive), especially between 62.0% (inclusive) and 69.0% (inclusive), or between 68.0% (inclusive) and 70.0% (inclusive), or between 70.0% (inclusive) and 76.0% (inclusive). The inoculation reagent or inoculant may contain one or more of the following elements, in weight % (inclusive), preferably including the indicated values each time:

[0145] - Calcium (Ca) is at least 0.5% (inclusive) and at most 2.1% (inclusive), especially between 1.2% (inclusive) and 2.1% (inclusive), or between 0.6% (inclusive) and 1.9% (inclusive), or between 0.75% (inclusive) and 1.25% (inclusive);

[0146] - Aluminum (Al) is at least 0.5% (inclusive) and at most 1.3% (inclusive), especially between 0.5% (inclusive) and 1.0% (inclusive), or between 0.55 and 1.3% (inclusive), or between 0.75% (inclusive) and 1.25% (inclusive);

[0147] - Zirconium (Zr) ≤ 4.5%, especially between 2.8% (inclusive) and 4.5% (inclusive);

[0148] - Manganese (Mn) ≤ 3.5%, especially between 2.5% (inclusive) and 3.5% (inclusive);

[0149] - Barium (Ba) ≤ 5.0%, especially between 3.0% (inclusive) and 5.0% (inclusive);

[0150] - Cerium (Ce) ≤ 2.0%, especially between 1.5% (inclusive) and 2.0% (inclusive);

[0151] - Bismuth (Bi) ≤ 1.3%, especially between 0.8% (inclusive) and 1.3% (inclusive);

[0152] The remaining inoculant is iron (Fe).

[0153] Advantageously, the inoculant is ferrosilicon alloy and contains calcium and elements selected from at least one of the following two groups, one group consisting of Zr, Mn, and Ba, and the other group consisting of Ce and Bi, within the above concentration ranges.

[0154] Examples of the inoculant composition are shown in Table 3 below (weight %, the rest is iron):

[0155] [Table 3]

[0156]

[0157] By using the inoculant in Table 3 above, the obtained flake graphite cast iron contains residual elements including calcium (Ca) and aluminum (Al). The content of residual elements calcium (Ca) and / or aluminum (Al) in the flake graphite cast iron is particularly greater than 0.0% (i.e., non-zero). The residual elements may also include one or more elements selected from the following: zirconium (Zr), manganese (Mn), and barium (Ba). The content of residual elements zirconium (Zr), manganese (Mn), and / or barium (Ba) in the flake graphite cast iron is particularly greater than 0.0% (i.e., non-zero). The residual elements may also include one or more elements selected from the following: at least one rare earth, particularly cerium (Ce) and bismuth (Bi). The content of residual elements composed of rare earth elements, particularly cerium (Ce) and / or bismuth (Bi), in the flake graphite cast iron is particularly greater than 0.0% (i.e., non-zero).

[0158] The tensile strength Rm of the obtained flake graphite cast iron is greater than 200 MPa, preferably greater than 340 MPa, particularly greater than 380 MPa.

[0159] The compressive strength Re of the obtained flake graphite cast iron is greater than 350 MPa, preferably greater than 490 MPa, particularly greater than 520 MPa.

[0160] In addition, the Brinell hardness HB of the flake graphite cast iron of the tubular object according to the present invention is less than or equal to 260 HB, particularly less than or equal to 230 HB.

[0161] The flake graphite cast iron advantageously has impact resistance according to the NF A 48-730 standard, including between 1.30 m (inclusive) and 2.00 m (inclusive). Although the standard NF A 48-730 is generally no longer applicable, it can still be used to define the impact resistance of flake graphite cast iron objects.

[0162] Referring again to Figure 1 , the pipe component 15 or the substrate 16 has an outer diameter DE and a wall thickness e . The pipe component 15 or the substrate 16 also has a nominal diameter DN . The nominal diameter DN is, for example, less than or equal to 400 mm or less than or equal to 300. The nominal diameter DN is greater than or equal to 100 mm.

[0163] The object or pipe manufactured by the device 2 or method according to the present invention includes a specific wall thickness DE depending on the outer diameter e . The relative mass MRL of each cylindrical part of the object or pipe may be one meter (1000 mm) long, which is a function of the outer diameter DE and the wall thickness e . The outer diameter DE and the wall thicknesse The relationship between them is shown in Table 4 below. Considering that the density of the tubular object according to the present invention is 7.15 kg / dm 3 , the relative mass MRL was calculated. For reference, the relevant nominal diameters are also indicated.

[0164] [Table 4]

[0165]

[0166] The wall thickness for each outer diameter is usually between the indicated minimum wall thickness and the indicated maximum wall thickness each time. Similarly, for each outer diameter in Table 4, the mass of the linear cylindrical part is included each time MRL of the limit value.

[0167] It should be understood that for pipes with socket ends, the wall thickness and / or the relative mass with respect to the length MRL values are considered only on strictly cylindrical fluid components, thus outside the socket ends.

[0168] For pipes including two flat ends, the above values can be considered only on the fluid components, thus outside the chamfered ends. For tubular fittings, the above values can be considered only on the fluid components outside the fitting ends.

[0169] Therefore, the fluid component is the component in the tubular object that does not include the socket end. Therefore, the fluid component can be a component in the shape of a hollow cylinder.

[0170] The wall thickness can also be between the indicated minimum wall thickness (inclusive) and the indicated maximum wall thickness (inclusive) each time.

[0171] In a variant, the wall thickness of the above tubular object is within the range of Table 5 below, where the maximum wall thickness is reduced compared to the above table:

[0172] [Table 5]

[0173] Nominal diameter (mm) Outer diameter (mm) Maximum wall thickness (mm) Minimum wall thickness (mm) 100 110 2.9 2 125 135 3.4 2.5 150 160 3.4 2.5 200 210 3.9 3 250 274 4.4 3.5 300 326 4.9 4

[0174] The following tests were carried out on a DN125 pipe made of flake graphite cast iron with the composition shown in Table 6 below:

[0175] [Table 6]

[0176]

[0177]

[0178] Pipe 1 is a comparative flake graphite cast iron pipe not according to the present invention, with a standard thickness of 3.8 mm. The thicknesses of Pipes 2 to 4 are 2.7 mm and they are manufactured according to the present invention. Table 7 below shows certain mechanical properties measured on the pipes thus obtained.

[0179] [Table 7]

[0180]

[0181] Figure 3 Shows a second embodiment of the manufacturing apparatus 2 according to the present invention.

[0182] The apparatus 2 according to the second embodiment and the method for manufacturing a pipe component differ from the above-described apparatus and method only in the following points. Similar elements have the same identification.

[0183] The apparatus 2 includes means (not shown) for applying a refractory material. This means is adapted to deposit a layer of temporary refractory material 50 on the inner mold surface 24 of the mold 10.

[0184] The temporary refractory material 50 itself is known and is, for example, a mixture of water, bentonite, and silica refractory products. The temporary refractory material layer 50 reduces the cooling rate of the cast iron poured into the mold 10. Alternatively, a temporary thermal insulation material is used instead of the temporary refractory material 50.

[0185] Use Figure 3 The manufacturing method of the shown apparatus 2 is a "wet spraying" manufacturing method. The method is as follows.

[0186] Before pouring the liquid cast iron into the mold 10, the temporary refractory material 50 is placed on the inner mold surface 24 and a layer of temporary refractory material is formed.

[0187] The next step is to pour the liquid cast iron onto the temporary refractory material layer.

[0188] Through the refractory material layer 50, the blank of the base body 16 or the blank of the cast iron tubular object contains no or very little cementite. The base body of the flake graphite cast iron is substantially ferrite with a low pearlite concentration, especially less than or equal to 10%, especially when the Si concentration is greater than 3.1%.

[0189] Figure 4 Shows Figure 3 a time / temperature graph during heat treatment of a blank of the base body 16 or a more general blank of a cast iron tubular object manufactured by the apparatus 2 according to the second embodiment shown according to the "wet spraying" manufacturing method.

[0190] After extraction from the mold 10, the blank of the substrate 16 or the blank of the cast iron tubular object is heat-treated. For this purpose, the blank of the substrate or the object is fed into the furnace at an inlet temperature higher than 800 °C and cooled in a first heat treatment step EW1 at a cooling rate lower than 40 °C / min to a ferrite formation end temperature lower than 740 °C, preferably between 700 °C and 740 °C. The first step EW1 is a ferrite formation step during which austenite is transformed into ferrite and graphite.

[0191] Then, in a second heat treatment step EW2, the blank of the substrate or the blank of the cast iron tubular object is cooled from the ferrite formation end temperature to a temperature lower than 100 °C, preferably between 20 °C and 100 °C (excluding). The cooling is carried out in air, i.e., at a rate between 30 °C / min and 70 °C / min, preferably between 40 °C / min and 60 °C / min, especially about 50 °C / min. The air temperature during the cooling process is between 10 °C and 40 °C.

[0192] Then, in a third heat treatment step EW3, the blank of the substrate or the blank of the cast iron tubular object is subjected to a stress relief heat treatment aimed at releasing the internal stresses initially present in the cast iron. This treatment includes first heating the blank of the substrate 16 or the blank of the cast iron tubular object from the above-mentioned temperature of 20 °C to 100 °C to a stress relief temperature of 600 °C to 700 °C, and then holding the blank of the substrate or the blank of the cast iron tubular object at the stress relief temperature for 10 minutes to 30 minutes.

[0193] Then, in a fourth step EW4, the blank of the substrate 16 or the blank of the cast iron tubular object is cooled to the ambient temperature (20 °C).

[0194] Through the above two manufacturing methods and the cast iron composition according to the present invention, the heat-treated finished product has a remarkable structure, and the carbon graphite particles on the outer edge are significantly denser and richer.

[0195] The chemical composition, especially in combination with the relatively thin wall thickness and the heat treatment applied at the mold outlet, enables significant gains in terms of the quality, size, and distribution of the particles, especially throughout the thickness. The uniform aggregation of graphite throughout the thickness of the cast iron tubular object contributes to obtaining a flake graphite cast iron (especially centrifugal flake graphite cast iron) with a new microstructure never seen before.

[0196] Figure 5 A micrograph of the structure of a prior art flake graphite cast iron tubular object near the mold side surface is shown. It can be seen that the graphite particles are relatively small and regularly distributed.

[0197] Figure 6 is Figure 5Microscopic photograph of the structure of the as - shown flake graphite cast iron tubular object near the surface on the side opposite to the mold. It can be seen that there are few graphite particles in the cast iron and their distribution is irregular.

[0198] Figure 7 is a microscopic photograph of the structure of the flake graphite cast iron tubular object according to the present invention. This image was taken on the surface of the object near the mold side, so in the case of a pipe, it is near the outer surface.

[0199] Figure 8 is Figure 7 a microscopic photograph of the structure of the as - shown flake graphite cast iron tubular object. This image was taken on the surface of the object near the side opposite to the mold, so in the case of a pipe, it is near the inner surface.

[0200] In Figure 7 and Figure 8 the graphite particles are grouped into "clusters", and these clusters are also regularly distributed throughout the thickness. Therefore, the flake graphite cast iron according to the present invention can contain variable high proportions of type II and / or type IV graphite as described in the standard NF EN ISO 945 - 1.

[0201] It should be noted that Figures 5 to 8 the scale in

[0202] corresponds to 200 μm. The pipe components manufactured by the above - mentioned method can be tubular elements other than socket - and - spigot pipes, such as cylindrical tubular elements.

[0203] The composition of the flake graphite cast iron according to the present invention can also be used to manufacture casting fittings. In this case, the manufacturing method of such a tubular object includes pouring liquid cast iron into a mold while inoculating. Then, after extracting from the mold and cooling to a temperature below 100 °C, stress - relief heat treatment is performed on the blank of the object in the cast iron. The treatment includes first heating the blank of the tubular object to a stress - relief temperature greater than 400 °C, preferably between 600 °C and 700 °C. Then, the blank of the cast iron tubular object is held at the stress - relief temperature for about 10 minutes to 30 minutes. Finally, the blank of the tubular object is cooled to ambient temperature. Compared with known fittings, the cast iron obtained at the end of the heat treatment can reduce the weight of the casting fittings while maintaining the same or improved mechanical strength, or at the same weight, it can improve the mechanical properties of the casting fittings.

[0204] Therefore, the flake graphite cast iron tubular object according to the present invention is used to obtain pipe components with a low wall thickness at a given mechanical strength or improved mechanical properties at a similar wall thickness. More specifically, the tubular object according to the present invention has significant impact - resistance, tensile - strength and compressive - strength properties at a given size. Therefore, it is economical in manufacturing and use, especially in transportation and handling.

Claims

1. A flake graphite cast iron tubular object (16), The flake graphite cast iron contains the following elements, by weight %: - Carbon (C) less than or equal to 3.7%, - Silicon (Si) between 2.0% (inclusive) and 3.9% (inclusive), - Phosphorus (P) between 0.05% (inclusive) and 0.2% (inclusive), Optionally: - Sulfur (S) between 0.10% (inclusive) and 0.14% (inclusive), - Manganese (Mn) < 0.7%, - Chromium (Cr) < 0.15%, - Nickel (Ni) < 0.5%, - Molybdenum (Mo) < 0.1%, - Vanadium (V) < 0.5%, - Copper (Cu) < 0.22%, - Titanium (Ti) < 0.065%, The balance is iron (Fe), as well as residual elements with a concentration below 0.01% resulting from the processing of cast iron and inevitable impurities with a concentration below 0.01%, where, The tubular object has an outer diameter (DE) and a wall thickness (e), and the wall thickness has one of the following values according to the outer diameter: 。 2. The tubular object according to claim 1, characterized in that, The silicon (Si) concentration of the flake graphite cast iron is one of the following: between 2.8% (inclusive) and 3.9% (inclusive), between 3.1% (inclusive) and 3.9% (inclusive), between 3.3% (inclusive) and 3.7% (inclusive).

3. The tubular object according to claim 1 or 2, characterized in that - The object is obtained by a preparation method in which when pouring liquid cast iron into a mold (10), the forming surface (24) has no temporary heat insulation or temporary refractory material (50), or - The object is obtained by a preparation method in which before the step of pouring liquid cast iron into a mold (10), a temporary refractory material (50) or a temporary heat insulation material is deposited on the forming surface (24).

4. The tubular object according to any one of claims 1 or 2, characterized in that, The tensile strength Rm of the flake graphite cast iron is greater than 200 MPa, preferably greater than 340 MPa, especially greater than 380 MPa.

5. The tubular object according to any one of claims 1 or 2, characterized in that, The compressive strength Re of the flake graphite cast iron is greater than 350 MPa, or greater than 490 MPa, or greater than 520 MPa.

6. The tubular object according to any one of claims 1 or 2, characterized in that, The Brinell hardness HB of the flake graphite cast iron is less than or equal to 260 HB, or less than or equal to 230 HB.

7. The tubular object according to any one of claims 1 or 2, characterized in that, The impact resistance of the flake graphite cast iron is between 1.30 m (inclusive) and 2.00 m (inclusive) according to the standard NF A 48-730.

8. The tubular object according to any one of claims 1 or 2, characterized in that, The residual elements include one or more elements selected from the following: calcium (Ca) and aluminum (Al).

9. The tubular object according to any one of claims 1 or 2, characterized in that, The residual elements include one or more elements selected from the following: zirconium (Zr), manganese (Mn) and barium (Ba).

10. The tubular object according to any one of claims 1 or 2, characterized in that, The residual elements include one or more elements selected from the following: at least one rare earth, especially cerium (Ce) and bismuth (Bi).

11. The tubular object according to any one of claims 1 or 2, characterized in that, The tubular object is an object manufactured in a mold (10).

12. The tubular object according to any one of claims 1 or 2, characterized in that, The flake graphite cast iron includes one or more of the following elements, by weight %: sulfur (S) between 0.10% (inclusive) and 0.14% (inclusive), manganese (Mn) < 0.7%, chromium (Cr) < 0.15%, nickel (Ni) < 0.5%, molybdenum (Mo) < 0.1%, vanadium (V) < 0.5%, copper (Cu) < 0.22%, titanium (Ti) < 0.065%.

13. A pipe component including a substrate (16), characterized in that, The matrix is the tubular object according to any one of claims 1 or 2.

14. The pipeline component according to claim 13, characterized in that, The component is a pipe, or a pipe including two flat ends or a pipe including a flat end and a socket end, or a tubular fitting.

15. A method for manufacturing a tubular object according to claim 1 or a pipe component according to claim 13, comprising the following consecutive steps: a) pouring liquid cast iron into a mold (10) having a forming surface (24), b) solidifying the liquid cast iron to obtain a blank of the object, c) heat-treating the blank of the object to obtain a cast iron object (16).

16. The manufacturing method according to claim 15, characterized in that, The heat treatment comprises or consists of any one of the following: - graphitization treatment, - ferritization treatment, or - ferritization treatment after graphitization treatment, and - stress relief treatment.

17. The manufacturing method according to claim 15 or 16, characterized in that before and / or during the step of pouring liquid cast iron into the mold, an inoculant is added to the cast iron, wherein the amount of silicon added by the inoculant accounts for 0.1% to 0.4% of the mass of the casting, wherein the silicon concentration added in the inoculation step is equivalent to the final silicon concentration of the flake graphite cast iron minus the silicon concentration present in the pouring ladle, and wherein the inoculant is an iron alloy, by weight, which contains a silicon (Si) concentration of at least 60.0% (inclusive) and at most 80.0% (inclusive), or between 62.0% (inclusive) and 69.0% (inclusive), or between 68.0% (inclusive) and 70.0% (inclusive), or between 70.0% (inclusive) and 76.0% (inclusive), and one or more of the following elements: - calcium (Ca) at least 0.5% (inclusive) and at most 2.1% (inclusive), or between 1.2% (inclusive) and 2.1% (inclusive), or between 0.6% (inclusive) and 1.9% (inclusive) or between 0.75% (inclusive) and 1.25% (inclusive), - aluminum (Al) at least 0.5% (inclusive) and at most 1.3% (inclusive), or between 0.5% (inclusive) and 1.0% (inclusive), or between 0.55% (inclusive) and 1.3% (inclusive) or between 0.75% (inclusive) and 1.25% (inclusive), - zirconium (Zr) ≤ 4.5%, or between 2.8% (inclusive) and 4.5% (inclusive), - manganese (Mn) ≤ 3.5%, or between 2.5% (inclusive) and 3.5% (inclusive), - barium (Ba) ≤ 5.0%, or between 3.0% (inclusive) and 5.0% (inclusive), - cerium (Ce) ≤ 2.0%, or between 1.5% (inclusive) and 2.0% (inclusive), - bismuth (Bi) ≤ 1.3%, or between 0.8% (inclusive) and 1.3% (inclusive), the balance being iron (Fe).

18. The manufacturing method according to claim 17, characterized in that, The inoculant is an iron alloy, by weight, having one of the following compositions: a) silicon (Si) between 68.0% (inclusive) and 70.0% (inclusive), calcium (Ca) between 1.2% (inclusive) and 2.1% (inclusive), aluminum (Al) between 0.5% (inclusive) and 1.0% (inclusive), the balance being iron (Fe); b) Silicon (Si) is between 62.0% (inclusive) and 69.0% (inclusive), calcium (Ca) is between 0.6% (inclusive) and 1.9% (inclusive), aluminum (Al) is between 0.55% (inclusive) and 1.3% (inclusive), zirconium (Zr) is between 2.8% (inclusive) and 4.5% (inclusive), manganese (Mn) is between 2.5% (inclusive) and 3.5% (inclusive), barium (Ba) is between 3.0% (inclusive) and 5.0% (inclusive), and the balance is iron (Fe); c) Silicon (Si) is between 70.0% (inclusive) and 76.0% (inclusive), calcium (Ca) is between 0.75% (inclusive) and 1.25% (inclusive), aluminum (Al) is between 0.75% (inclusive) and 1.25% (inclusive), cerium (Ce) is between 1.5% (inclusive) and 2.0% (inclusive), bismuth (Bi) is between 0.8% (inclusive) and 1.3% (inclusive), and the balance is iron (Fe).

19. The manufacturing method according to any one of claims 15 or 16, characterized in that, When pouring the liquid cast iron into the mold (10), the forming surface (24) has no temporary heat insulation or temporary refractory material (50), and the heat treatment includes: - The first step (ED1), heating the blank of the object for 2 to 10 minutes until the graphitization temperature is greater than 800 °C or greater than 900 °C but less than 1000 °C. The first step is to release the internal stress initially present in the cast iron, - The second step (ED2), graphitization, during which the blank of the flake graphite cast iron is held at the graphitization temperature for 5 to 30 minutes, or 15 minutes, - The third step (ED3), cooling to a temperature between 880 °C and 750 °C, or cooling to 800 °C, and the cooling time is less than 7 minutes, and - The fourth step (ED4), ferritization, during which the blank of the object in the cast iron is slowly cooled at a rate of less than 40 °C / minute within the temperature range of 700 °C to 780 °C.

20. The manufacturing method according to any one of claims 15 or 16, characterized in that, Before the step of pouring the liquid cast iron into the mold (10), a temporary refractory material (50) or a temporary heat insulation material is deposited on the forming surface (24), and the heat treatment includes: - The first step (EW1), ferritization, including slowly cooling the blank of the object from a furnace inlet temperature greater than or equal to 800 °C to a ferritization end temperature lower than 740 °C at a cooling rate of less than 40 °C / minute, - The second step (EW2), air cooling to a temperature lower than 100 °C, and - The third step (EW3), including heating the blank of the object in the cast iron to a stress relief temperature between 600 °C and 700 °C, and then holding the blank of the object in the cast iron at the stress relief temperature for 10 minutes to 30 minutes.

Images