Flake graphite cast iron tubular object, corresponding piping component and corresponding manufacturing process

Abstract

The flake graphite cast iron comprises, in % by weight, the following elements: - 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, the remainder being iron (Fe), and residual elements due to the production of the cast iron and unavoidable impurities. The tubular object has an outside diameter (DE) and a wall thickness (e), the wall thickness having, depending on the outside diameter, one of the following values: FIG. 1: AA%%%Table BB%%%Outside diameter (mm) (Tolerance (mm)) CC%%%Wall thickness (mm) = f(Outside diameter) DD%%%From EE%%%to

Description

[0001] TITLE: Tubular object made of cast iron with lamellar graphite, corresponding piping element and manufacturing method

[0002] The present invention relates to a tubular object made of lamellar graphite cast iron, in particular manufactured in a mold.

[0003] Current lamellar cast iron pipes have mechanical properties that must meet the EN877 standard.

[0004] A cast iron alloy is known, for example, as FR3060607A1. This alloy, however, is a spheroidal graphite cast iron alloy and not a lamellar grey cast iron alloy.

[0005] Furthermore, inoculants are known for the manufacture of cast iron objects. Such inoculants are for example described in document W00309314 which discloses a foundry inoculant based on Fe-Si-Bi-La or in W02004104252 which discloses inoculants based on Fe-Si + Bi + Ca + Al + rare earths (mainly La).

[0006] WO992991 1 describes an inoculant for lamellar or spheroidal graphite cast iron, comprising Si + (Ca and / or Sr and / or Ba) and optionally a rare earth, namely Ce and / or La, Mg, AI, Mn and / or Ti and / or Zr. This inoculant, however, also contains oxygen, in the form of metal oxides, and sulfur, in the form of metal sulfides. Table 6 of this document describes a commercial inoculant based on FeSi + Ca + Ba [Test no. P.] and a commercial inoculant based on FeSi + Ca + Bi + rare earth [Test no. Q].

[0007] Lamellar graphite cast iron pipes must generally have a tensile strength greater than or equal to 200 MPa, a crushing strength greater than or equal to 350 MPa and a Brinell hardness HB less than or equal to 260.

[0008] Known lamellar cast iron pipes have minimum wall thicknesses. These thicknesses depend on the nominal diameters of the pipes. These characteristics ensure the required mechanical performance.

[0009] The nominal diameters of these pipes are generally between 100 and 300 mm. The following Table 1 gives as an example the characteristics of known pipes: [Table 1]

[0010] The aim of the invention is to be able to propose a tubular object, for example a pipe or a tubular fitting, having given dimensions, which is light for these given dimensions, and which has mechanical properties at least in accordance with the standards in force.

[0011] More particularly, the tubular object according to the invention allows a weight saving advantageously between 15 and 35% compared to a similar object of the state of the art. Thus, thanks to the low weight, installation and handling are facilitated.

[0012] Known lamellar cast iron pipes have a significant wall thickness and require significant consumption of raw material in order to achieve a given crushing strength.

[0013] In particular, an aim of the invention is to provide tubular objects, such as cast iron pipes, with identical or improved mechanical strength and low raw material consumption. The aim of the invention also applies to tubular objects made of lamellar graphite cast iron other than pipes, such as tubular fittings. The invention seeks to reduce their weight while maintaining a given mechanical strength.

[0014] To this end, the invention relates to a tubular object made of lamellar graphite cast iron, in particular manufactured in a mold, the lamellar graphite cast iron comprising, in % by weight, the following elements:

[0015] - Carbon (C) less than or equal to 3.7%,

[0016] - Silicon (Si) between 2.0% inclusive and 3.9% inclusive,

[0017] - Phosphorus (P) between 0.05% inclusive and 0.2% inclusive, optionally:

[0018] - Sulphur (S) between 0.10% inclusive and 0.14% inclusive, - Manganese (Mn) < 0.7%,

[0019] - Chromium (Cr) < 0.15%,

[0020] - Nickel (Ni) < 0.5%,

[0021] - Molybdenum (Mo) < 0.1%,

[0022] - Vanadium (V) < 0.5%,

[0023] - Copper (Cu) < 0.22%,

[0024] - Titanium (Ti) < 0.065%, the remainder being Iron (Fe), and residual elements due to the production of cast iron at contents lower than 0.01% and unavoidable impurities at contents lower than 0.01%, and in which the tubular object has an outside diameter (OD) and a wall thickness (e), the wall thickness having, depending on the outside diameter, one of the following values:

[0025] [Table 2]

[0026] According to particular embodiments, the object according to the invention may comprise one or more of the following characteristics:

[0027] - the Silicon (Si) content of the lamellar graphite cast iron is between 2.8% inclusive and 3.9% inclusive, and is preferably between 3.1% inclusive and 3.9% inclusive, and is in particular between 3.3% inclusive and 3.7% inclusive;

[0028] - either the object is obtained by a manufacturing process in which a shaped surface is devoid of temporary thermal insulation or temporary refractory material when the liquid iron is poured into the mold, or the object is obtained by a manufacturing process in which a temporary refractory material or temporary thermal insulation is deposited on a shaped surface before the step of pouring the liquid iron into the mold;

[0029] - the lamellar graphite cast iron has a tensile strength Rm greater than 200 MPa, preferably greater than 340 MPa and in particular greater than 380 MPa; - the lamellar graphite cast iron has a crushing strength Re greater than 350 MPa, preferably greater than 490 MPa and in particular greater than 520 MPa;

[0030] - cast iron with lamellar graphite has a Brinell hardness HB less than or equal to 260HB, and in particular less than or equal to 230HB;

[0031] - the cast iron with lamellar graphite has an impact resistance according to standard NF A 48-730 of between 1.30m inclusive and 2.00m inclusive;

[0032] - residual elements include one or more of the elements taken from the list consisting of Calcium (Ca) and Aluminium (Al);

[0033] - the residual elements include one or more of the elements taken from the list consisting of: Zirconium (Zr), Manganese (Mn) and Barium (Ba); and

[0034] - the residual elements include one or more of the elements taken from the list consisting of: at least one rare earth, in particular cerium (Ce) and Bismuth (Bi).

[0035] The invention also relates to a piping element comprising a base body, characterized in that the base body is a tubular object as defined above.

[0036] According to particular embodiments, the piping element according to the invention is either a pipe, in particular a pipe comprising two plain ends or comprising a plain end and a socket end, or a tubular connector.

[0037] The invention also relates to a method for manufacturing a tubular object as defined above or a piping element as defined above, comprising the following successive steps: a) liquid cast iron is poured into a mold having a shaped surface, b) the liquid cast iron is allowed to solidify, obtaining a blank of the object, c) the blank of the object is subjected to a heat treatment, obtaining the cast iron object (16), in particular

[0038] - a graphitization treatment,

[0039] - a ferritization treatment, or

[0040] - a graphitization treatment followed by a ferritization treatment, and

[0041] - a relaxation treatment.

[0042] According to particular embodiments, the manufacturing method may comprise one or more of the following features:

[0043] - before the step of pouring the liquid cast iron into the mold and / or during the step of pouring the liquid cast iron into the mold, an inoculant is added to the cast iron, the quantity of silicon added by the inoculant is between 0.1 and 0.4% of the mass of the cast product, the silicon content added at this inoculation step corresponding to the final silicon content of the lamellar graphite cast iron less the silicon content present in the casting ladle, and the inoculant is a ferroalloy comprising, in % by weight, silicon (Si) at a 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 at a content of between 70.0% inclusive and 76.0% inclusive, and one or more of the following elements:

[0044] . Calcium (Ca) 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,

[0045] . Aluminum (Al) 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,

[0046] . Zirconium (Zi) < 4.5%, in particular between 2.8% inclusive and 4.5% inclusive,

[0047] . Manganese (Mn) < 3.5%, in particular between 2.5% inclusive and 3.5% inclusive,

[0048] . Barium (Ba) < 5.0%, in particular between 3.0% inclusive and 5.0% inclusive,

[0049] . Cerium (Ce) < 2.0%, in particular between 1.5% inclusive and 2.0% inclusive,

[0050] . Bismuth (Bi) < 1.3%, notably between 0.8% inclusive and 1.3% inclusive, the remainder being iron (Fe).

[0051] - the inoculant is a ferroalloy having, in % by weight, 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, and Aluminum (Al) between 0.5% inclusive and 1.0% inclusive, the remainder being iron (Fe); (b) Silicon (Si) between 62.0% inclusive and 69.0% inclusive, Calcium (Ca) between 0.6% inclusive and 1.9% inclusive, Aluminium (Al) between 0.55% inclusive and 1.3% inclusive, Zirconium (Zi) between 2.8% inclusive and 4.5% inclusive, Manganese (Mn) between 2.5% inclusive and 3.5% inclusive, Barium (Ba) between 3.0% inclusive and 5.0% inclusive, the remainder being iron (Fe); (c) Silicon (Si) between 70.0% inclusive and 76.0% inclusive, Calcium (Ca) between 0.75% inclusive and 1.25% inclusive, Aluminium (Al) between 0.75% inclusive and 1.25% inclusive, Cerium (Ce) between 1.5% inclusive and 2.0% inclusive, Bismuth (Bi) between 0.8% inclusive and 1.3% inclusive, the remainder being iron (Fe);

[0052] - the forming surface is free of temporary thermal insulation or temporary refractory material when the liquid iron is poured into the mold, and the heat treatment includes:

[0053] . a first step (ED1) of heating the blank of the object for a period of between 2 and 10 minutes until a graphitization temperature of more than 800°C is reached, and in particular more than 900°C, but less than 1000°C, this first step relaxing the internal stresses initially present in the cast iron,

[0054] . a second graphitization step (ED2) during which the blank of the object in lamellar graphite cast iron is maintained at the graphitization temperature for a period of between 5 and 30 minutes, preferably 15 minutes,

[0055] . a third step (ED3) of cooling to a temperature between 880°C and 750°C, preferably up to 800°C, lasting less than 7 minutes, and

[0056] . a fourth stage (ED4) of ferritization during which the rough cast object is cooled slowly, at a speed of less than 40°C / minute, within a temperature range of between 700°C and 780°C;

[0057] - a temporary refractory material or temporary thermal insulation is deposited on the forming surface before the step of pouring the liquid iron into the mold, and the heat treatment includes:

[0058] . a first ferritization step (EW1) consisting of cooling the blank of the object slowly, at a cooling rate of less than 40°C / minute, from an inlet temperature in a furnace, greater than or equal to 800°C to an end of ferritization temperature of less than 740°C,

[0059] . a second stage (EW2) of air cooling to a temperature below 100°C, and

[0060] . a third step (EW3) consisting of heating the blank of the cast iron object to a relaxation temperature of between 600°C and 700°C, then maintaining the blank of the cast iron object at this relaxation temperature for a period of between 10 minutes and 30 minutes.

[0061] The invention will be better understood by reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0062] [Fig 1] Figure 1 is a schematic view of a first embodiment of an installation for manufacturing a piping element forming a tubular object according to the invention;

[0063] [Fig 2] Figure 2 is a time / temperature diagram showing the different stages of the heat treatment of the blank of the tubular object according to the invention manufactured by the installation of Figure 1;

[0064] [Fig 3] Figure 3 is a schematic view of a second embodiment of an installation for manufacturing a piping element corresponding to a tubular object according to the invention; [Fig 4] Figure 4 is a time / temperature diagram showing the different stages of the heat treatment of the blank of the tubular object manufactured by the installation of Figure 3;

[0065] [Fig 5] Figure 5 is an image of a structure of a state-of-the-art lamellar graphite cast iron tubular object close to the mold-side surface of the object;

[0066] [Fig 6] Figure 6 is an image of the structure of the tubular cast iron object with lamellar graphite in Figure 5 close to the surface of the object on the side opposite the mold;

[0067] [Fig 7] Figure 7 is an image of a structure of a tubular object made of lamellar graphite cast iron according to the invention, the image corresponding to that of Figure 5; and

[0068] [Fig 8] Figure 8 is an image of the structure of the lamellar graphite cast iron tubular object of Figure 7, the image corresponding to that of Figure 6.

[0069] As a preliminary point, the term "rare earth" includes one or more elements from the list consisting of: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium and scandium.

[0070] Figure 1 shows an installation for manufacturing a pipe made of cast iron with lamellar graphite according to a first embodiment of the invention, designated by the general reference 2.

[0071] The installation 2 comprises a feeding bag 4, a pouring device 6, a casting channel 8, an inoculation device 9, a rotary mold 10, a cooling device 12 and an extraction device 14.

[0072] The installation 2 is used for the centrifugal production of pipe elements 15, such as pipes. The pipe element 15 forms a tubular object or a basic body 16 made of lamellar graphite cast iron.

[0073] Feed ladle 4 is a refractory crucible containing liquid metal, such as cast iron.

[0074] The pouring device 6, also called a "basket", has a volume corresponding to the quantity of liquid metal required to produce one or more base bodies 16. The pouring device 6 can be inclined into a position for pouring the liquid metal into the casting channel 8.

[0075] The casting channel 8 conducts the liquid metal from the pouring device 6 to the mold 10. It comprises an inlet 20 located near the pouring device 6 and an outlet 22 extending into the mold 10. The casting channel 8 is inclined relative to the horizontal so that the outlet 22 is located lower than the inlet 20, thus allowing the liquid iron to flow by gravity. The rotating mold 10, also called "shell", has a rotationally symmetrical shape, in the present example generally cylindrical, with axis XX, inclined relative to the horizontal so that it is parallel to the casting channel 8. In the following the expressions "axially" and "radially" will be used with reference to this axis XX. The mold 10 has an inner surface 24 of shape which is the negative surface of the base body 16, as well as a cylindrical outer surface 26.The inner surface 24 is provided with a controlled roughness called "peening", allowing the liquid metal to rotate during its pouring into the mold 10.

[0076] The mold 10 comprises a plain end 28, facing the inlet 20, and a socket end 30, which faces away from the inlet 20 and is provided with a core (not shown). The plain end 28 forms the plain end of the base body 16, while the socket end 30 forms the socket end of the base body 16.

[0077] The mold 10 can be driven in rotation about the axis XX. Furthermore, the mold 10 can be driven in translation along the axis XX between a casting start position, in which the outlet 22 is opposite the spigot end 30, and a casting end position, in which the outlet 22 is opposite the spigot end 28.

[0078] The cooling device 12 comprises a spraying means which is adapted to spray cooling liquid, for example water, onto the outer surface 26 of the mold 10. In a variant not shown, the cooling device may comprise a cooling means other than a means for spraying the outer surface of the mold, such as for example a water casing surrounding the outer surface of the mold.

[0079] The extraction device 14 is adapted to axially extract from the mold 10 the basic body blank 16 obtained after casting the liquid metal into the mold.

[0080] The pouring 6, cooling 12 and extraction 14 devices, the feed ladle 4 as well as the casting channel 8 are known per se and are not described in further detail. The mold 10 is for example entirely made of forged steel.

[0081] The installation also includes a heat treatment furnace 40.

[0082] The manufacture of the tubular object or the basic body 16 according to the invention using the installation 2 is carried out as follows.

[0083] The manufacturing process implemented is a process having the characteristics of the manufacturing process called “DeLavaud”.

[0084] Liquid cast iron is introduced into the feed ladle 4. The liquid cast iron in the ladle 4 is such that the tubular object or basic body 16 obtained with the manufacturing method according to the invention has the chemical composition defined below. The establishment of the final silicon content of the tubular object or basic body 16 can be done before the casting step in the mold 10, by additions of materials containing silicon, in particular FeSi alloys. Any silicon contributions resulting from inoculation treatments using silicon-based agents can be taken into account to determine the quantity of silicon to be added to the liquid metal to obtain a tubular object or basic body 16 having a silicon content in accordance with the invention.

[0085] Thus, the establishment of the final Silicon content of the tubular object or of the basic body 16, made before the casting step in the mold 10, can be carried out by adding to the cast iron a Silicon content equal to that of the object less the content provided by the inoculation.

[0086] Before the step of pouring the liquid cast iron into the mold and / or during the step of pouring the liquid cast iron into the mold, an inoculant is added to the cast iron. Advantageously, a so-called "late" inoculation step is implemented by adding the inoculant at least partially into the mold.

[0087] The amount of silicon added by the inoculant is between 0.1 and 0.4% of the mass of the cast product. The silicon content added at this inoculation step corresponds to the final silicon content of the lamellar graphite cast iron minus the silicon content of the cast iron present in the casting ladle or in the pouring device 6.

[0088] An increase in the silicon content of the lamellar graphite cast iron according to the invention should not be obtained by increasing the amount of silicon-based inoculating agent. Thus, in the case of the DeLavaud process, the silicon content in the cast iron of the tubular object provided by the inoculating agent is between 0.1% and 0.4%.

[0089] Liquid cast iron, corresponding to the quantity of cast iron required for the base body 16, is introduced into the pouring device 6 through the feed pocket 4.

[0090] The mold 10 is rotated around the axis XX and is brought into its casting start position.

[0091] Then, the liquid iron is poured from the pouring device 6 into the casting channel 8, flows along it and is poured into the mold 10 at the socket end 30.

[0092] Subsequently, the mold 10 is brought towards its end-of-casting position while the liquid iron is gradually poured onto the inner surface 24 of the mold and, before the liquid iron comes into contact with the inner surface 24, the inoculating device 9 deposits an inoculating agent, for example a FeSi-based powder, onto the inner surface 24 of the mold 10. Since the inoculating agent contains silicon, it is necessary to take this into account when establishing the final silicon content of the molded tubular object or basic body 16. In a variant not shown, the inoculating agent can be introduced entirely into the casting ladle or into the cast iron jet poured into the casting channel, even if this inoculation method is not preferred.

[0093] Before and during the casting step, apart from the inoculating agent, the inner surface 24 of the mold 10 is not covered with other materials and is in particular devoid of any temporary thermal insulation or temporary refractory material as used during the casting process called "Wetspray" (see also below concerning the installation of Figure 3).

[0094] Throughout the casting period, the mold 10 is cooled by the cooling device 12.

[0095] The liquid iron in the mold 10 is pressed against the inner surface 24 by centrifugation, solidifies and forms a blank 161 of the base body 16. Instead of the blank 161, a semi-finished product can be produced.

[0096] Then, the blank 161 of the base body 16 is extracted from the mold 10 by the extraction device 14.

[0097] Then, the blank 161 of the base body 16 is subjected to a heat treatment, which will be described in more detail below and, at the end of the heat treatment, the base body 16 is obtained.

[0098] In the context of the present invention, the contents are indicated each time in % by weight. When a content is indicated to a single digit after the decimal point, this indication also corresponds to the same content to two digits. For example, the indication of a content value 3.7% corresponds to the content value of 3.7% and to the content value of 3.70%.

[0099] The composition of the lamellar graphite cast iron used for the manufacturing process and therefore the composition of the base body 16 comprises, in % by weight, Carbon (C) at a content less than or equal to 3.7%, and Silicon (Si) at a content between 2.0% inclusive and 3.9% inclusive.

[0100] The composition of the lamellar graphite cast iron also includes, in % by weight, Phosphorus (P) between 0.05% inclusive and 0.2% inclusive.

[0101] Lamellar graphite cast iron may also include, in % by weight, the following elements:

[0102] - Sulphur (S) between 0.10% inclusive and 0.14% inclusive,

[0103] - Manganese (Mn) < 0.7%,

[0104] - Chromium (Cr) < 0.15,

[0105] - Nickel (Ni) < 0.5%,

[0106] - Molybdenum (Mo) < 0.1%, - Vanadium (V) < 0.5%,

[0107] - Copper (Cu) < 0.22%, and / or

[0108] - Titanium (Ti) < 0.065%.

[0109] The remainder of the flake graphite cast iron is Iron (Fe), and residual elements due to the production of the cast iron at contents less than 0.01% and unavoidable impurities at contents less than 0.01%.

[0110] In other words, flake graphite cast iron can consist of the elements listed above.

[0111] In particular, the composition of the lamellar graphite cast iron does not include Aluminum (Al), apart from the Aluminum possibly provided by inoculation [see below], so the Al content is less than 0.01%, preferably less than 0.005%. Similarly, the composition of the lamellar graphite cast iron does not include Magnesium (Mg), so the Mg content is less than 0.01%, preferably less than 0.005%.

[0112] Lamellar graphite cast iron may have a carbon equivalent CEQ = C (%) + 1 / 3 Si (%) + 1 / 3 P (%) less than or equal to 4.75%. These % are also indicated in % by weight.

[0113] Furthermore, the lamellar graphite cast iron may have a carbon equivalent CEQ = C (%) + 1 / 3 Si (%) + 1 / 3 P (%) less than or equal to 4.7%, preferably between 4.2% inclusive and 4.6% inclusive, and in particular between 4.2% inclusive and 4.5% inclusive and preferably equal to 4.3%.

[0114] The silicon (Si) content of the lamellar graphite cast iron is preferably between 2.8% inclusive and 3.9% inclusive, in particular between 3.1% inclusive and 3.9% inclusive, and in particular between 3.3% inclusive and 3.7% inclusive.

[0115] Figure 2 shows the time / temperature diagram during the heat treatment of the blank of the basic body 16 or more generally of a blank of the cast iron tubular object manufactured by the installation 2 of Figure 1 according to the “DeLavaud” manufacturing process. Hereinafter the terms “basic body 16” and “cast iron tubular object” will be used synonymously.

[0116] This “De Lavaud” manufacturing method comprises a step consisting of pouring liquid cast iron into the mold 10 and allowing the liquid cast iron to solidify, obtaining the rough cast iron tubular object made of lamellar graphite cast iron; then the rough cast iron object is subjected to a heat treatment. According to the DeLavaud method, the liquid cast iron is poured into the mold 10, the inner surface of shape 24 of which is devoid of temporary thermal insulation or temporary refractory material deposited on the inner surface 24.

[0117] After extraction from the mold, the blank of the basic body is at a temperature generally between 900°C and 1000°C, and in particular equal to approximately 950°C. At the entrance to the heat treatment furnace 40, the blank of the basic body is at a temperature generally between 550°C and 650°C, in particular at a temperature of approximately 600°C, forming the starting temperature of the heat treatment in the furnace.

[0118] In Figure 2 we then see that starting from this initial temperature, the blank of the cast iron tubular object is heated for a period of between 2 and 10 minutes during a first heat treatment step ED1, until reaching a graphitization temperature greater than 800°C and in particular greater than 900°C, but less than 1000°C. This first step ED1 of temperature increase makes it possible to relax the internal stresses present in the cast iron.

[0119] Then, in a second heat treatment step ED2, the cast iron tubular object blank is maintained at the graphitization temperature which in this case is approximately 950°C. The second heat treatment step ED2 lasts between 5 minutes and 30 minutes, and in this case lasts 15 minutes. During this second step, the cementite is dissolved and transformed into austenite and graphite.

[0120] Then, a third heat treatment step ED3, namely a cooling step, is implemented. During this step, the temperature is lowered, starting from the graphitization temperature, to a ferritization start temperature of between 880°C and 750°C, in this case equal to approximately 800°C. The temperature reduction during step ED3 is carried out over a period of less than 7 minutes, and for example between 4 and 7 minutes excluded, preferably less than or equal to 6 minutes.

[0121] Then, during a fourth heat treatment step ED4, which is a ferritization step, the cast iron tubular object blank is cooled slowly, i.e. at a cooling rate of less than 40°C / minute, preferably between 20°C / minute and 5°C / minute, within a temperature range of between 700°C and 780°C. During this fourth step, the austenite is transformed into ferrite and graphite.

[0122] Then, during a fifth step ED5, the cast iron tubular object blank is cooled from the end of ferritization temperature to a temperature below 100°C, and in particular to the ambient air temperature of 20°C.

[0123] Thus, we obtain the tubular object or basic body 16.

[0124] The inoculating agent or inoculant used in the context of the invention is a silicon-based ferroalloy, the silicon being at a content of at least 60% inclusive and at most 80% 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 the inoculating agent or inoculant may comprise, in % inclusive by weight, one or more of the following elements, the values ​​indicated preferably being included each time:

[0125] - Calcium (Ca) at least 0.5% inclusive and at most 2.1% inclusive, in particular 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;

[0126] - Aluminum (Al) at least 0.5% inclusive and at most 1.3% inclusive, in particular 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;

[0127] - Zirconium (Zi) < 4.5% inclusive, in particular between 2.8% inclusive and 4.5% inclusive;

[0128] - Manganese (Mn) < 3.5% inclusive, in particular between 2.5% inclusive and 3.5% inclusive;

[0129] - Barium (Ba) < 5.0% inclusive, in particular between 3.0% inclusive and 5.0% inclusive;

[0130] - Cerium (Ce) < 2.0% inclusive, in particular between 1.5% inclusive and 2.0% inclusive;

[0131] - Bismuth (Bi) < 1.3% inclusive, in particular between 0.8% inclusive and 1.3% inclusive; the remainder of the inoculant being iron (Fe).

[0132] Advantageously, the inoculant is a silicon-based ferroalloy and comprises calcium and the elements of at least one of the two groups consisting of Zr, Mn and Ba on the one hand and Ce and Bi on the other hand, in the content ranges mentioned above.

[0133] Examples of inoculant composition are shown in the following Table 3 (% by weight, the remainder being iron):

[0134] [Table 3]

[0135] Using the inoculating agent of Table 3 above, the resulting flake graphite cast iron contains residual elements that include Calcium (Ca) and Aluminum (Al). The content of these residual elements Calcium (Ca) and / or Aluminum (Al) in the flake graphite cast iron is in particular greater than 0.0% (i.e. not zero). The residual elements may also include one or more of the elements taken from the list consisting of: Zirconium (Zr), Manganese (Mn) and Barium (Ba). The content of these residual elements Zirconium (Zr), Manganese (Mn) and / or Barium (Ba) in the flake graphite cast iron is in particular greater than 0.0% (i.e. not zero). The residual elements may also include one or more of the elements taken from the list consisting of at least one rare earth, in particular Cerium (Ce) and Bismuth (Bi).The content of these residual elements consisting of a rare earth, in particular cerium (Ce) and / or Bismuth (Bi), in lamellar graphite cast iron is in particular greater than 0.0% (i.e. not zero).

[0136] The lamellar graphite cast iron thus obtained has a tensile strength Rm greater than 200 MPa, preferably a tensile strength Rm greater than 340 MPa and in particular greater than 380 MPa.

[0137] The lamellar graphite cast iron thus obtained has a crushing strength Re greater than 350 MPa, preferably greater than 490 MPa and in particular greater than 520 MPa.

[0138] Furthermore, the lamellar graphite cast iron of the tubular object according to the invention has a Brinell hardness HB less than or equal to 260HB, and in particular less than or equal to 230HB.

[0139] Lamellar graphite cast iron advantageously has an impact resistance according to the NF A 48-730 standard of between 1.30 m inclusive and 2.00 m inclusive. Although this NF A 48-730 standard is no longer generally applied, it makes it possible to define the impact resistance of an object made of lamellar cast iron.

[0140] Referring again to Figure 1, the pipe element 15 or the base body 16 has an outer diameter DE and a wall thickness e. The pipe element 15 or the base body 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.

[0141] The objects or pipes manufactured by the installations 2 or methods according to the invention comprise a specific wall thickness e as a function of the outside diameter DE. These objects or pipes may have a relative mass MRL per cylindrical section of one meter (1000mm) long which is a function of the outside diameter DE and the wall thickness e. The relationship between the outside diameter DE and the wall thickness e is indicated in the following table 4. The relative masses MRL were calculated by considering that the density of the tubular objects according to the invention is 7.15 kg / dm 3 . For information purposes, the associated nominal diameter is also indicated. [Table 4]

[0142] The wall thicknesses for each outside diameter are generally located each time between the minimum wall thickness indicated inclusive and the maximum thickness indicated inclusive. Similarly, the limiting values ​​between which the MRL masses of the linear cylindrical sections are located are each time included for each of the outside diameters in Table 4.

[0143] It is understood that for a pipe with a socket end, the values ​​of the wall thickness and / or relative mass in relation to the MRL length are considered exclusively on the strictly cylindrical running part and therefore excluding the socket end.

[0144] For a pipe with two plain ends, the above values ​​can be considered exclusively for the running part, therefore excluding ends provided with a chamfer. For a tubular fitting, the above values ​​can be considered exclusively for the running part, excluding the ends of the fitting.

[0145] The running part is therefore the part of a tubular object outside the fitting end. The running part can therefore be the part in the shape of a hollow cylinder.

[0146] Wall thicknesses can also be located at any time between the minimum wall thickness indicated inclusive and the maximum wall thickness indicated exclusive.

[0147] Alternatively, the wall thicknesses for the above-mentioned tubular objects are within the ranges of the following Table 5, in which the maximum wall thickness is reduced from the above-mentioned table: [Table 5]

[0148] The following tests were carried out on DN125 cast iron pipes with lamellar graphite having the compositions indicated in the following table 6: [Table 6]

[0149] Pipe 1 is a comparative pipe made of cast iron with lamellar graphite, which is not according to the invention and has a standard thickness of 3.8 mm. Pipes 2 to 4 have a thickness of 2.7 mm and were manufactured according to the invention. Table 7 below shows some mechanical properties measured on the pipes thus obtained.

[0150] [Table 7]

[0151] Figure 3 shows a second embodiment of a manufacturing installation 2 according to the invention. The installation 2 and the method for manufacturing the piping element according to this second embodiment differ from the installation and the method described above only in the following. Similar elements bear the same references.

[0152] The installation 2 comprises a device (not shown) for applying a refractory material. This device is adapted to deposit a layer of a temporary refractory material 50 on the inner surface 24 of the mold 10.

[0153] The temporary refractory material 50 is known per se and is, for example, a mixture of water, bentonite and silica-based refractory product. The layer of temporary refractory material 50 reduces the cooling rate of the cast iron poured into the mold 10. Alternatively, the temporary refractory material 50 is replaced by a temporary thermal insulation material.

[0154] The manufacturing process using installation 2 in Figure 3 is a “Wetspray” type manufacturing process. This process is as follows.

[0155] Before pouring the liquid iron into the mold 10, the temporary refractory material 50 is placed on the inner surface 24 and forms a layer of temporary refractory material.

[0156] The next step is to pour the liquid iron onto the layer of temporary refractory material.

[0157] Thanks to the layer of refractory material 50, the blank of the basic body 16 or the blank of the cast iron tubular object contains no or very little cementite. The lamellar graphite cast iron has an essentially ferritic matrix with a low pearlite content, in particular less than or equal to 10%, in particular when the Si content is greater than 3.1%.

[0158] Figure 4 shows the temperature / time diagram during the heat treatment of the blank of the basic body 16 or more generally of a blank of the cast iron tubular object manufactured using the “Wetspray” process by the installation 2 according to the second embodiment shown in Figure 3.

[0159] After extraction from the mold 10, the blank of the basic body 16 or of the cast iron tubular object undergoes a heat treatment. For this purpose, the blank of the basic body or of the object is introduced into a furnace at an inlet temperature above 800°C and, in a first heat treatment step EW1, is cooled at a cooling rate of less than 40°C / minute to a ferritization end temperature of less than 740°C and preferably between 700°C and 740°C. This first step EW1 is a ferritization step during which the austenite is transformed into ferrite and graphite.

[0160] Then, in a second heat treatment step EW2, the blank of the basic body or the cast iron tubular object is cooled from the end of ferritization temperature to a temperature below 100°C, and preferably between 20°C and 100°C excluded. This cooling takes place in air, i.e. at a speed between 30°C / min and 70°C / min and preferably between 40°C / min and 60°C / min and in particular at approximately 50°C / min. The air temperature during this cooling is between 10°C and 40°C.

[0161] Then, in a third heat treatment step EW3, the blank of the basic body or the cast iron tubular object undergoes a relaxation heat treatment intended to relax the internal stresses initially present in the cast iron. This consists first of all in heating the blank of the basic body 16 or the cast iron tubular object from the aforementioned temperature between 20°C and 100°C to a relaxation temperature between 600°C and 700°C, then in maintaining the blank of the basic body or the cast iron tubular object at this relaxation temperature for a period between 10 minutes and 30 minutes.

[0162] Then, in a fourth step EW4, the blank of the basic body 16 or the cast iron tubular object is cooled to room temperature (20°C).

[0163] With the two manufacturing processes described above and the cast iron compositions according to the invention, the finished product after heat treatment has a remarkable structure, with in particular graphite particles at the outer edge that are more compact and richer in carbon.

[0164] The chemical composition, particularly in combination with the relatively low wall thickness and the heat treatment applied at the mold outlet, allows for a significant gain in terms of quality, size and distribution of particles, particularly throughout the thickness. The homogeneous aggregation of graphite throughout the thickness of the tubular cast iron object allows for a new microstructure never observed before for gray cast irons with lamellar graphite, particularly centrifuged.

[0165] Figure 5 shows a micrograph of a structure of a state-of-the-art tubular cast iron object with lamellar graphite close to the surface of the object on the mold side. It can be seen that the graphite particles are relatively small and evenly distributed.

[0166] Figure 6 is a micrograph of the structure of the tubular cast iron object with lamellar graphite in Figure 5 close to the surface of the object on the side opposite the mold. It can be seen that the cast iron contains only a few graphite particles, which are also distributed irregularly.

[0167] Figure 7 is a micrograph of a structure of a tubular object made of lamellar graphite cast iron according to the invention, the image being taken close to the surface of the object on the mold side, therefore close to the outer surface in the case of a pipe. Figure 8 is a micrograph of the structure of the tubular object made of lamellar graphite cast iron of Figure 7, the image being taken close to the surface of the object on the side opposite the mold, therefore close to the inner surface in the case of a pipe.

[0168] In Figures 7 and 8, the graphite particles are grouped into "clusters", which are also distributed regularly over the entire thickness. The lamellar graphite cast iron within the meaning of the present invention may thus comprise a more or less high level of form II and / or IV graphite as described in standard NF EN ISO 945-1.

[0169] Note that the scale bar in Figures 5 to 8 corresponds to 200 pm.

[0170] The pipe element manufactured by the above methods may be a tubular element other than a socket pipe, for example a cylindrical tubular element.

[0171] The composition of the lamellar graphite cast iron according to the invention can also be used for the manufacture of foundry fittings. In this case, the manufacturing process for such tubular objects consists of pouring the liquid cast iron into a mold and inoculating it simultaneously. Then, after removal from the mold and cooling to a temperature below 100°C, the blank of the cast iron object is subjected to a relaxation heat treatment. This consists first of all in heating the blank of the tubular object to a relaxation temperature above 400°C and preferably between 600°C and 700°C. Then, the blank of the cast iron tubular object is maintained at this relaxation temperature for a period of between approximately 10 minutes and 30 minutes. Finally, the blank of the tubular object is cooled to room temperature.The cast iron obtained after this heat treatment makes it possible to reduce the weight of the foundry fitting compared to known fittings while maintaining identical or even improved mechanical resistance, or, at the same weight, makes it possible to increase the mechanical performance of the foundry fitting.

[0172] The tubular object made of lamellar graphite cast iron according to the invention therefore makes it possible to obtain piping elements having low wall thicknesses for a given mechanical strength or improved mechanical performance at similar wall thicknesses. In particular, the tubular objects according to the invention have significant impact, tensile and crushing strengths for given dimensions. Manufacturing and use, in particular transport and handling, are therefore economical.

Claims

CLAIMS 1. Tubular object (16) made of lamellar graphite cast iron, in particular manufactured in a mold (10), the lamellar graphite cast iron comprising, in % by weight, the following elements: - 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: - Sulphur (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 remainder being Iron (Fe), and residual elements due to the production of cast iron at contents lower than 0.01% and unavoidable impurities at contents lower than 0.01%, and in which the tubular object has an outside diameter (OD) and a wall thickness (e), the wall thickness having, depending on the outside diameter, one of the following values:

2. Tubular object according to claim 1, in which the Silicon (Si) content of the lamellar graphite cast iron is between 2.8% inclusive and 3.9% inclusive, and is preferably between 3.1% inclusive and 3.9% inclusive, and is in particular between 3.3% inclusive and 3.7% inclusive.

3. Tubular object according to claim 1 or 2, either in which the object is obtained by a manufacturing process in which a shaped surface (24) is devoid of temporary thermal insulation or temporary refractory material (50) when the liquid iron is poured into the mold (10), or in which the object is obtained by a manufacturing process in which a temporary refractory material (50) or a temporary thermal insulation is deposited on a shaped surface (24) before the step of pouring the liquid iron into the mold (10).

4. Tubular object according to any one of the preceding claims, in which the lamellar graphite cast iron has a tensile strength Rm greater than 200 MPa, preferably greater than 340 MPa and in particular greater than 380 MPa.

5. Tubular object according to any one of the preceding claims, in which the lamellar graphite cast iron has a crushing strength Re greater than 350 MPa, preferably greater than 490 MPa and in particular greater than 520 MPa.

6. Tubular object according to any one of the preceding claims, in which the lamellar graphite cast iron has a Brinell hardness HB less than or equal to 260HB, and in particular less than or equal to 230HB.

7. Tubular object according to any one of the preceding claims, in which the lamellar graphite cast iron has an impact resistance according to standard NF A 48-730 of between 1.30m inclusive and 2.00m inclusive.

8. A tubular object according to any preceding claim, wherein the residual elements comprise one or more of the elements taken from the list consisting of Calcium (Ca) and Aluminum (Al).

9. A tubular object according to any preceding claim, wherein the residual elements comprise one or more of the elements taken from the list consisting of: Zirconium (Zr), Manganese (Mn) and Barium (Ba).

10. Tubular object according to any one of the preceding claims, in which the residual elements comprise one or more of the elements taken from the list consisting of: at least one rare earth, in particular cerium (Ce) and Bismuth (Bi).

11. A piping element comprising a base body (16), characterized in that the base body is a tubular object according to any one of the preceding claims.

12. A pipe element according to claim 11, wherein the element is either a pipe, in particular a pipe comprising two plain ends or comprising a plain end and a socket end, or a tubular fitting.

13. Method for manufacturing a tubular object according to any one of claims 1 to 10 or a piping element according to one of claims 1 1 or 12, comprising the following successive steps: a) liquid cast iron is poured into a mold (10) having a shaped surface (24), b) the liquid cast iron is allowed to solidify, obtaining a blank of the object, c) the blank of the object is subjected to a heat treatment, obtaining the cast iron object (16), in particular - a graphitization treatment, - a ferritization treatment, or - a graphitization treatment followed by a ferritization treatment, and - a relaxation treatment.

14. Manufacturing method according to claim 13, in which, before the step of pouring the liquid cast iron into the mold and / or during the step of pouring the liquid cast iron into the mold, an inoculant is added to the cast iron, in which the quantity of silicon added by the inoculant is between 0.1 and 0.4% of the mass of the cast product, in which the silicon content added at this inoculation step corresponds to the final silicon content of the flake graphite cast iron less the silicon content present in the casting ladle, and in which the inoculant is a ferroalloy comprising, in % by weight, silicon (Si) at a 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: - Calcium (Ca) 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, Aluminium (Al) 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, Zirconium (Zi) < 4.5%, in particular between 2.8% inclusive and 4.5% inclusive, Manganese (Mn) < 3.5%, in particular between 2.5% inclusive and 3.5% inclusive, Barium (Ba) < 5.0%, in particular between 3.0% inclusive and 5.0% inclusive, Cerium (Ce) < 2.0%, in particular between 1.5% inclusive and 2.0% inclusive, Bismuth (Bi) < 1.3%, notably between 0.8% inclusive and 1.3% inclusive, the remainder being iron (Fe).

15. A manufacturing method according to claim 14, wherein the inoculant is a ferroalloy having, in % by weight, 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, and Aluminum (Al) between 0.5% inclusive and 1.0% inclusive, the remainder being iron (Fe); (b) Silicon (Si) between 62.0% inclusive and 69.0% inclusive, Calcium (Ca) between 0.6% inclusive and 1.9% inclusive, Aluminium (Al) between 0.55% inclusive and 1.3% inclusive, Zirconium (Zi) between 2.8% inclusive and 4.5% inclusive, Manganese (Mn) between 2.5% inclusive and 3.5% inclusive, Barium (Ba) between 3.0% inclusive and 5.0% inclusive, the remainder being iron (Fe); (c) Silicon (Si) between 70.0% inclusive and 76.0% inclusive, Calcium (Ca) between 0.75% inclusive and 1.25% inclusive, Aluminium (Al) between 0.75% inclusive and 1.25% inclusive, Cerium (Ce) between 1.5% inclusive and 2.0% inclusive, Bismuth (Bi) between 0.8% inclusive and 1.3% inclusive, the remainder being iron (Fe).

16. Manufacturing method according to one of claims 13 to 15, in which the forming surface (24) is devoid of temporary thermal insulation or temporary refractory material (50) when the liquid iron is poured into the mold (10), and in which the heat treatment comprises: - a first step (ED1) of heating the blank of the object for a period of between 2 and 10 minutes until a graphitization temperature of more than 800°C is reached, and in particular more than 900°C, but less than 1000°C, this first step relaxing the internal stresses initially present in the cast iron, - a second graphitization step (ED2) during which the blank of the object in lamellar graphite cast iron is maintained at the graphitization temperature for a period of between 5 and 30 minutes, preferably 15 minutes, - a third step (ED3) of cooling to a temperature between 880°C and 750°C, preferably up to 800°C, lasting less than 7 minutes, and - a fourth stage (ED4) of ferritization during which the rough cast object is cooled slowly, at a speed of less than 40°C / minute, within a temperature range of between 700°C and 780°C.

17. Manufacturing method according to one of claims 13 to 15, in which a temporary refractory material (50) or a temporary thermal insulator is deposited on the forming surface (24) before the step of pouring the liquid iron into the mold (10), and in which the heat treatment comprises: - a first ferritization step (EW1) consisting of cooling the blank of the object slowly, at a cooling rate of less than 40°C / minute, from an inlet temperature in a furnace, greater than or equal to 800°C to an end of ferritization temperature of less than 740°C, - a second air cooling step (EW2) to a temperature of less than 100°C, and - a third step (EW3) consisting of heating the blank of the cast iron object to a relaxation temperature of between 600°C and 700°C, then maintaining the blank of the cast iron object at this relaxation temperature for a period of between 10 minutes and 30 minutes.

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