WO2018114845A1

WO2018114845A1 - Spheroidal graphite cast iron object, corresponding component and corresponding manufacturing process

Info

Publication number: WO2018114845A1
Application number: PCT/EP2017/083378
Authority: WO
Inventors: Fabien BRUNESEAUX; Yana NASEDKINA; Rémi Rimlinger
Original assignee: Saint Gobain Pam
Priority date: 2016-12-19
Filing date: 2017-12-18
Publication date: 2018-06-28
Also published as: CN110268082A; ES2914548T3; EP3555335A1; FR3060607B1; FR3060607A1; CN110268082B; EP4050116A1; EP3555335B1; CN114774767B; CN114774767A

Abstract

This object (16) is made of spheroidal graphite cast iron, the steroidal graphite cast iron comprising, in % by weight, the following elements: carbon (C) less than or equal to 3.65% and silicon (Si) between 3.3% and 3.7%. Optionally, the cast iron comprises: phosphorus (P) ≤ 0.1%, and/or manganese (Mn) ≤ 0.6%, and/or chromium (Cr) ≤ 0.2%, and/or titanium (Ti) ≤ 0.15 %, and/or sulfur (S) ≤ 0.05%, and/or magnesium (Mg) between 0.005% inclusive and 0.07% inclusive, and/or copper (Cu) ≤ 0.3%, and/or nickel (Ni) ≤ 0.4%, and/or molybdenum (Mo) ≤ 0.02%, and/or aluminum (Al) ≤ 0.02%, and/or vanadium (V) ≤ 0.04%, the remainder being iron (Fe), and inevitable residual elements at contents of less than 0.01%. The spheroidal graphite cast iron has a carbon equivalent C_EQ = C (%) + 1/3 Si (%) + 1/3 P (%) of less than or equal to 4.75%. The spheroidal graphite cast iron has a resilience (E) greater than or equal to 9.49 J. Application to piping components or highway components.

Description

Spheroidal graphite cast iron object, element and method of manufacture

correspondents

The present invention relates to a spheroidal graphite cast iron object manufactured in a mold.

Current ductile iron pipes have mechanical properties that must meet standards, such as EN545 and EN598.

Ductile iron pipes must generally have the following characteristics:

a tensile strength greater than or equal to 420 MPa and in particular between 420 MPa and 460 MPa,

an elongation at break A greater than or equal to 10% for nominal diameters below or equal to 1000 mm and greater than 7% for nominal diameters greater than 1000 mm, and

a Brinell HB hardness less than or equal to 230.

The known ductile iron pipes lead to a large wall thickness and a high consumption of raw material in order to obtain a given crush strength.

Cast iron alloys are known for example from documents FR 2 139 866; US 3,891,432; DE 101 01 159 and JP-H-082 69614.

The object of the invention is to propose an object, and in particular a pipe element or a road element which is more economical than known objects and in particular which has optimized mechanical properties and a low weight for given dimensions.

In particular, an object of the invention is an increase in the mechanical strength of the cast iron, in order to make it possible to reduce the thickness of the pipes with respect to the current pipes by maintaining the pressure resistance at a given value, or to achieve a higher pressure resistance than current pipes for the same pipe thickness.

The object of the invention also applies to other objects made of spheroidal graphite ductile iron than pipes, such as tubular connectors and pieces of road obtained in the foundry. The invention seeks to reduce their weight and / or their wall thicknesses while maintaining a given mechanical strength.

For this purpose, the subject of the invention is a spheroidal graphite cast iron object manufactured in a mold,

spheroidal graphite cast iron comprising, in% by weight, the following elements:

- Carbon (C) less than or equal to 3.65%, - Silicon (Si) between 3.3% and 3.7%,

optionally:

- Phosphorus (P) <0.1%, and / or

- Manganese (Mn) <0.6%, and / or

- Chromium (Cr) <0.2%, and / or

Titanium (Ti) <0.15%, and / or

- Sulfur (S) <0.05%, and / or

- Magnesium (Mg) between 0.005% inclusive and 0.07% inclusive, and / or

- Copper (Cu) <0.3%, and / or

- nickel (Ni) <0.4%, and / or

- Molybdenum (Mo) <0.02%, and / or

- Aluminum (Al) <0.02%, and / or

- Vanadium (V) <0.04%,

the remainder being iron (Fe), and residual elements unavoidable at contents less than 0.01%, in which

the spheroidal graphite cast iron has a carbon equivalent C _E Q = C (%) + 1/3 If (%) + 1/3 P (%) less than or equal to 4.75% and in which

the spheroidal graphite cast iron has a resilience (E) greater than or equal to 9.49 J.

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

- The spheroidal graphite cast iron has a resilience (E), in particular measured according to the "Charpy" shock test, greater than or equal to 10 Joules or greater than or equal to 1 1 Joules at 20 ° C;

- The silicon content (Si) of spheroidal graphite cast iron is between 3.4% and 3.6%;

the silicon content (Si) of the spheroidal graphite iron is between 3.3% and 3.7%, preferably between 3.5% and 3.6%, and in particular in which the object is obtained by a manufacturing method in which a shaped surface is devoid of temporary thermal insulator or temporary refractory material when casting the molten iron into the mold;

the silicon content (Si) of the spheroidal graphite iron is between 3.3% and 3.5%, preferably between 3.4% and 3.5%, and in particular in which the object is obtained by a manufacturing method in which a temporary refractory material or a temporary thermal insulator is deposited on a shaped surface prior to the step of pouring the molten iron into the mold; the carbon equivalent C _EQ = C (%) + 1/3 If (%) + 1/3 P (%) of the spheroidal graphite cast iron is between 4.3% inclusive and 4.6% inclusive or between 4.4% inclusive and 4.6% inclusive, and is preferably between 4.45% inclusive and 4.55% inclusive and is in particular equal to 4.5%;

- spheroidal graphite cast iron has a tensile strength Rm greater than

470 MPa, preferably greater than 500 MPa and in particular greater than 530 MPa;

- Spheroidal graphite cast iron has an elongation at break A greater than or equal to 7% and in particular greater than or equal to 10%;

- Spheroidal graphite cast iron has a Brinell HB hardness less than or equal to 250HB, and in particular less than or equal to 230HB.

The invention also relates to a pipe element, such as a pipe or fitting, or a road element, such as a manhole or rainwater drain, comprising a base body, characterized in that the basic body is an object as defined above.

The invention also relates to a method of manufacturing an object as defined above or a pipe element or a road element as defined above, comprising the following successive steps:

a) pouring liquid iron into a mold having a shaped surface, b) allowing the molten iron to solidify by obtaining a blank of the object, and c) treating the blank of the iron with a heat treatment. object, especially a relaxation treatment by obtaining the cast iron object.

According to particular embodiments, the manufacturing method may include one or more of the following features:

before the step of pouring the molten iron into a mold, a step is implemented to establish the silicon content of the cast iron, in particular by adding in the melting furnace or in the ladle materials containing silicon, the silicon content added during this step corresponding to the final silicon content of the spheroidal graphite cast iron of the object minus the silicon content provided possibly by spheroidization and inoculation treatments.

the shaped surface is devoid of temporary thermal insulation or temporary refractory material when the liquid iron is poured into the mold, and wherein the heat treatment comprises:

. a first step of heating the blank of the object for a period of between 2 and 10 minutes until a graphitization temperature of greater than 800 ° C., and in particular greater than 900 ° C. but less than 1000 ° C. , this first step relaxing the internal stresses present initially in the cast, . a second graphitization step during which the blank of the cast iron object is maintained at the graphitization temperature for a period of between 5 and 30 minutes, in particular between 5 and 18 minutes, and preferably 15 minutes,

. a third cooling step to a temperature of between 880 ° C and 750 ° C, preferably up to 800 ° C, of less than 7 minutes, and

. a fourth ferritization step during which the blank of the cast iron object is cooled slowly, at a rate of less than 40 ° C / minute, within a temperature range between 700 ° C and 780 ° C ;

the heat treatment comprises:

. a step of cooling in air to a temperature below 100 ° C, and

. a relaxation step of heating the blank of the cast iron object at a relaxation temperature of 600 ° C to 700 ° C, and then maintaining the blank of the cast iron object at this relaxation temperature for a period of duration between 10 minutes and 30 minutes; and

depositing a temporary refractory material or a temporary thermal insulator on the shaped surface before the step of pouring the liquid iron into the mold, and wherein the heat treatment further comprises:

a first ferritization step of cooling the blank of the object slowly, at a cooling rate of less than 40 ° C / minute, of an inlet temperature in an oven, greater than or equal to 800 ° C until at a ferritization end temperature of less than 740 ° C,

the air cooling step being a second step and the relaxation step being a third step.

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

FIG. 1 is a schematic view of a first embodiment of an installation for manufacturing a pipe element forming an object according to the invention;

FIG. 2 is a time / temperature diagram showing the different steps of the heat treatment of the blank of the object according to the invention manufactured by the installation of FIG. 1;

FIG. 3 is a schematic view of a second embodiment of an installation for manufacturing a pipe element corresponding to an object according to the invention; FIG. 4 is a time / temperature diagram showing the different steps of the heat treatment of the blank of the object manufactured by the installation of FIG. 3;

FIG. 5 shows the tensile strength, as a function of the silicon content, of examples of spheroidal graphite cast iron pipes manufactured by the installations according to FIGS. 1 and 3;

FIG. 6 is a diagram showing the influence of the silicon content on the resilience of spheroidal graphite cast iron pipes manufactured by the two installations according to FIGS. 1 and 3; and

FIG. 7 shows the influence of the silicon content on the elongation at break of spheroidal graphite cast iron pipes manufactured by the two installations according to FIGS. 1 and 3.

In Figure 1 is shown an installation for manufacturing a spheroidal graphite cast iron pipe according to a first embodiment of the invention, designated by the general reference 2.

The installation 2 comprises a feed bag 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.

The plant 2 is used to centrifugally produce pipe elements 15, such as pipes. The pipe member 15 forms an object or base body 16 of spheroidal graphite cast iron.

The feed bag 4 is a refractory crucible containing liquid metal, such as cast iron.

The pouring device 6, also called "basket", has a volume corresponding to the amount of liquid metal needed to manufacture one or more basic bodies 16. The pouring device 6 can be inclined in a pouring position of the liquid metal in the channel casting 8.

The casting channel 8 conducts the liquid metal of 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 pouring 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 rotary mold 10, also called "shell", has a symmetrical shape of revolution, in the generally cylindrical example of axis XX, inclined relative to the horizontal so that it is parallel to the channel of 8. In what follows, the terms "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", for driving the liquid metal in rotation during its casting in the mold 10.

The mold 10 comprises a plain end 28, facing the inlet 20, and a plug end 30, which is turned away from the inlet 20 and which is provided with a core (not shown). The spigot end 28 forms the spigot end of the base body 16, while the spigot end 30 forms the interlocking end of the base body 16.

The mold 10 can be rotated about the X-X axis. Furthermore, the mold 10 can be driven in translation along the axis XX between a casting start position, in which the outlet 22 is in front of the end plug end 30, and a end of casting position , in which the outlet 22 is in front of the end end 28.

The cooling device 12 comprises a watering means which is adapted to project cooling liquid, for example water, onto the outer surface 26 of the mold 10. The extraction device 14 is adapted to extract axially from the mold The base body blank 16 obtained at the end of the casting of the liquid metal in the mold.

The pouring 6, cooling 12 and extraction 14 devices, the feed bag 4 and the pouring channel 8 are known per se and are not described in more detail. The mold 10 is for example entirely made of forged steel.

The installation also comprises a heat treatment furnace 40.

The manufacture of the object or base body 16 according to the invention with the installation 2 is performed as follows.

The manufacturing method used is a process having the characteristics of the manufacturing process called "DeLavaud".

Liquid cast iron is introduced into the feed bag 4. The liquid cast iron in the bag 4 is such that the object or base body 16 obtained with the manufacturing method according to the invention has the chemical composition defined below. and in particular the silicon content according to the invention. The establishment of the final silicon content of the object or of the base body 16 is made before the casting step in the mold 10, by additions of silicon-containing materials, especially FeSi alloys. These additions are for example made in the molten bath of electric furnaces or in feed pockets. Potential silicon inputs resulting from spheridisation and / or inoculation treatments using silicon-based agents must be taken in order to determine the amount of silicon to be added to the liquid metal to obtain an object or base body 16 having a silicon content according to the invention.

Thus, the establishment of the final silicon content of the object or of the base body 16, made before the casting step in the mold 10, is carried out by adding to the cast iron a silicon content equal to that of the less the content provided by inoculation and / or spheronization.

The increase in the silicon content of the spheroidal 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 amount of silicon in the melt of the object provided by the inoculation agent is between 0.1% and 0.3%.

Liquid cast iron, corresponding to the amount of cast iron necessary for the basic body 16, is introduced into the pouring device 6 by the feed bag 4.

The mold 10 is rotated about the X-X axis and is brought into its casting start position.

Then, the liquid iron is poured from the pouring device 6 into the pouring channel

8, flows along the latter and is poured into the mold 10 at the end plug-in end 30.

Successively, the mold 10 is brought to its end-of-casting position while the molten iron is gradually poured onto the inner surface 24 of the mold and, before the molten iron comes into contact with the inner surface 24, the device inoculation 9 deposits an inoculation agent, for example a FeSi-based powder, on the inner surface 24 of the mold 10. As described previously, when the inoculation agent contains silicon, it is necessary to take into account for the establishment of the final silicon content of the molded object or base body 16.

Before and during the pouring 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 in the casting process called "Wetspray" (see also below for the installation of Figure 3).

During the entire duration of the casting, the mold 10 is cooled by the cooling device 12.

The molten iron in the mold 10 is pressed against the surface 24 by centrifugation, solidifies and forms a blank 161 of the base body 16.

Then, the blank 161 of the base body 16 is extracted from the mold 10 by the extraction device 14. Then, the blank 161 of the base body 16 is subjected to a heat treatment, which will be described in more detail below and, after the heat treatment, the base body 16 is obtained.

The composition of the spheroidal graphite iron used for the manufacturing process and therefore the composition of the base body 16 comprises, in% by weight, carbon (C) at a content of less than or equal to 3.65%, and silicon (Si) at a level of between 3.3% inclusive and 3.7% inclusive.

Optionally, the spheroidal graphite cast iron comprises, in% by weight, the following element or elements:

- Phosphorus (P) <0.1%, and / or

- Manganese (Mn) <0.6%, and / or

- Chromium (Cr) <0.2%, and / or

Titanium (Ti) <0.15%, and / or

- Sulfur (S) <0.05%, and / or

- Magnesium (Mg) between 0.005% inclusive and 0.07% inclusive, and / or

- Copper (Cu) <0.3%, and / or

- nickel (Ni) <0.4%, and / or

- Molybdenum (Mo) <0.02%, and / or

- Aluminum (Al) <0.02%, and / or

Vanadium (V) <0.04%.

The remainder of the spheroidal graphite iron is iron (Fe), and other residual elements at contents less than 0.01%, due to the process of making the cast iron or unavoidable impurities.

Spheroidal graphite cast iron has a carbon equivalent C _E Q = C (%) + 1/3 If (%) + 1/3 P (%) less than or equal to 4.75%. These% are also indicated in% by weight.

Furthermore, the spheroidal graphite cast iron may have a carbon equivalent C _E Q = C (%) + 1/3 Si (%) + 1/3 P (%) less than or equal to 4.7%, preferably between 4.3% inclusive and 4.6% inclusive and preferably between 4.45% inclusive and 4.55% inclusive. Preferably, the carbon equivalent C _E Q is equal to 4.5%.

The silicon (Si) content is preferably between 3.4% inclusive and 3.6% inclusive, and preferably between 3.5% inclusive and 3.6% inclusive especially in the case of the use of the process DeLavaud as is the case of the present embodiment.

FIG. 2 shows the time / temperature diagram during the heat treatment of the blank of the base body 16 or more generally of a blank of the cast iron object manufactured by the installation 2 of FIG. 1 according to the method Manufacturing "DeLavaud". Subsequently the terms "base body 16" and "cast iron object" will be used synonymously.

For the record, this manufacturing process "Lavaud" comprises a step of pouring molten iron in the mold 10 and let solidify the molten iron by obtaining the blank of the cast iron object; then heat treatment is carried out on the blank of the cast iron object. According to the DeLavaud process, the molten iron is poured into the mold 10 whose inner surface of form 24 is devoid of temporary thermal insulation or temporary refractory material deposited on the inner surface 24.

After extraction of the mold, the blank of the base body is at a temperature generally between 900 ° C and 1000 ° C, and in particular equal to about 950 ° C. At the inlet of the heat treatment furnace 40, the blank of the base body is at a temperature generally of 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 oven.

In FIG. 2, it can be seen that, starting from this initial temperature, the blank of the cast iron object is heated for a duration of between 2 and 10 minutes during a first heat treatment step ED1, until to achieve 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 rise relaxes the internal stresses present in the cast iron.

Then, in a second heat treatment step ED2, the blank of the cast iron object is maintained at the graphitization temperature which in this case is equal to about 950 ° C. The second ED2 heat treatment stage has a duration of between 5 minutes and 30 minutes, and in this case has a duration of 15 minutes. During this second stage, the cementite is dissolved and converted into austenite and graphite.

Then, a third heat treatment step ED3 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 lowering of temperature during the stage

ED3 is carried out over a period of between 4 and 7 minutes, preferably less than or equal to 6 minutes.

Then, during a fourth heat treatment step ED4, which is a ferritization step, the blank of the cast iron object is cooled slowly, that is to say at a cooling rate of less than 40 ° C / minute. , preferably between

20 ° C / minute and 5 ° C / minute, within a range of temperatures between 700 ° C and 780 ° C. During this fourth step, the austenite is transformed into ferrite and graphite.

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

Thus, we obtain the object or the basic body 16.

The spheroidal graphite cast iron thus obtained has a tensile strength Rm greater than 470 MPa and preferably a tensile strength Rm greater than 500

MPa and in particular greater than 530 MPa.

As can be seen in FIG. 5, the spheroidal graphite cast iron having a silicon content as defined above and manufactured by the DeLavaud process described above meets this requirement.

Furthermore, the spheroidal graphite cast iron according to the invention has an elongation at break of greater than or equal to 7% and in particular greater than or equal to 8%, greater than or equal to 9% or greater than or equal to 10%.

Moreover, the spheroidal graphite cast iron of the object according to the invention has a resilience E greater than or equal to 9.49 Joules at ambient temperature (20 ° C.). This is achieved inter alia by the fact that the silicon content does not exceed 3.7%. Resilience

E is measured by the shock method "Charpy sheep". Thus, the artifacts comply with the American standard AWWAC151. Preferably, the resilience E measured according to the "Charpy" method is greater than or equal to 10 Joules or greater than or equal to

1 1 Joules.

This is shown in FIG. 6 which indicates that for silicon contents between 3.3% and 3.7%, the resilience E is located above or equal to 9.49 Joules for pipes according to the invention manufactured following the DeLavaud centrifugation process followed by the heat treatment described above.

In addition, the spheroidal graphite cast iron of the object according to the invention has a Brinell HB hardness of less than or equal to 230 HB.

Referring again to FIG. 1, the pipe member 15 or the base body 16 has a nominal diameter DN and a wall thickness e. The nominal diameter DN is for example less than or equal to 600 mm or less than or equal to 1000 mm or less than or equal to 1600 mm.

Pressure tests carried out on DN400 pipes show that at identical thickness, the pipes according to the invention have a tensile strength greater than 20% to 30% with respect to spheroidal graphite cast iron pipes having a in silicon less than 2.9%. Similarly, for the same breaking pressure and in the case of a DN400 pipe, the pipe obtained with the installation of Figure 1 and having undergone the heat treatment as described above with reference to FIG. 2 has a thickness of about 5.3 mm, whereas a pipe obtained with the conventional DeLavaud process and whose cast iron has a silicon content of less than 2.9% has a thickness greater than 6.5 mm.

FIG. 3 shows a second embodiment of a manufacturing installation 2 according to the invention.

The plant 2 and the method of manufacturing the pipe element according to this second embodiment differ from the installation and method described above solely by the following. Similar elements bear the same references.

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.

The temporary refractory material 50 is known per se and is for example a mixture of water, bentonite and refractory product based on silica. The temporary refractory material layer 50 reduces the cooling rate of the cast iron in the mold 10. Alternatively, the temporary refractory material 50 is replaced by a temporary thermal insulating material.

The manufacturing process using the installation 2 is a manufacturing process of the "Wetspray" type. This process is as follows.

Before pouring the molten iron into the mold 10, the temporary refractory material 50 is disposed on the inner surface 24 and forms a layer of temporary refractory material.

The next step is to cast the molten iron on the layer of temporary refractory material

Thanks to the layer of refractory material 50, the blank of the base body 16 or the blank of the cast iron object contains no or very little cementite. The spheroidal graphite cast iron has an essentially ferritic matrix with a low perlite content, especially less than or equal to 10%, since the Si content is greater than 3.2%.

FIG. 4 shows the temperature / time diagram during the heat treatment of the blank of the base body 16 or more generally of a blank of the cast iron object manufactured according to the "Wetspray" method by the installation 2 according to the second embodiment shown in Figure 3.

After extraction of the mold 10, the blank of the base body 16 or of the cast iron object undergoes a heat treatment, for this purpose, the blank of the basic body or the object is introduced into an oven 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 termination temperature of ferritization 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 converted into ferrite and graphite.

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

Then, in a third heat treatment step EW3, the blank of the base body or cast iron 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 base body 16 or of the cast iron object from the above-mentioned temperature situated between 20 ° C. and 100 ° C. at a relaxation temperature of between 600 ° C. and 700 ° C. ° C, then maintain the blank of the base body or cast iron object at this relaxation temperature for a period of between 10 minutes and 30 minutes.

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

The nominal diameter DN is for example greater than 600 mm.

Tests carried out show that, for an identical rupture pressure and in the case for example of a DN800 pipe, the pipe obtained with the installation of FIG. 3 and which has undergone the heat treatment described above with reference to FIG. Fig. 4 has a thickness of about 7.7 mm, whereas a pipe obtained with the conventional Wetspray process and whose cast iron has a silicon content of less than 2.9% has a thickness greater than or equal to 9.4 mm.

In Figure 5 we see that spheroidal graphite iron objects manufactured by the Wetspray process and comprising between 3.3% and 3.5% silicon have a tensile strength greater than 530 MPa.

Figure 6 shows the resilience E according to the "Charpy Sheep" impact test and shows that objects with spheroidal graphite cast iron contain between 3.3% and 3.5% of silicon and manufactured using the Wetspray process followed by a heat treatment ("WS Treaty ") as described above, have a resilience well beyond 10 Joules, unlike the spheroidal graphite cast iron obtained by the Wetspray process without subsequent heat treatment (" raw WS "in Figure 6) for which a Resiliency greater than 9.49 Joules is obtained only for silicon contents of less than 3%.

Similarly, FIG. 7 shows that the objects obtained by the Wetspray process followed by the heat treatment ("WS treated") according to the invention and having a silicon content of between 3.4 and 3.5% have a higher elongation A 15% and in particular between 18% and 22% approximately.

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

The composition of the spheroidal graphite cast iron according to the invention can also be used for the manufacture of a cast-iron road element such as a manhole or a rainwater drainage device, or for manufacturing foundry fittings. In this case, the method of manufacturing such objects is to cast the liquid iron in a mold and to inoculate simultaneously. Then, after extraction of 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 first consists in heating the blank of the object at a relaxation temperature greater than 400 ° C. and preferably between 600 ° C. and 700 ° C. Then, the blank of the cast iron object is maintained at this relaxation temperature for a period of between 10 minutes and about 30 minutes. Finally, the blank of the object is cooled to room temperature. The cast iron obtained at the end of this heat treatment makes it possible to reduce the weight of the road element or foundry connection relative to the known elements while maintaining a given mechanical strength, or else, at the same weight, makes it possible to increase the mechanical performance of the road element or foundry fitting.

In general, the resilience of the cast iron at room temperature (20 ° C) is greater than or equal to 10J or greater than or equal to 1 1 J. Resilience is measured in particular by the Charpy Sheep impact test. ".

The spheroidal graphite cast iron object according to the invention therefore makes it possible to obtain pipe elements or road elements with small wall thicknesses for a given mechanical strength or improved mechanical performance at similar wall thicknesses. Manufacturing and use, including transportation and handling, are therefore economical.

Claims

1. - Object (16) spheroidal graphite cast iron manufactured in a mold (10), the spheroidal graphite cast iron comprising, in% by weight, the following elements:

- Carbon (C) less than or equal to 3.65%,

- Silicon (Si) between 3.3% and 3.7%,

Optionally:

- Phosphorus (P) <0.1%, and / or

- Manganese (Mn) <0.6%, and / or

- Chromium (Cr) <0.2%, and / or

Titanium (Ti) <0.15%, and / or

- Sulfur (S) <0.05%, and / or

- Magnesium (Mg) between 0.005% inclusive and 0.07% inclusive, and / or

- Copper (Cu) <0.3%, and / or

- nickel (Ni) <0.4%, and / or

- Molybdenum (Mo) <0.02%, and / or

- Aluminum (Al) <0.02%, and / or

- Vanadium (V) <0.04%,

spheroidal graphite cast iron has a carbon equivalent C _E Q = C (%) + 1/3 If (%) +

1/3 P (%) less than or equal to 4.75% and in which

2. Object according to claim 1, wherein the spheroidal graphite cast iron has a resilience (E), in particular measured according to the "Charpy" impact test, greater than or equal to 10 Joules or greater than or equal to 1 Joules to 20 ° C.

3. Object according to claim 1 or 2, wherein the silicon content (Si) of the spheroidal graphite cast iron is between 3.4% and 3.6%.

4. Object according to any one of the preceding claims, wherein the silicon content (Si) of the spheroidal graphite cast iron is between 3.3% and 3.7%, preferably between 3.5% and 3, 6%, and in particular in which the object is obtained by a manufacturing method in which a shaped surface (24) is devoid of temporary thermal insulator or temporary refractory material (50) when casting the liquid iron in the mold (10).

5. Object according to any one of claims 1 to 3, wherein the silicon content (Si) of the spheroidal graphite cast iron is between 3.3% and 3.5%, preferably between 3.4% and 3.5%, and in particular in which the object is obtained by a manufacturing method in which a temporary refractory material (50) or a temporary thermal insulator is deposited on a shaped surface (24) before the step of pouring the molten iron into the mold (10).

6. Object according to any one of claims 1 to 5, wherein the carbon equivalent C _EQ = C (%) + 1/3 Si (%) + 1/3 P (%) of the spheroidal graphite cast iron is between 4.3% inclusive and 4.6% included or between 4.4% inclusive and 4.6% inclusive, and is preferably between 4.45% inclusive and 4.55% inclusive and is in particular equal to 4 , 5%.

7. Object according to any one of the preceding claims, wherein the spheroidal graphite cast iron has a tensile strength Rm greater than 470MPa, preferably greater than 500MPa and in particular greater than 530MPa.

8. Object according to any one of the preceding claims, wherein the spheroidal graphite cast iron has an elongation at break A greater than or equal to 7% and in particular greater than or equal to 10%.

9. Object according to any one of the preceding claims, wherein the spheroidal graphite cast iron has a Brinell hardness HB less than or equal to 250HB, and in particular less than or equal to 230HB.

10. A pipe element, such as a pipe or fitting, or a road element, such as a manhole or a rainwater drain, comprising a base body (16), characterized in that the basic body is an object according to any one of the preceding claims.

1 1. A method of manufacturing an article according to any one of claims 1 to 9 or a piping element or a road element according to claim 10, comprising the following successive steps:

a) pouring liquid iron into a mold (10) having a shaped surface (24),

b) the molten iron is allowed to solidify by obtaining a blank of the object; and c) the object blank is subjected to a heat treatment, in particular a relaxation treatment by obtaining the cast iron object (16).

12. Manufacturing process according to claim 1 1, wherein, before the step of pouring the molten iron in a mold, is implemented:

a step of establishing the silicon content of the cast iron, in particular by adding into the melting furnace or in a ladle silicon-containing materials, the silicon content added during this step corresponding to the final silicon content of the Spheroidal graphite cast iron of the object minus the silicon content eventually provided by spheroidization and inoculation treatments.

The manufacturing method according to claim 11 or 12, wherein the shaped surface (24) is free from temporary thermal insulator or temporary refractory material (50) when casting the molten iron into the mold (10). ), and wherein the heat treatment comprises:

a first step (ED1) for heating the blank of the object for a time of between 2 and 10 minutes until a graphitization temperature of greater than 800 ° C. is reached, and in particular greater than 900 ° C., but lower at 1000 ° C, this first step relaxing the internal stresses initially present in the cast,

a second graphitization step (ED2) during which the blank of the cast iron object is maintained at the graphitization temperature for a period of between 5 and 30 minutes, in particular between 5 and 18 minutes, and preferably 15 minutes,

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

a fourth ferritization step (ED4) during which the blank of the cast iron object is cooled slowly, at a rate of less than 40 ° C./minute, within a temperature range of between 700 ° C. and 780 ° C.

The manufacturing method according to claim 11 or 12, wherein the heat treatment comprises:

an air cooling step (EW2) up to a temperature of less than 100 ° C, and

a relaxation step (EW3) consisting of heating the blank of the cast iron object at a relaxation temperature of between 600 ° C. and 700 ° C. and then keeping the blank of the cast iron object at this temperature relaxation for a period of between 10 minutes and 30 minutes.

The manufacturing method according to claim 14, wherein a temporary refractory material (50) or a temporary thermal insulator is deposited on the shaped surface (24) prior to the step of pouring the molten iron into the mold (10). , and wherein the heat treatment further comprises:

a first ferritization step (EW1) of cooling the blank of the object slowly, at a cooling rate of less than 40 ° C / minute, of an inlet temperature in an oven, greater than or equal to 800 ° C up to a ferritisation end temperature below 740 ° C,

the step (EW2) of air cooling being a second step and the relaxation step being a third step (EW3).