Method for manufacturing cold-rolled corrugated stainless steel sheet

Abstract

To provide a method for manufacturing a sheet made of corrugated stainless steel involving a specific heat treatment enabling the structural modification of a material in a target zone, and to provide a sheet having good fatigue strength by improving the yield strength of a material of a sheet made of corrugated stainless steel.SOLUTION: A method for manufacturing a sheet made of corrugated stainless steel comprises: providing a sheet made of stainless steel (100); deforming a sheet made of stainless steel for making a corrugated sheet having a target zone exhibiting a geometric deformation ratio of 15-45% (110); heat treating a target zone at a temperature and for a heat treatment duration defined according to the composition of the stainless steel (120), in order to make the corrugated sheet having a recrystallized target zone; and cooling the corrugated sheet having the recrystallized target zone (130).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a corrugated stainless steel plate.

Background Art

[0002] This manufacturing method is, more specifically, intended to be implemented for the manufacture of corrugated stainless steel plates for use as a primary sealing membrane for the transport and / or storage of liquefied natural gas (also known by the initials LNG) within a tank.

[0003] The plate obtained by the manufacturing method of the present invention can be used, as a preferred but non-limiting exemplary example, for the manufacture of heat insulation and leak-proof walls of a support structure, for example, a tank incorporated into a ship's hull.

[0004] Such tanks are, for example, those used in liquefied gas carriers. They must be completely leak-proof and well-insulated in order to contain liquefied gas at low temperatures and limit its evaporation.

[0005] Referring to Figure 1A, these walls generally consist of two continuous sealing membranes, one of which is a primary 10 that contacts the product contained in the tank, and the other is a secondary 30 positioned between the primary membrane 10 and the support structure 50, with these two membranes alternating with two thermal barriers 20, 40. Thus, tank walls are known that consist of a primary thermal insulation material 20 associated with a primary membrane 10 made of stainless steel and a secondary thermal insulation material 40 associated with a flexible or rigid secondary membrane 30. This secondary membrane 30 includes, for example, at least one thin continuous metal plate, sandwiched and bonded between two glass fiber fabrics, made of aluminum, and a binder that can ensure the bond between the glass fabric and the aluminum. These tank thermal and leakproof walls are preferably manufactured from an assembly of prefabricated panels. Generally, each prefabricated panel has a general rectangular shape, and the primary insulation element 20 and secondary insulation element 40 have the form of a first rectangle and a second rectangle, respectively, with substantially parallel sides in a plan view, the length and / or width of the first rectangle being shorter than that of the second rectangle in order to form a perimeter boundary. The perimeter boundaries of adjacent secondary insulation elements 40 and the side walls of primary insulation elements 20 define a passage 24 that can extend throughout the entire length, width, or height of the tank. Continuity of the primary insulation 20 is achieved by inserting blocks 25 into the passage 24. To ensure the continuity of the secondary membrane 30, at the joint between two adjacent panels, the aforementioned perimeter boundary is covered with a strip of flexible ply 35 comprising at least one continuous thin metal plate, prior to the placement of the aforementioned blocks 25. The installation of these different panels involves a very rigorous work mode and high installation precision to ensure the insulation and sealing of the tank.

[0006] Another modification of the tank wall is partially shown in Figure 1B. In this modification, the wall also consists of two continuous sealed membranes, one primary 10 in contact with the product contained in the tank, and the other secondary 30 positioned between the primary membrane 10 and the support structure 50, with these two membranes alternating with two thermal insulation barriers 20, 40. In this modification, the secondary membrane 30 may be tightly stretched and can be made of corrugated primary membrane 10 made of Invar® or a high manganese content alloy and stainless steel. The thermal insulation panels of the thermal insulation barriers 20, 40 are preferably made of reinforced polyurethane foam.

[0007] The tanks of such ships are subjected to numerous stresses. Therefore, cooling the tanks before filling to very low temperatures, for example, around -160°C for methane, or even close to -170°C, can cause stress due to various thermal contractions of the materials forming the walls. Furthermore, ships are subjected to numerous stresses during navigation, such as swells, which can cause deformation of the hull and, consequently, the tank walls. The movement of cargo can also cause stress on the tank walls due to overpressure or backpressure.

[0008] It should be noted that the arrangement of one or more insulating elements and films is provided above as an example and is not limiting. More specifically, the present invention relates to the primary films described below.

[0009] The primary film 10 includes corrugations extending across its surface. The purpose of these corrugations is to give the primary film flexibility to adapt to the thermal contraction of the steel as the tank cools. Thus, as shown in Figure 2, the surface of the primary film can be defined by flat zones 11, waves 12, and nodes 13. These nodes 13 thus originate from the deformation and are the locations of metallurgical deformation of the material that constitutes the plate. As a result, the nodes 13 form geometric stress regions.

[0010] When liquefied natural gas is transported and / or stored, the primary membrane 10 comes into direct contact with the liquefied natural gas. Therefore, as described above, node 13 is an area where the risk of failure due to accumulated fatigue increases when the corrugated plate is used as a primary sealing membrane for transporting and / or storing LNG. In fact, the bending motion of the ship's keel beam acts on the ship's double hull, and thus the membrane. [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention aims to alleviate all or part of the above problems by proposing a method for manufacturing a corrugated stainless steel sheet having a specific heat treatment that allows for modification of the material structure within a target zone, and thus providing a sheet with better fatigue strength by improving its yield strength. [Means for solving the problem]

[0012] For this purpose, the subject of the present invention is a method for manufacturing corrugated cold-rolled stainless steel sheets, The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5% 16% ≤ Cr ≤ 20%, 0% <N≦0.2%、 0% <P≦0.045%、 0% <S≦0.015%、 To provide cold-rolled stainless steel sheets having a composition containing iron and residual elements resulting from the manufacturing process, Deformation of a stainless steel plate to obtain a corrugated plate having a target zone exhibiting a geometric deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%, To obtain a corrugated plate having a recrystallized target zone, heat treatment of the target zone of the corrugated plate at a temperature and heat treatment duration defined according to the stainless steel composition, and cooling of the corrugated plate having a recrystallized target zone, which is a method including.

[0013] In one embodiment, the nickel and nitrogen contents of the stainless steel represented by weight are -4%≦Ni≦8% -0.05%<N≦0.2% are such that

[0014] The duration of the heat treatment is defined according to the temperature of the heat treatment.

Table 1

[0015] In another embodiment, the nickel and nitrogen contents of the stainless steel represented by weight are -8%<Ni≦10.5% -0%<N≦0.1% are such that.

[0016] The duration of the heat treatment is defined according to the temperature of the heat treatment.

Table 2

[0017] Advantageously, the cooling of the corrugated plate having a recrystallized target zone is carried out at a rate of 50°C / second or more.

[0018] Advantageously, the heat treatment is carried out in a continuous furnace.

[0019] Advantageously, the heat treatment and / or cooling is carried out in an inert or reducing environment.

[0020] Advantageously, the heat treatment is carried out in a continuous furnace.

[0021] In another embodiment of the manufacturing method according to the present invention, the heat treatment may be carried out by applying a heating bell to the target zone.

[0022] Advantageously, the cooling of the corrugated plate having the recrystallized target zone is carried out by tempering in a tempering fluid.

[0023] Advantageously, cooling of the corrugated plate having the recrystallized target zone can preferably be carried out by pressurized injection of a tempering fluid at ambient temperature.

[0024] The manufacturing method according to the present invention may further include a step of cleaning the corrugated plate before heat treatment.

[0025] The present invention also relates to a sealed, insulated tank comprising at least one corrugated plate having a recrystallized target zone obtained by such a manufacturing method.

[0026] The present invention also, The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5% 16% ≤ Cr ≤ 20%, 0% <N≦0.2%、 0% <P≦0.045%、 0% <S≦0.015%、 Regarding corrugated cold-rolled stainless steel sheets having a composition containing iron and residual elements resulting from manufacturing, The corrugated plate has a waveform that defines at least one target zone exhibiting a geometric deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%, wherein at least one target zone is recrystallized.

[0027] Advantageously, the corrugated plate has a first waveform in a first direction and a second waveform in a second direction substantially perpendicular to the first direction, and there is a node at their intersection having at least one target zone.

[0028] The present invention also relates to a sealed, insulated tank comprising at least one such corrugated plate.

[0029] These features and advantages of the present invention, as well as other features and advantages, will become more apparent from the following description given with reference to the attached drawings, which are given as non-limiting examples. [Brief explanation of the drawing]

[0030] [Figure 1A] This is a schematic cross-sectional view of a conventional tank wall. [Figure 1B] This is a schematic diagram of another tank wall using conventional technology. [Figure 2] This represents different regions of conventional corrugated plates. [Figure 3] This diagram shows the steps of the manufacturing method according to the present invention. [Figure 4] The details of the nodes of the corrugated plate obtained after the plate deformation step of the manufacturing method according to the present invention are shown. [Figure 5] The steps of the heat treatment step and cooling step in a continuous furnace of the manufacturing method according to the present invention are schematically shown. [Figure 6] The microstructure details of the corrugated cold-rolled stainless steel sheet obtained by the manufacturing method according to the present invention are shown. [Figure 7] The microstructure details of a corrugated cold-rolled stainless steel sheet obtained by a method different from the manufacturing method according to the present invention are shown. [Figure 8] The results of tests conducted on different samples, one using the manufacturing method according to the present invention and the other not using it, are shown. [Figure 9] This diagram shows a simplified representation of the deformation of a plate. [Modes for carrying out the invention]

[0031] For clarity, the same element has the same reference number in different figures.

[0032] In the following, stainless steel sheets should be understood as stainless steel pieces obtained by cold rolling, having a rectangular, thin parallelepiped shape, for example, with a thickness of 0.15 to 5 mm. Furthermore, the term "corrugated" also means wavy, and corrugated sheets should be understood as sheets that exhibit a wavy or undulating surface.

[0033] Preferably, in the context of the present invention, the stainless steel plate has a thickness of 0.5 to 2 mm. Its width is preferably 200 cm or less, and its length is preferably 400 cm or less. However, other dimensions can be assumed by adapting the means used when carrying out the method of the present invention, in particular the size of the furnace which will be described below in the description of the present invention.

[0034] Figure 1A is a schematic cross-sectional view of a conventional tank wall. The plate manufactured by the method of the present invention can replace the primary film 10. This figure has already been described.

[0035] Figure 1B is a schematic diagram of another tank wall of the prior art. The plate manufactured by the method of the present invention can replace the primary membrane 10. This figure has already been described.

[0036] Figure 2 shows different regions of a conventional corrugated plate. This figure has already been explained.

[0037] Figure 3 shows a flowchart of the steps of the manufacturing method according to the present invention. The method for manufacturing corrugated cold-rolled stainless steel sheets according to the present invention is as follows: The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5% 16% ≤ Cr ≤ 20%, 0% <N≦0.2%、 0% <P≦0.045%、 0% <S≦0.015%、 The step 100 includes providing a cold-rolled stainless steel sheet having a composition including

[0038] Optionally, the composition of the stainless steel plate provided may include molybdenum (Mo ≤ 3%) in a weight-based content of 3% or less and / or copper (Cu ≤ 0.5%) in a weight-based content of 0.5% or less.

[0039] The remainder of the composition consists of unavoidable impurities resulting from the manufacture of iron and steel. The microstructure of this stainless steel is essentially austenitic (in the form of metastable austenite). The average size of the austenite grains, also called primary austenite, is between 6 μm (micrometers) and 35 μm (micrometers).

[0040] The manufacturing method includes, for example, step 110 of deforming a stainless steel plate by folding or stamping in order to obtain a corrugated plate that includes a waveform defining a target zone, which exhibits a geometric deformation ratio of 15% to 45% (preferably less than 35%) for deformation performed by folding, or a cross-sectional reduction ratio within the target zone of less than 25% for deformation performed by stamping.

[0041] The cross-sectional reduction ratio can be viewed as the ratio between the cross-sectional areas of the steel before and after deformation. Initial cross-section: 5 mm 2 Cross-section after deformation: 4.5 mm 2 The cross-sectional reduction ratio of a plate with a stamping type is 10%.

[0042] The geometric deformation ratio is a ratio that represents the geometric deformation of a plate in three dimensions. This can be determined by numerical calculation according to a formula known to those skilled in the art. Figure 9 is a simplified diagram showing the deformation of a plate. For illustrative purposes, in a simplified manner, considering only a single dimension, for a neutral fiber segment length Fn (indicated by a thick dotted line l0 in Figure 9) l0 = 100 mm and an outer fiber segment length ld = 110 mm (indicated by a thin dotted line in Figure 9, where ld = l0 + Δl), a folded plate of thickness Ep (see Figure 9) exhibits a deformation ratio of 10% such that the material along this outer fiber is not altered by the folding of the plate.

[0043] Step 110 of the plate deformation allows for the formation of corrugations or undulations on the plate. These corrugations 15 can be seen in Figure 4. The purpose of these corrugations is to give the plate flexibility for use in transporting and / or storing liquefied gases.

[0044] Figure 4 shows details of a node 13 of a corrugated sheet obtained after step 110 of sheet deformation. In Figure 4, after the deformation step, the corrugated sheet has a first wave 15 in a first direction and a second wave 16 in a second direction substantially perpendicular to the first direction. A node 13 is located at the intersection of the first wave 15 and the second wave 16. It comprises a target zone 14 exhibiting a deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%. This deformation / reduction ratio is specific to the deformation step and can be determined by calculation methods known to those skilled in the art. These deformation ratios result in the appearance of a greater martensite content in the target zone 14 of the node 13.

[0045] Step 110 of the plate deformation causes a change at the microstructural level of the stainless steel in the target zone 14. The metastable austenite of the stainless steel, which initially exists in the form of particles with an average size of 6 to 35 micrometers, transforms into a mixture of austenite and martensite. The martensite takes the form of lamellae with dimensions smaller than the primary austenite particles of the steel plate before deformation.

[0046] The deformation of primary austenite into martensite is partial. After deformation, the ratio of austenite to martensite depends on several factors, particularly the initial composition of the stainless steel and the level of deformation / section reduction of the sheet. In other words, given the same deformation, the ratio of austenite to martensite will differ for two stainless steel sheets of different compositions. Similarly, for a given initial steel composition, the ratio of austenite to martensite will differ depending on the point on the sheet considered (target zone, wave or flat zone) due to the difference in the deformation / section reduction ratio that occurs at that point on the sheet.

[0047] The target zone 14 exhibits a geometric deformation ratio between 15% and 45%, or a locally reduced cross-sectional area ratio within the target zone of less than 25%. The term geometric deformation ratio is used for the target zone obtained following the deformation step by folding. The term reduced cross-sectional area ratio is used for the target zone obtained following the deformation step by stamping. As previously explained, these target zones 14 form the geometrically stressed zones and are therefore zones that show a risk of failure due to increased fatigue. In the target zone 14, the austenite particles are transformed, at least partially, into martensite lamellae during the deformation step 110.

[0048] The steps of the manufacturing method according to the present invention, as described below, make it possible to improve the fatigue strength of the target zone 14 without degrading the mechanical properties of the zones adjacent to the target zone 14.

[0049] The manufacturing method according to the present invention includes, after step 110 of plate deformation, step 120 of heat treatment of the corrugated plate including the target zone 14, at a temperature and heat treatment duration defined according to the composition of the stainless steel, in order to obtain a corrugated plate having a recrystallized target zone. The recrystallization of the target zone is described below. In the context of the present invention, the recrystallization temperature is 700 to 900°C and the heat treatment duration is 5 seconds to 40 minutes.

[0050] In the context of the present invention, the heat treatment 120 of the component means heating the component and maintaining its temperature.

[0051] More specifically, -4%≦Ni≦8% -0.05% <N≦0.2% Regarding the nickel and nitrogen content of stainless steel expressed by weight, The duration of heat treatment 120 is defined as follows, according to the heat treatment temperature: [Table 3]

[0052] In other words, the duration of the heat treatment is directly related to the heat treatment temperature. For this nickel and nitrogen content of the steel under consideration, at a temperature of 700°C, the heat treatment duration is 15-40 minutes. At a temperature of 750°C, the heat treatment duration is 5-20 minutes, and so on.

[0053] moreover, -8% ≤ No ≤ 10.5% -0 <N≦0.1% Regarding the nickel and nitrogen content of stainless steel expressed by weight, The duration of heat treatment 120 is defined as follows, according to the heat treatment temperature: [Table 4]

[0054] It will be more generally apparent to those skilled in the art that various modifications can be made to the embodiments described above in light of the teachings disclosed herein. The present invention is defined by a range of heat treatment durations, for example, 750°C or 800°C. However, the present invention also applies to heat treatment temperatures within the indicated limits. For example, in the case of a heat treatment temperature of 775°C (i.e., between the indicated temperatures of 750°C and 800°C), those skilled in the art will know, based on the description of the present invention, that the heat treatment duration must be adapted to 4 to 8 minutes.

[0055] In step 120 of the heat treatment, the martensite lamellae present in the corrugated plate are broken down, transforming them into austenite particles smaller in size than the martensite lamellae (and therefore much smaller in size than the initial austenite particles in the steel of the plate before deformation). In other words, the heat treatment transforms the martensite in the target zone into austenite that has mostly fine particles. Typically, the percentage of residual martensite after heat treatment is 4% or less. These zones are called recrystallization target zones. In other words, the target zones are recrystallized when their martensite microstructure transforms into an austenite microstructure with fine particles, called a secondary microstructure. The production of these austenite nanoparticles, or more generally, the refinement of the austenite microstructure into smaller particles, allows for better performance in terms of the yield strength of the material. This improvement in yield strength has a beneficial effect on the fatigue strength of the target zones in question.

[0056] Finally, the manufacturing method according to the present invention includes a step 130 of cooling the corrugated plate having the recrystallized target zone. The step 130 of cooling the corrugated plate having the recrystallized target zone stops the growth of particles throughout the plate, and its purpose is to establish a microstructure in the form of austenite nanoparticles obtained by the heat treatment 120.

[0057] Figure 5 schematically shows the heat treatment step and cooling step in a continuous furnace of the manufacturing method according to the present invention.

[0058] In the embodiment shown in Figure 5, the heat treatment 120 is carried out in a continuous furnace 20. Advantageously, the heat treatment step 120 and the cooling step 130 are carried out in an environment that protects against surface contamination. It should be noted that the heat treatment 120 may alternatively be carried out in a vacuum furnace. The purpose of these particular environments is to prevent the formation of scale or any other contamination on the surface of the corrugated plate. These surface contaminations should be avoided in order to omit a descaling step (mechanical, chemical, or otherwise) after the heat treatment. However, the method according to the present invention may also include a descaling step after the heat treatment 120, particularly if the heat treatment environment is not protective against surface contamination.

[0059] Advantageously, the manufacturing method according to the present invention may further include a corrugated plate cleaning step 115 prior to the heat treatment 120. The purpose of the cleaning step 115 is to remove all trace contaminants, significant fatty substances, or metal chips present on the corrugated plate.

[0060] As shown in Figure 5, the corrugated sheet is placed on a moving floor 21, such as a set of mats or rollers, which passes directly through the furnace 20. As the floor 21 moves in direction 22, the corrugated sheet is displaced inward 20 into a first zone 23 called the input zone. The input zone 23 is an unheated zone. In contrast, in the case of a controlled environment, the input zone 23 is in a controlled environment. Thus, without disrupting the environment, by translating the floor in direction 22, the corrugated sheet is then transferred to a second zone 24 called the heating zone. The heat treatment step 120 is performed in the heating zone 24, which is the zone in which the corrugated sheet is exposed to the target temperature for an appropriate duration. As an example, for a stainless steel corrugated sheet with nickel and nitrogen content of 6% and 0.15% by weight, respectively, and the heating zone 24 set to 800°C, the exposure time is 5-10 minutes, for example, 8 minutes. Tests have been conducted by the applicant to determine the above exposure time range for a given temperature and composition of the stainless steel of the corrugated sheet.

[0061] The forward speed of the floor as it passes through the continuous furnace 20 is calculated as a function of the length of the heating zone 24 to obtain the desired exposure time. For example, in the case of a continuous furnace with a heating zone 10 m long and an exposure time of 5 minutes at 800°C, the floor speed is set to 2 m / min.

[0062] Alternatively, a gradual advancement of the floor could be considered, according to the dimensions of the corrugated board, to limit the time that the corrugated board exists in two steps simultaneously.

[0063] It should be noted that in this example, the floor is capable of translational movement. However, the same principle applies to other types of movement, particularly rotational movement using a rotating carriage furnace, and to parts of small dimensions, preferably, for example, about 30 cm x 50 cm (or larger depending on the size of the furnace). The present invention is based on heat treatment at a predetermined temperature and duration within a heating zone.

[0064] At the end of the exposure time in heating zone 24, the corrugated plate undergoes rapid cooling, such as over-tempering cooling.

[0065] The heat treatment step 120 and / or cooling step 130 are preferably carried out in an inert or reducing environment to avoid the formation of oxides on the surface of the plate. In the cooling step 130, a tempering fluid is then selected from among fluids that protect from oxidation. In both cases (heat treatment step 120 and cooling step 130), nitrogen hydride, argon, helium, or possibly pure hydrogen may also be considered. Alternatively, if cooling is not carried out in an inert or reducing environment, or further, if the corrugated plate has a recrystallized target zone, it may be subjected to a descaling step after the cooling step 130 to remove any undesirable residues that may be present on the surface of the plate.

[0066] In the case of the continuous furnace 20 shown in Figure 5, cooling 130 is performed by transferring the corrugated plate having the recrystallized target zone to the tempering zone 25 adjacent to the heating zone 24 in the forward direction 22 of the floor.

[0067] Advantageously, the cooling step 130 is carried out very quickly, for example, at a rate of 50°C / second or more.

[0068] For the reasons mentioned above, the heat treatment 120 and / or cooling 130 are preferably carried out in an inert or reducing environment.

[0069] In the case of heat treatment 120 in a vacuum furnace or a controlled environment, cooling 130 is carried out by pressurized injection of tempering fluid at ambient temperature.

[0070] In another embodiment, the heat treatment 120 can be carried out by applying a local heating means, such as a heating bell, to the target zone. For this purpose, the heating bell is positioned on the nodes enclosing the corrugated plate form. Inductive or convective heating means can also be envisioned, particularly for short-duration heat treatments.

[0071] As mentioned above, the heat treatment is performed on thin plates (typically having a thickness of 0.5 mm to 2 mm), and the immersion time is estimated to be close to the skin heating time. Therefore, the immersion time is considered to be shorter than the exposure time defined in the manufacturing method of the present invention.

[0072] If the heating means of the furnace's heating zone does not allow the placement of the plate to be processed in a heating zone already heated to the target temperature (e.g., a vacuum furnace), the effect of the temperature rise gradient is taken into account by shortening the time the target temperature is maintained. This shortening becomes even greater when the heat treatment temperature is high and the heating rate is slow. Note that if the heat treatment time is less than 5 minutes, it is not possible to raise the temperature gradually to the target temperature.

[0073] The manufacturing method may also include step 125 of adjusting the floor advance speed as a function of the temperature within the heating zone 24 in order to better control the duration of the heat treatment and, if necessary, take into account the temperature rise gradient. For example, for parts of greater thickness, the floor advance speed is adjusted to be less than the advance speed for parts of thinner thickness.

[0074] Therefore, the manufacturing method according to the present invention relies on a heat treatment optimized as a function of the chemical composition of the steel sheet. The heat treatment duration and temperature parameters are selected to obtain a satisfactory return of martensite to austenite within the target zone of the node, while limiting the growth of primary (i.e., within the non-deformable zone of the node) and secondary (within the deformable zone) austenite particles.

[0075] The manufacturing method of the present invention is based on a heat treatment specific to the target zone, a zone weakened for deformation to obtain a corrugation essential for planned liquefied gas transport / storage applications. The heat treatment of the present invention allows for the transformation of martensite present in the target zone into secondary austenite with smaller particle sizes. This results in better mechanical properties of the target zone. In other words, the present invention utilizes a partial transformation at the microstructural level of the target zone via martensite formed after heat treatment to obtain martensite lamellae and austenite particles smaller in size than the austenite particles initially present in the stainless steel.

[0076] A corrugated plate having a recrystallization target zone, manufactured by the manufacturing method according to the present invention, can be used as a component in the manufacture of a sealed membrane (primary membrane 10) for transporting and / or storing liquefied gas at cryogenic temperatures.

[0077] Figure 6 shows the microstructure details of a corrugated cold-rolled stainless steel sheet obtained by the manufacturing method according to the present invention. In this magnified view (1000x), the boundaries of the austenite particles 60 initially present in the cold-rolled stainless steel sheet can be seen. These particles are transformed into martensite in the form of lamellae 61, at least partially. Through the adapted heat treatment of the manufacturing method according to the present invention, the lamellae 61 are transformed into so-called secondary austenite in the form of fine particles 62 or nanoparticles. It is the refinement of the primary austenite particles 60 into secondary austenite nanoparticles 62 that makes it possible to obtain better mechanical properties by improving the yield strength of the sheet thus produced. The average size of the secondary austenite particles is 0.2 μm (micrometers) to 2 μm (micrometers), and may be less than 0.2 μm.

[0078] Figure 7 shows the microstructure details of a corrugated cold-rolled stainless steel sheet obtained by a method different from the manufacturing method according to the present invention. In this example, the corrugated sheet has undergone an excessively long heat treatment, i.e., a duration exceeding the heat treatment time of the method according to the present invention. In other words, the corrugated sheet detailed in Figure 7 is not obtained by the manufacturing method according to the present invention.

[0079] In this magnified view (500x), we can see the boundaries of austenite particles 60 that are similar in size to those initially present in cold-rolled stainless steel. Faint traces of martensite lamellae 61 are visible. As can be seen, excessive heat treatment time did not result in the formation of secondary austenite nanoparticles. On the contrary, the heat treatment annealed the material. The resulting microstructure contains a mixture of primary austenite particles and secondary austenite particles that have grown significantly to a size close to that of the primary austenite particles.

[0080] The microstructures shown in Figures 6 and 7 highlight the importance of the heat treatment step 120. In fact, it is essential, on the one hand, to consider the chemical composition of the steel used, and on the other hand, to match the duration of the heat treatment to the exposure time. If the duration of the heat treatment is less than the duration of the method of the present invention, a significant proportion of the martensite lamellae will not have time to be transformed into austenite nanoparticles. Also, if the duration of the heat treatment is longer than the duration of the method of the present invention, the martensite lamellae in the annealing material will be transformed back into larger austenite particles.

[0081] Figure 8 shows the results of tests performed on different samples using and without the manufacturing method according to the present invention. The x-axis represents the number of cycles to fracture (N). The Y-axis represents repeated elongation. In this particular case, the repeated elongation (Ec) is 0.55 mm. This coefficient is the same for all tests presented below. The samples are portions of cold-rolled corrugated sheets deformed according to step 110, and include a complete node. Each sample was repeatedly elongated, and the number of cycles to fracture of the sample was observed. Fracture may be reflected, for example, by cracks in the target zone.

[0082] As shown in Figure 4, two samples of stainless steel sheet that have been cold-rolled and then deformed (i.e., undergone deformation step 110), 304L of material with the following composition (weight percent): 0.0159% C, 0.57% Si, 1.135% Mn, 0.0243% P, 0.0027% S, 18.272% Cr, 9.310% Ni, 0.116% Cu, 0.039% Mo, and 0.0175% N. 301LN with a composition (weight percent) of 0.025% C, 0.52% Si, 1.70% Mn, 0.033% P, 0.003% S, 17.32% Cr, 6.63% Ni, 0.25% Cu, and 0.108% N. The test was conducted using a heat treatment step and a cooling step.

[0083] These samples underwent different heat treatments in a protected environment. The average life (number of cycles) calculated using the ISO-stress method is as follows: Unheat-treated 304L ("raw 304L") - 155147 cycles, 304L (by the method of the present invention) - 470467 cycles, heat-treated at 800°C for 6 minutes. 304L (outside range) - 134,400 cycles, heat-treated at 800°C for 10 minutes. Untreated 301LN ("raw 301LN") - 1,896,400 cycles, No fracture was observed in 301LN-2,000,000 cycles after heat treatment at 800°C for 5 minutes (within range) (the test was stopped at 2,000,000 cycles).

[0084] Please note that the number of cycles shown is an average obtained from several tests conducted under given conditions.

[0085] The raw sample 304L constitutes the reference sample, including target zone 14. Its lifetime is 155,147 cycles.

[0086] The same sample was subjected to the method of the present invention in a heat treatment step of 800°C for 6 minutes (304 L of sample at 800°C for 6 minutes). Its lifespan changed to 470,467 cycles (i.e., three times more than the reference sample).

[0087] The same sample was subjected to a heat treatment step of 800°C for 10 minutes (304L sample 800°C / 10 min) using a method not corresponding to the present invention. Its lifespan changed to 134,400 cycles. In other words, its lifespan decreased compared to the reference sample. Excessively long heat treatments can not only fail to improve the yield strength of the sample but can also adversely affect its lifespan.

[0088] The raw 301LN sample constitutes another reference sample containing target zone 14. Its lifetime is 1,896,400 cycles.

[0089] The same sample was subjected to the method of the present invention in a heat treatment step of 800°C for 5 minutes (301LN800°C / 5 min). Its lifespan was 2,000,000 cycles, after which no cracks were detected (i.e., at least 1.05 times longer than the reference sample).

[0090] Another test was performed at a higher load level ("high load level" with repeated elongation (Ec) of 0.7 mm), with one test per condition. The mean lifespan (number of cycles) given by the iso-stress method is as follows: Untreated 301LN ("raw 301LN") - 367,200 cycles, 301LN heat-treated at 750°C for 10 minutes (within the duration range corresponding to the method of the present invention) - 2,000,000 cycles without observed fracture (test stopped at 2,000,000 cycles).

[0091] The raw 301LN sample constitutes another reference sample, including target zone 14. Its lifetime at high load levels is 367,200 cycles.

[0092] The same sample was subjected to the method of the present invention in a heat treatment step of 750°C for 10 minutes (301LN 750°C / 10 min). The life at high load levels was 2,000,000 cycles without detection of cracks (i.e., at least 5.44 times greater than the reference sample). Tests performed on different samples with or without the manufacturing method according to the present invention clearly demonstrate the improved fatigue strength of the samples tested by the method of the present invention. Microscopic observations highlight the effect of heat treatment on microstructural formation and, consequently, on the yield strength performance level.

[0093] The present invention also, The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5% 16% ≤ Cr ≤ 20%, 0% <N≦0.2%、 0% <P≦0.045%、 0% <S≦0.015%、 Regarding corrugated cold-rolled stainless steel sheets having a composition including, The corrugated plate includes a waveform that defines at least one target zone 14 exhibiting a geometric deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%, wherein at least one target zone is recrystallized.

[0094] Advantageously, the corrugated plate has a first wave 15 in a first direction and a second wave 16 in a second direction substantially perpendicular to the first direction 15, with a node 13 at their intersection containing at least one target zone 14.

[0095] The present invention also relates to a sealed, insulated tank comprising at least one such corrugated plate.

[0096] It will become more common to those skilled in the art that various modifications can be made to the embodiments described above in light of the disclosed teachings. In the following claims, the terms used should not be construed as limiting the claims to the embodiments described herein, but rather as being intended to encompass, by their formulation, all equivalents within the scope of those skilled in the art based on general knowledge.

Claims

1. A method for manufacturing corrugated cold-rolled stainless steel sheets, The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5%, 16% ≤ Cr ≤ 20%, 0% < N ≤ 0.2%, 0% < P ≤ 0.045%, 0% < S ≤ 0.015%, The provision of a cold-rolled stainless steel sheet having a composition containing iron and residual elements resulting from the manufacturing process (100), Deformation (110) of the stainless steel plate to obtain a corrugated plate having a target zone exhibiting a geometric deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%, To obtain a corrugated plate having a recrystallized target zone, the target zone of the corrugated plate is heat-treated (120) at a temperature and heat treatment duration defined according to the composition of the stainless steel, The process includes cooling (130) the corrugated plate having a recrystallized target zone, The aforementioned manufacturing method -4% ≤ Ni ≤ 8% -0.05% < N ≤ 0.2% Regarding the nickel and nitrogen content of the stainless steel expressed by weight, The heat treatment duration (120) is defined according to the temperature of the heat treatment, Table 1 -8% < Ni ≤ 10.5% -0 < N ≤ 0.1% Regarding the nickel and nitrogen content of the stainless steel expressed by weight, A manufacturing method characterized in that the duration of the heat treatment (120) is defined according to the temperature of the heat treatment. Table 2

2. The manufacturing method according to claim 1, wherein the cooling (130) of the corrugated plate having the recrystallized target zone is carried out at a rate of 50°C / second or more.

3. The manufacturing method according to any one of claims 1 and 2, wherein the heat treatment (120) is carried out in a continuous furnace.

4. The manufacturing method according to any one of claims 1 and 2, wherein the heat treatment (120) and / or the cooling (130) are carried out in an inert or reducing environment.

5. The manufacturing method according to any one of claims 1 and 2, wherein the heat treatment (120) is carried out in a vacuum furnace.

6. The manufacturing method according to any one of claims 1 and 2, wherein the heat treatment (120) is carried out by applying a heating bell to the target zone.

7. The manufacturing method according to any one of claims 1 and 2, wherein the cooling (130) of the corrugated plate having a recrystallized target zone is carried out by tempering in a tempering fluid.

8. The manufacturing method according to any one of claims 1 and 2, wherein the cooling (130) of the corrugated plate having a recrystallized target zone is preferably carried out by pressurized injection of a tempering fluid at ambient temperature.

9. The manufacturing method according to any one of claims 1 and 2, further comprising the step (115) of cleaning the corrugated plate before the heat treatment (120).

10. The content is expressed by weight. 0.005% ≤ C ≤ 0.05% and preferably C ≤ 0.03% 0.1% ≤ Si ≤ 1%, 0.5% ≤ Mn ≤ 2%, 4% ≤ Ni ≤ 10.5%, 16% ≤ Cr ≤ 20%, 0% < N ≤ 0.2%, 0% < P ≤ 0.045%, 0% < S ≤ 0.015%, A corrugated cold-rolled stainless steel sheet having a composition containing iron and residual elements resulting from the manufacturing process, Corrugated cold-rolled stainless steel sheet, wherein the corrugated sheet has a waveform that defines at least one target zone (14) exhibiting a geometric deformation ratio of 15% to 45%, preferably less than 35%, or a cross-sectional reduction ratio within the target zone of less than 25%, and the at least one target zone is recrystallized.

11. The corrugated plate according to claim 10, wherein the corrugated plate has a first wave (15) in a first direction and a second wave (16) in a second direction substantially perpendicular to the first direction (15), and a node (13) having at least one target zone (14) is present at the intersection thereof.

12. A sealed, insulated tank comprising at least one corrugated plate as described in any one of claims 10 and 11.

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