A COATED STEEL SUBSTRATE

Abstract

The present invention relates to a coated stainless steel substrate comprising a coating comprising nanographites and a bonding agent being sodium silicate, wherein the stainless steel substrate has the following composition by weight percent: C = 1.2%, Cr = 11.0%, Ni = 8.0%, and on a purely optional basis, one or more elements such as: Nb = 6.0%, B = 1.0%, Ti = 3.0%, Cu = 5.0%, Co = 3.0%, N = 1.0%, V = 3.0%, Si = 4.0%, Mn = 5.0%, P = 0.5%, S = 0.5%, Mo = 6.0%, Ce = 1.0%, the remainder of the composition being iron and unavoidable impurities resulting from manufacturing. The invention also relates to a method for manufacturing this coated stainless steel substrate.

Description

A COATED STEEL SUBSTRATE The present invention relates to a proposed coating for protecting stainless steel used as components in the hot-dip coating process of steel strips from molten metal corrosion. The present invention also relates to the method for manufacturing the coated stainless steel and to the hot-dip coating process using the coated stainless steel. Typically, in steel rail production, steel strips are coated with a metallic coating deposited by hot-dip galvanizing or hot-dip aluminizing. This metallic coating contains elements usually selected from zinc, aluminum, silicon, magnesium, etc. These elements are melted in a bath through which the steel strip passes. To accomplish this, certain metal devices or parts, such as the nozzle, dip roll, stabilizing rollers, pipes, or pumping elements, are in direct contact with the molten bath. During contact, a reaction occurs between the molten metal and the submerged part. In particular, zinc and / or aluminum form intermetallic compounds with the iron in the metal device, resulting in embrittlement of the submerged part. To limit this molten metal-induced corrosion, metal devices or parts that will be used in contact with molten metal are usually made of stainless steel. Despite the improved resistance to molten metal corrosion, stainless steel in contact with molten metal is susceptible to corrosion, leading to deformation, embrittlement, and degradation. For example, the bottom of a nozzle made of stainless steel can be submerged for months in a molten bath. During this immersion, the molten metal attacks the nozzle, resulting in a thinner nozzle wall thickness which, combined with the high temperature, causes tool cracking.Due to molten metal corrosion, the nozzle often requires inspection, maintenance, and replacement. These regular inspections, maintenance, and replacements result in line stoppages, which severely disrupt the production of hot-dip coated steel strips. Patent application CN201172680 describes a nozzle for a galvanizing bath of cold-rolled steel strip that includes an upper frame and a lower frame, the upper frame being made of welded stainless steel plates and the lower frame being made of an aluminum oxide ceramic. However, this nozzle, which comprises two parts made of two materials—stainless steel and aluminum oxide ceramic—is difficult to produce. The aluminum oxide ceramic is melted to form the lower part of the nozzle. Aluminum oxide has a very high melting point, around 2000 °C. Consequently, new equipment is needed to produce this part, which significantly impacts the nozzle's cost. Therefore, the purpose of the invention is to provide a stainless steel substrate well protected against molten metal corrosion, such that inspections, maintenance, and replacements are minimized and embrittlement, deformation, and degradation are further prevented. Furthermore, the object of the invention is to provide an easy-to-implement method for producing this stainless steel substrate without replacing existing equipment in hot-dip galvanizing and hot-dip aluminizing lines. For this purpose, a first object of the present invention consists of a coated stainless steel substrate comprising a coating comprising nanographites and a bonding agent that is sodium silicate, wherein the stainless steel substrate has the following composition in weight percent: C <1.2%, Cr>11.0%, Ni > 8.0% and on a purely optional basis, one or more elements such as: Nb < 6.0%, B<1.0%, Ti < 3.0% Cu < 5.0%, Co < 3.0%, N < 1.0%, V < 3.0%, Si < 4.0%, Mn < 5.0%, P < 0.5%, S < 0.5%, Mo < 6.0%, Ce < 1.0%, the remainder of the composition being iron and unavoidable impurities resulting from processing. The coated stainless steel according to the invention may also have the optional characteristics listed below, considered individually or in combination: - the lateral size of nanographites is between 1 pm and 65 pm, - the width of the nanographites ranges from 2 pm to 15 pm, - the thickness of nanographites is between 1 nm and 100 nm, - the concentration of nanographites in the coating is between 5% and 70% by weight, - the concentration of sodium silicate in the coating is between 35% and 75% by weight, - the weight ratio of nanographites to the bonding agent is between 0.05 and 0.9, - the coating thickness is between 10 pm and 250 pm, - the coating also comprises clay, silica, quartz, kaolin, aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, triium oxide, zinc oxide, aluminum titanate, carbides or mixtures thereof. A second object of the invention is a method for manufacturing a coated stainless steel substrate comprising the following successive steps: A. The provision of a stainless steel substrate comprising by weight at most 1.2% C, at least 11.0% Cr and at least 8.0% Ni, the remainder of the composition being iron and unavoidable impurities resulting from manufacturing, B. The deposition on at least a portion of the stainless steel substrate of an aqueous mixture comprising nanographites and a bonding agent which is sodium silicate to form a coating, C. Optionally, drying the coating obtained in step B). The method for manufacturing a coated stainless steel according to the invention may also have the optional features listed below, considered individually or in combination: - in step B), the coating is depositioned by centrifugal coating, spray coating, dip coating or brush coating, - in step B), the aqueous mixture comprises from 40 g / L to 110 g / L of nanographites and from 40 g / L to 80 g / L of binder, - in step C), when drying is applied, the drying is carried out at a temperature between 50 °C and 150 °C, - in step O), when drying is applied, the drying is carried out for 5 to 60 minutes. A third object of the invention consists of a hot-dip coating process for a steel strip comprising a step of moving the steel strip through a molten metal bath comprising a piece of equipment at least partially immersed in the bath wherein at least a part of the piece of equipment is made of a coated stainless steel substrate according to the invention. A fourth object of the invention consists of a hot-dip coating installation comprising a molten metal bath comprising a piece of equipment at least partially immersed in the bath wherein at least a portion of the piece of equipment is made of a coated stainless steel substrate according to the invention. The piece of equipment for the hot-dip coating installation is optionally selected from a nozzle, an overflow, a dip roller, a stabilizer roller, a roller support arm, a roller flange, a pipe, and a pumping element. To illustrate the invention, several embodiments and non-limiting example tests will be described, particularly with reference to Figure 1 which illustrates the usual form of a nanographite according to the present invention. Other features and advantages of the invention will become evident from the following detailed description of the invention. The following terms are defined below: - Nanographite refers to a carbon-based nanomaterial made of graphene nanoplatelets, that is, stacks of a few graphene sheets that have a platelet shape as illustrated in Figure 1. In this figure, the lateral size means the greatest length of the nanoplatelet along the X-axis and the thickness means the height of the nanoplatelet along the Z-axis. The width of the nanoplatelet is illustrated along the Y-axis. Preferably, the lateral size of the nanographites is between 1 pm and 65 pm, advantageously between 2 pm and 15 pm and more preferably between 2 pm and 10 pm. Preferably, the width size of the nanographites is between 2 pm and 15 pm. Advantageously, the thickness of nanographites is between 1 nm and 100 nm, more preferably between 1 nm and 50 nm, even more preferably between 1 nm and 10 nm. Graphite nanoplatelet is a synonym for nanographite. The substrate refers to a material that provides the surface on which something is deposited. This material is not limited in terms of size, dimensions, or shape. It can be, notably, in the form of a strip, a sheet, a piece, a part, an element, a device, a piece of equipment, etc. It can be flat or any shape, created by any means. - “Coated” means that the substrate is coated at least locally with the coating. The coating may be limited, for example, to the area of ​​the substrate that will be immersed in the molten metal bath. “Coated” includes both “directly on” (without intermediate materials, elements, or space between them) and “indirectly on” (with intermediate materials, elements, or space between them). For example, coating the substrate may involve applying the coating directly onto the substrate without any intermediate materials / elements, as well as applying the coating indirectly onto the substrate with one or more intermediate materials / elements between them. - The hot-dip coating process refers to the hot-dip galvanizing process, when the coating is zinc-based, and the hot-dip aluminizing process, when the coating is aluminum-based. Without wishing to be limited to any particular theory, it appears that a coating comprising nanographites and a bonding agent, sodium silicate, on a stainless steel substrate acts as a barrier to molten metal attack and prevents the formation of Zn-Fe and / or Al-Fe intermetallic compounds. In fact, the coating according to the present invention is non-wetting with respect to the molten metal bath elements due to its graphite content. In particular, it appears that the nanographites are not wetted by liquid zinc and / or aluminum. Consequently, the nanographites act as the non-wetting agent, while the sodium silicate acts as a bonding agent and adhesion promoter to the stainless steel surface. The non-adhesion of the molten metal elements to the stainless steel surface leads to increased corrosion resistance, a reduced risk of substrate deformation, and a longer substrate lifespan.Furthermore, the coating that ccncnn / zznz / E / YiAi comprises, a sodium silicate, adheres well to the stainless steel substrate, thus providing it with additional protection. It also prevents the risk of coating cracking and peeling, which would expose the stainless steel substrate to deformation and attack from molten metal. These advantages of the coating according to the invention are provided in all kinds of molten bath compositions used in hot-dip coating lines. The molten metal bath composition can be zinc-based. Examples of zinc-based baths and coatings are: zinc comprising 0.2% Al and 0.02% Fe (HDG coating), zinc alloy comprising 5 wt% aluminum (Galfan™ coating), zinc alloy comprising 55 wt% aluminum, approximately 1.5 wt% silicon, the remainder consisting of zinc and unavoidable impurities due to processing (Aluzinc™, Galvalume™ coatings), zinc alloy comprising 0.5% to 20% aluminum, 0.5% to 10% magnesium, the remainder consisting of zinc and unavoidable impurities due to processing, and zinc alloys comprising aluminum, magnesium, and silicon, the remainder consisting of zinc and unavoidable impurities due to processing. The composition of the molten metal bath can also be aluminum-based. Examples of aluminum-based baths and coatings include: aluminum alloys comprising 8% to 11% by weight of silicon and 2% to 4% by weight of iron, the remainder consisting of aluminum and unavoidable impurities due to processing (AlusiMR coating), aluminum (AlupurMR coating), and aluminum alloys comprising zinc, magnesium, and silicon, the remainder consisting of aluminum and unavoidable impurities due to processing. The stainless steel substrate is an austenitic stainless steel. Therefore, it comprises at most 1.2 wt%, at least 11.0 wt% Cr, and at least 8.0 wt% Ni. Preferably, the amount of C is below or equal to 0.5% by weight and advantageously below or equal to 0.3% by weight. Preferably, the amount of Cr is below or equal to 30% by weight and more preferably below or equal to 25% by weight. Preferably, the amount of Ni is below or equal to 30% by weight and more preferably below or equal to 25% by weight. Optionally, the amount of Nb is below or equal to 3.0% by weight, more preferably below or equal to 2.0% by weight. Optionally, the amount of B is less than or equal to 0.3% by weight. Optionally, the amount of Ti is less than or equal to 0.1% by weight. Optionally, the amount of Cu is below or equal to 3.0% by weight, more preferably below or equal to 1.0% by weight. Optionally, the amount of Co is below or equal to 1.0% by weight. Optionally, the amount of N is below or equal to 0.5% by weight. Optionally, the amount of V is less than or equal to 1.0% by weight. ccncnn / zznz / E / YiAi Optionally, the amount of Si is between 0.5% and 2.5% by weight. Optionally, the amount of Mn is below or equal to 3.0% by weight, more preferably below or equal to 2.5% by weight. Optionally, the amount of P is below or equal to 0.1% by weight. Optionally, the amount of S is below or equal to 0.1% by weight. Optionally, the amount of Mo is between 0.5% and 2.5% by weight. Optionally, the amount of Ce is below or equal to 0.1% by weight. The possible unavoidable impurities that result from the processing are mainly P, S and N in the quantities described above. Examples of stainless steel substrates are 316 and 253MA. The stainless steel substrate can be any part or component that is at least partially immersed in a molten metal bath. Preferably, the stainless steel substrate is a nozzle, overflow, dip roll, stabilizer roll, roll support arm, roll flanges, pipe, or pumping element, or a part of these elements. The stainless steel substrate is at least partially coated with a coating comprising nanographites and a bonding agent that is sodium silicate. The concentration of nanographites in the coating is preferably between 1% and 70% by weight of dry coating, more preferably between 5% and 70% by weight, and even more preferably between 10% and 65% by weight. These concentrations provide a good balance between the non-adherence of the molten metal elements in the coating and the adhesion of the coating to the substrate. Preferably, nanographites contain more than 95% by weight of C and advantageously more than 99%. The bonding agent is sodium silicate. In other words, the bonding agent is derived from sodium silicate. This sodium silicate reacts during the drying phase to form rigid siloxane chains. It is believed that the siloxane chains bond to the hydroxyl groups present on the surface of the stainless steel substrate. It is also believed that the sodium silicate dissolved in the aqueous mixture applied to the substrate will penetrate all the surface crevices and, after drying, become hard and glassy, ​​thus anchoring the coating to the substrate. Sodium silicate refers to any chemical compound with the formula Na2xSiyO2y+xo (Na2O)x-(SiO2)y. It can notably be sodium metasilicate Na2SiO3, sodium orthosilicate Na4SiO4, sodium pyrosilicate Na2SiO3, Na2SiO3O3. The concentration of sodium silicate in the coating is preferably between 35% and 95% by weight of dry coating, more preferably between 35% and 75% by weight. These concentrations provide a good balance between the non-adherence of molten metal elements in the coating and the adhesion of the coating to the substrate. According to one variant of the invention, the coating further comprises additives, particularly to improve its thermal stability and / or abrasion resistance. These additives can be selected from clay, silica, quartz, kaolin, aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, triium oxide, zinc oxide, aluminum titanate, carbides, and mixtures thereof. Examples of clays are green montmorillonite and white kaolin clays. Examples of carbides are silicon carbide and tungsten carbide. If additives are added, their concentration in the dry coating can be up to 40% by weight and is preferably between 10% and 40% by weight, and more preferably between 15% and 35% by weight. When green montmorillonite is added, the ratio of graphene to green montmorillonite by weight is preferably between 0.2 and 0.8. According to one variant of the invention, the coating consists of nanographites, a sodium silicate-based bonding agent, and optional additives selected from clay, silica, quartz, kaolin, aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, triium oxide, zinc oxide, aluminum titanate, carbides, and mixtures thereof. Preferably, the dry coating thickness is between 10 µm and 250 µm. More preferably, it is between 110 µm and 150 µm. For example, the coating thickness is between 10 and 100 µm or between 100 µm and 250 µm. Preferably, the coating does not comprise at least one element selected from a surfactant, an alcohol, aluminum silicate, aluminum sulfate, aluminum hydroxide, aluminum fluoride, copper sulfate, lithium chloride, and magnesium sulfate. The invention also relates to a method for manufacturing the coated stainless steel substrate according to the present invention, comprising the following successive steps: A. The provision of a coated stainless steel substrate according to the present invention, B. The deposition on at least a portion of the stainless steel substrate of an aqueous mixture comprising nanographites and a bonding agent which is sodium silicate to form the coating according to the present invention, C. Optionally, drying the coated stainless steel substrate obtained in step B). In step A), the stainless steel substrate can be provided in any size, dimensions, and shape. It can be in the form of a strip, sheet, piece, part, element, device, or piece of equipment. It can be flat or shaped by any means. Preferably, in step B), the coating is deposition by spin coating, spray coating, dip coating or brush coating. Advantageously, in step B), the aqueous mixture comprises from 40 g / L to 110 g / L of nanographites. More preferably, the aqueous mixture comprises from 40 g / L to 60 g / L of nanographites. Advantageously, in step B), the aqueous mixture comprises from 40 g / L to 80 g / L of bonding agent. Preferably, the aqueous mixture comprises from 50 g / L to 70 g / L of bonding agent. Sodium silicate can be added to the aqueous mixture in the form of an aqueous solution. Sodium silicate can also be in a hydrated form, with the general formula (Na₂O)ₓ(SiO₂)ₓ·2H₂O, such as, for example, Na₂SiO₃·5H₂O or Na₂SiO₃·3H₂O. Advantageously, in step B), the weight ratio of the nanographites to the bonding agent is between 0.05 and 0.9, preferably between 0.1 and 0.5. According to one variant of the invention, the aqueous mixture of step B) further comprises additives, particularly to improve the thermal stability and / or abrasion resistance of the coating. These additives can be selected from clay, silica, quartz, kaolin, aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, yttrium oxide, zinc oxide, aluminum titanate, carbides, and mixtures thereof. Examples of clays are green montmorillonite and white kaolin clays. Examples of carbides are silicon carbide and tungsten carbide. The clays further help to adjust the viscosity of the aqueous mixture to facilitate its application. In this regard, when green montmorillonite is added, the ratio of graphene to green montmorillonite weight content is preferably between 0.2 and 0.8. In a preferred embodiment, the coating is dried, i.e., actively dried as opposed to natural air drying, in step C). It is believed that the drying step improves coating adhesion because water removal is better controlled. In a preferred embodiment, in step C), drying is carried out at a temperature between 50°C and 150°C, and preferably between 80°C and 120°C. The drying can be performed with forced air. Advantageously, in step C), when a drying is applied, the drying takes place for 5 to 60 minutes and, for example, between 15 and 45 minutes. In another modality, a drying step is not carried out. The coating is left to air dry. The invention also relates to the use of a coated stainless steel according to the present invention for the manufacture of a nozzle, an overflow, an immersion roller, a stabilizing roller, a roller support arm, a pipe, or a pumping element. The invention also relates to a hot-dip coating process of a steel strip comprising a step of moving the steel strip through a molten metal bath comprising a piece of equipment at least partially submerged in the bath wherein at least a part of the piece of equipment is made of a coated stainless steel substrate according to the invention. The invention also relates to a hot-dip coating installation comprising a molten metal bath comprising a piece of equipment at least partially immersed in the bath wherein at least a portion of the piece of equipment is made of a coated stainless steel substrate according to the invention. The invention will henceforth be explained based on tests carried out for informational purposes only. These are not limiting. Examples In the examples, the steel substrates used have the following composition in percent by weight: ccncnn / zznz / E / YiAi Steel C Mn Si PS Cr Ni Mo N Ce 1 0.08 2 0.75 0.045 0.03 17 12 2.5 0.1 - 2 0.08 0.8 1.8 0.04 0.03 21 11 - 0.2 0.06 ccncnn / zznz / E / YiAi Steel 1 corresponds to 316 stainless steel and steel 2 corresponds to 253MAMR stainless steel. Example 1: Coating adhesion tests For tests 1 and 2, stainless steels 1 and 2 were brush-coated with an aqueous mixture comprising 50 g / L of nanographites having a side length of 2 µm to 10 µm, a width of 2 µm to 15 µm, and a thickness of 1 nm to 100 nm, and 60 g / L of sodium silicate, as a bonding agent, in the form of an aqueous solution comprising 25.6% to 27.6 wt% SiO₂ and 7.5% to 8.5 wt% Na₂O. The coating was then dried in a hot-air oven for 60 minutes at 75 °C. The coating was 130 µm thick and comprised 45 wt% nanographites and 55 wt% bonding agent. For tests 3 and 4, stainless steels 1 and 2 were brush-coated with an aqueous mixture comprising 50 g / L of nanographites having a side length of 2 µm to 10 µm, a width of 2 µm to 15 µm, and a thickness of 1 nm to 100 nm, 100 g / L of green montmorillonite clay, and 60 g / L of sodium silicate, as a bonding agent, in the form of an aqueous solution comprising 25.6% to 27.6 wt% S1O2 and 7.5% to 8.5 wt% Na2O. The coating was then dried in a hot-air oven for 60 minutes at 75 °C. The coating was 130 pm thick and comprised 11 wt% nanographite, 69 wt% bonding agent and 20 wt% green montmorillonite clay. For tests 5 and 6, stainless steels 1 and 2 were brush-coated with an aqueous mixture comprising 90 g / L of nanographites having a side length of 2 µm to 10 µm, a width of 2 µm to 15 µm, and a thickness of 1 nm to 100 nm, and 60 g / L of sodium silicate, as a bonding agent, in the form of an aqueous solution comprising 25.6% to 27.6 wt% SiO2 and 7.5% to 8.5 wt% Na2O. The coating was then dried in a hot-air oven for 60 minutes at 75 °C. The coating was 130 µm thick and comprised 60 wt% nanographite and 40 wt% bonding agent. For tests 7 and 8, stainless steels 1 and 2 were brush-coated with an aqueous mixture comprising 50 g / L of reduced graphene oxide having a side length of 5 µm to 30 µm, a width of 5 µm to 30 µm, and a thickness of 1 nm to 10 nm, and 60 g / L of sodium silicate, as a bonding agent, in the form of an aqueous solution comprising 25.6% to 27.6 wt% SiO2 and 7.5% to 8.5 wt% Na2O. The coating was then dried in a hot-air oven for 60 minutes at 75 °C. The coating was 130 µm thick and comprised 45 wt% reduced graphene oxide and 55 wt% bonding agent. To evaluate coating adhesion, adhesive tape was applied to the test surfaces and then removed. Coating adhesion was assessed by visual inspection: 0 means that all the coating has remained on the stainless steel; 1 means that some parts of the coating have been removed; and 2 means that almost all of the coating has been removed. ccncnn / zznz / E / YiAi The results are shown in Table 1 below: Tests Steels Coating Adhesion Γ 1 Nanographites and sodium silicate 0 2* 2 Nanographites and sodium silicate 0 3* 1 Nanographites, montmorillonite green clay and sodium silicate 0 4* 2 Nanographites, montmorillonite green clay and sodium silicate 0 5* 1 Nanographites and sodium silicate 0 6* 2 Nanographites and sodium silicate 0 7 1 Reduced graphene oxide and sodium silicate 1 8 2 Reduced graphene oxide and sodium silicate 2 * according to the present invention. Tests according to the present invention show excellent coating adhesion. Example 2: Immersion by bath Tests 1 through 6 were immersed for two weeks in a zinc-based bath comprising 0.2% Al and 0.02% Fe. After two weeks, a thin, non-adherent zinc film was present on the tests. The zinc film peeled off easily. The coating of the present invention was still present in all tests. No zinc etching was observed. The tests according to the present invention were well protected against zinc attack. Tests 7 and 8 were also immersed for 8 days in an aluminum-based bath comprising 10% Si and 2.5% Fe. After 8 days, a thin, non-adherent metallic film was present on the tests. The metallic film was easily removed from the tests. The coating of the present invention was still present in both tests. No aluminum etching was observed. The tests according to the present invention were well protected against aluminum attack.

Claims

1. A coated stainless steel substrate comprising a coating comprising nanographites and a bonding agent being sodium silicate, wherein the stainless steel substrate has the following composition in weight percent: C <1.2%, Cr>11.0%, Ni > 8.0% and on a purely optional basis, one or more elements such as: Nb < 6.0%, B < 1.0%, Ti < 3.0%, Cu < 5.0%, Co < 3.0%, N < 1.0%, V < 3.0%, Si < 4.0%, Mn < 5.0%, P < 0.5%, S < 0.5%, Mo < 6.0%, Ce < 1.0%, the remainder of the composition being iron and unavoidable impurities resulting from manufacturing.

2. A coated steel substrate according to claim 1, wherein the lateral size of the nanographites is between 1 pm and 65 pm.

3. A coated stainless steel substrate according to any of claims 1 or 2, wherein the width size of the nanographites is between 2 pm and 15 pm.

4. A stainless steel substrate coated according to any of claims 1 to 3, wherein the thickness of the nanographites is between 1 nm and 100 nm.

5. A coated stainless steel substrate according to any of claims 1 to 4, wherein the concentration of nanographites in the coating is between 5% and 70% by weight.

6. A coated stainless steel substrate according to any of claims 1 to 5, wherein the concentration of sodium silicate in the coating is between 35% and 75% by weight.

7. A coated stainless steel substrate according to any of claims 1 to 6, wherein the weight ratio of the nanographites to the bonding agent is between 0.05 and 0.

9.

8. A coated stainless steel substrate according to any of claims 1 to 7, wherein the coating thickness is between 10 µm and 250 µm. ccncnn / zznz / E / YiAi 9. A coated stainless steel substrate according to any of claims 1 to 8, wherein the coating further comprises clay, silica, quartz, kaolin, aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, trio oxide, zinc oxide, aluminum titanate, carbides or mixtures thereof.

10. A method for manufacturing a coated stainless steel substrate comprising the following successive steps: A. Providing a stainless steel substrate comprising, by weight, at most 1.2% C, at least 11.0% Cr, and at least 8.0% Ni, the remainder of the composition being iron and unavoidable impurities resulting from manufacturing; B. Depositing on at least a portion of the stainless steel substrate an aqueous mixture comprising nanographites and a bonding agent being sodium silicate to form a coating; C. Optionally, drying the coating obtained in step B).

11. A method according to claim 10, wherein in step B), the deposition of the coating is carried out by centrifugal coating, spray coating, immersion coating or brush coating.

12. A method according to any of claims 10 or 11, wherein in step B), the aqueous mixture comprises from 40 g / L to 110 g / L of nanographites and from 40 g / L to 80 g / L of bonding agent.

13. A method according to any of claims 10 to 12, wherein in step C), when drying is applied, the drying is carried out at a temperature between 50 °C and 150 °C.

14. A method according to any of claims 10 to 13, wherein in step C), when drying is applied, the drying is carried out for 5 to 60 minutes.

15. Hot-dip coating process of a steel strip comprising a step of moving the steel strip through a molten metal bath comprising a piece of equipment at least partially immersed in the bath wherein at least a portion of the piece of equipment is made of a coated stainless steel substrate according to any of claims 1 to 9.

16. Hot-dip coating installation comprising a molten metal bath comprising a piece of equipment at least partially immersed in the bath wherein at least a portion of the piece of equipment is made of a coated stainless steel substrate according to any of claims 1 to 9.

17. Hot-dip coating installation according to claim 16, wherein the piece of equipment is selected from a nozzle, an overflow, a dip roller, a stabilizer roller, a roller support arm, a roller flange, a pipe, and a pumping element.