Annealing Method

Abstract

The present invention relates to a method for manufacturing steel sheets in an apparatus comprising a preheating zone, a heating zone with a maximum heating rate, and a soaking zone including a calibration step, a recrystallization annealing and soaking and coating step, the calibration step making it possible to define a low dew point that allows achieving predetermined quality targets.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a steel sheet. [Background technology]

[0002] During their manufacture, full hard steels are annealed to enhance their strength-ductility balance before being coated. During annealing, the steel strip is heated and maintained above its recrystallization temperature in a controlled atmosphere. The steel strip is then cooled and coated, usually by hot-dip galvanization in a galvanizing bath.

[0003] For example, a common practice is to heat a fully hardened steel plate from ambient temperature to a temperature above the recrystallization point of the steel (heating step) and then hold the steel at this temperature (soaking step). Both steps are performed in the same atmosphere and with the same dew point, e.g. an atmosphere containing 5% H2 by volume with inert gas and a dew point between -40°C and +10°C.

[0004] In the heating step, as the temperature gradually increases with the presence of oxygen, oxygen diffuses into the steel and two types of reactions occur. First, oxygen reacts with carbon to form gases such as CO2 and CO, which depletes the carbon atoms in the steel subsurface. But on the other hand, carbon atoms from the bulk diffuse into the carbon-depleted zone. As long as more carbon atoms leave the subsurface layer than enter the layer, the subsurface layer is decarburized. Second, oxygen reacts with steel alloying elements such as manganese (Mn), aluminum (Al), silicon (Si) or chromium (Cr), which have a higher affinity for oxygen than iron. It leads to the formation of oxides in the steel subsurface. The formation of said oxides in the subsurface reduces the amount of alloying elements available to form surface oxides.

[0005] The soaking step involves a higher temperature compared to the heating step. Due to the higher temperature of the soaking zone, alloying elements that did not form an internal oxide may diffuse from the bulk to the steel surface and form external selective oxides that are believed to have a negative effect on the wettability of the steel.

[0006] In a subsequent process step, these steels are usually coated with a metal alloy, such as a zinc-based coating, to improve their properties, such as corrosion resistance and / or phosphatability. The metal coating can be deposited by hot-dip or electroplating methods.

[0007] In the prior art, it is believed that the external selective oxides formed by the steel alloying elements on the steel sheet surface during the annealing step prevent reactive wetting between the substrate, i.e., the steel, and the coating, i.e., the aluminum or zinc-based coating. As a result, a discontinuous and non-uniform inhibitory layer is formed. This can result in areas of the final product that are free of coating, e.g., bare spots, or problems related to delamination of the coating that negatively affect the product quality.

[0008] EP3378965A1 describes a method for producing high-strength hot-dip galvanized steel sheet with excellent impact resistance and corrosion resistance at processed parts. The heating step is carried out up to 650°C in an atmosphere containing 0.1-20% by volume of H2 and satisfying the following conditions: -1.7≦log(PH20 / PH2)≦-0.6. Such parameters correspond to a dew point between -20°C and +10°C for a H2 concentration of 5%. The temperature rise rate is 0.5-5°C.s -1 The temperature rise of the steel plate is 5℃.s -1 is the limit because otherwise recrystallization in the surface layer of the steel sheet base material will proceed before internal oxide particles are formed, and the decarburized layer will not be obtained in time. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent Application Publication No. 3378965 Summary of the Invention [Problem to be solved by the invention]

[0010] The goal of the present invention is to increase the reliability of the annealing process, improve the wetting of the steel substrate and the quality of the coating. [Means for solving the problem]

[0011] This object is achieved by providing a method as claimed in claim 1. The method may also include any of the features of claims 2-15.

[0012] Other features and advantages of the present invention will become apparent from the following detailed description of the invention.

[0013] In order to illustrate the invention, various embodiments and non-limiting example trials are described with particular reference to the following figures. [Brief description of the drawings]

[0014] [Figure 1] 1 shows an embodiment of an annealing furnace and a hot dip plating facility. [Diagram 2] An embodiment of a coating that meets quality objective (A) and an embodiment of a coating that does not meet quality objective (B) are shown. [Diagram 3] Implement step v)a) of the calibration step. [Figure 4] Implement step v)b) of the calibration step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention relates to a method for producing a steel plate having a thickness t in an apparatus including a preheating section, a heating section having a maximum heating rate for the steel plate having a thickness t, and a soaking section, A) a calibration step, i) heating a steel sheet having a thickness t and the following chemical composition in weight percent: 0.05≦C≦0.50%, 0.3≦Mn≦8.0%, 0.01≦Si≦5%, and optionally one or more of the following elements in weight percent: 0.01%Al≦1.5%, B≦0.004%, Co≦0.1%, 0.001≦Cr≦1.00%, Cu≦0.5%, 0.001≦Mo≦0.5%, Nb≦0.1%, Ni≦1.0%, Ti≦0.1%, N≦0.01%, P<0.1%, S≦0.01%, V<0.2%, with the remainder of the composition being iron and unavoidable impurities, from room temperature to a temperature T1 below 600°C; ii) The steel plate is heated at the maximum heating rate from T1 to a recrystallization temperature T2 in the range of 720°C to 1000°C, containing 0.1 to 90% by volume of H2, the balance being inert gases and unavoidable impurities, and at a dew point DP CAL Heating in an atmosphere A1 having iii) Then, the steel sheet is maintained at a temperature T2 in an atmosphere A2 containing 0.1 to 90 volume % of H2, the remainder being an inert gas and unavoidable impurities, and having a dew point of at least -40°C; iv) The steel sheet is then hot-dip galvanized and the quality of the coating is evaluated; v) a) If the quality of the coating meets the predetermined quality target, calibration steps i) to iv) are repeated until the coating reaches a lower dew point DP CAL and repeating until the quality of the coating no longer meets the target, at the penultimate dew point DP CAL is defined as DP1, b) If the quality of the coating does not meet the quality target, calibration steps i) to v) are repeated until the coating reaches a higher dew point DP CAL Repeat until the quality of the coating meets the target, and the final dew point DP CAL a calibration step, which defines DP1 as B) A manufacturing step, in which a steel sheet having said thickness t and said chemical composition is - a recrystallization annealing step including successively a preheating step, a heating step, a soaking step and a cooling step, i) the preheating step comprises heating from room temperature to a temperature T1 less than 600° C.; ii) the heating step comprises heating from T1 to a recrystallization temperature T2 in the range of 720°C to 1000°C at a heating rate up to and including the maximum heating rate in an atmosphere A1 containing 0.1 to 90% H2, the balance being inert gases and unavoidable impurities, and having a dew point set at least to the DP1 value determined during a calibration step; iii) a recrystallization annealing step, in which the soaking step is held at a temperature in the range of T2-30°C to T2+30°C in an atmosphere A2 containing 0.1 to 90% H2, the remainder being inert gases and unavoidable impurities, and having a dew point DP2 set to -40°C or higher; a manufacturing method comprising a manufacturing step in which said steel sheet is subjected to a coating step in which said steel sheet is hot-dip galvanized in said coating bath.

[0016] As shown in Fig. 1, the apparatus 1' is an apparatus capable of performing heat treatment, such as an annealing oven or an annealing furnace. Such an apparatus includes a preheating section 2', a heating section 3', a soaking section 4' and a cooling section 5', and the temperature, heating rate and atmosphere of these sections can be set and controlled.

[0017] The temperature of the steel plate is increased in the pre-heating and heating sections. The maximum heating rate of the heating section is the maximum heating rate at which the manufactured steel plate having the thickness t can be heated during the heating section in manufacturing step ii). The maximum heating rate refers to the specific maximum heating rate of said heating section for a steel plate having the thickness t. The maximum heating rate relates to an average value.

[0018] The carbon content is between 0.05 and 0.50 percent by weight. If the carbon content is lower than 0.05 percent by weight, there is a risk of insufficient tensile strength. Furthermore, if the steel microstructure contains retained austenite, it will not have the stability required to achieve sufficient elongation. If the carbon content is higher than 0.5 percent by weight, the hardening of the weld increases.

[0019] The manganese content is 0.3-8.0 weight percent. Manganese is a solution hardening element that contributes to obtaining high tensile strength. Such an effect is obtained when the Mn content is at least 0.3 weight percent. However, if the Mn content is greater than 8.0 weight percent, it may cause the formation of a structure with excessively pronounced segregation zones that may adversely affect the mechanical properties of the weld. Preferably, the manganese content is 1.5-5.0 weight percent. This makes it possible to obtain a satisfactory mechanical strength without increasing the difficulties of industrial production of the steel and without increasing the hardenability in the weld.

[0020] The silicon content is 0.01-5 weight percent. Silicon retards the formation of carbides and stabilizes austenite. If the silicon content is more than 5 weight percent, the plasticity and toughness of the steel are significantly reduced.

[0021] The steel may optionally contain elements such as Al, B, Co, Cr, Cu, Mo, N, Nb, Ni, P, S, Ti, V for the following reasons:

[0022] Aluminum may be optionally contained in the steel sheet at a content of 0.01 to 1.5 weight percent. Al increases the Ms temperature and thus destabilizes the retained austenite. Furthermore, with an increase in the Al content above 1.5 weight percent, the Ac3 temperature increases, which causes difficulties in industrial production. Preferably, the aluminum content is 0.01 to 1.0 weight percent.

[0023] Boron may optionally be contained in the steel sheet at a content of up to 0.004 weight percent. By segregating to grain boundaries, B is beneficial in lowering grain boundary energy and thus increasing resistance to liquid metal embrittlement.

[0024] Chromium may optionally be included in the steel sheet in a content up to 1.00 weight percent, which allows the steel sheet to retard the formation of proeutectoid ferrite during the cooling step after the maximum temperature hold in the annealing cycle, making it possible to achieve higher strength levels. Its content is limited to 1.00 weight percent for cost reasons and to prevent excessive hardening.

[0025] Copper may optionally be included in the steel sheet at a content of up to 0.5 weight percent to harden the steel by precipitation of copper metal.

[0026] Molybdenum may optionally be included in the steel sheet in a content of up to 0.5 weight percent. This element retards the decomposition of austenite and is therefore effective in increasing hardenability and stabilizing the retained austenite.

[0027] Nickel may optionally be included in the steel plate, at a content of up to 1.0 weight percent, to improve toughness.

[0028] Titanium may optionally be contained in the steel plate in a content of up to 0.1 weight percent. Niobium may optionally be contained in the steel plate in a content of up to 0.1 weight percent. They harden and strengthen the steel by forming precipitates. However, if the amount of Nb exceeds 0.1 weight percent and / or the Ti content exceeds 0.1 weight percent, there is a risk that excessive precipitation will cause a decrease in toughness and must be avoided.

[0029] Vanadium may optionally be included in the steel sheet in a content of up to 0.2 weight percent, forming precipitation hardening and strengthening of the steel.

[0030] Phosphorus and sulfur are considered residual elements resulting from steelmaking. P may be present in amounts up to 0.04 weight percent. S may be present in amounts up to 0.01 weight percent.

[0031] Preferably, the chemical composition of the steel does not contain bismuth (Bi). Indeed, without wishing to be bound by any theory, it is believed that if the steel sheet contains Bi, the wettability is reduced and therefore the adhesion of the coating is reduced.

[0032] The calibration step is preferably performed using the same equipment as the manufacturing step. However, it is possible to use different equipment for the calibration step and the manufacturing step. Preferably, the equipment for the calibration step is an annealing furnace.

[0033] In calibration step iv), the quality of the coating can be assessed by visual inspection and / or inspection equipment, for example a scanning electron microscope (SEM) or field emission gun scanning electron microscopy (FEG-SEM).

[0034] Preferably, in calibration step v) a predetermined quality target is associated with the homogeneity of the coating on the steel sheet. Preferably, the predetermined quality target takes into account the absence of coating-free areas and / or the average coating thickness and / or the percentage of covered area.

[0035] For example, Figure 2 shows two coating qualities, one on the left that meets the target (A) and one on the right that does not meet the target (B). The one on the left meets the target because the entire sample is coated with a uniform thickness. The one on the right does not meet the target because part of the sample is not coated.

[0036] v) The repetition of the steps described in a) is shown in Figure 3. Dew point DP CAL1 and maximum heating rate (Max HR ) according to steps i) to iv), a first sample "A1" was prepared. As shown in the figure for sample "A1", the entire surface is coated (shown in grey), so the coating quality meets the predefined quality target. Then, DP CAL1 Lower dew point DP CAL2 and maximum heating rate (Max HRA second sample, "A2", was prepared according to steps i) to iv) in DP. As shown in the figure for sample "A2", the entire surface is coated (shown in grey), so the coating quality meets the predefined quality target. CAL2 Lower dew point DP CAL3 and maximum heating rate (Max HR A third sample "A3" was prepared according to steps i) to iv) in DP. As shown in sample "A3", some areas of the surface of sample "A3" are not coated (shown in white), so the coating quality does not meet the predefined quality target. CAL2 is defined as DP1.

[0037] Preferably, in step ii), DP CAL has a minimum value of −40° C. Even more preferably, in said step ii) of the calibration step A), DP CAL has a minimum value of -40°C, and in step v)a), the quality of the coating is CAL As a result, if a sample is produced using the maximum heating rate at a dew point of -40°C and the predefined coating quality is met, then -40°C can be defined as DP1.

[0038] v) The repetition of the steps described in b) is shown in Figure 4. CAL1 and maximum heating rate (Max HR The first sample "B1" was prepared according to steps i) to iv) in DP. The quality of the coating does not meet the predefined quality target due to the uncoated areas. CAL1 Higher dew point DP CAL2 and maximum heating rate (Max HR A second sample "B2" was prepared according to steps i) to iv) in DP. The quality of the coating does not meet the predefined quality target due to the uncoated areas. CAL2 Higher dew point DP CAL3 and maximum heating rate (Max HRThe third sample "B3" was prepared according to steps i) to iv) in DP. The quality of the coating met the predefined quality targets. CAL3 is defined as DP1.

[0039] It has been surprisingly observed that the key driving force for wettability of metal coatings is the heating rate and its relationship to dew point at that heating rate, and not the soak zone process parameters due to the formation of an outer oxide, contrary to what is believed in the prior art.

[0040] As a result, thanks to the calibration step, a limiting dew point (DP1) for the heating section can be defined, from which a predetermined coating quality can be achieved for any heating rate within the heating zone.

[0041] A preheating step is generally performed after the steel has been cold rolled. During this preheating, the steel sheet is heated from room temperature to a temperature T1 below 600°C. For example, this step can be performed in an RTF (radiant tube furnace) with an atmosphere composed of N2, H2 and inevitable impurities, or by induction or in a DFF (direct fired furnace) with an atmosphere with an air / gas (gaz) ratio < 1. However, in a DFF that includes several zones, for example 5 zones, it is possible to have an air / gas ratio > 1 in the last or last two zones.

[0042] Limiting the preheat temperature to less than 600° C. is advantageous since it reduces oxidation on the steel sheet, and is particularly advantageous in radiant tube furnaces (RTFs) since it makes it possible to avoid potentially harmful selective oxidation.

[0043] During the heating step, the steel sheet is heated from a temperature T1 to a recrystallization temperature T2 of 720°C-1000°C at a heating rate not greater than said maximum heating rate in an atmosphere A1 containing 0.1-90% by volume of H2, at least inert gases and unavoidable impurities and having a dew point DP1 as determined during the calibration step.

[0044] During the soaking step, the steel sheet is maintained in a temperature range of (T2-30°C) to (T2+30°C) in an atmosphere A2 containing 0.1-90% by volume of H2, at least inert gases and unavoidable impurities and having a dew point DP2 of at least -40°C. For example, if T2 is 950°C, the steel is maintained in the range of 920°C to 980°C in the soaking step iii).

[0045] The atmosphere for the heating and soaking steps can be achieved by introducing N2-H2 gas into a furnace using preheated steam and equipped with a H2 detector at different locations to monitor the dew point temperature of the atmosphere.

[0046] Preferably, the steel bulk chemistry has a ratio between manganese and silicon, in weight percent, that adheres to Mn / Si<4.

[0047] Preferably, the steel bulk chemical composition has a ratio between aluminum and magnesium, in weight percent, that adheres to Mn / Al<1.

[0048] Preferably, the bulk chemical composition of the steel has a ratio between manganese, aluminum and silicon, in weight percent, that adheres to Mn / (Al+(4×Si))<1.

[0049] All three compositions reduce the formation of FeO-MnO on the steel surface, improving coating adhesion and uniformity.

[0050] Preferably, in the preheating step i), the temperature T1 is lower than 550° C. Even more preferably, in the preheating step i), the temperature T1 is lower than 500° C. Apparently, by further limiting the temperature at the end of preheating (T1), the oxidation of the steel sheet can be further reduced, which also lowers the risk of potentially harmful selective oxidation in RTF.

[0051] Preferably, in said pre-heating step i), the heating rate is 50° C.s -1Higher heating rates in the preheat section allow for shorter length of this section and / or higher productivity.

[0052] Preferably, in the heating step ii), the atmosphere A1 contains between 1% and 20% by volume of H2 and at least an inert gas and inevitable impurities. Even more preferably, in the heating step ii), the atmosphere A1 contains between 3% and 8% by volume of H2 and at least an inert gas and inevitable impurities.

[0053] Preferably, said heating step ii) lasts for a period of 10 to 1000 seconds.

[0054] Preferably, in the soaking step iii), the steel sheet is maintained at a temperature of T2-10°C to T2+10°C.

[0055] Preferably, said soaking step ii) lasts for 10 to 1000 seconds.

[0056] Preferably, in the soaking step iii), the atmosphere A1 contains between 1 vol.% and 20 vol.% H2 and at least an inert gas and inevitable impurities. Even more preferably, in the soaking step iii), the atmosphere A1 contains between 3 vol.% and 8 vol.% H2 and at least an inert gas and inevitable impurities.

[0057] Preferably, the coating bath is a zinc-based coating bath, also known as hot-dip galvanizing, containing 0.1 to 0.3 weight percent aluminum and optionally magnesium.

[0058] Preferably, the coating bath is an aluminum-based bath containing 5 to 15 weight percent silicon.

[0059] Preferably, in the coating step C, the steel sheet is set at a temperature between 0 and 10°C higher than the hot dip galvanizing bath temperature which is maintained at a temperature between 420 and 470°C.

[0060] Preferably, the coating bath of step iv) of the calibration step A) and the coating bath of the coating step of the production step B) have the same base element.

[0061] Preferably, the coating bath of step iv) of the calibration step A) and the coating bath of the coating step of the production step B) are zinc-based coating baths containing 0.1 to 0.3 weight percent aluminum and optionally magnesium.

[0062] Preferably, the coating bath of step iv) of the calibration step A) and the coating bath of the coating step of the production step B) are aluminium-based baths containing 5-15% by weight of silicon. EXAMPLES

[0063] The following section deals with experimental results showing the wettability of steel as a function of the parameters of the heating zone.

[0064] A first series of experiments was carried out to evaluate the effect of the T1 temperature on the quality of the coating. In this first series of experiments, annealing cycles were applied to a cold rolled Fe-Si steel containing 0.03 wt% carbon, 3 wt% silicon, 0.2 wt% Mn and 0.01 wt% aluminium. In this first series of experiments, all parameters were constant except for T1. The heating rate was 4.4°C.s -1 The dew points in the heating and soaking zones are -20°C, the H2 concentration in the heating and soaking zones is 5% by volume, and the soaking time is 37.5 seconds. The quality of the coating is evaluated visually. Three experiments were performed for T1 values ​​of 500°C, 600°C, and 700°C. These parameters are summarized in Table 1.

[0065] As can be seen, when T1 is higher than 600° C., all other parameters remain constant, the coating quality does not meet the target. Also, it appears that the smaller T1 is, the better the coating quality is, all other parameters remain constant.

[0066] [Table 1]

[0067] A second series of experiments was carried out to reproduce the calibration step of the claimed process and thus find DP1. In this second series of experiments, an annealing cycle was applied to a cold-rolled Fe-Si steel containing 0.03 wt% carbon, 3 wt% silicon, 0.2 wt% Mn and 0.01 wt% aluminum. In this second series of experiments, all parameters were constant, except for the dew point of the heating zone. T1 was 600°C and the heating rate was 20°C.s -1 The dew point in the soaking zone is -20°C, the H2 concentration in the heating zone and the soaking zone is 5% by volume, and the soaking time is 37.5 seconds. The quality of the coating is evaluated visually. According to steps A)i) to A)v)a) of the claimed process, the coating is subjected to dew points DP of -10°C, -20°C, -25°C and -30°C. CAL Four experiments were performed for each value. Then, -25°C was defined as DP1 because it was the penultimate dew point in the calibration step, i.e. the last dew point where the coating quality met the target. These parameters are summarized in Table 2.

[0068] [Table 2]

[0069] A third series of experiments was carried out to evaluate the reliability of the claimed process. In this third series of experiments, the annealing cycle was applied to cold-rolled Fe-Si steels of the same steel grade as in the second series of experiments. In this third series of experiments, a calibration step was performed to verify the reliability of the claimed process. -1 DP1 for the maximum heating rate of 10°C was defined as -30°C. In this third series of experiments, all parameters were constant except the heating rate of the heating zone. T1 was 600°C, the dew point of the heating zone was -30°C, the dew point of the soaking zone was -20°C, the H2 concentration in the heating zone and soaking zone was 5% by volume, and the soaking time was 37.5 seconds. The quality of the coating was assessed visually. According to steps B)i) to B)iii) of the claimed process, the coating was heated at 10°C.s. -1 , 9.5℃.s -1 and 4.5°C.s -1Three experiments were performed for heating rate values ​​of 0.01 and 0.02, and the parameters are summarized in Table 3.

[0070] It can be observed that for any heating rate lower than the maximum heating rate in the heating zone, the coating quality meets the target.

[0071] [Table 3]

Claims

1. A method for manufacturing a steel plate having a thickness t in an apparatus including a preheating section, a heating section having a maximum heating rate for the steel plate having a thickness t, and a soaking section, comprising: A) a calibration step, i) A steel sheet having a thickness t and the following chemical composition in weight percent: 0.05≦C≦0.50%, 0.3≦Mn≦8.0%, 0.01≦Si≦5%, and optionally one or more of the following elements in weight percent: 0.01%≦Al≦1.5%, B≦0.004%, Co≦0.1%, 0.001≦Cr≦1.00%, Cu≦0.5%, 0.001≦Mo≦0.5%, Nb≦0.1%, Ni≦1.0%, Ti≦0.1%, N≦0.01%, P<0.1%, S≦0.01%, V<0.2%, with the remainder of the composition being iron and unavoidable impurities, is melted at a temperature T from room temperature to less than 600° C. １ Heat until ii) The steel plate is subjected to T １ to a recrystallization temperature T in the range of 720°C to 1000°C ２ At the maximum heating rate, 0.1 to 90% by volume of H ２ The remainder is inert gases and unavoidable impurities, and the dew point DP ＣＡＬ Atmosphere A having １ Heat it in iii) The steel plate is then heated to a temperature T ２ 0.1 to 90% by volume of H ２ The remainder is an inert gas and unavoidable impurities, and the atmosphere A has a dew point of at least -40°C. ２ Maintain in iv) The steel sheet is then hot-dip galvanized in a coating bath and the quality of the coating is evaluated; v) a) if the quality of the coating meets the predetermined quality target, repeat the calibration steps i) to iv) with a lower dew point DP ＣＡＬ and repeating until the quality of the coating no longer meets the target, at the penultimate dew point DP ＣＡＬ DP １ It stipulates that: b) If the quality of the coating does not meet the target, perform calibration steps i) to v) at a higher dew point DP ＣＡＬ Repeat until the quality of the coating meets the target, and the final dew point DP ＣＡＬ DP １ a calibration step defining B) A manufacturing step, in which a steel sheet having said thickness t and said chemical composition is manufactured as follows: a recrystallization annealing step including successively a preheating step, a heating step, a soaking step and a cooling step, i) the preheating step comprises heating from room temperature to a temperature T1 less than 600° C.; ii) The heating step comprises heating from T1 to a recrystallization temperature T2 in the range of 720° C. to 1000° C. at a heating rate up to the maximum heating rate with 0.1 to 90% H ２ with the remainder being inert gases and unavoidable impurities, and at least DP determined during the calibration step １ Atmosphere A having a dew point set to a value １ including heating in iii) The soaking step is performed at a temperature in the range of T2-30°C to T2+30°C, with 0.1 to 90% H ２ The remainder is inert gases and unavoidable impurities, and the dew point DP is set to -40°C or higher. ２ Atmosphere A having ２ a recrystallization annealing step in which the a manufacturing method comprising a manufacturing step in which said steel sheet is subjected to a coating step in which it is hot-dip galvanized in said coating bath.

2. 2. The method of claim 1, wherein the bulk chemical composition of the steel has a ratio between manganese and silicon, in weight percent, that adheres to Mn / Si<4.

3. 3. The method according to claim 1 or 2, wherein the bulk chemical composition of the steel has a ratio between aluminum and manganese, in weight percent, that adheres to Mn / Al<1.

4. 2. The method of claim 1, wherein the bulk chemical composition of the steel has a ratio, in weight percent, between manganese, aluminum and silicon that adheres to Mn / (Al+(4×Si))<1.

5. 5. The method according to claim 1, wherein in the preheating step i), the temperature T1 is lower than 550°C.

6. In the preheating step i), the heating rate is 50° C. s －１ The method according to any one of claims 1 to 5, wherein the

7. In the heating step ii), the atmosphere A1 is 1 to 20% by volume of H ２ The method according to any one of claims 1 to 6, comprising at least an inert gas and unavoidable impurities.

8. The method according to any one of claims 1 to 7, wherein the heating step ii) lasts for 10 to 1000 seconds.

9. The method according to any one of claims 1 to 8, wherein in the soaking step iii), the steel plate is maintained at a temperature of (T2-10°C) to (T2+10°C).

10. 10. The method according to any one of claims 1 to 9, wherein said soaking step iii) lasts for 10 to 1000 seconds.

11. In the soaking step iii), the atmosphere A2 is 1 to 20% by volume of H ２ 11. The method according to claim 1, further comprising at least an inert gas and unavoidable impurities.

12. The method of claim 11, wherein the coating bath is a zinc-based coating bath containing 0.1 to 0.3 weight percent aluminum and optionally magnesium.

13. The method of claim 11, wherein the coating bath is an aluminum-based bath containing 5 to 15 weight percent silicon.

14. In step ii) of the calibration step A), DP ＣＡＬ has a minimum value of −40° C., and in step v) a), the quality of the coating is −40° C. DP ＣＡＬ If the target is met, set -40°C as DP １ The method according to any one of claims 1 to 13, wherein

15. The method according to any one of the preceding claims, wherein the coating bath of step iv) of the calibration step A) and the coating bath of the coating step of the production step B) have the same base element.

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