HUE027485T2

HUE027485T2 - A steel sheet suitable for enamelling and method for producing such a sheet

Info

Publication number: HUE027485T2
Application number: HUE11713766A
Authority: HU
Inventors: Steenberge Nele Van; Marc Leveaux; Lode Duprez; Philippe Gousselot
Original assignee: Arcelormittal Investig Y Desarrollo S L
Priority date: 2011-04-08
Filing date: 2011-04-08
Publication date: 2016-09-28
Also published as: BR112013025885A2; CA2832357A1; ZA201307344B; CN103476955A; WO2012136270A1; EP2534271B1; MX2013011685A; SI2534271T1; US20190112684A1; BR112013025885B1; PL2534271T3; EA201391455A1; ES2545746T3; US20140065434A1; EP2534271A1; EA024029B1; KR20140014248A; CA2832357C; MX348721B; US20190112683A1

Description

Field of the Invention [0001] The present invention is related to a steel sheet suitable for enamelling, and to a method for the superficial decarburization of a steel sheet, as a preparation for enamelling the steel.

State of the art.

[0002] The carbon level of a steel sheet has an important influence on the results in terms of surface quality of an enamel layer applied on the surface of the sheet. A high carbon level at the steel surface may give rise to CO-gas bubble formation, which shows up as black spots and craters in the enamel surface. On the other hand, when a sufficiently high carbon level is present initially in the bulk, this carbon forms coarse cementite during hot rolling which cracks upon cold rolling. These cracks are capable of capturing hydrogen which enters the steel during the enamelling process. When hydrogen is insufficiently captured, pressure will rise at the steel/enamel surface which gives rise to the so-called ’fish-scale’ deformation of the enamel.

[0003] It is therefore advantageous to decarburize the steel only in a layer at the surface of the steel, i.e. to conduct a superficial decarburization. Document JP-A-2282421 describes such a method, wherein a continuously cast and annealed non-aging steel sheet for enamelling is produced, characterized in that a continuous-cast steel slab containing C between 0.0025 and 0.0050wt%, Si max. 0.03wt%, Mn between 0.1 and 0.6wt%, P between 0.005 and 0.03wt%, S between 0.005 and 0.03wt%, AI max. 0.01wt%, N max. 0.004wt%, Cu between 0.01 and 0.06wt%, O between 0.02 and 0.06wt%, V between 0.01 and 0.06wt%, the balance Fe and inevitable impurities, is hot-rolled with a finishing temperature higher than or equal to 800°C, and a coiling temperature of 600-800°C, cold-rolled with a reduction ratio higher than or equal to 60% and subjected to a decarburization annealing at 700-900°C for 30sec-3min, carried out in a continuous annealing furnace having a decarburizing atmosphere composed of 1-20% water vapour, gaseous hydrogen in an amount higher than or equal to twice the water vapour amount, and the balance being mainly gaseous nitrogen, so as to reduce the C-level to be less than or equal to 0.002wt%. JP-A-6116634 describes a similar method, but wherein the starting material has no vanadium and the initial C level is up to 0.015wt% and B is added instead of V for H-trapping.

[0004] Both prior art methods result in fully or superficially decarburized steel sheets which are suitable for enamelling by Direct White Enamelling (DWE), wherein one white enamel coating is applied on the surface, followed by one firing step. As the initial carbon level is quite low, fish-scale resistance due to cementite formation is not achieved. To compensate for this, a steel with a high oxygen level and a limited Al-level is used in the prior art together with specific alloying elements such as B, V. Thanks to the limited Al-content, oxides of Si and Mn and nitrides of B and V are formed within the bulk of the steel which are beneficial against fish-scaling. However, this alloying involves extra costs and leads to some technical difficulties, e.g. involving casting with V. Furthermore, the prior art decarburized sheets have rather low formability as testified by the values of the Lankford coefficient (rm). These values do not exceed 1.8 which is a concern when deep-drawing is foreseen. In particular, figure 1 of JP6116634 shows that rm values between 1.6 and 1.8 are only achieved for a very narrow range of carbon level before decarburizing annealing. Below 0.0050wt%C and above 0.0150wt%C, the rm value is deteriorated.

Aims of the invention [0005] The present invention aims to provide a partially decarburized steel sheet suitable for enamelling which do not suffer from the drawbacks of the above cited prior art.

Summary of the invention [0006] The invention is related to steel sheets and products and to a production method as disclosed in the appended claims. The invention is thus related to a rolled steel sheet suitable for enamelling, said sheet having a carbon profile, defined by a gradient in the C-level from a level Csurface at at least one surface of the sheet, to a level Cbu|k in the bulk of the sheet, Cbu|k being higher than Csurface, and with :

Cbuik higher than 0 and lower than or equal to 0.08wt%,

Csurface between 0 and 0.015wt%, AI between 0.012wt% and 0.07wt%,

Mn between 0.12wt% and 0.45wt%, O lower than 0.01wt% and optionally :

Cu between 0.025wt% and 0.1wt% S between 0.008wt% and 0.04wt%,

Ca between 0.0005wt% and 0.005wt% the balance being Fe and incidental impurities, and wherein the depth where the C-level reaches (Cbu|k+Csu[face)/2, is higher than 75μ(η.

[0007] According to a preferred embodiment, the steel sheet of the invention has an rm value between 1.8 and 2.1.

[0008] According to specific embodiments, Csurface is between 0.005wt% and 0.015wt%, or between 0 and 0.005wt%.

[0009] According to other specific embodiments, Cbu|k is between 0.02wt% and 0.08wt%, or between 0.025wt% and 0.08wt% or between 0.025wt% and 0.06wt%.

[0010] According to another embodiment, the Al-level is between 0.02wt% and 0.06wt%.

[0011] According to a further embodiment, said depth is between 130μ(η and 200μηι.

[0012] The invention is equally related to an enamelled steel sheet consisting of a steel sheet according to any of the above paragraphs, provided with an enamel layer.

[0013] The invention is further related to a steel product produced from a sheet according to the invention, and to an enamelled steel product consisting of a such a product, provided with an enamel layer.

[0014] The invention is also related to a method for producing a rolled steel sheetfor enamelling, comprising the steps of : subjecting a steel slab to hot rolling followed by coiling, and cold rolling, so as to obtain a cold-rolled steel sheet, said slab comprising the following initial composition : C between 0.02wt% and 0.08wt%, AI between 0.012wt% and 0.07wt%,

Mn between 0.12wt% and 0.45wt%, O lower than 0.01wt% and optionally :

Cu between 0.025wt% and 0.1wt%, S between 0.008wt% and 0.04wt%,

Ca between 0.0005wt% and 0.005wt%, the balance being Fe and incidental impurities, subjecting said cold-rolled sheet to continuous annealing step, wherein said sheet is exposed during a decarburizing time to a decarburizing atmosphere comprising water vapour and hydrogen gas, wherein the H2 content is between lvol% and 95vol%, the H20 content between 0.04vol% and 33vol%, the remainder being mainly nitrogen gas, the ratio pH20/pH2 being between 0.04 and 0.5.

[0015] According to a preferred embodiment, said continuous annealing takes place at an anneal temperature between 760°C and 850°C, and during a decarburizing time between 45s and 300s.

[0016] According to a specific embodiment, the anneal temperature is between 800°C and 850°C.

[0017] According to specific embodiments of the method of the invention, the initial C-level is between 0.025wt% and 0.08wt% or between 0.025wt% and 0.06wt%.

[0018] According to a further embodiment, the initial Al-level is between 0.02wt% and 0.06wt%.

[0019] According to a specific embodiment, the ratio pH20/pH2 is between 0.04 and 0.25.

[0020] The method of the invention may further comprise an over-ageing step at a temperature between 350°C and 450°C during a timespan between 100s and 500s. The method may further comprise a skinpass step with a reduction of between 0.3% and 1.5%.

Brief description of the figures [0021]

Figure 1 illustrates the carbon profile in a steel sheet according to the invention.

Figure 2 illustrates an example of an annealing step usable in the method of the invention.

Detailed description of the invention [0022] The steel sheet of the invention has a C-profile, defined by a gradient in the C-level from a lower value Csurface at the surface to a higher value Cbu|k in the bulk. The sheet is obtainable by a method which includes a continuous decarburization step, as will be described further in this text. Figure 1 illustrates the carbon-distribution across the thickness of two sheets according to the invention, with a thickness of 0.7mm. Curve 10 illustrates a sheet which comprises a bulk portion 11, where the C-level Cbu|k is substantially constant, and two surface portions 12 (one on each side of the sheet), each surface portion exhibiting the C-profile. The surface level is defined as the minimum value of the C-profile, measured by a suitable measurement technique (e.g. Glow Discharge Optical Emission Spectroscopy (GD-OES), which allows composition measurement as depth analysis). In a steel sheet according to the invention, the C-level at the surface is maximum 0.015wt%, whereas Cbu|k is higher than zero and lower than or equal to 0.08wt%. At the same time, Cbu|k is higher than CSU[face. According to an embodiment, Csurface is between 0.005wt% and 0.015wt%. According to another embodiment, Csu[face is between 0 and 0.005wt%.

[0023] Curve 10 is an example of a sheet where the decarburization has not taken place over the entire thickness of the sheet. This means that the level Cbu|k is equal to the initial C-level applied in the production method (described further in more detail). According to embodiments which correspond to embodiments of the method of the invention (see further), Cbu,k is then between 0.02wt% and 0.08wt%, or between 0.025wt% and 0.08wt, or between 0.025wt% and 0.06wt% or between 0.025wt% and 0.05wt%. Curve 13 illustrates the case where decarburization has continued until the middle plane of the sheet. In this case, Cbu!k is smaller than the initial C-level of the method, and the C-profile extends over each half-width of the sheet.

[0024] The decarburized sheet according to the invention further comprises AI, Mn and possibly S, Cu and Ca. Contrary to the prior art references, the oxygen level is to be kept lower than 0.01wt%. According to a preferred embodiment of the steel sheet of the invention, oxygen is not added deliberately to the composition, but is allowed only at impurity levels. Fish scaling resistance is ensured by the higher initial C-level, so no oxide formation is required for this purpose. This means that no special alloying elements such as V are included. Also, N is kept as low as possible.

[0025] The Al-level in the sheet of the invention is between 0.012wt% and 0.07wt%, which is higher than the allowed Al-level in the prior art references cited above. In the cited prior art documents AI needs to be limited to avoid deoxidation, so as to ensure the formation of the oxides that will work against fish-scaling. In the method of the invention (see further), AI is mandatory for deoxidation and binding of free N to avoid the ageing of the mechanical properties. When the Al-level is lower than 0.012wt%, insufficient deoxidation takes place, and binding of N is required through other means. Adding AI at levels higher than 0.07wt% means an increase in cost of the process, and a deterioration of the enamelling quality. A more preferred range for the Al-level, related to more optimized conditions in terms of deoxidation and cost/enamelling quality is between 0.02wt% and 0.06wt%.

[0026] Mn is present between 0.12wt% and 0.45wt%. This element is added to control the strength properties of the steel and to avoid the formation of free sulphur.

[0027] Copper, Sulphur and Calcium may optionally be added above the impurity level, more precisely in the ranges 0.025wt% to 0.1wt%, 0.008wt% to 0.04wt% and 0.0005wt% to 0.005wt% respectively. These elements improve the enamelling quality.

[0028] The balance of the composition of the steel sheet according to the invention consists of Fe and incidental impurities. The following elements may be present as impurities at levels which are preferably lower than the values (in wt%) given in table 1 :

Table 1 : impurity levels

(continued)

[0029] In a steel sheet of the invention, the depth of the C-profile, being defined as the depth where the C-level reaches (Cfciuik + Csurfare) is higher than 75μηι, to ensure good enamelling capability. According to an embodiment, said depth is between 130 μίτι and 200 μίτι.

[0030] Steel sheets according to the invention, i.e. with a C-level at the surface between 0 and 0.015wt% are suitable for 2C/1F enamelling, i.e. enamelling by applying a ground coat enamel, followed by an outer enamel coating, both coatings being subjected to one firing step, and for 1C/1F enamelling, i.e. enamelling by applying one enamel layer subjected to one firing step. Steel sheets with low C-levels (i.e. 0.005wt% and less) at the surface may be suitable also for Direct White Enamelling (DWE).

[0031] According to a preferred embodiment, the rm value of a steel sheet according to the invention is between 1.8 and 2.1. This means that the steel sheet has better formability than the prior art steel sheets referred to above. In the present description, the Y value refers to the plastic strain ratio (also known as the anisotropy factor), being the ratio of the true strain in the width direction to the true strain in the thickness direction when a sheet material is pulled in uniaxial tension beyond its elastic limit. The ’rm’ value is defined as 1Λ (r90 + 2*r45 + r0), with r90, r45 and r0 the r-values as defined above, measured on samples oriented respectively at 90°, 45° and 0° with respect to the rolling direction. In a steel sheet according to the invention, fish scaling resistance is ensured by the higher initial C-level applied in the method (see further).

[0032] The steel sheet of the invention can be produced by subjecting a steel slab with a specific initial steel composition to hot rolling, coiling and cold rolling, and by subjecting the cold-rolled sheet to continuous superficial decarburization. The initial composition is mainly characterized by a higher C-level compared to the prior art, and by a higher Al-level and a lower oxygen level. No deliberate addition of elements like V, Nb or B is done, while still allowing to produce enamelled steel sheets with a high fish scale resistance and good enamel surface quality. The initial C-level is between 0.02wt% and 0.08wt%, more preferably between 0.025wt% and 0.08wt%. This is higher than the initial C-levels disclosed in the prior art references referred to above. Despite such higher initial C-levels, the method of the invention allows to obtain steel sheets with improved formability characteristics compared to the prior art. Whereas JP6116634 indicates that above 0.015wt% of initial carbon, it is not possible to obtain acceptable decarburization and good formability, the starting composition of the invention does not encounter these problems. Decarburization is possible down to an acceptable level, while formability is excellent. When the initial C-level is lower than 0.02wt%, insufficient cementite formation occurs which deteriorates fish scale resistance. C-levels above 0.08wt% lead to too high strength levels and thus reduced formability. Specific ranges for the initial C-level, related to more optimized characteristics in terms offish scale resistance and strength/formability are between 0.025wt% and 0.06wt% and between 0.025wt% and 0.05wt%.

[0033] The initial steel composition according to the method of the invention further comprises AI, Μη and possibly O, S, Cu and Ca in the same ranges as the decarburized sheet described above, the balance being Fe and the incidental impurities listed in Table 1. A more preferred range for the initial Al-level, related to more optimized conditions in terms of deoxidation and cost/enamelling quality is between 0.02wt% and 0.06wt%. According to a preferred embodiment of the method of the invention, oxygen is not added deliberately to the composition, but is allowed only at impurity levels.

[0034] The method of the invention comprises standard steps of hot rolling and cold rolling a steel slab of the above composition. According to the preferred embodiment, the slab is (re)heated at a temperature above 1050°C, subjected to hot rolling with a finishing temperature between 850°C and 950°C, and coiling at coiling temperature between 620°C and 770°C. Still according to the preferred embodiment, cold rolling is performed with a reduction of minimum 50%. The final thickness of the cold rolled sheet is preferably between 0.2 and 2mm.

[0035] The decarburization anneal is done in an annealing furnace for continuous annealing (i.e. annealing while the cold-rolled sheet moves through the furnace at a given speed, said speed determining the anneal time, i.e. the time spent at the annealing temperature) as known in the art, possibly provided with a vapour injection device for applying a given annealing atmosphere.

[0036] Figure 2 shows an example of a lay-out of an annealing furnace usable in the method of the invention, starting with heating phase 1 wherein the temperature rises to the annealing temperature. Phase 2 represents the actual annealing (soaking) phase. Phase 3 is an overageing step. Phase 2 can consist of one or more periods with a different (constant or average) annealing temperature and a different annealing atmosphere in each period. Practically speaking, the different periods at different conditions can be obtained by dividing the annealing zone in subsections and by injecting H20 vapour into an atmosphere comprising H2, at various points along the annealing line (see example further in this description).

[0037] According to the invention, the superficial decarburization is done underadecarburizing atmosphere comprising water vapour and hydrogen gas, the remainder being essentially nitrogen gas, with the H2 content between 1vol% and 95vol%, the H20 content between 0.04vol% and 33vol%, the ratio of partial pressures pH20/pH2 being between 0.04 and 0.5, more preferably between 0.04 and 0.25. The above composition describes the atmosphere at the start of the decarburizing time. It is clear that during decarburization, the atmosphere composition will change, primarily due to the decarburization reaction taking place (formation of H2 and CO). Also at the start of the decarburizing time, small amounts of other gases may already have formed or may be present as impurities in the atmosphere. The total pressure under which the superficial decarburization anneal takes place may be atmospheric pressure, or a pressure different from atmospheric but within generally known boundaries applied in this type of annealing process.

[0038] According to one embodiment, the decarburizing atmosphere can be prepared with a mixture of H2 and N2 with between 1,5 and 5% H2 in which H20 vapour is injected so that pH20/pH2 is between 0.04 and 0.5. The minimum value of this ratio ensures that sufficient H20 is present to obtain decarburization according to the formula C + H20 ->· CO + H2. The maximum of said range ensures that oxidation of Fe and of the furnace is avoided. A more preferred range for pH20/pH2, related to more optimized conditions in terms of sufficient decarburization and avoiding the occurrence of Fe-oxidation is between 0.04 and 0.25.

[0039] In the method of the invention, the decarburizing atmosphere is applied during at least one of said periods with a different (constant or average) annealing temperature and a different annealing atmosphere in each period, preferably during the totality of phase 2. In the following, the "decarburizing time’ refers to the time spent under the conditions of the decarburizing atmosphere.

[0040] The decarburizing time and the anneal temperature are chosen so as to obtain a steel sheet according to the invention. It is within the skilled person’s knowledge to find suitable combinations of decarburizing time and anneal temperature based on the examples given further in this description. According to a preferred embodiment, the decarburizing time is between 45s and 300s and the anneal temperature between 760°C and 850°C. When the ratio pH20/pH2 is lower than about 0.1, the decarburizing time is preferably higher than 70s. A more preferred range of the anneal temperature, applicable in combination with any decarburizing time between 45s and 300s is between 800°Cand 850°C. The temperature is not necessarily constant during the decarburizing time. Fluctuations of the temperature may occur due to variations in the line speed for example. An over-ageing step may be applied at a temperature between 350°C and 450°C during a timespan between 100s and 500s. A skinpass may further be applied with a reduction of between 0.3% and 1.5%.

Examples [0041] Results from industrial trials performed by the applicant will be described hereafter, as well as a number of laboratory trials. All tested samples were produced from starting compositions according to the invention. The coiling temperature was 725°C. Two industrial trials were conducted. The thickness of the cold rolled sheet subjected to decarburization annealing in industrial trial 1 was 0.6mm; in the second industrial trial the thickness was 1 mm.

[0042] The continuous annealing line in which the industrial trials were conducted consists of a heating section, two soaking areas, a cooling and an overaging part. The annealing atmosphere consisted mainly of a mixture of H2 and N2, with Fl20 vapour being injected in the first and/or the second soaking area. In the first trial, H20 vapour was injected only in the second soaking area. In the second trial, H20 was injected in the first and the second soaking area. Overageing was performed in both trials at 400°C. The overageing time depended on the line speed, e.g. at 180m/min line speed, the overageing time was 232s. Table 2 shows the annealing conditions for both trials (numbered trial 1 and trial 2). Table 3 shows the composition besides C, for a number of the samples shown in table 1.

[0043] In industrial trial 1, the pH20/pH2 ratio is below the range of 0.04-0.5 in the first soaking area (due to the fact that no Fl20 injection is done). The decarburizing time in this trial is the time spent in the second soaking area, where the pH20/pH2 is within said range. This is an example therefore of a process wherein phase 2 as shown in figure 1 comprises a first period wherein the conditions of the present invention are not met, and a second period wherein these conditions are met. Such a process falls within the scope of the present invention.

[0044] In industrial trial 2, hi20-injection was performed in both soaking areas. The decarburizing time indicated here is the time spent in soaking areas 1 and 2. The anneal temperature is the average of the temperatures in soaking areas 1 and 2. The pH20/pH2 values indicated in table 1 are the average values in soaking area 1 in which more hl20 was injected. However, the pH20/pH2 in soaking area 2 is estimated to be also within the range of 0.04-0.5. In industrial trial 2, longerdecarburizing times could be achieved as compared to the first trial, forsimilar line velocities, leading to stronger decarburization.

[0045] The laboratory trials (marked ’trial 3’ in table 2), were conducted on samples which were subjected to a simulation of the continuous annealing step, at the conditions shown in table 2. These trials were conducted in an atmosphere of HNX with 5% H2, with H20 added to obtain pH20/pH2 in the range [0.04-0.5], [0046] Samples from all three trials were subjected to an enamelling process wherein a ground coat enamel is deposited, this enamel being designed especially to determine the role of C in the enamel characteristics. It was found that the adhesion of the enamelling layerwas good for all tested samples. The enamelling aspect was good for C-levels at the surface of maximum 0.015wt%, and for profile depths of 75μηι up to 250μηι, as shown in table 1. There is no reason to conclude from the results however that the enamelling quality deteriorates at higher depth values than 250μηη. Such higher depth values are therefore not excluded from the scope of the invention. All tested samples showed a good fish scale resistance.

[0047] Table 2 summarizes the results after decarburization in terms of the C-level at the surface (i.e. minimum level of the C-profile, measured by GD-OES), the depth of the C-profile, and the quality of an enamel layer produced on the surface of the samples. Samples 25 to 35 yielded a bad enamelling aspect, which can be ascribed to either an insufficient depth of the C-profile (as determined by the depth where the C-level reaches (Csurface+Cbu|k/2), and/or a C level at the surface which is too high. The reason for these negative results can be ascribed to the test conditions, either the anneal temperature which is too low, the decarburizing time too short, or the pH20/pH2 ratio too low, or a combination of these factors.

[0048] Table 4 shows the mechanical properties of a number of samples taken from the sheets of the industrial trials 1 and 2. Importantly, the formability in terms of the rm value is excellent, despite the initial C-level which is higher than in the prior art : rm is between 1.8 and 2.1. These results prove that the method of the invention allows to produce steel sheets suitable for enamelling, starting from an initial C-level higher than 0.02wt%, the resulting sheets allowing good enamelling quality and fish scale resistance, and having very good formability characteristics.

Table 2: Overview of experimental conditions and results

(continued)

[0049] The depth-values given in table 1 are values of the depth where the C-level reaches (Csurface+Cbu|k) /2. The depth measurements indicated with show the maximum depth which could be measured with the applied equipment. The real value is thus higher than this value. T able 3 : composition of samples (C-level in table 1, remaining elements are beneath impurity level, the remainder is Fe)

Table 4 : mechanical properties

Claims 1. A rolled steel sheet suitable for enamelling, said sheet having a carbon profile, defined by a gradient in the C-level from a level CSU[face at at least one surface of the sheet, to a level Cbu|k in the bulk of the sheet, Cbu|k being higher than Csurface, and with : - Cbu|k higher than 0 and lower than or equal to 0.08wt%, - Csurface between 0 and 0.015wt%, - AI between 0.012wt% and 0.07wt%, - Mn between 0.12wt% and 0.45wt%, - O lower than 0.01wt% and optionally : - Cu between 0.025wt% and 0.1wt% - S between 0.008wt% and 0.04wt%, - Ca between 0.0005wt% and 0.005wt%, the balance being Fe and incidental impurities, wherein said impurities may comprise (in wt%) : Si < 0.1, P < 0.03, Ti < 0.01, Cr < 0.2, Ni < 0.2, As < 0.02, Sn < 0.02, Nb < 0.01, V < 0.01, Sb < 0.02, Mo < 0.03, B < 0.0005, N < 0.007, and wherein the depth where the C-level reaches (Cbu|k+CSU[face)/2, is higher than 75μΐτι. 2. Steel sheet according to claim 1, having an rm value between 1.8 and 2.1. 3. Steel sheet according to claim 1 or 2, wherein Csu[face is between 0.005wt% and 0.015wt%. 4. Steel sheet according to claim 1 or 2, wherein Csu[face is between 0 and 0.005wt%. 5. Steel sheet according to any one of claims 1 to 4, wherein Cbu|k is between 0.02wt% and 0.08wt%. 6. Steel sheet according to claim 5, wherein Cbu|k is between 0.025wt% and 0.08wt%. 7. Steel sheet according to claim 5, wherein Cbu|k is between 0.025wt% and 0.06wt%. 8. Steel sheet according to any one of claims 1 to 7, wherein the Al-level is between 0.02wt% and 0.06wt%. 9. Steel sheet according to any one of claims 1 to 8, wherein said depth is between 130μ(η and 200μΓη. 10. Enamelled steel sheet consisting of a steel sheet according to any one of claims 1 to 9 provided with an enamel layer. 11. A method for producing a rolled steel sheet for enamelling, comprising the steps of : - subjecting a steel slab to hot rolling followed by coiling, and cold rolling, so as to obtain a cold-rolled steel sheet, said slab comprising the following initial composition : - C between 0.02wt% and 0.08wt%, - AI between 0.012wt% and 0.07wt%, - Mn between 0.12wt% and 0.45wt%, - O lower than 0.01wt% and optionally : - Cu between 0.025wt% and 0.1wt%, - S between 0.008wt% and 0.04wt%, - Ca between 0.0005wt% and 0.005wt%, - the balance being Fe and incidental impurities, wherein said impurities may comprise (in wt%) : Si < 0.1, P < 0.03, Ti < 0.01, Cr < 0.2, Ni < 0.2, As < 0.02, Sn < 0.02, Nb < 0.01, V < 0.01, Sb < 0.02, Mo < 0.03, B < 0.0005, N < 0.007, - subjecting said cold-rolled sheet to continuous annealing step, wherein said sheet is exposed during a decar-burizing time to a decarburizing atmosphere comprising water vapour and hydrogen gas, wherein the H2 content is between 1vol% and 95vol%, the H20 content between 0.04vol% and 33vol%, the remainder being mainly nitrogen gas, the ratio pH20/pH2 being between 0.04 and 0.5. 12. Method according to claim 11, wherein said continuous annealing takes place at an anneal temperature between 760°C and 850°C, and during a decarburizing time between 45s and 300s. 13. Method according to claim 12, wherein the anneal temperature is between 800°C and 850°C. 14. Method according to any one of claims 13 to 15, wherein the initial C-level is between 0.025wt% and 0.08wt%. 15. Method according to claim 14, wherein the initial C-level is between 0.025wt% and 0.06wt%. 16. Method according to any one of claims 11 to 15, wherein the initial Al-level is between 0.02wt% and 0.06wt%. 17. Method according to any one of claims 11 to 16, wherein the ratio pH20/pH2 is between 0.04 and 0.25. 18. Method according to any one of claims 11 to 17, further comprising an over-ageing step at a temperature between 350°C and 450°C during a timespan between 100s and 500s. 19. Method according to claim 18, further comprising a skinpass step with a reduction of between 0.3% and 1.5%. Patentansprüche 1. Emaillierungsfähiges Walzstahlblech, wobei das Blech ein Kohlenstoffprofil aufweist, das durch einen Gradienten in der C-Höhe von einer Höhe Cobe[f|âche auf zumindest einer Oberfläche des Blechs zu einer Höhe CMasse in der Masse des Blechs definiert ist, wobei CMasse größer als C0be[flache ist, und wobei: - CMasse größer als 0 ist und kleiner als oder gleich 0,08 Gew.-% ist; - Cobe[f|ache zwischen 0 Gew.-% und 0,015 Gew.-% beträgt; - AI zwischen 0,012 Gew.-% und 0,07 Gew.-% beträgt; - Mn zwischen 0,12 Gew.-% und 0,45 Gew.-% beträgt; - O weniger als 0,01 Gew.-% ist; und optional: - Cu zwischen 0,025 Gew.-% und 0,1 Gew.-% beträgt; - S zwischen 0,008 Gew.-% und 0,04 Gew.-% beträgt; - Ca zwischen 0,0005 Gew.-% und 0,005 Gew.-%; beträgt, wobei der Rest Fe und anfallende Verunreinigungen sind, wobei die Verunreinigungen (in Gew.-%): Si < 0,1, P < 0,03, Ti < 0,01, Cr < 0,2, Ni < 0,2, As < 0,02, Sn < 0,02, Nb < 0,01, V < 0,01, Sb < 0,02, Mo < 0,03, B < 0,0005, N < 0,007 umfassen können und wobei die Tiefe, bei der die C-Höhe (CMasse + Coberflache) / 2 erreicht, höher als 75 μηι ist. 2. Stahlblech nach Anspruch 1, das einen rm-Wert zwischen 1,8 und 2,1 aufweist. 3. Stahlblech nach Anspruch 1 oder 2, wobei Coberfläche zwischen 0,005 Gew.-% und 0,015 Gew.-% beträgt. 4. Stahlblech nach Anspruch 1 oder 2, wobei Coberflache zwischen 0 Gew.-% und 0,005 Gew.-% beträgt. 5. Stahlblech nach irgendeinem der Ansprüche 1 bis 4, wobei CMasse zwischen 0,02 Gew.-% und 0,08 Gew.-% beträgt. 6. Stahlblech nach Anspruch 5, wobei CMasse zwischen 0,025 Gew.-% und 0,08 Gew.-% beträgt. 7. Stahlblech nach Anspruch 5, wobei CMasse zwischen 0,025 Gew.-% und 0,06 Gew.-% beträgt. 8. Stahlblech nach irgendeinem der Ansprüche 1 bis 7, wobei die Al-Höhe zwischen 0,02 Gew.-% und 0,06 Gew.-% beträgt. 9. Stahlblech nach irgendeinem der Ansprüche 1 bis 8, wobei die Tiefe zwischen 130 μ(η und 200 μ(η beträgt. 10. Emailliertes Stahlblech, das aus einem Stahlblech nach einem der Ansprüche 1 bis 9 besteht, das mit einer Emailleschicht versehen ist. 11. Verfahren zum Herstellen eines Walzstahlblechs zum Emaillieren, das die Schritte umfasst: - Unterziehen einer Stahlbramme einem Warmwalzen, gefolgt von einer Wicklung und Kaltwalzen, um ein kaltgewalztes Stahlblech zu erhalten, wobei die Bramme die folgende Ausgangszusammensetzung aufweist: - C zwischen 0,02 Gew.-% und 0,08 Gew.-%; - AI zwischen 0,012 Gew.-% und 0,07 Gew.-%; - Mn zwischen 0,12 Gew.-% und 0,45 Gew.-%t; - O weniger als 0,01 Gew.-% ist; und optional: - Cu zwischen 0,025 Gew.-% und 0,1 Gew.-%; - S zwischen 0,008 Gew.-% und 0,04 Gew.-%; - Ca zwischen 0,0005 Gew.-% und 0,005 Gew.-%, wobei der Rest Fe und anfallende Verunreinigungen sind, wobei die Verunreinigungen (in Gew.-%) :Si < 0,1, P < 0,03, Ti < 0,01, Cr < 0,2, Ni < 0,2, As < 0,2, Sn < 0,02, Nb < 0,01, V < 0,01, Sb < 0,02, Mo < 0,03, B < 0,0005, N < 0,007 umfassen können:, - Unterziehen des kaltgewalzten Blechs einem kontinuierlichen Glühschritt, wobei das Blech während einer Entkohlungszeit einer entkohlenden Atmosphäre ausgesetzt wird, die Wasserdampf und Wasserstoffgas um fasst, wobei der H2-Gehalt zwischen 1 Vol.-% und 95 Vol.-% liegt, der H20-Gehalt zwischen 0,04 Vol.-% und 33 Vol.-% liegt, wobei der Rest vorwiegend Stickstoffgas ist, wobei das Verhältnis pH20/pH2 zwischen 0,04 und 0,5 liegt. 12. Verfahren nach Anspruch 11, wobei das kontinuierliche Glühen bei einer Glühtemperatur zwischen 760 °C und 850 °C und während einer Entkohlungszeit zwischen 45 s und 300 s erfolgt. 13. Verfahren nach Anspruch 12, wobei die Glühtemperatur zwischen 800 °C und 850 °C liegt. 14. Verfahren nach irgendeinem der Ansprüche 13 bis 15, wobei die anfängliche C-Höhe zwischen 0,025 Gew.-% und 0,08 Gew.-% liegt. 15. Verfahren nach Anspruch 14, wobei die anfängliche C-Höhe zwischen 0,025 Gew.-% und 0,06 Gew.-% liegt. 16. Verfahren nach irgendeinem der Ansprüche 11 bis 15, wobei die anfängliche Al-Höhe zwischen 0,02 Gew.-% und 0,06 Gew.-% liegt. 17. Verfahren nach irgendeinem der Ansprüche 11 bis 16, wobei das Verhältnis pH20/pH2 zwischen 0,04 und 0,25 liegt. 18. Verfahren nach irgendeinem der Ansprüche 11 bis 17, das darüber hinaus einen Überalterungsschritt bei einer Temperatur zwischen 350 °C und 450 °C innerhalb einer Zeitspanne zwischen 100 s und 500 s umfasst. 19. Verfahren nach Anspruch 18, das darüber hinaus einen Dressierungsschritt mit einer Verringerung von zwischen 0,3 % und 1,5% umfasst.

Revendications 1. Feuille d’acier laminée appropriée pour un émaillage, ladite feuille présentant un profil de carbone, défini par un gradient du niveau de C d’un niveau Csurface au niveau d’au moins une surface de la feuille, à un niveau Cmasse dans la masse de la feuille, Cmasse étant supérieur à Csurface, et avec : - Cmasse supérieur à 0 et inférieur ou égal à 0,08 % en poids, - Csurface entre 0 et 0,015 % en poids, - Al entre 0,012 % en poids et 0,07 % en poids, - Mn entre 0,12 % en poids et 0,45 % en poids, - O inférieur à 0,01 % en poids et optionnellement : - Cu entre 0,025 % en poids et 0,1 % en poids, - S entre 0,008 % en poids et 0,04 % en poids, - Ca entre 0,0005 % en poids et 0,005 % en poids, le reste étant du Fe et des impuretés accidentelles, dans laquelle lesdites impuretés peuvent comprendre (en % en poids) : Si < 0,1, P < 0,03, Ti < 0,01, Cr < 0,2, Ni < 0,2, As < 0,02, Sn < 0,02, Nb < 0,01, V < 0,01, Sb < 0,02, Mo < 0,03, B < 0,0005, N < 0,007, et dans laquelle la profondeur à laquelle le niveau de C atteint (Cmasse + Csurface)/2, est supérieure à 75 μπι. 2. Feuille d’acier selon la revendication 1, ayant une valeur rm entre 1,8 et 2,1. 3. Feuille d’acier selon la revendication 1 ou 2, dans laquelle Csurface est entre 0, 005 % en poids et 0,015 % en poids. 4. Feuille d’acier selon la revendication 1 ou 2, dans laquelle Csurface est entre 0 et 0, 005 % en poids. 5. Feuille d’acier selon l’une quelconque des revendications 1 à 4, dans laquelle Cmasse est entre 0,02 % en poids et 0,08 % en poids. 6. Feuille d’acier selon la revendication 5, dans laquelle Cmasse est entre 0,025 % en poids et 0,08 % en poids. 7. Feuille d’acier selon la revendication 5, dans laquelle Cmasse est entre 0,025 % en poids et 0,06 % en poids. 8. Feuille d’acier selon l’une quelconque des revendications 1 à 7, dans laquelle le niveau d’AI est entre 0,02 % en poids et 0,06 % en poids. 9. Feuille d’acier selon l’une quelconque des revendications 1 à 8, dans laquelle ladite profondeur est entre 130 μσι et 200 μ(η. 10. Feuille d’acier émaillée constituée d’une feuille d’acier selon l’une quelconque des revendications 1 à 9 présentant une couche d’émail. 11. Procédé de production d’une feuille d’acier laminée pour émaillage, comprenant les étapes consistant à : - soumettre une brame d’acier à un laminage à chaud suivi d’un bobinage et d’un laminage à froid, de manière à obtenir une feuille d’acier laminée à froid, ladite brame comprenant la composition initiale suivante : - C entre 0,02 % en poids et 0,08 % en poids, - Al entre 0,012 % en poids et 0,07 % en poids, - Mn entre 0,12 % en poids et 0,45 % en poids, - O inférieur à 0,01 % en poids et optionnellement : - Cu entre 0,025 % en poids et 0,1 % en poids, - S entre 0,008 % en poids et 0,04 % en poids, - Ca entre 0,0005 % en poids et 0,005 % en poids, - le reste étant du Fe et des impuretés accidentelles, dans lequel lesdites impuretés peuvent comprendre (en % en poids) : Si < 0,1, P < 0,03, Ti < 0,01, Cr< 0,2, Ni < 0,2, As < 0,02, Sn < 0,02, Nb < 0,01, V < 0,01, Sb < 0,02, Mo < 0,03, B < 0,0005, N < 0,007, - soumettre ladite feuille laminée à froid à une étape de recuit continu, dans lequel ladite feuille est exposée pendant une durée de décarburation à une atmosphère décarburante comprenant de la vapeur d’eau et un gaz d’hydrogène, dans lequel la teneur en H2 est entre 1 % en vol et 95 % en vol, la teneur en H20 entre 0,04 % en vol et 33 % en vol, le reste étant principalement du gaz d’azote, le rapport pH20/pH2 étant entre 0,04 et 0,5. 12. Procédé selon la revendication 11, dans lequel ledit recuit continu a lieu à une température de recuit entre 760 °C et 850 °C, et pendant une durée de décarburation entre 45 s et 300 s. 13. Procédé selon la revendication 12, dans lequel la température de recuit est entre 800 °C et 850 °C. 14. Procédé selon l’une quelconque des revendications 13 à 15, dans lequel le niveau de C initial est entre 0, 025 % en poids et 0,08 % en poids. 15. Procédé selon la revendication 14, dans lequel le niveau de C initial est entre 0,025 % en poids et 0,06 % en poids. 16. Procédé selon l’une quelconque des revendications 11 à 15, dans lequel le niveau d’AI initial est entre 0,02 % en poids et 0,06 % en poids. 17. Procédé selon l’une quelconque des revendications 11 à 16, dans lequel le rapport pH20/pH2 est entre 0,04 et 0,25. 18. Procédé selon l’une quelconque des revendications 11 à 17, comprenant en outre une étape de survieillissement à une température entre 350 °C et 450 °C pendant un laps de temps entre 100 s et 500 s. 19. Procédé selon la revendication 18, comprenant en outre une étape d’écrouissage avec une réduction située entre 0,3 % et 1,5 %.

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • JP 2282421 A [0003] · JP 6116634 B [0004] [0032] • JP 6116634 A [0003]

Claims

S & A1AÏMLMI QUESTIONS

1. enamel!) Get get get «« í í í í í í í í ez ez ez ez í í í amelynek amelynek amelynek amelynek amelynek amelynek ien ien ien ien ien ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében ében Ci Ci Ci Ci € fciJJ ^ and where: “Che« is greater than 8 and less than or equal to 8.08% by weight, - Caftte between 0 and 0.01% of weight, - between Al 0.812% and 00? WtmgH. - Mn 0.12 between ≤ g% and 0.45%, -O less than 0.81% by weight, and optionally between: Cn 0.025% by weight and 0.1% by weight, - S 0.888% by weight and 0.04% by weight, »Ca 8.0805 wt% to 0.005 wt%, where the residual Pé and any contaminants are at least one of the contaminants (masses: Si <0.1, P <(M> 3, Ti <0, 01, Cr <0.2, Hi <0.2, As <0.02, Sn <0.02, Nb <0.03, V < 0.03, Sb < 0.02, Mo < 0.03, i <0.0005, N <0.007, and aboi aza depth; greater than 75 μι »,.

Steel sheet according to claim 1, wherein the azr value is between 3.8 and 2.1.

3. A steel sheet according to claim 1 or claim 2 having a content of 0, 885% by weight and 0.015% by weight.

4. The steel plate of the!, Or 2, item G, where G & t is between 0 and 8,005 t8 meg%.

5, 1-4. Steel sheet according to any one of the claims, wherein the Csőső is between 0.02 and 0 and five. y.

The steel sheet according to claim 5, and the cylinders thereof, have a value of from about 8% to about 8.88%.

The steel sheet according to claim 1, wherein the * *, & $ 0.021 wt / wt.

8. Referring to Figures 1-7. Steel sheet according to any one of claims 1 to 3, wherein the Al-sine is between 0.02% and 0.06% by weight.

9. i-δ. any of the following claims are included.

II. steel plate, which is made of steel sheet, coated with enamel layer \ t

11. The procedure for the bite. seams for the production of steel sheet, which includes the following steps * steel rolls for hot rolling, then winding and cold rolling, to obtain a cold rolled steel sheet, the starting material of which is as follows: - C 0.02% to 0.08% by weight, : - AJ: 0.012 wt% to 0.07 wt% - Mn 0.12 wt%) and 0:, 45 wt%, - O smaller than wt% and optionally; - $ QMS to 0.1%, «$ 0.00 | % by weight to 0.04% by weight. - Ca between 0.0005% and 0.005% by weight, - the residual Fe and any impurity where the impurity mrtaimazliat is mentioned (in% by weight J: Si < 0.1, P < 0.03. Ti < 0 , 01, Cr <0.2, Ni <0.2, As <0.02, So <0.02, Nb <0.0 i, V <0.01, Sb <0.02, Mo <0, 03, B <0.0005, N <0.007, ~ mention cold-rolled plate under continuous firing step, where said plate is made by dehydrogenation of water vapor and hydrogen gas for a long time where H2 content is 11%. and 95% by weight, the H2O fuel content ranging from 0.04% to 33% by weight, the remainder being mainly nitrogen gas, where the ratio of P1 to PF1 is between Ö4 and OjS.

12. All. The process according to claim 1, wherein said continuous Exposure is at a temperature of between 7iOc € and SSfTC, and a dextrose between 45 sec and 300 sec.

13. The IJiris of claim 12, wherein the annealing temperature is SOON? and 850 ° C.

14. The 13-15. The process according to any one of claims 1 to 4, wherein the starting C content is from 0.025% to 0.08% by weight, IS The process of claim 14, wherein the starting C-taitai is 0.025% by weight and 0.06% by weight. 16th, the! 1 -IS. A process according to any one of claims 1 to 4, wherein the starting Al-blue is present in an amount of 0.02% by weight and 0.1% by weight of 17% by weight. A process according to any of the claims wherein the pH / pH pH ratio is 13.04 and 1), 25, IS. 11-17. A method according to any one of claims 1 to 4, further comprising a bowl burning step at a temperature between ^SOÎC and 4§0®C in a time period between sec0 sec to 500 sec, 19, A 1S. The method of claim 1, further comprising a dressing step with a reduction of from 0.3% to 1.5%.