JPH0678569B2 - Method for producing steel sheet for enamel having excellent adhesion and foam resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a steel sheet for enamel, and in particular, it has excellent press formability and adhesion of enamel after firing enamel, and causes occurrence of enamel bubble defects. The present invention relates to a method for manufacturing a cold rolled steel sheet for non-enamel.

<Prior Art> Enamel has a beautiful surface and excellent corrosion resistance, and is widely used in kitchen appliances, sanitary appliances, panels, chemical containers and the like.

Above all, steel sheets used for kitchen appliances and bathtubs are required to have excellent deep drawability. In order to improve the deep drawability, high ductility (El) and high Rankford value (r value) are required as mechanical properties of the steel sheet.

Further, the steel plate for enamel needs to be an ultra-low carbon steel and at the same time have a clean surface in order to suppress the occurrence of bubble defects and firing strain.

Furthermore, enameled steel sheets are produced by applying glaze to a steel sheet and firing it, but at the firing temperature of 800 to 850 ° C, hydrogen that has penetrated into the steel sheet agglomerates at the boundary between the steel sheet and the glaze during cooling, and the pressure causes glaze. A so-called “fly-out” that occurs when flipping is generated.

In general, as a method for preventing the wing, the oxygen content is increased to increase the inclusions in the steel, and Ti, B, N
A method of precipitating a large amount of second phase such as b, V, etc., carbide, nitride, sulfide, etc. has been used. However, if there are many inclusions and precipitates in the steel, the deep drawability deteriorates. Therefore, there is a limit to the production of enamel steel plates for applications requiring deep drawability.

The decarburized and denitrified annealed capped steel sheet satisfies these requirements and is excellent in press workability, and has been widely used as a steel sheet for enamel. However, this type of steel plate is inevitably high in cost because it needs decarburization and denitrification annealing in addition to ingot casting and slabbing rolling.

In order to solve such a problem, using a Ti-added ultra-low carbon steel excellent in press formability, which is the invention of Japanese Examined Patent Publication No. 42-12348, instead of decarburizing and denitrifying annealing, a continuous annealing method or a box annealing method is used. Many attempts have been made to produce steel plates for enamel. For example, as disclosed in JP-A-51-98619 and JP-A-54-125117, various methods have been proposed for producing a steel sheet for enamel which is excellent in press formability and knurling resistance.

In the case of Ti-added steel, Ti forms TiC, TiN, or Ti sulfide or Ti phosphide in the steel to improve the slab resistance, and at the same time, C, N and S are not in a solid solution state. Moldability is also good.

Therefore, it has been considered necessary to contain elements such as C, N, S, and P in the steel together with sufficient Ti in order to suppress the tabulation. However, the enamel steel sheet produced by the conventional method is inferior in the enamel adhesion to the decarburized and denitrified capped steel sheet, and particularly in the case of single-pass enamel coating, enamel bubble defects are likely to occur. And had a problem.

Due to these drawbacks, Ti-added ultra-low carbon steel has been used as a steel plate for enamel only for a very small number of applications, including enamel double crushing, while it has excellent press formability and resistance to tabulation. It was In particular, a glaze for enamel that does not contain Ni or Co, which promotes the interfacial reaction between the steel plate and the enamel glaze and has weak adhesion, could not be used directly for glazing and baking directly on the steel plate. .

On the other hand, as a method for improving the enamel adhesion of the steel sheet itself used for such a direct single-use enamel, for example, the methods disclosed in JP-A-51-27812 and JP-A-57-63661 are known. Has been.

Japanese Patent Laid-Open No. 51-27812 aims to improve adhesion by adding Co, As, Ni, etc. to steel, but in order to obtain good adhesion, 600 mg / dm ² or more is required. It is said that pickling weight reduction is required. However, in order to obtain such a large amount of pickling loss, there are problems in that not only the amount of acid to be reacted is large, but also the pickling solution deteriorates quickly and work management is difficult.

Further, in JP-A-57-63661, in order to solve the above problems, Cu: 0.02 to 0.06% by weight (hereinafter simply referred to as%
Is shown below), and (P + S) / Cu is set to 2.0 or less to obtain good adhesion at a small pickling loss value (200 mg / dm ² ) or more. However, there was a problem that bubble defects and black spot defects of enamel occurred. When the above-mentioned defects occur, re-baking by reworking is required, which causes a problem of cost increase due to reworking and reduction of adhesion force by rebaking.

<Problems to be Solved by the Invention> The present invention is to produce a steel plate for enamel which is excellent in enamel adhesion and foam resistance even with a single application of enamel without impairing the press formability and stab resistance of Ti-added steel. It provides a method.

<Means for Solving the Problems> The present invention provides (1) C: 0.001 to 0.005%, Mn: 0.05 to 0.5% by weight,
P: 0.003 to 0.020%, S: 0.005 to 0.04%, Sol.Al: 0.003 to 0.1
00%, N: 0.003 to 0.010%, Se: 0.002 to 0.020%, Ti: And Cu: 0.01-0.05% and Of the continuous casting slab containing Fe and the other balance of Fe and unavoidable impurities is hot-rolled, then bent so that the radius of curvature is in the range of 0.3 to 1.5 m.
Manufacture of enamel steel sheet with excellent adhesion and foam resistance, which is characterized by holding for 0 seconds to 30 minutes and then subjecting it to conventional hot finish rolling, cold rolling, recrystallization annealing and temper rolling. Method, and (2)% by weight C: 0.001 to 0.005%, Mn: 0.05 to 0.5%,
P: 0.003 to 0.020%, S: 0.005 to 0.04%, Sol.Al: 0.003 to 0.1
00%, N: 0.003 to 0.010%, Se: 0.002 to 0.020%, REM: 0.10
%, Ti: And Cu: 0.01-0.05% and Of the continuous casting slab that contains Fe and the other balance of Fe and unavoidable impurities, and then hot-rolled, and then bent so that the radius of curvature is in the range of 0.2 to 2.0 m.
Manufacture of enamel steel sheet with excellent adhesion and foam resistance, which is characterized by holding for 0 seconds to 30 minutes and then subjecting it to conventional hot finish rolling, cold rolling, recrystallization annealing and temper rolling. Is the way.

<Operation> First, the experiment on which the present invention is based will be described.

A 100 mm thick continuous cast slab of composition A, B and C shown in Table 1
After heating at 1250 ° C. for 3 hours, rough rolling was performed at 1100 ° C. for 3 passes to obtain a sheet bar having a thickness of 30 mm. Bending is then carried out at a radius of curvature of 0.25 to 1.8 m at 1000 ° C, that is, after winding for about 5 minutes with the radius of curvature in the above range, the finishing temperature is 860 ° C and the plate thickness is 3.2 mm in 3 passes. Was subjected to finishing hot rolling, and then cooled to room temperature by air cooling. After pickling,
Cold rolled to a sheet thickness of 0.8 mm, in an atmosphere of N ₂ : 93%, H ₂ : 3%, heating rate: 10 ° C / sec, soaking temperature / time: 830 ° C x 60 seconds,
Recrystallization annealing was performed at a cooling rate of 10 ° C./sec, and then temper rolling was performed with a # 50 dull rolling roll at a rolling reduction of 0.5%. Steel plate D in Table 1 is a capped steel plate that has been decarburized and denitrified by final annealing through conventional processes.

Next, the steel sheets A, B, C and D were pretreated as shown in FIG. 4 and then directly enameled once, and enamel firing at 820 ° C. for 60 seconds was performed in the atmosphere. Fig. 1 shows the foaming condition of the enamel surface at that time and the enamel adhesion [adhesion test method recommended by PEI (American Enamel Association): ASTM C313-59] together with the drawability (value) of the steel sheet.

By the way, the drawability value of a steel sheet is defined as follows.

Where r _{0 °} : Rankford value in rolling direction, r _{45 °} : Rankford value in _{45 °} direction to rolling direction, r _{90 °} : Rankford value in _{90 °} direction to rolling direction As a result, radius of curvature Steel sheets A and C that had been subjected to a bending work of 0.3 to 1.5 m had improved deep drawability and were superior to comparative steel B or conventional capped steel D. Further, in the range of the radius of curvature, no bubbles were observed on the steel plates A and C. Moreover, the enamel adhesion was similar to that of the conventional decarburizing and denitrifying capped steel.

In addition, a 100 mm thick sheet bar having the composition shown in Table 2 was set at 1300 ° C.
After heating for 1 hour at 1200 ° C ± 50 ° C, bended steel with a radius of curvature of 0.8 m (steel 1) and 1.0 m (steel 3) and unbent steel (steel 2) in 3 passes Finishing temperature 870 ℃, Plate thickness
Finishing hot rolling was performed so as to be 3.5 mm, and it was cooled to room temperature by air cooling. Then, after pickling, cold rolling is performed so that the plate thickness becomes 1.0 mm. 830 ℃ in an atmosphere of degreasing acid, hydrogen: 7%, nitrogen 93%
Recrystallization annealing was performed for × 40 seconds and temper rolling was performed with a rolling reduction of 0.8%.

After degreasing, the pickling time was changed within the range of 1 to 40 minutes, and then Ni dipping was performed for 10 minutes to directly subject the glaze and baking once to examine the adhesiveness of enamel and the occurrence of bubbles. The results are shown in FIG.

In Steel 1, enamel adhesion was good and no bubbles were generated after pickling for 5 minutes or more. However, Steel 2 which was not subjected to bending during hot rolling had a narrow pickling time region where good adhesion was obtained, and remarkable foam defects occurred.

In this experiment, the reason why the adhesion of the bent steel sheet was improved during hot rolling and the generation of bubbles was improved probably due to bending strain at high temperature, which facilitates precipitation of precipitates, especially in the surface layer. , And a large amount is deposited, the pickling speed increases,
It is considered that the adhesion was improved due to the formation of dense irregularities on the surface of the steel sheet after pickling and the accompanying increase in the amount of Ni precipitation after immersion in Ni.

On the other hand, in the case of a steel sheet with a low S content, which does not undergo bending during hot rolling, the adhesion is poor.
It is considered to be because S became S, and the pickling speed that would make the adhesion good was not obtained. That is, it is considered that the normal Ti-added extra-low C steel is preferentially pickled at the crystal grain boundaries, so that it is not possible to obtain a surface texture having fine unevenness that is advantageous for adhesion.

Further, although there is no established theory on the bubble generation mechanism itself, it is economically known that it easily occurs when the unevenness of the steel sheet surface after pretreatment is rough. It is considered that the generation of bubbles in this experiment could be suppressed because the steel sheet surface after pickling was densely corroded.

Next, the reasons for limiting the steel composition and manufacturing conditions in the present invention will be described below.

C: 0.001 to 0.005% As the C content decreases, the press formability improves, but
If less than 0.001%, TiC is hard to precipitate, and after enameling,
The lower limit is limited to 0.001% due to the occurrence of bite defects. Also, if it exceeds 0.005%, the deterioration of the material becomes significant, so
The upper limit is limited to 0.005%.

Mn: 0.05 to 0.5% Mn is an element effective in fixing S that causes red heat embrittlement, and it is necessary to contain at least 0.05%. However, the content of more than 0.5% hardens the material and reduces the workability, so that the range of the Mn content in the present invention is 0.05 to 0.5%.
Limited to

P: 0.003 to 0.020% If the P content exceeds 0.020%, the pickling rate at the pretreatment of enamel becomes fast and the smut, which has harmful enamel adhesion, is deposited on the surface of the steel sheet, so it is limited to 0.020% or less. Also 0.0
If it is less than 03%, the pickling speed is slow and the unevenness of the steel sheet surface, which is advantageous for adhesion, cannot be obtained. Therefore, 0.003% or more is required.

S: 0.005-0.04% Similar to C, the smaller the content of S, the more the press formability improves. However, if it is less than 0.005%, the pickling speed becomes slow as in the case of P, and the enamel adhesion is lowered. 0.04%
If it exceeds the range, bubble defects are likely to occur, so the S content in the present invention is limited to 0.005 to 0.04%.

Sol · Al: 0.003 to 0.100% Al is added as a deoxidizer at the steelmaking stage, but in order to complete deoxidation, it must be contained at least 0.003% in steel. However, the content of more than 0.100% raises the molten steel cost, so the Al content is set to 0.
The range was 003 to 0.100%.

N: 0.003 to 0.010% N is TiN that is effective in preventing the wing defects of enamels.
However, if the content is less than 0.005%, the precipitation amount of TiN is small, and it is difficult to prevent the lump defects. Further, if the content exceeds 0.010%, the amount of Ti added must be increased, which is disadvantageous in terms of cost. Therefore, the N content is limited to 0.005 to 0.010%.

Se: 0.002 to 0.020% The reason for adding Se is to lower the viscosity of molten steel during welding and to improve the bead shape after welding. 0.
If the content is less than 002%, there is no effect, and if it exceeds 0.020%, the pickling rate decreases and the adhesiveness deteriorates. Therefore, the content of Se is limited to 0.002 to 0.020%.

Ti: Ti is an element that is effective in forming TiC and TiN that prevent jump defects, and the amount necessary to fix C, S, and N that deteriorates the material, that is, Ti: It is necessary to contain the above. However, if the content exceeds 0.2%, not only the molten steel cost will increase, but also the pickling speed will increase and the enamel pretreatment conditions will become narrower.
In the present invention, the Ti content is Ti: Limited to

Cu: 0.01-0.05%, and Cu is an element effective in suppressing the pickling rate of Ti-added steel with a high pickling rate, but if the ratio with P (P / Cu) exceeds 0.8, there is no effect of Cu and the pickling rate is high. It is impossible to control.

If the ratio with P (P / Cu) is less than 0.2, the amount of pickling required to obtain fine irregularities and the Ni adhesion amount will be insufficient, resulting in poor adhesion. And the ratio is 0.
The content was set to 2 to 0.8, and if it is less than 0.01%, there is no effect of adding Cu, and if it exceeds 0.05%, the cost becomes high, so the content was made 0.01 to 0.05%.

The effects of the P content and Cu content on the enameled adhesion (PEI) will be described below.

Weight ratio C: 0.002%, Si0.01%, Mn: 0.2%, P: 0.01%,
Steel containing S: 0.02%, Al: 0.04%, N: 0.007%, Ti: 0.09%, Se: 0.01% and adjusting the Cu content to the ratio (P / Cu) to 0.15 to 1.35 is 1200 ℃. After heating for 2 hours, the radius of curvature is 0.7m at 1100 ℃
Was added for 5 minutes, and then finish rolling was performed so that the finishing temperature was 870 ° C and the plate thickness was 3.5 mm. After pickling, plate thickness
After cold-rolling a 0.8 mm plate and annealing it at 830 ° C for 90 seconds, 1.0
% Temper rolling was performed.

Then, under the conditions shown in FIG. 4, enamel pretreatment, direct enamel glazing and firing were performed once, and enamel adhesion (P, E, I) was examined, and the results are shown in FIG.

When the ratio of P and Cu (P / Cu) was within the range of 0.2 to 0.8, the enamel adhesion (P, E, I) was 90% or more, which was good. P / C
When u <0.2, PEI decreased rapidly, and when PEI> 0.8, PEI decreased gradually, and bubbles and sunspot defects tended to occur.

In the composition range of P / Cu <0.2, there is too much Cu, the pickling weight loss is slow, and the unevenness of the steel sheet surface that is advantageous for adhesion cannot be obtained.
Adhesion (P,
E, I) is presumed to have decreased significantly.

Further, in the range of P / Cu <0.8, it is considered that the amount of pickling, especially the corrosion of the crystal grain boundaries, progresses, and the precipitation of Ni also increases accordingly, causing bubble defects.

REM 0.10% REM is an element that is effective in trapping H ₂ that forms sulfides and causes scabbard defects, and also precipitates precipitates when bending strain is applied during hot rolling as in the present invention. Promote
Effective in improving material and enamel adhesion, but 0.1
If the content exceeds 100%, precipitates (Ti-Mn-REM
(S) etc. becomes difficult to control, and stable material and adhesion cannot be obtained, so REM
The upper limit of the content is limited to 0.1%.

Next, before the hot finish rolling step, the bending process with a radius of curvature of 0.3 to 1.5 m is performed in order to achieve good adhesion in steels in which precipitates are hard to precipitate, such as ultra-low C steels with low S content. For this purpose, it is effective to perform bending with a curvature radius of 1.5 m or less after rough rolling in the hot rolling process, especially before finish rolling. However, if the radius of curvature exceeds 1.5 m, precipitates that are effective for adhesion cannot be obtained, and in bending with a radius of curvature of less than 0.3 m, precipitates are evenly and finely precipitated in the steel plate thickness direction and In the present invention, the radius of curvature is limited to 0.3 to 1.5 because the mechanical properties such as drawability are deteriorated.

On the other hand, when REM is added, REM sulfides are formed instead of Ti-Mn-S, which increases the pickling speed during pre-enamel pretreatment, and pickling speed does not increase so much even when subjected to strong bending. It is possible to lower the lower limit of the radius of curvature to 0.2 m. In addition, by adding a very small amount of bending work to the REM-added material, it becomes possible to obtain dense irregularities on the surface of the steel sheet with good enamel adhesion during pretreatment, and the range of the optimum radius of curvature is better than that of the REM-free material. spread. The reason for this is presumed to be that Ti-Mn-REM (S) tends to be relatively spherical precipitates, and innumerable spherical precipitates were formed on the surface of the steel sheet when a work strain was applied. In order to obtain a radius of curvature of more than 2.0 m, the equipment has a large scale and other material properties and enamel properties are not very effective, so when REM is added, the range of the radius of curvature for bending is 0.2 to 2.0 m. Limited to

Bending is suitably performed after rough heating and finish rolling after heating the slab. That is, it is because the plate thickness is too thick to add bending before rough rolling, and after finish rolling, there is no difference from normal hot rolling and
This is because the plate thickness is thin at a low temperature of 500 to 700 ° C., so that the bending strain is small and precipitation of Ti-Mn-S, which is advantageous for pretreatment of enamel, does not occur. Therefore, the plate thickness and temperature during bending are preferably in the range of 20 to 50 mm and the temperature of 900 to 1200 ° C. under the conditions after rough rolling and before finish rolling. With a plate thickness of less than 20 mm, there is not much difference in the strain distribution from the steel plate surface to the inside, and precipitates are uniformly deposited in the plate thickness direction, and fine precipitates are dispersed in the steel plate surface layer as in the present invention, before enameling. It becomes difficult to form fine unevenness by pickling during the treatment.

The reason why the additional time for bending is set to 10 seconds to 30 minutes is that if the time is less than 10 seconds, precipitates are hard to deposit, and the material and enamel properties cannot be improved. Further, if held for more than 30 minutes, a large amount of precipitates or coarse precipitates are deposited, and the pickling rate during enamel pretreatment increases, so the bending work holding time in the present invention is increased. It was set to 10 seconds to 30 minutes.

<Example> A continuously cast slab having a thickness of 300 mm and having a steel composition shown in Table 3 was heated in a heating furnace at a temperature of 1200 to 1300 ° C for 1 to 3 hours, and then rough-rolled in 3 passes to obtain a plate thickness. 30mm seat bar was used. Continue to steel 1,2,3,4,7,8,9 and 100 before finish rolling.
Bending was performed by a coil box in the temperature range of 0 to 1100 ° C. For steels 5, 6, 10, 12, and 13, the rolling work was completed in the normal hot rolling process (without coil box threading).

Each of them was finished at a finishing temperature of 860 to 880 ° C. or higher of Ar ₃ transformation point and a hot rolled sheet having a thickness of 3.5 mm, and then wound at 550 to 620 ° C.
After pickling and cold rolling to a plate thickness of 0.8 mm, as shown in Table 4, steels 1 to 12 were continuously annealed and
Box-annealed (open-coil annealed) was applied to the 13 capped low-carbon steels to make decarburizing / denitrifying enamel steel sheets. Then, after temper rolling at a rolling reduction of 0.5 to 0.8%, samples are taken from the radius of curvature shown in Table 3 and subjected to enamel pretreatment shown in FIG. Conducted, enameled adhesion (P, E, I), bubble generation, scabbard defect generation and weldability were investigated.

Table 4 also shows the mechanical properties (YS, TS, El, values) of the steel sheet after annealing and temper rolling.

The weldability is smooth and there are no blowhole defects: ◯: There is a slight recess in the weld, no blowhole defect: △: There is considerable recess in the weld, blowhole defect occurs: × did.

As a result, steel N produced under the composition system and production conditions of the present invention
o.1,2,3,7,8,9 all had good mechanical properties, especially enamel adhesion, surface properties and knuckle resistance. Steel No. 13 is shown as a comparative example, but it is clear that the steel sheet of the present invention has far better mechanical properties. On the other hand, steel No. 4 has half curvature Since the diameter is as small as 0.2 m, mechanical properties and adhesion (PE
I), the occurrence of bubble defects was found. Steel Nos. 5 and 6 are steel sheets that have undergone the normal hot rolling process, and the enamel adhesion is inferior to that of the steels of the present invention. In addition, foam defects tended to occur.
Steel No. 10 was subjected to a normal hot rolling process and had a low N content, so that a slab defect was generated. Furthermore, since Se was not added, the weldability (irregularities after welding) was poor.

Steel No. 11 had a N content of 0.003% or less, so that a nail skipping defect was confirmed. Steel No. 12 is normally hot rolled and S
The content is high, bubble defects occur, and the material is deteriorated.

<Effects of the Invention> As described above, according to the present invention, it is possible to manufacture a steel plate for enamel which satisfies the press formability and stab resistance required for a steel plate for enamel and is excellent in enamel adhesion and foam resistance. It was

INDUSTRIAL APPLICABILITY According to the present invention, the steel plate for high grade enamel, which has been conventionally produced by the ingot making method, can be produced by the continuous casting method, which brings great advantages in terms of cost and energy saving.

[Brief description of drawings]

Figure 1 is a graph showing the effect of the radius of curvature of bending during hot rolling on the value, PEI value and bubble generation status. Figure 2 is
FIG. 3 is a diagram showing the effect of pickling time on PEI and foam generation, FIG. 3 is a diagram showing the relationship between PEI and P / Cu, and FIG. 4 is a diagram showing enamel pretreatment conditions.

Claims (2)

[Claims] 1. C: 0.001 to 0.005% in terms of weight%, Mn: 0.05 to
0.5%, P: 0.003 to 0.020%, S: 0.005 to 0.04%, Sol.Al: 0.00
3 to 0.100%, N: 0.003 to 0.010%, Se: 0.002 to 0.020%, Ti: And Cu: 0.01-0.05% and Of the continuous casting slab containing Fe and the other balance of Fe and unavoidable impurities is hot-rolled, then bent so that the radius of curvature is in the range of 0.3 to 1.5 m.
Manufacture of enamel steel sheet with excellent adhesion and foam resistance, which is characterized by holding for 0 seconds to 30 minutes and then subjecting it to conventional hot finish rolling, cold rolling, recrystallization annealing and temper rolling. Method. 2. C: 0.001 to 0.005% by weight%, Mn: 0.05 to
0.5%, P: 0.003 to 0.020%, S: 0.005 to 0.04%, Sol.Al: 0.00
3 to 0.100%, N: 0.003 to 0.010%, Se: 0.002 to 0.020%, REM:
0.10, Ti: And Cu: 0.01-0.05% and Of the continuous casting slab containing Fe and the remaining balance of Fe and unavoidable impurities is hot-rolled, then bent so that the radius of curvature is in the range of 0.2 to 2.0 m.
Manufacture of enamel steel sheet with excellent adhesion and foam resistance, which is characterized by holding for 0 seconds to 30 minutes and then subjecting it to conventional hot finish rolling, cold rolling, recrystallization annealing and temper rolling. Method.