JPH0543983A - Steel sheet for porcelain enameling excellent in deep drawability and aging resistance and its production - Google Patents

Abstract

PURPOSE:To produce a steel sheet for porcelain enameling excellent in deep drawability and aging resistance by preparing a steel sheet having a specific chemical composition in which respective contents of Nb, V, and Zr are specified. CONSTITUTION:A sheet of a steel having a composition which consists of, by weight, <=0.005% C, <=0.5% Mn, <=0.020% P, <=0.010% Al, 0.005-0.020& N, 0.008-0.030% O, 0.007-0.020% B, 0.010-0.100% Cu, <=0.050% Nb, further 0.001-0.100%, in total, of V and/or Zr, and the balance Fe with inevitable impurities and in which Nb/C is regulated to >=5.0 is prepared. Moreover, this steel sheet is produced by subjecting a steel slab stock having the above composition to hot rolling, to cold rolling at >=70% reduction of area, to continuous annealing at a temp. between 800 deg.C and the Ac3 transformation point. By this method, the steel sheet for porcelain enameling excellent in fishscale resistance, adhesive strength of porcelain enamel, and surface characteristics can be obtained at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a steel sheet for enamel which is excellent in press formability such as deep drawing and is also excellent in enamel properties such as resistance to snails, enamel adhesion, bubble resistance and black spot defect resistance. And a method for manufacturing the same.

[0002]

2. Description of the Related Art Enameled steel sheets are required to have a considerable deep drawability because they are subjected to severe press working as represented by the forming of sinks and baths. In addition, the enamel adhesiveness (particularly the adhesiveness when directly applying enamel once), firing strain characteristics, resistance to scabbing, foam resistance and black spot defect resistance must be satisfied. Conventionally, decarburized capped steel has been mainly used as a steel plate for enameling having good press workability, but nowadays, Ti-added steel by continuous casting is predominant. Regarding Ti-added steel, the C content is 0.005% by weight (hereinafter simply abbreviated as%)
In the following cases, excellent press workability can be obtained. JP-B-42-12348 and JP-B-44-18
Such a Ti-added steel is also disclosed in Japanese Patent Publication No. 066-066 and Japanese Patent Publication No. Sho 53-131919 and Japanese Patent Publication No. Sho 56-131919. No. 9357 is disclosed.

The Ti-added steel utilizes the fact that Ti is an element forming carbides, nitrides and sulfides, and these precipitates trap the hydrogen in the steel that causes the rust and resist the slag. It is intended to be useful for improving the jumpiness. However, it is disclosed in JP-A-61-276958 that the Ti-added steel causes defects such as poor weldability. Further, JP-A-60-110845 points out that it is inferior to conventionally used decarburized capped steels in terms of enamel adhesion, bubble resistance and black spot defect resistance. .. Regarding the poor weldability, S is described in JP-A-61-276958.
It is disclosed that by adding a small amount of e and Te, it is possible to improve a blowhole defect in a welded portion and to suppress a sink mark to improve a bubble defect and a streak defect caused by a defect in weldability. However, the Ti-added steel has a drawback in that bubbles and black spot defects are likely to occur in areas other than the welded portion.

In addition to Ti-added steel, B-added steel is widely known as a steel plate for enamel, which is disclosed in JP-B-54-3446 and JP-B-54-39808. The steel plate disclosed in each of the above publications,
It is intended to improve the rust resistance by using a precipitate such as BN formed by adding B.
There was no particular problem with regard to weldability. However, in all of these, the box annealing method is used as the annealing method,
Since the obtained steel sheet has remarkably poor mechanical properties, particularly r-value (rankfode value) showing deep drawability, it was unsuitable for applications where severe press forming is required.

On the other hand, Japanese Patent Publication No. 63-54049 discloses a manufacturing method for improving the r value of B-added steel. This method uses a heating rate of 150 ° C / h during annealing.
r. It is regulated within the following specific range. Such heating rate clearly implies box annealing. This process takes too many days to manufacture and also increases manufacturing costs.
Further, temperature unevenness easily occurs in the coil in the longitudinal direction and the width direction. In particular, temperature unevenness during annealing greatly affects the precipitation morphology of precipitates that are effective in preventing wing defects and the surface segregation that influences enamel adhesion, and also adversely affects the material inside the coil and enamel properties. It is accompanied by defects such as poor adhesion to the manufacturer and easy occurrence of bump defects.

Therefore, the inventors of the present invention have conducted extensive studies, and as a result, regarding a steel plate for enamel having excellent slab resistance and press formability, and a method for producing the same, high B, N, O (oxygen) containing Nb and Ti added thereto. Steel plate for enamel of Japanese Patent Laid-Open No. 3-10
No. 048 publication. However, according to the technique of this publication, a steel sheet having good press formability, particularly deep drawability can be obtained, but NbC is redissolved during annealing unless the manufacturing conditions are strict, and the amount of solid solution carbon increases. As a result, the aging resistance is deteriorated, and as a result, El (elongation) is deteriorated by aging, and the press formability is impaired.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a deep drawability,
Disclosed is a enamel steel sheet having good tubing resistance, and good aging resistance, and a method for producing the same, and further a steel sheet having good enamel characteristics such as adhesion as compared with a conventional steel sheet, It is an object to propose it together with its advantageous manufacturing method.

[0008]

The present invention is based on the weight composition of C: 0.005% or less and Mn: 0.5.
% Or less, P: 0.020% or less, Al: 0.010%
Hereinafter, N: 0.005-0.020%, O: 0.0
08-0.030%, B: 0.007-0.020
%, Cu: 0.010 to 0.100%, Nb: 0.05
0% or less, Nb / C is 5.0 or more, and one or both of V and Zr is 0.001 to 0.001 in total.
It is a steel sheet for enamel that contains 0.100% and the balance is Fe and unavoidable impurities and has good deep drawability and aging resistance. Further, 0.0001 to 0.050% Se by weight composition,
The deep drawability of the preceding paragraph formed by substituting the same amount of the remaining Fe, a enamel steel sheet having good aging resistance, and hot rolling using a steel slab having the composition of the preceding paragraph or the preceding paragraph as a raw material, The obtained hot rolled sheet has a rolling reduction of 70.
% Cold-rolling, followed by continuous annealing at a heating temperature of 800 ° C. or higher and an _AC3 transformation point or lower, which is a method for producing a steel sheet for enameling having good deep drawability and aging resistance. is there.

[0009]

The present invention limits the steel plate composition of the enamel steel plate to a certain specific range, and by carrying out continuous annealing treatment under specific conditions, good surface properties, adhesion, press formability and It is a manufacturing method for obtaining a enamel steel sheet that imparts aging resistance. More specifically, solid solution C is converted into NbC precipitate by addition of Nb, and even if it is re-dissolved during the annealing treatment, one or both of V and Zr is added to suppress the absolute amount, and enameled. It is intended to improve the mechanical properties and enamel properties of a steel sheet for use. Hereinafter, the reasons for limiting each component of the enameled steel sheet according to the present invention and the action thereof will be described in detail.

C: C is an infiltration type solid solution element, and is 0.00
When the content exceeds 50%, NbC precipitates are fine,
In addition, since a large amount of precipitates cause deterioration of the material, even if N
Even when b is contained, it is not preferable. Therefore C
Was limited to 0.005% or less. Mn: Mn is S that causes cracking during hot rolling.
It is an effective component for fixing as S and for forming unevenness on the surface of the steel sheet that makes the enamel adhesion good during pickling in the enamel pretreatment step. However, in order to exert this effect, at least 0.05% or more is desirable. On the other hand, if it exceeds 0.50%, the material is hardened and ductility and press formability are deteriorated. Therefore, the Mn content is limited to 0.50% or less.

B: B is an element to be added in the present invention for the purpose of improving the rust resistance, but if the content is less than 0.007%, BN or B ₂ O ₃ or the like is a habit defect. Since the amount of precipitates for preventing the occurrence of cracks is reduced and the lump defects are likely to occur, the lower limit value is set to 0.007%. On the other hand, if it exceeds 0.020%, the material deterioration becomes remarkable due to the influence of the solid solution B, so the upper limit was made 0.020%. Cu: Cu is an effective component for controlling the pickling rate at the time of pickling before enamel pretreatment, and in particular, the B-added steel as in the present invention is compared with the conventional decarburized capped steel, Since the pickling rate is 2-3 times faster, the inclusion of Cu is important. And at least 0.010% to bring out the effect
The above contents are required. However, in the component system of the present invention, if the Cu content exceeds 0.100%, the pickling rate becomes too slow, and the enamel adhesion on the pickling side is reduced for a short time, so in the present invention, .010 to 0.100
It was limited to the range of%.

Al: Al is usually used as a deoxidizer in the steelmaking stage, and in the present invention, Al is an effective component because it controls the O (oxygen) content. But 0.0
Since the content of more than 10% reduces the effective oxides that prevent the wing defects, the upper limit of the Al content of the present invention is 0.010%. O: O is an element effective for improving the rust resistance together with B and N, and at least 0.008% is required to bring out the effect. On the other hand, 0.030%
If it exceeds, it becomes easy to form blow holes during continuous casting, which also causes surface defects. Therefore, the O content is limited to the range of 0.008 to 0.030%.

N: N is a component which, like C, usually forms a solid solution in steel to deteriorate the quality of the material, but in the present invention, it is a B-added steel, and N forms and fixes BN precipitates. The material is not a problem. In addition, the precipitate is a desirable component because it forms a trap site for hydrogen which causes a dent defect. In order to completely prevent this snake-bit defect, the content of 0.005% or more is required. on the other hand,
If the content is 0.020% or more, the B content must be increased, and the risk of material deterioration increases. Therefore, in the present invention, the N content is 0.005 to 0.020%.
Limited to.

P: When the P content exceeds 0.020%, the material is hardened to deteriorate the press formability, and the pickling speed at the pretreatment of enamel is increased to increase the smut which causes bubbles and black spot defects. I will let you. Therefore, in the present invention, the P content is limited to 0.020% or less. Nb: an element for making C a precipitate of NbC that deteriorates the mechanical properties and enameled appearance properties of a steel plate in a solid solution state, and at least Nb / C is required to exert this effect. Is required to be 5.0 or more. However, if the Nb content exceeds 0.050%, the recrystallization temperature during the continuous annealing treatment will be remarkably increased, so the upper limit was made 0.050%.

Se: Se is an element effective for improving the weldability and the appearance of enamels (bubbles / black spot defects). Especially, it reduces the viscosity of molten steel to improve the sink mark of the welded portion, and the sulfuric acid for the pretreatment of enameling. In the invention, Se is added in an amount of 0.0001% or more because it has the effect of suppressing the generation of smut that adheres to the steel plate surface during pickling. However, if it exceeds 0.050%, the enamel adhesion is deteriorated. Therefore, the content is limited to the range of 0.0001 to 0.050%. V, Zr: V and Zr can suppress the absolute amount of NbC even if NbC is redissolved during annealing and the amount of solid solution C is increased. Therefore, it is extremely difficult to include one or both of them. Is effective for. Therefore, the total amount of V and Zr added must be at least 0.001%. On the other hand, when the content exceeds 0.10%, the oxides of V and Zr increase, which increases the amount of solid solution B and deteriorates the deep drawability. Therefore, its content is V and Z
The total amount of r is limited to the range of 0.001 to 0.10%.

Since other unavoidable impurities adversely affect the material and enamel characteristics, it is desirable to suppress the impurities as low as possible. In particular, S is preferably 0.020% or less. For the same reason, Si is preferably 0.03% or less.

Next, the invention of claim 3 which discloses the manufacturing method will be described. The steel slab according to the present invention can be manufactured by the ingot-slabbing rolling method or the continuous casting method. Further, the slab heating temperature does not need to be particularly limited, and if the steel composition is within the composition range of the invention of or, even if the steel composition is heated at a normal temperature of 1250 ° C., the subsequent cold rolling reduction, annealing temperature, etc. If the manufacturing conditions are satisfied, good deep drawability can be obtained. 1200 ° C for the purpose of obtaining a higher r value
The object can be achieved by heating at the following low temperature (for example, 1050 ° C.) and shortening the soaking time.

[0018] Hot rolling conditions: hot rolling condition is not particularly restricted, be terminated hot rolling in the usual A _r3 transformation point or above the temperature, make the following low-temperature finish A _r3 transformation point There is not much effect on the enameled properties. However, when the mechanical properties of the steel sheet are considered important, it is desirable to set the finishing temperature of hot rolling to the _{Ar 3} transformation point or higher. Also, regarding the winding temperature, if you want to ensure mechanical properties, high temperature, especially 6
It is preferably set to 00 ° C or higher. Cold rolling conditions: The reduction ratio of cold rolling is 70% or more.
Below this value, it is difficult to produce a cold-rolled steel sheet having excellent deep drawability (r value) and small in-plane anisotropy. The upper limit of the rolling reduction is not particularly specified, but if it exceeds 95%, the in-plane anisotropy becomes large, which is not preferable.

Continuous annealing conditions: A continuous annealing method is applied for recrystallization annealing. The reason is that the annealing process can be completed in a short time, and the surface concentration and grain boundary segregation of the components in the steel, which adversely affect the enameling properties, can be suppressed, and therefore the homogenization inside the coil can be achieved. Because you can. Further, the annealing temperature is set to a temperature range of 800 ° C. or higher and A _c3 transformation point or lower. The reason is that the r value is not improved at 800 ° C. or lower and press cracking occurs during press working. In the temperature range where the annealing temperature is the _{Ac 3} transformation point or higher, the recrystallization texture is randomized and deep drawing is performed. This is because the sex (r value) is reduced. The A _c3 transformation point is the temperature at which α iron transforms to γ iron and is usually around 910 ° C.

As described above, the steel sheet having the chemical composition according to the present invention and the steel sheet produced under the production conditions according to the present invention are the same as the conventional decarburized capped steel even if they are produced by the continuous casting slab. It is an excellent steel plate for enameling, which has better press workability and is less likely to cause bubbles and black spot defects even when it is directly enameled once. In addition, the characteristics of the enamel will not change even if it is used for applications other than direct enamelling.

[0021]

EXAMPLE Continuously cast slabs having various chemical compositions shown in Table 1 were prepared and subjected to recrystallization annealing by hot rolling, cold rolling and subsequent continuous annealing treatment under the manufacturing conditions shown in Table 2. .. Next, after subjecting to temper rolling with a reduction rate of 0.8%, mechanical properties and enamel properties were investigated.
The survey results are also shown in Table 2.

[0022]

[Table 1]

[0023]

[Table 2]

Mechanical properties of the annealed steel sheet were processed into JIS No. 5 tensile test pieces, and the yield point (YS) and tensile strength (YS) in 0 °, 45 ° and 90 ° directions with respect to the rolling direction were measured. T.
S. ), Elongation (El), and r-value (rank-ford value) were measured, and the average value X = (X ₀ + 2 × X ₄₅ + X ₉₀ ) / 4 calculated by the following equation was evaluated. In addition, Y. S. , T. S. , El and r values are all average values according to the previous equation. The aging index (AI) is also shown in Table 2. Here, the aging index (A.I.) was prestrained by 7.5% and (100 ° C., 30
Stress after aging treatment-absolute value of stress at 7.5% prestrain)
It showed with.

[0025]

[Table 3]

The surface characteristics of the enamel characteristics were evaluated by enamel treatment in accordance with the process shown in Table 3, the tendency of occurrence of bubbles and black spots was evaluated by visual judgment on the treated steel sheet, and the following characteristics were displayed. ◎: No occurrence, ○: Little occurrence, ×: Many occurrences. Also, the enamel adhesion is P. E. I. Adhesion test "P.
E. I. (American Enamel Association) recommended adhesion test method (ASTM C313-59) ",
This is expressed in%.

With respect to the snail resistance, three steel plates each were pretreated by pickling for 20 seconds without Ni dipping, and a commercial undercoating agent was applied and dried, and the dew point was 850 at 850.
After being inserted into a firing furnace at a temperature of 3 ° C. for 3 minutes to be fired, a accelerating treatment (160 ° C., 10 hours) of the knuckle characteristics was performed, and the result was visually judged and displayed as follows. ◎: No occurrence, ○: Little occurrence, ×: Many occurrences. Regarding the weldability, the occurrence of blowhole defects and sink marks was visually determined and displayed as follows. ◎: No occurrence, ○: Little occurrence, ×: Many occurrences. As is clear from the results shown in Table 2, the steel sheet according to the present invention is an enameled steel sheet having a good r-value and El and good aging resistance. On the other hand, the steel sheets shown in Comparative Examples are made of
Alternatively, either or both of the enamel properties were significantly inferior.

[0028]

The steel plate for enamel according to the present invention has deep drawability equivalent to or better than the conventionally used decarburized capped steel and Ti-added steel with good press formability. Resistance to slabs required for steel sheets,
It meets all enamel adhesion and surface properties. In particular, it overcomes the problems of bubbles and black spots that have been a problem with Ti-added steel, and can maintain the surface properties of decarburized capped steel or higher even if it is manufactured by a continuous casting method. Further, cold rolled steel sheets for high grade enamel which were conventionally produced by the ingot-slabbing method such as decarburized capped steel can be produced by the continuous casting method, and from the viewpoint of cost and energy saving. Also brings great benefits. Further, even if a hot-rolled sheet having the same composition system as this is subjected to enamel processing, there is no difference in enamel characteristics and weldability from the cold-rolled steel sheet, so there is no problem even if it is used as a hot-rolled steel sheet for enamel.

Claims (3)

[Claims] 1. A weight composition of C: 0.005% or less,
Mn: 0.5% or less, P: 0.020% or less, Al:
0.010% or less, N: 0.005 to 0.020%,
O: 0.008 to 0.030%, B: 0.007 to
0.020%, Cu: 0.010 to 0.100%, N
b: 0.050% or less, Nb / C is 5.0 or more, and one or both of V and Zr is 0.
A steel sheet for enamel, which contains 001 to 0.100% and the balance is Fe and unavoidable impurities and has good deep drawability and aging resistance. 2. A weight composition of 0.0001 to 0.050.
% Se replaced with the same amount of the remaining Fe.
Steel plate for enamel with good deep drawability and aging resistance. 3. A steel slab having the composition according to claim 1 or 2 is used as a raw material for hot rolling, and the obtained hot-rolled sheet is cold-rolled at a rolling reduction of 70% or more and then heated. A method for producing a steel sheet for enameling having a good deep drawability and aging resistance, which comprises performing continuous annealing at a temperature of 800 ° C. or higher and an _{AC 3} transformation point or lower.