JP5874771B2 - Steel plate for cans excellent in workability and rough skin resistance and method for producing the same - Google Patents

Description

  The present invention relates to a material for cans, and relates to a steel plate for cans excellent in workability and rough skin resistance and a method for producing the same.

  Cold rolled steel sheets used in the production of 2-piece cans such as deep-drawn cans, DRD (Drawn and Redrawn) cans, and DI (Drawn and Ironed) cans used in dry cell manufacturing, etc. have the following characteristics: Is required.

  (1) Excellent press workability and no defects such as cracks occur during processing.

  (2) The anisotropy is small, the earrings are excellent, and the occurrence of ears after deep drawing is small.

  (3) The surface roughness of the steel sheet after pressing is small and the finished appearance is good.

  Among these, regarding (2), for example, Patent Document 1 and Patent Document 2 disclose a technique for obtaining a steel sheet excellent in deep drawability and earring performance by adding Nb to ultra-low carbon steel.

  Regarding (3), it is known that the roughness resistance of the surface of the steel sheet after processing can be improved by reducing the crystal grain size. For example, Patent Document 3 discloses a technique for providing a steel sheet having a small surface roughness after molding using fine low-carbon steel.

JP 11-315346 A JP 2009-1555692 A Japanese Patent Laid-Open No. 10-30152

  However, the techniques described in Patent Document 1 and Patent Document 2 have problems that the crystal grains are coarse and rough skin occurs after press working, and that the cost of the steel sheet is increased by using expensive Nb. . In the technique of Patent Document 3, the yield strength of the obtained fine-grained low-carbon steel is increased, and workability such as cracking at the time of can molding and a decrease in mold life becomes a problem.

  An object of the present invention is to solve the above-described problems of the prior art and to provide a steel plate for cans excellent in workability and rough skin resistance and a method for producing the same.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the following points were found and the present invention was completed.

  First, by adding B to low-carbon steel and precipitating BN instead of AlN, the produced steel sheet becomes softer than B-free steel having the same ferrite average crystal grain size, and excellent processing Have sex.

  Secondly, by selecting and combining C and B contents in low carbon steel, hot rolling conditions, cold pressure ratio (rolling ratio during cold rolling), and annealing conditions, the ferrite crystal grain size becomes smaller and processed. Excellent resistance to rough skin afterwards.

  Based on the above knowledge, it is possible to obtain a steel plate for cans which is excellent in rough skin resistance, soft and excellent in workability. More specifically, the present invention provides the following.

  (1) As component composition, C: 0.010 to 0.050%, Si: 0.03% or less, Mn: 0.30% or less, P: 0.02% or less, S: 0.0. 02% or less, Al: 0.04% or less, N: 0.004% or less, B: 0.0010 to 0.0025%, the balance is made of Fe and inevitable impurities, and the average grain size of ferrite is 10.0 μm Hereinafter, including a BN precipitate having a yield strength of 280 MPa or less and a particle size of 80 nm or more, and an AlN precipitate having a particle size of 50 nm or less, the content of the BN precipitate is the content of the AlN precipitate. A steel plate for cans with excellent processability and rough skin resistance, characterized by the above.

  (2) The steel plate for cans having excellent workability and rough skin resistance as described in (1), having a plating film on the surface.

  (3) A method for producing a steel plate for cans having excellent workability and rough skin resistance as described in (1), wherein C: 0.010 to 0.050% and Si: 0.03% or less in mass%. Mn: 0.30% or less, P: 0.02% or less, S: 0.02% or less, Al: 0.04% or less, N: 0.004% or less, B: 0.0010 to 0.0025 %, The continuous cast steel slab having a composition composed of Fe and inevitable impurities is heated to 1100 ° C. or higher, finish-rolled at a temperature of 850 ° C. or higher, wound at a temperature of 540 to 590 ° C., and the reduction ratio Cold-rolled at 70 to 90%, heated at a temperature of 550 ° C. to the recrystallization start temperature within 5 seconds, and subjected to continuous annealing at a temperature of 650 to 750 ° C. Steel plate for cans with excellent workability and rough skin resistance, characterized by temper rolling at ~ 2.0% Manufacturing method.

  (4) The method for producing a steel plate for a can excellent in workability and skin roughness resistance according to (3), wherein the surface is plated after the temper rolling.

  The steel plate for cans of the present invention can be preferably applied to the production of any type of can such as for dry batteries and food cans. The steel plate for cans may be a cold rolled steel plate or a plated steel plate.

  According to the steel plate for cans obtained according to the present invention, since it is softer than before and the crystal grain size is smaller, it is possible to realize both workability and rough skin resistance that cannot be achieved with conventional steel.

  Moreover, since the steel plate for cans of this invention does not use expensive Nb, it can be manufactured at a low cost, and is excellent in workability and rough skin resistance.

It is a figure which shows the relationship between a particle size (ferrite average crystal grain size) and yield strength. It is a figure which shows BN in B addition steel. It is a figure which shows AlN in B additive-free steel.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

  First, how the present invention was completed will be described. The inventors consider that it is effective to reduce the degree of precipitation strengthening of the steel sheet in order to soften the steel sheet without coarsening the ferrite crystal grains, and the softening by adding B to the low carbon steel is considered. investigated.

  Low carbon hot rolled steel sheets having the components shown in Table 1 were aligned to a thickness of 2.0 mm by grinding, and cold rolled sheets having a thickness of 0.25 mm were formed by cold rolling. The cold rolled sheet was subjected to continuous annealing at 600 to 750 ° C.

The annealed sample was subjected to temper rolling with an elongation of 1.5%. About these steel plates, the ferrite average crystal grain size was measured by the cutting method based on JIS G0551 from the structure observation photograph. Moreover, about the steel plate after temper rolling, the yield strength was measured and evaluated by the tensile test using the half size test piece of JIS13B. These results are shown in FIG. 1 (the vertical axis is the yield strength, the horizontal axis is (grain size (ferrite average crystal grain size)) ^−1/2 , and the scale on the upper side of the graph represents the ferrite average crystal grain size) . It was confirmed that the B-added steel had a low yield strength and was softened by about 20 MPa as compared with the B-free steel compared with the same average ferrite grain size. The reason why the B-added steel is softer than the B-free steel is due to the difference in nitrided precipitates. Coarse BN precipitates in the B-added steel (FIG. 2), and fine AlN precipitates in the B-free steel (FIG. 3). The larger the precipitate diameter, the smaller the degree of precipitation strengthening, so the B-added steel became softer.

  Next, the details of the present invention will be described. “%” Representing the content of the component composition means “mass%”.

C: 0.010 to 0.050%
If the C content is less than 0.010%, the ferrite crystal grains become coarse, and as a result, the ferrite average crystal grain size becomes too large. For this reason, the minimum of content of C is made into 0.010%. On the other hand, if the C content exceeds 0.050%, the drawing processability decreases. For this reason, the upper limit of the C content is 0.050%. A preferable range of the C content is 0.016 to 0.040%.

Si: 0.03% or less Si is an element that remains in the steel as an impurity component even when intentional addition is not performed, and deteriorates the corrosion resistance of the steel sheet and the adhesion of the plating. In order to ensure good corrosion resistance, the Si content is set to 0.03% or less. A preferable range of the Si content is 0.02% or less.

Mn: 0.30% or less Mn prevents hot cracking of the slab by precipitating S in the steel as MnS. In order to precipitate and fix S, the Mn content is preferably set to 0.1% or more. However, Mn is a strengthening element. In the present invention, the upper limit of the Mn content is set to 0.30% in order to obtain soft characteristics.

P: 0.02% or less P segregates at the ferrite grain boundaries, embrittles the grain boundaries, and lowers the workability during drawing. P is an element that lowers the adhesion of plating. Therefore, the content of P is preferably as small as possible, and in the present invention, it is 0.02% or less.

S: 0.02% or less The content of S is preferably as small as possible from the viewpoint of preventing hot cracking of the slab. Therefore, the S content is 0.02% or less.

Al: 0.04% or less Al is sol. If the amount of Al exceeds 0.04%, precipitation of AlN increases, leading to hardening of the steel sheet. Therefore, the Al content is 0.04% or less. The preferable Al content is 0.03% or less.

N: 0.004% or less N tends to be deposited and detoxified as BN, but if it is too much, a large amount of solid solution N remains and cannot be rendered harmless, so the N content is 0.004% or less. To do. The preferable N content is 0.003% or less.

B: 0.0010 to 0.0025%
B is an important element of the present invention, and the B content is in the range of 0.0010 to 0.0025%. B reacts with solute N to form a BN precipitate (sometimes referred to as “BN” in the present specification). However, if the content of B is less than the above range, an AlN precipitate (hereinafter referred to as “AlN” in the present specification). In some cases) and the steel plate becomes hard. On the other hand, if the B content exceeds the above range, the anisotropy increases and the moldability deteriorates. The preferable B content is 0.0012 to 0.0020%.

  The balance is Fe and inevitable impurities.

  Next, the structure and properties of the steel plate for cans of the present invention will be described.

Ferrite average crystal grain size is 10.0 μm or less When the ferrite average crystal grain size is large, the surface roughness after can processing tends to deteriorate. Specifically, when the ferrite average crystal grain size exceeds 10.0 μm, the surface roughness of the surface deteriorates. For this reason, the ferrite average crystal grain size shall not exceed 10.0 μm. When the ferrite average crystal grain size is less than 5.0 μm, the yield strength is high and the workability may be inferior. Therefore, the ferrite average crystal grain size is preferably 5.0 μm or more. The method for measuring the ferrite average crystal grain size is based on JIS G0551.

Plate thickness is 0.60 mm or less The plate thickness of the steel plate for cans of the present invention is not particularly limited, but is preferably 0.60 mm or less from the viewpoint of cost and weight of the can body as a steel plate for cans. However, since excessive rolling increases costs, the plate thickness is preferably 0.10 mm or more.

The relationship between a BN precipitate having a particle size of 80 nm or more and an AlN precipitate having a particle size of 50 nm or less is expressed as BN ≧ AlN.
The precipitate particle size affects the degree of precipitation strengthening. The smaller the precipitate particle size, the greater the degree of precipitation strengthening. In the present invention, for the purpose of softening, N is precipitated as coarse BN while suppressing the precipitation of fine AlN. When the particle size of BN is 80 nm or more, the effect of precipitation strengthening becomes a value that can be almost ignored. When the particle size of AlN is 50 nm or less, the effect of precipitation strengthening exceeds 10 MPa, so the particle size is coarser than 80 nm. The relationship between the precipitation amount of BN and the precipitation amount of fine AlN having a particle size of 50 nm or less substantially governs the degree of precipitation strengthening. The relationship between the BN content (mass%) and the AlN content (mass%) in the steel sheet for cans of the present invention is BN content ≧ AlN content. If the above relationship is satisfied, the degree of precipitation strengthening can be suppressed more appropriately, and the steel plate for cans can be sufficiently softened.

  The particle diameters of AlN and BN can be obtained by observing the extracted replica obtained from the steel sheet with an electron microscope and measuring the diameter of the precipitate in which the target element is detected by elemental analysis (the diameter of BN). An example of how to determine is shown in Fig. 2 and an example of how to determine the diameter of AlN is shown in Fig. 3. The diameter is the diameter of the circumscribed circle. Further, the content of BN and the content of AlN are measured using an electrolytic extraction residue.

Yield strength is 280 MPa or less From the viewpoint of workability at the time of can molding and die life, the yield strength of the steel plate for cans is 280 MPa or less. Preferably it is 270 MPa or less.

Plating film From the viewpoint of improving the corrosion resistance, it is possible to apply a plating film such as Zn, Sn, Ni, and Cr to the steel sheet. The formation method of a plating film is not specifically limited, What is necessary is just to employ | adopt ordinary methods, such as hot dipping and electroplating. Further, in order to form a diffusion layer between the steel plate and the plated metal, diffusion annealing may be performed after plating.

  Then, although the preferable manufacturing method of the steel plate for cans of this invention is demonstrated, the manufacturing method of the steel plate for cans of this invention is not specifically limited to the following method.

Heating continuously cast steel slab to 1100 ° C or more After slab (continuous cast steel slab) obtained by continuous casting after melting steel having the above composition in a converter, or hot finishing directly Insert into a rolling mill and perform hot rolling. The slab heating temperature is set to 1100 ° C. or higher in order to decompose and re-dissolve AlN. The upper limit of the slab heating temperature is not particularly limited, but is preferably 1300 ° C. or lower in order to reduce the heating cost.

Finish rolling at a temperature of 850 ° C. or higher The finishing temperature of hot rolling is 850 ° C. or higher. When the hot-rolling finishing temperature is lower than 850 ° C., a texture is formed on the hot-rolled sheet, and the surface layer crystal grains may be coarsened or the processed structure may remain, resulting in deterioration of deep drawability. The upper limit of the finishing temperature is not particularly limited, but if the finishing temperature is too high, the crystal grain size of the hot rolled sheet becomes too large. For this reason, it is preferable that the said finishing temperature is 950 degrees C or less.

Winding at a temperature of 540 to 590 ° C. The winding temperature is 590 ° C. or lower in order to suppress the precipitation of AlN. The lower limit is set to 540 ° C. in consideration of variations in the coil width direction and the longitudinal direction.

Cold rolling at a rolling reduction of 70 to 90% After the hot-rolled steel sheet obtained above is pickled, cold rolling is performed. In order to reduce the in-plane anisotropy, the rolling reduction is in the range of 70 to 90%.

Continuous annealing at a temperature of 650 ° C. to 750 ° C. The annealing temperature of the continuous annealing is preferably equal to or higher than the recrystallization temperature in order to suppress a decrease in workability due to remaining unrecrystallized structure, and is set to 650 ° C. or higher. Moreover, in order to suppress the rough skin resulting from the coarsening by excessive grain growth, it shall be 750 degrees C or less. In order to suppress precipitation of AlN, the transit time from 550 ° C. to the recrystallization start temperature is set to be within 5 seconds. Preferably, it is within 3 seconds.

Temper rolling at an elongation rate of 1.0 to 2.0% Temper rolling is performed in this range because the occurrence of stretcher strain is prevented if the elongation rate is in the range of 1.0 to 2.0%.

  A continuous cast steel slab having the chemical components shown in Table 2 was heated to 1200 ° C., and then hot rolled at a finishing temperature of 890 ° C. and a winding temperature of 560 to 630 ° C. to obtain a hot-rolled steel plate having a thickness of 2.1 mm. The hot-rolled steel sheet was pickled and cold-rolled to obtain a cold-rolled sheet having a thickness of 0.25 mm. The rolling reduction is 88%. Thereafter, continuous annealing was performed at a temperature rising rate of 10 to 30 ° C./second and a temperature of 600 to 770 ° C., and temper rolling with an elongation rate of 1.5% was performed to obtain a steel plate. The conditions such as the annealing temperature are shown in Table 3. In addition, temperature rising time shows the time from 550 degreeC to recrystallization start temperature. The recrystallization start temperature indicates a temperature at which recrystallization is started even in a part of the rolled structure during annealing. The recrystallization start temperature is determined by preparing a sample which is cooled to room temperature after soaking at 550 ° C. to 700 ° C. for 10 seconds in advance, and confirming the cross-sectional microstructure of the sample. did.

  A JIS No. 5 tensile specimen and an optical microscope observation sample were collected from this steel plate, the yield strength was measured by a tensile test, and the ferrite average crystal grain size was measured by a cutting method based on JIS G0551. The results of yield strength and ferrite average crystal grain size are shown in Table 3.

  Also, after collecting a 100 mm diameter circular blank from this steel plate and forming it into a 14 mm diameter cylindrical shape by multistage drawing of 5 steps, the surface roughness Ra of the can body portion is measured based on JIS B0601; The moldability and rough skin were evaluated. As the evaluation of the moldability, 200 pieces of the above-mentioned drawing were performed, and “◯” was given when no defects such as cracks and wrinkles occurred, and “X” was given. In the evaluation of the rough skin property, the surface roughness Ra of the can body portion was “◎” when the surface roughness Ra was less than 0.5 μm, “◯” when 0.5 μm or more and less than 0.7 μm, and “X” when 0.7 μm or more. These evaluation results are shown in Table 3 (workability evaluation and rough skin evaluation in the table).

  In addition, the content of BN precipitates having a particle size of 80 nm or more and the content of AlN precipitates having a particle size of 50 nm or less are calculated in mass% by extraction residue analysis and TEM observation of the steel sheet, respectively. When BN ≧ AlN, “◯” was indicated, and when BN <AlN, “X” was indicated. The above results are shown in Table 3 (Evaluation of precipitates in the table).

  The weight of the precipitate was obtained by dissolving the sample with a 10% AA electrolyte solution (ethanol solution of acetylacetone tetramethylammonium chloride), and determining the residue from the residue by ICP emission spectrometry.

  TEM observation was performed using an extraction replica method at an acceleration voltage of 200 kV.

  Inventive Examples 1 to 7, which are invention steels, were excellent results as steel sheets for cans in terms of both workability and rough skin.

  Although the comparative example 1 used the steel slab 1, since the crystal grain coarsened because the annealing temperature was too high, etc., the ferrite average crystal grain size exceeded 10.0 μm, and the skin roughness evaluation was poor. is there.

  In Comparative Example 2, the steel slab 1 was used, but the annealing temperature was too low to be unrecrystallized, and almost no ferrite recrystallized grains were produced, so the yield strength, crystal grain size, workability and rough skin could not be evaluated. is there.

  In Comparative Example 3, the steel slab 1 was used. However, since the temperature rise time was long and precipitation of AlN could not be suppressed, the softening was insufficient.

  In Comparative Example 4, the steel slab 2 was used, but since the winding temperature was high and precipitation of AlN could not be suppressed, the softening was insufficient.

  Since the steel piece 4 used in Comparative Example 5 does not contain B, it is an example in which precipitation of AlN cannot be suppressed, it becomes hard, and workability is inferior.

  In Comparative Example 6, steel slab 5 was used, and B was less than the lower limit, and precipitation of AlN could not be suppressed, so that softening was insufficient.

  Comparative Example 7 uses a steel slab 6 and is an example in which B is added in excess of the upper limit, so that the anisotropy is high, an ear is generated at the time of molding, and the processing becomes defective (Comparative Example 7 is a comparative example). Earrings are bad).

  The comparative example 8 uses the steel piece 7, and the C amount exceeds the upper limit, and is an example inferior in workability.

  Comparative Example 9 is an example in which extremely low carbon steel of steel slab 8 is used, the ferrite crystal grains are coarse, and the ferrite average crystal grain size exceeds 10.0 μm, so that the rough skin evaluation is poor.

Claims (4)

As component composition, by mass%, C: 0.016 to 0.050%, Si: 0.03% or less, Mn: 0.30% or less, P: 0.02% or less, S: 0.02% or less Al: 0.04% or less, N: 0.004% or less, B: 0.0010 to 0.0025%, the balance is made of Fe and inevitable impurities, ferrite average crystal grain size is 10.0 μm or less, yield It includes a BN precipitate having a strength of 280 MPa or less and a particle size of 80 nm or more, and an AlN precipitate having a particle size of 50 nm or less, and the content of the BN precipitate is greater than or equal to the content of the AlN precipitate. Steel plate for cans with excellent processability and rough skin resistance.   The steel plate for cans having excellent workability and rough skin resistance according to claim 1, wherein the steel plate has a plating film on the surface. It is a manufacturing method of the steel plate for cans excellent in workability and rough skin resistance according to claim 1,
In mass%, C: 0.016 to 0.050%, Si: 0.03% or less, Mn: 0.30% or less, P: 0.02% or less, S: 0.02% or less, Al: 0 0.04% or less, N: 0.004% or less, B: 0.0010 to 0.0025%, and the continuous cast steel slab having a component composition consisting of Fe and inevitable impurities is heated to 1100 ° C. or higher, and 850 Finish rolling at a temperature of ℃ ℃ or more, winding at a temperature of 540-590 ℃, cold-rolling at a reduction rate of 70-90%, under the condition that the transit time from 550 ℃ to the recrystallization start temperature is within 5 seconds Steel plate for cans with excellent workability and rough skin resistance, characterized in that the temperature is raised, continuous annealing is performed at a temperature of 650 ° C. to 750 ° C., and temper rolling is performed at an elongation of 1.0 to 2.0%. Manufacturing method.   The method for producing a steel plate for cans having excellent workability and rough skin resistance according to claim 3, wherein the surface is plated after the temper rolling.