KR101167544B1 - Steel sheet for cans, hot-rolled steel sheet to be used as the base metal and processes for production of both - Google Patents

Abstract

When manufacturing a steel plate for cans, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005 By containing 0.10% and combining solid solution strengthening, precipitation strengthening, and fine grain strengthening, it is substantially a ferrite single phase structure, average grain size is 7 micrometers or less, and the characteristic after coating baking process is yield strength: 500 Mpa or more, yield ratio : 0.9 or more, total elongation: 10% or more, (DELTA) r: -0.50-0 The steel plate used will be obtained. In particular, hot rolling conditions are FT: 870 ° C or higher, cooling rate after hot rolling: 40 ° C / s or lower, CT: 620 ° C or higher, and the average grain size of the hot rolled steel sheet serving as a rolled material of the steel sheet for cans is 6 µm or more.

Steel sheet for cans, hot rolled steel sheet,

Description

Steel sheet for cans and hot rolled steel sheet used in its base material and manufacturing method thereof {STEEL SHEET FOR CANS, HOT-ROLLED STEEL SHEET TO BE USED AS THE BASE METAL AND PROCESSES FOR PRODUCTION OF BOTH}

The present invention relates to a tin mill black plate and a hot-rolled steel sheet for use in its base material. The present invention also relates to a steel sheet for cans and a method for producing the base material hot rolled steel sheet. Specifically, the present invention relates to a steel sheet for cans having high ductility, high strength, and low in-plate plastic anisotropy, a hot rolled steel sheet to be used for the base material thereof, and a manufacturing method thereof.

In recent years, in order to expand the demand for steel cans, measures have been taken to reduce can manufacturing costs and to market new cans such as bottle shaped cans and shaped cans.

Reducing the cost of the can production cost includes reducing the cost of the raw material. That is, even in the two-piece can which performs drawing, even in the three-piece can which mainly consists of simple cylindrical shaping | molding, the thinning of the steel plate used (gauge down: gauge down) is progressing.

However, if the steel sheet is simply thinned, the can body strength is lowered. Therefore, the steel sheet merely thinned cannot be used, and it is necessary to use a very thin and hard can steel sheet.

At present, such a very thin and hard steel sheet for cans is manufactured by the Double Reduce method (hereinafter referred to as DR method) which performs secondary cold rolling after annealing. The steel sheet produced by the DR method is characterized by high strength and low yield point elongation. In DRD cans with bottom forming, it is desirable that the yield elongation be as small as possible in order to prevent the occurrence of stretcher strain, in which the DR method is effective. Do. However, although the earing is required to be small in the DRD can, the ear tends to increase because the anisotropy tends to be large in the DR method, and the problem of reducing the anisotropy (denoted by Δr) to prevent the occurrence of the earing is a problem. There is.

On the other hand, mold release cans recently introduced to the market involve can body shaping of high workability. However, the DR material lacking ductility is difficult to be applied to a release can or the like because of poor workability. In addition, the production cost is high because the DR material also increases the manufacturing process as compared with the steel sheet subjected to temper rolling (rough pressure) after ordinary annealing.

In order to avoid such drawbacks of DR materials, secondary cold rolling is omitted, and in the Single Reduce method (SR method), which mainly controls the characteristics in the primary cold rolling and annealing processes, the high strength is obtained by using various strengthening methods. The method of manufacturing a steel plate or the method of manufacturing the steel plate with a small incidence of earrings is proposed as follows.

For example, Japanese Laid-Open Patent Publication No. 2001-107186 (Patent Document 1) adds a large amount of C and N (0.0050 mass% or more in total) to bake hardening to form a high strength can steel sheet equivalent to DR material. The technique to obtain is proposed. In this technique, the amount of N added, forced cooling after the end of hot rolling, prevention of AlN precipitation by low temperature winding (600 ° C. or lower), heat treatment conditions (for example, quenching after recrystallization annealing), and the like By this, the hardness obtained by aging is adjusted. The yield stress (also referred to as YS: yield strength (YP): yield point) after coating baking after lacquering is as high as 550 MPa or more.

In addition, Japanese Patent Laid-Open No. 11-199991 (Patent Document 2) also proposes a technique of increasing the strength by post-coating baking treatment, similarly to Patent Document 1. However, in the technique of this publication, in order to secure non-ageing properties, aging by solid solution C (about 5 to 15 ppm) is mainly used, and decarburization treatment is performed in continuous annealing. We carry out. In addition, N is not used as an aging element but precipitated and fixed as AlN by winding 600 degreeC or more (substantially about 680 degreeC) etc., and the resulting baking hardening amount is about 40-55 Mpa.

In JP 2005-336610 A (Patent Document 3), a combination of precipitation hardening by Nb carbide, solution hardening by Mn, P, and N, etc. is combined in combination, and the average grain size (average crystal grain size) having a ferrite grain structure of 7 µm or less, high strength (tensile strength TS: 550 MPa or more) and high ductility (elongation: 10% or more) It is proposed to obtain a combined steel sheet. Here, the refining of the ferrite is achieved by C content (0.04 mass% or more), coiling temperature (CT) (630 ° C. or less), or the like. Moreover, about 480-550 Pa are disclosed as YP obtained by this technique.

In Japanese Unexamined Patent Publication No. 59-129733 (Patent Document 4), the strain elongation is set to about 1.0% or less by suppressing C to 0.0030% or less and performing temper rolling of 10% or more. The production method which prevents generation | occurrence | production of and obtains the steel of the strength level equivalent to T4-T6 is proposed.

Japanese Patent Laid-Open No. 11-222647 (Patent Document 5) has an average grain size of 6 µm or less, obtained by primary cold pressure of 80 to 88%, no strain strain generation, and a low incidence of earrings (Δr Within ± 0.1) ultrathin steel sheet is proposed.

In addition, Japanese Laid-Open Patent Publication No. 2003-34825 (Patent Document 6) proposes a technique for obtaining a high strength steel sheet using finer grains by transformation. In this technique, the low carbon steel is hot rolled at the α + γ region and then cooled at high speed, and the heating rate of annealing is specified to refine the steel sheet to obtain a steel sheet having a tensile strength of 600 MPa and an overall elongation of 30% or more. have.

First, in order to reduce the thickness, securing of strength is essential. For example, the yield strength must be 500 MPa or more in order to obtain the current can body strength from a steel sheet having the same plate thickness (about 0.15 to 0.18 mm) as the DR material. Moreover, it is necessary to apply a high ductility steel plate to the can body which performs high can body processing, such as can expansion, and the can body which performs high flange processing. In addition, when steel having a high incidence of earrings is applied to two-piece cans such as DRD cans, the trim margin of the earring portion is increased and the yield is lowered. have.

In view of the above characteristics, in the above-described prior art, it is possible to manufacture a steel sheet that satisfies any of strength, ductility, and anisotropy, but a steel sheet that satisfies all cannot be manufactured.

For example, the method of increasing the strength by baking curability by adding a large amount of C and N described in Patent Document 1 is an effective method for increasing the strength. However, in the structure obtained by patent document 1, the anisotropy aimed at by this invention is not acquired. This is in contrast with the technique of the present invention described later. In the technique of Patent Literature 1, hot rolling is performed after starting hot rolling within 0.5 s after the end of hot rolling, winding at a winding temperature of 600 ° C. or lower, and cooling after rewinding. It may be considered that the grains of the steel sheet are related to not sufficiently growing.

In patent document 2, although it age-hardens by baking process, the tensile strength of the steel described in the Example is about 380 Mpa, and the yield strength 500 Mpa or more targeted by this invention is not obtained.

Although Patent Document 3 uses high strength by complex reinforcement by precipitation strengthening, solid solution strengthening, and the like, in general, steel using precipitation strengthening is poor in anisotropy, and in particular, in the hot rolling condition proposed in Patent Document 3, it is a target of the present invention. Anisotropy to be obtained is not obtained.

Although Patent Document 4 describes a steel having a T6 level at which the yield elongation is almost 0, it is necessary to perform temper rolling at a rolling rate of 10% or more, and it is substantially expensive by the same production method as the DR material. . Moreover, the base material which manufactures steel exceeding T6 is not seen. In addition, although it is not described about ductility in the specification, when rolling is carried out by 10% or more of reduction ratio, it is presumed that ductility is inferior.

In patent document 5, although the manufacturing method of the steel plate which suppresses generation | occurrence | production of an ear ring is disclosed by controlling manufacturing conditions, such as a component and hot rolling conditions, the yield strength of the steel described in the Example is to about 420 Mpa, and this invention It did not reach 500 MPa or more of this target.

The high strength by rapid cooling proposed by patent document 6 becomes expensive in operation. Moreover, in the structure obtained by patent document 6, the anisotropy aimed at by this invention is not acquired. This is in contrast to the technique of the present invention to be described later. In the technique of Patent Literature 6, after completion of hot rolling, cooling is performed over a temperature range of 80 ° C or higher at a cooling rate of 100 ° C / s or more within 1 s, and at 650 ° C or lower. Because of the winding, it may be considered that the crystal grains of the hot rolled steel sheet are not sufficiently grown.

This invention is made | formed in view of such a situation, The steel plate for cans which has a yield strength of 500 Mpa or more, a yield ratio of 0.9 or more, an overall elongation of 10% or more, and (DELTA) r becomes -0.50-0, and its base material after coating baking It is an object of the present invention to provide a hot rolled steel sheet and a method for producing the same.

MEANS TO SOLVE THE PROBLEM The present inventors earnestly researched in order to solve the said subject. As a result, the following findings were obtained.

The inventors have noted a complex combination of solid solution strengthening, precipitation strengthening, grain refinement, and age hardening. That is, solid solution strengthening is performed using solid solution strengthening elements, complex strengthening by solid solution strengthening, precipitation strengthening, and grain refining hardening by Nb, P, and Mn is strengthened while maintaining high elongation. In addition, by using solid solution C and solid solution N in steel, the strength increase by age hardening after coating baking is aimed at. By making the structure into a substantially ferrite single phase and defining the ferrite average crystal grain size, both high strength and high ductility are maintained, yield strength of 500 MPa or more and total elongation of 10% or more are obtained. In particular, in the present invention, attention is paid to the deterioration of anisotropy, which is a problem when using precipitation strengthening, and anisotropy can be improved by appropriately controlling hot rolling conditions, thereby enabling Δr to be -0.50 to 0.

In the present invention, the steel sheet for high strength and high ductility can and the manufacturing method thereof have been completed by comprehensively managing the components and the manufacturing method based on the above findings.

This invention is made | formed based on the above knowledge, The summary is as follows.

[1] In mass%, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005 It contains 0.10%, and has the composition which remainder consists of iron and an unavoidable impurity, and the structure which is substantially a ferrite single phase, the average crystal grain size of ferrite is 7 micrometers or less, and yield strength is 500 Mpa by the coating baking process. Above, yield ratio: 0.9 or more, total elongation: 10% or more, (DELTA) r: steel plate for cans which can acquire the characteristic of -0.50-0.

[2] In producing the steel sheet for cans according to the above [1], in mass%, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005% to 0.10%, the remainder of which is made of iron and unavoidable impurities by hot rolling at a finishing temperature (FT) of 870 DEG C or higher, and then wound up to 40 After cooling at an average cooling rate of 占 폚 / s or less, winding at a coiling temperature of 620 占 폚 or higher, and then cold rolling at a rolling reduction rate of 80% or higher, under conditions of a cracking temperature of 650 to 750 占 폚 and a crack time of 40 s or less. A continuous annealing is carried out, and temper rolling is performed by temper elongation of 1.5% or less, The manufacturing method of the steel plate for cans characterized by the above-mentioned.

[3] In mass%, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005 A hot-rolled steel sheet suitable for use as a steel sheet base material for cans containing -0.10%, having a composition consisting of iron and inevitable impurities, and a structure substantially in the form of ferrite single phase, and having an average crystal grain size of ferrite of 6 µm or more.

[4] In producing the hot rolled steel sheet according to the above [3], in mass%, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005% to 0.10%, and the remainder is hot rolled at a finishing temperature of 870 ° C or higher, and the balance of iron and inevitable impurities is 40 ° C / s or less. A method for producing a hot rolled steel sheet suitable for use as a steel sheet base material for cans, which is cooled at an average cooling rate and wound at a winding temperature of 620 ° C or higher.

In addition, in this specification, all% which shows the component of steel are mass%. For example, the description "Si: 0.005-0.5%" shall mean "Si: 0.005% or more and 0.5% or less" or "0.005% ≤ Si ≤ 0.5%".

In addition, in this invention, a coating baking process means the process which heat-processes 210 degreeC and 20 minutes equivalent to coating baking, and differs from what is called baking hardening process which gives a preliminary deformation and performs an aging treatment. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the relationship between the anisotropy ((DELTA) axis | shaft) (perpendicular axis) of the steel plate for cans (cold rolled steel), and the ferrite average crystal grain diameter (horizontal axis: micrometer) of the hot rolled steel plate which is a steel plate base material for cans.

Hereinafter, the present invention will be described in detail.

The steel sheet for cans of this invention is a high strength, high ductility can steel plate which can obtain the steel plate characteristics of yield strength 500 Mpa, yield ratio 0.9 or more, total elongation 10% or more, and (DELTA) -0.50-0 by coating baking process. Here, although the coating baking process is based on 210 degreeC and the process for 20 minutes, the equivalent effect is acquired substantially if it is a heat treatment of 180-265 degreeC and 2 to 30 minutes. In addition, you may perform lamination processing (heat laminating) instead of the coating baking process as heat processing to age-harden. Hereinafter, when it says the coating baking process, it shall include the same heat processing, such as a lamination process.

Moreover, the steel plate for cans provided with said steel plate characteristics which performed the coating baking process is also the steel plate of this invention. It is preferable that the coating baking process conditions in this case also comply with the said criteria, but there will be no limitation in particular as long as it is a condition which can obtain the said steel plate characteristic.

Usually, in the steel plate strengthened using DR method, elongation only shows several%. In contrast, the present invention is characterized by increasing the strength while maintaining a high elongation rate by producing a steel sheet subjected to solid solution strengthening, precipitation strengthening, and grain refinement strengthening with Nb, P, and Mn by continuous annealing. In addition, by remaining the appropriate amounts of solid solution C and N in steel, aging hardening of 30 MPa or more is caused by heat treatment essential in can manufacturing processes such as paint baking. That is, by increasing YP by aging hardening, it is possible to increase the pressure resistance at the bottom of the drawing can and the dent strength of the welding can.

Moreover, the value of (DELTA) r: -0.50-0 is obtained by making the finishing temperature at the time of hot rolling 870 degreeC or more, the subsequent cooling rate 40 degrees C / s or less, and winding temperature 620 degreeC or more.

These are the features of the present invention and are important requirements. In this way, the yield strength is 500 MPa or more, the yield ratio is 0.9 or more, and the total elongation is 10% or more, by adequacy of the components, structures, and manufacturing conditions centered on the solid solution strengthening element, the precipitation strengthening element, and the refinement strengthening element. And the steel plate for cans with (DELTA) r -0.50-0 is obtained.

Next, the component composition of the steel sheet for cans of this invention is demonstrated.

C: 0.01 to 0.12%

In the steel sheet for cans of the present invention, it is essential to achieve a predetermined or more strength (yield strength of 500 MPa or more) after continuous annealing and temper rolling, and to have a total elongation of 10% or more. It is necessary. When manufacturing the steel plate which satisfy | fills these characteristics, C content is important. In particular, since the amount and density of carbides are largely related to the strength of the steel sheet and the average grain size of the ferrite, it is necessary to ensure the amount of carbon available for precipitation. In addition, by depositing carbide at the grain boundary, grain boundary segregation of P can be suppressed, and the solid solution strengthening of P can be utilized to the maximum.

In order to acquire the above effect, the minimum of C addition amount is limited to 0.01%. On the other hand, when C content exceeds 0.12%, since an apocrystallization crack occurs in the cooling process at the time of steel making of steel, an upper limit is limited to 0.12%. A preferable minimum is 0.04% or more, and a preferable upper limit is 0.10% or less.

Si: 0.005 to 0.5%

Si is an element that increases the strength of steel by solid solution strengthening, but when contained in a large amount, corrosion resistance is significantly inhibited. Therefore, the upper limit of Si content is limited to 0.5%. Preferably it is 0.05% or less. On the other hand, in applications where high corrosion resistance is required, Si needs to be as low as possible, but the lower limit is limited to 0.005% in consideration of the reduction cost.

Mn: 0.3 to 1.5%

Mn increases the strength of the steel by solid solution strengthening and decreases the grain size. The effect of reducing the crystal grain size is remarkable is that the Mn content is 0.3% or more, and at least 0.3% Mn content is required in order to secure the target strength. Therefore, the minimum of Mn content is limited to 0.3%. On the other hand, when Mn is contained in a large amount, corrosion resistance is inferior. Therefore, an upper limit is limited to 1.5%. Preferably it is 1.1% or less.

ㆍ P: 0.005% to 0.2%

P is an element having a high solid solution strengthening ability, but when added in a large amount, corrosion resistance is remarkably impaired. Therefore, an upper limit is limited to 0.2%. Preferably it is 0.1% or less. On the other hand, in applications where high corrosion resistance is required, the amount of P added needs to be as low as possible, but the lower limit is limited to 0.005% in consideration of the reduction cost.

ㆍ Al: 0.10% or less

When the Al content increases, an increase in the recrystallization temperature is caused. Therefore, it is necessary to increase the annealing temperature. In this invention, since the recrystallization temperature rises also by the other element added in order to increase intensity | strength, and annealing temperature becomes high, it is preferable to avoid the raise of the recrystallization temperature by Al. Therefore, the upper limit of Al content is limited to 0.10%. In addition, it is preferable to contain more than 0.02% from a viewpoint of fully performing deoxidation and suppressing bubble generation in steel by the residual oxygen.

N: 0.012% or less

N is an element that is effective to increase aging hardening. In order to exhibit the effect of age hardening, it is preferable to add 0.005% or more, Preferably it is 0.0060% or more. On the other hand, when a large amount is added, hot ductility deteriorates and slab cracking becomes easy to generate | occur | produce in an unbending zone at the time of continuous casting. Therefore, the upper limit of N content is limited to 0.012%. When the aging hardening by N is not actively utilized, the content may be about 0.001% to 0.004%, but in that case, YS is slightly lowered unless a large amount of other reinforcing elements are added.

Nb: 0.005% to 0.10%

Nb is an important additional element in the present invention. Nb is an element with high carbide generating ability, and precipitates fine carbides to increase the strength. In addition, the strength is increased by making the ferrite finer. In addition, the particle diameter affects not only the strength but also the surface properties during drawing processing. When the ferrite average crystal grain size of the final product exceeds 7 µm, surface roughness occurs in part after the drawing process, and the surface appearance disappears. As mentioned above, intensity | strength and surface properties can be adjusted with Nb addition amount, and this effect arises when it exceeds 0.005%. Therefore, the lower limit is limited to 0.005%. Preferably it is 0.01% or more.

On the other hand, Nb brings about an increase in recrystallization temperature. For this reason, when it contains in more than 0.10%, in the continuous annealing performed by the cracking temperature of 650-750 degreeC, and the cracking time of 40 s or less prescribed | regulated by this invention, it will become difficult to anneal, for example, some recrystallization may remain | survive. If the annealing temperature is increased as a countermeasure, a recrystallized structure is obtained. However, the surface properties are inferior because elements in the steel are concentrated on the surface. Therefore, the upper limit of Nb addition amount is limited to 0.10%. Preferably it is 0.06% or less.

Remainder of the composition of a steel plate is made into Fe and an unavoidable impurity. S as an unavoidable impurity is mentioned, for example.

Next, the structure and steel plate characteristic of the steel sheet for cans of this invention are demonstrated.

ㆍ ferrite single phase structure, ferrite average crystal grain size: 7㎛ or less

First, in the present invention, the ferrite single phase structure is substantially made. Here, "substantially" means that it is equivalent to a ferrite single phase structure from the viewpoint of the effect of this invention. For example, even when it contains cementite etc. in about 1% or less, it is judged that it is substantially a ferrite single phase structure as long as the effect of this invention is shown.

Moreover, when the ferrite average crystal grain size exceeds 7 micrometers, the beauty of the surface appearance after can manufacture will disappear. This can be considered to correspond to extreme changes in surface roughness such as surface roughness. In particular, this phenomenon is confirmed in the can body of a two piece can and the can body of a three piece can which performs can enlargement. As mentioned above, ferrite average crystal grain diameter shall be 7 micrometers or less. Although the minimum of a ferrite average crystal grain size is not specifically limited, Usually, it becomes about 4 micrometers or more.

In addition, a ferrite crystal grain size is measured using the cutting method prescribed | regulated by JISG0551.

In addition, the ferrite average crystal grain size is mainly controlled by adjusting the steel sheet composition, cold rolling ratio, and annealing temperature to a target value. Specifically, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005 to 0.10% (Or these suitable ranges) (the remainder is iron and unavoidable impurities), hot rolled at a finishing temperature of 870 ° C. or higher, cooled to a winding at a rate of 40 ° C./s or less, and 620 ° C. or higher. After winding to a coil at a temperature and performing cold rolling with a reduction ratio of 80% or more, a crystal grain size of 7 µm or less can be obtained by performing continuous annealing under conditions of a cracking temperature of 650 to 750 ° C and a cracking time of 40s or less. .

Yield strength (YP): 500 MPa or more (after coating baking)

Yield strength is an important factor in securing the dent resistance of the welding can. In general, the dent strength is expressed by the relation between plate thickness and yield strength. When the present invention is applied to a use in which a conventional DR material has been used, the yield strength is set to 500 MPa or more in order to secure the dent strength at the thickness of the DR material (typically 0.15 to 0.17 mm). The upper limit of YP need not be limited, but generally it is about 700 MPa or less.

Yield ratio (YR): 0.9 or more (after coating baking)

When tensile strength is made high, the deformation resistance at the time of hot rolling or cold rolling becomes high, and the operability of rolling falls. On the other hand, it is necessary to ensure the yield strength to 500 Mpa or more from a viewpoint of can body strength. In other words, it is necessary to increase the yield strength and decrease the tensile strength, and the yield ratio is set to 0.9 or more as a condition for obtaining the above-mentioned characteristics without disrupting the operation. In particular, YR does not have an upper limit and may be a maximum value (= 1).

In addition, YP and TS mainly control steel plate composition, cold rolling rate, and annealing temperature to a target value. Specifically, C: 0.01 to 0.12%, Si: 0.005 to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: 0.10% or less, N: 0.012% or less, Nb: 0.005 to 0.10% (Or these preferred ranges) (the remainder is iron and unavoidable impurities), hot rolled at a finishing temperature of 870 ° C. or higher, cooled at a rate of 40 ° C./s or lower until winding, and a temperature of 620 ° C. or higher. After winding to a coil at 80 ° C. and performing cold rolling with a reduction ratio of 80% or more, it can be controlled to a target value by performing continuous annealing under conditions of a cracking temperature of 650 to 750 ° C. and a cracking time of 40 seconds or less.

Although YP and YR before coating baking are not specifically limited, About 450-550 Mpa and 85-95 are respectively.

ㆍ Elongation (El): 10% or more (after coating baking)

When the elongation rate (total elongation rate) is less than 10%, for example, application of the steel sheet to a can involving high can body processing such as can enlargement processing becomes difficult. Therefore, total elongation is made into 10% or more. Although the upper limit of total elongation does not need to specifically limit, Generally, about 50% is an upper limit. The above-described ferrite single-phase fine grain structure is particularly effective as a means for securing a total elongation of 10% or more.

Although El before coating baking is not specifically limited, It is about 15 to 50%.

ㆍ Δr: -0.50 ～ 0 (after coating baking)

In the present invention, Δr represented by the following formula is used as an index of the anisotropy.

_{Δr = (r 0 + r 90} - 2 × r 45) / 4

r ₀ is the tensile test in the rolling direction, r ₄₅ is the tensile test in the direction of 45 ° to the rolling direction, and r ₉₀ is the tensile test in the direction of 90 ° to the rolling direction. The r value of (Lankford value) is shown.

In a steel sheet having Δr of less than −0.50, for example, when processed into a DRD can, since the occurrence of earrings is large, the trim area is increased, and the yield of the steel sheet is lowered. That is, in order to suppress the amount of generation of earrings from the viewpoint of yield, Δr needs to be in the range of -0.50 to 0. In addition, when the absolute value of Δr is large, flange wrinkles are generated in the flange portion of the DRD can or the welding can due to the circumferential plate thickness distribution (deviation of the plate thickness). Therefore, a steel having Δr: -0.45 to 0 is used. It is preferable to use. In addition, in applications where the roundness of the can is important, it is preferable to suppress the plate thickness distribution in the circumferential direction as much as possible, so that Δr is preferably -0.30 to 0.

In addition, (DELTA) r mainly adjusts the finishing temperature at the time of hot rolling, the cooling rate after finishing, and the winding temperature, and controls it to a target value. Specifically, Δr can be hot rolled at a finishing temperature of 870 ° C or higher, cooled at a rate of 40 ° C / s or less until winding, and wound around a coil at a temperature of 620 ° C or higher to control to a target value.

Δr before coating baking is not particularly limited, but generally takes a close value after baking.

Next, the structure of the hot rolled sheet steel for steel plate base materials for cans is demonstrated.

ㆍ Hot rolled steel sheet structure: Ferrite single phase structure, average grain size 6㎛ or more

In the present invention, the structure of the hot rolled steel sheet is substantially a ferrite single phase structure. The meaning of “substantially” is the same as in the case of a cold rolled steel sheet (cold rolled, annealed, tempered rolled), and even in the case of containing about 1% or less of cementite or the like, substantially the ferrite is exhibited. We judge that it is single phase organization.

The anisotropy of the steel sheet after cold rolling, continuous annealing and temper rolling is greatly influenced by the ferrite grain size in the hot rolled steel sheet stage. For example, FIG. 1 shows the anisotropy of the cold rolled sheet steel obtained by performing continuous annealing of the cold rolling reduction ratio: 90%, a crack temperature: 710 degreeC, and a crack time: 30 s in the steel 1 shown to the Example mentioned later, and a hot rolled sheet steel. The relationship between the ferrite average crystal grain size in the step (hot rolled material) is shown. According to FIG. 1, when the ferrite average crystal grain size of a hot rolled material is less than 6 micrometers, (Dr) is less than -0.50, and the desired anisotropy value cannot be obtained. Therefore, it is preferable that the ferrite average crystal grain size in a hot rolled material shall be 6 micrometers or more. When using steel with (DELTA) r -0.45-0, it is more preferable that the ferrite average crystal grain size in a hot rolled material shall be 7 micrometers or more. When using steel with (DELTA) r -0.30-0, it is more preferable that the ferrite average crystal grain size in a hot rolled material shall be 8 micrometers or more. In addition, there is no upper limit in particular, Usually, the ferrite average crystal grain size in a hot rolled material is about 15 micrometers or less. The measurement method of the ferrite crystal grain size is the same as that of a cold rolled steel sheet.

In addition, the crystal grain size of a hot rolled material is mainly controlled to a target value by adjusting a component, the cooling rate to FT and CT at the time of hot rolling, and CT.

In addition, although a plate | board thickness and an aging index are not specifically limited in a claim, preferable conditions in implementing this patent are the range shown below.

Preferable plate thickness of steel sheet for cans: 0.2 mm or less, Preferred plate thickness of hot rolled steel plate: 2 mm or less

Since this invention mainly aims at application to the thinning of a drawing can and a welding can, plate | board thickness is mainly used in 0.2 mm or less.

In view of the operability of cold rolling, in order to make the steel of the strength level proposed by the present invention into a plate thickness of 0.2 mm or less, it is preferable to roll at a rolling rate of 94% or less or less. For this reason, it is preferable that the plate | board thickness of a hot rolled material shall be 2 mm or less.

ㆍ aging index: 30 MPa or more

In order to reliably obtain a yield strength of 500 MPa after coating baking or after lamination treatment, the aging index is preferably 30 MPa or more. In addition, in this invention, an aging index shows the amount of aging hardening at the time of 100 degreeC-60 minute heat processing, after providing 8% preliminary deformation.

Next, the manufacturing method of the steel plate for cans of this invention, and its base material hot-rolled steel sheet is demonstrated.

The molten steel adjusted to the above-mentioned chemical composition is produced by a commonly known steel making method using a converter or the like, and then a rolled material by a commonly used casting method such as a continuous casting method. (Ingot, especially slab).

Next, a hot rolled steel sheet is made by hot rolling using the rolled material obtained as described above. Prior to hot rolling, the rolled material is preferably heated to 1250 ° C. or higher (SRT ≧ 1250 ° C.). This is to completely employ N in the steel. As for crude rolling start temperature, 1350 degrees C or less is preferable.

The finishing temperature is at least 870 ° C. Moreover, it cools at the speed of 40 degrees C / s or less until winding, and winds up at the winding temperature of 620 degreeC or more. In addition, in view of anisotropy, the ferrite average crystal grain size of the hot rolled material obtained here is 6 micrometers or more. Although a base material hot rolled sheet steel is manufactured by the above process, you may perform pickling, etc. which are mentioned later.

When manufacturing a cold rolled steel plate for cans, although cold rolling is further performed, the scale which covers the steel plate surface beforehand is normally removed by pickling. Thereafter, after cold rolling at a reduction ratio of 80% or more, continuous annealing is performed under conditions of a cracking temperature of 650 to 750 ° C and a cracking time of 40 s or less, and temper rolling is performed at a roughness of 1.5% or less. Hereinafter, the detail of each requirement is demonstrated.

ㆍ Hot rolling finish temperature (FT): 870 ℃ or higher

The finish rolling temperature in hot rolling becomes an important item in controlling anisotropy. In order to secure Δr to -0.50 or more (0 or less) in the Nb-added steel, it is necessary to set the ferrite average crystal grain size of the hot rolled material to 6 µm or more and to control the texture. In order to obtain these, hot-rolling finishing temperature shall be 870 degreeC or more. In addition, FT is preferably at most 950 ° C from the viewpoint of suppressing defects resulting from scale.

ㆍ Average cooling rate after finishing rolling to winding up: 40 ° C./s or less

The anisotropy of the steel sheet for cans (cold rolled steel sheet) is greatly influenced by the ferrite average grain size of the hot rolled material. As mentioned above (refer FIG. 1), in order to make (DELTA) r into the range of -0.50-0, the ferrite average crystal grain size of a hot rolled material needs to be 6 micrometers or more. In order to make the ferrite average crystal grain size of a hot rolled material into 6 micrometers or more, the cooling rate after hot rolling needs to be made small, and as a condition, the average cooling rate after finishing shall be 40 degrees C / s or less. Here, the average cooling rate shall be divided by the elapsed time from the end of the hot rolling to the coil winding.

In order to reliably obtain steel with Δr of -0.45 to 0 in the entire width direction, it is preferable to set the ferrite average crystal grain size of the hot rolled material to 7 µm or more, and for this purpose, the average cooling rate needs to be 30 ° C / s or less. have.

In addition, in order to reliably obtain steel with (DELTA) r -0.30-0 in the whole width direction, it is preferable to make the ferrite average crystal grain size of a hot rolled material into 8 micrometers or more, and for this purpose, an average cooling rate shall be 20 degrees C / s or less. There is a need.

It is preferable to make an average cooling rate into 10 degreeC / s or more from a productivity viewpoint.

In addition, a cooling rate is controlled by the supply amount of cooling water, etc., for example. In a general industrial scale hot rolling facility, the cooling rate in the case of water cooling at maximum strength is about 80 to 100 ° C / s. In ordinary hot rolling, the steel sheet is water-cooled at least 50 ° C / s or more near this upper limit from the viewpoint of economy. do. On the other hand, the cooling rate in the case of not using the forced cooling means at all is about several degrees C / s, but since the winding temperature becomes high temperature and the defect resulting from a scale generate | occur | produces, it is unrealistic as an industrial production means.

Winding temperature (CT): above 620 ℃

In order to make the ferrite average crystal grain size of a hot rolled material into 6 micrometers or more, it is necessary to make coil winding temperature high and as a condition, winding temperature shall be 620 degreeC or more. From a viewpoint of making (DELTA) r -0.45-0, Preferably it is 640 degreeC or more. Moreover, in order to obtain the steel whose (Dr) r is -0.30-0, it is preferable to make winding temperature into 700 degreeC or more.

It is preferable to make winding temperature into 750 degreeC from a viewpoint of descaleability.

Cold rolling rate (rolling down rate): 80% or more

The reduction ratio in cold rolling is one of the important conditions in this invention. If the reduction ratio in cold rolling is less than 80%, it is difficult to produce a steel sheet having a yield strength of 500 MPa or more. In addition, in order to obtain the plate thickness (0.2 mm or less, normally about 0.17 mm) equivalent to DR material, it is necessary to make the plate thickness of a hot rolled sheet at least 1 mm or less at the rolling reduction rate of less than 80%, and it is difficult in operation. Do. Therefore, reduction ratio is made into 80% or more. In addition, in the capacity of a general rolling installation, in the case of an excessive cold rolling rate, since a rolling load increases and it becomes impossible to roll, it is preferable that the upper limit of a cold rolling rate shall be about 96%.

ㆍ Annealing Condition: Cracking Temperature 650 ℃ ～ 750 ℃, Cracking Time 40s or Less

Annealing shall be carried out by a continuous annealing method. In order to ensure favorable workability, the crack temperature in continuous annealing needs to be more than the recrystallization temperature of a steel plate, and in order to make structure more uniform, it is necessary to crack at the temperature of 650 degreeC or more. On the other hand, in order to continuously anneal above 750 degreeC, it is necessary to reduce speed as much as possible in order to prevent fracture | rupture of a steel plate, and productivity falls. It is set to 750 degrees C or less as a condition which does not reduce productivity. Since productivity cannot be ensured at the speed which becomes 40 second or more also about crack time, a crack time shall be 40s or less. There is no particular lower limit of the crack time, and there is no problem even if the crack time zero treatment is performed, for example, cooling immediately after reaching the crack temperature (highest temperature).

ㆍ Running pressure ratio: 1.5% or less

When the coarsening ratio (rolling-down rate due to temper rolling) increases, the ductility decreases because the deformation introduced at the time of processing increases, similar to the DR material. In this invention, since it is necessary to ensure 10% or more of total elongation with an ultra-thin material, a roughening ratio is made into 1.5% or less.

(Example 1)

The steel composition which contained the component composition shown in Table 1, and remainder melted in the converter by the steel which consists of Fe and an unavoidable impurity was obtained. After reheating the obtained steel slab at 1250 degreeC, hot rolling was started. Hot rolling was performed in the range of finish-rolling temperature of 880 degreeC-900 degreeC, it cooled by the average cooling rate 20-40 degreeC / s until winding, and it wound up in the coil in the range of winding temperature of 620-700 degreeC. Subsequently, after pickling, it cold-rolled at the reduction ratio of about 90 to 94%, and produced the thin steel plate of 0.17-0.2 mm. The obtained thin steel sheet reached 690-750 degreeC by the heating rate of 15 degreeC / sec, and performed continuous annealing for 690 degreeC-750 degreeC for 20 second. Subsequently, after cooling, temper rolling was performed so that the reduction ratio (measured by elongation) would be 1.5% or less, and ordinary chromium plating (electroplating) was carried out continuously to obtain tin-free steel. In addition, the crack temperature was adjusted in the range of 690 degreeC to 750 degreeC according to Nb addition amount.

After the coating baking process of 210 degreeC and 20 minutes was performed with respect to the plated steel plate (tin-free steel) obtained by the above, the tension test was done. In addition, the crystal structure and the average grain size were examined (in addition, the crystal structure and the grain size do not change particularly before and after the coating baking process). Moreover, also about a hot rolled sheet steel, the crystal structure and the average grain size were investigated. The investigation method is as follows.

The tensile test measured yield elongation, tensile strength, and elongation (total elongation) using the tension test piece of JIS No. 5 size (described in JIS Z 2201), and evaluated the strength and ductility. The r value measurement was performed using the tension test piece (width 12.5mm, parallel part 35mm, gage distance 20mm) of JIS No. 5 half size, and (DELTA) r was measured by the following method.

_{Δr = (r 0 + r 90} - 2 × r 45) / 4

In addition, when r ₀ is subjected to the tensile test in the rolling direction, r ₄₅ is subjected to the tensile test in the direction of 45 ° from the rolling direction, and r ₉₀ is the tensile test in the direction of 90 ° from the rolling direction. It shows r value at the time of doing.

The crystal structure (both hot rolled steel sheet and cold rolled steel sheet) polished the sample (rolling direction cross section), corroded the crystal grain boundary with nital (nital alcohol solution), and observed with an optical microscope. The average crystal grain diameter was measured using the cutting method prescribed | regulated to JISG0555 with respect to the crystal structure observed as mentioned above.

The obtained results are shown in Table 2.

From Table 2, examples of the present invention (Nos. 1 to 6, 20, 21) have a ferrite average crystal grain size of annealing material (plated steel sheet) structure of 7 µm or less, and uniformity not containing a mixed structure by structure observation. It was also confirmed that it was a fine ferrite single phase structure. Moreover, from Table 2, it is confirmed that the example of this invention is excellent in both strength and ductility. In addition, the aging index achieved 30 MPa in the invention examples (No. 1 to 6, 20) containing 0.005% or more of N, and the invention example (No. 1, 2, 4 to 6) containing N or 0.0060% or more. , 20) achieved 40 MPa.

On the other hand, in Comparative Example (No. 7) in which the Nb content is excessive, the anisotropy is insufficient, and in Comparative Example (No. 8) in which the Nb content is insufficient, the strength is insufficient.

In addition, in the invention example, the hot-rolled structure was a substantially ferrite single phase structure having an average particle diameter of 6 µm or more.

(Example 2)

A steel slab was obtained by containing the component composition shown in Table 3 (the same as No. 1 of Example 1), and the remainder being melted in the furnace before the steel which consists of Fe and inevitable impurities. After reheating the obtained steel slab at 1250 degreeC, hot rolling was started. Hot rolling performed the finish rolling temperature at 830-900 degreeC, cooled the average cooling rate to coiling at 16-45 degreeC / s, and wound up the coiling temperature in the range of 580-720 degreeC. Next, it cold-rolled at the reduction ratio of 75 to 94%, and produced the thin steel plate of 0.15-0.18 mm. The obtained thin steel sheet reached 630-740 degreeC by the heating rate of 20 degreeC / sec, and performed continuous annealing for 630-740 degreeC and 20-30 second. Subsequently, after cooling, temper rolling was performed so that a reduction ratio might be 1.5% or less, and normal chromium plating was performed continuously to obtain tin-free steel. Detailed manufacturing conditions are shown in Table 4.

After the coating baking process of 210 degreeC and 20 minutes was performed with respect to the plated steel plate (tin-free steel) obtained by the above, the tensile test was performed and the crystal structure and the average crystal grain size were investigated. The crystal structure and grain size were also examined for the hot rolled steel sheet. In addition, each test and irradiation method is the same method as Example 1.

The obtained results are shown in Table 5.

From Table 5, it turns out that in this invention example (No.9-12 etc.), the high strength steel plate with small anisotropy and high ductility is obtained by making cooling rate after finish rolling small and raising winding temperature.

On the other hand, in Comparative Examples (Nos. 13 to 15, etc.) in which the finish rolling temperature is low, the winding temperature is low, or the cooling rate after the finish rolling is large, the target value is reached for the strength and the ductility, but the winding temperature is low. It became a steel plate with large anisotropy. In the comparative example (No. 16 etc.) with a low crack temperature, although the target value was reached about intensity | strength and anisotropy, since recrystallization was not completed and some unrecrystallized crystal | crystallization remained, it became a ductile steel plate with small ductility.

Moreover, when drawing-processing about these steel plates, in the example of this invention (No. 9-12 etc.), the surface property of a steel plate is favorable, a surface roughness is not observed, and the amount of generation of an ear ring is also small. On the other hand, in the comparative example in which Δr is -0.50 or less, the amount of generation of earrings is large with respect to the steel sheet.

In addition, in the invention example, the hot-rolled structure was a substantially ferrite single phase structure having an average particle diameter of 6 µm or more.

ADVANTAGE OF THE INVENTION According to this invention, the high strength high ductility steel plate for cans which has a yield strength of 500 Mpa or more, a yield ratio of 0.9 or more, total elongation of 10% or more, and (DELTA) r becomes -0.50-0 is obtained.

Specifically, the present invention is solid solution strengthening using a solid solution strengthening element, and also by strengthening the composite strengthening (employment strengthening, precipitation strengthening and fine grain strengthening) by Nb, P, Mn, etc., while maintaining the high elongation In this case, the steel sheet having a yield strength of 500 MPa or more can be reliably produced even when the temper rolling after the annealing step is at a light pressure of about 1.5% or less.

As a result, even if the welding can is made thin by increasing the strength of the original plate (steel plate), high can body strength can be ensured. Moreover, also regarding the use of a positive pressure can which requires the pressure resistance strength of the bottom portion, it is possible to obtain high pressure resistance strength in the state of the current thickness. Moreover, by making ductility high, it is possible to perform high can body processing, such as can enlargement process.

In addition, in drawing cans, it is necessary to prevent the occurrence of earrings because the trim area of the can is increased to increase the yield, but in the present invention, the finishing temperature is 870 ° C or higher and the cooling rate up to winding is 40 ° C / s or less, By making winding temperature 620 degreeC or more, (Dr) r can be suppressed in the range of -0.50-0, and generation | occurrence | production of an ear ring can be prevented.

That is, according to this invention, since the steel plate excellent in all the characteristics of strength, ductility, and anisotropy is obtained, it is centered on three piece cans with high processability can body processing, and two piece cans which require pressure-resistant strength like positive pressure cans. It is most suitable as steel plate for cans.

Claims (4)

In mass%, C: 0.01% to 0.12%, Si: 0.005% to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: more than 0% and 0.10% or less, N: more than 0% and 0.012% or less, Nb: 0.005 to 0.10% Containing a composition consisting of iron and an unavoidable impurity, a structure having a ferrite single phase structure, and an average crystal grain size of ferrite is 7 µm or less, The steel plate for cans which can obtain the characteristics of yield strength: 500 Mpa or more, yield ratio: 0.9 or more, total elongation: 10% or more, (DELTA) r: -0.50-0 by the coating baking process. In mass%, C: 0.01% to 0.12%, Si: 0.005% to 0.5%, Mn: 0.3 to 1.5%, P: 0.005 to 0.2%, Al: more than 0% and 0.10% or less, N: more than 0% and 0.012% or less, Nb: 0.005 to 0.10% Containing, the remainder being hot rolled a steel consisting of iron and unavoidable impurities at a finishing temperature of 870 ° C. or higher, It is cooled by the average cooling rate of 40 degrees C / s or less until winding, winds up at the winding temperature of 620 degreeC or more, Subsequently, after cold rolling is carried out at a reduction ratio of 80% or more, continuous annealing is performed under conditions of a cracking temperature of 650 to 750 ° C and a cracking time of 40 s or less, and temper rolling at a roughness of 1.5% or less. The manufacturing method of the steel plate for cans which carries out. delete delete

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