JP4299858B2 - Steel plate for container and method for producing the same - Google Patents

Description

The present invention relates to a steel plate used for a metal container such as a beverage can and a manufacturing method thereof.
This application is based on Japanese Patent Application No. 2004-011139 filed on Jan. 19, 2004, and the contents thereof are incorporated.

Steel plates for containers represented by beverage cans, food cans, etc., are becoming thinner to reduce the cost of containers, and materials of 0.2 mm or less are also being applied. Problems that become apparent when a container is manufactured from such an ultrathin material include, for example, color tone, surface coating adhesion, and weldability deterioration due to difficulty in controlling the surface state.
It is known that the state of the steel sheet surface has a great influence on the color tone, surface coating adhesion, and weldability, and is disclosed in, for example, Patent Document 1, Patent Document 2, Patent Document 3, and the like. A method for controlling the surface roughness is disclosed in Patent Document 4. In these examples, since it is necessary to precisely control the manufacturing conditions in order to control the surface state, a decrease in productivity is inevitable. Further, in the control methods shown in these examples, the color tone, surface coating adhesion, and weldability of a container formed of the ultrathin material intended by the present invention cannot always be sufficiently improved.
JP 11-197704 A JP-A-8-3781 JP-A-6-57488 JP 7-9005 A

  One of the objects of the present invention is to determine the surface condition of the material in terms of the color tone of the container, the surface coating adhesion, and the weldability caused by the surface condition of the steel plate, which is a problem in containers manufactured using ultrathin materials. In addition to reforming by controlling the nitride form, it is possible to control the state of the steel sheet surface, and to avoid a special treatment that impedes productivity.

As described in Japanese Patent Application No. 2003-119381 and Japanese Patent Application No. 2003-100720, in order to dramatically improve the deformation resistance of the container without significantly reducing the ductility of the steel plate, It is possible to appropriately control the nitriding state in the plate thickness direction at the time of nitriding the steel plate. When the weldability of this material is evaluated, it is possible to apply a cathodic electrolytic treatment for the purpose of controlling the surface state, use a surfactant, fine control of Cr oxide, and roll accuracy as in the past. Even without specially controlled special rolling or the like, the surface state of the steel sheet is preferable. Therefore, the conditions which can improve significantly the color tone of the container, surface coating adhesiveness, and weldability resulting from the surface state of the steel plate, which has been a problem with containers made of ultrathin steel plates, were obtained.
That is, when increasing the amount of nitrogen in the steel by performing nitriding after cold rolling, the color tone of the can, the surface coating adhesion, and the weldability are not so much improved by simply creating the surface hardness. In the present invention, it is possible to preferably control the nitride form particularly on the outermost surface of the material surface layer by limiting the components, particularly the N amount, to a specific range and further optimizing the nitriding conditions. In addition, the unevenness on the surface of the steel sheet can be changed by this, and as a result, it is possible to improve the color tone, surface coating adhesion, and weldability of the can using the ultrathin material. According to each aspect of the present invention, the conditions and the control method thereof can be provided.

A first aspect of the steel plate for containers according to the present invention is a steel plate for containers having a plate thickness of 0.400 mm or less. This material contains C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less , the balance Consists of Fe and inevitable impurities . Further, the area ratio of nitride on the surface is 1.0% or more.
In the second aspect of the steel plate for containers according to the present invention, (nitride area ratio at the surface position of the steel sheet) / (nitride area ratio at the cross-sectional position of the steel plate thickness 1/4) is 1.5 or more. is there.
A third aspect of the container steel sheet according to the present invention, the number of independent nitrides or more in diameter 0.1μm at the surface is 0.001 pieces / [mu] m ² or more.
According to another embodiment of the steel plate for containers according to the present invention, the surface roughness may be 0.90 μm or less in Ra and 250 or more in PPI which is the peak number of irregularities per 1 inch in length. Furthermore, by mass%, Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, Cr: 2.0% or less May be. Furthermore, it may contain 0.1% or less in terms of mass% in total of Sn, Sb, Mo, Ta, V, and W.

The embodiment of the method for producing a container steel plate according to the present invention is a method for producing a container steel plate having a thickness of 0.400 mm or less. This material is, by mass%, C: 0.0800% or less, N: 0.0300% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less Contained, balance Fe and inevitable impurities. This steel is subjected to nitriding treatment at the same time as or after recrystallization annealing after cold rolling to increase the N content by 0.0002% or more and to make the nitride area ratio on the surface of the steel sheet 1.0% or more. Furthermore, N of a steel plate shall be 0.600% or less. However, the nitriding treatment is performed in an atmosphere containing 0.02% or more of ammonia gas and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C.
In the embodiment of the method for producing a steel plate for containers according to the present invention, steel is C: 0.0800% or less, N: 0.0300% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10% or less, S: 0.05 % Or less, Al: 2.0% or less, and may be composed of the balance Fe and inevitable impurities. After this steel is cold-rolled, nitriding is performed simultaneously with or after recrystallization annealing to increase the N content by 0.0002% or more, and the nitride area ratio on the surface of the steel sheet is set to 1.0% or more. Furthermore, N of a steel plate shall be 0.600% or less. However, the nitriding treatment is performed in an atmosphere containing 0.02% or more of ammonia gas and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C.

In another aspect of the method for producing a steel plate for containers according to the present invention, after cold rolling the steel, nitriding is performed simultaneously with or after the recrystallization annealing, and the N amount is increased by 0.0002% or more (the surface position of the steel plate). (Nitride area ratio) / (nitride area ratio at the cross-sectional position of the steel plate thickness 1/4) may be 1.5 or more. Furthermore, N of a steel plate shall be 0.600% or less. However, the nitriding treatment is performed in an atmosphere containing 0.02% or more of ammonia gas and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C.
According to still another aspect of the method for manufacturing a steel plate for containers according to the present invention, the steel is subjected to nitriding after cold rolling and simultaneously with or after recrystallization annealing, to increase the N amount by 0.0002% or more, The number of independent nitrides having a diameter of 0.1 μm or more on the surface of the steel plate may be 0.001 pieces / μm ² or more. Furthermore, N of a steel plate shall be 0.600% or less. However, the nitriding treatment is performed in an atmosphere containing 0.02% or more of ammonia gas and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C.
In another example of the present invention, when nitriding is performed simultaneously with or after the recrystallization annealing, (plate temperature at the start of nitriding (° C.) − 550) / (ammonia gas concentration at the start of nitriding (%)) <150 And
According to another aspect of the steel plate for containers according to the present invention, at least one steel plate for containers having a plate thickness of 0.400 mm or less, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less, with the balance consisting of Fe and inevitable impurities (after nitriding treatment) The nitride area ratio at the steel sheet surface position) / (nitride area ratio at the steel sheet surface position before nitriding treatment) is 1.5 or more.
In this case, the surface roughness in the at least part may be 0.90 μm or less in Ra, and the PPI which is the number of uneven peaks of the thickness per inch in the at least part region may be 250 or more.
Further, at least one of Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, Cr: 2.0% or less may be contained.
Further, the total of Sn, Sb, Mo, Ta, V, W may contain 0.1% or less.

  According to the steel plate for containers and the manufacturing method thereof of the present invention, the color tone, surface coating adhesion, and weldability of the container are avoided after avoiding complicated processing after nitriding treatment and productivity hindrance due to this complicated processing. Can be improved. Thus, the productivity of the steel sheet for ultrathin containers can be increased, and a remarkable effect on the production process can be exhibited.

First, the steel material component will be described. All steel components represent mass%.
The upper limit of the C amount is necessary to avoid deterioration of workability, and C: 0.0800% or less. Preferably it is 0.0600% or less, more preferably 0.040% or less.
In the steel according to the embodiment of the present invention in which the amount of N having the same properties as C is increased after annealing by nitriding, the C content required from the viewpoint of securing the strength may be low. C: Necessary strength can be ensured even at 0.0050% or less, and 0.0020% or less is acceptable. If it is 0.0015% or less, there is a balance with the amount of nitriding, but it becomes possible to produce extremely soft materials that are out of specification with ordinary container materials. Since the drawability is improved by improving the r value, it is preferable that the amount of C before nitriding is low.
Similarly to C, the upper limit of the N amount of the final product is necessary to avoid deterioration of workability, and it is preferable to set N: 0.600% or less. N is preferably 0.200% or less, more preferably N is 0.150% or less, and further preferably N is 0.100% or less. However, in order to obtain the effect of the aspect of the present invention, at least N for forming a considerable amount of nitride on the steel plate surface is necessary. With regard to this N amount, it depends on how much N distribution is generated in the thickness direction, but when using normal nitriding, naturally the N amount is increased compared to before nitriding. In particular, in the present invention, it is increased by 0.0002% or more. This appears to be very small as the N increase amount, but is very large considering the N increase amount on the steel sheet surface.
That is, the thickness corresponding to the surface component of the steel sheet is, for example, 1/100 of the plate thickness. In the case of a steel plate with a thickness of 0.20 mm, assuming that the 2 μm thick part is the surface layer part, the average thickness is N When the amount increases by 0.0002%, there is an increase of N amount of 0.0100% in the surface layer portion. As the N increase amount is increased, the amount of nitride on the surface required in the present invention is increased. Therefore, it is preferably 0.0005% or more, more preferably 0.0010% or more, further preferably 0.0020% or more, and further preferably 0.0050. % Or more, more preferably 0.0100% or more, further preferably 0.0200% or more, more preferably 0.0400% or more. In particular, if it is 0.0100% or more, the amount of N on the steel sheet surface is very high, the amount of nitride required is sufficient, and the effects of the present invention can be stably obtained. However, if the amount of increase in N is excessively large, a large number of thick and coarse nitrides are formed not only on the surface of the steel sheet but also inside the steel sheet, so that not only the workability is deteriorated but also surface defects may occur. So be careful. For these reasons, the upper limit of the average N content of the steel sheet should not be exceeded.
Similarly to C, the upper limit of the N amount before nitriding is necessary to avoid deterioration of workability, and N is preferably set to 0.0300% or less. Preferably, N is 0.0200% or less, more preferably N is 0.0150% or less, more preferably N is 0.0100% or less, more preferably N is 0.0050% or less, and even more preferably N is 0.0030% or less. Since the drawability is improved by improving the r value, it is preferable that the amount of N before nitriding is low. It should be noted that, as described later, N contained by nitriding after annealing is present to give good can color, surface coating adhesion, weldability, and exists before annealing. N is different in effect.

Si is added for strength adjustment, but if it is too much, workability and plating properties deteriorate, so 2.0% or less is preferable. In the steel according to the embodiment of the present invention, N and nitride that enter the steel by nitriding at the grain boundaries are formed, and not only brittle cracks are caused, but also the effects of the present invention may be impaired. , 1.5% or less, and further 1.0% or less may be required. In particular, in order to keep the moldability high, it is preferable that the Si amount is low. By controlling the Si content to 0.5% or less, further 0.1% or less, and further 0.07% or less, the moldability is improved and the formation of Si nitride is suppressed. Is possible.
Mn is added to adjust the strength, but if it is too much, the workability deteriorates, so 2.0% or less is preferable. In order to keep the moldability high, the Mn content is preferably low, and the moldability is improved by setting it to 0.6% or less, and further 0.2% or less.
P is added to adjust the strength, but if it is too much, not only the workability is deteriorated but also the nitriding of the steel sheet is inhibited. In order to keep the moldability high, the P content is preferably low, and the moldability is improved by setting it to 0.05% or less, and further 0.01% or less.
S deteriorates the hot ductility and becomes an impediment to casting and hot rolling, so 0.05% or less is preferable. In order to keep the moldability high, the S content is preferably low, and the moldability is improved by setting it to 0.02% or less, further 0.01% or less.
Al is an element added for deoxidation. However, if the content is high, casting becomes difficult, and there are harmful effects such as an increase in surface wrinkles. Therefore, the content is preferably 2.0% or less. Further, when the Al content is as high as 0.2% or more, there is an effect of combining with N that has entered the steel sheet by nitriding to form a large amount of AlN in the steel and hardening the nitrided portion. However, care must be taken because coarse AlN may be formed to cause embrittlement. In the sense that the formability of the steel sheet thickness center layer portion with a low degree of nitriding is kept high, it is preferable that the Al content is low, forming 0.2% or less, further 0.1% or less, forming a portion with a low degree of nitriding Can be improved.

The effects of elements considered in ordinary steel plates for containers other than the basic elements described above and the control thereof will be described below.
Ti increases the recrystallization temperature of the steel sheet, and remarkably deteriorates the annealing passability of the ultrathin steel sheet targeted by the present invention. Therefore, Ti is preferably 0.080% or less. In particular, it is not necessary to add Ti in a normal application that does not require a high r value, and it is 0.04% or less, more preferably 0.01% or less. In addition, Ti that is dissolved in the steel before nitriding has a strong effect of combining with N that has entered the steel sheet by nitriding to form fine TiN in the steel and hardening the nitrided portion. For this reason, even if the steel sheet thickness center layer with a low degree of nitriding may appear to be harder than necessary, the Ti content is preferably low when it is necessary to obtain a soft steel sheet, 0.005 % Or less, and further 0.003% or less can prevent the steel sheet from being hardened inadvertently. TiN formed on the surface of the steel sheet by nitriding is very fine, and the surface modification effect aimed by the present invention is small. Therefore, it is possible to enhance the surface modification effect using this. From this, it is also possible to add intentionally so that it may become in the addition amount range prescribed | regulated to this invention.
Nb has the same effect as Ti. Nb is preferably 0.080% or less in order to raise the recrystallization temperature of the steel sheet and significantly deteriorate the annealing passability of the ultrathin steel sheet targeted by the present invention. In particular, in normal applications that do not require a high r value, it is not necessary to add Nb, and it is preferably 0.04% or less, more preferably 0.01% or less. Further, Nb solid-dissolved in the steel before nitriding is combined with N that has entered the steel sheet by nitriding to form fine NbN in the steel and has a strong effect of hardening the nitriding part. For this reason, even if the steel sheet thickness center layer with a low degree of nitriding may appear more than necessary, the Nb content is preferably lower when it is necessary to obtain a soft steel sheet, 0.005 % Or less, and further 0.003% or less can prevent the steel sheet from being hardened inadvertently. On the other hand, NbN formed on the surface of the steel sheet by nitriding is very fine and has a small surface modification effect aimed by the present invention. However, it is possible to enhance the surface modification effect by using this. From this, it is also possible to add intentionally so that it may become in the addition amount range prescribed | regulated to this invention.

When B is added to a steel sheet containing about 0.01% or more of Ti and Nb, the recrystallization temperature of the steel sheet is raised, and the annealing passability of the ultrathin steel sheet targeted by the present invention is significantly deteriorated. On the other hand, when the content of Ti and Nb is small, the adverse effect on this point is small, and the recrystallization temperature is rather lowered, so that recrystallization annealing can be performed at a low temperature. Furthermore, since it also has the effect of improving the annealing passability, it can be positively added. However, if excessively added, cracking of the slab at the time of casting becomes remarkable, so the upper limit is preferably made 0.015%. For the purpose of improving the annealing passability by lowering the recrystallization temperature, it is sufficient to set B / N = 0.6 to 1.5 in relation to the content of N before nitriding.
B dissolved in the steel before nitriding combines with N that has entered the steel sheet by nitriding to form fine BN in the steel and has a strong effect of hardening the nitrided portion. When utilizing this hardening of the surface layer by BN, it is preferable to set the ratio of the B content and the N content before nitriding to B / N> 0.8. By setting this ratio to 1.5 or more, further 2.5 or more, hardening due to BN formation becomes remarkable. On the other hand, care should be taken because the hardening of the material may appear more than necessary due to the formation of BN, which may deteriorate the moldability. In the steel according to the embodiment of the present invention, if the hardening by BN formation is not particularly utilized, the ratio of the content of N before nitriding to the content of B is B / N <0.8, more strictly B / N < It should be 0.1. On the other hand, the BN formed on the surface of the steel sheet by nitriding is very fine, and although the surface modification effect targeted by the embodiment of the present invention is small , it is possible to enhance the surface modification effect using this. is there. From this, it is also possible to add intentionally so that it may become in the addition amount range prescribed | regulated to embodiment of this invention.

In addition, Cr: 20% or less, Ni: 10% or less, and Cu: 5% or less can be added in order to impart characteristics not specified in the present specification such as enhancing corrosion resistance. However, if excessively added, the nitriding ability essential for the steel of the present invention may be lowered, so Cr: 30% or less, Ni: 15% or less, Cu: 5% or less, more preferably Cr: 15% or less, Ni: 5% or less, Cu: 2% or less. In particular, Cr dissolved in the steel before nitriding is combined with N that has entered the steel sheet by nitriding, and has the effect of forming fine Cr nitride in the steel, particularly on the steel sheet surface. It is also possible to enhance the effect of the present invention by utilizing it. For this purpose, it is preferable to add 0.01% or more of Cr.
Cr increases the recrystallization temperature of the steel sheet. If excessively added, the annealing passability of the ultrathin steel sheet targeted by the present invention may be significantly deteriorated. In order to avoid the deterioration of the annealing passability due to the increase in the recrystallization temperature, it is preferable to add Cr to 2.0% or less, and if it is 0.6% or less, the increase in the recrystallization temperature is practically no problem. Can be suppressed.
Furthermore, even if Sn, Sb, Mo, Ta, V, and W are contained in total in an amount of 0.1% or less in order to impart characteristics not specified in the present invention, the effects of the present invention are not impaired.
Of the above-mentioned elements, P, B, Sn, and Sb may lower the nitriding efficiency, which is an important requirement of the present invention depending on the conditions, so pay attention to the upper limit content in consideration of the nitriding conditions. I need to pay. In particular, Sn and Sb are each preferably 0.06% or less, more preferably 0.02% or less, in order to prevent a significant decrease in nitriding efficiency.

As mentioned above, the division of the site | part of the steel plate thickness direction used by description in this specification is demonstrated using FIG.
In particular, the “plate thickness 1/4 position” represents the corresponding position in FIG. Sites corresponding to this “plate thickness 1/4 position” are present on both surfaces of the steel plate, but in the present invention, any one of them is within the scope of the present invention. It is relatively easy to change the front and back nitride distributions by a nitriding method, a surface treatment before nitriding, or some treatment after nitriding. In the embodiment of the present invention, steel sheets having such front and back different surface layers are also targeted. This is because the effect of improving the color tone, surface coating adhesion, and weldability intended by the present invention can be obtained even on only one side.
In the embodiment according to the present invention, the area ratio or number density related to the nitride is defined at a specific position in the plate thickness direction of the steel plate surface and the steel plate. The existing precipitates can be identified by a diffraction pattern such as an electron microscope or an attached X-ray analysis instrument. Of course, identification is possible by other methods such as chemical analysis. These diameter, area ratio, and number density described later can be quantified by, for example, observation with an electron microscope. In order to control the nitride size, area ratio, and number density, it is effective to appropriately control the temperature, time, and cooling rate immediately before entering this temperature range in the temperature range of 450 to 700 ° C described later. is there. Under normal conditions, similar to the formation of general precipitates, the nitride size becomes finer and denser as the cooling rate is higher and the temperature is lower, and the nitride size becomes coarser as the time increases.

The embodiment of the present invention is not limited to the precipitate of nitride alone, but is also applicable to the case of complex precipitation together with oxide, carbide, sulfide and the like. For example, when a composite precipitate is formed, it is difficult to specify the type of one precipitate and the size of each compound, but obviously one precipitate is divided into nitride and other compound parts . Unless it is divided, it is determined as one nitride.
The method for observing the nitride is not particularly limited, and may be directly observed using a scanning electron microscope with EDX or other surface observation apparatus, or an extraction replica obtained by the SPEED method may be observed. However, in the case of an extracted replica or the like, it is necessary to pay attention when creating the replica so that the replica includes only information on the observation surface on the steel plate. This is because, in the case of the SPEED method or the like, if the amount of electrolytic extraction is too large, information in the plate thickness direction is superimposed, and more precipitates are observed than when the steel plate is directly observed. For this reason, the amount of electrolytic extraction should be kept within 2 μm in terms of steel plate thickness. When the analysis is performed by EDX, the case where N is the mainly observed nonmetallic element is a nitride . In addition, because the size is small, even if the characteristic spectrum of N is not clear, Fe, Ti, Nb, B, Cr, etc. are detected, and clear spectra such as O, S are not observed, and nitride and Precipitates that can be almost determined to be nitrides from the comparison with other precipitates that can be identified are also considered as nitrides in the present invention. Moreover, you may use an electron beam diffraction pattern etc. for the qualification of a precipitate.

  The identification of the nitride is not limited to a technique using EDX or an electron diffraction pattern, and other analytical instruments may be used. In short, it is only necessary that the type, size, and number density of the precipitates can be determined by a method that is recognized as appropriate. Depending on the precipitate, it may be difficult to discriminate between carbide and nitride, but those that cannot be properly determined by a normal analytical instrument are excluded from the present invention. That is, those that are very small in size and cannot be qualitatively analyzed by EDX spectra or ordinary analytical instruments are excluded from nitrides to be considered in the present invention. According to an embodiment of the present invention, the minimum size of a qualitative precipitate in an analytical instrument for normal use is approximately 0.02 μm. Of course, if a finer nitride is taken into account using a more advanced analytical instrument, the area ratio and the like increase. In addition, when the arrangement of individual atoms is clearly specified, the problem is how far to determine the ultrafine atomic coalescence of N and metal atoms as nitrides. Exclude fine details.

Moreover, although the nitride which the shape extended | stretched may be seen, about the thing whose shape is not isotropic, let the average of a major axis and a minor axis be the diameter of the precipitate.
In the observation of the steel plate 1/4 thickness position cross section of the steel plate according to the embodiment of the present invention, it is necessary to polish the steel plate. Also in the observation of the steel sheet surface, it is possible to perform some kind of polishing treatment or etching treatment in order to clean the surface or to make a precise observation by clarifying precipitates. Needless to say, when the surface of the steel sheet is polished or etched , the observation surface is not strictly the surface of the steel sheet. Therefore, any method that does not require polishing or the like should be selected. When processing the surface, the reduction in plate thickness due to processing should be limited to about 2 μm or less.
In addition, not by observation from the surface direction of the plate (two-dimensional observation) but by observation from the cross-sectional direction (observation on the surface and 1/4 thickness position is not two-dimensional but one-dimensional), You may calculate an area ratio, a number density, a diameter, etc. The number of nitrides and the diameter can also be obtained using image analysis or the like.

Hereinafter, the state of the steel sheet surface, which is a preferred embodiment of the present invention, will be described.
In the embodiment of the present invention, the nitride form on the steel sheet surface is controlled. For example, the non-uniformity of the surface is increased by covering the surface of the steel plate with a material different from that of steel, and the characteristics related to the target surface state are improved. Further, since the characteristics related to the surface state depend on the form of the nitride formed on the surface, the nitride form is controlled by the thermal history after nitriding, the cooling conditions, and the like. Thus, the feature of the present invention is the state of nitride on the steel sheet surface. As a method for limiting this, in the embodiment of the present invention, the area ratio of nitride is used, and this is limited to 1.0% or more. Preferably 2.0% or more, more preferably 5.0% or more, more preferably 10% or more, more preferably 20% or more, more preferably 40% or more, and the entire surface of the steel sheet is covered with nitride. There is no problem.
However, the nitride formed in a film shape is easy to break, and it is not a little broken in the passing plate in the manufacturing process. It should be noted that the nitride film on the surface is very thick, which may be the starting point of the steel sheet breakage or may be recognized as some surface defect. Therefore, excessive surface enrichment of N content should be avoided.

  It can also be defined by the ratio of (nitride area ratio at the surface position of the steel sheet) / (nitride area ratio at the cross-sectional position of the steel sheet thickness 1/4), and this ratio is 1.5 or more, preferably 3 or more More preferably, it is 6 or more, more preferably 10 or more, more preferably 30 or more, and still more preferably 100 or more. When this ratio is small, the effect of the present invention is reduced and the intended steel sheet cannot be obtained. In addition, when nitriding is applied as a method for increasing the number density of nitride in the surface layer portion in this way, (nitride area ratio at the surface position of the steel sheet after nitriding treatment) / (at the surface position of the steel sheet before nitriding treatment) It can also be defined by the ratio of nitride area ratio. In this case as well, the ratio may be 1.5 or higher, preferably 3 or higher, more preferably 6 or higher, more preferably 10 or higher, more preferably 30 or higher, and still more preferably 100 or higher. Needless to say, the larger the ratio, the greater the effect of the present invention.

Further, as the form of the nitride on the surface, it is preferable to disperse the fine particles to a certain degree uniformly rather than to disperse coarse ones sparsely. However, too fine ones may have a small contribution to the surface modification effect intended by the present invention, and therefore preferably have a diameter of 0.10 μm or more. In the embodiment of the present invention, the number density is limited to an independent nitride region or an independent steel region on the steel sheet surface. In the aspect of the present invention, the numerical value of the higher number density is adopted among the nitriding region and the steel region. It is shown that the higher the numerical value, the more finely the region is dispersed on the steel plate surface. In the present invention, the number density is preferably 0.001 piece / μm ² or more. More preferably 0.003 / μm ² or more, more preferably 0.010 / μm ² or more, more preferably 0.030 / μm ² or more, more preferably 0.10 / μm ² or more, more preferably 0.30 / μm ² or more, The number is preferably 1.0 / μm ² or more, more preferably 3.0 / μm ² or more. FIGS. 2 and 3 schematically show the above-described area ratio and number density.

Next, control of the surface roughness of the steel sheet according to the embodiment of the present invention will be described. Various descriptions of the surface roughness can be considered. In the present invention, the surface roughness Ra and the PPI indicating the number of uneven peaks per inch of length are described. The measurement method is not particularly limited, and a method such as a stylus method or a laser method, or a commonly performed method such as two-dimensional or three-dimensional measurement is used.
In the present invention, Ra is 0.90 μm or less and PPI is 250 or more. If Ra is too high or PPI is too low, the properties such as color tone, adhesion, weldability and the like intended by the present invention deteriorate due to surface irregularities. Ra is preferably 0.80 μm or less, more preferably 0.70 μm or less, further preferably 0.60 μm or less, and further preferably 0.50 μm or less. The PPI is preferably 300 or more, more preferably PPI is 350 or more, more preferably PPI is 400 or more, more preferably PPI is 450 or more, and further preferably PPI is 500 or more. Qualitatively, it is preferable that unevenness with uniform height exists at a high density. The lower limit of Ra is not particularly limited, and is controlled to a value according to the purpose by nitriding conditions, temper rolling conditions, and the like. However, 0 is not included in the lower limit of Ra and is actually 0.02 μm or more.

  The upper limit of PPI is not limited, and is controlled according to nitriding conditions, temper rolling conditions, and the like. Basically, Ra is lower and PPI is higher when N is segregated so that the N concentration becomes higher near the surface. As one method for segregating N on the surface, nitriding is performed in a relatively short time in an ammonia atmosphere. Of course, the surface condition is the steel composition and crystal grain size before that, annealing temperature and cold rolling conditions, as well as rolling reduction and number of passes during temper rolling after nitriding, roll roughness, and plating when performing metal plating. It is also influenced by conditions. Therefore, although it is difficult to limit the surface state to a specific range, the basic control is the same as that normally performed, and can be controlled without any problems after several trials.

Conventionally, in order to control the roughness in this way, the unevenness of the rolling roll is transferred in the temper rolling after annealing, or the form control by a surface coating metal such as special electrolytic treatment or plating is performed. In addition, since the roughness strongly depends on the state of adhesion to the steel plate surface such as metal plating, the form control of the coating by plating has been performed precisely. However, in the embodiment of the present invention, since these conditions are hardly received, it is possible to enjoy a great advantage in production. For example, with regard to the unevenness of the rolling roll, since the unevenness of the rolling roll is conventionally worn out by rolling, it is necessary to frequently perform replacement of the rolling roll and uneven processing in order to define the unevenness on the surface of the steel sheet within a preferable range. Not only that, there was an excessive load in terms of productivity and labor.
On the other hand, according to the embodiment of the present invention, the surface state of the steel sheet is hardly affected by the temper rolling method, and it is possible to perform a large amount of processing without almost managing the wear of the unevenness of the rolling roll. Become. In addition, with regard to the form of metal plating, it is possible to uniformly disperse a very fine and uniform metal plating coating without particularly controlling the plating conditions and the like. Thereby, it is possible to greatly improve the productivity of the steel sheet. In general, temper rolling is often performed after annealing, but in the steel of the present invention, fine cracks on the surface of the steel sheet also by bending of the hearth roll when passing through the normal continuous annealing line, Since unevenness is formed, temper rolling is not essential.

The reason why the roughness of the steel sheet surface is hardly affected by the method and conditions that cause the roughness is considered to be because the cause of the roughness is the steel sheet itself, that is, the dispersion state of nitride on the steel surface. . This mechanism is described below. The steel according to the present invention is in a state different from that of a normal, basically homogeneous steel plate made of Fe by covering a very large portion of the steel plate surface with a nitride. When the surface of the steel sheet is partially covered with nitride, it is natural to expect that a difference in surface characteristics will occur between the nitride part and the exposed part of the steel sheet. Since the nitride covering the surface will be significantly different from the deformation characteristics of steel, the deformation due to the bending process associated with the skin pass and through-sheeting during steel plate production is reduced in the micro region. It is considered to be different from the exposed part. As a result, it is considered that the effect of processing conditions such as a skin pass is alleviated on the surface roughness and strongly depends only on the nitride state of the steel sheet surface. In addition, even when almost the entire surface is covered with nitride, it is considered that this nitride is finely crushed by slight deformation to form a uniform surface roughness.
Furthermore, with respect to such nitrides, the wettability and reactivity with the coating material covering the steel sheet surface formed by surface treatment such as plating is different from that of the steel sheet itself, and this is the purpose. It is considered that there is an effect that the characteristic changes in a preferable direction. That is, in the conventional steel plate in which no nitride exists, the coating material covers the steel plate surface relatively uniformly, whereas when nitride exists on a part of the steel plate surface, the portion where the nitride is exposed and the steel The formation state (thickness, etc.) of the coating material differs depending on the portion where the matrix phase is exposed. For this reason, the coating material at the time of the surface treatment is unevenly distributed depending on the presence of nitride on the surface of the steel sheet. . Therefore, it is possible to finely disperse the nitride or exposed steel surface on the steel plate surface at the time of steel plate production, or to cover the entire surface of the steel plate with finely crushed nitride, thereby covering the surface treatment The substance can be finely dispersed regardless of the surface treatment conditions. Such unevenly distributed coating material (that is, micro nonuniformity of the coating material) is considered to improve color tone, adhesion, and weldability.

  Next, nitriding conditions will be described. The nitriding treatment of the present invention is conveniently performed simultaneously with or after the recrystallization annealing after the cold rolling from the viewpoint of productivity, but is not particularly limited thereto. The annealing method can be applied regardless of batch type or continuous annealing. However, the continuous annealing method is much more advantageous from the viewpoint of the productivity of nitriding treatment and the uniformity of the material in the coil of the nitriding material. Further, in order to obtain a large effect by controlling the material of the inner surface layer as defined in the embodiment of the present invention, it is disadvantageous that the nitriding time and the subsequent thermal history are prolonged. It is preferable that at least the nitriding treatment is performed in a continuous annealing facility. If there is no special reason, it shall be applied to the continuously annealed material. In particular, in the continuous annealing process, the atmosphere in the furnace is partially controlled, and the recrystallization in the first half and the nitriding process in the second half are performed, and productivity, uniformity of material, easy control of the nitriding state, etc. There are benefits.

Further, if nitriding is performed before recrystallization is completed, recrystallization is remarkably suppressed, an unrecrystallized structure remains, and workability may be remarkably deteriorated. This limit is complicatedly determined by steel components, nitriding conditions, recrystallization annealing conditions, and the like. However, those skilled in the art can easily find a condition in which an unrecrystallized structure does not remain after an appropriate trial. Nitriding treatment takes into account not only the amount of N increase in the steel sheet due to nitriding, but also the steel composition and recrystallization annealing conditions, as well as the thermal history after nitriding, etc. It is necessary to determine the hardness change. If only the material determined by Rockwell hardness is used as an index, the preferred color tone, surface coating adhesion and weldability intended by the present invention cannot be obtained. This condition needs to be determined with reference to an appropriate number of trials in actual operation, but the basic idea is as follows, and the present invention is defined based on this.
That is, nitriding needs to be performed at a plate temperature of 550 to 800 ° C. This can also be achieved by setting the nitriding atmosphere to this temperature as in normal annealing, allowing the steel sheet to pass through the atmosphere to bring the plate temperature to this range, and simultaneously performing nitriding. Alternatively, the nitriding atmosphere may be set to a lower temperature, and nitriding may be advanced by allowing a steel sheet heated to a temperature in this range to enter the nitriding atmosphere. When the temperature of the nitriding atmosphere is raised to this temperature, the nitriding efficiency of the steel sheet may decrease due to alteration and decomposition of the atmosphere unrelated to the nitriding of the steel sheet, so the temperature is set to 550 to 750 ° C. The temperature is preferably 600 to 700 ° C, more preferably 630 to 680 ° C.
The nitriding atmosphere contains nitrogen gas in a volume ratio of 10% or more, more preferably 20% or more, more preferably 40% or more, more preferably 60% or more, and optionally, hydrogen gas is 90% or less, more preferably It may contain 80% or less, more preferably 60% or less, more preferably 20% or less, and may contain 0.02% or more of ammonia gas if necessary. The balance can be oxygen gas, hydrogen gas, carbon dioxide gas, hydrocarbon gas, or various inert gases.

In particular, ammonia gas is highly effective in increasing the nitriding efficiency, and a predetermined amount of nitriding can be obtained in a short time. Therefore, diffusion of N into the center of the steel sheet can be suppressed, and a favorable effect can be obtained for the present invention. Although 0.02% or less is sufficient for this effect, it is preferably 0.1% or more, more preferably 0.2% or more, more preferably 1.0% or more, and further preferably 5% or more. If it is 10% or more, a sufficient effect can be obtained even by nitriding in 5 seconds or less. From the viewpoint of nitriding efficiency, the ratio of main components other than ammonia gas, particularly the ratio of nitrogen gas to hydrogen gas (nitrogen gas) / (hydrogen gas) is preferably 1 or more, and this ratio is set to 2 or more. By doing so, more efficient nitriding becomes possible. Further, in normal annealing, annealing is performed under conditions that do not nitride in an atmosphere mainly composed of nitrogen gas and hydrogen gas. However, those skilled in the art are not limited to the above-described mixing of ammonia gas, and the dew point can be changed. It is possible to change the conditions to cause nitriding by mixing a trace gas or changing the gas ratio after an appropriate trial. The object of the present invention is that at least nitriding by heat treatment including annealing can be detected by the current analytical ability.

Although the holding time in the nitriding atmosphere is not particularly limited, in consideration of the steel sheet thickness of 0.400 mm at the maximum in relation to the temperature condition of the present invention of 550 ° C. or higher, if the holding time is too long, It is considered that N entering from the steel sheet surface by nitriding by diffusion of N in the steel reaches the central layer of the steel sheet, and the N distribution or hardness distribution intended by the present invention cannot be obtained, and the upper limit is 360 seconds. Further, even if the nitriding efficiency is improved, one second is required to obtain the nitriding amount and the nitrogen and hardness distribution in the thickness direction of the steel sheet, which are required by the present invention. The time is preferably 2 to 120 seconds, more preferably 3 to 60 seconds, further preferably 4 to 30 seconds, and further preferably 5 to 15 seconds. Needless to say, when controlling in a short time, it is necessary to increase the nitriding efficiency by increasing the ammonia concentration.
In the present invention, it is important to control the dispersion state of nitride on the surface of the steel sheet, and it is effective to control the nitriding conditions as a method for preferably controlling this. In the following, gas nitridation using particularly desirable ammonia gas will be described.

The technical aspects described later regarding this control are phenomena that can be easily understood by those skilled in the art, and it is relatively easy to apply this control concept to different nitriding methods. In the embodiment of the present invention, in order to preferably control the dispersion state of the nitride on the surface of the steel sheet, when performing the nitriding treatment, (the plate temperature at the start of nitriding (° C.) − 550) / (ammonia gas concentration at the start of nitriding) (%)) <150. The value represented by the formula (plate temperature at the start of nitriding (° C.) − 550) / (ammonia gas concentration at the start of nitriding (%)) is preferably 100 or less, more preferably 50 or less. When the plate temperature at the start of nitriding is 550 ° C. or lower, the value of the above equation is negative, but such a case is also included in the present invention. When the denominator is 0 in the above equation, a meaningful value cannot be obtained.However, when the denominator is 0, it means that nitridation has not substantially occurred. Is automatically excluded because it does not fit. The meaning of the above equation, that is, the technical significance of this control is considered as follows.
Since the dispersion state of nitride greatly depends on the initial state of forming nitride, in other words, the state at the time of nucleation of nitride, the condition at the start of nitridation affects the final dispersion state of nitride it is conceivable that. Nitride nucleation is considered to be a phenomenon in which nucleation occurs finely and finely at a low temperature in a state where the precipitated elements are dissolved in a supersaturated state at a low temperature, like precipitation in ordinary steel. That is, the supersaturated solid solution element tries to form some precipitates, but if the temperature at that time is low, sufficient diffusion does not occur and the diffusion distance becomes short, so that a fine precipitation form is obtained.

According to the embodiment of the present invention, the ammonia gas concentration is preferably high in order to control to a supersaturated state. However, if the temperature is too low, sufficient nitriding does not occur, and even if the ammonia gas concentration is high, it may not be possible to control to a sufficiently supersaturated state. Although it is difficult to completely formulate this situation and accurately present the optimum condition, it is basically expressed in the form of the restriction formula of the present invention in accordance with the above-mentioned idea. Become. The optimum situation is a temperature range where a certain degree of nitriding occurs sufficiently and diffusion does not occur excessively (for example, in the case of ammonia gas nitriding, a temperature range of about 550 to 700 ° C.), which is a relatively high gas. It is preferable to start nitriding at a concentration and to nucleate nitrides on the surface of the steel sheet. Although this does not include a temporal factor, it seems that fine nucleation can be achieved by performing nucleation over time at a low temperature where diffusion is further suppressed. In such a case, the value of the above equation is in a negative region, but it is included in the present invention as described above.
Since the above control concept is not limited to ammonia gas nitriding, the nitriding gas in gas nitriding is not limited to ammonia, and the nitriding method is not limited to gas nitriding. That is, it is controlled to finely disperse precipitation nuclei using a metallurgy of nucleation phenomenon that is generally known, and those skilled in the art who have knowledge about ordinary steel materials can perform specific nitriding. It is easy to set preferable conditions according to the method.

As mentioned above, although the case where the steel plate is gas-nitrided was described, the means for obtaining the steel plate of the present invention is not limited to gas nitriding, and can be performed by liquid nitriding, plasma nitriding, ion implantation or the like. In the present invention, since it is a necessary condition to cover a considerable area of the surface with nitride, other methods can be applied as long as N is concentrated on the surface. In particular, if the process is such that the N distribution in the thickness direction of the steel sheet is changed without increasing the total N content of the steel sheet and N is concentrated only on the surface, the change in workability of the steel sheet is small. Is convenient.
Further, the present invention can be realized not only in the process of nitriding the steel sheet but also in the process of modifying the steel sheet surface by attaching some N-containing substance to the steel sheet surface. In particular, if any nitride having low reactivity with the steel plate is attached to the surface, it is advantageous because the influence on the properties such as workability of the steel plate base material itself is reduced.
Oite the production of thin container steel sheet, there is a case where a re-cold rolling after recrystallization annealing for hardness adjustment and sheet thickness adjustment. This rolling reduction has been put to practical use from about 1%, which is close to a skin pass performed for shape correction, to 50% or more, which is the same as that for cold rolling. Also in the steel of the embodiment according to the present invention, as a result of experiments conducted by changing the rolling reduction ratio of recold rolling after nitriding in the range of 0 to 90% according to the application, the strength accompanying the increase of the recooling rolling ratio It was confirmed that the same characteristic changes as before, such as increase, ductility reduction, and deformation resistance after can molding were observed. However, it was also confirmed that the color tone, surface film adhesion, weldability, and the like attributed to surface precipitates, which are the characteristics of the present invention, maintain the same or higher level as conventional materials. That is, since the features of the present invention are not lost by re-cold rolling, the conditions for re-cold rolling may be determined as appropriate according to customer needs within the scope of conventional technical skill in the art. Re-cold rolling similar to conventional steel is applicable. When shape correction or the like is not necessary, it is possible to not perform re-cold rolling at all. For the purpose of shape correction or the like, rolling is performed at a reduction rate in the range of about 0.5% to about 2.5%, but the steel of the present invention is usually rolled to this extent. On the other hand, if the re-rolling ratio increases, the steel sheet itself becomes sufficiently hardened. Therefore, since it becomes possible to obtain sufficient can strength without controlling the material distribution in the thickness direction as in the embodiment of the present invention, the re-rolling ratio is increased to far beyond the normal application range. The significance is reduced.
Moreover, since workability will fall when a re-cold rolling rate becomes high, application of a high re-cold rolling rate should be avoided carelessly. From the above, when re-rolling is applied to the steel of the present invention, it is preferable to be up to about 70%. This limit is determined only in consideration of the can strength and ductility, but even if re-cold rolling exceeding 70%, for example, the surface characteristics by controlling surface precipitates, which is a feature of the present invention, The effect of improving weldability is not lost.

If re-rolling is performed in order to produce a hard material, it is needless to say that a higher re-rolling rate is preferable, and the re-rolling rate is preferably 6% or more, more preferably 10% or more, It is preferably 20% or more, more preferably 30% or more, and still more preferably 40% or more in terms of increasing hardness. On the other hand, if priority is given to ensuring ductility, it is needless to say that the re-rolling reduction ratio is preferably low. The re-rolling ratio is preferably 50% or less, more preferably 40% or less, and even more preferably 30%. % Or less, more preferably 20% or less, more preferably 10% or less, and even more preferably 5%, in order to ensure the ductility of the steel sheet. In the step of continuously performing recrystallization annealing and specific heat treatment, which is preferable from the viewpoint of productivity, the re-rolling time is after the specific heat treatment. However, when the recrystallization annealing and the specific heat treatment are performed as separate steps, it can be performed before the specific heat treatment.
Further, when considering a welded portion, it is pointed out that a normal material is softened locally by welding heat, and processing distortion is concentrated in flange forming or the like, resulting in deterioration of formability. In the steel of the present invention containing a large amount of N in the surface layer portion, since softening due to this welding heat is also suppressed, it is possible to obtain a merit with respect to the formability of the welded portion.
The embodiment of the present invention is applied to a steel plate having a thickness of 0.400 mm or less. This is because the color tone, surface coating adhesion, and weldability of the molded member are less likely to be a problem with steel plates having a thickness greater than this. A steel plate of preferably 0.300 mm or less, more preferably 0.240 mm or less is targeted, and a steel plate of 0.190 mm or less, further 0.160 mm or less can obtain a very remarkable effect. In this way, mainly by controlling the state of nitride on the surface of the steel sheet after nitriding, a material unique to the steel of the present invention that is not present in steel containing N or nitriding steel only for the purpose of creating surface hardness is used. To have. That is, by controlling the form of the nitride on the surface of the steel sheet based on the nitriding conditions defined in the present invention, it is possible to obtain very good color tone, surface coating adhesion, and weldability.

  The effect of the embodiment of the present invention does not depend on the heat history and the manufacturing history before annealing after the component adjustment. Slabs for hot rolling are not limited to manufacturing methods such as the ingot method and continuous casting method, and do not depend on the heat history up to hot rolling. The effects of the present invention can also be obtained by the CC-DR method in which hot rolling is directly performed without heating, and also by thin slab casting in which rough rolling or the like is omitted. The effect of the present invention can also be obtained by two-phase rolling in which the finishing temperature is α + γ, regardless of hot rolling conditions, or by continuous hot rolling in which a rough bar is joined and rolled.

Further, when using the steel according to the embodiment of the present invention as a container material having a welded portion, the softening of the heat-affected zone is suppressed, and in particular, the surface layer portion having a high N concentration is quenched and hardened. It also has the effect of improving strength. This becomes more prominent when elements such as B and Nb that normally suppress the softening of the heat-affected zone are added.
The steel plate according to the embodiment of the present invention includes a case where some surface treatment is performed. That is, in the steel sheet used by the user after the surface treatment, the color tone and weldability are necessary for the steel sheet after the surface treatment, and the preferable state of the steel sheet surface required for these characteristics was manufactured as described above. Steel sheets are not damaged by surface treatment. Of course, the absolute values of Ra and PPI change considerably by surface treatment, but a function that favors the surface state of the steel sheet generated by controlling the nitride form on the steel sheet surface, that is, many irregularities with small height are formed. This state can be sufficiently detected even by the steel sheet after the surface treatment. This effect provides very good color tone and weldability in the steel sheet after the surface treatment.

On the other hand, the surface state of the steel plate before the surface treatment is important in the adhesion of the surface coating such as metal plating, painting, and organic coating (laminate). With regard to this characteristic as well, by controlling the hardness in the thickness direction of the steel sheet according to the embodiment of the present invention, the surface state of the steel sheet is favored, that is, a state where a large number of irregularities having a small height are formed. This provides very good adhesion. As the surface treatment, in the case of metal plating, tin, chromium (tin-free), Ni, zinc, aluminum, etc., which are usually applied, are applied. Not only the adhesion of these coatings, but also the color tone and weldability after the coating is formed. In addition, in the case of coating a laminated steel sheet coated with an organic film that has been used in recent years, or coating directly on a steel sheet or after metal plating, etc., the effect of the present invention can enhance adhesion. It becomes possible.
The application can be used for all containers regardless of whether it is a two-piece can or a three-piece can, and can be applied when there is a problem similar to the above in some application.

As an example of the present invention, an Sn-plated steel plate, which is one of the most common steel plates for containers, was used, and the color tone, surface coating adhesion, and weldability were evaluated.
Adhesion is determined by performing a T-type peel test in a state where two pieces of epoxyphenol-based paint coated with 25 mg / m ^{2 on} both sides are heat-pressed with a nylon adhesive and wetted with tap water. It was measured. Of course, the one having high peel strength was judged to have good adhesion.
The color tone was defined by an L value obtained using a spectrocolorimeter after applying a transparent polyester resin at 10 μm and drying. The higher the L value, the better the color tone, and the value was judged as superior or inferior.
Welding is performed by changing the welding current in seam welding, which is normally applied to 3-piece cans. Splash generation during welding (chilli generation), weld strength by peel test (hain test), steel plate during welding The weldable current range was determined from the surface damage of the weld due to the arc current between the surface and the polar ring, and the range was determined by the range and the lower limit. A wider range is preferable because of high manufacturing stability, and a lower limit is preferable because plating peeling or material change due to a rise in the temperature of the weld is less likely to occur. The roughness was measured using a laser type three-dimensional roughness meter.
Although the steel sheet after nitriding has a considerable variation in N concentration in the thickness direction, the average value of the thickness is used in the present invention.

Various steel plates were manufactured by performing hot rolling, cold rolling, and recrystallization annealing on the steels of each component shown in Table 1. The amount of N described in Table 1 is the average amount of N before nitriding. For some materials, nitriding was carried out under the conditions shown in Table 1 by controlling the temperature, atmosphere, etc. of the nitriding furnace following the high temperature holding furnace for recrystallization annealing. All nitriding is performed during or after annealing, and it is assumed that recrystallization has been completed before nitriding occurs.
Furthermore, temper rolling was performed to produce a steel plate. Table 2 shows the rolling conditions, final plate thickness, nitrogen content analysis results, and property evaluation results for these steels. It can be confirmed that good color tone, surface coating adhesion, and weldability are obtained by controlling the state in the plate thickness direction within the specified range of the present invention using the production method of the present invention. For some materials that are not nitrided, we tried to adjust the surface roughness by making the temper rolling conditions special, but due to roll wear and the number of passes, efficient production was hindered. (Productivity evaluation column is “bad”). Moreover, although the evaluation value of steel plate roughness may reach the steel level of the present invention by such special rolling, the characteristics do not reach the level of the optimum steel material according to the embodiment of the present invention.

  The embodiments and other examples of the present invention have been described above, but the present invention is not limited to these embodiments and modifications. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention. Although various documents are cited in the present invention, their entire contents are incorporated herein.

FIG. 1 is a diagram showing each part in the thickness direction of the steel plate for containers of the present invention. FIG. 2 is a view showing a nitride region of the steel plate for containers according to the present invention. FIG. 3 is a view showing a steel region of the steel plate for containers according to the present invention.

Claims (20)

At least one steel plate for containers having a thickness of 0.400 mm or less, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10 %, S: 0.05% or less, Al: 2.0% or less, and the composition comprising the balance Fe and inevitable impurities,
A steel plate for containers, wherein the area ratio of nitride on the surface is at least 1.0%.   2. The container according to claim 1, wherein the surface roughness in the at least part is 0.90 μm or less in Ra, and the PPI which is the number of uneven peaks of the thickness per inch in the at least part region is 250 or more. Steel plate.   2. The composition according to claim 1, comprising at least one of Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, Cr: 2.0% or less. Steel plate for containers.   2. The steel plate for containers according to claim 1, containing 0.1% or less in total of Sn, Sb, Mo, Ta, V and W. At least one steel plate for containers having a thickness of 0.400 mm or less, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10 %, S: 0.05% or less, Al: 2.0% or less, and the composition comprising the balance Fe and inevitable impurities,
A steel plate for containers, wherein (the nitride area ratio at least at a part of the surface position) / (the nitride area ratio at the cross-sectional position of the at least a part of the plate thickness 1/4) is 1.5 or more.   6. The container according to claim 5, wherein the surface roughness in the at least part is 0.90 μm or less in Ra, and the PPI which is the number of uneven peaks of the thickness per inch in the at least part region is 250 or more. Steel plate.   6. The composition according to claim 5, comprising at least one of Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, Cr: 2.0% or less. Steel plate for containers.   6. The steel plate for containers according to claim 5, containing 0.1% or less in total of Sn, Sb, Mo, Ta, V, and W. At least one steel plate for containers having a thickness of 0.400 mm or less, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10 %, S: 0.05% or less, Al: 2.0% or less, and the composition comprising the balance Fe and inevitable impurities,
A steel plate for containers, wherein the number of independent nitrides having a diameter of 0.1 μm or more on at least a part of the surface is 0.001 pieces / μm ² or more.   10. The container according to claim 9, wherein the surface roughness in the at least part is 0.90 μm or less in Ra, and the PPI which is the number of uneven peaks of the thickness per inch in the at least part region is 250 or more. Steel plate.   10. The composition according to claim 9, containing at least one of Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, and Cr: 2.0% or less. Steel plate for containers.   10. The steel plate for containers according to claim 9, containing 0.1% or less in total of Sn, Sb, Mo, Ta, V, and W. A method for producing at least one steel plate for containers having a thickness of at least a portion of 0.400 mm or less, wherein the at least a portion is C: 0.0800% or less, N: 0.0300% or less, Si: 2.0% or less, Mn : Steel containing 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less, the balance being Fe and inevitable impurities,
(A) cold rolled,
(B) After the step (a), nitriding is performed simultaneously with or after the recrystallization annealing,
(C) A method for producing a steel plate for containers, wherein the N content is increased by 0.0002% or more, the area ratio of nitride on the surface of the steel plate is 1.0% or more, and the N content in the steel plate is 0.600% or less. .
However, the nitriding treatment in the step (b) is performed in an atmosphere containing ammonia gas at 0.02% or more and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C. A method for producing at least one steel plate for containers having a thickness of at least a portion of 0.400 mm or less, wherein the at least a portion is C: 0.0800% or less, N: 0.0300% or less, Si: 2.0% or less, Mn : Steel containing 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less, the balance being Fe and inevitable impurities,
(A) cold rolled,
(B) After the step (a), nitriding is performed simultaneously with or after the recrystallization annealing,
(C) Increase the amount of N by at least 0.0002% or more, (Nitride area ratio at the surface position of the steel sheet) / (Nitride area ratio at the cross-sectional position of the steel sheet thickness 1/4) is 1.5 or more, and within the steel sheet The manufacturing method of the steel plate for containers characterized by making N content of 0.600% or less.
However, the nitriding treatment in the step (b) is performed in an atmosphere containing ammonia gas at 0.02% or more and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C. A method for producing at least one steel plate for containers having a thickness of at least a portion of 0.400 mm or less, wherein the at least a portion is C: 0.0800% or less, N: 0.0300% or less, Si: 2.0% or less, Mn : Steel containing 2.0% or less, P: 0.10% or less, S: 0.05% or less, Al: 2.0% or less, the balance being Fe and inevitable impurities,
(A) cold rolled,
(B) After the step (a), nitriding is performed simultaneously with or after the recrystallization annealing,
(C) Increase the amount of N by at least 0.0002% or more, make 0.001 piece / μm ² or more of independent nitrides having a diameter of 0.1 μm or more on the surface of at least a part of the steel sheet, and the amount of N in the steel plate is 0.600% or less. The manufacturing method of the steel plate for containers characterized by performing.
However, the nitriding treatment in the step (b) is performed in an atmosphere containing ammonia gas at 0.02% or more and held for 0.1 seconds or more and 360 seconds or less so that the plate temperature becomes 550 to 800 ° C. (B) above the nitriding treatment step, (nitride starting plate temperature ° C. -550) / (ammonia gas concentration at the start nitride%) <any one of claims 13 to 15, characterized in that the 150 The manufacturing method of the steel plate for containers as described in a term . At least one steel plate for containers having a thickness of 0.400 mm or less, C: 0.0800% or less, N: 0.600% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.10 %, S: 0.05% or less, Al: 2.0% or less, and the composition comprising the balance Fe and inevitable impurities ,
A steel plate for containers, wherein (nitride area ratio at the steel sheet surface position after nitriding treatment) / (nitride area ratio at the steel plate surface position before nitriding treatment) is 1.5 or more. 18. The container according to claim 17 , wherein the surface roughness in the at least part is 0.90 μm or less in Ra, and the PPI which is the number of uneven peaks of the thickness per inch in the at least part region is 250 or more. Steel plate. 18. The composition according to claim 17 , containing at least one of Ti: 0.08% or less, Nb: 0.08% or less, B: 0.015% or less, Ni: 5.0% or less, Cu: 2.0% or less, Cr: 2.0% or less. Steel plate for containers. 18. The steel plate for containers according to claim 17 , containing 0.1% or less in total of Sn, Sb, Mo, Ta, V, and W.

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