JP5464223B2 - Surface-treated steel sheet for welding can and manufacturing method thereof - Google Patents

Description

  The present invention relates to a surface-treated steel sheet for a welding can excellent in flange crack resistance in a step of performing flange processing subsequent to neck-in processing in a neck-in welding can body used for beverage cans and the like by resistance seam welding, and a method for producing the same It is about.

  Among the can body joining methods, the resistance seam welding method has a steel plate yield superior to conventional soldering and resin bonding, and is widely used in beverage cans such as fruit juice and coffee, and aerosol cans for non-food cans. In the resistance seam welding method, the side seam portion of the can body is melted and crimped by electric resistance heat generated by the steel plate. After the side seam portion is pressure-bonded, both ends of the can body are projected outward in the diameter direction in order to attach the can lid. This is referred to as flange processing, and there may be a processing failure in which the protruding tip breaks at that time. This crack is called flange cracking, and the steel sheet characteristic that suppresses this cracking is called flange cracking resistance. Causes of flange cracking include insufficient bonding strength of the can body and insufficient ductility of the steel sheet. The former steel sheet factor causing insufficient bonding strength is a structural change in the vicinity of the weld, and the latter steel sheet factor causing insufficient ductility is included. Inclusions and precipitates.

  Recently, expensive aluminum is often used for the lid material, and it has become normal to reduce the diameter of the can lid for the purpose of reducing the amount of steel sheet used. Neck-in processing to narrow down has been performed once or multiple times. Since the neck-in process is a process prior to the flange process, a strong processing strain is applied to both ends of the can body, and the steel sheet ductility expressed by total elongation and uniform elongation is insufficient, which is a new cause of flange cracking. Further, from the viewpoint of resource saving, the thinning of steel sheets is progressing, and as a means of doing so, it is hot-rolled, cold-rolled, continuous annealing is selected to increase the steel sheet strength, and cold-rolled again to further strengthen. The law is being extended. The double cold rolling method is referred to as double reduction and abbreviated as 2CR. However, it also causes a strong processing strain on the steel plate as in the case of neck-in processing, which also causes a new flange crack.

  Several methods have already been proposed to solve these problems. For example, Patent Document 1 discloses a technique for controlling the fine ferrite structure and the amount of solute N by optimizing the manufacturing conditions of the DHCR manufacturing method from the viewpoint of suppressing cracking due to thinning of the steel sheet and securing the strength of the steel sheet. Yes. However, Patent Document 1 does not mention anything about the flange processing in a steel plate that has already undergone work hardening by neck-in processing, and the influence of inclusions in the steel, which is a problem in this case, is considered. Absent. In addition, in order to control the fine ferrite structure and the amount of solute N, the DHCR manufacturing method is indispensable and there are restrictions on the manufacturing technology.

  In addition, a manufacturing method in which the steel sheet is not strengthened even when continuous annealing is selected is disclosed in order to suppress the processing strain that is a new cracking factor. For example, the disclosed technology of Patent Document 2 is a continuous annealing method if the Al content [Al]% and the nitrogen content [N]% of the chemical components of the steel sheet have a relationship of [Al] / [N] ≧ 15. It is said that a soft steel sheet having a tempering degree T-3 or less can be obtained even if it is used. However, the method of Patent Document 2 is a method for producing a very soft steel sheet having a tempering degree of T-3 or less, and satisfies the purpose of securing the steel sheet strength by thinning the steel sheet being promoted from the viewpoint of resource saving. I can't. In addition, since the cementite precipitates in the recrystallized grains grow and become coarse due to the OA treatment, there is a problem that it is difficult to make the requirement [φ] / [t] ≦ 0.01 constituting the present invention.

  Patent Document 3 discloses a manufacturing method excellent in buckling strength against flange cracking due to inclusions and a reduction in steel plate strength due to thinning. Patent Document 3 specifies Al / N, annealing soaking temperature, and annealing soaking time to obtain a steel plate for thinned deep-drawn ironing cans with excellent buckling strength at the bottom of the can processed into a dome shape. However, the case where elongation is the main factor of machining as in flange processing is not taken into account, and, as in Patent Document 1 and Patent Document 2, the inclusion particle size that is the main factor in generating flange cracks due to thinning No mention is made of the size of the steel sheet and the proportion of uniform elongation in the total elongation of the steel sheet.

Japanese Patent Laid-Open No. 10-72640 Japanese Patent Laid-Open No. 8-73943 Japanese Patent Laid-Open No. 2003-183738

  Therefore, the present invention has been devised in view of the above-mentioned problems, and the object of the present invention is not to cause flange cracking in the flange processing step after neck-in processing by hitting a welded can, It aims at providing the surface treatment steel plate for welding cans which was excellent in advancing thickness reduction, and its manufacturing method.

  In order to solve the above-mentioned problems, the present inventors have observed in detail the defect portion of the can that has been cracked by performing flange processing after neck-in processing. As a result, it was confirmed that the flange crack occurred in the vicinity of the weld and was cracked at substantially the same position. The welded part referred to in the present invention is a part in which the steel sheet structure and mechanical property values are reinforced by the electric resistance heat and pressure applied through the current-carrying part at the time of making the weld can, and the vicinity of the welded part is the thickness of the base material. It is a part that is regarded as a heat-affected zone (hereinafter abbreviated as HAZ) that has limited resistance to electrical resistance heat. On the other hand, most parts not affected by welding heat are called base materials. The reason why flange cracks are likely to occur in the vicinity of the weld zone = HAZ is between the weld zone where the plate thickness is thicker than the base material portion and the base material that is not affected by heat and does not soften, and is relatively soft, so stress concentration tends to occur. This is probably because of this. In other words, if there is a large change in shape and it is relatively soft, stress concentrates there and cracks. Therefore, it is considered that the steel plate having flange cracking resistance can maintain the relationship of HAZ strength ≧ base material strength until the end of can making. As a result of intensive studies on the production method, the inventors of the present invention limited the [C] amount range of the chemical component to 0.02 to 0.06%, and the [Al] amount and [N] amount are [Al] / [[ N] was less than 4 or more than 7, and it was found that the steel sheet controlled so as not to become 4 to 7 had excellent flange crack resistance. A prototype of the weld can was made of the steel plate and the base material was examined. There was a relationship of [Uniform Elongation] and [Total Elongation] [Uniform Elongation] / [Total Elongation] ≧ 0.8, and the thickness of the weld can body It has been found that there is a relationship [φ] / [t] ≦ 0.01 between [t] and the included carbide average particle size [φ]. In the case of a welded can, the plate thickness of the body is equal to the plate thickness of the surface-treated steel plate that is the material. A steel plate having such a component has a property that the base material has a softer and more uniform strength than the HAZ strength, so that stress concentration hardly occurs and the base material is easily stretched. Further, the steel sheet combining the [C] amount, [Al] amount, and [N] amount of the present invention is temper-rolled at an elongation of 1 to 37%, and the HAZ strength is obtained even if neck-in processing is performed once or multiple times. ≥ It was confirmed that the relationship of the base metal strength was maintained.

That is, the present invention is mass%, C: 0.02 to 0.06%, Si: 0.0001 to 0.020%, Mn: 0.10 to 0.60%, P: 0.0001 to 0.02. %, S: 0.0001 to 0.02%, Total Al: 0.010 to 0.100%, N: 0.002 to 0.006%, and a chemical component comprising the balance Fe and inevitable impurities A steel piece having an Al content of [Al]% and a nitrogen content of [N]% of [Al] / [N] of less than 4 or more than 7 and heated to 1150 to 1250 ° C. Hot rolled to a plate thickness of 2.0 to 3.0 mm at a temperature, wound at a temperature of 450 to 650 ° C., pickled, primary cold rolled at an elongation of 85 to 95%, and a temperature of 600 to 660 ° C. Steel that has been continuously annealed with, temper rolled at an elongation of 1 to 37%, surface treatment for containers, and then turned into a welded can body [Uniform Elongation] and [Total Elongation] to [Uniform Elongation] / [Total Elongation] ≧ 0.8, Welding Can Body Thickness [t] and Encapsulated Carbide Average Particle Size [φ] to [φ] /[T]≦0.01, characterized by having a hardness of 62 to 85 in terms of HR30T, and a flange resistance in flange processing following neck-in processing with a plate thickness of 0.1 to 0.4 mm. It is a surface-treated steel sheet for welding cans with excellent cracking properties . According to the present invention, not only a steel plate for a thinned welding can excellent in neck formability is provided, but also a gauge down steel plate having various strength levels that can meet market demands for cost reduction and resource saving of the can. It is possible.

  According to the surface-treated steel sheet for welding cans to which the present invention is applied, having the above-described configuration, there is an advantage that a steel sheet having a thickness of 0.1 to 0.4 mm can be easily manufactured at low cost, and a commonly used welding machine Cans can be made, has excellent workability such as neck molding and flange molding, is resource-saving and energy-saving, so its economic value is extremely high.

It is a figure for demonstrating the tendency of the flange crack with respect to the relationship of [N] quantity and [Al] / [N] quantity.

  Hereinafter, the present invention will be described in detail. In the present invention, C: 0.02 to 0.06%, Si: 0.0001 to 0.020%, Mn: 0.10 to 0.60%, P: 0.0001 to 0.02% by mass% , S: 0.0001 to 0.02%, Total Al: 0.010 to 0.100%, N: 0.002 to 0.006%, and has a chemical component consisting of the balance Fe and inevitable impurities. In addition, the continuous cast steel slab in which the Al content [Al]% and the nitrogen content [N]% [Al] / [N] is less than 4 or more than 7 so that the relationship of 4 to 7 is eliminated. Is used. Hereinafter, the composition of each component is expressed by mass% with respect to the total mass, and when the mass% is expressed, it is simply expressed as%.

[C: 0.02 to 0.06%]
C is one of the important elements in the present invention. In order to ensure the strength of the base material and the HAZ flange crack resistance, the amount must be strictly controlled. If the content is less than 0.02%, not only is it difficult to ensure the strength, but in the region of 0.0001 to less than 0.02%, a slight change in the added amount causes a large variation in strength, and stable production of welded cans. Inhibits. On the other hand, if the content exceeds 0.06%, the base material becomes too hard and the flange workability is deteriorated, and the carbide precipitation is biased at the winding stage after hot rolling, resulting in flange cracking. Furthermore, the austenite phase is generated in the welded part and the HAZ by the electric resistance heat at the time of welding, and the hard phase is precipitated to cause flange cracking. For the above reasons, the lower limit of C is 0.02%, preferably 0.025%, more preferably 0.03%, and the upper limit of C is 0.06%, preferably 0.05%, more preferably 0.04%. %.

[Si: 0.0001 to 0.020%]
Si is an element harmful to the corrosion resistance of the steel plate for cans, but if it is 0.020% or less, no problem occurs during the distribution period of the practical cans. For ensuring corrosion resistance, 0.010% or less is desirable. The lower limit of Si does not need to be specified in particular, and it is preferable to reduce the content as much as possible, but 0.0001% is set as the lower limit from the viewpoint of the cost required for the reduction. For the above reasons, the lower limit of Si is 0.0001%, and the upper limit of Si is 0.020%, preferably 0.010%, more preferably 0.005%.

[Mn: 0.10 to 0.60%]
Mn is used to secure the strength of the steel sheet in the same manner as C. However, if the content is less than 0.10%, strengthening is not recognized, and if the content exceeds 0.60%, the alloy cost is remarkably increased and the attractiveness as a commercial steel sheet is lost, so it is 0.10 to 0.60%. To do. For the above reasons, the lower limit of Mn is 0.10%, preferably 0.20%, more preferably 0.30%, and the upper limit of Mn is 0.60%, preferably 0.50%, more preferably 0. 40%.

[P: 0.0001 to 0.02%]
P has the function of refining crystal grains and increasing the deformation resistance of the base material to promote stress concentration on the HAZ. It is also an element harmful to corrosion resistance like Si, and the upper limit was made 0.02%. The lower limit of P need not be specified in particular, and it is desirable to reduce the content as much as possible, but 0.0001% is set as the lower limit from the viewpoint of the cost required for the reduction. For the above reasons, the lower limit of P is 0.0001%, and the upper limit of P is 0.02%, preferably 0.010%, more preferably 0.005%.

[S: 0.0001 to 0.02%]
S is an element which causes red brittleness during hot rolling and generates S-induced soot, and is an element harmful to corrosion resistance like Si and P. Since red heat brittleness can be eliminated when Mn / S ≧ 8, the upper limit of S is made 0.02%. The lower limit is not particularly specified, and it is desirable to reduce the content as much as possible, but 0.0001% is set as the lower limit from the viewpoint of the cost required for the reduction. For the above reasons, the lower limit of S is 0.0001%, and the upper limit of S is 0.02%, preferably 0.010%, more preferably 0.005%.

[Total Al: 0.010 to 0.100%]
Al is an important element of the present invention together with N, and Al is added to deoxidize and fix N in steel as AlN. In particular, when N is not precipitated as aluminum nitride (hereinafter abbreviated as AlN) during hot rolling, ultrafine AlN is precipitated during continuous annealing, recrystallization is delayed, the base material strength is higher than HAZ, and flange cracking occurs. On the other hand, when AlN precipitation is promoted by high-temperature winding in the vicinity of the A1 point, a large amount of coarse AlN or the like is precipitated and becomes a flange crack starting point, and the base material strength or ductility is biased to promote flange cracking. The present inventors examined a preferable balance of [Al] and [N] that do not cause flange cracking in the winding temperature range where the inconvenient AlN state does not occur. As a result, it was found that flange cracking is likely to occur when the [N] amount is 20 to 60 ppm and [Al] / [N] is 4 to 7. Although the metallurgical mechanism is not clear, the flange crack induction region discovered by the present inventors is difficult to specifically precipitate AlN while being at a hot rolling coiling temperature of 450 to 650 ° C. preferable for AlN precipitation, and is extremely fine during continuous annealing. It is considered that AlN precipitates and delays recrystallization, and the strength of the base metal is higher than that of HAZ and induces flange cracking. In addition, the amount of Al must be strictly controlled to suppress flange cracking due to inclusions. Inclusions mixed in steelmaking cause flange cracking like coarse AlN, so it is important to add 0.010% or more to the molten steel as a deoxidizer to remove inclusions. On the other hand, an increase in the amount of Al leads to high costs and hardening of the base material, so the upper limit is made 0.100%. For the above reasons, the lower limit of Al is 0.010%, preferably 0.030%, more preferably 0.050%, and the upper limit of Al is 0.100%, preferably 0.080%, more preferably 0.060%. %.

[N: 0.002 to 0.006%]
N is an important element of the present invention as described in Al, and is an indispensable element for controlling the steel sheet strength to a hardness of 62 to 85 in terms of HR30T by solid solution strengthening. The solid solution strengthening effect can be stably obtained by adding 0.002% or more. On the other hand, if added over 0.006%, it causes steel slab cracking during continuous casting, and causes problems such as the formation of flange crack starting points by promoting coarse AlN precipitation during hot rolling, so the upper limit is 0.006%. To do. For the above reasons, the lower limit of N is 0.002%, preferably 0.003%, more preferably 0.004%, and the upper limit of N is 0.006%, preferably 0.0055%, more preferably 0.005. %.

[[Al] / [N] is less than 4 or more than 7]
As a result of an experimental study on the range where flange cracking does not occur, as shown in the examples described later, when [Al] / [N] is 4 or more and 7 or less, flange cracking is likely to occur. I found out. For this reason, in the present invention, [Al] / [N] is limited to less than 4 or more than 7 as a range in which flange cracking hardly occurs.

  In the present invention, the steel slabs having the above chemical components are hot-rolled, pickled, cold-rolled and continuously annealed, and then subjected to temper rolling with an elongation of 1 to 37%.

[Heating temperature of slab having the above chemical components: 1150 to 1250 ° C.]
Hot rolling is either a form in which the steel slab is cooled to below the Ar3 transformation point while it becomes a high-temperature steel slab after refining, or a form in which the steel slab is once cooled from below the Ar3 transformation point to room temperature and then reheated. Although it may be taken, since the steel sheet becomes a mixed grain structure when hot rolling below the Ar3 transformation point and the uniformity of the base material strength is impaired, the heating temperature of the slab having the above chemical components before hot rolling is preferably 1150 ° C or higher, When the temperature is higher than 1250 ° C., scale generation increases and yield reduction increases, so the upper limit is set to 1250 ° C.

  Since hot rolling is performed in air at normal temperature, the heat removal from the air and rolling roll is extremely large, and in order to hot-roll the entire length of the steel sheet at the Ar3 transformation point or more, the lower limit sheet thickness is preferably 2.0 mm or more. When the thickness is reduced to 3.0 mm, the cold rolling load increases and breakage during rolling tends to occur, so the upper limit is set to 3.0 mm.

  Finishing rolling is the process with the strictest temperature control in hot rolling, and if the temperature is higher than the Ar3 transformation point, the hot rolled steel sheet is uniformly sized, resulting in variations in the crystal grain size of the base material, uneven base material strength, and ductility. Can be suppressed. Since the Ar3 transformation point of a hot-rolled steel sheet varies depending on the chemical composition of the steel material used, it may be obtained experimentally from actual machine operation.

[Winding temperature: 450-650 ° C.]
Since the coiling temperature control is performed by water cooling, the temperature variation between the end and the center of the steel plate is likely to occur, and it is necessary to limit the coiling temperature range in which the variation is minimized. Low temperature winding with strong cooling to less than 450 ° C. is a preferable condition for minimizing steel plate temperature variation, but is a condition in which N is not precipitated as AlN, and the relationship of HAZ strength ≧ base material strength is impaired, so the lower limit is 450 ° C. To do. On the other hand, high temperature winding above 650 ° C. promotes AlN precipitation, and a large amount of coarse AlN precipitates to become the starting point of flange cracking. In addition, the base material strength and ductility are biased to promote flange cracking, so the upper limit is 650 ° C. To do.

[Cold rolling elongation: 85-95%]
The rolling rate at which a uniform sized structure is stably obtained after recrystallization by continuous annealing is applied. The lower the rolling rate, the larger and coarser the crystal grains constituting the recrystallized structure. The lower limit is preferably 85% or more, and the upper limit is preferably 95% corresponding to a general cold rolling functional force upper limit.

[Continuous annealing temperature: 600 to 660 ° C.]
In order to provide stable flange cracking resistance after neck processing, it is preferable to apply continuous annealing that can uniformly recrystallize the entire coil. When the continuous annealing temperature is less than 600 ° C., the base material is hardened without being completely recrystallized. Moreover, when it exceeds 660 degreeC, it will become easy to generate | occur | produce drawing and a fracture | rupture in a continuous annealing furnace. Accordingly, the lower limit temperature during continuous annealing is set to 600 ° C., and the upper limit is set to 660 ° C. The annealing time is 15 seconds or longer that does not impair the uniformity of the recrystallized structure, and even if it exceeds 60 seconds, the improvement in uniformity is slight.

[Temper rolling elongation: 1-37%]
After continuous annealing, temper rolling is performed. The purpose of temper rolling is to facilitate strength adjustment and thinning of the base metal by strengthening the work. The adjustment of thinning is preferably in the range of 1 to 37% elongation. This is because if the elongation is less than 1%, the steel sheet has poor work strengthening and it is difficult to obtain a hardness of 62 to 85 in terms of HR30T. On the other hand, if the elongation exceeds 37%, the base material loses its ductility, loses the plasticity that can be processed, and causes frequent buckling and cracking in neck processing and flange processing. For the above reasons, the lower limit of temper rolling is 1%, preferably 3%, more preferably 6%, and the upper limit of temper rolling is 37%, preferably 25%, more preferably 10%.

[Product thickness: 0.1 to 0.4 mm]
The final thickness of the temper-rolled steel sheet is 0.4 mm or less from the viewpoint of reducing the weight of the welding can by reducing the thickness and saving resources. Preferably it is 0.3 mm or less, More preferably, it is 0.15 mm or less. The steel plate obtained by such a method is used as a cut plate, a coil, or a steel foil. The type of surface treatment is not particularly limited, and an electrolytic chromate-treated steel sheet (tin-free steel), a tin-plated steel sheet, a thin tin-plated steel sheet, a Ni-plated steel sheet, or a composite-plated steel sheet combining them can be applied. . For chemical conversion treatment, chromium hydrated oxide, or electrolytic chromic acid-treated film with a two-layer structure consisting of a chromium hydrated oxide layer on the upper layer and a metal chromium layer on the lower layer, or Zr, P, Ti, phenol resin, silane coupling It is also possible to use a chemical conversion film produced by performing electrolytic treatment or coating treatment with a treatment liquid containing at least one agent or the like.

[Uniform elongation of welded can body base material / total elongation ≧ 0.8]
The cause of the flange cracking is insufficient bonding strength of the can body and insufficient ductility of the steel plate. The latter ductility-deficient steel sheet does not easily collapse even when subjected to electrical resistance heat and pressurization of the current-carrying part at the time of making the weld can, thereby forming a thick welded part. In addition, since the steel sheet with insufficient ductility is hard, the base material of the weld can is also hard. The HAZ that is between the welded portion having a thick plate thickness and the hard base material and has been softened by heating tends to concentrate stress and to be easily cracked. That is, if the HAZ has a large change in shape and is softer than the base material, stress concentrates and cracks there. The present inventors investigated the relationship between the total elongation value and the uniform elongation value, which are indicators of ductility, in order to determine the ease of crushing of the weld lap with a steel plate. As a result, if there is a relationship of [uniform elongation] / [total elongation] ≧ 0.8 between [uniform elongation] and [total elongation] of the steel plate used as the welded can body, the welded part easily collapses and flange cracks appear. I found it difficult.

  There are many metallurgical factors governing total elongation and uniform elongation, and it is difficult to say that the mechanism has been elucidated because it is very complex because it affects each other, but if it is a steel plate controlled within the scope of the present invention The preferable effect of the present invention can be obtained with certainty.

[The thickness t of the weld can body and the average carbide particle diameter φ included is φ / t ≦ 0.01]
Strong processing strain at both ends of the can body added by neck-in processing, as well as strong processing strain added by temper rolling used for thinning the steel plate from the viewpoint of resource saving, reduce the total elongation and uniform elongation values of the steel plate. Cause cracking of the flange. Flange cracking is a form of ductile fracture that occurs by processing that exceeds the ductility of HAZ, and inclusions and precipitates that always serve as starting points are present on the fracture surface. The present inventors investigated the relationship between the type and size of these impurities and the thickness of the welded can body. As a result, the main impurity is carbide, and if there is a relationship [φ] / [t] ≦ 0.01 between the plate thickness [t] of the weld can and the average carbide particle size [φ] included, the HAZ is flange processed. It was found that the flange cracking was difficult to withstand. The plate thickness of the welded can body is equal to the plate thickness of the surface-treated steel plate as the material. The carbide average particle diameter is obtained by taking 10 carbide grains present in the 200 μm × 200 μm field of view of the steel plate from the larger one, measuring the length of the long diameter, and averaging. Carbides are formed mainly by the influence of most of the components of the present invention on C. Those that are in a solid solution state, those that form precipitates that form the basis of carbides, and their amounts and types are very diverse. However, it is difficult to say that the mechanism has been elucidated due to its complexity, but the steel plate controlled within the scope of the present invention can surely obtain the preferable effects of the present invention.

  Examples will be described below. No. shown in Table 1 and Table 2 below. Steel pieces obtained by continuous casting of steels having chemical components 1 to 43 were hot-rolled to 2.5 mm, pickled, and rolled to 0.22 mm with a tandem six-high cold rolling mill. These No. Among the chemical components 1 to 43, No. 1 Nos. 1 to 12 are examples of the present invention satisfying the components in the range defined in the present invention and the production conditions are also included in the scope of the present invention. Nos. 13 to 43 are components in the range defined in the present invention described above (particularly N, Al / N), or a comparative example in which the manufacturing conditions (winding temperature) deviate from the scope of the present invention. Incidentally, the condition deviating from the components of the present invention is underlined.

  The steel sheet was subjected to temper rolling to 0.20 mm after continuous annealing and tin plating. Next, the steel sheet was coated, baked and dried except for the varnish portion for welding, cut into can body dimensions, and formed into a welded can body using a Suderonic welder FBB-1080. Thereafter, a two-stage neck-in process was performed with a can body dynecker, flanged, and flange cracking resistance was evaluated. The flange processing rate is larger than that of commercial cans, and the two-stage neck-in processing inner diameter [d] and flange outer diameter [D] are defined as [D] / [d] as the flange processing rate, and the condition is 1.25. It processed so that it might become. The number of flange cracking cans was obtained by producing 10,000 cans of each test material with a welding machine, applying neck-in and flange processing in succession, and visually observing the flange cracks of the resulting cans for each can. The flange crack occurrence rate was calculated by ([number of flange cracking cans] / 10,000 cans) × 100 (%). When a 0.15 mm thick steel plate that is most prone to flange cracking among tin-plated steel plates for welding cans already in general use was evaluated in advance by the same method, the flange crack occurrence rate was 0.05%. . With this as the practical upper limit, the flange crack resistance of the steel sheet of the present invention and the comparative steel sheet was evaluated.

  No. shown in Table 1 and Table 2. The steel sheet examples 1 to 43 satisfying the present invention have a flange crack occurrence rate of 0.05% or less, and have excellent workability equivalent to that of commercial steel sheets. The example had a flange crack generation rate of more than 0.05%, and was a characteristic that could not be used as a commercial steel sheet. In FIG. 1, the horizontal axis indicates [N] amount, the vertical axis indicates [Al] mass% / [N] mass% ratio, and the flange crack occurrence rate is expressed as ○ when less than 0.05%, and × when more than 0.05%. did.

  As shown in FIG. 1, the horizontal axis [N] amount is in the range of 0.002 to 0.006, and the vertical axis [Al] mass% / [N] mass% ratio is less than 4 or more than 7. Has shown that the flange cracking can be less than 0.5%. In contrast, when the horizontal axis [N] amount deviates from the range of 0.002 to 0.006, or even when the horizontal axis [N] amount is within the range of 0.002 to 0.006, the vertical axis [N] When the ratio of Al] mass% / [N] mass% is in the range of 4-7, it has been shown that flange cracking exceeds 0.5%.

From the above tendency of FIG. 1, in the present invention, N is 0.002 to 0.006%, and [Al] / [N] is less than 4 or more than 7.

Claims (2)

% By mass
C: 0.02 to 0.06%,
Si: 0.0001 to 0.020%,
Mn: 0.10 to 0.60%,
P: 0.0001 to 0.02%,
S: 0.0001 to 0.02%,
Total Al: 0.010-0.100%
N: 0.002 to 0.006%,
The balance is Fe and inevitable impurities, and the Al content [Al]% and the nitrogen content [N]% have a chemical component in which [Al] / [N] is less than 4 or more than 7. And [Uniform Elongation] and [Total Elongation] to [Uniform Elongation] / [Total Elongation] ≧ 0.8, and the thickness [t] and the included carbide average particle size [φ] to [φ] / [T] ≦ 0.01, characterized by having a hardness of 62 to 85 in terms of HR30T and resistance to flange processing following neck-in processing with a plate thickness of 0.1 to 0.4 mm. Surface-treated steel sheet for welding cans with excellent flange cracking properties .   The slab having the chemical component according to claim 1 is heated to 1150 to 1250 ° C, hot-rolled to a thickness of 2.0 to 3.0 mm at a temperature equal to or higher than the Ar3 transformation point, and wound at a temperature of 450 to 650 ° C. And pickling, primary cold rolling at an elongation of 85 to 95%, continuous annealing at a temperature of 600 to 660 ° C, temper rolling at an elongation of 1 to 37%, and surface treatment for containers. A method for producing a surface-treated steel sheet for welding cans according to 1.

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