JP4276388B2 - Thin steel plate for high-strength welding cans excellent in flange formability and method for producing the same - Google Patents

Description

【００４１】
【発明の効果】
以上説明したように、本発明では固溶Ｃ、固溶Ｎ量を適正量に制御することによりＨＡＺ部軟化を抑制すると共に、母材の伸びを十分に確保することにより、高強度溶接缶用薄鋼鈑において、優れたフランジ加工性を得られるようになったことは、省資源、省エネルギーに大きく寄与するところであり、その経済的効果は非常に大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin steel plate for a high-strength weld can excellent in flange formability and a method for producing the same.
[0002]
[Prior art]
In steel containers, there are so-called three-piece cans consisting of a canopy, a cylindrical barrel, and a bottom lid. The barrel is formed by forming a thin steel rod into a cylindrical shape, and then soldering and resin bonding. The method and the method by welding are performed. Among them, a method using welding, which has a small joining allowance and is advantageous for improving the material yield and has a high can-making speed, is the mainstream in recent years.
[0003]
In the body, after forming the body by welding, flange processing for tightening the canopy and the bottom cover is performed. When forming the flange portion of the body, a heat-affected zone in the vicinity of the welded portion (hereinafter referred to as HAZ portion) is formed. Thus, there is a drawback that the local necking (hereinafter referred to as necking) and necking due to the concentration of the flange processing distortion become long and the flange cracking is likely to occur.
[0004]
As a factor causing flange cracking and necking, the biggest problem in manufacturing a welded can is that the HAZ part is locally constricted during flange processing to cause necking and further flange cracking.
[0005]
In recent years, the plate thickness of can materials has been reduced from the viewpoint of resource saving and material cost reduction, and accordingly, the strength of steel plates has been increased (yield strength ≧ 450 Mpa) in order to ensure the strength of the can body. Such a steel sheet is manufactured by a double cold rolling method in which a hot rolled steel sheet is cold-rolled and then annealed and cold-rolled again at a temper rolling stage at a higher temper rolling rate than a conventional single-reduction steel plate. It is the mainstream to use a so-called double-reduced steel plate (hereinafter simply referred to as DR, DR steel plate).
[0006]
However, this DR steel sheet has a strong tendency to cause flange cracking during post-weld flanging. The cause is that the HAZ part is locally localized due to the so-called strain relief annealing effect in which the base metal that has been high in strength due to the cold-rolling strain due to DR is released and reduced by welding heat, and the cold-rolling strain of the HAZ part is reduced. There is a difference in strength between the softened and high-strength base metal and the weld point that has been improved by the heat of welding. It is considered that constriction due to unidirectional deformation occurs due to concentration of the overhang strain due to flange processing in the locally softened HAZ portion, resulting in flange cracking.
[0007]
In particular, the continuous annealing material has a higher incidence of flange cracking than the box annealing material. However, compared with continuous annealed materials, box annealed materials have drawbacks such as requiring a long annealing time and non-uniformity in material properties, so from the viewpoint of productivity and quality improvement, Various researches have been conducted on conversion of the manufacturing method to continuous annealing materials.
[0008]
And the invention of Unexamined-Japanese-Patent No. 60-24327 is proposed regarding the manufacturing method of the welded can thin steel plate excellent in the flange workability which overcomes the difficulty of this continuous annealing material.
[0009]
In the invention of Japanese Patent Laid-Open No. 60-24327, the hot rolling finish temperature is 800 to 600 ° C., the finish rolling is performed in a temperature range lower than the normal finish temperature, and the crystal grains after cold rolling and annealing are enlarged. In this method, the HAZ part is prevented from being softened at the time of welding, and coarse particles are prevented from being added. In addition, the amount of solid solution C is reduced to suppress softening and improve the flange workability.
[0010]
This invention increases the crystal grain size after annealing and reduces the solid solution C, thereby utilizing the delay in the HAZ recrystallization due to welding heat, that is, increasing the recrystallization temperature, thereby softening during welding. This is intended to suppress the flange workability.
[0011]
However, with this method, in the production of current materials that require high strength, the DR ratio must be increased to obtain the required strength of the steel sheet as the crystal grain size increases, and the cold rolled accumulated strain of the steel sheet must be ensured. The recrystallization temperature is increased and the recrystallization temperature is lowered, the progress of softening of the HAZ portion and the strength difference from the base material are increased, and the concentration of processing strain on the HAZ portion is promoted. Furthermore, the grain boundaries become brittle due to coarsening, leading to deterioration of flange workability, which is insufficient for improving the flange workability.
[0012]
Conventionally known technology has the idea of suppressing only the HAZ softening due to welding heat and mitigating the concentration of distortion due to flange processing, but the welding work uses high-temperature welding heat that causes steel fusion. Therefore, the softening of the HAZ part is inevitable, and the idea of preventing necking and cracking by suppressing only the thermal change of the HAZ part cannot be a fundamental improvement measure.
[0013]
[Problems to be solved by the invention]
Accordingly, the present invention provides a steel sheet for high-strength welding cans by a continuous annealing method that has an elongation equal to or greater than that of a steel sheet for welding cans by a box annealing method and that does not cause flange cracking by suppressing HAZ softening. It is an object to provide a manufacturing method.
[0014]
[Means for Solving the Problems]
As a result of repeated research in solving the above-mentioned problems, the present inventors have optimized the hot rolling finishing temperature, annealing conditions, overaging treatment conditions, secondary cold rolling rate, etc., in addition to the steel components, In particular, the inventors have found that flange workability is improved by limiting the amounts of solute C and solute N to an appropriate range, and have completed the present invention.
[0015]
The gist of the present invention is as follows.
(1) In mass%, C: more than 0.04% and 0.08% or less,
Si: 0.02% or less, Mn: 1.0% or less, P: 0.04% or less, S: 0.05% or less, Al: 0.1% or less, N: 0.005 to 0.02% or less Contains,
And the total of C and solid solution N dissolved in the steel sheet is 50 ppm ≦ solid solution C + solid solution N ≦ 200 ppm, the solid solution C in the steel sheet is 50 ppm or less, and the solid solution N in the steel sheet is 50 ppm or more. A thin steel plate for a high-strength weld can excellent in flange formability, characterized by comprising a range and the balance being Fe and inevitable impurities.
(2) In the thin steel sheet for high-strength welding cans as described in (1) above, Nb: 0.003 to 0.3%
Ti: 0.003 to 0.3%
B: 0.004 to 0.020%
Cu: 0.5% or less Ni: 0.5% or less Cr: 0.5% or less Mo: 0.5% or less
A thin steel plate for a high-strength weld can excellent in flange formability characterized by containing one or more elements selected from more.
(3) Using the continuously cast steel slab described in (1) or (2) above as a raw material, hot rolling was performed at a coiling temperature of 600 ° C. or less to form a hot-rolled steel sheet, and pickling and cold rolling were performed. After that, after the continuous annealing process at the recrystallization temperature or higher, perform an overaging treatment for 1 to 5 minutes in the range of 300 to 550 ° C., and make the secondary cold rolling 5% or more and 20% or less. The manufacturing method of the thin steel plate for high strength welding cans which was excellent in the flange formability characterized by this.
[0016]
The technical idea that led to the present invention will be described below.
Currently used box annealed materials have fewer flange cracks than continuous annealed materials. Considering this point, as a result of a detailed study of the means for improving flange cracking, two features and solutions were found.
[0017]
First, it is conceivable that the HAZ part softening of the box annealing material is smaller than that of the continuous annealing material. As a means to suppress the softening of the HAZ part with a continuously annealed material, the solid solution C state after annealing is precipitated as fine cementite, and by using it as a nucleus, the cold rolling strain in the DR is refined, and welding is performed. This is achieved by suppressing the coarsening of the crystal grain size during recrystallization with heat. By suppressing the coarsening of the crystal grain size, a reduction in the softening of the HAZ part is achieved. In addition, as a means of precipitation of fine cementite, it is achieved by an appropriate overaging treatment, and as a result, it can be detected in the form of a decrease in solid solution C.
[0018]
Secondly, it is considered that the elongation value of the box annealing material is larger than that of the continuous annealing material. That is, although the HAZ softening is also present in the box annealed material, it does not progress to flange cracking because the can end circumferential portion other than the welded portion has a large elongation, so that the entire region of the can circumference is also deformed simultaneously during flange processing. This is considered to be because stress concentration on the HAZ portion is alleviated. Therefore, by increasing the ductility of the base material, stress concentration on the HAZ part is alleviated. Therefore, it is only necessary to increase the elongation of the base material even in the continuous annealing material. However, in the conventional material, the improvement in the elongation and the increase in the strength are contradictory properties, and in order to ensure the necessary amount of strength, the DR ratio It has been common sense in the technology so far that the growth has decreased and the growth has been reduced accordingly. However, in the present invention, it was found that the DR ratio can be reduced by securing sufficient solid solution N and age strength is used to secure the required amount without reducing elongation. .
[0019]
Improvement of flange formability was confirmed by the combined effect of the above-mentioned two points, namely, the reduction of the solid solution C and the remaining of the solid solution N, and the present invention was completed.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the solid solution C reduction and the solid solution N residual type continuous annealing DR rolled material in the high strength thin steel sheet having excellent flange formability were studied. As a result, a preferred embodiment of the present invention will be described.
[0021]
C: More than 0.04% and 0.08% or less As a steel component, if the amount of C is excessive, the ductility is remarkably reduced due to hardening, and a predetermined elongation cannot be secured after reduction in can-making processability or DR, Excessive addition is not preferable from the viewpoint of reducing solid solution C. Therefore, the upper limit is made 0.08%. If the C content is 0.04% or less, the DR rate for securing the required strength increases, and as a result, the elongation decreases and the incidence of flange cracking increases.
[0022]
Al: 0.1 or less When there is a large amount of Al, it precipitates as AlN during annealing and heating, and the recrystallized grain growth of the annealed plate is suppressed, resulting in a non-uniform structure, and the amount of solute N necessary to ensure strength Since this causes problems such as reduction, the upper limit of Al content is set to 0.1%. From the viewpoint of securing solid solution N, it is desirable that the content be 0.02 to 0.07%.
[0023]
N: 0.005 to 0.02% or less N is an element necessary for increasing the strength of the steel sheet by the solid solution strengthening effect, and this effect can be stably obtained by adding 0.005% or more. If N is added in excess of 0.02%, the product will be remarkably hardened and the overall processability of can manufacturing will be hindered. In addition, it causes slab cracking during continuous casting, so the upper limit is made 0.02%. From the viewpoint of securing strength in consideration of the entire manufacturing process, it is preferable to contain it in the range of 0.005 to 0.012%.
[0024]
Solid solution C is obtained by the internal friction method, and solid solution N is obtained by subtracting the precipitation N (measured by the dissolution method using bromine ester) from the total N amount in the steel. If the value of solid solution C + solid solution N is not more than 50 ppm, sufficient solid solution strengthening amount and age-hardening amount cannot be secured, and there is a risk that the strength of the can body after canning is insufficient. On the other hand, if the content exceeds 200 ppm, the elongation decreases when aging progresses, and good flange workability cannot be obtained. Therefore, the total of solid solution C and solid solution N is contained in the range of 50 ppm ≦ solid solution C + solid solution N ≦ 200 ppm. In addition, it is preferable that solid solution C is 50 ppm or less from a viewpoint of HAZ softening prevention, and it is preferable that solid solution N is 50 ppm or more from a viewpoint of ensuring age-hardening property in that case.
[0025]
Si: 0.02% or less
If the amount of Si exceeds 0.02%, problems such as deterioration of surface treatment property and deterioration of corrosion resistance are caused, so the upper limit is made 0.02%. When particularly excellent corrosion resistance is required, the content is preferably 0.03% or less.
[0026]
Mn: 1.0% or less
Mn is an element that is effective in making crystal grains fine and preventing hot cracking due to S, and is preferably added according to the amount of S contained. Excessive addition deteriorates the corrosion resistance and deteriorates the cold rolling property due to hardening of the steel sheet, so the upper limit is made 1.0%. In addition, when better corrosion resistance and moldability are required, it is desirable to add in the range of 0.3% or less.
[0027]
P: 0.04% or less P is a harmful element that hardens steel, deteriorates flange workability and neck workability, and at the same time deteriorates corrosion resistance. Therefore, the upper limit is set to 0.04%. . If these characteristics are particularly important, the content is preferably 0.02% or less.
[0028]
S: 0.05% or less S is an element which exists as an inclusion in steel and reduces ductility and causes deterioration of corrosion resistance. Therefore, the upper limit is made 0.05%. In applications where particularly good workability is required, the content is preferably 0.005% or less.
[0029]
Nb: 0.003-0.3%
Nb is an element that is effective in making the steel structure finer, improving stretch flangeability, and preventing rough skin. It is necessary to add 0.003% or more for such an effect to be exerted, but if added over 0.3%, it becomes harder than necessary. Therefore, the amount of Nb added is set to 0.003 to 0.3%, but the range of 0.01% or less is more preferable in terms of the material.
[0030]
Ti: 0.003-0.3%
Ti also has the effect of refining the structure, just like Nb. In order to obtain this effect, 0.003% or more must be added. However, if it exceeds 0.3%, surface defects are prominent. Therefore, Ti can be added in a range of 0.003 to 0.3%, preferably 0.02% or less.
[0031]
B: 0.0004 to 0.020%
B is an element effective for refinement of the structure and adjustment control of aging, but is combined with N to be a precipitate. Such an effect is exhibited by addition of 0.0004% or more. However, addition over 0.020% is not preferable because the effect of N is reduced and the in-plane anisotropy of the steel sheet is increased. Therefore, B can be added in the range of 0.0004 to 0.020%.
[0032]
Cu: 0.5% or less, Ni: 0.5% or less, Cr: 0.5% or less, Mo: 0.5% or less All of these elements have the effect of increasing the strength of the steel sheet, and if necessary Add. However, if added over 0.5%, the cold rolling property is deteriorated, and the steel sheet is hardened more than necessary, and the can-making processability is deteriorated. Can be added.
[0033]
V: 0.3% or less, Zr: 0.5% or less, Ca: 0.01% or less These elements have almost similar material improving effects, and are added as necessary. However, the effect is saturated even if V and Zr are added in an amount exceeding 0.3% and Ca is added in an amount exceeding 0.01%.
[0034]
In the production method of the present invention, continuous cast steel pieces containing C: more than 0.04% and 0.08% or less, Al: 0.1% or less, and N: 0.005 to 0.02% or less by weight. The material is heated to 1050 ° C or higher, hot rolled at a coiling temperature of 600 ° C or lower to form a hot-rolled steel sheet, subjected to pickling and cold rolling, and soaking is performed at the recrystallization temperature. After the above-described continuous annealing process, an overaging treatment is performed. The required amount of solute C and solute N can be left in the steel sheet depending on the steel components, heating temperature and continuous annealing conditions. And a predetermined steel plate is obtained by giving twice cold rolling (DR) finish of elongation rate 5% or more and 20% or less.
[0035]
The term “overaging treatment” as used herein mainly refers to heat treatment at a low temperature for a long time as compared with a general annealing treatment for the purpose of reducing solute C. When the overaging treatment is performed after the continuous annealing, a soaking treatment is performed at 300 to 550 ° C. for 1 to 5 minutes. If it is less than 300 degreeC, the solid solution C cannot be reduced stably, but if it exceeds 550 degreeC, a crystal grain will coarsen. In addition, if it is less than 1 minute, the solid solution C cannot be reduced, and in order to perform a treatment exceeding 5 minutes, the furnace length is increased. In the overaging treatment performed after the continuous annealing, a treatment method called reheating overaging treatment with an annealing cooling end temperature of about 250 ° C. and reheating up to the overaging treatment temperature may be used.
[0036]
The overaging treatment may be performed by box annealing. The temperature and effect are the same as in the continuous annealing, but the heat treatment is performed for 2 to 10 hours. In this case, the solid solution C cannot be stably reduced in less than 2 hours, and the treatment in excess of 10 hours is not economically advantageous.
[0037]
The purpose of secondary cold rolling is to increase the strength of the material by strengthening the work, and to reduce the plate thickness and adjust the surface roughness and the like. When the rolling reduction of the secondary cold rolling exceeds 20%, the can workability is lowered and the ductility is deteriorated, and the flange workability which is the object of the present invention is reduced by increasing the strength more than necessary. It cannot be secured. Therefore, the rolling reduction of secondary cold rolling is 20% or less, preferably 15% or less, and it is desirable to make it 10% or less in applications where press formability is required. The lower limit of the rolling reduction is determined from the viewpoint of securing the required strength and the surface roughness management, but it is desirable to give 5% or more.
[0038]
【Example】
Examples of the present invention will be described below in comparison with comparative examples.
A steel plate for a welding can having a thickness of 0.18 mm was manufactured using the components and manufacturing conditions shown in Table 1. And the characteristic and flange workability of the obtained steel plate are shown in Table 1.
For evaluation of flange workability, the steel plate was formed into a 55 mmφ cylindrical shape and welded, and then flanged to a flange portion outer diameter of 70 mmφ to evaluate the presence or absence of cracks in the vicinity of the weld.
No. in Table 1 1-No. 7 is an example of the present invention, the range of the solid solution C and the solid solution N is kept at an appropriate amount, and the strength can be secured.
In addition, No. 8-No. No. 12 is a comparative example, and there are cases where the range of the solid solution C and the solid solution N deviates from an appropriate amount, and the strength is insufficient.
[0039]
That is, as apparent from Table 1, No. 1-No. No. 7 shows that the steel plate of the present invention has no flange cracking and has good flange workability. 8-No. In the case of 10 out of the scope of the present invention, a flange crack occurred.
[0040]
[Table 1]

[0041]
【The invention's effect】
As described above, in the present invention, the amount of solid solution C and solid solution N is controlled to an appropriate amount to suppress softening of the HAZ part, and by ensuring sufficient elongation of the base material, The ability to obtain excellent flange workability in thin steel plates greatly contributes to resource saving and energy saving, and its economic effect is very large.

Claims (3)

mass%, C: more than 0.04% and 0.08% or less,
Si: 0.02% or less, Mn: 1.0% or less, P: 0.04% or less, S: 0.05% or less, Al: 0.1% or less, N: 0.005 to 0.02% or less Contains,
And the total of C and solid solution N dissolved in the steel sheet is 50 ppm ≦ solid solution C + solid solution N ≦ 200 ppm, the solid solution C in the steel sheet is 50 ppm or less, and the solid solution N in the steel sheet is 50 ppm or more. A thin steel plate for a high-strength weld can excellent in flange formability, characterized by comprising a range and the balance being Fe and inevitable impurities. The thin steel plate for high-strength weld cans according to claim 1, further comprising Nb: 0.003 to 0.3%.
Ti: 0.003 to 0.3%
B: 0.004 to 0.020%
Cu: 0.5% or less Ni: 0.5% or less Cr: 0.5% or less Mo: 0.5% or less
A thin steel plate for a high-strength weld can excellent in flange formability characterized by containing one or more elements selected from more. Using the continuous cast steel slab according to claim 1 or 2 as a raw material, hot rolling at a coiling temperature of 600 ° C. or less to form a hot-rolled steel sheet, pickling and cold rolling, and then reheating soaking. After the continuous annealing process at a temperature equal to or higher than the crystal temperature, an overaging treatment is performed in the range of 300 to 550 ° C. for 1 to 5 minutes , and the secondary cold rolling is performed at a reduction rate of 5% to 20%. A method for producing thin steel sheets for high-strength welded cans with excellent properties.