JPS63500B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a cold-rolled steel plate for enameling, which has excellent press formability and enameling properties, and a method for manufacturing the same. <Prior art and its problems> Steel plates for enameling have excellent enameling properties such as enameling adhesion, firing strain characteristics, and resistance to chipping, and many enameled products undergo rigorous press forming. Therefore, it is necessary to have excellent press formability. It was reported in Japanese Patent Publication No. 42-12348 and Japanese Patent Publication No. 12348 that excellent press formability can be obtained when Ti is added to Ti-added steel, especially ultra-low carbon steel with a C content of 0.02% or less.
44-18066, etc. Patent Publication No. 45-40655 developed a technology for utilizing the excellent press formability of Ti-added steel and further obtaining excellent enameling properties.
No., JP-A-53-131919, or JP-A-56-
It is disclosed in No. 9357, etc. However, these techniques are techniques for improving not only good press formability but also chipping resistance among the enameling properties. In other words, by utilizing the fact that Ti forms carbides, sulfides, and nitrides in steel,
The aim is to increase the hydrogen storage capacity of steel sheets and suppress the occurrence of splatter. In order to fully exhibit this effect, it is necessary to add a sufficient amount of Ti, but when the amount of Ti is increased, there is a problem in that the adhesion to the enamel deteriorates. For this reason, although Ti-added steel has excellent press formability and chipping resistance, until now it has only been used in a limited number of applications as steel sheets for enameling. <Object of the Invention> The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a steel plate for enameling that has excellent press formability and enameling properties, and a method for manufacturing the same. <Structure of the invention> The reason why the enamel adhesion of Ti-added steel is poor is that a large amount of pickling products (FeSO ₄ · nH ₂ O) adheres to the steel plate surface during the sulfuric acid washing in the enamel pretreatment.
We have discovered that the adhesion of pickling products can be prevented by adding As, Sb, or Bi to steel. According to the first aspect of the present invention, C: 0.005% or less, Si: 0.03% or less, Mn: 0.50% or less, P: 0.02
% or less, S: 0.03% or less, N: 0.005% or more,
0.012% or less, Ti: 0.15% or less and Ti＞(48/12C
+48/14N+48/32S), Cu: 0.08% or less, As,
The total content of at least one element selected from the group consisting of Sb and Bi is 0.003% or more, 0.03%
Hereinafter, a cold-rolled steel sheet for enameling comprising the balance iron and unavoidable impurities will be provided. According to the second aspect of the present invention, when producing a cold-rolled steel sheet for enameling that has excellent press formability, enameling adhesion, and chipping resistance, C: 0.005% or less,
Si: 0.03% or less, Mn: 0.50% or less, P: 0.02% or less, S: 0.03% or less, N: 0.005% or more, 0.012%
Below, Ti0.15% or less and Ti > (48/12C + 48/14N
+48/32S)%, Cu: 0.08% or less, As, Sb and
Molten steel in which the total content of at least one element selected from the group consisting of Bi is 0.003% or more and 0.03% or less, the balance being iron and unavoidable impurities is continuously cast, hot rolled, cold rolled, and then recrystallized. Above the temperature
Provided is a method for producing a cold-rolled steel sheet for enameling, which is characterized by continuous annealing in a temperature range of Ac ₃ or lower. According to the third aspect of the present invention, press formability,
When producing cold-rolled steel sheets for enameling with excellent enameling adhesion and toe-slip resistance, C: 0.005% or less,
Si: 0.03% or less, Mn: 0.50% or less, P: 0.02% or less, S: 0.03% or less, N: 0.005% or more, 0.012%
Below, Ti0.15% or less and Ti > (48/12C + 48/14N
+48/32S+0.03)%, Cu: 0.08% or less, As, Sb
and Bi, the total content of at least one element selected from the group consisting of 0.003% or more and 0.03% or less,
Production of cold-rolled steel sheet for enameling, characterized in that molten steel consisting of residual iron and unavoidable impurities is continuously cast, hot-rolled, cold-rolled, and then box-annealed in a temperature range above the recrystallization temperature and below 800°C. A method is provided. The reasons for limiting the components of the cold-rolled steel sheet for enameling of the present invention will be described below. C: When C exists in a solid solution state in steel, the ductility and value of the steel sheet deteriorate. In steel to which a sufficient amount of Ti is added, C exists as TiC, and the degree of deterioration of ductility and value is small, but when the amount exceeds 0.005%, ductility particularly deteriorates. Furthermore, the amount of Ti required to fix C as TiC increases, which not only reduces the adhesion of the enamel but also causes an increase in cost. Therefore, the upper limit of the C content is set to 0.005%. Si: Si inhibits enamel adhesion, and if it exceeds 0.03%, the effect becomes strong, so it was limited to 0.03% or less. Mn: Mn is an unavoidable impurity in steel.
It is necessary to prevent hot embrittlement of the steel and obtain the necessary mechanical properties, but it is limited to 0.50% or less because if it exceeds 0.5%, it will inhibit enamel adhesion. P: P exists as an unavoidable impurity in steel. When the amount of P increases, not only does the ductility of the steel sheet deteriorate, but it also exhibits significant secondary work brittleness. Secondary work embrittlement is a phenomenon in which after a steel plate is press-formed, the press-formed product undergoes brittle fracture due to a slight stress.To avoid this, as described later, it is necessary to carry out continuous annealing or to apply sufficient Ti. It is effective to lower the amount of P in steel to 0.02% or less in addition to adding P. Therefore, the upper limit of P is set to 0.02%. S: Like P, S also exists as an unavoidable impurity in steel, and generally causes hot embrittlement of the steel and causes surface defects during hot rolling. It is also a harmful element that reduces the ductility of steel. However, when a sufficient amount of Ti is added, S turns into titanium sulfide, so the above-mentioned harm is reduced. However, as the amount of S increases, the amount of Ti required to be added increases, which causes an increase in cost. Therefore, the upper limit of the amount of S is set to 0.03%. N: In the steel sheet of the present invention, N is an element necessary to improve the chipping resistance among the enameling properties. In steel with Ti added, N exists as TiN, and as the amount increases, the chipping resistance of the steel sheet improves. That is, due to the presence of TiN, voids are formed in the steel during cold rolling, and hydrogen, which causes skipping, is occluded in the steel, thereby suppressing the occurrence of skipping. To completely suppress blockage
N of 0.005% or more is required. However, if the amount of N increases and a sufficient amount of Ti is added to fix it as TiN, bald defects may occur on the surface of the steel sheet. When the amount of N is 0.012% or less, it is extremely rare for such bald defects to occur. The range of N needs to be 0.005% or more and 0.012% or less. Ti: By adding Ti to steel, C, N,
S is fixed as TiC, TiN, and TiS, respectively, and this has the effect of not only reducing the adverse effects of these elements on the material of the steel sheet, but also preventing the occurrence of chipping. In order to fully exhibit this effect, a Ti amount sufficient to fix C, N, and S, ie, (48/12C+48/14N+48/32S)% or more is required. Furthermore, Ti forms a phosphide called TiFeP in steel. When cold-rolled steel sheets are continuously annealed, the cooling rate is high, so secondary work embrittlement does not occur. However, when box annealing is performed, the cooling rate is slow, so P segregates at grain boundaries during cooling, causing secondary work embrittlement. cause. Therefore, in the case of box annealing, in addition to Ti that becomes carbides, nitrides, and sulfides, sufficient Ti is added to form phosphides, and P is fixed as phosphides.
It is necessary to prevent grain boundary segregation and suppress secondary work brittleness. The amount of Ti required for this is (48/12C + 48/1
4N+48/32S+0.03)% or more. However, Ti
Excessive quantities not only lead to increased costs, but also
Continuous casting nozzles become easily clogged, causing sludge-like defects, and furthermore, enamel adhesion and weldability deteriorate. To avoid such problems, Ti
The amount must be 0.15% or less. Cu: Cu is 0.01% as an unavoidable impurity in steel.
The above-mentioned components have a significant effect on the pickling properties of steel sheets in sulfuric acid pickling performed as a pre-enamel treatment. In other words, as the amount of Cu in the steel increases, the pickling rate decreases significantly. However, as the amount of Cu increases, pickling products easily adhere to the enamel, causing a decrease in enamel adhesion. In particular, Cu promotes the tendency for the pickling rate to gradually increase when pickling is carried out for a long time, increasing the adhesion of pickling products. The effect of Cu on promoting pickling product adhesion can be reduced by adding As, Sb, Bi, etc., but in order to minimize the cost increase due to the addition of these elements, Cu should be kept at 0.08% or less. It is necessary. As, Sb, Bi: By adding these elements classified into group 5B on the periodic table, it is possible to suppress the pickling product from adhering to the surface. The mechanism by which these elements prevent the pickling products from adhering is not clear, but it is thought that they inactivate the adsorption sites of the pickling products (FeSO ₄ .nH ₂ O) on the steel sheet surface. In order to expect such an effect, the total of one or more of these elements must be 0.003
% or more is necessary, but if it is added in an amount of 0.03% or more, the pickling speed will be reduced and sagging defects will occur frequently during hot rolling. In order to avoid cost maps and to expect sufficient effects, it is preferable to add in a range of 0.005% or more and 0.03% or less. In addition, since secondary work embrittlement does not occur when cold-rolled steel sheets are continuously annealed,
Although it is possible to perform annealing at a temperature below Ac ₃ , in the case of box annealing, it is necessary to perform annealing at a temperature range above the recrystallization temperature and below 800°C in order to effectively form TiFeP. That is, the annealing temperature is 800℃
Above that, the solubility of Ti and P increases,
TiFeP becomes difficult to precipitate. Note that, from the viewpoint of cost and adhesion prevention, it is preferable that the annealing temperature is 750° C. or lower. <Example> The present invention will be explained based on an example. Example 1 Steel having the composition shown in Table 1 was made into a slab by continuous casting, and then hot rolled and cold rolled.
Continuous annealing was performed at 800°C for 20 seconds to obtain a cold steel plate. Furthermore, the material was subjected to 0.8% temper rolling and its mechanical properties and various enameling properties were investigated. Table 2 shows the materials of these steel plates. C amount is 0.008
Except for No. 10 of %, all other steel plates exhibit good press formability with an El of 48% or more and an r value of 1.8 or more. Table 2 also shows the results of the binding test for these steel plates. The binding test was performed by applying a commercially available glaze (L type manufactured by Nihon Ferro Co., Ltd.) after pickling for 20 seconds, and applying a glaze with a dew point of 30.
After enameling was fired at 820°C in a kiln at 820°C, the presence or absence of skipping was examined. Twenty specimens were fired for each steel plate, and the percentage of specimens in which splintering occurred was shown. Except for Nos. 8 and 9, which had a low N content, there was no occurrence of chipping, indicating that steel plates with excellent material quality and chipping resistance were obtained. However, enamel adhesion varies greatly depending on the steel plate. Figure 1 shows the amount of pickling products after washing with 10% sulfuric acid (70°C) for 15 minutes and the amount of commercially available Ti
This shows the adhesion of the enamel after applying white glaze and firing the enamel at 820℃. As an indicator of enamel adhesion
The PEI enamel adhesion index measured by the adhesion test established by PEI (American Enamel Institute) was used. Steel sheets that do not contain Sb, As, and Bi have a large amount of pickling products, and their enamel adhesion varies; even No. 7, which achieved the best adhesion, only achieved an adhesion of 60% according to the PEI index. Ta. However, with steel plates containing As, Sb, or Bi, the pickling products hardly adhered to the steel plates and good enamel adhesion was obtained. Example 2 A mesh having the composition shown in Table 3 was melted and made into a slab by continuous casting, followed by hot rolling and cold rolling.
Box annealing was performed for 10 hours. Next, 0.8% temper rolling was performed to obtain a cold rolled steel plate with a thickness of 0.7 mm. Table 4 shows the mechanical properties of these steel plates. Resistance to secondary processing brittleness is determined by forming into a cylindrical cup with a drawing ratio of 2.1, holding it at various temperatures from room temperature to -60℃, dropping a 5kg weight from a height of 1m, and measuring the temperature at which vertical cracking occurs. was evaluated as the critical temperature for cracking. In other words, the lower the critical temperature, the better the resistance to secondary work brittleness. All steel plates show excellent press formability of >1.8 and El >50%, but steel No. 16 has a small amount of Ti added.
No. 18 exhibited longitudinal cracking even at 0°C, and significant secondary work brittleness appeared. However, other steels containing sufficient Ti do not exhibit vertical cracking even at -60°C, indicating that they have good resistance to secondary work brittleness. FIG. 2 shows the results of examining enamel adhesion using the same method as in Example 1. Steel containing Sb, As or Bi can provide good enamel adhesion, but
Steel Nos. 17 and 18 that do not contain these elements have a large amount of pickling products deposited due to pickling, and good enamel adhesion cannot be obtained.

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[Table] Invention steel marked with ○

[Table] Invention steel marked with ○

【table】

[Table] Invention steel marked with ○

[Table] Invention steel marked with ○

[Brief explanation of the drawing]

FIG. 1 is a graph showing the enamel adhesion and the amount of pickling product deposited on each steel plate (continuously annealed material). FIG. 2 is a graph showing the enamel adhesion and the amount of pickling product deposited on each steel plate (box annealed material).

Claims (1)

[Claims] 1 C: 0.005% or less, Si: 0.03% or less, Mn:
0.50% or less, P: 0.02% or less, S: 0.03% or less,
N: 0.005% or more, 0.012% or less, Ti: 0.15% or less and Ti > (48/12C + 48/14N + 48/32S), Cu:
0.08% or less, the total of at least one element selected from the group consisting of As, Sb and Bi is 0.003
Cold-rolled steel sheet for enameling, consisting of % or more and 0.03% or less, the balance being iron and unavoidable impurities. 2. When producing cold rolled steel sheets for enameling with excellent press formability, enameling adhesion, and chipping resistance, C: 0.005% or less, Si: 0.03% or less, Mn:
0.50% or less, P: 0.02% or less, S: 0.03% or less,
N: 0.005% or more, 0.012% or less, Ti: 0.15% or less, and Ti > (48/12C + 48/14N + 48/32S)%,
Cu: 0.08% or less, the sum of at least one element selected from the group consisting of As, Sb and Bi,
Molten steel consisting of 0.003% or more and 0.03% or less, the balance iron and unavoidable impurities is continuously cast, hot rolled,
A method for producing a cold-rolled steel sheet for enameling, which comprises, after cold rolling, continuous annealing in a temperature range above the recrystallization temperature and below Ac ₃ points. 3. When manufacturing cold rolled steel sheets for enameling with excellent press formability, enameling adhesion, and chipping resistance, C: 0.005% or less, Si: 0.03% or less, Mn:
0.50% or less, P: 0.02% or less, S: 0.03% or less,
N: 0.005% or more, 0.012% or less, Ti: 0.15% or less and Ti > (48/12C + 48/14N + 48/32S + 0.03)
%, Cu: 0.08% or less, the total content of at least one element selected from the group consisting of As, Sb, and Bi is 0.003% or more and 0.03% or less, and the balance is iron and unavoidable impurities. A method for producing a cold-rolled steel sheet for enameling, which comprises hot rolling and cold rolling, followed by box annealing in a temperature range of at least a recrystallization temperature and at most 800°C.