JPH0416539B2 - - 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, enameling properties, and weldability, 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. Ti-added steel, especially ultra-low carbon steel with C content of 0.02wt% or less
It is reported that excellent press formability can be obtained when Ti is added.
It is disclosed in No. 18066 etc. Japanese Patent Publication No. 45-40655 describes a technology for utilizing the excellent press formability of Ti-added steel and further obtaining excellent enameling properties.
This is disclosed in JP-A No. 53-131919 or JP-A No. 56-9357. These technologies have good press formability and
This is a technology to improve the chipping resistance of enamel. In other words, the idea is to utilize the fact that Ti forms carbides, sulfides, and nitrides in steel to increase the hydrogen storage capacity of steel sheets and suppress the occurrence of splatter. However, in order to fully exhibit this effect, it is necessary to add a sufficient amount of Ti;
There was a problem that when the amount was increased, the adhesion to the enamel deteriorated. 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. On the other hand, steel plates for enameling are often subjected to various types of welding after forming. However, Ti-added steel has poor workability during welding compared to capped steel, which has traditionally been used for enameling, and is more prone to blowhole defects. Especially “sink” on welded parts
is large and leaves streaks during enamel firing,
There were problems such as bubble defects occurring in the blowhole area. Therefore, gapped steel is still used for welding purposes, and Ti-added steel has not been used for welding purposes. <Object of the invention> The present invention was made in view of the above-mentioned actual situation, and
The object of the present invention is to provide a steel plate for enameling that has excellent press formability, enameling properties, and weldability, 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.
The present inventors discovered that by first adding As, Sb, and Bi to the steel, the adhesion of pickling products could be prevented.
A method to improve the enamel adhesion of Ti-added steel was proposed. (Refer to Japanese Patent Application No. 59-22378) As a result of further investigation, we found that although the effect is not as great as that of As, Sb, and Bi, the addition of Se and Te has the same effect, and that the addition of Se and Te has the same effect. It was discovered that weldability could be improved, leading to the present invention. That is, in the first invention, C: 0.005wt% or less,
P: 0.02wt% or less, S: 0.03wt% or less, N:
0.005wt% or more, 0.012wt% or less, Ti: 0.15wt%
less than or equal to Ti≧ [(48/12)C+(48/14)N+
(48/32) A cold-rolled steel sheet for enameling consisting of S]wt%, Cu: 0.08wt% or less, Se and/or Te at 0.003wt% or more and 0.05wt% or less, the balance being iron and inevitable impurities. The second invention is to produce a cold-rolled steel sheet for enameling that has excellent press formability, enameling adhesion, and chipping resistance, and the following features: C: 0.005 wt% or less, P:
0.02wt% or less, S: 0.03wt% or less, N: 0.005wt
% or more, 0.012wt% or less, Ti: 0.15wt% or less, and
Ti≧[(48/12)C+(48/14)N+(48/32)S]
wt%, Cu: 0.08wt% or less, Se and/or Te
Molten steel consisting of 0.003 wt% or more and 0.05 wt% or less, the balance iron and unavoidable impurities is continuously cast, hot rolled, cold rolled, and continuously annealed in a temperature range above the recrystallization temperature and below Ac ₃ points. This is a method for producing a cold rolled steel plate for enameling, which is characterized by the following. The third invention provides a method for producing a cold rolled steel sheet for enameling which has excellent press formability, enameling adhesion, and chipping resistance, C: 0.005wt% or less, P:
0.02wt% or less, S: 0.03wt% or less, N: 0.005wt
% or more, 0.012wt% or less, Ti: 0.15wt% or less, and
Ti≧[(48/12)C+(48/14)N+(48/32)S
+0.03〕wt%, Cu: 0.08wt% or less, Se and/
Alternatively, molten steel containing 0.003wt% or more and 0.05wt% or less of Te, the balance iron and unavoidable impurities is continuously cast, and after hot rolling and cold rolling, the temperature is above the recrystallization temperature.
This is a method for producing cold-rolled steel sheets for enameling, which is characterized by box annealing in a temperature range of 800°C or lower. 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 steels with a sufficient amount of Ti added, C exists as TiC, and the degree of deterioration in ductility and value is small, but
When it exceeds 0.005wt%, 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 amount of C is set to 0.005wt%. 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, continuous annealing is performed as described later. Alternatively, in addition to adding sufficient Ti, it is effective to reduce the amount of P in the steel to 0.02 wt% or less. Therefore, the upper limit of P is set to 0.02wt%. 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 0.03wt%. 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 its 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 stumbling
N of 0.005wt% 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 wt% or less, it is extremely rare for such a bald-like defect to occur. The range of N is 0.005wt% or more,
It needs to be 0.012wt% 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 for this effect to be fully exhibited, the amount of Ti must be sufficient to fix C, N, and S, that is, [(48/12)C + (48/14)N + (48/21)S].
wt% 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 low, so P segregates at grain boundaries during cooling, causing secondary work embrittlement. wake up Therefore, when box annealing is performed, in addition to Ti that forms carbides, nitrides, and sulfides, sufficient Ti is added to form phosphides, fixing P as phosphides and preventing grain boundary segregation. , it is necessary to suppress secondary processing brittleness. The amount of Ti required for this is [(48/12)
C+(48/14)N+(48/32)S+0.03]wt% or more. However, an excessive amount of Ti not only causes an increase in cost, but also causes the continuous casting nozzle to become easily clogged and causes bald defects, and furthermore causes deterioration in enamel adhesion and weldability. In order to avoid such problems, the amount of Ti needs to be 0.15wt% or less. Cu: Cu is 0.01wt as an unavoidable impurity in steel
% or more, and has 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 effects of Cu that promote the adhesion of pickling products are As, Sb,
It can be reduced by adding Bi, Se, Te, etc., but in order to minimize the cost increase due to the addition of these elements, it is necessary to keep Cu at 0.08 wt% or less. The applicant has already disclosed that the adhesion of pickling products to the surface can be suppressed by adding elements classified as Group 5A on the periodic table, such as Se, Te: As, Sb, and Bi. There is. The mechanism by which these elements prevent pickling products from adhering is not clear, but pickling products (FeSO ₄ /
This is thought to inactivate adsorption sites for nH ₂ O). By adding Se and Te elements, As,
Although it is not as effective as adding Sb or Bi, it can suppress the adhesion of pickling products 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. Furthermore, workability during welding is improved and the occurrence of blowhole defects is suppressed.
It is not clear why these elements improve weldability, but it is thought that these elements lower the surface tension of iron during melting, making it easier to fuse even when welding speed is increased. It is necessary to add 0.003wt% or more of Se or Te in order to expect an effect of improving weldability and to suppress the adhesion of pickling products to the steel surface, but adding more than 0.05wt% will only increase costs. Instead, the continuous casting nozzle gets clogged and the material deteriorates. In order to avoid cost increase and have sufficient effect, it is desirable to add in a range of 0.005wt% or more and 0.05wt% or less. To manufacture the cold-rolled steel plate for enameling of the present invention,
It is preferable that molten steel in which the above-mentioned components are strictly adjusted to the above-mentioned quantitative ratios is continuously cast, hot-rolled, cold-rolled, and then continuously annealed or box-annealed. When continuously annealing cold rolled steel sheets, secondary work embrittlement does not occur, so it is possible to anneal at a temperature above the recrystallization temperature and below Ac ₃ points. However, when box annealing, TiFeP In order to form it effectively, it is necessary to anneal it in a temperature range above the recrystallization temperature and below 800°C. That is, when the annealing temperature exceeds 800°C, the solubility of Ti and P increases, making it difficult for TiFeP to precipitate. Note that, from the viewpoint of cost and adhesion prevention, it is preferable that the annealing temperature is 750° C. or lower. <Examples> The present invention will be described in more detail below with reference to Examples. 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-rolled steel plate with a thickness of 0.8 m/m. Furthermore, 0.8% temper rolling was performed to examine mechanical properties, enameling properties, and weldability. Table 2 shows these mechanical properties. The amount of C
Except for No. 21, which exceeds 0.005wt%, all other steel plates exhibit good press formability with an El of 50% or more and a value of 1.8 or more. Table 2 also shows the results of the toe jump test and the enamel adhesion test for these steel plates. The glaze test was carried out using a commercially available glaze (Japan Fellow) after 20 seconds of pickling.
Co., Ltd. L type) is glazed and fired in a kiln with a dew point of 30℃.
After enameling was fired at 820°C, the presence or absence of chipping was examined. Twenty specimens were fired for each steel plate, and the percentage of specimens in which splintering occurred was shown. Except for No. 17, No. 19, and No. 20, which had a low amount of N, there was no occurrence of any skipping. The amount of pickling product was measured after pickling with 10% sulfuric acid (70°C) for 15 minutes. After pickling _with 10% _H2SO4 (70℃) for 15 minutes, 2%
After pretreatment for 10 minutes by immersion in NiSO ₄ bath (65℃),
Table 2 also shows the enamel adhesion after applying a commercially available Ti white glaze and firing the enamel at 820°C. PE measured by the adhesion test established by PEI (American Enamel Institute) as an indicator of enamel adhesion.
I. Enamel adhesion index was used. Steel sheets containing no Se or Te could only achieve adhesion with a PEI index of 60 or less. On the other hand, each steel plate was welded using a plasma arc welder at a welding current of 65A and a welding speed of 1m/
After welding was carried out at min., the appearance shape of the welded part and transmitted X-ray observation were performed. The results are also shown in Table 2. In No. 1 to No. 6 and No. 17 to No. 21, which do not contain Se or Te, "sink marks" and blowhole defects occurred after welding. That is, if the steel is within the range of the present invention, it will have excellent press workability and chipping resistance, and it will be possible to obtain good enamel adhesion and weldability. Example 2 Steel having the composition shown in Table 3 was melted and made into a slab by continuous casting, and then hot rolled and cold rolled to form a slab at 720°C.
Box annealing was performed for 10 hours. Next, 0.8% temper rolling was performed to obtain a 0.8 mm cold rolled steel plate. Table 4 shows the results of examining the mechanical properties, various enameling properties, resistance to secondary work brittleness, and weldability of these steel plates. Note that the enameling test and welding test were conducted under the conditions described above. 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℃, and dropping a 5kg weight from a height of 1m, resulting in vertical cracking. This temperature was evaluated as the critical temperature for cracking. In other words, the lower this limit temperature is, the better the secondary work brittleness resistance is. All steel plates exhibited excellent press formability with a value of 1.9 or higher and an El of 53 or higher, and all comparison steels that did not contain Se or Te had sink marks and blowhole defects after welding. On the other hand, in No. 31 and No. 33, which had a small amount of Ti, vertical cracking occurred 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.

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【table】

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【table】

[Table] <Effects of the invention> The first invention Se and/or Te of the present invention
Cold-rolled steel sheets for enameling containing 0.003wt% to 0.05wt% are
As is clear from the test results shown in Tables 2 and 4, the enamel properties such as press formability, enamel adhesion, and chipping resistance are improved, and it also has excellent weldability and is resistant to secondary processing even when box annealed. Good brittleness. Se and/or Te of the second and third invention
The manufacturing method of cold-rolled steel sheets for enameling containing 0.003wt% to 0.05wt% involves continuous annealing in a predetermined temperature range or box annealing in a predetermined temperature range, which improves press formability, enameling adhesion, and chipping resistance. A cold-rolled steel sheet for enameling with improved enameling properties, excellent weldability, and good resistance to secondary work brittleness even when box annealed can be obtained.

Claims (1)

[Claims] 1 C: 0.005wt% or less, P: 0.02wt% or less,
S: 0.03wt% or less, N: 0.005wt% or more, 0.012wt
% or less, Ti: 0.15wt% or less and Ti≧ [(48/12)
C+(48/14)N+(48/32)S〕wt%, Cu:
0.08wt% or less, Se and/or Te 0.003wt%
Cold-rolled steel sheet for enameling, consisting of 0.05wt% or less, the balance being iron and unavoidable impurities. 2. When producing a cold rolled steel plate for enameling with excellent press formability, enameling adhesion, and chipping resistance, C: 0.005 wt% or less, P: 0.02 wt% or less,
S: 0.03wt% or less, N: 0.005wt% or more, 0.012wt
% or less, Ti: 0.15wt% or less and Ti≧ [(48/12)
C+(48/14)N+(48/32)S〕wt%, Cu:
0.08wt% or less, Se and/or Te 0.003wt%
The above is characterized in that molten steel consisting of 0.05wt% or less, balance iron and unavoidable impurities is continuously cast, hot rolled, cold rolled, and then continuously annealed in a temperature range above the recrystallization temperature and below Ac ₃ points. A method for producing cold-rolled steel sheets for enameling. 3. When producing a cold rolled steel plate for enameling with excellent press formability, enameling adhesion, and chipping resistance, C: 0.005 wt% or less, P: 0.02 wt% or less,
S: 0.03wt% or less, N: 0.005wt% or more, 0.012wt
% or less, Ti: 0.15wt% or less and Ti≧ [(48/12)
C+(48/14)N+(48/32)S+0.03〕wt%,
Cu: 0.08wt% or less, Se and/or Te
Molten steel consisting of 0.003wt% or more and 0.05wt% or less, balance iron and unavoidable impurities is continuously cast, hot-rolled, cold-rolled, and then box annealed in a temperature range of above the recrystallization temperature and below 800℃. Features: A method for producing cold-rolled steel sheets for enameling.