JPS6323247B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a steel plate for ultra-deep drawing enameling with excellent adhesion, and in particular, proposes a method that is advantageous for manufacturing at low cost through a continuous casting method. Conventional steel sheets for enameling have been manufactured by decarburizing cold-rolled steel sheets manufactured from low carbon rimmed steel by open coil annealing to reduce the C content to 0.008% or less. Rimmed steel is used because it contains a large amount of oxygen, so it has the advantage of being less likely to produce porosity defects during enamel firing, and because it is decarburized and annealed, it does not absorb heat during enamel firing. This is because the firing strain caused by stress is reduced, the ductility of the steel sheet is improved, and excellent formability can be obtained. However, steel sheets for enameling manufactured by such conventional methods inevitably suffer from (1) an increase in manufacturing costs due to open annealing; (2) It cannot be continuously cast to make rimmed steel. (3) Since it is a rimmed steel, the material quality is due to component segregation.
and the enamel properties are non-uniform, so the quality of the product is unstable. Moreover, in the case of the steel plate for enameling obtained through the above manufacturing process, it is required to have excellent press formability and so-called deep drawability in addition to the above-mentioned enameling properties, so it is common to use rimmed steel and decarburize annealing. Therefore, continuous casting is of course not possible, and oven annealing is indispensable, which has the disadvantage of increasing manufacturing costs. In addition, inclusion defects peculiar to agglomerated materials, non-uniformity of material due to segregation, and the fact that when a product steel strip is made, lumps are likely to occur in the rim layer and near the boundary line between the rim layer and the core layer, which can be said to be fateful. There were flaws. The object of the present invention is to overcome the above-described drawbacks of the conventional steel sheets for enameling, and to obtain a cold-rolled steel sheet for enameling that is excellent in quality and inexpensive and can be produced by continuous casting. The gist of the present invention, which is effective for achieving the desired effects in response to such purposes, is that, in weight percent, C: 0.003% or less, Mn: 0.50%.
Below, Al: 0.04% or more than twice the above C amount, excluding those containing 0.030% or less and Nb present as an oxide.
% or less, B 0.0020 to 0.0070% and N 0.0026
Continuously cast steel containing up to 0.0100%,
The cast slab is heated at a low temperature of 1000°C or higher and 1200°C or lower and then hot-rolled, and then cold-rolled to give a thickness of 0.01 to 2.0 g/m ² to the surface of the cold-rolled steel plate.
After applying Ni plating, the temperature is 1000℃ above the recrystallization temperature.
The present invention relates to a method for producing a steel plate for ultra-deep drawing enameling with excellent adhesion, which is characterized by performing recrystallization annealing at the following temperature. The details of the configuration will be explained below. The reasons for limiting the composition of molten steel are as follows. C weight %: C needs to be reduced to 0.003% or less. The reason for this is the enamel properties (firing strain,
The goal is to make ultra-low carbon steel from three points: improving the foam generation), improving the material quality, and preventing CO gas generation during continuous casting. General steel plate for enameling is C
If the carbon content is not low, CO gas will be generated during enamel firing, leading to bubble defects and firing distortion caused by α-γ transformation. Visual control is required. In contrast, the steel of the present invention has improved material properties such as elongation properties and value, and in order to prevent CO gas generation during continuous casting, the upper limit of C content has been lowered to 0.003% or less. And so.
This is because when the C content exceeds 0.003%, the amount of solid solute C before recrystallization annealing increases and the value deteriorates.
Material deterioration due to C aging also increases. Furthermore, CO gas is generated during continuous casting, making it impossible to obtain good surface quality. In short, it is this C content that makes continuous casting of enameling steel possible. Mn weight %: Mn is usually added in order to prevent hot brittle cracking caused by S so that the ratio is Mn/S10. In the case of killed steel, the smaller the amount of Mn, the better the material properties such as elongation (El) and area of area (value), so it is preferable to add a smaller amount of Mn.
The upper limit of the amount of Mn added is based on economic reasons, and in the present invention is set to 0.50% or less. Al weight %: Al is added to molten steel in order to deoxidize oxygen in molten steel and facilitate continuous casting. The role of this Al is to form nitrides in steel, similar to B, but unlike N that has become AlN, nitrogen that has become BN has a small effect on suppressing nitrides. When Al and B coexist, BN and AlN precipitate simultaneously, which reduces the effect of B addition, so the upper limit of Al was set at 0.03%. Nb weight%: Generally speaking, when a cast slab with an extremely low C of 40 ppm during melting is made into a cold-rolled steel sheet in a normal process, the in-plane anisotropy of elongation El and reduction of area (particularly 45° (D It is known that the El and r values in the ) direction become significantly large. In addition, during the recrystallization process in a continuous annealing furnace, solid solution C
remains, so the above value does not improve. In order to improve these drawbacks, adding Nb, which is a C-fixing element, improves these drawbacks. The amount of Nb added to meet these demands is naturally determined in relation to the amount of C, and it is 0.04 or more times the amount of C.
% or less. The reason is that when the Nb content is less than twice the C content, the anisotropy increases, and the average value of El and r values in the L (0°), C (90°), and D (45°) directions (, value) also deteriorates. On the other hand, the upper limit of the amount of Nb added is that if a large amount of Nb is added, precipitates such as NbC will increase too much, the crystal grain size after annealing will become smaller, and the El value will deteriorate. Also, since adding a large amount is not economical, the upper limit was set at 0.04%. Regarding the amount of Nb, the reason why oxides are excluded is that Nb oxides are not effective in fixing solid solution C. Weight % of B and N: The minimum addition amounts of B and N are determined from the viewpoint of preventing the occurrence of skipping, and the maximum addition amount is determined from the viewpoint of preventing material deterioration. First, the reason for determining the minimum addition amounts of B and N will be described. In the present invention, the main requirement is to add boron and nitrogen to precipitate BN, trap hydrogen around the BN precipitate, and prevent the occurrence of splatter. Figure 1 shows
C: 0.0018%, Mn: 0.18%, Nb: 0.10%,
Molten steel with N: 0.0040% and B content varying from 10 ppm to 85 ppm was slab-heated at 1150°C, a cold-rolled steel plate was pre-plated with 0.2 g/m ² of Ni, and then heated at 820°C. This is a graph showing the relationship between the amount of B, the value, and the occurrence of skipping when continuous annealing is performed for 40 seconds. Figure 2 also shows the relationship between the amount of B, the amount of BN, and the occurrence of skipping. It is a graph. From Figure 2, to prevent the occurrence of blockage,
It can be seen that the amount of BN precipitates is required to be 0.0046% or more. That is, B needs to be added in an amount of 0.0020% or more, and N is needed to be added in an amount of 0.0026% or more based on the formula below. NN (atomic weight) / BN (atomic weight) x BN (%) = 14 / (14 + 10.8) x 0.0046 = 0.0026% Also, from Figure 1, in order to obtain good drawability (value), the amount of B is 0.0070%. It turns out that you need to do the following. Note that if the amount of N is too large, the material will deteriorate, so the amount added should be 0.0100%.
Do the following. For the above reasons, it is necessary to control the amount of B to 0.0020% to 0.0070% and the amount of N to 0.0026% to 0.0100%. Next, the molten steel is continuously cast to produce a continuous cast slab. Conventional decarburized rimmed steel type enamel steel plates prevent the occurrence of skipping by making the molten steel component of the agglomerate high in oxygen (0≒450ppm). O causes a reaction,
Since CO gas was generated and a so-called rimming reaction occurred, continuous casting could not be used. In comparison, the steel of the present invention can be cast with extremely low C and O content, so no rimming reaction occurs.
Continuous casting became possible. Next, the above-mentioned casting slab is heated to 1000℃ or higher, 1200℃
After performing the following low-temperature heating, hot rolling is performed. This is because if the heating temperature exceeds 1200°C, BN precipitation during hot rolling will be impaired, an appropriate amount of BN precipitation will not be obtained, and the blockage resistance will deteriorate. However, as is well known, if the heating temperature is too low, the
Not only does hot rolling at ₃ or more Ar points become difficult, leading to deterioration of formability, but also the precipitated BN becomes excessively coarse, and the amount of BN precipitated becomes insufficient, reducing the ability to suppress lumping. Since this would cause instability, the lower limit of the heating temperature was set at 1000°C, which eliminates the risk of instability. Next, the hot rolled steel sheet is subjected to continuous annealing after cold rolling according to a conventional method. At this time, the method of the present invention is characterized in that the surface of the cold-rolled steel sheet is previously plated with Ni prior to the treatment. The reason for going through such processing steps will be described below. Figure 2 shows C: 0.0018%, Mn: 0.18%, Nb:
A slab obtained by continuous casting of molten steel containing 0.10%, N: 0.0030% to 0.0050%, and a B content of 10ppm and molten steel with a B content of 25ppm was heated to 1150°C, hot-rolled by the usual method, After pickling and cold rolling, 0 to 0.6 g of Ni was plated before entering the continuous annealing furnace, and the steel plate was used for enameling after recrystallization annealing, and the occurrence of lumps after normal enameling was investigated. This is the result.
In the case of the invention steel containing 25 ppm of B, 0.1
It can be seen that Ni plating of g/m ² can prevent the occurrence of skipping. However, the B content
In steel sheets having a concentration of 10 ppm outside the range of the present invention, even if the amount of Ni plating increases, the occurrence of skipping cannot be prevented.
Ni plating amount below 0.01g/m ² is too small to be effective, and the upper limit is 2.0g/m ² from the economic point of view.
I decided to. Another effect of such Ni plating is that good adhesion can be obtained even if pretreatment during enamel firing is omitted. Normally, when manufacturing enamel products, to improve adhesion and prevent flaking, degreasing, pickling with sulfuric acid, Ni dip in NiSO ₄ aqueous solution,
Perform pre-processing such as Such pretreatment increases costs and worsens the working environment due to waste acid treatment. However, according to the method of manufacturing a steel plate for enameling according to the present invention, even without such pretreatment, the adhesion is significantly improved by simply baking at 400 to 600°C for a few minutes, making it possible to Since it is also possible to prevent the occurrence of such problems, it is very effective in improving the working environment and omitting pre-treatment. Examples of the present invention will be described below.

【table】

[Table] Example As shown in Table 1, steel with a composition within the range of the present invention and steel with a composition outside the range as a comparative material were heated at a slab heating temperature of 1150°C, and then heated in the usual manner. After rolling, it is made into a 3.2mm hot-rolled coil and then pickled.
It was made into a 0.8mm cold rolled coil. Next, steels A to D were plated with 0.2 g/m ² of metallic Ni before recrystallization annealing.
E steel was not Ni-plated. Immediately thereafter, continuous annealing was performed at 820°C for 40 seconds, and after 0.4% skin pass rolling, mechanical properties, stubble tests, and adhesion tests were performed. For mechanical testing, JIS No. 5 test pieces were prepared at 0° (L direction), 46° (D direction), and 90° (C direction) with respect to the rolling direction, and tensile tests were performed. Measure the values of and calculate the average value of each expressed as L+C+2D/4,
El, was obtained as. Also, ΔEl indicates the difference between the maximum and minimum values in the L, C, and D directions, and Δr is Δr=・
It was determined by r _L + r _C + 2r _D /2. In addition, for the jump test, the sample was degreased and then pickled with 9% H ₂ SO ₄ at 70°C for 20 seconds.
It was enameled and fired at 830°C for 4.5 minutes. After that, accelerated treatment was performed at 160°C for 16 ^hours , and samples with no occurrence of skipping were evaluated as 〇.
Samples in which black kite appeared were evaluated as ×. On the other hand, in the adhesion test, the adhesion index was measured using a commercially available PEI tester. As shown in Table 2, the steels within the scope of the present invention are excellent in terms of material, flaking resistance, and adhesion; however, the steels outside the scope of the present invention are all poor in material quality, flaking resistance, and adhesion. is inferior. Example Using A steel and E steel in Table 1, dry baking was performed at 400°C for 5 minutes without pretreatment such as pickling or Ni dipping.
After that, it was directly enameled, fired at 830°C for 4.5 minutes, and then accelerated at 160°C for 16 ^hours , followed by a topping test and an adhesion test using a PEI tester.

[Table] As a result, steel E, which was not plated with Ni, had very poor adhesion and some skipping occurred, but steel A of the present invention was simply dry fired.
No skipping occurred and the adhesion was extremely good. As explained above, according to the method of manufacturing a cold rolled steel sheet for enameling of the present invention, it is possible to obtain a product that has excellent enameling properties such as zagging and blistering, as well as excellent press formability such as elongation and drawing. It will be done. Moreover, in the production of the present invention, continuous casting is possible, and decarburization by open annealing is not required, so normal tight annealing or continuous annealing can be performed and the product can be manufactured at low cost.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of B and the value and the presence or absence of skipping. Figure 2 is a graph showing the relationship between the amount of B, BN amount and the presence or absence of skipping. Figure 3 is a graph showing the relationship between the amount of B, the amount of BN, and the presence or absence of skipping. It is a graph showing the relationship between the amount and flaking resistance.

Claims (1)

[Claims] 1% by weight, including C: 0.003% or less, Mn: 0.50% or less, Al: 0.030% or less, and 0.04% or more twice the above C amount, excluding those in which Nb is present as an oxide.
Below, B is 0.0020~0.0070% and N is 0.0026~
Steel with a content in the range of 0.0100% is continuously cast, the cast slab is heated at a low temperature of 1000°C or higher and 1200°C or lower, hot rolled, and then cold rolled to form the surface of the cold rolled steel sheet in advance. 0.01~2.0g/m ² thick Ni
A method for producing a steel plate for ultra-deep drawing enameling with excellent adhesion, which comprises plating and then recrystallizing annealing at a temperature above the recrystallization temperature and below 1000°C.