JPS5912728B2 - Method for manufacturing deep-drawn aluminum killed hollow steel plate with excellent nail-skipping resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cold-rolled steel sheet for deep drawing aluminum killed enamel which has extremely excellent nail-skipping resistance.

Enamel steel sheets are often used in applications that require deep drawability, such as bathtubs, household tableware, and electrical appliances. Aluminum killed steel is sometimes used for such applications, but aluminum killed steel is cleaner than rimmed and cat 5 steel, so it has the disadvantage of being susceptible to surface defects called nail skipping after enamel firing. has.

As a countermeasure against this, the usual method is to increase the hydrogen absorption capacity of the steel by adding non-metallic inclusions such as oxides and sulfides to the steel, thereby improving the nail-skipping resistance. .

However, with this method, the workability deteriorates due to the addition of inclusions, and the addition of small amounts does not significantly improve the nail-skipping resistance. Therefore, manufacturing conditions that satisfy both the nail-skipping resistance and workability15 The range of steel sheets is narrow, and it is not easy to stably manufacture such steel sheets. Furthermore, in the production of aluminum-killed steel sheets by conventional box annealing, the following precautions are taken to improve deep drawability.

In other words, in order to ensure that At and N decomposed in the heating furnace remain in solid solution during and after hot rolling in the hot rolled sheet, the finishing temperature of the hot rolling is set as high as possible, preferably 870°C. C. or higher, and the winding temperature is as low as possible, preferably 600.degree. C. or lower, and the winding process is normally carried out for cooling. The reason for this is that, as is well known, solid solution At and solid solution nitrogen precipitate as AtN during recrystallization annealing after cold rolling, which is advantageous for deep drawing (1
11) Since the recrystallization orientation develops selectively30, it is important to select an appropriate heating rate for recrystallization annealing depending on the amount of solid solution At or the ratio of the amount of solid solution At and the amount of solid solute nitrogen. This was an essential condition for imparting drawability.

In this case, if aluminum killed steel is coiled at a temperature of 600°C or higher and cooled in air or slowly, AtN will precipitate due to the self-annealing effect of the coil, and (111) recrystallization orientation will be generated due to AtN precipitation during recrystallization annealing. It was common knowledge that the effect of this would be reduced or lost, making it impossible to obtain good deep drawability.

The present inventors have investigated the hot rolling winding temperature and the chemical composition in steel, especially Mn.
As a result of examining the effect of K,.
It has been found that when the Mn content is 0.15% or less, good deep drawability can be obtained even if the winding temperature is 600° C. or higher.

At the same time, it was also found that high-temperature rolling can provide excellent nail-skipping resistance without adding non-metallic inclusions to the steel. The present invention is provided based on the above knowledge, and its gist is as follows: CO. 1% or less, MnO. O3%
0.15% or less, oxygen 0.03% or less, acid-soluble At
O. A steel billet consisting of OO5% or more and 0.10% or less and Mn/S〉acid-soluble At7, 〉1.93, residual iron and inevitable impurity elements is hot rolled and heated to a temperature of 650°C or higher 8
Deep-drawn aluminum killed enamel with excellent nail-skipping resistance, characterized by being rolled at a temperature of 50°C or lower, cold-rolled according to a conventional method, and annealed in a recrystallization box at a temperature of 650°C or higher and 800°C or lower. It is in the manufacturing method of steel plate for industrial use.

The reason why the steel components are limited in the present invention will be explained below.

MnO. If l exceeds 5%, good deep drawability cannot be obtained in the box annealed material that has been subjected to high temperature winding.

In order to obtain good deep drawability, the content is preferably 0.13% or less. Furthermore, if the Mn content is less than 0.03%, there is a risk of red-hot embrittlement occurring due to S present as an inevitable impurity element in the steel. The amount of oxygen is set to 0.030% or less (
(preferably 0.01% or less).

In addition, S is Mn/S depending on the amount of Mn to prevent red-hot brittleness.
>7 (preferably Mn/S>10).
Next, acid-soluble AL is necessary to fix nitrogen, which exists as an unavoidable impurity element in steel, and to make the steel non-aging, and if it is less than 0.005 (fl), this purpose cannot be achieved. .

The content is preferably 0.010% or more.

In addition, the upper limit should be set to 0.10% (preferably 0.06%) since the action and effect will be saturated if it exceeds 0.10 (F6).Furthermore, in order to fix all the nitrogen in the steel with At and achieve non-aging. It is necessary to add At according to the amount of nitrogen in the steel so that the acid-soluble At/N>1.93.Next, the manufacturing process in the present invention will be explained.

First, after pre-deoxidizing if necessary during steel manufacturing, Mn<0.
The steel is tapped to a concentration of 15% and desulfurized if necessary. After that, 0.1 to 3 kf/TON of At is added to the molten steel. At may be added to the ladle, or may be added to the core of the steel ingot or slab during ingot formation or continuous casting. When At is added to the core portion of a steel ingot or slab, it is possible to particularly prevent the occurrence of defects caused by At on the steel surface. At the same time, it is also possible to prevent hollow defects such as bubbles caused by At present near the steel surface. Steel slabs (slabs obtained by blooming a steel ingot or cast slabs by continuous casting) are hot-rolled according to the usual method, and then 65
It is rolled up at a temperature of 0°C or higher (preferably 700°C or higher) and 850°C or lower (preferably 770°C or lower).

If the winding temperature is less than 650°C, the effect of improving the nail skipping resistance will be reduced.

In particular, when a remarkable effect of improving the nail-skipping resistance is expected, the winding temperature is preferably 700° C. or higher. If the winding temperature exceeds 850°C, it becomes difficult to adjust the plate temperature. After being wound, the coil is either air-cooled or allowed to stand for a time necessary for coarsening of the carbide, water-cooled, and then pickled and cold-rolled in a conventional manner. If the cold rolling reduction is less than 30%, desired deep drawability cannot be obtained. In addition, if it is more than 95 (f:I), the required hot rolling thickness becomes extremely large and is not practical.The coil after cold rolling is box annealed after electric cleaning if necessary.The annealing holding temperature in box annealing is 650 ℃ or higher and 850℃ or lower (preferably 700℃ or higher and 750℃ or lower).If the annealing temperature is lower than 650℃, deep drawability will decrease.
If it exceeds 0°C, the pores in the steel produced by cold rolling will be thermally fused and disappear, resulting in a decrease in the nail-skipping resistance, which is not preferable. In case of box annealing in which the coil is wound tightly, it is effective to hold the annealing for 10 hours or less in order to ensure the temperature of the coil's coldest point and eliminate variations in material. The steel plate is subjected to temper rolling if necessary. The present invention will be explained below based on examples.

Example 1 The component in molten steel is MnO. Steel is tapped in a converter so that the O2 content is 8% and the oxygen content is 0.05%, and the steel is desulfurized and At is reduced to 0 in a ladle.
．． After adding 8 to 1.5 k7/TON, steel slabs were formed by ingot making, blooming rolling, or continuous casting.

The steel piece was heated to 1200°C in a heating furnace, and the finishing temperature was 89°C.
After hot rolling at 0°C to a plate thickness of 2.8 to 3.5 Tfm, it was rolled up at a temperature of 680°C to 780°C and cooled in air. After pickling the steel coil, it was cold rolled to 0.8m and rolled to 70mm.
Box annealing was performed for 12 hours at a temperature of 0°C to 750°C, and 1% temper rolling was performed. Table 1 shows the chemical composition of the cold-rolled sheets of the invention steel and comparative steel, Table 2 shows the manufacturing conditions, and Table 3 shows the mechanical properties of the product sheets.

Next, a test piece with a size of 100 m x 200 m was applied twice and the number of nail skips that occurred after firing the enamel is shown in Table 4.

Furthermore, the nail-skipping resistance of a steel plate can also be evaluated by measuring the hydrogen permeation time.

In this method, hydrogen is generated by electrolysis on one side of a steel plate, and the time taken for the hydrogen to diffuse through the steel plate to come out on the other side of the plate is measured. The longer the hydrogen permeation time, the more hydrogen permeates through the steel plate. As the capacity is large, the nail-skipping resistance is excellent. Table 5 shows the results of measuring the hydrogen permeation time using this method. As will be seen, the steel of the present invention is non-aging and has both excellent deep drawability and nail skipping resistance. Furthermore, there were no surface defects after enameling twice.

Example 2 Molten steel tapped from a converter is desulfurized in a ladle so that Mn is 0.07 to 0.12 (f), and when bottom pouring is performed, the molten steel is poured into a mold from an injection pipe. The core was kept for 40 to 50 seconds, At 0.3 to 2.0 kf/TON was added to the core, and the core was bloomed into a slab.
Heated at 80°C to 1300°C, hot rolled at a finishing temperature of 900°C, rolled to a thickness of 3.2°, rolled up at a temperature of 690°C to 780°C, pickled, and 0.8°C. Cold rolled to 725℃10
Box annealing was performed for 1 hour and pressure was adjusted to 1 (fl).

Table 6 shows the chemical composition of the cold-rolled sheets of the invention steel and comparative steel, Table 7 shows the manufacturing conditions, and Table 8 shows the mechanical properties of the product sheets.

In addition, the firing test was conducted in the same manner as in Example 1, and the number of nails that occurred is shown in Table 9, and the measurement results of the hydrogen permeation time are shown in Table 1.
Shown in Table 0.

Claims (1)

[Claims] 1 C0.1% or less, Mn 0.03% or more and 0.15% or less, oxygen 0.03% or less, acid-soluble Al 0.005% or more and 0.10% or less, and Mn/S≧7, (acid-soluble Al)/
N≧1.93, a steel billet consisting of residual iron and unavoidable impurity elements is hot-rolled, rolled at a temperature of 650°C or higher and 850°C or lower, and then cold-rolled according to a normal method to obtain a steel slab of 650°C or higher and 850°C or higher.
A method for producing a steel plate for deep-drawn aluminum killed enamel with excellent nail-skipping resistance, characterized by recrystallization box annealing at a temperature of 00°C or lower.