JPS583441B2 - Manufacturing method of cold rolled steel plate by direct rolling of continuously cast stainless steel slab - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a stainless steel sheet by hot charging direct rolling of a continuously cast stainless steel slab.

The conventional process of manufacturing stainless steel plates from continuously cast slabs is shown in FIG.

In other words, since the surface of slabs continuously cast using conventional carbon-containing powder has surface defects such as carburization and micro-cracks caused by carburization, the slabs are cooled to room temperature and the entire surface of the slab is grinded. Alternatively, it may be necessary to grind with a planer (thus, approximately one section of this surface defect layer must be completely removed).

As a result, casting costs and yield declines are unavoidable.
There is a big problem.

Next, the cooled slab is charged into a heating furnace, reheated to a predetermined temperature, and hot rolled.

By the way, the surface temperature of the slab immediately after casting is 800-850℃.
Even though the slab is in a red-hot state and needs to be further heated for hot rolling, the slab has to be cooled down for the aforementioned caster, and approximately 150,000 Kcal/T of energy is wasted. It will be lost.

After hot-rolled steel sheets are annealed and pickled, it is necessary to use a coil grinder to remove surface defects such as roll flaws, scale flaws, indentation flaws, misalignment, and punching scratches caused by hot rolling.

Furthermore, in the conventional method, it is necessary to heat the slab at a high temperature of 1,100°C or more for a long time of 3 hours or more, resulting in a decrease in yield due to metal oxidation loss, and furthermore, the slab surface is locally damaged. It is severely oxidized and causes scale defects.

As mentioned above, it is clear that the conventional process is extremely unreasonable and disadvantageous in terms of yield, energy consumption, and production efficiency.

The present inventors have determined whether to produce slabs without surface defects that are the cause of cast defects, or even if defects exist, the defects are caused by the depth of the surface defects caused by hot rolling. We focused on the fact that if the defects were less than 100%, they could be removed by removing them by using a coil grinder on hot-rolled steel sheets, and as a result of numerous experiments and factory tests, we developed a new type of stainless steel that is completely different from conventional ones, as shown in Figure 2. Succeeded in manufacturing stainless steel plates from continuously cast steel slabs.

The inventors of the present invention conducted various experiments on methods of obtaining slabs without surface defects, and found that a method for casting slabs using powder in which nitride particles were added instead of carbon particles (hereinafter referred to as nitride-added powder) It was discovered that the resulting cast slabs had almost no carburization or microcracks caused by carburization, which is the cause of casting hand damage, and there was no need for casting hand work.

Figure 3 shows the surface properties of slabs cast using nitride-added powder in comparison with conventional methods.

Regarding the nitride-added powder, the present inventors have developed a powder that is the same as the carbon-containing powder by replacing the carbon particles with another substance that has the same effect as the carbon particles previously blended into the powder. From the viewpoint that it is possible to prevent carburization and carburization while maintaining melting characteristics and without impairing the effectiveness as a powder for continuous casting, Japanese Patent Application No. 50-71694.50-132490 and 50-1 1
As shown in No. 32492, we succeeded in developing a powder containing this substance.

That is, nitrides (BN, SI3N4, MnN,
As a result of repeated experiments, we discovered that by blending an appropriate amount with an appropriate particle size into powder, it has the same melting rate adjustment function as carbon particles, and the optimum range was found. This is a powder in which nitrides are specified, and if necessary, a powder reducing agent is added for the purpose of preventing a decrease in the melting point of the powder due to oxidation of the nitrides and maintaining the skeletal action of the nitrides at high temperatures.

Slabs without surface defects cast using nitride-added powder do not require surface maintenance, so the surface temperature can be maintained at 80℃ after casting.
It is possible to immediately send it directly to a heating furnace in a red-hot state of 0 to 850°C.

Of course, even if a slab is cast using nitride-added powder, if there are large local defects such as vertical cracks or engulfment, the defects must be removed, but it is not possible to carry out partial maintenance while still in a red-hot state. It is good to do this.

Furthermore, in order to prevent high-temperature oxidation loss of the slab in the heating furnace and the occurrence of scale defects due to local oxidation, the slab in the red-hot state may be coated with an optimal commercially available antioxidant depending on the steel type.

Conventionally, cooled slabs are sent to a heating furnace in the order of a preheating zone, a heating zone, and a soaking zone, and it takes about 4 to 5 hours of in-furnace time and about 500,000 yen to heat them to a predetermined hot rolling temperature. Kcal/T
However, with the process of the present invention, the red-hot slabs are immediately charged into the heating zone, and the time in the furnace can be shortened to 2 hours, resulting in significant energy savings with a heating fuel consumption of approximately 400,000 Kal/T. It has become clear that this will be the case.

Moreover, by applying the antioxidant, the amount of oxidation loss of the slab was reduced to 1/30 to 40 per unit area to be heated, and local oxidation was completely prevented.

The relationship between the amount of high-temperature oxidation loss of the slab and the presence or absence of antioxidant coating, and the temperature rise curves of the slab for the conventional method and the method of the present invention are shown in FIGS. 4 and 5.

As a result of investigating the surface properties of hot-rolled steel sheets manufactured by the process of the present invention, it was found that the present invention is effective in reducing scale defects caused by conventional high-temperature, long-time heating due to the short furnace time. became clear.

In addition, roll flaws, indentation flaws, misalignment caused by hot rolling,
Hot rolled steel sheet surface defects such as punching scratches occur in the same way as with conventional methods, so after annealing and pickling the hot rolled steel sheet,
%Thickness/Removal by grinding with a coil grinder on one side is necessary.

Incidentally, when stainless steel sheets are manufactured by the process of the present invention from slabs cast using conventional carbon-containing powder, the hot-rolled steel sheets undergo carburization, microcracks caused by carburization, heave defects, linear defects, and intergranular corrosion. , the surface grew rough, and even when it was removed by grinding with a coil grinder on more than 1% of the sheet thickness/one side of the hot-rolled steel sheet, it remained on the cold-rolled sheet and showed a significant decrease in yield.

In a preferred embodiment of the present invention, when stainless steel sheets are manufactured from continuous cast slabs, the continuous cast slabs are cast using nitride-added powder, and the red-hot slabs are left intact or, if necessary, partially After treatment, the hot rolled steel sheet is charged directly into a heating furnace, hot rolled, and after annealing and pickling, the thickness of the hot rolled steel sheet is reduced to 0.
Grinding is performed using a coil glider of 5 coefficient thickness/one side. Next, examples of the present invention will be shown.

Example 1 After continuous casting of molten SUS304 stainless steel into slabs with a size of 130 mm x 1060 mm using a nitride-added padder, the red-hot slabs with a surface temperature of 800°C were immediately sent directly to a heating furnace, and heated to 1200° C. in 2 hours in the furnace. ℃ and hot rolled to a plate thickness of 4. A 0 mm hot-rolled steel plate was produced, annealed and pickled, and then 20μ of one side was ground off using a coil grinder, and a stainless steel cold-rolled steel plate with a thickness of 1.0 mm was produced by one-stage cold rolling.

Example 2 After continuously casting SUS304 stainless molten steel into a slab of size 130 mm x 1060 mm using nitride-added powder, an antioxidant was applied by spraying, and the red-hot slab with a surface temperature of 750°C was immediately placed in a heating furnace. It was directly delivered, heated to 1250°C for 3 hours in the furnace, and hot rolled to a thickness of 4.
A 0 mm hot rolled steel plate was manufactured, and after annealing and pickling, 20 μm of one side was ground off using a coil grinder, and a stainless steel cold rolled steel plate with a thickness of 1.0 mm was manufactured by one-stage cold rolling.

Comparing the stainless steel sheet manufacturing cost, yield, and surface flaw score of cold rolled steel sheet in Examples 1 and 2 with the conventional method,
It is shown in Table 1 and Figure 6.

From Table 1, it is clear that according to the present invention, the yield, cost, and fuel consumption rate are significantly improved, and from FIG. 6, defects caused by hot rolling are reduced compared to the conventional method. I understand that.

Although the above examples were carried out on SUS304 stainless steel slabs, the effects of the present invention will naturally be exhibited even if the present invention is applied to other stainless steels that require a caster. be.

[Brief explanation of the drawing]

Fig. 1 is a conventional process diagram for producing stainless steel sheets, Fig. 2 is a process diagram showing an example of the method of the present invention, and Fig. 3 is a surface of a stainless steel slab cast using nitride-added powder. Figure 4 shows the properties of a slab in comparison with conventional slabs, Figure 4 shows the effect of preventing oxidation loss by applying an antioxidant, and Figure 5 shows that the heating time of slabs can be shortened by the method of the present invention. FIG. 6 is a diagram showing a comparison between the conventional method and the method of the present invention for the surface flaw rating of cold-rolled stainless steel sheets.

Claims (1)

[Scope of Claims] 1. In the production of cold-rolled stainless steel sheets, a red-hot slab continuously cast using powder to which nitride particles are added instead of carbon particles is directly sent to a heating furnace without any maintenance and subjected to hot heating. A method for producing a cold-rolled steel plate by direct rolling of a continuously cast stainless steel slab, characterized by rolling, annealing the hot-rolled steel plate, pickling, removing defects using a coil grinder, and then cold rolling. 2. In the production of stainless steel cold-rolled steel sheets,
After performing partial maintenance on a red-hot slab that was continuously cast using powder with nitride particles added instead of carbon particles,
A method for producing a cold-rolled steel plate by direct rolling of a continuously cast stainless steel slab, characterized by hot rolling, annealing the hot-rolled steel plate, pickling, removing defects using a coil grinder, and then cold rolling. . 3. A method for producing a cold-rolled steel sheet by direct rolling a continuously cast stainless steel slab according to claim 1 or 2, wherein the red-hot slab is coated with an antioxidant and then hot rolled.