KR20050068253A - Method for manufacturing hot-rolled high carbon steel sheets with excellent red scales surface appearance - Google Patents

Abstract

The present invention is to maintain the inlet temperature of the first descaling at 1173 ℃ or more in the first descaling step in order to remove red scale defects, including fayalite (Fe ₂ SiO ₄ ) generated during the hot rolling process In the sizing press, the width reduction ratio is applied at 5% or more in the sizing press, width rolling is performed, and then the second descaling step is performed. Provided is a method for producing a high carbon hot rolled steel sheet which descales.

Description

{Method for manufacturing hot-rolled high carbon steel sheets with excellent red scales surface appearance}

The present invention relates to a method for producing a hot rolled steel sheet. More specifically, the present invention relates to a method for producing a high carbon hot rolled steel sheet which has been completely removed on a ferayalite scale and has excellent surface quality.

In general, steel is classified as steel type according to carbon content among the constituent elements constituting the steel, and is classified as high carbon steel when the carbon content in steel is 0.4% or more.

Such high carbon steels have excellent mechanical strength and are mainly used for automobile parts and tools.

In the manufacturing process of high carbon steel products, the slab manufactured by continuous casting method or ingot process is heated above the recrystallization temperature and rolled in hot state to make hot rolled steel sheet in strip state, and then attached to the surface of steel sheet in pickling process. After removing the scale through the annealing and cold rolling process to produce a cold rolled steel sheet in the form of a coil. The cold rolled steel sheet thus prepared is subjected to heat treatment and then subjected to plating to give the required surface properties, and then to manufacture a final product.

As such, the steel sheet quality in the hot rolling process, which is an initial process, has an important effect in order to obtain excellent surface quality required for each customer after cold rolling and surface treatment. In particular, if the surface defects such as red scale and the like on the surface of the steel sheet in the hot rolling process, such surface defects also affect the subsequent product to give excellent quality to the final product.

It is known that the cause of the red scale surface defect in the process of manufacturing high carbon hot rolled steel sheet is due to the silicon (Si) in the range of 0.1-0.5 wt% contained in the high carbon steel.

To explain the causes of red scale surface defects, a general hot rolling process is briefly described first.

In the steelmaking process such as continuous casting process, the steel ingot manufactured in slab state is charged into the heating furnace and heated above the recrystallization temperature of the steel, and then the descaling apparatus removes the thick primary scale film attached to the surface of the slab and sizing Lightly press down in the width direction in the press to perform crack rolling while forming cracks on the scale on the slab, and another descaling device once again removes the cracked scale film on the surface of the slab, and then rolls it to a predetermined thickness and width in the rough mill. Do it.

And the rough bar (bar) before removing the scale to remove the scale generated on the bar surface during the rolling in the descaling apparatus before rolling into the finishing mill is rolled to the required thickness in the finishing mill and coiled in the coil state in the winder.

Thus, in order to hot roll the slab in a strip state, the heating is first performed at a recrystallization temperature or higher in a heating furnace. As shown, a liquid phase of fayalite (Feayalite, Fe ₂ SiO ₄ ) is produced between the iron component (Fe) and the scale iron oxide (FeO) of the steel sheet.

In this way, the Peayalite produced between the steel sheet and the scale is very close to the steel sheet and is not easily removed from the descaling apparatus, which is a subsequent process. It is a cause of surface defects.

Efforts have been made to suppress surface defects in the form of red scale, and among these studies, Japanese Patent Application Laid-open No. Hei 9-249914 and Japanese Patent Application Laid-open No. Hei 11-129015.

In Japanese Patent Laid-Open No. 9-249914, a method of heating the slab heating temperature in a heating furnace to 1173 ° C. or lower in which liquid phase feyalite is not produced is proposed. However, this method has a problem that the heating temperature is too low and the rolling load in the subsequent process is greatly increased, which makes it difficult to roll.

In Japanese Patent Laid-Open No. 11-129015, a method of greatly increasing the pressure of the descaling device is proposed. However, this method also has a problem in that the production cost is greatly increased because a new facility has to be installed and operated to increase the pressure of the tm kale removal device.

Therefore, the present invention is to solve such a problem, the object of the present invention is to adequately adjust the heating temperature of the slab furnace after the descaling devices before the rough rolling process to sufficiently remove the ferayite generated in the furnace In addition, the scale generated second in the rough rolling process is to provide a method for producing a high-carbon hot-rolled steel sheet having excellent red-scale surface quality by appropriately removing the side temperature of the finishing descaling apparatus.

In order to achieve the above object, the method for producing a high carbon hot rolled steel sheet according to the present invention is to produce a high carbon steel slab made of carbon content of 0.4 wt% or more, Si content of 0.1-0.5 wt%, balance of Fe, and other unavoidable impurities. Step; and

Heating the slab above a recrystallization temperature of the high carbon steel in a furnace; and

A first descaling step of removing scale from the heated slab by maintaining the temperature at the side of the slab formed on the surface of the slab at a temperature above the phase at which phase change of the phase into liquid phase;

A second descaling step of sizing the slab from which the scale is removed to at least a reduction ratio capable of peeling off the remaining felarite on the surface of the slab, and then peeling off the scale including the remaining felarite; Wow

Roughly rolling the slab from which the scale has been removed in a rough mill; and

A third descaling step of removing the scale including the secondary ferayalite by maintaining the temperature at the side of the roughly rolled bar at a temperature below the temperature at which the ferayalite generated in the rough rolling process is peeled off; And

Finishing rolling the scale bar in a finishing mill;

It provides a method of manufacturing a high carbon hot rolled steel sheet comprising a.

To this end, the present invention performs descaling by maintaining the inlet temperature of the first descaling at 1173 ° C. or higher in the first descaling step, and applying width reduction ratio to 5% or more in the sizing press, followed by width rolling. The descaling step is performed, and in the third descaling step, there is provided a manufacturing method of a high carbon hot rolled steel sheet which is descaled by setting the temperature of the third descaling step to 1000 ° C or less.

Hereinafter, a method of manufacturing a high carbon hot rolled steel sheet having excellent red scale surface quality of the present invention will be described in detail with reference to the accompanying drawings.

In order to explain the manufacturing method of the high carbon hot rolled steel sheet according to the present invention, first, the production equipment of the hot rolled steel sheet shown in FIG. 1 will be described.

In a steelmaking process such as a continuous casting process, a steel ingot manufactured in a slab state is charged into a heating furnace 1 and heated above the recrystallization temperature of the steel, and then a thick 1 attached to the slab surface in the descaling apparatus 1 (2). The secondary scale film is removed and lightly pressed in the width direction by the sizing press (3) to perform crack rolling while creating a crack on the scale on the slab, and the scale cracked on the surface of the slab once again in another descaling device (2). After the film is removed, the rough mill 5 is rolled to a predetermined thickness and width. And the roughly rolled bar removes the scale generated on the surface of the bar during rolling in the descaling apparatus 3 (6) before entering the finishing mill 7, and then rolls it to the required thickness in the finishing mill 7 It is wound in a coil state in the odor (not shown).

The present invention is characterized in that the slab heated in the heating furnace (1) by using such a hot rolling equipment is given a rolling condition for removing the feyalite in a subsequent process.

That is, the descaling apparatus 1 (2) is used to heat the high carbon steel slab containing 0.1-0.5 wt% of silicon (Si) to the normal temperature in the furnace 1 and then to sufficiently remove the felarite formed on the surface of the slab. The slab charged into the slab is kept at 1173 ° C. or more, which is the liquid formation temperature of the ferayarite. For this reason, the entrance temperature of the slab charged into the descaling apparatus 1 (2) is limited to 1173 ° C or more.

However, it is difficult to completely remove from the descaling apparatus 1 (2) because the feyalite generated in the furnace 1 can be produced non-uniformly on the slab surface.

Thus, the present invention adjusts the amount of deformation of the width rolling in the sizing press 3 to remove the waste night light that is not completely removed in the descaling apparatus 1 (2). That is, the amount of deformation in the sizing press 3 is applied at least 5% or more in order to peel off the remaining felarite which is not removed while passing through the descaling apparatus 1 (2).

Thus, while limiting the amount of reduction of the sizing press 3 to 5% or more, the Peayalite peeled off the sizing press is completely removed by the descaling apparatus 2 (4) provided in the roughing mill 5 entrance side.

However, according to the present invention in spite of the removal of the felarite over the second step in the rough rolling process newly thin solid and excellent adhesion can be produced in the solid phase.

Therefore, in the present invention, the secondary night light thus produced is removed from the mouth side of the finishing mill 7.

According to the basic research conducted to establish the rolling conditions proposed by the present invention, the lower the temperature of the entrance of the other descaling device 3 (6) installed at the entrance of the finishing mill 7, the better the peelability of the penayalite. appear. In particular, the peeling properties of the feyalite was found to be better than 1000 ℃. Therefore, in this invention, the entrance temperature of the finishing descaling apparatus 3 (6) provided in the entrance of the finishing mill 7 is set to 1000 degrees C or less.

Hereinafter, an embodiment of the present invention will be described.

Example 1

In the present Example 1, the influence of the side temperature of the descaling apparatus 1 (2) on the formation of a red scale defect was examined.

The steel subject to rolling used in the present Example 1 is a vacancy steel whose carbon content is 0.85 wt% and Si content is 0.2 wt%. The steel sheet to be rolled is heated to 1230 ° C. in a slab having a thickness of 250 mm and a width of 1000 mm, and then changed the entrance temperature of the descaling device 1 (2) at 10 ° C. intervals over 1160-1190 ° C. The scale produced in the furnace 1 was removed.

Then, the slab was subjected to a 100 mm width rolling amount in the sizing press 3, and then the scale cracked by the descaling apparatus 2 (4) was removed.

The slab descaled in this way is then rough-rolled in the roughing mill 5 to form a roughly rolling bar having a thickness of 35 mm, and thereafter, the descaling device 3 (6) of the descaling machine 7 installed at the inlet side of the finishing mill (7). The hot-rolled steel sheet having a thickness of 3.0 mm was manufactured by removing the scale generated during rough rolling at the entrance temperature at 990 ° C., followed by finishing rolling in the finishing mill 7.

The surface of the hot rolled steel sheet thus manufactured was observed to observe whether the red scale defect of the steel sheet manufactured was removed. Red scale defects were classified into five grades based on the following criteria.

Grade 1: Less than 5% of the area of red scale

Level 2: Red scale occurrence area less than 10%

Level 3: Red scale occurrence area 20% or less

Level 4: Red scale area less than 30%

Grade 5: Red scale area less than 40%

As such, the results of observing whether red scale defects were generated in the hot rolled steel sheet manufactured according to Example 1 are shown in Table 1 below. The experimental results shown in Table 1 show the effect of the entrance temperature of the descaling device 1 (2) on the formation of red scale defects, and in FIG. It is shown in a graph comparing the effect.

Example Entrance temperature of descaling device 1 (℃) Red scale defect grade of hot rolled steel Remarks Comparative Example 1 1160 4 - Comparative Example 2 1170 3 - Inventive Example 1 1180 2 - Inventive Example 2 1190 2 -

As shown in Table 1 and Figure 3 it can be seen that the red scale defect grade is lowered as the entrance temperature of the descaling apparatus 1 (2) is increased. This result shows that the surface of the slab charged in the descaling apparatus 1 (2) proposed in the present invention is maintained at 1173 ° C or higher, and the liquid phase penalite is separated and removed. It can be seen that quality can be obtained.

Example 2

In Example 2 of the present invention, the effect of the width rolling amount of the sizing press 3 on the formation of the red scale defect was examined.

The steel grade to be rolled was the same as that used in Example 1, and after heating the slab to 1230 ° C. in the heating furnace 1, the scale of the descaling device 1 (2) was adjusted to 1180 ° C., and then the sizing press 3 ), 0 to 100 mm of width rolling was carried out, and then the scale was removed using a descaling apparatus 2 (4), and rough rolling was performed to make a rough rolling bar having a thickness of 35 mm.

And then, the process was carried out in the same manner as in Example 1 to produce a hot rolled steel sheet having a thickness of 3.0mm.

The red scale observation results of the hot rolled steel sheet thus prepared are shown in Table 2 and FIG. 4.

The experimental results shown in Table 2 show the effect on the formation of red scale defects according to the reduction in the reduction ratio in the sizing press (3), and the red scale defect formation according to the reduction in the reduction ratio in the sizing press (3) in FIG. It is shown in a graph comparing the effect on.

Example Rolling amount of sizing press (mm) Rolling rate of sizing press (%) Red scale defect grade of hot rolled steel Remarks Comparative Example 3 0 0 4 - Comparative Example 4 30 3 3 - Inventive Example 3 60 6 2 - Inventive Example 4 100 10 2 -

As shown in Table 2 and Figure 4 it can be seen that as the sizing press reduction ratio is increased, the red scale defect formation grade is lowered. Therefore, it can be seen that at a reduction ratio of 5% or more of the sizing press proposed in the present invention, a defect grade of 2 can obtain very good surface quality.

Example 3

In Example 3 of this invention, the experiment result about the effect of the entrance temperature of the descaling apparatus 3 (6) in the entrance of the finishing mill 7 to the red scale defect is shown.

The steel sheet to be used in this embodiment is the same as the steel used in Example 1, and the scale is removed by heating the slab to 1230 ° C. in the furnace 1 and then adjusting the entrance temperature of the descaling device 1 (2) to 1180 ° C. Thereafter, a width of 100 mm was rolled in a sizing press, the scale was removed by the descaling apparatus 2 (4), and rough rolling was performed in the rough mill 5 to produce a rough rolled bar having a thickness of 35 mm.

Then, the rough-rolled bar was descaled at the entrance temperature of the descaling apparatus 3 (6) to 950-1050 ° C, and then subjected to finishing rolling in the finishing mill 7 to manufacture a hot rolled steel sheet having a thickness of 3.0 mm.

The observation results regarding the formation of red scale defects for the hot rolled steel sheets thus manufactured are shown in Table 3 and FIG. 5.

The experimental results shown in Table 3 show the effect of the entrance temperature of the descaling device 3 (6) on the formation of red scale defects. In FIG. It is shown in a graph comparing the effect.

Example Entry temperature of descaling device 3 (℃) Red scale defect grade of hot rolled steel Remarks Inventive Example 5 950 One - Inventive Example 6 970 2 - Inventive Example 7 990 2 - Comparative Example 5 1010 3 - Comparative Example 6 1030 3 - Comparative Example 7 1050 4 -

As shown in Table 1 and FIG. 3, it can be seen that as the entrance temperature of the descaling apparatus 3 (6) is lowered, the grade at which the red scale defect is formed decreases. Therefore, it can be seen that when the charging temperature of the descaling 3 proposed in the present invention is 1000 ° C. or lower, the defect grade is 2 and very good surface quality can be obtained.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and easily changed and equalized by those skilled in the art from the embodiments of the present invention. It includes all changes to the extent deemed acceptable.

The present invention provides suitable scale surface quality by appropriately controlling the entrance temperature of descaling device 1 to remove the generated ferayite on the surface of heated slab, the sizing press rolling amount and the entrance temperature of descaling device 3 at the finish rolling entrance. It is possible to manufacture an excellent hot rolled steel sheet has a significant contribution to improving the surface quality and workability of high carbon steel.

1 is a schematic diagram showing the layout of a hot rolling mill.

2 is a schematic diagram showing the structure of the scale generated on the surface of the slab in the furnace.

3 is a graph showing the effect of the entrance temperature of the descaling apparatus on the red scale defect.

4 is a graph showing the effect of the sizing press rolling rate on the red scale defect.

5 is a graph showing the effect of the entrance temperature of another descaling device on the red scale defect.

Claims (4)

 Preparing a high carbon steel slab comprising at least 0.4 wt% of carbon, 0.1 to 0.5 wt% of Si, and a balance of Fe and other unavoidable impurities; and Heating the slab above a recrystallization temperature of the high carbon steel in a furnace; and A first descaling step of removing scale from the heated slab by maintaining the temperature at the side of the slab formed on the surface of the slab at a temperature above the phase at which phase change of the phase into liquid phase; A second descaling step of sizing the slab from which the scale is removed to at least a reduction ratio capable of peeling off the remaining felarite on the surface of the slab, and then peeling off the scale including the remaining felarite; Wow Roughly rolling the slab from which the scale has been removed in a rough mill; and A third descaling step of removing the scale including the secondary ferayalite by maintaining the temperature at the side of the roughly rolled bar at a temperature below the temperature at which the ferayalite generated in the rough rolling process is peeled off; And Finishing rolling the scale bar in a finishing mill; Manufacturing method of high carbon hot rolled steel sheet having excellent red-scale surface quality comprising a.  The high-carbon hot rolled steel sheet having excellent red scale surface quality according to claim 1, wherein in the first descaling step, descaling is performed by maintaining the entrance temperature of the first descaling at 1173 ° C or higher. Manufacturing method.  3. The method of manufacturing a high carbon hot rolled steel sheet having excellent red scale surface quality according to claim 2, wherein the reduction ratio of the width reduction is 5% or more in the sizing press.  4. The red scale surface quality according to any one of claims 1 to 3, wherein in the third descaling step, descaling is performed at an entrance temperature of the third descaling step to 1000 ° C or less. Method for producing this excellent high carbon hot rolled steel sheet.