KR102360716B1 - Method of reducing scale of thick plate - Google Patents

Abstract

In the method for reducing the scale of a heavy plate by performing descaling by water spray while manufacturing a thick plate by rolling a slab, the rolling end temperature of the thick plate is controlled to 950 ° C or less, and the number of times of the descaling is increased to 5 times. The scale reduction method of the thick plate, characterized in that the following and the final pass of the descaling is completed before the (end pass - 1) pass, the surface scale thickness of the thick plate is controlled to a thin thickness of about 20 to 30 um can do.

Description

Method of reducing scale of thick plate

The present invention relates to a method for reducing the scale of a thick plate, and more particularly, a method for reducing the scale of a thick plate that can control the thickness of scale formed on the surface of a thick plate by optimizing a descaling pattern in a thick plate rolling process, and manufacturing of a thick plate accordingly It relates to a method and a plate manufactured therewith.

A thick plate, which generally refers to a thick steel plate having a thickness of 6 mm or more, is used in ships, bridges, construction machines, industrial machines, and the like.

Usually, in order to manufacture a heavy plate, molten iron is first made in the ironmaking process, the molten iron is refined in the steelmaking process, and it is poured into a mold and cooled and solidified while passing through a continuous casting machine, thereby producing a slab, an intermediate material. create

And in the heavy plate process, these slabs are heated in a heating furnace to make them hot, then transferred to a rolling mill to perform rolling to the thickness desired by the consumer, and the rolled blade is cut to the ordered width and length to manufacture the final plate product. At this time, in the thick plate process, the slab can be rolled in several stages to the plate thickness desired by the consumer by using a reversible rolling mill.

As such, scale occurs on the surface of the slab when the slab is heated in a heating furnace to manufacture the thick plate, or scale occurs on the surface of the thick plate as the slab discharged from the heating furnace is exposed to the atmosphere while being transferred to the rolling mill.

In order to remove the scale formed on the surface of the thick plate as described above, descaling is performed using a scale removal device. In general, descaling sprays a high-pressure fluid on the surface of the thick plate and peels and removes the scale formed on the surface of the thick plate by the impact force. do.

On the other hand, the surface beauty of the thick plate used as the outer plate of construction machines is important. When processing using a press or a jig to process the thick plate into a desired product shape, the scale on the surface of the plate is peeled off and the product is The problem of press-fitting on the surface often occurs. In order to prevent this, a customer using a thick plate requires a thick plate with a thin scale thickness of 20um or less from the plate manufacturer, but in general, a thick plate that has undergone hot rolling has a scale thickness of 50um or more. Therefore, in order to manufacture a thick plate that satisfies the needs of a customer, a rolling process capable of controlling the thickness of the scale on the surface of the thick plate is required, not the conventional rolling based on the thickness of the thick plate.

An object of the present invention is to provide a method for controlling the thickness of a scale formed on the surface of a thick plate in a plate rolling process to a set value or less.

Another object of the present invention is to reduce the thickness of the scale formed on the surface of the thick plate to prevent the scale peeled off from the surface of the plate from being pressed into the surface of the product.

In one embodiment of the present invention, in a method for reducing the scale of a thick plate in which descaling is performed by water spray while manufacturing a thick plate by rolling a slab, the rolling end temperature of the thick plate is controlled to 950 ° C or less, It provides a method for reducing the scale of a thick plate, characterized in that the number of times of descaling is set to 5 or less, and the final pass of the descaling is completed before the (end pass - 1) pass.

Another embodiment of the present invention is a method for manufacturing a thick plate of manufacturing a thick plate by rolling a slab while performing descaling to reduce scale, wherein the descaling is performed according to the above-described method for reducing scale of a thick plate It provides a method for manufacturing a thick plate.

Another embodiment of the present invention provides a thick plate manufactured according to the method for manufacturing a thick plate described above.

The details of other implementations are included in the detailed description below.

As described above, in the method for reducing the scale of a thick plate according to the present invention, the thickness of the scale on the surface of the thick plate can be controlled to a thin thickness of about 20 to 30 μm.

1 is a microstructure photograph showing scales formed on thick plates manufactured according to an experimental example of the present invention.
2 is a photograph showing a process of manufacturing a thick plate according to an experimental example of the present invention and cracks formed on the surface of the thick plate.
3(a), 3(b), and 3(c) are photographs showing the surfaces of thick plates manufactured according to an experimental example of the present invention.
4 is a graph showing the result of measuring the scale thickness according to the rolling end temperature, the blade thickness, and the number of descaling according to the experimental example of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

In the method for reducing the scale of a thick plate according to an embodiment of the present invention, in the method for reducing the scale of a thick plate by performing descaling by water spray while manufacturing a thick plate by rolling a slab, the rolling end temperature of the thick plate is 950 ° C or less, the number of times of the descaling is set to 5 or less, and the final pass of the descaling is completed before the (end pass - 1) pass.

In the method for manufacturing a thick plate according to another embodiment of the present invention, in the method for manufacturing a thick plate by rolling a slab while performing descaling to reduce scale, the method for manufacturing a thick plate is the method for reducing the scale of the thick plate, wherein the descaling is described above. It is characterized in that it is carried out according to

According to another embodiment of the present invention, there is provided a heavy plate manufactured according to the above-described method for manufacturing a thick plate.

It is preferable to control the rolling end temperature of the thick plate to 920 °C or less, and it is more preferable to control it to 900 °C or less.

It is preferable that the descaling after performing the descaling twice is performed by rolling rear spraying. .

It is preferable to set the number of descaling to 4, and in this case, when a total of 8 descalable passes, it is preferable to perform the descaling in 1, 2, 5, 6 passes.

In addition, it is more preferable to set the number of descaling to 5. In this case, when the total number of descalable passes is 8, it is more preferable to perform the descaling in 1, 2, 4, 5, 6 passes. do.

In addition, if the rolling end temperature of the thick plate is controlled to 920°C or less, the number of descaling is 4, and the number of descaling passes is 8 in total, the descaling passes are 1, 2, 5, 6 It is preferable to carry out the pass.

And when the rolling end temperature of the thick plate is controlled to 900°C or less, the number of descaling is 5 times, and the number of descaling passes is a total of 8 passes, 1, 2, 4, 5 passes of the descaling , it is more preferable to carry out in 6 passes.

Hereinafter, the present invention will be described in more detail through experimental examples.

[Experimental example]

(1st Experiment: Analysis of Factors Affecting Scale Thickness)

In order to analyze the factors affecting the thickness of the scale occurring on the surface of the thick plate while manufacturing the thick plate by rolling the slab, the plate was processed and descaling under the conditions according to the experimental examples in [Table 1] below. The microstructure photograph showing the scale and the thickness formed on the thick plates prepared according to the experimental example of [Table 1] is shown in FIG. 1 . The thickness of the scale was measured based on the microstructure photograph of FIG. 1 , and the results are also shown in [Table 1]. At this time, the thickness of the scale was described by measuring the thickness of two points on a continuous scale identified in the photograph of FIG. 1 , and averaging them. However, in Experimental Examples 4, 9, and 10 in which the thickness at some thickness measurement positions greatly deviated from the average, only one thickness at an appropriate position was selected as the scale thickness.

[Table 1]

[Evaluation of influence of rolling end temperature]

As can be seen from [Table 1], it can be seen that the difference in the scale thickness between Experimental Example 1 and Experimental Example 2, in which the rolling end temperature difference is less than 20 °C, and the scale thickness difference between Experimental Example 4 and Experimental Example 6 are not large. When the rolling end temperature difference is within 20 °C, it can be seen that the effect of the rolling end temperature on the scale thickness is not large.

However, in the case of Experimental Example 4 and Experimental Example 7, in which the rolling end temperature difference exceeds 20 °C, the difference in the thickness of the scale was large. Therefore, when the rolling end temperature exceeds 20 °C, it can be confirmed that the scale thickness is reduced under the condition that the rolling end temperature is low.

[Evaluation of the effect of the number of descaling]

As can be seen from [Table 1], the scale thickness difference between Experimental Example 2 and Experimental Example 3 with different descaling injection times, the scale thickness difference between Experimental Example 4 and Experimental Example 6, and Experimental Example 7 and Experimental Example 8 There was a large difference in scale thickness. Therefore, it can be seen that the thickness of the scale decreases as the number of descaling increases.

[Evaluate the impact of the descaling pass]

As confirmed in the evaluation of the effect of the number of descaling, the thickness of the scale decreases as the number of descaling increases, but Experimental Example 10 of [Table 1] has one more number of descaling times than Experimental Example 11, but the scale thickness was thicker, and in Experimental Example 11, although the number of descaling sprays was 3, the thickness of the scale was the thinnest. This is judged to be the effect of performing the final pass of the descaling injection in the last pass of descaling. Accordingly, it can be confirmed that the descaling pass is a factor affecting the thickness of the scale.

(2nd experiment: analysis of descaling pattern to optimize scale thickness)

In order to analyze the descaling pattern capable of optimizing the scale thickness, while changing the rolling end temperature, the number of descaling, and the descaling pass, which were identified as factors affecting the scale thickness according to the analysis results in [Table 1], As in the following [Table 2], descaling was performed under 4 different descaling patterns in 4 groups with a total of 4x4 conditions, that is, with different thicknesses, and the thickness of the final surface scale was measured, and the result is also shown in the following [Table 2] 2]. In addition, in the case of 24,85mm of blade thickness, the number of descaling injections was 4 times, the descaling passes were 1,2,6,7 passes, and the experiment in which the final pass was 7 passes was added as Experimental Example 1-5, The results are also shown in [Table 2].

[Table 2]

[Evaluation of the effect of the number of descaling]

Experimental Examples 3 and 4 of the experiments for each thickness in [Table 2] with different descaling times, that is, Experimental Examples 1-3 and 1-4, In Experimental Example 2-3 and Experimental Example 2-4, Experimental Example 3-3 and Experimental Example 3-4, Experimental Example 4-3 and Experimental Example 4-4, the difference in the thickness of the scale was confirmed to be about 2-5 μm. Therefore, as confirmed in the first experiment of [Table 1], it was confirmed that the thickness of the surface scale was reduced as the number of descaling increased in the second experiment of [Table 2].

However, if the number of descaling is increased, cracks are generated in the center of the blade width at the line/tail end of the blade during rolling. 2 is a photograph showing the process of manufacturing the thick plate and cracks formed on the surface of the thick plate manufactured in this way. Such cracks occur when the surface layer part is cooled by descaling spray, the blade line/tail part is intensively cooled and local cooling occurs, the ductility decreases in the corresponding part, and the surface layer part bursts during rolling, and this crack It is a phenomenon that remains on the surface even after this rolling is completed.

Therefore, in order to prevent the formation of cracks in the blade width, it is preferable to set the number of descaling not to exceed 4, and more preferably, the descaling spray added after 1 and 2 passes is not the rolling front spray. , it is desirable to set it based on the rear injection.

[Evaluate the impact of the descaling pass]

Experimental Example 2 and Experimental Example 3 of each thickness experiment, that is, Experimental Example 1-2 and Experimental Example 1-3, Experimental Example 2-2 and Experimental Example 2-3, Experimental Example 3-2 and Experimental Example 3-3, In Experimental Example 4-2 and Experimental Example 4-3, the number of descaling was applied equally 4 times, and only the descaling path was set differently to perform descaling, and thus the thickness of the scale formed on the surface of the manufactured heavy plate was measured. Thus, the results are described in [Table 2].

As can be seen in [Table 2], in Experimental Example 3 for each thickness in which the descaling pass was performed in 1,2,4,6 passes, each thickness in which the descaling spraying pass was performed in 1,2,3,4 passes Compared to Experimental Example 2, the thickness of the scale was formed to be about 5 to 8 μm thinner.

However, looking at the results of measuring the thickness of the scales formed in Experimental Example 1-5 in which descaling was performed 4 times and in Experimental Example 1-4 in which descaling was performed 6 times, Experimental Example 1-5 having a smaller number of descaling was performed Compared to Experimental Examples 1-5 in which the number of scaling is more, the scale thickness was small. This is judged because Experimental Example 1-5 performed the final pass at a further rear end compared to Experimental Example 1-4.

On the other hand, FIG. 3(a) is a photograph showing the surface of a thick plate manufactured by performing descaling twice using the descaling pass as 1 and 2 passes according to Experimental Example 1-1, and FIG. 3(b) ) is a photograph showing the surface of a thick plate manufactured by descaling four times using the descaling pass as 1,2,4,6 passes according to Experimental Example 1-3, and FIG. 3(c) is It is a photograph showing the surface of the thick plate manufactured by descaling 4 times using the descaling passes as 1,2,6,7 passes according to Experimental Example 1-5. As can be seen from these photos, the surface shown in Fig. 3 (a) has excellent appearance, but the surface shown in Figs. 3 (b) and 3 (c) has a stripe-shaped tiger mark (Tiger Mark). ) is formed. This is considered to have occurred by performing the final pass of descaling as a pass close to the end pass. In order to suppress the occurrence of the tiger mark on the surface of the thick plate as described above, it is preferable to terminate the descaling spray pattern in the previous pass except for the last pass as the final pass among the descalable passes when setting the descaling pattern. More preferably, if the descalable pass is 8 passes, it is desirable to complete it before 6 passes.

[Evaluation of influence of rolling end temperature]

Looking at the scale thickness of the experimental examples according to [Table 2], even if the number of descaling is increased up to 6 times and the final pass of descaling is performed in 6 passes, when the rolling end temperature exceeds 920 °C It can be seen that it is difficult to control the thickness of the scale below 24um. Accordingly, in order to control the scale thickness to 20 μm or less, as in Experimental Example 4, as in Experimental Example 4, as a result of descaling by lowering the rolling end temperature by 50 °C, a thick plate having a scale thickness close to 20um in Experimental Example 4-4 can be manufactured. there was.

Based on the blade thickness of [Table 2], the thickness of the scale according to the rolling end temperature and the number of descaling is summarized as shown in the graph of FIG. In addition, based on the above experimental examples, in order to control the scale thickness on the surface of the thick plate to a desired thickness in manufacturing the thick plate by rolling the slab, the preferred rolling end temperature and descaling pattern are summarized below [Table 3] same as

[Table 3]

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (13)

In the method of reducing the scale of a heavy plate by performing descaling by water spraying while manufacturing a thick plate by rolling a slab,
Controlling the rolling end temperature of the thick plate to 950 ° C or less, setting the number of times of descaling to 5 or less, and completing the final pass of the descaling before the (end pass - 1) pass A method of reducing the scale of a heavy plate. According to claim 1,
A method for reducing the scale of a thick plate by controlling the rolling end temperature of the plate to 920°C or less. According to claim 1,
A method of reducing the scale of a thick plate by controlling the rolling end temperature of the plate to 900°C or less. According to claim 1,
The descaling after performing the descaling twice is a method of reducing the scale of a thick plate by performing rolling rear spraying. 5. The method of claim 4,
When the descaling is performed twice, the scale reduction method of the thick plate is performed in 1 and 2 passes of the descaling. According to claim 1,
A method for reducing the scale of a heavy plate in which the number of times of the descaling is 4 times. 7. The method of claim 6,
A method of reducing the scale of a thick plate in which the descaling passes are 1, 2, 5, 6 passes when a total of 8 descalable passes. According to claim 1,
A method for reducing the scale of a heavy plate in which the number of times of the descaling is 5 times. 9. The method of claim 8,
A method for reducing the scale of a thick plate in which the descaling passes are 1, 2, 4, 5, 6 passes when a total of 8 descalable passes. According to claim 1,
If the rolling end temperature of the thick plate is controlled to 920°C or less, the number of descaling is 4, and the number of descaling passes is 8 passes, the descaling passes are 1, 2, 5, 6 passes. A method of reducing the scale of heavy plates carried out with According to claim 1,
When the rolling end temperature of the thick plate is controlled to 900°C or less, the number of descaling is set to 5, and the number of descaling passes is a total of 8 passes, the descaling passes are set to 1, 2, 4, 5, A method of reducing the scale of a heavy plate in 6 passes. In the method for manufacturing a thick plate by rolling a slab while performing descaling to reduce scale, the descaling is performed according to the method for reducing the scale of a thick plate according to any one of claims 1 to 11. A method for manufacturing a thick plate. A heavy plate manufactured according to the method for manufacturing a thick plate of claim 12.

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