JP3127278B2 - Manufacturing method of controlled cooling steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a controlled cooling steel material in hot rolling, which reduces the temperature deviation in the steel material at the end of cooling of the steel material to be cooled, makes the shape and the material of the steel material uniform, and reduces the deviation. And camber reduction.

[0002]

2. Description of the Related Art Conventionally, when a steel material manufactured by a continuous casting facility is transported to a heating furnace after passing through the end of the continuous casting facility, there is no descaling process, and the hot rolling line And a descaling step for removing scale due to atmospheric oxidation of the steel material being rolled in the heating furnace in the heating furnace up to the hot rolling mill.

[0003] Unless the above-mentioned scale is completely removed and rolled, the scale is pushed into the surface of the steel material during rolling and causes scale flaws on the product, or the residual scale unevenness on the surface reduces the surface effect of the cooling surface during cooling. A difference occurs and a temperature deviation occurs in the steel material. If a temperature deviation occurs in the steel material, there arises a problem that the shape (flatness, warpage, etc.) is deteriorated, or residual stress is accumulated inside the steel material, which leads to warpage and camber after cutting (Japanese Patent Laid-Open No. 2-1217).
No. 14).

[0004] In order to solve these problems, conventional techniques for controlling the heat pattern in the furnace, such as restricting the surface temperature of the steel material in the heating furnace to a high level when descaling the steel material, and descaling from the furnace extraction. There is one that regulates the elapsed time until the time is reached (Japanese Patent Publication No. 62-39044). In order to enhance the capacity of the descaling device installed after the heating furnace, low-pressure spray and high-pressure spray are installed stepwise, and the scale is levitated in the low-pressure spray zone and the scale pieces levitated in the high-pressure spray zone are scattered. (Japanese Unexamined Patent Publication No. 48-38242) and a means for removing the surface scale of steel using high-pressure water mixed with a predetermined amount of grinding powder (Japanese Unexamined Patent Publication No. 5-57332).
Has been implemented.

[0005]

The change in the furnace operating conditions of the heating furnace involves problems such as deterioration of materials, deterioration of rolling schedule and fuel consumption rate, and a problem that a large change in furnace operation cannot be performed. . In addition, in the capacity enhancement of the descaling device after the heating furnace, Si, Ni, Cu, Mo
It is very difficult to peel off the scale (Fig. 5) in which alloy elements such as are selectively oxidized in the heating furnace, and high pressure water descaling mixed with grinding powder causes abrasion of the nozzle and short life The conventional measures are not the most effective.

Further, the scale is generated not only in the heating furnace and the subsequent hot rolling process but also in the stage of casting in a continuous casting facility. There is also a problem that the influence of is excluded.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and the gist of the invention is to load a billet manufactured by a continuous casting facility into a billet heating furnace. Prior to the process, the scale of the steel slab is removed by a shot blasting device or a grinder device.

[0008]

The result of the test will be described below. The surface of a slab cast by a continuous casting facility is sampled, and after as-cast (AS), grinder (GR), shot blast (SB), and hot scarf (HS) -treated materials are heated under the same conditions, It was cooled to room temperature in an oxidizing atmosphere. As the material, a steel type excellent in fire resistance containing Mo: 0.5 wt% or more and two steel types of a thick plate 40K steel class were used. The heating was carried out in an electric furnace whose atmosphere was adjusted with a gas obtained by burning coke oven gas at an air ratio of 1.00, for a heating time of 3 hours and a heating temperature of 1200 ° C.

FIG. 6 shows the results. The amount of scale produced is changed from AS → HS → SB by changing the surface properties of the slab before heating.
→ It turns out that it becomes thin in the order of GR. In addition, the selectively oxidized region, which greatly affects the releasability of the scale, is also changed from AS → HS → SB → G
It can be seen that the layers become thinner in the order of R and the scale releasability improves (FIG. 7). In other words, the scale generated during casting on the slab surface before heating affects the scale generated during reheating, and by completely removing the scale during casting,
The scale thickness after heating and the selectively oxidized region that is difficult to peel due to high-pressure water descaling generated in steel containing Si, Ni, Cu, Mo, etc. can be reduced, the peelability of the scale can be improved, and the residual unevenness of the steel material scale can be reduced. Further, it is known that there is a strong correlation between the remaining scale and the steel material temperature as shown in FIG. 8, and that the temperature after controlled cooling tends to be lower in a portion where there is much scale remaining. Therefore, by removing the scale generated at the time of casting, the scale removability in the rolling step can be improved, unevenness of the scale remaining can be eliminated, and the temperature variation generated at the time of controlled cooling can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the present invention is applied to a plate mill will be described below. As shown in FIG. 1, before the steel material 12 manufactured in the continuous casting facility 1 was reheated in the heating furnace 3, the scale of the steel material 12 generated after the continuous casting was completely removed by the slab shot blasting device 10. Thereafter, the steel material 12 was charged into the heating furnace 3, heated, rolled, and controlled and cooled. In the figure, 2 is the end of a continuous casting apparatus, 5 and 6 are hot rolling apparatuses, 7, 8, and 9 are high-pressure descaling apparatuses, 1
1 is a control cooling device. Examination of the slab surface state after reheating confirmed that the selective oxidation region was reduced. Further, as cooling conditions, controlled cooling was started at 780 to 830 ° C. and stopped at 400 to 500 ° C., and the effect was evaluated for a material having a rolled size of 60 mm × 2255 mm × 14000 mm. As a result, the temperature deviation during cooling of the controlled cooling steel sheet is reduced due to the reduction of the scale remaining unevenness due to the reduction of the scale biting, and the shape defect (warpage re-correction rate, strip camber) caused by cooling is reduced.
It was improved as shown in

Further, the scale flaw repair rate due to the scale biting can be reduced as shown in FIG.

[0012]

As described above, according to the present invention, it is possible to manufacture a steel material which is excellent in shape and has little residual stress, in which the residual unevenness of the scale on the surface is reduced, the temperature deviation at the time of controlled cooling due to the surface effect can be reduced. Can be. In addition, since scale entrapment in the rolling step can be reduced, scale flaws on the steel material surface can also be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a step of transporting a steel material according to the present invention.

FIG. 2 is a diagram showing a change in a re-correction rate before and after implementation of the present invention.

FIG. 3 is a diagram showing a transition of a strip camber amount before and after implementation of the present invention.

FIG. 4 is a diagram showing changes in the scale flaw repair rate before and after the present invention is implemented.

FIG. 5 is a schematic sectional view showing a structure of a scale layer.

FIG. 6 is a view showing the influence of surface properties before heating on a scale layer.

FIG. 7 is a view showing the influence of surface properties before heating on the depth of a selective oxidation zone.

FIG. 8 is a view showing a relationship between scale remaining and steel material temperature.

[Description of Signs] 1 Continuous casting device 2 Machine end of continuous casting device 3 Heating furnace 5, 6 Hot rolling device 7, 8, 9 High-pressure water descaling device 10 Shot blasting device 11 Control cooling device 12 Steel material

Continuation of the front page (72) Inventor Hiroshi Akase 1 Kimitsu, Kimitsu City, Chiba Pref. Nippon Steel Corporation Kimitsu Works (56) References JP-A-2-121714 (JP, A) JP-A-1- 138013 (JP, A) JP-A-61-222611 (JP, A) JP-A-61-219448 (JP, A) JP-A-57-193222 (JP, A) JP-A-48-38242 (JP, A) JP-A-5-57332 (JP, A) JP-A-6-304639 (JP, A) JP-A-4-266416 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 45/06 B21B 1/46 B21B 13/22 B22D 11/12

Claims (1)

(57) [Claims] 1. A controlled cooling steel material, wherein a scale of a slab is removed by a shot blast device or a grinder device before charging a slab manufactured by a continuous casting facility into a slab heating furnace. Production method.