JPS6326203A - Method for decreasing surface defect at end in direct hot rolling of metallic piece to be rolled - Google Patents

Abstract

PURPOSE:To decrease the surface defects of a product steel sheet by heating the surface part of a rolled metallic piece until the temp. difference between the temp. in the central thickness part at the longitudinal end of said piece and the temp. in the surface part attains a prescribed temp. and rolling said piece. CONSTITUTION:The surface part at the end of the rolled metallic piece 2 is subjected to a heating treatment for a short period by a high-frequency induction heater 5 or gas burner heater 6 at the time of conveying the rolled metallic piece 2 by a roller table 2 toward an arrow 3 and feeding the same to a roughing mill 4 side. The temp. in the surface part 7 of the rolled metallic piece 2 at the time of rough rolling is kept at the temp. lower by about 50 deg.C than the temp. in the central part 8. The extension in the central part at the end is, therefore, largely suppressed by the increase of the temp. in the surface part, by which the surface defects are decreased.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides for rolling metal pieces such as high-temperature steel pieces rolled in a bloomer or high-temperature slabs cast in a continuous casting machine in a conventional manner. The present invention relates to the provision of a new means for reducing defects generated on the end surface of a rolled metal piece at both ends in the longitudinal direction when directly hot rolling is performed without heat treatment in a heating furnace.

(Prior art) To obtain rolled steel plates, high-temperature steel slabs rolled in a bloomer or high-temperature slabs cast in a continuous casting machine are directly hot-cast as they are, omitting the reheating process in a heating furnace. Needless to exemplify the hot direct rolling method, it is a well-known technology that has been widely used recently, and has a great advantage as a means that can significantly save energy, equipment, and production time. .

(Problems to be Solved by the Invention) The above-described hot direct rolling method has the following problems. In other words, during the period between being rolled as a bloomer, cutting to size, and rough rolling, which is the first stage of the rolling process, or after being cast in a continuous casting device, and before cutting and rough rolling, The drop in surface temperature of a rolled metal piece is large, especially the temperature difference between the center in the thickness direction and the surface at both front and rear ends of the rolled metal piece in the longitudinal direction. This is significantly larger than in the case of wood. For this reason, in the case of a blooming billet, the cross section of the billet may exhibit a rough fracture surface or warp may occur at the corner of the billet cross section when the billet is sheared, and in the case of a continuously cast billet, the billet If the gas slag from the primary gas cutting remains in the corner portions and is subjected to direct hot rolling in such a state, harmful defects will remain on the surface portions of the ends of the steel sheet. Depending on the shape of the steel plate end, defects that occur on the surface of the steel plate end may not be cut off as crops and may remain in the main body. This causes a decrease in yield. Conventionally, countermeasures have been taken to deal with this situation, such as strengthening the shape management of the shear blade for sizing cutting, and strengthening the management of the secondary gas cutting slag removal device, but none of these measures are fundamental. At present, no solution has been reached.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention applies a temperature compensation means by local heating to the ends in the longitudinal direction of a rolled metal piece, so that the inside and outside of the ends are It is designed to reduce the temperature difference, and specifically, when rolling a metal piece to be rolled by hot direct rolling means, at the longitudinal end of the metal piece to be rolled, the central part in the thickness direction The temperature difference between the temperature and the temperature of the surface in the same thickness direction is approximately 5
The surface portion is heated until the temperature drops to 0° C. or lower, and then subjected to rolling.

(Function) According to the above-mentioned technical means of the present invention, as shown in FIG.
(21 and as shown in FIGS. 2(1) and 2), the rolled metal piece 2 is transported by a conveying means such as a roller table 1,
When conveying in the direction of arrow 3 and sending it to the rough rolling mill 4 side which is the first stage of rolling forming, the end of the rolled metal piece 2 is
Figure 1 +11 (In the case of 21, the high frequency induction heating device 5 is used, and in the case of Figure 2 (1), the end surface is heated for a short time using the gas burner heating device 6. Effect can be obtained.

That is, in FIG. 3 (11, (2)), the example shows the case of a bloomed steel piece, but in FIG. 3 (1), which shows details of the longitudinal end of the rolled metal piece 2, 7 indicates a surface portion in the length direction l3 width direction 'yAW from the end of the rolled metal piece 2, and a portion 8 similarly extends in the length direction 1 from the end.
1. In the graph diagram showing the center part in the width direction (W) and the thickness direction (V2t), and also showing FIG. 3 (2), the vertical axis is the temperature;
The horizontal axis shows time, and the curve a in the same graph
is the surface temperature of the rolled metal piece 2 at the portion 7 shown in FIG. It shows the transition over rough rolling, and the curve is shown in Figure 3 (1).
This figure shows the change in the temperature at the center of the rolled metal piece 2 at the location 8 shown in Fig. 2 from the time of completion of casting in ingot making to charging into the scorching furnace, blooming rolling, and rough rolling. curve a
, b is the temperature transition in the conventional hot rolling method. That is, as is clear from both figures, during rough rolling, the temperature at the back surface portion 7 of the metal piece 2 to be rolled is 140° to 160° C. or more lower than the temperature at the center portion 8 of the metal piece 2. It becomes. Therefore, during rough rolling, the center extension of the end of the rolled metal piece 2 becomes larger than the surface extension of the end, and the end cross-section 9 of the metal piece 2 becomes larger.
A portion 10 of the end cross-sectional corner of the metal piece 2 remains as a harmful defect on the surface of the steel sheet after rough rolling. On the other hand, the curve C shown in FIG. 3(2) shows the back surface of the rolled metal piece 2 after the end surface portion has been heated by the heating device 5.6 previously explained in FIGS. 1 and 2. By heating the end surface portion according to the present invention, the temperature at the back surface portion 7 of the rolled metal piece 2 during rough rolling is lower than that of the rolled metal piece 2. The temperature at the central region 8 is reduced to 40° to 60°C lower, and the curve a shown earlier is
Compared to this, by increasing the surface temperature, the extension of the center of the end portion of the rolled metal piece 2 can be greatly suppressed, making it possible to reduce surface defects.

(Example) A suitable example of the method of the present invention will be explained with reference to Fig. 1 (1) (2) to Fig. 4 (11, (2). Fig. 1 + 1).
(21, In Fig. 2 (11F2), the rolled metal piece 2
As a heating device for locally heating the end surface of the front end or rear end in the longitudinal direction, Fig. 1 (1) +21 indicates a high frequency induction heating device 5, and Fig. 2 (1) (2) shows a gas burner heating device. Although device 6 is shown, there are not only two types of heating devices; any device that can perform effective heating in a short period of time can be freely adopted. It is standard that the temperature at the center is about 50°C lower than the temperature at the center. Further, the details of the hot direct rolling performed in the present invention, omitting the reheating step, are the same as those of the conventional method, and therefore, in the embodiment, components other than the rough rolling mill 4 are omitted. In short, just before starting direct hot rolling, the longitudinal end (front end or rear end) of the metal piece 2 to be rolled may be heat treated. Fourth
Figures (1) and (2) show the relationship between the temperature difference between the center of the end and the surface and the defects that occur, that is, to be more precise, they show the center part 8 of the metal piece 2 to be formed before rough rolling. and the temperature of the back surface portion 7 of the rolled metal piece 2, and the distance I! from the end of the steel plate 11 of the defect occurring on the surface of the steel plate 11. In the graph shown in FIG. 4 (2), the vertical axis indicates the defect occurrence position 12, and the horizontal axis indicates the center temperature - back surface temperature (temperature difference). d in the same graph is the curve a previously explained in Figure 3 (2).
Indicates the defect occurrence position in the case of (prior art), and e is
It shows the position of defect occurrence in the case of curve C according to the method of the present invention.

As is clear from the comparison of this figure, by the method of the present invention,
As the temperature difference between the center part 8 and the back part 7 of the rolled metal piece 2 decreases from the conventional 140° to 160°C to 40° to 60°C, the surface defect occurrence position of the steel plate 11 (product) is reduced. It has been confirmed that the amount decreases to less than %.

(Effects of the Invention) According to the present invention, surface defects observed at the longitudinal ends of a rolled metal piece that occur in the conventional hot direct rolling method can be eliminated by employing a temperature compensation means of local heating of the ends. It is excellent in that it can be reduced reliably and significantly. That is, as evidenced in the examples, by reducing the temperature difference between the center temperature and the back surface temperature at the end of the rolled metal piece 2 from 140° to 160°C to 40° to 60°C, The position of surface defects in the product steel sheet is reduced to below the conventional A, which naturally improves the product yield of the steel sheet, and is effective and effective as a solution to the problems in the hot direct rolling method. It has high utility value. It should be noted that the method of the present invention is sufficiently effective for metal materials other than the steel sheets used in the examples.

[Brief explanation of drawings]

Fig. 1 (1) (21, Fig. 2 + 1) (2) are both plane and front views of the embodiment of the method of the present invention, Fig. 3 (11,
(2) is an explanatory diagram of the temperature transition by location at the end of a bloomed steel slab, and Figures 4 (1) and (2) are the temperature difference between the center and surface of the rolled metal slab and the occurrence of defects on the steel plate surface. It is an explanatory diagram of the relationship with position. 1--roller table, 2--rolled metal piece, 4--rough rolling mill, 5--high frequency induction heating device, 6--gas burner heating device, 7--back surface portion, 8--center portion.

Claims (1)

[Claims] (1) When rolling a rolled metal piece by hot direct rolling means, at the longitudinal end of the rolled metal piece, the temperature at the center in the thickness direction and the temperature at the surface area in the same thickness direction 1. A method for reducing edge surface defects in hot direct rolling of a rolled metal piece, the method comprising heating the surface until the temperature difference between the two is approximately 50° C. or less, and then subjecting the same surface to rolling.