JPS58192607A - Rolling method of thick steel plate - Google Patents

Abstract

PURPOSE:To prevent the generation of seam flaw and the decrease in rolling efficiency by performing tapered rolling and rolling to a uniform thickness for broadside rolling of a thick steel plate then performing finish rolling in the longituidnal direction. CONSTITUTION:The rolling reduction of a roll 2' in the stage of bitting is decreased and a rolled material 3 of a tapered shape is rolled by increasing the rolling reduction successively during rolling in the 1st pass in broadside rolling of a thick steel plate. The gap of the rolls 2, 2' in the 2nd pass is kept intact, and the thin wall side is made bitting side. The rolling reduction in the stage of bitting is decreased and a rolled material 4 having a uniform thickness is rolled by increasing the rolling reduction successively. The prescribed broadside rolling is accomplished by repeatin the rolling stages for tapered rolling and rolling to a uniform thickness >=1 times alternately. The rolled material is rotated 90 deg. and is subjected to ordinary finish rolling in the longitudinal direction. The generation of seam flaw is prevented by the above-mentioned method without decreasing rolling efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rolling method for preventing seam defects that occur during rolling of thick steel plates.

There have been remarkable improvements in rolling technology for optimally thick steel plates.
The planar shape of the rolled material after hot rolling has come to be rolled into a shape close to the finished product dimensions. In other words, the rolling method uses an edger to control the planar shape of the rolled material, and the rolling method uses an edger to control the planar shape of the rolled material. A method for controlling the planar shape of the plane has been implemented.

As described above, when the rolled material after hot rolling approaches the finished product size, the cropping allowance becomes smaller and the rolling yield improves, but seam flaws occurring at the periphery of the rolled material, particularly on both sides, have become a problem.

-U/-Multiple flaws are minute flaws, and if the cropping allowance is large like in the past, they are cut off and do not pose a problem, but if the cropping allowance is smaller than mentioned above, seam flaws will remain on the finished steel sheet. 69, which has recently become the second biggest problem in the rolling of thick steel plates.

One way to prevent the occurrence of such seam defects is to bring the temperature of the front and back sides to JII when heating the slab and change the metal flow during rolling to better polish the front side, but this is not a complete solution. .

The inventors conducted various studies on the causes of such seam flaws.

One of the causes of seam defects is the low temperature of the edge of the rolled material during rolling, but another major cause is the swelling of the rolled material during biting. I discovered that. Furthermore, the bulge in the rolled material is
It is related to the pressure Fit when biting, and the amount of reduction when biting is lO
It has been found that when the temperature exceeds MII, the bulge in the rolled material increases and seam flaws are more likely to occur. However, if the rolling reduction amount at the time of biting is made small, the number of passes (the number of rolling times) increases and the rolling efficiency decreases.

This invention provides a rolling method that prevents the occurrence of seam defects by reducing the pressure Fll at the time of biting and does not reduce the rolling f1 ratio. In rolling, the amount of reduction at the time of biting is made small, and the amount of reduction is gradually increased during rolling to form a tapered rolled material, and then the thin side of the tapered rolled material is made the biting side, and during rolling. After repeating the rolling process of increasing the rolling head one by one to obtain a rolled material of uniform thickness once or multiple times until a predetermined width is reached, the rolled material is turned 90° and rolled in the longitudinal direction. This is characterized by carrying out nine finishing rolling steps as usual.

Generally, the rolling method for thick steel plates involves rolling a steel billet in the longitudinal direction by 1 to 2 rolls.
It is common to perform pass horizontal rolling (DBT pass), then turn 90 degrees and perform width rolling to a predetermined width width, and then turn further 90° to perform finish rolling in the length direction. It is.

In the widening rolling of such a thick steel plate, the present invention first reduces the amount of reduction at the time of biting, preferably 10 fl or less F, and sequentially increases the rolling force during rolling into a large comb and a tapered shape. Taper rolling is performed to form a material, and then the thin side of this tapered rolled material is set as the biting side, and the reduction amount at the time of biting is set to 101111 F or less, and the reduction amount is sequentially increased to obtain a rolled material of uniform thickness. Rolling is repeated one or more times alternately until - a predetermined cream width is reached. FIG. 1 is a diagram showing width rolling in the present invention.

The 11th cell shows the rolled material (1) before width rolling. That is, after polishing the piece with DBT passes in the longitudinal direction for 1 to 2 passes, the
It is rotated. ) in FIG. 1 shows the state of the l-th pass of taper rolling in iJ rolling. The roll (2) shown by the dotted line and the rolled material (1) shown by the dotted line show the state when biting, and the roll (2) shown by the solid line (and the rolled material (3) shown by the solid line show the state when released) .That is,
The amount of reduction at the time of biting is preferably small, preferably 10 fl or less, and the amount of reduction is gradually increased during rolling, and the thickness of the rolled material is rolled into a tapered material from tl to t□. It is. Figure 1 1c) shows 2
Shows the rolling of the bus. The roll (2) shown by the dotted line and the rolled material (3) shown by the dotted line show the state at the time of biting, and the roll (2) shown by the solid line and the rolled material (4) shown by the solid line show the state after two passes. be. That is, the amount of reduction during biting was made as small as 10M or more, similar to the previous pass of taper rolling, and the roll spacing was set at that ft, and the amount of rolling F was increased sequentially to obtain the rolled material (4) 1cEE rolling with a ladle-like thickness. It is something to do.

Such taper rolling and the rolling process to obtain a rolled material of uniform thickness are repeated once or multiple times to perform widening rolling to a predetermined width. The reason why it is done once or multiple times is because the specified width cannot be covered in one process! This is to obtain a predetermined width by repeating the process several times. The following in Figure 1 shows the case where it is repeated multiple times, and ] is for creampie 3
The tapered rolling passes are shown, and (5) shows the # side of the tapered rolled material after three passes of rolling. Figure 11) shows the rolling of a rolled material of uniform thickness in the 4th pass in the width-out pass, and (6) shows the rolled material of uniform thickness after 4 passes. After performing such widening rolling, the material is turned by 90 degrees and normal finish rolling is performed in the longitudinal direction.

As described above, in the rolling method of the present invention, the pressure Fl at the time of biting is
Since u is 1Off or less, there is no bulge in the rolled material, and seam flaws are prevented from occurring. Well, since taper rolling and rolling to obtain a rolled material of uniform thickness are carried out in combination, the number of passes is reduced and there is no reduction in rolling efficiency.

An example will be explained. This invention rolling method is applied to thick steel plate 4.
000T rolling was carried out. Table 1 shows the dimensions of the steel slab, the rolled material after finish rolling, and the finished steel plate.

111th! Two-pass DBT pass rolling bond of steel slab with dimensions shown in Table 1 90
After turning by 90 degrees and performing widening rolling until the specified width is 44591, it is turned 90 degrees and rolled to the specified length of 23500.
Finish rolling was performed to a weight of 1 g. FIG. 2 is a diagram showing the #R surface of the rolled material during width rolling. (a) is DB
Cross section of T-pass rolling rolled material, (b) is +iJ rolling l
The cross section after the pass, (C) shows the cross section after 2 passes, (d) shows the cross section after 3 passes, and (e) shows the cross section after 4 passes, and ridge) shows the cross section at the end of widening rolling. 2 out of 4000T conducted
000T is # after width l pass [t in fi (b), 3220m, t, -2001EII,
The amount of taper applied is t, -t, w 2QWn11,
Width rolling was performed with the taper amount of each taper rolling set to 20IO. The remaining 20007 is t, -220fl, t in cross section (b) after one pass of width adjustment.
, = 210 cod, diameter added jll ”l*1 =
The taper amount of each taper rolling is 1011 as lQg.
1 and width rolling was performed. Note that the rolling edge at the time of biting in each pass was 10 m. Thereafter, finish rolling was performed on the rolled materials having the dimensions shown in Table 1. From the obtained rolled material, the first
A finished steel plate having dimensions r shown in the table was measured.

Table 2 shows the results of investigating the occurrence of seam defects in this finished steel sheet in comparison with the conventional rolling method.

221st! As is clear from Table 2, in the conventional method, 300 steel slabs were rolled and 21 7-mm defects occurred, or 7.0%, but with the method of the present invention, 300 steel slabs were rolled. ,
When the taper amount was 20 fl, the occurrence was 3, 1.0%, and when the taper amount was 10 cm, the occurrence was only 1, 033 chi.

As described above, the rolling method of the present invention alternately performs taper rolling and rolling to achieve the same thickness during width rolling, thereby reducing the amount of reduction at the time of biting to 10 fl or less and preventing the occurrence of seam flaws. It prevents a decrease in rolling efficiency and improves the yield of thick steel plate rolling to a high level (IJ).

[Brief explanation of the drawing]

FIG. 1 is a diagram showing widening rolling in the present invention, and FIG. 2 is a diagram showing a cross section of a rolled material during widening rolling. In the figure, 1... Rolled material before width rolling, 2... Roll, 3... Rolled material after width 1 pass rolling, 4... Rolled material after width 2 pass rolling, 5 ...Rolled material after 3-pass widening rolling with a grinding trowel, 6...Rolled material after 4-pass width rolling.

Claims (1)

[Claims] During widening rolling of a thick steel plate, the amount of reduction at the time of biting is reduced, and the intermediate rolling pressure Fli is sequentially reduced to Oshima to form a tapered rolled material, and then the thin side of the tapered rolled material is rolled. is set as the biting side, and the pressure PI at the biting is made small, and the rolling intermediate pressure device is gradually increased to obtain a rolled material of uniform thickness.The process is alternately repeated one or more times to obtain a predetermined width. 1. A method for rolling a thick steel plate, characterized in that after rolling the material to its width, the rolled material is turned 90 degrees and normal finish rolling is performed in the longitudinal direction.