JPS5946682B2 - Thick plate rolling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thick plate rolling method that reduces crop loss and improves rolling yield in thick plate rolling.

Generally, when rolling a thick steel plate, the width of the steel plate after rolling increases, or a so-called crop loss occurs where the top and bottom parts are cut off due to poor shape.

In order to reduce such lot loss, a method has been proposed in which the growth of the crop is anticipated in advance and the thickness section of the sheet is subjected to tentering rolling to offset this growth.

In other words, if the cropped part of the rolled material protrudes outward in the longitudinal direction at its center, tenter rolling is performed to make the thickness of the rolled material thinner at the center than at both ends in a cross section perpendicular to the longitudinal direction; If the section is depressed inward in the longitudinal direction at the center, the rolled material is rolled by tenter rolling so that the thickness at the center is thicker than at both ends in a cross section perpendicular to the longitudinal direction.

However, since this method changes the thickness of the rolled material during tenter rolling, it cannot be applied to rolling thick steel plates that do not include width rolling.

So-called straight rolling, which does not include tentering rolling, is also frequently carried out in thick plate rolling, and there has been a need for a rolling method that reduces crop loss and can be applied to such straight rolling.

The object of the present invention is to reduce crop loss in plate rolling that does not include such tentering rolling.

The inventors conducted various studies on crop growth.

It is known that the growth of end crops is generally caused by widening of both sides of the front and rear sides of the rolled material.

FIG. 1 is a diagram showing the shape of a rolled material after rolling.

1 is widening and 2 is cropping.

Crop 2 grows with spread 1.

Further, if the width spread 1 is indicated by ΔW, ΔW is expressed by the following formula.

△W=f (h・Δh−T) ・・・・・・・・・
...m However, h: Thickness of the steel plate (mrIL) △h: Reduction amount (chi) T: Temperature ('C) As a result of various experiments conducted by the inventors regarding such width expansion, the rolling top during rolling of each pass It has been found that the amount of width expansion differs between the side (hereinafter referred to as the biting side) and the rolling bottom side (hereinafter referred to as the blowout side).

In other words, after heating the material, the reduction amount is the same on the engaging side and the unengaging side, and the thickness and temperature of the steel plate are also the same, and the material is rolled for one pass and cooled, and the amount of width expansion on the unengaging side and the unengaging side is I actually measured it.

FIG. 2 is a diagram showing the relationship between the amount of width expansion that occurs on the released side and the bited side.

The horizontal axis is the biting side width expansion amount ΔWi, and the vertical axis is the biting side width expansion amount ΔW.

It is.

As is clear from the figure, the amount of width expansion on the releasing side is 1.8 to 2.5 times the amount of width expansion on the biting side.

Based on this knowledge, this invention suppresses width expansion and prevents crop growth by making the amount of reduction on the non-biting side smaller than that on the biting side. In the initial rolling of plate rolling, the amount of reduction on the non-engaging side is 3 times the amount of reduction on the engaging side for each rolling pass.
Preferably 6 from the free side end so that the ratio is 0 to 60%.
The method is characterized in that after 4 to 8 passes of rolling are performed by changing the amount of reduction within a range of 0.00 mm or less, normal rolling is performed.

FIG. 3 is a diagram showing the order and shapes of the steel billet and rolled material in the case of reverse rolling in the rolling method of the present invention.

The marks in the figure are the rolling order, and the → marks are the rolling direction.

(2) is a steel billet after heating, and (2) indicates rolling during odd number passes (normal rotation), for example, shows the shape of the rolled material after one pass.

That is, the rolled material is bitten from the a1 side at the leading end and released on the b1 side, but during rolling, the amount of reduction is reduced within a range of 600 mm or less from the end of the side where it is released, and the amount of reduction is 30 to 60 times the reduction amount on the a1 side. It is something.

■ indicates rolling during even number passes (reverse rotation);
For example, it shows the shape of a rolled material after two passes,
For reverse rolling, the second pass involves biting from the b2 side and releasing on the a2 side, and the rolling amount on the a2 side is 30 to 60 of the rolling amount on the b2 side.
%.

After performing 4 to 8 passes of such rolling, normal rolling is performed and finish rolling is performed to a predetermined thickness.

In the present invention, the ratio of the reduction amount on the releasing side and the amount of reduction on the biting side is set to 30 to 60% because if it is less than 30%, the bite angle will be in the limited range and the biting tends to deteriorate.
If the ratio exceeds %, the effect of suppressing width expansion is small and the amount of crop reduction is small.

In addition, the number of passes is set to 4 to 8 passes.If the number of passes is less than 4 passes, the effect of suppressing width expansion is small and the amount of crop reduction is small. This is because they remain and cause a defective shape.

Further, the range of change in the rolling reduction amount is preferably 600 mm or less from the open end.

If it exceeds 600 mm, the effect of preventing width expansion will be small.

This will be described in more detail based on examples.

Thickness: 200 mu s Width: 1800 m, Length: 1500 ~
From a 2200mm steel piece, thickness 8-12mm, width 180mm
Thick steel plates having a length of 25,000 to 39,000 mm were manufactured by the method of the present invention and the conventional method.

In the method of the present invention, in each rolling pass in the range of 400 to 550 degrees from the end of the non-chewing side, the rolling reduction ratio of the biting side and the letting-off side is changed at the following constant ratio, and 4 passes out of 20 passes. Until the end,
Rolling was performed by changing the reduction amount up to the 6th pass and up to the 8th pass, and then normal rolling was performed.

Up to the 4th pass, there are 3 types of reduction ratio: 50%, 40%, and 30%. Up to the 6th pass, there are 4 types of reduction ratio: 60%, 50%, 40%, and 30 rice cakes. Up to the 8th pass, there are 4 types of reduction. Amount ratio: 70%, 60 parts, 50%, 40 parts.

The crop length (top part and bottom part) of the thick steel plates obtained by the above-mentioned manufacturing method were measured, and the difference △L in the cropping amount of the thick steel plates obtained by the method of the present invention and the conventional method was determined by FIG. 4 shows the results obtained by calculating the difference between the crop length of the top and bottom parts of the thick steel plate obtained using the conventional method.

FIG. 4 is a diagram showing the relationship between the rolling reduction amount ratio and the cropping amount difference ΔL for each number of passes.

The horizontal axis is the reduction amount ratio, which is the amount of reduction in pressure when releasing the bite/the amount of pressure increase on the biting side xioo.

In the figure, the solid line is the result of 4 passes, the dotted line is the result of 6 passes, and the dashed line is the result of 8 passes.

In addition, the shaded area in the figure is the biting angle limit range, which is the range in which the biting angle does not bite into the roll.

It is shown that this range occurs when the rolling reduction ratio is less than 30%.

When it is 30% or more and 60% or less, the difference ΔL in cropping amount increases for each number of passes, resulting in an improvement.

However, when it exceeds 60%, ΔL decreases.

Also, the higher the number of passes, the better the results.

In other words, good results cannot be expected with less than 4 passes.

However, if the number of passes exceeds 8, the plate thickness difference will remain until the final pass, and if an attempt is made to correct this difference, problems such as poor flatness will occur.

As is clear from the figure, by implementing the rolling method of the present invention, the crop amount could be reduced by 250 degrees on average, and the rolling yield could be improved by 0.8%.

As described above, the rolling method of the present invention significantly reduces crop loss by preventing the growth of crop amount, which could not be carried out in conventional thick plate rolling without tentering rolling, and has a great effect. be.

Although the present invention has been described with reference to the case of rolling thick plates by reverse rolling, it is also possible to use the method of the present invention when manufacturing steel plates with a continuous rolling mill.

For example, after rough rolling is performed by changing the amount of reduction on the biting side and the rolling side in each stand of a rough rolling mill, normal finishing rolling is performed in a finishing rolling mill.

[Brief explanation of drawings]

Figure 1 is a diagram showing the shape of a thick plate after rolling, Figure 2 is a diagram showing the relationship between the widening that occurs on the uncoupled side and the jammed side, and Figure 3 is a diagram showing the order of the rolling method of this invention and the steel plate. FIG. 4, which is a diagram showing the single shape, is a diagram showing the relationship between the rolling ratio ratio and the crop amount difference ΔL in each number of passes. In the figure, 1: Width spread amount, 2: Crop amount.

Claims (1)

[Claims] 1. In the initial rolling of thick plate rolling that does not include tentering rolling, for each rolling pass, the rolling bottom side end is rolled down so that the rolling bottom side rolling amount is 30 to 60% of the rolling top side rolling amount. A thick plate rolling method characterized by performing 4 to 8 passes of rolling with varying amounts and then performing normal rolling.