JP2001300604A - Method of manufacturing sheet by pack rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a sheet by pack rolling by which the wide thin materials of an alloy such as a heat resistant alloy and titanium alloy whose hot work is difficult are especially manufactured into products having small thickness deviation by hot rolling. SOLUTION: In the method for manufacturing sheets by which a pack rolled stock is formed by covering one or plural pieces of planar core materials with a spacer material and a cover material and the sheet is manufactured from the core material by rolling this pack rolled stock, by this manufacturing method of the sheet by pack rolling, draft is defined as >=15% about passes whose reduction ratio is >=3 to the initial thickness of the pack rolled stock.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled material formed by covering one or more plate-shaped core materials with a spacer material and a cover material, and hot-rolling the rolled material. The present invention relates to a method of manufacturing a thin plate by pack rolling for manufacturing a thin plate from a thin plate.

[0002]

2. Description of the Related Art In general, heat-resistant alloys and titanium alloys have a large temperature dependency of deformation resistance, and a processing load is increased due to a decrease in temperature during processing, so that processing is difficult. Further, there are materials having poor hot workability such as boron-added austenitic stainless steel. These materials are commonly referred to as difficult-to-machine materials.

[0003] As a thin plate rolling technique for these difficult-to-process materials,
Conventionally, a pack rolling (lamination rolling) method has been implemented. FIG. 8 is a sectional view showing an example of a rolled material. In FIG. 8, one or a plurality of plate-shaped core materials 1 which are materials to be rolled are covered with a spacer material 3 at four peripheral portions. The core member 1 and the spacer member 3 are sandwiched between upper and lower cover members 2. This figure shows an example of a rolled material in which two core materials 1 are covered with a spacer material 3 and sandwiched between cover materials 2.

As described above, since the plate-shaped core material to be rolled is covered with the spacer material and the cover material, the surface of the core material does not directly come into contact with a cold medium such as the outside air or a roll, so that the temperature of the core material is reduced. The reduction can be prevented, and the production of a thin plate material becomes possible.

For example, a Ti-6Al-4V alloy, which is well known as an α + β type titanium alloy, needs to be subjected to hot working in the α + β region in order to secure cold workability and superplasticity. However, the temperature dependence of the deformation resistance is very large, and when the temperature is 800 ° C. or less, the deformation resistance greatly increases, and the rolling beyond the allowable load of the rolling mill cannot be performed. Therefore, it is ideal to perform rolling in a temperature range of 800 to 950 ° C. where the deformation resistance is not so high below the β transformation point, and pack rolling in which the temperature drop is small is applied.

[0006] In pack rolling, between core materials,
And a release material is applied between the core material and the cover material,
Prevents pressing between core materials by rolling and pressing between core material and cover material. In addition, since the release material has a heat transfer resistance, it also contributes to preventing the core material from lowering in temperature. After the core material is surrounded by the spacer material and the cover material, the space between the spacer material and the cover material is welded to complete the assembly of the pack slab. In pack rolling, the pack slab thus assembled is hot rolled to produce a rolled material. Thereafter, the rolled pack material is dismantled, and a core material that has been rolled into a thin plate is taken out.

In such a pack rolling method, it is difficult to control the sheet thickness at the time of rolling because the core material as a product does not directly contact the rolling roll. Therefore, in order to increase the thickness accuracy of the product and improve the shape, various measures such as controlling the deformation resistance ratio and the temperature of the core material and the cover material have been devised.
For example, Japanese Patent Application Laid-Open No. 5-42302 discloses that, when rolling, the surface of a rolled material is cooled to increase the deformation resistance of a cover material so that the difference in deformation resistance value between the core material and the cover material is kept within a predetermined value. A technique for reducing the size has been proposed.

Further, in connection with this problem, there is a problem that the thickness of the end portion of the core material is increased in the pack rolled material. Since the defective thickness portion does not become a product, the yield is reduced. As a technique for preventing this, Japanese Patent Application Laid-Open No. Hei 10-216807 discloses a technique of managing the gap between the end of the core material and the spacer material in the state of assembling the rolled material to reduce the occurrence of thickness deviation. Methods to prevent this have been proposed. In this method, in the rolling of the pack rolled material, the amount of deformation of the core material in the side direction is predicted in advance,
The rolled pack is formed so that the above-mentioned gap is larger than this.

[0009]

However, the prior art has the following problems. According to the technique described in Japanese Patent Application Laid-Open No. 5-42302, the cover material is cooled so that the difference in the deformation resistance value from the core material is within a predetermined value. However, since the core material is surrounded by the cover material, Temperature cannot be measured. Therefore, in this technique, the temperature of the core material is estimated by simulation. However, since the temperature of the core material changes when the cover material is cooled, it is expected that the estimation calculation is actually quite complicated. In addition, there are many factors that depend on estimation, such as prediction of processing heat, and it is also questionable in terms of temperature accuracy.

[0010] Also, from the viewpoint of cooling technology, it is difficult to cool uniformly over a wide area of several meters square. Further, even if the above-described high-precision simulation calculation is possible, it is difficult for the existing cooling method to accurately cool to the target temperature by the ordinary cooling technique.

The technique described in Japanese Patent Application Laid-Open No. 10-216807 is effective for eliminating the thickness deviation at the width direction end, but when the rolling reduction ratio is large, the thickness deviation at the longitudinal direction end is considerably large. Therefore, it is not very effective. This is because a defective portion having a planar shape, that is, a so-called crop, which occurs at an end portion in the longitudinal direction with the progress of rolling grows and cannot be absorbed in a gap with a normal spacer material.

In view of this, it is conceivable to set a large gap in anticipation of the growth of the crop. But,
Even if such a large gap is provided, there is a problem that if the cover materials above and below the gap come into contact during rolling and the gap is closed, the effect is naturally lost.

[0013] The present invention solves the above problems, and can produce a wide and thin material of an alloy which is difficult to hot work such as a heat-resistant alloy or a titanium alloy by hot rolling, in particular, a product having a small thickness deviation. An object of the present invention is to provide a method for manufacturing a thin plate by pack rolling.

[0014]

The above object is achieved by the following invention. The invention provides a method of manufacturing a thin plate in which one or a plurality of plate-shaped core materials are covered with a spacer material and a cover material to form a rolled pack material, and the rolled pack material is rolled to manufacture a thin plate from the core material. In, for the pass where the reduction ratio is 3 or more with respect to the initial thickness of the rolled material,
A method for producing a thin plate by pack rolling, wherein the rolling reduction is 15% or more.

The present invention has been made while diligently studying the cause of the thickness deviation occurring in pack rolling. In the process, the deformation behavior of the rolled pack during rolling was examined, paying attention to the fact that the gap between the core material and the spacer material changed and a thickness deviation occurred. The occurrence of the thickness deviation at the front and rear ends in the longitudinal direction of the core material means that the substantial reduction ratio of the core material at that portion is smaller than the reduction ratio of the entire pack rolled material, and a method for preventing it. Were examined in various ways.

In the process, the amount by which the thickness of the sheet thickness deviation portion where the sheet thickness deviation occurs is relatively increased with respect to the normal portion is called the sheet thickness increase amount. It has been found that it changes depending on the rolling conditions. It has been found that the amount of increase in the thickness of each pass depends on the reduction ratio and the reduction ratio when the pass is reduced. Based on the examination results, in the present invention, at the stage where the rolling progresses and the reduction ratio becomes 3 or more,
By performing a strong reduction at a reduction ratio of 15% or more (0.15 in the figure) or more, the increase in the sheet thickness is suppressed.

The reasons for limiting the rolling conditions are as follows. First, in the region where the rolling reduction ratio is less than 3 at the beginning of rolling, it is desirable that the rolling reduction per pass is higher, but the increase in the sheet thickness can be reduced by increasing the rolling reduction without using a particularly strong rolling. However, in the region where the reduction ratio is 3 or more, when the reduction ratio per pass is low, the thickness increase tends to increase. Therefore, it is necessary to perform strong pressure reduction in this region. When the rolling reduction is less than 15%, there is no effect of reducing the amount of increase in sheet thickness, and it is necessary to be 15% or more. As described above, in a rolling pass having a reduction ratio of 3 or more, a strong reduction with a reduction ratio of 15% or more is performed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a mechanism in which a thickness deviation occurs in pack rolling will be examined for reference in practicing the present invention. For simplicity, consider a case where the gap between the core material and the spacer material before rolling is 0, that is, there is no initial gap. First, before the rear end portion of the core material is bitten into the roll bite, the core material and the cover material are subjected to a difference in the amount of elongation caused by a difference in deformation resistance and a difference in a substantial rolling reduction. There is a gap between the material and the spacer material. This gap is shown in FIG.
As shown in (1), the core material rear end 1B is already closed before coming out of the roll bite. The core material rear end 1B
The closed portion serves as a wall to suppress longitudinal elongation.

Further, since the substantial rolling reduction of the cover material 2 at the position where the gap 5 is closed is small, the amount of elongation of the cover material 2 is also small. Therefore, the difference in the relative elongation between the cover member 2 and the core member 1 is also reduced. For these reasons,
Since the rear end portion 1B of the core material is locally subjected to a compressive force in the longitudinal direction, the plate thickness increases near the rear end portion of the core material.

Next, at the leading end, a gap 5 is formed between the core material 1 and the spacer material 3 before the leading end 1T of the core material 1 is bitten into the roll bite similarly to the rear end 1B. Has occurred. Thereafter, when the core material tip 1T is bitten into the roll bite, the gap 5 is gradually closed and becomes a wall from a certain point, so that the elongation of the core material tip 1T is suppressed. Further, similarly to the core material rear end portion 1B, the difference in the relative elongation amount between the cover material 2 and the core material front end portion 1T also becomes small. Therefore, the thickness deviation also occurs at the leading end 1T of the core material, similarly to the trailing end 1B of the core material.

As the rolling progresses, the difference between the substantial rolling reduction of the core material and the cover material becomes a value purely corresponding to the difference of the deformation resistance, so that the influence of the longitudinal compressive force on the core material is eliminated. . The above-described phenomenon naturally occurs even when an initial gap exists between the core material and the spacer material.

By the way, there is a difference between the front end portion and the rear end portion in which one of the gap formed between the core material and the spacer material and the end portion of the core material is bitten into the roll bite first. The thickness deviation is larger at the rear end than at the front end. That is, at the rear end, the gap that is almost completely closed becomes a wall, and the elongation of the core material is suppressed. On the other hand, at the tip end, the gap that is closed from a certain position in the roll bite gradually becomes a wall, so that the elongation of the core material is also gradually suppressed. As a result, the thickness deviation does not become as large at the front end as at the rear end.

The difference in thickness deviation between the leading end portion and the trailing end portion can be confirmed by performing unidirectional rolling as a rolling method instead of reversing rolling which is usually performed by pack rolling.
FIG. 3 shows the experimental results. From this figure, it can be confirmed that the thickness deviation of the rear end portion is larger than that of the front end portion. In order to prevent the thickness deviation occurring at the front and rear ends in the longitudinal direction of the core material, it is difficult to close a gap generated between the core material and the spacer material, and a direction in which the thickness of the core material is suppressed from increasing. To apply force.

Here, attention was paid to the ratio ld / hm (roll gap shape ratio) of the contact arc length ld to the average plate thickness hm and the rolling reduction as parameters affecting these. FIGS. 4 and 5 show the results of a model rolling experiment performed to investigate the effect of this parameter in detail. In the figure, the reduction ratio indicates “the reduction ratio of the core material thickness deviation portion / the reduction ratio of the core material steady portion”. As this ratio is closer to 1, the reduction ratio of the sheet thickness deviation portion and the steady portion is reduced. The difference is small, which means that the thickness increase relative to the steady portion of the thickness deviation portion is small.

First, regarding the influence of the roll gap shape ratio ld / hm, as shown in FIG. 4, the reduction ratio becomes smaller as the reduction ratio is constant and ld / hm is larger, and the plate thickness deviation portion has a smaller thickness than the steady portion. The increase in thickness increases. This is considered to be because the larger the ld / hm, the easier the gap is to close. Also, as shown in FIG.
As the rolling reduction is constant at a constant m, the rolling reduction ratio increases and the increase in the thickness of the thickness deviation portion is small. This is because the larger the rolling reduction, the easier the gap is to be closed, but the greater the effect of suppressing the increase in the thickness of the core material at the end in the core material longitudinal direction.

As described above, in order to eliminate the thickness deviation at the front and rear ends of the core material, it is advantageous that the roll gap shape ratio ld / hm of each pass is smaller and the rolling reduction is larger. Understand. However, considering the actual operation, since the roll diameter is constant, ld / hm increases as the rolling reduction increases, and these two parameters cannot be controlled independently. Furthermore, in practice, it is necessary to consider the optimal balance between ld / hm and rolling reduction based on the transition of hot deformation resistance in each pass of the cover material and the core material.

FIG. 6 shows the relationship between the rolling reduction and the thickness increase in the actual operation. The relationship between the rolling reduction and the amount of increase in the thickness differs depending on the rolling reduction ratio.
Under condition 3, the greater the rolling reduction, the smaller the thickness increase. On the other hand, under the condition that the inlet side plate thickness is thin and the reduction ratio ≧ 3,
The increase in the sheet thickness hardly changed even when the rolling reduction was increased. However, a new finding was obtained that when the rolling reduction was 15% or more (0.15 in the figure) or more, the increase in the sheet thickness became smaller as the rolling reduction increased. From this, it is necessary to set the rolling reduction to 15% or more for the path where the rolling reduction of the rolled material becomes 3 or more.

[0028]

EXAMPLE According to the production method of the present invention, a thin plate of a Ti-6Al-4V alloy was produced by a pack rolling method. SS330 was used as a cover material and a spacer material, and two core materials of a Ti-6Al-4V alloy having a thickness of 10 mm were laminated, and a cover material having a thickness of 100 mm was laminated one above and below the core material. Rolling of 11 passes is performed on this 220 mm thick pack slab, and the final thickness is 32 mm.
As a result, the rolled material was dismantled to produce two thin plates having a thickness of 1.4 mm. As shown in Table 1, the pass schedule of the rolled material is as follows: a heavy rolling schedule (pattern 1) and a normal schedule (pattern 2: comparative example, all 15 passes).
And

[0029]

[Table 1]

The path where the reduction ratio becomes 3 or more (pattern 1:
The rolling reduction of the passes 7 to 10 and the pattern 2: the passes 8 to 15) is a strong reduction of about 20% in the pattern 1, whereas it is a light reduction of about 10% in the pattern 2. FIG. 7 shows the thickness deviation (final thickness increase) of the front and rear ends of each core material. The sheet thickness deviation is almost the same at the front and rear ends, and the larger value is shown in the figure. From this, the final thickness increase in the invention example (pattern 1) is 0.75 mm, whereas in the comparative example (pattern 2) it is 1.40 mm.
It can be seen that in the invention example, the strong reduction at the front and rear ends worked more effectively.

[0031]

According to the present invention, the reduction ratio of the rolled material is 3
With respect to the above paths, the substantial reduction at the front and rear end portions of the core material can be made close to the overall reduction ratio by applying a strong reduction at a reduction ratio of 15% or more. It is possible to make the deviation hard to occur. As a result, the yield is improved, and machining of the end portion for adjusting the thickness after rolling is not required, thereby improving the production efficiency and the economic efficiency.

[Brief description of the drawings]

FIG. 1 is a view showing a mechanism of occurrence of a sheet thickness deviation at a rear end portion of a core material.

FIG. 2 is a view showing a mechanism of occurrence of a thickness deviation at a core material tip.

FIG. 3 is a view showing a thickness deviation in a longitudinal direction of a core material when unidirectional rolling is performed.

FIG. 4 is a graph showing the influence of ld / hm on the reduction ratio.

FIG. 5 is a diagram showing the effect of the reduction ratio on the reduction ratio.

FIG. 6 is a diagram showing a relationship between a draft and a thickness increase.

FIG. 7 is a diagram showing a thickness deviation at front and rear ends.

FIG. 8 is a sectional view showing an example of a rolled material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core material 1T Core material front end 1B Core material rear end 2 Cover material 3 Spacer material 5 Gap 6 Release material

Claims (1)

[Claims] 1. A method for manufacturing a thin plate in which one or a plurality of plate-like core materials are covered with a spacer material and a cover material to form a rolled pack material, and the rolled pack material is rolled to manufacture a thin plate from the core material. In the method, for a pass having a reduction ratio of 3 or more with respect to the initial thickness of the rolled material, the reduction ratio is set to 15%.
A method for producing a thin plate by pack rolling, characterized in that: