JP2001300603A - 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 yield is improved, especially while raising the accuracy of thickness of the wide thin material of an alloy such as a heat resistant alloy and titanium alloy whose hot working is difficult. SOLUTION: In the manufacturing method of the sheet 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 sheets are manufactured from the core materials by rolling this pack rolled stock, by this manufacturing method of the sheet by the pack rolling, the initial thickness of the cover material is set so that the ratio of the thickness of the core material to the thickness of the pack rolled material is >=0.25. Furthermore, the rolling of the pack rolled stock is performed under conditions that the hot deformation resistance of the cover material is smaller than the hot deformation resistance of the core material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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, a pack rolling (lamination rolling) method has conventionally been implemented.
FIG. 12 is a sectional view showing an example of a rolled material. FIG.
In 2, a plate-shaped core material 1 which is one or a plurality of materials to be rolled is 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 exceeds the allowable load of the rolling mill and further rolling cannot be performed. Therefore, it is ideal to perform rolling in a temperature range of 800 to 950 ° C. below the β transformation point and at which the deformation resistance does not become so high. Therefore, pack rolling with a small decrease in temperature is applied.

[0006] In pack rolling, between core materials,
In addition, between the core material and the cover material, peeling is performed for the purpose of preventing pressure bonding between the core materials and between the core material and the cover material by rolling, and preventing a decrease in the temperature of the core material due to heat transfer resistance. The material is applied. 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 have been taken such as controlling the temperature and deformation resistance of the core material and the cover material. For example, in Japanese Patent Application Laid-Open No. 5-42302,
A technique has been proposed in which the surface of a rolled material is cooled to increase the deformation resistance of the cover material, thereby reducing the difference in deformation resistance value between the core material and the core material within a predetermined value.

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 gap between the ends of the core material is made larger to form a rolled pack material.

[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 the prediction of processing heat, and the temperature accuracy is questionable.

[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.

The present invention solves the above problems and improves the yield by increasing the thickness accuracy of a wide and thin material such as a heat-resistant alloy or a titanium alloy which is difficult to hot work by hot rolling, in particular. It is an object of the present invention to provide a method for manufacturing a thin plate by pack rolling.

[0014]

The above object is achieved by the following invention. According to a first aspect of the present invention, there is provided a thin plate, wherein 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 produce a thin plate from the core material. Wherein the initial thickness of the cover material is set to a thickness at which a ratio of the thickness of the core material to the thickness of the rolled material is at least 0.25 or more. It is a manufacturing method of.

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. As a result, it has been found that by increasing the ratio of the core material to the entire packed rolled material, the substantial rolling reduction of the core material approaches the rolling reduction of the whole packed rolled material.

In the present invention, the assembly ratio of the rolled material, that is, the ratio of the thickness of the core material to the total thickness is controlled.
When the thickness of the core material is thinner than that of the entire rolled material as in the prior art, the substantial reduction ratio of the front and rear ends of the core material is lower than the reduction ratio of the entire rolled material. Stop at. The ratio must be at least 0.25 or more. By controlling the ratio of the thickness of the core material in this way, it is possible to make it difficult for a thickness deviation to occur.

The initial thickness of the cover material is preferably as thin as possible, but the lower limit of the thickness is naturally determined from the heat retaining effect of the cover material. In particular, if a high finishing temperature is required for the core material, it goes without saying that the cover material is made thick to prevent the core material from lowering in temperature.

According to a second aspect of the present invention, there is provided the pack rolling device according to the first aspect, wherein the rolled material is rolled under a condition that the hot deformation resistance of the cover material is smaller than the hot deformation resistance of the core material. This is a method for manufacturing a thin plate.

According to the present invention, the cover material is rolled in a state where the hot deformation resistance is smaller than that of the core material so that the elongation of the cover material always exceeds the core material. Thereby, shape defects such as buckling of the core material can be prevented.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS For the sake of simplicity, it is assumed that a gap between a core material and a spacer material before rolling is zero, 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.
As shown in FIG. 1, this gap is already closed before the core material rear end 1B comes out of the roll bite. In the core material rear end 1B, the closed portion serves as a wall to suppress longitudinal elongation.

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

As shown in FIG. 2, the leading end 1T of the core material 1 is located 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, as shown in FIG. Has a gap 5. This gap 5 is provided at the tip 1 of the core material.
When T is bitten into the roll bite, it gradually closes and becomes a wall from a certain point.
Is suppressed. Also, like the core material rear end 1B,
The difference in the relative elongation between the cover material 2 and the core material tip 1T is also reduced. 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.

Note that, as the rolling progresses, the substantial reduction ratio of the core material and the cover material becomes a value purely corresponding to the difference in deformation resistance, so that the influence of the longitudinal compressive force on the core material is eliminated. In addition, the above phenomenon can be naturally observed 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. It can also be seen that the difference in thickness deviation between the front and rear ends is further promoted when the rolling method is inappropriate.

In order to prevent the thickness deviation occurring at the front and rear ends in the longitudinal direction of the core material, it is necessary to make it difficult to close the gap generated between the core material and the spacer material and to increase the thickness of the core material. Applying force in the direction of suppression.

Here, as parameters affecting these, 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. Note that these parameters are expressed as follows. ld = (R × ΔH) ^0.5 R: Work roll radius (mm) ΔH: Reduction amount (mm) hm = (h0 + h1 × 2) / 3 h0: Incoming plate thickness (mm) h1: Outgoing plate thickness (mm)

FIGS. 4 and 5 show the results of a model experiment conducted to investigate the effects of these parameters 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”, and the closer the ratio is to 1, the smaller the increase in the thickness of the thickness deviation portion is. Means

First, as for the influence of the roll gap shape ratio ld / hm, as shown in FIG. 4, the larger the ld / hm and the constant the reduction ratio, the smaller the reduction ratio and the greater the thickness.
This is considered to be because the gap becomes easier to close as ld / hm is larger. Regarding the effect of the rolling reduction,
As shown in FIG. 5, as ld / hm is constant and the rolling reduction is larger,
The reduction ratio increases, and the increase in sheet thickness decreases. this is,
The larger the rolling reduction, the easier the gap is to be closed, but the greater the effect of the force in the direction 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 of 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, in actual operation, since the roll diameter is constant, the ld / hm increases as the rolling reduction increases,
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.

The relationship between the roll gap shape ratio ld / hm and the reduction ratio in the actual machine is as shown in FIG. 6, for example. As described above, ld / hm is determined by the rolling reduction and the entry side plate thickness Hin. Therefore, the sheet thickness deviation is determined by the draft. Then, when investigating the relationship between the draft and the sheet thickness increase in the actual operation, it becomes as shown in FIG. From this figure, the entry side plate thickness Hi
When n is as thick as 60 mm or more, the increase in sheet thickness decreases as the rolling reduction increases, and when it is as thin as 50 mm or less, no change in the amount of sheet thickness depending on the rolling reduction is observed.

This is because when the inlet side thickness Hin becomes thinner, the roll gap shape ratio ld / hm becomes larger (FIG. 6), and the gap becomes easier to close, so that the thickness deviation at the front and rear ends of the core material cannot be eliminated. It is considered something. From this, the entry side plate thickness Hin
When the thickness is large (here, 60 mm or more), strong rolling is effective as a rolling method. As described above, it is effective to set a strong reduction in a certain range. However, in actual rolling, the amount of the strong reduction that can be taken is limited due to the load constraint and the torque constraint of the rolling mill, and a sufficient effect is always obtained. Not necessarily.

In order to obtain the same effect as under strong pressure, it is effective to apply a force in a direction to suppress an increase in the thickness of the core material. Therefore, in the present invention, as a method for obtaining the same effect as the above-mentioned high-pressure rolling schedule, the ratio of the thickness of the cored material to the total thickness, that is, the ratio of the thickness of the core material to the overall thickness, is controlled.

FIG. 8 is a diagram showing the relationship between the thickness ratio of the laminated plates and the reduction ratio of the core material described above. This figure shows the core material thickness
It is a summary of the results of one-pass rolling experiments performed by assembling pack rolled materials using cover materials of various thicknesses with a thickness of 10 mm. From the figure, the reduction ratio of the core material (the reduction ratio of the sheet thickness deviation portion / the reduction ratio of the steady portion) is low when the combined thickness ratio is around 0.1, and the reduction ratio of the sheet thickness deviation portion is low. Large thickness deviation. It can be seen that when the combined plate thickness ratio becomes 0.25 or more, the reduction ratio of the core material increases, and the plate thickness deviation decreases. Therefore, the laminated plate thickness ratio should be at least 0.2
If it is set to 5 or more, and as large as possible, the effect of preventing the thickness deviation becomes large. As described above, in order to reduce the sheet thickness deviation, it is necessary to increase the combined sheet thickness ratio so that the reduction ratio of the core material approaches 1. This means that the initial thickness of the cover material is reduced, and as a result, the stress in the thickness direction acting on the thickness deviation portion of the core material can be increased. The deviation is reduced.

When determining the initial thickness of the cover material, a point to be considered is that the hot deformation resistance of the core material is equal to that of the cover material until rolling is completed in order to prevent shape defects such as buckling of the core material. In some cases, when the finishing temperature of the core material is specified, it is necessary to ensure that temperature. Regarding the hot deformation resistance, when the core material is a difficult-to-process material, it is relatively easy to select a material that is easier to process as the cover material. When the finishing temperature of the core material is particularly high, the cover material is thickened accordingly to prevent the temperature of the core material from decreasing.

[0036]

EXAMPLE A thin plate of a Ti-6Al-4V alloy was manufactured by the manufacturing method of the present invention. A rolled pack was assembled using SS330 as the cover material and the spacer material. Core material, thickness 1
Two 7.5 mm Ti-6Al-4V alloys were stacked, and the cover material was changed in thickness to 35 mm (pattern 1: invention example) and 70 mm (pattern 2: comparative example).

The simulation result of the finishing temperature is as shown in FIG. 9, and when the initial plate thickness (Cover thickness) of the cover material is reduced, it decreases rapidly. In the case of the invention example, the thickness of the cover material is determined so that the lower limit of the finishing temperature of 720 ° C. shown by the broken line in the figure can be secured. Further, the hot deformation resistance during rolling is as shown in FIG. 10, and the core material always keeps at least twice the hot deformation resistance with respect to the cover material.

After the pack rolling of the rolled material is completed, the rolled material is disassembled, and a thin plate having a thickness of 1.6 mm is removed.
Manufactured one by one. FIG. 11 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. As a result, in the invention example (pattern 1), the final sheet thickness increase amount was 0.90 mm, whereas in the comparative example (pattern 2), it was 1.40 mm. It can be seen that it has acted on.

[0039]

According to the present invention, the assembling ratio of the rolled material, that is, the ratio of the thickness of the core material to the total thickness is set to a predetermined ratio or more, so that the front and rear ends of the core material can be substantially reduced. The rolling reduction can be made close to the overall rolling reduction, and the thickness deviation can be made hard to occur. Further, by rolling the rolled material under the condition that the hot deformation resistance of the cover material is smaller than the hot deformation resistance of the core material, shape defects such as buckling of the core material can be prevented. 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 reduction ratio and ld / hm.

FIG. 7 is a diagram showing a relationship between a draft and a thickness increase;

FIG. 8 is a view showing the relationship between the thickness ratio of the mating plates and the reduction ratio of the core material.

FIG. 9 is a view showing a simulation result of an initial plate thickness and a finishing temperature of a cover material.

FIG. 10 is a diagram showing hot deformation resistance during rolling.

FIG. 11 is a diagram showing a difference in a thickness deviation amount at an end of a core material depending on an initial thickness of a cover material.

FIG. 12 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 (2)

[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, the initial thickness of the cover material is adjusted so that the ratio of the thickness of the core material to the thickness of the rolled pack material is at least 0.
A method for producing a thin plate by pack rolling, wherein the thickness is set to 25 or more. 2. The method for producing a thin plate by pack rolling according to claim 1, wherein the rolled material is rolled under conditions where the hot deformation resistance of the cover material is smaller than the hot deformation resistance of the core material. .