JPH0245922B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for cold rolling a metal plate having a close-packed hexagonal crystal structure such as Ti, Ti alloy, Zr, or Zr alloy. The present invention relates to a method of manufacturing the same metal plate with good surface quality with good productivity.

[Conventional technology]

In the cold rolling of metal plates, it is essential to use rolling oil to prevent seizure, but on the other hand, if too much rolling oil is supplied, fluid lubrication will occur between the rolling rolls and the material to be rolled, and high-pressure rolling oil will cause It is known that unevenness (so-called oil pits) occurs on the free surface of the rolled material in contact with it. In particular, in metals such as the dense hexagonal metals, which have significantly different deformation resistance depending on the crystal orientation,
Since crystals in orientations with low deformation resistance are easily deformed, oil pits are likely to occur; for example, in cold-rolled Ti plates, it is not uncommon for the pits to reach a depth of more than ten microns. Since these oil pits significantly impede the surface precision of the final product, an important issue in cold rolling of this type of dense hexagonal metal sheet is how to reduce the size of the oil pits generated during the rolling process. . The allowable limit of the oil pit varies depending on the surface accuracy required depending on the product's use, but the depth is 1 to 1.
It is often required that the thickness be 2 μm or less.

On the other hand, if a rolling oil with poor lubricity is used to prevent the occurrence of oil pits, boundary lubrication will occur between the rolling rolls and the rolled material, which will increase the friction coefficient in the roll bite, increase the rolling load, and increase the rolling load. The material sticks to the roll. If rolling is continued in such a state, the rolled material will become locally stuck to the rolls, resulting in so-called seizure. When such seizure occurs during the rolling process, the coefficient of friction at the roll bite portion increases rapidly, making it impossible to continue rolling. Furthermore, if seizure occurs, the surface precision of the roll deteriorates and the surface precision of the cold rolled sheet also deteriorates significantly, making it necessary to re-grind the rolling roll. That is, it is believed that sticking at the early stage of rolling causes seizure, and conventionally rolling operations have been carried out to suppress sticking as much as possible from the early stage of rolling. In addition, in the final finishing pass, which greatly affects the surface accuracy of rolled products, if the rolling roll shows seizure phenomenon or even if only sticking occurs, the rolling operation should be immediately interrupted and the rolling roll replaced with a polished finishing roll. In addition to replacing the rolls and restarting operations, the rolling rolls with stuck metal to be rolled are being sent to the grinding and repair process.

[Problem that the invention seeks to solve]

Under these circumstances, when cold rolling dense hexagonal metal sheets as mentioned above, the main focus is on developing lubricating oil and setting operating conditions that can suppress oil pits as much as possible and prevent seizure. Research is underway to improve the oil pits, but attempts to suppress oil pits will cause seizures, and attempts to prevent seizures will make oil pits more likely to occur.
Because of this troublesome tendency, it was thought to be extremely difficult to improve both oil pits and seizure to a satisfactory degree. Under these circumstances, the present invention provides a cold rolling method for dense hexagonal metal plates that simultaneously solves the problems of oil pits and seizure, and that can yield the same metal plates with good surface precision with high productivity. This is what we are trying to provide.

[Means for solving problems]

The present invention uses a rolling roll whose surface is coated with a dense hexagonal metal coating with a thickness of 0.2 μm or more, and uses an emulsion-type rolling oil with a center grain size of 5 μm or less and a saponification value of 80 or more. The gist of this method is that it performs inter-rolling.

[Effect]

The dense hexagonal metal coating formed on the surface of the rolling roll used in the present invention is not a single layer with a smooth surface like plating, but a fine unevenness in units of length and width of 50 μm or less. This kind of film is created by passing a dense hexagonal metal plate of the same type as the rolled plate through a rolling roll in a poorly lubricated state and baking the dense hexagonal metal evenly onto the surface of the roll. It can be formed by In other words, as explained earlier, dense hexagonal metals have the property of being extremely susceptible to seizing, so for example, it is possible to use oil (including water) with poor lubricity, which is supplied to the rolling rolls without using a lubricant. The dense hexagonal crystal metal can be easily baked on the surface of the rolling roll by rolling, or by using a low-speed rolling method that can suppress the amount of lubricant incorporated. By using a rolling roll that has been subjected to a surface coating treatment, cold rolling can be carried out smoothly with almost no oil pits or seizures even when a normal lubricant is used.

Figure 1 shows a plate with a thickness of 0.9 using a small two-high rolling mill.
This figure shows the relationship between the average rolling force and cumulative strain for each pass when Ti plates with a thickness of 50 mm and a thickness of 50 mm are cold rolled. The diameter of the rolling roll used is
Two types of rolls were used: a 160mm roll with a grinding finish and a roll with a fixed Ti coating layer (approx. 1 μm) formed on the surface of the same roll (hereinafter sometimes referred to as a coating roll). A 2% concentration beef tallow emulsion lubricant (center particle diameter: 5 μm, saponification value: 180, particle size: 60 cst/40° C.) was used as the lubricant, and the rolling speed was 200 m/min. Reference photographs 1 and 2 show microscopic photographs of the surface of the cold-rolled sheet. As is clear from these photos, the surface of the plate rolled with coating rolls (reference photo 1) has no oil pits and has excellent surface precision, but the surface of the plate rolled with grinding rolls has excellent surface precision. (Reference photo 2) has a depth of 8 to 10 μm.
Significant oil pits are observed.

Furthermore, as is clear from FIG. 1, when the cumulative reduction rate at the initial stage of rolling is low, the rolling pressure with respect to strain is slightly higher in the coated roll than in the finished grinding roll, and the rolling efficiency is slightly lower. However, with a ground finish roll, the average rolling pressure gradually increases due to work hardening of the rolled material as the rolling reduction increases, whereas when a coated roll is used, the initial rolling pressure is lower than the ground finish roll. is also slightly high, but after that it tends to decrease and the average rolling pressure remains stable around 130Kg/mm ² despite the increase in work hardening (cumulative strain) of the rolled material. In other words, in the normal cold rolling method, the rolling pressure increases monotonically as the cumulative reduction rate increases, so the rolling pressure at the end of rolling becomes extremely large, but when coating rolls are used, the cumulative reduction rate is high. Since the rolling pressure remains stable at a relatively low value even as the temperature increases, cold rolling can be carried out smoothly to the end without causing seizure of the workpiece or significantly reducing rolling efficiency at the end of rolling. can.

Although the reason why the rolling pressure in the middle to late stages of rolling decreases due to the use of a coating roll is not necessarily clear, the surface of the rolled material (or the coating layer on the surface of the rolling roll) is It is thought that this is because the metal fine powder exfoliated from the surface produces lubricant and metal soap, which reduces the frictional resistance in the boundary lubrication region. Although it is not clear why the rolling pressure in the low cumulative reduction region when coating rolls are used is somewhat large, the formation of metal soap at the bit part is related to the amount of plastic deformation of the rolled material, and a large amount of metal soap is generated at the bit part. There is a theory that a certain amount of plastic deformation is necessary for metal soap to be generated, and because the amount of plastic deformation of the rolled material is small in the early stage of rolling, a sufficient amount of metal soap is not generated. It is presumed that this is the case.

The reason why oil pits are significantly suppressed by using a coating roll can be considered as follows. In other words, what is an oil pit?
As mentioned above, it is thought that the high-pressure rolling oil present in the roll bite pressurizes the surface of the rolled material, which is softer than the roll surface, causing unevenness.
In coated rolls, there is a relatively soft metal coating layer between the hard roll base material and the rolled material, so it is thought that this coating layer deforms preferentially and suppresses the deformation of the rolled material. .

Furthermore, when we conducted experiments to clarify the thickness of the coating layer in order to effectively exhibit the various effects described above, we found that the effects can be effectively exhibited if the thickness is 0.2 μm or more. confirmed. This thickness can also be considered to define the lower limit thickness for forming a uniform baked coating layer over the entire surface of the mill roll. In other words, it is technically extremely difficult to uniformly form a coating layer with a thickness of less than 0.2 μm over the entire surface of a rolling roll.
Uncoated portions may remain on a portion of the roll surface, causing local seizure or oil pits. There is no particular upper limit for the thickness of the coating layer, but since the thicker the layer, the better the performance, the most common range is 0.2 to 2 μm, considering the workability of forming the coating layer. It is. In addition, the surface of the coating layer is 0.2μm
max (same level as the surface roughness of the grinding finish roll)
It is preferable to have a roughness of at least a certain level of roughness, and by forming a coating layer with such a rough surface, the effect of suppressing seizure and oil pits can be further enhanced. A coating layer with such surface roughness can be easily formed by passing a dense hexagonal metal plate under insufficient lubrication, as explained earlier. It can be carried out at the end of the forming process, or at any time after installation in the cold rolling equipment and before the start of cold rolling.

The inventors of the present invention have previously proposed that ``In cold rolling a dense hexagonal metal sheet, the rolled metal is baked onto the roll surface by rolling with poor lubrication in the early stage of rolling, and then rolled under normal conditions. The company has proposed a method of cold rolling, which has succeeded in preventing seizure and oil pits.
The essential technical idea of the present invention is very similar to the above-mentioned earlier invention, but whereas this earlier invention is carried out in a series as a preliminary process of cold rolling,
The present invention clearly constitutes a separate invention in that a baked coating layer of a predetermined thickness is formed at an arbitrary time separate from the cold rolling process.

By forming a coating layer of a predetermined thickness on the surface of the rolling roll in this way, seizure and oil pits can be drastically reduced, but in order to obtain the high level of surface precision intended by the present invention, In addition to this configuration, use an emulsion-type lubricant in which the center particle diameter of the dispersed particles (for example, the particle diameter at the peak position in the emulsion particle size distribution as shown in Figure 2) is 5 μm or less and the saponification value is 80 or more. There is a need to.

Incidentally, Figure 3 shows the rolling reduction ratio [εi=In(ho/hi)] when using emulsion-type lubricants (concentration 1% or 0.5%) containing various tallow-based oils with different saponification values as dispersoids. This is a graph of experimental results examining the relationship between the average rolling pressure (Pm) and the average rolling pressure (Pm). However, the rolling conditions are: work roll diameter 254mm, rolling speed 12m/
The rolling reduction rate per pass is 10% in minutes, and the thickness is 1.0
A pure Ti plate with a thickness of 0.5 mm was rolled to a thickness of 0.5 mm. As is clear from Figure 3, the tendency for the average rolling pressure to increase as the rolling reduction rate increases varies markedly depending on the saponification value of tallow-based oil. It is thought that the rolling pressure will increase rapidly and the rolling operation will become substantially difficult. The higher the saponification value of tallow-based oil, the smaller the tendency for the rolling pressure to increase, but the rolling pressure observed when using a lubricant with a saponification value of 80 is the limit in actual operation.
If it is less than 80, the rolling pressure will be too high and actual operation will be difficult. For products using tallow-based oil with a rating of 80 or higher, the above-mentioned increasing trend becomes relatively slow, and the average rolling pressure reaches a plateau at about 170 kg/mm ² or less, and even if the rolling reduction rate is increased, the average rolling pressure increases even more. Rolling pressure does not increase. As is clear from these results, in order to suppress the threading resistance during rolling and smoothly perform cold threading, the oily dispersoid that makes up the emulsion-type lubricant must have a saponification value of 80 or more. It turns out that you should choose one.

Next, the following experiment was conducted to clarify the influence of the particle size of the oily dispersoid on the lubricating performance. That is, tallow-based oil (saponification value 180) was used as the oily dispersoid, an emulsion-type lubricant (concentration 1%) with different center particle diameters of the dispersoid was used, and a Ti plate (crystal particle diameter: approximately 5 μm) was used.
at a speed of 200m/min using a 200mmφ rolling roll.
The oil pit depth was compared when cold rolling was performed from 1.0 mmt to 0.5 mmt at 15%/1 pass. The results are shown in Figure 4. Using an emulsion-type lubricant with a center particle size of 5 μm or less can suppress the oil pit depth to 1 to 2 μm or less.
In particular, when using particles with a center particle size of 3 μm or less, the oil pit depth is almost zero (no oil pit). On the other hand, if an emulsion type lubricant with a center particle diameter exceeding 5 μm is used, the oil pit depth cannot be kept below 2 μm. Reference photo 3 is a micrograph used as a drawing to show an excerpt of the surface properties of the rolled plate obtained above. As is clear from this figure, emulsion-type lubrication with a center grain size of 5 μm or less (saponification value is 180) It can be seen that the surface precision of the rolled plate (pure Ti plate) obtained by combining the agent and the coating roll is extremely excellent.

〔Effect of the invention〕

The present invention is constructed as described above, and by using a special baking coating roll,
It has become possible to obtain a dense hexagonal metal rolled plate with excellent surface precision and no oil pits or seizure. Moreover, since the rolling pressure during rolling can be kept low, there is no fear of excessive load being applied to the work rolls, and cold rolling with good operability can be smoothly performed.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between cumulative strain and average rolling pressure during cold rolling, Figure 2 is a graph to explain the meaning of central grain size, and Figure 3 is a graph when tallow-based emulsion lubricant is used. Reduction rate at [εi=In
(ho/hi)] and the average rolling pressure (Pm), and FIG. 4 is a graph showing the relationship between the central particle diameter of the same lubricant and the oil pit depth.

Claims (1)

[Claims] 1. Cold rolling is carried out using a rolling roll with a dense hexagonal metal coating with a thickness of 0.2 μm or more on the surface, and an emulsion type rolling oil with a center grain size of 5 μm or less and a saponification value of 80 or more. A method of cold rolling a dense hexagonal metal plate, characterized by: