JPH0469483B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to rolling process rolls formed with a composite film, particularly cold rolling mills, skin pass mills,
This is a proposal regarding rolls for cold rolling processes used in rolling equipment for manufacturing cold rolled steel sheets, such as recoilers. [Conventional technology] Generally, cold-rolled steel sheets and various types of plating base plates, etc.
After going through the steps of steelmaking, blooming, and hot rolling, it is manufactured by performing pickling, cold rolling, annealing, and temper rolling.
Various rolling process rolls used in cold rolling processes are required to have the following characteristics. (1) It must have an appropriate coefficient of friction against the running material and exhibit so-called gripping properties. In other words, (a) a preset tension can be applied, (b) the threaded material does not slip, (c) it has a function to prevent the threaded material from meandering, and (2) the threaded material has no surface scratches, impressions, etc. (3) It is difficult for foreign matter (oil, iron ore powder, other general dust, etc.) to adhere to the surface; (4) The above functions can be maintained for a long period of time. Conventionally, rolls for rolling processes that meet these demands have been used whose surfaces are electroplated with chrome. [Problems to be Solved by the Invention] However, although the conventionally used electrochrome plating rolls are excellent in that they do not cause surface flaws on the threaded material, they still have the following drawbacks. (1) Insufficient wear resistance and short life. (2) When subjected to high temperature history (over 300°C), the hardness of the chrome plating layer decreases and the wear resistance deteriorates dramatically. (3) In order to improve wear resistance, it is necessary to increase the hardness, but there are limits to the chrome plating method, and it is difficult to increase the hardness beyond the current hardness (Hv850-930). Furthermore, even if a material with high hardness can be obtained, it is very brittle, and therefore the threaded material is scratched by small lumps of peeled chrome plating, which shortens the life of the chrome plating. As explained above, electrochrome plated rolls, which have been commonly used as rolls for cold rolling processes, have the fatal drawback of short lifespan, as well as demands for high functionality and improved productivity for threading materials. There was also the problem that it was not possible to satisfy the requirements. This invention aims to take advantage of the advantages of conventional chrome-plated rolls while at the same time providing the hardness of a metal-carbide cermet spray coating and the smoothness of an electroplated coating. By doing so, the purpose is to provide a roll with a composite film that is softer than carbide and has plastic deformation performance. [Means for Solving the Problems] The present inventors have conducted extensive research to solve the above problems regarding rolls for rolling processes, and have obtained the following findings. (1) When electroplating is applied on the above composite film, this electroplated film has the same level of smoothness as chrome plating and the ability to prevent the adhesion of foreign substances. (2) Even if the outermost layer is an electroplated film, if there is a cermet sprayed layer underneath, the carbide cermet particles in the base can provide an appropriate amount of frictional force with the threaded material, which conventional chrome plating lacks. You can make up for it. (3) Although it is a base, the carbide sprayed layer is extremely hard and has excellent wear resistance, so even if it becomes a composite film, it will continue to perform well for a long time. (4) The carbide cermet film has excellent adhesion not only to the roll base material but also to the electroplated film, and the particles of the film are strongly bonded to each other, so it does not come in contact with the plate material. It also does not peel off, and there is no local peeling phenomenon like chrome plating. This invention was made based on such knowledge,
After thermal spraying a composite material such as tungsten carbide, chromium carbide, titanium carbide, etc. with cobalt, nickel, or nickel-chromium alloy on the surface of the roll, the sprayed surface is then coated with nickel plating or nickel-iron. This paper proposes a roll on which a composite film is formed by electroplating an alloy. In addition, in the present invention, if the type of plating liquid is appropriately selected during the above-mentioned plating, a plated layer having a wide range of hardness can be obtained. [Operation] Generally, the carbide cermet coating sprayed on the roll surface is harder (Hv 1100-1300) and has better wear resistance than electrochrome plating (Hv 850-930), but when the surface is observed microscopically, The structure has a forest of carbide particles with acute angles.
For this reason, such a thermal spray roll is capable of applying high tension to the threading material and can maintain excellent threading performance over a long period of time without causing slippage. However, on the other hand, there was a problem in that the threaded material was susceptible to scratches and depressions. As a solution to the above-mentioned problems, the inventors previously proposed in Japanese Patent Application No. 62-243614 a composite film forming roll in which electroless nickel plating is applied on a metal carbide cermet sprayed film. Although this roll proposed earlier shows extremely good performance, there is little equipment for electroless nickel plating, especially for large rolls, and even if plating equipment for large rolls were installed, the equipment cost would be high. Since the amount of work could not be expected to be enough to amortize the cost, the cost problem remained, in that the electroless nickel plating process required a considerable amount of expense. The present invention utilizes the characteristics of the carbide cermet thermal spray coating as is, similar to the prior art proposed technique, while overcoming the above-mentioned problems by applying electronickel plating to the surface of the coating in place of the electroless nickel plating. Alternatively, we focused on applying electric nickel-iron alloy plating. In other words, when such an electroplating process is performed on a thermally sprayed coating, carbide fine particles with acute angles in the base coating are completely covered with nickel or nickel-iron alloy precipitates, resulting in moderate frictional threading. It is possible to extend the lifespan while retaining the properties. In addition, in the present invention, the reason why electroplating is possible when forming a composite film is that normally, a single carbide has poor electrical conductivity and cannot be electroplated, but in the case of a cermet film, the metal components mixed in the film are This is because it has a current-carrying effect. The electroplated coating formed in this way is advantageously deposited even in the depressions (concave portions) of the base coating, so that the surface of the thermal spray coating can be uniformly and completely covered. Moreover, by changing the composition of the nickel plating solution during electroplating, the hardness of the plating film can be controlled over a fairly wide range. Furthermore, nickel/iron alloy plating is better against the pressure received from the threaded material than nickel plating. As mentioned above, the rolling process roll of the present invention, which is coated with a composite coating of a thermal spray coating and an electroplated coating, exhibits properties equivalent to conventional electrochrome plated rolls in the initial stage of use, and has appropriate wear resistance. It maintains smoothness and smoothness, and at the same time there is no fear of scratches occurring in the threaded material. That is, when a roll is actually used, as the period of use becomes longer, the nickel plating film on the part that is in contact with the threading material wears out, and the carbide fine particles are exposed and begin to come into contact with the threading material. However, in the case of the roll of the present invention, the exposed WC fine particles are surrounded by a nickel plating film that is softer than the carbide particles, so the contact with the threading material is limited to minute point contact, which prevents the occurrence of scratches. It suppresses On the other hand, the recesses that do not come into contact with the running material are covered with nickel plating and are relatively smooth, so even if iron rust or other solid dust adheres to them, they are easily discharged out of the system and remain clean. can do. Furthermore, as the period of use of the roll increases and the wear of the nickel plating film progresses, the number of contact areas between the carbide particles and the threading material increases. However, the rate of increase in the contact area is generally slow, so
It is thought that there is no occurrence of large flaws as seen in the contact area when the thermal spray coating is applied alone, and rather the two are in a state where they are easily compatible. In this invention, a thermal spray material made of metal carbides such as WC, CrC, and TiC, and Co, Ni, Cr, and alloys thereof is used. For example, the following composition is used. WC(X)−Co(Y) Cr ₃ C ₂ (X)−Co(Y) TiC(X)−Co(Y) WC(X)−Ni(Y) WC(X)−Ni(Y)−Cr (Z) However, X = 95wt% to 68wt% Y = 5wt% to 28wt% Z = 5wt% to 25wt% Also, nickel and nickel-iron alloy are used as the base to be applied on the thermal spray coating. Next, the manufacturing process of a roll for a rolling process having a composite coating of the present invention will be explained based on FIG. First, the surface of the roll to be treated is blasted using alumina grains to remove rust and foreign matter from the roll surface and to give it an appropriate roughness as a base for thermal spraying. Thereafter, a carbide cermet spray coating of a predetermined thickness is formed on the carbide cermet material by jet coat spraying or plasma spraying using a hydrocarbon-oxygen combustion flame as a heat source. After that, it is possible to proceed directly to the electroplating process, but depending on the sheet material, electroplating may be applied after lightly mechanically polishing the sprayed coating, or after polishing, the surface may be blasted again using fine alumina particles. Electroplating may be performed after dulling the surface to a uniform roughness. [Example] Example 1 (1) Conditions for implementation (a) Roll used: Material: JIS G5101 (1978) carbon steel casting SC42 Dimensions: Diameter 800 x Length 1650 mm (b) Cermet thermal spray material: (a) WC ( 88%) - Co (12%) (b) WC (73%) - Cr (20%) - Ni (7%) Thickness 100μm (c) Types of electroplating and plating conditions: As shown in Table 1. be. In other words, normal pure nickel plating 2 is used as nickel plating.
Types: 1 type each with semi-gloss nickel plating, glossy nickel plating, 1 type with nickel/iron alloy plating
A total of 5 types. The plating conditions were as follows: The roll was immersed in a plating solution bath maintained at 50℃±2℃, and treated to a thickness of 3μm at a cathode current density of 3A/ ^dm2 , and the roughness of the composite coating surface was reduced to Ra2. .0~3.5μ
Adjusted to m. (d) Hardness of precipitated metal: As shown in Table 1, the hardness of precipitated metal varies depending on the type of plating solution, and in normal nickel plating, it is generally soft and Hv220.
~240, slightly harder for nickel/iron alloys
The hardness is Hv350-390, 520-570 for semi-gloss, and Hv700-850 for glossy, showing extremely high hardness.
Therefore, regarding the roll according to the present invention,
A material having a hardness of Hv220 to 850 is appropriately selected. Now, the film performance of the roll manufactured through the above-described process was investigated using it as a bridle roll of a cold rolling skin pass mill shown in FIG. 2. As you can see from the diagram, structural steel plate (width 1200 x thickness 2.3 mm) is supplied from the recoiler.
1 is given tension by bridle rolls 2, 3, 4, and 5 provided on the mill entrance side, and guided to the mill body by the action of a work roll 6 and a back-up roll 7 that supports it. Rolled. Thereafter, it passes through bridle rolls 8, 9, 10, and 11 on the mill exit side to become a product. Therefore, in this example, the rolling equipment shown in FIG. 2 was operated continuously, and the presence or absence of scratches on the threaded material and the state of damage to the film on the roll surface were evaluated primarily by visual observation. As comparison rolls, a conventionally used hard chrome plated roll and a roll coated with only a WC cermet thermal spray coating were used, each with the same surface roughness as the composite coating of the present invention.
It was finished to Ra2.0-3.5μm and tested. Table 2 summarizes the above survey results. As can be seen from these results, the coating made of WC cermet alone caused scratches on the threaded material, and the coating made of chrome plating alone exhibited good performance against scratches, but it had a short lifespan and only required one month of operation. Later, peeling of the film occurred. On the other hand, the composite coating of the present invention does not cause any scratches on the rolling material, maintains a healthy condition even when inspected one year later, and has less iron rust and foreign matter adhering to the roll surface. It was good and warm.

【table】

【table】

[Table] Example 2 Using the test roll of Example 1, the following metal carbide cermet was thermally sprayed to a thickness of 100 μm, and then the first
In addition to electroplating as shown in the table, the surface roughness of the composite film is Ra2.0.
Finished to ~3.0 μm. Thermal spraying material: (c) Cr ₃ C ₂ (80%) - 20% (80Ni - 20Cr) (d) TiC (75%) - 25% (80Ni - 20Cr) Also in this example, the cold Continuous operation was performed using a rolling line, and the occurrence of scratches on the threaded material and peeling of the composite coating were investigated. As a comparison example roll, the surface was coated with Ra2.0 to 3.0 as it was sprayed.
I used the finished product. Table 3 summarizes the results. The roll having the composite film of the present invention did not cause any scratches on the running material and was in good condition even when inspected one year later. As is clear from this result, it was found that the composite coating of the present invention can be used not only with WC but also with Cr ₃ C ₂ and Ti as the carbide, and also in the electrolytic nickel plating on the thermally sprayed coating. It was found that all of the five types listed in Table 1 can be applied under the following conditions. However, regarding soft plating (A and B in Table 1), there was a tendency for the electroplated film to be easily scratched when the roll was handled, but this was a handling problem and the roll film function No problems were found. On the other hand, the comparison roll with only a thermal spray coating caused small scratches on the running material, although its surface roughness was equivalent to that of the composite coating of the present invention. An investigation into the reasons for the superiority of this composite film revealed the following. In other words, even if the surface roughness is the same, the composite film of the present invention has electroplating applied to the outermost layer, so when it comes into contact with a running material, this electroplated layer is destroyed first, and the lower part is destroyed. The carbide particles present in the plate are exposed and come into contact with the threading material. However, the number of such particles is much smaller than that of a simply thermally sprayed coating, and the area around the carbide particles is covered with an electroplated coating, which acts as a kind of buffer and makes the contact with the running material gentle. , it is thought that it did not cause any scratches. That is, FIG. 3 schematically illustrates this phenomenon, and in the figure, 3-1 is a schematic cross-sectional view of the state where the carbide cermet spray coating 2 is still formed, and 3-2 is a schematic cross-sectional view of the state where the carbide cermet spray coating 2 is still formed. 3-3 is a schematic cross-sectional view of an example of a composite film of film 3 which is electroplated on film 2 of No. 1, and 3-3 is a schematic cross-sectional view of the composite film of No. 3-2 after it has been brought into contact with a passing plate material. It is.

〔Effect of the invention〕

As explained above, according to the present invention, it has excellent wear resistance, does not cause scratches on the threaded material, and has the advantage of minimizing the adhesion of iron rust and foreign substances. A roll for a rolling process with excellent properties can be obtained. Moreover, the present invention does not lose the inherent characteristics of carbide cermets, which have seizure resistance and appropriate gripping properties, and is therefore suitable as a composite coating for rolls at low cost.

[Brief explanation of the drawing]

Figure 1 is a manufacturing process diagram of the roll for the rolling process of the present invention, Figure 2 is a schematic diagram showing the trial situation of a skin pass mill and tension bridle roll to which the roll of the present invention is applied, and Figure 3 is a composite coating film. 1 shows a state in which only a carbide cermet sprayed coating is formed, and 2 shows a schematic diagram of a cross section.
3 shows the state after electroplating has been applied to the film 1, and 3 shows the state after the film 2 has been brought into contact with the plate material. 1...Roll, 2...Thermal spray coating, 3...Electroplated coating.

Claims (1)

[Scope of Claims] 1. A composite coating obtained by forming an electroplated coating of nickel or nickel-iron alloy on the sprayed coating on the surface of a roll having a carbide cermet sprayed coating. Rolls for rolling process. 2 The above thermal spray coating is made of tungsten carbide,
The roll for a rolling process according to claim 1, which is a carbide cermet made of a metal carbide such as chromium carbide or titanium carbide, and a metal such as cobalt, nickel, chromium, or an alloy thereof.