JP2624278B2 - Conductor roll and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductor roll, particularly to a conductor roll suitably used for continuous electroplating of a steel sheet, and a method for producing the same.

The conductor roll proposed in the present invention is also applied in the fields of continuous electrolytic polishing (iron and steel, non-ferrous metals), electrolytic degreasing of metallic materials, electrolytic descale, and anodizing of aluminum and its alloys. is there.

[Conventional technology]

In general, electroplating of a thin steel plate is generally performed by passing a steel plate to be plated through a plating tank through a cathode conductor roll at a predetermined speed. For example, FIG. 1 shows an outline of a continuous electroplating apparatus. In this apparatus, a steel plate 1 to be plated first enters a plating tank 3 filled with a plating solution 2 and contacts a conductor roll 4 of a cathode, and at the same time, maintains a potential as a cathode and moves up and down (or one of them). Pass between the anodes 5 installed in parallel. The steel plate 1 to be plated is plated while passing through the anode 5, and then goes out of the tank to be a product through processes such as water washing and drying.

Conductor rolls used in the above-mentioned equipment must have the following characteristics in terms of their functions and durability: a. Good current-carrying performance, b. Excellent corrosion resistance, and c. Excellent wear resistance. , Three performances are required.

On the other hand, conventional conductor rolls for electroplating use the following materials and
Structured rolls have been used.

Commercially available Hastelloy C alloy (16Cr-4W-5Fe-17Mo-remaining Ni)
Rolls made by electroplating Ni or Cr on the surface of steel rolls, rolls sprayed with metal carbide, and rolls in which a corrosion-resistant Ni-based alloy (for example, Hastelloy C alloy) is weld-welded on the steel roll surface.

However, such a conventional conductor roll has a drawback that, although excellent in certain properties, it cannot satisfy other properties. For example, in the case of the above Hastelloy C roll, even if it exhibits excellent corrosion resistance to the plating solution, because it is soft (around Hv200), it will cause wear damage within a short period of time due to contact with the passing material (steel plate). In the case of the above-mentioned Ni or Cr plating roll, there is a problem that the film thickness is thin and easily corroded by an acidic plating solution, and the life of the roll is short. metal carbides (WC, TiC, Cr, etc. ₃ C ₂₎ when the roll was sprayed, in particular acidic strong plating solution (e.g.
When used in a pH range of 2 or less, the plating solution that has penetrated through the pores of the thermal spray coating corrodes the steel roll of the base metal, causing the thermal spray coating to peel off and fall off. The overlaid roll is
In addition to the drawback that the steel plate that comes into contact during use is easily damaged by wear, the dendritic structure generated during welding due to the corrosive action of the plating solution emerges on the roll surface (just like a macro-etched state). There was a problem that the pattern was transferred to the plated steel sheet and the quality was significantly reduced.

[Problems to be solved by the invention]

In the case of the above-mentioned conventional technology in which a Ni-based alloy is weld-welded on the roll surface, the problematic dendritic structure (hereinafter referred to as “bead mark”) of the weld overlay depends on the corrosion resistance and wear resistance of the overlay material. It is said to appear. In particular, in the current situation where the line speed has been increased recently to improve productivity (thereby a tendency to lower the pH of the plating solution as a means of improving the cathode current efficiency and plating adhesion efficiency). The problem is getting bigger and bigger.

In short, an object of the present invention is to improve the corrosion resistance and corrosion and abrasion resistance while suppressing the appearance of bead marks, and to propose a conductor roll that can solve all the above-mentioned technical problems of the prior art, Another object is to propose a method for producing such a roll advantageously.

[Means for solving the problem]

According to the study of the present inventors, the corrosion resistance and the wear resistance of the conductor roll were investigated based on past damage cases, and it was found that both were in a very close relationship.
That is, the wear phenomenon on the roll surface can be roughly explained as follows.

The material (metal) of the roll is corroded by the plating solution,
The corrosion products generated here are usually carried away by the contacting plate.

When the material of the roll is an alloy, only a specific alloy element is selectively eluted into the plating solution to form a porous film. Since the porous film has a small mechanical strength, it is removed by contact with the sheet material.

By selective elution of the alloy element, a bead mark mainly due to a dendritic structure generated at the time of weld overlaying appears, and this is transferred to a threaded material (plated steel sheet).

What can be known from the above phenomena is that if the roll surface is overlaid by a welding method that uses a hard and corrosion-resistant alloy and does not precipitate a dendritic structure, a conductor roll that can solve the above-mentioned problems can be solved. Manufacturing is possible. Further, it was also found that if the heat treatment is performed after the overlay welding, the overlay welding structure is further stabilized, and a weld overlay having excellent corrosion resistance and wear resistance is obtained.

The present invention based on such knowledge, on the surface of the steel roll, at least the outermost layer is a submerged arc welding layer
The purpose of the present invention is to form a multilayer weld overlay of a Co-base weld overlay alloy as a basic problem-solving means.Furthermore, in addition to the above-described processing, in order to stabilize the overlay structure, As a more preferable means for solving the problem, a heat treatment layer obtained by heating this build-up layer to a temperature of 1050 ° C. or more for 10 minutes or more is adopted.

The Co-based welding overlay alloy is one of the alloys containing Co as a main component and Cr-W-Fe, Cr-W-Fe-Ni, or Cr-Fe-Ni-Mo added thereto. Alloy, and the multi-layer weld overlay is composed of a plurality of sub-arc weld layers alone or a plurality of sub-arc weld layers, the lower surface of which includes a plasma powder overlay weld layer. It is.

[Action]

As a roll overlaying alloy used in the present invention, a known Hastelloy C alloy (16Cr-17Mo-5Fe-4.5W-
Ni) An alloy that is harder, has at least equivalent corrosion resistance, and is capable of overlay welding is required.

Table 1 shows the chemical composition and hardness of the weld overlay alloy and the known Hastelloy C alloy used in the roll of the present invention.

As can be seen from Table 1, the weld overlay welding alloys (A to E) of the present invention contain Co as a main component, and contain Cr-W-Fe and Cr-WF.
e-Ni, Cr-Fe-Ni-Mo is a high hardness Co alloy with the addition of Hastelloy C alloy (F).
It is a Ni-based alloy of Ni and has a hardness of around 200 Hv and is soft.

The following investigation was performed using these alloys (AF). That is, the plasma powder overlay welding method (hereinafter “PTA
Method) and the submerged arc welding overlay method (hereinafter referred to as the "submerged method").
The surface of the base material of TKM13A was overlaid using the above-mentioned A to F alloys, and the thickness of all the layers was finished to 20 mm. (After the first layer, the surface was smoothed by grinding. The second layer was overlaid and the surface was ground again.) Then, the surface of the overlay is etched using aqua regia, and the presence or absence of bead marks due to the dendritic structure peculiar to the weld overlay and the incorporation of iron into the overlay due to the dissolution of base metal components. Was examined for some.

Table 2 shows these results. In the build-up layer obtained by the PTA method, severe bead marks were generated in all the alloys regardless of the chemical composition of the alloys.

FIG. 2 shows typical bead marks. When the bead marks are classified according to their shapes, they are rippled bead marks, boundary bead marks, and droplet-shaped bead marks.
Of these, と means that there is a part that is strongly affected by heat at the time of overlaying and a part that is not affected, so that different phases of the metal structure are formed at the boundary, and this becomes a bead mark, and Depending on the shape of the solidification line in the part, a round macrostructure may be formed, and in some cases, the lower bead may locally appear in a round shape due to cutting or polishing (wear reduction) of the upper bead.

With respect to conductor rolls, the appearance of the above-mentioned "droplet beads" is the most problematic.

The above-mentioned bead marks can be reduced to some extent by heating to a high temperature after the cladding to make the structure uniform. However, a temperature of 1200 ° C. or more is required for complete extinction. At such a high temperature, adverse effects such as deformation of the roll base material, coarsening of the crystal of the base material and reduction in strength occur.

On the other hand, as shown in FIG. 3, the layer layered by the submerged welding method has some ripples and bead marks at the boundary, but the degree is small, and the melting point is considered to be the most harmful. No drop bead marks are generated.

The reason is considered as follows. That is, the PTA method generally has a low heat input and a small amount of so-called base metal penetration, so that when the second layer is built up, the first layer has a small penetration amount, and furthermore, weaving is required.
The dendritic structure of the layer appears clearly on the surface, and droplet beads are easily formed between the layers. On the other hand, in the submerged method, since the heat input is large and the penetration is large, most of the first layer is also melted when the second layer is built up, and both solidify as a substantially integrated weld metal. No bead marks are generated.

For these reasons, when attention is paid to the presence or absence of the appearance of a bead mark, it is found that it is more advantageous to employ the submerge method to form the weld overlay by applying the present invention to the present invention.
However, in this process, if the two-layer overlay welding is performed by the submerged method, the amount of heat input into the base material (roll) increases due to the large amount of heat input in this method, and the iron in the base material component becomes There is a tendency to penetrate the upper layer. This incorporation of iron into the build-up layer is not preferred because it promotes a reduction in the corrosion resistance of the build-up layer to the plating solution.

In the present invention, in order to overcome the problem of iron contamination in the base material, first, the first layer of plating is overlaid by a PTA method with a small heat input using a hard alloy, and then the second layer is plated thereon. We have come up with a method of overlay welding on the plating of aluminum by the submerge method with a large heat input. It has been found that by performing such multi-layer welding overlay, it is possible to form a build-up layer having few bead marks and having excellent corrosion resistance and corrosion wear resistance on the steel roll surface.

As a more preferred roll structure in the present invention,
A heat treatment of the multi-layer weld overlay layer after the overlay weld homogenizes the structure of the overlay layer, and it is better to transform the overlay weld layer into a build-up layer peculiar to a mixed structure that is less susceptible to macro-etching action due to local corrosion. It turns out.

Table 3 shows the overlays obtained by the method of the present invention,
After holding at various temperatures, etching was performed with aqua regia to investigate the occurrence of bead marks. As is clear from the results in Table 3, the bead mark was 1000 ° C.
At the following temperatures, there was no change, but at 1050 ° C, the temperature was reduced by maintaining the temperature for 10 minutes or more, and at 1,150 ° C, almost disappeared.

Next, corrosion resistance and corrosion wear resistance of the weld overlay and the heat treated weld overlay formed on the surface of the steel conductor roll will be described based on experimental results.

The experimental conditions of the corrosion resistance and the corrosion wear resistance described below are as follows.

Types of overlaying alloys: 6 types of the above (A to F alloys) Roll base material: JIS G 3445 (1983) STKM13A Overlaying method: 1st layer 8 mm by PTA method 2nd layer submerging method The method of the comparative example-Both the first and second layers were 15 mm in total by the PTA method. Heat treatment: 1150 ° C for 15 minutes About the corrosion resistance evaluation method of the overlay and the test results As a simulated electroplating solution, sodium sulfate 70 g / l Solution and add sulfuric acid to it to reduce the hydrogen ion concentration.
Prepare a specimen adjusted to 1.3 and heated to 60 ° C, into which a test piece (length 20 × width 20 × thickness 10m) collected from the overlay
m) is immersed, and a pulse current is applied to the test piece as a cathode for 0.2 seconds and stationary for 0.6 seconds at 1 A / cm
^The current was applied for 24 hours at a strength of ² (test piece area), and the corrosion resistance was evaluated by measuring the appearance change and corrosion current after the test.

FIG. 4 (a) shows the pulse current supply device, and FIG. 4 (b) shows the pulse current waveform. In the figure, a test piece 41 is contained in a glass test water tank 44 together with a simulated plating solution 42 and a platinum counter electrode 43, and the tip of the test piece 41 is connected to a terminal of the pulse generator 5. The counter electrode of platinum is connected to the terminal so that a predetermined pulse current can be applied to both electrodes. On the other hand, a capillary 46 made of a glass tube is provided on the front surface of the test piece 41, and the inside of the capillary 46 is filled with a simulated plating solution. This capillary 46 is connected to a beaker 47 filled with the same liquid and a reference electrode (Ag / AgC
l) It is also connected to a beaker 49 in which a 48 is installed via a salt bridge 50 made of a glass tube. The beaker 49 contains 1
The prescribed potassium chloride aqueous solution 51 is filled.

The reference electrode is connected to a potentiometer 53 by a lead 52, and the test piece 41 is also connected to the potentiometer by a lead 54. In short, the potential of the test piece surface due to the pulsed current is always recorded by a potentiometer based on the Ag / AgCl electrode, and the change in polarization potential and current causes the corrosion current ( Corrosion).

Tables 4 and 5 show the ratio between the change in appearance of the test piece by the pulse current test and the corrosion current value obtained from the polarization characteristics.

As is clear from Tables 4 and 5, all the specimens of the build-up layer obtained by applying the PTA method turned black regardless of heat treatment, and it was recognized that a large corrosion current was flowing. Was. The black color change of the test piece was due to the corrosion product of the test piece material covering the surface. When the black coating was removed using 1N hydrochloric acid, a sharp weld bead shape was observed. Therefore, the weld overlay obtained by the PTA method was found to be unsuitable as a conductor roll material.

On the other hand, the test piece subjected to submerged arc welding according to the method of the present invention has an extremely glossy appearance even after the test, and the corrosion current value is only about 50% of the comparative example.
It was confirmed that excellent corrosion resistance was exhibited.

In this test, the Hastelloy C alloy used as a comparative example was also examined. However, only the corrosion resistance was good, and the alloy exhibited the same performance as the alloy of the present invention.

Evaluation Method and Test Results of Corrosion-Abrasion Resistance Using the same simulated electroplating solution used in the above-described corrosion-resistance evaluation method, corrosion-wear characteristics were investigated by a method as shown in FIG. That is, test rolls 61 (diameter 50 × length 100 mm) manufactured by various methods are set on the plating solution tank 62. The test roll 61 is rotated 25 times per minute by a motor (not shown).

On the surface of the test roll 61, a plating solution 63 is provided with a pipe 64.
And a roll of stainless steel wool mat 65 is pressed against the surface of the roll so that the wool mat 65 reciprocates in the longitudinal direction of the roll, which rotates 25 times per minute. . Therefore, the roll 61
Is always wet with the plating solution. On the other hand, the solution collected in the plating solution tank 62 is sent to the plating solution storage tank 67 by the pump 66, and circulates so as to drop again on the roll surface.

Table 6 shows changes in the roll surface and the amount of weight loss before and after the test, which was conducted for 100 hours by the above-described method. In the weld overlay of the PTA method as a comparative example, clear bead marks all appeared regardless of the type of alloy. As for the weight reduction ratio, the Co-based alloy (A
In the case of using (E), the reduction amount was small, and was about 10 to 20% of that of the Hastelloy alloy (F). Hastelloy alloy showing good corrosion resistance showed a large weight loss,
Since the alloy itself is soft, it is considered that it was strongly affected by the frictional action of the stainless steel wool mat 65, and it was experimentally determined that it was unsuitable as a conductor roll to be used in a strongly acidic plating solution. Proven to.

On the other hand, it was confirmed that the composite overlayer welded by the first-layer PTA method and the second-layer submerged method had a small bead mark even in the case of using a Hastelloy alloy having low corrosion and wear resistance (however, the weight was low). Large decrease). In addition, the roll overlaid by welding using the Co-based alloy of the present invention has a smaller weight loss than that of the Hastelloy C alloy, even if the overlaid by the PTA method.
It turns out that it is excellent in corrosion wear resistance. On the other hand, the results are summarized as follows: Rolls that have been overlaid by the composite overlay welding of Co-based alloys have very little bead marks, have a small weight loss, and are used in strongly acidic plating solutions. This indicates that the conductor roll is excellent.

As shown in Table 2, the first and second layers, both of which are built up by the submerged welding method, have a feature that bead marks are extremely small. However, the penetration of the base metal component is large, and there is a concern that the corrosion resistance may be reduced due to the incorporation of iron.
Therefore, even in a multi-layer weld overlay formed only by the submerged method, it can be used satisfactorily in an environment where the pH of the plating solution is high and the corrosiveness is mild, since the wear resistance is excellent.

Therefore, the present inventors used the overlaying alloys A and D,
Layered specimens and two-layer specimens were prepared by the PTA method as a submerged welding method and a comparative example, and the pH of the simulated plating solution was adjusted to 1.6,
The corrosion resistance of the build-up layer was investigated using the apparatus shown in FIG. 4 while changing to 2.3 and 3.0. Table 7 shows the results.
PTA is used for the submerged welding method for the overlay layer with only the layer
It was clearly inferior to that obtained by the method, and a decrease in corrosion resistance due to the incorporation of base metal iron was evident.

However, since the iron mixing ratio of the two-layer submerged weld overlayer is smaller than that of the single-layer overlayer, the corrosion current amount is 25 at pH 1.6.
%, But at pH values above 2.3 the difference was around 10%. Therefore, it was found that a conductor roll having a small appearance of bead marks could sufficiently withstand practical use in an environment of a plating solution having a pH of 2.3 or more.

In addition, when the same type of test as described above was conducted by performing three-layer overlaying by the submerged welding method, the corrosion resistance was improved as compared with the two-layer overlaying. This is because the iron content of the base metal is reduced by overlaying the overlay, and if the overlay is increased even if the submerged welding method is used, the overlay by the combination of the PTA method and the submerged welding method It is evident that corrosion resistance comparable to that of.

[Example] Example-1 A weld overlay (first-layer PTA method, second-layer submerge method) of the present invention and a comparative example were mounted on a roll made of JIS G3445 (1983) STKM13A having a diameter of 350 mm and a length of 2100 mm. Both layers were welded by the PTA method to a thickness of 15 mm. There are six types of overlaying alloys A to F. Conductive rolls were prepared for each of the as-welded and heat-treated at 1050 ° C. for 30 minutes after the overlaying. Inspection of the machined surface by the color check method revealed no weld cracks or blowholes. The surface hardness after cutting was within the measurement range shown in Table 1 for each alloy.

Next, continuous electrogalvanizing and tin plating of the steel sheet were performed using these rolls. Table 8 shows the chemical components and plating conditions of both plating solutions, each having strong acidity and plating at a high current density.
This is an extremely harsh environment for a conductor roll.

After operating continuously for 5000 hours as a conductor roll, it was withdrawn from the plating solution and its surface was observed.

After that, it was further operated continuously for 5000 hours under the same conditions, and the surface was observed.After heat treatment at 1050 ° C. for 30 minutes, the surface condition did not change at all and maintained a good surface state. There was found. However, the surface of the roll, which was not welded but still welded, was slightly etched and exhibited a completely matte shape. However, generation of bead marks was not recognized, and it had a function as a conductor roll.

In contrast, the rolls welded only by the PTA method of the comparative example used under the same conditions suffered severe corrosion wear after 5000 hours of operation (alloy F), and although the corrosion wear was slight, a clear bead mark was formed. Appearance, such as the phenomenon that this is frequently transferred to the plated steel sheet, was observed.

In the case of the weld overlay by the PTA method, which was subjected to a heat treatment at 1150 ° C. for 30 minutes, the appearance of the bead marks was somewhat slow, but transfer to the plated steel sheet was observed.

FIG. 6 (a) shows a microstructure photograph of the roll surface according to the present invention using alloy E, and FIG. 6 (b) shows a build-up layer obtained by the PTA method of a comparative example using the same alloy. 5 is a microstructure photograph of a roll surface having the following. As is clear from these photographs, the build-up layer formed on the roll of the present invention has an extremely stable austenite structure, whereas the build-up layer formed on the roll of the comparative example has a typical dendritic structure. It was found that a large difference was obtained in the metallurgical properties of the overlays obtained even when alloys of the same components were used.

Example 2 Each of the roll base materials used in Example 1 was subjected to the submerged welding method and the PTA method using the overlaying alloys A and D, respectively.
After the layer welding was performed, the plate was subjected to a heat treatment at 1150 ° C. for 30 minutes, and was used as a conductor roll for 5000 hours in an environment in which the pH of the plating solution in Table 8 was adjusted to 2.3. As a result, in the weld overlay by the PTA method, a clear bead mark was observed although little corrosion loss was observed. On the other hand, the rolls on which the weld overlay was formed by the submerged method of the present invention had a small amount of corrosion thinning, no bead marks were observed, and it was confirmed that the rolls were sufficiently practical even in the present pH environment.

〔The invention's effect〕

As described above, the conductor roll of the present invention and its manufacturing technique have the following effects.

(1) It is possible to provide a hard overlay conductor roll in which the iron content from the roll base material is small and a bead mark does not appear during overlaying.

(2) It is possible to provide a conductor roll that is not corroded by a strongly acidic plating solution and is not corroded and worn even when it comes into contact with a steel sheet, and is effective for continuous electroplating extremely efficiently.

(3) The roll heated to 1050 ° C. or higher after the cladding can provide a conductor roll with more excellent corrosion resistance and corrosion resistance of the cladding layer.

(4) The conductor roll as described above can be manufactured reliably and with excellent high yield.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a continuous electroplating tank for a steel sheet using a conductor roll, FIG. 2 is an explanatory view of a droplet-shaped bead mark appearance seen on a weld overlay by a PTA method, and FIG. FIG. 4 (a) is a schematic diagram of a pulse current test device and FIG. 4 (b) is a pulse current waveform, and FIG. The figure is a schematic diagram of the corrosion and wear test apparatus, FIG. 6 (a) is a metallographic micrograph of the overlay layer of the conductor roll of the present invention, and FIG. 6 (b) is the meat of the conductor roll shown as a comparative example. It is a metallographic micrograph of an embossed layer. DESCRIPTION OF SYMBOLS 1 ... Steel plate to be plated, 2 ... Plating solution, 3 ... Plating tank, 4 ... Conductor roll, 5 ... Anode, 41 ... Test piece, 42 ... Simulated plating solution, 43 ... Platinum counter electrode, 44 …… Test tank, 45 …… Pulse generator, 46 …… Capillary, 47
…… Beaker, 48 …… Reference electrode, 49 …… Beaker, 50 ……
Shiohashi, 51 ... Potassium chloride aqueous solution, 52 ... Conductor, 53 ...
Potentiometer, 54 ... Conductor, 61 ... Test roll, 62 ... Plating solution tank, 63 ... Plating solution, 64 ... Piping, 65 ... Wool mat, 66 ... Pump, 67 ... Plating solution storage tank .

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C25F 1/02 C25F 1/02 7/00 7/00 M

Claims (4)

(57) [Claims] 1. A Co-based welding overlay alloy having at least an outermost layer as a submerged arc welding layer on a surface of a steel roll,
A conductor roll having a multi-layer weld overlay. 2. The multi-layer welding build-up layer is composed of a plurality of heat treatment layers in which only a submerged arc welding layer or a plurality of heat treatment layers in which a surface layer including a plasma powder build-up welding layer as a lower layer is a submerged arc welding layer. The conductor roll according to claim 1. 3. Co-based welding overlay comprising Co as a main component and Cr-W-Fe, Cr-W-Fe-Ni or Cr-Fe-Ni-Mo added to the surface of a steel roll. The alloy was subjected to submerged arc welding or plasma powder buildup welding to form a lower buildup weld layer first, and then submerged arc welding to form an upper buildup layer, thereby forming a multilayer weld buildup layer. A method for manufacturing a conductor roll. 4. A Co-based weld overlay alloy comprising Co as a main component and Cr-W-Fe, Cr-W-Fe-Ni, Cr-Fe-Ni-Mo on the surface of a steel roll. By submerged arc welding or plasma powder buildup welding to form a lower buildup weld layer first, then submerge arc welding to form an upper buildup layer, thereby forming a multilayer weld buildup layer, A method for manufacturing a conductor roll, comprising heating the multilayer weld overlay to a temperature of 1050 ° C. or more for 10 minutes or more.