JPS5839906B2 - Roll for hot wire rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot wire roll, and more particularly to a hot wire roll made of cemented carbide having an alloy binder phase consisting of nickel (Ni), cobalt (co) and chromium (Cr). Pertains to rolls for wire rods.

In recent years, rolls made of cemented carbide have been increasingly used for rolling and guiding rolls of hot wire rods.

Due to the characteristics of cemented carbide, such as its high hardness and rigidity at room temperature and hot temperatures, as well as its excellent surface finish, the lifespan of the roll due to wear and surface roughness is significantly longer than that of conventional cast iron rolls. This is because it can be improved.

As is well known, cemented carbide is mainly made of WC (tungsten carbide), Co (cobalt), Ni (nickel),
It is a sintered alloy bonded with iron group metals such as Fe (iron), and W
In addition to C, there is Ti (titanium).

It often contains carbides such as Ta (tartan) and Nb (obium).

As a cemented carbide for rolls, it is necessary to use a material with a high transverse rupture strength with emphasis on toughness, so WC with a relatively large grain size of 1 to 5 μ is bonded with 10 to 30 wt of Co, and Ti
.

Compositions that do not contain carbides such as Ta and Nb at all or contain only a few percent or less are mainstream, but metals other than Co have so far been hardly used as the binder phase.

Cemented carbide rolls for hot wire rods have a satisfactory performance in terms of wear resistance due to their excellent hardness, but due to the brittleness that arises due to their hardness, for example, the caliber surface of the roll has some problems in practical use. It tends to generate countless minute cracks and cause so-called surface roughening.

This rough surface is printed on the surface of the workpiece material, that is, the wire rod, and causes a significant deterioration of the surface quality of the product.

Therefore, an object of the present invention is to provide a roll for hot wire rods which has excellent copper plate roughening properties by preventing minute cracks occurring on the surface and preventing surface roughening as much as possible.

Generally, the manufacturing method of cemented carbide is as follows: After preparing a desired composition of powders such as Co and WC, they are pulverized and mixed using a means such as a ball mill, and then this mixed powder is shaped into a desired shape. After rolling and forming, this molded body is
The roll of the present invention is sintered at a temperature of 350 to 1500°C, and the manufacturing method is the same as the conventional method.

The roll for hot wire rod according to the present invention has a hard carbide phase of WC, TiC, TaC, and NbC with an average grain size of 1 μ to 5 μ (however, TiC, TaC, and NbC have a total weight of 10 wt.
) and the total amount of N for 12 weight type and 30 weight rice cake.
i and a ternary alloy binder phase of Co and Cr,
Cr in the bonded phase is 0.0% relative to the sum of Ni and Co.
30 or less and 0.05 or more with respect to the total bonded phase, and furthermore, Ni has a value of 0.05 or more with respect to the sum of Ni and Co.
33 to 0.90, and the polarization potential is 0.3 V or more with respect to cooling general industrial water.

Hereinafter, the causes of rough skin on the roll surface and embodiments of the present invention will be described with reference to the drawings.

The conditions under which the roll is used are extremely severe, such as wire temperature of 900 to 1100°C and rolling speed of 10 to 6 Qm/s.
ec, subjected to forced cooling with high pressure water at a rolling pressure of 10 to 40 kg/-.

Therefore, for example, a portion of a mill roll is used in a state where it is repeatedly subjected to thermal stress due to rapid heating and cooling in extremely short cycles and mechanical stress due to rolling stress.

On the other hand, the process by which roughness occurs on the roll surface is extremely complicated, but the general outline is as follows.

Before use, the roll surface is ground smooth with a diamond grindstone, so that the unevenness is less than 2 to 3 microns.

The surface roughness that appears in the early stages of processing such as rolling usually begins as traces of detachment of lumps with a depth of 10 to 20 microns and a width of about 20 to 30 microns.

In other words, as shown in Fig. 1, there are minute cracks below the surface.
It occurs parallel to the surface at a depth of 20μ and develops into shedding of lumps.

As a result, a gentle surface roughness is formed with 2 as the top and 3 as the bottom.

In addition, the same rough surface as described above is often caused not by the falling off of lumps but also by fine cracks generated perpendicular to the surface.

That is, the fine cracks shown in FIG. 2 and 4 are generated on the surface, and the vicinity of the opening 5 of the crack is worn out or missing, resulting in a gradual roughening of the surface as shown in FIG.

After such initial rough skin continues for a while, full-scale rough skin begins to develop.

Some of the cracks that first appeared perpendicular to the surface grew further to a depth of 50 to 100 μm, and now
The skin changes to a state where it cannot return to the gradual rough skin described above.

An example of such a state is shown in FIG. 3, where the entrance to the crack enters inward in the shape of a wedge as shown at 6, and a crack like number 7 exists deeper from the tip of the wedge.

In many cases, fragments or scales of the workpiece steel such as 8 are present in the opening of the wedge-shaped crack.

The surface layer of the wire rod processed during this period was press-fitted into the cracks of the roll and was pulled out when separated from the roll.

In other words, the opening of a wedge-shaped crack is caused by repeated press-fitting and detachment of the workpiece material.

On the other hand, in areas where the pressure applied to the roll during processing is locally large, large clumps fall off or small pieces fall off, resulting in large depressions as illustrated in FIG. 4.

In many cases, a crack like 10 is generated from the corner 9 of this large depression or from a place close to the corner 9 at a right angle to the surface, and as this crack continues to progress, it promotes the falling off of the lumps, and in the initial stage of processing. Severe surface roughness occurs, which is different from the gradual roughness caused by dry skin.

Moreover, since the cracks that grow perpendicular to the surface are perpendicular to and parallel to the direction of the caliber of the roll, these cracks are combined to form a net-like appearance.

Next, at the end of rolling, that is, when it is necessary to regrind the rolls, the gap between the cracks is further widened, and as shown in Fig. 5, the gap inside the crack is wider than at the entrance, that is, near the surface. Something like this is coming.

Looking at the crack surface structure inside the crack, a portion 12 where the Co phase of the alloy structure of WC-C,o has disappeared can be found.

Furthermore, as shown in Figure 6, even if the gap inside the crack is not wider than the gap at the entrance, the Co phase disappears at the bottom of the crack and the W
A portion 13 in which only C particles remain is often found.

The remaining WC particles are held by a small amount of remaining Co phase, and such a portion 12 or 13 gradually develops parallel to the surface and finally develops to the point where a portion 14 surrounded by a network of cracks falls off. This results in surface pitting as shown at 15 in FIG.

The size of this pitting is about 200μ x 200μ, and its depth is often about 100μ.
This causes deterioration of the surface quality of the wire rod, which is the workpiece.

Now, considering the cause of the crack that is wider inside than the opening shown in Figure 5, when the surface area of the wire material to be processed completely fills the crack, it is press-fitted and pulled out again. It is extremely difficult to think about this, and the reason for the propagation of cracks parallel to the surface and the disappearance of the Co phase shown in Figure 6 is that the wire surface layer is press-fitted to the bottom of the cracks that are perpendicular to the roll surface. It is also difficult to think that only the Co phase was selectively removed due to mechanical factors such as adhesion when the Co phase was drawn out.

That is, factors other than mechanical factors must be considered as the cause of such a phenomenon.

Next, when observing the propagation path of the above-mentioned growing crack, as shown in FIG. 8, it often propagates selectively through the grain boundaries 16 between the WC grains and the Co phase.

This is in contrast to the phenomenon in which when a crack propagates due to tensile fracture or the like, it often propagates through the WC particles.

In other words, one way to prevent the growth of cracks, which is a major factor in the roughening of the roll surface, and to obtain rolls with excellent roughening resistance is to strengthen the interface between the carbide particles and the binder phase and prevent the growth of cracks. This is a necessary condition.

The conditions for using the roll are as described above, but the cooling water used at that time is pressurized by a pump, and furthermore, it is drawn in by the wire material being processed and easily penetrates into the cracks that exist on the roll surface. do.

Also, some of the cooling water turns into superheated steam due to the red-hot wire and enters the crack.

The cooling water used here is almost without exception industrial water, and contains many impurities.

The impurity contents are SO,-, C1-+. NO
It also contains acid radicals such as 3-''''.

As is well known, these acid radicals tend to combine with positively charged metals to form water-soluble metal salts, and
Water, which is not originally a good conductor of electricity, can be easily changed into a good conductor.

On the other hand, cemented carbide consists of a carbide phase such as WC and a metal bonding phase such as Co, and it is well known that there is a large difference in standard potential between the carbide and the metal.

Also, carbides and metals are of course good conductors of electricity.

As is well known, in an environment where substances that are good electrical conductors but have large differences in standard potential exist adjacent to each other, and where electrons and ions can freely move around them, a local battery is formed. Innumerable small cells called WC phase 20 are formed as shown in a schematic cross-sectional view in FIG.
A potential is generated between the Co phase 21 and Co phase 21, and metal ions such as Co are eluted even under conditions of room temperature and pressure, and the binder phase of the cemented carbide is lost.

This is a phenomenon called wet corrosion.

On the other hand, cemented carbide rolls are subject to residual stress caused by manufacturing processes such as polishing, and mechanical stress generated during use such as wire processing, and these pressures can collectively reach several hundred kg/-. It extends.

Moreover, the cooling water and the surface of the roll are also heated by the red-hot workpiece.

It is also well known that under such high temperature and pressure conditions, the process progresses even more violently.

In addition, when we microscopically observe the surface of the rolls that are used as they rotate, the rolls that are used as they rotate come into contact with the workpiece at certain points, and are subject to stress each time they are processed. Become.

It is a well-known fact that when a material is subjected to repeated stress in a corrosive environment, the progress of corrosion is accelerated and the fatigue strength of the material is significantly reduced, resulting in a phenomenon called corrosion fatigue.

In order to obtain a cemented carbide roll with excellent surface roughness resistance, it is necessary to develop a material that prevents the above-mentioned crack growth, prevents such corrosion, and has high fatigue strength.

In order to prevent crack growth, as mentioned above, it is important to strengthen the grain boundaries between the carbide and the binder phase. In order to prevent the corrosion of the binder phase, the following three steps are necessary to prevent the corrosion of the binder phase. Improvements are possible.

That is, either the potential of the bonded phase with a low potential is increased as much as possible to eliminate the formation of local batteries, the surface of the bonded phase is made to form an insoluble film to make it passivate, or, for example, by using oil etc.
Either a protective film is created on the surface layer.

The effect of creating a protective film with oil and retarding skin roughness can be demonstrated, for example, by spraying lubricating oil instead of cooling water onto the part where the wire is caught in the rolls used for hot rolling.

It is thought that the effect of using lubricating oil is to reduce the coefficient of wear and prevent corrosion.

Next, it is possible to try to increase the potential of the bonded phase to improve its corrosion resistance, for example by using a noble metal with a high standard potential as the bonding phase, but it is difficult to use expensive noble metals. Not only is it industrially difficult, but it is extremely difficult to obtain a cemented carbide with sufficient mechanical strength that uses these metals or alloys as a binder phase and has no residual pores. It is impossible to realize this.

However, it was not impossible to achieve a high standard potential and passivation by using an alloyed binder phase instead of the conventional single Co phase as the binder phase.

As a result of experiments, the inventor found that carbides such as W, Ti, Ta, and Nb were added to an alloy consisting of Ni and Co, and a small amount of Cr was added to the alloy.
It was bonded by an alloy binder phase with added .

It has been found that a roll made of cemented carbide can prevent rough skin caused by the process described above and can provide the desired high quality wire rod.

The present invention increases the potential of the bonded phase and prevents the formation of local batteries caused by the potential difference with the carbide phase, while passivating the bonded phase itself, which prevents corrosion of the bonded phase caused by cooling water that comes in contact with it during use. In addition to preventing
The present invention relates to a cemented carbide roll for hot wire rods that has no residual holes and has excellent mechanical strength.

First, the hard compound that is the most important composition of cemented carbide is W
It is C.

The hard compound in the present invention is also WC.

This is due to the mechanical properties of cemented carbide, mainly made of WC, which have a large Young's modulus and high rigidity, as well as a large specific gravity, making it easy to obtain the weight and strength required for rolls. Part of WC is TiC,T
Even if it is replaced with a hard compound such as aC or NbC, the object of the present invention will not be impaired in any way.

However, if the content of these TiC, TaC, and NbC is too large, the strength will decrease and the material will become unsuitable as a hot wire roll material, so the total amount of TiC, TaC, and NbC should be 10 weight φ or less.

Second, the total amount of the binder phase must not be less than 12 parts by weight and must not be more than 30 parts by weight.

As shown in the data in Figure 10, this means that the total amount of bonded phase is 1.
When the weight is less than 2 φ, the hardness of the roll obtained is higher than necessary, and due to the resulting brittleness, the transverse rupture strength, which is a typical value of mechanical strength, is low, and cracks that occur will grow very easily, making it difficult to use. This results in undesirable results.

In addition, when the total amount of the binder phase exceeds 30% by weight, the hardness is low and the surface roughness caused by wear becomes thicker, and the stress received during use causes significant plastic deformation, resulting in cracks that even lead to the roll's destruction. It is easy to cause the growth of

Similarly, as shown in FIG. 10, the hardness of the cemented carbide roll of the present invention is lower than that of the conventional cemented carbide having only Co as a binder phase, even with the same carbide weight.

This may seem contradictory to cemented carbide, which generally requires high hardness, but in reality, the binder phase has high toughness, and due to its strong bond with the carbide phase, it is prone to cracking due to large stress. This has extremely important significance in that it suppresses the occurrence of cracks and also prevents the growth of cracks that have occurred.

Here, it is effective to further improve the roughness of the copper plate on the roll surface by further adding Cr to the binder phase consisting of Ni and Co.

This is because Cr has excellent corrosion resistance, and the addition of Cr significantly improves the corrosion resistance of the binder phase. However, as is well known, Cr tends to combine with carbon to form carbides. strong.

If it becomes a G carbide, the proportion of solid solution in the binder phase will be reduced, and not only will it not be possible to achieve the intended strengthening of the binder phase, but also the mechanical strength will be reduced, which will not satisfy the purpose of the present invention. I can't.

In order to achieve the present invention, it is a matter of course that the amount of carbon must be sufficiently adjusted in the entire roll manufacturing process.

However, when the ratio of the amount of Cr added to the sum of Ni and Co exceeds 0.30, it becomes difficult to adjust the amount of carbon, and part of the Cr becomes carbide, reducing the strength. This is not preferred because it becomes difficult to obtain a product with few residual pores.

Therefore, in the present invention, the amount of Cr added is 9 weight φ or less, and 0% with respect to the sum of Ni and Co.
．． It needs to be 30 or less.

However, Cr fixed in the binder phase has the important function of forming a dense oxide film on the surface of the binder phase in contact with cooling water, causing so-called passivation and improving corrosion resistance. Therefore, if the amount of Cr added is too small, the object of the present invention cannot be fully achieved.

Therefore, the amount of Cr added is equal to the total amount of bonded phase, i.e., N
It is necessary that the sum of i, Co, and Cr be 0.05 or more.

Next, the size of hard carbide particles, which has an important effect on the properties of cemented carbide, is also one of the important points in the roll of the present invention.

That is, as shown in FIG. 11, when the particle size is smaller than 1μ, the distance between hard carbide particles, that is, the thickness of the binder phase becomes smaller, and therefore the hardness increases even with the same amount of binder phase. Toughness is reduced, and therefore cracks are more likely to occur and the life of the roll is reduced.

On the other hand, if the particle size is larger than 5μ, the thickness of the binder phase becomes too large, resulting in too low hardness, and even a small stress easily causes large plastic deformation, resulting in a very short roll life. .

Furthermore, the corrosion resistance of the binder phase, which has an important effect on the roughness of the copper plate of the roll, is affected by the passivation by the addition of Cr mentioned above, but as mentioned above, the corrosion resistance of the binder phase, which has an important effect on the roughness of the copper plate, is In this case, addition of Cr alone is not sufficient.

That is, the object of the present invention cannot be achieved if the binder phase is only Co or Ni and only Cr is alloyed with it.

The object of the invention is achieved only if the binder phase consists of a range of alloys of Ni and Co, to which Cr is added.

As can be seen from the data shown in Figure 12 regarding the axiality of this bonded phase, Cr is added to a single metal of Co or Ni.
In a bonded phase in which Cr is added, or in a bonded phase in which only Cr is added to an alloy in which the ratio of Co and Ni is outside a certain range, the curve starts to rise sharply, that is, the so-called polarization occurs, where a large current begins to flow. The potential is still low, and the corrosion resistance is
I can't say that it has improved enough.

Here, in an alloy to which Cr is added, there is a process in which the curve that once started to rise becomes parallel to the horizontal axis again.

This shows the process of passivation.

Here, the ratio of Co and Ni in the binder phase is as shown in FIG.
Taking the case where the r amount is 1% by weight as an example, if the Ni content in the binder phase is larger than 0.33 relative to the sum of Ni and Co, the polarization potential will reach a stable level. The size increases rapidly, the corrosion resistance is significantly improved, and the performance of the resulting roll is extremely excellent.

However, when the Ni content in the bonding phase becomes too large and the above value exceeds 0.9, the voltage at which the curve begins to rise sharply becomes lower, and the corrosion resistance deteriorates. Moreover, the performance of the resulting roll is unsatisfactory.

This is because, as can be seen from the data of the co-Ni alloy shown in FIG. 13, a higher potential than each single metal can be obtained in a certain range.

This will be explained in more detail below with reference to Examples.

Example 1 13% by weight of Ni powder and C were added to WC powder with an average particle size of 2.5μ.
6% by weight of O powder and 1.5% by weight of Cr powder were added and thoroughly mixed in a ball mill. 1kg of camphor was added to 100kg of powder obtained. This mixture was molded into a bottom mold by applying a pressure of 1ttrn/crA. , vacuum sintering at a temperature of 1380°C to produce a rolling roll with a diameter of 160 mm and a thickness of 70 mm.

When a steel wire was hot rolled using this roll, it was found that a conventional cemented carbide roll with only Co as a binder phase could only roll to about 1,200 tEn at most due to surface roughness, but it was rolled to 2,000 tEn. became possible.

The hardness of the cemented carbide at this time is 80.8 in HRO, the transverse rupture strength is 295 kg/-, and the polarization potential is 804-1 in acid radical concentration.
65ppm, Cl-30ppm, NO310ppm p
The voltage was 0.98V for the cooling water H8.5.

Example 2 A rolling roll was made at the same time as in Example 1, except that the particle size of WC was 3.8 μm and the Cr content was 1.0% by weight.

With this roll, rolling of 2,300 m was also possible.

The cemented carbide at this time has an HRO hardness of 81 and an O transverse rupture strength of 305.
kg/door d, and the polarization potential was 0.92■.

Example 3 A guide roll with a diameter of 45 ridges and a thickness of 25 mm was made from the mixed powder obtained in Example 2, and this was used as a guide during hot rolling of steel wire. The lifespan of the cemented carbide guide roll, which was limited to about 2,500 m due to rough skin, was able to last up to 4,800 m.

Example 4 The rolling rolls obtained in Examples 1 and 2 were observed and compared with a conventional roll using only Co as a binder phase during rolling.

In Figure 14, only Co is used as the binder phase, and the binder phase weight is 20
Figures 15 and 16 are the results of observing surface roughness after rolling to 1200ttIrL of a roll with weight%.
The figures show rolls 1 and 5 obtained in Examples 1 and 2, respectively.
This is an observation result of surface roughness after rolling to 00t0rL.

In Fig. 14, in which only Co is used as the binder phase, the crack openings 17 are wide and many pittings 15 can be observed, but in the roll of the present invention, the cracks are small in both Figs. 15 and 16. , I can't find any pitting either.

Furthermore, when the cross section was observed, there were no cracks that spread inside, as shown in Figure 5, which were often observed with rolls with only Co as a binder phase, and no phenomenon of disappearance of the binder phase occurred. Ta.

In addition, the average length of cracks as shown in FIG. 4 10 was 150μ in the roll with only Co as a binder phase, whereas the average length was 80μ in the roll of Example 1, and the average length of cracks in Example 2 was 150μ.
The roll was 95μ.

Example 5 WC powder with an average particle size of 5μ, 5μ TiC, 2μ TaC
, 3p NbC powder was used in an amount of 82 parts, and a total amount of Ni powder), Co powder, and Cr powder was added in an amount of 18 parts to fabricate a Morgan roll having the alloy composition shown in Table 1.

Regarding the amount of rolling, a ternary alloy with a binder phase of Co-Ni-Cr showed good results.

It was also found that the polarization potential of the ternary type was 0.3 V or higher, indicating excellent corrosion resistance against industrial water.

As described above, the roll of the present invention is a wire hot rolling roll,
Kite rolls and pinch rolls exhibit excellent performance in the field of processing wire rods in hot conditions using cooling water containing impurities, but the workpiece material is not only wire rods, but also works under similar conditions, such as plate materials. It shows excellent performance when used in

[Brief explanation of drawings]

1A and B to 6A and B are photographs and explanatory diagrams of the cross-section of a roll for hot wire rod during use, and are diagrams illustrating the process of roughening that occurs on the surface of the roll; Figures A and B are photographs and explanatory diagrams of the surface of a roll that has reached the end of its service life due to severe roughening.
Figures A and B are photographs showing the propagation paths of cracks and their explanatory diagrams; Figure 9 is a diagram explaining the corrosion phenomenon that occurs in the binder phase of cemented carbide; Figure 10 is a diagram showing the alloy material of the present invention and conventional cemented carbide. A graph showing the mechanical properties with the alloy, Fig. 11 is a graph showing the relationship between the particle size of hard carbide and the life of the obtained roll, and Fig. 12 shows the surface of the binder phase of the obtained cemented carbide. 4. A polarization curve diagram showing the corrosion property. Figure 13 is a graph diagram showing the relationship between the polarization potential and the composition of the binder phase. Figures 14 to 16 are the conventional rolls and books with only Co as the binder phase. This is a photograph comparing the practical performance with the roll according to the invention in terms of copper plate roughening resistance. In addition, in FIG. 10, -0- indicates the conventional cemented carbide having CO as a binder phase, and . . . indicates N according to the present invention.
With i+Co as the bonding phase, N i /N i +Co same,
75 is the cemented carbide, ----mu--- is the N of the present invention.
Ni/Ni+Co=0.75 with i+Co as the bonding phase
It is a cemented carbide with Cr=1.0. In addition, Fig. 13 shows so, -1 = 65 ppm, cl - =
78 ppm, No3-= 10 ppm, pH=
These are the results when cooling water of 8.5 was used.

Claims (1)

[Claims] WC having an average particle size of 11μ to 5μ, or a hard carbide phase in which a part of the WC is replaced with one or more of TiC, TaC, and NbC of 10 weight φ or less (however, TiC, TaC, NbC) (with a total weight of 10% by weight or less) and a ternary alloy binder phase of Ni, Co, and Cr with a total amount of 12 to 30 weight φ, and Cr in the binder phase is the sum of Ni and Co. 0.30 or less for the total bonded phase, and 0.05 or more for the total bonded phase, and furthermore, Ni
and Co, from 0.33 to 0.90,
A roll for hot wire made of cemented carbide, characterized in that the polarization potential is 0.3 V or more with respect to cooling general industrial water.