JPH0790293A - Lubricant for hot rolling of stainless steel - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent seizure of stainless steel on the rolling rolls during hot rolling of stainless steel with a lubricant, and to obtain a product with no surface defects. [Composition] Fe ₂ O ₃ having an average particle size of 0.1 μm or more and less than 1 μm
One or two kinds of powder or Fe ₃ O ₄ powder: 5% by weight to
30% by weight, acrylic acid-based water-soluble polymer: A lubricant for hot rolling of stainless steel obtained by mixing the balance water with an amount sufficient to make the viscosity of the lubricant 1000 to 50,000 cP (centipoise).

Description

Detailed Description of the Invention

[0001]

The present invention relates to a lubricant composition suitable for preventing the seizure of stainless steel on a rolling roll during hot rolling of stainless steel and obtaining a product having good surface properties. Regarding

[0002]

2. Description of the Related Art Since stainless steel products are required to have a beautiful surface, it is necessary to prevent the occurrence of surface defects as much as possible in the manufacturing process. However, when hot-rolling stainless steel with a hot rolling facility such as a tandem mill, flaws often occurred on the surface of the steel sheet due to seizure of the stainless steel on the rolling rolls.

It is said that this seizure is caused by the metal surface of the hot rolling roll and the metal surface of the hot rolling material being in close contact (metal touch). Particularly in stainless steel, the oxide film (scale) is difficult to form, and even when it forms, the rate of its formation is slow, so there is more chance of metal touch during multi-stage rolling, and seizure frequently occurs.

If the surface of the hot-rolled stainless steel sheet is flawed due to this seizure, even a slight flaw is not suitable for mirror finishing applications. As a result, the use of the obtained stainless steel sheet is restricted. In addition, stainless steel plates with surface flaws require additional surface care such as polishing. Furthermore, if the degree of flaws is significant, it cannot be used as a product and is scrapped. Thus, the flaws on the surface of the steel plate reduce the yield and increase the manufacturing cost.

Therefore, in order to suppress the occurrence of surface defects during hot rolling as much as possible, various means such as reducing the load on the rolling rolls, selecting the rolling conditions, selecting the roll material, and improving the lubricant have been tried. Has been. For example, as a lubricant, various methods have been proposed to prevent seizure by supplying animal fats and oils, vegetable fats and oils, mineral lubricants, synthetic lubricants and the like to the surface of a rolling roll. In addition, a method is also being investigated in which a powder having lubricity is dispersed and mixed in rolling oil and then supplied to the surface of a rolling roll by an injection method.

However, in these methods, since the hot rolling of stainless steel is under severe conditions, seizure cannot be completely prevented, and the surface defects are caused. is there.

On the other hand, Japanese Patent Application Laid-Open No. 64-83309
The publication describes a lubricant for hot rolling of stainless steel in which iron oxide powder is dispersed in a viscous aqueous solution in an amount of 1 to 30% by weight. According to the invention of this publication, as described in the publication, if it is difficult to generate oxide scale to cause seizure during hot rolling of stainless steel, the iron oxide should be positively replenished from the outside. It is based on the idea that the cause will be resolved.

[0008]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
─ For the invention proposed in 83309 publication, we continued the test research based on the above idea, but in the lubricant described in the publication, immediately after mixing the iron oxide powder with the viscous aqueous solution, Although a uniform dispersion was obtained, when the lubricant was preserved, the iron oxide powder settled in the storage bath, and there were cases where stable dispersion and retention of the iron oxide powder could not be obtained for a long time.

When the dispersion and retention of iron oxide powder is unstable,
During hot rolling, iron oxide powder cannot be stably supplied to the surface of the rolling roll. As a result, seizure may occur and the stainless steel may be flawed. In addition, it was found that iron oxide accumulates on the joints of the pipe that supplies the lubricant, causing problems such as clogging of the pipe and insufficient supply of the lubricant.

On the other hand, in recent years, there is a tendency that stainless steel, which has a high Cr equivalent and is excellent in high temperature oxidation resistance, is used as an exhaust gas member for automobiles. The higher the Cr equivalent, the thinner the scale thickness produced by hot rolling, and the more marked the occurrence of seizure defects. A lubricant capable of completely preventing seizure even for such a material having a high Cr equivalent is disclosed in JP-A-64
─ Has not been developed so far, including those of the 83309 publication.

Therefore, an object of the present invention is to obtain a lubricant capable of further improving the seizure flaw prevention effect as compared with the conventional one, and particularly capable of hot rolling without causing seizure even in a stainless steel having a high Cr equivalent. To do.

[0012]

According to the present invention, the average particle size is
Fe ₂ O ₃ powder or Fe ₃ O ₄ powder of 0.1 μm or more and less than 1 μm, 1 or 2 kinds: 5 wt% to 30 wt%, acrylic water-soluble polymer: viscosity of lubricant composition after mixing is 1000
Enough to reach ~ 50,000 cP (centipoise),
Remainder: Mixing water, the viscosity is 1000 to 50000
A lubricant for cP stainless steel hot rolling is provided.

[0013]

In the case of a lubricant for dispersing iron oxide powder in a viscous aqueous solution as proposed in Japanese Patent Application Laid-Open No. 64-83309, the iron oxide powder is retained and dispersed in the viscous aqueous solution and applied to a rolling roll. If the lubricant is rolled up, the rolling characteristics of the lubricant (strictly speaking, the adhesiveness to the roll and the rolling bit in the roll bite) required to completely prevent metal contact with the rolled material are completely seized. From the perspective of becoming a key point of prevention,
The present inventors have conducted extensive testing and research on the types of thickeners, powder properties of iron oxide, physicochemical properties of lubricants, and the like.

As a result, among a wide variety of water-soluble thickeners, the cross-linked acrylic acid polymer has the effect of significantly improving the above-mentioned dispersion retention characteristics and the rolling-in characteristics of the lubricant, as compared with others. I knew it was. The iron oxide powder used is Fe ₂ O ₃ or Fe _{3 with} a size of 0.1 μm or more and less than 1 μm.
It was also revealed that it was good that it was a powder of O ₄ .

As a medium for supplying the iron oxide powder,
Oils and fats and lubricating oils can be considered, but it is difficult to uniformly disperse iron oxide powder because it does not necessarily have lipophilicity.

Hereinafter, the function and effect of each element constituting the lubricant for hot rolling of stainless steel according to the present invention will be individually described.
Clarify the grounds for limiting these numbers.

[Type of iron oxide] In general, iron oxide is FeO, Fe
Some are represented by the chemical formula of ₃ O ₄ , Fe ₂ O ₃ . Of these, Fe ₂ O ₃ has the highest hardness. Thus, although less preferred the direction of FeO and Fe ₃ O ₄ in terms of hardness involved in wear or the like of the roll, when seen from the viewpoint of anti-seizing of rolled Fe ₂
It does not matter if O ₃ is used. On the other hand, FeO is difficult to obtain industrially stable. Therefore, iron oxide is Fe ₃ O ₄
It is practical to use Fe ₂ O ₃ or a mixture thereof in view of cost. The purity does not necessarily have to be high, and oxides such as SiO ₂ and MnO and those containing metallic iron as impurities can be used.

[Particle Size of Iron Oxide] The particle size of the iron oxide powder is uniformly dispersed in the viscous aqueous solution and stability of the dispersion over time. Have an important effect on sex. When the average particle size of iron oxide is 1 μm or more, if it is 10 μm or less, uniform dispersion can be obtained when the lubricant is mixed by adjusting the viscosity of the viscous aqueous solution. However, when the lubricant is stored for a long period of time, iron oxide powder may settle in the storage tank, or iron oxide may accumulate at the joints of the lubricant supply pipe within a long period of time. To do. In addition, since the ratio of the area that coats the supply surface becomes smaller for coarser particles, the coating efficiency of the supply surface decreases when the same weight of iron oxide is supplied. Therefore, the average particle size of iron oxide powder must be less than 1 μm.

As described above, a small average particle size is advantageous in terms of uniform dispersibility and coating efficiency on the supply surface, but when the average particle size is less than 0.1 μm, it is mixed with a viscous aqueous solution. In this case, since the fine powder has a strong cohesive force, it is extremely difficult to disperse it uniformly. Therefore, the average particle size of iron oxide powder must be 0.1 μm or more.

[Particle Shape of Iron Oxide Powder] The individual particles of the iron oxide powder have various shapes such as a rectangular parallelepiped, a needle shape, an octahedron, and a sphere. It was found that the seizure prevention effect can be further obtained by using spherical iron oxide. The spherical shape does not necessarily mean that it has a spherical surface, but refers to a rounded particle shape with few corners.

[Fixed Amount of Iron Oxide] The content of iron oxide in the lubricant composition is regulated within an appropriate range in order to obtain a desired roll baking effect and at the same time ensure a stable supply of the lubricant. . If the iron oxide content is 1% by weight or more, the seizure prevention effect will appear, but in practice seizure may occur due to fluctuations in the rolling conditions, etc. in order to obtain a stable seizure prevention effect. Requires a content of 5% by weight or more. On the other hand, when the content exceeds 30% by weight, the supply stability tends to decrease with time, and when spraying the lubricant on the surface of the rolling roll, excessive discharge energy is required, which is not practical. A problem arises. Therefore, the iron oxide content must be 5 to 30% by weight.

[Type of Thickener] A characteristic feature of the lubricant composition of the present invention is that a water-soluble acrylic acid-based polymer, especially a cross-linked acrylic acid polymer, is used as a thickener.

Various substances are known as industrially usable thickeners for obtaining a viscous aqueous solution, but the present inventors conducted many tests using various thickeners. As a result, it was found that among the many water-soluble polymers with thickening effect, the above-mentioned cross-linked acrylic acid polymer has a unique effect on the dispersion retention of iron oxide powder and the seizure prevention property of stainless steel during hot rolling. It was

Even if a water-soluble cellulose derivative such as methyl cellulose or carboxymethyl cellulose is used, a temporary viscosity can be obtained, but the iron oxide powder does not necessarily have a good dispersion holding property, and the amount added in order to obtain a stable dispersion holding. To increase the viscosity. When the viscosity is high, it becomes difficult to mix the iron oxide powder and the liquid-feeding property of the lubricant is significantly reduced. On the other hand, the cross-linked acrylic acid polymer and the like are capable of extremely stably dispersing and retaining the iron oxide powder in the viscosity range described below, and are also excellent in the adhesiveness to the rolling rolls.

As is well known, there are cross-linked acrylic acid polymers obtained by subjecting polyacrylic acid to a cross-linking reaction and a copolymer of an acrylic acid monomer and a cross-linking agent. Both are distinguished from linear polyacrylic acid. Among these cross-linked acrylic acid polymers, there are some special ones that do not dissolve in water or swell water, but such a polymer cannot be used in the lubricant of the present invention. In the invention, a water-soluble cross-linked acrylic acid polymer is used.

Typical cross-linking acrylic acid polymers that can be used in the present invention include those whose main component is polyacrylic acid, those whose main component is sodium polyacrylate or its copolymer, and whose main component is Examples include ammonium polyacrylate. Therefore, the cross-linked acrylic acid polymer as referred to in the present invention means a water-soluble one of polyacrylic acid or a salt thereof as a main component, or a cross-linked polymer having a copolymer thereof as a main component. To tell. In the lubricant of the present invention, the amount of the crosslinked acrylic acid polymer blended is such that the viscosity of the lubricant after blending the iron oxide powder is 1000 to 5000.
It is the amount necessary to reach 0 cP (centipoise).

[Viscosity of Lubricant] The lubricant of the present invention has a viscosity of 100 from the viewpoint of dispersion retention of iron oxide powder and liquid feeding of the lubricant.
It is necessary to set 0 to 50,000 cP. Viscosity 1
If it is less than 000 cP, it is difficult to uniformly disperse and retain the iron oxide, which causes problems such as settling of the iron oxide in the lubricant storage tank and deposition in the lubricant supply conduit. On the other hand, the higher the viscosity is, the more advantageous it is for maintaining the dispersion of the iron oxide powder. However, if the viscosity is unnecessarily increased, not only it becomes extremely difficult to uniformly disperse the iron oxide powder,
A large amount of energy needs to be supplied to supply the lubricant, which increases the equipment cost and impracticality. Therefore, in the present invention, the lubricant viscosity is 1000 to 50.
The range is 000 cP.

[Adjustment of pH] The lubricant of the present invention is slightly acidic as it is because of the use of the cross-linked acrylic acid polymer. Therefore, considering the corrosiveness of the rolling equipment, it is preferable to adjust the pH to neutral or weakly alkaline. However, in the case where the original action of the crosslinked acrylic acid polymer is changed in an undesired direction by the addition of alkali, it is necessary to sufficiently consider the type and addition amount of the alkali agent.

[Method of Applying Lubricant] When the lubricant according to the present invention is applied to hot rolling of stainless steel, it is practical to carry out as follows.

The lubricant is stored in a tank after mixing,
From this tank, liquid is sent through a pump to a conduit leading to a rolling roll. The pump may be selected as appropriate, but since it has a higher viscosity than simple water, a pressure of several tens of kgf / cm ² or more is usually required, so it is suitable to use a plunger type pump or the like.

A nozzle is attached to the tip of the conduit,
A lubricant is sprayed from the nozzle onto the roll surface in the rolling stand. The rolling stand on which the lubricant is sprayed is not particularly limited, and is appropriately selected from a finishing rolling stand and a rough rolling stand in the hot strip mill, and which roll is sprayed should be determined taking into consideration the degree of the effect. You can select it. During the spraying, it may be sprayed on the roll surface over the entire width in contact with the rolled material, and because of the remarkable peeling of the oxide scale in relation to the plastic deformation behavior in the widthwise rolling during rough rolling. It may be selectively sprayed in the vicinity of the edge of the rolled material, where seizure is relatively likely to occur.

The amount of lubricant supplied to the rolling rolls is appropriately adjusted in consideration of the liquid feeding pressure, the capacity of the nozzle at the tip of the conduit, the rotational speed of the rolling rolls, and the like. For example, it is preferable to adjust the area of contact of the rolling roll with the rolled material to about 0.1 liter / m ² to several liters / m ² .

Although ordinary rolling lubricating oil may be used in the hot rolling of stainless steel, the use of the lubricant according to the present invention does not hinder the combined use of lubricating oil and reduces the rolling load. A lubricating oil for such purposes may be used in combination.

[0034]

【Example】

(Example 1) Table 1 shows representative lubricants tested.
As shown in Table 1, iron oxide has various particle sizes Fe ₂ O ₃
Alternatively, Fe ₃ O ₄ was used alone or as a mixture, and this was dispersed in a viscous aqueous solution to which a thickener was added to prepare lubricants Nos. 1 to 13.

The cross-linked acrylic acid polymers used are those marked with (○) in the table under the trade name Rheogic manufactured by Nippon Pure Chemical Co., Ltd. (cross-linked acrylic acid polymer whose main component is sodium polyacrylate). The product with the (●) mark is Hibiswako (trade name, a cross-linked acrylic acid polymer whose main component is polyacrylic acid) manufactured by Wako Pure Chemical Industries, Ltd.

The methyl cellulose used as a comparative example is Metrose manufactured by Shin-Etsu Chemical Co., Ltd., and the carboxymethyl cellulose is CMC Daicel manufactured by Daicel Chemical Industries.

[0037]

[Table 1]

The test of dispersion / holding property of each lubricant was conducted as follows. First, each thickening agent is dissolved by stirring in water to obtain a water-soluble viscous liquid, and a predetermined iron oxide powder is added to it, and the mixture is further stirred, mixed and dispersed to prepare a lubricant. 1 liter of lubricant is transferred to a beaker, and the lubricant is sampled in the upper layer part, the central part and the lower layer part of the beaker, and the iron oxide content at each position (upper part, central part, lower layer part) is measured. It was measured. Then, this beaker was left still for 1 week.

After standing for one week, the lubricant inside the beaker was collected again in the upper layer portion, the center portion and the lower layer portion while avoiding stirring the lubricant inside the beaker.
The content of iron oxide was measured at each position (upper layer portion, central portion, lower layer portion). The results are shown in Table 2.

[0040]

[Table 2]

The lubricant within the scope of the present invention has a content of iron oxide at each position of the upper layer portion, the central portion, and the lower layer portion, which is almost the same as that immediately after stirring, even after standing for 1 week, and is left standing for a long period of time. However, it can be seen that the dispersed state of iron oxide is stable.

On the other hand, in the lubricants of the comparative examples which are out of the scope of the present invention, although iron oxide was uniformly dispersed immediately after mixing,
After standing for 1 week, the iron oxide content was higher in the lower layer than in the upper layer, except for the lubricant of No. 12. Therefore, in the lubricants of Comparative Examples, there is a concern that iron oxide may settle to the bottom in the storage tank or iron oxide may be deposited in the supply conduit to the rolling rolls over time.

In the lubricants of Nos. 1, 11, and 12 (all comparative examples), the iron oxide content was already partially biased and non-uniform immediately after mixing, or the iron oxide powder aggregated. It was

(Example 2) Thickness 200 mm, width 1030
~ 1240mm, single weight 10 ~ 14ton ferritic stainless steel (Chemical composition: 0.01 ~ 0.02% C, 0.0
46-0.57% Si, 0.20-0.30% Mn, 18.
3 to 19.6% Cr, 0.11 to 0.13% Ni, 0.41
A slab of 0.49% Nb, 0.46 to 0.58% Cu) was hot rolled in a hot strip mill. First, the slab was heated to 1200 to 1250 ° C., then roughly rolled to a rough bar having a thickness of 25 mm, and then rolled to a hot coil having a thickness of 3.0 mm by a finishing rolling mill group consisting of 7 stands. After changing the work rolls of the finishing rolling mill group (replacement with grinding-finished rolls), 14 to 41 slabs (slabs for one rolling cycle) are continuously hot-rolled. Lubrication conditions were kept constant.

Pipes were supplied to the work rolls of the first to third stands of the finishing rolling mill group so as to supply the lubricant, and the lubricant was sprayed onto the rolling rolls from the upper and lower nozzles of 3 to 4 provided on the rolling stand. . At that time, the lubricant of the storage tank was operated at 40 kgf /
Liquid was sent at a pressure of mm ^{2 and} the lubricant was ejected from each nozzle. The flow rate of the lubricant supplied from the nozzle to the roll was adjusted to about 0.3 liter / m ² with respect to the roll surface.

The viscosity (cP) of each lubricant used at this time,
Fe ₃ O ₄ and Fe ₂ O ₃ composition ratio (wt%), average particle size (μ
m), the content (% by weight) and the type of thickener are shown in Table 3. The marks attached to the types of thickeners are as described in Example 1.

In these rollings, the conventionally used rolling oil was supplied to the backup roll by water injection. The material of the work rolls of the first to third finish rolling mills was a high chrome roll. No. 14 only supplied the rolling oil and did not supply the lubricant.

All the coils after hot rolling were passed through a continuous annealing pickling line, the surface skin of each coil after descaling was observed, and the occurrence of surface defects due to roll seizure was investigated. . The results are shown in Table 4.

[0049]

[Table 3]

[0050]

[Table 4]

From the results shown in Table 4, in the cases of Nos. 17, 18, 22, and 24 using the lubricant of the present invention, surface flaws do not occur even after the 26th or more rolling rolls are changed, and roll baking is effectively performed. It can be seen that sticking is prevented.

On the other hand, when only the rolling oil is supplied and no lubricant is supplied, or when a lubricant outside the scope of the present invention is used, surface flaws occur and seizure is not always effectively prevented. could not.

That is, in No. 14 without a lubricant, surface flaws were caused from the second seizure due to roll seizure, and then surface flaws were generated on all the coils rolled by the seizure-occurred roll. Nos. 16 and 21, which used lubricants having a low iron oxide content, showed a slight seizure prevention effect, but surface defects occurred when the rolling progressed to 5 to 7.

No. 15 containing excessively fine iron oxide
For Nos. 19 and 23, which have excessively high viscosities, surface flaws occurred from the 9th to 13th coils. The cause of this is thought to be that iron oxide is not uniformly dispersed.
When the nozzle was observed after hot-rolling the slab for cycles, it was found that the nozzle tip was clogged. It is expected that the lubricant was not sufficiently supplied in the hot rolling around the 10th line where surface defects occurred.

No. 2 using iron oxide having an excessively large particle size
In No. 0, surface defects were generated from the 5th line. It is considered that this is because seizure occurred because the roll surface could not be sufficiently covered with iron oxide.

[0056]

According to the lubricant of the present invention, since the iron oxide powder can be stably dispersed and held for a long period of time, even if the lubricant is stored in the storage tank for a long period of time, it does not settle, and the surface of the rolling roll is prevented. Iron oxide powder can be uniformly supplied, roll seizure during stainless steel hot rolling can be effectively prevented, and high-quality products without surface defects can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C10M 107: 28) C10N 10:16 20:02 20:06 40:24 (72) Inventor Yuichi Higo 11-11 Showa-machi, Kure-shi, Hiroshima Inside Steel Research Institute, Nisshin Steel Co., Ltd. (72) Inventor Akifumi Hiramatsu 11-11, Showa-machi, Kure-shi, Hiroshima Inside Steel Research Institute, Nisshin Steel Co., Ltd.

Claims (3)

[Claims] 1. Fe ₂ having an average particle size of 0.1 μm or more and less than 1 μm
One or two kinds of O ₃ powder or Fe ₃ O ₄ powder: 5% by weight
~ 30% by weight, acrylic acid water-soluble polymer: viscosity of the lubricant is 100
Lubricant for hot rolling of stainless steel, which is a mixture of water and a sufficient amount so as to be 0 to 50,000 cP (centipoise). 2. The lubricant according to claim 1, wherein the water-soluble acrylic acid-based polymer is a cross-linked acrylic acid polymer. 3. The lubricant according to claim 1, wherein the lubricant is supplied to the roll surface during hot rolling of stainless steel.