JPH07310088A - Lubricant for hot rolling of stainless steel having high chromium content - Google Patents

Abstract

PURPOSE:To obtain the subject lubricant capable of preventing seizure of a roll and providing a high-quality product free from surface flaw in hot rolling of stainless steel having high Cr content by dispersing fine powder of iron hydroxide into a viscous water solution and specifying the apparent viscosity of the resultant lubricant. CONSTITUTION:This lubricant is continuously fed, while at least carrying out rolling, to the surface of a rolling roll contacting with a material to be rolled when a stainless steel having high Cr content is subjected to hot rolling and obtained by dispersing 10-40wt.% of powder of iron hydroxide [preferably iron oxyhydroxide of the formula, FeO(OH)] having 0.1-1mum average particle diameter into a viscous water solution obtained by dissolving a thickener consisting of a water soluble high polymer (preferably a water-soluble crosslinked acrylic acid polymer) in water and has 1000-50000cp apparent viscosity. Large effect is preferably obtained by applying the lubricant to hot rolling of stainless steel having a high Cr content of >=20% Cr equivalent defined by the formula {the brackets represent the content (wt.%) of the each component element in the steel}.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seizure-preventing lubricant which is supplied between a roll surface and a material to be rolled during hot rolling of stainless steel having a high Cr content.

[0002]

2. Description of the Related Art A stainless steel strip or steel sheet (abbreviated as "steel sheet" in the present specification) is required to have a beautiful surface, so that the production of surface defects is prevented as much as possible. There is a need to. However, when hot rolling stainless steel with a hot rolling facility such as a tandem mill,
Defects due to seizure of stainless steel on the rolling rolls were often generated on the surface of the steel sheet.

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-metal touch). In particular, the higher the Cr content, the more difficult it is for an oxide film (scale) to form on the surface, and even if it forms, the rate of formation is extremely slow. Therefore, in the hot rolling of high Cr stainless steel, the above-mentioned metal-
The chances of metal touching tend to increase and seizure on the rolls tends to occur frequently. When the seizure occurs, the surface quality of the roll deteriorates and the deteriorated shape is transferred to the surface of the material to be rolled, so that the surface quality of the material to be rolled deteriorates.

If a flaw is generated on the surface of the hot-rolled stainless steel sheet due to the seizure on the roll, even a slight flaw will be an unsuitable product for the purpose of performing mirror finishing in the final step. . In addition, a separate process for removing surface flaws by polishing the surface is required. In some cases, if the degree of flaw is remarkable, it cannot be used as a product and is scrapped. Therefore, the defects cause a decrease in the manufacturing yield of steel sheet products and increase the manufacturing cost.

In order to avoid such a problem, conventionally,
Various improvement measures have been tried, such as reduction of rolling load of rolling rolls, selection of rolling conditions, selection of roll material and selection of lubricant.

[0006] For example, for the lubricant, animal fats and oils,
Various methods have been proposed to prevent seizure by supplying rolling oil such as vegetable oil, mineral lubricating oil or synthetic lubricating oil to the surface of the rolling roll. A method is also being investigated in which powder having a lubricating function is dispersed and mixed in rolling oil and then supplied to the surface of the rolling roll by an injection method. However, these methods cannot completely prevent seizure, especially when high Cr stainless steel is hot-rolled, and in reality, cause surface defects.

Japanese Unexamined Patent Publication No. 64-83309 discloses 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 the occurrence of oxide scale on the surface is a cause of roll seizure during hot rolling of stainless steel, the iron oxide powder is positively replenished from the outside. This is based on the idea that this cause will be eliminated. The iron oxide powder used includes Fe ₂ O ₃ and Fe ₃ O ₄ powder having a particle size of 10 μm or less. As the viscous aqueous solution, a thickener such as an acrylic acid polymer or a carboxyvinyl polymer is dissolved in water. What was done is illustrated.

JP-A-63-254195 discloses a composition in which iron oxide powder is suspended in lubricating oil, or a polymeric substance which is soluble in lubricating oil but not water and iron oxide powder are added to the lubricating oil. A lubricating oil for hot rolling of stainless steel comprising the composition is disclosed, and it is described that this lubricating oil can also suppress seizure on rolls.

On the other hand, unlike the idea of supplying such iron oxide from the outside between the roll and the material to be rolled, there was also the idea of actively oxidizing the surface of the roll. For example, Japanese Patent Publication No. 54-35985 describes a method in which iron hydroxide is supplied to the roll surface during rolling through water as a medium to form a coating film containing triiron tetraoxide as a main component on the roll surface. . In this case, as the roll material, use easily oxidizable adamite (alloy name of cast iron for rolls),
When 5% suspension water of ferric hydroxide was sprayed from the roll water cooling nozzle to the roll being hot-rolled, and when 10-20% suspension water of ferric hydroxide was contacted with the roll surface. It is described that an artificial black skin is formed on the roll surface when applied through a felt installed in a wiper shape. However, the target is ordinary hot rolling of ordinary steel, and there is no description of hot rolling of stainless steel.

Japanese Unexamined Patent Publication (Kokai) No. 60-184405 discloses a method of positively oxidizing the metal surface of the material to be rolled with iron hydroxide, as opposed to oxidizing the roll surface described above. In the hot rolling process of stainless steel for rough rolling and finish rolling, by supplying iron hydroxide to the material to be rolled between the rough rolling passes or between the rough rolling final pass and the final rolling first pass. In this paper, we propose a method in which the oxide scale on the surface of the material to be stripped peels off while the metal surface is exposed while passing through the previous pass, and oxide scale is generated on the exposed metal surface. ing. Here, iron hydroxide is supplied to the surface of the material to be rolled by spraying colloidal iron hydroxide with a carrier gas, or by suspending iron hydroxide in water or rolling lubricant. Then, a method of spraying on the surface of the material to be rolled is shown. As described above, it is described that when the rolled material is regenerated with the oxide scale and then passed through the hot rolling roll, seizure on the rolling roll is suppressed and the surface of the rolled material is improved.

Further, Japanese Unexamined Patent Publication No. 52-142704 discloses a lubricant for hot rolling in which a polymer emulsion based on rolling oil is entrained with a substance having a lubricating function. This lubricant has a higher friction coefficient and improved biteability, but this lubricant is intended for ordinary steel with a low Cr content and has a high Cr content like stainless steel. It is considered insufficient to prevent seizure in steel.

[0012]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
The invention proposed in Japanese Patent Publication No. 4-83309 was continued to be tested and researched based on the above-mentioned idea. However, in the lubricant described in that publication, immediately after mixing iron oxide powder with a viscous aqueous solution, It was possible to obtain a uniform dispersion, but the iron oxide powder settled in the storage tank where it was stored, and we experienced that it was not possible to obtain stable dispersion retention of the iron oxide powder for a long time. If the dispersion and retention of the iron oxide powder is unstable, the iron oxide powder cannot be stably supplied to the surface of the rolling roll in the actual operation. That is, iron oxide is deposited on the joint portion of the conduit for supplying the lubricant to the rolling rolls, which causes clogging of the pipe and insufficient supply of the lubricant.

Therefore, there is a possibility that the purpose of preventing image sticking may not be fulfilled completely. In particular, in recent years, high Cr stainless steel, which has a high Cr equivalent as a constituent and is excellent in high temperature oxidation resistance, tends to be used for exhaust gas members for automobiles. However, the higher the Cr equivalent, the higher the Cr equivalent becomes. Since the scale formed on the surface becomes thinner, seizure is likely to occur. Even if the above-mentioned lubricant using iron oxide powder is effective in preventing seizure of stainless steel with a relatively low Cr, It has been found that even with stainless steel having a high Cr equivalent, seizure cannot be completely prevented. Therefore, one of the objects of the present invention is to solve such a problem.

It is to be noted that the one proposed in Japanese Patent Publication No. 54-35985 discloses the formation of a Fe ₃ O ₄ film on the surface of an amadite roll which is easily oxidized and which is often used for hot rolling of ordinary steel. However, it is unlikely that a similar coating will form stably on high-chrome rolls or high-speed steel rolls used for hot rolling of stainless steel. Even if the Fe ₃ O ₄ coating is formed on the roll surface, if the thickness is small, it is effective in preventing seizure when the stainless steel is hot-rolled for a long time with the high-speed rotating roll. I can't think of that. This can be said even when an iron oxide film is to be positively formed on the surface of the material to be rolled before entering the roll, as proposed in JP-A-60-184405. In particular, when the material to be rolled is stainless steel having a high Cr content, the iron oxide coating is difficult to form, and even if formed, it becomes thin. Therefore, one object of the present invention is to overcome the limitation of the known method of forming an iron oxide film on the surface of the roll side or the material to be rolled and then rolling, and to prevent seizure even in hot rolling of high Cr stainless steel. Is to provide a lubricant capable of solving the above problem, and particularly to provide a lubricant having a property that can be stably supplied to the entire roll surface and having an excellent anti-seizure effect even in high Cr stainless steel. .

The term "high Cr stainless steel" as used herein means a stainless steel having a Cr equivalent of 20% or more, which is defined by the following formula.

[0016]

According to the present invention, a high Cr content is achieved.
When hot rolling stainless steel, it is a lubricant for hot rolling continuously supplied to the surface of the rolling roll in contact with the material to be rolled, at least while the rolling is being performed. 10 to 40% by weight of iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm is dispersed in a viscous aqueous solution obtained by dissolving a thickener composed of molecules in water, and an apparent viscosity of 1000. Provided is a lubricant for hot rolling of high Cr stainless steel of -50000 cP (centipoise).

Here, the iron hydroxide is preferably of the general formula Fe
It is iron hydroxide represented by O (OH). The thickener is preferably a water-soluble cross-linked acrylic acid polymer or a water-soluble biogum. If desired, the lubricant of the present invention may be added with an appropriate amount of a nonionic surfactant, for example, an ester-based one such as ethylene glycol fatty acid ester or propylene fatty acid ester.

The lubricant for hot rolling of the present invention can prevent seizure on the roll even during hot rolling of high Cr stainless steel having a Cr equivalent defined by the following formula (1) of 20% or more. Cr equivalent (%) = [Cr] +2 [Si] +2.5 [Al] +1.2 [Mo] -30 [C] -15 [N] -2 [Ni]-[Mn] ・ ・ ・ (1) , [] In the formula represents the content (% by weight) of the constituent element in the steel.

[0019]

[Function] The cause of roll seizure in hot rolling of stainless steel is that the generation rate of surface scale is slow due to the excellent oxidation resistance of stainless steel. In this case, the scale layer sufficient to protect this new surface is not generated by the next pass. This phenomenon remarkably appears in a material having a high Cr equivalent and excellent in high temperature oxidation resistance. Particularly high Cr
Equivalent stainless steel has a property that even if a scale is formed on the surface, the scale has a high Cr ₂ O ₃ concentration and an Al ₂ O ₃ concentration and is thin, so that it is easily cracked. For this reason, an exposed portion of the metal is likely to occur on the rolled material, and this metal directly contacts and adheres to the metal of the roll, causing seizure on the roll surface.

The present inventors have found that the iron seizure can be prevented even with high Cr stainless steel by supplying iron hydroxide powder dispersed in a viscous aqueous solution to the surface (metal) of the rolling roll. It was More specifically, an extremely fine iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm is dispersed in an appropriate amount in a viscous aqueous solution in which an appropriate thickener is dissolved, and then, on the roll surface or roll bite. If it is supplied and interposed between the roll and the material to be rolled during rolling, seizure does not occur even in hot rolling of high Cr stainless steel. Although the reason for this is not clear, when the lubricant of the present invention is applied to the roll surface and comes into contact with a high-temperature material to be rolled, iron hydroxide powder, for example, FeO (OH) fine powder in the lubricant is generated. , 2FeO (OH) → Fe ₂ O ₃ + H ₂ O decomposes instantly, and the Fe ₂ O ₃ generated covers the exposed metal part of the material to be rolled during rolling, and this exposed metal part is the roll metal. Prevent direct contact with
The lubricant of the present invention lowers the coefficient of friction between the material to be rolled and the roll by the lubricating action, and the decomposition reaction is an endothermic reaction. It is considered that the phenomena of removing heat from the metal and lowering its temperature, and relaxing this metal-metal adhesion are interrelated.

The respective elements constituting the lubricant of the present invention will be individually described below.

Types of Iron Hydroxide The lubricant of the present invention has an average particle size of substantially 0.1 μm or more 1
The content of iron hydroxide powder having a particle size of less than μm is 10 to 40% by weight. Generally, for iron hydroxide, FeO (OH), Fe (O
There are forms such as H) ₂ and Fe (OH) ₃ . Any iron hydroxide can be used for the lubricant of the present invention in principle, but Fe (O
H) ₂ and Fe (OH) ₃ are industrially difficult to obtain as solid powders, but FeO (OH) powder is the most stable industrially available, so FeO (OH) 3 as iron hydroxide It is practical to use.

Further, the lubricant of the present invention comprises iron hydroxide powder
It suffices if the content is 0 to 40% by weight, and it is permissible to contain, for example, iron oxide in an appropriate amount in addition to the iron hydroxide. Iron oxide has the forms of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ , but it is difficult to obtain FeO industrially stably. Therefore, when iron oxide is mixed, it is preferable to use Fe ₂ O ₃ and / or Fe ₃ O ₄ powder.

However, when a high Cr stainless steel having a Cr equivalent of 20% or more is targeted, a lubricant containing only iron hydroxide powder without mixing iron oxide is preferable. This is because the iron hydroxide powder has a function that iron oxide can prevent the seizure of the roll even if it is made of high Cr stainless steel by the decomposition reaction. However, iron hydroxide may be contained substantially in an amount of 10 to 40% by weight, and its purity does not necessarily have to be high. Iron hydroxide containing iron oxide, SiO ₂ , MnO or other metal or oxide as an impurity in a usual range, for example, 5 wt% or less can be used.

The particle size of the particle size iron hydroxide powder iron hydroxide powder stability over time of the uniform dispersibility and the dispersion state of the viscous aqueous solution, more uniform spray resistance and the rolling when supplying the rolling roll surface Since the rollability between the material and the roll is greatly affected, it is important to select the particle size appropriately. Even if the average particle size of iron hydroxide is 1 μm or more, if it is 10 μm or less, a uniform dispersion can be obtained at the time of mixing when mixing using a viscous aqueous solution whose viscosity is adjusted to be higher. However, when it is stored for a long period of time, iron hydroxide powder precipitates. Further, if the viscosity is high, there is a problem in supply to the surface of the rolling roll. It has been found that when the particle size is less than 1 μm, such a problem is less likely to occur, and a good dispersion state can be maintained for a long time by selecting an appropriate thickener and adjusting the viscosity. Further, if the content of iron hydroxide is the same, the efficiency with which the iron hydroxide particles coat the roll surface becomes better as the particles become finer, and the coating efficiency improves as the particle size of the iron hydroxide becomes smaller. And
The finer the particles, the more uniform the iron oxide film formed by the decomposition reaction can be secured. Therefore, the average particle size of the iron hydroxide powder used is preferably less than 1 μm.

On the other hand, if the average particle size is too small, for example, if the average particle size is less than 0.1 μm, it is easy to coagulate. It will be extremely difficult. Further, the ultrafine powder having a particle size smaller than 0.1 μm is industrially difficult to manufacture, which causes an increase in cost. Therefore, the lubricant of the present invention uses iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm. Although iron hydroxide is often finer than iron oxide, it is easy to obtain iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm, although it depends on the production method. Thus, when iron hydroxide fine powder having an average particle size of 0.1 μm or more and less than 1 μm is used, since this is fine powder,
It becomes easy to enter a crack in the scale on the surface of the material to be rolled, and the amount of winding between the material to be rolled and the roll also increases, which effectively acts to prevent metal-metal touch.

Content of Iron Hydroxide Powder The content of iron hydroxide powder in the lubricant is proper in order to obtain a desired roll seizure prevention effect and to obtain a stable supply of the lubricant to the roll surface. Must be limited to a certain range. In particular, the Cr equivalent defined by the formula (1) is 20%.
Regarding the above, it was found that the seizure prevention effect appears when the content of the iron hydroxide powder is 5% by weight or more. However, in practice, seizure may occur due to changes in rolling conditions, etc., and in order to obtain a stable seizure prevention effect, a content of 10% by weight or more is required.
The higher Cr equivalent stainless steel is, the more advantageous the lubricant containing the iron hydroxide powder is. However, its content is 40
Lubricants exceeding 10% by weight tend to decrease the retention of dispersion over time and increase the apparent viscosity of the lubricant due to the large content, which results in an increase in the viscosity of the rolling roll. It was found that spraying lubricant from the nozzle requires a large amount of discharge energy, making spraying difficult in practice. Therefore, the content of the hydroxide powder in the lubricant must be 5-40% by weight, preferably 10-40%, and more preferably 10-30%.

It is possible to use mere water as a medium for supplying the viscous aqueous solution iron hydroxide powder to the roll surface, but when water alone is used as a medium, the adhesion of the iron hydroxide powder to the roll surface is poor. Moreover, it was found that the iron hydroxide powder was significantly deposited in the conduit for pumping this fluid, which was not suitable for actual use. Further, using fats and oils or lubricating oil as a medium for the iron hydroxide powder makes it difficult to form a uniformly dispersed fluid because the iron hydroxide powder does not necessarily have lipophilicity.
On the other hand, it has been found that the above-mentioned problems can be almost completely solved by using a viscous aqueous solution in which an appropriate amount of a suitable thickener is dissolved in water as a supply medium for iron hydroxide powder.

Kinds of Thickeners Very many thickeners are known that dissolve in water to impart thickening properties. Typical water-soluble polymer thickeners include those based on cellulose ethers and polyacrylic acid. The present inventors have attempted to disperse iron hydroxide powder in a viscous aqueous solution using various types of these thickeners. As a result, it was found that a viscous aqueous solution using a cellulose ether type such as methyl cellulose or carboxymethyl cellulose does not necessarily have sufficient dispersion retention when the iron hydroxide powder is mixed with the viscous aqueous solution. Further, even if the polyacrylic acid-based water-soluble polymer is a straight-chain type, sufficient dispersion retention cannot be obtained as in the case of cellulose ethers.

However, it has been found that the water-soluble substance composed of the cross-linked acrylic acid polymer generally exhibits good dispersion retention with respect to the iron hydroxide powder. As is well known, crosslinked acrylic acid polymers include those obtained by subjecting polyacrylic acid to a crosslinking reaction and those obtained by copolymerizing an acrylic acid monomer and a crosslinking agent. In any case, unlike linear polymers, the fact that the polymer in a three-dimensional network in a cross-linking state is dissolved in water contributes to the dispersion retention of iron hydroxide powder. It is considered to be something. However, it is thought that sodium polyacrylate has a large number of electrolytic groups that dissolve in water and dissociate, but it was found that it has a function of holding iron hydroxide powder in a good dispersed state.

Furthermore, when xanthan gum obtained by fermenting carbohydrates using a water-soluble biogum, particularly a strain of the genus Xanthomonas, is dissolved in water to form a viscous aqueous solution, the iron hydroxide powder has further improved dispersion retention. It turned out to be good. In particular, when the lubricant is diluted with water by mixing with water in a conduit for feeding the lubricant, the powder particles tend to aggregate, but when xanthan gum is used as the thickener, It was found that this phenomenon is unlikely to occur and nozzle clogging is unlikely to occur.

The cross-linking acrylic acid polymers, sodium polyacrylates, and thickeners such as biogum such as xanthan gum used in the lubricant of the present invention are all available on the market.

Amount of Thickener Added When iron hydroxide powder is dispersed in a viscous aqueous solution in which the above thickener is dissolved, the apparent viscosity of the lubricant in the dispersed state is in the range of 1,000 to 50,000 cP. First, it is necessary to adjust the amount of thickener added. The value of this viscosity was measured using a B-type viscometer with a shear rate of 1.2 /
Second, the value when the viscosity of the lubricant is measured at a measurement temperature of 20 ° C. The addition amount of the thickener is adjusted in the range of 0.1 to 3% by weight so that the above-mentioned viscosity can be obtained according to the amount of the mixed iron hydroxide and the type of the thickener used. can do.

Surfactant The lubricant of the present invention can increase the anti-seizure effect by adding an appropriate amount of a surfactant. That is, the addition of a certain kind of surfactant improves the dispersion state of the iron hydroxide powder, and the wettability between the roll and the lubricant is improved during spraying onto the rolling roll, increasing the amount of lubricant adhering to the roll. Can be made. As a result, the amount of iron hydroxide powder entrained in the roll bite increases, which brings about a remarkable effect in preventing seizure. In particular, ester-based surfactants such as ethylene glycol fatty acid ester,
The use of nonionic surfactants such as propylene fatty acid esters is preferred. If this surfactant is added in an amount exceeding 5% by weight, the viscosity of the lubricant will be reduced and the retention of iron hydroxide will be reduced, so the addition amount must be 5% by weight or less.

Viscosity of Lubricant In order to obtain stable dispersion retention of the iron hydroxide powder, the particle size and content of the iron hydroxide powder, and the type and addition amount of the thickener are appropriately adjusted as described above. However, if the viscosity of the obtained lubricant is lower than 1000 cP, the adhesion of the iron hydroxide powder to the roll will be poor, and the dispersibility in a viscous aqueous solution and its retention will not be good either. Then, deposits and accumulations will occur in the storage tank or in the pipe that feeds the liquid from the storage tank to the nozzle. On the other hand, with a lubricant having a high apparent viscosity exceeding 50,000 cP, it becomes difficult to uniformly disperse the iron hydroxide powder, and it becomes difficult to carry out pressure feeding to the nozzle and injection from the nozzle. For this reason, the viscosity of the lubricant is 1000 to 50000 cP, preferably 40.
It is preferably in the range of 2000 to 20000 cP, which increases the amount of iron hydroxide wound in the roll bite and effectively prevents metal-metal touch.

The lubricant of the present invention thus constituted is preferably adjusted to pH neutral or weakly alkaline so as not to cause corrosion of rolling equipment and related equipment.

Method of Applying Lubricant The lubricant according to the present invention is preferably applied as follows in hot rolling of stainless steel. First, the lubricant is prepared and stored in a tank while maintaining its dispersed state. From this tank, it is pumped through a conduit to a nozzle mounted near the rolling roll. This pumping is usually a number 1
Since a pressure of about 0 kgf / cm ² or more is required, it is suitable to use a plunger type pump or the like.

The lubricant thus pressure-fed to the nozzle is continuously sprayed from the nozzle toward the surface of the rotating roll in the rolling stand at least during rolling. . The rolling stand to which this lubricant is applied is not particularly limited, but is appropriately selected from the group of finishing rolling stands and the group of rough rolling stands in the hot strip mill. When spraying the lubricant onto the roll surface, it is usually good to spray this lubricant evenly over the entire roll width in contact with the material to be rolled.
At the edge of the material to be rolled, oxide scale delamination becomes particularly noticeable in relation to the plastic deformation behavior during rough rolling. In some cases, therefore, a lubricant may be selectively added near the edge of the material to be rolled. You may spray.

The supply amount of the lubricant to be sprayed onto the surface of the rolling roll is appropriately adjusted in consideration of the rolling speed and the like, but it is from about 0.1 liter / m ² to several per unit area where the rolling roll contacts the material to be rolled. It is good that it is about liter / m ² .
This lubricant is characterized in that it prevents seizure of rolls of high Cr stainless steel, and also contributes to the reduction of the friction coefficient. However, this lubricant has been used in the past during hot rolling of stainless steel. It can also be used in combination with an ordinary lubricating oil or the like used for the purpose of reducing the rolling load.

Representative examples of the lubricant of the present invention will be shown below by way of examples. As shown in these examples, when hot rolling is performed on high Cr stainless steel using the lubricant of the present invention, seizure on rolls occurs. As a result, a novel hot rolling method for high Cr stainless steel with good surface properties is provided. That is, according to the present invention, when hot rolling high-Cr stainless steel, the hot-rolled high-Cr stainless steel is directed toward the surface of the rolling roll.
An iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm in a viscous aqueous solution obtained by dissolving a thickener made of a water-soluble polymer in water from a spray nozzle installed near the roll. An apparent viscosity of 100% by dispersing 40% by weight is 100.
A hot rolling method for high Cr stainless steel, characterized in that a lubricant of 0 to 50000 cP (centipoise) is continuously sprayed at least while the material to be rolled is in contact with the roll. The hot rolling referred to here means hot rolling under the normal hot rolling conditions of ordinary high Cr stainless steel, which is composed of, for example, rough rolling and finish rolling.
This method exerts a great effect especially when it is applied to the hot rolling of stainless steel having a Cr equivalent of 20% or more shown in (1) above, by using the lubricant having the constitution described in detail above. To do.

[0041]

【Example】

[Example 1] Lubricants Nos. 1 to 19 shown in Table 1 were prepared. FeO (OH), Fe
_One or _{two of 2} O ₃ or Fe ₃ O ₄ was used, and the powder composition thereof was shown in the table by weight%. Also, the average particle size of each powder
(μm) and the content (% by weight) of each powder in the lubricant are shown in the table. The types of thickeners used for each lubricant, the presence or absence of surfactants, and the viscosity (cP) of the lubricant are shown in the table. The viscosity of the lubricant was measured using a B-type viscometer at a shear rate of 1.2 / sec and a measurement temperature of 20 ° C.

In the preparation of each lubricant, first, the powder was added to water while stirring, and then a solution prepared by separately adding a predetermined thickening agent and, in some cases, a surfactant to water was added to the above powder. It was added to water and mixed with stirring, and finally caustic soda was added as needed to obtain a lubricant having a pH of 7.

Among the thickeners used, the one designated as a cross-linking acrylic acid polymer was a trade name "Junron PW110" manufactured by Nippon Pure Chemical Co., Ltd. Further, as the indicated sodium polyacrylate, the trade name “Rheogic 306L” manufactured by Nippon Pure Chemical Co., Ltd. was used. As the water-soluble cellulose derivative shown, "Metroze 4000" manufactured by Shin-Etsu Chemical Co., Ltd. was used. The amount of these thickeners added is the amount required for the apparent viscosity of the final lubricant to reach the indicated value. The surfactants used were ethylene glycol fatty acid ester-based or propylene fatty acid ester-based surfactants, and the former used "Junron PW11" as a thickener.
0 ”is used, the latter is used as a thickener,“ Rheogic 3
"06L" was used. The amount of these surfactants added was expressed as the concentration (% by weight) in the lubricant.

Each of the lubricants Nos. 1 to 19 in Table 1 has a high C content.
r During hot rolling of stainless steel, it was used under the following conditions. First, hot rolling is performed with a thickness of 200 mm and a width of 10
A slab of ferritic stainless steel having a weight of 30 to 1240 mm and a weight of 10 to 14 tons is heated to 1200 to 1250 ° C., rough-rolled to a rough bar having a thickness of 25 mm, and then finished by a finishing rolling mill group consisting of 7 stands. It was rolled into a 3.0 mm hot coil.

The chemical composition of the tested stainless steel is% by weight, C: 0.01 to 0.06%, Si: 0.22 to 0.2.
68%, Mn: 0.18 to 0.74%, Cr: 17.9 to
22.1%, Ni: 0.11 to 0.34%, Mo: 0.03
~ 2.0%, Nb: 0 ~ 0.49%, Cu: 0 ~ 0.58
%, Al: 0.02 to 4.0%, Ti: 0 to 0.32%,
N: It is in the range of 0.006 to 0.013%. These stainless steels have Cr equivalents represented by the formula (1) of the text of about 20 to 23%, about 23 to 26%, and about 26 to 29%.
%, And by applying each lubricant to 20 stainless steel slabs of each rank, hot rolling can be performed on each slab with a total of 60 slabs. went.

Actually, after changing the work rolls of the finishing rolling mill group (replacement with grinding finished rolls), 20 slabs of each lubricant were continuously hot-rolled,
The type and amount of lubricant were constant during this one cycle.
Lubricants are supplied to the upper and lower work rolls of the first to third stands of the finishing rolling mill group, and four nozzles are provided on each of the upper and lower work rolls (eight in total for each stand). Liquid was sent from the lubricant storage tank to the nozzle of No. 1 by a plunger type pump at a pressure of 40 kgf / mm ² through a conduit. The amount of lubricant supplied to each roll surface was adjusted to be about 0.3 liter / m ² with respect to the roll surface. The material of the work rolls of the first to third finish rolling mills is a high chrome roll.

In the above rolling operation, the conventionally used rolling oil was supplied to the backup roll by water injection. The coils after hot rolling were passed through a continuous annealing pickling line, and the surface texture of each coil obtained after descaling was observed to investigate the number of surface defects caused by roll seizure. The results are shown in Table 2.

The dispersion retention, dispersibility, sprayability and adhesion of each lubricant were evaluated in the laboratory as follows. The results are also shown in Table 2.

The dispersion retention was evaluated by the degree of sedimentation of iron hydroxide powder. The degree of sedimentation is as follows:
The upper liquid amount (separated liquid volume) of the lubricant was measured and calculated by the following formula. Sedimentation degree% = (separated liquid volume after 1 week) / (total volume) x 1
00

As shown in Table 3, those having a sedimentation degree of 2% or less are marked with ∘, those with a sedimentation degree of 2 to 10% are marked with ∘, and 10
.About.20% was evaluated by .DELTA., And 20% or more was evaluated by 4 levels of X.

The dispersibility of each lubricant (the state in which particles are dispersed in a viscous aqueous solution) was evaluated by the dispersed particle size (dispersion maximum particle size). The dispersed particle size was measured by laser diffraction. As shown in Table 3, the dispersed particle size (dispersion maximum particle size) is 4
◎ mark for less than 0 μm, ○ for 40-80 μm
The evaluation was made on the basis of four levels, in which the mark, the mark of 80 to 160 μm, and the mark exceeding 160 μm were designated as Δ and X, respectively.

The jetting property was judged by the stability of jetting when it was supplied to an elliptical spray nozzle having a diameter of 0.5 × 1.0 mm at a jetting pressure of 40 kg / cm ² and the jetting width of the lubricant.
It was rated at 4 levels according to the criteria shown in.

The adhesion was measured by measuring the film thickness of the lubricant formed on the surface of the roll using a laser film thickness meter, and the thickness was evaluated according to the criteria shown in Table 3 to 4 levels.

In the column of comprehensive evaluation criteria in Table 2, the suitability of the high Cr stainless steel as a lubricant is determined by the laboratory property evaluation of lubricants and the situation where seizure occurs in actual hot rolling. This is a comprehensive evaluation.
A mark indicates insufficient effect, and a mark indicates no effect.

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

[Table 3]

As can be seen from the results in Table 2, the lubricant No.
When hot-rolled with 5, 10, 11, 13, 15, 16 and 18, no surface flaw occurs even if 20 rolls are rolled after changing the rolling roll within the range where the Cr equivalent is up to 29%. Roll seizure was prevented, and the operation was stable without nozzle clogging. With these lubricants, the same results were obtained even when the Cr equivalent was lower than that shown, for example, when the Cr equivalent was 16-18 or 18-20.

On the other hand, in the comparative example of No. 1 which does not use a lubricant and the comparative example of No. 2 in which iron oxide is simply mixed with water, the Cr equivalent is already in a relatively low range of 20 to 23%. Most of the coils were flawed.

Although a thickener was added, N containing iron oxide alone was added.
In the case of the o.3 lubricant, the number of flaws increased as the Cr equivalent increased, and surface flaws occurred in all the coils at the Cr equivalent of 26 to 29%. Therefore, it cannot be applied to high Cr equivalent stainless steel.

A No. 4 lubricant similar to No. 3 except that a surfactant was added has some seizure prevention effect, but is not sufficient.

In the case of the lubricant No. 6 which contains iron hydroxide but whose thickener is a water-soluble cellulose derivative, the Cr equivalent is 26 to 29%, the number of surface defects is 20, and all the coils are rolled. Surface defects due to seizure occurred. It is considered that this is because, as shown in the property evaluation in Table 2, the retention of the lubricant was poor and the iron hydroxide powder separated and settled.

No. 7 containing excessively fine iron hydroxide
When hot rolling is performed using the above lubricant, this may be related to the poor uniformity of iron hydroxide, but when the nozzle was observed after hot rolling, the nozzle tip was clogged. As a result, it is estimated that the lubricant was not sufficiently supplied during hot rolling from around the 13th coil.
The coil was damaged after that.

The lubricant of No. 8 containing iron hydroxide and having a cross-linked acrylic acid polymer and a surfactant added thereto, but having a remarkably low viscosity, shows almost no effect on the surface flaw prevention. Absent.

With the lubricant No. 9 having a low iron hydroxide content, a slight seizure-preventing effect was recognized, but the occurrence of flaws was not sufficiently suppressed.

No. 12 containing iron hydroxide having an excessively large particle size
Nozzle clogging was observed when the nozzles after rolling were observed with the lubricant of. Therefore, although this No. 12 lubricant has the effect of preventing seizure, it is difficult to supply it to the roll surface in a stable manner, so that it is not practical.
In the case of the lubricant of No. 14 having an excessive amount of surfactant, a tentative effect is recognized in the Cr equivalent of 20 to 26%, but a sufficient effect cannot be obtained in the Cr equivalent of 26 to 29%.

With a No. 19 lubricant having an excessively high viscosity,
Since the viscosity was too high and the injection condition was unstable, flaws occurred around the 10th coil regardless of the Cr equivalent. It is considered that this is due to nozzle clogging.

Example 2 Lubricants No. 21 to 26 shown in Table 4 were prepared in the same manner as in Example 1. Among the thickeners used, “Xanthan gum” shown in Table 4 was trade name Rheozic 100 manufactured by Nippon Pure Chemical Industries, Ltd.
This is xanthan gum consisting of a heteropolysaccharide obtained by fermenting carbohydrates using a strain of the genus Xanthomonas. Agar was used as the "agarose polysaccharide" and starch was used as the "amylose polysaccharide". The "crosslinked acrylic acid polymer" is Junron PW110 manufactured by Nippon Pure Chemical Co., Ltd. as in Example 1, and the "water-soluble cellulose ether" is also manufactured by Shin-Etsu Chemical Co., Ltd. as in Example 1. Is.

With respect to the sedimentation property of each of the obtained lubricants, the lubricants were left for one week after production, and the upper volume of the separated or precipitated lubricants was measured. The results are shown in Table 5.

The dispersibility of each lubricant (the state in which particles are dispersed in a viscous aqueous solution) was evaluated by the dispersed particle diameter (dispersion maximum particle diameter). The dispersed particle size was measured by laser diffraction and evaluated on the basis of four criteria shown in Table 6, and the results are shown in Table 5
It was shown to.

Furthermore, if the lubricant is diluted with water for some reason, it will aggregate and cause nozzle clogging troubles.
The "cohesiveness due to water dilution" of the lubricant was examined. That is,
The agglomerated particle size of the lubricant diluted with water was measured with an optical microscope, and evaluated in four levels according to the criteria shown in Table 6, and the results are shown in Table 5.
It was shown to. Here, the concentration of the lubricant diluted with water is 4% by weight.
Is. The cohesiveness due to this water dilution evaluates the cohesiveness when the lubricant is diluted with water in the conduit to the nozzle when water is mixed into the conduit to the nozzle while waiting for the next rolling. .

Each lubricant was supplied to the roll surface in the same manner as in Example 1 during hot rolling of stainless steel. However, high-speed steel (high speed steel) was used as the material of the rolls of the first to third stands to which the lubricant was supplied. The chemical composition value of the applied stainless steel is% by weight, C: 0.01 to 0.06.
%, Si: 0.22 to 0.68%, Mn: 0.18 to 0.7
4%, Cr: 17.9 to 22.1%, Ni: 0.11 to 0.1.
34%, Mo: 0.03 to 2.0%, Nb: 0 to 0.49
%, Cu: 0 to 0.58%, Al: 0.02 to 4.0%,
Ti: 0 to 0.32%, N: 0.006 to 0.013%, and its slab is 1200 to 1250 ° C.
After rough heating, rough rolling is performed on a rough bar with a thickness of 25 mm, and then with a finishing rolling mill group consisting of 7 stands, a thickness of 3.0 m.
m hot coil. At that time, after changing the work rolls of the finishing rolling mill group, 10 slabs were continuously hot-rolled, and the lubricating condition was kept constant during this one cycle. After rolling, 10 slabs were rolled again under the same conditions with the injection equipment and the storage tank kept unchanged until the next rolling opportunity, and the presence or absence of nozzle blockage before and after that was investigated.

The lubricant injection position, supply method, and supply amount were the same as in Example 1, and the conventionally used rolling oil was supplied to the backup roll by water injection.

Nozzle clogging and seizure resistance were investigated during rolling using each lubricant, and the results are also shown in Table 5.
The nozzle clogging property was checked by inspecting the nozzle before and after rolling.
For the seizure property, the presence or absence of seizure was examined by determining the roll skin after rolling and the steel plate surface skin after pickling. Nozzle clogging and seizure resistance were evaluated as x when 10 coils were rolled using each lubricant and nozzle clogging or seizure occurred even with one coil.

Further, comprehensive evaluation was carried out according to the same criteria as in Example 1, and the results are shown in Table 5.

[0077]

[Table 4]

[0078]

[Table 5]

[0079]

[Table 6]

From the results of Table 5, the following is clear.

Nos. 21 and 22 are lubricants using iron oxide as a thickener made of a water-soluble synthetic polymer. In these lubricants, iron oxide is apt to settle, and dilute agglomerated particles with water that most affect nozzle clogging. The diameter is also large. For this reason, nozzle clogging eventually occurred and seizure could not be prevented. No. 24 and 25 lubricants that used vegetable polysaccharides as thickeners caused nozzle blockage, and No. 24 lubricants did not have a seizure prevention effect due to the low powder content. , Also N
In the case of o.25, seizure occurred because the water-diluted aggregate particle size was large.

On the other hand, N using biogum as a thickener
With the lubricants of o.23 and 26, neither nozzle clogging nor seizure was suppressed. That is, by using these lubricants, aggregation due to water dilution was suppressed, stable injection was possible in terms of lubricant supply, and nozzle clogging did not occur before and after rolling. It was also found that there is no sedimentation after 1 week of production, so that it is excellent in long-term holding stability, and a stable effect can be obtained in terms of preventing seizure of stainless steel. In particular, FeO (O
The product using H) has no sedimentation at all, has a small dispersed particle size and a water-diluted agglomerated particle size, and is extremely excellent in nozzle clogging resistance and roll seizure resistance.

[0083]

As described above, according to the lubricant of the present invention, it is possible to stably prevent roll seizure during hot rolling of high Cr stainless steel, and to obtain a high quality product having no surface flaw. can get. Also, damage to the rolling rolls is reduced and the roll unit is also reduced. Since the manufactured stainless steel plate has a clean surface property, surface grinding can be omitted, and it is possible to manufacture a stainless steel plate with high productivity and high added value such as a mirror finishing application.

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Claims (5)

[Claims] 1. A hot rolling lubricant which is continuously supplied to the surface of a rolling roll in contact with a material to be rolled during hot rolling of high Cr stainless steel, at least while the rolling is being performed. Then, 10 to 40% by weight of iron hydroxide powder having an average particle size of 0.1 μm or more and less than 1 μm is dispersed in a viscous aqueous solution obtained by dissolving a thickener composed of a water-soluble polymer in water. And the apparent viscosity is 1000 ~ 50000cP
(Centipoise) high Cr stainless steel hot rolling lubricant. 2. The high Cr content according to claim 1, wherein the iron hydroxide is iron oxyhydroxide represented by the general formula FeO (OH).
Lubricant for hot rolling of stainless steel. 3. The lubricant for hot rolling of high Cr stainless steel according to claim 1, wherein the thickener is a water-soluble crosslinked acrylic acid polymer. 4. The hot rolling lubricant according to claim 1, wherein the high Cr stainless steel has a Cr equivalent defined by the following formula of 20% or more, Cr equivalent (%) = [Cr] +2 [ Si] +2.5 [Al] +1.2 [Mo] -30 [C] -1
5 [N] -2 [Ni]-[Mn] However, [] in the formula represents the content (% by weight) of the constituent element in the steel. 5. The lubricant for hot rolling according to claim 1, further comprising 5% by weight or less of a surfactant.