JPH04130194A - Lubricant for hot rolling of stainless steel - Google Patents

Abstract

PURPOSE:To obtain the title lubricant which can prevent the seizure to rolling rolls when stainless steel is hot-coiled under a high load by dispersing specified fine inorganic particles in a viscous aqueous solution. CONSTITUTION:1-30wt.% fine inorganic particles of which particles having a diameter of 10mum or smaller account for at least 90wt.% and which comprise a compound selected from MoS2, BN, PbO, PbS, CaF2, alumina, titania, nickel oxide, chromium oxide, and an inorganic silicate are dispersed in a viscous aqueous solution, if necessary having a water-soluble high-molecular thickening agent incorporated therein, having a viscosity of 1X10<3> to 5X10<5>cP to give the title lubricant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot rolling lubricant that suppresses seizing on rolling rolls, particularly when hot rolling stainless steel under high load.

[Prior Art] Stainless steel products are required to have excellent surface texture, so it is strictly avoided that scratches occur on the surface of the steel plate during the manufacturing process. However, when stainless steel is hot rolled using conventional hot rolling equipment such as a tandem mill, scratches due to seizure of the rolling rolls often occur on the surface of the steel sheet. If surface flaws occur, even if the flaws are mild, the product is unsuitable for mirror finishing purposes. As a result, the uses of the obtained steel sheet are subject to restrictions. Furthermore, it is necessary to perform surface care on a stainless steel plate with surface flaws through a polishing process. Furthermore, if the degree of damage is significant, the product cannot be shipped.
It becomes scrap. Therefore, the yield decreases,
This causes an increase in manufacturing costs.

In order to suppress the occurrence of surface flaws caused by seizure on the surface of stainless steel, various means have been studied in the past. For example, it has been reported that the occurrence of surface defects can be suppressed by reducing the load on the rolling rolls, selecting rolling conditions, selecting roll materials, improving lubricants, etc.
Among them, Glenroll is said to be effective in preventing seizure.

[Problems to be Solved by the Invention] Incidentally, as a recent trend, a large rolling load has been adopted as a means of increasing productivity of a hot rolling line and improving material quality. Further, under conventional rolling conditions, for example, in a tandem mill, the rolling load at the pre-finishing stage corresponding to the first to third stands of the finishing rolling group is set to be large.

If grain rolls are used in a stand with a large rolling load, the rolls will wear thickly (and the degree of freedom of width reverse rolling, which is essential in recent rolling technology, will be lost).

Further, even if the problem of roll seizure is solved, systems that perform mixed rolling of stainless steel and ordinary steel have the disadvantage that the surface texture grade of ordinary steel products is slightly lowered. For these reasons, the adoption of grain rolls is not a sufficient measure to prevent surface defects in recent rolling technologies that are based on schedule-free rolling, mixed rolling of different steel types, and the like.

Furthermore, various attempts have been made to prevent the occurrence of surface flaws by improving lubricants. Various types of lubricants have been developed in the field of rolling ordinary steel because they are present between the rolling rolls and the rolled material and have the effect of lowering the coefficient of friction. A similar effect is expected in hot rolling of stainless steel, and is considered to be effective in preventing seizure. However, the current situation is that existing animal or vegetable oils, mineral or synthetic lubricating oils, etc. do not have sufficient anti-seizure effects.

Therefore, the present invention uses a substance that prevents metal-to-metal contact between the stainless steel and the rolling roll and also has a lubricating action as an alternative to these conventional lubricants, thereby preventing seizure of the rolling roll. The purpose is to produce hot-rolled stainless steel sheets with excellent surface properties.

[Means for Solving the Problems] In order to achieve the object, the hot rolling lubricant of the present invention contains M o S 2 , BN , P b O, P
bS, CaF2. It is characterized in that one or more types of inorganic fine particles selected from alumina, titania, nickel oxide, chromium oxide, and inorganic silicates are dispersed in a viscous aqueous solution at a ratio of 1 to 30% by weight.

Here, it is preferable to use inorganic fine particles in which 90% by weight or more is fine powder with a particle size of 10 LLm or less. In addition, a water-soluble polymer thickener is added to the viscous aqueous solution to increase the viscosity by lXl.
It is preferable to adjust it to ×103 to 5X10' cP.

[Function] In mixed rolling of different steel types, schedule-free rolling, etc., high Cr rolls are used as work rolls in the pre-finishing stage where the rolling load is large. However, high Cr
The roll has a similar composition to the stainless steel to be rolled, and is highly compatible with the material to be rolled. Therefore, it has the disadvantage that seizure tends to occur during hot rolling of stainless steel.

The cause of surface flaws on stainless steel during hot rolling is
The problem is that the material to be rolled sticks to the rolling roll, and the seizure is repeatedly transferred to the material to be rolled. For this reason, it is not possible to freely change the steel type and roll it.
Production efficiency is suppressed. In addition, a rolling roll with seizure must be replaced with a roll having a good surface quality, which unavoidably lowers operating efficiency due to an increase in roll consumption, an increase in rolling downtime, and the like.

The present inventors have been conducting research on roll seizure in hot rolling of stainless steel for many years. During this time, we have experienced that roll seizure tends to occur during high-speed rolling under high pressure as slabs become larger, and is particularly noticeable in stainless steel.

This is due to the fact that stainless steel has excellent oxidation resistance, has a slow scale formation rate, and when a new surface occurs during multi-stage rolling, there is not enough time to form a scale layer that protects the new surface. It turned out that. In particular, problems occur frequently in tandem mills with high rolling speeds, and there are fewer cases of surface flaws in Steckel mills, etc., which also indicates the importance of the protective effect of scale.

Therefore, the present inventors have considered preventing seizure by replenishing the missing scale from the outside and preventing metal-to-metal contact between the material to be rolled and the rolling roll.

In this series, the use of iron oxide powder dispersed in a viscous aqueous solution as a lubricant was discovered in JP-A-64-
83309, and the use of a graphite powder dispersed in a viscous aqueous solution as a lubricant was introduced in JP-A-1-167396.

When using this type of lubricant, even if a high Cr roll is used as a work roll,
Even when hot rolling is performed at a high temperature of 200° C. while applying a high load of 10 to 50 kgf/mm”, roll burning of stainless steel can be prevented.

The present inventors subsequently investigated and researched substances other than iron oxide powder and graphite in order to prevent seizure by further avoiding metal-to-metal contact. As a result, MoS, BN, Pb0P b S , Ca F
2+ alumina, titania, nickel oxide, chromium oxide,
It was discovered that inorganic silicates and the like act as similarly effective lubricant components, leading to the present invention. Note that these inorganic fine particles may be dispersed in the viscous aqueous solution alone or in combination.

The amount of inorganic fine particles dispersed in the viscous aqueous solution must be maintained at 1 to 30% by weight. This amount of dispersion is 1% by weight.
If it is less than that, the anti-seizure effect due to the addition of inorganic fine particles will be small. Conversely, in the case of a viscous aqueous solution in which fine inorganic particles are dispersed in an amount exceeding 30% by weight, it is required to significantly increase the ejection energy when spraying the aqueous solution onto a rolling roll. This not only impairs economic efficiency, but also tends to cause troubles such as clogging of conduits due to precipitation and accumulation of inorganic particles.

Further, the particle size of the inorganic fine particles is preferably such that 90% by weight or more has a particle size of 10 μm or less in order to maintain a homogeneous dispersion state in an aqueous solution. 90% by weight or more has a particle size of 10μ
m or less, a homogeneous dispersion state is maintained even after an aqueous solution in which inorganic fine particles are dispersed is left for one week. In addition, by reducing the particle size, a good dispersion state can be obtained even in a relatively low viscosity aqueous solution. Furthermore, by reducing the particle size, it is possible to suppress the adverse effects of inorganic fine particles on the stainless steel surface.

The viscosity of the aqueous solution in which the inorganic fine particles are dispersed can be increased to 1×1×10 3 to 5 by adding a water-soluble polymer thickener.
It is preferable to adjust to X1×10 3 cP (centipoise). When the viscosity is maintained within this range, adhesion to the mill rolls is adequate.

Among the inorganic fine particles, molybdenum disulfide M o S * is known as a solid lubricant having a layered structure that is easily sheared. When this is supplied to hot rolling rolls, contact between nucleus metals is suppressed while utilizing lubricity. As a result, an anti-seize effect is exhibited.

Boron nitride BN has a 60,000-grade layered crystal structure and is known as a substance that has a lubricating effect similar to molybdenum disulfide. Additionally, it has a high melting point of 3000°C and is a stable substance. Therefore, a large effect of suppressing metal-to-metal contact between the material to be rolled and the rolling roll is exerted.

Lead oxide PbO and lead sulfide PbS have relatively low melting points;
In the hot rolling temperature range of stainless steel, it is in a molten or semi-molten state. By covering the surface of the rolling roll with this melt, metal-to-metal contact is avoided and seizure is prevented.

Calcium fluoride Ca F 2 has a high melting point of 1373° C., exhibits excellent lubricity at high temperatures, prevents metal-to-metal contact, and suppresses seizure on rolling rolls.

Alumina AJ2. Titania Tioi, nickel oxide N 10 + chromium oxide Cra○8, etc. are all hard oxides that are stable at high temperatures. These oxides are the above-mentioned M o S z, BN,
Slightly inferior to PbO, PbS, etc. However, forming a stable oxide film between the rolled material and the rolling roll prevents metal-to-metal contact between the two, which has a large effect on seizure prevention. In addition, since the amount of lubricant supplied to the surface of the rolled material is small, even if it remains on the surface of the rolled material, even though it is a hard oxide, it will reduce the wear of the rolling rolls. There is little risk that it will be promoted. Moreover, since it is a stable oxide, it does not penetrate into the rolled material, is easily removed in the subsequent pickling process, and does not have any adverse effect on pickling properties.

Inorganic silicates are composite oxides of silica and metal oxides, and typical examples include mica and glass. Inorganic silicates can be used at hot rolling temperatures of stainless steel from 1250 to 850.
In the temperature range of °C, most of the material is in a molten state, forming a film on the surface of the rolling roll as a melt, and direct contact with the material to be rolled is avoided.

Furthermore, the type of water-soluble polymer thickener added to adjust the viscosity of the viscous aqueous solution is not particularly limited. However, when considering the corrosivity of the lubricant when it scatters and adheres to surrounding rolling equipment, a neutral or weakly alkaline lubricant is preferable. Furthermore, it is preferable to use a thickener that exhibits stable viscosity even when the pH of the lubricant is adjusted. Examples of such thickeners include acrylic acid polymers and carboxyvinyl polymers.

[Examples] Hereinafter, the present invention will be specifically described by way of examples with reference to the drawings.

! A stainless steel plate 5US430LX with a thickness of 20 mm, a width of 50 mm, and a length of 150 mm was used as the material to be rolled, and the rolling temperature was 9.
Hot rolling was carried out by one pass rolling at 00° C. and a rolling reduction of 70%. At this time, as the rolling roll, hot work tool steel 5KD
A roll made in No. 61 was used. Further, the material to be rolled was heated for a short time in a furnace into which an inert gas was introduced, and the amount of scale generated on the surface of the material to be rolled was suppressed as much as possible so that the film thickness was approximately ILLm.

A lubricant was sprayed onto the surface of a roll having a diameter of 350 mm and a barrel length of 300 mm during hot rolling. That is, as shown in FIG. 1, the lubricant contained in the lubricant container L is sent to the injection nozzle 3 via the supply conduit 2 using a pump with a pressure of 100 kgf/cm''. The lubricant droplets 4 were sprayed onto the circumferential surface of a rolling roll 5 rotating at 40 rpm.The spray width was 20 rpm.
0 mm, and the injection time was set to 3 seconds.

As a result, a total weight of 5 g of lubricant was supplied to the circumferential surface of the rolling roll 5. This amount corresponds to forming a liquid film having a film thickness of about 20 μm.

After injecting the lubricant onto the circumferential surface of the rolling roll 5, the water contained in the high-pressure water container 6 is pumped through the nozzle 7 at a pressure of 3
kg f / cm '' as water droplets 8. This water supply corresponds to the supply of roll cooling water in a hot rolling mill. If the amount of lubricant is appropriate, the rate of lubricant flowing down will be reduced, and the rate of attachment of the lubricant to the rolling roll 5 will be increased.

As shown in Table 1, the lubricant has an average particle size of 1.1
A viscous aqueous solution containing various inorganic fine particles having a maximum particle size of 5 μm or less and an acrylic acid polymer as a thickener was used. After rolling, the surfaces of the rolling roll 5 and the rolled material were observed to check for occurrence of seizure. The results are shown in Table 1.

As is clear from Table 1, Mo5a according to the invention,
A lubricant containing BN, PbO, PbS, CaFz, etc. exhibits an anti-seizure effect that is comparable to the lubricant in which iron oxide powder, graphite powder, etc., as proposed in the previous application, is dispersed. It turns out that it is something. Furthermore, the lubricity was also sufficient.

(Hereinafter, the margin of this page) The stability of fine particle dispersion was investigated in lubricants prepared by varying the amount of inorganic fine particles such as BN and Al2-Oa dispersed in a viscous aqueous solution and the viscosity of the viscous aqueous solution. Dispersion stability was determined by preparing a lubricant, placing it in a beaker, and allowing it to stand still, and determining the state of dispersion of the fine particles one week later. The investigation method is to collect a lubricant sample from the upper part of the beaker and measure the content of fine particles contained in the sample liquid.
The ratio with the content at the initial stage of preparation was determined.

As for the particle size of the inorganic fine particles, as in Example 1, those having an average particle size of 1.1 μm and a maximum particle size of 5 μm or less were used. Furthermore, an acrylic acid polymer was used as a thickener for the viscous aqueous solution.

The results of the investigation of fine particle dispersibility are shown in Table 2.

(Hereinafter, the margin of this page) As is clear from Table 2, the amount of dispersion of inorganic fine particles is
As long as the viscosity of the viscous aqueous solution is maintained at ~30% by weight, and as long as the viscosity of the viscous aqueous solution is set to 1 x 103 to 5 x 10'cP, even after being left for one week, the amount of dispersed inorganic fine particles contained in the viscous aqueous solution in the upper layer of the beaker will be: It was almost the same as the initial stage of preparation.

In other words, it can be seen that no sedimentation of fine particles occurred and a stable dispersion state was obtained.

This stable dispersion state indicates that the lubricant can be supplied to the rolling rolls under stable conditions for a long period of time without causing problems such as settling or clogging in the lubricant supply conduit or supply nozzle.

[Effects of the Invention] As explained above, when the lubricant of the present invention is used, a stable lubricant film is formed on the circumferential surface of the rolling roll, and the metal-metal gap between the rolling roll and the rolled material is Contact can be avoided. As a result, the rolled material is prevented from sticking to the circumferential surface of the rolling roll, and a hot rolled steel sheet free of defects such as surface flaws can be obtained. This hot rolled steel sheet has excellent surface properties and is used for various purposes including mirror finishing. Moreover, since the work load of surface care in subsequent steps is eased, manufacturing costs can also be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a mechanism for spraying lubricant onto rolling rolls. 1: Lubricant container 2: Supply conduit 3: Spray nozzle 4: Lubricant droplet 5: Roll roll 6: High pressure water container 7; Nozzle 8: Water droplet

Claims (3)

[Claims] (1) MoS_2, BN, PbO, PbS, CaF_2
, alumina, titania, nickel oxide, chromium oxide, and inorganic silicate, one or more types of inorganic fine particles are dispersed in a viscous aqueous solution at a ratio of 1 to 30% by weight. Lubricant for hot rolling of stainless steel. (2) A lubricant for hot rolling of stainless steel, wherein 90% by weight or more of the inorganic fine particles according to claim 1 are fine powders having a particle size of 10 μm or less. (3) For hot rolling of stainless steel, characterized in that a water-soluble polymer thickener is added to the viscous aqueous solution according to claim 1, and the viscosity is adjusted to 1 x 10^3 to 5 x 10^5 cP. lubricant.