JPH083111B2 - Lubricant for hot working of stainless steel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricant suitable for obtaining a product having good surface properties by preventing seizure of stainless steel on a working roll during hot working of stainless steel.

[0002]

2. Description of the Related Art Since stainless steel products are required to have a clean surface, it is necessary to prevent surface scratches in the manufacturing process as much as possible. Surface scratches on stainless steel products are caused by various factors in the steelmaking process, hot rolling process, cold rolling process and the like. Among them, in the hot rolling process, the stainless steel plate is often seized on the rolling roll to cause surface scratches. A stainless steel sheet with surface scratches is not suitable for a mirror-finished application even if the surface scratches are mild. Also, if the degree of scratches is significant, it is returned to the steelmaking stage as scrap, and the yield as a steel plate decreases. When shipping a stainless steel plate with surface scratches as a product requiring a good surface condition, it is necessary to remove the surface scratches by a polishing process such as buffing. However, if the occurrence of surface scratches in the rolling process can be suppressed, the polishing process can be reduced or omitted, and the productivity is improved.

In order to prevent the occurrence of surface scratches caused by seizure during hot rolling, various studies have been conventionally conducted on reducing roll load by adjusting rolling conditions, improving material of rolling rolls, improving lubricants, and the like. It is being appreciated. For example, various lubricants based on existing animal fats and oils, vegetable fats and oils, mineral lubricants, etc. have been researched and developed. But,
At present, it has not been possible to obtain a sufficient anti-seizure effect.

The inventors of the present invention effectively prevent seizure of a stainless steel plate on a rolling roll when using a mixed solution of powdered iron oxide and graphite dispersed in a viscous aqueous solution as a lubricant for hot rolling. It has been found that Japanese Patent Application Laid-Open No. 64-83309 and Japanese Patent Application Laid-Open No. 1-16
It was introduced in Japanese Patent No. 7396. This lubricant has a significantly better seizure prevention effect than the conventional hot rolling lubricant.

[0005]

However, even if the above-mentioned lubricant is used, surface scratches may occur in some cases. In particular, if the pass schedule is changed or the rolling temperature is changed in the hot rolling process, the load on the roll may increase beyond the action of the lubricant that suppresses the occurrence of seizure. As a result, surface scratches cannot be completely prevented. By the way, the environment in which stainless steel products are used is becoming severer year by year, and the required service life is also becoming longer. To meet these demands,
Stainless steel containing a large amount of alloy elements such as Cr and Al has begun to be used. When hot rolling a stainless steel sheet having such a composition and composition with high oxidation resistance, the amount of oxide scale produced on the surface of the steel sheet during rolling is smaller than that of conventional stainless steel. Therefore, a metal-metal touch occurs between the roll and the roll, and seizure on the roll easily occurs.

The lubricant previously proposed by the inventors of the present invention is effective in reducing the degree of seizure when used in hot rolling of such a stainless steel sheet. It cannot be completely prevented. As a result, the stainless steel sheet may become a hot rolled coil with surface scratches depending on the hot rolling cycle. The surface scratches are not limited to hot rolling, but surface scratches may also occur in other hot working methods such as hot extrusion in which a stainless steel material is extruded into a predetermined shape at a high temperature.

The present invention has been devised in order to solve such problems, and by utilizing the endothermic action and releasing action of iron hydroxide, it is possible to change the rolling conditions and change the material to be rolled. The object of the invention is to obtain a hot-working product that has a sufficient anti-seizure effect and has no surface scratches.

[0008]

In order to achieve the object, the lubricant for hot working of stainless steel according to the present invention is 1-30.
It is characterized in that the iron hydroxide powder of weight% is dispersed in a viscous aqueous solution. This lubricant is 1 to 30% by weight
It is also possible to include the iron oxide powder (1) in a total amount of 2 to 30% by weight with iron hydroxide. 90% by weight or more of each of iron oxide and iron hydroxide is preferably fine powder having a particle size of 10 μm or less. The viscous aqueous solution is prepared by dissolving a polymeric thickening agent in water, and preferably has a viscosity of 10 to 500 poise.

[0009]

The phenomenon that the material to be rolled seizes on the hot working roll is considered to be caused by the following mechanism, taking hot rolling as an example. Stainless steel plate
It is plastically deformed by pressing with a rolling roll, and a new surface is revealed. The nascent surface is derived from the base metal that is not covered with oxide scale and has an active surface state. When the newly formed surface becomes a metal-metal touch in which it directly contacts the metal surface of the rolling roll, mutual metal atoms cause thermal diffusion and adhere at the contact interface in a high temperature state.

The present inventors have considered that the adhesion is suppressed when a substance that prevents the mutual diffusion of metal atoms is present on the contact surface of the metal-metal touch between the stainless steel plate and the rolling roll. In addition, since adhesion is a kind of reaction involving thermal diffusion, it was considered that reducing the thermal activity is also an effective means of suppressing adhesion.

As means for lowering the thermal activity of the contact interface between the stainless steel plate and the rolling roll, means for lowering the plate temperature or enhancing cooling of the rolling roll are conceived. However, the reduction of the plate temperature increases the rolling load, which causes the load on the roll to increase, and is not necessarily effective in preventing seizure. Further, when the cooling water is increased in order to strengthen the roll cooling, the temperature in the roll bite where the stainless steel plate and the rolling roll come into contact with each other can be lowered even if the roll surface temperature in the state immediately before the rolled material is caught can be lowered. There is a limit to lowering. Iron hydroxide dissociates into iron oxide and water according to the following reaction when the temperature is raised to about 300 ° C. 2FeOOH → Fe ₂ O ₃ + H ₂ O

This dissociation is an endothermic reaction. Therefore, a part of the iron hydroxide supplied into the roll bite causes a dissociative endothermic reaction to lower the temperature of the contact surface of the stainless steel plate and the rolling roll. The iron oxide produced by the reaction is
It intervenes at the contact interface together with unreacted iron hydroxide and coats the surface of the stainless steel plate and the rolling roll. As a result, the metal-metal touch contact is blocked, and the mutual diffusion of metal elements is suppressed. As described above, iron hydroxide prevents seizure of the stainless steel plate on the rolling roll by both of the endothermic action and the coating action.

For iron hydroxide, FeOOH, Fe (OH)
_There are various chemical structures such as ₂ . The iron hydroxide used in the present invention is not particularly limited in its type as long as it is stable in the air and industrially available. Generally speaking, iron hydroxide has the advantage that it is industrially manufactured stably and is relatively inexpensive in price. However, other metal hydroxides such as magnesium hydroxide Mg (OH) ₂ , manganese hydroxide Mn (OH) ₂ and calcium hydroxide Ca (OH) ₂ which cause a similar endothermic reaction are used at the reaction temperature, the amount of absorbed heat, etc. In consideration of the reaction characteristics, price, etc., it is possible to replace with iron hydroxide or blend it as an optional component. The iron hydroxide powder is supplied to the peripheral surface of the rolling roll by using the viscous aqueous solution as a carrier. The blending ratio of iron hydroxide to the viscous aqueous solution is restricted in terms of seizure prevention effect, supply method and the like.

If the blending ratio of iron hydroxide is too small, the amount of heat absorbed by the dissociation reaction is small, and the surface of the stainless steel plate and the rolling roll cannot be sufficiently covered.
As a result, the anti-seizure effect is reduced. In order to obtain a given effect with a lubricant containing a small amount of iron hydroxide, it is necessary to increase the absolute amount of lubricant supplied.
It becomes difficult to supply the lubricant in a state suitable for actual operation. On the other hand, if the blending ratio of iron hydroxide is too large, the proportion that does not contribute to the dissociative endothermic reaction increases, the seizure prevention effect is saturated, and iron hydroxide is wasted. Therefore, the mixing ratio of iron hydroxide to the viscous aqueous solution is 1 to 3.
It should be 0% by weight.

The lubricant of the present invention may contain iron oxide in addition to iron hydroxide. The iron oxide that can be used is not particularly limited, but FeO, Fe ₃ O ₄ , and Fe ₂ O _{3 can be used.}
However, any iron oxide and a mixture thereof can be used in the present invention. The iron oxide intervenes in the contact surface between the stainless steel plate and the rolling roll in the roll bite, prevents the metal-metal touch contact, and exhibits a release effect of suppressing pseudo-attachment. As a result, seizure of the stainless steel plate on the rolling roll is prevented. Iron oxide is mixed in the viscous aqueous solution so that the total amount of iron oxide and iron hydroxide is 2 to 30% by weight. When the blending ratio of iron hydroxide exceeds 30% by weight, not only the coating action on the stainless steel plate and the rolling roll is saturated, but also the dispersed state in the viscous aqueous solution becomes unstable. Therefore, when left for a long period of time, iron oxide precipitates and the physical properties of the lubricant change. Further, troubles such as blockages easily occur in the piping system that supplies the lubricant to the rolling rolls. However, if the blending ratio is less than 1% by weight, the effect of preventing seizure due to iron oxide is insufficient.

Iron oxide and iron hydroxide not only make it difficult to effectively coat the surface of the rolling roll and the stainless steel plate with a too large particle size, but also tend to settle in the state of being mixed with a viscous aqueous solution, so that they are homogeneous. It becomes difficult to maintain such a dispersed state. In particular, the finer the iron hydroxide, the easier the dissociation reaction is initiated, and the iron hydroxide works effectively for cooling the surfaces of the rolling roll and the stainless steel plate. In this respect, it is preferable that the particle size of iron oxide and iron hydroxide is 90% by weight or more and fine particles of 10 μm or less.

The viscosity of the viscous aqueous solution is important for maintaining the mixed iron oxide and iron hydroxide in a homogeneous dispersion state. If the viscosity is too low, the suspended iron oxide and iron hydroxide tend to settle, and the characteristics of the stored lubricant change,
It causes troubles such as blockage in the piping system that supplies the lubricant. However, if the viscosity is too high, it is necessary to set a very high discharge pressure when supplying the lubricant to the peripheral surface of the rolling roll, and the lubricant suitable for the mounting industry cannot be supplied. Therefore, the addition of a polymer-based thickener causes 10 to 5
The viscosity of the viscous aqueous solution is adjusted in the range of 00 poise. The type of viscous aqueous solution is not particularly limited as long as it satisfies the conditions relating to viscosity. The viscosity of a viscous aqueous solution can be easily adjusted by adding a trace amount of a thickener. As the thickener, various polymer thickeners such as acrylic acid polymers are used.

[0018]

EXAMPLES Example 1: C: 0.006% by weight, Si:
0.15 wt%, Mn: 0.23 wt%, P: 0.02
4% by weight, S: 0.001% by weight, Ni: 0.16% by weight, Cr: 18.23% by weight, Mo: 1.03% by weight,
From ferritic stainless steel containing Ti: 0.41 wt% and Al: 0.23 wt%, plate thickness 25 mm, width 40
A hot rolling test piece having a length of 200 mm and a length of 200 mm was cut out.

The hot rolling conditions were one pass rolling with a rolling temperature of 900 ° C. and a rolling reduction of 75%. The rolling roll has a diameter of 350 mm and a body length of 30 made of hot work tool steel SKD61.
A 0 mm roll was used. Further, the test piece which is the material to be rolled was heated to 950 ° C. in an inert gas atmosphere in order to suppress the generation of scale. The scale formed on the surface of the test piece after heating was thin with a film thickness of about 1 μm or less.

Prior to hot rolling, a lubricant was sprayed on the surface of the rolling roll as shown in FIG. That is, the pressure of the lubricant contained in the lubricant container 1 is 100 kgf.
/ Cm ² pump is used to send to the injection nozzle 3 via the supply conduit 2 and from the injection nozzle 3 as fine lubricant droplets 4 to 20 r.p.m. p. m. It was jetted onto the circumferential surface of the rolling roll 5 rotating at. At this time, the injection width was set to 200 mm and the injection time was set to 3 seconds.

A total weight of 5 g of lubricant was supplied to the peripheral surface of the rolling roll 5. This supply amount corresponds to forming a liquid film having a film thickness of about 20 μm on the peripheral surface of the rolling roll 5.
After the lubricant is sprayed on the peripheral surface of the rolling roll 5, the water contained in the high-pressure water container 6 is pressured from the nozzle 7 to 3 kgf / c.
It was jetted as a water drop 8 at m ² . This supply of water corresponds to the supply of roll cooling water, and if the viscosity of the lubricant is appropriate, the rate of runoff is reduced, and the rate of adhesion of the lubricant to the rolling rolls 5 is increased.

As the lubricant, as shown in Table 1, a viscous aqueous solution containing an acrylic acid polymer as a thickener was used.
As the iron hydroxide dispersed in the viscous aqueous solution, a fine powder having an average particle diameter of 0.8 μm and a proportion of powder having a particle diameter of 10 μm or less of 99% by weight was used. Further, in iron oxide, 99% of powder having an average particle size of 1.2 μm and particle size of 10 μm or less
A fine powder was used, which accounted for wt%.

[0023]

[Table 1]

Hot rolling was performed under the condition that a lubricant film was formed on the surface of the rolling roll 5 by spraying each lubricant, and after rolling, the surface of the rolling roll 5 and the test piece were observed to check whether seizure occurred. investigated. As is clear from Table 1 showing the investigation results, in an example using a lubricant in which iron hydroxide was dispersed at a ratio of 1 to 30 wt% and a lubricant in which 1 to 30 wt% of iron oxide was further mixed In that case, seizure did not occur in any of them, and the hot-rolled sheet had good surface properties. The supply amount and the adhesion amount in Table 1 were calculated based on the total amount of iron hydroxide and iron oxide.

Example 2 The influence of the viscosity of the viscous aqueous solution, the amount of iron hydroxide and iron oxide dispersed, the particle size, etc. on the stability of fine particle dispersion in the prepared lubricant was investigated. Iron hydroxide and iron oxide were mixed with the viscous aqueous solution to prepare a lubricant, which was then placed in a beaker and allowed to stand. Then, the dispersion state of iron hydroxide and iron oxide after one week was investigated. As a survey method, a lubricant sample was taken from the upper part of the beaker,
The method of measuring the contents of iron hydroxide and iron oxide contained in the sample liquid and comparing the contents with the contents at the initial stage of preparation was adopted. The survey results are shown in Table 2.

[0026]

[Table 2]

As is apparent from Table 2, most of the particle diameters of iron hydroxide and iron oxide are 10 μm or less, and the total dispersion amount is 30 μm.
When the viscosity of the viscous aqueous solution is 10% or more by weight, the sample solution collected from the upper layer of the beaker after standing for 1 week contains iron hydroxide and iron oxide having almost the same contents as the lubricant at the initial stage of preparation. Included. This indicates that the lubricant prepared according to the present invention maintains a stable fine particle dispersion state without causing fine particle sedimentation. Therefore, the lubricant can be supplied to the circumferential surface of the rolling roll 5 under stable conditions for a long period of time without causing the supply conduit 2, the injection nozzle 3 and the like to be blocked. In addition, in the above-mentioned Examples, an example in which the lubricant of the present invention was used for hot rolling of stainless steel was described. However, the lubricant of the present invention is not restricted to this, and is similarly applied to other hot working methods such as hot extrusion of a stainless steel material into a predetermined shape.

[0028]

As described above, the lubricant of the present invention cools the stainless steel and the working roll by the dissociative endothermic reaction, and at the same time, uses iron hydroxide as an active ingredient which exhibits a coating action on the stainless steel and the working roll. Contains. When this lubricant is applied to the peripheral surface of a working roll to hot work stainless steel, roll seizure is effectively prevented, and a high-quality product without surface scratches can be obtained.
In addition, damage to the processing rolls is reduced, and the unit consumption of rolls is also reduced. Since the manufactured hot-worked product has a clean surface, surface polishing can be reduced or omitted, and it is possible to manufacture stainless steel materials with high productivity and high added value such as mirror finishing applications. .

[Brief description of drawings]

[Fig. 1] Mechanism for spraying lubricant to rolling rolls

[Explanation of symbols]

1 Lubricant Container 2 Supply Conduit 3 Injection Nozzle 4 Lubricant Droplet 5 Rolling Roll 6 High Pressure Water Container 7 Cooling Water Nozzle 8 Water Droplet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C10M 145: 14) C10N 10:16 20:02 20:06 Z 40:24 Z

Claims (4)

[Claims] 1. A lubricant for hot working of stainless steel, wherein 1 to 30% by weight of iron hydroxide powder is dispersed in a viscous aqueous solution. 2. 1-30% by weight of iron hydroxide and 1-30
A lubricant for hot working of stainless steel, characterized in that a total of 2 to 30% by weight of iron oxide is dispersed in a viscous aqueous solution. 3. A lubricant for hot working of stainless steel, wherein 90% by weight or more of each of iron oxide and iron hydroxide according to claim 1 or 2 is fine powder having a particle size of 10 μm or less. 4. A lubricant for hot working of stainless steel, wherein the viscous aqueous solution according to claim 1 or 2 is adjusted to have a viscosity of 10 to 500 poises by adding a polymeric thickening agent.