JPH0454522B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is capable of stably manufacturing steel strip products with good surface properties without causing seizure defects caused by rolling rolls near the edge of the steel strip or defects in biting of the rolled material into the rolling rolls. The present invention relates to a method for hot rolling stainless steel. <Prior art and its problems> When hot rolling steel strips, generally the friction coefficient between the work roll and the material to be rolled is lowered to reduce wear and roughness of the work roll and to reduce rolling power. Therefore, hot rolling oil made of mineral oil, fat, synthetic ester, etc. is widely used. However, when the material to be rolled is stainless steel, the rolling temperature is higher and the deformation resistance is higher than when rolling carbon steel strips.
Even if the above-mentioned rolling oil is used, there is a problem that its lubricating effect is not sufficiently exhibited, and therefore it is very difficult to stably maintain good working conditions. Furthermore, in this case, the temperature near the edge of the steel strip is lower than that at the center, and the amount of secondary oxide scale produced is small, so the lubricating effect of the secondary oxide scale cannot be expected.
Therefore, it has been pointed out that the surface roughness of the work roll caused by baking between the roll and the steel strip is particularly severe in this area. For this reason, conventionally, when hot rolling stainless steel strips, "baking" and "roughening" occur.
In order to more reliably deal with such problems, we use oils and synthetic oils with high oil film strength and heat resistance, or lubricants with solid lubricants such as graphite, molybdenum disulfide, mica, and talc added to these as rolling oil. (Japanese Unexamined Patent Publication No. 57-80495), rolling oil is supplied concentratedly to a predetermined location (near the edge, etc.) (Jikkosho
55-12968) was applied. However, these measures to strengthen lubrication lower the coefficient of friction more than necessary, which in turn causes problems such as poor biting and slippage in the rolling rolls, and conversely creates new problems such as the inability to perform stable rolling operations. was pointed out. In this way, especially in the hot rolling of stainless steel strips, under lubrication conditions that do not cause poor biting or slippage, measures to prevent seizure between the roll and the steel strip are insufficient, and conversely, roughening of the surface due to seizure may occur. Under safe lubrication conditions, problems such as poor biting and slippage occur, making it impossible to ensure stable work, which is a contradictory problem, and there is a strong need for improvement measures. <Means for solving the problem> From the above-mentioned viewpoint, the present inventors have solved the problem of "seizing defects" without causing "biting defects" or "slips" in hot rolling of stainless steel strips.
We conducted extensive research to provide a method for stably manufacturing stainless steel strip products with good surface quality while preventing the occurrence of A lubricant with a specific amount of one or more solid powders selected from iron oxide, silicic anhydride, and alumina dispersed and whose friction coefficient is adjusted to a specific value is supplied to the roll surface near the edge of the steel strip. The above-mentioned problems are fully resolved by hot rolling, and hot-rolled stainless steel strips with good surface quality can be manufactured with stable workability.'' It is. This invention was made based on the above findings, and when hot rolling a stainless steel strip, a mixture of iron oxide, silicic anhydride, and alumina is applied to the surface of at least the edge of the steel strip at a position corresponding to rolling. By rolling while supplying a dispersion liquid in which the friction coefficient is adjusted to 0.2 to 0.4 by adding 1% by volume or more of seeds or more, there is no occurrence of poor biting or slipping.
Moreover, it is possible to stably produce stainless steel strips with good surface quality without the occurrence of seizure defects.
It has the following characteristics. The "position of the rolling roll corresponding to the rolling of the steel strip edge" referred to here refers to the surface portion of the work roll that comes into contact with the edge of the stainless steel strip being rolled, and the dispersion liquid is supplied from this point. Although it is efficient and economical to limit the range to only the vicinity including the part, it is of course possible to limit the range to the entire roll surface including the part. In addition, "iron oxide" dispersed in the liquid is represented by the chemical symbols Fe ₂ O ₃ and Fe ₃ O ₄ , and these iron oxides, silicic anhydride, or alumina have a particle size of 0.1
It is preferable to use ~50 μm. Furthermore, the reason for numerically limiting the "friction coefficient of the dispersion" and the "total amount of iron oxide, silicic anhydride, and alumina to be dispersed in the dispersion" as described above is as follows. In other words, if the friction coefficient of the dispersion is less than 0.2, it will not be possible to sufficiently prevent slips from occurring when the dispersion is bitten into the roll;
This is because when it exceeds 0.4, the rolling load becomes high.
Further, if the amount of one or more of iron oxide, silicic anhydride, or alumina in the dispersion is less than 1% by volume,
Even if the friction coefficient of the dispersion liquid is within the range of 0.2 to 0.4, the effect obtained by dispersing iron oxide, silicic acid anhydride, or alumina powder will be insufficient, and it will not be possible to suppress defective biting and occurrence of seizure. This is because the The friction coefficient of the dispersion liquid can be easily adjusted by adjusting the amount of iron oxide, silicic anhydride, or alumina to be dispersed. Figure 1 also shows a "water-dispersed lubricant" in which various solid powders are dispersed in water, and an "oil-dispersed lubricant" in which various solid powders are dispersed in mineral oil (equivalent to #120 machine oil with a viscosity of 50 cst at 40°C). This is a graph showing the ``relationship between the type and amount of lubricant and the coefficient of friction'' investigated through a cylinder block type friction test under the following conditions. A) Dispersed solid powder in the test lubricant Types of solid powder: Al <sub>2</sub> O <sub>3</sub> , SiO <sub>2</sub> Fe <sub>2</sub> O <sub>3</sub> , natural mica, graphite. Particle size of solid powder: 1 μm in each case. Amount of solid powder added: 0, 0.5, 2, 5, 10, 20, 30 and 40% by volume. B) Friction test Work material (block): Material...SUS 304 stainless steel, dimensions...10t x 20b x 70. Processing tool material (cylinder): Material: High chrome cast iron (2.5%C,
15% Cr, 1% Ni, 1.5% Mo), dimensions...100φ x 40h. Workpiece temperature: 1000℃. Work material pressing load: 100Kgf. Machining tool rotation speed: 10rpm. Lubricant supply method: Continuously apply to the surface of the processing tool (30g/m <sup>2</sup> ). Test (friction) time: 30 seconds. C) Calculation method of friction coefficient Measure the rotational torque (T) when pressing the workpiece to find the friction force (F), and calculate the friction coefficient (μ) using the formula μ=F/T. From this Figure 1, it can be seen that by using Al <sub>2</sub> O <sub>3</sub> , SiO <sub>2</sub> or Fe <sub>2</sub> O <sub>3</sub> as the solid powder dispersed in the liquid and adjusting the amount added to 1 to 40% by volume, the lubricant has a coefficient of friction. is adjusted to a range of 0.2 to 0.4. The results are also shown in Figure 2 below). On the other hand, Figure 2 shows the ``type and amount of lubricant and slip occurrence status'' investigated by a biting test using a small rolling mill under the following conditions using the same test lubricant as the one used to obtain the results in Figure 1. In addition to showing the relationship between the occurrence of jamming when the rolled material is pressed against the roll gap, we also show the relationship between the type and amount of lubricant and the occurrence of seizure defects obtained in the previous friction test. This graph is also shown, and the occurrence of slips (no biting) is indicated by an "x" mark, and the occurrence of burn-in flaws is indicated by "black lines", respectively, on the curve of the coefficient of friction. [Bite test conditions] Roll: Material…Ni grain cast iron (3.3% C, 1.7
%Cr, 4.5%Ni, 0.5%Mo). Diameter…100mmφ. Rolled material: Material...SUS 304 stainless steel, Dimensions...3.0t x 30b x 100. Rolled material temperature: 1000℃. Roll gap: 2.0mm. Rolling speed: 30m/min. Lubricant supply method: Apply to the surface of the rolling roll (30g/m ² ). Pressing force on rolled material: 1Kgf. This figure 2 also shows that the solid powder to be dispersed in the liquid is Al ₂ O ₃ , SiO ₂ or Fe ₂ O ₃ and the friction coefficient is adjusted by adjusting the amount added. It can be seen that by increasing the amount by volume % or more, not only the defective biting into the rolling roll is eliminated, but also the occurrence of seizure is eliminated. Next, the present invention will be specifically explained with reference to Examples. <Example> In addition to using a tandem mill with 4 layers and 7 stands, the pre-stage stand (especially the first stand here), which has many "slips during biting and rolling" and "occurrence of roll seizure defects," was While supplying the lubricant shown in Table 1 to the upper and lower roll surfaces in the vicinity of the rolling material edge including the part where it is rolled, the SUS304 stainless steel strip slab (thickness: 20
mm, width: 1000mm, weight: 1000 tons, temperature: 1000~
(1050°C) was continuously rolled under the following conditions to produce a hot rolled stainless steel strip.

[Rolling conditions of the first stand]

Roll material: High chrome cast iron (2.5%C, 15
%Cr, 1%Ni, 1.5%Mo). Roll diameter: 740mmφ. Rolling speed: 150m/min. Rolling reduction rate: 30%. Supply of lubricant: Among the lubricants shown in Table 1, the water-dispersed lubricants (test numbers 3 and 9) were diluted 3 times, and the other lubricants were added to 5% by volume in water using the injection method. The edges of the rolled material of the upper and lower rolls are distributed at a pressure of 3 kg/cm ² and a flow rate of 5/min, respectively, from a nozzle with a pressure of 3 kg/cm 2 and a flow rate of 200 kg/min.
mm”.The total supply amount is 20/mm”.
min. At this time, "slip conditions during rolling material biting and rolling", "presence or absence of seizing defects on the roll surface after rolling 1000 tons", and "1000
The degree of wear on the roll surface after ton rolling was observed, and the results were as shown in Table 1. That is, test number 1 shows the conventional example of rolling with mineral oil supplied as a lubricant. However, in this case, although there is no slippage, seizure defects occur and the roll wear is significant.In test number 2, rolling was performed using mineral oil with 40% by volume of rapeseed oil added as a lubricant. In this case, although the degree of roll wear is milder than in Test No. 1, slips occur and even seizure defects occur. 10% by volume of acrylic resin
This shows a conventional example of rolling by supplying a lubricant containing water containing 10% by volume of graphite with a particle size of 1 μm, but in this case, no seizure defects occur and there is little roll wear. Slips occur during biting and rolling, making stable rolling impossible. Test No. 4 is an example in which rolling was performed using the clouding lubricant (mineral oil) used in Test No. 1 with 0.5% by volume of Fe ₂ O ₃ with a particle size of 1 μm added as a lubricant. In this case, no slipping occurred and roll wear was milder than in Test No. 1, but seizure defects occurred. On the other hand, in test number 5, particle size: 1 μm was applied to mineral oil.
Test No. 6 was a lubricant with 1% by volume of Fe ₂ O ₃ added to mineral oil, test number 7 was a lubricant with 30% by volume of Fe ₂ O ₃ of 5 μm particle size added to mineral oil, and test number 7 was a mineral oil with a particle size of 50 μm. of
This shows an example of the present invention in which a lubricant containing 5% by volume of Fe ₂ O ₃ was supplied for rolling, and the amount of solid powder supplied per unit area was 0.4 g/m ^{2 .} , 13.0g/m ² and 2.1g/m ² . In this case, it can be seen that no slips or seizure defects occur, and roll wear is slight. In test number 8, 10% by volume of Al ₂ O ₃ with a particle size of 1 μm was added to the lubricant used in test number 2.
30% by volume of Fe ₂ O ₃ with a diameter of 5 μm was supplied as a lubricant (the amount supplied as a solid powder was 5.4
g/m ² ) This is an example of rolling. In this case as well, no slips or seizure defects occurred, and the degree of roll wear was slight. In test number 9, 20% by volume of Fe ₂ O ₃ with a particle size of 1 μm was added to water containing methylcellulose and supplied as a lubricant (the amount supplied as a solid powder was
8.7 g/m ² ) This is an example of rolling. In this case as well, no slips or seizure defects occurred, and the degree of roll wear was slight. In test number 10, 2 SiO ₂ particles with a particle size of 0.1 μm were added to mineral oil.
This is an example of rolling with % by volume added as a lubricant (supplied amount as solid powder is 0.4 g/m ² ), but in this case as well, there were no slips or seizure defects, and the roll was smooth. The degree of wear was also slight. From the results of these test numbers 5 to 10, it is clear that Fe ₂ O ₃ , Fe ₃ O ₄ , Al ₂ O ₃ and SiO ₂ are present in liquids such as water or mineral oil.
When stainless steel is hot rolled using a lubricant containing at least 1% by volume of one or more of these solids and the friction coefficient adjusted to 0.2 to 0.4, slips and seizure defects almost never occur. It is clear that it becomes possible to stably produce hot-rolled stainless steel strips with good surface quality and good workability. <Summary of the Invention> As explained above, according to the present invention, it is possible to hot-roll a stainless steel strip without causing "defects in biting" or "slips during rolling", and moreover, it is possible to hot-roll stainless steel strips near the edge of the steel strip. Since the occurrence of seizure defects with the rolling rolls is prevented as much as possible, it is possible to stably produce high-quality stainless steel strips with good surface properties, and the lifespan of the rolling rolls is also extended by reducing roll wear. This brings about extremely useful effects industrially.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the type and amount of lubricant and the coefficient of friction, which was investigated by a cylinder block friction test using lubricants in which various solid powders were dispersed. ,cylinder·
``The relationship between the type and amount of lubricant and the occurrence of seizure defects'' investigated using a block friction test.
This graph also shows the relationship between the type and amount of lubricant and the occurrence of slippage, which was investigated using a small rolling mill and a bite test using a lubricant in which various solid powders were dispersed. .

Claims (1)

[Claims] 1. When hot rolling a stainless steel strip, at least 1% by volume of one or more of iron oxide, silicic anhydride, and alumina is added to the surface of the rolling roll at least at the edge of the steel strip at a position corresponding to rolling, to increase the friction coefficient to 0.2. A method for hot rolling a stainless steel strip, characterized in that rolling is carried out while supplying a dispersion liquid adjusted to a concentration of ~0.4.