JPH05179276A - Lubricating agent for hot rolling of stainless steel - Google Patents

Abstract

PURPOSE:To obtain the subject product effective for preventing the seizure in hot-rolling, increasing the draft and the rolling speed and enabling the rolling of stainless steel in high efficiency by adding a specific dialkyl polysulfide and a phosphorous acid ester to a base oil. CONSTITUTION:The objective product having a viscosity of 100-500cst at 40 deg.C is produced by compounding (A) a base oil having a molecular weight of >=500 with (B) 20-70wt.% of a dialkyl polysulfide having a sulfur content of >=30wt.% (preferably 6-13C compound) and (C) 3-10wt.% of a phosphorous acid ester (preferably an alkyl phosphite having 6-18C alkyl group). The adjustment of the viscosity of the product is carried out e.g. by using a mineral oil having a molecular weight of 500-1,000 and a synthetic ester having a molecular weight of 724-892 as the base oil and varying the mixing ratio of the components. The product is applied generally at a rate of 0.5-30g/m<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a lubricant used during warm rolling, which is preheated to 400 ° C and rolled.

[0002]

2. Description of the Related Art Conventionally, since stainless steel, especially austenitic stainless steel, is markedly hardened by rolling, 400 mm is produced by a Sendzimir mill with a roll diameter of 100 mm or less.
Rolling was performed at a low rolling speed of m / min or less, and the efficiency was very low.

In recent years, in order to improve rolling efficiency, the roll diameter is
High-speed rolling is being carried out with a levers mill or tandem mill of 250 mm or more. However, since the roll diameter is large, there is a problem that the rolling load becomes high, the rolling reduction is restricted and the number of passes increases, or seizure occurs and the rolling speed cannot be increased.

Therefore, in order to suppress the work hardening caused by rolling, a warm rolling method has been tried in which the temperature of the rolled material is raised to a high temperature (JP-A-2-220701). This is because work hardening of austenitic stainless steel occurs due to the generation of martensite having a large deformation resistance by rolling, but when the temperature is high, the generation amount thereof decreases as shown in FIG. However, the temperature of the rolled material is 150 ℃
In the case of the above, the deformation resistance is reduced and the rolling load is reduced, but the lubrication state between the roll and the rolled material is deteriorated, seizure is more likely to occur, and high efficiency rolling cannot be realized.

[0005]

SUMMARY OF THE INVENTION The present invention solves the problem of seizure at the time of warm rolling in which the rolling temperature is raised and the rolling reduction is increased.
An object of the present invention is to provide a rolling lubricant for reducing the number of rolling passes and increasing the rolling speed to roll stainless steel, particularly austenitic stainless steel, with high efficiency.

[0006]

[Means for Solving the Problems] To prevent seizure during rolling,
Generally, it is effective to interpose a thermally stable lubricant between the roll and the rolled material. For example, rolling oil has been conventionally used for rolling steel materials. Oils, synthetic esters, fatty acids, etc., which are generally used as rolling oil, exhibit lubricity by being adsorbed or chemically reacted on the surface of the rolled material. However, since the surface of stainless steel is covered with a stable oxide film, adsorption and chemical reaction are unlikely to occur.
In addition, even if slightly adsorbed or chemically reacted, the lubricity sharply decreases at a high temperature of 150 ° C or higher. Therefore, the above-mentioned object could not be achieved with the conventional steel lubricant.

As a result of exploration of a lubricant for warm rolling of stainless steel, the present inventors formed a strong reaction film of iron sulfide, iron phosphate, etc. at a high temperature by a reaction with stainless steel or a roll. The inventors have reached the present invention by knowing that the above object can be achieved by adding an appropriate amount of dialkyl polysulfide and phosphite to a base oil.

According to the present invention, 20 to 70% by weight of a dialkyl polysulfide having a sulfur content of 30% by weight or more and a phosphite ester of 3 to 10 are added to a base oil having a molecular weight of 500 or more.
% By weight, and the viscosity at 40 ° C is 100-500 cSt
The subject is a lubricant for warm rolling of stainless steel.

The lubricant of the present invention is useful for warm rolling of any stainless steel, but particularly when it is applied to austenitic stainless steel, the rolling efficiency can be remarkably increased and its usefulness is great. In the present invention, warm rolling of stainless steel means rolling performed by heating stainless steel to 150 ° C or higher. The warm rolling temperature is generally in the range of 150 to 400 ° C.

[0010]

The structure and operation of the present invention will be described in detail below.
The lubricant of the present invention comprises dialkyl polysulfide 20-70.
% Of phosphite and 3 to 10% by weight of phosphite in a base oil. As the dialkyl polysulfide, those having an alkyl carbon number of about 6 to 13 are preferable. Further, the phosphite ester is a phosphite alkyl ester having an alkyl group having about 6 to 18 carbon atoms,
Either a diester or a triester may be used.

The dialkyl polysulfide and phosphite are extreme pressure additives, which react with rolled materials and rolls under high temperature and high surface pressure to produce iron sulfide and iron phosphate, and exert a lubricating effect. is there.

However, in the case of dialkyl polysulfide, the lubricating effect greatly differs depending on the sulfur content and the amount added to the lubricant. That is, when the sulfur content of the dialkyl polysulfide is 30% by weight, excellent seizure resistance is exhibited. However, such a high sulfur content causes a high friction coefficient, which is not preferable as a lubricant. It has been found that the addition of a small amount of phosphite ester together is effective for lowering the friction coefficient, whereby a rolling lubricant having excellent seizure resistance and a low friction coefficient can be obtained.

The amount of dialkyl polysulfide added is 20
If the addition amount of the phosphite is less than 3% by weight or less than 3% by weight, sufficient seizure resistance cannot be obtained. The higher the amount of dialkyl polysulfide added, the better the anti-seizure property. However, when it exceeds 70% by weight, the friction coefficient does not decrease even when phosphite is used in combination, so the amount added was limited to 70% by weight. In addition, phosphite ester
Even if it is added in an amount of more than 10% by weight, its friction coefficient lowering effect remains unchanged. Moreover, if the addition amount exceeds 10% by weight, the corrosiveness increases, and the rolls, rolling mills, and even the circulation supply device for the lubricant are corroded, so the upper limit of the addition amount of the phosphite is 10% by weight did.

In order to fully exert the lubricating effect of the lubricant of the present invention obtained by incorporating the above-mentioned dialkyl polysulfide and phosphite into the base oil, a sufficient amount of lubrication is provided between the roll and the rolled material. It is necessary to introduce agents.
Therefore, the viscosity of the lubricant is preferably 100 cSt or more at 40 ° C. If the viscosity is less than this, the lubricating effect will be insufficient. On the other hand, if the viscosity exceeds 500 cSt at 40 ° C, lubrication becomes too high during rolling and slip occurs, which is not preferable. Further, if the viscosity is higher than 500 cSt, the cleaning property after rolling may be deteriorated.

The viscosity can be adjusted freely by changing the composition of two or more base oils having different molecular weights. For example, mineral oil with a molecular weight of 500-1000 and molecular weight of 724-
By adding 892 synthetic ester, 100 at 40 ℃
Viscosity can be adjusted within the range of ~ 500 cSt.

As the base oil (base oil), any base oil that has been conventionally used for lubricants can be used. For example,
One or more selected from mineral oils, fats and oils and synthetic esters can be used as the base oil.

The reason why the molecular weight of the base oil is limited to 500 or more is that if the molecular weight is less than 500, the heat resistance is inferior and the lubricity of dialkyl polysulfide or phosphite is impaired. In addition, since the base oil having a molecular weight of less than 500 has a low viscosity, it is difficult to set the viscosity of the obtained lubricant to 100 cSt or more. There is no particular upper limit to the molecular weight of the base oil, but it will usually be 2000 or less. When two or more base oils are used, the average molecular weight should be 500 or more.

The present inventors confirmed the relationship between the molecular weight of the base oil and the heat resistance by the following tests. 50 mg of the sample oil (mineral oil and synthetic ester each having different molecular weight and 4 kinds of beef tallow) was placed in a container with a diameter of 5 mm and a height of 5 mm, and heated in a nitrogen gas atmosphere at a heating rate of 5 ° C / min, The evaporation amount of the sample oil was measured. The result is shown in FIG. As can be seen from FIG. 2, the amount of evaporation almost behaves according to the molecular weight,
The higher the molecular weight, the higher the evaporation temperature, but there is not much difference between mineral oils, synthetic esters, fats and oils. In addition, if the molecular weight is 500 or more in any type, 300 ℃
Evaporation weight loss is less than 30%.

The lubricant of the present invention may consist of only the above-mentioned base oil, dialkyl polysulfide and phosphite, but may contain other additives in a small amount. Examples of such additives include base oils having a molecular weight of less than 500, or various additives commonly used in lubricants, such as antioxidants, viscosity index improvers, rust preventives and defoamers.

When the stainless steel is warm-rolled by using the lubricant of the present invention, the lubricant may be directly applied to the rolling rolls, or may be diluted in the form of an emulsion in water. When used as an emulsion, an appropriate amount of emulsifier is added to the lubricant and emulsified in water to obtain an emulsion of about 0.2 to 20% by weight. When this emulsion is supplied to the rolling roll, the water vaporizes as soon as it comes into contact with the hot roll surface, and the lubricant remains on the roll surface. By forming an emulsion, a small amount of lubricant can be easily and uniformly applied. Further, by using this emulsion as cooling water, the temperature of the rolling roll can be controlled.

The coating amount of the lubricant of the present invention varies depending on the rolling conditions, but it is generally about 0.5 to 30 g / m ² .

[0022]

EXAMPLES Next, the action and effect of the lubricant of the present invention will be specifically illustrated by the following examples. However, the present invention is not limited to the mode described in the embodiments.

Example 1 A friction test was conducted to explain the action of the lubricant of the present invention. The friction test was carried out using a Bowden type friction tester (Fig. 3) in which a steel ball is pressed against a heated flat plate for friction, and the lubricity was evaluated by the presence or absence of seizure and the measurement of the friction coefficient. In the illustrated tester, the flat plate slides in the direction perpendicular to the paper and rubs against the steel ball.

<Test conditions> Flat plate: SUS 304 2B (1.0 mm thickness x 10 mm width x 100 mm length) Steel ball: SUJ-2 (diameter 3/16 inch) Load: 3 kgf (Hertz stress 240 kgf / mm ² ) Friction speed: 4 mm / sec (reciprocating friction with a friction stroke of 10 mm) Temperature: 50, 100, 150, 200, 250, 300, 350, 400 ° C Lubricant amount: 30 g / m ² applied on a flat plate < Test lubricant> No. main composition ¹⁾ (% by weight) Viscosity (cSt / 40 ℃ ) 1 Mineral oil 50%, Synthetic ester 35%, Oil and fat 10%, Sono and others 5% 70 (Conventional example) 2 Mineral oil 60%, Dialkyl polysulfide 35%, Sono and others 5% 270 (Comparative example) 3 Mineral oil 65%, Fats and oils 25%, Phosphorous diester 5%, Sono and others 5% 200 (Comparative example) 4 Mineral oil 55%, Dialkyl polysulfide 35%, Suba Phosphoric acid ester 5%, sono 5% 230 (Example of the present invention) ─────────────────────────────────── ── 1) Dialkyl polysulfide: Alkyl group with 9 carbon atoms, Io C Content 36% by weight Phosphorous acid ester: 12 carbon atoms of alkyl group, etc .: 1.5% emulsifier, 1.5% fatty acid, 1% rust inhibitor, 1% antioxidant Figure 1 shows the friction test results under the above test conditions. Shown in. The friction coefficient is shown as an average value after five reciprocating frictions at a predetermined temperature. With the conventional lubricant of sample lubricant No. 1, seizure occurs above 150 ° C. The lubricant containing No. 2 dialkyl polysulfide does not cause seizure even at high temperatures, but has a high friction coefficient. The lubricant containing No. 3 phosphite has a low friction coefficient and does not cause seizure up to 200 ° C. However, it begins to burn at temperatures above 250 ° C. On the other hand, the No. 4 lubricant of the present invention containing the dialkyl polysulfide and the phosphite added together does not cause seizure from 50 ° C to 400 ° C, and has a low friction coefficient and excellent lubricity. Shows.

Example 2 Using a 3% concentration emulsion of the same four kinds of lubricants as used in Example 1, a lever roll mill with a work roll diameter of 300 mm was used to heat SUS 304 with a thickness of 4.0 mm and a width of 1023 mm. The rolled and annealed stainless steel material (pickled) was warm-rolled. The rolling was performed by preheating this stainless steel material to 200 ° C. and rolling at the rolling reduction and rolling speed shown in Table 1. The lubricant emulsion is
Flow rate of 100 l / min per nozzle from each of 10 nozzles arranged along the roll axis on the inlet side of each of the 4 rolls, the upper and lower work rolls and the backup roll.
It was supplied at 4000 l / min). The amount of lubricant applied to the surface of each roll was approximately 10 g / m ² . The rolling load during this rolling and the presence or absence of seizure were measured, and the results are shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2]

As shown in Table 2, only the lubricant of the present invention of No. 4 could be rolled and seizure did not occur.
With other lubricants, No. 2 did not seize, but the rolling load was so high that the mill specification limit was reached, so rolling was stopped at the third pass. In addition, the No. 1 and No. 3 lubricants caused significant seizure, and the rolling was stopped at the first and third passes, respectively.

The rolling result is relatively in good agreement with the result of the friction test with the Bowden tester shown in FIG.
This means that the Bowden tester can be used for actual evaluation.

Example 3 Based on the results of Example 2, using a Bowden tester,
A friction test was conducted in the same manner as in Example 1 while changing the components, the addition amount and the viscosity of the lubricant of the present invention. In this example, the temperature was evaluated at 250 ° C. The lubricants tested were based on a mixture of mineral oil having a molecular weight of 500 to 1000 and synthetic ester having a molecular weight of 724 to 892 in various combination weights of 1: 1 of mineral oil and ester. It was prepared by adding a predetermined amount of acid ester. If the viscosity exceeds 500 cSt (40 ° C), polybutene was added to adjust the viscosity. The test results are shown in Table 3 below.

[0031]

[Table 3]

As is clear from the results shown in Table 3, the lubricant of the present invention has no seizure and has a coefficient of friction within an appropriate range of 0.05 to 0.10.

Example 4 A representative 9 out of the lubricants tested for lubricity in Example 3 was used.
A seed was chosen and a rolling experiment was carried out with a revers mill in the same manner as described in Example 2. The rolled material was the same SUS 304 material as used in Example 2, and was rolled according to the rolling schedule shown in Table 1.
It was carried out in two ways. Measure the increase / decrease of rolling load during warm rolling (200 ° C) against rolling load when rolling at 50 ° C.
The lubricity was evaluated. The smaller the load during warm rolling, the higher the lubricity.

Further, rolling is performed by changing the rolling reduction in each pass (the rolling reduction is reduced when seizure occurs, the rolling reduction is increased when seizure does not occur), and the maximum rolling reduction (No seizure occurs) The lubricity was also evaluated by determining the seizure limit rolling reduction). The results are shown in Table 4 below.

[0035]

[Table 4]

As can be seen from the results in Table 4, in Conventional Examples 4 and 5 in which a lubricant containing no dialkyl polysulfide or phosphite ester was used as in the present invention, seizure occurred and hot rolling was performed. On the contrary, the rolling load is slightly higher than the value when rolling at 50 ° C. That is, the lubricity was poor in the warm state, and the seizure limit rolling reduction was 10 to 15%. Further, even if it contains a dialkyl polysulfide and a phosphite, the lubricants of Comparative Examples whose types, compositions or viscosities are outside the scope of the present invention also have low lubricity,
The seizure limit reduction rate was as low as 15 to 25%.

On the other hand, all of the lubricants of the present invention are excellent in lubricity during warm rolling, the rolling load is reduced by 20 to 30% in warm rolling as compared with 50 ° C. rolling, and the seizure limit is The rolling reduction was 30 to 35%, which was 2.5 to 3 times that of the conventional example.

[0038]

By using the lubricant of the present invention, seizure of stainless steel, especially austenitic stainless steel, can be prevented during warm rolling, and at the same time, the friction coefficient can be lowered to reduce the rolling load. Thereby, the rolling reduction in each pass can be increased, the number of rolling passes can be reduced, and rolling can be performed with high efficiency. In addition, high-speed rolling becomes possible as compared with the conventional Sendzimir mill. Therefore, the rolling efficiency of the austenitic stainless steel is significantly increased due to the reduction of the number of rolling passes and the high speed rolling.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in mechanical property values and amounts of martensite with temperature of austenitic stainless steel.

FIG. 2 is a diagram showing weight loss of mineral oils and synthetic esters of various molecular weights and fats and oils (beef tallow) in a nitrogen atmosphere.

FIG. 3 is a schematic explanatory view of a Bowden friction tester.

FIG. 4 shows the test results of a friction test using a Bowden tester,
It is a figure shown in relation with a test temperature, a friction coefficient, and a seizure condition.

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Claims (1)

[Claims] 1. A dialkyl polysulfide 20 having a sulfur content of 30% by weight or more in a base oil having a molecular weight of 500 or more.
Lubricant for warm rolling of stainless steel, containing ~ 70% by weight and 3-10% by weight of phosphite and having a viscosity of 100-500 cSt at 40 ° C.