JP2927185B2 - Lubricant for hot plastic working and processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot plastic working lubricant for use in hot plastic working of metals, particularly steel, such as hot rolling and hot forging, and a hot plastic working method using the same. And about. More specifically, the lubricant of the present invention is suitable for use by being adhered to the surface of a high-temperature workpiece before hot plastic working. Particularly, in the process of producing a seamless pipe, elongation rolling (mandrel Before mill rolling, assell mill rolling, plug mill rolling, pilger mill rolling, etc.), it is suitable for use by attaching to the inner surface of a high-temperature hollow shell which is a workpiece.

[0002]

2. Description of the Related Art For example, a process of producing a seamless pipe by mandrel mill rolling will be described with reference to FIG. 1. A hollow shell (also called a hollow shell) as a workpiece is obtained by heating a round steel slab as a raw material. After heating in a furnace, it is made by hot piercing with a piercer. In the mandrel mill rolling process, the high temperature from the piercer (usually 9
A mandrel bar is inserted into the hollow shell of (00 to 1200 ° C.), and while this bar is inserted, a pair of hole-shaped two rolls are shifted in the circumferential direction by 90 degrees for each unit to form a tandem 7 to 7 mm. 8
Rolling is performed by a mandrel mill placed on a table to obtain a thick tube. Thereafter, the thick-walled tube is usually re-heated in a re-heating furnace, stretched by a stretch reducer to reduce the outer diameter and to a small extent, and cooled to complete a seamless tube of a predetermined size.

[0003] When the hollow shell is stretched and rolled, a gap between the inner surface of the hollow shell and the outer surface of the mandrel bar (working interface)
Causes relative slip. It is important for this rolling to ensure a good lubrication state at the working interface so that the relative slip proceeds smoothly. Therefore, a lubricant is applied to this interface to secure a low and stable friction coefficient, prevent seizure between the hollow shell and the mandrel bar, and obtain good inner surface quality and dimensional accuracy of the product. Have been done.

[0004] As such a lubrication method, a water-dispersed lubricant mainly composed of graphite and a resin-based organic binder is applied to the surface of a mandrel bar before being inserted into a hollow shell. And then drying to form a dry solid lubricating film. That is, the method
(Hereinafter referred to as Method A) in which a lubricant is formed as a solid lubricating film on a (mandrel bar). Attempts have been made to improve the high-temperature lubricating performance of the lubricant used in the method A by adding additives (for example, see JP-A-61-2797).
No.). Even when a seamless pipe is formed from a work material that is easily seized with a mandrel bar such as stainless steel, the seizure resistance can be improved by changing the composition of the lubricant.

For the purpose of further improving the lubricity when lubrication is insufficient only by the above-mentioned method A, or for the purpose of removing the oxide scale from the inner surface of the hollow shell, the processing surface of the workpiece is heated. It is also known to apply a lubricant or descaling agent to the inner surface of a heated high temperature hollow shell. The lubrication by this method is a lubrication method (hereinafter, referred to as a B method) in which a lubricant is attached to a processing surface of a high-temperature workpiece and the lubricant is melted by heat of the workpiece to form a fluid lubricating film. .

For example, JP-A-46-30581 discloses that a descaling agent having a melting point lower than the hot working temperature (eg, salt, borax, phosphate, a mixture of these and carbon, etc.) is used at a high temperature. It is described that the descaling agent is sprayed into the hollow of the hollow shell, and the melted descaling agent is coated on the inner surface of the shell by rotating the shell.

[0007] JP-A-61-37987 and JP-A-1-278903 each disclose air, an inert gas or the like on the inner surface of a high-temperature hollow shell before inserting a mandrel bar, in combination with the above-mentioned method A. It describes that a lubricant or a descaling agent is blown as a carrier gas. Lubricant / pickling agent used in this method
As a descaling agent, JP-A-61-37989 contains a boric acid compound (borax, etc.) and a solid lubricant (graphite, etc.) as main components, and adds various inorganic and organic compounds as necessary. Compositions are described.

[0008]

According to the experience of the present inventors, in mandrel mill rolling, the material to be processed is carbon steel, the mandrel bar is hot tool steel SKD6, and the surface is scaled skin. In this case, lubrication is sufficient only with method A, and the combined use of method B is not always necessary. However, even if the work material is carbon steel, if the mandrel bar is Cr plated on the surface to improve its life,
It is necessary to use Method B as auxiliary lubrication for Method A.

On the other hand, when the material to be processed is stainless steel that is liable to seize and the surface of the mandrel bar is a scale skin, or in particular, when plating such as Cr plating is applied, the A method is used. Even when the method B is used in combination, the lubrication is still insufficient, and a problem often occurs in product quality due to seizure.

In an attempt, a solid lubricating film was formed on a mandrel bar having a surface uniformly coated with Cr to a thickness of about 50 μm according to the above method A, and then a stainless steel (SUS3
When the mandrel mill rolling of the hollow shell made of 04) was performed, the inner surface of the product (seamless tube) had an inner surface flaw with a depth of 0.5 mm or more, and the Cr plating on the mandrel bar surface was sharply excavated. Seizure flaws resulting from adhesion of stainless steel components occurred.

On the other hand, on the inner surface of the hot hollow shell before rolling,
According to the method B, the composition mainly composed of borax and graphite described in JP-A-61-37989 was sprayed, melted to form a fluid lubricating film, and then subjected to mandrel mill rolling under the same conditions as above. In the case (that is, the combined use of the A method and the B method), the inner surface flaw of the product after rolling was somewhat reduced to a depth of about 0.3 to 0.2 mm, but the lubrication was still insufficient and the surface of the mandrel bar was insufficient. Damage also occurred.

An object of the present invention is to provide a hot plastic working lubricant suitable for the above-mentioned Method B and a hot plastic working method using the same. More specifically, even if the work material is stainless steel in which seizure easily occurs, and the tool is a plating tool that requires a high degree of lubrication, in particular, even if it is a Cr plating tool, it is applied to a high-temperature work material. Thereby, the friction coefficient between the two interfaces can be remarkably reduced, and by using in combination with the method A, seizure can be prevented even in hot plastic working under severe conditions such as seamless tube elongation rolling. It is an object of the present invention to provide a lubricant capable of obtaining a high-quality product with reduced surface defects and a hot plastic working method using the same.

[0013]

As a lubricant that can achieve the above object, according to the solution to ## by the present invention, alkali metal salts consisting of (a) alkali metal carbonates and alkali metal carboxylates
A lubricant for hot plastic working, comprising 10 to 100% by weight and (b) 0 to 90% by weight of graphite is provided.

[0014] The composition of the lubricant of the present invention is an alkali metal salt.
(a) is 100% by weight (that is, graphite (b) is 0%). In other words, the lubricant of the present invention comprises only the alkali metal salt (a) or a mixture of the alkali metal salt (a) at 10% by weight or more and the graphite (b) at 90% by weight or less.

The lubricant is suitable for use in Method B described above. That is, this is a hot plastic working method in which the lubricant is attached to the working surface of a workpiece heated to a predetermined hot plastic working temperature and then hot plastic working is performed using a tool.

In a preferred embodiment, the tool is a metal-plated tool, particularly a Cr-plated tool, which is liable to seize, and the workpiece is a hollow shell for a seamless pipe, particularly a stainless steel pipe. It is a hollow shell made of steel. That is, according to the present invention, even in a processing state in which seizure is likely to occur, in which hot plastic working of stainless steel is performed using a Cr-plated tool, seizure can be prevented and good product quality can be ensured. You can.

[0017]

Hereinafter, the lubricant and the hot plastic working method of the present invention will be described in detail. However, in the following, a mandrel mill rolling may be described as an example to simplify the description. Alkali metal salts (a) in the lubricants of this invention, (b) an alkali metal carbonate and (ii) an alkali metal carboxylate, may be used one or two or more kinds.

Examples of the alkali metal carbonate (a) include sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium sesquicarbonate and the like.
Since these have a melting point of 1200 ° C. or less, when they come into contact with the workpiece heated to the hot plastic working temperature, they are melted and thermally decomposed into oxides. Reacts with the scale (iron oxide) generated on the surface, so the adhesion to the surface of the work material is increased. As a result, during hot plastic working, it functions as a stable and good fluid lubricant. For example, sodium carbonate has a melting point of 852 ° C.
At this temperature, it is easily thermally decomposed, becomes sodium oxide, and reacts with iron oxide.

Examples of the alkali metal carboxylate (b) are as follows:
Sodium and potassium salts of saturated or unsaturated fatty acids having 6 to 30 carbon atoms. Examples include sodium and potassium salts of octylic acid, myristic acid, stearic acid, palmitic acid, oleic acid, linoleic acid, ricinoleic acid and the like. Also, alkali metal salts of natural fatty acids such as tall oil fatty acids (eg, a mixture of fatty acid sodium salts having 6 to 18 carbon atoms) can be used. Further, in addition to such aliphatic monocarboxylic acids, alicyclic carboxylic acids such as naphthenic acid, polycarboxylic acids, and alkali metal salts of aromatic carboxylic acids can also be used.

The alkali metal carboxylate melts relatively easily at a lower temperature of 1000 ° C. or less, and functions as a fluid lubricant at a relatively low temperature during rolling. In addition, uniform adhesion to the surface of the workpiece at high temperature is also good. Therefore, both the alkali metal carbonate (a) and the alkali metal carboxylate (b) used as the alkali metal salt (a) melt when they come into contact with the surface of the workpiece at high temperature and adhere to the surface of the workpiece. And functions as a fluid lubricant.

[0021] The carboxylate alkali metal carbonate (b) (ii), in order to exhibit the respective characteristics were above mentioned, using a mixture of both as an alkali metal salt (a). The mixing ratio in the case of its the carbonate at a weight ratio of carboxylic acid salt, 1: 2 to 10: 1, especially 1: 1 to 8: 1 and, carbonate
It is preferable to increase (b). This is because the carboxylate has a relatively low boiling point and is lost by evaporation on the surface of the workpiece at a high temperature. If the amount of the carboxylate is too large, the lubricity may decrease.

This carbonate (a) or carboxylate (b)
However, salts with divalent or higher valent metals (eg, alkaline earth metal carbonates) have a high melting point, making it difficult to function as a fluid lubricant. For example, calcium carbonate is 890
Decomposes into calcined lime CaO by thermal decomposition at ℃, the melting point of which is 2572
℃, the temperature to react with iron oxide is also around 1150 ℃,
It cannot perform the same action as the sodium carbonate described above. The divalent or higher valent metal carboxylate is called a metal soap and has been used as a lubricant. However, it is chemically unstable and stable under the hot plastic working conditions of the present invention. In many cases, a harmful low-melting-point metal compound such as lead stearate that causes solder embrittlement with the workpiece is often included.

Further, an alkali metal oxide may be used in place of the alkali metal carbonate (a) or carboxylate (b), but it is expensive, is chemically unstable, and may be used as a lubricant. There is a problem with storage management.

Further, when the alkali metal salt is a borate, for example, borax, the melting point of the borax is 878 ° C. and the reactivity with the work material is good, so that a certain degree of lubricity can be obtained. As shown in the examples, due to the relatively high viscosity of the melt, good product quality cannot be obtained by mandrel mill rolling.

The lubricants of this invention can be comprised of only the above-mentioned (i) a carbonate Contact <br/> by beauty (ii) an alkali metal salt consisting of carboxylic acid salts (a), graphite thereto When (b) is blended, the lubricating properties of graphite can be increased by blending a small amount of graphite. The graphite may be either natural graphite or chemically synthesized artificial graphite. However, graphite remains powder even at high temperatures and does not react with the surface (scale) of the workpiece, so it only burns. Therefore, alkali metal salts that melt and adhere to the surface of the workpiece
Without the help of (a), it does not adhere to the work material and cannot be used alone. That is, since at least 10% by weight of the alkali metal salt (a) is required for this adhesion, the proportion of graphite is set to 90% by weight or less. When graphite (b) is blended, the preferred amount is 70% by weight or less, more preferably 50% by weight or less.

The preferred mixing ratio of the lubricant of the present invention is such that the alkali metal carbonate (a) in the alkali metal salt (a) is 20 to 20%.
90% by weight, 5 to 40% by weight of alkali metal carboxylate (b) and 0 to 70% by weight of graphite (b). More preferably,
(A) is 50-80% by weight, (b) is 10-30% by weight, graphite (b) is
10 to 50% by weight and all three components are mixed in appropriate amounts. If the amount of the alkali metal carbonate (a) is too large, the uniform adhesion to the surface of the workpiece at a relatively low temperature may decrease. On the other hand, if the amount of the alkali metal carboxylate (b) is too large, the lubricity may decrease due to evaporation as described above. If the amount of graphite is too large, the amount of the alkali metal salt (a) decreases, and the adhesion of the lubricant to the surface of the workpiece decreases.

The purity of each component (especially natural graphite)
85% by weight, preferably 90% by weight or more. The powder particle size of each component is not particularly limited, but in order to ensure uniformity of blowing with a blowing machine and rapid meltability upon contact with a high-temperature workpiece, the average particle size is 500 μm. Hereinafter, it is advantageous to set the thickness to preferably 100 μm.

[0028] The lubricant of the present invention comprises a work material heated to a predetermined hot plastic working temperature (preferably 900 to 1200 ° C).
(For example, in the case of seamless mandrel mill rolling, a hollow shell is used). That is, B
Lubrication method. Tools (e.g., mandrel bar)
It is preferable that a graphite-based solid lubricating film is formed on the surface according to Method A described above. Since there is a fluid lubricating film formed on the surface of the workpiece due to the adhesion of the lubricant of the present invention, consumption of the solid lubricating film applied to the tool surface is suppressed, and this film can be used effectively for a long time. That is, the use of the lubricant of the present invention not only improves the lubricity, but also has the effect of extending the life of the lubricating film on the tool surface.

The material of the material to be processed is not particularly limited, and can be applied to hot plastic working of various metals such as carbon steel, stainless steel, and Ni-based alloy. Since the lubricant of the present invention can prevent seizure even under severe hot plastic working conditions, it is advantageous to apply the lubricant to stainless steel in which seizure easily occurs, particularly austenitic stainless steel.

The lubricating properties of tools for plastic working differ greatly depending on the surface condition. The scale surface and the nitrided surface have a low coefficient of friction, and the plated surface has a high coefficient of friction. Therefore, when the lubricant of the present invention is applied to a tool plated with a metal such as Cr, Ni, and Fe, particularly a tool plated with Cr, a great effect can be obtained. As a result, the conventional method such as mandrel mill rolling of an austenitic stainless steel hollow shell with a Cr-plated mandrel bar causes seizure and the occurrence of internal flaws on the product (seamless tube) even when the method A and the method B are used together. By using the lubricating method of the present invention in combination with the method A even under hot plastic working conditions where it was not possible to prevent the seizure, it is possible to prevent seizure and obtain a product of good quality.

The method of supplying the powdered lubricant of the present invention to the surface of the workpiece is not particularly limited, and any method capable of uniformly applying the lubricant in accordance with the form of the work surface to be lubricated can be adopted. For example, when the workpiece is a plate material or the processing surface requiring lubrication is the outer surface of the tube, the lubricant may be simply sprayed. However, in order to uniformly apply the lubricant to the inner surface of the hollow shell described as an example, it is preferable to supply the lubricant by a blowing method in which powder is blown using a carrier gas. Air can be used as the carrier gas, but an inert gas such as nitrogen or argon is preferable. For example, using a nitrogen gas at a pressure of about 4 kg / cm ² as a carrier gas, about 300 to 400 g of lubricant is blown uniformly from a blow nozzle inserted about 50 mm from the end face of the hollow shell. The agent can be attached to the inner surface of the hollow shell. The supply amount of the lubricant of the present invention varies depending on the situation, but is usually 5 to 5.
It is in the range of 200 g / m ² , preferably 100-150 g / m ² .

Although the above description has been made with reference to an example of seamless pipe making, particularly mandrel mill rolling, the lubricant and hot plastic working method of the present invention include other hot rolling and hot forging. Applicable to hot plastic working in general.

[0033]

【Example】

[0034]

Example 1 A number of lubricants comprising one or more powders of the following components were prepared.

Powder component used (a) Alkali metal salt (a) Alkali metal carbonate: sodium carbonate (Na ₂ CO ₃ ) (average particle size 50 μm) Potassium carbonate (K ₂ CO ₃ ) (average particle size 60 μm) (b) ) Alkali metal carboxylate: Sodium fatty acid (mixed fatty acid Na salt with 6 to 18 carbon atoms) (average particle size 20 μm) Potassium fatty acid (mixed fatty acid K salt with 6 to 18 carbon atoms) (average particle size 30 μm) (c) Others: Borax (Na ₂ B ₄ O ₇ · 10H ₂ O) (average particle size 40 μm) Calcium carbonate (CaCO ₃ ) (average particle size 50 μm) (b) Graphite: Natural graphite (purity 85% by weight) (average particle size) 40 μm) Artificial graphite (purity: 99% by weight) (average particle size: 10 μm) The lubricating performance of the obtained lubricant was examined by a ring compression test.

The ring compression test is a method generally used as a simple method for evaluating the performance of a lubricant used for forging or the like. FIG. 2 shows a conceptual diagram of the ring compression test. Illustrated ring (In this embodiment, outer diameter 24 mm × inner diameter 6.0 mm ×
The thickness of the workpiece is 4.0 mm) and the die is used as a tool to compress the ring in the thickness direction of the ring while changing the compression ratio. The relationship between the dimensional change rate of the ring inner diameter after the compression processing and the compression rate is applied to the diagram shown in FIG. 3 to determine the friction coefficient.
At the time of this compression test, the state of seizure can be directly observed visually.

In this embodiment, after each lubricant is sprayed on the upper surface of the workpiece (ring) (spray amount: 50 g), the workpiece is heated uniformly (1000 ° C. × 10 minutes) in an electric furnace. The high temperature workpiece to which the molten lubricant had adhered was immediately subjected to the compression test described above. The tools were not subjected to lubrication. The material of the workpiece (ring) and the material and surface treatment of the tool (die) were as follows.

Work material (ring) Material SUS304 (Austenitic stainless steel), 13Cr steel (Martensitic stainless steel for oil country tubular goods), or S45C
(General high carbon steel). The composition of each steel is as shown in Table 1.

Material of tool (die) and surface treatment material: Tool steel SKD6 (composition is as shown in Table 2) Surface treatment: scale skin 0.01 mm thickness (Vickers hardness 4
50) Cr plating 0.04 mm thickness (Vickers hardness 1000) Ni plating 0.04 mm thickness (Vickers hardness 400) Fe plating 0.04 mm thickness (Vickers hardness 350) Nitriding 0.1 mm thickness (Vickers hardness 1000) This was produced by processing at 1020 ° C. × 20 minutes soaking → quenching → 620 ° C. × 20 minutes soaking → air cooling. For Cr plating, use a sulfuric acid-containing chromic acid bath (CrO ₃ concentration 250 g /
L), Ni plating was performed by an electroplating method using a Watt bath (sulfate / chloride bath), and Fe plating was also performed by a sulfate / chloride bath. Nitriding treatment is 900 ℃ x 30 in 30% ammonia gas
The heat treatment was performed for a long time.

Table 3 shows the compositions of the tested lubricants, and the test results when the workpiece was SUS304, 13Cr steel, and S45C.
(Coefficient of friction) are shown in Tables 4, 5, and 6, respectively. When the material of the workpiece is SUS304 or 13Cr stainless steel, the coefficient of friction is higher if the coefficient of friction exceeds 0.2, and it is considered difficult to apply it to forging and rolling of actual machines. , 0.2 or less are judged as acceptable levels. However, when the tool (die) has a scale surface or a nitrided surface that is difficult to seize, the coefficient of friction is lower than that of the plated surface.

On the other hand, when the material of the material to be processed is carbon steel (S45C) in which seizure is unlikely to occur, a friction coefficient exceeding 0.15 is judged as a high friction coefficient when the tool is a plated surface, and a friction coefficient of 0.15 or less is judged as an allowable level. On the scale surface or nitriding surface, a coefficient of friction exceeding 0.10 is judged to be a high coefficient of friction, and a coefficient of 0.10 or less is judged to be an acceptable level.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

As can be seen from Tables 4 to 6, in the lubricant of the present invention, the friction coefficient is reduced to an allowable level or slightly higher than the allowable level in almost all cases, and the lubricant can be sufficiently rolled and forged in an actual machine. Showed lubricity. In particular, a lubricant containing both an alkali metal carbonate and an alkali metal carboxylate as the component (a) and further containing graphite reduced the friction coefficient.

On the other hand, in the comparative example, although the friction coefficient was lower than that in the comparative example 9 in which no lubricant was used, all the examples showed a high friction coefficient that greatly exceeded the allowable level. That is, if borax or calcium carbonate is used instead of the alkali metal carbonate, or if the compounding amount of graphite exceeds 90% by weight, the lubricity of the lubricant will be significantly reduced, making it impossible to perform rolling and forging on a real machine. It turns out that it becomes.

The coefficient of friction is low when the die surface is the scale surface and the nitriding surface, and high when the die surface is plated. In particular, the coefficient of friction was high in the case of the Cr-plated and Ni-plated surfaces, but even in that case, the lubricant of the present invention could reduce the friction coefficient to an allowable level. Also,
There was no difference in the performance of the lubricant depending on the type of plating, and it was found that the same lubricating performance was exhibited for all types of plating.

[0051]

Example 2 A powdery lubricant having the composition shown in Table 7 was prepared in the same manner as in Example 1. This lubricant was tested on a Mannesmann-type mandrel mill rolling line for seamless pipes to evaluate lubrication performance.

In the mandrel mill rolling, a lubricant is blown into the inner surface of a high-temperature hollow shell (hollow shell) immediately after being pierced by a piercer, and then a graphite-organic binder-based lubricant is applied and dried to form a solid lubricant film on the surface. Was inserted into the hollow shell, and the hollow shell containing the bar was stretched and rolled by a mandrel mill. The lubricant injection and rolling conditions were as follows.

Experimental conditions Rolling device: Semi-float type 7-stand mandrel mill Rolled material: SUS304 (austenitic stainless steel), 13Cr steel (martensitic stainless steel for oil country tubular goods), S45C (general high carbon steel) (composition) Table 1) Rolling dimensions: Hollow shell after drilling Outer diameter 181 x wall thickness 17.5 x length 65
Outer diameter 151 x wall thickness 6.5 x length 20 after rolling 50 mm mandrel mill
000 mm Product dimensions Outer diameter 113 x wall thickness 6.5 x length 27
140 mm Inner surface temperature: Hollow shell after drilling 1230 ° C after drilling → 1180 ° C before mandrel mill rolling Immediately after mandrel mill rolling About 1000 ° C Mandrel bar: Outer diameter 134 x length 23000 mm Material: SKD6 (see Table 2) Surface condition: Cr Plating (50μm thickness) Lubrication: Apply graphite-organic binder-based water-soluble lubricant uniformly at room temperature and use after drying (average lubrication film thickness about 50μm) Blowing lubricant into hollow shell: pressure about 4kg / cm ² About 300 g of lubricant is blown into the hollow shell from a nozzle inserted into the hollow shell about 50 mm from the end face of the hollow shell using the nitrogen gas as the carrier gas.The friction coefficient of the mandrel mill rolling interface and the retained force of the mandrel bar during rolling are measured at each stand. Was calculated as the value obtained by dividing by the sum of the rolling loads. Further, the product quality of the inner surface of the seamless pipe after rolling was visually and ultrasonically examined, and the inner surface quality was determined based on the following criteria. Further, based on the results of the coefficient of friction and the inner surface quality, a comprehensive evaluation of the lubricant was performed according to the following criteria.

Judgment Criteria When the material to be rolled is SUS304 stainless steel Inner surface quality ×: Depth 0.32 mm (thickness)
5%) Above scratches △: Depth of 0.10mm or more and less than 0.32mm depth at least in part in the pipe axis direction ○: Defects of less than 0.10mm depth in the pipe axis direction Overall evaluation Friction coefficient less than 0.100 → X, △, same as quality
Evaluation of ○ Quality ○, low coefficient of friction (<0.035, stable rolling, good dimensional accuracy) → ◎ Quality ×, high coefficient of friction (> 0.100, unstable rolling) → ×× When the material to be rolled is 13Cr stainless steel Inner surface quality Same evaluation criteria as SUS 304 stainless steel Overall evaluation Friction coefficient is less than 0.08 → same as quality ×, △, ○
Evaluation of quality ○, low coefficient of friction (<0.035, stable rolling, good dimensional accuracy) → ◎ Quality ×, high coefficient of friction (> 0.08, unstable rolling) → ×× When the material to be rolled is high carbon steel S45C Inner surface quality ×: Depth of 0.20mm (part of wall thickness)
3%) or more flaws Δ: flaws with a depth of 0.10 mm or more and less than 0.20 mm at least partially in the pipe axis direction ○: flaws with a depth of less than 0.10 mm in the pipe axis direction Overall evaluation Friction coefficient less than 0.08 → ×, △, ○ same as quality
Evaluation of quality ○, low coefficient of friction (<0.030, stable rolling, good dimensional accuracy) → ◎ Quality ×, high coefficient of friction (> 0.08, unstable rolling) → ××

[0055]

[Table 7]

[0056]

[Table 8]

As can be seen from Table 8, when the lubricant of the present invention was used for the lubrication method of Method B, the friction coefficient was low, the depth was 0.32 mm for stainless steel, and 0.20 for carbon steel. The generation of deep flaws exceeding mm 2 was completely prevented, and the evaluation was Δ to ◎. Alkali metal salt (a)
As alkali carbonate (a) and alkali carboxylate
(B) together with a small amount of graphite (specifically, (b) 50-80%, (b) 10-30%, (b)
場合 50%), a particularly high evaluation (◎) was obtained.

On the other hand, in the comparative example, although the friction coefficient is lower than that in the comparative example 21 in which no lubricant is used,
Seizure could not be prevented, and the deep flaws described above occurred on the inner surface of each product. Therefore, the evaluation is ×××
X markedly decreased. Therefore, since the lubricity of the lubricant is significantly reduced, rolling and forging in an actual machine is practically impossible.

[0059]

The lubricant of the present invention, when applied to a high-temperature workpiece, sufficiently lowers the friction coefficient even if the tool surface and / or the workpiece is easily seized. , Seizure can be prevented. As a result, the lubricant is applied to the lubrication method of the above-mentioned method B, and is used in combination with the lubrication method of the method A. Prevent seizure even under hot plastic working conditions such as mandrel mill rolling of stainless steel hollow shells with plated (especially Cr-plated) tools (mandrel bars) that could not prevent flaws. It is possible to obtain a good quality product.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a mandrel mill rolling line.

FIG. 2 is an explanatory diagram of a ring compression test.

FIG. 3 is a graph showing a relationship between a processing amount (a compression ratio and an inner diameter change ratio) in a ring compression test and a friction coefficient.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI C10N 40:24 (58) Investigated field (Int.Cl. ⁶ , DB name) C10M 105/22 C10M 103/06 C10M 125/10 C10M 129/26 C10N 10:02 C10N 40:24

Claims (5)

(57) [Claims] 1. A hot plasticity comprising (a) 10 to 100% by weight of an alkali metal salt comprising an alkali metal carbonate and an alkali metal carboxylate, and (b) 0 to 90% by weight of graphite. Processing lubricant. 2. The method according to claim 1, wherein the lubricant according to claim 1 is adhered to a processing surface of a workpiece heated to a predetermined hot plastic working temperature, and then subjected to hot plastic working using a tool. Hot plastic working method. 3. The hot plastic working method according to claim 2, wherein the tool is a metal-plated tool. 4. The hot plastic working method according to claim 3, wherein said metal plating is Cr plating. 5. The hot plastic working method according to claim 2, wherein the workpiece is a hollow shell for seamless pipe making.