JP2002001402A - Roll die in cold pilger mill and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll die in cold Pilger mill and its manufacturing method excellent in both wear and abrasion resistance and corrosion resistance, and lasting for a long time. SOLUTION: The roll die is made of steel stock having C: 0.2-0.6%, Cr: 3-9%, Mo: 0.5-3%, P: not more than 0.02%, S: not more than 0.005% in mass percentage and having hardness of 52HRC to 60HRC, and the Sharpy impact value not less than 5 J/cm2 at normal temperature and a metal flow in the roll axis direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll dice for a cold pilger mill used for cold rolling of a metal tube and a method for producing the same.

[0002]

2. Description of the Related Art As a method for manufacturing a metal tube by cold working, a cold rolling method using a cold pilger mill is known. FIG. 1 is a perspective view showing an example of a main part of a cold pilger mill, and FIG. 2 is a view for explaining a rolling method, in which a roll die is developed and shown.

In FIG. 1, a cold pilger mill includes a pair of upper and lower roll dies 10. The roll die 10 has a hole die 11 formed on the peripheral surface thereof, and a roll stand 20 formed by a rotating shaft (not shown) provided at an axis.
It is supported by. One end of the rotating shaft has a rotating diameter (PCC.
A pinion gear 21 whose D) is slightly smaller than the outer diameter of the roll die 10 is provided in a state in which the pinion gear 21 meshes with a horizontal rack gear 22.

The roll stand 20 reciprocates in the direction of arrow A by driving a connecting rod (not shown). Along with this, the roll die 10 reciprocates in the direction of arrow a and reciprocates in the direction of arrow b during this reciprocation. The die 11 formed on the peripheral surface of the roll die 10 has a cross-sectional shape that is substantially half of a substantially elliptical shape whose major axis side is the width direction of the die, and a processing start point a to a processing end point b shown in FIG. The processing portion 11a whose diameter (depth) continuously decreases toward the shape, the forming portion 11b whose cross-sectional shape is substantially half of a substantially perfect circle, and whose diameter (depth) is equal from the processing end point b to the forming end point c. , A relief portion 11c provided on the bottom dead center Sb side of the forming portion 11b and a top dead center Sa from the processed portion 11a.
It is constituted by a relief portion 11d formed on the side. In addition,
The reference numeral 11e in FIG.
1 shows the bottom of the hole shape when expanded and shown, and the reference numerals Sa and Sb denote the top dead center and the bottom dead center of the roll die that reciprocates (reciprocally rotates).

[0005] A mandrel 30 is provided between the pair of upper and lower roll dies 10,10. Mandrel 30
Is provided with a tapered portion 31 whose outer diameter decreases toward the tip and an equal-diameter portion 32 formed following the small-diameter side of the tapered portion 31. It is arranged to face the moving area of the part 11a and the forming part 11b.

When the pipe P is rolled by the pilger mill configured as described above, the roll stand 20 is reciprocated, and the area of the relief portion 11d of the die 11 or the relief portion 1 is formed.
In the area of 1d and the escape portion 11c, the pipe P is fed by a predetermined length along the mandrel 30 from the left side in FIG. 2 and rotated by a predetermined angle around the pipe axis. By this operation, the pipe P is reduced in diameter from the tip thereof to the processing portion 11a of the die 11 provided on the roll die 10 and the tapered portion 31 of the mandrel 30, and then the die 11 is formed. It is formed by the portion 11b and the equal diameter portion 32 of the mandrel 30. During rolling, lubricating oil is used for lubrication between the pipe P, the roll die 10 and the mandrel 30.

[0007] The rolling of the pipe by the pilger mill is performed at a high working ratio in which the area reduction Y defined by the following equation is 75% or more.

Y = ((X ₀ −X ₁ ) / X ₀ ) × 100 Formula X ₀ : Cross-sectional area of pipe before processing X ₁ : Cross-sectional area of pipe after processing Such cold pilger Roll dies used for mills are required to have the following properties from the viewpoint of the service life. (1) Abrasion Resistance and Seizure Resistance As described above, the hole-shaped processed portion provided on the roll die has a cross-sectional shape that is approximately half of a substantially elliptical shape whose major axis side is the width direction of the hole die. The diameter (depth) changes continuously in the circumferential direction of the roll die. When the tube is rolled by rotating the roll dies, whose diameter (depth) of the die is changed, by a pinion gear having a constant rotation diameter, the peripheral velocity at the bottom of the die at each position in the circumferential direction of the roll dies is reduced. different. Also in one section of the die, the peripheral speed at each position on the die surface is different. For this reason, almost all portions of the groove form slip with the pipe to be rolled, and the slipped portion may be worn. Therefore, wear resistance for preventing wear due to slip is required.

The degree of slip differs depending on the position of the die. If abrasion occurs, the amount of wear varies depending on the degree of slip. Therefore, wear resistance is required also from the viewpoint of dimensional control of the die. . Further, since seizure may occur due to wear, seizure resistance is also required. (2) Hardness In rolling of a pipe by a Pilger mill, the degree of work (area reduction rate) is extremely high. Therefore, the tube during rolling is work-hardened, and a high surface pressure is generated in the die for rolling the work-hardened tube. Appropriate hardness is required to withstand this high surface pressure. (3) Toughness Rolling of a pipe by a Pilger mill is intermittent rolling by reciprocating movement and reciprocating rotation of a roll die as described above. Therefore, an impact force is applied to the roll die. In particular, when the reciprocating speed of the roll stand is increased to increase the rolling efficiency, the impact force applied to the roll dies increases. To withstand this large impact force, toughness is required.

Further, when the feed amount of the tube fed every time the roll die is stopped becomes larger than a set amount, or when the mandrel is broken during rolling and the broken portion is fed in the rolling direction together with the tube feed. In this case, an impact load is applied to the roll die, and the roll die may be broken from the bottom of the die. To withstand such a shocking load,
Toughness is required. (4) Corrosion resistance In the rolling of a tube by a Pilger mill, a chlorine-based extreme pressure additive (for example, chlorinated paraffin) and a mineral oil are main components for lubrication between a tool (roll die, mandrel) and the tube. Lubricating oils may be used. In this lubricating oil, most of the chloride ions generated by the extreme pressure reaction become iron chloride, which prevents seizure between the tool and the pipe. However, the released chlorine ions are contained in the lubricating oil. Since chlorine ions contained in the lubricating oil come into contact with the roll dies, the roll dies are corroded and wear and the fatigue life is reduced. Therefore, when the above-mentioned lubricant is used, corrosion resistance to chlorine ions is required.

Conventionally, as a roll dice for a cold pilger mill, which is required to have many properties, JIS
Bearing steel specified in SUJ5 of G 4805 and alloy tool steel for cold dies specified in SKD11 of JIS G4404 were used, but none of them satisfied the above requirements.

Roll dies having a longer life than those of the conventional roll dies are disclosed in JP-A-4-172113 and JP-A-10-85806.

The roll dice disclosed in Japanese Patent Application Laid-Open No. 4-172113 has a chemical composition according to JIS G4404.
Has a hardness of 52 HRC to 56 HRC and a metal flow in the roll axis direction, based on the alloy tool steel specified in SKD11.

This roll die has a hardness of 52 HRC, which is the hardness of the alloy tool steel usually used at a hardness of 60 HRC or more.
By reducing the RC to 56 HRC, the toughness is improved, and the crack resistance and wear resistance are enhanced. However, since the steel is a high C-high Cr steel, a huge carbide is inevitably generated, and the improvement in toughness corresponding to the decrease in hardness cannot be obtained.

The roll die disclosed in Japanese Patent Application Laid-Open No. 10-85806 is a roll die in which the surface of the die is nitrided to generate a compressive residual stress at the bottom of the die, thereby preventing cracking.

However, in this roll die, while the hardness of the surface of the nitrided die increases, the toughness extremely decreases to increase the susceptibility to cracking. Progress is remarkable.

As described above, the roll dies disclosed in the above-mentioned publications are particularly insufficient in toughness and do not satisfy all the above requirements. Recently, tubes made of difficult-to-machine materials (for example, duplex stainless steel and nickel-base alloy) are subject to rolling, and high-speed rolling at a high working ratio is required. Is desired.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide a roll dice for a cold pilger mill, which has a good balance between hardness and toughness and is excellent in abrasion resistance and corrosion resistance, and a method for producing the same.

[0019]

The gist of the present invention is to provide the following (1) a roll die of a cold pilger mill and (2)
In its manufacturing method. (1) In mass%, C: 0.2 to 0.6%, Cr: 3 to 9
%, Mo: 0.5 to 3%, P: 0.02% or less, S:
Made of steel containing 0.005% or less, hardness is 52HRC
~ 60HRC and Charpy impact value at room temperature is 5
A roll dice for a cold pilger mill, having a metal flow in the roll axis direction at J / cm ² or more. (2) A method for producing a roll die of a cold pilger mill, comprising the following steps (A) to (F). (A) In mass%, C: 0.2 to 0.6%, Cr: 3 to 9
%, Mo: 0.5 to 3%, P: 0.02% or less, S:
Using cast material made of steel containing 0.005% or less as an electrode to produce a slab by secondary melting (B) Forging or rolling the slab heated to 1100 ° C. or more to have a metal flow in the axial direction Manufacture a cylindrical body. (C) The cylindrical body is annealed by heating at 800 to 880 ° C. for 3 hours or more and then cooling the furnace. (D) The cylindrical body is cut in a direction perpendicular to its axis to obtain a disk material. (E) A through hole is formed in the axis of the disk material, and a hole shape is formed on the outer peripheral surface to form a roll material. (F) The roll material is quenched from 1000 to 1100 ° C and 500 to 600 ° C. Tempering

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The roll dice of the cold pilger mill of the present invention will be described in the order of chemical composition, hardness, Charpy impact value, and metal flow. The percentages representing the contents of the chemical compositions are all mass%. <Chemical composition> C: C increases the hardness of the martensite structure and forms carbides of Cr and Mo to improve wear resistance. For that purpose, 0.2% or more is required. on the other hand,
If it exceeds 0.6%, precipitation of giant carbides of Cr and Mo becomes significant during solidification after melting, and the toughness decreases. Therefore, the content of C is set to 0.2 to 0.6%. In addition,
A preferred range is 0.3-0.5%. Cr: Cr forms a solid solution in the base material during quenching to enhance the quenchability. In addition, a Cr carbide is formed to improve wear resistance. For that purpose, 3% or more is required. But 9%
If it exceeds 200, large carbides are likely to precipitate during solidification after melting, and toughness is reduced. Therefore, the content of Cr is set to 3 to 9%. In addition, a preferable range is 4 to 6%. Mo: Mo dissolves in the base material during quenching, forms carbides, improves wear resistance, and further enhances heat resistance. To exhibit these effects, 0.5% or more is required. However, when the content exceeds 3%, not only the effect is saturated, but also the hot workability is reduced. Therefore, the content of Mo is set to 0.5 to 3%. In addition, when a lubricating oil containing a large amount of chlorine as an extreme pressure additive is used in pilger mill rolling, chlorine ions are generated by the extreme pressure reaction during rolling. Most of this chloride ion
Although it becomes iron chloride and prevents seizure at the contact portion between the roll die and the tube to be rolled, a part is mixed into the lubricating oil.
Since the roll dies are constantly in contact with the lubricating oil mixed with the chloride ions during rolling, the fatigue life may be reduced and corrosion and wear may progress due to the chloride ions. Mo
Prevents the reduction of the fatigue life and the progress of corrosive wear due to the chlorine ions. In order to obtain this effect, the lower limit of Mo is set to 1
%. P: P is an element contained as an impurity and reduces toughness and hot workability. In addition, it promotes tempering embrittlement.
Therefore, the upper limit of the content is set to 0.02%. A preferred upper limit is 0.01%. S: S is an element contained as an impurity, and exists as a sulfide, and lowers toughness and hot workability similarly to P. Therefore, the upper limit of the content is set to 0.005%. A preferred upper limit is 0.003%. The chemical composition of the roll die of the present invention is composed of steel containing the above elements, but may further include the following alloy elements depending on the purpose of use. Ni: Ni improves the toughness by forming a solid solution in the base material. To obtain this effect, 0.1% or more is required. However, even if it exceeds 2%, the effect is saturated. Therefore,
If contained, the content is 0.1 to 2%. Nb: Nb prevents austenite grains from coarsening and improves strength and toughness. For that purpose, 0.1% or more is required. However, if it exceeds 2%, the hot workability is reduced. Therefore, when the content is to be contained, 0.1 to 2%
And V: V prevents austenite grains from coarsening and forms fine carbides to improve wear resistance and hardenability. To obtain this effect, 0.1% or more is required. However, when the content exceeds 2%, the workability decreases. Therefore, when it is contained, it is 0.1 to 2%. W: W enhances heat resistance and forms carbides to improve wear resistance. For that purpose, 0.1% or more is required. However, if it exceeds 3%, the hot workability decreases. Therefore, when it is contained, it is set to 0.1 to 3%. Si: Si is effective as a steel deoxidizing agent. When Si is used as a deoxidizing agent, it is easily deformed even if it is present in steel as an inclusion as compared with the case where Al is used, so that it is extended in the direction of metal flow. For this reason, in the roll die of the present invention in which the direction of the metal flow is controlled to improve the crack resistance, the influence on the crack can be reduced, so that deoxidation by Si is suitable. Also,
Si has the effect of increasing the hardness after high-temperature tempering. When it is added as a deoxidizing agent, it may be contained in steel at an unavoidable level, but need not always be left. When it is contained for the purpose of increasing the hardness after high-temperature tempering, if it is contained in a large amount, the hot workability and the toughness decrease, and if it is contained, the content is made 0.01 to 3.0%. A preferred range for the content is 0.01 to 2.0%. Further, in order to make deoxidation more complete and prevent toughness from being reduced by oxygen, the lower limit is preferably set to 0.1%. Mn: Mn is effective as a deoxidizing agent and a desulfurizing agent for steel. In addition, there is an effect of improving hardenability. When it is added as a deoxidizing agent and a desulfurizing agent, it may be contained in steel at an unavoidable level, but need not always be left. When added for the purpose of improving the quenchability, if contained in a large amount, the workability is reduced.
1 to 2.0%. A preferred range for the content is 0.01 to 1.0%. <Hardness> In the roll die of the present invention, JIS Z 22
The hardness measured on the C scale in the Rockwell hardness test specified in 45 is 52 to 60 HRC. When the hardness is less than 52 HRC, the abrasion resistance is poor.
If it exceeds C, the toughness is insufficient and cracks occur, and in each case, the life is short.

In the roll dies of the pilger mill, slip occurs between the groove and the tube to be rolled as described above.
Typical wear caused by this slip includes pitting-like wear and peeling-like wear.

[0022] These abrasions are caused by the fact that, after being rolled into an elliptical shape by one reciprocation of a roll stand, a pipe provided with an axial feed and rotation around the axis is rolled by one reciprocation of the next roll stand. In addition, since the long diameter portion of the tube comes into contact with the die first, the contact portion has a high surface pressure.

In order to prevent such abrasion, the hardness of the porous surface layer portion is set to 52 HRC by, for example, surface quenching.
That is all. However, even if the hardness of only the surface portion of the groove is increased, if the surface layer of the hole is worn out by use for a long time, the internal hardness is sharply reduced and the life is shortened.
Therefore, in the roll die of the present invention, the lower limit of the hardness is set to 52 HRC.

In the rolling by the Pilger mill, a flaw called a pipe end mark may be generated on the surface of the roll die. This tube end mark is formed on the surface of the groove by the corner of the tube end when the corner of the end of the tube to be rolled comes into contact with the groove, and reduces the surface properties and dimensional accuracy of the rolled tube. Invite. In order to prevent the occurrence of the tube end mark, hardness of 52 HRC or more is required.

Rolling by a pilger mill is intermittent rolling in which the roll die repeats reciprocating movement (reciprocating rotation) and stopping as described above. For that purpose, the roll dies are required to have appropriate toughness. Furthermore, when the feed amount of the tube fed every time the roll die is stopped becomes larger than the set amount, or when the mandrel breaks during rolling and the broken portion is sent in the rolling direction together with the tube feed, An impact load is applied to the roll die, and the roll die may be broken from the bottom of the die. To prevent such cracking, appropriate toughness is required. Upper limit of hardness is 60HRC
If so, the required toughness is almost satisfied. <Charpy impact value> JIS Z
Using a U-notch test piece (notch depth 2 mm) specified in 2202, a test was performed at room temperature by a metal material impact test method specified in JIS Z 2242, and the determined absorbed energy was measured at the notch bottom of the test piece. The value is divided by the area, and this value is set to 5 J / cm ² or more.

The toughness required for a roll die is determined by the Charpy impact value together with the hardness described above. When the upper limit of the hardness is set to 60 HRC and the Charpy impact value is set to 5 J / cm ² or more, the toughness is improved, and cracking of the roll die can be prevented. <Direction of metal flow> The direction of the metal flow of the roll die is the axial direction. This is to prevent the roll die from breaking from the bottom of the die. When the non-metallic inclusions and giant carbides do not exist in the alloy tool steel constituting the roll die at all, there is no need to regulate the direction of metal flow.

However, in general, non-metallic inclusions and giant carbides are present in the alloy tool steel of interest to some extent. The roll dies are subjected to processing such as rolling and forging during the production thereof. In this processing, the inclusions and the large carbides are extended in a direction in which the material is extended (hereinafter, referred to as a metal flow direction). It is. If the non-metallic inclusions and the giant carbides extended in the direction of the metal flow are present on the surface of the roll die or directly below it in a state of extending in the radial direction of the roll die, the width of the die during rolling is reduced. The roll dice may be broken by the tensile force in the direction.

In the roll die of the present invention, even if a small amount of inclusions and giant carbides are present, the direction in which they extend is perpendicular to the radial direction of the roll die.
The direction of the metal flow is defined as the roll axis direction.

Next, the method for producing the roll die of the pilger mill of the present invention will be described.

First, it is melted and refined by a conventional method, and a columnar cast material made of alloy tool steel having the above-mentioned chemical composition is produced by an ingot method or a continuous casting method.

The cast material is secondarily melted as an electrode to produce a columnar cast piece. The secondary melting is generally performed with a primary purpose of reducing segregation, while separating and removing inclusions in the steel to give a clean steel. In the present invention, in addition to these, the toughness is adversely affected. Performed to reduce or eliminate macro carbides.

That is, since the casting material before the secondary melting takes a long time for solidification at the time of casting, a huge carbide is generated in the solidification process. In the secondary melting and refining, a cast material in which a huge carbide is generated is used as an electrode, and this electrode is partially melted from the end to form a micropool in the mold sequentially, and then solidification from the bottom by cooling. proceed.

In the micropool, the components of the molten metal are homogenized, and solidification by cooling thereafter produces a more stable and finer MC-type secondary carbide than the carbide formed in the cast material before the secondary melting. During the solidification, it is rapidly cooled, so that the MC type secondary carbide is prevented from becoming coarse. Therefore, it is possible to obtain a slab having extremely small amount of giant carbide.

As the secondary melting method, there are various methods depending on a combination of a melting atmosphere (in vacuum, in air, in an inert gas) and a heating method (arc, molten slag, electron beam, plasma arc). In the present invention, any method can be used as long as it is a method capable of increasing the solidification rate and solidifying and solidifying the micropool in which the cast material is locally melted, and the specific method is not limited. Such methods include, for example, vacuum arc remelting (VAR) and electroslag remelting (ES).
R) and electron beam remelting (EBR).

There is also a method of subjecting a cast material to diffusion heat treatment in order to convert a huge carbide into a fine MC-type carbide. However, this method requires a long processing time and a part of the huge carbide. May remain without being decomposed into MC type carbide.

Subsequently, the columnar slab is heated to 1100 ° C. or higher, and then forged or rolled. Heating temperature 11
The reason why the temperature is set to 00 ° C. or higher is to facilitate the deformation of the slab by forging or rolling and to decompose the huge carbide remaining in the slab into fine MC-type carbide.

In forging or rolling, instead of rolling down in the axial direction of the columnar slab, rolling down is performed in a direction perpendicular to the axial direction of the columnar slab, and the columnar slab is extended in the longitudinal direction to form a cylindrical body. And In the cylindrical body manufactured in this way, the direction of the metal flow is the axial direction of the cylindrical body.

Solidification segregation accompanying lamination solidification occurs in the slab after the secondary melting and refining. This solidification segregation is a lighter segregation than the segregation existing in the cast material before the secondary melting. However, when used under severe conditions such as a roll die of a cold pilger mill, it is preferable to control the direction of even this slight segregation in a direction that does not lead to cracks in the roll die.

[0039] In the slab after the secondary melting and refining, inclusions and giant carbides may be slightly present. These cause cracks depending on the direction as described above. In order not to cause cracking of the roll die, even if segregation, inclusions and small amounts of large carbides are present,
The direction of the metal flow is set to the axial direction of the cylindrical body, and in the subsequent step, the processing is performed so that the axial direction of the cylindrical body matches the axial direction of the roll die.

In order to set the direction of the metal flow to be the axial direction of the cylindrical body, it is preferable that the working ratio expressed by the ratio of the sectional area after the processing to the sectional area before the processing is 4 or more.

The cylindrical body is annealed by heating to 800 to 880 ° C. for 3 hours or more and then cooling the furnace. This annealing is performed in order to remove the processing distortion caused by the forging or rolling. The reason that the annealing temperature is set to 800 to 880 ° C. and the holding time is set to 3 hours or more is that the annealing temperature is 80
If the temperature is less than 0 ° C. or the holding time is less than 3 hours, the processing strain is not sufficiently removed, while if the annealing temperature exceeds 880 ° C., giant carbide is precipitated.

Subsequently, the cylindrical body is cut into a predetermined length from a direction perpendicular to the axis to obtain a disk material. The cutting length is
It is almost equal to the axial length of the roll die.

Next, a hole is formed in the outer peripheral surface of the disk material, and a through hole is formed in the axis to obtain a roll material. The mold is, for example, a mold 11 shown in FIGS.
The through hole is a hole for attaching the roll die to the rotating shaft by shrink fitting or the like. The die and the through hole are formed by cutting, and the side and peripheral surfaces are also shaped by cutting.

Subsequently, 1000 to 11
Quenching from 00 ° C and tempering at 500 to 600 ° C are performed.

The quenching is for obtaining a high hardness by changing the structure of the roll die to a martensite structure.
After heating to 0 to 1100 ° C, the mixture is air-cooled or oil-cooled. By this quenching, a hardness of about 52 to 63 HRC is obtained. If the quenching temperature is less than 1000 ° C., sufficient hardness cannot be obtained, while if the quenching temperature exceeds 1100 ° C., the structure becomes coarse and the toughness decreases.

For tempering, the hardness is 52 HRC to 60 HRC.
After heating to 500 to 600 ° C. and holding for 1 hour or more, air-cooling is performed. Tempering temperature is 500
If the temperature is out of the range of ６００600 ° C. or the holding time is less than 1 hour, a predetermined hardness cannot be obtained.

FIG. 3 is a diagram showing an example of a tempering temperature curve of steel H described later. As can be seen from the figure, if the quenching temperature is different, the hardness after quenching (the hardness shown as quenched in the figure) is also different. Further, even when the quenching temperature is the same, the hardness is different if the tempering temperature is different. This tendency also depends on the chemical composition of the roll die. Therefore, the tempering temperature is set to 5 depending on the chemical composition and the quenching temperature so that a hardness of 52 to 60 HRC is obtained.
An appropriate temperature in the range of 00 to 600 ° C. may be selected.

Since the tempering temperature range in the present invention is a high temperature range near or higher than the secondary curing temperature, retained austenite is decomposed and almost disappears, and tensile residual stress is easily released. This tempering is preferably performed a plurality of times in order to further reduce retained austenite.

The quenched and tempered roll dies are then polished to adjust the surface roughness of the die and correct the dimensions due to distortion.

[0050]

EXAMPLES Example 1 An alloy tool steel having a chemical composition shown in Table 1 was melted in an electric furnace, and the diameter was 800 m by an ingot method.
m was produced. In Table 1,
Steel V is a tool steel, steel W specified in JIS SKD11.
Is tool steel specified in the above-mentioned Japanese Patent Application Laid-Open No. 4-172113.

[0051]

[Table 1] The cast material was subjected to electroslag remelting (ESR) or vacuum arc remelting (VAR) to produce a cylindrical slab having the same diameter as the cast material. Subsequently, after the cylindrical slab is heated to 1150 ° C., it is subjected to rolling or forging for working from the radial direction to produce a cylindrical body having a diameter of 380 mm (working ratio 4.4). After holding for a period of time, annealing was performed to cool the furnace.

Subsequently, the cylindrical body was cut into a length of 210 mm to obtain a disc material, and a tube having an outer diameter of 64 mm was cut into an outer diameter of 30 mm.
A groove for rolling into a 6 mm tube is formed on the outer peripheral surface, and a through hole for shrink-fitting the rotary shaft is formed on the axial center, and the outer peripheral surface and the end surface are formed by machining. Roll material was manufactured.

The roll material was added at 1050 ° C. or 11
After oil quenching after heating to 00 ° C,
After heating to 00 to 600 ° C. and holding for 6 hours or 12 hours, tempering by air cooling was performed twice, and then the entire surface was polished to produce three roll dies each having an outer diameter of 370 mm and a length of 170 mm. In addition, one test material was manufactured by the same process as that described above except that the machining of the die and the through hole was omitted.

As a comparative example, three roll dies and one test material were manufactured by a method in which one of the conditions specified in the manufacturing method of the present invention was not satisfied. Type of secondary melting, classification of rolling or forging processing from the radial direction,
Table 2 shows the quenching temperature and the tempering temperature. Table 2
, The holding time in tempering was no. 11 in 1
Except for 2 hours, all were 6 hours.

[0055]

[Table 2] Collect a test piece from the test material manufactured by the above method,
A hardness test and a Charpy impact test were performed. Further, rolling the tube using a roll die manufactured by the above method,
The life of the roll dies was investigated. These results are also shown in Table 2.

In the hardness test, test specimens were sampled from the above-described test materials from three circumferential positions in the outer peripheral area where the mold was formed, and the Rockwell hardness specified in JIS Z 2245 was determined for each test specimen. Measurement was made at three points on the C scale (HRC) of the test method. The hardness shown in Table 2 indicates the average of these measured values.

The Charpy impact test uses the above-described test material in the same manner as the hardness test, and uses JIS Z220 from the vicinity of the position where the hardness test piece is collected in the range where the mold is formed.
U-notch specimen specified in 2 (notch depth 2 mm)
Was collected from the axial direction of the test material, and JIS
Absorbed energy was determined by testing at room temperature according to the metal material impact test method specified in Z2242. The impact value shown in Table 2 indicates the average of values obtained by dividing the absorbed energy by the cross-sectional area of the notch bottom of the test piece.

The life was determined by rolling a roll of a stainless steel tube having a chemical composition specified in JIS SUS304 having an outer diameter of 64 mm and a thickness of 5.5 mm, which was rolled into a product tube having an outer diameter of 30.6 mm and a thickness of 2 mm. It was expressed as the total length of the product pipe rolled before replacement. The rolling conditions were as follows: the rolling stroke was 991 mm, the number of strokes was 135 times per minute, the tube feed amount between strokes was 9 mm, the rotation angle around the axis during the tube feed was 57 degrees, and chlorine was used as the lubricating oil. (PL-17) (Yushilo Chemical Co., Ltd., trade name) containing 30% by mass.

As can be seen from Table 2, no. 1 to N
o. In the twenty-first example of the present invention, both the hardness and the impact value are excellent, and the life is 300 km or more. On the other hand, no.
In Comparative Examples 22 to 25, although the chemical composition was steel H in the range specified by the present invention, the manufacturing conditions were out of the conditions specified by the present invention, so that either one of the hardness and the impact value or Both deviate from the conditions stipulated in the present invention, and have a very short life.

Further, No. 1 having a chemical composition outside the range specified in the present invention. 26 to No. 26 The comparative example of 36 has a short life regardless of the manufacturing method. In addition, No. 32 and No. 32. The comparative example of No. 33 satisfies the conditions specified in the present invention in terms of hardness and impact value. However, in these comparative examples, C or even higher Cr causes cracks in the hole-shaped portion due to the influence of Cr carbide. It is presumed to have occurred. <Example 2> An alloy furnace steel having a chemical composition shown in Table 3 was melted in an electric furnace, and a test piece was collected from a test material manufactured in the same manner as in Example 1, and the method specified in JIS Z 2274 was used. A rotary bending fatigue test was performed. The test piece was a No. 1 test piece (parallel portion diameter: 10 mm) and was sampled from the same direction as the Charpy impact test piece.

[0061]

[Table 3] Test should be done either in air or lubricating oil used in the rolling ^- was carried out while spraying a (Cl 100 ppm) in the test piece. The resulting SN curve is shown in FIG. Further, the time intensity σ (A10 ³ ) at the number of repetitions of 10 ³ was determined, and the intensity ratio (time intensity in lubricating oil / time intensity in air × 10 ³ ) was obtained.
0 (%)) is also shown in Table 3.

FIG. 3 shows that the greater the Mo content, the greater the number of repetitions. Further, as shown in Table 3, the content of Mo is out of the range of the present invention.
Is 64%, while the strength ratio of steel H, steel Hb, steel Hc and steel Hd within the range where the content of Mo is specified in the present invention is as good as 75% or more. It is.

[0063]

The roll die of the present invention has a good balance of hardness and toughness and is excellent in corrosion resistance.
Its life is extremely long. Further, according to the method of manufacturing a roll die of the present invention, the above-mentioned roll die can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a main part of a cold pilger mill.

FIG. 2 is a view for explaining a rolling method using a cold pilger mill, and is an expanded view of a roll die.

FIG. 3 is a diagram showing an example of a tempering temperature curve.

FIG. 4 is an SN diagram showing the results of a repeated bending test of an example.
It is a curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Roll die 11 Hole type 11a Processing part 11b Forming part 11c, 11d Escape part 11e Hole bottom 20 Roll stand 21 Pinion gear 22 Rack gear 30 Mandrel 31 Tapered part 32 Equal diameter part a Processing start point b Processing end point c Forming end point

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/00 302 C22C 38/00 302E 38/22 38/22 (72) Inventor Noriaki Hirohata Higashi Amagasaki City Hyogo Prefecture No. 1 Nishinomachi, Mukojima F-term (reference) in Sumitomo Metal Industries, Ltd. Kansai Works Special Pipe Works 4E016 AA09 CA08 DA06 EA03 EA13 EA23 FA01 FA04 FA18 4K042 AA20 AA25 BA02 BA03 DA01 DA02 DA03 DC02 DC03 DE04

Claims (2)

[Claims] (1) In mass%, C: 0.2-0.6%, Cr:
3 to 9%, Mo: 0.5 to 3%, P: 0.02% or less,
S: made of steel containing 0.005% or less, and having a hardness of 52H
A roll dice for a cold pilger mill, which has a RC of 60 to 60 HRC, a Charpy impact value at room temperature of 5 J / cm ² or more, and a metal flow in a roll axis direction. 2. A method for producing a roll dice for a cold pilger mill, comprising the following steps (A) to (F). (A) In mass%, C: 0.2 to 0.6%, Cr: 3 to 9
%, Mo: 0.5 to 3%, P: 0.02% or less, S:
Using cast material made of steel containing 0.005% or less as an electrode to produce a slab by secondary melting (B) Forging or rolling the slab heated to 1100 ° C. or more to have a metal flow in the axial direction Manufacture a cylindrical body. (C) The cylindrical body is annealed by heating at 800 to 880 ° C. for 3 hours or more and then cooling the furnace. (D) The cylindrical body is cut in a direction perpendicular to its axis to obtain a disk material. (E) A through hole is formed in the axis of the disk material, and a hole shape is formed on the outer peripheral surface to form a roll material. (F) The roll material is quenched from 1000 to 1100 ° C and 500 to 600 ° C. Tempering