JPH1081937A - Forging roll for seamless steel tube and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a forging roll for rolling a seamless steel pipe having a good gripping wear resistance by forming the roll of a high carbon cast alloy cast steel contg. specified amounts of C, Si, Mn, Ni and Cr and specifying the ratio of the area of spheroidal carbide to be occupied in the metallic structure of the roll. SOLUTION: A high carbon alloy cast steel contg., by weight, 1.10 to 1.85% C, 0.3 to 1.2% Si, 0.4 to 1.5% Mn, Ni and Cr respectively by 0.5 to 2.0%, and the balance iron is subjected to hot forging into a roll shape, which is thereafter cooled to <=600 deg.C at a cooling rate of >=2.5 deg.C/min. After that, this steel is held at (Acm-10 deg.C) to (Acm-100 deg.C) for >=5hr as primary carbide spheroidizing heat treatment and is then subjected to secondary carbide spheroidizing heat treatment. Then, the area of spheroidal carbide is regulated to 35 to 55% in the metallic structure of the roll. Furthermore, the high carbon alloy cast steel may be added with one or more kinds among Mo, V and W respectively by 0.1 to 1.0%, and the total content of elements harmful for forging such as P, S, Cu, As, Sn, Pb or the like is regulated to <=0.2%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling roll used for manufacturing a seamless steel pipe and a method for manufacturing the same, and more particularly, to a roll characteristic of a rolling mill used in manufacturing a seamless steel pipe by a Mannesmann pipe manufacturing method. In other words, this is a technique for improving abrasion resistance, heat crack resistance, biting properties, skin roughness resistance, and the like by changing the components of the roll and the metallographic structure (hereinafter referred to as the metal structure).

[0002]

2. Description of the Related Art In the production of a seamless steel pipe by the Mannesmann method, in order to exert the effect of rotary forging on a roll used for rolling (hereinafter referred to as a single roll), the rollability of a rolled material into the roll (hereinafter simply referred to as a single roll) is described. Is an important factor.
For this reason, a slightly soft material has been employed for the rolls used, for example, the piercer roll or the elongator roll, at the expense of abrasion resistance. However, in order to reduce the production cost of a seamless steel pipe, it is extremely important to reduce the unit consumption of rolls. Further, when a stainless steel pipe is manufactured using a roll made of a material that sacrifices wear resistance, there is a problem in securing the surface quality of the inner and outer surfaces of the steel pipe. Therefore, a roll made of a so-called adamite-based material was manufactured by centrifugal casting and used on a test basis. However, before the abrasion resistance was exhibited, the above-described problem of the biting property occurred.

More specifically, the piercer roll 1 is different from a normal roll because the roll arrangement on the stand is inclined as shown in FIG. Rolling part 3 and rolling material 5
The part 4 which sends out the three parts. Since each part plays a different role, the characteristics required as the roll material differ for each part even for the same roll. In other words, in a portion (hereinafter, referred to as an entry side) 2 into which the rolling material 5 enters, it is important that the rolling material (hereinafter, the material) bites into the roll, and the surface of the portion has a certain degree of friction. The rough skin condition must be maintained. Moreover, the part 3 which contributes to rolling,
That is, in the center portion of the roll, the properties of the roll material need to be abrasion resistance and rough surface resistance, and the portion (outside portion) 4 where the rolled material 5 is sent out needs to hold the rolled material 5 stably. Therefore, a certain degree of surface roughness and wear resistance are required. Satisfying different material requirements in different parts of the same roll,
It is difficult with current technology. For this reason, conventionally, a roll material that improves the biting property at the expense of the abrasion resistance of the roll has been selected.

However, in the piercer roll 1 in which abrasion resistance is sacrificed and a roll material having a good biting property is adopted, work hardening is severe near the entry side portion 2 and the roll center portion 3 contributing to rolling. This causes a problem that remarkable wear occurs. In order to improve the wear resistance, a roll material having a high carbon content (for example, C: 1.9% by weight) may be employed. Thereby, the roughened surface state of the roll surface is temporarily improved. However, during operation, a biting defect due to work hardening occurred in the entry side portion 2, causing another problem that the rolled material 5 slipped and seized, resulting in a scratch on the product. In particular, when the poor biting is remarkable, the rolling material 5 cannot be bitten, and the rolling may not be possible. When a tool steel material having a lower carbon content than the above-mentioned roll material (C: about 1.1% by weight) but relatively high hardness is used, excellent wear resistance is exhibited, and biting at the entry side 2 portion is achieved. Sex was maintained. However, there is a disadvantage that a deep heat crack (surface crack) occurs in the portion 3 contributing to rolling and the roll surface is chipped off.

[0005]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a seamless roll which simultaneously has two contradictory characteristics which are considered impossible to be realized with the same roll, namely, biting properties and wear resistance. An object of the present invention is to provide a forging roll for rolling a steel pipe and a method for manufacturing the same.

[0006]

Means for Solving the Problems In order to achieve the above object, the inventor focused on forging in the roll manufacturing technique and repeatedly examined the components and metal structure using various roll materials. Of new knowledge. (1) In order to exhibit abrasion resistance, a spherical hard carbide is used for the soft base of the roll (Shore hardness Hs 29 to 34).
Degree). In that case, as is apparent from FIG.
Coarse carbides of φ show better wear resistance. In addition, in order not to hinder the biting property, the spherical carbide is set to 35 to 55 area% of the metal structure of the roll, and the coarse rod / lump carbide is set to 3 area% or less of the metal structure.

(2) In order to completely eliminate the network-like carbide which appears in the adamite-based roll material and is inconvenient for abrasion resistance by only heat treatment, it is not possible to reduce the carbon content to 1.5 wt% or less. It is necessary to apply a mechanical force called forging. (3) Deterioration of the biting property is caused by work hardening of the roll material and smoothing of the surface. However, if the shore hardness Hs of the roll surface is suppressed to 29 to 34 and a large amount of spherical carbide is precipitated there, as the wear of the roll surface progresses, the surface is always in a uniform roughened state, and a good bite is obtained. Embedment is obtained.

(4) The roll surface deteriorates due to deep heat cracks or plastic flow of the roll material.
The deterioration can be avoided by allowing spherical carbides grown to 1-2 μmφ to exist in the matrix. From the above findings, the inventor has found that the distribution state of carbides in the roll base is most important for achieving the above object, and in particular, it is important to find heat treatment conditions for realizing complete spheroidization of the carbides. And concluded. In addition, the hardness of the roll surface (in terms of Shore hardness Hs) is determined from the balance between work hardening and the rate of progress of wear.
Is 29 to 3 which is considerably lower than the conventional common sense of around 40.
It turned out that we had to set it to 4. Below this hardness, the ability of the carbide to grasp the material is insufficient, and the wear resistance of the roll is reduced. In addition, when the hardness is higher than this, a biting defect occurs particularly when rolling a material having a high high-temperature deformation resistance such as stainless steel. Furthermore, in order to properly adjust these two properties (wear resistance and biting properties), the chemical composition of the roll material is important, and the appearance of mesh-like carbides that are inconvenient for achieving the purpose is due to the cooling rate after forging. It was expected that all of them could be avoided by securing the temperature and spheroidizing heat treatment over two stages.

In order to realize such knowledge, the inventor has selected high-carbon cast steel as a roll material, and conducted intensive research on the combination of forging and heat treatment applied thereto, thereby completing the present invention. That is, the present invention relates to carbon 1.10
1.85 wt%, silicon 0.3-1.2 wt%, manganese 0.4-1.5 wt%, nickel 0.5-2.0
wt.%, 0.5-2.0% by weight of chromium, with the balance substantially consisting of a high carbon cast iron alloy, with spherical carbides comprising 35-55% by area of the metallographic structure of the roll. It is a forging roll for rolling seamless steel pipes.

[0010] The present invention also relates to the high carbon alloy cast steel,
Molybdenum 0.1-1.0 wt%, vanadium 0.
1-1.0wt%, tungsten 0.1-1.0wt
% Or more of the forged harmful elements of phosphorus, sulfur, copper, arsenic, tin, lead, zinc, antimony and bismuth in the high carbon alloy cast steel.
A forging roll for rolling a seamless steel pipe, wherein the forging roll has a content of 2 wt% or less.

Further, the present invention is characterized in that less than 10% by area of the metal structure of the roll has a pearlite structure, or the roll surface has a hardness of 29 to 34 Hs. Forging rolls. In addition, a method for producing the roll is also described as an invention.
0.3-1.2wt%, manganese 0.4-1.5wt
%, Nickel 0.5-2.0wt%, chromium 0.5
After hot forging a high carbon alloy cast steel containing -2.0 wt% and substantially balance iron, the steel is cooled to 600 ° C or less at a cooling rate of 2.5 ° C / min or more, and then cooled to the first temperature. (Acm-10 ° C) ~ (Acm
(−100 ° C.) for 5 hours or more, and then a second stage carbide spheroidizing heat treatment is performed.

[0012] In addition, the present invention relates to the high carbon alloy cast steel, wherein molybdenum 0.1-1.0 wt%, vanadium 0.1-1.0 wt%, tungsten 0.1-1.0 wt%.
1.0 wt% of one or more of them, or phosphorus, sulfur, copper, arsenic, tin,
A method for producing a forging roll for rolling a seamless steel pipe, wherein a total content of forged harmful elements of lead, zinc, antimony, and bismuth is set to 0.2 wt% or less, and the second-stage carbide sphere is formed. A method for producing a forged roll for rolling a seamless steel pipe, wherein the chemical heat treatment is performed within a temperature range of 700 to 840 ° C.

In the present invention, the forging roll for seamless steel tube rolling is broken by using a ferrite base as a main body, breaking conventional wisdom.
Based on the epoch-making idea of distributing spherical carbides there, it is possible to secure biting properties with softness and maintain wear resistance by spheroidizing carbides. as a result,
Conventionally, it was considered impossible to realize the same roll 2
The present invention has made it possible to provide a forging roll for seamless steel tube rolling and having a method for manufacturing the same, which simultaneously has the two properties, biting properties and wear resistance.

In the present invention, a sample was taken from the vicinity of the surface layer of the roller, and the metal structure of the roll was examined by observing the sample with a microscope. That is, the area of the spherical carbide and the like was determined by processing the image obtained by observation.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The constitution of the present invention is as described above. Therefore, the chemical composition of the forged roll according to the present invention, the cooling after forging, the first and second stages of spheroidizing heat treatment, The reason why the metal structure is substantially limited to a state in which two phases of ferrite and spherical carbide are present will be described. Chemical composition Carbon: 1.10 to 1.85 wt% Carbon is a central component for the roll to exhibit wear resistance as a carbide forming element, and at least 1.10 w
t% or more is required. If the content is not more than 1.10 wt%, coarse spheroidization of the carbide is unlikely to occur, and if the content is not less than 1.85 wt%, a large amount of eutectic carbide is generated, which causes surface roughening. In addition, the most preferable carbon content is 1.3 to 1.80 wt%.

Silicon: 0.3 to 1.2 wt% Silicon is an unavoidable alloy element of cast iron and needs to be at least 0.3 wt%. Due to the action, carbon is excessively precipitated on the matrix during the heat treatment and deteriorates the biting property of the roll. Therefore, the upper limit is set to 1.2 wt%.

Manganese: 0.4 to 1.0 wt% Manganese is added together with silicon for deoxidation of molten metal during the steel making process, and is present in an amount of 0.4 wt% or more. Since the toughness is reduced, the upper limit is set to 1.0 w
t% or less. Chromium: 0.5-2.0 wt% Chromium is essential for carbide formation, and in particular, 0.5 wt% or more is required to make spherical carbide coarse. However, when added in an amount of 2.0 wt% or more, the heat crack resistance of the roll is deteriorated.

Molybdenum: 0.1-1.0 wt% Molybdenum is an important element for carbide formation, but its effect becomes effective at 0.1 wt% or more, and when added simultaneously with chromium as a main alloying component. , There is a tendency to gradually increase the amount of carbide. Further, if added in an amount of 1.0 wt% or more, the formation of coarse rod-like carbides during the heat treatment cannot be prevented, so that the upper limit was set.

Vanadium: 0.1 to 1.0 wt% Vanadium is an important element for carbide formation. Its effect becomes effective at 0.1 wt% or more, and when added at the same time as chromium as a main alloying component. , There is a tendency to gradually increase the amount of carbide. Further, if added in an amount of 1.0 wt% or more, the formation of coarse massive carbides by heat treatment cannot be prevented, so that the upper limit was set. Tungsten: 0.1 to 1.0 wt% Tungsten also has the same effect on carbide formation as molybdenum. It becomes effective when added at 0.1 wt% or more, and when added at the same time as chromium as a main alloy component,
There is a tendency to gradually increase the amount of carbide. However, 1.0
If it is added in an amount of not less than wt%, it is not possible to prevent the formation of coarse rod-like carbides due to the heat treatment.

Total amount of harmful elements for forging: 0.2 wt% or less According to a detailed study on the effect of impurity elements on forgeability, it is found that when each of the impurity elements exists alone,
In particular, phosphorus must not exceed 0.03 wt%, and sulfur, tin and arsenic must not exceed 0.02 wt%. This is because, when each of the above-mentioned impurity elements exceeds the above-mentioned amounts, the roll crack characteristics such as heat crack resistance and toughness are remarkably deteriorated. Also,
In general, hypereutectoid cast steel having a component range according to the present invention,
Poor forgeability, content of impurity element is 0.2
If the content exceeds wt%, it is difficult to achieve more uniform forging. However, the present invention is not intended to improve the forgeability by reducing the content of each of the impurity elements to 0.2 wt% or less, and to reduce the total content of the impurity elements to 0.2 wt% or less. By doing so, the performance of the roll is improved. -Heat treatment conditions 1) Cooling after forging In order to always maintain good biteability, it is necessary to adjust the distribution of spherical carbides. That is, the roll is given a densification of the metal structure by forging and the toughness accompanying it,
It is necessary to prevent the network carbide from precipitating on the roll base during slow cooling from the austenitic state.

For this purpose, it is necessary to increase the grain boundary area on the metal structure and to make the cooling rate relatively high. According to a detailed investigation by the inventor, a training ratio of 1.5
When a roll having a microstructure (large grain boundary area) forged by ~ 3S is cooled to 600 ° C in a temperature range of 900 to 800 ° C at a cooling rate of 2.5 ° C / min or more, a subsequent spheroidizing heat treatment is performed. It was found that the reticulated carbide was easily spheroidized. However, if the cooling rate is lower than 2.5 ° C./min, the network carbide is not easily decomposed by the spheroidizing heat treatment in the next step. Therefore, in the present invention, it must be strictly adjusted to maintain this cooling rate. 2) First stage spheroidizing heat treatment of carbide In the roll in the component range according to the present invention, (Acm-1
By maintaining the temperature in a temperature range of 0 ° C. to (Acm-100 ° C.) for 5 hours or more, the network carbide can be decomposed. This is because the first spheroidization is performed by a synergistic effect with the cooling after the forging. When maintained at a temperature higher than the above temperature, the crystal structure may be completely austenitized, in which case, the network carbide is not eliminated,
Roll biting performance is poor. In addition, (Acm-100
When the first-stage spheroidizing heat treatment is started at a temperature lower than the temperature of (.degree. C.), coarse rods or massive carbides remain in a network. In such a case, the heat crack resistance of the roll is deteriorated, and the roll surface is likely to be chipped, similarly to the conventional cast adamite roll. 3) Heat treatment for spheroidizing carbides in the second stage For rolls having a component range related to the present invention, 700 to 8
The second stage carbide spheroidizing heat treatment can be performed in a temperature range of 40 ° C. to make the spherical carbide coarse. By maintaining the temperature in this range, only the relatively large-diameter carbides generated in the first-stage spheroidizing heat treatment are dispersed as nuclei, and subsequently grow at a slow rate into large carbides. I do.

An important point in the production of the roll according to the present invention is to utilize the crystal structure refined by forging. In addition to the decomposition of the network-like carbide, the base of the roll is mostly (90% or more) is a ferrite phase. The reason is that the ferrite phase, which is harder to harden than the pearlite phase, is advantageous because the deterioration of the roll bite is caused by the work hardening of the matrix. The lower limit of the pearlite phase in Shore hardness Hs is about 35, which is already close to the limit hardness required for biting properties. For this reason,
In the present invention, the ferrite phase was selected as the base of the roll.
It should be noted that there is no conventional example in which a ferrite phase having inferior wear resistance is actively used for a base in a forging roll for seamless steel pipe rolling requiring wear resistance, and this is a feature of the present invention.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the production and use of a roll for seamless steel pipe rolling according to the present invention will be described below. (Production Example 1) The invention 1 shown in Table 1 was melted and refined in an electric furnace.
The molten metal adjusted to the chemical composition shown in (1) was degassed by vacuum treatment, and then cast to form a steel ingot. Next, the steel ingot was discharged from
Forging was performed at a total forging ratio of 1.8 to 2.3 S so as to form a sleeve roll having a diameter of 5 mm, an inner diameter of 508 mm, and a length of 780 mm, and the metal structure was refined. The roll after this forging is once cooled to 600 ° C. by forced air cooling at a cooling rate of approximately 3 ° C./min on the surface of the roll material, and then reheated to 900 ° C. as a first stage spheroidizing heat treatment. After that, the roll material was air-cooled in a temperature range of 900 to 600 ° C. at a cooling rate of approximately 3.5 ° C./min on the surface of the roll material. After the center of the roll is cooled to 600 ° C., it is subsequently reheated to 830 ° C. as a second stage spheroidizing heat treatment, kept at that temperature for 10 hours, and then again to 600 ° C. at 9.5 ° C./hour. It was gradually cooled at a cooling rate. Finally, these heat-treated forgings were machined to complete sleeve rolls.

[0024]

[Table 1]

(Example of use) The above-mentioned sleeve roll is made by JI
SG 4105 It was shrink-fitted to an arbor (core material) by SCM440 specified for chromium-molybdenum steel, assembled into a piercer roll, set in a Mannesmann-type piercer, and pierced and rolled with a rolled material. The use result is evaluated by the number of rolled materials passed until the roll change, and compared with rolls manufactured by conventional casting (hereinafter, cast rolls)
It is shown in Table 2. According to Table 2, the rolling material has a large deformation resistance.
In the case of 3Cr stainless steel, the difference from the conventional roll is remarkable, and it can be seen that the service life is at least three times that of the conventional roll. When used for piercing and rolling of carbon steel,
A life improvement of 50% or more has been achieved. In addition, 13Cr
The use of the roll according to the present invention has eliminated the problem of poor biting which has frequently occurred during rolling of the stainless steel.

[0026]

[Table 2]

The roll according to the present invention, the conventional forged high-hardness roll and the casting-type roll are used for piercing the same kind of material, respectively, and the surface Shore hardness (hereinafter simply referred to as hardness) distribution on the above-mentioned portion of the roll is used. Is shown in FIG. FIG.
As a result, the hardness of the forged high-hardness roll in which the biting failure occurred was high before use, but the hardness of the entry side portion 2 and the center portion 3 was further increased by use. Rough skin progresses,
In the case of cast steel rolls with degraded product skin and the rolls according to the present invention, the result was that the increase in hardness due to use was small.

FIG. 2 shows the surface roughness of the center portion 3 of the roll. According to FIG. 2, the roll according to the present invention shows that the roughening progresses as compared with the high hardness roll, which is advantageous for maintaining the biting property. The roll of the present invention exerts a self-healing force as the wear progresses, and can always maintain an appropriate surface roughness.

[0029]

As described above in detail, in the present invention, the metal structure of the roll is such that spherical coarse carbides (about 1 to 2 μmφ) are dispersed in the matrix of the ferrite phase.
An appropriate roll surface roughness can be maintained, and excellent biting properties and abrasion resistance can be exhibited. As a result, the effect of improving the roll life was remarkable, and in the production of a seamless steel pipe, the basic unit of the roll used was remarkably improved, and the trouble of poor biting could be solved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in a Shore hardness distribution before and after use with respect to a portion (position) of a piercer roll.

FIG. 2 is a diagram showing a comparison of the central part surface roughness before and after using a piercer roll.

FIG. 3 is a diagram showing the relationship between the size of spherical carbides dispersed in a roll base and wear reduction obtained in a wear test.

FIG. 4 is a perspective view showing the structure of a piercer roll.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 piercer roll 2 part where rolling material enters (entrance part) 3 part contributing to rolling (center part) 4 part that sends out rolling material (outside part) 5 rolling material 6 plug 7 plug bar 8 traveling direction 9 Direction of rotation

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B21K 1/02 B21K 1/02 C21D 6/00 C21D 6/00 E 9/38 9/38 A C22C 38/56 C22C 38/56 (72) Inventor Itsu Seo, 1-98 Shimoshin Nisso-cho, Toyama City Inside the Taiyo Steel Co., Ltd. Toyama Works (72) Inventor Satoshi Matsuoka 1-98, Shimoshin Nisso-cho, Toyama City In the Toyama Works of Taiheiyo Steel Co., Ltd. Kawasaki Steel Corporation Chita Works (72) Inventor Akira Ito 1-1 1-1 Kawasaki-cho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works

Claims (9)

[Claims] 1. Carbon 1.10 to 1.85 wt%, silicon 0.3 to 1.2 wt%, manganese 0.4 to 1.5 w
t%, nickel 0.5-2.0 wt%, chromium 0.
A seamless steel pipe containing 5 to 2.0 wt%, with the balance substantially consisting of a high carbon alloy cast steel of iron, wherein the spherical carbide occupies 35 to 55 area% of the metallographic structure of the roll. Forging roll for rolling. 2. The high-carbon alloy cast steel is made of molybdenum.
0.1-1.0wt%, vanadium 0.1-1.0w
The forging roll for seamless steel tube rolling according to claim 1, wherein one or more of t% and 0.1 to 1.0 wt% of tungsten are added. 3. The high carbon alloy cast steel according to claim 1, wherein the total content of harmful forging elements of phosphorus, sulfur, copper, arsenic, tin, lead, zinc, antimony and bismuth is 0.2 wt% or less. Item 3. A forging roll for rolling a seamless steel pipe according to item 1 or 2. 4. 10% by area of the metallographic structure of the roll
2 is a pearlite structure.
4. A forged roll for rolling a seamless steel pipe according to any one of claims 3 to 3. 5. The forging roll for rolling a seamless steel pipe according to claim 1, wherein the surface hardness is 29 to 34 Hs. 6. Carbon 1.10 to 1.85 wt%, silicon 0.3 to 1.2 wt%, manganese 0.4 to 1.5 w
t%, nickel 0.5-2.0 wt%, chromium 0.
After hot forging a high-carbon alloy cast steel containing 5 to 2.0 wt% and substantially balance iron, into a roll shape, the steel is cooled to 600 ° C or less at a cooling rate of 2.5 ° C / min or more, and then cooled to 600 ° C or less. (Acm-10 ° C) to (Ac)
m-100 ° C) for 5 hours or more,
A method for producing a forging roll for rolling a seamless steel pipe, comprising performing a carbide spheroidizing heat treatment in a step. 7. The high carbon alloy cast steel according to claim
0.1-1.0wt%, vanadium 0.1-1.0w
7. The method for producing a forged roll for rolling a seamless steel pipe according to claim 6, wherein one or more of t% and 0.1 to 1.0 wt% of tungsten are added. 8. The high carbon alloy cast steel according to claim 1, wherein the total content of forged harmful elements of phosphorus, sulfur, copper, arsenic, tin, lead, zinc, antimony and bismuth is 0.2 wt% or less. Item 8. The method for producing a forged roll for rolling a seamless steel pipe according to item 6 or 7. 9. The second stage carbide spheroidizing heat treatment is performed at 70
The method for producing a forged roll for rolling a seamless steel pipe according to any one of claims 6 to 8, wherein the process is performed within a temperature range of 0 to 840 ° C.