JP2683861B2 - Hot pipe making tool and method of manufacturing the same - 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 pipe manufacturing tool (such as an inner surface rolling tool) used in piercing rolling or drawing rolling when manufacturing a seamless pipe by the Mannesmann method, and the hot rolling. The present invention relates to a method for manufacturing a pipe tool.

[0002]

2. Description of the Related Art The seamless pipe manufacturing process by the Mannesmann system is roughly divided into two types: a tilt roll type two-roll type piercer, a three-roll type piercer and a hole type roll.
It consists of a piercing and rolling process that uses a rolling machine such as a roll type press roll piercing mill, and a drawing and rolling process that uses a sloping roll type two roll elongator (drawing machine). However, in these rolling processes, tools for inner surface rolling (piercer plug, mandrel, etc.), which are excellent in heat resistance and wear resistance, cannot be omitted.

As a material for the tool for inner surface rolling, for example, a tool for piercing and rolling (piercer plug), a steel of 3% Cr-1% Ni base (hereinafter referred to as "steel") which has been conventionally developed for processing ordinary steel. ,% Representing the component ratio is taken as% by weight) was generally used. However, it cannot be said that high-temperature strength is sufficient with the above materials, and when drilling stainless steel or the like with high deformation resistance, high surface pressure is applied and melting damage occurs at the tip and tools must be scrapped in a short period of time. I had to do it.

Therefore, for stainless steels and high Cr steels, a material in which the proportions of Cr content and Ni content of the above 3% Cr-1% Ni base steel are modified and appropriate amounts of W and Mo are added ( JP-A-56-
130457, Japanese Examined Patent Publication No. 64-7146), and a piercing and rolling tool using a material to which Ti and Zr have been added (Japanese Examined Patent Publication No. 64-7147) have been proposed. In addition, a heat-resistant alloy or ceramic material as a base material or a surface-modifying material was also experimentally proposed.

However, although the tools according to the above-mentioned JP-A-56-130457, JP-B-64-7146 or JP-B-64-7147, which are expected to have high performance as a practical material, certainly have high temperature strength, The tool life was only 1.5 to 2.0 times as long as that of the 3% Cr-1% Ni base steel mentioned above. This extension of the service life is caused by "seizure", and the seizure generated in the body of the tool subjected to severe shear deformation has been a factor that hinders the improvement of the service life of the tool.

Therefore, it has been proposed that a piercing / rolling tool or the like made of these materials is heat-treated in an oxidizing atmosphere to form an oxide scale layer having high lubricity on the surface thereof (special feature). Kai 57-152446, JP 61-264163, JP 63-69948, JP 63-282241, JP 3-204106
No. 4-147706, No. 4-270003). However, even with these tools, when a material having a large deformation resistance such as stainless steel is to be processed, it is still impossible to sufficiently prevent seizure.

By the way, when examining the damage state of the drilling tool in this case, most of the damage was due to seizure due to abrasion or peeling of the produced oxide scale layer. It has been confirmed that the scale layer formed on the tool surface is seized in the pipe making to cause seizure particularly when processing a material having a high deformation resistance such as stainless steel.

According to Japanese Patent Application Laid-Open No. 63-228241, "When the Cr content is 0.95% or more, the scale structure formed on the surface is mainly FeCr ₂ O ₄ and the rolled material can be easily rolled. The life is short because it is scraped off, and if the Cr content is less than 0.95%, the oxide scale formed by heat treatment becomes a FeO-based surface scale that firmly adheres to the tool surface, resulting in a longer tool life. However, if the material with the Cr content adjusted to less than 0.95% is simply subjected to the scale-forming treatment, the life extension effect is not sufficiently satisfactory, and the above-mentioned 3% Cr-1% Ni alloy is not sufficient. -It has stopped at about 2.5 to 3.0 times that of stainless steel.

Moreover, when heat treatment for producing an oxide scale is performed on the tool surface, remarkable decarburization occurs on the tool surface, and as a result, the vicinity of the tool surface (~ 2 mm) is significantly softened and plastic deformation occurs at high temperature use. It was also found that it becomes easier and causes melting loss, seizure, and deformation.

In view of the above, the object of the present invention is to establish means for stably providing a hot pipe manufacturing tool that guarantees a long service life even in the case of manufacturing a material having high deformation resistance. Was to do.

[0011]

In order to achieve the above object, the inventors of the present invention ensure a sufficient high temperature deformation resistance of a hot pipe manufacturing tool and take a more stable seizure prevention measure. As a result of repeated studies from the viewpoint of necessity, the following findings were obtained.

A) It is known that it is effective to increase the C content in the material steel and to add Mo and W in order to increase the high temperature deformation resistance of the hot pipe manufacturing tool. If you take proper measures, the toughness during quenching will decrease significantly,
The tool easily breaks due to quenching cracks, impact during transportation, or impact at the start of drilling. However, as a method of improving this, the Ac ₃ point temperature of the material steel is raised so as to minimize the area where quenching occurs, so that even if the surface temperature rises during pipe making, it will not exceed the Ac ₃ point. it is conceivable to, but which may not be prevented from grilled enters for increasing shortage of Ac ₁ point temperature in that case, also simultaneously solved the problem of easily softened to Ac ₁ point temperature is low Was difficult. However, by adding a large amount of Mo and W, it becomes possible to effectively solve these problems.

B) On the other hand, for preventing seizure, it is most effective to form a low melting point oxide scale layer having excellent lubricity and hardly peeling on the tool surface. Fe oxide is effective as an oxide scale, but in order to further improve lubricity and ensure sufficient seizure resistance, a thick scale layer that is dense and has excellent peel resistance and wear resistance is used. Need to be formed. for that reason,
Spinelization of the scale by adding Cr to the base steel has been conventionally used, but in addition to Mo and W, a large amount of Ni is contained and the content of Ni and W is set to a predetermined level. When the surface is oxidized by using a base steel adjusted to a range, the oxide scale layer formed on the surface is "a metal piece highly enriched in Ni" or "Mo, W". Becomes a state in which the low-melting-point compound produced by bonding with FeO is dispersed.
Even in the case of thick scale, the scale structure changes from the general grain boundary oxidation type to the internal oxidation type, and the peeling resistance (adhesion with the base material) and wear resistance are greatly improved, and seizure prevention The effect is further improved.

C) However, when the surface is subjected to an oxidation treatment for forming a scale having lubricity, decarburization is inevitably generated on the surface layer of the base material, and there is a problem that the material softens due to decarburization. is there. However, if a large amount of Mo and W are added to the base steel and Ni and Mn are used to suppress the formation of ferrite, the above problems can be reduced to the extent that they are practically acceptable.

D) In order to obtain a hot pipe forming tool having excellent seizure resistance, the composition design of the base material is optimized to form a dense oxide scale layer having excellent peeling resistance and wear resistance. It is of course necessary to increase the thickness of the scale before use, as described above, but to ensure a precise and sufficient thickness of the scale. In this case, the heat treatment conditions for forming the oxide scale layer play an important role, so it is necessary to regulate the heat treatment conditions.

The present invention has been completed after further studies based on the above-mentioned findings and the like. "The hot pipe-making tool is C: 0.08 to 0.65%, Si: 0.1 to 2.0%. , Mn: 0.2 ~
3.0%, Ni: 0.2 to 7.0%, sol.Al: 0.005 to 0.2%, one or more of Mo and W: A total of 1.5 to 8.0%, and an amount satisfying 7W (%) + 8Ni (%) ≤ 56. Contains or further Cr: 5.0% or less, Co: 5.0% or less, V: 2.0 or less,
Nb: 2.0 or less, Ti: 2.0 % or less, Zr: 0.5% or less, B: 0.2% or less, one or more of Mg, Ca, La, Ce and Y: Includes 0.5 or less in total and the balance Fe and unavoidable Steel substrate as an impurity, or the content of N, O, P and S in the unavoidable impurities is 0.02% or less, 0.02% or less, 0.035% or less, respectively.
It is characterized in that the surface of a steel base body regulated to 0.030% or less has an internal oxidation-type scale layer having a thickness of 250 to 1000 μm ”, and further,“ C: 0.08 to 0.65%, Si: 0.1-2.0%, Mn: 0.2
~ 3.0%, Ni: 0.2 ~ 7.0%, sol.Al: 0.005 ~ 0.2%, one or more of Mo and W: A total of 1.5 ~ 8.0% and an amount satisfying 7W (%) + 8Ni (%) ≤ 56 Or further contains Cr: 5.0% or less, Co: 5.0% or less, V: 2.0%
Below, Nb: 2.0% or less, Ti: 2.0% or less, Zr: 0.5%
Below, B: 0.2% or less, one or more of Mg, Ca, La, Ce and Y: a steel containing at least one of 0.5% or less in total and the balance being Fe and inevitable impurities, or further N, O in unavoidable impurities,
Content of P and S is 0.02% or less, 0.02% or less,
After forming the steel controlled to 0.035% or less and 0.030% or less into a predetermined tool shape, soaking is performed at 800 to 1100 ° C for 4 to 10 hours in an oxidizing atmosphere with an atmospheric oxygen concentration or less, and subsequently. 800 to 5 at a cooling rate of 50 ° C / hr or less
By gradually cooling to 00 ° C, the surface has a thickness of 250-1
By forming an internal oxidation type scale layer having a thickness of 000 μm, it is possible to stably manufacture a hot pipe manufacturing tool having a long service life ”.

[0017]

Next, in the present invention, the composition of the steel, the oxide scale thickness of the tool substrate surface, the roughness of the steel substrate surface, and the reasons for limiting the tool manufacturing conditions as described above will be explained together with the action. Detailed description.

(A) Steel composition a) C C is an effective component for improving the high-temperature strength of steel, but if its content is less than 0.08%, sufficient strength cannot be secured. On the other hand, when the C content exceeds 0.65%, the hardness of the surface layer portion where quenching occurs due to cooling after pipe making becomes too high, and quench cracking easily occurs. Therefore, the C content is 0.08 to 0.65.
The range is defined as%.

B) Si Si is an effective component for deoxidation, increase in Ac ₁ point, densification of oxide scale on the tool surface, etc., but if the content is less than 0.1%, the desired effect is obtained. On the other hand, if the content exceeds 2.0%, not only the toughness is deteriorated, but also a scale layer having a sufficient thickness cannot be obtained and the lubricating performance is insufficient. Therefore, the Si content is set to 0.1 to 2.0%.

C) Mn When adding a large amount of Mo and W as in the steel of the present invention, the addition of Mn is effective to secure the austenite single phase at high temperature, and suppresses the formation of δ-ferrite. Therefore, addition of Mn is necessary to prevent deterioration of toughness and deterioration of high temperature strength. However, if the content is less than 0.2%, the above effect is not sufficient. On the other hand, if Mn exceeds 3.0%, Mn in the oxide scale deteriorates the denseness of the scale and also increases the melting point of the scale to deteriorate its lubricity. Therefore, the Mn content was set to 0.2-3.0%.

D) Ni Ni has an action of improving the toughness of the hardened phase formed in the surface layer of the tool by cooling after pipe making, but in order to obtain the desired effect due to the above action, 0.2% or more It is necessary to secure the Ni content of. Also, the Ni added to the steel is
It remains without being oxidized in the scale layer formed by the oxidation scale treatment, has a composite strengthening action, and has a function of greatly improving the peeling resistance of the scale. Is Ni
It becomes remarkable when the content exceeds 0.2%. Further, Ni also has an action of suppressing the formation of δ-ferrite when a large amount of Mo or W is added, thereby preventing a decrease in toughness and a decrease in high temperature strength. However, if Ni is contained in an amount of more than 7.0%, the generation of scale is suppressed, which rather deteriorates the lubricity. In addition, when the content is in the range of "7W (%) + 8Ni (%)>56" in relation to the W content, the scale becomes a grain boundary oxidation type similar to the conventional oxide scale type plug. Becomes detached during perforation. Therefore, the Ni content is 0.2-7.0%, and "7W (%) + 8
Ni (%) ≤ 56 "was satisfied.

E) Mo, W Containing one or two or more of these components in a specific amount or more is extremely effective in improving the high temperature strength, and increases the Ac ₁ point to burn the surface layer of the tool after drilling. It also has the function of reducing the number of parts that enter and preventing quenching cracks. These effects are equivalent in Mo and W, and in the total amount of [Mo + W]
If it is less than 1.5%, the above effect is insufficient, and deformation and melting loss easily occur during pipe making. (As for toughness, W is better than Mo, especially for drilling tools where toughness is important. Mo should be suppressed to 3.5%). On the other hand, if the total content of Mo and W exceeds 8.0%, ferrite will remain even at high temperatures, conversely the high temperature strength will decrease and the toughness will also deteriorate. Therefore, the total content of Mo and W is
It was defined as 1.5 to 8.0%. From the viewpoint of toughness, it is preferable to contain W rather than Mo, and especially for tools in which toughness is important, the Mo content should be suppressed to 3.5% or less.

F) sol.Al sol.Al is an effective component as a deoxidizer. In particular, it is necessary to secure the strength at a high temperature in the material for pipe manufacturing tools, and therefore the strength is inevitably high even at room temperature. In this case, it is important to suppress the oxygen content in the steel in order to secure the toughness, It is desirable that the content be 200 ppm or less. O
When the content is 30 ppm or less, the toughness is further improved. However, if the sol.Al content is less than 0.005%, the deoxidizing effect is insufficient. On the other hand, if the sol.Al content exceeds 0.2%, the deoxidizing effect is not only saturated, but rather the viscosity of molten steel during tool casting increases. This may cause casting defects. Therefore, the sol.Al content is set to 0.005 to 0.2%.

G) Cr, Co, V, Nb, Ti, Zr, B, Mg, Ca,
La, Ce and Y These components have the function of improving the toughness of steel materials, the deformation resistance at high temperatures, and the function of improving the lubricating characteristics of the scale. Although they are added, the content of each component is individually limited for the following reason.

Cr Cr is a component particularly effective for densifying the oxide scale layer and improving the adhesion between the base material and the lubricating film (oxide scale layer), but its content is 5.0%. If it exceeds 0.1%, the oxidation resistance is excessively improved and the lubricating oxide scale layer having a desired thickness cannot be formed. Therefore, the Cr content is set to 5.0% or less. However, when the Cr content is 0.95% or more, the structure of the surface scale is mainly FeCr ₂ O ₄ and it is easy to peel off, and the melting point of the scale is increased to deteriorate the lubricity. Therefore, it can be said that it is preferable to keep the Cr content below 0.95%.

Co Co is a component that exerts the same toughness improving action as Ni and the scale peeling resistance improving action without significantly reducing Ac ₁ point and Ac ₃ point, but its content is If the ratio exceeds 5.0%, it is impossible to secure the improvement effect commensurate with the cost increase.

V, Nb, Ti, Zr, Mg, Ca, La, Ce and Y Any of these components is particularly effective for grain refinement of the material, not only improving the toughness of the steel material but also the scale layer. Although it also has the effect of densifying, if its content exceeds the respective upper limit values, the embrittlement phase precipitates and the toughness deteriorates.

[0028] The B B, is maintained at a high temperature during piercing and O - strengthen grain boundaries of austenite and became tool surface layer, there is an effect of improving the deformation resistance, deformability at high temperature, a 0.2% If it is contained in excess, the toughness deteriorates due to precipitation of the brittle phase.

H) Inevitable impurity N is contained in an amount of 0 to prevent defects during melting (solidification).
02% or less, and O is preferably 0.02% or less to secure desired toughness as described above. Further, P and S also adversely affect the toughness, so in order to secure the desired toughness, the respective contents are 0.035% or less and
It is desirable to limit it to 0.03% or less.

(B) Thickness and Structure of Oxide Scale on Surface of Hot Pipe Making Tool Scale of oxide scale layer formed on steel substrate surface of hot pipe making tool is less than 250 μm. -Since the lubricity of the resin and the desired heat resistance to the base material cannot be obtained, and the desired tool life cannot be obtained, the thickness thereof is set to 250 μm or more. In addition, if the oxide scale layer becomes too thick, the scale
Since the rule layer becomes porous and peeling easily occurs,
The thickness of the oxide scale layer formed on the surface of the tool substrate is 100.
It is desirable to control it to 0 μm or less.

The oxide scale formed on the tool substrate surface
As shown in FIG. 1 or 2, the rule layer is generally divided into two layers, an inner scale layer (a portion of thickness A in the figure) and an outer scale layer, which is referred to in the present invention as “oxidation scale”. Layer thickness "
Is the total scale thickness [B in the figure]. In addition,
Generally, the outer layer side is a relatively porous scale mainly composed of FeO.
And the inner layer side is a dense scale layer of spinel / composite oxide type. The interface between the inner scale layer and the base material is a grain boundary oxidation type depending on the components and the heat treatment conditions (shown in FIG. 1 and obtained in Test No. 37 of Examples described later).
And internal oxidation type (shown in FIG. 2 and obtained in Test No. 5 of the Example described later). Of course, in the present invention, the internal oxidation type scale layer is indispensable, and this is realized by appropriately controlling the component design of the base material as described above (oxidation to the grain boundary after casting and solidification). Segregation of easily prone components (W, Ti, etc.) results in a grain boundary oxidation type, and these provide excellent peeling resistance of the scale layer (adhesion at the interface between the scale layer and the base material). .

(C) Manufacturing conditions for hot pipe forming tools a) Forming into tool shape For manufacturing hot pipe forming tools (piercer plugs, elongator rolling plugs, plug mill rolling plugs, etc.) In this case, first, steel having a predetermined component composition is melted and then cast, and then a plastic working such as forging is performed or a shape is finished by cutting without a plastic working such as a tool shape.

B) Scale Layer Forming Heat Treatment Conditions <Atmosphere> The heat treatment atmosphere affects the structure of the scale produced. In the present invention, the oxygen concentration in the atmosphere is adjusted to be equal to or lower than the atmospheric oxygen concentration. However, if the oxygen concentration in the atmosphere is higher than the atmospheric oxygen concentration, iron oxide grows rapidly during the heat treatment, so that the thickness is thick but the compactness is poor. It becomes a porous scale and easily peels off. The oxygen concentration is generally 5 to 1
About 0% is desirable, and CO and H ₂ O gas are mixed if necessary.

<Temperature> The heat treatment temperature affects the structure and growth rate of the generated scale. In the present invention, the heat treatment temperature is 8
The temperature is set to be 0 to 1100 ° C. The reason for this is that if the temperature is lower than 800 ° C., a very long heat treatment time is required due to poor oxide forming ability, and it is not suitable for actual operation.
This is because if the temperature exceeds ℃, the scale growth becomes remarkably fast, the scale becomes unstable and porous, and peeling easily occurs.

<Time> The heat treatment time affects the thickness and structure of the scale produced. In the present invention, the heat treatment time is 4 to 1
Although it was set as 0 hr, the reason is that if it is less than 4 hr, the scale thickness is not sufficient for the component system, while if it exceeds 10 hr, the scale growth becomes excessive and the scale thickness becomes excessive. Is too thick, and the scale becomes porous and peeling easily occurs.

<Cooling Rate / Temperature after Soaking> The cooling rate after soaking affects the denseness of the scale. In the present invention, after soaking, it was decided to gradually cool to 800 to 500 ° C. at a cooling rate of 50 ° C./hr or less, but if the cooling rate exceeds 50 ° C./hr, cracks and peeling of the scale Dropout occurs. It is desirable to gradually cool at a cooling rate of 20 to 30 ° C./hr or less. If the end temperature of the slow cooling is higher than 800 ° C, peeling and dropping of the scale will occur in the subsequent rapid cooling. On the other hand, if the end temperature of the slow cooling is lower than 600 ° C, the cooling time will be too long and the operation will be continued. It becomes an upper problem.

The tool of the present invention obtained as described above has a longer service life than conventional ones, and the drilling tool used under severe conditions is used as an example.
Compared to tools with 1% Ni base steel, it has a life of over 3.0 to 10.0 times.

Next, the effects of the present invention will be described more specifically by way of examples.

Example First, steel of each chemical composition shown in Table 1 and Table 2 was melted in a small (500 kg) high frequency induction electric furnace, and each of these charges was cast into a sand mold and then machined. Finishing was performed to form a piercer plug with a maximum outer diameter of 147 mm.
Then, the mechanical properties of these were investigated.

[0039]

[Table 1]

[0040]

[Table 2]

Next, the above piercer plug material was subjected to a scale heat treatment. The plug surface scale heat treatment is
It was carried out in a butane gas combustion atmosphere (air-fuel ratio 31) at a predetermined temperature, time, cooling rate, and slow cooling end temperature. Then, the surface scale layer thus obtained was actually measured from a cross-sectional microphotograph of the central portion of the plug, and the scale structure was specified.

Next, the piercer plug thus prepared was subjected to a drilling test in an actual machine to evaluate its life. In the drilling test, SUS heated to 1230 ℃
420 equivalent steel (13% Cr steel), SUS304 equivalent steel (18% Cr
For a round billet of -8% Ni steel) with an outer diameter of 187 mm and a length of 1770 mm, the drilling ratio is 3.1 and the piercer-outlet shell outer diameter is 19
Perforation rolling was performed with a length of 2 mm and a length of 5500 mm. The perforation time was about 7.5 seconds. Here, the actual piercer conditions were as follows. Cross angle: 10 °, inclination angle: 14 °, plug diameter: 147φ, tip draft rate: 6.0%.

Tables 3 to 5 show the heat treatment conditions of the test steels, the actual measurement values of the oxide scale layer thickness, the oxide scale structure, the mechanical properties and the results of the actual machine perforation test. The mechanical properties are toughness and Charpy impact value at room temperature (10 mm × 10 mm, 2 mm U
Notch) and the deformation resistance are shown by the result of the 800 ° C compression test. (Here, the toughness value is 0.9 kg-m / cm ² or more in order to withstand the influence of thermal and mechanical stress of the actual machine as a piercer plug. , It is desirable that the deformation resistance is 25 kgf / mm ² or more). Real machine test
In the test, the plug life was evaluated by the perforation of one plug.
The number of lines, that is, the number of passes. The plug provided
If it is discarded due to melting of the tip, peeling of the scale, etc., drilling
The time was 8-10 seconds.

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

As shown in Tables 3 and 4, in the present invention, the desired toughness and high strength can be obtained with each of the component materials, and the surface scale thickness can be properly adjusted by the proper heat treatment conditions for the oxidation scale. The plug that is the value is obtained. As a result of the drilling test, a sufficiently long life was achieved when the number of possible drillings was 7 to 15 passes for the subject SUS420 steel and 4 to 10 passes for SUS304 steel.

On the other hand, in the comparative examples, except for the test number 32, the toughness and the high temperature strength were out of the desirable ranges, so that cracking of the plug and melting at the tip occurred at the time of drilling, and the number of drillable cycles was SUS420 steel. Was 3 passes or less, and SUS 304 steel was 1 pass. Also, in test number 32, the number of perforations possible was SU because the amount of Ni and the scale thickness after heat treatment were excessive.
S420 steel and SUS304 steel had 5 passes and 2 passes, respectively, and no improvement in life was obtained.

Test Nos. 41 to 47 and 49 are the oxide scale application temperature or time, Test No. 48 is the scale application time and the slow cooling end temperature, and Test Nos. 50 to 53 are the cooling rate. And, in the test numbers 54 to 57, the slow cooling end temperature was out of the conditions specified in the present invention, respectively, except for the test numbers 46, 49 and 50, the scale thickness after heat treatment was the present invention. However, the life was not improved because the number of perforations was 6 passes or less for SUS420 steel and 3 passes or less for SUS304 steel.

Even if the surface scale thickness is within the range specified in the present invention, in Test Nos. 46, 49 and 50 in which the treatment conditions do not satisfy the specified conditions of the present invention, the scale structure is intragranular. Oxidation type, but the scale is not dense and porous, or the scale is insufficient, so the scale
Is easily peeled off and abraded, resulting in S
The US420 steel had 5 to 6 passes, and the SUS304 steel had 2 to 3 passes, so that life improvement could not be obtained.

Even when the "steel A" used in Test Nos. 49 to 51 is applied, the heat treatment conditions defined in the present invention (Test No. 5) are those having a dense intragranular oxidation type scale structure. As a result, SUS420 steel has 12 passes, and SUS304 steel has 7 passes, and life has been improved.

Test Nos. 37 and 38 are steels having a composition according to "steel E", but "7W (%) + 8Ni (%)>56" are examples. "Steel E" is used. Test No. 5 has an internal oxidation type scale structure, whereas Test Nos. 37 and 38 have a grain boundary oxidation type scale structure.
The plug life is getting shorter.

FIG. 1 is a photomicrograph of the cross section of the grain boundary oxidation type scale of the plug obtained in Test No. 37 (magnification: 200).
2 is a photomicrograph (magnification: 200) of the cross-section of the intragranular oxidation-type scale of the plug obtained in Test No. 5. Further, in the example of the present invention in this example, steel containing N, O, P and S in the unavoidable impurities as 0.02% or less, 0.02% or less, 0.035% or less, 0.030% or less was used as a tool material. However, in the composition of the above-mentioned example of the present invention,
It has also been confirmed that even if the contents of O, P and S are slightly above the above range, the corresponding properties superior to those of the conventional materials are exhibited.

[0054]

[Summary of Effects] As described above, according to the present invention, it is possible to realize a hot pipe manufacturing tool (piercer plug, etc.) exhibiting an extremely long service life, and to reduce the manufacturing cost of a seamless pipe. Industrially useful effects such as a significant reduction can be brought about.

[Brief description of the drawings]

FIG. 1 is a photograph of a metal structure showing a typical example (test number 37) of a grain boundary oxidation type scale observed with a microscope.

FIG. 2 is a photographic diagram of a metal structure showing a typical example (test number 5) of an intragranular oxidation-type scale observed with a microscope.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidenori Kinugasa, 1850 Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Works (72) Inventor Kiyoshi Hasegawa, 1-13 Shinjuku-cho, Kawagoe-shi, Saitama In-house stock company (72) Inventor Tetsuji Noguchi 5-13-1 Shinjuku-cho, Kawagoe City, Saitama Prefecture In-house stock company Shinhokoku Steel Co., Ltd. (56) Reference JP-A-4-74848 (JP, A)

Claims (9)

(57) [Claims] 1. A weight ratio of C: 0.08 to 0.65%, Si:
0.1 to 2.0%, Mn: 0.2 to 3.0%, Ni: 0.2 to 7.0
%, Sol.Al: 0.005 to 0.2%, one or more of Mo and W:
A total of 1.5 to 8.0%, and an amount of 250 to 1000 μm of internal oxidation type on the surface of the steel base body containing the amount satisfying 7W (%) + 8Ni (%) ≤ 56 and the balance being Fe and unavoidable impurities. A hot pipe manufacturing tool having a scale layer. 2. The hot pipe manufacturing tool according to claim 1, wherein the steel substrate also contains Cr: 5.0% or less in weight ratio in place of a part of the remaining components. 3. The hot pipe manufacturing method according to claim 1 or 2, wherein the steel substrate also contains Co: 5.0% or less in weight ratio in place of a part of the remaining components. tool. 4. The steel substrate is one or more of V: 2.0 % or less, Nb: 2.0 % or less, Ti: 2.0 % or less, and Zr: 0.5% or less in weight ratio in place of a part of the remaining components. Is also included,
The hot pipe manufacturing tool according to any one of claims 1 to 3. 5. The steel substrate is characterized in that it also contains B: 0.2% or less by weight instead of a part of the balance component.
The hot pipe manufacturing tool according to any one of 1. 6. The steel substrate is characterized in that it also contains, in place of a part of the remaining components, one or more of Mg, Ca, La, Ce and Y in a weight ratio: 0.5 % or less in total. Yes, claims 1 to 5
The hot pipe manufacturing tool according to any one of 1. 7. N in unavoidable impurities in a steel substrate,
The content of O, P and S is 0.02% by weight.
The hot pipe manufacturing tool according to any one of claims 1 to 6, wherein the tool is regulated to 0.02% or less, 0.035% or less, and 0.030% or less. 8. A weight ratio of C: 0.08 to 0.65%, Si:
0.1 to 2.0%, Mn: 0.2 to 3.0%, Ni: 0.2 to 7.0
%, Sol.Al: 0.005 to 0.2%, one or more of Mo and W:
The total content is 1.5 to 8.0% and the content of 7W (%) + 8Ni (%) ≤ 56 is satisfied, or Cr: 5.0% or less, Co: 5.0% or less, V: 2.0% or less, Nb: 2.0 %
Below, Ti: 2.0% or less, Zr: 0.5% or less, B: 0.2
% Or less, one or more of Mg, Ca, La, Ce and Y: In total
Includes at least one of 0.5% or less, with the balance being Fe
And steel inevitable impurities are formed into a predetermined tool shape, and then 800-
Heat soak for 4 to 10 hours at 1100 ℃, then 50 ℃ / h
A method for producing a hot pipe manufacturing tool, characterized in that an internal oxidation-type scale layer having a thickness of 250 to 1000 μm is formed on the surface by gradually cooling to 800 to 500 ° C. at a cooling rate of r or less. 9. A weight ratio of C: 0.08 to 0.65%, Si:
0.1 to 2.0%, Mn: 0.2 to 3.0%, Ni: 0.2 to 7.0
%, Sol.Al: 0.005 to 0.2%, one or more of Mo and W:
The total content is 1.5 to 8.0% and the content of 7W (%) + 8Ni (%) ≤ 56 is satisfied, or Cr: 5.0% or less, Co: 5.0% or less, V: 2.0% or less, Nb: 2.0 %
Below, Ti: 2.0% or less, Zr: 0.5% or less, B: 0.2
% Or less, one or more of Mg, Ca, La, Ce and Y: In total
Includes at least one of 0.5% or less, with the balance being Fe
And unavoidable impurities, and N, O, P in the impurities
And S content is 0.02% or less, 0.02% or less,
After steel with 0.035% or less and 0.030% or less is formed into a predetermined tool shape, soaking is performed at 800 to 1100 ° C for 4 to 10 hours in an oxidizing atmosphere having an atmospheric oxygen concentration or less, and then 50 ° C / It is characterized in that an internal oxidation type scale layer having a thickness of 250 to 1000 μm is formed on the surface by gradually cooling to 800 to 500 ° C. at a cooling rate of hr or less.
Method for manufacturing hot pipe manufacturing tool.