JPH0426739A - Steel for hot pipe making tools and hot pipe making tools - Google Patents

Abstract

PURPOSE:To obtain a steel for a hot tube manufacturing tool excellent in strength, toughness, hot deformation resistance and seizing resistance by specifying the compsn. constituted of C, Si, Mn, Ni, Mo, W, Al and Fe and regulating the content of N, O, P and S in impurities. CONSTITUTION:This is a steel for a hot tube manufacturing tool having a compsn. contg., by weight, <=0.65% to 1.0% C, 0.1 to 2.0% Si, 0.2 to 3.0% Mn, 0.5 to 7.0% Ni, total 1.5 to 8.0% of one or more kinds of Mo and W and 0.005 to 0.2% sol. Al, furthermore contg., at need, one or more kinds among 0.2 to 5.0% Cr, 0.2 to 5.0% Co, 0.1 to 2.0% V, 0.1 to 2.0% Nb, 0.05 to 2.0% Ti, 0.01 to 0.5% Zr, 0.001 to 0.2% B and total 0.01 to 0.5% of one or more kinds among Mg, Ca, La, Ce and Y and the balance Fe with inevitable impurities and in which the content of N, O, P and S in the impurities is each regulated to <=0.02%, <=0.01%, <=0.035% and <=0.030%. By using this steel and forming oxidized scale having 50 to 250mum thickness on the surface, the hot tube manufacturing tool excellent in durability can be obtd.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tool steel suitable for use as a hot pipe forming tool for manufacturing seamless pipes, and a hot pipe forming tool with excellent durability. It is something.

<Prior art and its problems> At present, methods such as the Mannesmann method, plug mill method, and Eugene hot extrusion method are generally known as industrial methods for producing seamless steel pipes. Plugs, guide shoes, and plugs used in plug mill methods.

Hot pipe making tools such as dies used in the Eugene hot extrusion method are used under extremely harsh operating conditions, both in terms of surface temperature and surface pressure, and as a result, the tools are prone to deformation and seizure, making it difficult to extend their service life. had become a major issue. In particular, in recent years, the demand for seamless pipes made of stainless steel and Ni alloys has been increasing, so the above problem has become more urgent.

For example, the material for the Mannesmann drilling plug, which has the harshest operating conditions among the above tools, is "Fe-0,2χG-
0,2χS+ -0,5%Mn -1χCr-2χN+
−1,5χ(M.

+W) Steel (hereinafter, % representing the component ratio is expressed as weight %)
” has been used for boat fishing, but a perforated plug made of this material can withstand 200 bass perforations when the material to be perforated is carbon steel, but it cannot withstand 0.2χC-13XCr steel (
For SUS420) material, at most 3 passes, and further 5US30
When using 4-steel materials, deformation occurs even in one bus.
There was a problem in that stable production could not be achieved without repairs.

Therefore, a predetermined amount of C+Si+Mn was used as the material for pipe making tools.
A proposal was made to extend tool life by applying cast steel containing , Cr, Ni, and B, and subjecting it to nitriding treatment and oxide scale formation treatment (Japanese Patent Laid-Open No. 59-1430).
No. 76).

However, the pipe-making tools obtained by the above method not only have less than satisfactory deformation resistance at high temperatures, but also
Decarburization occurs during oxidation treatment carried out by heating to 00 to 1250°C, leading to softening of the tool surface layer, resulting in deformation and melting damage during hot tube manufacturing.

It was difficult to prevent seizure from occurring.

In addition, we have made improvements to the composition of the steel material for pipe making tools.
There have been several proposals to improve the strength and toughness during use, as well as the ability to form oxide scales and their properties in order to ensure wear resistance and seizure resistance (for example, Japanese Patent Laid-Open No. 1983-1999). 264163, JP-A-63-282241, etc.), none of the above-mentioned JP-A-63-282241 has insufficient deformation resistance at high temperatures, and Cr, Mo, and W are added to improve strength, toughness, and wear resistance. In the case of the steel material according to No. 1982-61264163, if the Cr content is too high, scales of sufficient thickness will not be formed in the oxidation treatment, and the Cr and Mo
It has also been pointed out that when the amount of W added increases, ferrite remains even at the quenching temperature, resulting in insufficient strength at room temperature or high temperature.

Therefore, with these conventional pipe-making tools, especially when performing hot pipe-making of materials with high deformation resistance such as stainless steel or Ni-based alloys (Alloy 825, etc.), the tip of the tool, etc., which is subject to high surface pressure, melts. In addition to being prone to damage, the tool body, which is subjected to severe shear deformation, was prone to seizure (seizure is the majority of damage when the workpiece is stainless steel).
In many cases, the inconvenience of having to discard the tool after only a short amount of use was unavoidable. Here, if the workpiece material is "carbon steel" or "low alloy steel with a Cr content of less than 13%", heating before processing will make the surface (also the inner surface during drilling) rich in lubricity. A scale mainly composed of Fe oxide is generated, which is transferred to the tool surface treated with a lubricating film and lubricates the tool. In the case of alloys, etc., the lubricating scale does not transfer from the workpiece to the tool surface, so the tool inevitably suffers from severe damage.

Moreover, in the case of perforated plugs, the following phenomenon has also become a major problem. In other words, the temperature of the plug surface rises to more than 1 AC point due to drilling, which is a severe process, but for this reason, subsequent cooling (more than air cooling: water cooling is used to increase the frequency of use of the plug with the aim of improving productivity). often)
This is a phenomenon in which the surface becomes hardened, and as this process is repeated every time a hole is drilled, cracks (thermal cracks) form on the surface, resulting in breakage of the plug.

Although it is effective to reduce the strength of the tool and improve its toughness in order to prevent cracking, this method has the disadvantage that deformation and melting damage are more likely to occur.

Therefore, the purpose of the present invention is to provide sufficient strength, toughness, and hot resistance even when making pipes from materials that have high deformation resistance and are prone to seizure, such as stainless steel and Ni-based alloys. The object of the present invention is to provide a hot pipe making tool that exhibits deformation resistance, seizure resistance, and excellent durability.

Means for Solving the Problems> Therefore, the present inventors conducted intensive research to achieve the above object, and as a result, were able to obtain the following knowledge. That is, (al C1M to increase the high temperature deformation resistance of tool steel
Although it is known that the addition of O and W is effective, the addition significantly reduces the toughness during quenching, and there is a risk of breakage due to impact during tool transport or when drilling begins. A possible solution to this problem is to raise the AC1 point of the tool material so that the temperature rise during tube manufacturing that exceeds the AC3 point temperature and causes quenching is limited to the very surface layer of the tool. However, in order to achieve this goal and prevent softening of the parts that are not hardened, Mo,
It is necessary to add a large amount of W.

(bl) Also, it is extremely effective to form a scale layer with a low melting point to prevent seizure, and therefore a Fe oxide layer is preferable as the scale layer, but in order to ensure sufficient lubricity, the scale layer must be It is necessary to have a thickness of 50p or more and to form a dense scale.

The realization of such a scale layer is possible by adding a large amount of Ni to the steel, and the scale layer formed on the surface of the steel containing a relatively large amount of Ni has a high degree of Ni. Concentrated metal flakes are present in a dispersed manner, and the peeling resistance and wear resistance of the scale are greatly improved.

(C) Furthermore, as mentioned above, pipe-making tools suffer from hardening during cooling after pipe-making processing, resulting in high hardness and low toughness of the surface layer, making them susceptible to cracking and thermal cracking. This problem can be solved by adding a large amount of C to lower the Ms point and adjusting the composition so that austenite exists dispersed even at room temperature.

The present invention was made based on the above-mentioned findings, etc. rC: 0.65 to 1.0%, Si: 0.1 to
2.0%.

Mn: 0.2-3.0%, Ni: 0.
5-7.0%.

One or more types of Mo and W: 1.5 to 8.0% in total.

So! ．． Contains Al: 0.005-0.2%, or further contains Cr: 0.2-5.0%, Co: 0.
2-5.0%.

V:Q, l~2.0%, Nb:0.1~2,
0%.

Ti: 0.05-2.0%, Zr:
0.01-0.5%.

B: 0.001-0.2%.

Contains one or more of Mg+ Ca, La, Ce, and Y: 0.01 to 0.5% in total, and the remainder consists of Fe and unavoidable impurities, and N, 0 in the impurities゜The content of P and S is 0.02% or less and 0.01% or less, respectively.
By configuring the steel for hot pipe making tools to have an ingredient composition of 0.035% or less and 0.030% or less, it has excellent high temperature deformation resistance, cracking resistance, and heat cracking resistance that are fully satisfactory as hot pipe making tools. It is characterized by the fact that it has realized a steel for hot pipe making tools that has excellent anti-seizure effects (lubricity, peeling resistance, wear resistance) and is easy to form a skull. ``Durability has been significantly improved by making the hot pipe making tool made of steel with the above-mentioned composition and having an oxide scale lubricating film with a thickness of 50 to 250 mm on the surface.'' ” is also featured.

Next, in the present invention, the reason why the composition of the steel and the thickness of the oxide scale lubricating film formed on the tool surface are limited as described above will be explained in detail along with their effects.

<Function> (A) Composition of steel a) C C is an effective component for improving the high temperature strength of steel materials, but if its content is less than 0.65%, the necessary strength cannot be secured and the toughness is also poor. Furthermore, since a sufficient reduction in the Ms point cannot be expected, a sufficiently dispersed austenite structure cannot be achieved at room temperature, resulting in a "surface layer area that is hardened after pipe making".
The hardness of the steel becomes too high, making it more likely that cracks will occur. In addition, the amount of carbide in the scale layer on the tool surface formed by the oxidation scale treatment is insufficient, resulting in poor lubricity and significant wear and tear during pipe manufacturing. On the other hand, C content is 1.0%
If it exceeds this, the austenite becomes excessive and the strength at room temperature to high temperature decreases, and the tool becomes more likely to suffer from melting damage. Furthermore, when a lubricating scale layer is formed on the tool surface by oxide scale treatment, the metal base in the tool surface layer is severely decarburized, making it impossible to secure the desired surface hardness. Therefore, the C content is 0.65-1
．． It was set as 0%.

In addition, in the steel according to the present invention, it is desirable that the amount of austenite at room temperature is 10 to 30% by volume in view of the balance between strength and toughness. This is because the amount of austenite at room temperature is 1
This is because if it is less than 0% by volume, it tends to be insufficient in toughness, while if it exceeds 30% by volume, it tends to be insufficient in strength.

b) 5t Si is an effective component for deoxidizing, increasing Ac, points, and densifying the oxide scale on the plug surface, but if its content is 0
．． If it is less than 1%, the desired effect cannot be obtained; on the other hand, 2.0%
If the content exceeds 100%, not only will the toughness deteriorate, but also a scale layer of sufficient thickness will not be obtained, leading to insufficient lubrication performance. Therefore, the Si content was determined to be 0.1 to 2.0%.

c) Mn As in the steel of the present invention (when adding a large amount of Mo, W,
Addition of Mn is effective in ensuring a single austenite phase at high temperatures. In this case, the Mn content is 0.2%
If the content is less than 3%, the above effects will not be sufficient, while if the content exceeds 3%, Mn entering the scale will deteriorate the denseness of the scale and increase the melting point of the scale, thereby deteriorating the lubricity. Therefore, the Mn content was determined to be 0.2 to 3%.

d) Ni Ni has the effect of improving the toughness of the hardened phase formed on the surface layer of the tool by cooling after pipe making, and in order to obtain this toughness improvement effect, it is necessary to add 0.5% or more of Ni. It is necessary to ensure the Ni content. Furthermore, Ni added to the steel
remains unoxidized in the "scale layer formed by oxidized scale treatment" and has a composite reinforcing effect that greatly improves the peeling resistance of the scale, and this effect is due to the Ni-containing It becomes noticeable when the amount is 3.0% or more, and 5.
When it exceeds 0%, even more remarkable effects are exhibited. However, 7
．． If Ni is contained in an amount exceeding 0%, the formation of scale will be suppressed, and in addition to deteriorating the lubricity, an excessive amount of austenite will remain at room temperature, resulting in a large decrease in strength. Therefore, the Ni content is 0.5~
It was set at 7.0%.

e) Mo, W Containing one or more of these components in a specific amount or more is extremely effective in improving high-temperature strength, and also increases the Ac point and reduces the hardening of the surface layer of the tool after pipe forming. It also has the effect of reducing the amount of penetration and preventing cracking. These effects are equivalent for MO and W, and if the total amount of (Mo+W) is less than 1.5%, the above effects are insufficient and deformation and melting damage easily occur during pipe manufacturing. On the other hand, Mo,
If the total content of W exceeds 8.0%, ferrite will remain even at high temperatures, and the high temperature strength will not only decrease, but also the toughness. Therefore, the total content of Mo and W was set at 1.5 to 8.0%.

From the viewpoint of toughness, it is more preferable to contain W than MO, and especially in tools where toughness is important, the MOC content is 3.
It is best to suppress it to 5% or less.

f) Sol, AI! sol and AI are effective components as deoxidizing agents. In particular, pipe manufacturing tool materials must maintain high strength at high temperatures.
Therefore, it inevitably has high strength even at room temperature, but in this case, it is important to suppress the amount of oxygen in the steel to ensure toughness, and it is necessary to keep the zero content to at least 1100 pp or less. 0
When the content is 30 ppm or less, the toughness is further improved.

But sof, Aj! If the content is less than 0.005%, the deoxidizing effect is insufficient; on the other hand, if the content exceeds 0.2%, the deoxidizing effect not only becomes saturated, but also reduces the viscosity of molten steel during casting of pipe making tools. This increases the risk of casting defects. Therefore, the sol, AJ) content is 0.005
It was set at ~0.2%.

g> Cr+ Co, v+ Nb, Ti, Zr,
B, MglCa.

La, Ce, Y These components have the effect of improving the toughness of the steel material, the deformation resistance at high temperatures, and the effect of improving the lubrication properties of the scale, so one or more of them may be added if necessary. However, the reason why the content of each component is individually limited numerically is as follows.

Cr Cr is an effective component to particularly densify the oxide scale layer and improve the adhesion of the lubricating film (oxide scale layer), but if its content is less than 0.2%, the desired above effects cannot be obtained. On the other hand, if the content exceeds 5.0%, the oxidation resistance will improve too much, making it impossible to form a lubricating oxide scale layer with a desired thickness.

O Co is a component that exhibits the same toughness improvement effect as Ni and scale peeling resistance improvement effect without significantly lowering Ac, point, especially when its content is 0.2 If the content is less than 5.0%, the desired effect due to the above action cannot be obtained, and on the other hand, if the content exceeds 5.0%, it is not possible to ensure an improvement effect commensurate with the cost increase.

V, Nb, Tt, Zr, M, CaLa
Ce Y All of these components are particularly effective in refining the grains of materials, and have the effect of not only improving the toughness of steel materials but also densifying the scale layer, but their content is limited to the lower limit of each. If the content is less than the above, the desired effect cannot be obtained, while if the content exceeds each upper limit, a brittle phase may precipitate, resulting in deterioration of toughness.

In particular, B has the effect of strengthening the grain boundaries of the tool surface layer, which has become austenite due to being held at high temperatures during tube manufacturing, and improving deformation resistance and deformability at high temperatures. If the content is less than 0.001%, the desired effect due to the above action cannot be obtained, while if the content exceeds 0.062%, the toughness will deteriorate.

h) The content of impurity N is reduced to 0 to prevent defects during melting (solidification).
．． 0.02% or less, and the O, P, and S contents are each reduced to 0.01% or less to ensure the desired toughness.
It is necessary to limit it to 0.035% or less and 0.030% or less.

(B) Thickness of oxide scale on the tool surface If the thickness of the oxide scale formed on the surface of the pipe making tool is less than 50 marks, the lubricity will be insufficient and the desired tool life will not be obtained; When the oxide scale thickness exceeds 250 am, the scale layer becomes porous and easily peels off.
After all, it becomes impossible to ensure a sufficient tool life.

Therefore, the thickness of the oxide scale formed on the surface of the pipe making tool was limited to 50 to 250 mm.

In addition, in order to form the oxide scale with the above-mentioned predetermined thickness, a) casting is performed using steel having the above-mentioned composition as a material.

TI) External milling after casting.

c) After forging, the tool produced by external cutting or other means may be heated and held at 900 to 1200° C. for 1 to 5 hours in the air or in a steam-added atmosphere, and then air-cooled or furnace-cooled.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> First, steel with each chemical composition shown in Table 1 is melted by air melting, vacuum melting, AOD, or VOD process, and after casting, it is externally machined to produce the most severe steel among tools. It is finished in the shape of a plug for drilling holes in Mannesmann pipes, which is used under such conditions.

Then, during tube manufacturing, each of the above-mentioned plugs was heated to 900 to 1200° C. in an atmosphere containing water vapor to generate oxide scale on its surface. The heating temperature and time were adjusted with consideration given to obtaining the best possible oxide scale thickness and adhesion depending on the composition of the steel.

Charpy impact value of each piercing plug obtained in this way (crackability evaluation index value: room temperature test with 2 mU notch)
And the investigation results of compressive deformation resistance value at 1000℃,
It is shown in Table 2 along with the oxide scale thickness.

Next, a drilling test was carried out on 5US420 and 5US304 stainless steel using each of the plugs subjected to the oxide scale formation treatment, and the number of possible drillings (
(excluding repair use), and the results are listed in Table 2 along with the factors that caused the plugs to be discarded.

As is clear from the results shown in Table 2, in the drilling plug made of the steel according to the present invention, it is possible to form an oxide scale with a thickness of 85 to 186 μm, which is very preferable on the lubricating surface. In addition to exhibiting sufficient lubricity and scale peeling resistance, compressive deformation resistance at 1000℃:
It has excellent high-temperature strength of 30 kgf/- or more and impact value at room temperature: 1 kg-m/cn or more and exhibits sufficient tool life, but under the conditions specified in the present invention. In the comparative examples that did not meet the requirements, "tip melting due to low high temperature strength", "cracking due to insufficient toughness", or "seizing due to thin scale layer or insufficient peeling resistance" occurred, resulting in perforation. It can be seen that the number of times is extremely low.

Summary of Effects> As explained above, according to the present invention, excellent durability can be achieved even in hot pipe manufacturing of materials that have high deformation resistance and are prone to seizure, such as high alloy steel, stainless steel, and Ni-based alloys. It is possible to provide a hot pipe-making tool that exhibits the above-mentioned properties, and it is possible to stably supply high-quality seamless pipes industrially, which brings about extremely useful effects industrially.

Claims (3)

[Claims] (1) Weight percentage: C: 0.65-1.0%, Si: 0.1-2.0%, M
n: 0.2-3.0%, Ni: 0.5-7.0%, Mo
and one or more kinds of W: 1.5 to 8.0% in total, sol.
Contains Al: 0.005 to 0.2%, the remainder consists of Fe and unavoidable impurities, and the content of N, O, P, and S in the impurities is 0.02% or less and 0.01%, respectively. Hereinafter, a steel for hot pipe making tools, characterized in that the content is 0.035% or less, 0.030% or less. (2) Weight percentage: C: 0.65-1.0%, Si: 0.1-2.0%, M
n: 0.2-3.0%, Ni: 0.5-7.0%, Mo
and one or more kinds of W: 1.5 to 8.0% in total, sol.
Contains Al: 0.005-0.2%, further Cr: 0.2-5.0%, Co: 0.2-5.0%, V
:0.1-2.0%, Nb:0.1-2.0%, Ti:
0.05-2.0%, Zr: 0.01-0.5%, B:
0.001 to 0.2%, one or more of Mg, Ca, La, Ce, and Y: 0.01 to 0.5% in total, and the remainder is Fe and unavoidable impurities. and the content of N, O, P and S in the impurities is 0.02% or less, 0.01% or less, and 0.
．． 0.035% or less, 0.030% or less steel for hot pipe making tools. (3) A hot pipe making tool made of the steel according to claim 1 or 2 and having an oxide scale lubricating film with a thickness of 50 to 250 μm on its surface.