JPH0835010A - Production of steel and steel tube, excellent in high temperature characteristic - Google Patents

Abstract

PURPOSE:To produce a steel having high strength at high temp. and excellent in oxidation resistance by subjecting a steel, in which the ranges of the amounts of alloying elements, an OR value, and an MC value are respectively specified, to hot rolling at specific temp., to coiling, and then to holding at a temp. not lower than the Ms point. CONSTITUTION:This steel has a composition which consists of, by weight, 0.3-3.0% Si, 0.02-2% Mn, 3.5-9.9% Cr, 0.01-1.0% Al, <=0.03% C, <=0.03% P, <=0.03% S, <=0.02% N, and the balance Fe with inevitable impurities and in which the OR value given by equation I is regulated to >=6.5. Further, V, Ti, Zr, and Hf are added, and the MC value given by equation II is regulated to >=0. A slab of this high Cr steel is heated to 1100-1300 deg.C, and hot rolling is finished at >=850 deg.C. The resultant steel strip is coiled and then held at a temp. not lower than the Ms point of the steel for >=60min, by which the metallic structure is essentially formed into ferrite. While roll-forming the steel strip into cylindrical state, both ends of the steel strip are welded to form into a steel tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing steel and a steel pipe having excellent high temperature characteristics, and more specifically, to an exhaust manifold attached to an automobile engine, an exhaust gas purifying catalyst holding substrate, and an automobile exhaust system. The present invention relates to a method for producing low cost steel or steel pipe having excellent properties such as oxidation resistance, strength and workability as the steel pipe of the front part of the above.

[0002]

2. Description of the Related Art In recent years, there is an increasing number of cases in which an exhaust manifold (hereinafter referred to as "exhaust manifold") of an automobile uses a stainless steel exhaust manifold instead of a conventional cast iron exhaust manifold. This is because the exhaust manifold made of stainless steel can make the wall thickness thinner, which is very useful for reducing the weight of the automobile. Austenitic stainless steel such as JIS (Japanese Industrial Standard) SUS310 has excellent heat resistance and workability, and is therefore widely used for general heat resistance applications. However, this type of steel is generally expensive, and has a large thermal expansion coefficient, and thus has a drawback of being inferior in thermal fatigue characteristics.

On the other hand, ferritic stainless steels generally have a smaller coefficient of thermal expansion than austenitic stainless steels and therefore have excellent thermal fatigue properties, and are therefore suitable for applications such as exhaust manifolds that undergo a temperature cycle of heating and cooling. Can be said. Therefore, SUS410L, SUS430LX and the like defined in JIS G4305 have already been put to practical use as exhaust manifolds and the like. Furthermore, for example, JP-A-64-
In Japanese Patent No. 8254 and Japanese Patent Laid-Open No. 2-175843, C
A ferritic stainless steel containing a large amount of r and having improved high temperature strength has been proposed.

However, these ferritic stainless steels are very expensive, and when used in exhaust manifolds,
There is a drawback that the cost is significantly higher than that of the cast iron exhaust manifold, and the cost is high even for an exhaust gas purification catalyst.
Further, since it contains a large amount of Cr, it cannot be said that the workability is good, and in order to form a complicated shape such as an exhaust manifold or an exhaust gas purification catalyst, the manufacturing process becomes complicated and the processing cost is high. There is a drawback that

[0005]

In view of such a situation, the present invention provides a steel and a steel pipe for use in an automobile exhaust system, etc., which has high strength at high temperature, excellent oxidation resistance and good workability. It is intended to provide a method of manufacturing at a cost.

[0006]

In order to achieve the above object, the inventors of the present invention develop a steel having excellent oxidation resistance and high temperature strength in a high temperature environment including an exhaust system and a method for producing the steel. Therefore, we have studied from various viewpoints.

As a result of various studies to achieve the above object, the inventors of the present invention added Si to steel containing Cr in a relatively small amount of 3.5 to 9.9% as opposed to the conventional stainless steel. By doing so, it is possible to greatly improve the oxidation resistance at high temperatures, and if the range of the amount of alloying elements is strictly controlled so as to satisfy specific conditions, the oxidation resistance at high temperatures will be further improved. V, Ti, Zr, Ta, Hf
It was found that the addition of Al improves the workability, and the addition of Mo and W further improves the high temperature strength.

Further, the inventors of the present invention continued to study a method for producing such steel and steel pipe at low cost, and as a result, when converting high Cr steel from a billet into a hot-rolled steel, or further forming a pipe. In doing so, it was found that a steel or a steel pipe suitable for the above purpose can be obtained if the process conditions are selected precisely.

The present invention has been made based on these findings, and is characterized by the following matters. (1) By weight, Si: 0.3 to 3.0%, Mn:
0.02-2.0%, Cr: 3.5-9.9%, Al:
0.01-1.0%, C: 0.03% or less, P: 0.0
3% or less, S: 0.03% or less, N: 0.02% or less,
Containing the balance Fe and unavoidable impurities, the OR value given by the following equation is 6.5 or more, OR value = [% Cr] +4 [% Si] -17 [% C] -3
[% N] Further, high Cr whose MC value given by the following equation is 0 or more.
MC value = 12 + 18 [% N] +15 [% C] +0.6
[% Ta] +0.3 [% Mn]-([% Cr] +2 [%
Si] +2 [% W] +2 [% Hf] +3 [% Mo] +5
[% Nb] +5 [% V] +5 [% Zr] +8 [% Ti]
+11 [% Al] +17 [% S] +33 [% P]) After heating to a temperature of 1100 to 1300 ° C, 850 ° C
It is characterized in that hot rolling is completed at the above temperature to form a strip steel, which is wound and then held at a temperature of Ms point of the steel or more for 60 minutes or more to substantially change the metal structure to ferrite. And a method for producing steel having excellent high temperature characteristics. (2) In the steel described in (1) above, after hot-rolled steel is wound up, it is held at a temperature of 650 ° C. or higher for 30 minutes or longer, and the metallographic structure is substantially ferrite. A method of manufacturing steel with excellent properties. (3) The high Cr steel slab according to (1) or (2) above may further contain V, Ti, N as an additional component in a weight percentage.
A method for producing a steel having excellent high-temperature properties, characterized by containing 0.01% or more and 1.0% or less in total of one or more of b, Zr, Ta, and Hf. (4) The high Cr steel piece according to any one of (1) to (3) above is 0.03% or more, 3.0% or more as a total of one or two kinds of Mo and W in addition by weight as an additional component. % Or less, a method for producing a steel having excellent high temperature characteristics. (5) Weight%, Si: 0.3 to 3.0%, Mn:
0.02-2.0%, Cr: 3.5-9.9%, Al:
0.01-1.0%, C: 0.03% or less, P: 0.0
3% or less, S: 0.03% or less, N: 0.02% or less,
Containing the balance Fe and unavoidable impurities, the OR value given by the following equation is 6.5 or more, OR value = [% Cr] +4 [% Si] -17 [% C] -3
[% N] Further, a high C value in which the MC value given by the following equation is 0 or more.
r steel billet, MC value = 12 + 18 [% N] +15 [% C] +0.6
[% Ta] +0.3 [% Mn]-([% Cr] +2 [%
Si] +2 [% W] +2 [% Hf] +3 [% Mo] +5
[% Nb] +5 [% V] +5 [% Zr] +8 [% Ti]
+11 [% Al] +17 [% S] +33 [% P]) After heating to a temperature of 1100 to 1300 ° C, 850 ° C
The hot rolling was completed at the above temperature to form a strip steel, which was wound and then held at a temperature of the Ms point or higher of the steel for 60 minutes or longer to substantially change the metal structure to ferrite. A method for producing a steel pipe having excellent high-temperature properties, characterized in that the steel strip is cut into a predetermined width and then the steel strip is welded at both ends while continuously forming a cylindrical shape by roll forming. (6) In the method for manufacturing a steel pipe according to (5) above,
In the winding process of hot strip steel, at a temperature of 650 ° C or higher after winding, 3
A method for producing a steel pipe having excellent high-temperature properties, which is retained for 0 minutes or more and the metal structure of the steel strip is substantially ferrite. (7) The high Cr steel billet according to (5) or (6) above may further contain V, Ti, N as an additional component in a weight percentage.
A method for producing a steel pipe having excellent high-temperature characteristics, characterized by containing one or more of b, Zr, Ta, and Hf in a total amount of 0.01% or more and 1.0% or less. (8) The high Cr steel piece according to any one of (5) to (7) further contains, as an additive component, one or two kinds of Mo and W in a total amount of 0.03% or more and 3. 0% or less is contained, The manufacturing method of the steel pipe excellent in the high temperature characteristic characterized by the above-mentioned. (9) In the method for manufacturing a steel pipe according to any one of (5) to (8), the total strain amount ε added to the steel from the stage of the steel strip to the time it is manufactured as a steel pipe is defined by the plate thickness t of the steel strip. (Mm),
With respect to the final outer diameter D (mm) of the steel pipe, ε ≦ t / D + 0.
The method for producing a steel pipe having excellent high temperature characteristics, characterized in that (10) The method for producing a steel pipe having excellent high-temperature characteristics according to (5) to (9), wherein both ends of the steel strip are welded by electric resistance welding to produce an electric resistance welded steel pipe. (11) The method for producing a steel pipe having excellent high temperature characteristics according to (5) to (9), wherein both ends of the steel strip are welded by laser welding to produce a steel pipe. (12) The method for producing a steel pipe having excellent high-temperature characteristics according to (5) to (9), wherein the means for welding both ends of the steel strip is a composite welding of electric resistance welding and laser welding.

The present invention will be described in detail below. First,
The reason for limiting the range of each component in the high Cr steel of the present invention will be described. Si: When Si is added in combination with steel containing 3.5% or more of Cr, the effect of improving oxidation resistance at high temperatures is remarkable,
It is also an element necessary to secure the ferrite structure. If the content is less than 0.3%, the effect is not sufficient, and if the content exceeds 3.0%, toughness and workability at room temperature decrease, so the content range is 0.3% to 3.0%. Limited to

Mn: Necessary as a deoxidizing agent for steel,
It is necessary to contain 02% or more. Even if the content exceeds 2.0%, not only is the effect saturated,
If Mn is excessively contained, it is difficult to secure a ferrite single-phase structure, so the upper limit content is 2.0%.

It is necessary to add Cr: Si in combination to contain 3.5% or more in order to secure the required corrosion resistance and oxidation resistance. However, if the content exceeds 9.9%, not only the cost is unnecessarily increased, but also the workability is deteriorated, so the upper limit content is made 9.9%.

Al: 0.01% or more is required to be added as a deoxidizing agent for steel, and it is a useful element for securing a ferrite structure. If added in excess of 1.0%, coarse oxide-based inclusions are formed and workability is reduced, so the content is limited to 0.01-1.0%.

C and N: C and N form a compound with Cr to reduce the oxidation resistance and also the workability.
Further, it is desirable that the content is small as it becomes a factor to inhibit the formation of ferrite structure, and the upper limits of the content are 0.03% for C and 0.02% for N.

P: If present in a large amount, the hot workability and the workability are deteriorated, so it is preferable that the amount is small, and the upper limit content is 0.03%. S: If present in a large amount, the hot workability and the workability are deteriorated, so it is preferable that the amount be small, and the upper limit content is 0.03%.
And

OR value: As a combination of the contents of the respective elements,
The OR value defined by the following formula must be 6.5 or more. OR value = [% Cr] +4 [% Si] -17 [% C] -3
[% N] This is a finding based on the results of the present inventors' detailed study on the optimum component composition and combination for obtaining the characteristics as the steel for automobile exhaust system. If the OR value is less than 6.5, the oxidation resistance at high temperature, which is the most important property for exhaust system steel, is insufficient. For example, assuming that the operating temperature in an automobile exhaust system is 800 ° C or higher, the OR
If the value is less than 6.5, abnormal oxidation occurs and it cannot be used.
In order to withstand use as an automobile exhaust system, it is necessary to secure an OR value of 6.5 or more. According to the study by the present inventors, the steel containing 3.5% or more of Cr has the effect that Si has a four-fold effect on the oxidation resistance as compared with Cr.
It has been found that both C and N form a compound with Cr and impair the oxidation resistance.

MC value: In the present invention, it is further necessary that the MC value given by the following equation is 0 or more. MC value = 12 + 18 [% N] +15 [% C] +0.6
[% Ta] +0.3 [% Mn]-([% Cr] +2 [%
Si] +2 [% W] +2 [% Hf] +3 [% Mo] +5
[% Nb] +5 [% V] +5 [% Zr] +8 [% Ti]
+11 [% Al] +17 [% S] +33 [% P])

This is a finding based on the results of the present inventors' detailed examination of the manufacturing method for obtaining the characteristics as the steel for automobile exhaust system. When the MC value is smaller than 0, a ferrite structure exists in the metal during hot rolling, and the metal structure at the end of hot rolling becomes a mixed structure of ferrite and austenite. When the ferrite structure is present during hot rolling,
The hot workability and the workability after winding are remarkably deteriorated, resulting in a poor yield and a lack of workability required as a material for an automobile exhaust system. If the MC value is 0 or more, it is possible to realize an austenite single phase state, and it is possible to manufacture steel having excellent properties as an automobile exhaust system material by precisely controlling the manufacturing conditions. The weighting of each component in the formula of MC value is obtained by the present inventors from the results of various component studies.

The basic composition and the constraining conditions of the steel for automobile exhaust system, which is the object of the present invention, have been described above. In the present invention, the following elements are further added as necessary to further improve the characteristics. It also covers steel. Needless to say, even when the following components are added, the conditions of OR value and MC value must be satisfied.

V, Ti, Nb, Zr, Ta, Hf: These elements are effective in improving workability when they are compounded and added to steel containing 3.5% or more of Cr. The total content of one or more of these elements is 0.01%
If it is less than the above, the effect is not sufficiently exhibited. On the other hand, 1.0%
If it is added in excess, the effect will be saturated, but the cost will be unnecessarily increased, and coarse precipitates may be formed to lower the toughness.
Therefore, the total content of one or more of these elements is 0.01% or more and 1.0% or less.

Mo and W: These elements have a Cr content of 3.5.
%, It is effective to further increase the high temperature strength when added in combination with steel. If the total content of one or two kinds of Mo and W is less than 0.03%, the effect is not sufficiently exhibited. On the other hand, even if added in excess of 3.0%, the effect is already saturated, but it only unnecessarily increases the cost, so one or two of Mo or W is added.
The total content of the seeds is 0.03% or more and 3.0% or less.

In the steel of the present invention, in addition to the above-mentioned components, Ni, Cu, B and other components are contained as impurities mixed in from scraps or raw materials or for the purpose of adjusting toughness, workability and the like. You can Further, a rare earth element, Ca can be contained for the purpose of improving hot workability and improvement of oxidation resistance at high temperature, and the present invention can be achieved even if Ni, Cu, B, rare earth element, Ca or the like is added. It does not deviate from the range. The rare earth elements referred to here are elements having atomic numbers 57 to 71 and 89 to 103 and Y.

Next, the manufacturing conditions of the present invention and the reasons for limitation thereof will be described. Billet heating temperature: Uniformly heat the billet to its center,
It is necessary to secure hot workability in hot rolling. However, heating above 1300 ° C. is not preferable because melting of the slab occurs and material loss due to the formation of oxide scale becomes significant and the yield decreases. On the other hand, if the heating temperature is less than 1100 ° C, the deformation resistance in hot rolling becomes too large. Therefore, the billet heating temperature is set to 1100 to 1300 ° C.

Hot rolling: For hot rolling, a conventional plate rolling process can be used. Rolling end temperature: For the purpose of ensuring ductility after hot rolling, the rolling end temperature needs to be in a temperature range in which the metal structure is substantially an austenite single phase, and the rolling end temperature is 8
Must be above 50 ° C. In the present invention, the hot working strain is released by the γ → α transformation after the end of hot rolling to achieve high ductility. The accumulated hot working strain is not released and the workability of the hot rolled sheet deteriorates. Strictly speaking, the temperature range of the austenite single phase differs depending on the component composition of the steel, the hot working conditions, etc., but in the steel within the range of the present invention, it is generally 850 ° C. or higher, and more preferably 9 or more.
By setting the temperature to 00 ° C. or higher, the austenite single phase state can be substantially realized.

Cooling after hot rolling: As described in the previous section, in the present invention, the working strain accumulated during hot rolling is released by the γ → α transformation after the end of hot rolling, and the hot rolled sheet is used. Has achieved high ductility. If the temperature becomes lower than the Ms point while the γ → α transformation after the hot rolling is incomplete, martensite is generated and the ductility of the hot rolled sheet is significantly reduced. Therefore, after completion of hot rolling, it is necessary to hold at a temperature of Ms point or higher for at least 60 minutes or more to make the metal structure ferrite. However, the holding temperature does not necessarily have to be constant, and even if the strip steel is in the cooling process, the purpose can be achieved if it is above the Ms point, so after the hot rolling is finished, wind the strip steel at a high temperature. The strip steel temperature may stay above the Ms point for 60 minutes or more.

Winding temperature: The optimum holding temperature and time strictly differ depending on the chemical composition of the steel, etc., but according to the results of studies by the present inventors, the steel of the present invention has a temperature of 650 ° C. or higher for 30 minutes. It has been found that a ferrite structure can be obtained with the above retention. At a temperature lower than 650 ° C., the rate of γ → α transformation remarkably decreases, so that the holding time required to obtain the ferrite structure becomes extremely long. Also, 3
If the retention time is less than 0 minutes, the γ → α transformation is not completed. At the same time, the inventors have found that the higher the retention temperature and the longer the retention time, the smaller the variation in ductility, and the retention conditions of 700 ° C. or higher and 60 minutes or longer are more preferable. In these cases as well, the holding temperature does not necessarily have to be constant, so if the strip steel is wound at a high temperature, the purpose can be achieved in the cooling process. The winding temperature at this time depends on the size and weight of the steel strip, but is preferably 750 ° C. or higher.

Forming and Welding of Steel Pipes: Conventional steel pipe manufacturing processes can be applied to forming and welding of steel pipes. A steel strip is cut into a predetermined width according to the outer diameter required for a steel pipe for an automobile exhaust system, and then roll-formed and welded to produce a steel pipe. As the welding, ordinary electric resistance welding, ordinary laser welding, or combined welding of electric resistance welding and laser welding can be used.

In the present invention, the total strain amount at the time of pipe making is further limited according to the degree of workability required for the steel pipe, and the reason is as follows. According to a study by the present inventors, for example, as a steel pipe for an automobile exhaust system, when particularly high workability is required for bending or expanding, it is manufactured as a steel pipe from the stage of the strip steel obtained by hot rolling. It is effective to reduce as much as possible the total strain ε added to the steel before being piped. The plate thickness t of high Cr steel targeted by the present invention
(Mm), with respect to the final outer diameter D (mm) of the steel pipe, ε is t
If the steel pipe is manufactured so as to have a ratio of /D+0.03 or less, a steel pipe having particularly excellent workability can be obtained.

In the manufacturing process of the steel sheet or steel pipe manufactured according to the present invention, it is not necessary to subject the steel sheet or steel pipe to descaling treatment or pickling treatment for the purpose of obtaining the surface properties of the steel sheet or predetermined characteristics of the steel pipe. The present invention does not depart from the essence of the present invention and is included in the scope of the present invention. If necessary, a normal descaling step or pickling step can be added.

When the steel produced by the method of the present invention is used as an exhaust manifold, for example, the steel sheet may be produced as a steel sheet, then the steel sheet may be press-formed, and further processed / welded to produce the exhaust manifold. Further, the steel plate may be formed into a shape of a steel pipe, for example, as an electric resistance welded steel pipe, and then processed into an exhaust manifold by secondary processing and welding. Steels having a composition and a combination of elements that are limited in the present invention, including other processes, are all targets of the present invention, and an optimal exhaust manifold manufacturing process is selected depending on the cost and constraints of existing manufacturing equipment. No matter which exhaust manufacturing process is selected, it does not depart from the scope of the present invention. When it is used as an exhaust gas purification catalyst supporting substrate, it is generally used as a steel plate, and when it is used as a front pipe, it is generally used as a steel pipe. Therefore, the object of the steel or the steel pipe targeted by the method of the present invention is, of course, not limited to these product shapes.

[0031]

EXAMPLES The present invention will be described below based on examples. Example 1 A steel having the components shown in Table 1 was melted and hot-rolled into a strip steel having a thickness of 2.0 mm. During hot rolling, the billet heating temperature is 1200 ° C., and the hot rolling finish temperature is 900 to 95.
It was set to 0 ° C. Table 2 shows the presence or absence of α phase at the end of hot rolling,
It shows the time when the strip steel temperature after winding is 650 ° C or higher. Test pieces are taken from these steel plates and the JIS standard G
High temperature tensile test at 800 ° C according to 0567 and 80
A continuous high temperature oxidation test at 0 ° C. for 100 hours and a thermal fatigue test with a maximum heating temperature of 800 ° C. were performed. Also,
A tensile test was performed at room temperature to examine the elongation at break.

[0032]

[Table 1]

The results of these tests are also shown in Table 2. In the high-temperature tensile test results in Table 2, ◎ is 0.2% yield strength 22N / mm ² or more, ○ is 17N / mm ² or more, 2
2N / mm less than ^2, also × indicates that it was less than 17N / mm ^2.

[0034]

[Table 2]

In the high temperature oxidation test results, ⊚ indicates an increase in oxidation of less than 1 mg / cm ² , ∘ indicates 1 mg / cm ² or more and less than 10 mg / cm ² , and x indicates 10 mg / cm ^2.
It shows that it was above.

In the results of the thermal fatigue test, ∘ indicates that the number of repetitions up to fracture was 500 times or more, and ×
Indicates less than 500 times.

Regarding workability, ⊚ indicates that the elongation at break was 35% or more, ∘ indicates 30% or more and less than 35%, and x indicates less than 30%.

As is apparent from Table 2, the steel of the present invention, Sample No. 1-9 are high temperature strength, oxidation resistance, heat fatigue resistance,
While excellent in all of the workability, the sample No. which is a comparative example. 10 to 14 are inferior in any of the characteristics.

Example 2 The steel strip of Example 1 was cut and formed into a steel pipe by roll forming and welding. Electric welding was used for all welding, and the dimensions of the steel pipe were an outer diameter of 38.1 mm and a wall thickness of 2.0 mm. Table 3 shows the total strain amount ε applied to the steel from the stage of the steel strip to the time when it is manufactured as a steel pipe. Test pieces were taken from these steel pipes and the same tests as in Example 1 were performed. The test results are also shown in Table 3. The meanings of the symbols in Table 3 are the same as in Example 1.

[0040]

[Table 3]

As is clear from Table 3, the steel pipe of the present invention, Sample No. 1 to 9 are excellent in high temperature strength, oxidation resistance, heat fatigue resistance and workability, while
Sample No. which is a comparative example. 10 to 14 are inferior in any of the characteristics.

[0042]

As described above, according to the present invention, it is possible to provide a method for manufacturing steel and steel pipe having excellent high temperature properties at low cost.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/00 301 A A 302 Z 38/28

Claims (12)

[Claims] 1. Si: 0.3 to 3.0% by weight, M
n: 0.02 to 2.0%, Cr: 3.5 to 9.9%, Al: 0.01 to 1.0%, C: 0.03% or less, P: 0.03% or less, S : 0.03% or less, N: 0.02% or less, and the balance Fe and unavoidable impurities, and the OR value given by the following equation is 6.5 or more, OR value = [% Cr ] +4 [% Si] -17 [% C] -3
[% N] Further, high Cr whose MC value given by the following equation is 0 or more.
MC value = 12 + 18 [% N] +15 [% C] +0.6
[% Ta] +0.3 [% Mn]-([% Cr] +2 [%
Si] +2 [% W] +2 [% Hf] +3 [% Mo] +5
[% Nb] +5 [% V] +5 [% Zr] +8 [% Ti]
+11 [% Al] +17 [% S] +33 [% P]) After heating to a temperature of 1100 to 1300 ° C., hot rolling was completed at a temperature of 850 ° C. or higher to form a strip steel, which was wound. After that, hold for 60 minutes or more at a temperature of Ms point of the steel or more,
A method for producing steel having excellent high-temperature properties, characterized in that the metal structure is substantially ferrite. 2. The method for producing steel according to claim 1, wherein
A method for producing a steel having excellent high-temperature properties, characterized in that, after winding the hot-rolled steel, it is held at a temperature of 650 ° C. or higher for 30 minutes or more to make the metal structure substantially ferrite. 3. The high Cr steel slab according to claim 1 or 2, further comprising V, Ti, Nb, Z as an additional component in a weight percentage.
0.0 of 1 or 2 or more of r, Ta and Hf in total
1% or more and 1.0% or less are contained,
A method for manufacturing steel with excellent high temperature properties. 4. The high Cr steel slab according to claim 1, 2 or 3 further comprises, as an additive component, one or two of Mo and W in total of 0.03% or more and 3 or more. 0.0% or less,
A method for producing steel having excellent high-temperature characteristics, characterized by containing it. 5. Si: 0.3-3.0% by weight, M
n: 0.02 to 2.0%, Cr: 3.5 to 9.9%, Al: 0.01 to 1.0%, C: 0.03% or less, P: 0.03% or less, S : 0.03% or less, N: 0.02% or less,
It consists of the balance Fe and unavoidable impurities, and the OR value given by the following equation is 6.5 or more. OR value = [% Cr] +4 [% Si] -17 [% C] -3
[% N] Further, a high C value in which the MC value given by the following equation is 0 or more.
r steel billet, MC value = 12 + 18 [% N] +15 [% C] +0.6
[% Ta] +0.3 [% Mn]-([% Cr] +2 [%
Si] +2 [% W] +2 [% Hf] +3 [% Mo] +5
[% Nb] +5 [% V] +5 [% Zr] +8 [% Ti]
+11 [% Al] +17 [% S] +33 [% P]) After heating to a temperature of 1100 to 1300 ° C., hot rolling was completed at a temperature of 850 ° C. or higher to form a strip steel, which was wound. After that, hold for 60 minutes or more at a temperature of Ms point of the steel or more,
It is characterized in that the metal structure is substantially ferrite, and further, after this steel strip is cut to a predetermined width, the steel strip is welded at both ends to form a steel pipe while being continuously formed into a cylindrical shape by roll forming. , A method of manufacturing a steel pipe having excellent high temperature characteristics. 6. The method for producing a steel pipe according to claim 5, wherein in the step of winding the hot-rolled steel strip, it is held at a temperature of 650 ° C. or higher for 30 minutes or more after the winding to substantially change the metallographic structure of the steel strip. A method for producing a steel pipe having excellent high temperature characteristics, characterized in that ferrite is used as the material. 7. The high Cr steel slab according to claim 5 or 6,
In addition, as an additional component, V, Ti, Nb, and Z are added by weight%.
0.0 of 1 or 2 or more of r, Ta and Hf in total
1% or more and 1.0% or less are contained,
A method for manufacturing a steel pipe having excellent high temperature characteristics. 8. The high Cr steel slab according to claim 5, 6 or 7, further comprising, as an additive component, one or two kinds of Mo and W in a total of 0.03% or more and 3 or more. 0.0% or less,
A method for producing a steel pipe having excellent high temperature characteristics, characterized by containing. 9. The method for manufacturing a steel pipe according to claim 5, 6, 7 or 8, wherein the total strain amount ε added to the steel from the stage of the steel strip to the production of the steel pipe is defined as the strip steel. With respect to the plate thickness t (mm) and the final outer diameter D (mm) of the steel pipe,
t / D + 0.03, The manufacturing method of the steel pipe excellent in the high temperature characteristic characterized by the above-mentioned. 10. An electric resistance welded steel pipe is produced by welding both ends of a steel strip by electric resistance welding.
7. A method for producing a steel pipe having excellent high temperature characteristics according to 7, 8 or 9. 11. The method for producing a steel pipe having excellent high-temperature characteristics according to claim 5, 6, 7, 8 or 9, wherein the both ends of the steel strip are welded by laser welding to produce a steel pipe. 12. A means for welding both ends of a steel strip is a composite welding of electric resistance welding and laser welding.
8. The method for producing a steel pipe having excellent high temperature characteristics according to 8 or 9.