JP3265022B2 - Method for producing steel and steel pipe with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing steel having excellent corrosion resistance, and more particularly to a method for producing steel and steel pipe having excellent corrosion resistance in an exhaust system of an internal combustion engine such as an automobile or a ship. .

[0002]

2. Description of the Related Art Conventionally, in an exhaust system of an internal combustion engine mainly for an automobile, steel in which ordinary steel is plated with aluminum or zinc has been used in order to suppress corrosion from the inside or outside. However, in recent years, a catalyst or the like for purifying exhaust gas has been provided in an exhaust system for the purpose of suppressing environmental pollution, so that such a plated steel material has become insufficient in corrosion resistance. Therefore, steel containing 5 to 10% of Cr for the purpose of improving the corrosion resistance of a steel base is disclosed in
No. 143240 and Japanese Patent Application Laid-Open No. 63-143241. However, along with the extension of the service period and the warranty period of vehicles in recent years, high-grade stainless steel further containing about 18% of Cr or further adding Mo is widely used in exhaust systems. However, even such a high-grade stainless steel does not always have sufficient corrosion resistance, for example, local corrosion like pitting may occur. Such high-grade stainless steels are made of Cr or M
The processability is poor due to the large amount of o contained, and in order to form a complicated shape such as an exhaust system member, it is extremely difficult to manufacture, and the manufacturing process becomes extremely complicated. There is a drawback that it becomes expensive. Also, the material cost is high.

[0003] As a representative of the above-mentioned exhaust system, Cr is generally used.
In steels containing a certain amount of steel, local corrosion tends to occur when the environment becomes severe. To improve the resistance to corrosion, it is very common to increase the Cr or Mo content in order to improve the resistance to corrosion. It was a means.

[0004]

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide a method for producing steel and a steel pipe having high resistance to a corrosive environment such as an exhaust system of an internal combustion engine at a low cost. .

[0005]

In order to achieve the above object, the present inventors have developed various viewpoints in order to develop a method for producing steel and a steel pipe having excellent corrosion resistance in a corrosive environment such as an exhaust system. Has been considered since. First, the present inventors examined the corrosion environment of the exhaust system, and found that corrosion of the exhaust system of the internal combustion engine occurs in an environment in which chlorides, sulfate ions, and the like contained in the exhaust gas are heated to 80 to 150 ° C. I found it. Furthermore, as a result of various investigations on means for improving corrosion resistance in the corrosive environment, Cr was reduced to 5.5 to 9.9%, contrary to conventional stainless steel.
It has been found that steel to which 0.3 to 3.0% of Al is added exhibits extremely excellent corrosion resistance in a corrosive environment such as an exhaust system. Furthermore, the present inventors have continued their studies as a better steel, and found that C and N of steel containing 5.5 to 9.9% of Cr and 0.3 to 3.0% of Al were reduced. It is effective in improving corrosion resistance and workability, that Si and Mn are appropriate as deoxidizing and strengthening elements, and that Cu, Mo, W, Sb, and Ni are added to the above steel alone or in combination. It has been found that better corrosion resistance can be obtained.

Further, the present inventors have continued to study a method for producing such steel at low cost, and as a result, when high Cr steel is converted into a steel strip from a steel slab and finally subjected to recrystallization annealing or further pipe forming. It has been found that if the process conditions are selected precisely, a steel or steel pipe suitable for such purpose can be obtained.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) By weight%, Si: 0.01% or more and less than 1.2%,
Mn: 0.02 to 2.0%, Cr: 5.5 to 9.9
%, Al: 0.3 to 3.0%,
C: 0.02% or less, P: 0.03%
Below, S: 0.01% or less, N: 0.
This is a method for producing steel having excellent corrosion resistance, characterized in that high Cr steel slabs, which are reduced to not more than 02% and the balance of Fe and unavoidable impurities are formed into steel sheets sequentially in the following steps. After heating the billet to a temperature of 1150-1300 ° C,
A step of hot-rolling a hot strip having a plate thickness of 1.6 mm or more and 6.0 mm or less at a rolling completion temperature of 680 ° C. or more, and winding it as a steel strip; A step of forming a cold-rolled steel strip by adding cold rolling, the above-mentioned cold-rolled steel strip is heated to a temperature of 760 ° C. or more for 0.5 min.
(2) In the step (1), before cold rolling the hot-rolled strip steel, the heat treatment of maintaining the temperature at 740 ° C. or more for 0.5 min or more. And (3) a high Cr steel slab to which the invention of the above item (1) or (2) is applied, further comprising:
, Cu: 0.05-3.0%, Mo: 0.
05 to 3.0%, W: 0.05 to 3.0%,
Sb: 0.01 to 0.5%, Ni: 0.01 to 2.0
%, One or more of the following: (4) In the high Cr steel slab targeted by each of the inventions of the above (1) to (3), further as an additional component ,
Rare earth elements: 0.001 to 0.1% by weight, C
a: 0.0005 to 0.03% of one or two steels.

Further, the present invention provides: (5) Si: 0.01% or more and less than 1.2% by weight.
Mn: 0.02 to 2.0%, Cr: 5.5 to 9.9
%, Al: 0.3 to 3.0%,
C: 0.02% or less, P: 0.03%
Below, S: 0.01% or less, N: 0.
A method for producing a steel pipe having excellent corrosion resistance, characterized in that high Cr steel slabs, which are reduced to not more than 02% and the balance of Fe and unavoidable impurities are sequentially formed into steel pipes in the following steps.

After heating the billet to a temperature of 1150-1300 ° C., hot rolling to a hot strip having a plate thickness of 1.6 mm or more and 6.0 mm or less with a rolling completion temperature of 680 ° C. or more and winding it as a strip. A step of subjecting the hot-rolled steel strip to a cold-rolled steel strip by cold rolling with a cumulative rolling reduction of 40% or more, and applying the cold-rolled steel strip to a temperature of 760 ° C. or more for 0.5 min.
The above-mentioned heat treatment for holding and recrystallizing. After cutting the above-mentioned steel strip into a predetermined width, the both ends of the steel strip are welded by electric resistance welding while being continuously formed into a cylindrical shape by roll forming. The process of forming a sewn steel pipe.
(6) The total strain ε applied to the steel from the stage of the steel strip recrystallized by the process of the invention of the above (5) until the steel pipe is formed as an ERW steel pipe is represented by the thickness of the steel strip. t (mm) and ε ≦ t / D + 0.06 with respect to the final outer diameter D (mm) of the ERW steel pipe.
(7) In the above (5) or (6), before cold-rolling the hot-rolled strip steel, the steel pipe is heated to a temperature of 740 ° C. or more for 0.5 min.
This is a method for producing a steel pipe having excellent corrosion resistance, which is recrystallized by performing the heat treatment held as described above. (8) In the invention of the above (5), (6) or (7), the steel pipe is formed as an electric resistance welded steel pipe, Replace the steel pipe on the outside diameter with 7
(9) A method for producing a steel pipe having excellent corrosion resistance, wherein the steel pipe is recrystallized by performing a heat treatment at a temperature of 60 ° C. or more for 1 minute or more, and (9) the method described in the above (5), (6), (7) or (8). In the high Cr steel slab targeted by the present invention, Cu: 0.05 to 3.0% by weight as an additional component,
Mo: 0.05 to 3.0%, W: 0.05 to
3.0%, Sb: 0.01 to 0.5%, N
i: 0.01 to 2.0%, which is a method for producing a steel pipe having excellent corrosion resistance containing one or more kinds of (10) the above (5), (6), (7), (8) ) Or high-Cr steel slab which is the object of the invention of item (9), and as an additional component, by weight%, rare earth element: 0.001
-0.1%, Ca: 0.0005-0.03%, 1
Kind Code: A1 A method for producing a steel pipe having excellent corrosion resistance containing one or two kinds.

[0010]

First, the reason why the range of each component is limited in the high Cr steel slab to which the method of the present invention is applied will be described. Si: The addition of Si as a deoxidizing agent and a strengthening element to steel containing 5.5% or more of Cr is effective. However, if the content is less than 0.01%, the deoxidizing effect is not sufficient, and .
When the content is more than 2%, the effect is no longer saturated and the processability is reduced. Therefore, the content range is limited to 0.01% or more and less than 1.2%.

Mn: Mn is required as a deoxidizing agent for steel,
Although it is necessary to contain 0.02% or more, even if it exceeds 2.0%, the effect is not only saturated anymore, but if Mn is excessively contained, the workability is reduced. The content is 2.0%.

Cr: Cr must be contained in an amount of 5.5% or more in order to ensure corrosion resistance.
%, The cost is unnecessarily increased and the workability is reduced. Therefore, the upper limit content is set to 9.9%.

Al: Al is C in order to secure corrosion resistance.
It is an important element in addition to r. As described above, if the content of Al is less than 0.3%, the effect of suppressing the occurrence of pitting corrosion is not sufficient. Since the effect saturates, but reduces workability, the Al content is limited to 0.3% or more and 3.0% or less.

C, N: C and N reduce the workability of the steel sheet, and also, C forms carbides with Cr to lower the corrosion resistance, and N lowers the toughness. It is desirable that the content is as small as possible, and the upper limit content is 0.02% in each case.

P: If P is present in a large amount, the toughness is reduced. Therefore, it is desirable that P is small, and the upper limit content is 0.03%.
And S: Since the presence of a large amount of S also lowers the pitting corrosion resistance, a smaller amount is desirable, and the upper limit content is 0.01%.

The basic components of steel having excellent corrosion resistance to be produced by the method of the present invention are described above. In the present invention, one or more of the following elements may be added as required. Steels with further improved properties are also targeted. Cu: Cu contains not less than 5.5% of Cr and 0.3 of Al
Addition of 0.05% or more to steel containing not less than 0.05% has the effect of improving the resistance to general corrosion. However, adding more than 3.0% not only saturates the effect, but also reduces the hot workability. Therefore, the upper limit content is 3.0%.

Mo: Mo has an effect of suppressing the occurrence and growth of pitting corrosion when added to steel containing 5.5% or more of Cr and 0.3% or more of Al by 0.05% or more. 3.
Even if added in excess of 0%, not only the effect is saturated, but also the workability is reduced, so the upper limit content is set to 3.0%.

W: W also contains 5.5% or more of Cr and contains Al
When the addition of 0.05% or more to steel containing 0.3% or more has the effect of suppressing the occurrence and growth of pitting corrosion,
%, The effect is not only saturated but also lowers the workability. Therefore, the upper limit content is set to 3.0%.

Sb: When Sb is added to steel containing 5.5% or more of Cr and 0.3% or more of Al in an amount of 0.01% or more, Sb has an effect of improving resistance to pitting corrosion and general corrosion. , More than 0.5% decreases the hot workability, so the upper limit content is 0.5%.

Ni: Ni has an effect of suppressing pitting corrosion by adding 0.01% or more to steel containing 5.5% or more of Cr and 0.3% or more of Al. If added in excess, not only the effect is saturated, but also the hot workability is reduced and the cost is increased, so the upper limit content is 2.0%.
And

Rare earth element (REM), Ca: Rare earth element and Ca are elements effective for improving hot workability and pitting corrosion resistance.
When the content is less than 0.001% for Ca and less than 0.0005% for Ca, the effect is not sufficient.
In the case of a, if added in excess of 0.03%, coarse non-metallic inclusions are respectively formed and hot workability and pitting corrosion resistance are degraded. Therefore, the upper limit content is 0.1% for rare earth elements,
Ca is set to 0.03%. In the present invention, the rare earth element has an atomic number of 57-71 and 89-10.
Indicates the third element and Y.

In steels and steel pipes to which the method of the present invention is applied, Nb, V, Ti, Zr, Nb, V, Ti, Zr, and the like are added as impurities mixed from scrap and the like, or for the purpose of adjusting toughness and workability. Ta, Hf, B and the like can be contained, all of which are objects of the present invention, and can be added according to the purpose.

Next, the steps of the present invention and the reasons for limiting the steps will be described. Billet heating temperature: Heat the billet uniformly to its center,
It is necessary to ensure hot workability in hot rolling. However, heating above 1300 ° C. is not preferable because slab burn-through occurs and material loss due to the formation of oxide scale becomes significant and yield decreases. on the other hand,
If the heating temperature is lower than 1150 ° C., the deformation resistance in hot rolling becomes too large. Therefore, the billet heating temperature is 11
50 to 1300 ° C.

Hot rolling: For hot rolling, a normal plate rolling process can be used. In order to satisfy the properties as a sheet while securing the productivity in the subsequent cold rolling, it is appropriate that the sheet thickness after hot rolling is 1.6 mm or more and 6.0 mm or less. Further, from the viewpoint of productivity in the subsequent cold rolling, the shape of the plate is a hot coil.

Rolling Completion Temperature: For the purpose of ensuring ductility after hot rolling, the end temperature of hot rolling needs to be 680 ° C. or higher.

Cold Rolling: In order to secure good workability when manufacturing parts and steel pipes using the steel sheet according to the method of the present invention, the cumulative rolling reduction in cold rolling must be 40.
% Or more. If this cumulative rolling reduction is satisfied, a normal rolling process can be applied as cold rolling, and it is possible to select a thickness before cold rolling according to the thickness of the final product.

Heat treatment: In order to ensure good workability when manufacturing parts and steel pipes using the steel sheet according to the method of the present invention, in order to heat-treat the steel sheet after cold rolling, a temperature of 760 ° C. or more is required. However, if the holding temperature is lower than 760 ° C., it takes a very long time to recrystallize, so that it is difficult to apply industrially. If the heating time is less than 0.5 min, the required heating temperature becomes too high, which causes oxidation of the steel sheet and deterioration of the surface properties. If the above conditions are satisfied, any of a continuous heat treatment facility for steel sheets and a batch (box) heat treatment facility may be used as the heat treatment.

Forming and ERW Welding on Steel Pipes: A normal ERW steel pipe manufacturing process can be applied to forming and ERW welding on steel pipes, and a predetermined width is set according to the outer diameter required as a steel pipe for an automobile exhaust system. After cutting the steel strip, it can be formed into a steel pipe by roll forming and electric resistance welding.

In the present invention, the following steps may be further added in addition to the above steps, if necessary, for the following reasons.

[0030] Total strain: When a steel pipe is required to have particularly high workability for bending, expanding, or the like, from the stage of the strip steel recrystallized in the heat treatment process after the cold rolling, the electric resistance welding is performed. Total strain ε added to steel before it is made into a steel pipe
It is effective to reduce as much as possible. It is manufactured so that ε is not more than t / D + 0.06 with respect to the plate thickness t (mm) of the Cr-reduced stainless steel and the final outer diameter D (mm) of the ERW steel pipe to which the method of the invention is applied. If this is the case, a steel pipe with particularly excellent workability can be obtained.

Heat treatment before cold rolling: According to the study of the present inventors, for example, as a steel pipe for an automobile exhaust system or a bent pipe,
Particularly when high workability is required, it is more effective to recrystallize the hot-rolled strip before cold rolling. For this purpose, the holding temperature needs to be 740 ° C. or more, and the holding time needs to be 0.5 min or more. By performing such heat treatment before cold rolling, the final product can be obtained. Particularly excellent workability can be obtained even at the steel pipe stage. If the above conditions are satisfied, any of a continuous heat treatment facility for steel sheets and a batch (box) heat treatment facility may be used as the heat treatment.

Post-pipe heat treatment: When workability as an ERW steel pipe is extremely strictly required, the pipe is formed as an ERW pipe, the steel pipe having the final outer diameter is annealed, and the steel pipe as the final outer diameter is formed. It is effective to remove the strain introduced up to this point, and for this purpose, the holding temperature needs to be 760 ° C. or more, and the holding time needs to be 1 min or more.

In the production process of the steel sheet produced by the method of the present invention, descaling or pickling of the steel sheet is performed for the purpose of obtaining the surface properties of the cold-rolled sheet and the predetermined properties as a steel pipe. It does not deviate from the essence of the method of the present invention at all, and all of them are included in the scope of the present invention, and if necessary, a usual descaling step or pickling step may be added. it can.

The steel produced according to the method of the present invention may be used in various kinds of corrosive environments such as an exhaust system of an internal combustion engine, an environment in which an aqueous solution containing chloride and sulfate ions is exposed to high temperatures, and an environment in which heating and cooling are repeated. Can be applied to

[0035]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below.
A steel strip having the components shown in Table 1 was melted and hot-rolled into a steel strip having a thickness of 4.0 mm, and then subjected to cold rolling and heat treatment under the conditions shown in Table 2 to produce a steel strip. In the hot rolling, the billet heating temperature was 1250 ° C. The present invention
No. In Nos. 9 and 12, heat treatment was performed before cold rolling under the conditions shown in Table 2. In Comparative Example No. 18 is SUS410
Steel corresponding to L.

Subsequently, test pieces were taken from these steels,
A room temperature tensile test and a corrosion resistance test were performed. The room temperature tensile test was carried out in accordance with JIS Z2241 using a No. 13B tensile test piece specified in JIS Z2201, and the ductility, that is, the elongation at break was examined as an index of workability. The corrosion resistance test is
A test piece having a width of 50 mm and a length of 70 mm was sampled and subjected to a corrosion test. In the corrosion test, the test piece was immersed in 50 cm ³ of an aqueous solution containing 100 ppm of sulfate ions, 100 ppm of chloride ions, and 500 ppm of bicarbonate ions as ammonium salts, and the test solution was completely maintained by keeping the test container in an atmosphere at 130 ° C. Evaporation and volatilization as one cycle, 2
A test in which 0 cycles were repeated was performed. This corresponds to the corrosion conditions of the vehicle exhaust system. The maximum pit depth of the test specimen after the test was measured and used as the test result. If the maximum pit depth is 0.2 mm or less, the result is ◎.
Those with a maximum pit depth of more than 0.4 mm and less than 0.8 mm are marked with X, those with a maximum pit depth of more than 0.4 mm and less than 0.4 mm are marked with X, and those with a maximum pit depth of more than 0.8 mm are marked with XX. As a matter of fact,
The results are shown in Table 2 together with the results of the room temperature tensile test.

[0037]

[Table 1]

[0038]

[Table 2]

As is clear from Table 2, the present invention is an example of the present invention in which components are selected and production conditions are selected based on the method of the present invention.
No. Nos. 1 to 12 have excellent ductility at normal temperature and also have excellent corrosion resistance in severe corrosive environments. On the other hand, it is a comparative example
No. In Nos. 13 to 16 and 18, the elongation at break at normal temperature is small, the workability is poor, or the corrosion resistance is insufficient, and none of them satisfy the required properties. In Comparative Example No. No. 17 generates cracks by cold rolling due to insufficient ductility after hot rolling,
Could not be steel.

(Example 2) Steel having the components shown in Table 3 was melted, and hot-rolled under the conditions shown in Table 4 to obtain a steel strip having a thickness of 4.0 mm. After being subjected to cold rolling and heat treatment, a steel pipe having the dimensions shown in Table 2 was formed by forming and electric resistance welding. In the hot rolling, the billet heating temperature was 1260 ° C. Invention Example No. 1
In Nos. 9 and 30, heat treatment was performed before cold rolling under the conditions shown in Table 4; In No. 28, heat treatment was performed under the conditions shown in Table 4 after forming the ERW steel pipe. Example No. In Nos. 29 to 30, the total strain applied to the steel from the heat treatment after the cold rolling to the completion of the ERW steel pipe forming was controlled to the value shown in Table 4. In the comparative examples, No. No. 35 is a case where SUS410L which is a conventional steel is applied.

Subsequently, test specimens were taken from these steel pipes and subjected to a room temperature tensile test and a corrosion resistance test. The room temperature tensile test was performed using a No. 12A tensile test piece specified in JIS Z2201 in accordance with JIS Z2241, and ductility, that is, elongation at break was examined as an index of workability. Also,
In the corrosion resistance test, a test piece having a width of 15 mm and a length of 70 mm was sampled from a steel pipe and subjected to a corrosion test.

The corrosion test and the measurement of the pit depth performed after the test were performed in the same manner as in Example 1, and the results are shown in Table 4.

[0043]

[Table 3]

[0044]

[Table 4]

As is apparent from Table 4, N is an example of a steel pipe in which components are selected and production conditions are selected based on the method of the present invention.
o. Nos. 19 to 30 have excellent ductility at normal temperature and extremely excellent corrosion resistance. On the other hand, in Comparative Example No. 31-
In the case of No. 35, the elongation at break at normal temperature is small and workability is poor,
The high-temperature strength is insufficient or the corrosion resistance is poor, and none of them satisfy the required properties.

[0046]

As described above, the present invention provides a method for producing steel having excellent corrosion resistance, and is extremely significant in contributing to industrial development.

Continuation of the front page (51) Int.Cl. ⁷ identification code FI C22C 38/60 C22C 38/60 (58) Field surveyed (Int.Cl. ⁷ , DB name) C21D 8/00-8/10 C21D 9 / 08 C21D 9/46-9/48 C22C 38/00-38/60

Claims (10)

(57) [Claims] 1. wt%, Si: 0.01% or more and less than 1.2%, Mn: 0.02-2.0%, Cr: 5.5-9.9%, Al: 0.3- C: 0.02% or less, P: 0.03% or less, S: 0.01% or less, N: 0.02% or less, with the balance being Fe and unavoidable impurities High Cr consisting of
A method for producing steel having excellent corrosion resistance, wherein a billet is sequentially formed into a steel plate in the following steps. After heating the billet to a temperature of 1150-1300 ° C,
Rolling completion temperature of 680 ° C or more and sheet thickness of 1.6mm or more and 6.0
hot rolling to a hot strip of not more than mm, and winding as a steel strip, a step of applying the cold rolling of the hot rolled steel strip having a cumulative rolling reduction of 40% or more to a cold rolled steel strip, Cold rolled steel strip is heated to 760 ℃ or more for 0.5min.
A step of subjecting to the above-mentioned heat treatment for recrystallization. 2. The steel with excellent corrosion resistance, wherein the hot-rolled steel strip according to claim 1 is recrystallized by subjecting it to a heat treatment at a temperature of 740 ° C. or more for 0.5 min or more before cold rolling. Manufacturing method. 3. The high chromium slab according to claim 1, further comprising, as an additional component, Cu: 0.05 to 3.0%, Mo: 0.05 to 3.0%, W: 0. 0.05 to 3.0%, Sb: 0.01 to 0.5%, Ni: 0.01 to 2.0%, steel having excellent corrosion resistance characterized by containing one or more of the following: Manufacturing method. 4. The high-Cr steel slab according to claim 1, 2, or 3, further comprising, as an additional component, 0.001 to 0.1% by weight of a rare earth element, 0.0005 to 0.03% of Ca, A method for producing steel having excellent corrosion resistance, comprising one or two of the following. 5. In weight%, Si: 0.01% or more and less than 1.2%, Mn: 0.02-2.0%, Cr: 5.5-9.9%, Al: 0.3- C: 0.02% or less, P: 0.03% or less, S: 0.01% or less, N: 0.02% or less, with the balance being Fe and unavoidable impurities High Cr consisting of
A method for producing a steel pipe having excellent corrosion resistance, wherein a steel slab is sequentially formed into a steel pipe in the following steps. After heating the billet to a temperature of 1150-1300 ° C,
Rolling completion temperature of 680 ° C or more and sheet thickness of 1.6mm or more and 6.0
hot rolling to a hot strip of not more than mm, and winding as a steel strip, a step of applying the cold rolling of the hot rolled steel strip having a cumulative rolling reduction of 40% or more to a cold rolled steel strip, Cold rolled steel strip is heated to 760 ℃ or more for 0.5min.
A step of subjecting to the above-mentioned heat treatment for recrystallization. A step of cutting the above-mentioned steel strip into a predetermined width, welding the both ends of the steel strip by electric resistance welding while continuously forming the steel strip into a cylindrical shape by roll forming, and forming a pipe as an electric resistance welded steel pipe. 6. The total strain ε applied to the steel from the stage of the steel strip recrystallized by the process of claim 5 to the steel pipe as an ERW pipe is determined by the thickness t (mm) of the steel strip. ), Ε ≦ t / D + 0.06 with respect to the final outer diameter D (mm) of the ERW steel pipe.
The method for producing a steel pipe having excellent corrosion resistance according to claim 5, characterized in that: 7. The steel sheet according to claim 5, wherein before the hot-rolled strip is cold-rolled, a heat treatment is performed at a temperature of 740 ° C. or more for 0.5 minutes or more to recrystallize. Steel pipe manufacturing method. 8. A steel pipe according to claim 5, 6 or 7, wherein the steel pipe having a final outer diameter is heat-treated at a temperature of 760 ° C. or more for 1 minute or more to be recrystallized. A method for manufacturing steel pipes with excellent corrosion resistance. 9. The high chromium slab according to claim 5, 6, 7 or 8, further comprising: Cu: 0.05 to 3.0%, Mo: 0.05 to 3.0% by weight. , W: 0.05-3.0%, Sb: 0.01-0.5%, Ni: 0.01-2.0%, Corrosion resistance characterized by containing one or more of the following: Excellent method of manufacturing steel pipe. 10. The high chromium steel slab according to claim 5, 6, 7, 8 or 9, further comprising, as an additional component, 0.001 to 0.1% by weight of a rare earth element, 0.0005 to 0.05% of Ca. A method for producing a steel pipe excellent in corrosion resistance, characterized by containing one or two kinds of 0.03%.