JPH06212256A - Production of steel and steel pipe excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To produce steel and a steel pipe of the exhaust system of an internal combustion engine high in corrosion resistance at a low cost by reducing the content of C and N in steel in which the content of Cr is reduced to specified value and contg. specified value of Al. CONSTITUTION:A high Cr slab having a compsn. contg., by weight, 0.01 to 1.2% Si, 0.02 to 2.0% Mn, 5.5 to 9.9% Cr and 0.3 to 3.0% Al and in which the content of C is reduced to <=0.02%, P to <=0.03%, S to <=0.01% and N to <=0.02%, and the balance Fe with inevitable impurities is formed, This slab is heated to 1150 to 1300 deg.C and is subjected to hot rolling into a hot strip in such a manner that the rolling finishing temp. is regulated to >=680 deg.C and the sheet thickness is regulated to 1.6 to 6.0mm. Successively, cold rolling is executed to regulate the cumulative draft to >=40%. This cold rolled band steel is subjected to heat treatment of holding to >=760 deg.C for >=30sec.

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 the exhaust system of an internal combustion engine mainly for automobiles, in order to suppress corrosion from the inner surface or the outer surface, steel obtained by plating ordinary steel with aluminum or zinc has been used. However, in recent years, the exhaust system is equipped with a catalyst for purifying exhaust gas for the purpose of suppressing environmental pollution, and thus the corrosion resistance of such plated steel materials has become insufficient. Therefore, a steel containing 5 to 10% of Cr for the purpose of improving the corrosion resistance of the steel base is disclosed in JP-A-63-63.
-143240 and JP-A-63-143241. However, along with the extension of the service life and warranty period of vehicles in recent years, high-grade stainless steel further containing Cr up to about 18% or further adding Mo is often used in the exhaust system. However, even such a high-grade stainless steel may not always have sufficient corrosion resistance, since local corrosion like pitting may occur. In addition, such high-grade stainless steel is made of Cr or M.
Since a large amount of o is contained, the workability is poor, and in order to form a complicated shape such as an exhaust system member, it is extremely difficult to manufacture, and the manufacturing process is remarkably complicated. It has the drawback of becoming expensive. And the material cost is high.

As a representative of the above exhaust system, Cr is generally used.
In a steel containing a certain amount of steel, local corrosion is likely to occur when the environment becomes harsh, and in order to improve resistance to corrosion as a means against this, it is a very general technical matter to increase the content of Cr or Mo. It was a means.

[0004]

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

[0005]

In order to achieve the above object, the present inventors have various viewpoints for developing a method for producing steel and a steel pipe having excellent corrosion resistance in a corrosive environment including an exhaust system. I have been considering from. First, the present inventors examined the corrosive environment of the exhaust system, and found that the corrosion of the internal combustion engine exhaust system occurs in an environment in which chlorides, sulfate ions, etc. contained in the exhaust gas are heated to 80 to 150 ° C. I found it. Furthermore, as a result of various studies on means for improving corrosion resistance in the corrosive environment, Cr was reduced to 5.5 to 9.9%, which is completely opposite to that of conventional stainless steel.
It has been found that the steel to which Al is added in an amount of 0.3 to 3.0% exhibits extremely excellent corrosion resistance in a corrosive environment including an exhaust system. Further, as a result of further studies by the present inventors as a superior steel, as a result of reducing C and N of a steel containing 5.5 to 9.9% Cr and 0.3 to 3.0% Al. It is effective in improving corrosion resistance and workability, Si and Mn are suitable as deoxidizing and strengthening elements, and 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 inventors of the present invention continued to study a method for producing such a steel at low cost, and as a result, when finally recrystallizing annealing a high Cr steel from a steel strip to a strip steel, or further forming a pipe. It has been found that a steel or a steel pipe suitable for such a purpose can be obtained by precisely selecting the process conditions.

The present invention has been made on the basis of such findings, and the gist thereof is as follows.
That is, (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 to 3.0%,
C: 0.02% or less, P: 0.03%
Hereinafter, S: 0.01% or less, N: 0.
It is a method for producing steel with excellent corrosion resistance, characterized in that high Cr steel slabs with a balance of Fe and unavoidable impurities reduced to 02% or less are successively formed into steel plates in the following steps. After heating the billet to a temperature of 1150-1300 ° C.,
A step of hot rolling to 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 as a strip steel. The above hot-rolled strip steel has a cumulative rolling reduction of 40% or more. A step of applying cold rolling to obtain a cold rolled steel strip, the cold rolled steel strip is heated to a temperature of 760 ° C. or higher for 0.5 min.
The step of performing a heat treatment for holding the above for recrystallization, and (2) the heat treatment of holding the temperature of 740 ° C. or more for 0.5 min or more before cold rolling the hot rolled steel in the item (1). A method for producing a steel having excellent corrosion resistance, which comprises subjecting to recrystallization, and (3) in the high Cr steel slab targeted by the invention of the item (1) or (2), as an additional component, a further weight%
And Cu: 0.05 to 3.0%, Mo: 0.
05-3.0%, W: 0.05-3.0%,
Sb: 0.01 to 0.5%, Ni: 0.01 to 2.0
%, One or two or more of them are contained in the high Cr steel slab targeted by the inventions of (4) above (1) to (3). ,
% Rare earth element: 0.001-0.1%, C
a: 0.0005 to 0.03%, a method for producing a steel containing one or two kinds.

The present invention further provides (5)% by weight of Si: 0.01% or more and less than 1.2%,
Mn: 0.02-2.0%, Cr: 5.5-9.9
%, Al: 0.3 to 3.0%,
C: 0.02% or less, P: 0.03%
Hereinafter, S: 0.01% or less, N: 0.
A method for producing a steel pipe having excellent corrosion resistance, characterized in that high Cr steel billets reduced to 02% or less and containing the balance Fe and unavoidable impurities are sequentially formed into steel pipes in the following steps.

After heating the steel slab to a temperature of 1150 to 1300 ° C., it is hot-rolled into a hot strip having a rolling completion temperature of 680 ° C. or more and a plate thickness of 1.6 mm or more and 6.0 mm or less, and wound as a strip steel. A step of cold rolling the above hot-rolled steel strip by cold rolling at a cumulative rolling reduction of 40% or more, the above cold-rolled steel strip at a temperature of 760 ° C or higher for 0.5 min
The above heat treatment for holding and recrystallizing, after cutting the above strip steel into a predetermined width, while continuously forming it into a cylindrical shape by roll forming, both ends of the steel strip are welded by electric resistance welding The process of making as a sewing steel pipe.
In addition, (6) the total strain amount ε added to the steel from the stage of the steel strip recrystallized by the step of the invention of the above (5) to the time it is manufactured as an electric resistance welded steel pipe is defined by the plate thickness of the steel strip. t (mm), final outer diameter D (mm) of ERW steel pipe, ε ≦ t / D + 0.06
(7) The method for producing a steel pipe having excellent corrosion resistance according to (7) above, in (5) or (6), the cold rolling of the hot rolled steel strip is performed at a temperature of 740 ° C. or higher for 0.5 min.
A method for producing a steel pipe having excellent corrosion resistance, which is obtained by subjecting to the above heat treatment for recrystallization, comprising: The steel pipe in the outer diameter is 7
A method for producing a steel pipe having excellent corrosion resistance, which comprises performing heat treatment for holding at a temperature of 60 ° C. or more for 1 min or more to recrystallize, and (9) above (5), (6), (7) or (8) In the high Cr steel slab targeted by the present invention, as an additional component, further, by weight%, Cu: 0.05 to 3.0%,
Mo: 0.05-3.0%, W: 0.05-
3.0%, Sb: 0.01 to 0.5%, N
i: 0.01 to 2.0%, and a method for producing a steel pipe having excellent corrosion resistance, containing one or more of (10) the above (5), (6), (7), (8) ) Or in the high Cr steel slab targeted by the invention of item (9), the rare earth element: 0.001 as an additional component in a weight percentage.
~ 0.1%, Ca: 0.0005-0.03%, 1 of
It is a method for producing a steel pipe having excellent corrosion resistance, which contains one or two kinds.

[0010]

First, the reason why the range of each component is limited in the high Cr steel bill targeted by the method of the present invention will be described. Si: Si is effective to be added as a deoxidizing agent and a strengthening element to steel containing 5.5% or more of Cr, but if the content is less than 0.01%, the deoxidizing effect is not sufficient and 1 ．
If the content is 2% or more, the effect is already saturated and the workability is deteriorated. Therefore, the content range is limited to 0.01% or more and less than 1.2%.

Mn: Mn is necessary as a deoxidizing agent for steel,
It is necessary to contain 0.02% or more, but even if the content exceeds 2.0%, the effect is already saturated, and if Mn is contained excessively, the workability is deteriorated. The content is 2.0%.

Cr: Cr is required to be contained in an amount of 5.5% or more in order to secure corrosion resistance.
If it is contained in excess of%, not only the cost is unnecessarily increased, but also the workability is deteriorated, so the upper limit content is made 9.9%.

Al: Al is C in order to secure corrosion resistance.
It is an important element along with r, and as described above, if the Al content is less than 0.3%, the effect of suppressing the occurrence of pitting corrosion is not sufficient, while if it is added in excess of 3.0%, Since the effect is saturated but the workability is lowered, the Al content is limited to 0.3% or more and 3.0% or less.

C, N: C and N deteriorate the workability of the steel sheet, and C forms a carbide with Cr to deteriorate the corrosion resistance. Further, N deteriorates the toughness. It is preferable that the content is as small as possible, and the upper limit content is 0.02% in each case, and the smaller the content, the better.

P: If P is present in a large amount, it lowers the toughness, so it is desirable that the amount be small, and the upper limit content is 0.03%.
And S: S is also preferable if it is present in a large amount, since it lowers the pitting corrosion resistance, and the upper limit content is made 0.01%.

The above is the basic composition of the steel excellent in corrosion resistance, which is the object of production by the method of the present invention, but in the present invention, one or more of the following elements may be added, if necessary. , Steel with improved properties is also targeted. Cu: Cu contains 5.5% or more of Cr and contains 0.3% of Al.
%, The addition of 0.05% or more to steel has the effect of improving the resistance to general corrosion, but addition of more than 3.0% saturates the effect and reduces hot workability. Therefore, the upper limit content is made 3.0%.

Mo: Mo has the 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 in an amount of 0.05% or more. 3.
Even if added over 0%, not only the effect is saturated but also the workability is lowered, so the upper limit content is made 3.0%.

W: W also contains 5.5% or more of Cr and is Al
Addition of 0.05% or more to steel containing 0.3% or more of Al has the effect of suppressing the occurrence and growth of pitting corrosion.
If added in excess of%, not only the effect will be saturated but also the workability will be deteriorated, so the upper limit content is made 3.0%.

Sb: Sb also has the effect of improving resistance to pitting corrosion and general corrosion when added in an amount of 0.01% or more to steel containing Cr in an amount of 5.5% or more and Al in an amount of 0.3% or more. If added in excess of 0.5%, the hot workability is deteriorated, so the upper limit content is made 0.5%.

Ni: Ni has the effect of suppressing pitting corrosion when added in an amount of 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 will be saturated, but also the hot workability will be reduced and the cost will increase, so the upper limit content is 2.0%.
And

Rare earth elements (REM), Ca: Rare earth elements and Ca are elements that are effective in improving hot workability and pitting corrosion resistance.
If it is less than 01% and Ca is less than 0.0005%, the effect is not sufficient, and if it is less than 0.1% for rare earth elements, C
a), when added in excess of 0.03%, coarse non-metallic inclusions are generated and conversely deteriorate hot workability and pitting corrosion resistance, so the upper limit content is 0.1% for rare earth elements,
Ca is 0.03%. In the present invention, the rare earth element has an atomic number of 57 to 71 and 89 to 10.
Refers to element 3 and Y.

In the steel and steel pipe to which the method of the present invention is applied, in addition to the above components, Nb, V, Ti, Zr, Nb, V, Ti, Zr, Ta, Hf, B and the like can be contained, and these are all objects of the present invention and can be added according to the purpose.

Next, the process of the present invention and the reason for limiting the process 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 the slab will be burned down and the material loss due to the formation of oxide scale will be significant and the yield will be reduced. on the other hand,
If the heating temperature is less than 1150 ° C, the deformation resistance in hot rolling becomes too large. Therefore, the billet heating temperature is 11
It is set to 50 to 1300 ° C.

Hot rolling: For hot rolling, a conventional plate rolling process can be used. In order to satisfy the properties as a plate while ensuring the productivity in the subsequent cold rolling, it is appropriate that the plate 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: The end temperature of hot rolling must be 680 ° C. or higher for the purpose of ensuring ductility after hot rolling.

Cold rolling: When manufacturing parts and steel pipes using the steel sheet according to the method of the present invention, in order to ensure good workability, the cumulative rolling reduction is 40 in cold rolling.
It must be at least%. If this cumulative reduction ratio is satisfied, a normal rolling process can be applied as cold rolling, and it is possible to select the plate thickness before cold rolling according to the plate thickness of the final product.

Heat treatment: At the time of heat-treating a steel sheet after cold rolling, a temperature of 760 ° C. or higher is required in order to ensure good workability when manufacturing parts, steel pipes, etc. using the steel sheet according to the method of the present invention. However, if the holding temperature is lower than 760 ° C, it takes a very long time to recrystallize, and it is difficult to industrially apply the holding time. This is because if it 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. As long as the above conditions are satisfied, either a continuous heat treatment equipment for steel sheets or a batch (box) heat treatment equipment may be used as the heat treatment.

Forming into steel pipe and ERW welding: A normal ERW steel pipe manufacturing process can be applied to forming into a pipe and ERW welding, and the pipe has a predetermined width depending on the outer diameter required as a steel pipe for automobile exhaust system. The steel strip can be cut, and then roll-formed and electric resistance welded to form a steel pipe.

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

Total strain amount: When particularly high workability is required for bending, expanding, etc., as a steel pipe, from the stage of re-crystallized strip steel in the heat treatment process after cold rolling to electric resistance welding Total strain amount ε added to steel before being manufactured as a steel pipe
Is effective as much as possible. The method of the present invention shall be applied so that ε is t / D + 0.06 or less with respect to the plate thickness t (mm) of the Cr-reduced stainless steel and the final outer diameter D (mm) of the electric resistance welded steel pipe. If so, a steel pipe having particularly excellent workability can be obtained.

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

Post pipe heat treatment: When workability as an electric resistance welded steel pipe is required extremely severely, pipe forming as an electric resistance welded steel pipe is performed, and a steel pipe having a final outer diameter is annealed to obtain a steel pipe having a final outer diameter. It is effective to remove the strain introduced up to this point. For this purpose, the holding temperature must be 760 ° C. or higher, and the holding time must be 1 min or longer.

In the production process of the steel sheet produced by the method of the present invention, the descaling treatment or the pickling treatment of the steel sheet is performed for the purpose of obtaining the surface texture of the cold-rolled sheet and the predetermined characteristics of the steel pipe. It does not depart from the essence of the method of the present invention, and any of them is included in the scope of the present invention. If necessary, a normal descaling step or a pickling step may be added. it can.

The steel produced according to the method of the present invention has various 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 temperature, and an environment in which heating and cooling are repeated. Can be applied to.

[0035]

【Example】

Example 1 An example of the present invention will be described below.
Steel having the components shown in Table 1 was melted and hot-rolled into a strip steel having a thickness of 4.0 mm, and then cold-rolled and heat-treated 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 under the conditions shown in Table 2 before cold rolling. In addition, Comparative Example No. 18 is SUS410
Steel corresponding to L.

Subsequently, test pieces were taken from these steels,
A normal 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 ductility, that is, 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. For the corrosion test, the test piece was completely immersed by immersing the test piece up to half in 50 cm ³ of an aqueous solution containing 100 ppm of sulfate ion, 100 ppm of chloride ion and 500 ppm of bicarbonate ion as an ammonium salt, and keeping the whole test container in an atmosphere of 130 ° C. One cycle is to evaporate and volatilize into 2
A test was repeated with 0 cycles. This corresponds to the corrosive conditions of the automobile exhaust system. The maximum pitting depth of the test piece after the test was measured and used as the test result. ◎ for maximum pitting depth of 0.2 mm or less, maximum pitting depth of 0.
Those with a maximum pitting depth of more than 2 mm and 0.4 mm or less are marked with ○, those with a maximum pitting depth of more than 0.4 mm and less than 0.8 mm are marked with x, and those with a maximum pitting 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 apparent from Table 2, it is an example of the present invention in which the components are selected and the production conditions are selected based on the method of the present invention.
No. 1 to 12 are excellent in ductility at room temperature and also excellent in corrosion resistance in a severe corrosive environment. On the other hand, it is a comparative example
No. In Nos. 13 to 16 and 18, the elongation at break at room temperature was small and the workability was poor, or the corrosion resistance was insufficient, and none of them satisfied the required characteristics. In addition, Comparative Example No. No. 17 has cracks in cold rolling due to insufficient ductility after hot rolling,
Could not be steel.

(Example 2) Steels having the components shown in Table 3 were melted and hot-rolled under the conditions shown in Table 4 to obtain strip steels having a thickness of 4.0 mm, which were then cooled under the conditions shown in Table 2. After hot 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. Inventive Example No. 1
In Nos. 9 and 30, heat treatment was performed before cold rolling under the conditions shown in Table 4, and No. In No. 28, heat treatment was performed under the conditions shown in Table 4 after the ERW steel pipe was manufactured. Example No. In Nos. 29 to 30, the total strain amount applied to the steel after the post-cold rolling heat treatment and before the completion of the production of the electric resistance welded steel pipe was controlled to the values shown in Table 4. Further, among the comparative examples, No. No. 35 is a case where SUS410L which is a conventional steel is applied.

Subsequently, test pieces 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 carried out in accordance with JIS Z2241 using a No. 12A tensile test piece specified in JIS Z2201, and ductility, that is, breaking elongation was examined as an index of workability. Also,
For 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 pitting depth after the test were carried out in the same manner as in Example 1, and the results are also shown in Table 4.

[0043]

[Table 3]

[0044]

[Table 4]

As is clear from Table 4, N is an example of a steel pipe in which components are selected and manufacturing conditions are selected based on the method of the present invention.
o. Nos. 19 to 30 have excellent ductility at room temperature and very excellent corrosion resistance. On the other hand, No. which is a comparative example. 31-
No. 35, the elongation at break at room temperature is small and the workability is poor,
The high temperature strength is insufficient or the corrosion resistance is inferior, and neither satisfies the required characteristics.

[0046]

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

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C22C 38/38

Claims (10)

[Claims] 1. By weight%, Si: 0.01% or more and less than 1.2%, Mn: 0.02-2.0%, Cr: 5.5-9.9%, Al: 0.3- 3.0%, C: 0.02% or less, P: 0.03% or less, S: 0.01% or less, N: 0.02% or less, and the balance Fe and unavoidable impurities Consisting of high Cr
A method for producing steel having excellent corrosion resistance, characterized in that steel pieces are sequentially formed into steel sheets in the following steps. After heating the billet to a temperature of 1150-1300 ° C.,
When the rolling completion temperature is 680 ° C or more, the plate thickness is 1.6 mm or more and 6.0
a step of hot-rolling to a hot strip of mm or less and winding as a strip steel, a step of cold-rolling the hot-rolled strip steel having a cumulative rolling reduction of 40% or more into a cold-rolled strip steel, Cold-rolled steel strip at a temperature above 760 ℃ for 0.5min
The step of recrystallizing by performing the above heat treatment. 2. A steel excellent in corrosion resistance, characterized in that the hot-rolled steel strip according to claim 1 is recrystallized by being heat-treated at a temperature of 740 ° C. or higher for 0.5 min or longer before cold rolling. Manufacturing method. 3. The high Cr steel slabs according to claims 1 and 2 further contain, as an additional component, by weight, Cu: 0.05 to 3.0%, Mo: 0.05 to 3.0%, W: 0. Steel having excellent corrosion resistance, characterized in that it contains one or more of 0.05 to 3.0%, Sb: 0.01 to 0.5%, and Ni: 0.01 to 2.0%. Manufacturing method. 4. The high Cr steel slabs according to claims 1, 2 and 3 as an additional component, further in weight%, rare earth element: 0.001 to 0.1%, Ca: 0.0005 to 0.03%, 1. A method for producing steel having excellent corrosion resistance, which comprises one or two of the above. 5. By weight%, Si: 0.01% or more and less than 1.2%, Mn: 0.02-2.0%, Cr: 5.5-9.9%, Al: 0.3- 3.0%, C: 0.02% or less, P: 0.03% or less, S: 0.01% or less, N: 0.02% or less, and the balance Fe and unavoidable impurities Consisting of high Cr
A method for producing a steel pipe having excellent corrosion resistance, characterized in that steel pieces are sequentially formed into steel pipes in the following steps. After heating the billet to a temperature of 1150-1300 ° C.,
When the rolling completion temperature is 680 ° C or more, the plate thickness is 1.6 mm or more and 6.0
a step of hot-rolling to a hot strip of mm or less and winding as a strip steel, a step of cold-rolling the hot-rolled strip steel having a cumulative rolling reduction of 40% or more into a cold-rolled strip steel, Cold-rolled steel strip at a temperature above 760 ℃ for 0.5min
The step of recrystallizing by performing the above heat treatment. A step of cutting the above strip steel into a predetermined width and then continuously forming a cylindrical shape by roll forming while welding both ends of the steel strip by electric resistance welding to form an electric resistance welded steel pipe. 6. The total strain amount ε added to the steel from the stage of the steel strip recrystallized by the process of claim 5 to the time it is manufactured as an electric resistance welded steel pipe is defined by the plate thickness t (mm ), Ε ≦ t / D + 0.06 with respect to the final outer diameter D (mm) of the electric resistance welded steel pipe
The method for producing a steel pipe having excellent corrosion resistance according to claim 5, wherein 7. The corrosion-resistant steel according to claim 5 or 6, characterized in that, before cold-rolling the hot-rolled steel strip, it is re-crystallized by being heat-treated at a temperature of 740 ° C. or higher for 0.5 min or longer. Steel pipe manufacturing method. 8. The method according to claim 5, 6 or 7, wherein a steel pipe formed as an electric resistance welded steel pipe and having a final outer diameter is subjected to a heat treatment of holding it at a temperature of 760 ° C. or more for 1 min or more to recrystallize it. A method for manufacturing a steel pipe having excellent corrosion resistance. 9. The high Cr steel slab as an additional component according to claim 5, 6, 7 or 8, further comprising Cu: 0.05 to 3.0% and Mo: 0.05 to 3.0% by weight. , W: 0.05 to 3.0%, Sb: 0.01 to 0.5%, Ni: 0.01 to 2.0%, and one or more types of corrosion resistance. Excellent steel pipe manufacturing method. 10. The high Cr steel piece according to claim 5, 6, 7, 8 or 9, further comprising, by weight, a rare earth element: 0.001 to 0.1%, and Ca: 0.0005. 0.03% of 1 type or 2 types is contained, The manufacturing method of the steel pipe excellent in corrosion resistance characterized by the above-mentioned.