JPH1099595A - Stainless steel clothes-drying bar and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel clothes-drying bar which is made very strong and has a good flexure resistance. SOLUTION: This clothes-drying bar is constituted of a high strength stainless steel pipe which includes 20-95vol.% of martensite which is made by cold-rolling chrome stainless steel and heating it to an (α+γ) two-phase region of Ac1 or above and then rapidly cooling it at the rate of at least I deg.C/second, with the rest part of it being substantially ferrite and which has a ferritet martensite multiphase structure of a 0.2% proof stress of at least 400MPa. As for a method for manufacturing the pole, a stainless steel band is formed into a pipe by a roll-less forming method after it is heat-treated and then the welded pipe is cut to size to obtain a wash-line pole. Due to the ferrite+martensite multiphase structure, the pipe can be made very strong without any deterioration in Young's modulus and flexural rigidity and therefore can be made thin for a clothes-drying bar.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hanging rod made of stainless steel which has excellent flexural rigidity and can be made thinner, and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a clothespin made of a metal tube, there is an ordinary steel tube coated with a resin, but stainless steel having excellent appearance and durability has also been used. In this type of clothespin, a stainless steel clad tube in which a stainless steel tube having a thickness of about 0.1 mm is wound around a normal steel tube having a wall thickness of about 0.5 to 0.6 mm, an austenitic or ferritic stainless steel having a wall thickness of about 0.6 mm is used. Steel pipes and the like are used. Stainless steel clad pipe is made of ordinary steel, so rust generated inside flows out from the end,
There is a risk of soiling the laundry. A clothes rod made of austenitic or ferritic stainless steel is excellent in weather resistance and corrosion resistance, but has a disadvantage in that it is expensive because the material cost is higher than resin-coated pipes or stainless clad pipes. Therefore, in Japanese Patent Application Laid-Open No. 5-285298,
The material is made of stainless spring steel whose strength is increased by work hardening, and the material cost is reduced by making it thinner.

[0003]

The clothespin made of stainless spring steel, whose strength has been enhanced by work hardening, is equal to or better than conventional materials with respect to destruction or permanent deformation even if the material is thinned due to its high strength. Of sufficient strength. However, in a metal material whose strength has been increased by cold rolling, a decrease in Young's modulus in accordance with an increase in proof stress and tensile strength cannot be avoided. The bending stiffness of a clothesline is governed by the secondary moment of area, which depends on the diameter and thickness, and the Young's modulus of the material. Therefore, in a clothesline made thinner due to an increase in strength, the bending rigidity is remarkably reduced due to the combination of the thickness reduction and the decrease in Young's modulus. Further, in a welded pipe made of stainless spring steel whose strength has been increased by work hardening, the strength near the welded portion is reduced due to the heat history at the time of welding. In addition, when welding this kind of material after forming it by the roll forming method, it is difficult to form the material by the roll forming method due to the high strength of the material, resulting in a welded pipe having poor roundness and the like. The present invention has been devised to solve such a problem. By using stainless steel having a ferrite + martensite dual-phase structure, it is possible to suppress a decrease in flexural rigidity due to thinning, and to reduce the cost. It aims to provide a high-quality clothesline.

[0004]

In order to achieve the object, a stainless steel clothesline according to the present invention is obtained by cold rolling chromium-based stainless steel and then heating it to an (α + γ) two-phase region of A _c1 or more. Thereafter, the martensite formed by the heat treatment of quenching at a rate of 1 ° C./sec or more has a ferrite + martensite dual phase structure of 20 to 95% by volume and the balance substantially consisting of ferrite, and a 0.2% proof stress of 400 MPa or more. The high strength stainless steel pipe is used as a rod material. The ratio of wall thickness / outer diameter of the high-strength stainless steel pipe is 0.1%.
Preferably it is in the range of 75-2%. The stainless steel clothespole, after a chromium-based stainless steel strip was cold rolled, then was heated to A _c1 or more (α + γ) 2-phase region 1
By performing a heat treatment of quenching at a rate of at least
When the martensite is 30% by volume or more and the remainder substantially consists of ferrite, a ferrite + martensite dual phase structure is generated, and a small-diameter bending roll is arranged parallel to the steel strip width direction to restrain free deformation in the longitudinal direction. The stainless steel strip after heat treatment is continuously plastic-bent / bent-backed with the inner surface of the pipe as the inner side, and then the stainless steel strip is formed into a tube with the product curvature using the widthwise bending of the stainless steel strip. It is manufactured by joining the abutting portions of the stainless steel strip in the width direction and cutting the obtained welded pipe to a fixed size.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The chromium stainless steel used in the present invention is, for example, C: 0.10% by mass or less, Si: 2.0% by mass or less, Mn: 4.0% by mass or less, P: 0.040% by mass. %, S: 0.030% by mass or less, Ni: 4.0% by mass or less, Cr: 10.0 to 20.0% by mass, N: 0.
12% by mass, O: 0.02% by mass or less, Cu: 4.0% by mass or less, with the balance being Fe and impurities,
C + N is 0.01 to 0.20 mass%, Ni + (Mn + C
u) / 3 is regulated to 0.2 to 5.0% by mass. This stainless steel contains 17% Cr-2% Ni as a main component, and SUS304 containing 18% Cr-8% Ni as a main component.
It is cheaper than a stainless steel spring material obtained by increasing the strength of stainless steel by cold rolling, and is advantageous in terms of cost when compared with the same diameter and the same thickness. Above all, a composition with a high Cu content exhibits antibacterial properties, so that a clothesline excellent in hygiene can be obtained.

C and N are strong and inexpensive austenite-forming elements as compared with Ni, Mn, Cu and the like, and have a large martensite strengthening ability. And effectively acts to increase the strength. Therefore, in order to obtain a desired high strength and good ductility after the continuous heat treatment step to substantially form a double phase structure of ferrite and martensite, even if an austenite forming element such as Ni, Mn, or Cu is added. , (C +
N) At least 0.01% by mass or more is required. However, if the amount of (C + N) is too high, the amount of martensite after the heat treatment for multi-phase formation increases, and in some cases, the amount of martensite is 1%.
Since the martensite becomes 00% by mass and the hardness of the martensite phase itself becomes very high, high strength is obtained but ductility is reduced. Therefore, the amount of (C + N) is set to 0.20% by mass or less, and 0.01% by mass ≦ (C +
N) It is necessary to satisfy the relationship of 0.20% by mass.

Further, when a large amount of C is contained, the toughness is reduced, and not only the productivity and the characteristics of the product are adversely affected, but also a dual-phase heat treatment in which the continuous heat treatment furnace heats and rapidly cools to a ferrite + austenite two-phase temperature region. In, the chromium carbide once dissolved in the heating re-precipitates at the ferrite or austenite (martensite after cooling) grain boundaries during the cooling, causing a so-called sensitization to form a Cr deficient layer near the grain boundaries, and the corrosion resistance is remarkably deteriorated. There are cases. Therefore, the amount of C is set to 0.10% by mass or less. N is
It is difficult to add a large amount due to the solubility, and addition of a large amount causes an increase in surface defects. Since Si is a ferrite-forming element and has a strong solid solution strengthening ability for both ferrite and martensite phases, it effectively acts to control the amount of martensite and the strength level. However,
Since addition of a large amount causes deterioration in hot workability and cold workability, the upper limit is 2.0% by mass.

[0008] Ni, Mn, and Cu are austenite-forming elements and are elements that effectively act on the control of the amount and strength of martensite after the dual-phase heat treatment. Ni, M
By adding n and Cu, the content of C can be reduced, thereby improving ductility as soft martensite, suppressing precipitation of chromium carbide at grain boundaries, and preventing deterioration of corrosion resistance due to sensitization. it can. Further, Ni, M
n and Cu have an effect of remarkably lowering the A _c1 point of the steel, that is, the temperature at which the austenite phase starts to be generated when the temperature is increased by heating. This has an important significance in improving workability as a fine ferrite + martensite mixed structure which is a feature of the present invention.

In the dual-phase stainless steel to which the present invention is applied, an austenite phase is formed in the ferrite ground during the dual-phase heat treatment after cold rolling to obtain a mixed structure. In this case, a fine structure is obtained. It is necessary to finely disperse the generated austenite phase. This means:
(1) A dual-phase treatment is performed in a continuous heat treatment furnace in which rapid heating is performed in the state of cold rolling, and austenite is simultaneously formed in a ferrite matrix in which the processing strain due to cold rolling remains (the austenite formation). (Increase of nucleation sites) is important, and (2) N that lowers the A _c1 point near or below the recrystallization temperature of the ferrite phase
Addition of i, Mn, and Cu is necessary and effective. In addition, even if the multi-phase heat treatment is performed as it is in the cold rolling state, when the A _c1 point is considerably higher than the recrystallization temperature of the ferrite phase,
Austenite formation starts after the ferrite phase is completely recrystallized. In this case, the austenite nucleation site is limited to the ferrite grain boundary, and the martensite becomes large.

[0010] Ni has the largest effect on the austenite forming ability per unit mass% and the _Ac1 point, and Mn and Cu are about 1/3 of Ni. Therefore, in determining the amounts of Ni, Mn, and Cu to obtain the above-described functions and effects, the amounts of Ni, Mn, and Cu are regulated using the relational expression of Ni + (Mn + Cu) / 3.
It is necessary to add 2% by mass or more. However, if added in large amounts, the product becomes expensive and economical efficiency is impaired. Therefore, Ni, Mn, and Cu are each set to 4.0% by mass or less, and Ni + (Mn + Cu) / 3 is set to 5.0% by mass or less. P is an element having a large solid solution strengthening ability, but may have an adverse effect on toughness. If S is too high, it has a bad influence on corrosion resistance and hot working, so it is preferably as low as possible, and the upper limit is 0.030% by mass.

[0011] Cr is an element that has the most important effect on the corrosion resistance of stainless steel. In order to maintain the minimum required corrosion resistance as stainless steel, at least 10.0
If the Cr content is too high, the amount of austenite-forming elements required to generate a martensite phase and obtain high strength increases, leading to an increase in product cost and toughness and workability. 20. to provide a reduction.
The upper limit is 0% by mass. O forms oxide-based nonmetallic inclusions and lowers the cleanliness of the steel. Therefore, O is preferably lower, and is set to 0.02% by mass or less. The amount of martensite after the dual-phase heat treatment is a main factor that governs the strength (hardness). As the martensite amount increases, the strength increases while the ductility decreases. The amount of martensite is, for example, γ
_The maximum amount that can be produced can be controlled by the component balance represented by _max , and even the same component can be changed by the multi-phase heat treatment, particularly by the heating temperature. If the amount of martensite is less than 20% by volume, it is difficult to obtain a hardness of HV 200 or more, while if the amount of martensite exceeds 95% by volume, the decrease in ductility becomes large and the absolute value of elongation becomes low. The significance of a ferrite + martensite composite structure is impaired. Therefore, the amount of martensite after the dual-phase heat treatment is defined as 20 to 95% by volume.

The chromium-based stainless steel is subjected to hot rolling and cold rolling to produce a cold-rolled steel strip. The cold-rolled steel strip is passed through a continuous annealing furnace and heated to a ferrite + austenite two-phase temperature range of A _C1 or more, and then from the maximum heating temperature to 100 ° C.
Cooling to an average cooling rate of 1 to 1000 ° C./sec to obtain a ferrite + martensitic duplex stainless steel strip.
The dual phase heat treatment is performed by passing a steel strip as cold rolled through a continuous heat treatment furnace to obtain a microstructure. In order to obtain a mixed structure of ferrite + martensite after heat treatment,
It is an essential condition to heat to the two-phase region of ferrite + austenite. In the practice of the method of the present invention, in the vicinity of the temperature (A _c1 point) at which austenite starts to form when heated from a low temperature in a continuous heat treatment furnace, the variation in the amount of austenite with respect to the temperature change, that is, the variation in the amount of martensite after rapid cooling, is reduced. Large and stable hardness (strength) may not be obtained.

In the range of steel components targeted by the present invention, such a change in hardness does not substantially occur when the steel is heated to a high temperature range of A _c1 point + 100 ° C. or higher. The temperature is preferably higher than the A _c1 point + 100 ° C. On the other hand, as for the upper limit of the heating temperature, if the temperature is too high, not only does the hardness rise saturate, but the temperature also decreases, which is disadvantageous in terms of manufacturing cost. In the two-phase region of ferrite + austenite during the heat treatment for forming a dual phase, an amount of austenite phase is generated in an almost equilibrium state in a short time, so that the heating time may be short, and heating may be performed within about 10 minutes. Regarding the cooling rate during the dual phase heat treatment, at least 1 ° C. /
Although it is necessary to set the cooling time to at least 1000 seconds, it is substantially difficult to obtain a cooling rate of 1000 ° C./second or more. Therefore, in the present invention, cooling from the two-phase region heating temperature is 1 to 1000 ° C.
At a cooling rate in the range of / s. The cooling rate is an average cooling rate from the maximum heating temperature to the normal temperature. However, it is not always necessary to use this cooling rate in the cooling process after austenite is transformed into martensite.

The stainless steel strip adjusted to a ferrite + martensite dual phase structure by heat treatment has a 0.2% proof stress of 400 MPa or more, and is comparable to a stainless steel spring material obtained by increasing the strength of SUS304 stainless steel by cold rolling. Proof stress and tensile strength. The elongation at break and the Young's modulus in the rolling direction show higher values than those of stainless steel spring materials obtained by increasing the strength of SUS304 stainless steel by cold rolling. When the flexural rigidity is the same, a stainless steel having a ferrite + martensitic dual phase structure can be thinner than a stainless steel spring material obtained by increasing the strength of SUS304 stainless steel by cold rolling, and is a less expensive material. Becomes Therefore, when stainless steel having a dual phase structure of ferrite and martensite is used as a rod material of a clothes-line, it is possible to reduce the wall thickness due to high strength and has a high Young's modulus. Is minimized. Further, since there is little decrease in hardness, which is an index of the strength of the welded portion, it is an advantageous rod material in terms of strength.

The stainless steel used in the present invention is a material whose structure is made to have a high strength by forming a ferrite + martensite double phase. When forming and welding such a high-strength material into a welded pipe, if the pipe is formed by a normal roll forming method, it is difficult to perform good forming due to excessive springback at the time of forming, and the quality and sectional shape of the welded part are deteriorated It is difficult to obtain a high quality welded pipe. Therefore, in the present invention, a high-quality, high-strength, thin-walled rod material for a clothesline is manufactured by a rollless forming method in which a steel strip is bent by prestrain and formed into a cylindrical shape. The present inventors have disclosed the rollless forming method itself in Japanese Patent Publication No. 6-77773 and Japanese Patent Publication No. 7-29147.
This is the tube-making method introduced in the official gazette. As shown in FIG.
The stainless steel strip 2 unwound from the pay-off reel 1 is pre-strained by plastic bending and unbending by the small-diameter bending roll 3 and the auxiliary forming roll 4 curls the stainless steel strip 2 in the width direction to form a cylindrical shape. . Next, the stainless steel strip 2 is constrained in a tubular shape by the seam guide roll 5 and both ends in the width direction are butt or overlapped by the squeeze roll 6,
Weld with a welding torch 7. Thereby, even if the material has high strength, the effect of springback is suppressed, and a welded pipe 8 having a good shape can be obtained.

In order to improve the roundness of the welded pipe 8, the welded pipe 8 is flattened by the flat roll 9, and the welded pipe 8 sent out by the transport roll 10 is again formed into a substantially circular cross section by the straightening roll 11. You can also. Flattening → reforming releases the residual stress of the welded pipe 8 and prevents the vicinity of the cut portion from being deformed by the residual stress when the welded pipe 8 is cut. Therefore, even after cutting the welding pipe 8 to the length of the clothesline, there is no deformation such as opening and closing of the mouth, and a clothesline having good roundness over the entire length can be obtained. In the flattening at this time, the welded pipe 8 is flattened so that the distance from the pipe bottom to the welded portion is 3 to 15% smaller than the target product diameter. In order to secure the required bending rigidity for use as a clothesline, the ratio of the thickness / outer diameter of the welded pipe 8 is set to 0.
It is preferably at least 75%. However, when the thickness / outer diameter ratio exceeds 2.0%, the cost merit as compared with the conventional product is reduced.

The obtained welded pipe 8 is cut to a stainless steel rod 12 having an effective length of a clothesline. As shown in FIG. 2, caps 13 made of resin or the like are attached to both ends of the stainless steel rod material 12 and the openings at both ends are closed, whereby a stainless steel clothesline is obtained. Alternatively, as shown in FIG. 3, a stretchable clothesline can be used. In this case, a structure in which a small-diameter stainless steel pipe 15 is inserted into a large-diameter stainless steel pipe 14 so as to be able to expand and contract is adopted. A cap 13 is attached to the outer end of the small-diameter stainless steel pipe 15,
A stopper 16 is provided at the end of the large-diameter stainless steel pipe 14.
Is attached. The stopper 16 abuts on a joint 17 attached to an end opening of the large-diameter stainless steel pipe 14 to prevent the small-diameter stainless steel pipe 15 from falling off the large-diameter stainless steel pipe 14.

[0018]

【Example】

Example 1 A cold rolled steel strip having a thickness of 0.35 mm was prepared by hot rolling and cold rolling stainless steel having the components shown in Table 1. After subjecting the cold-rolled steel strip to continuous annealing at 1020 ° C. for 3 minutes, it was cooled to 100 ° C. at an average cooling rate of 20 ° C./sec.

[0019]

The heat-treated stainless steel strip had a 75% by volume martensite ferrite + martensite dual phase structure and a 0.2% proof stress of 1000 MPa. In addition, as shown in Table 2, the mechanical strength was substantially the same as the proof stress and tensile strength of the conventional SUS304 stainless steel, but the Young's modulus and the bending resistance were remarkably excellent. The comparative example in Table 2 is a stainless steel spring material obtained by increasing the strength of SUS304 stainless steel by cold rolling. As shown in FIG. 4, the stainless steel of the comparative example showed a tendency for the Young's modulus in the rolling direction to decrease as the rolling reduction during cold rolling increased, as shown in FIG. On the other hand, since the stainless steel according to the present invention does not depend on cold rolling for strengthening, the initially high Young's modulus is maintained.

[0021]

After cutting the stainless steel strip to a predetermined width of 91.9 mm, a stainless steel pipe having a diameter of 29.4 mm was formed by the rollless forming method shown in FIG. Using a roll having a diameter of 8 mm as the small-diameter bending roll 3, a stainless steel was pre-strained by plastic bending and unbending and formed into a cylindrical shape, and then both ends in the width direction were TIG-welded at a welding speed of 10 m / min. After welding, the flat roll 9 flattened the product by about 2 mm from the target outer diameter, and the straightening roll 11 formed the welded pipe 8 into a perfect circular shape. The obtained welded pipe 8 was cut into a length of 3 m, and the outer surface of the pipe was polished.
The welded pipe after cutting was supported at two points at a distance between fulcrums of 1500 mm, and a one-point concentrated load was applied to the center between the fulcrums to measure the amount of deflection at the center between the fulcrums, thereby evaluating the bending resistance.
As can be seen from the measurement results in FIG. 5, it can be seen that the stainless steel rod according to the present invention has a smaller amount of bending than the SUS304 stainless steel rod and is excellent in bending resistance.

In the welded portion, as shown in FIG. 6, there is little decrease in hardness as an index of the material strength, and the strength is uniform over the entire circumference of the pipe. On the other hand, SUS30 of the comparative example
In the 4 stainless steel welded pipe, the hardness is significantly reduced at the welded portion, and the strength distribution in the circumferential direction varies. The stainless steel rod material according to the present invention is once flattened after welding and straightened into a perfect circle. As a result, no deformation such as opening and closing of the mouth due to residual stress occurs on the cut end face, and good roundness was maintained at any of the front end, the center, and the rear end as shown in FIG. . Further, as shown in FIG. 8, the diameter at the front end, the center, and the rear end did not fluctuate greatly in the circumferential direction. On the other hand, in the stainless steel rod material of the comparative example, as shown in FIG. 9, the diameters of the front end portion and the rear end portion varied greatly in the circumferential direction. When a stainless steel tube having a martensite + ferrite dual phase structure formed by a rollless forming method is cut into a predetermined length and used as a rod material for a clothesline, a conventional stainless steel clothesline is used. As compared with a rod, a clothesline with much better quality characteristics such as shape and strength and an inexpensive clothesline was obtained.

Example 2 A stainless steel strip having a thickness of 0.30 mm was formed from a stainless steel having the components shown in Table 3 by hot rolling and cold rolling. The cold rolled steel strip was subjected to a soaking process at 1000 ° C. for 1 minute and a dual phase heat treatment at 20 ° C./sec.

[0025]

The heat-treated stainless steel had a composite structure of ferrite and martensite with about 50% by volume of martensite, and had a 0.2% proof stress of 620 MPa. After cutting this stainless steel strip to a predetermined width of 70.4 mm, a 25.4 mm diameter stainless steel pipe was formed by the rollless forming method shown in FIG. The tube forming conditions are almost the same as in the first embodiment. The stainless steel pipe manufactured in this way has high strength and an elongation of about 13%, and can be bent at an angle of 90 degrees with a radius of about 150 mm. It had excellent workability applicable not only to applications but also to applications such as clothes racks that require bending.

[0027]

As described above, the clothesline of the present invention uses a duplex stainless steel pipe whose strength has been increased by adjusting the structure to two phases of ferrite and martensite by heat treatment as a rod material. I have. With this organizational adjustment,
Since the strength is increased without lowering the Young's modulus and the flexural rigidity, a clothesline having a thinner thickness than a conventional stainless steel clothesline is provided. In addition, since there is no variation in strength and the roundness is excellent, it is used as a high-quality clothesline in combination with the beautiful appearance and corrosion resistance unique to stainless steel.

[Brief description of the drawings]

Fig. 1 Tube making process by rollless forming method

[Fig. 2] Clothesline pole using stainless steel pipe

Fig. 3 Telescopic clothesline using stainless steel tubes

FIG. 4 is a graph showing the effect of the cold rolling reduction on the Young's modulus of a stainless steel strip.

FIG. 5 is a graph comparing the amount of deflection of a stainless steel rod according to the present invention with the amount of deflection of a conventional SUS304 stainless steel rod.

FIG. 6 is a graph comparing the hardness distribution near the welded portion of the stainless steel rod according to the present invention with that of the conventional SUS304 stainless steel rod.

FIG. 7 is a graph showing the effect of flattening and straightening after welding on roundness.

FIG. 8 is a graph showing that there is little variation in the diameter in the circumferential direction at each of the longitudinal portions of the stainless steel rod according to the present invention.

FIG. 9 is a graph showing that the diameter in the circumferential direction of each of the stainless steel rod members of the comparative example varies greatly in the longitudinal direction.

[Explanation of symbols]

1: Payoff reel 2: Stainless steel strip 3: Small diameter bending roll 4: Auxiliary forming roll 5: Seam guide roll
6: Squeeze roll 7: Welding torch 8: Welded pipe 9: Flat roll
10: Conveyance roll 11: Straightening roll 12: Stainless steel rod 1
3: Cap 14: Large diameter stainless steel pipe 15: Small diameter stainless steel pipe 16: Stopper 17: Joint

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takeo Kitaoka 1 Tsurumachi, Amagasaki-shi, Hyogo Nisshin Steel Co., Ltd.Amagasaki Works (72) Inventor Hiroshi Fujimoto 4976 Nomuraminamicho, Shinnanyo-shi, Yamaguchi Nisshin Steel Inside the Technical Research Institute Co., Ltd. (72) Katsuhisa Miyakusu 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Pref. Nisshin Steel Co., Ltd. (72) Inventor Yoshio Morii 3-4-1 Marunouchi, Chiyoda-ku, Tokyo Sun Inside Shin Steel Co., Ltd.

Claims (3)

[Claims] 1. A chromium-based stainless steel is cold-rolled, heated to an (α + γ) two-phase region of A _c1 or more, and then heated to 1 ° C. /
A martensite formed by a heat treatment of quenching at a speed of not less than 2 seconds has a ferrite + martensite dual phase structure of 20 to 95% by volume and a balance substantially consisting of ferrite.
A stainless steel clothesline made of a high-strength stainless steel pipe having a 2% proof stress of 400 MPa or more. 2. The stainless steel clothesline according to claim 1, wherein the ratio of the thickness / outer diameter of the high-strength stainless steel pipe is in the range of 0.75 to 2%. 3. The chromium-based stainless steel strip is cold-rolled, heated to an (α + γ) two-phase region of A _c1 or more, and then heated to 1 ° C. /
By applying a heat treatment of quenching at a speed of at least 2 seconds, a ferrite + martensite double phase structure in which martensite is 20 to 95% by volume and the balance is substantially ferrite is generated, and the small-diameter bending roll is rolled in the steel strip width direction. When the stainless steel strip after heat treatment is continuously plastic-bent / bent-backed with the inner surface of the pipe as the inner side when the free deformation in the longitudinal direction is restrained and the pipe is bent in the longitudinal direction, the widthwise bending of the stainless steel strip is performed. A method for manufacturing a stainless steel clothesline in which a stainless steel strip is formed into a tubular shape having a product curvature by using the same, the abutting portions in the width direction of the stainless steel strip are joined, and the obtained welded pipe is cut to a fixed size.