KR101008180B1 - Ferritic stainless steel having excellent formability of welded zone, welded pipe using the same and method for manufacturing the welded pipe - Google Patents

Abstract

The present invention relates to a ferritic stainless steel, laser welded steel pipe and a method for producing the welded steel pipe excellent in workability of the weld.

In the present invention, by weight%, C: 0.01% or less, N: 0.01% or less, Si: 0.8-1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3%, Nb: 0.3- It provides 0.4%, Ti: 0.1 to 0.2%, and the rest provides a stainless steel having excellent workability of the weld portion, characterized in that consisting of Fe and other unavoidable impurities.

In another aspect, the present invention provides a stainless steel welded steel pipe excellent in the workability of the welded portion when the hardness ratio (HAZ / base material) of the steel pipe is 0.98 to 1.05 when manufacturing the welded steel pipe from the stainless steel, and provides a method for producing the welded steel pipe.

FERIITIC STAINLESS STEEL, LASER WELDED STEEL, FORMATBLILITY

Description

Ferritic stainless steel with excellent processability of welded parts, welded steel pipes using the same, and a method for manufacturing the same

The present invention relates to a ferritic stainless steel having excellent workability of a welded part, a welded steel pipe using the same, and a method for manufacturing the welded steel pipe. More particularly, softening of the welded part immediately after the pipe is made by appropriately controlling the composition of the steel and the amount of heat input. The present invention relates to a ferritic stainless steel welded steel pipe having excellent workability by preventing phenomenon.

Recently, the automobile industry is required to improve fuel efficiency by tightening and reducing exhaust gas regulations, and automobile manufacturers are adopting ferritic stainless steel having excellent corrosion resistance and heat resistance in place of existing castings or aluminum plated steel sheets. .

Exhaust system parts are composed of press-formed products of plate and pipe-formed products, and they are mostly manufactured and assembled by welding. Therefore, it can be said that securing the quality characteristics of the welded portion is a very important factor that determines the performance of the exhaust system components.

Since the shape of the exhaust system is quite complicated, in forming, steel sheets or steel pipes are subjected to harsh processing. Ferritic stainless steel welded steel pipes (steel pipes manufactured by high frequency welding, TIG welding, laser welding, etc.) are welded metals or heat affected zones when secondary processing such as bending or expansion is applied. In some cases, weld cracks are generated in the HAZ, and even though the workability of the base material is excellent, the workability of the base material cannot be exhibited due to the decrease in the workability of the welded part. This phenomenon occurs more prominently when molding in winter or at low processing temperatures.

On the other hand, as described above, it is common to adopt high alloy ferritic stainless steel for the purpose of securing high temperature characteristics of the steel used as the temperature of the exhaust gas increases due to the strengthening of environmental regulations. This further deterioration is pointed out as a problem.

As a result of applying high frequency welding, TIG welding, and laser welding to the heat resistant 14Cr ferritic stainless steel, this study was unable to secure sufficient processing characteristics for high frequency welding and TIG welding steel tubes. In the case of high frequency welded steel pipe, coarse Ti and Nb-based precipitates accumulate at the interface of the joint and act as a cracking point during processing, and work hardening occurs in the vicinity of the weld due to plastic deformation during high temperature welding. In the case of TIG welding, the welding efficiency was lowered, and thus the width of the hardened welded part was wider than that of other welding, and the grain size was also coarsened, resulting in poor workability.

On the other hand, in the case of laser welding, low heat input welding is possible compared to high frequency welding and TIG welding, so that the width of the weld is narrow and there are no welding defects, so that good quality characteristics can be obtained. However, when laser welding was applied to high alloy ferritic stainless steel, softening occurred for a certain time after welding. This is presumably caused by excessively increasing the hardness of the raw material due to work hardening of the raw material at the time of forming the pipe, and causing some loosening phenomenon during welding. The softening phenomenon of the welded part was found to exhibit good quality characteristics when the welded steel tube was processed after a few days after the hardness was restored due to the aging phenomenon. However, it is pointed out as a problem that parts production is delayed due to waiting for a few days after pipemaking and that quality inspection of steel pipes after pipe welding is difficult.

Conventional well-known techniques for securing the processability of high-Cr-based ferritic stainless steel pipes, which are typical steel grades used in high temperature parts, are as follows.

Japanese Patent Laid-Open Publication No. 1997-125209 discloses a method of welding a tube by electric resistance welding (ERW) of a heat-resistant ferritic stainless steel containing Nb, followed by post-heat treatment at a high temperature of 850 to 1000 ° C. and rapidly cooling to 1 ° C./sec or more. Japanese Patent Laid-Open Publication No. 2006-193770 discloses a Vickers hardness HV _W and a base material of a welded ferritic single-phase stainless steel welded steel pipe containing 0.1 to 0.5% of Ti or Nb as one or two weight percents, respectively. The hardness difference ΔHV (= HV _W -HV _M ) from the negative Vickers hardness HV _M is in the range of 10 to 40, and the ratio RT (= T _W / T _M ) between the bead width T _W and the base material thickness T _M is 1.05 to 1.3 After molding and welding (ERW, GTAW), the calibration is carried out with a deformation amount of 0.5 to 2.0% in the longitudinal direction, and a post-heat treatment method is proposed in the temperature range of 700 to 850 ° C. However, the present invention is to apply the annealing heat treatment after welding the pipe for the purpose of reducing the work hardening of the welded steel pipe, these methods are effective in improving the workability of the welded steel pipe, but the cost increase and surface oxidation There is a problem.

In Japanese Patent Laid-Open No. 2000-326079, a ferritic stainless steel containing less than 1% of Ti and Nb alone or in combination is formed into an open pipe, and when the butt face is laser welded, the weld pipe passes through a straightening roll. When the hardness difference ΔHV (HVwHVb) between the Vickers hardness HVw of the welded part and the Vickers hardness HVb of the base material is in the range of 10 to 80, the temperature of the material becomes 150% or more of the room temperature. It provides a way to control. This method is a laser tube welding technique, which is a correction method that controls the temperature of the material to be 80% or more of room temperature at 150 ° C or lower after welding in order to secure the hardness difference between the weld metal part and the base metal to a certain level. Since the laser tube welding is much larger than other welding methods in the welding heat cycle, it does not require separate management because it reaches the room temperature level in the correction line after welding, and there is no effect on the softening phenomenon of the welding heat affected zone required by the present invention. Judging.

Japanese Patent Application Laid-Open No. 1996-155665 discloses a method for miniaturizing the crystal grains of a ferritic stainless steel weld metal part, which is subjected to penetration welding with a first laser beam, and after the temperature of the weld part is 400 ° C. or lower, 2 provides a method of partial welding by irradiating a laser beam. However, this method uses two laser beams to refine the grain size of the weld metal, but it is considered that the cost increase due to the additional installation of the laser welder and the softening problem of the weld heat affected zone are not related.

Japanese Laid-Open Patent Publication No. 1993-277769 discloses a method of improving the workability by preheating the ferrite stainless steel to 250 ° C. or higher before welding, welding the inner bead protrusion height to 0.15 mm or more, and reducing the welded portion in the plate thickness direction. to provide. However, this method is a method of preheating at 250 ° C or higher before laser tube welding, welding the protruding height of the inner surface bead at 0.15mm or more, and reducing the welded portion in the plate thickness direction to improve workability. The low heat input welding method has a problem that it is difficult to stably secure the inner bead protrusion height more than 0.15mm.

Known techniques as a steel manufacturing method for securing the weldability of the heat-resistant ferritic stainless steel as follows.

 In Japanese Patent Laid-Open No. 1999-256286, C: 0.02% or less, Si: 0.7-1.0%, Mn: 1.0-1.5%, Cr: 13.5 ~ in order to omit the post-heat treatment of heat-resistant ferritic stainless steel to ERW steel pipes. 15.5, N: 0.02% or less, Nb: 0.3 to 0.6%, Cu: 0.02 to 0.24%, Al: 0 to 0.03%, and the processing arsenic satisfying the relationship of 1.45≥Nb + Si and 1.35≤Nb + 1.2Si Provides dull welded steel pipes. However, in the present invention, it was confirmed that it is difficult to secure sufficient workability for deep processing applications such as expansion of the bending part.

Japanese Patent Laid-Open Publication No. 1995-266072 discloses an atmosphere nitrogen concentration in the vicinity of a weld seam in order to prevent nitrogen absorption of stainless steel laser welds and improves workability. temperature T (℃) and determined by the allowable nitrogen content [% N] _WM of the weld metal of _{[% N] at, log (} [% N] at) ≤ 2log ([% N] WM) - 2 × (518 / T + 1.068)-2 × (0.046 [% Cr] -0.00028 [% Cr] ² ). However, it is difficult to control the process variables in real time in the actual piping process.

Japanese Patent Laid-Open Publication No. 2002-80943 discloses Co, V, and B in a ferritic stainless steel containing Cr: 11 to 20% and Nb: 0.2 to 0.8%, respectively, Co: 0.01 to 0.3%, V: 0.01 to 0.3%, and B. : Provides a method of securing secondary processing brittleness and high temperature fatigue characteristics in the welded part by complex addition in the range of 0.0002 ~ 0.005%. However, this method is a method to secure secondary processing brittleness and high temperature fatigue characteristics by adding Co, V, and B complex, but it is difficult to apply deep processing usage theory such as re-expanding the vicinity after bending. .

The present invention is to provide a heat-resistant 14Cr ferritic stainless steel excellent in workability of the weld.

In addition, the present invention provides a welded steel pipe and a method of manufacturing the welded steel pipe to improve the productivity of the steel pipe material and to ensure the quality even in harsh processing conditions by preventing the softening phenomenon of the weld immediately after the pipe, when the laser tube welding is applied.

In the present invention, by weight%, C: 0.01% or less, N: 0.01% or less, Si: 0.8-1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3%, Nb: 0.3- It provides 0.4%, Ti: 0.1 to 0.2%, and the rest provides a stainless steel having excellent workability of the weld portion, characterized in that consisting of Fe and other unavoidable impurities.

In addition, the present invention is a weight%, C: 0.01% or less, N: 0.01% or less, Si: 0.8-1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3%, Nb: 0.3 ~ 0.4%, Ti: 0.1 ~ 0.2%, the remainder is made of Fe and other unavoidable impurities, the workability of the weld, characterized in that the hardness ratio (HAZ / base material) of the steel pipe when welding the steel pipe is 0.98 ~ 1.05 This excellent stainless steel welded pipe is provided.

In addition, the present invention is a weight%, C: 0.01% or less, N: 0.01% or less, Si: 0.8 ~ 1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3%, Nb: 0.3 ~ 0.4%, Ti: 0.1 ~ 0.2%, the remainder of the weld heat input (output / speed, KW / m / min) is 0.86 ~ in the protective gas when manufacturing stainless steel pipe made of Fe and other unavoidable impurities It is to provide a method for producing a stainless steel welded steel pipe having excellent workability of a welded part, comprising the step of laser welding in the range of 1.28 KW · min / m.

Ferritic stainless steel laser welded steel pipe of the present invention is usually applied to high alloy ferritic stainless steel welded steel pipe by reducing Cu and (Ti + Nb) / (C + N) of the steel to an appropriate level and controlling the laser welding heat input. After the heat treatment can be omitted, it is possible to greatly contribute to the improvement of the processing quality characteristics and productivity by preventing the softening phenomenon of the weld. This result is very useful in terms of utilization because it can be improved in the same way not only 14Cr system of the present invention, but also high Cr, high alloy welded steel pipe.

Hereinafter, the stainless steel of the present invention will be described in detail.

The stainless steel of the present invention satisfies the following component ranges (hereinafter,% by weight).

The contents of carbon (C) and nitrogen (N) are each 0.01% or less. Since C and N are elements which reduce the workability of the base metal and the welded part, it is preferable to make them as small as possible, but it is preferably 0.01% or less in consideration of the increase in manufacturing cost in steelmaking technology.

The content of silicon (Si) is 0.8 to 1.0%. Si is an effective element that improves oxidation resistance at high temperature exposure. The minimum content for securing oxidation resistance is 0.8%, and when added excessively, the workability of the steel decreases, the work hardening during the pipework deepens, and the softening phenomenon of the weld heat affected zone is promoted, so the upper limit is limited to 1.0%.

The content of copper (Cu) is 0.1 to 0.3%. Cu is an element that improves the workability of steel materials, but when it is added excessively, it increases the n value (work hardening index) in the pipe forming process before welding, which deepens the work hardening of the steel pipe material and promotes softening of the weld heat affected zone. The range is limited to 0.1 to 0.3%.

The content of chromium (Cr) is 13.7 to 14.3%. Cr needs 13.7% or more to ensure corrosion resistance and oxidation resistance, but the upper limit is set to 14.3% as the Cr content increases.

The content of titanium is 0.1 to 0.2%, and the content of niobium (Nb) is 0.3 to 0.4%. Ti and Nb are elements that improve steel workability, high temperature strength and high temperature thermal fatigue properties. When adding Ti and Nb more than an upper limit, there exists a problem that workability deteriorates by the increase of solid solution Nb and Ti amount. Therefore, the content of Ti is 0.1 to 0.2%, the content of Nb is 0.3 to 0.4%.

The rest consists of Fe and unavoidable impurities.

The stainless steel of the present invention satisfies 0.982 ≦ 1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N) ≦ 1.05. In the above formula, the lower limit and the upper limit represent the hardness ratio (HAZ / base metal) of the welded steel pipe. In the present invention, the hardness distribution of the 14Cr ferritic stainless steel laser welded steel pipe was measured, and the workability was evaluated. As a result, it was found that the hardness ratio and the workability of the welded steel pipe had a close relationship. That is, in the hardness ratio of 0.982 or less, the softening phenomenon that the hardness value of the welded heat affected zone (HAZ) is lower than that of the base material is generated, and cracks occur during processing. If the hardness ratio is 1.05 or more, the welded portion hardens and the workability is lowered.

In addition, as a result of examining the hardness ratio between the component elements contained in the steel and the welded steel pipe through a regression equation, it was confirmed that Cu and (Ti + Nb) / (C + N) became the dominant factors. In particular, it was found that the influence of Cu is remarkable. Elements such as Cu, Ti, and Nb are solid solution strengthening elements in ferrite, and when the material is molded in the tube welding process, it is necessary to control the amount of addition downward.

Hereinafter, the welded steel pipe of the present invention will be described in detail.

The welded steel pipe of the present invention is a weight% as described above, C: 0.01% or less, N: 0.01% or less, Si: 0.8-1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3 %, Nb: 0.3-0.4%, Ti: 0.1-0.2%, and the rest consists of Fe and other unavoidable impurities.

In addition, the welded steel pipe of the present invention satisfies 0.982 ≦ 1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N) ≦ 1.05.

The welded steel pipe of the present invention has a value that the hardness ratio (HAZ / base material) of the steel pipe is 0.98 ~ 1.05. Hardness ratio is the value measured at 1hr after welding of the pipe, and it is set as 0.98 as the lower limit to prevent softening of the initial welding heat affected zone, and the upper limit 1.05 means that the welded heat affected zone is slightly hardened compared to the base metal. If the above is exceeded, there is a possibility that the weld is excessively hardened and brittle cracks are generated at the time of forming the steel pipe.

Hereinafter, a method for manufacturing a laser welded steel pipe will be described in detail.

In order to manufacture the welded steel pipe of the present invention, by weight%, C: 0.01% or less, N: 0.01% or less, Si: 0.8-1.0%, Mn: 0.5% or less, Cr: 13.7-14.3%, Cu: 0.1-0.3 %, Nb: 0.3 ~ 0.4%, Ti: 0.1 ~ 0.2%, and the remainder is welded heat input (output / speed, KW / m / min) of stainless steel consisting of Fe and other unavoidable impurities, 0.86 ~ 1.28 kW Laser welding at min / m Weld heat input is controlled by laser power and welding speed. If the welding heat input is small, penetration welding is difficult, and if the welding heat input is excessively applied, bead sagging occurs in the weld section, and the upper part of the bead underfill and the lower part of the bead protrusion are increased, thereby correcting and forming the shape of the steel pipe. Difficult to secure sex In the present invention, the welding heat input of the steel is limited to 0.86 to 1.28 kW · min / m in order to include the sagging length of the welded portion and the protruding length of the lower portion of the bead in the steel pipe within -0.15 to 0.25 mm.

In the present invention, an inert gas is used as a shielding gas in both the upper and lower portions of the bead during the laser welding. The protective gas is effective for preventing the incorporation of impurities from outside air during welding. In the case of laser welding, the temperature of molten metal is much higher than that of general arc welding, and it is easy to mix nitrogen and oxygen in the air. Therefore, when the protective gas is not treated on both the upper and lower beads, the brittleness of the weld portion is increased by nitrogen and oxygen mixed therein. Therefore, in the present invention, a protective gas is used on both the upper and lower beads to prevent brittleness of the weld.

In the protective gas, the bead upper part is blown with He gas at a flow rate of 15 to 20 L / min, and the lower part of the bead is preferably treated with an atmosphere of Ar gas. If the protective gas He has a flow rate of less than 15 L / min, the weld surface surface is insufficient to facilitate the mixing of external air, and if it exceeds 20 L / min, the molten metal scatters during welding, making it difficult to secure a healthy bead shape. Therefore, the flow rate of He is limited to 15-20 L / min. At the bottom of the bead, it is sufficient to treat the atmosphere with Ar gas, and there is no need to limit the flow rate.

Hereinafter, embodiments of the present invention will be described in detail.

(Example)

As shown in Table 1, a ferritic stainless steel having Fe-14Cr-0.9Si as the basic composition and changing the Cu and (Ti + Nb) / (C + N) ratios to 0.16 to 0.5% and 18.6 to 41.8, respectively. Eight kinds of solvents were prepared, and a coil having a thickness of 1.5 mm was manufactured through a process of hot rolling, annealing, cold rolling, and annealing. As an application of the present invention, steel 3 is 0.278% Cu, (Ti + Nb) / (C + N) ratio 37, steel 8 is 0.164% Cu, (Ti + Nb) / (C + N) ratio 41.8.

In general, the tubing process adopts a continuous roll forming method applied to an exhaust system, and manufactured a welded steel tube having an outer diameter of 33 mm by forming, laser welding, straightening, and cutting. 12KW CO ₂ laser welding machine was used for the laser welding. The laser power and welding speed were changed during welding, and the optimum conditions without defects of the welded parts were derived. The protective gas is effective to prevent the incorporation of impurities from outside air. In laser welding, the temperature of molten metal is much higher than that of general arc welding, and nitrogen is easily mixed in the air. Therefore, the upper protective gas was He gas at a flow rate of 15 ~ 20L / min, the atmosphere was treated with Ar gas at the bottom of the bead.

division Chemical composition (wt%) Hardness ratio
(Article 1h
After HAZ /
Base material) Flat test
(Article 1h
Hot after
Mercury)
Remarks C Si Mn Cr Cu Nb Ti N (Ti + Nb) /
(C + N) Steel 1 0.0090 0.81 0.30 14.2 0.5 0.290 0.140 0.009 23.9 0.8822 ● Comparative example Steel 2 0.0070 0.827 0.201 14.21 0.466 0.357 0.139 0.013 24.8 0.9364 ● Comparative example Steel 3 0.0083 0.825 0.217 14.21 0.278 0.385 0.181 0.007 37.0 0.9823 ○ Inventive Example Steel 4 0.0090 0.784 0.31 14.13 0.478 0.294 0.147 0.010 23.3 0.9396 ● Comparative example Steel 5 0.0080 0.778 0.302 14.2 0.468 0.290 0.121 0.010 22.9 0.9670 ◑ Comparative example Steel 6 0.0080 0.776 0.30 14.16 0.46 0.282 0.125 0.009 24.0 0.9645 ◑ Comparative example Steel 7 0.0080 0.815 0.216 14.17 0.452 0.297 0.136 0.009 25.5 0.9408 ● Comparative example Steel 8 0.0098 0.932 0.195 14.15 0.164 0.354 0.144 0.006 41.8 1.0318 ○ Inventive Example

* Based on the number of cracks generated (20 times in total): ○ 0, ◑ 1 ~ 4, ● 5 or more

The laser welded steel pipes were subjected to 20 times of flat tests in which the welded welds were perpendicular to each other and perpendicular to the direction of the load to be loaded as shown in FIG. In addition, the hardness of the welded part of the steel pipe and the base material was measured using a micro Vickers hardness tester, and the hardness ratio (HAZ / base material) was obtained. In hardness measurement, the area including the base material and the welded part was measured three times at 0.2 mm intervals with a load of 500 g and a holding time of 10 sec.

In order to confirm the quality characteristics of the plate laser welding portion, the Ericsson test was conducted. Ericsson (Erichsen) value was measured by measuring the height to the crack occurrence point of the weld while pushing up the punch on the lower surface of the plate weld. The higher the Erichsen value, the better the formability.

2 is a result of examining the defect occurrence state of the welded part according to the change of the process variable during laser welding. As the laser power decreases and the welding speed increases, the unperforated area expands, and when the laser power increases excessively or the welding speed decreases, the bead underfill increases in the weld portion, making it difficult to secure good beads. It can be seen that. If the appropriate welding heat input amount is calculated | required from the inclination of the straight line which shows a suitable welding range in FIG. 2, it will be 0.86-1.28 KW * min / m.

Table 1 is a result of welding the tube for 8 types of steel at 6KW laser welding speed and 5m / min of the proper welding conditions, and evaluated the weld hardness ratio and workability. In order to quantitatively evaluate the softening phenomenon of the tube welding part, the weld hardness measurement and the flatness test were performed within 1hr immediately after the tube welding.

For steel pipes of steels 3 and 8, which are the dominant components in the hardness ratio of welded steel pipes, no cracking occurred 1 hour after the pipe was produced. Occurred. The hardness ratio indicates that the value of steel 3 represents the lower limit, and when the value becomes about 0.982 or more, cracking prevention is possible. As a result of regression analysis using these results, the following equation is satisfied. The adjusted R square (R-Sq), which represents the reliability of the regression equation, was relatively good at 80.4%.

Hardness Ratio (HAZ / Material) = 1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N)

From the above formula, it is judged that sufficient workability can be secured by adjusting Cu and (Ti + Nb) / (C + N) downward to an appropriate level.

FIG. 3 shows the results of performing an Ericsson test on steel 1, steel 3, and steel 8 welded at a base metal, a laser output of 6KW, and a welding speed of 5 m / min. Steel 1 had cracks in the weld heat affected zone and steel 3 and 8 had cracks in the weld metal zone, respectively. In other words, the softening phenomenon of the weld heat affected zone is reduced in the steels 3 and 8 compared to the steel 1. In addition, when comparing the Ericsson (Erichsen) value of the welded portion for each steel type, it can be seen that the welded portion of the steel 3 and the steel 9 has better forming characteristics than the steel 1.

1 is a schematic view of a flat test of a laser welded steel pipe.

2 is a result of examining the defect occurrence state of the welded part according to the change of the process variable during laser welding.

3 shows the results of the Erichsen test on steels 1, 3, and 8. FIG.

Claims (8)

By weight%, C: 0.01% or less (excluding 0%), N: 0.01% or less (excluding 0%), Si: 0.8 ~ 1.0%, Mn: 0.5% or less (excluding 0%), Cr: 13.7 ~ 14.3%, Cu: 0.1-0.3%, Nb: 0.3-0.4%, Ti: 0.1-0.2%, the remainder is composed of Fe and other unavoidable impurities, 0.982 ≦ 1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N) ≦ 1.05 The stainless steel with excellent workability of the welded part characterized by the above-mentioned. delete By weight%, C: 0.01% or less (excluding 0%), N: 0.01% or less (excluding 0%), Si: 0.8 ~ 1.0%, Mn: 0.5% or less (excluding 0%), Cr: 13.7 ~ 14.3%, Cu: 0.1-0.3%, Nb: 0.3-0.4%, Ti: 0.1-0.2%, the remainder is composed of Fe and other unavoidable impurities, 0.982 ≦ 1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N) ≦ 1.05 The stainless steel welded steel pipe with excellent workability of welded parts. 4. The stainless steel welded steel pipe having excellent machinability according to claim 3, wherein the hardness ratio (HAZ / base metal) of the steel pipe is 0.98 to 1.05. By weight%, C: 0.01% or less (excluding 0%), N: 0.01% or less (excluding 0%), Si: 0.8 ~ 1.0%, Mn: 0.5% or less (excluding 0%), Cr: 13.7 ~ 14.3%, Cu: 0.1-0.3%, Nb: 0.3-0.4%, Ti: 0.1-0.2%, the remainder consists of Fe and other unavoidable impurities, 0.982≤1.55-0.847Cu-0.00899 (Ti + Nb) / (C + N) ≤ 1.05 stainless steel welded steel pipe manufacturing method characterized in that it comprises the step of laser welding under a protective gas when manufacturing a welded steel pipe. The method of claim 5, wherein the laser welding step of the weld heat input (output / speed, KW / m / min) of 0.86 ~ 1.28KW · min / m of the welded stainless steel pipe having excellent workability Manufacturing method. The method of manufacturing a stainless steel welded steel pipe according to claim 5 or 6, wherein an inert gas is used at both the upper and lower portions of the bead as the protective gas. The method of claim 7, wherein the protective gas is a He gas at a flow rate of 15 ~ 20L / min at the top of the bead, the atmosphere is treated with Ar gas at the bottom of the bead production of stainless steel welded steel pipe excellent in the processability of the weld. Way.

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