WO2008093888A1 - Ferritic stainless steel for exhaust gas passage member - Google Patents

Abstract

Disclosed is a stainless steel for an automobile exhaust gas passage member, which comprises the following components (by mass): C: 0.03% or less, Si: 1% or less, Mn: 1.5% or less, Ni: 0.6% or less, Cr: 10-20%, Nb: more than 0.5% and not more than 0.7%, Ti: 0.05-0.3%, Cu: more than 1% and not more than 2%, V: 0.2% or less, N: 0.03% or less, B: 0.0005-0.02%, optionally Al: 0.1% or less, and optionally at least one member selected from Mo, W, Zr and Co in the total amount of 4% or less, with the remainder being Fe and unavoidable impurities, wherein the stainless steel has such a structure that a Cu phase and a Nb compound phase each having a longer diameter of 0.5 μm or more is contained at a ratio of 10 pieces/25 μm2 or less. The stainless steel can show excellent thermal fatigue properties and low-temperature stiffness when used as an exhaust gas passage member of a higher peak temperature type or a lower peak temperature type.

Description

 Ferritic stainless steel for exhaust gas path members

 The present invention relates to a ferritic stainless steel used as an exhaust gas path member typified by an exhaust stoma hold, a catalytic converter case (outer cylinder), a front pipe, and a center pipe, and an automobile bright exhaust gas path member using the same.

 Rice field

 Conventional technology

 For heat exhaust path members such as Exostoma Honoredo, hornworm medium comparator cases, front pipes, center one pipes, etc., highly heat-resistant SUS 4 44-based materials are often used. In addition, as materials with improved high-temperature acid resistance and high-temperature strength in a high-temperature region exceeding 700 ° C., Patent Documents 1 and 2 include ferrite containing about 1 to 2 mass% of Cu. Stainless steel is disclosed. Cu in steel precipitates as a Cu phase by heating and has the effect of improving high temperature strength and thermal fatigue properties. This kind of Cu-containing steel is particularly suitable for exhaust gas path members connected to the type of engine with a high exhaust gas temperature.

 Patent Document 1: International Publication No. 0 3 Z O 0 4 7 1 4 Pamphlet

 Patent Document 2: Japanese Patent Laid-Open No. 2 0 06-1 1 7 9 8 5 Problem to be Solved by the Invention

 In recent years, there has been an increasing need for housing exhaust gas path members of automobile engines in a limited space as the number of various devices mounted around the engine increases, and there are increasing cases of severe processing being used. . For this reason, members applied to engines whose exhaust gas temperature is not so high have been required to have extremely excellent thermal fatigue properties and excellent low temperature toughness.

As means for improving the high-temperature strength and thermal fatigue characteristics of ferritic stainless steel, there is known a means of adding an appropriate amount of Cu as described in Patent Documents 1 and 2 mentioned above. Nb up to a maximum of 0.6% by mass for the purpose of increasing the high temperature strength in the high temperature range exceeding C The method of making it contain is adopted. However, according to detailed investigations by the inventors, the Cu-containing steels of Patent Documents 1 and 2 have good thermal fatigue characteristics (for example, 200 to 900 ° C) when the maximum temperature reached is high. However, it has been found that the thermal fatigue characteristics (for example, 200 to 750 ° C) when the maximum temperature is low may be slightly inferior to those of SUS444-based materials. For this reason, the steels of Patent Documents 1 and 2 are advantageous for application to a vehicle equipped with a high-power engine having a high exhaust temperature, and are not very suitable for application to a vehicle equipped with a small engine having a relatively low exhaust temperature. Also, even in the case of a high-power engine, the exhaust temperature may fluctuate depending on how it is used. Therefore, it is desirable to use a material that exhibits good thermal fatigue characteristics as the exhaust gas path member even when the maximum temperature reached is low.

 An object of the present invention is to provide a ferritic stainless steel that exhibits excellent thermal fatigue characteristics and is excellent in low-temperature toughness when applied to any exhaust gas passage member having a high maximum temperature or a low maximum temperature. To do. Means for solving the problem

 As described above, the thermal fatigue characteristics when the maximum temperature reached is as high as 900 ° C or higher, for example, can be improved by utilizing the precipitation of the Cu phase. However, as a result of further studies, it was found that the thermal fatigue characteristics when the maximum temperature reached is as low as about 750 ° C or less, for example, can be improved by controlling the Nb precipitation mode. That is, with Cu phase

By controlling the precipitation form of the Ni compound phase, a ferritic stainless steel can be realized that can cope with both high and low maximum temperatures.

In the present invention, in mass%, C: 0.03% or less, S i: 1% or less, Mn: 1.5% or less, N i: 0.6% or less, C r: 10 to 20%, Nb: more than 0.5 to 0.7%, T i: 0.05 to 0.3%, Cu: more than 1 to 2%, V: 0.2% or less, N: 0.03% or less, B: 0.00 05 to 0.02%, and A 1: 0.1% or less as needed Contains one or more of Mo, W, Zr, and Co in a total range of 4% or less, and consists of the balance Fe and unavoidable impurities, and is defined by the following formula (1) [T i] Depending on the value, the [Nb] value defined by the following formula (2) or (3) is in the range of 0.5 to 0.65, and 10 Cu phases with a major axis of 0.5 μπι or more / 25 μηι ² or less , Chikaratsu diameter 0.5 mu m or more N b compound phase 1 0 / / 25 m for exhaust gas passage components of stainless steel having an adjusted organization ² below Hisage Provided.

 [T i] = T i -4 (C + N) …… (1)

 When [T i] 0, [Nb] = Nb ...... (2)

 When [T i] is 0, [Nb] = Nb + 0.5 [T i] ...... (3)

 The value of the content of the element expressed in mass% is assigned to the locations of Ti, C, and N in (1), and Nb in (2) and (3). As the exhaust gas path member, for example, an automobile exhaust stoma hold, a catalytic converter, a front pipe, and a center pipe are suitable targets. Of course, it may be used as various exhaust gas path members other than automobiles.

 According to the present invention, the thermal fatigue characteristics when the maximum ultimate temperature is high (for example, 200 to 900 ° C) and the thermal fatigue characteristics when the maximum ultimate temperature is low (for example, 200 to 750 ° C) are simultaneously improved. Ferritic stainless steel material was realized. Accordingly, the ferritic stainless steel of the present invention can be widely applied from the case where it is used as an exhaust gas path member at a high exhaust gas temperature to the case where it is used at a low exhaust gas temperature. In addition, this steel material has the basic heat resistance (high-temperature oxidation resistance, high-temperature strength) required for automobile exhaust gas path members, and is excellent in low-temperature toughness. It is extremely useful as a route member. Preferred embodiments of the invention

 The steel of the present invention contains Cu and Nb, and different types of precipitated phases of Cu phase and Nb compound phase are formed in the actual use environment. However, it exhibits excellent thermal fatigue properties.

As a result of various investigations, in the steel satisfying the composition described later, the number of Cu phases with a major axis of 0.5 ^ m or more is 10 // 25 μπι2 or less, and the number of Nb compound phases with a major axis of 0.5 μπι or more is 10 or less Z25 ^ _m 2 It has been found that when it is in an adjusted microstructure, heating during use sufficiently forms fine precipitates, resulting in a significant improvement in thermal fatigue properties. In other words, in both the Cu phase and the Nb compound phase, if a large number of precipitated phases with a major axis of 0.5 μηι or more are present in the material at a density exceeding 10/25 μπι ² in advance, As a result, fine precipitate phases are not generated sufficiently, and stable improvement in thermal fatigue characteristics cannot be expected. Cu Alternatively, if Nb is excessively contained outside the provisions described below, heat can be generated if a fine precipitate phase can be produced even if a coarse Cu phase or Nb compound phase is present in the material. In some cases, fatigue characteristics can be improved. In this case, however, the presence of a coarse precipitate phase is not preferable because it causes adverse effects such as low temperature toughness.

The Cu phase is a so-called ε-Cu precipitate phase, which usually grows in one direction, and usually has a rod shape. The Nb compound phase is a precipitate mainly composed of Fe ₂ Nb, and when it contains Mo, it generally takes the form of Fe 2 (Mo, Nb). This Nb compound phase also tends to grow in one direction, so it usually has a rod shape. Therefore, it is reasonable to evaluate the size of these precipitate phases by the major axis. Specifically, the major axis of the precipitate appearing in the image observed with a transmission electron microscope (TEM) (corresponding to the projected length on the observation surface) may be adopted as the major axis here. Whether it is a Cu phase or an Nb compound phase can be identified using an analyzer (such as EDX) equipped with TEM. Nb carbide and Nb nitride are excluded from the Nb compound phase mentioned here. Carbides and nitrides are often massive or spherical, and can be distinguished from the Fe ₂ Nb-type precipitated phase relatively easily by their shape. If it is difficult to distinguish from the shape, it can be identified using the analyzers described above (EDX, etc.).

 When the maximum temperature reached during use is about 900 ° C or higher, Cu is sufficiently re-dissolved by heating, and a fine Cu phase precipitates mainly at 500 to 7 ° C. The This improves the fatigue characteristics (ie, thermal fatigue characteristics) during repeated heating. On the other hand, Cu does not re-dissolve sufficiently in repeated heating where the maximum temperature reached is as low as about 750 ° C or lower. For this reason, the effect of improving the thermal fatigue characteristics due to the fine precipitation of the Cu phase cannot be obtained sufficiently.

In the present invention, thermal fatigue characteristics when the maximum temperature reached is not sufficiently improved by the Cu phase alone are captured by fine precipitation of the Nb compound phase. The Nb compound phase brings about precipitation strengthening by heating at 700 to 750 ° C for a very short time. It was found that this short-time precipitation strengthening phenomenon markedly improved the thermal fatigue characteristics in the range of 200 to 750. Although there are many unclear points about the mechanism at this time, the short-term precipitation strengthening by the Nb compound phase suppresses pulsation due to ratchet deformation and compressive stress at the initial stage of repeated heating. Works well for fatigue properties It is guessed that it is used.

 Hereinafter, components and formation will be described.

 When C and N are contained in an excessive amount, which is generally considered an effective element for improving high-temperature strength such as creep strength, the oxidation characteristics, caloe properties, low-temperature toughness, and weldability deteriorate. In the present invention, both C and N are limited to 0.03% by mass or less.

 Si is effective in improving high-temperature acid resistance. In addition, it combines with the oxygen in the atmosphere during welding to prevent oxygen from entering the steel. However, if the Si content is excessive, the hardness increases and the workability and low temperature toughness are reduced. In the present invention, the Si content is limited to 1% by mass or less, and may be limited to 0.1 to 0.6% by mass, for example.

 Mn improves high-temperature oxidation resistance, especially scale peel resistance. Also, like Si, it combines with the oxygen in the atmosphere during welding to prevent oxygen from entering the steel. However, excessive addition hinders workability and weldability. In addition, Mn is an austenite stabilizing element, so if it is added in a large amount, a martensite phase is likely to be formed, which causes a decrease in workability. Therefore, the Mn content is limited to 1.5% by mass or less, and more preferably 1.3% by mass or less. For example, it may be specified to be less than 0.1 to 1% by mass.

 Ni is a stable austenite element. If it is contained in excess, it causes the formation of a martensite phase and causes a decrease in workability and the like, similar to Mn. Ni content is allowed up to 0.6% by mass.

 Cr stabilizes the ferrite phase and contributes to the improvement of oxidation resistance, which is important for high-temperature materials. However, excessive Cr content leads to a decrease in workability of the steel material. Therefore, the Cr content is 10 to 20% by mass. The Cr content is preferably adjusted according to the use temperature of the material. For example, when excellent high-temperature oxidation resistance up to 9500 ° C is required, a Cr content of 16 mass% or more is desired, and if it is up to 900 ° C, 1 2 to 16 mass% The range is acceptable.

Nb is an extremely effective element for securing high-temperature strength in a high-temperature region exceeding 700 ° C. This improvement in high-temperature strength is considered to contribute greatly to the solid solution strengthening of Nb in this component system. In addition, N b fixes C and N, and is effective in preventing toughness 'I' life loss. Although the action of these N b is generally conventional, in the present invention, N b compound is further added. By utilizing the fine precipitation of the phase, the thermal fatigue characteristics when the maximum temperature reached It aims to improve (as mentioned above). In order to sufficiently obtain such Nb action, it is necessary to secure an Nb content exceeding 0.5% by mass, and it is more effective to secure an Nb content exceeding 0.6% by mass. However, excessive N addition leads to a decrease in raw material II, low temperature toughness, and increased weld hot cracking susceptibility, so the Nb content is limited to 0.7 mass% or less.

 On the other hand, it is easy to combine with N1 ^ C and N. If Nb is consumed as carbides or nitrides, improvement in high-temperature strength by solute Nb and improvement in thermal fatigue properties by Nb compound phase will be insufficient. Therefore, the [Nb] value defined by the following equation (2) or (3), that is, the effective Nb amount, is defined according to the [Ti] value defined by the following equation (1).

 [T i] = T i -4 (C + N) …… (1)

 When [T i] ≥0, [Nb] = Nb (2)

 When [T i] is 0, [Nb] = Nb + 0.5 [T i] (3)

 When the Ti content is more than the amount that can bind to C and N, that is, when the effective Ti content [T i] is 0 or more, the value of the Nb content is expressed as in (2). The effective Nb amount [Nb] may be adopted as it is. On the other hand, when the effective Ti amount [T i] is smaller than 0, it is necessary to secure the Nb content to compensate for the effective Ti amount, and a value smaller than the Nb content is also valid as shown in (3). The amount of Nb [Nb] is adopted.

 In the present invention, the Nb content is in the range of more than 0.5 to 0.7 mass%, and the effective Nb content [Nb] is further specified in the range of 0.5 to 0.65. In other words, strictly defining the Nb content within an extremely narrow range is important for improving thermal fatigue characteristics when the maximum temperature is low, in addition to high temperature strength and low temperature toughness.

T i generally fixes C and N and is effective in improving formability and preventing toughness deterioration. In particular, in the present invention, it is necessary to strictly control the Ti content from the viewpoint of securing the effective Nb amount as described above. Specifically, the Ti content is 0.05 mass. / ₀ or more must be secured. However, excessive addition of Ti causes deterioration of the surface properties due to the formation of a large amount of TiN, and also adversely affects weldability and low temperature toughness. For this reason, the Ti content is specified to be 0.05 to 0.3% by mass.

A1 is a deoxidizer and an element that improves high-temperature oxidation resistance. In the present invention, A 1 can be contained in the range of 0.1% by mass or less. Excess A 1 content during welding A large amount of acid oxide is formed on the surface, which may act as a starting point for processing cracks.

 Cu is an important element for increasing the high temperature strength. That is, in this effort, as described above, the Cu phase fine dispersion precipitation phenomenon is used to increase the strength at 500 to 700 ° C, especially when the maximum temperature reached is as high as 900 ° C or higher. For that purpose, Cu content exceeding 1% by mass is necessary. However, excessive Cu content reduces workability, low temperature toughness, and weldability, so the Cu content is limited to 2 mass% or less.

 V contributes to the improvement of high-temperature strength by the combined addition of Nb and Cu. In addition, coexistence with Nb improves workability, low temperature toughness, intergranular corrosion susceptibility, and toughness of weld heat affected zone. However, excessive addition leads to workability and low temperature toughness, so it should be contained in the range of 0.2% by mass or less. The V content is desirably in the range of 0.01 to 0.2% by mass, and more preferably 0.03 to 0.15% by mass.

 B is effective for improving secondary work brittleness. It is surmised that the mechanism is due to the decrease in grain boundary solid solution C and the strengthening of grain boundaries. However, excessive addition of B deteriorates manufacturability and weldability. In the present invention, B is contained in the range of 0.0005 to 0.02 mass%.

 Mo, W, Zr, and Co are effective for improving the high-temperature strength of the ferritic stainless steel of this component system, and one or more of these can be added as necessary. However, since a large amount of additive causes brittleness of the steel, when these elements are added, the total content should be 4% by mass or less. It is more effective to add so that the total content is in the range of 0.5 to 4% by mass.

Ferritic stainless steel having the above composition can be melted by a general steelmaking process of stainless steel, and thereafter, for example, a process of “hot rolling → annealing → pickling”, or even “cold”. By performing the process of “rolling—annealing → pickling” once or multiple times, an annealed steel sheet having a thickness of about 1 to 2.5 mm is obtained. However, in finish annealing, it is important to set an appropriate cooling rate in each of the Nb precipitation temperature range and the Cu precipitation temperature range. For example, as the finish annealing condition, the steel is heated to 950 to 1100 ° C, preferably 1000 to 1100 ° C, and then the average cooling rate of 1000 to 700 ° C, which is the precipitation temperature range of the Nb compound phase (heating temperature is 1000 ° C). When the temperature is lower than C, the average cooling rate from the heating temperature to 700 ° C) is over 30 to 100 ° C / second, and the average cooling rate of 700 to 400 ° C, which is the Cu phase precipitation temperature, is 5 to 50 °. The condition of C / second can be adopted. Above composition adjustment With such heat treatment conditions, 10 steel phases with a major axis of 0.5 μηι or more, 25 μm ² or less, and 10 Nb compound phases with a major axis of 0.5 μηι or more, adjusted to 10 or less 25 μπι ² or less in the microstructure state (annealing) Steel plate). Here, “finish annealing” is the final annealing performed in the steel production stage.

 An exhaust gas path member is constructed using this annealed steel sheet. In the case of a tubular member, the annealed steel plate is roll-formed into a predetermined tube shape, and the butt portion of the material is welded to produce a welded steel pipe. As a welding method, a known pipe making welding method such as TIG welding, laser welding, or high frequency welding can be applied. The obtained steel pipe is subjected to a heat treatment process and a pickling process as necessary, and then molded into an exhaust gas passage member. Example

A ferritic stainless steel having the composition shown in Table 1 was melted and an annealed steel sheet with a thickness of 2 mm was obtained in the process of “hot rolling—annealing / pickling → cold rolling → finish annealing / pickling”. . In addition, a round bar with a diameter of about 25 mm was made by hot forging using a part of the forged slab, and this was finish-annealed. Finish annealing on sheet materials and finishing annealing on bar materials, except for steel No. l 9, the average cooling rate from 1000 ° C to 700 ° C exceeds 30 ° C after holding 1050 ° CX soaking for 1 minute. The temperature was in the range of 100 ° C / second, and the conditions were such that the average cooling rate from 700 to 400 ° C was in the range of 5 to 50 ° CZ seconds. For steel No.19, finish annealing was performed under the same conditions as in the other examples except that the average cooling rate from 1000 to 700 ° C was controlled in the range of 10 to 20 ° C / sec. (Same conditions for both board and bar).

■ ¼ffl¾¾n½ «: Stop

When the rolling direction of the plate and the longitudinal direction of the bar are referred to as the L direction, the metal structure was observed in the cross section perpendicular to the L direction for the plate and bar after finish annealing. Use a transmission electron microscope (TEM) to examine the size of the Cu phase opium Nb compound phase, 25; the number of Cu phase opium Nb compound phases with a major axis of 0.5 / m or more observed per um ² Was measured. At least 10 visual fields were observed per sample, and the average was taken. The types of precipitated phases were classified by quantitatively measuring Fe, Nb, Mo, and Cu using an EDX (energy dispersive X-ray fluorescence spectrometer) attached to the TEM. When the precipitated phase is fine, the constituent elements of the steel substrate are detected together. Therefore, in the analysis values of the above four elements that are aimed at the precipitated phase, the Cu phase is the one that has a Cu content of 50% by mass or more. Those with Nb of 30% by mass or more were classified as Nb compound phases. The results are shown in the column for Cu phase in Table 2, with 10 Cu phases with a major axis of 0.5 / m or more and no more than 25 μπι ² as ◯ (good) and the others as X (bad). . The results are shown in the column of Nb compound phase in Table 2 with 10 Nb compound phases with a major axis of 0.5 μπι or more, Z25 μπι ² or less with ◯ (good), and others with X (bad). . For each steel, there was no difference in the results between the plate and the bar, so the evaluation of the precipitated phase shown in Table 2 also applies to the deviation and deviation of the plate and bar.

 Using the plate material, an impact test was conducted to evaluate low temperature toughness. Take a V-notch impact test piece so that the direction of impact is the rolling direction of the plate, and perform an impact test of JISZ 2242 at a 25 ° C pitch in the range of _75 to 50 ° C to determine the ductile brittle transition temperature. It was. A transition temperature lower than 125 ° C (exhibiting a ductile fracture surface even at 25 ° C) was evaluated as ◯ (good), and the others were evaluated as X (defect).

 Thermal fatigue tests were conducted using rods, and the thermal fatigue characteristics at 200 to 750 ° C and 200 to 900 ° C were investigated. Cut the gap between the gauge points so that the diameter is 10 mm and the parallel part length is 2 Omm (length between the gauge points is 15 mm), and R = 5.7 mm so that the diameter is 7 mm at the center position between the gauge points. A round bar test piece with a notch was prepared and tested and evaluated under the following conditions in air. The number of repetitions when the stress drops to 75% of the stress at the time of cracking is defined as the thermal fatigue life.

 (Thermal fatigue characteristics at 200 to 750 ° C)

The restraint rate (ratio of applied strain to thermal expansion) is 25%, and "200 ° C x 0.5 min hold → temperature rise to about 750 ° C at about 3 ° C / sec → hold at 750 ° C for 2.0 min → Cooling rate approx. 3 ° C / Repeated heat cycle with `` cooled to 200 ° C in seconds '' as one cycle, thermal fatigue life is 8 (good) if it is 1800 cycles or more, △ 150,000 cycles or more and less than 1800 cycles (Slightly bad), less than 150 thousand cycles was evaluated as X (bad), and 〇 evaluation was accepted.

 [Thermal fatigue characteristics at 2 00-900 ° C]

 The restraint ratio (ratio of applied strain to thermal expansion) is set to 20%, “20 ° CX 0 · 5 minutes hold → temperature rise to 9 ° 0 ° C at about 3 ° CZ seconds → 9 0 0 Hold for 0.5 min at ° C → Cool to about 200 ° C at a cooling rate of about 3 ° C / sec. Repeat the heat cycle to 1 cycle, and the thermal fatigue life is more than 900 cycles (good) , Less than 90 cycles were evaluated as X (defect), and 〇 evaluation was accepted.

 These results are shown in Table 2. Table 2

 Precipitation phase Thermal fatigue properties

 Category No. Steel Low temperature toughness

 Cu phase Nb compound phase 200-750 ° C 200-900. C

 1 A ○ ○ ○ ○ ○

2 "B ○ ○ O ○ O

3 C ○ ○ O ○ ○

■ 4 D O O O O O

5 E ○ ○ O ○ ○

 Departure 6 F ○ ○ ○ ○ ○

 7G ○ ○ ○ • O ○

 Example

 8 H ○ O O ○ O

9 I ○ ○ O ○ ○

.10 J 〇 〇 〇 .〇 〇

11. K 〇 〇 〇 o 〇

12 L 〇 〇 〇.

 13 M ○ ○ ○ .X O

14 N 〇 〇 〇 X 〇

15 0 ○ ○ Δ

 Ratio 〇 〇

 16 P X X X ○ ○

 Example 17 Q ○ O O Δ ○

 18 R ○ ○ O Δ ○

19 B ○ XX Δ ○ As can be seen from Table 2, the examples of the present invention satisfying the chemical composition specified in the present invention and the precipitation form of the Cu phase and Nb compound phase have thermal fatigue characteristics (200 to 900 ° C) when the maximum temperature reached is high. ) And thermal fatigue properties (200 to 750 ° C) when the maximum temperature reached is low, and low-temperature toughness was also good.

 On the other hand, Nos. 13-15 and 17 as comparative examples have low Nb content and lack of effective Nb content [Nb]. Therefore, when the maximum temperature reached is as low as 750 ° C, a fine Nb compound phase is formed. Was insufficient and the thermal fatigue characteristics were inferior at 200 to 750 ° C. Since N o .16 contains excessive Cu and Nb, it was possible to improve the thermal fatigue properties despite the presence of many coarse Cu and Nb compound phases. And low temperature toughness. : ^ 0.18 is a conventional steel equivalent to 3113444, which has a low Cu content, but a high Mo content, so its thermal fatigue characteristics at 200 to 900 ° C were good. However, since the effective Nb content was insufficient, the thermal fatigue characteristics at 200-900 ° C were not improved. No. 19 is a steel having the composition specified in the present invention. In the finish annealing, the cooling rate in the Nb compound phase precipitation temperature range is too slow, resulting in the formation of a coarse Nb compound phase. Since the fine Nb compound phase did not sufficiently precipitate by heating, the thermal fatigue characteristics at 200 to 750 ° C were inferior. Also, low temperature toughness is inferior due to the influence of coarse Nb compound phase.

Claims

1. In mass%, C: 0.03% or less, Si: 1% or less, Mn: 1.5% or less, Ni: 0.6% or less, Cr: 10-20%, Nb: more than 0.5 to 0.7%, T i: 0.05 to 0 · 3%, Cu: more than 1 to 2%, V: 0.2% or less, N: 0.03. /. B: 0.0005-0. It consists of 02%, the balance Fe and unavoidable impurities, and the [Nb] value defined by the following formula (2) or (3) is 0.5 depending on the [T i] value defined by the following formula (1). The composition is in the range of ~ 0.65, and the Cu phase with a major axis of 0.5 μη or more is adjusted to 10/25 μηι ² or less, and the Nb compound phase with a major axis of 0.5 μηι or more is adjusted to 10/25 μm ² or less. Stainless steel for exhaust gas path members with a structured structure.  [T i] = T i 1 4 (C + N) ...... (1) Enclosure  When [T i] ≥0, [Nb] = Nb ...... (2)  When [T i] is 0, [Nb] = Nb + 0.5 [T i] (3) 2. The stainless steel for exhaust gas passage member according to claim 1, further having a composition containing A 1: 0.1% by mass or less. 3. The ferritic stainless steel for exhaust gas passage members according to claim 1 or 2, further comprising a composition containing at least one of Mo, W, Zr, and Co in a total range of 4% or less. 4. The automobile exhaust gas path member according to any one of claims 1 to 3, wherein the exhaust gas path member is one of an automobile exhaust hold, a catalytic converter, a front pipe, and a center pipe.