JP2003213381A - High corrosion resistant low strength stainless steel with excellent workability and toughness of welds and its welded joints - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a stainless steel having, at the same time, the three characteristics of corrosion resistance, welded toughness and workability at the same time by optimizing the steel composition. SOLUTION: C: less than 0.02% by mass, Si: 1.0% by mass or less, Mn: 1.5% by mass or less, Cr: 11% by mass or more, 15% by mass
Hereinafter, a component composition containing Ni: more than 1.0% by mass and 2.5% by mass or less, Al: less than 0.1% by mass, and N: less than 0.02% by mass within a range satisfying a predetermined formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to structural materials for vehicles such as railroads, automobiles and buses, and structural materials for civil engineering and the like, and has high workability and toughness at the welded portion after welding, high corrosion resistance and low strength. TECHNICAL FIELD The present invention relates to stainless steel, and particularly to stainless steel which is suitable for welded structures, is applied to visible parts requiring corrosion resistance, and is suitable as a base material for welded joints.

[0002]

2. Description of the Related Art A relatively low-strength welded structural stainless steel is suitable for the above-mentioned applications, but a conventional low-strength welded structural stainless steel having a tensile strength of, for example, 500 MPa, is
Cr content is about 11% by mass, the lowest of all stainless steels, and since Ni and Mo, which improve corrosion resistance, are not added, the corrosion resistance is insufficient to be applied to parts exposed to the outdoors. was there.

To address this problem, for example, in Patent Document 1, Ni and Mo are added, and the volume ratio of the heat-affected zone to the welding heat affected zone is increased.
A stainless steel for construction has been proposed which has improved corrosion resistance and toughness in the heat affected zone by forming a martensite structure of 50% or more.

However, when a martensite structure of 50% by volume or more is formed in the heat-affected zone of the weld, the strength of the heat-affected zone of the weld is remarkably increased and the elongation is lowered, so that the workability of the weld is significantly deteriorated. Since it appears, it was not suitable for applications where processing is performed after welding.

As a stainless steel having excellent corrosion resistance, a martensitic stainless steel used for oil well pipes and line pipes is known. The stainless steel usually contains Ni in an amount of 3% by mass or more. Therefore, the structure after annealing is martensite, and the tensile strength is as high as 800 MPa or more, which makes it unsuitable for applications that require processing such as bending.

[0006]

[Patent Document 1] Japanese Patent Laid-Open No. 11-302795

[0007]

As described above, at present, no steel grade has been found that simultaneously achieves the three properties of corrosion resistance, toughness and workability of the welded portion. Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide a stainless steel in which the three properties of corrosion resistance, weld toughness and workability are simultaneously established by optimizing the steel components. .

[0008]

In order to achieve the above-mentioned object, the inventors have made a detailed description of the effects of the components of stainless steel on the corrosion resistance, the toughness and workability of the weld, the strength and elongation of the base metal. Upon investigation, (a) the addition of Cr and Ni significantly improved the corrosion resistance, and (b)
By optimizing the amounts of C, N, Cr, Mn and Ni and setting the amount of martensite produced in the weld heat affected zone to 5% by volume or more and less than 50% by volume, excellent toughness and workability are achieved in the welded zone. , (C) By controlling the amount of Ni, Mn and C that suppress the ferrite transformation and making the metal structure after annealing of the base material ferrite + carbide, low tensile strength of 600 MPa or less and 25% or more of The inventors have newly found that high elongation can be obtained, and completed the present invention.

That is, the structure of the present invention is as follows. (I) C: less than 0.02 mass%, Si: 1.0 mass% or less, Mn:
1.5 mass% or less, Cr: 11 mass% or more and 15 mass% or less, Ni:
It contains more than 1.0% by mass and less than 2.5% by mass, Al: less than 0.1% by mass and N: less than 0.02% by mass in a range satisfying the following formulas (1) to (4), and P and S are respectively P: High corrosion resistance and low strength stainless steel with excellent workability and toughness, characterized by containing 0.04% by mass or less and S: less than 0.01% by mass, with the balance being essentially the composition of Fe and inevitable impurities. steel. Note [Cr] + 1.2 × [Ni] ≧ 15.0 ---- (1) [Cr] + 23 × [C] + 18 × [N] −1.2 × [Mn] −0.4 × [Ni] ≦ 16.0 --- (2) [Ni] + 0.5 × [Mn] + 30 × [C] ≦ 3.0 ----- (3) 0.015 <[C] + [N] <0.03 ----------- --------- (4) Where, [Cr], [Ni], [C], [N] and [Mn]
Are the contents of Cr, Ni, C, N and Mn (% by mass)

(Ii) In addition to the component composition described in (i) above, Cu: 2 mass% or less, Mo: 2 mass% or less and Co:
A high-corrosion-resistant low-strength stainless steel excellent in workability and toughness of a welded portion, containing 1% or more of 2% by mass or less and satisfying the following formulas (5) to (8). Note [Cr] ＋ 1.5 × [Mo] ＋ 1.2 × [Ni] ＋ 0.5 × [Cu] ＋ 0.3 × [Co] ≧ 15.0 ---- (5) [Cr] ＋ 1.2 × [Mo ] + 23 × [C] + 18 × [N] −1.2 × [Mn] −0.4 × [Ni] −0.2 × [Cu] ≦ 16.0 ---- (6) [Ni] + 0.5 × ([Mn] + [Mo] + [Cu]) + 30 × [C] ≦ 3.0 ---- (7) 0.015 <[C] + [N] <0.03 ----------------- --- (8) where [Cr], [Mo], [Ni], [Cu], [Co],
[C], [N] and [Mn] are Cr, Mo, Ni and C, respectively.
Content of u, Co, C, N and Mn (% by mass)

(Iii) In the above (i) or (ii), Ti: 0.2 mass% or less, Nb: 0.2 mass% or less, V: 0.2 mass% or less, Zr: 0.2 mass% or less and Ta: 0.2 mass% or less. A high-corrosion-resistant low-strength stainless steel excellent in workability and toughness of a weld, characterized by containing one or more of the following.

(Iv) In any one of (i) to (iii) above, B: 0.005% by mass or less and Ca: 0.005% by mass.
A high-corrosion-resistant low-strength stainless steel excellent in workability and toughness of a weld, characterized by containing one or two of the following.

(V) Any one of the above (i) to (iv), further containing one or two kinds of W: 0.1 mass% or less and Mg: 0.01 mass% or less. High corrosion resistance and low strength stainless steel with excellent workability and toughness.

(Vi) In any of the above (i) to (v), a high corrosion resistance low strength stainless steel excellent in workability and toughness of a welded portion, which has a tensile strength of 600 MPa or less.

(Vii) Any one of the above (i) to (vi)
Welded joint made of stainless steel of
The ratio of martensite structure in the heat-affected zone is 5% by volume
Above 50% by volume, and the charpy of the welding heat affected zone
-Shock value is 30 J / cm at -50 ° C ²It is characterized by the above
Weld joint to be.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The stainless steel of the present invention (hereinafter referred to as the present invention steel) will be described in detail below. First, the basic composition of the steel of the present invention will be described in detail. C: less than 0.02% by mass C is an element that increases the strength of steel and deteriorates workability, and also decreases the toughness of the welded part. When the content is 0.02% by mass or more, its adverse effect becomes remarkable, so 0.02% by mass Limited to less than%. In particular, from the viewpoint of weld toughness, it is desirable that the content be 0.012 mass% or less.

Si: 1.0% by mass or less Si is an element necessary as a deoxidizer, and for that purpose,
It is preferable to contain 0.1% by mass or more. However, if it exceeds 1.0 mass%, the steel is remarkably embrittled and the toughness of the welded part is also lowered, so the content is limited to 1.0 mass% or less. From the viewpoint of weld toughness, it is desirable that the content be 0.3 mass% or less.

Mn: 1.5% by mass or less Mn increases the strength of steel and lowers the workability, and also reduces the corrosion resistance, so it is limited to 1.5% by mass or less.
From the viewpoint of corrosion resistance, it is recommended to limit the content to preferably less than 1.0% by mass, more preferably 0.5% by mass or less.

Cr: 11% by mass or more and 15% by mass or less Cr is an elemental component effective in improving the corrosion resistance which is a characteristic of stainless steel, and 11% by mass is necessary for obtaining sufficient corrosion resistance.
The above is necessary, and this is the lower limit. Particularly, from the viewpoint of corrosion resistance, it is preferable to add Cr in an amount of 12 mass% or more. More preferably, it is in the range of more than 13% by mass. On the other hand, Cr lowers the toughness of the steel, and when it is contained in excess of 15% by mass, the toughness is remarkably deteriorated, so this is made the upper limit. From the viewpoint of toughness, it is desirable that Cr be 14 mass% or less.

Ni: more than 1.0% by mass and 2.5% by mass or less Ni improves the corrosion resistance, which is a characteristic of stainless steel, and promotes the formation of an austenite phase at high temperatures (approximately 1000 to 1100 ° C.), and By forming a martensite structure of 5% by volume or more, the weld toughness, which is a characteristic of structural stainless steel, is improved. In order to obtain the effect, it is necessary to add more than 1.0% by mass. In particular, from the viewpoint of weld toughness, it is preferable to add more than 1.5% by mass. On the other hand, the addition of more than 2.5% by mass saturates the effect of improving the toughness of the welded part and only increases the cost of the material, so it is limited to 2.5% by mass or less.

Al: less than 0.1% by mass Al is necessary as a deoxidizer for steelmaking, and preferably 0.01
It is contained in an amount of not less than 0.1% by mass, but excessive addition thereof lowers the toughness, so the content is limited to not more than 0.1% by mass.

N: less than 0.02% by mass N is an element that lowers the toughness of the welded portion like C, and if the content is 0.02% by mass or more, its adverse effect becomes remarkable, so N is limited to less than 0.02% by mass. . Particularly, from the viewpoint of weld zone toughness, the upper limit is preferably 0.012% by mass.

Here, with respect to C and N, satisfying the above equation (4) or (8), that is, C + N is
It should be less than 0.03% by mass. Because C + N is
This is because if the content is 0.03% by mass or more, the toughness of the welded part is significantly reduced. Particularly, from the viewpoint of weld toughness, it is desirable that the content be 0.02 mass% or less. On the other hand, 5 in the heat affected zone
In order to form a martensite structure of volume% or more, C + N needs to exceed 0.015 mass%, and this is the lower limit.

P: 0.04 mass% or less P is an element that reduces hot workability, and it is advantageous to suppress P as much as possible in order to secure manufacturability. However, if it is made too low, the steelmaking cost will rise, so 0.04 mass% is made the upper limit. From the viewpoint of hot workability, the content is more preferably 0.02 mass% or less.

S: less than 0.01 mass% S, like P, has a high hot workability as in the case of P, but 0.01% by mass is economically limited due to the economic limitation on the de-S treatment during steelmaking.
It is less than mass%. However, from the viewpoint of hot workability,
It is desirable that the content be 0.005 mass% or less.

Further, in the steel of the present invention, it is essential that the above-mentioned basic component compositions satisfy the above formulas (1) to (3). First, in order to obtain excellent corrosion resistance, which is one of the characteristics of the steel of the present invention, addition of Cr and Ni is effective, and in order to obtain that effect, the above formula (1), that is,
It is necessary that the value of [Cr] + 1.2 × [Ni] is 15.0 or more. Especially, when importance is attached to corrosion resistance, it is preferably 16.0
Or more, more preferably 17.0 or more.

On the other hand, the addition of Cr may increase the ferrite equivalent, and the ferrite structure may become coarse in the heat-affected zone of the weld and the toughness of the weld may be reduced. Therefore, when adding Cr, the amount of addition of Cr is regulated. is necessary. This is because an excessive increase in ferrite equivalent is suppressed, and at the same time, Mn and Ni are added to increase the austenite equivalent and the amount of martensite in the weld heat affected zone is secured at 5% by volume or more.

The martensite structure in the heat-affected zone of welding is effective in suppressing coarsening of the ferrite structure and improving the toughness by the fine structure itself. For that purpose, 5% by volume or more is required. It is necessary to secure it. Particularly, from the viewpoint of weld toughness, it is preferably 10% by volume or more, more preferably 20% by volume or more. On the other hand, when the content is 50% by volume or more, the heat-affected zone of the weld is significantly hardened and the bending workability of the weld is significantly deteriorated. Therefore, it is necessary to limit the content to less than 50% by volume. Furthermore, the welding heat-affected zone has a Charpy impact value of 30 J / cm ² or more at -50 ° C, more preferably 50 J / cm ²
It is necessary to be above. That is, when the Charpy impact value is less than 30 J / cm ² at −50 ° C., the welded portion may be brittlely fractured when used as a vehicle structural material or a civil engineering structural material in a cold region.

FIG. 1 shows the relationship between the amount of martensite in the heat affected zone of welding and the toughness and workability of the welded portion. That is, FIG. 1 shows that the C and N contents are 0.02 mass% C-0.
02% by mass N: 0.01% by mass C-0.01% by mass N, fixed at two levels, (12-14% by mass) Cr- (0.2-1.5% by mass) Mn-
(1-2 mass%) Within the composition range of Ni, the composition of the components is adjusted to change the amount of martensite in the heat-affected zone of welding,
For each weld with a different amount of martensite, the Charpy test fracture surface brittleness ductility transition temperature (vTr
s) and bending workability.

First, as a structural material, the minimum condition is that the brittle ductile transition temperature is 0 ° C. or lower. For that purpose, at 0.02 mass% C-0.02 mass% N, the martensite content is 50% by volume. It is necessary to be above. However,
According to the bending test of the weld heat affected zone, it has been found that cracking occurs when the amount of martensite is 50% by volume or more regardless of the C and N contents. In order to reduce the amount of martensite to less than 50% by volume, it is necessary to reduce C and N. In fact, with 0.01 mass% C-0.01 mass% N, a brittle ductile transition temperature of 0 ° C. or lower was obtained even when the amount of martensite was 50 vol% or lower.

Here, C and N have the effect of increasing the austenite equivalent, but as shown in FIG. 1, they lower the toughness of the material, so they must be reduced to improve the toughness of the welded part. Further, the above formula (2) is satisfied between Cr, which is regulated for the reason of increasing the ferrite equivalent, and Mn and Ni, which compensate for the lack of the austenite equivalent, that is, [Cr] + 23 × [C] + 18 × [N] −1.2 × [Mn] −
It is important to set the value of 0.4 × [Ni] to 16.0 or less. From the viewpoint of weld toughness, it is preferably 15.0 or less, more preferably 14.0 or less.

That is, the left side of the above equation (2) is
When it exceeds 16.0, the toughness of the weld zone becomes remarkable due to the coarsening of the ferrite structure grains in the heat-affected zone of the weld due to the increase of the ferrite equivalent or the toughness decrease due to the increase of the C and N contents, or both. descend.

Next, in order to improve the workability of the base material,
It is necessary to transform the martensite structure generated by hot rolling into a soft ferrite structure by heat treatment such as annealing. To that end, Ni, which increases the resistance of ferrite transformation,
It is necessary to suppress the addition of Mn and C, and the value of the above formula (3), that is, [Ni] + 0.5 × [Mn] + 30 × [C] is limited to 3.0 or less. In particular, from the viewpoint of workability of the base material, 2.5
The following is preferable. By following the above formula (3), it becomes possible to reduce the tensile strength to 600 MPa or less by the usual annealing method.

Here, when the tensile strength exceeds 600 MPa, the workability of the base material is significantly reduced. Therefore, the tensile strength is limited to 600 MPa or less. Particularly, from the viewpoint of workability of the base material, the tensile strength is preferably 550 MPa or less.

In the steel of the present invention, in addition to the above-mentioned basic components, one or two of Cu, Mo and Co described later is used.
It is possible to add more than one kind, and in this case, instead of the above formulas (1) to (3), the above formulas (5) to (3) can be added.
It is essential to satisfy (7). However, equation (5)-
The meaning represented by (7) is the same as in the above equations (1) to (3).

In the steel of the present invention, in addition to the above basic components, the following components can be added as required. Cu: 2% by mass or less, Mo: 2% by mass or less, and Co: 2% by mass or less, one or more kinds First, Mo is an element component effective for improving the corrosion resistance, and a sufficient corrosion resistance improving effect is obtained. Therefore, it is preferable to add more than 0.5% by mass, particularly from the viewpoint of corrosion resistance,
It is preferable to add 0.7 mass% or more. On the other hand, if the content is more than 2% by mass, not only the effect of improving the corrosion resistance is saturated, but also the steel is hardened and the workability is deteriorated, so this is the upper limit. The effect of improving the corrosion resistance can be sufficiently obtained by adding 1.5% by mass or less.

Cu and Co, like Mo, are elemental components effective in improving corrosion resistance. In the present invention, it is not an essential component, but in order to obtain a sufficient effect of improving corrosion resistance, it is preferable to add each in an amount of 0.3% by mass or more. On the other hand, when the content of each exceeds 2% by mass, not only the effect is saturated, but also
Since steel hardens and workability such as bending decreases, this is the upper limit.

0.2% by mass or less of one or more of Ti, Nb, V, Zr, and Ta, respectively. Ti, Nb, V, Zr, and Ta are elements that improve the workability of steel, and if necessary, And add. However, 0.2
If it is added in an amount of more than mass%, the toughness will decrease, so the upper limit is 0.2 mass%. Since the effect of adding Ti, Nb, V, Zr and Ta can be obtained even by adding a small amount, it is not necessary to set a lower limit.

[0039] B: 0.005 mass% or less and Ca: 0.005 mass% or less of one or two kinds B and Ca have the effect of increasing the toughness of steel even if added in a small amount, and are added as necessary. However, not only is the effect saturated when added in excess of 0.005 mass%,
In order to reduce the corrosion resistance, the upper limit is 0.005% by mass.
Since the effect of adding B and Ca can be obtained even by adding a trace amount, it is not necessary to set a lower limit.

W: 0.1% by mass or less and Mg: 0.01% by mass
The following 1 or 2 types W and Mg have the effect of improving the corrosion resistance of steel, and are added as necessary. When W and Mg are contained in excess of 0.1% by mass and 0.01% by mass, respectively, the toughness decreases, so this is made the upper limit. Since the effect of adding W and Mg can be obtained even by adding a trace amount, it is not necessary to set a lower limit.

The steel of the present invention consists essentially of Fe and inevitable impurities other than the above components. That is, being substantially composed of Fe means that the balance contains a small amount of an alkali metal, an alkaline earth metal, a rare earth element, a transition metal, and the like in addition to Fe. The inclusion of a small amount of these elements does not hinder the effects of the present invention.

Here, the method for producing the steel of the present invention is not particularly limited, and may be in accordance with general production of stainless steel. For example, in steelmaking, the basic components and components added as necessary are melted in a converter or an electric furnace, and VO
D (Vacuum Oxygen Decarburization) or AOD (Arg
On Oxygen Decarburization) is preferable. The melted molten steel can be made into a steel material according to a known casting method, but from the viewpoint of productivity and quality, it is preferable to apply the continuous casting method. The steel material obtained by continuous casting is heated to 1000 to 1250 ° C. and hot-rolled into a hot-rolled plate having a desired plate thickness. This hot-rolled sheet is preferably subjected to batch annealing at 600 to 900 ° C., if necessary, and then descaled by pickling or the like to obtain a product. Depending on the application, it may be cold rolled to 700-8
It is also possible to make a cold rolled annealed plate by pickling after continuous annealing at 00 ° C, and then to make a thin plate product.

The welding method applied to the steel of the present invention is MI
Welding methods such as G, MAG, TIG, spot, and laser are all applicable. Since the steel of the present invention reduces C and N and prevents weld cracking, it does not require post heat treatment after welding and can be sufficiently used for structural applications as it is, but for strength adjustment, etc. Alternatively, post heat treatment may be performed.

[0044]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention. First, a 50 kg steel ingot having the chemical composition shown in Table 1 was melted in a high-frequency vacuum melting furnace, and a hot-rolled sheet having a thickness of 3 mm was formed by ordinary hot rolling. Then, after annealing at 670 ° C. for 15 hours and then gradually cooling in an argon atmosphere, the surface scale was removed by pickling to obtain a test material. Using these test materials, the volume ratio of martensite structure, toughness, and bending of the heat-affected zone, which is considered to be the poorest in the rusted area ratio of the base metal after the combined cycle corrosion test (CCT) The tensile strength and elongation of the base material in the rolling direction were investigated.

Here, CCT was a cycle test in which salt spray according to JIS Z2371 was combined with dry and wet. A 70 mm x 150 mm plate was sampled from the test material and subjected to 30 cycles of salt spray: 35 ° C for 2 hours, drying: 60 ° C for 4 hours, and wetness: 50 ° C for 2 hours for a total of 8 hours. The rust area ratio of the test surface was measured.

Further, the test piece taken from the test material was MIG butt welded (wire Y308, current: 150A, voltage: 19V,
Welding speed: 9 mm / s, shielding gas: 100% Ar 20 liter / min, root gap: 1 mm), cut out a cross section perpendicular to the welding direction of the weld, and etch with aqua regia.
The volume ratio of the martensite structure in the heat affected zone was measured.

The bending test was carried out by grinding the weld excess and measuring the size 25.
A test piece of mm × 70 mm is cut out so that the longitudinal direction is perpendicular to the welding direction and the welding heat affected zone is at the center, a bending test of the welding heat affected zone is performed, and the outside of the bend is observed with a magnifying glass to check for cracks. Existence was checked. Bending test: inner radius 1.5 mm, bending angle 180
Went at °.

Further, in order to evaluate the toughness of the welded portion, as shown in FIG.
After collecting a test piece of the size shown in, and grinding the weld surplus, the weld heat-affected zone is notched, and the Charpy impact value according to JIS Z2242 indicates that the Charpy impact value at -50 ° C (test number 5 Was measured.

A JIS Z2201 No. 13 B-shaped test piece was sampled, and the tensile strength and elongation in the rolling direction were measured by a tensile test according to JIS Z2241. Table 1 shows the above measurement and evaluation results.

The rust area ratio of CCT is 30% or less, and the Charpy impact value (vE-
50 ° C) is 30 J / cm ² or more, and the elongation at break is 25% or more,
This means that the characteristics of the present invention are excellent and the expected performance is obtained.

[0051]

[Table 1]

As is clear from Table 1, the steels of the present invention are excellent in corrosion resistance, as well as in the toughness and bending workability of the weld heat affected zone. Also, it can be seen that the base material has a low strength of 600 Mpa or less and a high elongation. One of the comparative steels is inferior to the inventive examples.

[0053]

As described above, according to the present invention, it is possible to provide a stainless steel having three of corrosion resistance, toughness of a weld heat affected zone, workability of a base material and a weld heat affected zone. Is. INDUSTRIAL APPLICABILITY The steel of the present invention is suitable for civil engineering structures, vehicle structural parts such as railways and automobiles.

[Brief description of drawings]

FIG. 1 is a diagram showing an amount of martensite in a heat-affected zone of welding, a Charpy test fracture surface brittleness ductility transition temperature, and a bending test result.

FIG. 2 is a view showing the shape of a bending test piece in a heat-affected zone of welding.

FIG. 3 is a diagram showing the shape of a Charpy impact test piece in a heat-affected zone of welding.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Osamu Furu             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F-term (reference) 4E001 AA03 CA03 EA10

Claims (7)

[Claims] 1. C: less than 0.02 mass%, Si: 1.0 mass% or less, Mn: 1.5 mass% or less, Cr: 11 mass% or more and 15 mass% or less, Ni: 1.0 mass% or more and 2.5 mass% or less, Al: Less than 0.1% by mass and N: less than 0.02% by mass are contained within a range satisfying the following formulas (1) to (4), and P and S are respectively P: 0.04% by mass or less and S: less than 0.01% by mass. The high corrosion resistance and low strength stainless steel excellent in workability and toughness of the welded part, characterized in that the balance is substantially the composition of Fe and unavoidable impurities. Note [Cr] + 1.2 × [Ni] ≧ 15.0 ---- (1) [Cr] + 23 × [C] + 18 × [N] −1.2 × [Mn] −0.4 × [Ni] ≦ 16.0 --- (2) [Ni] + 0.5 × [Mn] + 30 × [C] ≦ 3.0 ----- (3) 0.015 <[C] + [N] <0.03 ----------- --------- (4) Where, [Cr], [Ni], [C], [N] and [Mn]
Are the contents of Cr, Ni, C, N and Mn (% by mass) 2. The component composition according to claim 1, further containing one or more of Cu: 2 mass% or less, Mo: 2 mass% or less and Co: 2 mass% or less, and the following formula: A high corrosion resistance low strength stainless steel excellent in workability and toughness of a weld, which is characterized by satisfying (5) to (8). Note [Cr] ＋ 1.5 × [Mo] ＋ 1.2 × [Ni] ＋ 0.5 × [Cu] ＋ 0.3 × [Co] ≧ 15.0 ---- (5) [Cr] ＋ 1.2 × [Mo ] + 23 × [C] + 18 × [N] −1.2 × [Mn] −0.4 × [Ni] −0.2 × [Cu] ≦ 16.0 ---- (6) [Ni] + 0.5 × ([Mn] + [Mo] + [Cu]) + 30 × [C] ≦ 3.0 ---- (7) 0.015 <[C] + [N] <0.03 ----------------- --- (8) where [Cr], [Mo], [Ni], [Cu], [Co],
[C], [N] and [Mn] are Cr, Mo, Ni and C, respectively.
Content of u, Co, C, N and Mn (% by mass) 3. The method according to claim 1, further comprising Ti: 0.2% by mass or less, Nb: 0.2% by mass or less, V: 0.2% by mass or less, Zr: 0.2% by mass or less and Ta: 0.2% by mass or less. Alternatively, a high-corrosion-resistant low-strength stainless steel excellent in workability and toughness of a weld portion, characterized by containing two or more kinds. 4. The workability and toughness of a welded part according to claim 1, further comprising one or two of B: 0.005 mass% or less and Ca: 0.005 mass% or less. Excellent corrosion resistance and low strength stainless steel. 5. A welded part according to any one of claims 1 to 4, further containing one or two of W: 0.1% by mass or less and Mg: 0.01% by mass or less. High corrosion resistance, low strength stainless steel with excellent workability and toughness. 6. A high-corrosion-resistant low-strength stainless steel having excellent workability and toughness at a welded portion according to any one of claims 1 to 5, which has a tensile strength of 600 MPa or less. 7. A welded joint using the stainless steel according to any one of claims 1 to 6 as a base material, wherein the ratio of martensite structure in the heat-affected zone of the weld is not less than 5% by volume.
A welded joint which is less than volume% and has a Charpy impact value of 30 J / cm ² or more at −50 ° C. in a heat-affected zone of welding.