JPH08209309A - Molybdenum-containing austenitic stainless steel excellent in nitric acid corrosion resistance in weld heat-affected zone - Google Patents

Abstract

PURPOSE: To produce a molybdenum-containing austenitic stainless steel requiring no secondary treatment such as post weld heat treatment and excellent in nitric acid corrosion resistance in a weld heat-affected zone. CONSTITUTION: This steel has a chemical composition consisting of, by weight, <=0.02% C, <=0.5% Si, 1-2% Mn, <=0.03% P, <=0.01% S, 6-22% Ni, 13-27% Cry 2-3% Mo, <=0-01% sol-Al, 0.03-0.1% N, <=0.3% Cup <=0.0010% B, and the balance Fe with inevitable impurities and satisfying inequality Ni+30(C+N)+0.5Mn-1.1 Cr-1.1Mo%-1.5Si+7.4>=0. It is desirable that, in addition to this composition, an inequality Ni+30(C+N)+0.5Mn+0.8Cr+0.8Mo+1.2Si-31.4>=0 is satisfied. It is more desirable that, in addition of either of the above compositions, B is regulated to <=0.0005%, and further <=1.0% (not including an addition-free case), in total, of one or more elements among Ti, Nb, V, Zr, Hf, and Ta are incorporated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molybdenum-containing austenitic stainless steel material having excellent nitric acid corrosion resistance in the heat-affected zone of welding, and particularly severe nitric acid resistance such as nitric acid plant and nuclear fuel reprocessing plant. The present invention relates to a molybdenum-containing austenitic stainless steel suitable for a structural steel material used in an environment where corrosiveness is required.

[0002]

2. Description of the Related Art Conventionally, austenitic stainless steel excellent in nitric acid corrosion resistance has been used as a material for nitric acid plants and nuclear fuel reprocessing plants. In these steel sheets, precipitation of chromium carbides such as Cr ₂₃ C ₆ in the heat-affected zone tends to significantly promote intergranular corrosion, and in order to prevent this, the C content in the steel was reduced. Low carbon stainless steel or Ti or / and N
Stabilized stainless steel that fixes C by adding b or the like has been developed.

Among these, austenitic stainless steels used in an environment in which salts such as nitrates are present and which require pitting corrosion resistance in addition to nitric acid corrosion resistance have pitting corrosion resistance. Mo is often added for the purpose of improvement.
However, in the austenitic stainless steel containing Mo such as SUS316, the nitric acid corrosion resistance of the heat affected zone of the welded portion tends to deteriorate even in the low carbon stainless steel or the stabilized stainless steel. On the other hand, SUS3
In the case of austenitic stainless steel containing no Mo such as 04, low carbon stainless steel or stabilized stainless steel does not cause such a problem of deterioration of nitric acid corrosion resistance after welding.

Conventionally, as a means for preventing deterioration of nitric acid corrosion resistance of a heat-affected zone of a weld containing Mo-containing austenitic stainless steel, the first layer of the weld metal, which is in contact with the nitric acid solution in the weld, does not contain Mo. A technique using an additive is disclosed in JP-A-3-273194 and JP-A-1.
-62278 discloses a technique of heat treating a surface layer which is in contact with a nitric acid solution after welding, disclosed in JP-A-4-93699 and JP-A-62-120425, and containing Mo containing Sn and V. Σ phase (FeCr intermetallic compound), Laves phase (Fe ₂ Mo), which causes corrosion of austenitic stainless steel, and
Techniques for suppressing the precipitation of the χ phase (Fe ₁₈ Cr ₆ Mo ₅ ) at the grain boundaries are disclosed in JP-B-57-28740 and JP-A-6-184631.

[0005]

However, the technique of (1) is an invention relating to a filler material, particularly a filler material forming an initial layer, and a useful effect can be obtained for a weld heat affected zone of a base material. Absent. In addition, the technique (1) is not an appropriate method in consideration of the case where the welding process becomes a complicated process and the repair or the like is performed later. Regarding this point, the technology is the same, both have advanced technology for welding work, and
It cannot be applied to all parts.
Is an invention related to the base material, but in reality, the σ phase,
Even if the Laves phase and the χ phase are not precipitated at the crystal grain boundaries, deterioration of nitric acid corrosion resistance in the heat-affected zone of the weld may be observed, which is not a fundamental solution.

Therefore, an object of the present invention is to solve the above-mentioned problems, so that it is not necessary to perform a secondary treatment such as heat treatment after welding, and moreover, a stable supply can be achieved. An object of the present invention is to provide a molybdenum-containing austenitic stainless steel having excellent nitric acid corrosion resistance in the heat affected zone.

[0007]

In order to solve the above problems, the present inventors have investigated the causes of deterioration of nitric acid corrosion resistance in the weld heat affected zone of Mo-containing austenitic stainless steel. As a result, as for the corrosion of the weld heat affected zone, Mo is remarkably concentrated at the interface between the δ ferrite phase and the austenite phase, which deteriorates the nitric acid corrosion resistance. Therefore, this deterioration phenomenon occurs at the interface between the δ ferrite phase and the austenite phase due to the presence of the δ ferrite phase in the steel. By this, the σ phase, Laves
It is possible to explain the phenomenon that the nitric acid corrosion resistance of the heat-affected zone of the weld deteriorates even if the phases and χ phase are not precipitated. Further, since the factor of deterioration of nitric acid corrosion resistance is due to Mo concentrated at the interface between the δ ferrite phase and the austenite phase, in an austenitic stainless steel containing no Mo such as SUS304, In the case of low carbon stainless steel or stabilized stainless steel, deterioration of nitric acid corrosion resistance of the heat affected zone of welding is not recognized.

From the above, in order to maintain strict nitric acid corrosion resistance in general Mo welding austenitic stainless steel without subjecting secondary heat treatment to Mo-containing austenitic stainless steel, δ ferrite A steel material having a chemical composition such that no phase is formed in the steel is required. The present invention has been made based on the above-mentioned findings, and is characterized by having the following configurations.

The molybdenum-containing austenitic stainless steel (hereinafter referred to as the first invention) having excellent resistance to nitric acid corrosion in the heat-affected zone of the present invention has a C: 0.02 wt.% Or less, Si: 0. 5 wt.% Or less, Mn: 1-2 wt.%,
P: 0.03 wt.% Or less, S: 0.01 wt.% Or less, N
i: 6 to 22 wt.%, Cr: 13 to 27 wt.%, Mo:
2-3 wt.%, Sol.Al: 0.01 wt.% Or less (including no addition), N: 0.03-0.1 wt.%, Cu: 0.3
wt.% or less (including no addition) and B: 0.001
0 wt.% Or less, the balance: Fe and unavoidable impurities, and the following formula (1): Ni + 30 (C + N) + 0.5Mn-1.1Cr-1.1Mo-1.5Si + 7.4 ≧ 0 − ------------- (1) However, for Ni, C, N, Mn, Cr, Mo and Si,
It is characterized by having a chemical composition that satisfies the content (wt.%) Of each element.

More desirable molybdenum-containing austenitic stainless steel of the present invention (hereinafter referred to as the second invention) is added to the stainless steel of the first invention, and further, its chemical composition is the following (2). Formula: Ni + 30 (C + N) + 0.5Mn + 0.8Cr + 0.8Mo + 1.2Si-31.4 ≧ 0 ------------ (2) However, Ni, C, N, Mn, Cr, Mo And Si is
It is characterized by satisfying the content (wt.%) Of each element.

An even more desirable feature of the molybdenum-containing austenitic stainless steel of the present invention is that, in addition to the stainless steel of the first invention or the second invention, boron (B): 0.0005 wt.%. And at least one element selected from the group consisting of titanium (Ti), niobium (Nb), vanadium (V), zirconium (Zr), hafnium (Hf) and tantalum (Ta). Is contained in a total amount of 1.0 wt.% Or less (not including no additive).

[0012]

The reason why the chemical composition of the stainless steel of the present invention is limited as described above will be explained.

(1) C: When the C content exceeds 0.02 wt.%, Cr is formed in the crystal grain boundaries of the steel due to heating during welding.
The precipitation of ₂₃ C ₆ carbide is promoted and a Cr-deficient layer is formed along the grain boundary, resulting in deterioration of nitric acid corrosion resistance in this portion. Therefore, the C content should be limited to 0.02 wt.% Or less.

(2) Si: Si is an element added as a deoxidizing agent for molten steel, and is a strong ferrite phase forming element. However, if Si is added in an amount of more than 0.5 wt.%, The corrosion potential of stainless steel is increased, the precipitation of harmful σ phase and η phase is promoted, and nitric acid corrosion resistance is significantly deteriorated. Therefore, the Si content should be limited to 0.5 wt.% Or less.

(3) Mn: Mn is an austenite phase stabilizing element, and has the effect of improving weld crack resistance. However, if the Mn content is less than 1 wt.%, The effect is not sufficiently exhibited. On the other hand, its content is 2 wt.%
If it exceeds the limit, the workability deteriorates. Therefore, the Mn content is 1 to
It should be limited to the range of 2 wt.%.

(4) P: P is an impurity that segregates at the grain boundaries and adversely affects nitric acid corrosion resistance and weld crack resistance. If the P content exceeds 0.03 wt.%, The nitric acid corrosion resistance and the weld crack resistance deteriorate in the present invention.
Therefore, the P content should be limited to 0.03 wt.% Or less.

(5) S: S accelerates the formation of sulfide as the content increases, and the selective corrosion originating from this accelerates the deterioration of nitric acid corrosion resistance and pitting corrosion resistance.
Similarly to S, S is an impurity that adversely affects the weld crack resistance. If the S content exceeds 0.01 wt.%, Nitric acid corrosion resistance, pitting corrosion resistance, and weld crack resistance deteriorate. Therefore,
The S content should be limited to 0.01 wt.% Or less.

(6) Ni: Ni has the effect of stabilizing the austenite phase. However, if the Ni content is less than 6 wt.%, Such effects in austenitic stainless steel are not sufficiently exhibited. On the other hand, Ni
Since is an expensive element, excessive addition causes an increase in manufacturing cost. Therefore, the Ni content should be limited to the range of 6 to 22 wt.%.

(7) Cr: Cr is a basic element having a function of passivating the surface of stainless steel, and the addition of Cr has the effect of improving nitric acid corrosion resistance. However, if the Cr content is less than 13 wt.%, The effect cannot be sufficiently obtained. On the other hand, since Cr is a ferrite phase stabilizing element, if its content exceeds 27 wt.%, The stability of the austenite structure is significantly impaired and the precipitation of σ phase, which is harmful to nitric acid corrosion resistance, is promoted. . Therefore, the Cr content should be limited to the range of 13 to 27 wt.%.

(8) Mo: Mo is an element effective in improving pitting corrosion resistance, and when salts such as nitrates are present and nitrification corrosion resistance and pitting corrosion resistance are required, It is an element to be added. However, Mo content is 2 wt.%
If it is less than the above range, the above-mentioned effects are not sufficiently exhibited. On the other hand, Mo
Is a ferrite phase forming element and is an element harmful to nitric acid corrosion resistance, and if its content exceeds 3 wt.%, Its harmful effect appears. Therefore, the Mo content should be limited to the range of 2-3 wt.%.

(9) sol.Al: Al is added during deoxidation of molten steel. However, excessive addition of Al deteriorates the toughness, forms non-metallic inclusions in the crystal grains and in the grain boundaries, and deteriorates the nitric acid corrosion resistance. If the sol.Al content exceeds 0.01 wt.%, the above-mentioned harmful effects will appear. Therefore, the sol.Al content should be limited to 0.01 wt.% Or less. The present invention includes the case where sol.Al is not added (0 wt.%).

(10) N: N is an austenite phase forming element and is an element effective for improving strength. However, if it is less than 0.03 wt.%, The effect is not sufficient. On the other hand, when the N content exceeds 0.1 wt.%, The precipitation of nitrides is promoted and the nitric acid corrosion resistance is adversely affected. Therefore, the N content should be limited to the range of 0.03 to 0.1 wt.%.

(11) Cu: Cu is an element effective in improving pitting corrosion resistance. However, when the content is 0.
If it exceeds 3 wt.%, Segregation of P crystal grain boundaries is promoted. Therefore, the Cu content should be limited to 0.3 wt.% Or less. In the present invention, Cu is not added (0 wt.%
) Is included.

(12) B: B is an impurity element in the austenitic stainless steel of the present invention, which segregates at the grain boundaries and forms a boride rich in Cr, which makes it resistant to nitric acid corrosion. Adversely affect. B content is 0.0
Above 005 wt.%, The above-mentioned adverse effects begin to appear, and 0.001
Above 0 wt.%, This adverse effect becomes particularly noticeable. This adverse effect is particularly noticeable with relatively high concentrations of nitric acid, such as 65% nitric acid. Therefore, when the application to a relatively high concentration nitric acid environment is expected, the B content is 0.0010 wt.
% Or less, and more preferably 0.00
It should be limited to less than 05 wt.%.

(13) Ti, Nb, V, Zr, Hf, and Ta: Ti, Nb, V, Zr, Hf, and Ta suppress the precipitation of Cr ₂₃ C ₆ by fixing C in any element. However, it is an element effective for improving the sensitization resistance. By adding one or more of these elements, the above-mentioned effects are achieved. However, if the total amount of these elements added exceeds 0.1 wt.%, The nitric acid corrosion resistance deteriorates. Therefore, in order to obtain an austenitic stainless steel that is more excellent in nitric acid corrosion resistance after welding,
The content of Ti, Nb, V, Zr, Hf and Ta is limited to 1.0 wt.% Or less (including no addition) in total of one or more elements selected from these elements. Should be added.

In the stainless steel of the present invention, even if only the content of each element in the chemical composition is within the scope of the present invention, if the δ ferrite phase is formed in the steel material, the welding work is performed. At times, Mo concentrates at the interface between the δ ferrite phase and the austenite phase and deteriorates nitric acid corrosion resistance. Therefore, it is necessary to suppress the formation of the δ ferrite phase in the manufacturing process of the steel material. Therefore, the above δ
"J" and "L" are used as the ferrite phase generation suppression index by the following formulas (3) and (4): J = Ni + 30 (C + N) + 0.5Mn-1.1Cr-1.1Mo-1.5Si + 7.4- --------------- (3) L = Ni + 30 (C + N) + 0.5Mn + 0.8Cr + 0.8Mo + 1.2Si-31.4 ------------ --Defined as (4).

Steel sheets of austenitic stainless steel having the above-mentioned chemical composition and austenitic stainless steel not having the above-mentioned chemical composition were retained at a temperature of 1100 ° C. for 30 minutes and then solid-soluted. After the treatment, the temperature was kept at 650 ° C. for 2 hours, and then the sensitization treatment was performed. A corrosion test using 65% boiling nitric acid was performed on a test piece collected from the steel sheet subjected to the sensitization treatment, and the corrosion rate was obtained. Then, it was divided into three classes of ⊚, ○ and × in order from the one excellent in nitric acid corrosion resistance. The corrosion test method with nitric acid and the evaluation method of nitric acid corrosion resistance will be described in detail in the section of Examples.

FIG. 2 is a graph in which the corrosion rate of each test piece is arranged by the values of J and L calculated from the chemical composition of each test piece using the equations (3) and (4). is there. In the subscripts of the plots in the figure, "main-number" and "ratio-number" indicate "specimen of the present invention No." and "specimen for comparison No." in Table 1 described later.

In order to obtain an austenitic stainless steel material excellent in nitric acid corrosion resistance, that is, a product marked with ⊚ or ○, from FIG. 2, at least J ≧ 0, that is, the following formula (1): It is understood that Ni + 30 (C + N) + 0.5Mn-1.1Cr-1.1Mo-1.5Si + 7.4 ≧ 0 ------------ (1) should be satisfied. And, in order to obtain an austenitic stainless steel material excellent in nitric acid corrosion resistance, that is, the one marked with ⊚ among these, in addition to at least satisfying the formula (1), L ≧ 0,
That is, the following formula (2): Ni + 30 (C + N) + 0.5Mn + 0.8Cr + 0.8Mo + 1.2Si-31.4 ≧ 0 ------------ (2) should be satisfied.

On the other hand, in FIG. 2, even when J ≧ 0 and when J ≧ 0 and L ≧ 0, there are some which are not excellent in nitric acid corrosion resistance (marked by X). In each case, the content of each element is not within the range of the present invention described above.

From the above, in order to obtain an austenitic stainless steel material excellent in nitric acid corrosion resistance, the content of each element is within the range of the present invention described above, and at least (1) The formula should be satisfied, and in order to obtain an even better one, the formula (2) should be satisfied in addition to this.

[0032]

Next, the present invention will be described in more detail with reference to Examples. Using a vacuum high frequency induction melting furnace, shown in Table 1,
Alloy steel having a chemical composition within the scope of the present invention (hereinafter,
Ingots of "the alloy of the present invention") and alloy steels having chemical composition outside the scope of the present invention (hereinafter referred to as "comparative alloy") were melted.

In Table 1, the comparative alloy Nos. 1 to 4 are
The content of each element is within the scope of the present invention. However, the comparative alloys No. 1 and 2 among these do not satisfy the above-mentioned formulas (1) and (2) which are the conditions of the present invention,
Comparative alloys No. 3 and 4 do not satisfy the above formula (1). Further, in Comparative Alloys Nos. 5 and 6, any one element is out of the scope of the present invention with respect to the content of each element, and in Comparative Alloys Nos. 7 and 8, (1)
And, although the formula (2) is satisfied, any one of the elements is out of the scope of the present invention with respect to the content of each element.

[0034]

[Table 1]

Each steel ingot thus obtained was
After heating to ℃, it was hot rolled to prepare a steel plate having a plate thickness of 10 mm. The above steel sheets prepared from the respective ingots of the present invention alloy and the comparative alloy are hereinafter referred to as “invention specimen” and “comparative specimen”, for example, ingot of the invention alloy No. 1 The above-mentioned steel sheet prepared from the above is referred to as "specimen of the invention No. 1".

Next, each of the sample of the present invention and the sample for comparison was held at a temperature of 1100 ° C. for 30 minutes and then subjected to a solution treatment. Next, two steel plates were prepared by cutting along the center line of the width of each steel plate, and one of the steel plates was held at a temperature of 650 ° C. for 2 hours and then subjected to a sensitization treatment (hereinafter, this Steel sheet is called "sensitized heat treatment material". The other steel plate was left as a solution treatment (hereinafter,
This steel sheet is called "solution heat treatment material".

From the solution heat treated material and the sensitized heat treatment material for each of the present invention specimen and the comparative specimen,
A corrosion test piece having a thickness of 2 mm, a width of 20 mm and a length of 30 mm was collected. Each of these test pieces is immersed in boiling nitric acid at 65% for 48 hours for the first corrosion, and then the nitric acid is replaced with fresh 65% boiling nitric acid for immersion for 48 hours for the second corrosion. In this process, a corrosion test was carried out up to the fifth corrosion.

Next, by measuring the corrosion weight loss of each test piece after each corrosion, the corrosion rate was determined 5 times for each test piece, and the average value was defined as the "corrosion rate". The corrosiveness was evaluated.

The above-described sensitization treatment of the steel sheet corresponds to a severer condition than the usual welding conditions of the steel sheet. For example, when welding a steel plate with a thickness of 10 mm, when TIG welding is performed with an average heat input per pass of about 10 kJ / cm at the X groove, the heat history received by the surface layer on the side that comes into contact with the liquid reaches the maximum. The temperature does not exceed 650 ° C, and the time of heating to 600 ° C or higher is less than 20 seconds. Therefore, it is understood that the heat effect of the steel sheet by the sensitization treatment is much severer than the heat effect of ordinary welding.

FIG. 1 shows the results of the above corrosion test on the solution heat-treated material and the sensitized heat-treated material of the present invention sample No. 1 and the comparative sample No. 1 in 65% boiling nitric acid. It is a graph shown.

According to FIG. 1, in the test sample No. 1 for comparison, the nitric acid corrosion resistance was remarkably deteriorated when the sensitization treatment was applied, whereas the test sample No. 1 of the present invention was used. In No. 1, no deterioration in nitric acid corrosion resistance was observed even after the sensitization treatment. The reason is as follows. Since the comparative sample No. 1 is within the range of the chemical composition of the conventional Mo-containing ultra-low carbon austenitic stainless steel, the δ-ferrite phase has already been formed in the solution heat treated material, Therefore, due to the sensitization treatment, Mo was remarkably concentrated at the interface between the δ ferrite phase and the austenite phase, so that corrosion proceeded at this interface.
On the other hand, since the sample No. 1 of the present invention has the chemical composition within the range of the present invention, the formation of the δ ferrite phase was suppressed. As a result, the sample No. 1 of the present invention did not have an interface between the δ ferrite phase and the austenite phase, and therefore Mo concentration did not occur even by the sensitization treatment.
Corrosion as in the comparative sample No. 1 did not occur.

Table 2 shows the evaluation results of the nitric acid corrosion resistance of the sensitized material of each of the present invention specimen and the comparative specimen.

[0043]

[Table 2]

The evaluation criteria for nitric acid corrosion resistance shown in Table 2 are shown below. ⊚: Corrosion rate is less than 0.20 mm / year, ◯: Corrosion rate is 0.20 mm / year or more, 0.30 m
Less than m / year, x: Corrosion rate is 0.30 mm / year or more The nitric acid corrosion resistance of the comparative specimen is all X, whereas that of the specimen of the present invention is all ◎ or ○. .

In FIG. 2 described above, the evaluation results of nitric acid corrosion resistance shown in Table 2 are summarized by the values of J and L of the δ ferrite phase formation inhibition index, which are determined according to the chemical composition of each specimen. It is a graph.

The following matters are apparent from Table 2 and FIG. That is, the samples Nos. 1 to 16 of the present invention show excellent nitric acid corrosion resistance even when subjected to the strict sensitization treatment as described above, and among them, the δ ferrite phase production suppression index: J In the samples No. 1 to 4 and 9 to 12 of the present invention in which the values of L and L are both 0 (zero) or more,
Particularly excellent nitric acid corrosion resistance is exhibited.

The inventors of the present invention showed that the solution heat-treated materials of Nos. 1 to 16 of the present invention shown in Table 1 were subjected to TIG welding with an average heat input per pass of 10 kJ / cm at the X groove. According to the above, a welded joint was produced, and the weld heat affected zone was tested for the amount of δ ferrite phase. As a result, it was not possible to recognize the presence of the δ ferrite phase in the weld heat affected zone in any of the samples of the present invention. Therefore, it is considered that the sensitized heat-treated material of the sample of the present invention also suppressed the formation of the δ ferrite phase, and exhibited excellent nitric acid corrosion resistance.

On the other hand, in any one of the comparative specimens containing even one condition outside the scope of the present invention, the nitric acid corrosion resistance deteriorates when the above-mentioned sensitization treatment is applied. That is, in Comparative Samples No. 1 to 4, the content of each element is within the range of the present invention, but at least the value of J is less than 0 (zero) in the δ ferrite phase production suppression index. Since it is outside the range of the present invention, and in the comparative samples No. 5 to 8, the value of J is 0 out of the δ ferrite phase production suppression index.
(Zero) or more and within the scope of the present invention, but regarding the content of each element, No. 5 has a C content, No. 6 has a Si content, No. 7 has a Mo content, and , No. 8 had a high Al content outside the range of the present invention, and therefore no excellent nitric acid corrosion resistance was obtained in any of the comparative specimens.

[0049]

As described above, according to the stainless steel of the present invention, the steel material exhibits excellent nitric acid corrosion resistance in the heat-affected zone even when it is affected by heat during welding during welding. Therefore, it is not necessary to perform heat treatment after welding. Therefore, according to the present invention, the nitric acid corrosion resistance of the welding heat affected zone for producing an austenitic stainless steel material extremely suitable as a structural steel material used in a nitric acid plant, a nuclear fuel reprocessing plant, etc. It is possible to provide an excellent molybdenum-containing austenitic stainless steel, which brings an extremely useful effect industrially.

[Brief description of drawings]

FIG. 1 Inventive sample No. 1 and comparative sample No. 1
3 is a graph showing the results of a nitric acid corrosion test for each of the solution heat treated material and the sensitized heat treatment material.

FIG. 2 is a graph showing the relationship between the nitric acid corrosion resistance and the δ ferrite phase inhibition index: J and L values of the test sample of the present invention and the test sample for comparison that have been subjected to the sensitization treatment.

Claims (3)

[Claims] 1. Carbon (C): 0.02 wt.% Or less, Silicon (Si): 0.5 wt.% Or less, Manganese (Mn): 1-2 wt.%, Phosphorus (P): 0. 03 wt.% Or less, sulfur (S): 0.01 wt.% Or less, nickel (Ni): 6 to 22 wt.%, Chromium (Cr): 13 to 27 wt.%, Molybdenum (Mo): 2 3 wt.%, Acid-soluble aluminum (sol.Al): 0.01 wt.% Or less, nitrogen (N): 0.03 to 0.1 wt.%, Copper (Cu): 0.3 wt.% Or less (Including no addition) and boron (B): 0.0010 wt.% Or less, balance: iron (Fe) and inevitable impurities, and the following formula (1): Ni + 30 (C + N) +0 .5Mn-1.1Cr-1.1Mo-1.5Si + 7.4 ≧ 0 ------------ (1) However, Ni, C, N, Mn, Cr, Mo and Si are
A molybdenum-containing austenitic stainless steel excellent in nitric acid corrosion resistance of a heat-affected zone of welding, characterized by having a chemical composition satisfying the content (wt.%) Of each element. 2. Carbon (C): 0.02 wt.% Or less, silicon (Si): 0.5 wt.% Or less, manganese (Mn): 1-2 wt.%, Phosphorus (P): 0. 03 wt.% Or less, sulfur (S): 0.01 wt.% Or less, nickel (Ni): 6 to 22 wt.%, Chromium (Cr): 13 to 27 wt.%, Molybdenum (Mo): 2 3 wt.%, Acid-soluble aluminum (sol.Al): 0.01 wt.% Or less, nitrogen (N): 0.03 to 0.1 wt.%, Copper (Cu): 0.3 wt.% Or less (Including no addition) and boron (B): 0.0010 wt.% Or less, balance: iron (Fe) and unavoidable impurities, and the following formulas (1) and (2): Ni + 30 (C + N) + 0.5Mn-1.1Cr-1.1Mo-1.5Si + 7.4 ≧ 0 -------------- (1) Ni + 30 (C + N) + 0.5Mn + 0 8Cr + 0.8Mo + 1.2Si-31.4 ≧ 0 ------------ (2) where, Ni, C, N, Mn, Cr, Mo and Si,
A molybdenum-containing austenitic stainless steel excellent in nitric acid corrosion resistance of a heat-affected zone of welding, characterized by having a chemical composition satisfying the content (wt.%) Of each element. 3. In addition to the chemical composition according to claim 1 or 2, boron (B): 0.0005 wt.% Or less, and further titanium (Ti), niobium (Nb). , Vanadium (V), zirconium (Zr), hafnium (Hf)
And one or two selected from tantalum (Ta)
A molybdenum-containing austenitic stainless steel excellent in nitric acid corrosion resistance of a heat-affected zone of welding, characterized in that it contains 1.0 wt.% Or less (not including any additive) in total of at least one element.