ES2608460T3 - Ferritic stainless steel - Google Patents

Abstract

Ferritic stainless steel consisting of, in mass%, C: from 0.001% to 0.030%, Si: from 0.03% to 0.80%, Mn: from 0.05% to 0.50%, P: 0.03% or less, S: 0.01% or less, Cr: from 19.0% to 28.0%, Ni: from 0.01% to less than 0.30%, Mo: from 0, 2% to 3.0%, Al: from more than 0.15% to 1.2%, V: from 0.02% to 0.50%, Cu: less than 0.1%, Ti: from 0, 05% to 0.50%, N: from 0.001% to 0.030%, and Nb: less than 0.05%, in which the expression (1) is satisfied, optionally also one or more elements selected from Zr: 1 , 0% or less, W: 1.0% or less, REM: 0.1% or less, Co: 0.3% or less, and B: 0.1% or less, and the rest It is Faith and unavoidable impurities, Nb x P <= 0.0005 ... (1) where each element symbol represents the content (in mass%) of the element.

Description

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DESCRIPTION

Phenolic stainless steel Technical field

The present invention relates to phenolic stainless steel that is less likely to cause sensitization of a welded area, which produces high corrosion resistance of a tempering color in a welded area, and which is less likely to cause weld cracking in a welding cord formed by double welding, using ferntic stainless steel in applications where a structure is manufactured by welding, for example, car exhaust system materials such as muffler materials, hot water storage tank materials for electric water heaters, or building materials such as cerrajena materials, ventilation opening materials and duct materials.

Prior art

Ferntic stainless steel has several characteristics that are superior to those of austemotic stainless steel, such as high profitability in corrosion resistance, good thermal conductivity of heat, a small coefficient of thermal expansion, and resistance to cracking by corrosion under stress. . Therefore, ferntic stainless steel has been used in a variety of applications such as in the production of automobile exhaust system elements, construction materials such as roofing and cerrajena materials, and materials used in wet conditions such as furniture kitchen, water tanks and hot water tanks.

In order to manufacture these structures, in many cases, a stainless steel sheet is cut and shaped to give an appropriate shape and subsequently a joint is made by welding. However, when phenolic stainless steel is used, welding cracking can occur in a double welding zone, such as a part where three plates are joined together or the start and end of a circumferential weld, in which welding again on a weld seam. As the shapes of the welded elements have become increasingly complicated, the double welding zone described above has increased and the appearance of welding cracking has become a problem.

The double welding zone is not flat and welding is performed again in a part where the shell is present. Therefore, oxygen, nitrogen and the like are likely to be mixed in a weld seam, which degrades corrosion resistance. However, in the related art, there have been some findings regarding these problems in double welding zones.

Patent literature 1 discloses phenolic stainless steel that has high corrosion resistance and good weldability. This phenolic stainless steel produces both corrosion resistance and ease of weld penetration due to Mg added to the fernt stainless steel and an appropriately controlled S content. However, nothing is mentioned about cracking in a double welding zone or the corrosion resistance of a double welding zone.

In fact, when welding is performed using the ferntic stainless steel disclosed in patent literature 1, in some cases cracking occurs in a double welding zone.

Patent literature 2 discloses phenolic stainless steel that has good weldability. However, although this ferntic stainless steel has an improved weld penetration facility and improved workability after welding, there is no mention of possible problems in double welding zones, such as welding cracking.

Appointment List

Patent Bibliography

PTL 1: Japanese Patent Application Publication without examining No. 8-246105 PTL 2: Japanese Patent Application Publication without examining No. 2009-91654

JP2006257544 teaches phenolic stainless steel that has excellent corrosion resistance as a welded part in which ferric stainless steel contains, in bulk, 0.001 to 0.02% C, 0.001 to 0.02% N, from 0.01 to 0.3% of Si, from 0.05 to 1% of Mn, <0.04% of P, from 0.15 to 3% of Ni, from 11 to 22% of Cr, from 0 , 01 to 0.5% of Ti, and 0.0002 to 0.002% of Mg, contains one or two or more classes of Mo, Nb and Cu with 0.5 to 3.0% of Mo, of 0, 02 to <0.6% of Nb, from 0.1 to <1.5% of Cu, the rest consisting of Fe and unavoidable impurities.

Summary of the invention

Technical problem

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In the light of the prior problems of the prior art, an objective of the present invention is to provide ferntic stainless steel that is less likely to cause sensitization of a welded area, which produces a high corrosion resistance of a tempering color in a welded area, and that is less likely to cause weld cracking in a weld seam when double welding.

Solution to the problem

In order to address the problems described above, in the present invention, the influence of various elements on weld cracking that occurs in double welding was extensively studied. Note that the term "double welding" in this document refers to the fact of welding the same part two or more times, and the term "double welding zone" in this document refers to a part and the periphery of the part which has repeatedly undergone the process of melting and solidifying two or more times due to double welding, such as a part in which welding cords overlap between each other at the beginning and at the end of the welding when circumferential welding is performed or a part in which welding cords overlap each other when cross welding is performed.

A part in which welding cracking due to double welding was cut and the fracture surface was observed with an SEM (scanning electron microscope). A precipitation of film type of Nb was observed on the fracture surface. For comparison, a part was cut in which no welding cracking had occurred and observed with an SEM. A film-like precipitate of Nb was not observed as observed on the fracture surface described above. A film-like precipitation of Nb is considered to be responsible for the appearance of weld cracking.

The influence of various elements on welding cracking in a double welding zone was studied and, as a result, it was found that no welding cracking occurs in a steel that has a low P content and a low Nb content. Cross welding was performed by welding of bead on sheet using various ferrous stainless steels, and the presence or absence of weld cracks in a double weld zone was examined using an optical microscope. Figure 1 shows the results. In Fig. 1, a ferntic stainless steel in which welding cracks were absent is marked with a circle, and a ferntic stainless steel in which welding cracks were present is marked with a cross. It is shown that no welding cracking occurred in the range in which Nb is less than 0.05%, P is 0.03% or less, and Nb x P is 0.0005 or less.

It is clear that a reduction in Nb content leads to a suppression of weld cracking. However, since Nb is an element that is effective in suppressing the sensitization of a weld bead, the reduction of the Nb content can disadvantageously increase the risk of sensitization. Also, since the surface of a double weld zone is not flat and scale forms on the surface of the double weld zone, impurities are likely to mix in a weld seam. Therefore, a double welding zone is in disadvantageous welding conditions from the point of view of sensitization. Therefore, the influence of various elements on the sensitization of a weld bead was examined. As a result, it was clear that, in addition to the reduction of Nb, the addition of V and Al was also effective in suppressing the sensitization of a welded area. This is supposedly because V and Al form VN and AlN, respectively, which suppress the formation of a Cr nitride.

In addition, an oxide layer called "tempering color" is formed on a weld seam and, as a result, Cr deficiency occurs as in the case of sensitization, which degrades corrosion resistance. Therefore, the influence of various elements on the corrosion resistance of a tempering color was evaluated. As a result, the following findings were obtained. When Si, Al and Ti are concentrated in a tempering color, a dense oxide layer is formed that has a good protective function. In addition, the amount of oxidized Cr due to welding is reduced, which suppresses Cr deficiency due to oxidation. Therefore, when the contents of Si, Al and Ti are properly established, the corrosion resistance of a weld bead is enhanced.

Additional studies have been carried out based on the findings described above and, as a result, the present invention has been performed. The summary of the present invention is described below.

[1] Ferntic stainless steel containing, in mass%, C: from 0.001% to 0.030%, Si: from 0.03% to 0.80%, Mn: from 0.05% to 0.50%, P : 0.03% or less, S: 0.01% or less, Cr: from 19.0% to 28.0%, Ni: from 0.01% to less than 0.30%, Mo: from 0.2% to 3.0%, Al: from more than 0.15% to 1.2%, V: from 0.02% to 0.50%, Cu: less than 0.1%, Ti: from 0.05% to 0.50%, N: from 0.001% to 0.030%, and Nb: less than 0.05%,

in which the expression is satisfied (1)

Nb x P <0.0005 ... (1)

optionally also one or more elements selected from Zr: 1.0% or less, W: 1.0% or less, REM: 0.1% or less, Co: 0.3% or less, and B : 0.1% or less and the rest is inevitable Fees and impurities

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where each element symbol represents the content (in mass%) of the element.

Advantageous effects of the invention

According to the present invention, ferric stainless steel is provided which, when double welding is performed, is less likely to cause sensitization of a welded area, which produces high corrosion resistance of a tempering color in a welded area, and which is less likely to cause weld cracking in a weld seam.

Brief description of the drawings

Figure 1 is a diagram to explain the effects of Nb content and P content on weld cracking in a double weld zone.

Figure 2 is a schematic diagram illustrating cross welding.

Description of the realizations

The reasons for the limitations on the constituent elements of the present invention are described below.

1. Composition

First, the reasons for the limitations on the composition of the steel according to the present invention are described. Note that, when referring to a composition, "%" always indicates "% by mass."

C: from 0.001% to 0.030%

C is an element that is inevitably contained in steel. A high C content increases the mechanical strength of steel. A low C content enhances the workability of steel. The C content of 0.001% or more is adequate to achieve sufficient mechanical strength of the steel. If the C content exceeds 0.030%, the degradability of the workability of the steel becomes significant and a Cr carbide is precipitated, which increases the risk of degradation of the corrosion resistance due to the local deficiency of Cr. therefore, the C content is set at 0.001% to 0.030%, preferably set to 0.002% to 0.018%, and more preferably set to 0.002% to 0.010%.

Yes: from 0.03% to 0.80%

If it is an element that is useful for deoxidation. In the present invention, Si is an important element that concentrates on a tempering color formed by welding together with Al and Ti, thereby enhancing the protective function of an oxide layer, and therefore enhances the corrosion resistance of a welded area This effect is obtained when the content of Si added is 0.03%. However, if the Si content exceeds 0.80%, the degradability of steel workability becomes significant, which leads to difficulty in a forming process. Therefore, the Si content is set at 0.03% to 0.80%, preferably it is set to more than 0.30% to 0.80%, and more preferably it is set to 0.33% at 0.50%

Mn: from 0.05% to 0.50%

Manganese is an element that is inevitably contained in steel and has an effect on increasing mechanical strength. This effect is obtained when the content in Mn is 0.05% or more. However, if the content of Mn exceeds 0.50%, the precipitation of MnS is increased, which acts as a source of corrosion, which degrades the corrosion resistance. Therefore, the Mn content is set at 0.05% to 0.50% and preferably is set at 0.08% to 0.40%.

P: 0.03% or less

Phosphorus is an element that is inevitably contained in steel. An excessively high P content degrades the weldability of steel and increases the risk of intergranular corrosion. In the present invention, it was found that an increase in P content results in the appearance of weld cracking in a double weld zone. An increase in the P content reduces the solidification temperature of the ferntic stainless steel, and consequently an Nb carbonitride precipitates in the liquid phase and forms a film-like shape. This inhibits the flow of a fusion bath in a solidification process and the formation of crystal grains. Therefore, it is considered that welding cracking is likely to occur in a ferntic stainless steel that has a high P content. The risk of welding cracking is considered to increase particularly in double welding because the repetition of the fusion process and solidification causes an additional condensation of Nb and, as a result, it becomes probable that Nb precipitation occurs. If the P content exceeds 0.03%, the adverse effect of P on welding cracking becomes significant. Therefore, the P content is set at 0.03% or less and preferably is set at 0.025% or less.

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S: 0.01% or less

Sulfur is an element that is inevitably contained in steel. In the event that the S content exceeds 0.01%, the corrosion resistance is degraded, because the formation of water-soluble sulfides such as CaS and MnS is enhanced. Therefore, the S content is set at 0.01% or less, more preferably it is set at 0.006% or less, and additionally preferably it is set at 0.003% or less.

Cr: from 19.0% to 28.0%

Cr is an element that is very important to maintain the corrosion resistance of stainless steel. If the Cr content is less than 19.0%, it is not possible to obtain a sufficient corrosion resistance in a weld seam or the periphery thereof in which the Cr content in the surface layer is reduced due to the oxidation caused by welding. On the other hand, if the Cr content exceeds 28.0%, the workability and ease of production of the steel are degraded. Thus, the Cr content is set at 19.0% to 28.0%, preferably set to 21.0% to 26.0%, and more preferably set to 21.0% to 24, 0%

Ni: from 0.01% to less than 0.30%

Nor is it an element that enhances the corrosion resistance of stainless steel and suppresses the progression of corrosion in a corrosive environment in which a passive film cannot be formed and active dissolution occurs. This effect is obtained when the content of Ni added is 0.01% or more. However, if the content of Ni added is 0.30% or more, the workability of the steel is degraded and the cost is increased because Ni is an expensive element. Therefore, the Ni content is set at 0.01% to less than 0.30%, preferably set to 0.03% to 0.24%, and more preferably set to 0.03% at less than 0.15%.

Mo: from 0.2% to 3.0%

Mo is an element that promotes the repasivation of a passive film and enhances the corrosion resistance of stainless steel. The effect described above becomes more significant when Mo is contained in the steel together with Cr. Mo produces the effect of enhancing corrosion resistance when the Mo content is 0.2% or more. However, if the Mo content exceeds 3.0%, the mechanical strength of steel is increased and the rolling load on the steel is increased accordingly, which leads to the degradation of the ease of production of the steel. Therefore, the Mo content is set at 0.2% to 3.0%, preferably set to 0.6% to 2.4%, more preferably set to 0.6% to 2.0 %, and additionally preferably is set at 0.8% to 1.3%.

Al: from more than 0.15% to 1.2%

Aluminum is an effective element for deoxidation. In the invention, Al improves the corrosion resistance of the weld by concentrating on a tempering color formed by welding together with silicon and titanium.

In addition, Al has a stronger affinity for nitrogen than Cr and forms AlN. This inhibits the formation of a Cr nitride. In this way, this element also suppresses the sensitization of a weld bead. This effect is obtained when the Al content exceeds 0.15%. However, if the Al content exceeds 1.2%, the diameter of ferrite glass grains is increased, which degrades the workability and ease of production of the steel. Therefore, the Al content is set at more than 0.15% to 1.2% and preferably is set at 0.17% to 0.8%.

V: from 0.02% to 0.50%

V is an element that enhances the corrosion resistance and workability of steel and reduces the risk of welding cracking. This element is combined with nitrogen to create VN and thereby suppresses sensitization of a welded area. Although it is known that adding Nb and Ti in combination is effective in suppressing sensitization of a welded area, in the present invention, there is a need to reduce the Nb content in order to suppress weld cracking in a double weld zone. . However, if Ti is added to steel alone, a sufficient sensitization suppression effect may not be achieved. Therefore, the addition of V and Al as alternatives to Nb is effective in suppressing the sensitization of a welded area. This effect is obtained when the content of V is 0.02% or more. On the other hand, if the V content exceeds 0.50%, the workability of the steel is degraded. Therefore, the V content is set at 0.02% to 0.50% and preferably set to 0.03% to 0.40%.

Cu: less than 0.1%

Cu is an impurity that is inevitably contained in steel. In ferntic stainless steel that has high corrosion resistance and that has a Cr content and a Mo content such as in the present invention, Cu increases the passivity maintenance current, thus causing a passive film to be unstable, and, as a result, degrading corrosion resistance. The effect of degrading corrosion resistance becomes significant if the Cu content is 0.1% or more. Therefore, the Cu content is set at less than 0.1%.

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Ti: from 0.05% to 0.50%

Ti is an element that is preferably combined with C and N and thereby suppresses the degradation of corrosion resistance caused by the precipitation of a Cr carbonitride. In the present invention, Ti is an element that is important for suppress sensitization of a welded area. In addition, this element concentrates on a tempering color of a welded area in combination with Si and Al and thereby enhances the protective function of an oxide layer. This effect is obtained when the Ti content is 0.05% or more. However, if the Ti content exceeds 0.50%, the workability of the steel is degraded and the size of a Ti carbonitride is increased, which causes surface defects. Therefore, the Ti content is set at 0.05% to 0.50%, preferably set to 0.08% to 0.38%, and more preferably set to 0.25% to 0, 35%

N: from 0.001% to 0.030%

N is an element that is inevitably contained in steel and has an effect of increasing the mechanical strength of steel due to the reinforcement of a solid solution similar to C. This effect is obtained when the N content is 0.001% or more. However, if precipitation of a Cr nitride occurs, corrosion resistance is degraded. Therefore, an appropriate N content is 0.030% or less. Therefore, the N content is set at 0.001% to 0.030%, preferably set to 0.002% to 0.018%, and more preferably set to 0.007% to 0.011%.

Nb: less than 0.05%

Generally, Nb is considered to be an element that is preferably combined with C and N and thereby suppresses the degradation of corrosion resistance caused by the precipitation of a Cr carbonitride. The element also precipitates in the form of a film in a double weld zone and thereby causes weld cracking in the double weld zone. Therefore, the Nb content is preferably set low. Significant welding cracking occurs if the Nb content is 0.05% or more. Therefore, the Nb content is set to less than 0.05% and preferably set to less than 0.02%.

Nb x P: 0.0005 or less

where each element symbol represents the content (in mass%) of the element.

Nb precipitates in the form of a film in a double weld zone, which causes weld cracking to occur. The precipitation of Nb depends mainly on the product of the Nb content and the P content. As shown in Figure 1, significant welding cracking occurs if Nb x P exceeds 0.0005. Therefore, Nb x P is set at 0.0005 or less.

The fundamental chemical composition according to the present invention was described above, and the rest is inevitable Fees and impurities. In addition, Zr, W, REM, Co and B can be added to the steel as optional elements in order to enhance the corrosion resistance and toughness of the steel.

Zr: 1.0% or less

Zr is combined with C and N and thus produces an effect of suppressing sensitization. This effect is obtained when the content of Zr is 0.01% or more. However, an excessive addition of Zr degrades the workability of steel and leads to an increase in cost because Zr is a very expensive element. Therefore, when Zr is added to the steel, the Zr content is preferably set at 1.0% or less and more preferably set at 0.2% or less.

W: 1.0% or less

W has an effect of enhancing corrosion resistance in a manner similar to Mo. This effect is obtained when the content of W is 0.01% or more. However, an excessive addition of W increases the mechanical strength of the steel, which degrades the ease of production of the steel. Therefore, when W is added to the steel, the W content is preferably set at 1.0% or less and more preferably set at 0.5% or less.

REM: 0.1% or less

A REM (rare earth element) enhances oxidation resistance and thereby suppresses oxidation scale formation. This suppresses the formation of a Cr depletion region immediately below a tempering color of a welded area. This effect is obtained when the REM content is 0.001% or more. However, an excessive addition of REM degrades the ease of production of steel, such as ease of acid pickling, and leads to an increase in cost. Therefore, when a REM is added to the steel, the REM content is preferably set to 0.1% or less.

Co: 0.3% or less

Co is an element that enhances the toughness of steel. This effect is obtained when the Co content is 0.001% or more. However, an excessive addition of Co degrades the ease of steel production. So,

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when Co is added to the steel, the Co content is preferably set at 0.3% or less and more preferably set at 0.1% or less.

B: 0.1% or less

B is an element that improves the resistance to fragility of secondary machining. The B content of 0.0001% or more is appropriate in order to obtain the effect. However, an excessively high B content causes the degradation of ductility due to solid dissolution reinforcement. Therefore, when this content B in the steel, the content in B is preferably set at 0.1% or less and more preferably is set at 0.01% or less.

2. Manufacturing conditions

Next, a preferred method of manufacturing the steel according to the present invention is described. Steel having the composition described above is produced by fusion by a known method using a converter furnace, an electric furnace, a ford melting furnace, or the like and is shaped to give a steel raw material (roughing) by continuous casting or Ingot casting. Subsequently, the steel raw material is heated to 1100 ° C to 1300 ° C and then hot rolled at a finishing temperature of 700 ° C to 1000 ° C and a winding temperature of 500 ° C to 850 ° C . Therefore, a steel strip having a thickness of 2.0 to 5.0 mm is prepared. The hot-rolled strip prepared at 800 ° C to 1200 ° C is coated, subjected to pickling with acid and then laminated in fno. The laminated sheet is coated in fno at 700 ° C to 1000 ° C. After annealing, the laminated sheet is subjected to pickling with acid to remove the scale. Optionally, the steel strip laminated in fno, from which the scale has been removed, can be subjected to adjustment lamination.

Example 1

Next, the present invention is described based on examples.

The stainless steels shown in Table 1 were prepared by fusing in vat and then heated to 1200 ° C. Subsequently, the stainless steels were hot rolled to a thickness of 4 mm, annealed at 800 ° C to 1000 ° C and then subjected to acid pickling to remove the scale. The resulting stainless steels were laminated in fno to a thickness of 0.8 mm, annealed at 800 ° C to 1000 ° C and subjected to acid pickling. Therefore, test materials were prepared.

[Table 1] Chemical compositions of test materials (mass%)

 No.

 C Yes Mn P S Cr Ni Mo Al V Nb Ti N Cu Other elements NbxP Remarks

 one

 0.005 0.36 0.15 0.027 0.001 22.5 0.11 1.08 0.27 0.10 0.011 0.32 0.009 - 0.00030 Example of the invention

 2

 0.008 0.38 0.14 0.021 0.001 21.0 0.09 1.08 0.27 0.10 0.001 0.32 0.009 0.01 0.00002 Example of the invention

 3

 0.006 0.38 0.15 0.012 0.001 21.0 0.10 1.07 0.27 0.10 0.040 0.35 0.010 0.01 0.00048 Example of the invention

 4

 0.008 0.33 0.14 0.011 0.002 23.6 0.09 1.08 0.26 0.21 0.010 0.28 0.011 - 0.00011 Example of the invention

 5

 0.008 0.67 0.14 0.018 0.001 23.6 0.10 1.07 0.26 0.19 0.001 0.28 0.010 - 0.00002 Example of the invention

 6

 0.007 0.34 0.14 0.020 0.001 23.7 0.10 0.79 0.18 0.19 0.002 0.28 0.010 - 0.00004 Example of the invention

 7

 0.008 0.33 0.15 0.022 0.001 23.8 0.10 0.82 0.77 0.19 0.001 0.29 0.010 - 0.00002 Example of the invention

 8

 0.006 0.34 0.15 0.022 0.001 23.7 0.11 0.84 0.50 0.05 0.001 0.39 0.011 - 0.00002 Example of the invention

 9

 0.005 0.34 0.15 0.020 0.001 23.7 0.09 0.84 0.49 0.29 0.018 0.18 0.009 - 0.00036 Example of the invention

 10

 0.005 0.33 0.16 0.019 0.001 23.7 0.09 0.83 0.50 0.42 0.019 0.18 0.008 - 0.00036 Example of the invention

 eleven

 0.005 0.37 0.16 0.020 0.001 21.9 0.08 1.31 0.50 0.12 0.001 0.47 0.009 - 0.00002 Example of the invention

 12

 0.006 0.37 0.21 0.028 0.001 21.9 0.08 1.32 0.32 0.12 0.012 0.27 0.009 0.02 Zr: 0.04, W: 0.2 0.00034 Example of the invention

 13

 0.007 0.42 0.21 0.025 0.001 21.8 0.08 1.32 0.32 0.11 0.001 0.27 0.008 - Zr: 0.02, REM: 0.02 0.00003 Example of the invention

 14

 0.007 0.44 0.21 0.026 0.001 21.9 0.11 1.32 0.17 0.11 0.001 0.32 0.008 0.06 Co: 0.04 0.00003 Example of the invention

 fifteen

 0.008 0.44 0.20 0.025 0.001 21.8 0.10 1.32 0.17 0.11 0.001 0.31 0.010 0.01 W: 0.1, 0.00003 Example of

 REM: 0.001, B: 0.0005 invention

 16

 0.008 0.42 0.15 0.029 0.002 22.1 0.10 1.05 0.18 0.15 0.243 0.23 0.012 - 0.00705 Comparative Example

 18

 0.008 0.35 0.14 0.022 0.001 22.3 0.09 1.04 0.09 0.14 0.001 0.19 0.010 0.6 0.00002 Comparative example

 19

 0.007 0.35 0.13 0.023 0.001 22.3 0.09 1.05 0.31 0.01 0.001 0.19 0.009 - 0.00002 Comparative example

 twenty

 0.007 0.36 0.13 0.063 0.001 22.1 0.09 1.05 0.31 0.15 0.002 0.32 0.009 - 0.00013 Comparative example

 twenty-one

 0.007 0.36 0.13 0.028 0.001 22.1 0.09 1.05 0.31 0.15 0.030 0.29 0.009 - 0.00084 Comparative example

 22

 0.004 0.09 0.32 0.016 0.001 24.7 0.10 1.01 0.23 0.07 0.008 0.28 0.007 - B: 0.0005 0.00013 Example of the invention

 2. 3

 0.008 0.18 0.29 0.017 0.001 25.0 0.09 1.01 0.22 0.07 0.010 0.25 0.010 - 0.00017 Example of the invention

The underlined parts are outside the range of the invention

Cross welding was performed as shown in Figure 2 with the test materials prepared by welding TIG cord on sheet at a welding current of 90 A and a welding speed of 60 cm / min. The protective gas used was 100% Ar gas both on the front side (torch side) and on the rear side. The flow rate was set at 15 l / min on the front side and 10 l / min on the rear side. The width of a weld seam on the front side was approximately 4 mm.

The presence or absence of weld cracks in double weld areas of weld beads prepared using an optical microscope was examined. Table 2 shows the results.

[Table 2] Results of the evaluation of properties of test materials

 No.

 Presence or absence of weld cracks Potential corrosion by pitting Vc'100 in the weld seam Presence or absence of corrosion determined by a neutral corrosion test of neutral salt spray Observations

 mV versus SCE

 one

 Absent 22 Absent Example of the invention

 2

 Absent 24 Absent Example of the invention

 3

 Absent 27 Absent Example of the invention

 4

 Absent 14 Absent Example of the invention

 5

 Absent 38 Absent Example of the invention

 6

 Absent 12 Absent Example of the invention

 7

 Absent 52 Absent Example of the invention

 8

 Absent 41 Absent Example of the invention

 9

 Absent 28 Absent Example of the invention

 10

 Absent 28 Absent Example of the invention

 eleven

 Absent 49 Absent Example of the invention

 12

 Absent 23 Absent Example of the invention

 13

 Absent 28 Absent Example of the invention

 14

 Absent 22 Absent Example of the invention

 fifteen

 Absent 21 Absent Example of the invention

 16

 Present - Present Comparative Example

 18

 Absent -197 Present Comparative Example

 19

 Absent -202 Present Comparative Example

 twenty

 Present - Present Comparative Example

 twenty-one

 Present - Present Comparative Example

 22

 Absent 13 Absent Example of the invention

 2. 3

 Absent 32 Absent Example of the invention

There was no welding cracking in test materials # 1 to 15, 22 and 23, which are examples of the invention. However, among test materials No. 16 and 18 to 21, which are comparative examples, weld cracks were present in test material No. 16 in which the Nb and Nb x P content were out of the range of the invention, the test material No. 20 in which the P content was outside the range of the invention, and the test material No. 21 in which Nb x P was outside the range of the invention. Parts with weld cracks of these test materials were cut and the surfaces of their fractures were observed with an SEM. A precipitation of film type of Nb was observed in each sample.

A 20 mm square test tube was taken which inclines a double weld zone of the weld seam

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prepared from each test material, except for test materials # 16, 20 and 21 in which welding cracks were present. Each specimen was covered with a sealing material so that a 10 mm square plane to be measured was not covered with the sealing material. The potential for pitting corrosion of each specimen was measured in a 3.5% aqueous NaCl solution at 30 ° C without removing a tempering color formed by welding the specimen. The specimens were not subjected to polishing or passivation treatment. The measurement method stages other than those described above complied with JIS G 0577 (2005). Table 2 shows the corrosion potentials by pitting measured V'cioo. In test materials Nos. 1 to 15, 22 and 23, which are examples of the invention, V'ci00 was 0 mV versus SCE or more. On the other hand, in test materials # 18 and 19, which are comparative examples, V'c100 was less than 0 mV compared to SCE. Therefore, it was confirmed that high corrosion resistance was achieved in the examples of the invention.

A 40x40 mm specimen was taken that includes a double weld zone of the weld seam of each of test materials # 1 to 23 shown in table 1. A neutral neutral salt spray corrosion test was performed according to JIS H 8502 (1999) using the front side of the specimen as the plane to be examined. The number of cycles was set to three. After completion of the test, the presence or absence of corrosion of the weld bead was visually examined. Table 2 shows the results. In test materials Nos. 1 to 15, 22 and 23, which are examples of the invention, corrosion was absent. On the other hand, in test materials Nos. 16 and 18 to 21, which are comparative examples, corrosion was present. Therefore, it was confirmed that the weld seams of the examples of the invention have high corrosion resistance.

Industrial applicability

Ferntic stainless steel according to the present invention is suitably used in applications where a structure is manufactured by welding, for example, car exhaust system materials such as muffler materials, hot water storage tank materials for electric water heaters, or building materials such as cerrajena materials, ventilation opening materials and duct materials.

Claims (1)

1. Ferntic stainless steel consisting of, in mass%, C: from 0.001% to 0.030%, Si: from 0.03% to 0.80%, Mn: 0.05% to 0.50%, P: 0.03% or less, S: 0.01% or less, Cr: 19.0% to 28.0%, Ni: 0 , 01% to less than 0.30%, Mo: from 0.2% to 3.0%, Al: from more than 0.15% to 1.2%, V: from 0.02% to 0.50 %, Cu: minus 5 of 0.1%, Ti: from 0.05% to 0.50%, N: from 0.001% to 0.030%, and Nb: less than 0.05%, in which the expression (1) is satisfied, optionally also one or more elements selected from Zr: 1.0% or less, W: 1.0% or less, REM: 0.1% or less, Co : 0.3% or less, and B: 0.1% or less, and the rest is inevitable Fees and impurities, Nb x P <0.0005 ... (1) 10 where each element symbol represents the content (in mass%) of the element.