WO2020203939A1

WO2020203939A1 - Stainless steel sheet

Info

Publication number: WO2020203939A1
Application number: PCT/JP2020/014407
Authority: WO
Inventors: 修幸岡田; 雄介及川; 柘植　信二; 純平犬塚; 文則江目
Original assignee: 日鉄ステンレス株式会社
Priority date: 2019-03-29
Filing date: 2020-03-27
Publication date: 2020-10-08
Also published as: JPWO2020203939A1; KR20210139296A; CN113396238A; JP7008873B2

Abstract

Through a two-phase stainless steel sheet which includes 0.001-0.03% C, 0.05-1.5% Si, 0.10-3.00% Mn, 22.00-27.00% Cr, 4.00-7.00% Ni, 0.50-2.50% Mo, 0-1.50% W, and 0.10-0.25% N and satisfies equation 1 and equation 2, it is possible to obtain, even without solution heat treatment, a steel sheet which has corrosion resistance adequate for application in a river structure, industrial machine, chemical industrial tank, or other structure, and which has both strength and toughness equal to or greater than SUS304N2-X.　(Equation 1): PREW = Cr + 3.3(Mo + 0.5W) + 16N. (Equation 2): TS (°C) = 4Cr + 25Ni + 11(Mo + W) × (Mo + W) + 41(Mo + W) + 5Si – 6Mn – 30N + 550.

Description

Stainless steel plate

The present invention relates to stainless steel. For example, SUS304N2-X, which is an austenitic stainless steel, and SUS329J4L, which is a duplex stainless steel, can be substituted.

Stainless steel is used as a countermeasure against corrosion in river structures, industrial machinery, chemical industry tanks, etc. When stainless steel is used as a structural member, a high-strength material is required for the purpose of weight reduction by thinning, so austenitic stainless steel SUS304N2-X containing N in SUS304 and omitting solution heat treatment is used. May be used.

However, since the corrosion resistance of SUS304N2-X is inferior to that of SUS316L, it may not be applicable in terms of corrosion. Cr and Mo are known as elements that improve corrosion resistance, but in order to make the austenite phase single phase, the content of Ni, which is an austenite phase forming element, must be increased at the same time in addition to these elements, which is significant. It leads to an increase in cost.

Two-phase stainless steel is said to have lower expensive Ni content and higher strength than austenitic stainless steel. However, duplex stainless steels that have undergone solution heat treatment do not have the strength of SUS304N2-X. Further, in SUS329J4L, which is a typical steel type of duplex stainless steel, precipitation of σ phase is unavoidable during hot rolling. Therefore, if solution heat treatment is omitted in order to obtain strength, σ phase remains in the product. Corrosion resistance and toughness are greatly deteriorated.

The stainless steel shown in Patent Document 1 has been proposed as a duplex stainless steel having increased strength by omitting solution heat treatment. This steel saves Mo and focuses on suppressing the precipitation of Cr nitrides.

Japanese Unexamined Patent Publication No. 2012-153953

River structures, industrial machinery, chemical industry tanks, etc. may be in a severe corrosive environment due to chloride ions and acids in the contacting fluid. In such a place, the amount of Cr is small, and the desired corrosion resistance cannot be secured with SUS304N2-X that does not contain Mo.

In the hot-rolled steel sheet disclosed in Patent Document 1, attention is paid to the suppression of precipitation of Cr nitride, but in duplex stainless steel having a large content of Cr and Mo, σ-phase precipitation has a great influence on toughness and corrosion resistance. Cr nitride is a compound that precipitates by the interaction of Cr and N, and reduction of N and inclusion of austenite phase-forming elements (for example, Ni and Mn) are effective for suppressing precipitation of Cr nitride. On the other hand, the σ phase is an intermetallic compound precipitated by the interaction of Cr and Mo, and Ni accelerates the precipitation of the σ phase. Further, Mn is an element that is effective in suppressing Cr nitride precipitation but deteriorates corrosion resistance. Therefore, in duplex stainless steels having a large content of Cr and Mo, the effects of contained elements such as Ni and Mn on the formation of precipitates and intermetallic compounds and the corrosion resistance are significantly different. That is, the hot-rolled steel sheet disclosed in Patent Document 1 has a limit in corrosion resistance because it does not consider deterioration of toughness and corrosion resistance due to precipitation of the σ phase, and a steel sheet having further enhanced corrosion resistance and toughness is required. Has been done.

Against this background, the present inventors have sufficient corrosion resistance to be applied to structures such as river structures, industrial machinery, and chemical industry tanks, and further have strength and toughness equal to or higher than that of SUS304N2-X. The subject is to obtain a stainless steel plate.

In order to solve the above problems, the present inventors have high strength even if solution heat treatment is omitted by designing a component that can avoid σ phase precipitation during hot rolling while ensuring corrosion resistance. However, it was thought that a stainless steel sheet with excellent corrosion resistance and toughness could be obtained. That is, a new estimation formula was found for the σ-phase precipitation temperature TS, and using steel materials with different TSs according to this formula, the entry side temperature TF of the final finish rolling pass of hot rolling and 800 ° C. after the completion of hot rolling The cooling rate in the section of 600 ° C. was changed, and the strength, impact characteristics, and corrosion resistance of the obtained hot-rolled steel sheet were evaluated.
Through the above experiments, the present invention has been completed, which clearly indicates the stainless hot-rolled steel sheet without the solution heat treatment.

That is, the gist of the present invention is as follows.
[1]
By mass%
C: 0.001 to 0.030%,
Si: 0.05 to 1.50%,
Mn: 0.10 to 3.00%,
Cr: 22.00 to 27.00%,
Ni: 4.00 to 7.00%,
Mo: 0.50 to 2.50%,
W: 0 to 1.50%,
N: 0.10 to 0.25%,
Co: 0 to 1.00%,
Cu: 0 to 3.00%,
V: 0 to 1.00%,
Nb: 0 to 0.200%,
Ta: 0 to 0.200%,
Ti: 0 to 0.030%,
Zr: 0 to 0.050%,
Hf: 0 to 0.100%,
B: 0 to 0.0050%,
Al: 0 to 0.050%,
Ca: 0 to 0.0050%,
Mg: 0 to 0.0050%,
REM: 0 to 0.100%, and Sn: 0 to 0.100%,
The rest is Fe and unavoidable impurities,
O as an impurity: 0.006% or less,
P: 0.05% or less,
S: Steel limited to 0.003% or less,
The PREW obtained by the formula 1 is 25.0 or more and 36.0 or less, and the σ phase precipitation temperature TS (° C.) obtained by the formula 2 is 800 ° C. or more and 950 ° C. or less.
0.2% proof stress is 450MPa or more,
Charpy impact value at -20 ° C is 70 J / cm ² or more,
The pitting potential measured at 50 ° C. is 0.40 V vs. A stainless steel plate characterized by being SSE or higher.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N (Equation 1)
TS (° C.) = 4Cr + 25Ni-11 (Mo + W) x (Mo + W) + 100 (Mo + W) + 5Si-6Mn-30N + 550 (Equation 2)
However, each element symbol in the formulas 1 and 2 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
[2]
The component in the stainless steel sheet is mass%,
Co: 0.01-1.00%,
Cu: 0.01-3.00%,
V: 0.01-1.00%,
Nb: 0.005 to 0.200%,
Ta: 0.005 to 0.200%,
Ti: 0.001 to 0.030%,
Zr: 0.001 to 0.050%,
Hf: 0.001 to 0.100%,
B: 0.0001 to 0.0050%,
Al: 0.003 to 0.050%,
Ca: 0.0005-0.0050%,
Mg: 0.0001 to 0.0050%,
REM: 0.005 to 0.100%, and Sn: 0.005 to 0.100%
The stainless steel sheet according to [1], which contains one or more of them.

The stainless steel sheet obtained by the present invention has strength equal to or higher than that of SUS304N2-X, sufficient toughness as a structural material, and corrosion resistance higher than that of SUS304N2-X. On the other hand, the alloy cost is also reasonable, so the economy is good. As a result, by using the stainless hot-rolled steel sheet according to the present invention for river structures, industrial machinery, chemical industry tanks, etc., both performance and cost are improved, and it contributes extremely to the industrial and environmental aspects. It's big.

The reason for limiting the composition of the stainless steel according to the present invention will be described. Unless otherwise specified in the present specification,% for a component represents mass%.

C is limited to a content of 0.030% or less in order to ensure the corrosion resistance of stainless steel. If it is contained in excess of 0.030%, Cr carbides are generated during hot rolling, and corrosion resistance and toughness deteriorate. On the other hand, 0.001% is set as the lower limit from the viewpoint of cost of reducing the amount of C in stainless steel.

Si is contained in an amount of 0.05% or more due to deoxidation. Preferably, it is 0.20% or more. On the other hand, if it is contained in excess of 1.50%, the toughness deteriorates. Therefore, it should be 1.50% or less. Preferably, it is 1.00% or less.

Mn has the effect of increasing the austenite phase and lowering the σ phase precipitation temperature, so it is preferable to contain Mn at 0.10% or more. On the other hand, Mn is an element that lowers the corrosion resistance of stainless steel, so Mn should be 3.0% or less. Preferably 2.50% or less, 2.00% or less, 1.50% or less, 1.00% or less, 0.50% or less, 0.45% or less, 0.40% or less, or 0.35% or less. It is good to set it to.

Cr is contained in an amount of 22.00% or more in order to ensure basic corrosion resistance. Preferably 23.00% or more, 24.00% or more, 25.00% or more, 25.10% or more, 25.20% or more, 25.30% or more, 25.40% or more, or 25.50% or more. It is good to set it to. On the other hand, since Cr is an element that promotes the precipitation of the σ phase, the content is limited to 27.00% or less. It is preferably 26.90% or less, 26.80% or less, 26.70% or less, 26.60% or less, or 26.50% or less.

Ni is an element that promotes the formation of an austenite structure and at the same time has the effect of suppressing the formation of Cr nitrides and has the effect of improving the corrosion resistance to various acids. Therefore, it is preferable to contain 4.00% or more. Preferably, the content is 4.50% or more, 5.00% or more, 5.10% or more, 5.20% or more, 5.30% or more, 5.40% or more, or 5.50% or more. On the other hand, Ni is an element that promotes the precipitation of the σ phase, and when the σ phase is precipitated, a Cr-deficient phase is formed and the local corrosion resistance deteriorates. Therefore, it is preferable to contain Ni in 7.00% or less. It is preferably 6.90% or less, 6.80% or less, 6.70% or less, 6.60% or less, or 6.50% or less.

Mo is a very effective element that enhances the corrosion resistance of stainless steel, and it is preferable to contain 0.50% or more in order to impart corrosion resistance of 304N2-X or more. Preferably, 1.00% or more, 1.30% or more, 1.35% or more, 1.40% or more, 1.45% or more, 1.50% or more, 1.55% or more, 1.60% or more, It should be 1.65% or more, or 1.70% or more. On the other hand, Mo is an element that promotes the precipitation of the σ phase, and the local corrosion resistance deteriorates. Therefore, it is preferable to contain Mo in an amount of 2.50% or less. It is preferably 2.40% or less, 2.30% or less, 2.10% or less, and 2.00% or less.

W has the effect of improving the corrosion resistance of stainless steel, similar to Mo. In the steel of the present invention, it is preferable to contain 1.50% as the upper limit for the purpose of enhancing the corrosion resistance. On the other hand, since it is also an expensive element, it does not have to be contained in particular. The preferable content is preferably 0.02% or more.

N (nitrogen) is an effective element that enhances the strength and corrosion resistance of stainless steel, so it is recommended that it be contained in an amount of 0.10% or more. It is preferably 0.15% or more. On the other hand, since N produces Cr nitride and inhibits corrosion resistance, its content is preferably 0.25% or less. Preferably, it is 0.20% or less.

The rest is Fe and unavoidable impurities. The unavoidable impurities are elements contained in the raw material, elements unintentionally contained during production, and the like. Of the impurities, O, P, and S are limited for the following reasons.

O (oxygen) is an element that is inevitably mixed and is an element that inhibits the hot workability, toughness, and corrosion resistance of stainless steel, so it is preferable to reduce it as much as possible. Therefore, the O content is preferably 0.006% or less.

P is an element that is inevitably mixed from the raw material, and since it deteriorates hot workability and toughness, it should be as small as possible and limited to 0.05% or less. Preferably, it is 0.03% or less.

S is an element that is inevitably mixed from the raw material, and it also deteriorates hot workability, toughness, and corrosion resistance. Therefore, it should be as small as possible, and the upper limit should be 0.003% or less.

Further, instead of Fe, one or more of the following elements (Co, Cu, V, Nb, Ta, Ti, Zr, Hf, B, Al, Ca, Mg, REM, Sn) are contained. May be good. Since these elements do not have to be contained, the content range includes 0%.

Co is an element effective for enhancing the corrosion resistance of steel and may be contained. Even if Co is contained in an amount of more than 1.00%, it is an expensive element and therefore an effect commensurate with the cost is not exhibited. Therefore, it is preferable to contain Co in an amount of 1.00% or less. It is preferably contained in an amount of 0.50% or less. In order to obtain the effect, it is preferable to contain 0.01% or more, preferably 0.03% or more.

Cu may be contained because it is an element that additionally enhances the corrosion resistance of stainless steel to acid. If Cu is contained in an amount of more than 3.0%, εCu is precipitated in excess of the solid solubility during cooling after hot rolling and embrittlement occurs. Therefore, it is preferable to contain Cu in an amount of 3.00% or less. It is preferably contained in an amount of 2.00% or less. When Cu is contained, it is preferable to contain it in an amount of 0.01% or more, preferably 0.20% or more in order to obtain the effect.

Since V, Nb, and Ta are elements that form carbides and nitrides in steel and additionally enhance corrosion resistance, they may be contained. On the other hand, if a large amount is contained, the toughness will be inhibited by excessively formed carbides and nitrides. Therefore, the contents of V, Nb and Ta are 1.00% or less, 0.200% or less and 0, respectively. .200% or less is recommended. When these elements are contained, they are preferably contained in an amount of 0.01% or more, 0.005% or more, and 0.005% or more, respectively, in order to obtain the effect.

Ti, Zr, and Hf may be contained because they are elements that form carbides and nitrides in steel to refine crystal grains. On the other hand, if a large amount is contained, the toughness will be inhibited by excessively formed carbides and nitrides. Therefore, the contents of Ti, Zr, and Hf are 0.030% or less, 0.050% or less, and 0, respectively. It should be 100% or less. When these elements are contained, they are preferably contained in an amount of 0.001% or more, 0.001% or more, and 0.001% or more, respectively, in order to obtain the effect.

B is an element that improves the hot workability of steel and may be contained. On the other hand, if it is contained in a large amount, the nitride of B is precipitated and the toughness is inhibited. Therefore, the content may be 0.0050% or less. When B is contained, it is preferable to contain 0.0001% or more, preferably 0.0005% or more in order to obtain the effect.

Al is an element for deoxidizing steel and may be contained. On the other hand, if it is contained in excess, Al nitride is generated and the toughness is inhibited. Therefore, the content should be 0.050% or less. It is preferably 0.030% or less. When Al is contained, it is preferably 0.003% or more, preferably 0.005% or more in order to obtain the effect.

Ca and Mg may be contained in order to enhance hot workability. On the other hand, if it is excessively contained, the hot workability is adversely affected. Therefore, the Ca and Mg contents are preferably 0.0050% or less and 0.0050% or less, respectively. When these elements are contained, it is preferable to set them to 0.0005% or more and 0.0001% or more, respectively, in order to obtain the effect.

REM may be contained because it is an element that improves the hot workability of steel. On the other hand, excessive content lowers hot workability and toughness, so when REM is contained, it is preferably 0.100% or less. When REM is contained, 0.005% or more may be contained in order to obtain the effect. Here, the content of REM is the sum of the contents of lanthanoid rare earth elements such as La and Ce.

Sn may be contained because it is an element that enhances the corrosion resistance of steel to acid. On the other hand, if it is contained in excess, it impairs hot workability. Therefore, when Sn is contained, it is preferably 0.100% or less. When Sn is contained, it is preferable to make it 0.005% or more in order to obtain the effect.

PREW is an index for the pitting corrosion resistance of stainless steel, and is calculated by Equation 1 using the contents (%) of the alloying elements Cr, Mo, W, and N. If the PREW of stainless steel is less than 25.0, it cannot exhibit corrosion resistance in brackish water / seawater environment and chloride ion environment such as chemical industry tank. The upper limit is not particularly limited, but if the alloying element is contained in excess of 36.0, the cost will increase. Therefore, the PREW range is preferably 25.0 or more and 36.0 or less.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N (Equation 1)
However, each element symbol in the formula 1 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.

Chloride ions cause corrosion in river structures, industrial machinery, chemical industry tanks, etc., causing corrosion. In order to ensure sufficient corrosion resistance in the environment, the PREW value may be 25.0 or more by containing Cr, Mo, N, and W. From the viewpoint of ensuring corrosion resistance, the lower limit of PREW is preferably 26.0, 27.0, 28.0, 29.0, 29.5, 30.0, 30.5, or 31.0. On the other hand, if the Cr and Mo contents are excessively increased in order to increase PREW, the σ phase is precipitated as described above, and if the N content is excessive, the toughness is deteriorated and other adverse effects appear. Considering the influence on these characteristics, the upper limit of PREW should be 36.0.

In general stainless steel sheets (especially duplex stainless steel sheets), even if the σ phase is precipitated in hot rolling, the σ phase disappears in the subsequent solution heat treatment. However, since the strength is lowered by the solution heat treatment, in order to secure the strength, it is preferable to omit the solution heat treatment and leave the strain introduced in the steel during hot rolling in the final product.

The precipitation temperature of the σ phase is determined by the chemical composition of the steel, and the temperature range in which the σ phase can precipitate in a chemical equilibrium state can be estimated by thermodynamic calculation. For example, it can be calculated using commercially available software called Thermocalc (registered trademark) and a thermodynamic database (FE-DATA version 6 or the like). Using the above software and database, the present inventors obtained Equation 2 for estimating the upper limit of the σ-phase precipitation temperature region (hereinafter referred to as σ-phase precipitation temperature, which is indicated by TS). Further, in order to suppress the precipitation of the σ phase and obtain the desired characteristics, the TS is preferably 950 ° C. or lower. Preferably, the TS is 930 ° C or lower, or 910 ° C or lower. The lower the TS, the more difficult it is for the σ phase to precipitate, but this leads to a decrease in Cr, Mo, and W, resulting in insufficient corrosion resistance. Therefore, the lower limit of TS may be set to 800 ° C. It is preferably 820 ° C. or higher, 830 ° C. or higher, or 840 ° C. or higher.
TS (° C.) = 4Cr + 25Ni-11 (Mo + W) x (Mo + W) + 100 (Mo + W) + 5Si-6Mn-30N + 550 (Equation 2)
However, each element symbol in the formula 2 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
The following formula 2'may be used as the estimation formula for the σ phase precipitation temperature TS. Within the scope of the present invention, both Equation 2'and Equation 2 are equivalent.
TS (° C.) = 4Cr + 25Ni + 71 (Mo + W) -11.4 (Mo-1.3) * (Mo-1.3) + 5Si-6Mn-30N + 569 (Equation 2')

The hot rolling process will be described below.
The slab heating temperature before the start of rolling may be appropriately determined, for example, in the range of 1150 to 1250 ° C.

Next, regarding the pass schedule, if the finishing temperature TF (steel surface temperature at the entrance of the final pass of hot rolling) is too high and is close to the solution heat treatment temperature, sufficient strain does not remain in the hot-rolled steel sheet, and the desired hardness is obtained. Cannot be obtained. On the other hand, if the TF is too low, precipitation of the σ phase is unavoidable. However, since TS is an estimated value of the σ-phase precipitation temperature when the steel sheet is held in a chemical equilibrium state, that is, for an infinite time, the actual hot rolling is completed in a finite time, so that the TF does not need to exceed TS. Equation 3 may be satisfied as long as the component range is specified in the present invention. The conditions other than the finishing temperature are not particularly limited, and for example, the rolling amount for each pass may be determined according to the capacity of the rolling mill.
TF-TS ≧ -100 (Equation 3)

After hot rolling, in order to suppress σ phase precipitation in the cooling process, cooling may be performed at a cooling rate of 1 ° C./s or more in the section of 800 ° C. to 600 ° C. within the component range specified in the present invention. The cooling method is not particularly limited, and water cooling or air cooling may be used depending on the plate thickness. As described above, it is not necessary to carry out solution heat treatment on the hot-rolled steel sheet thus obtained.

The strength should be equal to or higher than SUS304N2-X, that is, 0.2% proof stress of 450 MPa or higher. It may be preferably 480 MPa or more.

Stainless steel is used outdoors as a river structure and in chemical plants together with cooling equipment, so it may be exposed to temperatures below room temperature. In order to use it as a structural member in such an environment, toughness at low temperature is required, and specifically, the Charpy impact value of the hot-rolled steel sheet at −20 ° C. may be 70 J / cm ² or more.

Sufficient corrosion resistance against chloride ions, which cause corrosion, is required in the above applications. Specifically, the pitting potential of a hot-rolled steel sheet at 50 ° C. is 0.40 V vs. It may be SSE or higher. Here, vs. SSE indicates that the potential is based on a silver-silver chloride reference electrode using a saturated KCl aqueous solution at 25 ° C. as an electrolyte.

Of the precipitated σ phases, the ones that affect the corrosion resistance are those precipitated during the hot rolling and subsequent cooling processes. Therefore, hot rolling and subsequent hot rolling are performed based on the difference ΔCr between the amount of Cr extraction residue of the hot-rolled steel sheet and the amount of Cr extraction residue of the steel sheet obtained by subjecting the hot-rolled steel sheet to solution heat treatment at 1000 to 1100 ° C. and then water-cooling. The effect of precipitation during the cooling process was quantified. As a result, when ΔCr exceeds 0.010% in terms of Cr content in the steel sheet, the corrosion resistance of the hot-rolled steel sheet tends to decrease. Therefore, it is preferable that ΔCr is 0.010% or less.

Examples are described below. Table 1 shows the chemical composition, PREW, and TS of the test steel. Among the components of steel, the components not shown in Table 1 are Fe and unavoidable impurity elements. These steels were obtained using a vacuum melting furnace. Regarding the components shown in Table 1, the portion where the content is not described is the unavoidable impurity level. REM means lanthanoid rare earth elements, and the content indicates the total of these elements. The slabs obtained by vacuum melting were heated at 1200 ° C. for 2 hours, and then hot forged to obtain steel ingots having a predetermined shape. Here, the shape of the ingot was 110 mm width × 150 mm length × 60 mm thickness when the plate thickness after finish rolling was 20 mm or less, and 110 mm width × 150 mm length × 100 mm thickness when the plate thickness exceeded 20 mm.

Table 2 shows the conditions of the hot rolling and the subsequent cooling rate performed to make the ingot into a steel sheet, and the values of 0.2% strength, Charpy absorption energy, and pitting corrosion potential of the obtained hot-rolled steel sheet. In the production of the hot-rolled steel sheet, first, the ingot obtained by the above-mentioned forging was soaked in heat at 1200 ° C. for 60 minutes. Then, the TF was reduced to the temperature shown in Table 2 and cooled so that the cooling rate in the section of 800 ° C. to 600 ° C. became the value shown in the table. The cooling method was water cooling.

The method of measuring 0.2% proof stress is described. The No. 4 test piece described in JIS Z2241: 2011 was cut out from the steel plate after hot rolling by machining. The measurement method was carried out in accordance with JIS Z2241: 2011.

The method of measuring Charpy absorbed energy is described. The test piece described in JIS Z2242: 2018 was cut out from the steel sheet after hot rolling by machining. The notch shape was a V notch. When the standard test piece could not be collected due to insufficient thickness of the steel plate, a subsize test piece was collected as shown in Table 2. The measurement was carried out in accordance with JIS Z2242: 2018. However, the test temperature was −20 ° C.

The method of measuring the pitting potential is described below. A sample having a width of 15 mm, a length of 30 mm, and a thickness of 2 mm was cut out by machining from the surface layer of the steel sheet after hot rolling, and after grinding 0.5 mm from the surface layer, a test piece having a measurement surface of # 600 wet polishing finish was prepared. A resin was applied to this test piece, leaving a portion of 10 mm × 10 mm on the measurement surface. The test was carried out using this test piece according to the method of JIS G0577: 2014. However, in JIS G0577: 2014, the temperature of the test was changed from 30 ° C to 50 ° C. The measurement was carried out until the anode current density reached 1 mA / cm ² , and the pitting potential was the potential at the time when the current density exceeded 100 μA / cm ² .

As can be seen from the above examples, it has been clarified by the present invention that a stainless hot-rolled steel sheet having strength and toughness suitable for structural members, excellent corrosion resistance, and good economic efficiency can be obtained.

The stainless steel sheet according to the present invention has strength equal to or higher than that of existing stainless steels (SUS304N2-X and SUS329J4L), has toughness and corrosion resistance suitable for structural members, and is also excellent in economy. It can be used for all industrial equipment and structures such as for chemical plants.

Claims

By mass%
C: 0.001 to 0.030%,
Si: 0.05 to 1.50%,
Mn: 0.10 to 3.00%,
Cr: 22.00 to 27.00%,
Ni: 4.00 to 7.00%,
Mo: 0.50 to 2.50%,
W: 0 to 1.50%,
N: 0.10 to 0.25%,
Co: 0 to 1.00%,
Cu: 0 to 3.00%,
V: 0 to 1.00%,
Nb: 0 to 0.200%,
Ta: 0 to 0.200%,
Ti: 0 to 0.030%,
Zr: 0 to 0.050%,
Hf: 0 to 0.100%,
B: 0 to 0.0050%,
Al: 0 to 0.050%,
Ca: 0 to 0.0050%,
Mg: 0 to 0.0050%,
REM: 0 to 0.100%, and Sn: 0 to 0.100%,
The rest is Fe and unavoidable impurities,
O as an impurity: 0.006% or less,
P: 0.05% or less,
S: Steel limited to 0.003% or less,
The PREW obtained by the formula 1 is 25.0 or more and 36.0 or less, and the σ phase precipitation temperature estimation formula TS (° C.) obtained by the formula 2 is 800 ° C. or more and 950 ° C. or less.
0.2% proof stress is 450MPa or more,
Charpy impact value at -20 ° C is 70 J / cm 2 or more,
The pitting potential measured at 50 ° C. is 0.40 V vs. A stainless steel plate characterized by being SSE or higher.
PREW = Cr + 3.3 (Mo + 0.5W) + 16N (Equation 1)
TS (° C.) = 4Cr + 25Ni-11 (Mo + W) x (Mo + W) + 100 (Mo + W) + 5Si-6Mn-30N + 550 (Equation 2)
However, each element symbol in the formulas 1 and 2 indicates the content (mass%) of the element, and if it is not contained, 0 is substituted.
The component in the stainless steel sheet is mass%,
Co: 0.01-1.00%,
Cu: 0.01-3.00%,
V: 0.01-1.00%,
Nb: 0.005 to 0.200%,
Ta: 0.005 to 0.200%,
Ti: 0.001 to 0.030%,
Zr: 0.001 to 0.050%,
Hf: 0.001 to 0.100%,
B: 0.0001 to 0.0050%,
Al: 0.003 to 0.050%,
Ca: 0.0005-0.0050%,
Mg: 0.0001 to 0.0050%,
REM: 0.005 to 0.100%, and Sn: 0.005 to 0.100%
The stainless steel sheet according to claim 1, which contains one or more of them.