JP3363628B2 - Stainless steel excellent in corrosion resistance to molten salt and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to stainless steel having excellent corrosion resistance against molten salt, and more particularly to a material for a separator of a molten carbonate fuel cell.

[0002]

2. Description of the Related Art A molten carbonate type fuel cell separator material is required to have corrosion resistance so that molten carbonate as an electrolyte does not cause molten salt corrosion. Conventionally, as a separator material for such a molten carbonate fuel cell,
High grade stainless steels such as SUS316L and SUS310S have been used.

It is said that the corrosion resistance to molten carbonate is generally proportional to the amount of Cr in stainless steel, and therefore, a substance having a large amount of Cr such as SUS310S is often used. In addition, in the stainless steel having a high Cr content, the Ni content is also high in order to stabilize the austenite phase.

On the other hand, by coating the surface of these stainless steels with alumina, high corrosion resistance is imparted,
There is also an example in which this is used as the separator material.

Regarding the improvement of corrosion resistance of stainless steel against molten carbonate, JP-A-62-294153, "Separator material for fuel cell" and JP-A-1-252757.
The "Fe-based alloy excellent in molten carbonate corrosion resistance" of Japanese Patent Publication is known. The former JP-A-62-294153 teaches that the corrosion resistance to molten carbonate is improved by adding Al to the steel.

However, if a large amount of Al is added to the stainless steel in order to improve the corrosion resistance against molten salt, the hot workability of the steel is significantly deteriorated, and large cracks are likely to occur during hot rolling for steel sheet production. become. Therefore, the size of steel sheet that can be manufactured is limited, and the product yield is low and the manufacturing cost must be high. For such a problem of hot workability of Al-containing austenitic stainless steel, a small amount of δ-ferrite is precipitated during solidification,
Alternatively, a method for improving the hot workability of stainless steel by adding a rare earth element such as La or Ce is disclosed in JP-B-55.
No. 4,43498, and JP-A-60-262.
Japanese Patent No. 945 proposes a method of preventing cracking by hot rolling at a temperature in the range of 1000 to 1200 ° C.

[0007]

Since the molten carbonate of a fuel cell has an extremely strong corrosive action, it cannot be said that even if a high-grade stainless steel such as SUS316L or SUS310S is used as the separator material, it has sufficient corrosion resistance. is the current situation. Especially in SUS310S, Cr
Since the Ni content is high, the raw material cost becomes high and the workability also deteriorates. From a product price perspective,
The challenge is to reduce the content of Cr and Ni, especially the content of Ni as much as possible. In this respect, JP-A-62-29
"Fuel cell separator material" of 4153 publication is 25%
Cr-20% Ni steel is used as the basic composition, the raw material cost is high, and the workability is not so good.

[0008] In the case of a method of coating the surface of stainless steel with alumina to improve the corrosion resistance of the separator material, there is a problem that coating and heat treatment are required and the whole manufacturing process becomes complicated.

The Fe-based alloy described in JP-A-1-252757, which has excellent resistance to molten carbonate corrosion, must have a particularly low Si content. For this reason, special consideration must be given to the production of steel, which also raises the production cost.

JP-B-55-43498 and JP-A-6-
Japanese Patent Laid-Open No. 0-262945 discloses an Al-containing stainless steel having excellent heat resistance and oxidation resistance and good hot workability. However, it is a molten salt environment with high heat and very strong corrosiveness and complicated corrosion mechanism. There is no useful teaching for improving corrosion resistance in.

Therefore, the present invention is an inexpensive fuel cell for a fuel cell which has excellent resistance to molten carbonate corrosion and excellent workability or hot workability while suppressing the contents of Cr and Ni as much as possible. The purpose is to develop a stainless steel separator material.

[0012]

According to the present invention, the weight percent is
C: 0.1% or less, Mn: 2.0% or less, Ni: 7.
5% or more and less than 15.0%, Cr: 14.0 to 20.0%,
Si: more than 0.2% and 4.0% or less, Al: 1.0 to 4.0
%, And in some cases further 3.0% or less C
u, Mo less than 3.0%, Ti less than 1.0%, 1.0%
Zr, 0.5% or less of Y or 0.5% or less, preferably 0.05% or less of one or more kinds of REM (rare earth element), and Si% / Al% ≤ 1. 0, preferably Si% / Al% ≦
Provided is a stainless steel which satisfies the relationship of 0.4 and has excellent corrosion resistance to a molten salt, the balance of which is Fe and inevitable impurities.

The stainless steel of the present invention is preferably adjusted in the content of components so as to further satisfy the following relationship. (Si% + Al%) / Ni% ≦ 0.47

More preferably, in the stainless steel of the present invention, the amount of each component is adjusted so that the value of δ (%) represented by the following formula is in the range of 0.5 to 4.0. δ (%)
For steels with, the hot rolling is terminated at a temperature of 1000 ° C or higher during hot rolling (the material temperature on the delivery side of the finishing mill is 1000
The hot-rolled steel sheet can be advantageously manufactured by adopting the hot-rolling condition that the temperature is not less than 0 ° C. δ (%) = 1.57 ・ Cr + 0.7 ・ Si + 3.89 ・ A
1-1.57, Ni-0.16, Mn-38.5, C-7.
65. In that case, if REM is contained, its content should be 0.
It should be less than 05%.

[0015]

The present inventors have conducted extensive research on the corrosion behavior of stainless steel in the environment of molten carbonate fuel cells. However, when the amounts of Si and Al in steel are added together within a certain range, , It has been found that a stainless steel having excellent corrosion resistance to molten carbonate can be obtained without significantly increasing the contents of Cr and Ni. That is, details thereof will be shown in Examples (FIGS. 1, 2 and 4) described later. Preferably Si% / Al% ≦
Addition so as to satisfy the relationship of 0.4 gives a stainless steel showing excellent corrosion resistance to molten carbonate.
It can be considered that this is an action due to the formation of the Al oxide layer and the Si oxide layer on the surface of the stainless steel.

Further, when such Si and Al are added in combination, the workability of the steel becomes inferior. This point is shown in the example (FIG. 3) described later, where (Si% + Al%) / Ni It has been found that the problem can be solved if Ni is contained so that the relationship of% ≦ 0.47 is satisfied.

Further, a steel containing Al such as the steel according to the present invention generally has poor hot workability, and there is a risk of breakage when a hot rolled steel sheet is produced by ordinary hot rolling equipment. As shown in Examples (FIGS. 5 and 7) described later, the amount of each component was adjusted so that the value of δ (%) was in the range of 0.5 to 4.0, and at 1000 ° C. or higher. It was found that this could be solved by finishing hot rolling. At that time, RE
When M is added, it is preferably 0.05% or less (Fig. 6).

[Detailed Description of the Invention] The action of each component in the steel of the present invention and the reason for controlling the content are individually explained as follows.

C: If the C content is too high, the hot workability of the steel is impaired, so the C content is 0.1.
% Or less. In addition, in order to improve the high temperature strength of steel, it is preferable to contain a C content exceeding 0.03%.

Mn: Mn is an austenite forming element and is used as a deoxidizing agent and a desulfurizing agent during melting.
% Of Mn. However, excessive addition deteriorates the corrosion resistance to molten salt, so the Mn content in the steel of the present invention is set to 2.0% or less.

Ni: Ni is an austenite-forming element and must be contained in an amount of 7.5% or more in order to maintain the austenite phase. However, if contained too much, the product price will rise, so the upper limit is 15.0.
It was less than%.

Cr: Cr plays an important role in improving the corrosion resistance of steel against molten carbonate. For this purpose, it is necessary to contain 14.0% or more of Cr. However, if Cr is contained too much, the austenite phase becomes unstable and the hot workability deteriorates.
The amount of r should be 20.0% or less.

Si: Si acts to improve the high temperature strength and oxidation resistance of steel. Since Si has a large oxygen affinity, when the steel of the present invention is used as a separate material for a fuel cell, the vicinity of the interface between the oxide layer formed on the steel surface by molten carbonate corrosion and the stainless steel base material is used. Near the grain boundary of
An i-oxide is formed. This Si oxide layer prevents the diffusion of atoms that try to pass through the grain boundaries and serves to suppress the corrosion of stainless steel. This action is promoted by the inclusion of Al as described later. In order to improve the corrosion resistance to molten carbonate, the Si content is required to exceed 0.2%. However, if added in a large amount, the manufacturability and hot workability are impaired, so the Si content should be 4.0% or less.

Al: Al has a deoxidizing action and an action of improving the corrosion resistance to molten carbonate. To obtain sufficient corrosion resistance to molten carbonate, it is necessary to add Al in an amount of 1.0% or more, but if too much is added, manufacturability and hot workability will deteriorate. Is 1.0
It was set to ˜4.0%.

The steel of the present invention is characterized in that the molten carbonate corrosion resistance is improved by the combined addition of Si and Al. This fact is also shown in Examples described later (FIGS. 1, 2, and 4), and the action and effect of this composite addition can be considered as follows.

As described above, the Si oxide layer formed at the interface between the oxide layer on the outermost surface and the stainless steel base material by containing a proper amount of Si prevents diffusion of atoms from inside and outside the stainless steel. Acts as a kind of barrier and has the effect of increasing the corrosion resistance of stainless steel. However, according to the experiments by the present inventors, it was found that this Si oxide has low stability (that is, high solubility) with respect to the molten carbonate, and therefore the molten carbonate has an oxide on the outermost surface of the steel. When the layer penetrates and penetrates into the Si oxide layer, the Si oxide is dissolved and it becomes impossible to exhibit a sufficient corrosion resistance effect.

However, when an appropriate amount of Al is contained in the steel, an Al oxide layer is formed outside the Si oxide layer, and this outer Al oxide layer protects the Si oxide from the molten carbonate, and In either case, the coexistence of the Si oxide layer and the Al oxide layer having a small atomic diffusion coefficient can further suppress the corrosion of the stainless steel itself.

Such action and effect can be achieved when the contents of Si and Al satisfy the relationship of Si% / Al% ≦ 1.0 in the above range, and more preferably Si% / Al%. It was found that when ≦ 0.4, the corrosion resistance to molten carbonate was very good.

In addition to the above basic composition, Cu, M
If one or more of o, Ti, Zr, Y or REM is added in an appropriate amount, the corrosion resistance to molten carbonate can be further improved. The preferred contents of these elements are as follows.

Cu: Cu has the effect of improving the corrosion resistance to molten carbonate. However, if too much is added, the hot workability deteriorates, so the Cu content is 3.0.
% Or less.

Mo: Mo has the effect of improving the corrosion resistance to molten carbonate. However, if too much is added, the weldability and hot workability deteriorate, so the Mo content should be 3.0% or less.

Ti: Ti has the effect of improving the high temperature strength of steel and also the effect of improving corrosion resistance to molten carbonate. However, if a large amount is added, the toughness deteriorates, so the Ti content is made 1.0% or less.

Zr: Zr has the effect of improving the high temperature strength of steel and the effect of improving the corrosion resistance to molten carbonate. However, if a large amount is added, the weldability and the cleanliness of the steel are impaired, so the content of Zr is 1.0%.
Below.

Y: Y has the effect of improving the corrosion resistance to molten carbonate. However, if a large amount is added, the hot workability deteriorates, so the Y content is 0.5% or less by weight.

REM: REM (rare earth element) has the effect of improving the corrosion resistance to molten carbonate, and
Improves hot workability by adding a small amount. However, if added in a large amount, the hot workability deteriorates, so the content of REM is set to 0.5% or less by weight. Particularly, in order to improve hot working, it is desirable to contain REM in an amount of 0.05% by weight or less.

Next, the stainless steel containing a large amount of Si or Al, like the steel of the present invention, generally has a tendency that the hardness of the steel increases and the workability deteriorates, but (Si% + Al%) / Ni% ≦ If Ni is contained so as to satisfy the relationship of 0.47, the hardness of the steel can be lowered and the workability can be improved (Fig. 3 in the example described later).

Further, stainless steel containing a large amount of Al has a problem that the hot workability is remarkably deteriorated and a large crack is generated in the hot rolled sheet during hot rolling.
The steel containing 1 has severe cracking, and it is difficult to manufacture a hot-rolled steel strip by a usual method. As a result of repeated experiments to solve this problem, by controlling the amount of δ-ferrite and the temperature of the hot-rolled sheet during hot rolling, even if Al, which is necessary to maintain the corrosion resistance to molten salt, is contained, It was found that hot rolling can be satisfactorily produced by hot rolling.

That is, as an expression for predicting the amount of δ-ferrite appearing in the ingot or slab of the steel of the present invention from the content of each component, δ (%) = 1.57 · Cr + 0.7 · Si + 3.89 · A
1-1.57, Ni-0.16, Mn-38.5, C-7.
65 was obtained. However, this formula is applicable only when δ (%) is 0
The range is up to 6, and if it exceeds 6, the hit rate becomes low. When the amounts of the respective components are adjusted so that δ (%) represented by this equation is in the range of 0.5 to 4.0, as shown in Examples (FIGS. 5 and 7) described later. It was also revealed that this steel has excellent hot workability. Therefore, in this case, it becomes possible to manufacture the hot-rolled steel strip by the normal hot rolling equipment.

However, it became clear that even in the steel in which this δ (%) is in the range of 0.5 to 4.0, a drastic change in ductility occurs between 900 and 1000 ° C. Therefore, hot rolling is performed. In some cases, the material temperature when exiting the final pass is 10
It was found that the temperature should be 00 ° C or higher. That is,
If the hot rolling is completed at a temperature of 1000 ° C. or higher, a cracked edge or the like does not occur and a hot rolled sheet of good quality can be stably manufactured.

[0040]

【Example】

[Example 1] Samples a to q and samples r to z used in the test
The chemical component values (% by weight) of are shown in Table 1 and Table 2, respectively. Samples a to q in Table 1 are steels of the present invention, and samples r to z in Table 2 are comparative steels.

[0041]

[Table 1]

[0042]

[Table 2]

Samples aq (inventive steels) and samples rz
(Comparative steels) were all melt-cast in a 30 kg vacuum melting furnace, and the cast pieces were hot-rolled and annealed to obtain hot-rolled sheets. Then, after annealing, cold rolling, and annealing, specimens for corrosion tests were taken. Sample y in Table 2 is a commercially available SUS316
L and sample z are commercially available SUS310S, and steel plates of these commercially available steels were also subjected to the same corrosion test.

The corrosion test was carried out using 62 mol% Li ₂ CO ₃ -38
Each of the samples a to z is immersed in a molten carbonate containing mol% K ₂ CO ₃ and kept at a temperature of 650 ° C. for 70 hours in an atmosphere of 70 vol% air-30 vol% CO ₂ gas. .
The corrosion product generated on the surface of the sample after this test is removed and the difference in the sample weight before and after the test is measured.
/ Cm ² ) to evaluate molten carbonate corrosion resistance. The results are shown in Fig. 1. The following can be seen from the results of FIG.

First, Cu, Mo, Ti, Zr, Y, RE
In samples a to i (inventive steels) to which none of M was added, sample c in which the Al content was approximately 2% compared to samples a, b, and f in which the Al content was close to 1% , G and i have less corrosion. Further, as compared with these samples c, g and i, the samples d, h and p having an Al content of about 3% have a smaller amount of corrosion. And these samples d, h, p
In comparison with Samples e and q whose Al content is approximately 4%, and Samples j, k, l, m, n, which contain any of Cu, Mo, Ti, Zr, Y and REM. o has a smaller amount of corrosion.

Further, as compared with the samples r and s (comparative steels) in which the Si content is less than 0.2%, all of the samples a to q (inventive steels) in which the Si content is 0.2% or more. Small amount of corrosion.
However, in the samples t, u, v, and w (comparative steels), although the addition amounts of Si were all 0.2% or more, and while containing a certain amount of Al, the samples a to q (the present invention) were used. The result is that the amount of corrosion is greater than that of steel.

Then, the relationship between the amount of corrosion and the ratio of Si% / Al% was arranged, and the results shown in FIG. 2 were obtained. It can be seen from FIG. 2 that the corrosion resistance to molten carbonate is improved only when the content ratio of Si and Al satisfies Si% / Al% ≦ 1.0. More preferably, when the relationship of Si% / Al% ≦ 0.4 is satisfied, the corrosion resistance to molten carbonate is further improved.

Then, a test piece was cut out from the plate obtained in the same manner as in the corrosion test, and a Vickers hardness test was conducted.
The result of the test is (Si% + Al%) / of the steel used for the test.
FIG. 3 shows the Ni% as the horizontal axis and the Vickers hardness (Hv) as the vertical axis.

From the result of FIG. 3, (Si% + Al%) / N
It can be seen that the Vickers hardness changes abruptly when i% is around 0.47. And (Si% + Al
%) / Ni% ≦ 0.47, the Vickers hardness (Hv) is about 180 or less, and it is understood that the workability is good because the hardness is low.

Example 2 A cold-rolled annealed steel plate having the chemical composition values (% by weight) shown in Table 3 was prepared in the same manner as in Example 1, and the test piece thereof was subjected to the same corrosion test as in Example 1. I served. The result is the same as in the case of FIG. 2 above, Si% / Al%
The results are shown in FIG.

[0051]

[Table 3]

From the results shown in FIG. 4, it can be seen that the molten carbonate corrosion resistance is good when Si% / Al% ≦ 1.0 in the alloy, as in Example 1. In FIG. 4, sample 1q,
Corrosion amount of 1r and 1s is especially large, but this is due to Si%
/Al%>1.0. Sample 1p is S
i% / Al% is as small as 0.12, but Si content is 0.2%
Since it is less than the above, the amount of corrosion is large.

Example 3 A 2% Al-containing steel having the chemical composition value of sample 1d in Table 3 was melted and cast in a 30 kg vacuum melting furnace, and a slab having a thickness of 35 mm was cut from the steel ingot by cutting. Was produced. This slab was soaked at 1230 ° C for 1 hour, then at a reduction rate of 30-35% per pass,
Hot rolling was performed so that the material temperature (final pass temperature) when passing through the final finish rolling roll was 700 to 1050 ° C., and a hot rolled sheet having a thickness of 5 mm was manufactured. When the final pass temperature and the degree of edge cracking of the hot rolled sheet were examined, the results shown in Table 4 were obtained.

[0054]

[Table 4]

From the results of Table 4, the final pass temperature is 1000
It can be seen that if the temperature is at least ℃, hot-rolled sheets can be produced without causing ear cracks. The δ (%) of sample 1d is 1.6
Is. A hot tensile test at 1000 ° C. was performed to obtain the cross-section reduction rate at the time of tensile fracture, and the relationship between this cross-section reduction rate and the edge crack during hot rolling was investigated.
It was revealed that if the cross-section reduction rate at 0 ° C is 55% or more, almost no edge crack occurs during rolling at the final pass temperature of 1000 ° C. Therefore, in order to prevent the occurrence of edge cracks during hot rolling, it is desirable that the cross-section reduction rate at 1000 ° C is 55% or more.

[Example 4] Each sample in Table 3 was melted in a 30 kg vacuum melting furnace to form an ingot, and a round bar test piece for a hot tensile test was prepared from the ingot by cutting to 1000
It was subjected to a hot tensile test at ℃, and the cross-section reduction rate when tensile rupture was measured. Then, δ (%) of each test piece was obtained by the formula described in the text, and the test results are shown in Fig. 5 with the δ (%) as the horizontal axis and the measured cross-section reduction rate as the vertical axis. .

As is apparent from FIG. 5, when δ (%) is large, the cross-section reduction rate decreases and the hot workability deteriorates. Conversely, δ
If the (%) is too small, the area reduction rate will decrease. According to Fig. 5, the area reduction rate is 55% or more when δ (%) is 0.
It is in the range of 5 to 4.0%, and it can be seen that in this case the hot workability becomes good. Sample 1p has good hot workability, but as shown in FIG. 4, it has poor molten carbonate corrosion resistance.

Next, among the samples shown in Table 2, 2% Al-containing steel and REM-added steel and a hot tensile test (1000
The relationship with the cross-sectional reduction rate at (° C) was investigated. The results are shown in Fig. 6. From this figure, it is understood that the cross-section reduction rate (hot ductility) is improved by the addition of REM, but it is decreased when the content exceeds a certain amount. It is considered that when excessive REM exists in the steel, inclusions such as oxides increase, which adversely affects the hot workability. In any case, it can be seen that when the REM content is 0.05% or less, more specifically, the hot workability becomes the best at around 0.02%.

Example 5 A sample having the chemical component values (% by weight) shown in Table 5 was prepared in the same manner as in Example 1 and subjected to the same molten carbonate corrosion resistance test as in Example 1. Further, a sample was prepared in the same manner as in Example 4, and a hot tensile test was performed at 1000 ° C. in the same manner as in Example 4 to obtain the cross-section reduction rate. The results are summarized in Fig. 7.

[0060]

[Table 5]

From the results shown in FIG. 7, the steels of Samples 2a to 2f having the composition ranges specified in the present invention each had a corrosion amount in molten carbonate of about 1/2 or less of that of SUS310S (2j), indicating good corrosion resistance. It can be seen that the molten carbonate exhibits corrosiveness. Further, the δ (%) of the steels of the present invention (2a to 2f) are all in the range of 0.5 to 4.0 as shown in Table 5, but the cross-sectional reduction rate at 1000 ° C of these steels is Is 55% or more, and hot working is also good.

On the other hand, since the sample 2h has Si% <0.2 and the sample 2i has Si% / Al%> 1.0, the corrosion resistance is poor. In addition, sample 2g is δ
(%) Is out of the range of 0.5 to 4.0, the hot workability is poor.

[0063]

As described above, according to the present invention,
Even for stainless steels having relatively low Cr and Ni contents, stainless steels having improved corrosion resistance to molten carbonate were obtained. This stainless steel has a relatively large amount of A
Despite containing l, hot rolling is possible with high yield. Accordingly, it is possible to provide a fuel cell separator material that is inexpensive and has excellent durability, which is an alternative to the conventional fuel cell separator material.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Si content in steel and the amount of corrosion of steel in molten carbonate.

FIG. 2 is a diagram showing the relationship between the ratio of Si% / Al% in steel and the amount of corrosion of steel in molten carbonate.

FIG. 3 is a diagram showing a relationship between (Si% + Al%) / Ni% in steel and Vickers hardness of steel.

FIG. 4 is a diagram showing the relationship between the ratio of Si% / Al% in steel and the amount of corrosion of steel in molten carbonate.

FIG. 5 shows the value of δ (%) in steel and the hot tensile test (10
It is a figure which shows the relationship with the cross-section reduction rate at the time of (00 degreeC).

FIG. 6: REM content in steel and hot tensile test of steel (10
It is a figure which shows the relationship with the cross-section reduction rate at the time of (00 degreeC).

FIG. 7: Hot tensile test (1000
It is a figure which shows the cross-section reduction rate at the time of using (), and the amount of corrosion when using for a molten carbonate corrosion test.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-247852 (JP, A) JP-A-1-252757 (JP, A) JP-A-62-294153 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22C 38/00-38/06 C21D 8/02

Claims (8)

(57) [Claims] 1. By weight%, C: 0.1% or less, Mn: 2.
0% or less, Ni: 7.5% or more and less than 15.0%, Cr: 1
4.0 to 20.0%, Si: more than 0.2% and 4.0% or less,
A stainless steel containing Al: 1.0 to 4.0%, satisfying the relationship of Si% / Al% ≤ 1.0, and the balance being Fe and inevitable impurities, which is excellent in corrosion resistance against a molten salt. 2. By weight%, C: 0.1% or less, Mn: 2.
0% or less, Ni: 7.5% or more and less than 15.0%, Cr: 1
4.0 to 20.0%, Si: more than 0.2% and 4.0% or less,
Al: 1.0 to 4.0%, further, 3.0% or less Cu, 3.0% or less Mo, 1.0% or less Ti, 1.0.
One or more of Zr of 0% or less, Y of 0.5% or less or REM (rare earth element) of 0.5% or less,
A stainless steel that satisfies the relationship of Si% / Al% ≦ 1.0, and has excellent corrosion resistance to molten salts with the balance being Fe and inevitable impurities. 3. The stainless steel according to claim 1, which satisfies the relationship of Si% / Al% ≦ 0.4. 4. (Si% + Al%) / Ni% ≦ 0.47
The stainless steel according to claim 1, 2 or 3, which satisfies the relationship of. 5. The value of δ (%) represented by the following formula is 0.5 to 0.5.
The stainless steel according to claim 1, 2, 3 or 4, wherein the amount of each component is adjusted to fall within the range of 4.0, δ (%) = 1.57 · Cr + 0.7 · Si + 3.89 · A.
1-1.57, Ni-0.16, Mn-38.5, C-7.
65. 6. The stainless steel according to claim 5, wherein the REM content is 0.05% or less. 7. By weight%, C: 0.1% or less, Mn: 2.
0% or less, Ni: 7.5% or more and less than 15.0%, Cr: 1
4.0 to 20.0%, Si: more than 0.2% and 4.0% or less,
Al: 1.0 to 4.0% is contained, and the relationship of Si% / Al% ≦ 1.0 is satisfied, and δ (%) = 1.57 · Cr + 0.7 · Si + 3.89 · A
1-1.57, Ni-0.16, Mn-38.5, C-7.
65. The amount of each component is adjusted so that the value of δ (%) represented by is within the range of 0.5 to 4.0, and the rest is austenitic stainless steel containing Fe and unavoidable impurities and hot-rolled. A method for producing stainless steel having excellent corrosion resistance to molten salt, which comprises terminating hot rolling at a temperature of 1000 ° C. or higher when forming a steel strip. 8. The stainless steel has a C content of 3.0% or less.
u, Mo less than 3.0%, Ti less than 1.0%, 1.0%
Zr below, Y below 0.5% or R below 0.05%
The manufacturing method according to claim 7, which contains one kind or two or more kinds of EM (rare earth elements).