JP3473083B2 - Cr-containing steel with excellent high-temperature salt damage characteristics, toughness and high-temperature strength - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to members used in waste incinerators, exhaust ducts, etc., which are required to have high temperature salt damage characteristics. More specifically, Cr (chrome), S
Cr content for high temperature salt damage resistance, which is superior in high temperature salt damage characteristics, toughness and high temperature strength to steels that have been conventionally used (hereinafter referred to as conventional steels) due to the optimum balance of i (silicon) and the addition of appropriate stabilizing elements. Related to the technical field of steel. The present invention also relates to a member used for the above-mentioned applications, which is required to have high temperature salt damage characteristics and processability. More specifically, while reducing the amount of expensive Cr added to reduce the cost of these members, even low-Cr-containing steel is superior to conventional steel by adding Si and an appropriate stabilizing element. TECHNICAL FIELD The present invention relates to a technical field of high-temperature salt-damaged Cr-containing steel having high-temperature salt-damage properties and excellent manufacturability and workability.

[0002]

2. Description of the Related Art Conventionally, SUH409 and SUS4 are used for members such as waste incinerators and exhaust ducts that operate at relatively low temperatures.
Steel such as 30J1L and SUS304 is used. Such waste incinerators, exhaust ducts, etc. are used in an environment in which chlorides, molten salts, etc. adhere to duct materials, etc., and are further heated to around 650 ° C., so-called high temperature salt damage poses a problem. The high temperature salt damage resistance is required for the member.

On the other hand, since the exhaust duct material is also a structural member, there is a portion where a large high temperature strength is required. However, in general, steel having improved high-temperature strength has drawbacks that good toughness cannot be obtained and manufacturability is poor. There was no inexpensive material that was strong against salt damage at high temperature, had high strength at high temperature, and had excellent toughness. The conventional steel described above cannot be said to be an inexpensive material because it contains a large amount of expensive Cr even if it is a ferritic steel.
Since S304 contains Ni (nickel), it is a more expensive material.

Further, since these members are bent and welded, the workability of the base material portion and the workability of the welded portion are important. In the case of bending, it is rare that the material is worked close to the fracture, and rather, it is easy to work and the YS is low (here, YS is the yield stress).
It is an abbreviation for s (yield stress). ) Is desired. Often, the Erichsen value of the weld is also important, as some of the weld is often machined in order to optimize the exhaust gas flow.

In addition to such high temperature salt damage characteristics or workability, it is also important that the cost is low. The fact that it is inexpensive depends on the manufacturability of the material manufacturer as well as the Cr content. Although the annealing temperature is one of the indicators of manufacturability, if low-temperature annealing is possible, the manufacturing cost can be reduced accordingly.

[0006]

Under such a condition, an inexpensive material having a high temperature salt damage property, a high temperature strength and a high toughness which are superior to those of conventional steels, and high temperature salt damage property, manufacturability and workability are obtained. There is a strong demand for the development of excellent and inexpensive materials. As a material having improved high temperature salt damage characteristics, there is JP-A-5-125491 relating to ferritic stainless steel. Japanese Unexamined Patent Publication No. 5-125491 discloses a steel that achieves improvement in high temperature salt damage characteristics at 650 ° C. by adding Si. However, in this case, expensive Cr is added in an amount of 10% or more, and the reduction of the material price is not considered. Further, since Nb (niobium) is added, high-temperature annealing is required from the viewpoint of manufacturability, and it cannot be manufactured at low cost. When the element to be added is changed from Nb to Ti (titanium) or Zr (zirconium), it becomes possible to anneal at a relatively low temperature, but in this case, the workability of the welded portion, that is, the Erichsen value is lowered. There's a problem.

The steel conventionally used as an exhaust duct material mainly contains Cr in an amount of 11.5 wt% or more. However, considering the cost, the amount of expensive Cr added should be reduced as much as possible. Preferably. Since austenitic stainless steel contains more expensive Ni, the cost is high.

The inventors of the present invention set the addition amount of Cr to 1
High temperature salt damage characteristics in the area reduced to less than 0.0%,
The present invention has been completed through repeated research on toughness, high temperature strength, manufacturability and workability. The present invention provides SUH409, which has been conventionally used for its excellent high temperature salt damage property.
It is an object of the present invention to provide a Cr-containing steel that is more inexpensive than SUS430J1L, further improves high temperature salt damage characteristics, and is excellent in toughness and high temperature strength. Further, the present invention is an inexpensive C which is excellent in high temperature salt damage property, manufacturability and processability.
It is intended to provide r-containing steel.

[0009]

In general, in stainless steel, in order to secure corrosion resistance and oxidation resistance, Cr is 11.
5% or more is contained. For example, JIS G 430
4 hot rolled stainless steel plate or JIS G 43
The stainless steel plate specified by 05 cold rolled stainless steel plate has a C content of 11.5 wt% or more in any steel type.
It contains r.

The inventors of the present invention investigated the effects of elements added to various alloys on high temperature corrosion under the condition that chlorides coexist, that is, on high temperature salt damage characteristics, and found that the optimum range of Cr addition amount was I found that there is. Further, it became clear that the high temperature salt damage property was remarkably improved by the addition of Si, and even if the addition amount of Cr was less than 10.0 wt%, by increasing the addition amount of Si, SUS3
It was found that it exhibits a high temperature salt damage resistance of 04 or more.

That is, if the Cr content in the steel is large, intergranular corrosion is likely to occur, so that the corrosion progresses remarkably in a part and the maximum value of the maximum erosion depth becomes large. Here, the maximum erosion depth is defined by the sum of the corrosion thinning amount (μm) and the intergranular corrosion depth (μm). On the contrary, if the Cr content is small, it is considered that the general corrosion is severe and the corrosion resistance becomes insufficient, and as a result, the maximum erosion depth becomes deep. Therefore, in order to exert the high temperature salt damage characteristic, there is an optimum range of the Cr content as described above.

FIG . 1 shows the high temperature salt damage resistance for steels with different amounts of Cr and Si added. High temperature salt damage resistance is
After performing 10 cycles with a step of immersing in a saturated saline solution for 5 minutes in the atmosphere of 650 ° C. for 2 hours as one cycle, the maximum erosion depth on one side of the test piece was evaluated. FIG. 1 shows that the maximum erosion depth becomes smaller when the Cr addition amount is in the range of 2 wt% or more and less than 10 wt%. Figure
1 is currently used SUH409, SUS4
The results of performing the same test with 30J1L and SUS304 are also shown. From FIG. 1 , it was shown that when the Cr content was within the range of the present invention, the high temperature salt damage property was good.

The inventors of the present invention have studied in detail the effects of Si, Cr and stabilizing elements, and as a result, as described above, there is an optimum Cr addition range for improving the high temperature salt damage characteristics. , Steel with low Cr content (low Cr steel)
However, it has been found that the addition of Si significantly improves the high temperature salt damage characteristics. Further, by reducing the addition amount of Cr, good workability of the base material can be obtained, and Ti, Z
It has been found that the workability of the welded portion can be improved more than that of the conventional steel even by the steel having a large Si content by the action of r and V. In addition, by using the appropriate stabilizing element,
The present invention has been completed by finding that it can be annealed at a low temperature and can be produced at a lower cost than conventional steel.

Addition of Ti and Zr based on low Cr steel achieves low YS and a recrystallization temperature of 950.
Since it can be kept below ℃, it has been used conventionally.
Unlike the case of 30J1L, there is no need to heat to about 1000 ° C., and it can be manufactured at low cost. Furthermore, as a result of a detailed study of weldability, it was found that in a steel containing Cr—Ti or Zr, the addition of a small amount of V significantly improved the Erichsen value. Obtaining such a vast amount of research results, the steel of the present invention has Cr and Si contents in the optimum range, and by adding an optimum stabilizing element, high temperature salt damage characteristics superior to conventional steels and We have succeeded in developing a low-cost Cr-containing steel that has the workability of the material and weld.

The first invention of the present invention is: C: 0.01 wt% or less, Mn: 2.0 wt% or less, Si: 0.6 wt% or more and 5.0 wt% or less, Cr: 2.0 wt% or more 10. Less than 0 wt%, Al: 0.1 wt% or less, N: 0.01 wt% or less, Ni: 2.0 wt% or less , V: 0.05% or more and 1% or less, and further 1 of Ti and Zr species or two or containing less 0.01 wt% or more 1.0 wt%, and, C, N, Ti, Zr content is adjusted so as to satisfy the following following formula (1), the balance being substantially Fe In addition, it is a Cr-containing steel excellent in high temperature salt damage characteristics consisting of inevitable impurities, manufacturability, and workability. Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Equation ( 1 )

The second invention is that C: 0.01 wt% or less, Mn: 2.0 wt% or less, Si: 0.6 wt% or more and 5.0 wt% or less, Cr: 2.0 wt% or more and 10.0 wt%. %, Al: 0.1 wt% or less, N: 0.01 wt% or less, Ni: 2.0 wt% or less, V: 0.05% or more and 1% or less, and one of Ti and Zr Or 0.01 wt% or more and 1.0 wt% or less, and the contents of C, N, Ti, and Zr are adjusted so as to satisfy the formula ( 1 ), and one of Ca and REM Alternatively, it is a Cr-containing steel that contains 0.01 wt% or more and 0.2 wt% or less in total of two types, and that the balance substantially consists of Fe and unavoidable impurities and is excellent in high temperature salt damage characteristics, manufacturability, and workability.

Further, the third invention is C: 0.01 wt% or less, Mn: 2.0 wt% or less, Si: 0.6 wt% or more and 5.0 wt% or less, Cr: 2.0 wt% or more and 10.0 wt% %, Al: 0.1 wt% or less, N: 0.01 wt% or less, Ni: 2.0 wt% or less, V: 0.05% or more and 1% or less, and Ti, Zr: 0.01 wt% At least 1 wt% or more and 1.0 wt% or less are contained, and the contents of C, N, Ti, and Zr are adjusted so as to satisfy the above formula ( 1 ), and Mo, Cu: 0. It is a Cr-containing steel that contains one or two kinds of 05 wt% or more and 3.0 wt% or less, and the balance is substantially Fe and unavoidable impurities, and is excellent in high temperature salt damage characteristics, manufacturability, and workability.

Further, the fourth invention is C: 0.01 wt% or less, Mn: 2.0 wt% or less, Si: 0.6 wt% or more and 5.0 wt% or less, Cr: 2.0 wt% or more and 10.0 wt% %, Al: 0.1 wt% or less, N: 0.01 wt% or less, Ni: 2.0 wt% or less, V: 0.05% or more and 1% or less, and one of Ti and Zr Or 0.01 wt% or more and 1.0 wt% or less, and the contents of C, N, Ti, and Zr are adjusted so as to satisfy the formula ( 1 ), and one of Ca and REM Or 0.01 wt% or more and 0.2 wt% or less in total, 0.05 wt% or more and 3.0 wt% or less of one or two types of Mo and Cu, and the balance substantially Fe and unavoidable Excellent in high-temperature salt damage characteristics consisting of impurities, manufacturability, and processability It was a Cr-containing steel.

In addition, the fifth aspect of the present invention is 0.006 wt% C.
% Or less, the first to fourth inventions characterized by being contained
The Cr-containing steel according to any one of 1.

[0020]

The reason for limiting the range of each component in the above composition of the present invention will be explained below. C is an element that greatly affects the high temperature salt damage characteristics, and the lower the content, the better in order to enhance the toughness and in terms of manufacturability, and is preferably 0.01% or less. It is particularly preferably 0.006% or less.

Mn has a deoxidizing action and a desulfurizing action,
If added excessively, the oxidation resistance of the steel is lowered and the workability of the steel is deteriorated. Further, excessive addition is a problem from the viewpoint of maintaining a stable ferrite structure, and the upper limit was made 2.0%. The preferable range of adding Mn is 0.03% or less.

Si is one of the features of the present invention, and is an element necessary for enhancing the high temperature salt damage resistance. The effect becomes remarkable when the added amount of Si is 0.6% or more, and even if added by 5.0% or more, it is not further improved. Further, if Si is added more than necessary, the workability of steel is deteriorated. Therefore, the range of the addition amount is set to 0.6% to 5.0%. The range of 1.0% or more and 2.0% or less is more preferable.

Ni may be added especially when it is desired to improve the toughness. Since the improvement in toughness due to addition is saturated by the addition of 2.0% or more, the upper limit was made 2.0%. When it is not necessary to improve the toughness, it is an element that does not need to be added originally, so its content is set to 2.0% from the content level of unavoidable impurities. The preferable range of the addition amount of Ni is 0.2% or less.

Since Cr is an expensive element, adding more than necessary causes an increase in cost. Further, as described above, with respect to the high temperature salt damage characteristics, if the addition amount is too large, intergranular corrosion is severe and local corrosion proceeds. On the other hand, if the addition amount is small, general corrosion proceeds. Therefore, the Cr content is 2.0
% Or more and less than 10.0%, preferably 4.0%
More preferably, it is in the range of 9.0% or less.

Al is an element necessary as a deoxidizing agent, but if the addition amount is too large, the toughness of steel is lowered and the manufacturability is deteriorated. Further, since the workability is deteriorated due to the solid solution strengthening, the upper limit of the added amount is set to 0.1%. The preferable range of the added amount of Al is 0.03% or less.

N, like C, adversely affects the high temperature salt damage characteristics of steel. Further, in order to improve the toughness and workability of steel, the smaller the content, the better. Further, N is an element that greatly affects the workability of the weld, and if the content is large, the workability of the weld deteriorates, so the upper limit was made 0.01%.
It is more preferably 0.006% or less.

Ti and Zr combine with C and N to reduce YS and improve workability. Also, by adding together with V, the Erichsen value of the welded portion is improved and the workability becomes higher than that of the conventional steel. In order to bring out the effect of the solid solution V sufficiently, it is necessary to add V in an amount of 0.01% or more and 1.0% or less and satisfy the following formula ( 1 ). Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Formula ( 1 ) When the added amount of V is within this range, the effects of Ti and Zr are equal. However, the addition amount of each component is 0.01
If it is less than 1%, the effect does not appear, and if it exceeds 1%, inclusions increase and workability deteriorates. Therefore, the addition amount is set to 0.01% or more and 1.0% or less. The addition amounts of Ti and Zr satisfy the above formula ( 1 ) and are preferably 0.2% or less. Further, since these elements lower the recrystallization temperature as compared with Nb, the manufacturability is improved and the manufacturing cost can be reduced.

V is an important element for the present invention.
In the case of a steel having a low Cr content and a high Al content as in the present invention, the workability of the weld is poor when only one or two of Ti and Zr are added, and as in Comparative Steels H and I described later, When the amount of V added was small, it did not reach the level of conventional steel. But,
By adding V in addition to one or two of Ti and Zr, the workability of the welded portion was significantly improved. This effect appears when the addition amount of V is 0.05% or more, but if the addition amount of V exceeds 1%, the workability decreases, so the upper limit of the addition amount is 1%.
%. The preferable addition amount of V is 0.05 to 0.2%
Is the range. Further, since the solid solution V contributes to exert such an effect, the solid solution V should be added so that the binding force with Ti and Zr, which has a larger binding force with C and N than V, satisfies the above formula ( 1 ). is necessary.

Since Ca and REM improve the oxidation resistance of steel at high temperatures, it is advisable to add one or two if necessary. Here, REM is a rare earth element, and specifically, Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), N
It is a group of lanthanoid series elements such as d (neodymium).
In order to improve the oxidation resistance, these elements should be added to 0.0
It is necessary to add 1% or more, but if added excessively, the toughness of the steel is deteriorated, and the hot workability is deteriorated. Therefore, the addition amount range is 1 type or 2 types in total. .0
It is limited to 1% or more and 0.2% or less.

One or two kinds of Mo and Cu may be added, if necessary, in order to improve the room temperature corrosion resistance of steel. The effect becomes remarkable when the added amount is 0.05% or more, but if it is excessive, the workability is lowered and the cost is increased. For this reason, the range of addition amount is 0.5% or more and 3.0% or less in total of one kind or two kinds.

[0031]

(Example) (Example 1) Cr-containing steel having a predetermined chemical composition shown in Table 1 was melted in a vacuum melting furnace to obtain a 30 kg steel ingot. Hereinafter, a 4 mm thick plate was hot-rolled by a known method, annealed, a 2 mm thick plate was cold-rolled, and finish annealing was performed. A test piece was prepared using the 2 mm cold rolled annealed plate obtained as described above.
The invention steels 1 to 13 and the comparative steels A to J were subjected to a high temperature salt damage test at 650 ° C., a base material workability test and a welded part workability test. Each physical property evaluation test was performed as follows and evaluated.

[0032]

[Table 1]

[0033]

[Table 2]

(Physical property evaluation test) (1) High temperature salt damage test (Example 1) Using each cold rolled annealed plate manufactured in the manufacturing example, a test piece having a thickness of 2 mm, a width of 20 mm and a length of 30 mm was prepared. . These test pieces were immersed in a 26% saturated saline solution for 5 minutes , placed in an atmosphere of 650 ° C. for 2 hours each, and then cooled for 5 minutes, each cycle consisting of 10 cycles. The erosion depth was measured. The maximum erosion depth was the maximum value of the amount of corrosion thinning (μm) plus the intergranular corrosion depth (μm). Evaluation of the maximum erosion depth, 5 0
A is less than μm, B is 50 μm or more and less than 100 μm, and C is 100 μm or more.

( 2 ) Measurement of recrystallization temperature, base material workability test and weld workability test The recrystallization temperature was determined by changing the finish annealing temperature, and finish annealing was performed at the recrystallization temperature. The base material processability was evaluated by the YS value, because the YS value is important for practical use, as described in the section of the prior art. The evaluation is that the YS value is 350.
A of less than or equal to MPa is shown as A, one of more than 350 MPa and less than 400 MPa is shown as B, and one of 400 MPa or more is shown as C. The weldability was evaluated by welding under the conditions of a welding speed of 600 mm / min, a welding current of 130 A, and a surface of 10 L / min of an argon gas shield, and the portion was subjected to an Erichsen test. As a result of the Erichsen test, 8 mm or more is shown as A, 5 mm or more and less than 8 mm is shown as B, and 5 mm or less is shown as C.

(Evaluation of Physical Properties) The results of the tests (1) and (2) are shown in Table 2 .

[0037]

[Table 3]

As shown in Table 2 , the high temperature salt damage characteristics of the invention steels 1 to 13 were all evaluated as A, and the high temperature salt damage characteristics were remarkably improved as compared with the conventional steels shown in the comparative steels A to C.
It was noted that all of the present invention steels 1 to 13 are low Cr steels, but show much higher temperature salt damage characteristics than SUS304 shown in comparative steel C containing 8% of expensive Ni. Further, the recrystallization temperature of the invention steels 1 to 13 is 950 ° C.
It is as follows, and it can be manufactured at a lower cost than the conventional steel SUSU430J1L. Further, the workability of the base material and the welded portion was also evaluated to be higher than that of the conventional steels shown in Comparative Steels A to C , and it was shown that the workability was practically no problem.

In Comparative Steel D having a low Si content, sufficient improvement in high temperature salt damage characteristics was not observed, and in Comparative Steel E having an excessive Si content, the workability of the base material and the welded portion was inferior to that of the conventional steel, It wasn't practical. Further, since Comparative Steel F contains N in an excessive amount, the workability of the base metal and the weld zone is comparative Steel A to.
It was inferior to the conventional steel shown in C. Comparative Steel G had a high recrystallization temperature because Nb was added as a stabilizing element, and the weldability was also the same as that of the conventional steels shown in Comparative Steels A and B. Comparative steels H and I had a low V content and were inferior in weldability. Further, the comparative steel J has Ti and Z.
Since the content of r was small, the workability of the base material and the welded portion was inferior to the conventional steels shown in Comparative Steels A to C , which was not practical.

[0040]

As described above, according to the present invention , low C
Even for r steel, by optimizing the balance of Cr, Si or stabilizing elements, SUH409, SUS43
It has a high temperature salt damage property of 650 ° C. far superior to 0J1L, has base metal, weldability, and manufacturability that are higher than those of conventional steel, and an inexpensive steel can be obtained. The steel of the present invention is not limited to the exhaust duct material and the cold-rolled annealed sheet, and high temperature salt damage, toughness, high-temperature strength, workability, cost, etc. are members of the cold rolled sheet, hot rolled sheet, Casting condition, etc.
It can be applied regardless of the mode.

[Brief description of drawings]

FIG. 1 Fe—Ti—Cr—Si based steel and Fe—T
High temperature salt of i-Cr-Mo-Si steel at 650 ° C
It is a graph which shows the influence of Cr and Si which acts on a damage characteristic.
It

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-279807 (JP, A) JP-A-5-125491 (JP, A) JP-A-1-100241 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (5)

(57) [Claims] 1. C (carbon) : 0.01 wt% or less; Mn (manganese) : 2.0 wt% or less; Si (silicon) : 0.6 wt% or more and 5.0 wt% or less; Cr (chromium) : 2. 0 wt% or more and less than 10.0 wt%; Al (aluminum) : 0.1 wt% or less; N (nitrogen) : 0.01 wt% or less; Ni (nickel) : 2.0 wt% or less ; V (vanadium): 0.05 % Or more and 1% or less;
Further, it contains one or two of Ti (titanium) and Zr (zirconium) in an amount of 0.01 wt% or more and 1.0 wt% or less; and the content of C, N, Ti, and Zr is represented by the following formula ( 1 ). A Cr-containing steel which is adjusted to satisfy the above conditions and whose balance consists essentially of Fe (iron) and inevitable impurities and which is excellent in high temperature salt damage characteristics and workability . Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Equation ( 1 ) 2. C: 0.01 wt% or less, Mn: 2.0 wt% or less; Si: 0.6 wt% or more and 5.0 wt% or less; Cr: 2.0 wt% or more and less than 10.0 wt%; Al: 0 1 wt% or less; N: 0.01 wt% or less; Ni: 2.0 wt% or less; V: 0.05% or more and 1% or less; and one or two of Ti and Zr. 01 wt% or more and 1.0 wt% or less, and the contents of C, N, Ti, and Zr are adjusted to satisfy the following formula (1) , and further Ca (calcium) and REM
One or two of (rare earth elements) total 0.01
A Cr-containing steel containing not less than wt% and not more than 0.2 wt% with the balance being substantially Fe and unavoidable impurities and having excellent high temperature salt damage characteristics and workability . Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Formula (1) 3. C: 0.01 wt% or less, Mn: 2.0 wt% or less; Si: 0.6 wt% or more and 5.0 wt% or less; Cr: 2.0 wt% or more and 10.0 wt% or less; Al: 0 1 wt% or less; N: 0.01 wt% or less; Ni: 2.0 wt% or less; V: 0.05% or more and 1% or less; and one or two of Ti and Zr. 01 wt% or more and 1.0 wt% or less; and the contents of C, N, Ti, and Zr are adjusted to satisfy the following formula (1) , and further Mo (molybdenum) and Cu (copper)
One or two of them are 0.05 wt% or more and 3.0 wt%
% Or less, and the balance is Cr-containing steel excellent in high temperature salt damage characteristics and workability, which is substantially Fe and unavoidable impurities in the balance. Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Formula (1) 4. C: 0.01 wt% or less; Mn: 2.0 wt% or less; Si: 0.6 wt% or more and 5.0 wt% or less; Cr: 2.0 wt% or more and less than 10.0 wt%; Al: 0 1 wt% or less; N: 0.01 wt% or less; Ni: 2.0 wt% or less; V: 0.05% or more and 1% or less; and one or two of Ti and Zr. 01 wt% or more and 1.0 wt% or less; and the contents of C, N, Ti, and Zr are adjusted so as to satisfy the following formula (1) , and one or two of Ca and REM are added in total. 0.01
wt% or more and 0.2 wt% or less, one or two kinds of Mo and Cu are contained in 0.05 wt% or more and 3.0 wt% or less, and the balance is high-temperature salt damage characteristics and processing consisting essentially of Fe and unavoidable impurities Cr-containing steel with excellent properties . Ti% / 48 + Zr% / 91 ≧ C% / 12 + N% / 14 ... Formula (1) 5. The C content is 0.006 wt% or less.
Cr according to any one of claims 1 to 4, characterized in that
Containing steel.