JP2008195985A - Cast ferritic stainless steel having excellent acid resistance, and cast member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide cast ferritic stainless steel excellent in acid resistance and desirably having superior machinability and also to provide a cast member excellent in acid resistance composed of the cast ferritic stainless steel. <P>SOLUTION: The cast ferritic stainless steel with excellent acid resistance has a composition consisting of, by mass, 18.0 to 27.0% Cr, 0.8 to 3.5% Cu, 0.5 to 2.0% Si, 0.5 to 1.5% Mo, ≤2.5% Nb, ≤0.6% Ni, ≤0.12% C, ≤1.0% Mn, ≤0.10% Al, ≤0.15% P, ≤0.15% S, ≤0.10% N and the balance Fe with inevitable impurities and satisfying (Cu+Si)>2.0%. The cast member is manufactured using the cast ferritic stainless steel. The cast member may be a switching valve member for switching the flow passage of exhaust gas. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is suitable for use in gas pipes, cooler parts, switching valves, etc., which are exhaust gas recirculation system member members exposed to exhaust gas exhausted from engines such as aircraft and automobiles. Related to cast stainless steel. The present invention also relates to a cast member made of the ferritic stainless cast steel and excellent in acid resistance.

For example, in an aircraft, an automobile, and the like, many systems that recirculate a part of exhaust gas discharged from an engine to an intake system to suppress a combustion temperature and suppress generation of NOx are often used. This is a so-called exhaust gas recirculation (hereinafter referred to as EGR) system.
In an EGR system, for example, exhaust gas recirculation system members (hereinafter referred to as EGR members) exposed to exhaust gas such as the gas pipes, cooler parts, and switching valves described above are often used. In order to prevent corrosion due to exhaust gas exhibiting the above, excellent acid resistance is desired.

As a material having corrosion resistance and acid resistance, stainless steel defined in JIS-G4303 is often used. Stainless steel is generally classified into austenite, ferrite, austenite / ferrite two-phase, martensite, and precipitation hardening due to the characteristics of the structure. Among these, austenite is more resistant to corrosion than ferrite. It is known that it has excellent acid resistance.
For example, in a valve housing (hereinafter referred to as an EGR valve) having a mechanism for switching an exhaust gas circulation path, SUS304, which is one of the well-known austenitic stainless steels, is known as a material that can withstand corrosion of exhaust gas. Is used.

  Further, in order to solve the problem of corrosion due to such strongly acidic exhaust gas, for example, in Japanese Patent Application Laid-Open No. 2003-193205 (Patent Document 1), C: 0 in mass% and excellent in sulfuric acid corrosion resistance. 0.5% or less, Si: 2% or less, Mn: 3% or less, S: 0.2% or less, Ni: 8-18%, Cr: 12-25%, Mo: 0-4%, W: 0 2% and (Mo + 0.5W): 0 to 4%, Cu: 0.5 to 6%, and (Ni / Cu): 2% or more, Nb: 0 to 2.5%, balance: Fe and There has been proposed an exhaust gas recirculation system component substantially composed of an austenitic stainless cast steel containing inevitable impurities.

  Further, for example, in Japanese Patent Application Laid-Open No. 2002-121653 (Patent Document 2), by mass, C: 0.020% or less, Si: more than 0.30 to 1.00%, Mn: more than 0.50 to 1 0.000%, P: 0.040% or less, S: 0.005-0.020%, Cu: 1.0% or less, Ni: 1.0% or less, Cr: 13.0-20.0%, Mo: more than 0.50 to 2.00%, Al: 0.020% or less, N: 0.020% or less, Nb: 0.20 to 0.50%, O: 0.010% or less, C + N: 0 A ferritic stainless steel containing 0.010% or more and having the balance of Fe and inevitable impurities and excellent in cold workability, corrosion resistance, machinability, and weldability has been proposed.

JP 2003-193205 A JP 2002-121653 A

  The present inventor is not easily corroded by strong acid exhaust gas and is suitable for EGR members. For example, the above-mentioned EGR valve is machined for attaching a switching valve or the like to study stainless cast steel excellent in acid resistance. Therefore, in addition to acid resistance, we examined stainless cast steel with as good machinability as possible.

  The exhaust gas recirculation system parts made of austenitic stainless cast steel proposed by Patent Document 1 described above certainly have extremely excellent sulfuric acid corrosion resistance. In addition, austenite-ferrite duplex cast stainless steel, although not as much as austenite, has acid resistance. However, the two-phase system of austenite and austenite / ferrite is disadvantageous in terms of manufacturing cost because the cost of the alloy itself increases because there are many expensive additive elements such as Ni. Further, since the machinability is inferior to that of ferrite, it is disadvantageous in terms of machining cost, and further improvement has been desired.

Since the above-mentioned austenitic stainless steel has a face-centered cubic lattice structure, work hardening is likely to occur. Therefore, in terms of machinability, a ferrite-based structure having a body-centric lattice structure is generally used. Stainless steel is advantageous.
The ferritic stainless steel proposed by Patent Document 2 described above is a forging steel having salt water resistance, and has hot workability and cold workability by addition of Si and Nb. It is also excellent in that machinability is obtained by adding Mn. However, according to the study of the present inventor, the content of Cu and Si is suppressed to 1.0% by mass or less, and cold workability as forging steel is provided. In terms of acid resistance to this, it was insufficient.

  An object of the present invention is to provide a ferritic stainless cast steel having excellent acid resistance and desirably good machinability. Moreover, it is providing the cast member excellent in the acid resistance which consists of said ferritic stainless cast steel.

  In view of the above-mentioned problems, the present inventor studied that the ferritic stainless steel proposed in Patent Document 2 described above is used as a base composition and has acid resistance against sulfuric acid or the like. In other words, the main additive elements for Fe, such as Cr, Cu, Si, Mo, and Nb, Ni, C, Mn, Al, P, S, N are studied and the addition effect of these main elements is examined. The present inventors have found that the acid resistance can be improved by optimizing the above.

  That is, this invention is a mass%, Cr: 18.0-27.0%, Cu: 0.8-3.5%, Si: 0.5-2.0%, Mo: 0.5-1. 5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% or less, Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less , S: 0.15% or less, N: 0.10% or less, and (Cu + Si): more than 2.0%, and the balance containing Fe and inevitable impurities and having excellent acid resistance. It is.

In the present invention, it is desirable to have excellent acid resistance by mass%, including Cr: 18.0 to 22.0%, Cu: 0.8 to 2.2%, and Si: 1.0 to 1.5%. Ferritic stainless cast steel.
Desirably, it is a ferritic stainless cast steel excellent in acid resistance containing (Cu + Si): 2.8% or more by mass%.

  Moreover, the cast member excellent in acid resistance can be obtained using the ferritic stainless steel cast steel of this invention mentioned above. That is, in mass%, Cr: 18.0-27.0%, Cu: 0.8-3.5%, Si: 0.5-2.0%, Mo: 0.5-1.5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% or less, Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less, S: Cast member excellent in acid resistance, made of ferritic stainless cast steel with 0.15% or less, N: 0.10% or less and (Cu + Si): more than 2.0%, the balance containing Fe and inevitable impurities Can be obtained.

Moreover, the cast member mentioned above is the ferritic stainless steel which contains Cr: 18.0-22.0%, Cu: 0.8-2.2%, Si: 1.0-1.5% by the mass%. A cast member made of cast steel is desirable.
Further, a cast member made of ferritic stainless cast steel containing (Cu + Si): 2.8% or more by mass% is desirable.
The casting member may be a switching valve member that switches an exhaust gas flow path.

  The ferritic stainless cast steel excellent in acid resistance of the present invention is a stainless cast steel that is hardly corroded by acidic exhaust gas or the like. Therefore, the cast member using the stainless cast steel of the present invention is a cast member having excellent acid resistance. For example, when applied to an exhaust gas recirculation system member (EGR member) such as the switching valve member (EGR valve) described above, excellent performance can be exhibited. Also, since it is ferritic stainless cast steel, not austenitic, it also has good machinability, so that the above-described switching valve member (EGR valve), which is often machined, is efficiently industrially produced. Can do.

As described above, an important feature of the ferritic stainless cast steel of the present invention is that excellent acid resistance is imparted by optimizing the addition range of elements such as Cr, Cu, Si, and Mo.
Specifically, in terms of mass%, Cr: 18.0 to 27.0%, Cu: 0.8 to 3.5%, Si: 0.5 to 2.0%, Mo: 0.5 to 1. 5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% or less, Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less , S: 0.15% or less, N: 0.10% or less, and (Cu + Si): more than 2.0, with the balance containing Fe and unavoidable impurities.

Hereinafter, the ferritic stainless cast steel of the present invention will be described in detail with respect to the content of Fe and the reasons for limiting the content of each component.
Cr: 18.0 to 27.0 (mass%)
Cr is contained at 18.0% or more in order to obtain acid resistance. However, if the content is increased, the acid resistance is improved, but the toughness may be impaired, so the content is suppressed to 27.0% or less. Further, considering the oxidation of the molten metal due to the Cr content, etc., if castability is desired, it is desirable to contain it in the range of 18.0 to 22.0%. In addition, if high acid resistance is desired, the content is more than 20.0% and not more than 27.0%. In addition to this, if castability is desired, the content is more than 20.0% and not more than 22.0%. It is desirable to contain.

Cu: 0.8 to 3.5 (mass%)
In the present invention, Cu is an especially important element for imparting acid resistance. It also contributes to improved heat resistance. Therefore, at least 0.8% or more is contained. Further, Cu is generally considered as an element to be suppressed in forging steel, and if it is contained in a large amount, the toughness is remarkably deteriorated and the hot workability and the cold workability may be impaired. However, in the ferritic stainless cast steel of the present invention, which is a steel for casting, a desired shape can be obtained by casting, and since there is no substantial plastic working, the content exceeds 1.0%. can do. However, even if the content is increased, not only an improvement in acid resistance commensurate with it can be expected, but castability may be impaired, and even if it is a steel for casting, a great deterioration of toughness should be avoided. Therefore, the content is suppressed to 3.5% or less. Further, if considering castability in addition to acid resistance, 1.5 to 2.5% is desirable, and if considering castability, it is desirable to keep it to 2.2% or less.

Si: 0.5 to 2.0 (mass%)
Si is an element that is useful as a deoxidizing element for stainless steel and also improves acid resistance. Moreover, it has the effect | action which suppresses that a large amount of Cr oxide which impairs toughness is formed and disperse | distributed. Therefore, 0.5% or more is contained. However, if the content is too large, a large amount of Si compound is formed and the toughness may be impaired, so the content is controlled to 2.0% or less. Desirably, it is contained in the range of 1.0 to 1.5%. Further, from the viewpoint of castability, it is desirable to contain more than 1.0%.

Mo: 0.5 to 1.5 (mass%)
Mo is an element that has an effect of improving the corrosion resistance and improving the strength by strengthening the solid solution, and contributes to suppressing high-temperature oxidation and improving high-temperature strength. Therefore, the high-temperature strength is improved by using 0.5% or more by using solid solution strengthening at high temperature. However, if the content is too large, the toughness may be impaired, and this is disadvantageous in terms of cost, so the content is limited to 1.5% or less. Further, considering from various aspects such as acid resistance, castability, and cost, it is desirable to contain in the range of 0.8 to 1.2%.

Nb: 2.5 or less (mass%)
Nb is an element that improves high-temperature strength by solid solution strengthening or precipitation strengthening. In the present invention, Nb is contained in a range of 2.5% or less. Further, in the present invention, by forming carbides and nitrides with affinity for C and N, the effect of reducing the amount of solute C and the amount of solute N, suppressing the increase in hardness, and improving the machinability. Can also be expected. However, if the amount of Nb is too large relative to the content of C or N, the effect of reducing the amount of solid solution C or the amount of solid solution N is saturated, and the machinability is reduced by the excess Nb itself. Therefore, the content is limited to 2.5% or less. Desirably, about 10 times the amount of (C + N) is contained by mass%, and excess Nb is not left while suppressing an increase in the amount of solid solution C or the amount of solid solution N. Nb carbide and Nb nitride are generated preferentially over Cr carbide that impairs intergranular corrosion, thereby suppressing precipitation of Cr carbide and suppressing intergranular corrosion.

Ni: 0.6 or less (mass%)
Ni is an element that contributes to improvement of acid resistance and solid solution strengthening. However, if the content exceeds 0.60%, an austenitic structure that is inferior in machinability to a ferrite type is formed. Moreover, since it is an expensive material, material cost will also increase. Desirably, it is 0.30% or less, which is disadvantageous in productivity, but more desirably 0.20% or less.

C: 0.12 or less (mass%)
C is an unavoidable element and contributes to the improvement of castability. However, if contained in a large amount, the acid resistance and toughness may be deteriorated, and is desirably limited to 0.12% or less. More desirably, it is 0.08% or less. Further, although it is disadvantageous in productivity, it is suppressed to 0.05% or less.

Mn: 1.0 or less (mass%)
Mn is an element necessary as a deoxidizer during the production of cast steel, and also produces MnS and has an effect of improving machinability. However, since MnS is also a compound that reduces acid resistance, it is desirably limited to 1.0% or less. More desirably, it is 0.70% or less. Further, although it is disadvantageous in productivity, it is suppressed to 0.50% or less.

Al: 1.0 or less (mass%)
Al is an element known as a more effective deoxidizer than Si and Mn, and can also be used during the production of cast steel. However, Al generates an oxide, and when this oxide remains on a machined surface, it loses its aesthetics and may become a starting point of corrosion, resulting in deterioration of oxidation resistance. Therefore, it is desirably limited to 0.10% or less. Although it is disadvantageous in productivity, it is more preferably limited to 0.05% or less.

P: 0.15 or less (mass%)
P is an unavoidable element, which may cause toughness deterioration and cause cracking during casting, and is desirably limited to 0.15% or less. Although it is disadvantageous in productivity, it is more preferably suppressed to 0.10% or less.

S: 0.15 or less (mass%)
S is an unavoidable element and has an effect of improving machinability by generating MnS. However, since MnS is also a compound that reduces acid resistance, it is desirably limited to 0.15% or less. Although it is disadvantageous in productivity, it is more preferably suppressed to 0.10% or less.

N: Below 0.10 (mass%)
N, like C, is an inevitable element and has the effect of improving the toughness by refining crystal grains. However, a large amount of Cr precipitates Cr nitride, which deteriorates toughness and acid resistance. There is. Therefore, it is desirably limited to 0.10% or less. More desirably, it is disadvantageous in productivity, but is suppressed to 0.05% or less.

(Cu + Si): exceeding 2.0 (mass%)
As described above, in the present invention, Cu: 0.8 to 3.5% and Si: 0.5 to 2.0% are contained by mass%. However, if the content of Cu and Si, that is, the total amount of (Cu + Si) is too small, the effect of improving acid resistance becomes insufficient, so (Cu + Si): more than 2.0% is contained. However, Cu and Si are not included beyond the respective contents. Further, although there is a possibility that the toughness is somewhat deteriorated, (Cu + Si): 2.8% or more can be contained in order to obtain higher acid resistance.

The balance is Fe and inevitable impurities In the present invention, elements such as Mg, Ti, B, V, Co, As, and O are also unavoidable in addition to the elements such as C, P, S, and N described above as unavoidable. It is an element. However, since it cannot be contained substantially at all, it may be contained as long as the effects of the present invention are not inhibited.
For example, Mg originally forms an oxide and becomes a crystallization nucleus of TiN, and an effect of refining ferrite grains can be expected. However, excessive content may lead to deterioration of acid resistance, and preferably 0. Suppressed to 50% by mass or less. Although it is disadvantageous in productivity, it is more preferably suppressed to 0.30% by mass or less.

For example, Ti originally binds to C, N, and S to improve acid resistance and intergranular corrosion resistance, and has a fixing action of C and N, but excessive inclusion causes deterioration of castability and toughness. It is desirable that the content be suppressed to 0.50% by mass or less. Although it is disadvantageous in productivity, it is more preferably suppressed to 0.20 mass% or less.
For example, B originally forms TiB and brings about the effect of refining ferrite grains, but excessive inclusion may lead to deterioration of acid resistance and toughness, and is preferably suppressed to 0.10% by mass or less. Although it is disadvantageous in terms of productivity, it is more preferably limited to 0.05% by mass or less.
In addition, other V, Co, As, and O are desirably suppressed to 0.10% by mass or less, and further 0.05% by mass or less so as not to affect the acid resistance.

Next, the cast member excellent in acid resistance of the present invention will be described.
The cast member of the present invention is obtained by casting using the above-described ferritic stainless cast steel of the present invention, and has the same composition and mechanical properties as this ferritic stainless cast steel. Therefore, the cast member of the present invention is formed as a cast member suitable for use in an environment exposed to acidic gas or liquid, for example, an exhaust gas recirculation system member exposed to exhaust gas. By applying to gas pipes, cooler parts, EGR valves, and the like, it is possible to obtain an exhaust gas recirculation system member that does not corrode for a long time.
Moreover, as a cast member of this invention, there exist a gas piping, cooler components, an EGR valve, etc. which are used in the EGR system mentioned above, for example. Since the cast member of the present invention is good in terms of machinability, it is preferably applied to a body of an EGR valve that is often machined, that is, a member for a switching valve that switches an exhaust gas flow path, and improves productivity. Can contribute significantly.

  As a method for producing the exhaust gas recirculation system member of the present invention, a conventionally known casting method such as sand casting can be applied. In terms of productivity, it is advantageous to apply a precision casting method such as lost wax casting in which a casting mold is manufactured from a vanishing model having substantially the same shape as the product. Furthermore, a method can be used in which a casting obtained by casting is subjected to heat treatment such as HIP processing, machining such as cutting or grinding, post-treatment such as deburring or polishing, etc., if necessary. .

(Evaluation of acid resistance of ferritic stainless cast steel)
In order to evaluate the acid resistance of the ferritic stainless cast steel of the present invention, each composition shown in Tables 1 and 2 (Examples of the present invention: 1 to 3, Comparative Examples: 4 to 10, Conventional Examples: SUS430, SUS304) A round bar-shaped specimen (outer diameter 10 mm, length 20 mm, total surface area 785 mm ² ) for the corrosion test was prepared. There are elements not shown in Tables 1 and 2, but the remainder and inevitable impurities are contained in Fe.
In manufacturing the test body, first, a predetermined amount of raw materials are melted in the air in a high-frequency furnace, and the molten metal is controlled to 1620 to 1640 ° C., then cast into a Y block mold and then machined to the size and shape of the test body. A casting material was obtained. Then, the casting material was machined to obtain each test body having the above shape.

Next, a corrosion test for evaluating acid resistance was performed using the above-mentioned test specimen. In the corrosion test, sulfuric acid, nitric acid, formic acid, acetic acid and hydrochloric acid are mixed in the corrosive solution to obtain sulfuric acid concentrations of 0.25%, 1.0%, 3.0% and 5.0%. Four types of acidic aqueous solutions were used in a glass beaker. In the corrosion test, the test specimen supported by the nylon thread was thoroughly washed with alcohol only for the first time, and then immersed in the above acidic aqueous solution that was hot-watered on a hot stirrer and temperature-controlled at 80 ° C. ± 3 ° C. for 1 hour. Then, the specimen was pulled up and dried with a dryer, and the mass of the specimen was measured to obtain a weight loss of the specimen due to corrosion. Then, the procedure of immersing the test specimen again in the acidic aqueous solution for 1 hour, lifting and drying, and measuring the mass was repeated until the weight loss of the test specimen became zero.
The results of the corrosion test are shown in Table 3. In addition, the corrosion degree g / m < ² > * h < ^-1 > (JIS-Z8401) was used for evaluation of corrosion.

From Table 3, in Examples 1-3 of the present invention, corrosion rates for the sulfuric acid concentration from 0.25 to 5.0% of the acidic aqueous solution, even the largest Example 2 0.99~354.57g ^{/ m} 2 · h ⁻¹ and 400 g / m ² · h ⁻¹ or less. Further, a more preferred third embodiment the 0.00~182.24g ^/ m 2 · ^{h -1,} has been a 200g ^/ m 2 · ^{h -1} or less.
On the other hand, the corrosion degree of the conventional SUS430 which is the same ferritic stainless cast steel was 18.99 to 670.85 g / m ² · h ⁻¹ . In Comparative Example 4-8, and the smallest Any Comparative Example ^{4 63.82~769.17g / m 2 · h -1} , that does not extend to Example 2 of about 400g ^/ m 2 · ^{h -1} I understood.

  From the above, it has been confirmed that the ferritic stainless cast steel of the present invention has excellent acid resistance as compared with conventional SUS430 and Comparative Examples 4-8. In addition, it was found that the ferritic stainless cast steel of the present invention having the composition of Example 3 has particularly excellent acid resistance when the sulfuric acid concentration of the acidic aqueous solution is 1.0% or less.

(Example of cast member)
Next, as an embodiment of the cast member of the present invention, for the purpose of switching the exhaust gas flow path, which is one of the exhaust gas recirculation system members (EGR members) schematically shown in FIG. The switching valve member used (hereinafter referred to as EGR valve 1) was cast and formed by the lost wax precision casting method. The manufactured EGR valve 1 has a housing 2 having a flange surface 6, a low-temperature side passage 3 serving as a flow path for low-temperature exhaust gas such as when the engine is started, and a flow path for sending high-temperature exhaust gas to the cooler. A high temperature side passage 4, a shaft hole 5 for inserting a shaft (not shown) for attaching a butterfly valve (not shown), a mounting hole 7 for the shaft, stoppers 3a, 4a for abutting the butterfly valve, and the housing A fixing hole 8 is provided. Moreover, the material which has the composition of the ferritic stainless steel cast shown in Table 1 as Example 3 was used for material.

  First, a mold having substantially the same space shape (cavity) as the EGR valve 1 is formed, and commercially available wax (Pattern Wax A7-TCF / RR, Bryson Japan Co., Ltd.) is injected into this cavity, and the EGR valve An extinction model having substantially the same shape as 1 was obtained. Specifically, the above disappearable model was simultaneously injection-molded with a hot water, a runway, and the like made of the same wax as this, to obtain a drum-shaped model in which the hot water, the runway, and the like were integrated. The drum-shaped model was repeatedly coated with a slurry containing refractory colloidal silica and stucco containing zircon sand to obtain a mold having a plurality of refractory layers.

Then, after the mold is sufficiently dried, a drum-shaped model made of wax, that is, a vanishing model having substantially the same shape as that of the EGR valve 1, a feeder and a runway, is obtained from the mold by a high-temperature steam autoclave. Etc. were melted by heating and completely dissolved and removed to obtain a casting mold.
Next, the material having the composition shown in Table 1 as Example 3, that is, by mass, Cr: 19.65%, Cu: 1.81%, Si: 1.21%, Mo: 0.96%, Nb : 0.41%, Ni: 0.11%, C: 0.04%, Mn: 0.07%, Al: 0.02%, P: 0.02%, S: 0.01%, N: A melt containing 0.01% and the balance: Fe and inevitable impurities (Cu + Si): 3.02% was obtained by melting in the atmosphere. Then, the molten metal is suction cast into the mold while being controlled at 1620 to 1640 ° C., the mold is disassembled after cooling, the mold waste and the like are removed by sand shot, and then blow-cleaned to provide an EGR valve that is an embodiment of the present invention 1 casting material (outer shape 70 mm × 105 mm × 30 mm, mass 683 g) was obtained.

Exhaust gas of the present invention is produced by subjecting the cast material of the EGR valve 1 manufactured as described above to blow cleaning after sand shot, and further machining the shaft hole 5, flange surface 6, mounting hole 7 and the like. A switching valve member (EGR valve) having an outer shape of 70 mm × 105 mm × 29 mm and a mass of 614 g, which is an example of a recirculation system member and is used for switching an exhaust gas flow path shown in FIG. I was able to.
Since the EGR valve thus obtained has the same composition as the ferritic stainless cast steel having excellent acid resistance according to the present invention, it can be provided as a high-performance EGR valve having acid resistance against strong acids such as sulfuric acid. it can. Further, it is excellent in machinability as compared to the austenite system and is advantageous in terms of machining cost, and therefore can be provided as an inexpensive EGR valve.

It is a schematic diagram of the appearance of an EGR valve that is an example of the exhaust gas recirculation system member of the present invention.

Explanation of symbols

1. 1. RGR valve, Housing, 3. Low temperature side passage, 3a. Stopper, 4. High temperature side passage, 4a. Stopper, 5. Shaft hole, 6. 6. flange surface; Mounting holes, 8. Fixing hole

Claims (7)

  In mass%, Cr: 18.0-27.0%, Cu: 0.8-3.5%, Si: 0.5-2.0%, Mo: 0.5-1.5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% or less, Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less, S: 0.0. 15% or less, N: 0.10% or less, and (Cu + Si): more than 2.0%, and the balance contains Fe and inevitable impurities, and ferritic stainless cast steel having excellent acid resistance.   The mass% contains Cr: 18.0 to 22.0%, Cu: 0.8 to 2.2%, Si: 1.0 to 1.5%. Ferritic stainless cast steel with excellent acid resistance.   The ferritic stainless cast steel with excellent acid resistance according to claim 1 or 2, characterized by containing (Cu + Si): 2.8% or more by mass%.   In mass%, Cr: 18.0-27.0%, Cu: 0.8-3.5%, Si: 0.5-2.0%, Mo: 0.5-1.5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% or less, Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less, S: 0.0. 15% or less, N: 0.10% or less, and (Cu + Si): more than 2.0%, and the balance is made of ferritic stainless cast steel containing Fe and inevitable impurities. Cast parts.   It is made of a ferritic stainless cast steel containing, in mass%, Cr: 18.0 to 22.0%, Cu: 0.8 to 2.2%, and Si: 1.0 to 1.5%. The cast member excellent in acid resistance according to claim 4.   The cast member with excellent acid resistance according to claim 4 or 5, wherein the cast member is made of a ferritic stainless cast steel containing (Cu + Si): 2.8% or more by mass%.   The cast member with excellent acid resistance according to any one of claims 4 to 6, wherein the cast member is a switching valve member for switching a flow path of exhaust gas.

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