JP2917450B2 - Stainless steel with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention]

(Industrial application field) The present invention relates to a stainless steel having excellent corrosion resistance, which is suitably used as a material for parts or the like which are required to have excellent corrosion resistance. (Prior Art) Conventionally, in order to improve the corrosion resistance of components, it has been considered effective to add a large amount of a corrosion resistance improving element such as Mo, Cr, or Ni to steel as a component material. (Problems to be Solved by the Invention) However, when a large amount of corrosion resistance improving elements such as Mo, Cr and Ni are added to steel, there is a problem that the cold castability of steel may be deteriorated. I was (Object of the Invention) The present invention has been made in view of such a conventional problem, and has a good cold forgeability, is capable of processing a near net shape, and has a higher corrosion resistance than before. It is an object of the present invention to provide a stainless steel excellent in corrosion resistance, which is suitable as a material of a component capable of maintaining high reliability for a long time.

Configuration of the Invention

(Means for Solving the Problems) The stainless steel excellent in corrosion resistance according to the present invention is, by weight%, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less,
P: 0.030% or less, S: 0.015% or less, Cr: 4 to 30%, Al: 0.01
-10%, N: 0.050% or less, O: 0.010% or less, and Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Zr: 1.
One or two selected from 5% or less, V: 1.5% or less
One or more selected from the group consisting of at least one of the following, also Cu: 5.0% or less, Ni: 20.0% or less, Mo: 10.0% or less, and Pb: 0.03 to 0.30%, Bi as required : 0.002-0.
020%, Ca: 0.002 ~ 0.020%, Te: 0.01 ~ 0.20%, Se: 0.03 ~
Including one or more selected from 0.30%,
Consists balance of Fe and impurities, Al ₂ O on the surface by heat treatment
It is characterized by having a structure where ₃ is formed and the corrosion resistance is further improved, and the surface state is uniformed by polishing if necessary, further improving the corrosion resistance The present invention is characterized in that the stainless steel structure having excellent corrosion resistance is a means for solving the above-mentioned conventional problems. Next, the reasons for limiting the component composition (% by weight) of the stainless steel having excellent corrosion resistance according to the present invention will be described. C: 0.015% or less C is an element that lowers the corrosion resistance and toughness of the member and also deteriorates the cold forgeability.
015% or less. Si: 4.0% or less Si has an effect of improving corrosion resistance, but such an effect saturates at about 4.0%, and the addition of more than 4.0% significantly deteriorates cold forgeability. 4.
0%. Mn: 0.30% or less If a large amount of Mn is contained, the cold forgeability is impaired, so the upper limit of the Mn content was set to 0.30%. P: 0.030% or less If a large amount of P is contained, the cold forgeability is lowered. For such a reason, the upper limit of the P content is set to 0.030%. S: 0.015% or less If a large amount of S is contained, the cold forgeability is lowered. For such a reason, the upper limit of the S content is set to 0.015%. Cr: 4 to 30% Cr is an element effective for improving the corrosion resistance. To obtain such an effect, the Cr content is set to 4% or more. But 30
%, The Cr content is set to 30% or less, since the cold forging property is deteriorated when the Cr content exceeds 30%. _{Al: 0.01~10% Al Al 2 O} 3 on the surface of the member by a heat treatment such as vacuum annealing
Is an element effective for further improving the corrosion resistance by forming, and is also an element effective for increasing the volume resistance. Therefore, the content is set to 0.01% or more so that these effects can be obtained. However, even if the content exceeds 10%, the effect is hardly improved, and if the content exceeds 10%, the cold forgeability is rather deteriorated. Therefore, the Al content is set in the range of 0.01 to 10%. N: 0.050% or less N, like C, is an element that lowers the corrosion resistance and toughness of the member and also deteriorates the cold forgeability, so the upper limit of the N content was made 0.050%. O: 0.010% or less O generates oxide-based inclusions and deteriorates cold forgeability, and lowers the coercive force by lowering the oxygen content to improve electromagnetic characteristics. The upper limit of the amount was 0.010%. Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Zr: 1.5% or less, V: 1.5% or less C or N is cold as described above Although it is an element that causes deterioration in forgeability, in order to reduce the adverse effects of C and N, one of Nb, Ta, Ti, Zr, and V, which is a carbonitride forming element, is used.
It is also desirable to add seeds or two or more kinds as necessary to reduce the size of crystal grains. Then, for example, when Ti is added to reduce the adverse effects of C and N as described above, the Ti promotes the formation of TiC and TiN, and improves cold forgeability and toughness. Such action is due to Nb, Ta,
The same applies to Zr and V. However, if too much is added, the cold forgeability is deteriorated, or the machinability is lowered, thereby impairing the processing performance. Therefore, even if added, the upper limit of each element is set to 1.5%. One or more selected from Cu: 5.0% or less, Ni: 20.0% or less, and Mo: 10.0% or less Cu, Ni, and Mo are effective elements for improving corrosion resistance. It is also possible to add one or more of these as needed. However, if too much is added, the cold forgeability is deteriorated. Therefore, even if it is added, 5.0% or less for Cu, 20.0% or less for Ni, M
It is necessary to make o less than 10.0%. Pb: 0.03-0.30%, Bi: 0.002-0.020%, Ca: 0.002-0.020
%, Te: 0.01 to 0.20%, Se: 0.03 to 0.30% One or more selected from among Pb, Bi, Ca, Te, Se is an element effective for improving machinability, For example, such an effect is obtained because cold forging is an element effective for improving machinability in the case of forming a fine drill hole by processing a near net shape close to the shape of the part. For this purpose, one or more of these elements may be added as necessary. However, if it is added in a large amount, the cold forgeability is reduced, so it is better to add it within a range that does not impair such properties. For Pb, 0.03 to 0.30%, for Bi, 0.002 to 0.020%, and for Ca, May be added in the range of 0.002 to 0.020%, for Te in the range of 0.01 to 0.20%, and in the range of 0.03 to 0.30% for Se. Highly corrosion resistant stainless steels of the present invention are those having a chemical composition as described above, the Al ₂ and the Al ₂ O ₃ on the surface by heat treatment such as vacuum annealing are formed
Corrosion resistance is further improved by the presence of O ₃ . When performing a heat treatment for further improving the corrosion resistance by forming Al ₂ O _{3 on} such a surface, the total pressure is 10 ⁻¹⁰ Torr to 10 atm, and the oxygen partial pressure is 0 ≦ Po It is desirable that the process be performed under the conditions of ₂ ≦ 1 (that is, 0% ≦ Po ₂ ≦ 100%) and a temperature of 400 ° C. to 1300 ° C. In addition, by polishing the surface to make the surface state uniform, it is possible to further improve the corrosion resistance. In this case, it is desirable to appropriately select a polishing means. (Operation of the Invention) Since the stainless steel having excellent corrosion resistance according to the present invention has the above-mentioned component composition, it is C, Si, Mn, P, S, N,
Appropriate regulation of O results in good cold forgeability, and addition of an appropriate amount of Al increases electrical resistance while keeping tensile strength low, and significantly improves corrosion resistance by heat treatment and surface polishing. Therefore, application to high frequency electromagnetic materials is promising, and furthermore, crystal grains are refined due to the effect of adding an appropriate amount of Nb, Ta, Ti, Zr, V and the regulation of C, N, O. In addition, due to the effect of adding appropriate amounts of Cr, Cu, Ni, and Mo, the corrosion resistance is also good, and the machining is also achieved by the effect of adding appropriate amounts of Pb, Bi, Ca, Te, and Se. The properties are also good. (Examples) After stainless steels having the component compositions shown in Table 1 were melted, the mechanical properties, corrosion resistance, machinability, electric resistance and magnetic flux density of each stainless steel were investigated. These results are
It is shown in the table. The machinability was investigated by a drilling test using a 2 mm diameter drill. In Table 2, ◎ indicates that the machinability was good, ○ indicates that the machinability was normal, and Δ Indicates that the machinability was not very good. In addition, in evaluating the corrosion resistance of each stainless steel shown in Table 1 by the atmospheric exposure test, surface polishing (# 400)
The corrosion resistance was evaluated for the case where the heat treatment was performed and no heat treatment was performed, the case where neither the surface polishing nor the heat treatment was performed, and the case where the surface polishing was not performed and the heat treatment (850 ° C. × 2 hr; vacuum 10 ⁻⁵ Torr) was performed. Was done. These results are also shown in Table 2. In the corrosion resistance evaluation shown in Table 2, A shows that there was no rust, B showed that there was substantially no rust, C showed that there was very little rust, D
Indicates that rust was generated, and E indicates that red rust was generated. As shown in Tables 1 and 2, in Comparative Example No. 1 in which the Cr content was too small, the corrosion resistance was considerably inferior, and the volume resistivity was not sufficiently increased, so that the electric resistance was extremely low. In Comparative Example No. 2 where the C content is too high, the corrosion resistance is not so good. In Comparative Example No. 3 where the Al content is too high, the corrosion resistance after the heat treatment is low. Although it is good, it shows a high value of electric resistance, and because of its high tensile strength, it is inferior to cold forgeability and magnetic properties and machinability, and furthermore, Si Comparative Example No. 4 with too much content
In the case of the heat treatment, the corrosion resistance is rather poor, and the tensile strength is large and the cold forgeability is poor.Also, the Al content is too small. In the case of .5, the corrosion resistance is rather poor due to the heat treatment,
It is recognized that the electric resistance is small, and further, in the case of Comparative Example No. 6 where the O content is too large, the machinability, corrosion resistance and cold forgeability are not very good. Was done. In contrast, C, Si, Mn, P, S, N, O content is regulated within an appropriate range, and the present invention Nos. 1 to 11 in which the Cr, Al content is appropriate. In the case, the surface polishing is more excellent in the corrosion resistance than the case where neither the surface polishing nor the heat treatment is performed, and the corrosion resistance is further improved by performing the heat treatment. ,
It has excellent cold forgeability and good electrical resistance and magnetic flux density. Further, by adding one or more of Pb, Bi, Ca, Te, and Se, It has been confirmed that it is possible to further improve the machinability. Then, for the test materials of Example No. 8 of the present invention and Comparative Example No. 5, an Auger-Esca elemental strength analysis up to a depth of 1000 mm was performed. In Example No. 8 of the present invention, FIG. As shown, heat treatment causes outward diffusion of Al and
_The formation of ₂ O ₃ increases the amount of Al and O in the surface layer, and Al ₂ O ₃ is formed on the surface, suppressing Cr removal during heat treatment and suppressing inward diffusion of O. Thus, it was recognized that further improvement in corrosion resistance was realized. On the other hand, in Comparative Example No. 5, it was recognized that since Cr was removed by the heat treatment, the corrosion resistance after the heat treatment was rather inferior to that before the heat treatment.

【The invention's effect】

Since the stainless steel having excellent corrosion resistance according to the present invention has the above-described composition, C, Si, Mn, P, S, N,
Appropriate regulation of O improves the cold forgeability.Also, the effect of adding an appropriate amount of Al, Nb, Ta, Ti, Zr, V and the regulation of C, N, O Has been refined, and the electromagnetic properties have been further improved, and the corrosion resistance has been improved by the action of adding an appropriate amount of Cr, Cu, Ni, Mo,
By adding an appropriate amount of Al to the surface by heat treatment such as vacuum annealing
Corrosion resistance is further improved by allowing Al ₂ O _{3 to} be formed, and furthermore, corrosion resistance is further improved by ensuring that the surface state is uniform, In addition, the machinability is improved by the action of adding appropriate amounts of Pb, Bi, Ca, Te, and Se, and the electromagnetic characteristics are improved along with the improvement of the corrosion resistance and cold forgeability of various parts. And a remarkably excellent effect that high reliability of components can be maintained for a long period of time is brought about.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are graphs illustrating the results of analyzing the amounts of Fe, Cr, Al, and O in the surface layer portions of the test materials of Example No. 8 of the present invention and Comparative Example No. 5, respectively.

Claims (9)

(57) [Claims] (1) In weight%, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less, C:
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
A stainless steel having excellent corrosion resistance, comprising the following: Fe and impurities, wherein Al ₂ O ₃ is formed on the surface by heat treatment to improve corrosion resistance. 2. In% by weight, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less,
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Zr: 1.5% or less, V: 1.5% or less, the balance being Fe and impurities Consisting of
Stainless steel with excellent corrosion resistance, characterized in that Al ₂ O ₃ is formed on the surface by heat treatment and the corrosion resistance is further improved. 3. In% by weight, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less, C:
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
The following, and one or more selected from among Cu: 5.0% or less, Ni: 20.0% or less, and Mo: 10.0% or less, with the balance being
A stainless steel with excellent corrosion resistance, characterized by being made of Fe and impurities, and having Al ₂ O ₃ formed on the surface by heat treatment to have improved corrosion resistance. 4. In% by weight, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less, C:
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
Below, and Pb: 0.03-0.30%, Bi: 0.002-0.020%, Ca:
0.002 to 0.020%, Te: 0.01 to 0.20%, Se: One or more selected from 0.03 to 0.30%, with the balance being Fe and impurities, heat treatment forms Al ₂ O _{3 on the} surface Stainless steel with excellent corrosion resistance, characterized in that it has improved corrosion resistance. 5. The composition according to claim 1, wherein C: 0.015% or less, Si: 4.0% or less,
Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less, Cr: 4
Up to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010% or less, Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Z
r: 1.5% or less, V: 1.5% or less, one or more selected from among them, Cu: 5.0% or less, Ni: 20.0% or less, Mo: 1
Contains one or more selected from 0.0% or less, with the balance being Fe and impurities.
A stainless steel having excellent corrosion resistance, characterized in that Al ₂ O ₃ is formed and the corrosion resistance is further improved. 6. In weight%, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less,
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Zr: 1.5% or less, V: 1.5% or less, and Pb: 0.03 to 0.30 %, Bi: 0.002-0.
020%, Ca: 0.002 ~ 0.020%, Te: 0.01 ~ 0.20%, Se: 0.03 ~
Including one or more selected from 0.30%,
Consists balance of Fe and impurities, Al ₂ O on the surface by heat treatment
Stainless steel with excellent corrosion resistance, characterized in that the steel is formed with ₃ and the corrosion resistance is further improved. 7. In% by weight, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less,
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
Or less, and one or more selected from among Cu: 5.0% or less, Ni: 20.0% or less, Mo: 10.0% or less, and Pb:
0.03 ~ 0.30%, Bi: 0.002 ~ 0.020%, Ca: 0.002 ~ 0.020%, T
e: 1 selected from 0.01 to 0.20%, Se: 0.03 to 0.30%
A stainless steel having excellent corrosion resistance, characterized in that it contains one or more species, the balance being Fe and impurities, and Al ₂ O ₃ is formed on the surface by heat treatment to improve corrosion resistance. 8. In% by weight, C: 0.015% or less, Si: 4.0% or less, Mn: 0.30% or less, P: 0.030% or less, S: 0.015% or less,
r: 4 to 30%, Al: 0.01 to 10%, N: 0.050% or less, O: 0.010%
Nb: 1.5% or less, Ta: 1.5% or less, Ti: 1.5% or less, Zr: 1.5% or less, V: 1.5% or less, and Cu: 5.0% or less , Ni: 20.0% or less, M
o: One or more selected from 10.0% or less,
Furthermore, Pb: 0.03-0.30%, Bi: 0.002-0.020%, Ca: 0.0
02-0.020%, Te: 0.01-0.20%, Se: One or more selected from 0.03-0.30%, with the balance being Fe and impurities, heat treatment forms Al ₂ O _{3 on the} surface Stainless steel with excellent corrosion resistance, characterized in that it has improved corrosion resistance. 9. The corrosion resistance according to claim 1, wherein the surface state is made uniform by polishing, and the corrosion resistance is further improved. Excellent stainless steel.