JP2013049918A - Electromagnetic stainless steel and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic stainless steel which has high electromagnetic resistivity suitable to the application of a rotor and a stator of a solenoid valve such as a fuel injector in an automobile exposed to the severe environment, and excellent corrosion resistance, and a method of manufacturing the same.SOLUTION: The electromagnetic stainless steel is composed of, by mass%, ≤0.04% C, 0.3-1.2% Si, 0.3-1.0% Mn, 0.01-0.05% S, ≤1.0% (not including 0%) Ni, >16.0% to ≤18.0% Cr, 0.2-0.5% Al, 0-0.05% Ti and the balance Fe with impurities.

Description

  The present invention relates to electromagnetic stainless steel having high electrical resistivity and excellent corrosion resistance, and a method for producing the same.

Conventionally, electromagnetic stainless steel having excellent electric field responsiveness to a dynamic magnetic field and excellent corrosion resistance has a high electrical resistivity as a component of a mover or stator of an electromagnetic valve such as an automobile fuel injection device. It has been adopted.
For example, in Patent Document 1, C: 0.05% or less, N: 0.04% or less, Al: more than 0.50% to 3.0% or less, Si: 0.30-2. 50%, Mn: 0.50% or less, S: 0.03% or less, Ti: 0.01-0.50%, Cr: 5.0% -20.0%, B: 0.0005-0. There has been proposed an electromagnetic stainless steel containing 01%, with the balance being inevitable impurities and substantially Fe. The first feature of the composition proposed in Patent Document 1 is that Ti and B are added together and S is reduced as much as possible. The second feature is that Al is contained in a relatively large amount. As a result, the electrical resistivity is increased and the corrosion resistance and magnetic properties are improved. In addition, Pb: 0.30% or less may be included as one of selective elements for the purpose of improving machinability.
Moreover, in patent document 2 by this applicant, C: 0.03% or less, N: 0.03% or less, Al: 0.2-1.5%, Si: 0.3-1. 2%, Mn: 0.5-1.0%, S: 0.008-0.06%, Cr: 8-16%, the electromagnetic stainless steel which the remainder consists essentially of Fe is proposed. This proposal is based on a 13Cr-Fe alloy, and by optimizing the contents of Al, Si, Mn, and S, it has high electrical resistivity, excellent soft magnetism and cold forging without sacrificing machinability. Is realized. In Patent Document 2, the amount of S and Mn is adjusted to adjust the amount of MnS, which is a non-metallic inclusion having good machinability, so that it does not contain Pb which is an element harmful to the environment. It is an excellent technique in that soft magnetism and machinability can be obtained.

JP-A-6-010101 JP-A-2-061028

As described above, the electromagnetic stainless steel disclosed in Patent Document 1 is intended to realize an increase in electrical resistivity, an increase in maximum magnetic permeability, and a decrease in coercive force by positively adding Al. When Al is raised, workability deteriorates. Further, Pb added to obtain excellent machinability is a substance harmful to the environment.
In addition, the electromagnetic stainless steel disclosed in Patent Document 2 can obtain machinability without containing Pb, but when exposed to a harsh environment, there is a problem that the electromagnetic stainless steel rusts due to salt damage. . For example, when electromagnetic stainless steel is applied to the parts of the mover and stator of the fuel injection device, if rusting occurs in these parts, the function as the electromagnetic valve is impaired, which causes a problem. In addition, in order to increase the electrical resistivity and improve the magnetism, Al is slightly increased and contained, which may cause problems in workability.
Thus, electromagnetic stainless steel is required to have various properties such as electrical resistivity, corrosion resistance, soft magnetism, workability, machinability, etc., but in recent years, particularly high electrical resistivity and excellent corrosion resistance are required. There is a tendency. In response to this requirement, there has been a problem that conventionally disclosed electromagnetic stainless steel is insufficient.
An object of the present invention is to solve this problem and to provide an electromagnetic stainless steel having a high electrical resistivity and excellent corrosion resistance and a method for producing the same.

The present inventor excluded a harmful substance such as Pb, and again investigated the relationship between the chemical composition of electromagnetic stainless steel and the electrical resistivity, corrosion resistance, and magnetic properties. As a result, it was found that the Cr content is optimally around 17%. In addition, Al added positively in order to improve magnetic properties in conventional electromagnetic stainless steel is excellent in high permeability and low coercive force even if it is reduced to a range where workability is not deteriorated by increasing Cr. The inventors have found that soft magnetism can be obtained and have reached the present invention.
That is, in the present invention, by mass%, C: 0.04% or less, Al: 0.2-0.5%, Si: 0.3-1.2%, Mn: 0.3-1.0%, S: 0.01 to 0.05%, Ti: 0 to 0.05%, Cr: more than 16.0% and 18.0% or less, Ni: 1.0% or less (not including 0%), The balance is electromagnetic stainless steel made of Fe and impurities.
In the present invention, preferable Al, Cr and Ti ranges are as follows: Al content is mass%, 0.2 to 0.35%, Cr content is mass%, 16.5 to 18.0%, Ti content The amount is 0.008 to 0.05% by mass.
Moreover, this invention is a manufacturing method of the electromagnetic stainless steel which obtains a hot work material by obtaining the steel ingot which has the above-mentioned composition, and heating to 950-1150 degreeC and hot-working.
Furthermore, this invention is a manufacturing method of the electromagnetic stainless steel which anneals at 850-1050 degreeC after the said hot working process.

  Since the electromagnetic stainless steel of the present invention has a high electrical resistivity, the magnetic field responsiveness to a dynamic magnetic field is excellent. It also has excellent corrosion resistance under harsh environments. Furthermore, it is excellent in terms of soft permeability with high magnetic permeability and low coercivity. Therefore, for example, magnetic field responsiveness is required, and it is suitable for an electromagnetic valve component of a fuel injection device used in a harsh environment.

It is a photograph which shows the external appearance after the salt spray test of the electromagnetic stainless steel of this invention. It is a photograph which shows the external appearance after the salt spray test of the electromagnetic stainless steel of a comparative example.

As described above, an important feature of the present invention is that the relationship between the chemical composition, electrical resistivity, corrosion resistance, and soft magnetism of the electromagnetic stainless steel is studied and the chemical composition is within an appropriate range. The reason why each chemical composition is defined in the electromagnetic stainless steel of the present invention is as follows. Unless otherwise specified, the mass% is indicated.
C: 0.04% or less Since C is an element that combines with Cr and Ti to form carbides and degrades the corrosion resistance and soft magnetism of electromagnetic stainless steel, the content is preferably as low as possible. Therefore, C is one of the elements that should be restricted in the present invention. If C is in the range of 0.04% or less, significant corrosion resistance deterioration and soft magnetic deterioration will not occur. Therefore, the upper limit was made 0.04%. A preferable lower limit of C is 0%, and a preferable upper limit of C is 0.02%.
Al: 0.2-0.5%
While Al is an element that has the effect of increasing the electrical resistivity of electromagnetic stainless steel and improving soft magnetism, it is an element that deteriorates workability, so that the content is desirably low. In the present invention, it is possible to reduce Al as compared with conventional electromagnetic stainless steel by setting Cr to be close to 17%. However, when the Al content is less than 0.2%, the effect of improving the electrical resistivity and soft magnetism is small, and conversely, when the Al content exceeds 0.5%, the hardness of the electromagnetic stainless steel is increased and the plastic workability is lowered. Therefore, the upper limit was made 0.5%. The minimum with preferable Al is 0.22%, More preferably, it is 0.24%. On the other hand, the preferable upper limit of Al is 0.45%, and more preferably 0.35%.

Si: 0.3-1.2%
Si is an element that has the effect of increasing the electrical resistivity of electromagnetic stainless steel and improving soft magnetism. Therefore, it is essential and added in the present invention. However, if Si is less than 0.3%, the effect of increasing the electrical resistivity and soft magnetism is small, and conversely in the range exceeding 1.2%, the hardness of the electromagnetic stainless steel increases and the workability is lowered. Was 1.2%. The lower limit of Si is preferably 0.5%, more preferably 0.6%. On the other hand, the preferable upper limit of Si is 1.0%, more preferably 0.9%.
Mn: 0.3 to 1.0%
Mn is an element that combines with S to become MnS of non-metallic inclusions and ensures the machinability of electromagnetic stainless steel. However, if Mn is less than 0.3%, it is insufficient to fix S. Conversely, if Mn is more than 1.0%, the magnetic flux density of the electromagnetic stainless steel is lowered. % Range. The minimum of preferable Mn is 0.4%, More preferably, it is 0.45%. On the other hand, the preferable upper limit of Mn is 0.9%, more preferably 0.8%.

S: 0.01 to 0.05%
S is also an element that becomes MnS and ensures the machinability of the electromagnetic stainless steel. However, if S is less than 0.01%, the amount of MnS is small and the effect of improving the machinability is small. Conversely, if it exceeds 0.05%, the amount of MnS is too large and soft magnetism is deteriorated. Therefore, the range was 0.01 to 0.05%. A preferable lower limit of S is 0.02%, and more preferably 0.025%. On the other hand, the preferable upper limit of S is 0.04%, more preferably 0.035%.
Ti: 0 to 0.05%
Ti is an element that fixes C and N and prevents deterioration of soft magnetism due to solid solution of C and N in the parent phase of electromagnetic stainless steel. On the other hand, Ti is the parent phase. Since there is a possibility that the soft magnetism may be deteriorated by dissolving in a solid solution, it may be added as necessary, or it may be added (0%). The upper limit in the case of adding Ti is set to 0.05% for the reason described above. The preferable lower limit in the case of adding Ti is 0.008%, more preferably 0.01%. On the other hand, the preferable upper limit of Ti is 0.03%, and more preferably 0.02%.

Cr: more than 16.0% and not more than 18.0% Cr is the most important element for the electromagnetic stainless steel of the present invention, but the desired effect cannot be expected even if Cr is too little or too high. Therefore, it is adjusted to an extremely narrow range. As described above, the composition with the Cr content increased to around 17% is optimal for increasing the electrical resistivity, corrosion resistance, and magnetic properties, and by adjusting the Cr content within a very narrow range, Can be reduced. However, when Cr is in the range of 16.0% or less, for example, the possibility of rusting is increased in the electromagnetic stainless steel under a severe environment such as salt damage, so Cr needs to be contained in excess of 16.0%. is there. On the other hand, even if it is in the range exceeding 18.0%, although it is advantageous for increasing the electrical resistivity and improving the corrosion resistance, the magnetic flux density is significantly reduced. Therefore, the upper limit is defined as 18.0%. The lower limit of Cr is preferably 16.5%, more preferably 16.7%. On the other hand, the upper limit of preferable Cr is 17.8%, more preferably 17.5%.
Ni: 1.0% or less (excluding 0%)
Ni, like Cr, is an essential element of the present invention that is effective in improving corrosion resistance and has an effect of increasing electrical resistivity. Further, by dissolving Ni in the ferrite structure, there is an effect of increasing the strength of the electromagnetic stainless steel by solid solution strengthening. However, in the range exceeding 1.0%, soft magnetism is deteriorated, so the upper limit is defined as 1.0%. In order to obtain the effect of improving the corrosion resistance of Ni more reliably, the lower limit of Ni is preferably set to 0.3%. A more preferable lower limit of Ni is 0.35%, and a more preferable upper limit of Ni is 0.7%.

The balance is Fe and impurities. The balance is Fe and impurities inevitably mixed in the manufacturing process. A lower impurity content is preferred. The upper limit of typical impurities may be in the following range.
P ≦ 0.05%, N ≦ 0.04%, O ≦ 0.01%

Next, the manufacturing method of this invention is demonstrated.
In the present invention, a steel ingot having the aforementioned composition is produced. The method for producing the steel ingot may be a conventional method, but if the composition is such that active Ti is added, it is preferable to produce the steel ingot by performing vacuum melting.
The obtained steel ingot is hot-worked to obtain a hot-worked material. This is because by performing hot working on the steel ingot, the electromagnetic stainless steel is recrystallized and it becomes easy to obtain excellent soft magnetism.
If the heating temperature at the time of hot working is less than 950 ° C., there is a concern that deformation resistance at the time of hot working increases and cracking occurs in the electromagnetic stainless steel during hot working, so the lower limit of the heating temperature is 950 C. A more desirable lower limit temperature is 980 ° C., and a more desirable lower limit temperature is 1000 ° C. On the other hand, if the heating temperature during hot working exceeds 1150 ° C., the ferrite grains become coarse and there is a concern of intergranular cracking, so the upper limit of the heating temperature was set to 1150 ° C. A more desirable upper limit temperature is 1120 ° C, and a more desirable upper limit temperature is 1100 ° C.
The hot working in the present invention refers to a known hot working technique such as hot forging, hot pressing, hot rolling and the like.

Next, annealing is performed after the hot working process described above.
Annealing is for annealing the dynamic recrystallized structure formed during hot working to adjust the ferrite grain size and to obtain excellent soft magnetism. In addition, it is preferable that the shape of the electromagnetic stainless steel at the time of annealing is performed after processing into a part shape.
The reason why the lower limit of the heating temperature in the annealing process is set to 850 ° C. is that the effect of regulating the ferrite grains is small at a temperature lower than 850 ° C. A more preferable lower limit temperature is 880 ° C., and a more preferable lower limit temperature is 900 ° C. On the other hand, when the heating temperature exceeds 1050 ° C., soft magnetism is improved by increasing the ferrite grain size, but after processing into a part shape, deformation of the electromagnetic stainless steel or part shape at a high temperature exceeding 1050 ° C. This is because a problem of bonding between the two occurs. A more desirable upper limit temperature is 1020 ° C, and a more desirable upper limit temperature is 1000 ° C.
As described above, the electromagnetic stainless steel of the present invention to be described has higher electrical resistivity and superior corrosion resistance than conventional electromagnetic stainless steel. Moreover, since it also has excellent soft magnetism, it is suitable, for example, for parts of a mover or a stator of an electromagnetic valve such as an automobile fuel injection device.

The following examples further illustrate the present invention.
Ten types of ingots of 10 kg electromagnetic stainless steel were melted in a vacuum melting furnace. Table 1 shows the chemical composition of each electromagnetic stainless steel.
No. in Table 1 Alloys 1-8 are within the chemical composition of the electromagnetic stainless steel of the present invention. On the other hand, no. No. 11 is a comparative alloy containing Pb, which is a harmful substance, while the amounts of the alloy, Mn, S, and Cr are out of the scope of the present invention. Moreover, No. of the comparative example. In 12, Al is outside the scope of the present invention.

No. of the present invention. Nos. 1 to 8 and Comparative Example No. No. 11 alloy and no. A steel ingot of each alloy stainless steel of 12 alloys was heated to 1100 ° C. and hot forging was performed to obtain a round bar with a diameter of 30 mm.
After removing the oxide scale at the time of hot forging, a salt spray test piece having a diameter of 20 mm and a plate thickness of 2 mm was cut out from this round bar, and one side was polished to # 500 with emery paper. In addition, a 4 mm × 4 mm × 80 mm electrical resistance measurement piece, an outer diameter of 20 mm, an inner diameter of 15 mm, a plate thickness of 5 mm, and an electromagnet test piece of 5 mm × 10 mm × 30 mm were cut out from each round bar.
These salt spray test pieces, electrical resistance measurement pieces, ring test pieces, and electromagnet test pieces were held in a hydrogen atmosphere furnace at 950 ° C. for 2 hours, and then subjected to magnetic annealing to cool the furnace, and electrical resistance measurement, salt spray test and It used for the magnetic measurement. The electrical resistance was measured using an electrical resistance measuring device based on the four probe method. In the salt spray test, a 5% NaCl aqueous solution having a temperature of 35 ° C. was sprayed for 168 hours to confirm the occurrence of rust.
The measurement of the magnetic characteristics is performed by winding the small ring test piece 100 times primary and 10 times secondary, and applying the maximum applied magnetic field Hm = 800 A / m, 2000 A / m, 4000 A / m, and 8000 A / m. DC magnetic properties were measured. Further, the DC magnetic characteristics were measured on the electromagnet test piece under the condition of the maximum applied magnetic field Hm = 40000 A / m.

No. of the present invention. Nos. 1 to 8 and Comparative Example No. No. 11 alloy and no. Table 2 lists the electrical resistivity, corrosion resistance, and magnetic properties of the 12 alloys. In addition, as an example of the salt spray test result, No. 1 of the present invention. A photograph of the appearance of the alloy 1 after the salt spray test is shown in FIG. The appearance of the 11 alloy after the salt spray test is shown in FIG.
From FIG. In the case of one alloy, a starting point of rust is slightly seen at the end, but no remarkable rust is seen. On the other hand, no. After the salt spray test of Alloy 11, noticeable red rust is seen. From this, No. The corrosion resistance of Alloy 1 is No. 1. It turns out that it is superior to 11 alloy. In Table 2, the corrosion resistance was marked as ◯ when no significant rust was observed, and marked as x when significant rust was observed. Except for alloy No. 11, all were No. The rusting was the same as that of 1 alloy.
Further, when attention is paid to the electrical resistivity of each electromagnetic stainless steel, No. 1 of the present invention. In the alloys 1 to 8, an electrical resistivity of 0.71 μΩm or more was obtained. No. 11 alloy and no. The electrical resistivity of alloy 12 was lower than 0.71 μΩm.
Further, when focusing attention on the magnetic characteristics, the No. 1 of the present invention. No. 1 alloy, no. No. 2 alloy and No. 2 In the case of alloy 5, the maximum permeability μm is higher than in the comparative example, and the soft magnetism is also excellent.

  From the above results, No. 1 of the present invention. Nos. 1 to 8 are comparative examples. No. 11 alloy and no. It can be seen that it has a high electrical resistivity with respect to 12 alloys and is excellent in corrosion resistance.

  The electromagnetic stainless steel of the present invention has a high electric resistivity and excellent corrosion resistance. For example, a fuel injection device for an automobile that requires a magnetic field response to a dynamic magnetic field and is exposed to a harsh environment. It can be applied to the use of a mover or stator of a solenoid valve.

Claims (6)

  C: 0.04% or less in mass%, Al: 0.2-0.5%, Si: 0.3-1.2%, Mn: 0.3-1.0%, S: 0.01- 0.05%, Ti: 0 to 0.05%, Cr: more than 16.0% and 18.0% or less, Ni: 1.0% or less (excluding 0%), the balance from Fe and impurities Electromagnetic stainless steel characterized by   The electromagnetic stainless steel according to claim 1, wherein the Al content is 0.2% to 0.35% by mass.   The electromagnetic stainless steel according to claim 1 or 2, wherein the Cr content is 16.5 to 18.0% by mass.   The electromagnetic stainless steel according to any one of claims 1 to 3, wherein the Ti content is 0.008 to 0.05% by mass.   After obtaining the steel ingot which has a composition in any one of Claims 1 thru | or 4, a hot work material is obtained by heating to 950-1150 degreeC and hot-working, The electromagnetic stainless steel characterized by the above-mentioned Production method.   The method for producing electromagnetic stainless steel according to claim 5, wherein annealing is performed at 850 to 1050 ° C. after the hot-heating step.