TW201313922A - Electromagnetic stainless steel and manufacturing method thereof - Google Patents

Abstract

An electromagnetic stainless steel and manufacturing method thereof are provided. The electromagnetic stainless steel has high electrical resistivity and good corrosion resistance which can be applied to a rotor or a stator in an electromagnetic valve of automobile fuel injection devices always exposed to harsh environment. The electromagnetic stainless steel has a composition containing a mass percentage of: less than 0.04% of C, 0.3% to 1.2% of Si, 0.3% to 1.0% of Mn, 0.01% to 0.05% of S, less than 1.0%(not including 0%) of Ni, more than 16.0% and less than 18.0% of Cr, 0.2% to 0.5% of Al, 0% to 0.05% of Ti, and remaining parts being Fe and impurities.

Description

Electromagnetic stainless steel and manufacturing method thereof

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

In the past, a rotor or a stator of a solenoid valve such as an automobile fuel injection device is required to have a high electrical resistivity, and an electromagnetic stainless steel excellent in magnetic field responsiveness to a dynamic magnetic field and excellent in corrosion resistance is used.

For example, Patent Document 1 proposes: C: 0.05% or less, N: 0.04% or less, Al: more than 0.50% and 3.0% or less, Si: 0.30% to 2.50%, and Mn: 0.50% or less, in terms of % by mass. : 0.03% or less, Ti: 0.01% to 0.50%, Cr: 5.0% to 20.0%, B: 0.0005% to 0.01%, and the rest are electromagnetic stainless steels having unavoidable impurities and substantially Fe composition. The first feature of the composition proposed in Patent Document 1 is that Ti and B are added in combination, and S is strongly reduced; and the second feature is to increase resistivity and improve corrosion resistance and magnetic properties by containing a relatively large amount of Al. characteristic. Further, in order to improve the machinability, Pb: 0.30% or less may be contained as one of the selection elements.

Further, Patent Document 2 of the applicant of the present application proposes that C: 0.03% or less, N: 0.03% or less, Al: 0.2% to 1.5%, Si: 0.3% to 1.2%, and Mn: 0.5% by mass%. ~1.0%, S: 0.008% to 0.06%, Cr: 8% to 16%, and the rest is substantially Fe stainless steel. This proposal is based on the 13Cr-Fe alloy to optimize the content of Al, Si, Mn, and S, and achieve high resistivity and excellent quality without impairing machinability. Different soft magnetic and cold forgeability. This Patent Document 2 is an excellent technique for adjusting the amount of MnS which is a non-metallic inclusion which is excellent in machinability by adjusting the amounts of S and Mn, and does not contain an environmentally harmful element, Pb, and Corrosion resistance, soft magnetic properties, and machinability are obtained.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 6-010101

[Patent Document 2] Japanese Patent Laid-Open No. Hei 2-061028

As described above, in the electromagnetic stainless steel disclosed in Patent Document 1, the increase in the resistivity, the increase in the maximum magnetic permeability, and the decrease in the coercive force are achieved by the active addition of Al. However, when Al is increased, the workability is deteriorated. In addition, Pb added in order to obtain excellent machinability is an environmentally harmful substance.

Further, although the electromagnetic stainless steel disclosed in Patent Document 2 does not contain Pb and can obtain machinability, when exposed to a severe environment, there is a problem that the electromagnetic stainless steel is rusted by salt damage. For example, when electromagnetic stainless steel is applied to a rotor or a stator component of a fuel injection device, if these components are rusted, there is a problem that the function as a solenoid valve is hindered. Further, in order to increase the electrical resistivity and increase the magnetic properties, the Al content is slightly increased, so that there is a problem in workability.

As described above, the electromagnetic stainless steel is required to have various characteristics such as electrical resistivity, corrosion resistance, soft magnetic properties, workability, and machinability, and in recent years, there is a tendency that a particularly high resistivity and excellent corrosion resistance are required. With regard to this requirement, the electromagnetic stainless steel disclosed so far has an unsatisfactory problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic stainless steel having high electrical resistivity and excellent corrosion resistance and a method for producing the same.

The inventors excluded these harmful substances like Pb, and again investigated the relationship between the chemical composition of the electromagnetic stainless steel and the electrical resistivity, corrosion resistance, and magnetic properties. As a result, it was found that the amount of Cr was about 17%. Further, it has been found that in the conventional electromagnetic stainless steel, Al is actively added in order to improve the magnetic properties, but by increasing the Cr, the Al can be reduced to a range where the workability is not deteriorated, and high magnetic permeability and low coercive force can be obtained. Excellent soft magnetic properties have thus completed the present invention.

That is, the present invention is an electromagnetic stainless steel comprising, in mass%, C: 0.04% or less, Al: 0.2% to 0.5%, Si: 0.3% to 1.2%, Mn: 0.3% to 1.0%, S: 0.01%~0.05%, Ti: 0%~0.05%, Cr: more than 16.0% and 18.0%, Ni: 1.0% or less (excluding 0%), and the rest are Fe and impurities.

In the present invention, the preferred range of Al, Cr and Ti is that the Al content is 0.2% to 0.35% by mass%, the Cr content is 16.5% to 18.0% by mass%, and the Ti content is 0.008% by mass%. ~0.05%.

Further, the present invention is a method for producing an electromagnetic stainless steel which, after obtaining a steel block having the above composition, is heated to 950 ° C to 1150 ° C for hot working to obtain a hot worked material.

Further, the present invention is a method for producing an electromagnetic stainless steel which is annealed at 850 ° C to 1050 ° C after the above thermal processing step.

The electromagnetic stainless steel of the present invention has a high resistivity and is dynamic The magnetic field has excellent magnetic field responsiveness. In addition, it has excellent corrosion resistance in a harsh environment. Moreover, it is quite excellent in the soft magnetic properties of high magnetic permeability and low coercive force. Therefore, it is suitably applied to, for example, a component for a solenoid valve of a fuel injection device that requires magnetic field responsiveness and is used in a severe environment.

As described above, an important feature of the present invention is to study the relationship between the chemical composition, electrical resistivity, corrosion resistance, and soft magnetic properties of electromagnetic stainless steel, and to obtain an appropriate range of chemical composition. In the electromagnetic stainless steel of the present invention, the reason for specifying each chemical composition is as follows. In addition, unless otherwise indicated, it is described as mass %.

C: 0.04% or less

C is an element which is bonded to Cr or Ti to form a carbide and deteriorates the corrosion resistance and soft magnetic properties of the electromagnetic stainless steel. Therefore, the content is preferably small. Therefore, C is one of the elements which should be limited in the present invention. When C is in the range of 0.04% or less, significant deterioration in corrosion resistance and deterioration of soft magnetic properties are not caused. Therefore, the upper limit is set to 0.04%. A preferred lower limit of C is 0%, and a preferred upper limit of C is 0.02%.

Al: 0.2%~0.5%

Al is an element which has an effect of improving the electrical resistivity of the electromagnetic stainless steel and improving soft magnetic properties. On the other hand, it is an element which deteriorates workability, and therefore it is preferable that the content is low. In the present invention, by setting Cr to about 17%, Al can be reduced as compared with the prior electromagnetic stainless steel. However, when Al is less than 0.2%, the effect of improving the high resistivity and soft magnetic properties is small, whereas in the range where Al exceeds 0.5%, the hardness of the electromagnetic stainless steel becomes high, and the plastic workability is improved. Lower, so set the upper limit to 0.5%. A preferred lower limit of Al is 0.22%, more preferably 0.24%. On the other hand, the preferred upper limit of Al is 0.45%, more preferably 0.35%.

Si: 0.3%~1.2%

Si is an element having an effect of improving the electrical resistivity of the electromagnetic stainless steel and improving soft magnetic properties. Therefore, it must be added in the present invention. However, when Si is less than 0.3%, the effect of increasing the specific resistance and improving the soft magnetic properties is small. On the other hand, in the range where Si exceeds 1.2%, the hardness of the electromagnetic stainless steel is increased to deteriorate the workability, so the upper limit is made 1.2%. The lower limit of the preferred Si is 0.5%, more preferably 0.6%. On the other hand, a preferred upper limit of Si is 1.0%, more preferably 0.9%.

Mn: 0.3% to 1.0%

Mn can be bonded to S to form a non-metallic inclusion MnS, and is an element that ensures the machinability of the electromagnetic stainless steel. However, when Mn is less than 0.3%, the amount of S is not sufficient. On the other hand, in the range where Mn exceeds 1.0%, the magnetic flux density of the electromagnetic stainless steel is lowered, so that it is in the range of 0.3% to 1.0%. A preferred lower limit of Mn is 0.4%, more preferably 0.45%. On the other hand, a preferred upper limit of Mn is 0.9%, more preferably 0.8%.

S: 0.01%~0.05%

S is also an element of MnS, ensuring the machinability of electromagnetic stainless steel. However, when S is less than 0.01%, the amount of MnS is small, and the effect of improving machinability is small. On the other hand, in the range where S exceeds 0.05%, the amount of MnS is excessive and the soft magnetic property is deteriorated, so it is set to 0.01%. 0.05% range. A preferred lower limit of S is 0.02%, more preferably 0.025%. On the other hand, a preferred upper limit of S is 0.04%, more preferably 0.035%.

Ti: 0%~0.05%

Ti is an element having an effect of fixing C or N and preventing soft magnetic deterioration caused by C or N solid solution in the mother phase of electromagnetic stainless steel. On the other hand, since Ti is solid-dissolved in the matrix phase, soft magnetic properties are obtained. There is a possibility of deterioration, so it may be added as needed, or may be added (0%). For the above reasons, the upper limit when Ti is added is set to 0.05%. A preferred lower limit when Ti is added is 0.008%, more preferably 0.01%. On the other hand, a preferred upper limit of Ti is 0.03%, more preferably 0.02%.

Cr: more than 16.0% and less than 18.0%

Cr is the most important element for the electromagnetic stainless steel of the present invention, and Cr is too small or too high to obtain the desired effect, and thus is adjusted in an extremely narrow range. As described above, in order to achieve an increase in resistivity, corrosion resistance and magnetic properties, a composition in which the amount of Cr is increased to about 17% is an optimum composition, and Al can be adjusted by adjusting the Cr content in an extremely narrow range. reduce. However, when Cr is in the range of 16.0% or less, it is possible to increase the possibility of rusting of the electromagnetic stainless steel in a severe environment such as salt damage, and therefore it is necessary to contain more than 16.0% of Cr. On the other hand, when Cr is in the range of more than 18.0%, it is advantageous for improvement in high electrical resistivity and corrosion resistance, but the decrease in magnetic flux density is remarkable, so the upper limit is made 18.0%. A preferred lower limit of Cr is 16.5%, more preferably 16.7%. On the other hand, the upper limit of the preferable Cr is 17.8%, more preferably 17.5%.

Ni: 1.0% or less (excluding 0%)

Ni is an essential element of the present invention and, like Cr, has improved corrosion resistance. Sexual effect, and has the effect of increasing resistivity. Further, there is also an effect of improving the strength of the electromagnetic stainless steel by solid solution strengthening by dissolving Ni in the ferrite iron. However, in the range where Ni exceeds 1.0%, soft magnetic properties are deteriorated, so the upper limit is made 1.0%. In order to obtain the effect of improving the corrosion resistance of Ni more reliably, it is preferable to set the lower limit of Ni to 0.3%. More preferably, the lower limit of Ni is 0.35%, and the upper limit of Ni is more preferably 0.7%.

The rest is Fe and impurities

The remainder is Fe and impurities that are inevitably mixed in manufacturing. Less impurity content is preferred. If the upper limit of the representative impurities is in the following range, it may be any case.

P≦0.05%, N≦0.04%, O≦0.01%

Next, the production method of the present invention will be described.

In the present invention, a steel block having the above composition is produced. Although the steel block may be used in a usual production method, if the active Ti is added to the composition, it is preferable to carry out vacuum dissolution to produce a steel block.

The obtained steel block is thermally processed to form a hot worked material. The reason for this is that the electromagnetic stainless steel is recrystallized by hot working on the steel block to easily obtain excellent soft magnetic properties.

When the heating temperature at the time of hot working is less than 950 ° C, the deformation resistance during hot working becomes high, and the electromagnetic stainless steel during hot working may be broken. Therefore, the lower limit of the heating temperature is 950 ° C. A more desirable lower limit temperature is 980 ° C, and particularly preferably a lower limit temperature of 1000 ° C. On the other hand, if hot When the heating temperature at the time of processing exceeds 1150 ° C, the grain of the ferrite grains is coarsened and the grain boundary is broken. Therefore, the upper limit of the heating temperature is set to 1150 ° C. A more desirable upper limit temperature is 1120 ° C, and a particularly desirable upper limit temperature is 1100 ° C.

Further, the term "thermal processing" as used in the present invention refers to a well-known hot working technique such as hot forging, hot press working, or hot rolling.

Next, annealing is performed after the above thermal processing step.

The reason for the annealing is to obtain an excellent soft magnetic property by annealing the dynamic recrystallized structure appearing in the thermal processing to adjust the particle size of the ferrite iron. In addition, it is preferred that the electromagnetic stainless steel is processed into a part shape and then annealed.

The reason why the lower limit of the heating temperature in the annealing step is 850 ° C is that the effect of forming the granules of the granules at a temperature of less than 850 ° C is inferior. A more preferable lower limit temperature is 880 ° C, and particularly preferably a lower limit temperature of 900 ° C. On the other hand, if the heating temperature exceeds 1050 ° C, although the particle size of the granules is large and uniform, and the soft magnetic properties are improved, after processing into a part shape, deformation of the electromagnetic stainless steel or part shape occurs at a high temperature exceeding 1050 ° C. The next question of each other. A more desirable upper limit temperature is 1020 ° C, and a particularly desirable upper limit temperature is 1000 ° C.

As described above, the electromagnetic stainless steel of the present invention described has a higher electrical resistivity and more excellent corrosion resistance than the prior electromagnetic stainless steel. Further, since it also has excellent soft magnetic properties, it is suitably applied to a rotor or a stator component of a solenoid valve such as an automobile fuel injection device.

[Example]

The invention is illustrated in more detail by the following examples.

Ten steel blocks of 10 kg of electromagnetic stainless steel were dissolved by a vacuum melting furnace. The chemical composition of each electromagnetic stainless steel is shown in Table 1.

The No. 1 to No. 8 alloys of Table 1 are within the range of the chemical composition of the electromagnetic stainless steel of the present invention. On the other hand, No. 11 of the comparative example is a comparative example alloy in which the amounts of Mn, S, and Cr are outside the range of the present invention and contain Pb as a harmful substance. Further, in No. 12 of the comparative example, Al was outside the scope of the present invention.

The No. 1 to No. 8 alloy of the present invention and the steel blocks of the electromagnetic stainless steel of the No. 11 alloy and the No. 12 alloy of the comparative example were heated to 1,100 ° C for hot forging to obtain a round bar material having a diameter of 30 mm.

After the oxide film at the time of hot forging was removed, a salt spray test piece having a diameter of 20 mm and a thickness of 2 mm was cut out from the round bar material, and one side was finished by grinding with a sandpaper up to #500. In addition, from each round bar material A 4 mm × 4 mm × 80 mm resistance measuring piece, an annular test piece having 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.

These salt spray test pieces, resistance measurement pieces, ring test pieces, and electromagnet test pieces were placed in a hydrogen gas atmosphere furnace at 950 ° C for 2 hours, and then subjected to furnace cooling and magnetic annealing for resistance measurement and salt spray test. With magnetic determination. The resistance was measured using a resistance measuring device using a four-terminal method. Further, in the salt spray test, a 5% NaCl aqueous solution having a temperature of 35 ° C was sprayed for 168 hours, and the occurrence of rust was confirmed.

The magnetic properties were measured by winding a small annular test piece at a time of 100 cycles of 1 time and 10 times, at a maximum applied magnetic field of Hm=800 A/m, 2000 A/m, 4000 A/m, 8000 A/m. The DC magnetic properties were measured under each condition. Further, DC magnet characteristics were measured on the electromagnet test piece under the conditions of the maximum applied magnetic field Hm = 40000 A/m.

The electrical resistivity, corrosion resistance and magnetic properties of No. 1 to No. 8 alloys of the present invention and No. 11 alloys and No. 12 alloys of Comparative Examples are shown in Table 2. In addition, the appearance photograph after the salt spray test of the No. 1 alloy of the present invention as an example of the salt spray test results is shown in FIG. 1 , and the appearance of the No. 11 alloy of the comparative example after the salt spray test is shown in FIG. 2 . .

According to Fig. 1, in the No. 1 alloy of the present invention, only a small amount of rust was observed at the edge portion, but no significant rust was observed. On the other hand, after the salt spray test of the No. 11 alloy of the comparative example, red rust was observed. From this, it is understood that the No. 1 alloy is more excellent in corrosion resistance than the No. 11 alloy. In addition, if the corrosion resistance of Table 2 is that no obvious rust is observed, ○ When the rust was observed to be clearly marked as ×, it was found that the degree of rust was substantially the same as that of the No. 1 alloy except for the No. 11 alloy of the comparative example.

Further, focusing on the specific resistance of each of the electromagnetic stainless steels, the results are No. 1 to No. 8 alloys of the present invention, and a resistivity of 0.71 μΩm or more is obtained, but the resistances of the No. 11 alloy and the No. 12 alloy of the comparative examples are obtained. The rate is below 0.71 μΩm.

Further, when focusing on the magnetic properties, the No. 1 alloy, the No. 2 alloy, and the No. 5 alloy of the present invention have higher maximum magnetic permeability μm and more excellent soft magnetic properties than the comparative examples.

According to the above results, the No. 1 to No. 8 alloy of the present invention has higher electrical resistivity and higher corrosion resistance than the No. 11 alloy and the No. 12 alloy of the comparative example.

[Industrial availability]

Since the electromagnetic stainless steel of the present invention has high electrical resistivity and excellent corrosion resistance, it is suitably applied to, for example, a rotor of a solenoid valve that requires magnetic field responsiveness to a dynamic magnetic field and is exposed to a vehicle fuel injection device or the like in a severe environment. The purpose of the stator.

Fig. 1 is a photograph showing the appearance of a stainless steel spray test of the present invention after a salt spray test.

Fig. 2 is a photograph showing the appearance of the electromagnetic stainless steel of the comparative example after the salt spray test.

Claims (6)

An electromagnetic stainless steel comprising: C: 0.04% or less, Al: 0.2% to 0.5%, Si: 0.3% to 1.2%, Mn: 0.3% to 1.0%, S: 0.01% by mass% 0.05%, Ti: 0% to 0.05%, Cr: more than 16.0% and 18.0%, Ni: 1.0% or less (excluding 0%), and the balance being Fe and impurities. 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 from 0.008% to 0.05% by mass%. A method for producing an electromagnetic stainless steel, characterized in that after obtaining a steel block having the composition according to any one of claims 1 to 4, heating to 950 ° C to 1150 ° C for hot processing to obtain heat Processing materials. The method for producing an electromagnetic stainless steel according to claim 5, wherein the annealing is performed at 850 ° C to 1050 ° C after the hot addition.