JPH0649916B2 - Corrosion resistant steel for soft magnetic rod tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a soft magnetic rod or steel for pipes used for an iron core of a solenoid valve or the like, and more specifically, electromagnetic characteristics, corrosion resistance,
The present invention relates to a rod-shaped or tubular iron core material which has excellent machinability and also has excellent cold forgeability.

(Prior art and problem to be solved) Generally, iron core materials such as solenoid valves have hitherto been pure iron, silicon steel, 13Cr-2Si steel, 13Cr-0.8 Si-0.25Al-.
Pb steel, etc., is used as a fixed iron core for solenoid valves, plungers, etc. Recently, various soft magnetic materials (for example, Cr, Al, etc.) have been added or added to improve corrosion resistance, magnetism, and others. JP-A-59-185762, 59-232258, 62
-146249, 63-45350) have been developed and have been partially commercialized.

These fixed iron cores and plungers are made from round bars or pipes by cold forging and cutting, but in order to promote the rationalization of machining processes, they have excellent machinability and, in addition, have a small and complex shape. In order to cope with cold forging, which is becoming more and more severe in recent years, such as cold forging of products, it is required to reduce the hardness of the material (Hv ≦ 120). As for electromagnetic characteristics, a material with better operability at a lower power consumption, that is, excellent magnetic characteristics (magnetic flux density B ₂ 8000G
Or more, B ₅ 10000G or more, B ₂₅ 11000G or more, coercive force Hc 1.0
A material having a high specific resistance (ρ ≦ 70 μΩcm) on top of 0e or less) is required. Also, in iron solenoid valves widely used from factory robots to consumer products (coolers, gas stoves, etc.), injectors for electronically controlled automatic fuel injection devices for automobiles, etc. Not only may the rusting part peel off and become clogged with the sliding part, significantly impairing the operability of the solenoid valve, the electromagnetic characteristics of the iron core itself, and even leading to a serious accident. Therefore, prevention of rusting is an extremely important request, and for that purpose, a material having corrosion resistance equal to or higher than that of 13% Cr steel is required.

However, among the steels conventionally used, pure iron and silicon steel have poor machinability and corrosion resistance, and 13Cr-2Si steel has improved corrosion resistance but poor machinability, and 13Cr-0.8Si-
0.25Al-Pb steel has improved corrosion resistance and machinability, but its hardness is high (Hv ≥ 136) and it is insufficient to support cold forging, which has become increasingly severe in recent years. There was no material that satisfied all of these characteristics. Further, for the recently developed steel, electromagnetic sustainability, corrosion resistance, machinability, cold forgeability and the like have been improved, but especially for the purpose of improving cold forgeability, electromagnetic characteristics, No proposal has been made yet for a technique for reducing the hardness of a material without impairing the corrosion resistance.

(Means for Solving the Problems) The present invention solves the above-mentioned problems of conventional magnetic steels as soft magnetic rods or steels used for iron cores of solenoid valves and the like, and has excellent electromagnetic characteristics and corrosion resistance. It also has excellent cold forgeability and machinability, and has a high specific resistance (ρ ≧ 70μΩcm) and excellent magnetic properties due to the extremely low impurity element content and the addition of appropriate amounts of Cr and Al. With corrosion resistance,
Furthermore, by keeping the hardness low (Hv ≤ 120), it has excellent cold forgeability that can cope with severe cold forging, and if necessary, free cutting elements Pb, Bi, Se, Te, etc. A steel for a corrosion-resistant soft magnetic rod tube, which is capable of imparting excellent machinability by adding an appropriate amount thereof, and has the following gist.

The first invention steel of the present invention has a weight ratio of C ≦ 0.01% N ≦ 0.01% Si ≦ 0.10% Mn ≦ 0.15% S ≦ 0.015% Cr: 5 to 15% Al: 1.0 to 1.9% is included, and Cr and Al are further included in Log ₁₀ (% Cr) + 0.861 × (% Al) ^2/3 ≧ 1.90.
(1) (% Cr) + 2.88 × (% Al) ≦ 18.3 ... (2) A corrosion resistant soft magnetic rod tube steel characterized by comprising balance iron and unavoidable impurities. In the second invention steel, the weight ratio of C ≦ 0.01% N ≦ 0.01% Si ≦ 0.10% Mn ≦ 0.15% S ≦ 0.015% Cr: 5-15% Al: 1.0 to 1.9%, Pb: 0.03 to 0.40%, Bi: 0.
03-0.40%, Se: 0.03-0.40%, T
e: contains at least one or more of 0.01 to 0.20%, and further contains Cr and Al as Log ₁₀ (% Cr) + 0.861 × (% Al) ^2/3 ≧ 1.90.
(1) (% Cr) + 2.88 x (% Al) ≤ 18.3 ... (2) It is a corrosion resistant soft magnetic rod and tube steel consisting of balance iron and unavoidable impurities.

(Operation) Table 1 shows the chemical composition and main characteristics of the present invention steel, comparative steel, and conventional steel.

These are melted in a vacuum induction furnace and cast into a 50kG steel ingot,
After forging to φ30, annealing was performed to prepare test pieces, which were used for each measurement. The magnetic measurement is 850 ℃ × 4Hr in vacuum.
Was performed after the strain relief annealing was performed. Then, the correlation between these measured values and the contents of Cr and Al and others were investigated, and the results are summarized in FIGS. The subscripts in FIGS. 1, 2, 6 and 7 indicate the sample numbers in Table 1.

FIG. 1 shows the effect of Cr content on the DC magnetic properties of the material. As is clear from the figure, the value of B ₂₅ decreases linearly as the Cr content increases. As mentioned at the beginning, magnetic flux density B ₂₅ 11000G or more is required to obtain excellent operating characteristics in a solenoid valve, but the Cr content is 1
It is understood that if it exceeds 5%, it will not be possible to stably obtain B ₂₅ 11000G or more.

FIG. 2 shows the effect of Al content on the DC magnetic properties of the material. As is clear from the figure, the values of the magnetic flux densities B ₂ , B ₅ , and B ₂₅ decrease linearly as the Al content increases. Similarly, as mentioned at the beginning, the magnetic flux density B ₂ 8000G or more, B
₅ 10000 G above is required, if the Al content exceeds 1.9% B ₂ 8000G or more, B ₅ 10000 G or more it can be seen that it is impossible to stably obtain.

FIG. 3 is a plot of the relationship between the specific resistance ρ (μΩcm) and the contents of Cr and Al, and the contour lines as shown for ρ can be drawn, from which the following empirical formula (a) was obtained.

ρ (μΩcm) = 31.8 x LoG ₁₀ (% Cr) + 27.4 x
(% Al) ^2/3 +9.6 (a) FIG. 4 is a plot of the relationship between the hardness Hv and the contents of Cr and Al. The hardness contour lines are straight lines as shown. From this, the following empirical formula (b) was obtained.

Hv = 0.123 × ((% Cr) +2.88 (% Al)) ² +7
9.0 …… (b) From Fig. 3 and Fig. 4, the Cr content increases up to about 10% and both the specific resistance and hardness increase remarkably.
If it exceeds 15%, the increase of the specific resistance becomes gradual, and if it is 15% or more, only the hardness increases and the effect of increasing the specific resistance becomes small. On the other hand, the effect of increasing the addition amount of Al is
Since the effect of increasing the specific resistance is large and the effect of increasing the hardness is small, it can be understood that the addition of Al is effective for increasing the specific resistance.

By the way, as mentioned at the beginning, it is necessary to keep the specific resistance of the iron core material used to be 70 (μΩcm) or higher in order to achieve better operability with less power consumption by solenoid valves. Since this is necessary, substituting this into equation (a) gives 31.8 × Log ₁₀ (% Cr) + 27.4 × (% Al) ^2/3 +9.6.
≧ 70 That is, Log ₁₀ (% Cr) + 0.861 × (% Al) ^2/3 ≧ 1.90 ……
(1) is obtained. In FIG. 3, the range of Cr and Al contents according to the formula (1) is shown by hatching.

Next, as also mentioned above, in order to cope with the severe cold forging, it is necessary to suppress the hardness to Hv120 or less, so by substituting this into the formula (b), 0.123 × ((% Cr) + 2.88 × (% Al)) ² + 79.0 ≦ 1
20 That is, (% Cr) + 2.88 × (% Al) ≦ 18.3 (2) is obtained. In Fig. 4, the range of Cr and Al contents according to the formula (2) is shown by diagonal lines.

FIG. 5 shows whether the corrosion resistance of the material is good or bad (indicated by ◯, Δ, ×).
And the Cr and Al contents are plotted, and the ranges of the curves of the above formulas (1) and (2) are also overlaid and plotted on it. The corrosion resistance test is
The corrosion weight loss of the material was examined by immersing it in a 3% NaCl solution at 25 ° C. for 24 hours. As is clear from the figure, satisfactory results cannot be obtained unless Cr exceeds 10%, but Al is 1
It can be seen that it can be pushed down to 5% by adding more than%. After all, in order to obtain the corrosion resistance required for the intended use of the present invention, Cr needs to be 5% or more and Al needs to be 1% or more. When this is added to the above-mentioned direct current magnetic characteristics, specific resistance, and limitation by hardness, the Cr and Al contents are in a thinly painted range, and by controlling in this region,
For the first time, it was found that a material having excellent electromagnetic characteristics, cold forgeability, and corrosion resistance was obtained.

Next, FIGS. 6 and 7 show a characteristic comparison between the conventional steel and the steel of the present invention.

FIG. 6 shows the relationship between the hardness Hv and the specific resistance ρ (μΩcm). It can be seen that the steel of the present invention has a lower hardness relative to the specific resistance value than the conventional steel, that is, a steel having improved cold forgeability.

FIG. 7 shows DC magnetic characteristics (magnetic flux density B ₂ (kG), coercive force Hc
(0e)) and the specific resistance ρ (μΩcm). It can be seen that the steel of the present invention has a larger magnetic flux density B ₂ (kG) and a smaller coercive force Hc (0e) for the same specific resistance value than the conventional steel, and is therefore a steel type with improved soft magnetism.

From the above, it can be concluded that the steel of the present invention is a steel which has not only excellent electromagnetic characteristics, corrosion resistance and machinability, but also cold forging property remarkably improved as compared with the conventional steel.

Next, the reason for limiting the component composition in the present invention will be explained.

<C, N> C and N form carbides and nitrides that adversely affect the soft magnetic properties, or dissolve in crystals to distort the crystal lattice, resulting in deterioration of magnetism and remarkable increase in hardness. The smaller the better. If the C and N contents exceed 0.01%, the magnetic properties and cold forgeability targeted by the present invention cannot be obtained depending on the relationship with the amounts of other components.

Therefore, the upper limits of C and N are set to 0.01%.

<Si> Si, like C and N, forms a solid solution in the crystal and significantly increases the hardness of the material, and thus improves the cold forgeability and, in addition, other main properties (corrosion resistance, magnetic property, In consideration of the effect on (resistivity), the smaller the content, the more desirable.

For example, Si does not have the effect of improving corrosion resistance like Cr and Al,
Although the effect of increasing the specific resistance and improving the direct current magnetic characteristics is smaller than that of Al, the solid solution strengthening effect is about 2 times as much as Al and about 5 times as much as Cr, and the hardness is increased. However, it is not necessary for the intended use of the present invention because it significantly reduces the cold forgeability of the material.

In the main component (Cr, Al) range of the present invention, the Si content is
If it exceeds 0.10%, the hardness may be high depending on the relationship with other ingredients.
If Hv120 is exceeded and the cold forgeability targeted by the present invention is not obtained, or if the increase in hardness due to Si is compensated for by reducing the Cr and Al contents, corrosion resistance and specific resistance decrease, and the present invention Therefore, the desired corrosion resistance and resistivity cannot be obtained.

Therefore, the upper limit of Si is set to 10%.

<Mn> Mn, like Si, forms a solid solution in the crystal and significantly increases the hardness, so cold forgeability is impaired, and since it is an austenite stabilizing element, magnetic properties are impaired, and corrosion resistance is also reduced, so the content is The less the better.

For example, Mn does not have the effect of improving corrosion resistance like Cr and Al,
Although the effect of increasing the specific resistance is smaller than that of Al and further impairs the direct current magnetization characteristics, the solid solution strengthening action is larger than that of Cr and Al. Therefore, similar to Si, for the purpose and purpose of the present invention, It is unnecessary.

In the main component (Cr, Al) range of the present invention, the Mn content is
If it exceeds 0.15%, the hardness may be increased depending on the relationship with other components.
Since it exceeds Hv120, the cold forgeability that is the object of the present invention cannot be obtained, or when the hardness increase due to Mn is compensated for by reducing the Cr and Al contents, corrosion resistance and a decrease in specific resistance are caused. Inventive corrosion resistance, the specific resistance can not be obtained,
Also in terms of magnetic characteristics, magnetic flux density B ₂ 8000G or more, B ₅ 100G
Since it is not possible to stably obtain a value of 00G or more and Hc of 1.00e or less, the magnetic characteristics targeted by the present invention cannot be obtained.

Therefore, the upper limit of Mn is set to 0.15%.

<S> Since S forms a sulfide that adversely affects cold forgeability and corrosion resistance, it is preferable that the content of S is as small as possible. S content is 0.
If it exceeds 015%, the cold forgeability and corrosion resistance targeted by the present invention cannot be obtained.

Therefore, the upper limit of S is set to 0.015%.

<Cr, Al> Cr and Al have been described in detail above, but will be summarized below.

Cr is an element effective for enhancing the corrosion resistance, but as shown in FIG. 1, excessive addition of Cr causes a decrease in magnetic flux density, and when the Cr content exceeds 15%, for example, it is necessary in the present invention. It becomes impossible to stably obtain the magnetic flux density B _{25 of} 11,000 G or more. Therefore, the upper limit of the Cr content is set to 15%.
However, as is clear from FIG. 5, when the Cr content is less than 5%, the corrosion resistance becomes insufficient for the intended use of the present invention, so the lower limit is made 5%.

Al is an element effective in increasing the specific resistance and improving the corrosion resistance. However, as shown in FIG. 2, excessive addition causes a decrease in the magnetic flux density, and when the Al content exceeds 1.9%, for example, The magnetic flux densities B ₂ 8000 G or more and B ₅ 10000 G or more required in the present invention cannot be stably obtained. Therefore, the upper limit of the Al content is 1.9%. However, as is clear from FIG. 5, when the Al content is less than 1%, the corrosion resistance becomes unstable, so the lower limit is made 1%.

Further, regarding specific resistance and hardness, Cr and Al are closely correlated with each other, and regarding specific resistance value, 70 (μ
Ωcm) or more, the range shown in FIG. 3, that is, the range of formula (1) must be satisfied, and the hardness is
In order to obtain the target Hv120 or less in the present invention, it was found that it is necessary to set the range of FIG. 4, that is, the range of the formula (2), and the present invention has been completed.

<Pb, Bi, Se, Te> The second invention steel of the present invention is particularly suitable for applications in which machinability is a problem, and Pb, Bi,
At least one of Se and Te is added, 0.03 to 0.40% for Pb, Bi, and Se, and 0.01 to 0.20 for Te. Addition of Pb, Bi, Se, and Te above their respective upper limit values saturates the effect of improving machinability, and further lowers electromagnetic characteristics and cold forgeability. There is almost no improvement effect. Therefore, the addition amount is as described above for each.

(Example) Next, No. 4 steel added with Pb was selected as the steel of the present invention, and No. 47 steel and No. 48 steel were selected as conventional steels, and a cold upsetting test was performed. The movable iron core and the fixed iron core were processed, and the actual machine test was performed. As a result of the cold upsetting test, the work hardening index (K value) of No. 4 steel was 12% lower than that of No. 47 steel and 17% lower than that of No. 48 steel. According to the results of the actual machine test, the power consumption of No. 4 steel is 6% lower than that of conventional steel and 6% lower than that of No. 47 steel. Demonstrated more stable performance. Furthermore, since the No. 4 steel of the present invention steel is also free-cutting steel,
Compared with the conventional steel No. 48 steel and No. 49 steel, the tool life during product processing was also improved by about 15 to 35%.

(Effect) As is clear from the above description, the steel of the present invention is a material having excellent cold forgeability, electromagnetic characteristics, corrosion resistance and machinability, and is particularly advantageous as an electromagnetic material for corrosive environments. It is used, for example, when used as an iron core material of a solenoid valve for electronically controlled automatic fuel injection device for pulse-operated automobiles, due to high specific resistance and excellent magnetic characteristics,
It exhibits superior operating characteristics (greater suction power and more sensitive reaction) with lower power consumption than those using conventional materials. Furthermore, since it has both excellent cold forgeability and excellent machinability, it is possible to perform cold forging that is more severe than conventional materials, and it is possible to further rationalize the part processing process.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Cr content and the magnetic flux density B ₂₅ ,
FIG. 2 is a diagram showing the relationship between the Al content and the magnetic flux densities B ₂ , B ₅ , B ₂₅ , and the coercive force Hc, and FIG. 3 is a diagram showing the relationship between the Cr and Al contents and the specific resistance value. 4 is a diagram showing a relationship between Cr and Al contents and hardness, and FIG. 5 is a diagram showing Cr and Al contents and hardness,
Figure 6 that summarizes the relationship between specific resistance and corrosion resistance
FIG. 7 is a diagram comparing the hardness and specific resistance of the present invention steel and conventional steel, and FIG. 7 is a diagram comparing the direct current magnetic characteristics and specific resistance of the present invention steel and conventional steel.

Claims (2)

[Claims] 1. C ≦ 0.01% N ≦ 0.01% Si ≦ 0.10% Mn ≦ 0.15% S ≦ 0.015% Cr: 5-15% Al: 1.0-1.9 %, And Cr and Al in Log ₁₀ (% Cr) + 0.861 x (% Al) ^2/3 ≥ 1.90
(1) (% Cr) + 2.88 × (% Al) ≦ 18.3 …… (2) The balance is controlled by the balance iron and inevitable impurities, and the corrosion-resistant soft magnetic rod tube steel 2. C ≦ 0.01% N ≦ 0.01% Si ≦ 0.10% Mn ≦ 0.15% S ≦ 0.015% Cr: 5-15% Al: 1.0-1.9 %, Pb: 0.03 to 0.40%, Bi: 0.
03-0.40%, Se: 0.03-0.40%, T
e: contains at least one or more of 0.01 to 0.20%, and further contains Cr and Al as Log ₁₀ (% Cr) + 0.861 × (% Al) ^2/3 ≧ 1.90.
(1) (% Cr) + 2.88 × (% Al) ≦ 18.3 …… (2) The balance is controlled by the balance iron and inevitable impurities, and the corrosion-resistant soft magnetic rod tube steel