JPH0463248A - Soft magnetic stainless steel having high magnetic flux density and low coercive force and excellent in machinability - Google Patents

Abstract

PURPOSE:To obtain a soft magnetic stainless steel having the properties of high magnetic flux density and low coercive force and excellent in corrosion resistance and machinability by specifying a compsn. constituted of C, Si, Mn, Ni, Cr, Cu, Al, O, N, Ca, Bi, Pb, S, Se, Te, Zr and Fe. CONSTITUTION:This is soft magnetic stainless steel having high magnetic flux density and low coercive force and excellent in machinability, which has the characteristic of contg., by weight, <=0.010% C, <=0.10% Si, <=0.10% Mn, <=0.10% Ni, 11 to 13% Cr, <=0.10% Cu, 0.05 to 0.15% Al, <=0.0070% 0, <=0.0100% N and <=0.015% C+N, furthermore contg. one or >=two kinds among 0.002 to 0.02% Ca, <=0.30% Bi, <=0.040% S and <=0.040% Se, and at the time of incorporating one or more kinds of S and Se, contg. one or two kinds of 0.002 to 0.040% Te and 0.02 to 0.15% Zr and the balance Fe with inevitable impurities. This stainless steel permits the miniaturization of the magnetic circuit of a solenoid valve or the like.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a high magnetic flux device with excellent magnetic properties, electrical properties, and corrosion resistance that is used in electronic fuel injection devices (EFI), solenoid valves, magnetic sensors, etc. of automobiles, etc. It concerns low density, coercive force, soft magnetic stainless steel.

(Prior art) Before 1975, JIS steel 5O3430, 5U was used as the magnetic core material for parts that required corrosion resistance in electronic fuel injection devices, solenoid valves, magnetic sensors, etc. used in automobiles.
5410 etc. have been used. Later, in the early 1970s, Fe was developed to improve the corrosion resistance and electromagnetic properties of JIS steel.
-13Cr-ISi-0,25AI steel was developed and is in use to date. However, in line with the recent trend toward miniaturization of actuators such as solenoid valves, there has been an extremely strong demand for miniaturization of magnetic circuits, and since a cutting process is often involved in manufacturing each component of the magnetic circuit, it is difficult to cut easily. There is also a growing demand for improvement. In this situation, Fe-13Cr-ISi-0,25AI
Steel is no longer suitable for this purpose, and Fe-13Cr-ISi-
There has been a strong desire to develop a new material that has even higher magnetic flux density and superior soft magnetic properties than 0.25AI steel, and also has excellent free machinability.

(Problems to be Solved by the Invention) The present invention was made in order to solve the above-mentioned drawbacks of conventional steel, and the miniaturization of magnetic circuits such as electronic fuel injection devices and solenoid valves, which has recently been strongly demanded. The purpose of the present invention is to provide a soft magnetic stainless steel that has the characteristics of high magnetic flux density and low coercive force necessary to enable this, and has excellent corrosion resistance and free machinability.

(Means for solving the problem) Materials used for electronic fuel injection devices, solenoid valves, etc. are cold worked when manufacturing the parts, so in order to prevent deterioration of magnetic properties due to the effects of processing strain, Heat treated to improve magnetic properties. In order to obtain excellent magnetic properties, especially low coercive force, it is necessary to perform heat treatment at a high temperature of 900°C or higher, but with conventional steels such as 5US430.5US410,
A T-loop exists near 800-1100°C, and 800°C
When heat treated at a temperature higher than 0.degree. C., the processing strain disappears, but since transformation occurs, the transformation strain remains after cooling, resulting in deterioration of the magnetic properties. On the other hand, when the heat treatment was performed at a low temperature of less than 800°C, the processing strain did not completely disappear and a low coercive force could not be obtained. On the other hand, Fe-13Cr-
Although ISi-0,25AI steel does not exhibit T transformation at high temperatures, the magnetic flux density decreases due to the inclusion of Sl and AI, making it impossible to obtain satisfactory magnetic properties.

The present inventors focused on the fact that in conventional steels, it was not possible to obtain excellent magnetic flux density because the γ-loop region was made smaller and the ferrite phase was stabilized by the composite addition of Si, 81. It is possible to obtain both low coercive force and high magnetic flux density by reducing the T-loop area through efficient component adjustment and enabling heat treatment at a high temperature of 900 to 1200°C. The present invention was developed as a result of extensive research into the amount of components to be added that makes it possible to obtain excellent magnetic properties.

In order to reduce the T-loop region, austenite former elements such as Ni, Cu, C+N, Mn
Si, which is a ferrite former element,
It has been conventionally said that it is sufficient to add A1 or the like.

However, it is currently not known exactly how effective each element is individually. In addition, in order to obtain high magnetic flux density, C
It is necessary to reduce all elements except r as much as possible. By utilizing recent excellent steelmaking technology, the present inventors were able to remove Cr (C+N, Si, Mn, Ni, Cu) to a level that could not be reached with conventional metallurgical methods.
Elements such as XAl and 0 were reduced, and the presence or absence of T loops was measured. However, it was found that if only the elements other than Cr are lowered, the γ loop becomes smaller to some extent, but it still exists in the heat treatment temperature range. Therefore, as a result of further research on the effects of the ferrite former elements Si, Al, Mo, and Ti, it was found that A
It was discovered that I has the greatest effect of reducing the r-loop region, and together with the effect of reducing austenite former elements, a single ferrite phase can be obtained in all temperature ranges of 800°C or higher. It was also found that AI has a smaller negative effect on reducing magnetic flux density than Si.
Since it also serves as a deoxidizer, it has been discovered that a very large effect can be obtained by adding a small amount.

That is, as a result of thorough investigation and research into the influence of alloys on 13Cr stainless steel, the present inventors have reduced other elements as much as possible except for Cr, which ensures corrosion resistance, and
The minimum amount of A necessary to reduce the loop area and obtain the deoxidizing effect.
By adding I, we succeeded in securing magnetic properties (high magnetic flux density and low coercive force) at a level that could not be predicted conventionally.

Furthermore, the present inventors aimed to improve the free machinability of the material developed based on the above knowledge.
Free-machining elements such as , Bi, , Ca, Te, and Zr were added, and the adverse effects on magnetic properties and the effect of improving free-machinability were investigated. As a result, we determined the amount of the above-mentioned component elements that can improve the free machinability without significantly deteriorating the magnetic properties and corrosion resistance, and arrived at the present invention.

That is, in the present invention, C: 0.010% or less in weight ratio,
Si: 0.10% or less, Mn: 0.10! Below, Ni
: 0.10% or less, Cr: 11-13%, Cu: 0.1
0% or less, AI: 0.05-0.15%, 0:0.00
70% or less, N: 0.0100X or less, C+N: 0.0
Contains 15z or less, and further Ca: 0.002 to 0.0
22, Bj: 0.30Z or less, Pb: 0.30! Contains one or more of the following: S: 0.040Z or less, Se: 0.040"A or less, and further contains S, S
When containing one or more types of e, Te: 0.002~
0.040%, Zr: Contains one or two of 0.02 to 0.152, and the balance is Fe and impurity elements.High magnetic flux density, low coercive force soft material with excellent free machinability. Made of magnetic stainless steel.

Next, the reasons for limiting the composition of the high magnetic flux density soft magnetic stainless steel of the present invention will be explained.

C, 0,0102 or less C is an element that adversely affects magnetic properties and corrosion resistance, and in the present invention, it is desirable to reduce it as much as possible.
The upper limit was set to 0.010χ. Note that in order to further improve magnetic properties, it is desirable that the content be 0.005% or less.

Si: 0.10% or lessSi is a deoxidizing element, but it deteriorates magnetic properties, so
It is desirable to reduce it as much as possible, and the upper limit is 0.
It was set to 10χ.

Mn: 0.10X or less Since the content of Mn significantly impairs corrosion resistance and magnetic properties, it is desirable to reduce it as much as possible, and the upper limit is set at 0.10
I set it as X.

Cr; 11-132 Cr is an essential basic element for ensuring the necessary corrosion resistance, and at the same time has the effect of narrowing the temperature range of the γ phase.

In order to fully obtain the above effects, it is necessary to contain at least 11% or more. However, even if the content exceeds 13χ, the effect of improving corrosion resistance is not large and the magnetic properties are also impaired, so the upper limit was set at 13χ.

Al; 0.05~0.15X Al is an important element that makes the most of the features of the present invention,
It is the optimal element for narrowing the γ-loop region and obtaining a single phase of ferrite in the heat treatment temperature range, and is also highly effective as a deoxidizing agent.To obtain this effect, it must be contained at 0.05% or more. be. However, if the content exceeds 0.15χ, the magnetic flux density and coercive force deteriorate, so the upper limit was set at 0.15χ.

0; 0.0070% or less Since 0 lowers the magnetic flux density and worsens the magnetic properties, it is desirable to have as little as possible, but in consideration of actual manufacturability, the upper limit was set at 0.0070χ.

N: 0.0100% or less N is contained in steel as an impurity, but limiting it to 0.0100% or less is effective in improving magnetic properties, so the upper limit was set to 0.0100χ.

C+N: 0.015% or less C and N are elements that combine with Cr to form carbonitrides, lowering corrosion resistance and also deteriorating magnetic flux density and coercive force. It also has the effect of being an austenite former element and expands the T-loop region.
It is necessary to reduce the value as much as possible, and the upper limit is set to 0.0152.

Ni: 0.10% or less, Cu: 0.10X or less Although Ni and Cu are elements that improve corrosion resistance, they are austenite former elements and are elements that expand the T-loop region and deteriorate magnetic properties.

In the present invention, since the magnetic properties are the most important, it is necessary to reduce them as much as possible, and the upper limit is 0.10 for both.
It was set as χ.

Next, the reasons for limiting the composition of additive components to improve free machinability will be explained.

S, 0.040% or less S is added to improve machinability, but a large amount of S impairs cold workability as well as magnetic properties and corrosion resistance.
The upper limit was set to 0.040χ.

Se; 0.040% or less Se is added to improve machinability, but since a large amount of Se impairs cold workability as well as magnetic properties and corrosion resistance, the upper limit was set to 0.040χ.

Pb: 0.30% or less, Bi: 0.30% or less P
b. Bi is an element that improves machinability, but since a large amount of Bi impairs magnetic properties, corrosion resistance, and cold workability, the upper limit was set to 0.30χ.

Ca; 0.002 to 0.020I Ca is added to improve machinability, but in order to obtain the above effect, the content must be 0.002% or more. However, if the content exceeds 0.020χ, it will impair magnetic properties, corrosion resistance, and cold workability, so the upper limit should be set at 0.02
It was set to 0χ.

Te; 0.002 to 0.040χ Te has the effect of neutralizing the influence of S and Se on cold workability, and in order to obtain this effect, 0.002
% or more. However, the upper limit was set at 0.040χ because a large amount of Ni impairs cold workability and also deteriorates magnetic properties and corrosion resistance.

Zr; 0.02 to 0.15χ Zr is an element that makes MnS and MnSe spheroidal and improves cold workability, and must be contained in an amount of at least 0.02%. However, since a large amount of Ni impairs cold workability and also deteriorates magnetic properties and corrosion resistance, the upper limit was set at 0.15χ.

(Example) Next, the features of the present invention will be clarified by comparing them with conventional steel and comparative steel through examples. Table 1 shows the chemical composition of the test steel.

(Left below) In Table 1, steels 1 to 7 are steels of the present invention, and steels 8 to 21 are steels of the present invention.
The steel is a comparison steel, and 22!1iil is a conventional steel, Fe.
-13Cr-ISi-0,25AI steel.

The test steels in Table 1 were melted in an electric furnace, hot rolled,
Heat treatment was performed at 0°C for 2 hours at a cooling rate of 100°C/hour, and magnetic flux density, coercive force, corrosion resistance, machinability, and presence or absence of transformation to T phase at high temperatures were measured.

For the magnetic properties, a ring test piece with an outer diameter of 24 mm, an inner diameter of 16 mm, and a thickness of 16 mm was prepared as a test piece using a DC type BH) laser, and the magnetic flux density and coercive force were measured.

Regarding corrosion resistance, a salt spray test was conducted in accordance with JIS Z2371, and the rust rate was measured. If the rust rate was less than 25%, it would be ○, if it was 25% or more and less than 50%, it would be Δ, if it was 50% or more. was marked as ×.

Regarding machinability, a drilling test was performed using a test piece with a thickness of 10n+m at a rotation speed of 725r, p, m, and a load of 4kg using a high-speed steel drill with a diameter of 5mm, and the time required to drill the hole was determined. This is what was measured.

The presence or absence of transformation to the T phase at high temperatures was determined by preparing a test piece with a diameter of 3 mm and a length of 10 mm, heating it to 1000°C, and then measuring the change in size of the test piece during cooling using a Formaster tester. It is.

The measured magnetic flux density, coercive force, corrosion resistance, machinability, and presence or absence of transformation to T phase are shown in Table 2.

(Left below) Table 2 As is clear from Table 2, the 8 steels used for comparison are Cr
Because of its high content, although it has excellent corrosion resistance, it has a poor magnetic flux density; 9fiil has a low Cr content, so it has a poor coercive force due to its corrosion resistance and γ transformation;
Since 0 steel has a low AI content, its magnetic properties such as magnetic flux density and coercive force are inferior due to the influence of γ transformation, and the ill
12M has a high content of Si and AI, so its magnetic flux density is inferior, and 12M has a high content of C+N, so it has poor corrosion resistance and transforms to the T phase at high temperatures, which causes transformation strain during heat treatment, which deteriorates the magnetic properties. 13 steel is inferior to N.
i, Steel 14 has a high content of Cu, so it has poor magnetic properties due to transformation strain like Steel 14m, Steel 14 has a high Mn content, so it has poor magnetic properties like Steel 12.13, and Steel 15 has a high Mn content, so it has poor magnetic properties like Steel 12. Steels 16 to 21 have poor magnetic properties and free machinability because they have a high Cr content and no free machinability improving elements are added. Although it has excellent free machinability, it has poor magnetic flux density and corrosion resistance.

On the other hand, the conventional steel Fe-13Cr-ISi-0,25
22 steel, which corresponds to AI steel, has less Si and A than the steel of the present invention.
Since the I content is high, the magnetic flux density and coercive force are significantly inferior.

On the other hand, the steels of the present invention, grades 1 to 7, do not undergo T-phase transformation, have a magnetic flux density of 14,000 G or more, and a coercive force of 0.
500. It has significantly superior magnetic properties compared to conventional steels, as well as superior corrosion resistance and free machinability.

(Effects of the Invention) As detailed above, the high magnetic flux density, low coercive force soft magnetic stainless steel with excellent free machinability of the present invention ensures corrosion resistance by adding the necessary minimum amount of Cr, and has austenitic former. - By reducing all elements as much as possible and adding a small amount of AI, which is a ferrite former element, T
It has become possible to perform heat treatment at 800°C or higher to reduce the loop area and completely eliminate processing distortion without causing transformation, and it has become possible to significantly improve both magnetic flux density and coercive force compared to conventional steel. , and also has excellent free machining properties. Therefore, the present invention enables miniaturization of magnetic circuits such as electromagnetic valves, and has high practicality in industry.

Claims (1)

[Claims] 1. Weight ratio: C: 0.010% or less, Si: 0.1
0% or less, Mn: 0.10% or less, Ni: 0.10% or less, Cr: 11-13%, Cu: 0.10% or less, Al
: 0.05-0.15%, O: 0.0070% or less, N
: 0.0100% or less, C+N: 0.015% or less, further Ca: 0.002 to 0.02%, Bi: 0
．． 30% or less, Pb: 0.30% or less, S: 0.040
% or less, Se: 0.040% or less, and when containing one or more of S and Se, Te: 0.002 to 0.040%, Zr: 0. 0
Contains one or two of 2 to 0.15%, and the remainder is F.
A soft magnetic stainless steel with high magnetic flux density and low coercive force that has excellent free machinability and is characterized by consisting of E and impurity elements.