JPH0758536B2 - Magnetic recording steel material and manufacturing method thereof - Google Patents

Description

The present invention relates to an information recording medium utilizing magnetism, particularly a magnetic recording steel material suitable for use under severe conditions such as a high temperature environment and a corrosive environment, and its production. It is related to the method, and specifically, it can be used for industrial applications such as control sensors for various automation devices and material tracking in factories, as well as for consumer applications where durability and record protection are strongly required. The present invention relates to a magnetic recording steel material and a manufacturing method thereof.

(Prior Art) Information media that use magnetism, such as magnetic tapes and magnetic cards, are widely used for recording information. This is because the recording / reproducing system is easy to adapt to automation, and easy to manufacture and inexpensive. Yes, and because it is highly reliable. In addition, compared with printing, which has been an information recording means for a long time, the recording capacity is large and the confidentiality is high because the recorded contents are not visible, which is also an advantage.

Generally, a magnetic tape or a magnetic card is made of plastic or paper as a base material and magnetic powder such as ferrite is applied onto the base material. As the base material, appropriate rigidity, mechanical strength, water resistance, chemical resistance, processability, printability, etc. are required,
Various materials are selected according to the purpose. Currently, plastic films and sheets are the mainstream because of their ease of handling and cost. As a magnetic material, γ-Fe ₂ O
Ferrite powders such as ₃ are often used, and various technological developments are being made to increase recording density. Also,
In order to prevent loss of recording and accidental loss of recording due to contact with products that use permanent magnets, studies are underway on magnetic materials with high coercive force. In addition to magnetic properties, wear resistance and external appearance properties of magnetic materials are a problem.

On the other hand, although not as flashy as for consumer use, attempts to apply magnetic recording are being actively made in various industries such as manufacturing. For example, in order to operate or control an automated device such as a robot, it is necessary to detect a length, an angle, and a position, and a magnetic scale is being considered as the sensor. As the magnetic scale, a magnetic tape on which an information pattern is recorded is partly put to practical use, like a magnetic tape. However, since the Curie point of ferrite (the temperature above which it loses magnetism) is low, the operating temperature is usually limited to 50 ° C or lower.

In the manufacturing industry, automation of material tracking in factories is also a major issue. For this reason, a bar code type material identification method has been studied, and a ceramic thin film bar code seal has been developed for high temperatures. However, since these basically perform optical detection, they cannot be used if the surface changes due to wear or dirt. In addition, paper perforated tape is still the mainstream for controlling NC lathes, but this is largely due to the fact that magnetic recording is susceptible to external magnetic fields and heat and has a problem with reliability. is there.

(Problems to be Solved by the Invention) Although magnetic recording has many advantages over optical and mechanical recording, it is not always fully utilized for industrial use. This is because industrial use requires higher reliability than consumer use, but the environment in which it is used is poor and there is no recording medium that can withstand it.

The first problem with environmental resistance is heat resistance.
As described above, ferrite, which is often used as a recording medium, cannot be used at high temperatures due to its characteristics. Also, the base material itself cannot be used at high temperatures, such as paper and plastic. From this point, the metal material is most suitable.

Further, for industrial use, it is often used in an environment where corrosion and wear are severe, and conventional recording media cannot handle it. Also in this respect, metallic materials are advantageous, and austenitic stainless steel shows good corrosion resistance.

Japanese Patent Publication No. 62-32407 proposes that the surface of a metal material is locally heat-treated to form a magnetically altered portion, which is used for displacement detection. However, the means for providing the magnetically altered portion disclosed herein is a heat treatment of heating and quenching at a temperature below the melting point, and the difference in magnetic characteristics between the treated portion and the untreated portion is not so large. Moreover, when heat is applied, the metal structure (precipitate or strain) produced by the rapid cooling changes, and the difference becomes smaller. In addition, in order to increase the difference in magnetic characteristics, the metal material is expensive Ni Ag (Fe25%-
This method is unsuitable for stable production of a recording body that is inexpensive and has excellent magnetic characteristics, such as the need to use Ni75% alloy).

The present inventors have succeeded in producing a magnetic displacement portion by using a Fe-based material different from the magnetic recording body disclosed in Japanese Patent Publication No. 62-32407 and melting a part of the material. , Previously filed as Japanese Patent Application No. 60-225737.
62-83620). The invention of this prior application is that cold-plastic working is performed on metastable austenitic stainless steel to cause processing-induced transformation to convert it into a ferromagnetic material, and this is irradiated and melted with a high energy density beam to locally become a non-magnetic material. After conversion, a magnetic scale (magnetic scale) is constructed using this non-magnetic-ferromagnetic pair. This principle can also be applied to recording information. This utilizes the phase change in the cold-worked state and the melt-processed state in the metastable austenitic stainless steel. The difference in characteristics is extremely large. However, in this method as well, when heat of 300 to 400 ° C. or higher is applied, the work-induced martensite generated by the cold working is decomposed into austenite again, so that the recording is left open.

As described above, the conventional method does not always have sufficient heat resistance, and in general, when a heat history exceeding 300 ° C. is received, the recording is usually rapidly lost. Further, as seen in the method of Japanese Patent Publication No. 62-32407, the S / N ratio of the output signal is often low, which requires a high level of detection technology.

In view of the above situation, the present invention is a magnetic recording medium that can withstand a high temperature of 300 ° C. or higher, and has excellent corrosion resistance and wear resistance, and that has a high S / N ratio of the output signal and is easy to detect at low cost. The purpose is to provide.

(Means for Solving the Problems) It is generally known that the magnetic properties of metallic materials change depending on the type and composition of alloy elements or the metallurgical structure. In a simple metal, only Fe, Ni, and Co exhibit ferromagnetism. In practical steel, carbon steel and ferritic stainless steel are ferromagnetic, and austenitic stainless steel is usually nonmagnetic.

The invention of JP-A-62-53620, mentioned above, records information by applying this principle to a ferromagnetic base material to locally make it a non-magnetic structure. However, this method does not have sufficient heat resistance. This is because, as described above, the ferromagnetism of the base material was obtained as a result of cold-working metastable austenite to generate work-induced martensite, and thus returns to non-magnetic austenite when heat is applied. Because. In addition, when detecting the difference in magnetic characteristics, compared to the case where there is a local non-magnetic part in the ferromagnetic base material,
In general, a non-magnetic substrate having a ferromagnetic portion is easier to detect and has a higher S / N ratio.

Therefore, in order to improve heat resistance and detection sensitivity, the inventors of the present invention irradiate a steel material having different kinds of metals adhered to the surface layer of a non-magnetic substrate with a high-density energy beam, and the composition itself of the portion. Various studies were carried out on the method of changing.
As a result, it was revealed that there is an appropriate combination of the base material and the surface layer member and an appropriate thickness of the surface layer member.
Therefore, the gist of the present invention is the following method of manufacturing a magnetic recording body with a magnetic recording body.

Heat resistance characterized by comprising a base material of austenitic stainless steel and a chromium layer on its surface, and a predetermined local part of the surface is a ferromagnetic material formed by melting and homogenizing the base material and the chromium layer. Magnetic recording steel with excellent corrosion resistance.

After depositing chromium having a thickness t (μm) satisfying the following formula on the surface of austenitic stainless steel,
A method for producing a magnetic recording steel material having excellent heat and corrosion resistance, which comprises irradiating a predetermined position on the surface with a high energy density beam to locally melt the beam and making the part ferromagnetic.

Here, X and Y are the Ni equivalent and Cr equivalent of the austenitic stainless steel, respectively, and D is the average penetration depth (μm) after the beam irradiation.

(Operation) First, the basic concept of the present invention will be described with reference to FIG.

FIG. 1 (a) is an enlarged cross-sectional view of the surface local portion showing a state in which the chromium layer 2 is formed on the surface of the austenitic stainless steel base material 1. When a high energy density beam is irradiated onto a predetermined part of this surface to melt it, as shown in FIG. 1 (b), the austenitic stainless steel of the base material and the chromium layer are melt-mixed and the Cr content is high. A portion 3 made of ferromagnetic ferritic stainless steel is formed.

That is, when a high energy density beam is irradiated onto a steel material having a non-magnetic austenitic stainless steel surface with a certain appropriate thickness of Cr, that portion is melted and changed to a ferromagnetic ferritic stainless steel, and the magnetic properties Produces different parts of. Information is recorded by irradiating a beam in accordance with a target pattern, and the information is read by detecting this pattern by an inductive sensor system using a magnetic head as shown in FIG. 1 (c).

The base material of the base may be any non-magnetic austenitic stainless steel. Base material cost
Considering to make the required thickness of the Cr layer as thin as possible,
Although SUS 201 and SUS 301 systems having a low Ni content are advantageous, they need to be careful because they tend to form work-induced martensite and become ferromagnetic when they are cold-worked.

Chromium in the surface layer is necessary for producing partially ferromagnetic ferritic stainless steel by irradiation with a high energy density beam. Fe may be considered for the same purpose, but since Fe itself is magnetic, it needs to be removed in a later step and is not suitable. Al and Si are also ferrite-forming elements,
Easy to oxidize and difficult to process.

The thickness of chromium in the surface layer portion depends on the Ni equivalent and Cr equivalent in the austenitic stainless steel of the base material and the penetration depth after beam irradiation, and there is an appropriate range. The lower limit thickness is necessary to stably produce ferritic-stainless steel in the beam irradiation area, and if it is less than the lower limit, a sufficient S / N ratio cannot be obtained. On the other hand, the upper limit is necessary to make the composition of the locally melted portion formed by beam irradiation uniform, and if the upper limit is exceeded, the S / N ratio also deteriorates.

The method of determining the upper limit and the lower limit of the chromium layer thickness will be specifically described below.

FIG. 2 is a diagram schematically showing the cross-sectional shape of the fusion zone by beam irradiation.

In FIG. 2, where t: thickness of chromium layer (μm) D _M : maximum penetration depth (μm), the average penetration depth (μm) is: A × D _M

Here, A is a coefficient depending on the cross-sectional shape of the fusion zone, and if the cross-section of the fusion zone is completely rectangular, A = 1.0, and if it is triangular, A = 0.5.
Is. Since the actual cross-sectional shape is in the middle of this range, A is usually in the range of 0.6 to 0.9.

The main factors that determine the metallographic structure of stainless steel are the Ni and Cr contents. The former is an austenite-stabilizing element, the latter is a ferrite-stabilizing element, and in terms of suppository, the dimension is a non-magnetizing element and the latter is a ferromagnetizing element. Regarding components other than Ni and Cr, it is divided into austenite stabilizing element group and ferrite stabilizing element group, and taking into account the degree of each action effect, Ni equivalent and Cr equivalent are defined as follows. There is.

Ni equivalent (%) =% Ni + 30 ×% C + 0.5 ×% Mn Cr equivalent (%) =% Cr +% Mo + 1.5 ×% Si + 0.5 ×% Nb (% indicates weight%.) Diagram showing the relationship between the Ni equivalent and Cr equivalent and the organization (from the Nikkan Kogyo Shimbun "Stainless Steel Handbook").

Now, assuming that the Ni equivalent of the base material is X% and the Cr equivalent is Y%, the average Ni equivalent and Cr equivalent of the melted portion are considered to be that the chromium layer on the surface melts uniformly, Becomes

It is considered that the presence of 50% or more of ferrite is necessary for the fused part to become ferromagnetic. When this condition is seen in FIG. 3, it is the area below the line a. Straight line a Therefore, the area under the straight line b is Ni equivalent ≦ [Cr equivalent −10] /1.65 ・ ・ ・, and by substituting the formula and the Ni equivalent and Cr equivalent of the formula into this formula, Becomes

On the other hand, regarding the upper limit of the chromium layer thickness t, since the Curie point of the fusion zone needs to be room temperature or higher, Cr (%) ≤ 65 based on Fig. 4 (from Asakura Shoten "Magnetic Handbook") ... .... By substituting the Cr equivalent (%) of the equation into this equation, Becomes

From Fig. 3, it is 10% to produce 50% or more of ferrite.
Since the above Cr equivalent is required, when this value is used, t ≦ 0.6 × ...

Since elements other than Cr also affect the Curie point,
Strictly speaking, there is a problem in substituting the Cr equivalent of the formula into the Cr (%) of the formula. However, for Ni, the main element, the Curie point tends to increase when diluted with Cr,
There is no problem because it is on the stable side. The content of other elements is small, and in practice, there is no problem in using the formula or the formula.

The method for adhering chromium to the surface of the base material may be any method such as electroplating, vapor deposition, laminating a chrome foil, and rolling clad. At present, electroplating is most desirable in consideration of the ease of adjusting the thickness and the manufacturing cost.

The high energy density beam may be a laser beam, an electron beam, a plasma beam, or the like, but it is practical to use a laser beam that does not require a vacuum device.

The penetration depth can be controlled by changing the energy density of the beam, and can be selected according to the shape of the steel material and the purpose of use.

Information can be read using a magnetic head to detect magnetic flux by applying high frequency and electromagnetic induction, or after magnetically detecting a magnetic flux using a Faraday element, or by detecting leakage magnetic flux with a Hall element. It is possible.

(Example) As the base material, a cold rolled sheet of 1 mm thick of typical austenitic stainless steels SUS 301 and SUS 316 was solution-treated at 1100 ° C. Chromium layers of various thicknesses were electroplated on the surface of these substrates. Then, using a single mode carbon dioxide gas laser oscillator, a beam was oscillated with an output of 100 w, and the light was focused on a diameter of 100 μm by a lens and irradiated on the surface of the steel sheet. The feed rate of the steel sheet was scanned at 5 m / min and a pitch of 0.5 mm, and a linear pattern having an average penetration depth () of 30 μm was recorded.

A sample of the thus-obtained recording medium as it was irradiated with laser and 50
The S / N ratio of the sample after heating at 0 ℃ was evaluated by applying a high frequency of 900 kHz by the inductive sensor method, detecting the magnetic flux due to electromagnetic induction. The results are shown in Table 1.

In Comparative Example 1 in Table 1, austenitic stainless steel (SUS 301) was cold-rolled and irradiated with a laser beam to a base material which was made ferromagnetic by the work-induced transformation to locally melt it to make it non-magnetic. And is equivalent to that proposed in JP-A-62-83620. Comparative example 2 is Japanese Patent Publication No. 62-
According to the method disclosed in Japanese Patent No. 32407, 25% Fe-7
It is a heat treatment by irradiating a laser beam of a Ni-based alloy of 5% Ni.

From the test results in Table 1, it is apparent that the samples corresponding to the examples of the present invention have excellent S / N ratio even after heating at 500 ° C. and have excellent heat resistance. In Comparative Example 1, before heating, an S / N ratio comparable to that in Part 1 of the present invention was obtained. This is because the difference between ferromagnetism and non-magnetism is detected in principle, as in the example of the present invention. However, since the base material is ferromagnetic, it does not reach the high S / N ratio level obtained by the present invention. Further heating to 500 ° C will result in the loss of any records. This is because the work-induced martensite, which supports the ferromagnetism of the substrate, becomes austenite and becomes specific magnetism.

Comparative Example 2 merely utilizes the difference in the metal structure (which is considered to be the difference in precipitates and strain) due to the rapid cooling after the laser beam irradiation, so the S / N ratio before heating is small. Not only that, but the record disappears due to heating. On the other hand, in the example of the present invention, since the difference in magnetic characteristics based on the difference in the metal structure itself between the base material and the laser beam irradiation portion is utilized, a high S / N ratio can be obtained even at high temperature. That is,
The magnetic recording material of the present invention can withstand temperatures up to the melting point of the material in principle.

It can be said from the results shown in Table 1 that the thickness of the chromium layer on the surface desirably satisfies the condition described in claim 2.

(Effects of the Invention) The magnetic recording steel material of the present invention has higher heat resistance and S / N ratio than the magnetic recording bodies known so far, and has excellent corrosion resistance and wear resistance in terms of material properties. Is also excellent. Further, due to the characteristics of magnetic recording, the confidentiality of the recorded contents is high, and the protection of the recording against an external magnetic field is extremely high. Therefore, the industrial application range is very wide as an industrial magnetic recording medium which is subject to severe environmental changes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining the basic concept of a magnetic recording steel material of the present invention, (a) is a cross-sectional view of a state in which a chromium layer is attached to a base material, and (b) is Sectional drawing which formed the fusion | melting part (ferromagnetic part) locally, (c) is a figure which shows a recording detection method. FIG. 2 is an enlarged sectional view of the fusion zone. FIG. 3 is a diagram showing the relationship between the Ni equivalent and the chromium equivalent and the metallurgical structure. FIG. 4 is a diagram showing the relationship between the Cr content and the Curie point in the Fe—Cr binary system.

Continuation of front page (56) Reference JP-A-63-259413 (JP, A) JP-A-57-20921 (JP, A) JP-B 1-32448 (JP, B2)

Claims (2)

[Claims] 1. A base material of austenitic stainless steel,
A magnetic recording steel material having excellent heat and corrosion resistance, comprising a chromium layer on the surface thereof, and a predetermined local portion of the surface being a ferromagnetic material formed by melting and homogenizing a base material and a chromium layer. 2. A surface of austenitic stainless steel,
After depositing chromium having a thickness t (μm) satisfying the following formula, a high energy density beam is irradiated to a predetermined position on the surface to locally melt it, and the part is made ferromagnetic. A method of manufacturing a magnetic recording steel material having excellent heat and corrosion resistance. Here, X and Y are the Ni equivalent and Cr equivalent of the austenitic stainless steel, respectively, and D is the average penetration depth (μm) after the beam irradiation.