JPS61130459A - High-hardness non-magnetic shaft having superior corrosion resistance - Google Patents

Abstract

PURPOSE:To improve surface hardness, non-magnetic properties, and corrosion resistance, by incorporating prescribed percentage of C, Si, Mn, Ni, Cr, N, and Fe and by carrying out rolling and working under prescribed conditions. CONSTITUTION:The steel consisting of, by weight, 0.1-0.5% C, <=0.6% Si, 14-20% Mn, 0.3-2% Ni, 16-18% Cr, 0.04-0.4% Ni, and the balance Fe is refined. The steel is hot-rolled at 1,000-1,050 deg.C and cooled at >=15 deg.C/sec cooling rate. The cooled steel stock is subjected to cold wire drawing, and the resulting wire rod is subjected to cold shearing with a cutting edge and then to cold compression forming by use of rolls. In this way, the high-hardness non-magnetic shaft having >=Hr500 surface hardness, <=1.01 permeability and superior corro sion resistance can be obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a high hardness non-magnetic shaft with excellent corrosion resistance, especially for use in video tape recorders, video cameras, video tape cassettes, and audio recording devices (VTRs). Surface hardness of Hv 500 or more, used as various shafts in devices that utilize magnetism (hereinafter sometimes simply referred to as "magnetic devices") such as tape recorders, audio discs, direct drive motors, computer storage devices, etc. The present invention relates to a highly hard non-magnetic shaft having a magnetic permeability of 1°01 or less and excellent corrosion resistance.

(Prior Art) The shafts used in devices that utilize magnetism as described above include cylinder shafts, capstan shafts, guide shafts (guides, guide balls, guide pins, guide rollers, etc.) used in VTRs, and even There are rotating shafts of magnetic disks (hereinafter collectively referred to as "shafts" in this specification), and strict requirements are placed on them not only in terms of magnetic properties but also in mechanical properties.

For example, a cylinder shaft used in a VTR is assembled integrally with a magnetic head, and transmits rotation from a motor directly connected to the cylinder shaft to the magnetic head. In this case, when the strong magnetism of the motor is induced into the cylinder shaft, it destabilizes the magnetism of the magnetic head directly connected to it, causing distortion in the recording and playback of images and sounds. In order to prevent such magnetic induction, non-magnetic properties are important for the cylinder shaft. Furthermore, when the cylinder shaft wears out, uneven rotation occurs, making the running of the magnetic tape unstable and distorting recording and playback. In order to minimize shaft wear, excellent mechanical properties such as shaft surface hardness are required.

The capstan shafts of video tape recorders and audio tape recorders run in direct contact with the magnetic tape. on the other hand,
The capstan shaft of a direct drive motor rotates due to changes in the strong magnetic field of the motor that is directly connected to this shaft. Therefore, in any case, if magnetism is induced in the capstan shaft or magnetic flux remains, the memory of the magnetic tape that comes into contact with it will be disturbed.

Note that an oil-impregnated alloy metal is used to support the rotation of the capstan shaft, but if the metal contact surface of this shaft wears out, the rotation of the shaft becomes uneven and the running of the magnetic tape becomes unstable. This is fatal for a high quality magnetic device.

Magnetic tape guide shafts such as guides, guide poles, guide bins, and guide rollers for VTRs, VTR cameras, and VTR cassettes come into direct contact with the magnetic tape, so they not only need to be non-magnetic, but also must be non-magnetic. The guide shaft must be resistant to sliding wear as the tape slides at high speed, and if the shaft is scratched, the contact tape will also be scratched, so it must be resistant to sliding wear and less susceptible to scratches. be done.

Similarly, magnetic disks in audio equipment, floppy disks in computers, and electronic still cameras use magnetic disks. The rotating shaft of the magnetic disk and the guide shaft of the magnetic head of this device are required to have excellent non-magnetism and resistance to sliding wear.

In recent years, devices using magnetism have made remarkable progress, and the required characteristics have become increasingly strict. Currently, the target properties for a non-magnetic shaft are a magnetic permeability of 1.01 or less and a surface hardness of Hv 500 or more.

That is, the guide shafts of devices that use magnetic tapes, magnetic disks, and magnetic heads, and the rotating shafts of direct drive motors that rotate in strong magnetic fields, are designed to minimize magnetic induction and residual magnetic flux density. Upper magnetic permeability is 1.01
It is necessary that the following is true.

At the same time, rotating shafts such as cylinder shafts and direct drive capstan shafts that are directly connected to motors need to minimize sliding wear on their contact surfaces with metal. moreover,
The guide shaft that guides the magnetic tape needs to minimize sliding wear on its contact surface with the tape. For this reason, shafts for magnetic devices are required to have high surface hardness, and practically require a Vickers hardness of Hv 500 or more.

By the way, devices using magnetic tapes, magnetic disks, magnetic heads, etc. must be free from rust. Rust peels off easily and has residual magnetism.

This is because if the rust that develops on the shaft peels off and adheres to the tape, disk, or head, recording and playback will be disrupted and become unstable. Furthermore, if the peeled rust adheres to the rotating or sliding parts of the shaft, the shaft will be more likely to wear out. On the other hand, if it adheres to the tape, it may cause scratches on the tape, so it is particularly required to have excellent corrosion resistance and resistance to induction. For example, 60℃, 9
Excellent corrosion resistance (herein, unless otherwise specified, such corrosion resistance is simply referred to as "corrosion resistance") is required, with no slight rust occurring even after 100 hours of storage in a 5% constant temperature and humidity chamber.

That is, the temperature of the shaft for a magnetic device increases during operation, and decreases when the device is stopped. It is also affected by the rise and fall of the outside temperature. If the temperature of the shaft suddenly drops, water vapor in the outside air may condense and moisture may adhere to it. Rust that occurs as a result disturbs magnetic acquisition and reproduction and inhibits smooth rotation and sliding, so moisture and humidity must not cause rust. It is necessary to have corrosion resistance that does not cause rust even under the atmospheric conditions of the natural environment, such as high temperature (60°C) and high humidity (95%).

Conventionally, the shaft used for such applications is SUS 30, which is non-magnetic, has a magnetic permeability of 1.01 or less, has high surface hardness, and has excellent corrosion resistance.
4, SO5305, 5IIS 316 (7) Manufactured from austenitic stainless steel or high Mn austenitic steel.

S [IS 304.5 IJS 305, SO5316
Although it has excellent corrosion resistance, when trying to impart non-magnetic properties with a magnetic permeability of 1.01 or less, it becomes soft with a hardness of Hv 320 or less. When hardened as much as possible to obtain wear resistance, 5IIS 304 already has a magnetic permeability of 2.5 or more at Hv 370, SOS 305 has a magnetic permeability of 1.03 or more at Hv 340, and SUS 316 has an Ilv 380.
The magnetic permeability is high, with a magnetic permeability of 1.02 or more, and the magnetic permeability is 1.02.
It is not possible to obtain a shaft that is non-magnetic with a surface hardness of 0.01 or less and has wear resistance with a surface hardness of Hv 500 or more.

By the way, a non-magnetic shaft with excellent wear resistance, a surface hardness of Hv 500 or more, and a magnetic permeability of 1.01 or less can be obtained from high Mn steel. It rusts easily, making it impossible to obtain a shaft with excellent corrosion resistance.

(Problems to be Solved by the Invention) The object of the present invention is to provide a material with excellent corrosion resistance,
Another object of the present invention is to provide a shaft for a magnetic device that has excellent nonmagnetic properties and mechanical properties, such as a magnetic permeability of 1.01 or less and a surface hardness of Hv 500 or more.

(Means for Solving the Problems) The inventor of the present invention continued his intensive research to achieve the above-mentioned purpose, and found that among many non-magnetic steels, those with a specific composition have particularly excellent corrosion resistance and work hardening ability. They discovered this and completed the present invention.

That is, the gist of the present invention is, in weight %, c: 0.10-0.50%, Si: 0.60
% or less, Mn: 14-20%, Ni: Q
, 3-2.0%, Cr: 16-18%, N
: Made of steel having a composition of 0.04 to 0.4%, the balance Fe and unavoidable impurities, and hot rolled at a temperature of 1050°C or higher, 15°C/ Surface hardness Hv 500 or more and magnetic permeability 1.01 or less obtained through cooling at a cooling rate of sec or more, cold wire drawing, cold shear cutting with a shear blade, and cold compression processing with a roll. This is a highly hard, non-magnetic shaft with excellent corrosion resistance.

As described above, according to the present invention, high plastic deformation is applied to the shaft surface by applying cold shear cutting with a shear blade and cold compression processing with a roll to a cold drawn steel wire. A layer with a thickness of over 500 Hv is cold compressed.
A high surface hardness of ~570 can be obtained, and a surface hardness of Hv 500 or higher, which is necessary for the required sliding wear resistance, can be obtained.

According to one aspect of the present invention, the steel has the above-mentioned composition.
This is a magnetic tape guide shaft with excellent corrosion resistance, a surface hardness of Hv 500 or more, and a magnetic permeability of 1.01 or less.

According to yet another aspect, the steel has the above-mentioned composition, has excellent corrosion resistance, has a surface hardness of lv 500 or more, and has a magnetic permeability of 1.
This is a cylinder shaft for driving a magnetic device of 01 or less.

In addition, according to yet another aspect, having the above steel composition,
This is a capstan shaft for magnetic tape with excellent corrosion resistance, a surface hardness of Hv soo or more, and a magnetic permeability of 1.01 or less.

(Function) (13 Characteristics of steel composition: As mentioned above, in the present invention, the content of Mn and Cr is high (contains Ni and N, so it can be made into a stable austenitic system, and Surface hardness Hv 50 due to processing
Even when the axis is 0 or more, the magnetic permeability is generally 1.002 to 1.
, 008, which is non-magnetic and fully satisfies the objective of the present invention, which is a magnetic permeability of 1.01 or less.

Furthermore, the C content is 16% or more, and at 60℃, 95%
Even if kept in a constant temperature and humidity chamber for 100 hours, the diameter remains 0°5 μm.
It is a shaft with excellent corrosion resistance that does not cause even the slightest rust.

The reason why the steel composition is limited as described above in the present invention is as follows.

C (Carbon) C is an element that stabilizes austenite and at the same time contributes to solid solution strengthening, and in the present invention, it must be contained in an amount of 0.10% or more to ensure strength. On the other hand, 0.5
If it exceeds 0%, a large amount of carbide will precipitate at the austenite grain boundaries, which will deteriorate the ductility of the wire and lead to a decrease in cold workability and corrosion resistance. Therefore, in the present invention, the C content is limited to 0.10 to 0.50%.

Si (Silicon) Si is normally added to molten steel as a deoxidizing agent during the refining process, but if it exceeds 0.60%, nonmetallic inclusions will increase and the cleanliness of the steel will deteriorate, so the upper limit should not be exceeded. It was set at 0.60%.

Mn (Manganese) Mn has the effect of stabilizing the austenite structure at low cost, but in the present invention, it is an element necessary to make the steel non-magnetic. For this purpose, it is necessary to contain 14% or more. On the other hand, since sufficient improvement cannot be obtained even if it exceeds 20%, the present invention sets it at 14 to 20%. Further, a more desirable range is 15 to 18% to further satisfy both nonmagnetism and corrosion resistance.

Ni) Ni is an effective element for stabilizing the austenite structure and improving corrosion resistance, and for the purpose of the present invention, it is necessary to add at least 0.3% or more. However, if it exceeds 2.0%, it is not only undesirable for stabilizing the austenite composite fibers, but also increases costs.

Therefore, in the present invention, the upper limit of the Ni content is set to 2.0
%. Preferably, 1. It is O~2.0%.

Cr (Chromium) Cr makes the austenite structure of steel containing Mn-Ni extremely stable, and has the effect of increasing work hardening ability by reducing the H1 layer defect energy. In the present invention, in order to improve corrosion resistance in addition to these effects, the content must be 16% or more. But 18%
If it exceeds this, no further improvement in the above effect will be observed.

Therefore, in the present invention, the content of C' is 16 to 18
%. In such a narrow range, particularly excellent effects can be obtained as a non-magnetic shaft.

N (M element) Like C, N is an element that stabilizes the austenite structure and at the same time contributes to solid solution strengthening. N also has the effect of improving stress corrosion cracking resistance, and for this purpose, in the present invention, it is necessary to contain it in an amount of 0.04% or more. This allows N to stabilize the austenite structure and improve corrosion resistance.
It is also possible to avoid adding a large amount of expensive elements such as i.

On the other hand, a high Nm content exceeding 0.4% is undesirable because it may cause defects due to blowholes in the cast steel ingot. Therefore, the N content is 0.04-0.4%
It was determined that

(2) Features in terms of magnetic properties and mechanical properties: According to the present invention, hot rolling is performed at a temperature of 1000°C or higher and 1050°C or lower, and then cooling is performed at a cooling rate of 15°C/second or higher. This is because when hot rolling a high alloy steel such as the steel used in the present invention, it is necessary to dissolve precipitates such as carbides into the matrix again, so the steel is heated to a high temperature within the above range.

In addition, carbides such as Mn and Cr are likely to precipitate in such high alloy steel, and the precipitation of these carbides cannot be avoided unless the wire is forcedly cooled at a rate of 15°C/sec or more after winding. That's because there isn't. Precipitation of these carbides causes a decrease in ductility, cold workability, and corrosion resistance.

The hot rolled wire rod thus obtained is cold drawn, and the cold drawn steel wire is subjected to cold shear cutting and cold compression processing using rolls. Through a series of such cold workings, it is possible to obtain a surface hardness of Hv 500 or more, and even in that case, the magnetic permeability is 1.01 or less, which is satisfactory as a non-magnetic shaft for a magnetic device. It has characteristics.

Next, the present invention will be further explained by examples.

Example electric furnace: C: 0.10-0.50%, St: 0.
60% or less.

Mn: 14-20%, Ni: 0.3-2.0%
, Cr: 16-18%, N: 0.04-0.4
After melting a steel ingot with the chemical composition of Experiment N [L1 to 4 in Table 1, which contains % Fe and some unavoidable impurities, Hot rolling was carried out at a cooling rate of I5°C/sec after rolling.
The wire rod having a diameter of 5.511II11 cooled at the above cooling rate was cold drawn into a wire having a diameter of 2.72 m+e.

A wire with a diameter of 2.72 mm was subjected to cold plastic shearing with a shearing blade, and then subjected to cold compression plastic processing with a roller, and straight flea 2.
I made a 60mm shaft.

The thus obtained shaft according to the present invention and conventional shafts (indicated by experimental fish 5 to 10 in Table 1) were compared in terms of their magnetic properties, surface hardness, and corrosion resistance.

The results are also summarized in Table 1, but the corrosion resistance test was 6
The shafts were immersed for 100 hours in a constant temperature and humidity chamber at 0°C and 95%. After the test, shafts with no trace of rust with a diameter of 0.5 μm are marked with an ○, and shafts with poor corrosion resistance and easy to rust are marked with an X. Shown.

Among the conventional shafts, the shafts in experiments 11h5 and 6 were susceptible to rust (they could not actually be used.The shafts in experiments 7 to 10 had a hardness of H).
When v is as low as 400 or less, a shaft with magnetic permeability of 1.02 or more and the required hardness and non-magnetic properties cannot be obtained.

However, the shafts according to the present invention (experiments 1 to 4) have excellent corrosion resistance, do not rust, and have a surface hardness of H
v 513-539, suitable for sliding wear resistance requirements. It can be seen that it is non-magnetic, with a magnetic permeability of 1.002 to 1.008, and is especially suitable for use as a non-magnetic shaft used in magnetic devices.

Claims (1)

[Claims] In weight%, C: 0.10 to 0.50%, Si: 0.60% or less, M
n: 14-20%, Ni: 0.3-2.0%, Cr: 1
6 to 18%, N: 0.04 to 0.4%, balance Fe and unavoidable impurities, and hot rolling at a temperature of 1000°C or higher and 1050°C or lower; After cooling at a cooling rate of 15°C/sec or more, cold wire drawing, cold shear cutting with a shear blade, and cold compression processing with a roll, the surface hardness is Hv500 or more and the magnetic permeability is 1. A high hardness non-magnetic shaft with excellent corrosion resistance, characterized by a hardness of .01 or less.