JPS6143423B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing an A-base alloy plate for magnetic disks, and in particular, (1) reduces non-metallic inclusions and intermetallic compounds in the matrix and uniformly and finely disperses them, and (2) improves the quality of the matrix. The macrostructure is made uniform and fine, and it can be easily cut and polished to provide a disk base with excellent smoothness.
The present invention relates to a method for manufacturing an A-base alloy plate for magnetic disks. The magnetic disk substrate, which is most commonly used as a storage medium in electronic computers, has a structure in which the surface of an A-based alloy plate is cut to a predetermined thickness, and then a thin magnetic film is coated on the precision-polished or precision-cut surface. By magnetizing this magnetic thin film, signals are stored. This type of magnetic disk substrate is generally required to have the following characteristics. (1) In order to maintain a constant gap between the magnetic head and the magnetic disk base and stabilize the memory response characteristics, the surface accuracy after precision polishing or precision cutting must be good. In other words, there should be little distortion or slight waviness in the entire base. (2) There are few and small surface defects such as protrusions and holes that have an adverse effect on maintaining a constant thickness of the magnetic thin film. Also, even if the defects are minute, they do not form an aggregate. (3) It must be able to stably perform cutting and polishing when manufacturing the base, and have sufficient mechanical strength to withstand high-speed rotation during use. (4) Be non-magnetic and lightweight. (5) Good corrosion resistance and a certain degree of heat resistance. On the other hand, the AA standard 5086 alloy is currently the most commonly used substrate for magnetic disks, but in recent years there has been an increasingly strong demand for larger capacities and higher densities for magnetic disks, and the magnetized area per bit has become smaller and smaller. As the magnetic disks become more compact, it is desired to reduce the thickness of the magnetic film and the gap between the magnetic head and the magnetic disk. However, the above-mentioned AA5086 alloy is not suitable for high density in terms of surface precision and surface defects among the above-mentioned properties. Under the above-mentioned circumstances, the present inventors first conducted research to find out the reason why good surface precision could not be obtained, and the following facts were confirmed. [A] When the surface of conventional disk bases is precisely polished, they elongate in a direction parallel to the rolling direction of the material, with a period of about 0.5 to 2 mm and a maximum height of 0.10 to 0.15.
There was slight waviness on the order of μRmax. When we investigated the cause of this, we found the following. (1) The period of micro-waviness after surface polishing of the disk base corresponds to the macrostructure, and the rougher the macrostructure, the larger the height of the micro-waviness. (2) - One of the causes of the formation of a coarse macrostructure in the normal DC casting method (ingot thickness of approximately 300 to 600 mm) is the roughness of the substructure of the ingot (uneven distribution of intermetallic compounds). If the ingot structure is made finer, the macrostructure of the product will also be made finer, reducing minute waviness. (2) - Another reason why a coarse macrostructure is formed when rolling from a normal ingot is as follows. The macrostructure after hot rolling is usually a structure in which the crystal grains at the initial stage of hot rolling are elongated. In other words, recrystallization during hot rolling is dynamic recrystallization, and even if the working amount is small, recrystallization occurs one after another, so even if the individual recrystallized grains are fine, they are very different from the grain size at the initial stage of hot rolling. There is a close relationship, and recrystallized grains with slightly different orientations exist within the initial elongated grains. Therefore, in order to reduce minute waviness using a normal casting method, it is necessary to control the casting conditions and hot rolling conditions to make the macrostructure fine. [B] In the disk base made of AA5086 alloy, there are many intermetallic compounds with a diameter or length of about 15 μm in the matrix, and these intermetallic compounds are mainly composed of A-Fe-Mn eutectic compounds and Mg. ₂ Si-based eutectic compounds. These compounds are discontinuous with the matrix and have higher hardness than the matrix, so when the substrate is cut and polished, they remain as protruding defects on the surface or fall off. Then a hole defect is formed. As a result, even if sufficient cutting and polishing are performed, the surface precision cannot be sufficiently improved. Based on the above-mentioned research results, the present inventors have determined that the surface precision of the A-based alloy sheet can be significantly improved by making the crystallized substances formed in the ingot as fine as possible and preventing micro-segregation. We thought that it would be possible, and in order to realize this idea, we have been conducting intensive research on the types and amounts of added alloying elements, casting conditions, etc.
As a result, by limiting the type and amount of additive alloying elements and by making the castings manufactured by continuous casting as thin as possible, the crystallized material becomes significantly finer due to the rapid cooling effect, and the crystal structure is reduced. It was found that the above objectives were successfully achieved as the particles were made finer and micro-segregation was drastically reduced. The present invention was completed based on this knowledge, and its composition includes Mn as an alloying element: 0.9
Continuously cast an A-based alloy molten metal containing Ti: 0.03 to 0.08% and/or B: 0.01% or less to a plate thickness of 4 to 15 mm,
The gist lies in the fact that it is further rolled. First, the added alloying elements will be explained. Mn is an essential component for increasing the mechanical strength and corrosion resistance of the alloy plate, and if it is less than 0.9%, these effects will not be effectively exhibited. However, if it is too large, the amount of intermetallic compounds produced increases, causing segregation and coarsening of crystallized substances, so it should be kept at 1.4% or less. Ti and B are essential elements for refining the ingot structure and preventing micro-segregation, and in order to effectively exhibit these effects, Ti: 0.03% or more and a trace amount of B (preferably 0.0005% or more) must be used alone or in combination. However, Ti is 0.08%, B
If it exceeds 0.01%, most of the excess will be removed during the molten metal passage treatment stage using a filter that applies electrochemical adsorption phenomena, so adding any more is wasteful. In addition, A used as the base metal in the present invention is
It has a purity of 99% or more, and as long as the Fe, Si, etc. that are unavoidably contained in A are at the level of impurities, there is almost no coarsening of crystallized substances and no actual harm is caused. In the present invention, after melting Alloy A having the above-mentioned composition, it is passed through a filter that applies an electrochemical adsorption phenomenon to remove nonmetallic inclusions in the molten metal, and then continuous casting is performed. In order to achieve this goal, the plate thickness must be reduced to 4 to 15 mm using a continuous casting process. Traditional continuous casting method has a thickness of 300 to 600 mm
It is customary to obtain slabs of the order of mm. However, the results confirmed by the inventors through experiments show that if the slab is thick, rapid cooling becomes difficult and the crystallized substances become coarse during solidification. It is not possible to make the size smaller than 3 μm. However, in the continuous casting process, the plate thickness
When the thickness is set to 15 mm or less, the cast plate is cooled extremely rapidly, and as a result, the crystallized substances can be made extremely fine, and the crystal grains can also be made fine. In particular, since the composition used in the present invention is an A--Mn alloy that is susceptible to supercooling, the effect of quenching to refine crystallized substances is clearly exhibited. By the way, the thickness obtained by conventional continuous casting method is 300 to 600 mm.
The size of crystallized particles in a slab of about mm is about 12 μm, but if the thickness is set to 15 mm or less, the cooling rate can be increased by more than 10 times, and the size of crystallized particles can be reduced to 3 μm or less. Become. Moreover, since the crystal grains can be made finer, micro-segregation hardly occurs. Therefore, the A-base alloy plate obtained by subsequent hot, warm or cold rolling can be obtained in a state in which extremely fine crystallized substances are uniformly dispersed, and this can be obtained by machining and polishing. Also, there is no risk of causing unevenness caused by coarse crystallized substances or ripple phenomena caused by micro-segregation. As is clear from the above effects, the thinner the plate thickness during continuous casting, the better, but cold rolling of at least 50% or more is required from the viewpoint of accuracy in punching, cutting, and polishing of the disk base. Yes, the lower limit was set at 4 mm. On the other hand, if the plate thickness exceeds 15 mm, the cooling rate cannot be increased sufficiently, and the effect of refining crystallized substances cannot be satisfactorily exhibited. In the present invention, continuous casting includes semi-continuous casting. The present invention is roughly constructed as described above, and its effects can be summarized as follows. (1) In addition to limiting the type and amount of additive alloying elements, the thickness of the plate during continuous casting was made as thin as possible and the plate material was rapidly cooled, so crystallized substances could be made extremely fine and the matrix can be uniformly dispersed throughout. Therefore, surface irregularities caused by coarse crystallized substances and ripple phenomena caused by micro-segregation can be prevented as much as possible, and an A-based alloy plate for magnetic disks with high surface precision can be obtained. (2) Therefore, it is possible to reduce the thickness of the magnetic film and the gap between the magnetic head and the magnetic disk, making it possible to adapt to larger capacities and higher densities of magnetic disks. (3) Mechanical strength, heat resistance, and corrosion resistance are the same as or better than conventional products, and the manufacturing method is simple, so it can be provided at a price comparable to conventional products. Next, examples of the present invention will be shown. Example A molten A-based alloy having the composition shown in Table 1 was passed through a commonly used filter that applied the electrochemical adsorption phenomenon to remove nonmetallic inclusions.
It was continuously cast to a thickness of 5 mm and further cold rolled to a plate material of 2 mm thickness. This plate material was strain-relief annealed at 300°C for 2 hours, then cut to 0.1 mm according to the usual process for disk substrate processing, and strain-relief annealed at 340°C for 2 hours. It was then buffed and finished, and its performance as a disk base was examined, and the following results were obtained.

[Table] [Performance test results] Micro waviness: 0.01μmRmax (usually about 0.1μmRmax) Maximum crystallized size: 2μm (usually about 15μm) Mechanical properties Proof strength (Kg/mm ² ): 17.6 Tensile strength (Kg/mm ² ): 20.4 Elongation (%): 12.5 As is clear from the above results, the A-based alloy plate obtained by the present invention exhibits extremely high surface precision and also has good mechanical properties.

Claims (1)

[Claims] 1 Contains Mn: 0.9 to 1.4% as an alloying element, as well as Ti: 0.03 to 0.08% and/or B: 0.01%
The A-base alloy molten metal containing the following has a plate thickness of 4 to 4
A method for producing an A-based alloy sheet for magnetic disks, which is characterized by continuous casting to a thickness of 15 mm and further rolling.