JPS6366894B2 - - Google Patents

Description

[Detailed description of the invention]

A. Field of Industrial Application The present invention relates to a method for manufacturing an alloy plate material such as a molten metal target material for use in a magnetic recording medium as a target material for forming a metal thin film by sputtering. B. Conventional technology The conventional method for producing alloys such as molten alloy target materials involves casting heated molten metal into a metal case, solidifying and cooling it, and then hot working and machining it into the final shape. . C. Problems to be Solved by the Invention However, when target material for magnetic recording media is cast by the conventional method, cracks occur on the surface of the steel ingot near the center or top during the solidification and cooling process in the mold. Especially when manufacturing flat steel ingots, the cracks are deep and the steel ingots are often divided. Therefore, it is necessary to remove a large amount of surface defects before the next step, hot working, or a steel ingot with the minimum required dimensions cannot be obtained. As a countermeasure to this problem, attempts have been made to fill the inner surface of the metal case with refractories or to raise the preheating temperature of the case, but the former causes foreign matter to be mixed in due to peeling of the refractory during casting, and the latter causes the alloy to be cast to be mixed into the case. It is easy to weld and has the opposite effect.
Neither can be improved significantly. The present invention solves these problems and provides a method for efficiently producing an alloy by producing an ingot with a solid and smooth surface. D. Means for Solving the Problems The present invention uses a refractory ceramic mold preheated to a high temperature as a mold for casting an alloy used as a target material, etc., thereby making it possible to perform low-temperature casting, thereby reducing the shrinkage of the cast alloy immediately after solidification. This is because the temperature gradient of the steel ingot is reduced during the process, and no cracks occur on the surface of the steel ingot. Furthermore, the solidified surface easily slips between the refractory on the inner surface of the mold in contact with the molten metal, and by lowering the compressive strength of the back-up portion, the mold collapses during the solidification process and the alloy contracts. When a molten alloy is cast into a mold and solidified and cooled, solidification generally produces a rapidly cooled skin on the surfaces in contact with the mold, that is, the bottom and side surfaces, and then inward in the direction of the temperature gradient. Crystals then grow. During this process, tensile stress acts on the surface of the steel ingot due to volumetric contraction. The strength of the alloy at high temperatures just below the freezing point is extremely low, and cracks easily occur in the steel ingot due to partial welding to the mold case that prevents shrinkage, or when inserted into the small gap between the mold case and the lower surface plate. . This phenomenon progresses along grain boundaries in the solidification structure, and high-purity alloys are more susceptible to cracking than conventional super-heat-resistant alloys mainly composed of Ni or Co. The reason for this is that conventional alloys have a large difference between the solidification start temperature and solidification completion temperature of 50 to 100°C, while target materials generally have a narrow temperature difference and solidify in a form close to that of pure metals. It is thought that the supercooling phenomenon during solidification also increases. Therefore, in order to solidify the high-purity alloy in a directional manner using the metal case, it is necessary to increase the gradient, which is not economical as a steel ingot shape for producing plate material, which is the general shape of the target material. On the other hand, ceramic molds, especially molds made using the lost wax method, are coated with slurry made of refractory and binder, and sprinkled with refractory granules to fix this coating, which are repeatedly applied to the model. There is an advantage that the composition of the binder can be selected from a wide range. As a result, the inner wall of the mold that comes into contact with the molten metal has a relatively high strength composition similar to the conventional lost wax method in order to withstand erosion caused by the molten metal during casting, and the middle layer, which is backed up, is designed to withstand the erosion of the molten metal during casting. If a high-purity alloy is cast using a mold with a bonding agent that has the minimum strength necessary to withstand the above-mentioned metal case, and the outer wall coating layer is made to have relatively high strength like the inner wall, the Defects such as welding of the alloy to the mold and mold wrinkles due to low mold preheating temperature or low pouring temperature are greatly reduced, and an ingot with a smooth surface is obtained. In addition, with regard to the occurrence of cracks due to shrinkage of the cast steel during the solidification and cooling process, low-temperature casting is possible by preheating the mold, so the refractory does not seize, so it does not easily slip and cause cracks. Furthermore, even if the desired shape of the ingot prevents shrinkage, the inner surface of the mold and the boundary between the intermediate layer, which has low strength, are likely to move, so that the mold with a thin inner surface collapses and shrinks. The details will be explained below using examples. Example 1 As a high-purity alloy, it has a structure of Co88wt%Crwt% and the total impurity content is 0.1wt%<Σ(C, Si, Mn, P,
S, Ni, Mo, Cu, Al, Fe, Mg, Zr, Ca, O,
The final shape is 2mm thick with the target material being N, H).
An example of manufacturing a board with a width of 120 mm and a length of 380 mm will be described. 99.97% purity Co and purity as melting raw material
1×10 ^-4 to 5× in a vacuum melting furnace using 99.98 Cr
Dissolved in an atmosphere of 10 ^-4 Torr. Zirconia stabilized with 4% calcia was used as the melting crucible. The composition after dissolution is shown in Table 1.

[Table] * Elements with arrows in the constituent elements column indicate that they are in the impurity element column.
(1) The above alloy is placed in a metal case with internal dimensions of 35 mm
It has a width of 300mm x 150H and has a feeder at the top, and the cross-sectional shape is 35mm at the bottom x 50mm at the top x 300mm width x 50mm.
It was cast in a mold case marked with H. The casting conditions were a case preheating temperature of approximately 150°C, and an injection temperature of 120°C above the solidification start temperature of the alloy (approximately 1470°C). After casting, the steel ingot was cooled to approximately 700°C in a vacuum, and then taken out into the atmosphere and observed. Regarding the surface condition of the steel ingot, surface defects in the form of hot water wrinkles were observed in the lower part, but no cracks were observed. However, a penetrating crack occurred in the upper part of the steel ingot at a position approximately 20 mm below the feeder, and a steel ingot with the desired shape could not be obtained after hot working. (2) The case of casting using a ceramic mold having a cavity having the same shape as the metal case is shown below. As a mold manufacturing method, a mold having a cavity with the same dimensions as the metal case was manufactured by using a combination of refractory mud having the composition shown in Table 2 and refractory granules (statuko material) for fixing the slurry film. . The manufacturing process of the mold is the same as the lost wax precision casting method, as shown in Figure 1. (1) A wax model steel ingot part 1 of the desired shape has a feeder part 3 made of the same material, a sprue cup 2, and a gas vent hole. (2) Fixing the coating with the refractory mud and the coating with the stucco material (3) Drying the coating layer with the refractory (4) Repeating the steps (2) and (3) above until 7~
Step of making the model 10 mm thick (5) Melting out the model by heating (6) Firing step to burn off the residual wax and sinter the mold The mold 5 obtained through the above steps is as shown in Figure 2. Placed in a heat-resistant steel box 10 before casting,
Approximately 10 meshes of back-up refractory material 9, such as sandstone, are filled into the gap and preheated in a heating furnace. 6, 7, and 8 are the keys for the sprue cup, riser, and ingot, respectively.

[Table] 〓Surfactant
Small amount〓
Studco material 48-80 mesh alumina grain

Claims (1)

[Claims] 1 Mo, V, or any one of Ni-Fe and Co-Cr
Contains one or more of W and Nb,
A method for producing a refined alloy containing impurities with a balance of 0.1% or less, which is characterized by forming an ingot using a ceramic casting mold preheated to 300 to 950°C, and then hot working the alloy. Method. 2. The method for manufacturing an alloy according to item 1, characterized in that a mold manufactured by a lost wax precision casting method is used as the ceramic mold.