JPH0527490B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is capable of sufficiently suppressing deformation-induced transformation even at a low drawing area reduction rate in order to economically and stably produce a ferromagnetized metastable austenitic steel bar suitable as a magnetic scale material, etc. The present invention relates to a method for drawing metastable austenitic steel that promotes . In recent years, the use of "magnetic scales" has become more prominent for measuring the amount of displacement, displacement speed, etc. of piston rods, etc. A "magnetic scale" is a scale formed by regularly arranging linear or band-shaped magnetically altered parts on the surface of a base made of a metal material, etc., and a magnetic scale placed close to and facing the surface of the scale. The sensor measures the relative displacement between the base and the magnetic sensor by reading the scale. <Prior Art and its Problems> As a conventional "magnetic scale" of this kind, one is known in which air gap grooves are carved out in a base made of a ferromagnetic material and the air gap grooves are utilized as magnetically altered parts. However, although the "magnetic scale" manufactured in this way had good magnetic scale characteristics and could obtain high output, its structure made it difficult to use it for sliding shafts such as piston rods and guide shafts. The problem was that the grooves had to be filled, making it impractical due to manufacturing costs and mechanical strength. In addition, as seen in Japanese Patent Application Laid-Open No. 57-16309, "magnetic A method of manufacturing "scale scales" was also proposed, but although the manufacturing method itself is simple, in this case, only a product with a small difference in magnetic properties between the base material (base part) and the heat-treated part can be obtained, and it is difficult to use. However, there are problems in that an expensive detection device is required or the reliability of the product is not sufficient. However, the above proposal also mentions measures to improve magnetic properties, and the 25%
Examples have been given of applying very expensive magnetic materials such as Fe-75%Ni alloy, but the products obtained in this way are not only expensive but also have poor strength and wear resistance. Not only that, but there are many limitations in terms of use, and the magnetic properties are also far from perfect. In other words, in the case of a "magnetic scale," it has already been mentioned that theoretically, by forming an air gap groove, the maximum magnetic output can be obtained at that part. Therefore, the above statement indicates that ``a combination of ferromagnetic material and non-magnetic material is the best magnetic scale.'' However, in the "magnetic scale" using the Fe-Ni alloy proposed above, both the base material (base part) and the heat-treated part are ferromagnetic, and the scale is formed simply by the difference in magnetic permeability between them. Therefore, it cannot necessarily be said that it is an ideal product in terms of magnetic properties. Furthermore, apart from these, a thin film (0.2~
We have also proposed a "magnetic scale" in which a thin film (0.3 mm thick) is formed as a base, and magnetically altered parts are created at predetermined intervals in a thin film on the base by partial electrical heating or heating with a particle beam such as a laser. (Unexamined Japanese Patent Publication No. 1983-
No. 7517). However, in the above-mentioned "thin plating film mainly composed of Ni and P that is partially heat-treated to form altered areas," the S/N ratio is said to be poor because the reading sensitivity of the scale is relatively low. However, in order to increase the sensitivity, the thickness of the thin film must be considerably thickened, which is an economic disadvantage, and if the surface of the magnetic scale is required to have wear resistance, it is necessary to use chrome plating, etc. There was a problem in that it was necessary to apply a wear-resistant coating, complicating the processing process, and there was also a risk that damage such as cracks would occur in the heat-treated plating thin film. Under these circumstances, the present inventors first
Most of the problems of the conventional method have been solved. proposed a magnetic scale characterized by an austenite structure. The above magnetic scale proposed by the present inventors is
It is a scale made by irradiating a base material made of metastable austenitic steel that has been cold-worked to become ferromagnetic to form localized non-magnetized areas, and has extremely good magnetic properties. However, in order to make the metastable austenitic steel ferromagnetic, a high degree of cold working is required, and therefore, manufacturing constraints are unavoidable, such as the need for large-scale drawing equipment. That is, there was no need to actively induce deformation-induced transformation in metastable austenitic steel to make it ferromagnetic, and thus such a drawing method had not been established in the past. This is because metastable austenitic steel has the property of becoming extremely hard due to the formation of a martensitic structure due to deformation-induced transformation, and problems such as "die seizure" and "wire breakage" are likely to occur during the drawing operation. Therefore, when drawing metastable austenitic steel materials for normal use, conventionally,
The main focus is on "suppressing deformation-induced transformation as much as possible," and generally speaking, as shown in Figure 3, "by drawing out the necessary area reduction in one pass in a warm process, deformation-induced transformation can be suppressed as much as possible.""Means to suppress and improve efficiency" were simply adopted. In addition, in FIG. 3, the reference numeral 1 indicates a drawing material, and the reference numeral 2 indicates a drawing die. <Means for Solving the Problems> In view of the above-mentioned circumstances, the present inventors have devised a method to achieve sufficient ferromagnetism by promoting deformation-induced transformation as much as possible, which was not previously intended. “Ferromagnetic drawing method for metastable austenitic steel”
In order to establish the Recognizing that this is not at all industrially desirable as it leads to the reinforcement of large drawing equipment and auxiliary equipment, which leads to a significant increase in costs and increases work troubles, we have developed As a result of repeated research in pursuit of the possibility of promoting deformation-induced transformation as much as possible while keeping the drawing area reduction rate as low as possible during drawing, we have found the following (a):
The findings shown in ~(d) were obtained. That is, (a) When obtaining a sufficiently ferromagnetic metastable austenitic steel drawn bar suitable as a material for magnetic scales by drawing, the inlet drawing temperature is suppressed to 140°C or less. need to be
There is no problem if the drawing temperature is kept particularly below 140°C, but if it exceeds that temperature, sufficient ferromagnetization will not be achieved. (b) However, in order to obtain a drawn rod product with the structure and strength required for equipment components, the required product can be obtained in one pass from a material with normal diameter dimensions (sufficient area reduction is expected). When drawing to the required dimensions, it is impossible to keep the drawing temperature of the metastable austenitic steel bar material below 140℃ due to processing heat, and problems such as die seizure and cutting of the material occur due to hardening due to transformation. becomes more likely to occur. (c) However, if the number of drawing passes is multiple during drawing to reduce the area reduction rate per pass, the rise in temperature of the material due to processing heat will be suppressed, and the inlet drawing temperature until the required diameter is finished will be kept below 140°C. At the same time, the strength of the finished product to the required diameter is sufficiently high, and troubles such as die seizure and cutting of the material can be stably prevented. In addition, at this time, if the heat dissipation of the material is slightly insufficient between each pass, the material temperature will increase with each pass, and in reality it will reach 140 degrees Celsius in the final pass.
However, even in that case, since the deformation-induced transformation is sufficiently promoted in the previous pass, ferromagnetization is sufficiently improved. (d) However, in order to increase the drawing efficiency and achieve sufficiently stable ferromagnetization, it is effective to forcefully cool the material between each pass. It is now possible to stably keep the drawing temperature below 140℃ without waiting for heat dissipation, and by arranging multiple drawing dies in a straight line, a single gripping device installed at the exit of the final die can handle all passes. It is also convenient for carrying out high-efficiency multiple die drawing, which involves simultaneously drawing out the dies. This invention was made based on the above knowledge, and it is based on the following: ``When drawing a metastable austenitic steel bar, by making a plurality of drawing passes and reducing the area reduction rate per pass, the drawing temperature in each pass can be reduced. of
Either perform cold drawing while maintaining the temperature at 140°C or less, or use multiple drawing passes to reduce the area reduction rate per pass, and forcefully cool the intermediate material before each pass to remove the drawing die immediately before it. By suppressing the temperature rise due to passage, the drawing temperature in each pass can be reduced.
Cold drawing is carried out while maintaining the temperature below 140℃, thereby actively causing deformation-induced transformation and improving the strength, resulting in a stable metastable austenitic steel bar with sufficiently high ferromagnetism and strength. It is characterized by the fact that it can be manufactured using The above “metastable austenitic steel” is
For example, when stainless steels such as SUS301 and SUS304 undergo solution treatment, they become completely austenitic and exhibit non-magnetic properties, but subsequent cold working causes strain-induced transformation, resulting in a martensitic structure that becomes ferromagnetic. However, when applied to the present invention, the type is not critical. This invention will be explained in more detail below. First, it is extremely important to use a plurality of drawing passes in the method of the present invention, but this is because it takes not "one pass" but "two passes" to achieve a predetermined area reduction rate to obtain a drawn product. Pass or better”
This means that the passes are divided into two, and as this reduces the heat generated during processing per pass, it is possible to sufficiently promote processing-induced transformation. By the way, when a large area reduction rate is required in general drawing processing, and it is impossible to draw the material in one pass due to breakage of the material or limitations on the capacity of the drawing machine, it is necessary to divide the material into multiple passes. This is a method that has been used in the past. However, multi-pass drawing in this case is carried out only from the perspective of "performing the drawing work without operational trouble", and is only adopted when it is impossible to perform the drawing work in one pass. It is a means of On the other hand, in the method of the present invention, we target metastable austenitic steel as the material to be drawn, and the area reduction rate that can be drawn in one pass is This is done from the perspective of "reducing the area reduction rate per pass in order to prevent the temperature from rising to the point where the process-induced transformation of the drawn material is inhibited," and the purpose of dividing the drawing pass into multiple passes is completely They are different. In other words, the purpose of dividing the passes in the method of the present invention is to lower the material temperature during drawing, and the drawing temperature can be significantly lowered by lowering the area reduction rate during drawing, thereby significantly promoting deformation-induced transformation. It will be done. Therefore, when carrying out the method of the present invention, 1
It is possible to increase the number of drawing dies on the drawing line, which is impossible with the above-mentioned ``multi-pass drawing'' from the conventional perspective, which requires drawing with a drawing device for each pass (one die). A method of arranging the dies in a straight line and pulling out the total area reduction in one drawing operation using one drawing device (referred to here as the ``multiple die method'').''
is also possible and sufficient.
Fig. 1 is a conceptual diagram of the above-mentioned "multiple die method", in which a plurality of drawing dies 2, 2,... are arranged in a straight line, and even in one drawing operation, the required area reduction rate is achieved all at once. This figure shows how the drawing material 1 is pulled out. Since this "multiple die method" can complete processing in one step, it is an extremely preferable method as it ensures superior productivity compared to conventional multi-pass drawing. However, if productivity is not emphasized, the conventional It goes without saying that the effect of promoting deformation-induced transformation can also be obtained by the multi-pass drawing method. In addition, previously published Japanese Patent Application Laid-open No. 58-221611 discloses a method that uses two dies and one drawing device and uses this to pull out the drawn material at once. This is done to ensure dimensional accuracy and pass center when inspecting the surface flaws of the material between dies, and it goes without saying that this is essentially different from the method of the present invention. Now, as mentioned above, in the method of the present invention, control of the inlet drawing temperature is extremely important, and plays a dominant role in determining the performance as a material for, for example, a magnetic scale. If the inlet drawing temperature exceeds 140°C, sufficient ferromagnetization of the drawn product cannot be achieved, and when applied to magnetic scales, the ferromagnetic properties are insufficient and a satisfactory product cannot be obtained. Therefore, it is necessary to set the number of drawing passes until the specified area reduction rate is reached so that the inlet drawing temperature does not exceed 140°C, or divide the number of passes to reduce the rise in drawing temperature, and then perform drawing at the die entrance. It is necessary to supplementally cool the material. However, especially when the multiple die method is applied, the temperature of the material increases with each pass due to insufficient cooling between the dies, and it is actually conceivable that the upper limit of 140°C may be exceeded in the final pass. As mentioned above, even in such a case, if measures such as the method of the present invention are basically taken, the deformation-induced transformation will be sufficiently promoted in the previous pass, and the magnetic properties will be sufficiently improved. For this reason, in practice, the desired purpose can be fully achieved by multiple passes in the air at room temperature, but if more powerful suppression of temperature rise is desired, a refrigerant below room temperature such as liquefied gas may be used. The material may be cooled at the die entrance before passing through the die. Forced cooling improves the ferromagnetic effect accordingly. When performing forced cooling using the multiple die method,
Specifically, as shown in FIG. 2, there are methods such as spraying a gas or liquid coolant 3 onto the drawn material 1 between the dies 2 and 2, or immersing the entire drawn material in a cooling liquid. Can be adopted. In this case, it is even more advantageous to apply a cooling liquid that exhibits a lubricating effect during drawing. By the way, a method known as the "direct cooling wire drawing method" in which the material immediately after exiting the die is directly cooled with a refrigerant is known, but this method involves drawing with high carbon steel wire, etc. This is applied to suppress static strain aging due to line temperature. On the other hand, since the deformation-induced transformation ends while the material remains in the die, it is meaningless to cool the metastable austenitic steel material after it leaves the die, as in the case of the direct cooling wire drawing method. Reducing the temperature at the inlet is an important issue. Therefore, in the method of the present invention, there is no need to perform forced cooling at the exit of the final die. Next, the present invention will be specifically explained using examples. <Example> Example 1 First, C: 0.05%, Si: 0.50%, Mn: 1.40%,
A metastable austenitic steel containing 6.81% Ni, 0.02% N, and the remainder substantially Fe was hot rolled into a 27mmφ bar, and heated to 1100℃ for 2 hours.
After soaking and solution treatment for a period of time, the surface was peeled to obtain a drawn material rod of 25 mmφ. Next, this was subjected to a fluorine-based resin film treatment to form a lubricating base film, and this was drawn out to a diameter of 21.6 mm under various conditions. Then, the drawn bar was passed through a two-roll rotary bend straightening machine to obtain a straight bar with a straightness of 0.3 to 0.5 mm/m. As shown in Table 1, the drawing conditions are one-pass drawing or multi-die drawing using 1 to 4 drawing dies, intermediate cooling is natural cooling or forced air cooling, and the drawing speed is 0.5 m at the final die exit. / minute.
In addition, the material temperature at the exit of each die was measured with a thermocouple type contact thermometer. A test piece of 10 mmφ was cut out from the straight bar obtained in this way, and its DC magnetization characteristics were measured to determine the saturation magnetic flux density [Bs] as a measure of ferromagnetization.
The results are also shown in Table 1. In addition, when evaluating ferromagnetization, the position detection accuracy on the magnetic scale mentioned above is determined by the saturation magnetic flux density [Bs]
Another study by the present inventors has revealed that practical accuracy can be achieved with "Bs≧5KG", and this was used as the standard for evaluation. As is clear from the results shown in Table 1,
It can be seen that sufficient ferromagnetism cannot be achieved with one-pass drawing, and that the more passes the number of passes yields better results. Also, from Table 1, when forced air cooling was applied, a cooling effect of 3 to 8 degrees Celsius was observed and the temperature decreased overall, but in the final pass it was rather

【table】

[Table] It is clear that the temperature is higher than in the case of a pass, but the low temperature in the previous pass is effective, and the effect of improving the saturation magnetic flux density [Bs] is greater than in the case of natural cooling. I know it's noticeable. Example 2 First, a drawn material bar with a diameter of 20.5 mm was obtained using the same materials as in Example 1 and the same steps as in Example 1. Next, this was drawn out under the conditions shown in Table 2 to make a bar with a diameter of 18 mmφ, and then a straight bar with a straightness of 0.3 to 0.5 mm/m was made using a rotary bend straightening machine. The material was cooled by a water spray method, and other drawing conditions and straightening conditions were the same as in Example 1. A test piece of 10 mmφ was cut out from the straight bar obtained in this way, and its DC magnetization characteristics were measured to determine the saturation magnetic flux density [Bs] as a measure of ferromagnetization.
The results are also shown in Table 2. In this example, since the cooling was sufficient, the drawing temperature was considerably lower and was below 140°C for all passes, which resulted in a sufficient improvement in magnetic properties as is clear from the results shown in Table 2. was gotten. <Summary of Effects> As explained above, according to the present invention, it is possible to stably provide a metastable austenitic steel drawn bar material that is sufficiently ferromagnetic without requiring special high-capacity equipment. This brings about industrially useful effects, such as making it possible to obtain products with excellent performance at low cost by applying it to materials such as magnetic scales.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the multiple dice method according to the present invention. FIG. 2 is a conceptual diagram showing a multiple die method using a cooling means according to the present invention. Third
The figure is a conceptual diagram showing a one-pass drawing method, which is a conventional bar drawing method. In the drawings, 1... Drawing material, 2... Drawing die, 3... Refrigerant.

Claims (1)

[Claims] 1. When drawing a metastable austenitic steel bar, a plurality of drawing passes are performed to reduce the area reduction rate per pass, thereby maintaining the inlet drawing temperature at 140°C or less in each pass. A method of drawing a metastable austenitic steel bar to make it ferromagnetic, which is characterized by performing cold drawing to actively cause deformation-induced transformation and to improve its strength. 2. The method for ferromagnetizing a metastable austenitic steel bar according to claim 1, wherein a plurality of drawing dies are arranged in a straight line and all passes of drawing are completed in one drawing operation. 3. When drawing a metastable austenitic steel bar, the number of drawing passes is made to reduce the area reduction rate per pass, and the intermediate material before passing through each pass is forcibly cooled to reduce the temperature caused by passing through the drawing die immediately before that. By suppressing the rise, cold drawing is performed while maintaining the inlet drawing temperature in each pass below 140℃,
A method for drawing a metastable austenitic steel bar to make it ferromagnetic, which is characterized by actively causing deformation-induced transformation and improving its strength. 4. The method for ferromagnetizing a metastable austenitic steel bar according to claim 3, wherein a plurality of drawing dies are arranged in a straight line and all passes of drawing are completed in one drawing operation.