JPH0724855B2 - Processing method of Ni-Ti type shape memory alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for processing a Ni-Ti type shape memory alloy (hereinafter abbreviated as NT alloy), and in particular solves the problems of warpage and twist due to processing. is there.

[Conventional technology]

NT alloys are alloys containing Ni and Ti as their main components.The shape memory effect that the deformation in the martensite phase is restored to the original shape of the matrix by heating above the As point of the martensite transformation, and the martensite transformation In the parent phase above the As point, there is a superelastic effect of returning to the original shape even if a strain of about several% is applied, and further, a vibration damping effect due to hysteresis during transformation of the alloy is exhibited. Such a characteristic is an effect that is not found in ordinary metals, and its utilization as various actuators, fasteners, and the like has been studied, and it has been partially put to practical use.

[Problems to be solved by the invention]

NT alloys belong to the category of difficult-to-machine materials from the perspective of ordinary metals, and have extremely hard work hardening and poor ductility. For this reason, it takes a considerable number of man-hours just to process a round wire or a square wire with a diameter of several mm from the ingot.
Most alloys are used for coil materials that are relatively easy to process. Recently, however, plate materials and the like have been processed, but the processing has hardly been clarified.

In general, when a metal material is processed, the material rarely uniformly extends in the longitudinal direction due to the processing, and the resulting processed product causes shape defects in the longitudinal direction such as warpage and twist. For this reason, the straightness of the processed product is ensured by applying tension to the processed product on the delivery side of processing or by repeatedly applying tension bending by a tension leveler or the like. However, the repeated tension bending is often an independent device, and the shape of the cross section may be deteriorated depending on the processed product, which is also a problem in terms of cost.

Depending on the metal material, it may be possible to obtain sufficient straightness by stretching in the longitudinal direction simply by applying tension to the processed product at the processing output side, but with NT alloy, when processing in the temperature range of the martensite phase, it becomes tentatively straight. When processed, if the temperature is raised to a temperature above the As point of the martensitic transformation, the shape of the martensitic deformation is restored and the straightness of the processed product deteriorates significantly.
Further, in the case of processing in the temperature range of the mother phase, even if a tension is applied, the elongation in the longitudinal direction due to it is almost elastic, and the warp or twist of the processed product is not improved. Similarly to general metal materials, NT alloys can be heated to the recrystallization temperature and applied with tension to remove residual stress and strain, and can be warped and twisted. However, this method has problems in terms of characteristics such as surface oxidation and reduction in mechanical strength.

[Means for solving problems]

As a result of various studies in view of this, the present invention can remove warpage and twist of a processed product without deteriorating the characteristics.
This is a developed NT alloy processing method.

One of the processing methods of the present invention is characterized in that, in the processing of an NT alloy, the alloy processed into a desired shape is held at 100 ° C. or higher to apply tension.

Another one of the processing methods of the present invention is roll forming of an NT alloy that is drawn by a drawing machine through a forming roll, a heating device is provided between the forming roll and the drawing machine, and the alloy formed by roll forming is 100 ° C. or higher. It is characterized in that it is held at and the tension is applied.

Still another one of the processing methods of the present invention is a roll forming process of an NT alloy which is drawn by a drawing machine through a forming roll, a heating device is provided between the forming roll and the drawing machine, and the Af point of the martensitic transformation is 50 or less. It is characterized in that an alloy roll-formed in a temperature range from a temperature higher than ℃ or higher to 200 ℃ is held at 100 ℃ or higher to apply tension.

That is, the present invention, cold rolling of the same kind as a general metal, wire drawing, when processing an NT alloy into a desired shape, depending on the NT alloy compounding ratio and processing conditions, the processed product warps And twisting occurs. By holding this at 100 ° C or higher and applying tension in the longitudinal direction, warpage and twist of the processed product are corrected. For example, as shown in FIG. 1, a heating device (3) is provided between the rolling mill (1) and the take-up winder (2) on the outlet side, and the rolled NT alloy (a) is passed through the heating device (3) to obtain 100 The NT alloy (a) is maintained at a temperature of not lower than 0 ° C and tension is applied by the winder (2). As shown in the figure, capstans (4) and (5) may be provided before and after the heating device (3) to apply tension to the NT alloy (a) that is passed through the heating device (3).

Further, as shown in FIG. 2, in the roll forming process, a heating device (3) is provided between the final forming stand (b) and the take-up stand (7), and the roll-formed NT alloy (a) is applied to the heating device (3). The temperature is maintained at 100 ° C. or higher, and tension is applied to the NT alloy (a) by the take-up stand (7). In the figure, (8) shows an inert gas introduction pipe. Further, in the roll forming process, the NT alloy is subjected to roll forming process in a temperature range from 50 ° C or more higher than the Af point of the martensitic transformation to 200 ° C, and this is held at 100 ° C or more and tension is applied in the longitudinal direction. Is added.

[Action]

The processing method of the present invention is 100 ° C. after processing in the martensite phase, instead of processing at the recrystallization temperature which causes deterioration of properties until now.
By maintaining the temperature range applicable to the cold working machine as described above and applying tension in the longitudinal direction, it is possible to remove the warp and twist of the processed product.

However, maintaining the temperature above 100 ° C and applying tension effectively removes the warp and twist of the processed product, but below 100 ° C the warp and twist are insufficiently removed even if the tension is increased. This is because. Further, in the roll forming, when the pipe is not welded and the forming is performed cold (martensite phase), some shape restoration occurs in the temperature range of the parent phase, and an opening occurs at the butt portion. In order to eliminate this, the roll forming is strongly bent by an amount corresponding to the amount of shape restoration, or the roll forming is performed in a temperature range of from 50 ° C higher than the Af point of the martensitic transformation to 200 ° C. By doing so, it is possible to eliminate the shape restoration in the temperature range of the mother phase. However, at a height of less than 50 ° C from the Af point of the martensitic transformation, shape restoration cannot be eliminated, and when it exceeds 200 ° C, the properties of the alloy deteriorate due to oxidation and the like.

<Example (1)> NT alloys also cause warpage and twist during cold rolling, similar to general metals, and the degree thereof varies depending on the alloy composition ratio and processing conditions. Therefore, the width obtained by rolling is 10 mm, the thickness is 0.3 mm,
Create an NT alloy with a length of 500 mm and a radius of curvature of 100 mm, attach the NT alloy (a) to the support (9) and attach a weight (10) that moves up and down in the guide (11) to the lower end as shown in FIG. Mounting, NT
The radius of curvature after heating the alloy (a) to a constant temperature for 1 second was measured. The results are shown in FIG.

As is clear from the figure, when the heating temperature was set to 100 ° C or higher, many effects were shown in reducing the warp. This effect becomes greater when the weight (tension) is increased, but excessive tension caused breakage or deformation of the cross-sectional shape. The twist was also greatly improved by heating and holding at 100 ° C or higher with the weight straightened.

Next, an NT alloy tape having a width of 10 mm, a thickness of 0.3 mm, and a radius of curvature of 100 mm is heated by a heating device (temperature 300 ° C, furnace length 500 mm) at a linear velocity of 2 m / min (tension 5 kg) with both capstans as shown in Fig. 1. Tension was applied to the NT alloy tape through the. As a result, the radius of curvature of the tape could be 10 m or more.

<Example (2)> Generally, in roll forming, a warp is likely to occur due to a difference in track length between an edge and a bottom in a forming process. So NT
A roll-formed alloy tape was used to create a round open tube with a diameter of 3 mm.
A warp of about 500 mm occurred. On the other hand, as shown in Fig. 2, a heating device is placed between the final molding stand and the take-up stand, and the heating temperature is 200 ° C. Rolled NT alloy tape was passed with a tension of 5 kg. As a result
I was able to raise it to about 10,000 meters. For comparison, the heating device was passed through without applying tension, but no improvement in the radius of curvature was observed.

If the pipe is not welded and the forming is performed cold (martensite phase), the shape may be somewhat restored in the temperature range of the parent phase, and an opening may occur at the joint. In such a case, bend strongly by an amount corresponding to the amount of shape restoration in pre-roll forming, or when performing roll forming, deform the NT alloy tape from the Af point of martensitic transformation to 50 ° C or more. If the temperature is maintained from a high temperature to 200 ° C, the radius of curvature can be improved without causing the opening of the mating portion even if heated to 200 ° C or higher by the heating device.

〔The invention's effect〕

As described above, according to the present invention, it is possible to remove warpage and twist in the longitudinal direction instead of processing at the recrystallization temperature which causes deterioration of the characteristics so far, and it is extremely easy to form a secondary processed product with an accurate shape. It is possible to provide significant advantages in industry.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of the processing method of the present invention, FIG. 2 is an explanatory view showing another example of the processing method of the present invention, and FIG. 3 is an explanatory view showing a test method in one embodiment of the present invention. FIG. 4 is a relationship diagram of a radius of curvature and a heating temperature showing an example of the test result. Formed NT alloy 1. Rolling mill 2. Winding machine 3. Heating device 4.5. Capstan 6. Forming final stand 7. Pulling stand 9. Support part 10. Weight 11. Weight guide

Claims (3)

[Claims] 1. A method for processing a Ni-Ti-based shape memory alloy, characterized in that, in the processing of a Ni-Ti-based shape memory alloy, the alloy processed into a desired shape is held at 100 ° C. or higher to apply tension. 2. A roll forming process of a Ni-Ti type shape memory alloy which is drawn out by a take-out machine through a forming roll, a heating device is provided between the forming roll and the take-out machine, and the alloy formed by roll forming is heated to 100 ° C. or higher. A method for processing a Ni-Ti shape memory alloy, which is characterized by holding and applying tension. 3. A roll forming process of a Ni-Ti type shape memory alloy which is drawn by a take-out machine through a forming roll, a heating device is provided between the forming roll and the take-out machine, and 50 ° C. or more from the Af point of martensitic transformation. A processing method for a Ni-Ti-based shape memory alloy, characterized in that an alloy roll-formed in a temperature range from a high temperature to 200 ° C is held at 100 ° C or more to apply tension.