JPH0210849B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for processing a Fe-Mn-Si shape memory alloy. (Prior art) Fe-Mn-Si shape memory alloys are known, for example, from the Japan Institute of Metals Autumn Conference General Lecture Abstracts (October 1984).
Known for its 550 pages. However, when this alloy is deformed at room temperature, cracks occur when the amount of processing exceeds a certain value, making further processing difficult. The reason for this is thought to be that the ε phase with a dense hexagonal structure is introduced into the matrix together with dislocations during processing. (Problems to be Solved by the Invention) By the way, if thin sheets and wire rods of the above-mentioned shape memory alloys can be manufactured, the range of their applications will be significantly expanded. There is a processing limit to reducing the diameter. (Means for Solving the Problems) The present invention solves the above problems. In other words, the present inventors believe that the ε phase is generated during processing at room temperature because the temperature at which the γ→ε transformation occurs due to deformation (Md point) is above room temperature. If this is done, the formation of ε phase will be prevented,
We thought that processing could be done easily without causing cracks. Therefore, the present invention has found that by heating the Fe-Mn-Si alloy of the present invention to a temperature above the Md point and performing rolling and wire drawing processing, it is possible to manufacture thin plates and wires with good surface properties. I understand. However, in the as-processed state, the shape memory effect deteriorates, but by further heating it to a temperature of 400°C or higher for a predetermined period of time, the results show that it once again exhibits excellent shape memory properties. The present invention has been made based on this knowledge. That is, in the present invention, Mn: 20 to 40%, Si: 3.5 to 8
% and the remainder is Fe and unavoidable impurities, or in addition to the above components, 10% or less Cr, Ni, Co, 2% or less
By processing a Fe-Mn-Si shape memory alloy containing Mo, 1% or less of one or more of C, Al, and Cu, with the remainder consisting of Fe and unavoidable impurities, at a temperature above the Md point. This processing method is characterized by suppressing the formation of the ε phase, making it easier to manufacture thin plates and wire rods, and then restoring their shape memory ability by annealing at a temperature equal to or higher than the Af point for a predetermined period of time. Here, the reasons for limiting each component and heat treatment conditions in the present invention will be explained. When the amount of Mn is less than 20%, the α' phase is also introduced along with the generation of the ε phase due to stress induction, reducing the shape memory effect. Conversely, when the Mn content exceeds 40%, the γ phase is stabilized, and sliding deformation of the γ phase occurs preferentially over the γ→ε transformation. Although Si is an element that promotes γ→ε transformation, its sufficient effect can be obtained by adding 3.5% or more. However, if more than 8% of Si is added, the workability and formability of the alloy will be impaired. Cr facilitates the γ → ε transformation, improves shape memory properties, and also helps improve corrosion resistance, but only 10%
If it is added in excess of this amount, it will form a low melting point intermetallic compound with Si, making it impossible to melt the alloy. Ni contributes to improving toughness without deteriorating shape memory properties, but when added in excess of 10%, hot workability deteriorates. Although Co improves shape memory properties and has good hot workability, it is expensive and the effect is not significant even when added in large amounts, so the upper limit was set at 10%. Mo improves shape memory properties as well as heat resistance, but when added in excess of 2%, hot workability worsens and conversely, shape memory properties also deteriorate. Although C improves the shape memory effect, addition of more than 1% significantly deteriorates toughness. Al acts as a deoxidizing agent and improves the shape memory effect, but there is no change in the effect if it is added in excess of 1%. Cu improves corrosion resistance without deteriorating the shape memory effect, but an upper limit of 1% is sufficient for its addition. In addition, the reason why warm rolling or wire drawing is performed at a temperature above the Md point after hot rolling is to prevent the formation of the ε phase as described above, and also for a predetermined time (5 minutes) at a temperature above the Af point. Above) The reason for annealing is to recover the deterioration in shape memory properties caused by processing at temperatures above the Md point. (Example) Next, an example of the present invention will be shown. Table 1 shows the alloy components, processing temperatures, surface textures, annealing temperatures, and shape recovery rates. If the surface quality is good, it is marked with ◯, if it is somewhat poor, it is marked with △, and if cracks or the like occur, it is marked with ×. In addition, the shape recovery rate was measured using a 0.4 x 2 x 30 (mm) test piece at room temperature.
It is shown as the percentage of the angle that returned after bending 90° and heating to 400°C. It can be seen that according to the present invention, it is possible to produce a thin plate with good surface properties and excellent shape memory ability. (Effect of the invention) As explained above, according to the present invention, Fe−Mn−
The Si-based shape memory alloy can be easily processed into thin plates or wires without affecting the shape memory effect, which is highly effective.

【table】

[Table] - indicates that annealing was not performed.

Claims (1)

[Claims] 1 Mn: 20-40%, Si: as weight percentage
Fe-Mn-Si shape memory alloy containing 3.5 to 8%, the remainder consisting of Fe and unavoidable impurities, or in addition to the above components, 10% or less of Cr, Ni, Co, 2% or less of Mo, 1% or less 1 or 2 of C, Al, Cu
After hot rolling, a Fe-Mn-Si type shape memory alloy containing at least 100% of Fe-Mn-Si, with the remainder consisting of Fe and unavoidable impurities, is subjected to warm rolling or wire drawing in a temperature range of at least the Md point, and then to the A _f point. A method for processing a Fe-Mn-Si shape memory alloy, characterized by annealing at a temperature above.