JPH044391B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention has high strength, high toughness, excellent shape memory effect, and has corrosion resistance and hot workability when necessary.
This relates to Fe-Mn-Si shape memory alloys. (Prior Art) Many alloys exhibiting a shape memory phenomenon are known, including Ti--Ni alloys, copper-based alloys, and iron-based alloys (for example, "Metal", March 1983 issue, p. 38). Among these, for example, patent application No. 187403 filed by the present applicant.
The Fe-Mn-Si alloy shown in the above issue exhibits excellent shape memory properties even when manufactured by the usual melting and rolling method. However, 100% shape memory effect has not yet been demonstrated. (Problem to be solved by the invention) Now, when Fe-Mn-Si alloys are deformed at temperatures below the temperature at which martensite occurs (Md point), for example at room temperature, the austenite (γ) matrix with a face-centered cubic structure forms. Martensite with dense hexagonal structure (ε)
transform into Thereafter, when heated above the reverse transformation end temperature (Af point), this ε martensite transforms back to the original γ matrix and exhibits a shape memory effect. At this time, it is sufficient that only ε martensite is generated by the transformation, but sliding deformation of the γ matrix also occurs at the same time. This γ
Slip causes irrecoverable strain when heated, and the shape recovery rate is low in Fe-Mn-Si alloys.
This is considered to be one of the reasons why it does not reach 100%. Also Fe−
Mn-Si alloys have problems in corrosion resistance, heat resistance, and toughness when used as practical materials. (Means for solving the problem) In order to enhance the shape memory effect of Fe-Mn-Si alloys, the stress that occurs during γ→ε transformation should be made relatively lower than the stress that occurs during γ sliding deformation. do it. Both γ and ε have densest structures, and the difference in structure is the difference in lamination. Therefore, it is thought that if the stacking fault energy is lowered, the γ→ε transformation will occur more easily. The stacking fault energy is greatly affected by the addition of alloying elements, and in the case of γ iron alloys, Cr, Mo, Co, C,
It is known that the addition of Al lowers this value. Therefore, the present inventors added these alloying elements. However, it has been found that the γ→ε transformation becomes easier and the shape memory properties are improved. We also found that adding a small amount of Cu can improve corrosion resistance without deteriorating shape memory properties, and that Ni can improve toughness without deteriorating shape memory properties. The present invention is based on this knowledge, and the present invention is based on the knowledge that Mn is 20 to 40% and
In addition to 3.5 to 8% Si, 10% or less Cr, Ni, Co,
The gist of the present invention is a shape memory alloy containing 2% or less of Mo, 1% or less of one or more of C, Al, and Cu, and the remainder being substantially Fe. That is, the present invention is characterized by improving shape memory properties and imparting corrosion resistance, heat resistance, and high toughness by adding various alloying elements to a Fe-Mn-Si shape memory alloy. In the present invention, the above-mentioned basic components including Mn and Si include
Co, Mo, C, Al to improve shape memory properties
Cr and Cu are added to improve corrosion resistance, and Ni is added to add toughness. The effects of adding these alloying elements are classified based on the main effects, and depending on the individual element, multiple effects may be observed as described below. That is, the present invention is a shape memory alloy characterized by having the composition shown below. (1) Mn20~40%, Si3.5~ as weight percentage
8% plus less than 10% Co, less than 2%
A shape memory alloy containing one or more of Mo, 1% or less of C, and 1% or less of Al, with the remainder being substantially Fe. (2) Mn20~40%, Si3.5~ as weight percentage
8% plus less than 10% Co, less than 2%
One or more of Mo, 1% or less C, 1% or less Al, 10% or less Cr, 1% or less Cu
Contains one or two of the following, with the remainder substantially
A shape memory alloy characterized by being made of Fe. (3) Mn20~40%, Si3.5~ as weight percentage
8% plus less than 10% Co, less than 2%
1. A shape memory alloy containing one or more of Mo, 1% or less C, and 1% or less Al, and 10% or less Ni, with the balance substantially consisting of Fe. (4) Mn20~40%, Si3.5~ as weight percentage
8% plus less than 10% Co, less than 2%
Contains one or more of Mo, 1% or less C, 1% or less Al, 10% or less Cr, 1% or less Cu, and 10% or less Ni, with the balance A shape memory alloy characterized in that substantially consists of Fe. Here, the reason for limiting the amount of alloying elements contained in the alloy of the present invention will be explained. If Mn is less than 20%, the α' phase is also introduced along with the formation of the ε phase due to stress induction, resulting in a decrease in the shape memory effect. Conversely, when Mn exceeds 40%, γ is stabilized, and γ slip deformation occurs preferentially over 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 helps improve corrosion resistance, but when added in excess of 10%, it forms a low melting point intermetallic compound with Si, making it difficult to melt the alloy. Also, Cr is γ→ε
It is also effective in facilitating transformation and improving shape memory properties. Ni contributes to improving toughness without deteriorating shape memory properties, but when added in excess of 10%, hot workability deteriorates. Although Co improves the shape memory effect and 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 the shape memory effect and heat resistance, but if it is added in an amount exceeding 2%, hot workability deteriorates, and conversely, the 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 an amount of 1% or more. Cu improves corrosion resistance without deteriorating the shape memory effect, but an upper limit of 1% is sufficient for its addition. (Example) Examples are shown below. Examples Table 1 shows the components of alloys produced using a high-frequency heating atmospheric furnace. These are all 1250 ~ after ingot formation.
Hold at 1050℃ for 1 hour, cut out a 0.5 x 1.5 x 30 mm plate material by rolling to obtain a 13 mm thick plate material, apply bending deformation of ~45° at room temperature, and calculate the recovery angle when heated above the Af point as the bending angle The degree of shape memory effect was determined and displayed based on the value divided by . Regarding hot formability, judge from the surface properties of the slab rolled to 13 mm after heating at 1200℃ for 1 hour. If so, it is indicated with an x. Regarding corrosion resistance, a test piece with a shape of 2 x 100 x 100 mm was exposed to the atmosphere for one year, and the amount of corrosion of Fe-30Mn-6Si alloy was set as 100. If it was 20 or less, it was rated ◎. For some, the corrosion resistance was evaluated by a salt spray test (JISZ2371), and red rust occurrence rate after 24 hours of spraying was rated ◎ if it was less than 20%, ○ if it was 20% or more and less than 50%, and △ if it was 50% or more. These results show that the alloy of the present invention not only has excellent shape memory properties, but can also be provided with corrosion resistance if necessary. Table 2 shows the results of impact tests on alloys with added Ni produced in the same manner as above. It can be seen that the absorbed energy at room temperature is improved in the alloy containing Ni.

【table】

[Table] * indicates evaluation by salt spray test.

[Table] (Effects of the Invention) As explained above, according to the present invention, a shape memory alloy having excellent shape memory properties, corrosion resistance, and hot workability can be obtained using a relatively inexpensive alloy component system.

Claims (1)

[Claims] 1. Mn 20-40%, Si 3.5-40% by weight
In addition to 8%, Co of 10% or less, Mo of 2% or less,
A shape memory alloy containing one or more of 1% or less of C and 1% or less of Al, with the remainder being substantially Fe. 2 Mn20~40%, Si3.5~ as weight percentage
In addition to 8%, Co of 10% or less, Mo of 2% or less,
Contains one or more of 1% or less C, 1% or less Al, and 10% or less Cr, 1% or less Cu, with the balance essentially consisting of Fe. A shape memory alloy characterized by 3 Mn20~40%, Si3.5~ as weight percentage
In addition to 8%, Co of 10% or less, Mo of 2% or less,
A shape memory alloy containing one or more of 1% or less of C, 1% or less of Al, and 10% or less of Ni, with the balance substantially consisting of Fe. 4 Mn20~40%, Si3.5~ as weight percentage
In addition to 8%, Co of 10% or less, Mo of 2% or less,
Contains 1% or less of C, 1% or less of one or more of Al, 10% or less of Cr, 1% or less of Cu, and 10% or less of Ni, with the remainder being substantially A shape memory alloy characterized by being essentially composed of Fe.