Shape memory stainless steel excellent in stress corrosion crack

Metal treatment – Stock – Mechanical memory

Patent

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

148563, C21D 800, C22C 3838

Patent

active

051980410

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a shape memory stainless steel excellent in shape memory effect and a method for enhancing shape memory effect thereof. More particularly, the invention relates to a shape memory stainless steel excellent in resistance to stress corrosion cracking which can advantageously develop its shape memory effect when used as fixing or fastening parts of machines, or as a pipe joint.


BACKGROUND OF THE INVENTION

As alloys exhibiting shape memory effect, there are known nonferrous-metal alloys including Ni--Ti alloys and Cu alloys as well as ferrous metal alloys such as Fe--Pd alloys, Fe--Ni alloys and Fe--Mn alloys. Among others, Fe--Mn alloys are inexpensive, and thus, because of their commercial value, various alloys of this Fe--Mn series are reported in patent literatures, for example, Fe--(15.9-30.0%) Mn alloys in JP A 55-73846, Fe--Mn--(Si, Ni, Cr) alloys in JP A 55-76043, Fe--(20-40%)Mn--(3.5-8%)Si alloys in JP A 61-76647 and Fe--(15-30%)Mn--N alloys in JP A 63-216946. furthermore, JP A 62-112720 discloses a method for enhancing shape memory effect of a Fe--Mn--Si alloy wherein a so-called training effect by repeating a cycle of working at a rate of up to 20% and heating to a temperature of at least 400.degree. C. is utilized.
However, ferrous metal shape memory alloys are generally disadvantageous in low corrosion resistance. JP A 61-201761 discloses examples of Fe--Mn--Si alloys whose corrosion resistance is improved by adding Cr. However, the Cr content taught is too low, i.e. not more than 10.0%, to achieve corrosion resistance well comparable with that of stainless steels. Furthermore, JP A 63-216946 teaches to improve corrosion resistance of ferrous metal shape memory alloys by adding Cr. Again, however, the Cr content disclosed is 10% or less and it is not taught how to realize a desired level of shape memory characteristics with the ferrous metal shape memory alloys having Cr, which is a ferrite former, in excess of 10% incorporated therein.
On the other hand, as to general stainless steels, "Scripta Metallurgica, 1977, vol. 5, pp.663.about.667" reports that SUS304 steel exhibits shape memory effect, if it is deformed at -196.degree. C. and then heated to room temperature, however, its shape recovery is too small to put it to practical use.


OBJECT OF THE INVENTION

An object of the invention is to provide a shape memory alloy containing more than 10% of Cr, which alloy is capable of exhibiting such a shape memory effect that even though the temperature of secondary deformation is not very low, for example, even though the temperature of secondary deformation is slightly below room temperature, when it is heated to moderately elevated temperature after the secondary deformation, it can recover its primary shape prior to the secondary deformation, and which alloy does not substantially suffer from stress corrosion cracking that may be a problem when the alloy is used as a pipe joint or the like.


DISCLOSURE OF THE INVENTION

According to the invention, there is provided a shape memory stainless steel excellent in resistance to stress corrosion cracking, which comprises, by weight, up to 0.10% of C, 3.0 to 6.0% of Si, 6.0 to 25.0% of Mn, up to 7.0% of Ni, more than 10.0% and not more than 17.0% of Cr, 0.02 to 0.3% of N, 2.0 to 10.0% of Co and more than 0.2% and not more than 3.5% of Cu, and optionally at least one selected from up to 2.0% of Mo, 0.05 to 0.8% of Nb, 0.05 to 0.8% of V, 0.05 to 0.8% of Zr, 0.05 to 0.8% of Ti, the balance being Fe and unavoidable impurities, the alloying components being adjusted so that a D value is not less than -26.0, wherein the D value is defined by the following equation: r+1.6.times.Si+Mo+1.5.times.(Nb+V+Zr+Ti)].
When the steel having the above defined chemical composition is processed to an article of a predetermined shape, annealed to memorize the shape, deformed at a temperature of not higher than room temperature, heated to a temperature of at least 100.degree. C. and allowed to cool to room temperature, the mem

REFERENCES:
patent: 4933027 (1990-06-01), Moriya et al.
patent: 5032195 (1991-07-01), Shin et al.

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Shape memory stainless steel excellent in stress corrosion crack does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Shape memory stainless steel excellent in stress corrosion crack, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shape memory stainless steel excellent in stress corrosion crack will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-1278558

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.