CA2225679A1 - Iron-based shape memory and vibration damping alloys containing nitrogen - Google Patents
Iron-based shape memory and vibration damping alloys containing nitrogen Download PDFInfo
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- CA2225679A1 CA2225679A1 CA 2225679 CA2225679A CA2225679A1 CA 2225679 A1 CA2225679 A1 CA 2225679A1 CA 2225679 CA2225679 CA 2225679 CA 2225679 A CA2225679 A CA 2225679A CA 2225679 A1 CA2225679 A1 CA 2225679A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Abstract
The invention concerns a steel composition, in which, in addition to iron and manganese, there is possibly silicon, and in which nitrogen is an essential part. The composition may also include such conventional elements that are used in metallurgy to improve the desired properties. The composition contains, in addition to iron, (in percentages by weight) Mn 5.0-50.0 %, Si 08.0 % and N 0.01-0.8 %, as well as, if desired, one or more of the following elements: Cr 0.1-20.0 %, Ni 0.1-20.0 %, Co 0.1-20.0 %, Cu 0.1-3.0 %, V 0.1-1.0 %, Nb 0.1-1.0 %, Mo 0.1-3.0 %, C 0.001-1.0 %, rare earth metals (e.g. Sc, Y, La, Ce) 0.0005-0.02 %, and that it fulfils the following equation: Ni + Co + 0.5Mn + O.3Cu + 20N + 25C>=0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo). The composition has good shape memory and damping properties, as well as mechanical and corrosion resistance properties.
Description
CA 0222~679 l997-l2-23 W O 97/03215 P~l/~61.
Iron-based shape memory and vibration damping alloys containing nitrogen.
This invention co. ,ce- ns r-iL u96n-containing shape memory and vibration damping 5 metals, particularly shape memory steels.
In the following text, reference is often made to only shape memory metals or shape ",e.nory steels, even though this means metals and especi~lly steels whichhave both shape mer"o"/ and damping properties. How great a ~ropo, Lio- ~ can be10 counted as memory properties, or correspondingly as damping properties, depends on the composition used.
Shape memory metals mean metallic materials, in which a so-called one or two-way shape .ne,--oiy effect appears. The shape ~e~oly effect is based on the 15 ~ on of a l..a- lensilic ~n~ro...lc.lion. When, in a one-way memory effect, an austenitic (austel-ilê is a phase that is stable at high temperatures) sample iscoolecl, it forms martensite. If the formation of the martensite does not favour any direction, for example due to external stress, the shape of the piece does not change. When the material is deformed (generally less than 10 %), the twin 20 structure of the martensite phase of the material is rea, .anyed so that the twins that are in an advantageo~ ~s orientation with the stress grow at the expense of the others and new Illdl lensile can arise as a result of the stress. When the piece is el,edled above the te,nperdl-Jre of auslenile fo.~alion, the material may return to its form preceding the deformation.
In some materials, martensite does not arise during cooling, but forms during cl~ru., . I~Liul 1. Rec~ ~se twinning occurs in three dimensions, the shape of the piece may even cl ,a"ge during deror---dlion in a very complicated manner, and nevertheless still return to its original shape when heated. A one-way shape 30 memory effect can be exploited, for example in aLLacl.r.,enl, tensioning and prestressed structures.
When a rod-like sample dero,.ned by straining is heated to the austenite range, the s~.-"~le will recover its length before cJeror.naLion, if the shape memory effect CA 0222~679 1997-12-23 W O 97/03215 PCT/~ 5/~ZI~
is complete. Recovery may also be partial. If, for example the recoverable strain is half of the strain arising from sl, elcl ~i"y it is said that the recovery rate is 50 %.
The stress ~ Ised by recovery is called recovery stress.
5 In a two-way shape memory effect the maleri21 Ureme,,~bers two shapesr, which are achieved by heating and cooling. The te""~eralure dirrerel,ce between the states may even be 1~C. Among the most i"~o, IdnllllelllUIy effect applicaliGI ,s are so~alled ~ct~ l~tors in active viL,r~lior, damping, in robotics, valves heat relays and cGr"posile structures.
The most illlpolla"t memory metals used at ,ul-ese,,t are Ni-Ti and Cu-based.
These memory metals are quite eAI~e~ ~sive, which is the reason that the develop",enl of iron-based memory metals, i.e. memory steels, has been begun.
It is possi~le to divide ",e",oly steels into the following ~ ~sses accordi. ,y to the 15 type of lattice structure in the ",a,lel.sile that is obtained: BCT (Body-centred tel,dgo,)al), BCC (Body ce"l,~d cubic) and HCP (Hex~gsnal close-packed). In Fe-Ni-Co-Ti steel, BCT ma,lel)sile is formed from the FCC (Face-centeral cubic) auslel,ila phase. BCT rllallellsite is generally formed in such an alloy in which there is a high stacking fault energy. A large change in specific volume is 20 ~ssoci~led with the lrallsron~)alio,-. In this kind of ",~,lensile the derol",alion mechanism is often slip in ~dition to twinning. The fact that the deformation based on slipping is non-recoverable weakens the shape ~emo~y properties of this kind of alloy. If however the material is alloyed in such a way that it has so-called invar properties slip dero,l"alion is prevented and the memory properties25 may be good.
In Fe-Mn-Si-based "~e"~oly steels HCP r"~,lensile arises in der~"",alion. HCP
martensite generally arises in such alloys in which there is a small stacking-fault energy and a small change in specific volume. The memory propei lies are based 30 on the fact that derorl"~lion takes place by twinning nor does slip practically appear.
Examples of such memory steels, in which HCP ~a~lei~sile arises in deror",alion are given in US Patents 4 780,1~4 4,933,027 and 4 929 289.
CA 0222~679 1997-12-23 W O 97/03215 PCTn~6100408 The first one rerened to is based on an iron-based alloy composed of the following cG,IsliLuents:
Mn 20 - 40 % (weight %) Si 3.5 - 8.0 % and at least one of the following eler"enls;
Cr-10 % Ni -10 % Co -10 % Mo -2 % C -1 % Al -1 % Cu -1 % which is balanced with iron and random impurities.
The sec~"d of the pd~enls f~rel, ~ d to is also an iron-based " ,er"o, y steel in which there is Cr 5 - 20 % Si 2 - 8 % and at least one of the following elements: Mn 0-1 -~0 14.8 % Ni 0.1 - 20 % Co 0.1 - 30 % Cu 0.1 - 3 % N 0.001 - 0.3 % and in which Ni + 0.5Mn ~ 0.4Co + 0.06Cu + 0.002N ~ 0.67 (Cr + 1.2Si) - 3.
The last patent rerer, ed to depicls an iron-based ~en~o~ y steel in which there is Cr 0.1 - 5.0 % Si 2.0 - 8.0 % Mn 1.0 - 14.8 % and at least one of the following ele",enls. Ni 0.1 - 20 % Co 0.1 - 30 % Cu 0.1 - 3.0 % N 0.001 - 0.400 %, and in which Ni + 0.5Mn ~ 0.4Co + 0.06Cu + 0.002N 2 0.67 (Cr + 1.2Si) which is balanced with iron and random impurities.
The first of the memory steels referred to achieved a recovery rate of 75 - 90 %.
The addition of at least one element from the group Cr Ni Co or Mo is intended to improve co" OSiOI, r~sislance. However corrosion resistance is not very good in these steels on account of the high manyanese coule"L In ~d~ition these alloys oxidize at high te~ eraL-Ires. Oxidation may occur already when the sample is being heated to the austenite range to recover the original shape after deformation. The addition of cl-ro"~ium to the alloy in which there is 20 - 40 %",an~,anese and 3.5 - 8.0 % silicon may lead to the rorl"dlion of a brittle o-phase which reduces the shape memory properties fo""ability and ductility of steel.
Also the steels according to US Patents 4 933 027 and 4 929 289 do not have good ductilityvalues and rul",abili4 cha,~-~e,islics. In addition their strengths and corrosion properties are quite poor. In many cases corrosion resistance is also insurricienl.
Practical applications require such memory steels that have good shape memory CA 0222~679 1997-12-23 W O 97103215 PCT/~ 1~8 ~,upel lies high s~ ts. Iyll ~ and ductility and good corrosion resistance. They should also not oxi~ e at high temperatures.
On the other hand the damping of vibration in ",acl,i.,es, equ;t,",e"l and 5 structures has become increasingly il,.po.lanl with industrialization. Vibration causes both structural fatigue and reduces the performance of equipme~ ll. Further vibration and noise may be del,i",ei.lal to peo~le's health. An effective way ofreducing the level of vibr~lio- - is to use da-- "~;ng m~lerials in the manufacture of a ",acl-i.,e causing vibration. This is often not possible, bec~use sl~iPhle d~lllping 10 construction materials are not available. The iron-based damping constructionmaterials that are most in use are grey cast irons. Their mecl.a"ical properties, above all ductility are quite modest which limits their use.
Certain ferrite steels have a high damping capacily. The dam~i"y is based on 15 " ,ayl lelo el~-~ticity. Their use is limited by the fact that their da" ,piny properties are substantially weakened by derol"~alion or welding. In addition their strength isonly at the level of mild structural steel (Fe37) and they are cold-brittle.
The phase boundary between the c-...a~lel~sile phase appearing in certain iron 20 and manganese alloys and the austenite phase is sensitive to the mechanical loading of the material. This movement has been shown to damp vibration (C.-S.
Choi et al. Proc. of the Int. Conf. on Mal le~ Isilic Transror",~lions ICOMAT92, ed.
C.M. Wayman and J. Perkins, 1993 pp. 509 - 514). The structure of the e-llldl lensile phase is hexagonal close-packed and that of auslel ,ile is face-centred 25 cubic. In binary iron-based Fe~n alloys, the highest .lalllpi. ~y ~p~city is achieved with a composition Fe -17 (mass) % Mn. This col.,~osilion has been selected as the reference material for this invention.
It is the intention of this invention to create depending on the use either memory 30 steels or damping steels or prerer~Lly both simullal)eously which have the aforementioned good cl ,aracleri~lics. In other words they have excellent shape " ,e" ,o~ prùpel lies high slrenylh and ductility and good corrosion r~sisla"ce, as well as high te,-"~eralure oxidalion resislance. The intention is to also achieve a high dalllping cA~AciLy. In addition, the steels should retain a high damping CA 0222~679 l997-l2-23 W O 97/03215 PCT~g6/00408 capacity even when the material is cold-worked. A nitrogen alloy has a central siyl ,iricance in the achievement of the above prope, lies.
The dror~r"entioned excellent pro~e,lies are achieved using steels with the 5 c hd~d~;teristic features described in the accompanying Claims.
The invention is described in the following text by desc,ibi,)g compositions accor-Ji"y to the invention, without limiting them ~rec;sely to those des~ iL ed in any way wl,alsoever. Rerereilce is also made to the accompanying patent 10 draw;. ~y:~ in which:
Figure 1 (a) shows the stress-strain yl ~,uhs of two example steels (curve 1 = steel number 4 and curve 2 = steel number 2) to be described later, 15 Figure 1 (b) shows the stress-temperature graphs of the same example steels in Figure 1(a) measured during the heating cycle carried out after the treatment desc;,il,ecl. During the heating cycle, the length of the samples was kept consla"l.
The treal",e,)ls shown in the figures were carried out five times and the curvesshow the fifth treatment, Figure 2 shows the length of a 6 % deformed sample of one alloy according to theinvention (steel number 5) as a function of temperature, Figure 3 shows the damping ~l~cil~ (loga, ill "nic decrement) of one steel (steel 25 number 25) as a function of the vibration amplitude cor"pared to the rererence steel (steel number 27) and Figure 4 shows the stress of the same steels as a function of strain.
30 In orderfor HCP ~d~lensile Illelllo~ steel to have good shape memory properties, the following conditions must be fulfilled:
1. Before deformation. the amount of martensite must be as small as possible.
Iron-based shape memory and vibration damping alloys containing nitrogen.
This invention co. ,ce- ns r-iL u96n-containing shape memory and vibration damping 5 metals, particularly shape memory steels.
In the following text, reference is often made to only shape memory metals or shape ",e.nory steels, even though this means metals and especi~lly steels whichhave both shape mer"o"/ and damping properties. How great a ~ropo, Lio- ~ can be10 counted as memory properties, or correspondingly as damping properties, depends on the composition used.
Shape memory metals mean metallic materials, in which a so-called one or two-way shape .ne,--oiy effect appears. The shape ~e~oly effect is based on the 15 ~ on of a l..a- lensilic ~n~ro...lc.lion. When, in a one-way memory effect, an austenitic (austel-ilê is a phase that is stable at high temperatures) sample iscoolecl, it forms martensite. If the formation of the martensite does not favour any direction, for example due to external stress, the shape of the piece does not change. When the material is deformed (generally less than 10 %), the twin 20 structure of the martensite phase of the material is rea, .anyed so that the twins that are in an advantageo~ ~s orientation with the stress grow at the expense of the others and new Illdl lensile can arise as a result of the stress. When the piece is el,edled above the te,nperdl-Jre of auslenile fo.~alion, the material may return to its form preceding the deformation.
In some materials, martensite does not arise during cooling, but forms during cl~ru., . I~Liul 1. Rec~ ~se twinning occurs in three dimensions, the shape of the piece may even cl ,a"ge during deror---dlion in a very complicated manner, and nevertheless still return to its original shape when heated. A one-way shape 30 memory effect can be exploited, for example in aLLacl.r.,enl, tensioning and prestressed structures.
When a rod-like sample dero,.ned by straining is heated to the austenite range, the s~.-"~le will recover its length before cJeror.naLion, if the shape memory effect CA 0222~679 1997-12-23 W O 97/03215 PCT/~ 5/~ZI~
is complete. Recovery may also be partial. If, for example the recoverable strain is half of the strain arising from sl, elcl ~i"y it is said that the recovery rate is 50 %.
The stress ~ Ised by recovery is called recovery stress.
5 In a two-way shape memory effect the maleri21 Ureme,,~bers two shapesr, which are achieved by heating and cooling. The te""~eralure dirrerel,ce between the states may even be 1~C. Among the most i"~o, IdnllllelllUIy effect applicaliGI ,s are so~alled ~ct~ l~tors in active viL,r~lior, damping, in robotics, valves heat relays and cGr"posile structures.
The most illlpolla"t memory metals used at ,ul-ese,,t are Ni-Ti and Cu-based.
These memory metals are quite eAI~e~ ~sive, which is the reason that the develop",enl of iron-based memory metals, i.e. memory steels, has been begun.
It is possi~le to divide ",e",oly steels into the following ~ ~sses accordi. ,y to the 15 type of lattice structure in the ",a,lel.sile that is obtained: BCT (Body-centred tel,dgo,)al), BCC (Body ce"l,~d cubic) and HCP (Hex~gsnal close-packed). In Fe-Ni-Co-Ti steel, BCT ma,lel)sile is formed from the FCC (Face-centeral cubic) auslel,ila phase. BCT rllallellsite is generally formed in such an alloy in which there is a high stacking fault energy. A large change in specific volume is 20 ~ssoci~led with the lrallsron~)alio,-. In this kind of ",~,lensile the derol",alion mechanism is often slip in ~dition to twinning. The fact that the deformation based on slipping is non-recoverable weakens the shape ~emo~y properties of this kind of alloy. If however the material is alloyed in such a way that it has so-called invar properties slip dero,l"alion is prevented and the memory properties25 may be good.
In Fe-Mn-Si-based "~e"~oly steels HCP r"~,lensile arises in der~"",alion. HCP
martensite generally arises in such alloys in which there is a small stacking-fault energy and a small change in specific volume. The memory propei lies are based 30 on the fact that derorl"~lion takes place by twinning nor does slip practically appear.
Examples of such memory steels, in which HCP ~a~lei~sile arises in deror",alion are given in US Patents 4 780,1~4 4,933,027 and 4 929 289.
CA 0222~679 1997-12-23 W O 97/03215 PCTn~6100408 The first one rerened to is based on an iron-based alloy composed of the following cG,IsliLuents:
Mn 20 - 40 % (weight %) Si 3.5 - 8.0 % and at least one of the following eler"enls;
Cr-10 % Ni -10 % Co -10 % Mo -2 % C -1 % Al -1 % Cu -1 % which is balanced with iron and random impurities.
The sec~"d of the pd~enls f~rel, ~ d to is also an iron-based " ,er"o, y steel in which there is Cr 5 - 20 % Si 2 - 8 % and at least one of the following elements: Mn 0-1 -~0 14.8 % Ni 0.1 - 20 % Co 0.1 - 30 % Cu 0.1 - 3 % N 0.001 - 0.3 % and in which Ni + 0.5Mn ~ 0.4Co + 0.06Cu + 0.002N ~ 0.67 (Cr + 1.2Si) - 3.
The last patent rerer, ed to depicls an iron-based ~en~o~ y steel in which there is Cr 0.1 - 5.0 % Si 2.0 - 8.0 % Mn 1.0 - 14.8 % and at least one of the following ele",enls. Ni 0.1 - 20 % Co 0.1 - 30 % Cu 0.1 - 3.0 % N 0.001 - 0.400 %, and in which Ni + 0.5Mn ~ 0.4Co + 0.06Cu + 0.002N 2 0.67 (Cr + 1.2Si) which is balanced with iron and random impurities.
The first of the memory steels referred to achieved a recovery rate of 75 - 90 %.
The addition of at least one element from the group Cr Ni Co or Mo is intended to improve co" OSiOI, r~sislance. However corrosion resistance is not very good in these steels on account of the high manyanese coule"L In ~d~ition these alloys oxidize at high te~ eraL-Ires. Oxidation may occur already when the sample is being heated to the austenite range to recover the original shape after deformation. The addition of cl-ro"~ium to the alloy in which there is 20 - 40 %",an~,anese and 3.5 - 8.0 % silicon may lead to the rorl"dlion of a brittle o-phase which reduces the shape memory properties fo""ability and ductility of steel.
Also the steels according to US Patents 4 933 027 and 4 929 289 do not have good ductilityvalues and rul",abili4 cha,~-~e,islics. In addition their strengths and corrosion properties are quite poor. In many cases corrosion resistance is also insurricienl.
Practical applications require such memory steels that have good shape memory CA 0222~679 1997-12-23 W O 97103215 PCT/~ 1~8 ~,upel lies high s~ ts. Iyll ~ and ductility and good corrosion resistance. They should also not oxi~ e at high temperatures.
On the other hand the damping of vibration in ",acl,i.,es, equ;t,",e"l and 5 structures has become increasingly il,.po.lanl with industrialization. Vibration causes both structural fatigue and reduces the performance of equipme~ ll. Further vibration and noise may be del,i",ei.lal to peo~le's health. An effective way ofreducing the level of vibr~lio- - is to use da-- "~;ng m~lerials in the manufacture of a ",acl-i.,e causing vibration. This is often not possible, bec~use sl~iPhle d~lllping 10 construction materials are not available. The iron-based damping constructionmaterials that are most in use are grey cast irons. Their mecl.a"ical properties, above all ductility are quite modest which limits their use.
Certain ferrite steels have a high damping capacily. The dam~i"y is based on 15 " ,ayl lelo el~-~ticity. Their use is limited by the fact that their da" ,piny properties are substantially weakened by derol"~alion or welding. In addition their strength isonly at the level of mild structural steel (Fe37) and they are cold-brittle.
The phase boundary between the c-...a~lel~sile phase appearing in certain iron 20 and manganese alloys and the austenite phase is sensitive to the mechanical loading of the material. This movement has been shown to damp vibration (C.-S.
Choi et al. Proc. of the Int. Conf. on Mal le~ Isilic Transror",~lions ICOMAT92, ed.
C.M. Wayman and J. Perkins, 1993 pp. 509 - 514). The structure of the e-llldl lensile phase is hexagonal close-packed and that of auslel ,ile is face-centred 25 cubic. In binary iron-based Fe~n alloys, the highest .lalllpi. ~y ~p~city is achieved with a composition Fe -17 (mass) % Mn. This col.,~osilion has been selected as the reference material for this invention.
It is the intention of this invention to create depending on the use either memory 30 steels or damping steels or prerer~Lly both simullal)eously which have the aforementioned good cl ,aracleri~lics. In other words they have excellent shape " ,e" ,o~ prùpel lies high slrenylh and ductility and good corrosion r~sisla"ce, as well as high te,-"~eralure oxidalion resislance. The intention is to also achieve a high dalllping cA~AciLy. In addition, the steels should retain a high damping CA 0222~679 l997-l2-23 W O 97/03215 PCT~g6/00408 capacity even when the material is cold-worked. A nitrogen alloy has a central siyl ,iricance in the achievement of the above prope, lies.
The dror~r"entioned excellent pro~e,lies are achieved using steels with the 5 c hd~d~;teristic features described in the accompanying Claims.
The invention is described in the following text by desc,ibi,)g compositions accor-Ji"y to the invention, without limiting them ~rec;sely to those des~ iL ed in any way wl,alsoever. Rerereilce is also made to the accompanying patent 10 draw;. ~y:~ in which:
Figure 1 (a) shows the stress-strain yl ~,uhs of two example steels (curve 1 = steel number 4 and curve 2 = steel number 2) to be described later, 15 Figure 1 (b) shows the stress-temperature graphs of the same example steels in Figure 1(a) measured during the heating cycle carried out after the treatment desc;,il,ecl. During the heating cycle, the length of the samples was kept consla"l.
The treal",e,)ls shown in the figures were carried out five times and the curvesshow the fifth treatment, Figure 2 shows the length of a 6 % deformed sample of one alloy according to theinvention (steel number 5) as a function of temperature, Figure 3 shows the damping ~l~cil~ (loga, ill "nic decrement) of one steel (steel 25 number 25) as a function of the vibration amplitude cor"pared to the rererence steel (steel number 27) and Figure 4 shows the stress of the same steels as a function of strain.
30 In orderfor HCP ~d~lensile Illelllo~ steel to have good shape memory properties, the following conditions must be fulfilled:
1. Before deformation. the amount of martensite must be as small as possible.
2. The surface energy of the stacking fault of the austenite must be as small as CA 0222~679 l997-l2-23 W O 97/03215 PCT/~
possible. In ~ddilicsl 1 r-rl)dl lensiLe must form in the deror",alion and the quantity of a-",a,le"sile must be as small as possi~le.
possible. In ~ddilicsl 1 r-rl)dl lensiLe must form in the deror",alion and the quantity of a-",a,le"sile must be as small as possi~le.
3. The sLI er,gU I of the austenite must be as high as possible. In a strong matrix, the derorllldLion of auslellile through slipping ~ecGIIles difficult.
5 4. The temperature of fol"lalion of malle,lsile Ms must be above the Neel temperature TN~ at which anlirerl o"~ayl letic orderil l9 takes place.
There is abundant data in theory on the assumed and proven effects of various el~llellls on the properties of .,-e...û.~ steels. One exd..lple that can be given is the description in US Patent 4 933,027 referred to above as the state of the artwhich quite e,cte, Isively desca iL,es the significance of dirrer~- IL ele m enl~ in memory steels.
The aforementioned and other ractor~ have naturally been studied in the 15 develo,c " le, It work on the ~l lemory steel according to the invention. On the basis of this clesc;, iplio, I and of practical expel il l le, lls, the contents given in the Claims were arrived at for essentially the following reasons.
1. Manganese. Ma. .yanese stabilizes austenite strongly and increases the 20 s . - Ihility of, .it, oge. " which also stabilizes ausler,ile. When the Mn-content is less than 5 % a-ma,le,-sile begins to form (in ~d~ition to e-rllarLellsile) to such an extent that memory and damping ,~,ru,c,ellies begin to s~ nlially worsen. In chromium silicon and ,,il,ogell-cûlllailling alloys the reduction of the ~l~allganese conlenl may cause the ro,ll)dlion of o-ferrite during the cooling following melting 25 which leads to the forlll~liol- of porosity ber~se the solubility of nilro~aen in ~-ferrite is very small. If, on the other hand the ,nd"ya"ese conlenL Pxceeds 50 ~/0 the Neel tel"peraLure rises too much nor can even the addition of silicon and nitrogen reduce it sufficiently from the point of view of the shape memory effect.
30 2. Silicon. Silicon redoces the stacking fault energy of austenite, increasesstrength and red~ ~ces the Neel temperature. If the content is less than 2 % thedesired ~,ru~Je,Lies are ye.lerally no longer obtained. Nonetheless, thanks to nitrogen alloying the Illel,lor~/ effect is also presel,L in such alloys in which there is no silicon at all. At silicon co,-LenLs in excess of 8 % the ductility of steels CA 0222~679 l997-l2-23 W O 97/03215 PCTn~6/00408 diminishes and the hot and cold-workability is red~ ~cer~
3. Nibogen. NiLIugen has been selected as part of the alloy heG~ se it reinforces au~l6"ile (and ."a, lensile) more than any other element and stabilizes austenite 5 as well as improving corrosion resistance. Nitrogen improves both shape n,e",o, y and da" ,,.,i, Iy p, ope~ lies in the alloys accordi"g to the invention. Nill ogen prevents the fo""alion of the brittle c~-phase which recl~ces ductility. An ~ ro,criale Neel te""~erdlure can be set by -~le~i-ly a s~-it~hle ratio of llilloyel) and ",a"y~nese.
The alloying of llillc,gen and ",a"gd"ese has o~,uosile effects on the Neel 10 temperature. When the r,il,~ye., colllellt is less than 0.01 % the effects described above are insignificant. If the CGI ~te~ IL is above 0.8 % the steel becomes brittle.
5 4. The temperature of fol"lalion of malle,lsile Ms must be above the Neel temperature TN~ at which anlirerl o"~ayl letic orderil l9 takes place.
There is abundant data in theory on the assumed and proven effects of various el~llellls on the properties of .,-e...û.~ steels. One exd..lple that can be given is the description in US Patent 4 933,027 referred to above as the state of the artwhich quite e,cte, Isively desca iL,es the significance of dirrer~- IL ele m enl~ in memory steels.
The aforementioned and other ractor~ have naturally been studied in the 15 develo,c " le, It work on the ~l lemory steel according to the invention. On the basis of this clesc;, iplio, I and of practical expel il l le, lls, the contents given in the Claims were arrived at for essentially the following reasons.
1. Manganese. Ma. .yanese stabilizes austenite strongly and increases the 20 s . - Ihility of, .it, oge. " which also stabilizes ausler,ile. When the Mn-content is less than 5 % a-ma,le,-sile begins to form (in ~d~ition to e-rllarLellsile) to such an extent that memory and damping ,~,ru,c,ellies begin to s~ nlially worsen. In chromium silicon and ,,il,ogell-cûlllailling alloys the reduction of the ~l~allganese conlenl may cause the ro,ll)dlion of o-ferrite during the cooling following melting 25 which leads to the forlll~liol- of porosity ber~se the solubility of nilro~aen in ~-ferrite is very small. If, on the other hand the ,nd"ya"ese conlenL Pxceeds 50 ~/0 the Neel tel"peraLure rises too much nor can even the addition of silicon and nitrogen reduce it sufficiently from the point of view of the shape memory effect.
30 2. Silicon. Silicon redoces the stacking fault energy of austenite, increasesstrength and red~ ~ces the Neel temperature. If the content is less than 2 % thedesired ~,ru~Je,Lies are ye.lerally no longer obtained. Nonetheless, thanks to nitrogen alloying the Illel,lor~/ effect is also presel,L in such alloys in which there is no silicon at all. At silicon co,-LenLs in excess of 8 % the ductility of steels CA 0222~679 l997-l2-23 W O 97/03215 PCTn~6/00408 diminishes and the hot and cold-workability is red~ ~cer~
3. Nibogen. NiLIugen has been selected as part of the alloy heG~ se it reinforces au~l6"ile (and ."a, lensile) more than any other element and stabilizes austenite 5 as well as improving corrosion resistance. Nitrogen improves both shape n,e",o, y and da" ,,.,i, Iy p, ope~ lies in the alloys accordi"g to the invention. Nill ogen prevents the fo""alion of the brittle c~-phase which recl~ces ductility. An ~ ro,criale Neel te""~erdlure can be set by -~le~i-ly a s~-it~hle ratio of llilloyel) and ",a"y~nese.
The alloying of llillc,gen and ",a"gd"ese has o~,uosile effects on the Neel 10 temperature. When the r,il,~ye., colllellt is less than 0.01 % the effects described above are insignificant. If the CGI ~te~ IL is above 0.8 % the steel becomes brittle.
4. Chromium. The acldilio~- of cl,ror"ium red~ces the stacking fault energy and improves cGr, OSiOI, r esisla"ce and high temperature oxidation resislal ,ce.
15 Chromium also i"~ ases the solubility of nilrogel). If the chromium content is less than 0.1 % the above effects are insignificantly small. If on the other hand thechromium conlenl is above 20 % o-ferrite may form during the solidification stage of the smelting of the steel. In the same way during the solidification or during the heat treatment stage of steel brittle cJ-phase may form.
15 Chromium also i"~ ases the solubility of nilrogel). If the chromium content is less than 0.1 % the above effects are insignificantly small. If on the other hand thechromium conlenl is above 20 % o-ferrite may form during the solidification stage of the smelting of the steel. In the same way during the solidification or during the heat treatment stage of steel brittle cJ-phase may form.
5. Nickel. Nickel stabilizes austenite sl~ongly and improves the corrosion resistance of steel and its high temperature oxidation resisldl,ce. At co"le,1ls of less than 0.1 % the effects are insiy"irical,l. At conle,.l~ of more than 20 % the temperature at which "~a~lensile still forms with the aid of derc"",alion becomes 25 very low when the amount of ~"a,lensite rolll,i~,y decreases and finally no , l lal lensile forms at all.
6. Cobalt. Cobalt improves the memory and hot-working properties of steel. At conlel lls of less than 0.1 % the effects are insiyl liricantly small while if the conlenL
30 grows to more than 20 ~/0 no further improvel"enls are gained.
30 grows to more than 20 ~/0 no further improvel"enls are gained.
7. Copper. Copper stabilizes austenite and improves corrosion resisl~"ce. The adval,tageous effects of copper appear if the conlel,l is more than 0.1 %. If the copper conlenl exceeds 3 % the rollllalioll of c-lllallensile in deformation is CA 0222~679 1997-12-23 W O 97/03215 PcT/~
prevented, becAuse copper ir,~ eases the slackiny fault energy of austenite.
prevented, becAuse copper ir,~ eases the slackiny fault energy of austenite.
8. Vanadium and niobium. Vanadium and niobium i,~ 3ase yield sl~n~lll. They also increase the solubility of nil.os~e.. in a molten state, which is i...po,lar,l from 5 the point of view of manufacture. If the cG,-le"ls are less than 0.01 %, the effects are insignificant, while if they exceed 1 %, shape ~--~r..ory pr~pe,lies and thefGrmaL,ility of the steel weaken. Vanadium and niobium form finely dispersed I lib ides, which r ,;. I~u.ue steel, which in turn may ina ease the recoverable strain of the shape ..-e,..Gry effect.
9. Molybdenum. Molybdenum recl~ ~ces the slacking fault energy and improves hightemperature oxiddlion resistance. If the conlenl is smaller than 0.1 %, the effects are i"siy, .iricanlly small, and if the conlenl is ~aler than 3 %, the memory and hot-workability properties of the steel worsen.
10. Carbon. Carbon has been selected as an alloying component, because it reinforces and stabilizes austenite and improves the shape " ,ei "o"/ effect.
Conle"ls of less than 0.001 % have no effect on the properties, and if the content e~ eeds 1 %, ductility begins to diminish sl ~hsPntially.
Conle"ls of less than 0.001 % have no effect on the properties, and if the content e~ eeds 1 %, ductility begins to diminish sl ~hsPntially.
11. Rare earth metals (e.g. Sc, Y, La, Ce). Rare earth metals prevent the prec;,.,il~lion of ele",~l)ls at the grain boundaries, which improves corrosion resisl~"ce. If the contents are less than 0.0005 %, the effects are insignificantly small. If the contents are more than 0.02 %, the mechanical properties and 25 workability of the steel weaken decisively.
12. The ratio of the total amount of the elements stabilizing the austenite to the total amount of the elemenls stabilizing the ferrite.
30 In the steels that are the object of this invention, it is important that the material is completely ausl~, lilic, or at least that the amount of psssihle a-mal LensiLe is small, before derc,r",aiion. Due to this, the following equation must be conrul",ed to, in addition to the above limiLaLions;
CA 0222~679 l997-l2-23 W O 97/03215 PCTn~96/00408 Ni + 0.5Mn + Co + 0.3Cu + 20N + 25C 2 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo) The ability of the ele",e,)ls in the steel to stabiiize auslenile can be cl~ ted by the nickel equivalent Ni~qu~ which is the left-hand side of the above e~ tion. The 5 right-hand side depi~;t-~ the ability of the elements to stabilize ferrite, this being termed the cl ,rur..ium equivalent and marked Cr.quh,.
30 In the steels that are the object of this invention, it is important that the material is completely ausl~, lilic, or at least that the amount of psssihle a-mal LensiLe is small, before derc,r",aiion. Due to this, the following equation must be conrul",ed to, in addition to the above limiLaLions;
CA 0222~679 l997-l2-23 W O 97/03215 PCTn~96/00408 Ni + 0.5Mn + Co + 0.3Cu + 20N + 25C 2 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo) The ability of the ele",e,)ls in the steel to stabiiize auslenile can be cl~ ted by the nickel equivalent Ni~qu~ which is the left-hand side of the above e~ tion. The 5 right-hand side depi~;t-~ the ability of the elements to stabilize ferrite, this being termed the cl ,rur..ium equivalent and marked Cr.quh,.
13. Impurities. The phosphorus and sulphur col lle- llS must be less than 0.02 %.
When all of the ~,ope, lies des~ ibed above are taken into account, then the result according to the invention is a ~emo~y steel cGIl~osiliol~, which, in ~d~ition to iron, Col .Lains the following elel"e"ls in the cor,le"ls given (weight-%):
Mn5.0-50.0%,SiO-8.0%andNO.01 -0.80%.
In order to improve certain properties, one or more of the following elements may be added to the composition:
CrO.1 -20.0 %
Ni 0.1 -20.0 %
CoO.1 -20.0%
Cu 0.1 - 3.0 %
VO.1 - 1.0 %
NbO.1 -1.0%
MoO.1-3.0~/O
C 0.001 - 1 .0 %
Rare earth metals (e.g. Sc, Y, La, Ce) 0.0005 - 0.02 %.
The following equation too should be valid:
Ni + Co + 0.5Mn + 0.3Cu +20N + 25C 2 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo), balanced with the aid of iron and ran-lo m impurities.
The nitrogen alloying was observed, according to the invention, to suL,sla"lially CA 0222~679 1997-12-23 W O 97/03215 PCT/r~5/~
improve not only the shape r"ên ,o. y ~ ~, lies of Fe-Mn-based l"e" ,o"/ steels but also theim"e~l Idl ~ I prope, lies including da",ping prope, lies. Other ad~,anlages of "~e" ,o, ~ and damping steels accor Ji. ~ to the invention are ease of manufacture working and joining by weldills~. BecA~se a weld also has shape Illelllor~
5 properties the areas of the joints do not form points of ~lisconli",~ity in for example prestressed structures. In Addition ~ ~il- ogel ~ improves co., OSiOI, resisldnce and high temperature oxid~tion resisld"ce. Other alloy cor,.~.o"e"ts used in memory steel (such as Mn and Cr) increase the scl ~hility of the llilloyel"
so that the nil,uyen alloyin9 is brought surricienll~ high by using the normal 10 smelting methods used in the steel industry. By carrying out smelting in a high-pressure nitrogen atmosphere or by using powder metallurgical manl~Actl~ring Ill~lhGdS, it is possible to inc;.~ase the nitrogen conlenl of steel still further but the higher cost of the man~ ring ."elhoc~s may then limit the al-pli~li4,,5 of the steel.
The following ~Jer"o"~lr~les with the aid of examples the effect of nitrogen alloying on the properties of memory and damping steels. All of the steel examples were manufactured by conventional induction melting in an argon-nitrogen atmosphere the partial pressure of the nitrogen being varied in order to obtain a certain 20 t liLI oge n conlênl in the alloy. After smelting the steels were hot-rolled into 5 mm-thick bars at a te."~ erdl.lre of 1273 - 1373 K and then cold-drawn into 3 mm wires.
When the damping properties were invesfi~te~ the steel alloys were drawn into 1 mm wires which were annealed at a temperature of 1273 K for half an hour and then quenched in water.
Table 1 Compositions of example steels A~oy Mn Si Cr Ni V N Co Cu Nb C
No.
1 17.40 5.10 13.00 3.45 - 0.22 2 16.40 5.48 8.09 3.67 3 17.50 5.28 8.56 3.85 - 0.20 4 18.40 5.10 9.70 3.73 0 20 0.20 CA 0222~679 1997-12-23 W O 97/03215 PCT~96/00408 13.90 4.68 13.10 4.80 0.20 6 14.90 7.60 0.20 18.00 0.04 7 18.20 5.47 0.40 0.042 17.00 8 16.90 2.87 8.00 12.00 0.12 2.80 9 17.50 5.28 8.56 3.85 0.13 28.80 5.24 0.20 0.11 0.20 11 26.90 5.48 4.00 2.00 0.14 12 24.80 5.44 5.18 0.15 0.51 13 24.00 5.42 8.47 3.80 0.18 1 0 14 34.30 5.87 10.10 0.39 30.10 5.91 8.20 0.20 0.52 0.28 16 40.50 5.94 12.00 0.6 0.20 17 45.00 2.21 18.30 0.59 18 16.00 5.20 9.10 4.30 0.14 1~ 19 18.30 4.50 2.30 2.50 0.50 0.01 0.50 6.00 6.10 12.60 12.60 0.22 21 14.00 11.60 0.23 10.00 22 20.00 6.00 7.00 0.22 1.00 23 20.40 5.10 9.50 3.43 0.20 24 15.30 2.00 0.22 3.70 0.20 0.004 26 15.3 0.11 0.004 27 17.5 0 005 2~ Alloy 27 = reference alloy Note: Alloy 18 also 1.2 Mo and 0.001 Ce; Alloys 26 - 28 also 0.001 P.
The properties of the above alloys were investigated in the manner described in the following text:
1. Mechanical properties The yield and ulli",ale ~l,e"~Lhs and fracture strains are given in Table 2. TheinvesLigdlion of yield ~ nyll, and fracture strains was carried out for several other CA 0222~679 l997-l2-23 W O 97/03215 PCT/r-.S."C1~~
steels. The displacement rate in the testing machine fixture was 1 mm/min. The measured length of the samples was 100 mm and the thicknesses 0.8 mm.
Table 2 Yield ~lr~ U) (Roa2)~ ultimate tensile ~ l h (Rm) and fracture strain (R30) 5 of example steels 1 - 4 Alloy Yield sl,enyLI, Ultimate tensile Fracture strain (MPa) sl.enytl, (Mpa) (%) 2~i 16 950 10 CA 0222~679 l997-l2-23 W O 97/03215 PCTn~6/00408 ~ The nitrogen alloying was shown to increase the yield sllellylll and ullirllale 5 sll ~, Iyl h of the steel but it was not observed to reduce the fracture strain. Figure 4 shows stress-strain plots for materials 25 and 27 (rere, e~ ~ce alloy). Material 25 clearly work-llar~le"s more than ..,dlerial 27 and the y~dlesl value for strain measured for the r~ilruyen alloyed Illalel ial 25 was more than 50 % gredler than for the rerere"ce Illalerial 27. The test cler-o--al-dles that rlilluyell alloying cleariy 10 improves precisely the mechanical prol~ellies of dallll~i,ly steel. The damping r~p:~cjly was retained at quite a high level even in worked steel up to a reduction of a few percent.
2. Shape ."e..,oly properties Shape ")e",o,y prupe,lies were investigated on a materials testing r"acl,ir,e using sampies of 3 mm Ihick ar nealed wire with a dime, ~sional length of 30 mm. The samples were stretched by 5 mm and then heated above Af temperature (at this te""~er~lure all rl~a~le~lsile has c;l,anged into austenite). The recovery of the strain in relation to the original strain (preceding heating) was used as a criterion of the shape memory properties. Depending on how great this value was three quality cl-sses were set for this ratio (shape recovery rate).
Class 1: ratio greater than 70 %
Class 2: ratio 30 - 70 %
Class 3: ratio less than 30 %
The cl ~-sses of the steels are given in Table 3.
The effect of nitrogen alloying on the recovery stress was also investigated andthe results are given as graphs in Figure 1 for steels 2 and 4.
The nitrogen-alloyed sample 4 also co"lai,~ed Cr and V-r lill ides. Figure 1 (a) CA 0222~679 1997-12-23 W O 97/03215 PCTi~-.S/.ClD~
shows the i~ ase of stress during al- dil li~ 19. ~-llldl Lel ,siLe arises in derorm~Lion.
The stress level (aLr~n~u,Ll ,) of the nitrogen-alloyed steel 4 is clearly g,~aler than that of steel 2, which does not conlai. ~ "ilroye". The values for Fe-Mn-Si-based non-nitrogen steels given in the literature are clearly lower than those of steel 4.
Once the stress was removed, the te" ,per~lure of the samples was raised to about 800 K and after that back to room tel,.l~er~l-Jre, keeping the strain (= length of sample) CGI laldl ll during the entire cycle. Stress was observed to i- ~c. ~ase at the beginning of the I .ealing stage, bec~ ~-ce the Illdl lensile beca,ne auslel ~ile and then 10 diminished, as a result of the thermal e~l~a~-sio-- of the sample. The r-~il"um values for the recovery stress of steel 4 were about 300 MPa, while the value for the nitrogen-free steel 2 was only about 200 MPa. The recovery stress values given in the literature for nil,uyel ,-free Fe-Mn-Si-based memGIy steels are 150 -200 MPa.
Ni~ uge- ,-alloying thus clearly i"creases recovery stress. Recovery stress is a very i..,po.lanL variable in shape memory steel applications (e.g. tighteners, fasteners and preslressed structures), often even more i-.,po,Lanl than recoverable strain.
The recoverable strains of nil- oyen-alloyed memory steels are 1.5 - 4 %. Thermo-20 mechanical cycling, i.e. the so-called lrdini,.g of mel.,o,y steel, was observed to increase the recoverable strain and to yenerally move the fGr...alion of auslenile to a lower temperature in nil.ogen-alloyed steels too. In Figure 1 (b), thermo-mechanical cycling was repealed five times and the curves of the Figure were measured from the fifth cycle. The ratio between recoverable strain and the 25 original defo-malion also increased as a result of training. Its value was generally 0.6 - 1. Complete recovery was observed with a strain of as much as 3 %, for example in steel number 22.
When the temperature in Figure 1 was brought back to room te~"peraLure, a 30 pe""d,)enl stress of about 700 MPa remained in nitrogen-alloyed sample 4. In the .IiLIoge,I-free sa~ le, the stress was less than 400 MPa. In many applications (e.g.
~lLacl.,.,el.Ls, tensioners and the presL.essing of cGncrele), the magnitude of the residl ~~1 stress is an excellent advantage.
CA 0222~679 l997-l2-23 W O 97/03215 PCTn~g6/00408 Nil,oye"-alloyed steels accorc~ s3 to the invention have good shape memory properties and mech~"ical ~rupe, lies, even at cryc,ge"ic ter"~,eralures.
Recoverable strains of a few per cent were measured in tensile tests carried out at liquid rlill o~~eo tel "per~l-Jres.
Nitrogen-alloyed shape memory steels were also observed to have a two-way shape memory phenomenon. The recoverable strain in one and two-way shape ",emo,y effect is given in Figure 2. The example steel is steel 5 of Table 1. When a sample ~l~ror",ed by a 6 % stretch is hedled, the sample si,o,lens by 3.5 %, which is the recoverable strain of a one-way shape ",el"oly effect. When the sample is cooled and healed after this to between -196~ C - 750~ C, a loop is obtained, which ~lepic1s a two-way ",el"or~/ ~.I,el,o",el,on. In this steel its ",ay"ilude is about 0.4 % after the third cycle.
3. Vibration damping properties The damping capacities of rnalelials 25 and 27 (rererence steel) are given in Figure 3 as ful)uLiuns of the amplitude of the vibration. At a small amplitude with a value of 0.00005 the damping capacity (loy~rillll-lic decrement) is about 0.02. As the vibration amplitude increases the damping ca,uacily of both materials increases but the damping capacity of alloy 25 increases more rapidly and at an amplitude value of 0.0002 it is more than 50 % ~-~aler than that of alloy 27. The effect of nitrogen-alloying in improving damping capacily is obvious. A high d~ Jil lg capaciLy was shown to be retained over a broad range of temperatures.
The damping values of steel 26 were between those of steels 25 and 27.
The properties of shape ",el"o,~ and damping steels according to the invention are excellent according to all the criteria given. The values also clearly exceeded the values given in the literature.
The dalllping ~p~ y (1092,iU",.:c decrel"ent) of steels accordi"g to the invention is typically 0.01 - 0.08 at small vibration amplitudes (relative defor" ,dlion 10~ - 10-5). At greater amplitudes (c. 10~) the damping ca,uacil~/ is as much as 0.1. Steel number 23 is an example of a steel which combines excellent mechanical CA 0222~679 1997-12-23 ~ope~lies corr~sion ,esislance and IllelllGIY properties (a dero""dLion of 2.5 % is recovered completely) as well as a high da~ iny ca~,acily.
4. Corrosion resistance The corrosion resisla"ce of the steels was ev~ te~ metallographically after the Sdll ~l~s had been in the at",ospl)er~ for one year. The steels were divided into three c~ ~sses on the basis of the following criteria.
10 Class 1: No corrosion products at all observed Class 2: Cor, USiol, products were observed to some extent on the sur~ace of the s~" ",1~
Class 3: The surface was entirely coated with co" UsiGn pro~ ctc 15 Table 3 also shows the results of this test.
5. High temperature oxidation resistance The samples were heated to 600~ C in an air atmosphere and ll ,er~3arler the same 20 kind of ev~ tion as in Section 3 was carried out. The steels were divided into three cl~sses on the basis of the following criteria.
Class 1: No co" uSiGI, products at all observed Class 2: Corrosion products were observed to some extent on the surface of the 2~; sample Class 3: The surface was entirely coated with corrosion products.
The results are given in Table 3.
CA 0222~679 1997-12-23 W O 97tO3215 PCT/r~5/~
Table 3 Com~dl iso" of shape me,ool y steels according to the invention Alloy Shape Co"osio-~ High tel"~,er~ re oxidation ",el"o~y resistance resislance ,~,ropel ly Nitrogen-alloyed "~el"oly steels according to the invention are the first shape memory materials whose propellies and prices permit the exlel,sive industrial application of shape memory materials. Nitrogen-alloyed memory steels are CA 0222~679 l997-l2-23 W O 97/03215 PCT/~ 5/~CI~
When all of the ~,ope, lies des~ ibed above are taken into account, then the result according to the invention is a ~emo~y steel cGIl~osiliol~, which, in ~d~ition to iron, Col .Lains the following elel"e"ls in the cor,le"ls given (weight-%):
Mn5.0-50.0%,SiO-8.0%andNO.01 -0.80%.
In order to improve certain properties, one or more of the following elements may be added to the composition:
CrO.1 -20.0 %
Ni 0.1 -20.0 %
CoO.1 -20.0%
Cu 0.1 - 3.0 %
VO.1 - 1.0 %
NbO.1 -1.0%
MoO.1-3.0~/O
C 0.001 - 1 .0 %
Rare earth metals (e.g. Sc, Y, La, Ce) 0.0005 - 0.02 %.
The following equation too should be valid:
Ni + Co + 0.5Mn + 0.3Cu +20N + 25C 2 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo), balanced with the aid of iron and ran-lo m impurities.
The nitrogen alloying was observed, according to the invention, to suL,sla"lially CA 0222~679 1997-12-23 W O 97/03215 PCT/r~5/~
improve not only the shape r"ên ,o. y ~ ~, lies of Fe-Mn-based l"e" ,o"/ steels but also theim"e~l Idl ~ I prope, lies including da",ping prope, lies. Other ad~,anlages of "~e" ,o, ~ and damping steels accor Ji. ~ to the invention are ease of manufacture working and joining by weldills~. BecA~se a weld also has shape Illelllor~
5 properties the areas of the joints do not form points of ~lisconli",~ity in for example prestressed structures. In Addition ~ ~il- ogel ~ improves co., OSiOI, resisldnce and high temperature oxid~tion resisld"ce. Other alloy cor,.~.o"e"ts used in memory steel (such as Mn and Cr) increase the scl ~hility of the llilloyel"
so that the nil,uyen alloyin9 is brought surricienll~ high by using the normal 10 smelting methods used in the steel industry. By carrying out smelting in a high-pressure nitrogen atmosphere or by using powder metallurgical manl~Actl~ring Ill~lhGdS, it is possible to inc;.~ase the nitrogen conlenl of steel still further but the higher cost of the man~ ring ."elhoc~s may then limit the al-pli~li4,,5 of the steel.
The following ~Jer"o"~lr~les with the aid of examples the effect of nitrogen alloying on the properties of memory and damping steels. All of the steel examples were manufactured by conventional induction melting in an argon-nitrogen atmosphere the partial pressure of the nitrogen being varied in order to obtain a certain 20 t liLI oge n conlênl in the alloy. After smelting the steels were hot-rolled into 5 mm-thick bars at a te."~ erdl.lre of 1273 - 1373 K and then cold-drawn into 3 mm wires.
When the damping properties were invesfi~te~ the steel alloys were drawn into 1 mm wires which were annealed at a temperature of 1273 K for half an hour and then quenched in water.
Table 1 Compositions of example steels A~oy Mn Si Cr Ni V N Co Cu Nb C
No.
1 17.40 5.10 13.00 3.45 - 0.22 2 16.40 5.48 8.09 3.67 3 17.50 5.28 8.56 3.85 - 0.20 4 18.40 5.10 9.70 3.73 0 20 0.20 CA 0222~679 1997-12-23 W O 97/03215 PCT~96/00408 13.90 4.68 13.10 4.80 0.20 6 14.90 7.60 0.20 18.00 0.04 7 18.20 5.47 0.40 0.042 17.00 8 16.90 2.87 8.00 12.00 0.12 2.80 9 17.50 5.28 8.56 3.85 0.13 28.80 5.24 0.20 0.11 0.20 11 26.90 5.48 4.00 2.00 0.14 12 24.80 5.44 5.18 0.15 0.51 13 24.00 5.42 8.47 3.80 0.18 1 0 14 34.30 5.87 10.10 0.39 30.10 5.91 8.20 0.20 0.52 0.28 16 40.50 5.94 12.00 0.6 0.20 17 45.00 2.21 18.30 0.59 18 16.00 5.20 9.10 4.30 0.14 1~ 19 18.30 4.50 2.30 2.50 0.50 0.01 0.50 6.00 6.10 12.60 12.60 0.22 21 14.00 11.60 0.23 10.00 22 20.00 6.00 7.00 0.22 1.00 23 20.40 5.10 9.50 3.43 0.20 24 15.30 2.00 0.22 3.70 0.20 0.004 26 15.3 0.11 0.004 27 17.5 0 005 2~ Alloy 27 = reference alloy Note: Alloy 18 also 1.2 Mo and 0.001 Ce; Alloys 26 - 28 also 0.001 P.
The properties of the above alloys were investigated in the manner described in the following text:
1. Mechanical properties The yield and ulli",ale ~l,e"~Lhs and fracture strains are given in Table 2. TheinvesLigdlion of yield ~ nyll, and fracture strains was carried out for several other CA 0222~679 l997-l2-23 W O 97/03215 PCT/r-.S."C1~~
steels. The displacement rate in the testing machine fixture was 1 mm/min. The measured length of the samples was 100 mm and the thicknesses 0.8 mm.
Table 2 Yield ~lr~ U) (Roa2)~ ultimate tensile ~ l h (Rm) and fracture strain (R30) 5 of example steels 1 - 4 Alloy Yield sl,enyLI, Ultimate tensile Fracture strain (MPa) sl.enytl, (Mpa) (%) 2~i 16 950 10 CA 0222~679 l997-l2-23 W O 97/03215 PCTn~6/00408 ~ The nitrogen alloying was shown to increase the yield sllellylll and ullirllale 5 sll ~, Iyl h of the steel but it was not observed to reduce the fracture strain. Figure 4 shows stress-strain plots for materials 25 and 27 (rere, e~ ~ce alloy). Material 25 clearly work-llar~le"s more than ..,dlerial 27 and the y~dlesl value for strain measured for the r~ilruyen alloyed Illalel ial 25 was more than 50 % gredler than for the rerere"ce Illalerial 27. The test cler-o--al-dles that rlilluyell alloying cleariy 10 improves precisely the mechanical prol~ellies of dallll~i,ly steel. The damping r~p:~cjly was retained at quite a high level even in worked steel up to a reduction of a few percent.
2. Shape ."e..,oly properties Shape ")e",o,y prupe,lies were investigated on a materials testing r"acl,ir,e using sampies of 3 mm Ihick ar nealed wire with a dime, ~sional length of 30 mm. The samples were stretched by 5 mm and then heated above Af temperature (at this te""~er~lure all rl~a~le~lsile has c;l,anged into austenite). The recovery of the strain in relation to the original strain (preceding heating) was used as a criterion of the shape memory properties. Depending on how great this value was three quality cl-sses were set for this ratio (shape recovery rate).
Class 1: ratio greater than 70 %
Class 2: ratio 30 - 70 %
Class 3: ratio less than 30 %
The cl ~-sses of the steels are given in Table 3.
The effect of nitrogen alloying on the recovery stress was also investigated andthe results are given as graphs in Figure 1 for steels 2 and 4.
The nitrogen-alloyed sample 4 also co"lai,~ed Cr and V-r lill ides. Figure 1 (a) CA 0222~679 1997-12-23 W O 97/03215 PCTi~-.S/.ClD~
shows the i~ ase of stress during al- dil li~ 19. ~-llldl Lel ,siLe arises in derorm~Lion.
The stress level (aLr~n~u,Ll ,) of the nitrogen-alloyed steel 4 is clearly g,~aler than that of steel 2, which does not conlai. ~ "ilroye". The values for Fe-Mn-Si-based non-nitrogen steels given in the literature are clearly lower than those of steel 4.
Once the stress was removed, the te" ,per~lure of the samples was raised to about 800 K and after that back to room tel,.l~er~l-Jre, keeping the strain (= length of sample) CGI laldl ll during the entire cycle. Stress was observed to i- ~c. ~ase at the beginning of the I .ealing stage, bec~ ~-ce the Illdl lensile beca,ne auslel ~ile and then 10 diminished, as a result of the thermal e~l~a~-sio-- of the sample. The r-~il"um values for the recovery stress of steel 4 were about 300 MPa, while the value for the nitrogen-free steel 2 was only about 200 MPa. The recovery stress values given in the literature for nil,uyel ,-free Fe-Mn-Si-based memGIy steels are 150 -200 MPa.
Ni~ uge- ,-alloying thus clearly i"creases recovery stress. Recovery stress is a very i..,po.lanL variable in shape memory steel applications (e.g. tighteners, fasteners and preslressed structures), often even more i-.,po,Lanl than recoverable strain.
The recoverable strains of nil- oyen-alloyed memory steels are 1.5 - 4 %. Thermo-20 mechanical cycling, i.e. the so-called lrdini,.g of mel.,o,y steel, was observed to increase the recoverable strain and to yenerally move the fGr...alion of auslenile to a lower temperature in nil.ogen-alloyed steels too. In Figure 1 (b), thermo-mechanical cycling was repealed five times and the curves of the Figure were measured from the fifth cycle. The ratio between recoverable strain and the 25 original defo-malion also increased as a result of training. Its value was generally 0.6 - 1. Complete recovery was observed with a strain of as much as 3 %, for example in steel number 22.
When the temperature in Figure 1 was brought back to room te~"peraLure, a 30 pe""d,)enl stress of about 700 MPa remained in nitrogen-alloyed sample 4. In the .IiLIoge,I-free sa~ le, the stress was less than 400 MPa. In many applications (e.g.
~lLacl.,.,el.Ls, tensioners and the presL.essing of cGncrele), the magnitude of the residl ~~1 stress is an excellent advantage.
CA 0222~679 l997-l2-23 W O 97/03215 PCTn~g6/00408 Nil,oye"-alloyed steels accorc~ s3 to the invention have good shape memory properties and mech~"ical ~rupe, lies, even at cryc,ge"ic ter"~,eralures.
Recoverable strains of a few per cent were measured in tensile tests carried out at liquid rlill o~~eo tel "per~l-Jres.
Nitrogen-alloyed shape memory steels were also observed to have a two-way shape memory phenomenon. The recoverable strain in one and two-way shape ",emo,y effect is given in Figure 2. The example steel is steel 5 of Table 1. When a sample ~l~ror",ed by a 6 % stretch is hedled, the sample si,o,lens by 3.5 %, which is the recoverable strain of a one-way shape ",el"oly effect. When the sample is cooled and healed after this to between -196~ C - 750~ C, a loop is obtained, which ~lepic1s a two-way ",el"or~/ ~.I,el,o",el,on. In this steel its ",ay"ilude is about 0.4 % after the third cycle.
3. Vibration damping properties The damping capacities of rnalelials 25 and 27 (rererence steel) are given in Figure 3 as ful)uLiuns of the amplitude of the vibration. At a small amplitude with a value of 0.00005 the damping capacity (loy~rillll-lic decrement) is about 0.02. As the vibration amplitude increases the damping ca,uacily of both materials increases but the damping capacity of alloy 25 increases more rapidly and at an amplitude value of 0.0002 it is more than 50 % ~-~aler than that of alloy 27. The effect of nitrogen-alloying in improving damping capacily is obvious. A high d~ Jil lg capaciLy was shown to be retained over a broad range of temperatures.
The damping values of steel 26 were between those of steels 25 and 27.
The properties of shape ",el"o,~ and damping steels according to the invention are excellent according to all the criteria given. The values also clearly exceeded the values given in the literature.
The dalllping ~p~ y (1092,iU",.:c decrel"ent) of steels accordi"g to the invention is typically 0.01 - 0.08 at small vibration amplitudes (relative defor" ,dlion 10~ - 10-5). At greater amplitudes (c. 10~) the damping ca,uacil~/ is as much as 0.1. Steel number 23 is an example of a steel which combines excellent mechanical CA 0222~679 1997-12-23 ~ope~lies corr~sion ,esislance and IllelllGIY properties (a dero""dLion of 2.5 % is recovered completely) as well as a high da~ iny ca~,acily.
4. Corrosion resistance The corrosion resisla"ce of the steels was ev~ te~ metallographically after the Sdll ~l~s had been in the at",ospl)er~ for one year. The steels were divided into three c~ ~sses on the basis of the following criteria.
10 Class 1: No corrosion products at all observed Class 2: Cor, USiol, products were observed to some extent on the sur~ace of the s~" ",1~
Class 3: The surface was entirely coated with co" UsiGn pro~ ctc 15 Table 3 also shows the results of this test.
5. High temperature oxidation resistance The samples were heated to 600~ C in an air atmosphere and ll ,er~3arler the same 20 kind of ev~ tion as in Section 3 was carried out. The steels were divided into three cl~sses on the basis of the following criteria.
Class 1: No co" uSiGI, products at all observed Class 2: Corrosion products were observed to some extent on the surface of the 2~; sample Class 3: The surface was entirely coated with corrosion products.
The results are given in Table 3.
CA 0222~679 1997-12-23 W O 97tO3215 PCT/r~5/~
Table 3 Com~dl iso" of shape me,ool y steels according to the invention Alloy Shape Co"osio-~ High tel"~,er~ re oxidation ",el"o~y resistance resislance ,~,ropel ly Nitrogen-alloyed "~el"oly steels according to the invention are the first shape memory materials whose propellies and prices permit the exlel,sive industrial application of shape memory materials. Nitrogen-alloyed memory steels are CA 0222~679 l997-l2-23 W O 97/03215 PCT/~ 5/~CI~
excellently applicable as ~.,aler;als for alla~ enls (e.g. machine components, stones), te,lsioner:, (e.g. pipe co""ec~ions) and various pre:,l,essed structures (e.g. co, Icrete reinrorceme,-l steels).
5 The use of ~l~emo~y steels in the above applicalions is based on the fact thatdeformation is carried out on mer"ol~ steel products before they are inst~e~l Separ~te derol .,~ic" l is not always required, hec~ ~se the normal working of steel, such as the drawing of wire or the ~ressing, ~or~ y or cold-rolling of a plate or similar can act as the necess~ry dero,mdlion. This pellllils cc,lsiderdLle savings 10 in costs. During the deror,llalion, mal lel ~sile forms, the twin structure of which is o, ienled due to the stress held, or the twin structure of rl ,a, lensile that has already formed is re-oriented. After inst~ fion, the memory steel product is heated to the austenite range (typically 100 - 350~C), in which case part (or all) of the Illdl lel ,sile Chdl ,~3es to austenite. The product then tries to retum to its pre~lerc n"dlion shape, 15 which c~uses the desired stress in the structure in which the product has been installed.
It should be further noted, that nitrogen-alloyed shape memory steels manufactured accordi"g to the invention have yet one more excellent property, i.e.
20 the ability to exploit the for",alion of nitrides to reinforce the colll~,osilio". For example, one ,c, ocedure is that after cold-working the steel is aged by healil .9, e.g.
to about 300 - 600~C. The aging ~ses nitrides to form and in this way the sl, enyl h of the steel is further improved.
2~ The use of shape memory steel, for example in the prestressing of concrele (or rather in presll essing that is carried out afterwards) provides construction design with quite new opportunities, be~use shape memory steel can be installed in the desired shape inside the mass. When the mass has l,arde"ed, the state of prestressing can be set suitably by heating the steel at a selected point, for 30 example using induction heating or by an electric current led to the steel or other suitable ",a"ner. The use of ~I~e~l~ory steel as a presllessing method also makes it possible to increase the stress by means of heating carried out later, if the",a,lensile phase has been left in the steel during the first heating.
CA 0222~679 l997-l2-23 W O 97/03215 PcT/~ c1D~
5 The use of ~l~emo~y steels in the above applicalions is based on the fact thatdeformation is carried out on mer"ol~ steel products before they are inst~e~l Separ~te derol .,~ic" l is not always required, hec~ ~se the normal working of steel, such as the drawing of wire or the ~ressing, ~or~ y or cold-rolling of a plate or similar can act as the necess~ry dero,mdlion. This pellllils cc,lsiderdLle savings 10 in costs. During the deror,llalion, mal lel ~sile forms, the twin structure of which is o, ienled due to the stress held, or the twin structure of rl ,a, lensile that has already formed is re-oriented. After inst~ fion, the memory steel product is heated to the austenite range (typically 100 - 350~C), in which case part (or all) of the Illdl lel ,sile Chdl ,~3es to austenite. The product then tries to retum to its pre~lerc n"dlion shape, 15 which c~uses the desired stress in the structure in which the product has been installed.
It should be further noted, that nitrogen-alloyed shape memory steels manufactured accordi"g to the invention have yet one more excellent property, i.e.
20 the ability to exploit the for",alion of nitrides to reinforce the colll~,osilio". For example, one ,c, ocedure is that after cold-working the steel is aged by healil .9, e.g.
to about 300 - 600~C. The aging ~ses nitrides to form and in this way the sl, enyl h of the steel is further improved.
2~ The use of shape memory steel, for example in the prestressing of concrele (or rather in presll essing that is carried out afterwards) provides construction design with quite new opportunities, be~use shape memory steel can be installed in the desired shape inside the mass. When the mass has l,arde"ed, the state of prestressing can be set suitably by heating the steel at a selected point, for 30 example using induction heating or by an electric current led to the steel or other suitable ",a"ner. The use of ~I~e~l~ory steel as a presllessing method also makes it possible to increase the stress by means of heating carried out later, if the",a,lensile phase has been left in the steel during the first heating.
CA 0222~679 l997-l2-23 W O 97/03215 PcT/~ c1D~
When considering purely damping properties in this case too the pr~ e, lies and price of r,il,uge,, alloyed steels accor:li"y to the invention permit their wideindustrial arplic~tion. They can be used either as cast cGI"ponenls or as products that have been worked in various ways. They are s~it~hlc for use in large 5 constructions too bec~ ~se they can be joined by welding.
-Steels accordi"y to the invention are also suitable for such applications in whichthe .,.alerial must absorb impact energy and shock waves (e.g. v~hic1~5 and military applicalio"s). An ~ ;liu~ ~al advantage of ~"dl~rial accordi. .y to the10 invention co" "~a, ed to many other metallic damping malerials (e.g. Mn-Cu) is their high mod~ s of elasticity and high strength.
Practical tests using ~-.emc,.y steels acco~di.-g to the invention were carried out on some ar pli~tions that were reyarl:leJ as suitable.
As stated above shape memory steels are excellently suitable for many attacl""enl and tensioning applications. Pre-deformations can be carried out at room temperature at which it is also possible to store the deformed components (co""~are Ni-Ti-cryofit connectors). The moduli of elasticity of the steels are high 20 (the moduli of el~sticity of Cu and Ni-Ti-based me",ory metals for example are suLslzi"lially smaller which means that the greater part of the recoverable strain of these metals may be in elastic strain). Col- "oar~d to many other memory steels the advanlages of steels accordi. ,9 to the invention are great recovery forces and recoverable strain high mechanical sl~ enytl ~ and ductility good cGr. usion 25 ,esislance and high le",per; lure oxidation resistance excellent steel working and ."acl ,i"i"g properties. In addition the steels can be joined by welding. The weld too has been shown to have a shape l"~",or~r p~ u,~el l~/. This can also be exploited in applications. A practical demo,-sl, dlion was made by bending a butt weld andstraightening it by heating. Further steels according to the invention can be 30 economically manufactured by conventional methods used in the steel industry.
Shape ",e",o,y metals according to the invention have also an excellent ability to damp shock waves and impact energy be~ se the defor",alion of auslenile steel to martensite consumes a great deal of energy. In many applications the CA 0222~679 1997-12-23 W O 97/03215 PCT~6/00408 derc"llldlions may be very great, he~u-se the dero""alion mechanism is (up to a certain degree of deror-"dlion) the ror"~dlion of l~,d~lensile, instead of plastic deformation. Due to this, the limit of defor",2lion of the Illalelidl is very high.
Applications of this include vehicle frame structures and certain military 5 applications.
The presl, essit,g of concrete carried out with the aid of shape memory steel was tested/de",G"sl,dle.l by man~ ctl~ring two reinrol~ed steel beams (16 x 16 x 60 mm3). Inside both beams there were four 1 mm-thick longitudinal shape memory 10 steel rei"ru' ~" ,enLs acco~ dil ~ to the invention, which were sp~ced at 10 mm from one another. Ties were placed round the reinforcements at intervals of about 7 mm. Separate pre-deror",alion was not carried out on the memory steel wires, instead normal cold-drawing of the wire to a thicklless of 1 mm served as pre-~Jeru".,dlion. The wires placed inside one of the beams were heated to a 15 temperature of 250~C, at which most of the l,~a~lel,sile that had arisen in thedeformation changed to austenite and the wires simultaneously shortened. The wires placed inside the other beam were not heated. Both steel pillars were placed inside a form and the form was filled with concrete. The concrete was composed of normal Portland cement and sand, which was sieved through a 1.5 mm sieve.
20 After casli"y~ the con~ele mass was vibrated to reduce voids. When the concrete beams had hardened for 6 weeks, they were heated to 250~C. A cG",plessive stress then arose in the beam, the reinrorcel"ent wires of which had not been previously heated, as a consequence of the steel wires trying to shorten as the martensite changed to austenite. When both beams were bent, the prestressed 25 beam broke under a greater load. This demonstrates that prestressing, carried out with the aid of shape memory steel, works.
Also the attachment of pipe connections/machine col"~onents to an axle can be carried out using shape memory steel accordi"g to the invention. Machine 30 COIllpGl ,enls, e.g. flywheels and parts of electric motors, are allacl ,ed to an axle by exploiting ll ,e, Illd~ t,Udl ~SiUI 1. The toleral ~ce required is achieved by either heating the ",acl ,i"e component or by cooling the axle with e.g. Iiquid nitrogen. The shape memory eKect can also be exploited in atta~:l""enl. The changes in dimension achieved with memory steels are much yrealer than those caused by thermal CA 0222~679 1997-12-23 W O 97/03215 PCTn~96/00408 e~ansion. Attachment can take place by means of e.g a sleeve made from shape memory steel. The sleeve can be pre~erorl"ed by drawing the sleeve in the direction of the axle. Vvhen the sleeve is placed between the axle and the machine component and heali"g is carried out to the au~ ile range the sleeve tries to 5 return to its pre-drawing form. The thickness of its wall i"creases and simulla"eously it tightens the machine co~ onent onto the axle. If the sleeve ismade from two-way shape memory steel the removal of the ~acl ,i"e COIllpOl ,ant takes place by cooling to a le"~peralure that has been selected with the aid of the alloying of the ~ "amo~ ~/ steel and lhe~ " ,o" ,ecl ~ ical ll aaln ,e, ll so much lower than 10 the operating temperature of the machine that uni~ ILenliGI ,al detacl ""anl cannot take place.
A pipe connection made from memol~ steel is a sleeve the inner dian,ater of which is smaller than the outer diameter of the pipe. The inner dia",aler of the15 sleeve is enlarged to be greater than the diameter of the pipe by deforming the sleeve e.g. by means of a ~"a"dlal. The enlaryed sleeve is placed over a butt joint between two pipes. The sleeve tightens the pipes together when it is heated to the austenite range.
20 The attachment of a memory steel sleeve around an axle and pipe was de",on~l,aled by manufacturing a sleeve from the l"amoly steel to be palenled with a length of 10 mm an intemal did",ater of 8 mm and a wall thickness of 2 mm.
Attacl""e"l took place by heating the sleeve to 300~C. The ti~.3hlening sl,asseswere ascertained with the aid of changes in dimension.
A sepa~ale all~;l " "enl cor, ,,uonenl made from rl ~a~ "ory steel is not always required bec~l Ise in many instances the product itself can be made from memory steel.
It is possible to exploit the invention in the allach~enl of a rivet screw or other 30 allacl ,r"ent member in which a change of dimension takes place in the direction of the axle. In many attachment applications (e.g. plates machine components) attachment can be carried out by means of such an attachment member which has been derc"ned by drawing in the direction of the axle before allacl Iment. After installation tiyl,lel,i"g takes place by heating the alLachment member to the CA 02225679 l997-l2-23 W O 97/03215 PcT/k~5 austenite range. I le~ ,9 can also take place in such a way that the central part of the ,ner.ll,er is heated to a higher te,ll,~er~lure than the outer surface. In this case, rnore au~leniLe arises in the inner parts than in the surface parts. A tensile stress then arises inside the member and a cor", ressive stress in the surface. Fractures 5 an. d stress co" oSiG,) do not easily arise in a surface subject to col "pressive stress.
=The exploitation of the stress gradients c~l ~sPd by the partial I ,eali,)g of memory steel is a new innovation, which can be utili~Pd in many applications.
.-~
. ~ ~ .
~, w Cons~truction al-plic~lions dt:",a".li.)g high resisla"ce to fatigue can aiso utilize the 10 ~--~vention. Because nitrogen-alloyed shape memory steels are strong, and they have so-called super-elastic properties, they easily wilhsland fatigue loa~ yS at even high loading amplit~ es When steel is sllessed, the derorllldlioll mechanism is (up to a certain limit) twinning and not slipping. This ...ecl,anis", is recoverable and ",~terial fatigue is then very small. Be~ ~se steels accordi,)g to the invention 15 are, in addiliGIl, cheap and easily worked and easily welded together, they are highly sl ~it~hle as construction materials for large steel structures and machines in which they are subject to great fatigue loadings.
-Steels accordi"y to the invention are also suitable for such applications in whichthe .,.alerial must absorb impact energy and shock waves (e.g. v~hic1~5 and military applicalio"s). An ~ ;liu~ ~al advantage of ~"dl~rial accordi. .y to the10 invention co" "~a, ed to many other metallic damping malerials (e.g. Mn-Cu) is their high mod~ s of elasticity and high strength.
Practical tests using ~-.emc,.y steels acco~di.-g to the invention were carried out on some ar pli~tions that were reyarl:leJ as suitable.
As stated above shape memory steels are excellently suitable for many attacl""enl and tensioning applications. Pre-deformations can be carried out at room temperature at which it is also possible to store the deformed components (co""~are Ni-Ti-cryofit connectors). The moduli of elasticity of the steels are high 20 (the moduli of el~sticity of Cu and Ni-Ti-based me",ory metals for example are suLslzi"lially smaller which means that the greater part of the recoverable strain of these metals may be in elastic strain). Col- "oar~d to many other memory steels the advanlages of steels accordi. ,9 to the invention are great recovery forces and recoverable strain high mechanical sl~ enytl ~ and ductility good cGr. usion 25 ,esislance and high le",per; lure oxidation resistance excellent steel working and ."acl ,i"i"g properties. In addition the steels can be joined by welding. The weld too has been shown to have a shape l"~",or~r p~ u,~el l~/. This can also be exploited in applications. A practical demo,-sl, dlion was made by bending a butt weld andstraightening it by heating. Further steels according to the invention can be 30 economically manufactured by conventional methods used in the steel industry.
Shape ",e",o,y metals according to the invention have also an excellent ability to damp shock waves and impact energy be~ se the defor",alion of auslenile steel to martensite consumes a great deal of energy. In many applications the CA 0222~679 1997-12-23 W O 97/03215 PCT~6/00408 derc"llldlions may be very great, he~u-se the dero""alion mechanism is (up to a certain degree of deror-"dlion) the ror"~dlion of l~,d~lensile, instead of plastic deformation. Due to this, the limit of defor",2lion of the Illalelidl is very high.
Applications of this include vehicle frame structures and certain military 5 applications.
The presl, essit,g of concrete carried out with the aid of shape memory steel was tested/de",G"sl,dle.l by man~ ctl~ring two reinrol~ed steel beams (16 x 16 x 60 mm3). Inside both beams there were four 1 mm-thick longitudinal shape memory 10 steel rei"ru' ~" ,enLs acco~ dil ~ to the invention, which were sp~ced at 10 mm from one another. Ties were placed round the reinforcements at intervals of about 7 mm. Separate pre-deror",alion was not carried out on the memory steel wires, instead normal cold-drawing of the wire to a thicklless of 1 mm served as pre-~Jeru".,dlion. The wires placed inside one of the beams were heated to a 15 temperature of 250~C, at which most of the l,~a~lel,sile that had arisen in thedeformation changed to austenite and the wires simultaneously shortened. The wires placed inside the other beam were not heated. Both steel pillars were placed inside a form and the form was filled with concrete. The concrete was composed of normal Portland cement and sand, which was sieved through a 1.5 mm sieve.
20 After casli"y~ the con~ele mass was vibrated to reduce voids. When the concrete beams had hardened for 6 weeks, they were heated to 250~C. A cG",plessive stress then arose in the beam, the reinrorcel"ent wires of which had not been previously heated, as a consequence of the steel wires trying to shorten as the martensite changed to austenite. When both beams were bent, the prestressed 25 beam broke under a greater load. This demonstrates that prestressing, carried out with the aid of shape memory steel, works.
Also the attachment of pipe connections/machine col"~onents to an axle can be carried out using shape memory steel accordi"g to the invention. Machine 30 COIllpGl ,enls, e.g. flywheels and parts of electric motors, are allacl ,ed to an axle by exploiting ll ,e, Illd~ t,Udl ~SiUI 1. The toleral ~ce required is achieved by either heating the ",acl ,i"e component or by cooling the axle with e.g. Iiquid nitrogen. The shape memory eKect can also be exploited in atta~:l""enl. The changes in dimension achieved with memory steels are much yrealer than those caused by thermal CA 0222~679 1997-12-23 W O 97/03215 PCTn~96/00408 e~ansion. Attachment can take place by means of e.g a sleeve made from shape memory steel. The sleeve can be pre~erorl"ed by drawing the sleeve in the direction of the axle. Vvhen the sleeve is placed between the axle and the machine component and heali"g is carried out to the au~ ile range the sleeve tries to 5 return to its pre-drawing form. The thickness of its wall i"creases and simulla"eously it tightens the machine co~ onent onto the axle. If the sleeve ismade from two-way shape memory steel the removal of the ~acl ,i"e COIllpOl ,ant takes place by cooling to a le"~peralure that has been selected with the aid of the alloying of the ~ "amo~ ~/ steel and lhe~ " ,o" ,ecl ~ ical ll aaln ,e, ll so much lower than 10 the operating temperature of the machine that uni~ ILenliGI ,al detacl ""anl cannot take place.
A pipe connection made from memol~ steel is a sleeve the inner dian,ater of which is smaller than the outer diameter of the pipe. The inner dia",aler of the15 sleeve is enlarged to be greater than the diameter of the pipe by deforming the sleeve e.g. by means of a ~"a"dlal. The enlaryed sleeve is placed over a butt joint between two pipes. The sleeve tightens the pipes together when it is heated to the austenite range.
20 The attachment of a memory steel sleeve around an axle and pipe was de",on~l,aled by manufacturing a sleeve from the l"amoly steel to be palenled with a length of 10 mm an intemal did",ater of 8 mm and a wall thickness of 2 mm.
Attacl""e"l took place by heating the sleeve to 300~C. The ti~.3hlening sl,asseswere ascertained with the aid of changes in dimension.
A sepa~ale all~;l " "enl cor, ,,uonenl made from rl ~a~ "ory steel is not always required bec~l Ise in many instances the product itself can be made from memory steel.
It is possible to exploit the invention in the allach~enl of a rivet screw or other 30 allacl ,r"ent member in which a change of dimension takes place in the direction of the axle. In many attachment applications (e.g. plates machine components) attachment can be carried out by means of such an attachment member which has been derc"ned by drawing in the direction of the axle before allacl Iment. After installation tiyl,lel,i"g takes place by heating the alLachment member to the CA 02225679 l997-l2-23 W O 97/03215 PcT/k~5 austenite range. I le~ ,9 can also take place in such a way that the central part of the ,ner.ll,er is heated to a higher te,ll,~er~lure than the outer surface. In this case, rnore au~leniLe arises in the inner parts than in the surface parts. A tensile stress then arises inside the member and a cor", ressive stress in the surface. Fractures 5 an. d stress co" oSiG,) do not easily arise in a surface subject to col "pressive stress.
=The exploitation of the stress gradients c~l ~sPd by the partial I ,eali,)g of memory steel is a new innovation, which can be utili~Pd in many applications.
.-~
. ~ ~ .
~, w Cons~truction al-plic~lions dt:",a".li.)g high resisla"ce to fatigue can aiso utilize the 10 ~--~vention. Because nitrogen-alloyed shape memory steels are strong, and they have so-called super-elastic properties, they easily wilhsland fatigue loa~ yS at even high loading amplit~ es When steel is sllessed, the derorllldlioll mechanism is (up to a certain limit) twinning and not slipping. This ...ecl,anis", is recoverable and ",~terial fatigue is then very small. Be~ ~se steels accordi,)g to the invention 15 are, in addiliGIl, cheap and easily worked and easily welded together, they are highly sl ~it~hle as construction materials for large steel structures and machines in which they are subject to great fatigue loadings.
Claims (14)
1. A shape memory and vibration damping steel composition, characterized in that it contains, in addition to iron, (in percentages by weight) Mn 5.0 - 50.0 %, Si 0 - 8.0 % and N 0.01 - 0.8 %, as well as, if desired, one or more of the following elements:
Cr 0.1 - 20.0 %, Ni 0.1 - 20.0 %, Co 0.1 - 20.0 %, Cu 0.1 - 3.0 %, V 0.1 - 1.0 %, Nb 0.1 -1.0 %, Mo 0.1 - 3.0 %, C 0.001 - 1.0 %. rare earth metals (e.g. Sc, Y, La, Ce) 0.0005 - 0.02 %, and that it fulfils the following equation:
Ni + Co + 0.5Mn + 0.3Cu + 20N + 25C ~ 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo).
Cr 0.1 - 20.0 %, Ni 0.1 - 20.0 %, Co 0.1 - 20.0 %, Cu 0.1 - 3.0 %, V 0.1 - 1.0 %, Nb 0.1 -1.0 %, Mo 0.1 - 3.0 %, C 0.001 - 1.0 %. rare earth metals (e.g. Sc, Y, La, Ce) 0.0005 - 0.02 %, and that it fulfils the following equation:
Ni + Co + 0.5Mn + 0.3Cu + 20N + 25C ~ 0.3 x (Cr + 2Si + 5V + 1.5Nb + 1.5Mo).
2. A composition according to Claim 1, characterized in that it contains, in addition to iron, Mn 8.0 - 45.0 %, Si 0 - 7.5 % and N 0.05 - 0.6 %, as well as, if desired, the aforementioned other elements.
3. A composition according to Claim 1, characterized in that it contains, in addition to iron, Mn 10.0 - 40.0 %, Si 0 - 7.0 % and N 0.1 - 0.5 %, as well as, if desired, the aforementioned other elements.
4. A composition according to Claim 1, characterized in that it contains, in addition to iron, Mn 13.0 - 35.0 %, Si 2.0 - 6.0 % and N 0.1 - 0.4 %, as well as, if desired, the aforementioned other elements.
5. A composition according to Claim 1, characterized in that it contains, in addition to iron, Mn 14.9 - 35.0 %, Si 3.0 - 6.5 %, and N 0.1 - 0.4 %, as well as, if desired, the aforementioned other elements.
6. A composition according to Claim 1, characterized in that it contains, in addition to iron, manganese, silicon and nitrogen, one or both of the following substances: Cr 0.1 - 20.0 % and Ni 0.1 - 20.0 %.
7. A composition according to Claim 1, characterized in that it contains, in addition to iron, manganese, silicon and nitrogen, one or more of the following substances; Cr 0.1 - 20.0 %, Ni 0.1 -20.0 %, Co 0.1 - 20.0 %, Cu 0.1 - 3.0 % V 0.1 - 0.8 % Nb 0.1 - 0.8% Re 0.0005 - 0.02 %.
8. A composition according to Claim 1 characterized in that it contains in addition to iron manganese, silicon and nitrogen also C 0.005 - 0.6 %.
9. The use of a steel according to Claim 1 in attachments, tensioners and various prestressed structures.
10. The use according to Claim 9 in the prestressing of concrete structures.
11. The use of a steel according to Claim 1 on account of the two-way memory phenomenon, to produce movement or force in actuator applications.
12. The use of a steel according to Claim 1 in objects requiring vibration damping.
13. The use of a steel according to Claim 1 in objects requiring the damping of impact loadings and shock waves.
14. The use of a steel according to Claim 1 in objects requiring high fatigue resistance.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI953393A FI953393A0 (en) | 1995-07-11 | 1995-07-11 | Kvaevelegerade minnismetaller |
| FI953393 | 1995-07-11 | ||
| FI960866A FI960866A (en) | 1995-07-11 | 1996-02-26 | memory metals |
| FI960866 | 1996-02-26 | ||
| FI961922 | 1996-05-07 | ||
| FI961922A FI961922A0 (en) | 1996-05-07 | 1996-05-07 | Daempningsstaol |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2225679A1 true CA2225679A1 (en) | 1997-01-30 |
Family
ID=27241642
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2225679 Abandoned CA2225679A1 (en) | 1995-07-11 | 1996-07-11 | Iron-based shape memory and vibration damping alloys containing nitrogen |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0846189A1 (en) |
| JP (1) | JP2000501778A (en) |
| AU (1) | AU6361396A (en) |
| CA (1) | CA2225679A1 (en) |
| RU (1) | RU2169786C2 (en) |
| WO (1) | WO1997003215A1 (en) |
Cited By (2)
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| CN103173695A (en) * | 2011-12-22 | 2013-06-26 | 空中客车印度工程中心 | Shape memory stainless steels with rare earth elements Ce and La |
| CN111500946A (en) * | 2020-05-25 | 2020-08-07 | 徐州优尚精密机械制造有限公司 | Stainless steel casting for ship hardware fitting and preparation process thereof |
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| CN1062060C (en) * | 1997-12-31 | 2001-02-14 | 天津大学国家教委形状记忆材料工程研究中心 | Shape-memory stainless steel joint for pipeline |
| FI982407A0 (en) | 1998-03-03 | 1998-11-06 | Adaptamat Tech Oy | Controls and devices |
| JP3864600B2 (en) * | 1999-01-27 | 2007-01-10 | Ｊｆｅスチール株式会社 | Method for producing high Mn non-magnetic steel sheet for cryogenic use |
| JP3542754B2 (en) * | 2000-02-09 | 2004-07-14 | 独立行政法人物質・材料研究機構 | Shape memory alloy |
| CN1128244C (en) * | 2000-10-26 | 2003-11-19 | 艾默生电气（中国）投资有限公司 | Fe-Mn-Si base marmem containing Cr and N and its training method |
| SE528991C2 (en) | 2005-08-24 | 2007-04-03 | Uddeholm Tooling Ab | Steel alloy and tools or components made of the steel alloy |
| EP1767659A1 (en) | 2005-09-21 | 2007-03-28 | ARCELOR France | Method of manufacturing multi phase microstructured steel piece |
| EP2141251B1 (en) * | 2008-06-25 | 2016-12-28 | EMPA Dübendorf | Shape memory alloys based on iron, manganese and silicon |
| JP2010156041A (en) * | 2008-12-04 | 2010-07-15 | Daido Steel Co Ltd | Two-way shape-recovery alloy |
| RU2443795C2 (en) * | 2010-04-16 | 2012-02-27 | Тамара Федоровна Волынова | MULTI-FUNCTION ANTIFRICTION NANOSTRUCTURE WEAR-RESISTANT DAMPING ALLOYS WITH SHAPE MEMORY EFFECT ON METASTABLE BASIS OF IRON WITH STRUCTURE OF HEXAGONAL ε-MARTENSITE, AND ITEMS USING THESE ALLOYS WITH EFFECT OF SELF-ORGANISATION OF NANOSTRUCTURE COMPOSITIONS, SELF-STRENGTHENING AND SELF-LUBRICATION OF FRICTION SURFACES, WITH EFFECT OF SELF-DAMPING OF VIBRATIONS AND NOISES |
| RU2494162C1 (en) * | 2012-10-05 | 2013-09-27 | Юлия Алексеевна Щепочкина | Iron-based wear resistant alloy |
| JP6182725B2 (en) * | 2012-12-28 | 2017-08-23 | 国立研究開発法人物質・材料研究機構 | Damping alloy |
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| WO2020064126A1 (en) * | 2018-09-28 | 2020-04-02 | Thyssenkrupp Steel Europe Ag | Shape-memory alloy, flat steel product made therefrom with pseudo-elastic properties, and method for producing such a flat steel product |
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| US4929289A (en) * | 1988-04-05 | 1990-05-29 | Nkk Corporation | Iron-based shape-memory alloy excellent in shape-memory property and corrosion resistance |
| CA1323511C (en) * | 1988-04-05 | 1993-10-26 | Hisatoshi Tagawa | Iron-based shape-memory alloy excellent in shape-memory property, corrosion resistance and high-temperature oxidation resistance |
| JPH02228451A (en) * | 1989-02-28 | 1990-09-11 | Nippon Steel Corp | Iron-base shape memory alloy |
| JPH02301514A (en) * | 1989-05-15 | 1990-12-13 | Nisshin Steel Co Ltd | Method for allowing shape memory stainless steel to memorize shape |
| JPH0328319A (en) * | 1989-06-26 | 1991-02-06 | Nisshin Steel Co Ltd | Pipe joint made of stainless steel and its production |
| JPH0382741A (en) * | 1989-08-25 | 1991-04-08 | Nisshin Steel Co Ltd | Shape memory staiinless steel excellent in stress corrosion cracking resistance and shape memory method therefor |
| FR2654748B1 (en) * | 1989-11-22 | 1992-03-20 | Ugine Aciers | STAINLESS STEEL ALLOY WITH SHAPE MEMORY AND METHOD FOR PRODUCING SUCH AN ALLOY. |
-
1996
- 1996-07-11 JP JP9505533A patent/JP2000501778A/en not_active Ceased
- 1996-07-11 WO PCT/FI1996/000408 patent/WO1997003215A1/en not_active Application Discontinuation
- 1996-07-11 EP EP96922913A patent/EP0846189A1/en not_active Ceased
- 1996-07-11 RU RU98102127/02A patent/RU2169786C2/en not_active IP Right Cessation
- 1996-07-11 AU AU63613/96A patent/AU6361396A/en not_active Abandoned
- 1996-07-11 CA CA 2225679 patent/CA2225679A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103173695A (en) * | 2011-12-22 | 2013-06-26 | 空中客车印度工程中心 | Shape memory stainless steels with rare earth elements Ce and La |
| CN103173695B (en) * | 2011-12-22 | 2015-10-21 | 空中客车印度工程中心 | Shape memory stainless steel containing rare earth element ce and La |
| CN111500946A (en) * | 2020-05-25 | 2020-08-07 | 徐州优尚精密机械制造有限公司 | Stainless steel casting for ship hardware fitting and preparation process thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0846189A1 (en) | 1998-06-10 |
| JP2000501778A (en) | 2000-02-15 |
| AU6361396A (en) | 1997-02-10 |
| WO1997003215A1 (en) | 1997-01-30 |
| RU2169786C2 (en) | 2001-06-27 |
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