NO122041B

NO122041B -

Info

Publication number: NO122041B
Application number: NO0603/70A
Authority: NO
Inventors: M Bergquist; O Kaellstroem; G Lagerberg; N Oekvist
Original assignee: Sandvikens Jernverks Ab
Priority date: 1969-02-21
Filing date: 1970-02-20
Publication date: 1971-05-10
Also published as: GB1252238A; SE323525B; DE2008320B2; JPS5020938B1; DE2008320C3; US3664825A; FR2035397A5; DE2008320A1

Description

Fremgangsmåte ved fremstilling Method of manufacture

av zirkoniumlegeringer. of zirconium alloys.

Oppfinnelsen angår en fremgangsmåte ved fremstilling av zirkoniumlegeringer av kjent type som foruten zirkonium og en ubetydelig mengde forurensninger hovedsakelig inneholder 0,2-2,5 vektprosent tinn og en samlet mengde av 0,1-3,0 vektprosent av ett eller flere av metallene jern, krom, nikkel og niob for derved å oppnå legeringer med en hoyere duktilitet enn vanlig og for-bedrede overflateegenskaper. The invention relates to a process for the production of zirconium alloys of a known type which, in addition to zirconium and an insignificant amount of impurities, mainly contain 0.2-2.5 weight percent tin and a total amount of 0.1-3.0 weight percent of one or more of the metals iron , chromium, nickel and niobium in order to obtain alloys with a higher ductility than usual and improved surface properties.

Legeringer av denne type, som "Zircaloy 2" hhv. "Zircaloy h", som foruten tinn inneholder små mengder jern, krom og nikkel hlw. jern og krom, har vist seg å være spesielt godt egnede for an-vendelse som kapslingsror for atomreaktorer på grunn av sin gode holdfasthet, sin korrosjonsbestandighet ved hoyere temperaturer Alloys of this type, such as "Zircaloy 2" or "Zircaloy h", which, in addition to tin, contains small amounts of iron, chromium and nickel hlw. iron and chromium, have proven to be particularly well suited for use as containment tubes for nuclear reactors due to their good holding strength, their corrosion resistance at higher temperatures

og sitt lave tverrsnitt for noytronabsorpsjon. and its low neutron absorption cross section.

Når en slik legering avkjoles fra en hoy temperatur, f.eks. fra 1000°C, forekommer det en omvandling fra en hoytemperaturfase P (kubisk romsentrert gitter) til en lavtemperaturfase a (tett-pakket hexagonalt gitter). Under omvandlingen dannes små plater (skiver) av a-fase fra kjerner i p-krystallene, og disse små plater vokser derefter langs spesifikke krystallplan i p-krystallene, When such an alloy is cooled from a high temperature, e.g. from 1000°C, a transformation from a high-temperature phase P (cubic space-centered lattice) to a low-temperature phase a (close-packed hexagonal lattice) occurs. During the transformation, small plates (discs) of a-phase are formed from nuclei in the p-crystals, and these small plates then grow along specific crystal planes in the p-crystals,

dvs. de såkalte habitusplan. Omvandlingstypen er i og for seg velkjent og betegnes med Widmanståtten-omvandling. i.e. the so-called habitus plan. The transformation type is well known in and of itself and is referred to as the Widmanståten transformation.

Som regel foregår omvandlingen slik at hver p-krystall gjen-nomtrenges av grupper av i det vesentlige parallelle skiver av a-fase. Det er mulig at kjernedannelsesstedene for a-faseskivene hovedsakelig har befunnet seg i p-krystallenes korngrenser, og dette har medfort at inntil hverandre liggende kjerner i en slik korngrense har hatt sterkt lignende betingelser for sin dannelse som har medfort en vekst av ensartet orienterte skiver. Den derved dannede struktur betegnes i fortsettelsen som "A-struktur". As a rule, the transformation takes place so that each p-crystal is penetrated by groups of essentially parallel slices of a-phase. It is possible that the nucleation sites for the a-phase disks have mainly been located in the grain boundaries of the p-crystals, and this has meant that adjacent nuclei in such a grain boundary have had very similar conditions for their formation, which has led to the growth of uniformly oriented disks. The resulting structure is referred to in the following as "A-structure".

Det har nu vist seg at kjernedannelse kan oppnåes inne i p-krystallene. Kjernedannelsestedene befinner seg da inntil partikler i krystallene. Ved hver slik partikkel dannes kjernene for flere a-faseskiver som derefter vokser i forskjellige retninger. Skiver som har vokst fra forskjellige kjernedannende partikler, vil krysse hverandre, og dette forer til at strukturen ser ut som et flett - verk som ofte betegnes som en "kurvfletningsstruktur". Denne struktur er i fortsettelsen betegnet som "B-struktur". It has now been shown that nucleation can be achieved inside the p-crystals. The nucleation sites are then located next to particles in the crystals. At each such particle, the nuclei form for several a-phase discs which then grow in different directions. Discs that have grown from different nucleating particles will cross each other, and this causes the structure to look like a braid - a work often referred to as a "basket weave structure". This structure is hereafter referred to as "B-structure".

B-strukturen er i flere henseender mer fordelaktig enn den ovenfor'angitte A-struktur, bl.a. hva gjelder materialets duktilitet og overflateegenskaper. The B-structure is in several respects more advantageous than the above-mentioned A-structure, i.a. in terms of the material's ductility and surface properties.

Som et eksempel på hvorledes overflateegenskapene er avhengige av strukturen, kan det nevnes at ved fremstillingen av kapslingsror utfores som regel en varmebehandling innen p-faseområdet slik at omvandlingen til A-struktur forekommer fra forholdsvis grove p-fasekrystaller. På grunn av de store enheter av jevnt orienterte a-faseplater som derved dannes og på grunn av selve a-fasens mekaniske anisotropi blir materialflytningen ved en efterfolgende plastisk bearbeidelse uregelmessig, og dette forer til uregelmes-sige overflater og et derav folgende nedsatt utbytte. Hvis derimot As an example of how the surface properties are dependent on the structure, it can be mentioned that in the production of casing tubes, a heat treatment is usually carried out within the p-phase area so that the transformation to A-structure occurs from relatively coarse p-phase crystals. Due to the large units of uniformly oriented a-phase plates that are thereby formed and due to the mechanical anisotropy of the a-phase itself, the material flow becomes irregular during a subsequent plastic processing, and this leads to irregular surfaces and a consequent reduced yield. If however

en B-struktur oppnåes, blir overflatene jevne. a B-structure is achieved, the surfaces become smooth.

Som angitt ovenfor er B-strukturen langt bedre enn A-strukturen hva gjelder duktiliteten. Ved f.eks. fremstilling av brenselelementer hvor brenselstaver innkapslet med den ovenfor angitte legering sammenfoyes ved lodding, gjennomgår en del av kapslingsroret inntil loddefugen faseomvandlingen a-B-a. Dersom omvandlingen p-a gir A-struktur, nedsettes duktiliteten betrakte-lig sammenlignet med dersom omvandlingen gir B-struktur. As stated above, the B structure is far better than the A structure in terms of ductility. By e.g. production of fuel elements where fuel rods encapsulated with the alloy specified above are joined by soldering, a part of the casing tube undergoes the phase transformation a-B-a until the solder joint. If the transformation p-a gives an A-structure, the ductility is reduced considerably compared to if the transformation gives a B-structure.

For zirkoniumlegeringer av den ovenfor angitte type er det derfor viktig at omvandlingen av p-fase til a-fase forer til B-strukturen. For zirconium alloys of the above-mentioned type, it is therefore important that the conversion of p-phase to a-phase leads to the B structure.

Det har nu ved omfattende forsok vist seg at den onskede B-struktur kan oppnåes ved den angitte faseomvandling ved å til-sette en egnet mengde av et metallcarbid når legeringsbestand-delene smeltes sammen. Den forholdsvise mengde av det tilsatte metallcarbid bor noyaktig reguleres slik at den ferdige legering får et sluttcarboninnhold av minst lM-O, fortrinnsvis 150, og hoyst 300 vektdeler pr. million .vektdeler av legeringen (1<*>4-0 - 300 ppm). Som tilsetningsmateriale. anvendes som regel zirkoniumcarbid, ;men det er mulig helt eller delvis å erstatte zirkoniumcarbidet med. ett eller flere metallcarbider som jern-, krom- og niobcarbid. ;Som regel bor zirkoniumcarbid og/eller et annet metallcarbid tilsettes i en .slik mengde at legeringen får et sluttcarboninnhold ikke over 300, fortrinnsvis l<>>+0-300, ppm. Dersom carboninn-holdet er lavere enn den ovenfor angitte, nedre grense av-l^fO ppm, fåes ikke den onskede B-struktur. Dersom på den annen side den c5vre grense av~300 overskrides, går dette ut over korrosjonsbe-standigheten. Det har dessuten vist seg at metallcarbidet fortrinnsvis bor tilsettes i form av et pulver for å oppnå det gun-stige resultat ifolge oppfinnelsen. ;Da zirkonium lett danner oxyder og absorberer atmosfæriske og andre forurensninger ved forhoyede temperaturer, bor legerings-bestanddelene smeltes under vakuum i en lysbueovn. Ved smeltingen anvendes som regel zirkoniumsvamp og zirkoniumskrap som utgangsmateriale, og onskede mengder av de bvrige legeringselementer tilsettes. Det har ifolge oppfinnelsen vist seg nbdvendig at zir-koniumbestanddelene samlet ikke må inneholde mer carbon enn 100 ppm, fortrinnsvis ikke over 75 ppm. Det tilsettes ifolge oppfinnelsen også zirkoniumcarbid og/eller andre metallcarbider i en slik mengde at den ferdige legering får det ovenfor angitte carbon-innhold. Råmaterialene bor være så rene som mulig, men det kan ofte ikke unngåes at ubetydelige mengder forurensninger, bl. a. carbon, kan forekomme i disse. Ifolge oppfinnelsen er det av vesentlig betydning at disse forurensninger er tilstede i en lav mengde og at minst 50 %, fortrinnsvis minst 80 %, av carbonet i sluttlegeringen er carbon som er blitt tilfort ved tilsetningene av zirkoniumcarbid og/eller andre metallcarbider. Det kan i denne forbindelse nevnes at i visse tilfeller kan ubetydelige mengder oxygen og/eller silicium være tilstede i legeringen som aktiv bestanddel. ;Oppfinnelsen vil bli nærmere'beskrevet i form av et eksempel i forbindelse med fremstilling av "Zircaloy 2" inneholdende 1,<*>+ vektprosent tinn,0,12 vektprosent jern, 0,10 vektprosent krom, 0,06 vektprosent nikkel og resten zirkonium med ubetydelige mengder forurensninger. It has now been shown by extensive testing that the desired B-structure can be achieved by the indicated phase transformation by adding a suitable amount of a metal carbide when the alloy components are fused together. The relative amount of the added metal carbide should be precisely regulated so that the finished alloy has a final carbon content of at least 1M-0, preferably 150, and at most 300 parts by weight. million .parts by weight of the alloy (1<*>4-0 - 300 ppm). As an additive. as a rule, zirconium carbide is used, but it is possible to completely or partially replace the zirconium carbide with. one or more metal carbides such as iron, chromium and niobium carbide. As a rule, zirconium carbide and/or another metal carbide should be added in such an amount that the alloy has a final carbon content not exceeding 300, preferably 1<>>+0-300, ppm. If the carbon content is lower than the above-mentioned, lower limit of -1^f0 ppm, the desired B structure is not obtained. If, on the other hand, the upper limit of ~300 is exceeded, this exceeds the corrosion resistance. It has also been shown that the metal carbide should preferably be added in the form of a powder in order to achieve the favorable result according to the invention. As zirconium easily forms oxides and absorbs atmospheric and other pollutants at elevated temperatures, the alloy components must be melted under vacuum in an arc furnace. During the melting, zirconium sponge and zirconium scrap are usually used as starting material, and desired amounts of the other alloying elements are added. According to the invention, it has proved necessary that the zirconium components must not contain more carbon than 100 ppm, preferably not more than 75 ppm. According to the invention, zirconium carbide and/or other metal carbides are also added in such a quantity that the finished alloy has the above-mentioned carbon content. The raw materials must be as clean as possible, but it often cannot be avoided that insignificant amounts of contamination, e.g. a. carbon, can occur in these. According to the invention, it is of significant importance that these contaminants are present in a low amount and that at least 50%, preferably at least 80%, of the carbon in the final alloy is carbon that has been added by the additions of zirconium carbide and/or other metal carbides. In this connection, it can be mentioned that in certain cases negligible amounts of oxygen and/or silicon may be present in the alloy as an active ingredient. The invention will be described in more detail in the form of an example in connection with the production of "Zircaloy 2" containing 1.<*>+ weight percent tin, 0.12 weight percent iron, 0.10 weight percent chromium, 0.06 weight percent nickel and the rest zirconium with negligible amounts of impurities.

Utgangsmaterialene for smeltingen som ble utfort under vakuum i en lysbueovn, var zirkoniumsvamp, zirkoniumskrap og onskede mindre mengder av de andre legeringsbestanddeler. Carbon-innholdet i utgangsmaterialet var ca. 0,005 vektprosent. Til det ovenfor angitte utgang.smateriale ble 0,15 vektprosent zirkoniumcarbid tilsatt. The starting materials for the melting, which was carried out under vacuum in an electric arc furnace, were zirconium sponge, zirconium scrap and desired smaller amounts of the other alloy constituents. The carbon content in the starting material was approx. 0.005% by weight. 0.15% by weight of zirconium carbide was added to the starting material indicated above.

En sammenligning mellom strukturen til materialet (I) fremstilt ved foreliggende fremgangsmåte og strukturen til et til-svarende •materiale (II) fremstilt fra et vanlig utgangsmateriale på vanlig måte, viste at materialet' I hadde en jevn B-struktur og at materialet II hadde en jevn A-struktur efter varmebehandling innen B-området, som ved lodding. Ved et spesielt strekkforsok med et materiale behandlet på denne måte, ble det for materialet I oppnådd en forlengelse av 13 % og en forlengelse av 6 % for materialet II. Efter en varmebehandling innen B-området fikk materialet I en jevn overflate mens materialet II hadde en uregel- A comparison between the structure of the material (I) produced by the present method and the structure of a corresponding material (II) produced from a common starting material in the usual way showed that the material I had a uniform B structure and that the material II had a uniform A structure after heat treatment within the B area, as with soldering. In a special tensile test with a material treated in this way, an elongation of 13% was achieved for material I and an elongation of 6% for material II. After a heat treatment in the B area, material I had a smooth surface, while material II had an irregular

my.-;;;ig og grov overflate. my.-;;;ig and rough surface.

Ved et ytterligere forsok ble "Zircaloy K" inneholdende 1,5 vektprosent tinn, 0,21 vektprosent jern, 0,12 vektprosent krom og resten zirkonium med ubetydelige mengder forurensninger fremstilt ved under vakuum i en lysbueovn å smelte et materiale som, med unntagelse av en tilsatt mengde av 0,12 vektprosent kromcarbid, var praktisk talt fritt for carbon. Efter varmbear-bsidelse innen B-området hadde legeringen en jevn overflate mens en legering av den ovenfor angitte type og fremstilt på vanlig måte hadde en uregelmessig og grov overflate. In a further attempt, "Zircaloy K" containing 1.5% by weight of tin, 0.21% by weight of iron, 0.12% by weight of chromium and the remainder zirconium with negligible amounts of impurities was produced by melting under vacuum in an electric arc furnace a material which, with the exception of an added amount of 0.12 weight percent chromium carbide, was practically free of carbon. After heat treatment within the B range, the alloy had a smooth surface, while an alloy of the above-mentioned type and produced in the usual way had an irregular and rough surface.

De fremstilte legeringsprodukter ved hvert av disse forsok hadde et sluttcarboninnhold av 150-300 ppm. The alloy products produced in each of these trials had a final carbon content of 150-300 ppm.

Claims

1. Process for the production of a zirconium alloy which, in addition to zirconium and a negligible amount of impurities, contains 0.2 - 2.5 weight percent tin and a total amount of 0.1 - 3.0 weight percent of one or more of the metals iron, chromium , nickel and niobium, and also carbon, as the alloy has a B-phase structure at higher temperatures and an a-phase structure at lower temperatures, characterized by one or more zirconium constituents with a total carbon content not exceeding 100 parts by weight. million parts by weight are melted with the addition of one or more metal carbides together with the additional components necessary to achieve the necessary composition for the alloy, whereby the metal carbide or carbides are added in such an amount that the zirconium alloy has a final carbon content of 1 -0 - 300 parts by weight per parts per million by weight of the zirconium alloy.

2. Method according to claim 1, characterized in that metal carbide is added in such an amount that the zirconium alloy has a final carbon content of over 150 parts by weight. parts per million by weight of the zirconium alloy.

3. Method according to claim 1 or 2, characterized in that the metal carbide is added in the form of a powder. k.

Method according to claims 1-3? characterized in that zirconium carbide is added as metal carbide.

5. Method according to claim l-<*>f, characterized in that the metal carbide is added in such an amount that the zirconium alloy has a final carbon content of 170-300 parts by weight. parts per million by weight of the zirconium alloy.

6. Method according to claims 1-5, characterized in that metal carbide is added in such an amount that it gives at least 50 percent by weight of the final carbon content in the alloy. •7. Method according to claims 1-6, characterized in that metal carbide is added in such an amount that it gives at least 80 percent by weight of the final carbon content in the alloy.