Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1994-11-10
1996-10-01
Andrews, Melvyn
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148421, C22C 1600, C22F 118
Patent
active
055607900
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates in general to the manufacture of products or articles from corrosion-restant alloys used as construction materials of the active core of nuclear reactors, more specifically to a material based on zirconium, products used in the active core of nuclear reactors, and a process for producing such products.
BACKGROUND ARTS
The aforesaid material and product made therefrom are to meet quite a number of requirements as for strength characteristics, corrosion-resistance in water and in high-temperature steam, hydrogenation-proofness, and resistance to radiation growth and to creep. The material should possess high processibility characteristics as being aimed at making, e.g., thin-walled pipes for fuel claddings, spacer grids, and other construction elements of the nuclear reactor core.
Most suitable for the purpose are zirconium-based materials, containing 0.5-1.5 wt. % Nb, 0.9-1.5 wt. % Sn, and 0.3-0.6 wt. % Fe, up to 0.2 wt. % Cr in combination therewith. Said materials, when compared with alloys, wherein the maximum content of the third component is within 0.28 wt. %, feature a higher corrosion resistance, including higher resistance to nodular corrosion, as well as a higher resistance to radiation growth and to creep.
Known in the art is a zirconium alloy (SU, Al, 1,751,222), consisting essentially of the following components on a weight percent basis;
Sn--0.9-1.2
Fe--0.3-0.6
Nb--0.5-1.1
Zr--being the remainder.
The aforesaid alloy features fairly high corrosion-resistance and mechanical properties: tensile strength up to 490-580 MPa (20.degree. C.) and 275-365 MPa (at 350.degree. C.), yield point up to 345-390 MPa (at 20.degree. C.) and 185-245 MPa (at 350.degree. C.) corrosion resistance when exposed to the effect of a steam-and-water mixture at 300.degree. C. irradiation, until formation of fluences 3.7 10.sup.24 m.sup.2 (3400 h) and 1 10.sup.25 m.sup.-2 (7840 h) in terms of weight gain) up to 30-40 mg/sq dm and 80-95 mg/sq dm, respectively, and a rate of creep at 350.degree. C. and under a lead of 100 MPa up to (1.3-3.6) 10.sup.-5 %/h.
The alloy in question, however, is featured by liability to form a banded arrangement of large-size particles (up to 1.5 m) of a fairly stable intermetallide enriched in iron (ZrFe.sub.3) in the ingot and at early stages of its processing, which leads during plastic working of this alloy with high reduction ratios, to origination of microcracks at the places of aggregation of such particles. To eliminate large-size particles in the alloy structure involves beta-treatment of an ingot with prolonged holding periods at high temperatures, with the resultant higher metal consumption due to an increased thickness of the gas-saturated layer being removed and hence higher cost of finished products.
Furthermore, despite the use of beta-treatment, rather large (up to 1.0 m) particles of the ferriferous intermetallides (ZrFe.sub.3 inclusive) are reestablished in the structure of finished products made of said alloy, with the result that a total density of particles in the alpha-zirconium matrix is noticeably reduced. This can be explained by a high tendency of such intermetallides to coagulation at the temperatures of recrystallization alpha-annealing between the stages of multiply repeated cold straining which are applied when making products from said alloy. Presence of large particles of intermetallides featuring a reduced distribution density in the matrix affects adversely corrosion resistance and breaking strength characteristics of the material the product is made of.
Known in the art are a zirconium alloy for making components for light-water reactors and a method for its treatment with a view to attaining a definite creep level thereof (U.S. Pat. No. 5,125,985).
Said alloy consists essentially of, on a weight percent basis;
0.5 to 2.0 Nb;
0.7 to 1.5 Sn;
0.07 to 0.28 of at least one metal selected from the group consisting of the group of elements incorporating Fe, Ni, and Cr;
up to 220 mln.sup.-1 C;
the remainder being Zr.
Use
REFERENCES:
patent: 5211774 (1993-05-01), Garde et al.
patent: 5241571 (1993-08-01), Pati et al.
patent: 5244514 (1993-09-01), Garde
Bibilashvili Jury K.
Dubrovsky Valery A.
Gusev Anatoly J.
Ivanov Anatoly N.
Kotrekhov Vladimir A.
A.A. Bochvar All-Russian Inorganic Materials Research Institute
Andrews Melvyn
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