JPS636624B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for homogenizing the segregation of tin contained in a zirconium alloy and to a zirconium alloy in which this segregation is homogenized. In metals and gold, the term "stringer" is often used to describe the "string-like" features of the microstructure. These may be alloy segregation, second phase particle segregation and/or impurity segregation. In zirconium alloys, without exception for other metal alloy systems, the term "stringer" is used, for example in Picklesimer's U.S. Pat.
2894866 and is used to describe "string-like" impurities such as stringers and carbon, phosphorous, silicon, etc. The present invention deals with stringers that have long been believed to be carbon rich. Because of this belief and the known limited solubility of zirconium in carbon,
Homogenization by heat treatment is considered impossible, and known attempts to homogenize by this method have not been carried out. Recent advances in electronic analysis techniques have revealed that stringers previously believed to be carbon are tinnitus. These tin stringers are believed to be a heterogeneous product of the vacuum arc melting process. The segregation of these tin lichens appears as irregularly shaped lumps that are somewhat shorter than the elongated shapes in the ingot. As the ingot is worked, the segregation is elongated in the working direction and exhibits string-like features when examined parallel to the working direction. The above-mentioned US Pat. No. 2,894,866 discloses a method for removing second-phase segregated stringers from zirconium-based alloys using a heat treatment method. This patent describes a method of beta-quenching the alloy at a temperature of 975° C. for one hour. This treatment redistributes the second phase but leaves the tin stringers in the microstructure. Other patents relating to heat treatment of zirconium alloys include U.S. Pat. No. 3,645,800 to Nock and Wiener et al.
et al., U.S. Pat. No. 3,689,324, these patents disclose heat treatment methods that are either too low in temperature or too short to remove the tin stringers in this case. . Due to the presence of these tin stringers, it has been found that, depending on the application, corrosion develops at these locations of segregation or stringers, and furthermore, mechanical weakening develops at these locations. In some molding processes, especially those involving sharp curvatures, segregation can cause cracking, resulting in an undesirable product. The present invention is directed to a method for removing tin stringers or segregation in zirconium alloys by homogenization in order to provide zirconium products that are less susceptible to corrosion and cracking. The invention consists of heat treating the zirconium alloy at an elevated temperature of about 1000° C. or higher, generally 1100° C. or higher, for a time sufficient to homogenize the tin stringer. The correlation between time and temperature in the heat treatment process is
It is determined by the following general formula: [Temperature] 1225-70 ln [Time] In the formula, [Temperature] is the heating temperature °C, and [Time] is the heating time h. (Targeting the natural logarithm, i.e. the logarithm based on e) According to the present invention, the temperature at which the alloy is processed is higher than that normally used in beta quenching, and It is carried out for a longer time than is generally necessary, in some cases from 8 to 24 hours.
It also becomes time. The treatment time is inversely proportional to the increase in heating temperature. Zirconium alloys can be processed in this way at most stages of production, from ingot preheating to final size. The higher the segregation thickness, the higher the temperature and/or
Or you have to spend a longer time. The term "zirconium alloy" as used herein means an alloy in which the following components constitute the main alloy elements. Tin: 3% by weight from traces, Iron: 0.3% by weight from traces, Chromium: 0.15% by weight from traces, Nickel: 0.1% by weight from traces, Carbon: 0.05% by weight from traces, Oxygen: 0.2% by weight from traces, Silicon: Trace to 0.03% by weight, Zirconium: Residual However, other zirconium alloys are also included. According to the general formula mentioned above, the above alloy is heated to about 1000℃.
By heating to a temperature above, the stringer type alloy segregation is homogenized in the zirconium alloy. In this way, an alloy with greater corrosion resistance and formability is produced. A 0.08 inch (0.2 cm) thick sheet of zirconium alloy within the above composition range with tin stringers approximately 0.1 to 1 micron thick;
Typical examples of times and temperatures used are listed in the table below.

[Table] In the drawing, the points mentioned above are plotted on the graph shown therein, and the line defining the area in which segregation is removed is represented by the general formula mentioned above. The size of the final segregation to be homogenized depends both on the initial size in the as-cast ingot and on the amount of subsequent processing during which it is reduced to size for heat treatment. It is possible that there is thicker segregation in material that has undergone greater reduction than in comparison pieces from other source ingots. The times and temperatures calculated by the general formulas above provide guidelines for suitable parameters for removing tin stringers from zirconium alloy products of all sizes. As an example,
A 4-inch (approximately 18 cm) thick zirconium alloy plate was treated at 1200° C. for 4 hours to remove segregation, ie, to homogenize the tin stringers. Accordingly, the present invention is directed to a method for removing tin stringers from zirconium alloys by heat treatment according to mathematically related time and temperature tables. Modifications are possible within the scope of the invention.

[Brief explanation of the drawing]

The drawing is a graph showing the area where segregation is removed depending on the temperature and time of heat treatment.

Claims (1)

[Claims] 1. A method for homogenizing the segregation of a zirconium alloy in which the segregation of tin-rich contained in the zirconium alloy is reduced and corrosion and cracking are less likely to occur, according to the following general formula: [Temperature]≧1225−70 1n [time], where [temperature] is the heating temperature °C, [time] is the heating time h, and in order to homogenize the segregation in the zirconium alloy, the zirconium alloy is
A segregation homogenization method characterized by heating at a temperature of 1400°C for 8 hours to 10 minutes. 2 The zirconium alloy contains: tin: traces ~ 3% by weight, iron: traces ~ 0.3% by weight, chromium: traces ~ 0.15% by weight, nickel: traces ~ 0.1% by weight, carbon: traces ~ 0.05% by weight, oxygen: traces ~ 2. A method according to claim 1, characterized in that it has a composition consisting of: 0.2% by weight, silicon: trace to 0.03% by weight, zirconium: remainder.