JPS63216954A - Production of zr based alloy plate having excellent cold workability - Google Patents

Abstract

PURPOSE:To produce a Zr based alloy having good cold workability to which cold working can be executed without a heat treatment, by heating the Zr based alloy to a specific temp., subjecting said alloy to hot rolling and thereafter quenching the same at a specific cooling speed. CONSTITUTION:The Zr based alloy is heated to 850-950 deg.C and is subjected to the hot rolling in such a manner that FeZr deposited at the time of blooming is allowed to form a solid solution, the grain coarsening of the alloy by the pre-treatment of the hot rolling is prevented and the fine granulation of the same is executed by the hot rolling. Said alloy is then quenched at the cooling ratio of 50 deg.C/sec to control the new deposition of FeZr. The Zr based alloy having the good cold workability (ductility) to which the cold working (cold rolling and cold molding) can be executed without the heat treatment is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a Zr (zirconium)-based alloy sheet having excellent cold workability, particularly ductility.

[Conventional technology]

Zr-based materials, ie, pure Zr and Zr alloys, have excellent corrosion resistance and heat resistance and have a small thermal neutron absorption cross section, so they have recently been increasingly used as corrosion-resistant and heat-resistant alloys and as materials for nuclear reactors.

This Zr plate is produced by hot rolling, or in the case of a thin product,
Manufactured using a combination of hot rolling and cold rolling methods.

A method for producing a material for cold rolling is a method in which a Zr-based alloy is heated to a β-phase region (beta transformation point or higher) after final hot working, and then rapidly cooled (Japanese Patent Laid-Open No. 61-143571).
No., Zr is heated at 810℃ or higher, 810℃~
A method (Japanese Patent Publication No. Sho 62-4463) has been disclosed in which hot rolling is carried out between the β transformation point, followed by rapid cooling and further annealing. All of these methods involve hot working, heat treatment, and then cold working.

[Problem that the invention seeks to solve]

However, the former method has poor cold deformability due to coarsening of crystal grains, and the latter method requires an annealing step, which increases the cost accordingly. Although Zr-based alloys have excellent properties in terms of applications, the main reason why they are reluctant to use them not only for industrial purposes but also for nuclear power equipment is that the raw material costs are extremely high. be. Therefore, it was necessary to at least reduce processing costs as much as possible while ensuring excellent workability.

However, until now, there has been little known theoretical research on the above-mentioned processability from a material perspective, and there have been few reports on specific measures to improve processability, and currently no effective measures have been found. It is.

Therefore, an object of the present invention is to provide a method for manufacturing a Zr-based alloy with good cold workability (ductility), which can be subjected to cold working without heat treatment after hot working.

[Means for solving problems]

In order to solve the above problems, the present invention is aimed at producing a Zr-based alloy sheet by hot rolling at a temperature of 850 to 950.
It is characterized by heating at 0.degree. C., hot rolling, and then rapidly cooling at a cooling rate of 50.degree. C./second or more. here,
Examples of Zr-based alloys include pure Zr and low-alloy zirconium known as Zircaloy-2 and Zircaloy-4.

[For production]

As will be described later, the deterioration in workability of Zr-based alloy sheets is largely due to the influence of coarse Fe and Zr precipitated at grain boundaries during cooling after hot working, and the influence of crystal grain size. Therefore, if the hot rolling step, which is the final step of hot working, is performed within the above temperature range, coarse Fe2Zr can be converted into a solid solution. Furthermore, if cooling after hot rolling is performed with the cooling rate in the above speed range, coarse Fe
, Zr redecipitation can be prevented, and crystal grains can be made finer, so workability can be significantly improved.

[Specific structure of the invention]

The present invention will be explained in more detail below.

First, the process that led to the completion of the present invention will be explained. The present inventors have repeatedly investigated the causes of deterioration in workability in Zr-based alloy sheets, and have obtained the following knowledge.

(1) The main cause of deterioration in workability is that the intermetallic compound Fe2Zr precipitates and grows at grain boundaries.

(2) During the cooling process after blooming rolling, these Fe and Zr precipitate at grain boundaries and become coarse due to the slow cooling rate, and remain even after the subsequent hot rolling process, deteriorating cold workability. .

(3) Even if a solution treatment for the purpose of dissolving FezZr is performed after the blooming rolling, Fe2Zr precipitates again at the grain boundaries in the subsequent hot rolling process and deteriorates the workability.

(4) Solutionization of FezZr does not necessarily need to be carried out at a high temperature above the β-transformation point as conventionally done, and heating at 850 to 950°C, which is near the top and bottom of the β-transformation point, is sufficient. .

(5) If the hot rolled material has fine grains and has little processing strain, it will have high cold deformability (ductility).

Based on the above findings, in order to suppress the precipitation of FezZr in the product production process after blooming and to obtain a fine-grained material, (1) Coarse Fe and Zr precipitated after blooming are dissolved.

■ Low-temperature hot rolling at an appropriate temperature.

■ Suppress redecipitation of Fe and Zr during the hot rolling process.

The present invention has been developed while keeping in mind that new processes such as solution treatment and strain relief annealing are not required, and that conventional processes are omitted in order to manufacture the product at low industrial cost. This is the completed version.

That is, in the present invention, the heating temperature before hot rolling is 850 to 950°C.
As a result, Fe and Zr precipitated during blooming were dissolved in solid solution, and grain coarsening due to heating before hot rolling was prevented, grain refinement was performed by hot rolling, and the cooling rate after hot rolling was set to 50°C/ S or more suppresses new precipitation of Fe and Zr,
This product has improved cold workability of the Zr-based alloy sheet.

Next, the reason for the above numerical limitation in the hot rolling process will be explained with reference to the drawings. Figure 1 shows the ductility (=elongation rate) of sample material A shown in Table 1 after hot rolling and cooling at a cooling rate of 100°C/S.

This figure shows the effect of hot rolling heating temperature on EJ), and it can be seen that El is best when the heating temperature is in the range of 850 to 950°C.

The reason for this is considered to be that when the temperature is 850° C. or lower, coarse FezZr existing before hot rolling does not become a solid solution during heating and remains in the final product, resulting in poor El. Moreover, at 950° C. or higher, the steel becomes a single β phase during heating, resulting in coarse grains, resulting in coarse α grains even after hot rolling, which deteriorates ductility.

In normal processes, the finishing temperature can be controlled within a range of 150°C lower than the heating temperature, but if it falls below approximately 700°C due to problems during hot rolling, it will be in a state close to cold working. Therefore, it is desirable to control the temperature to about 700° C. or higher, since this results in a large amount of processing strain and reduces ductility.

Next, Figure 2 shows the influence of the cooling rate on El after hot rolling when the hot rolling heating temperature for specimen A is the optimum temperature of 900°C. Shows excellent El in cooling rate.

This is considered to be because when the cooling rate is less than 50° C./S, FezZr precipitates at grain boundaries and deteriorates ductility.

As a practical cooling method, methods such as immersion treatment in a water tank or spray cooling immediately after hot rolling can be used.

In addition, before subjecting to cold processing such as cold rolling and cold forming,
It goes without saying that mild cold working such as straightening and surface conditioning such as pickling are included within the scope of the present invention.

〔Example〕

Next, examples will be shown.

Pure Zr(A) with the composition shown in Table 1, Zircaloy-2
(B), Silka O E 4 (C) Ingot (VAR
After forging and blooming a 1 ton ingot) at a temperature of 1000℃, hot rolling under various hot rolling conditions without solution treatment and immediately cooling with spray water. Tensile tests and microstructural observations were conducted on the as-rolled material.

As is clear from Table 2, the hot rolling heating temperature is 700
Magnetic No. 1, which has a low heating temperature of 1000° C., shows precipitation of FezZr and is poor in El, while Magnetic No. 5, which has a high heating temperature of 1000° C., has coarse grains and a low El. Furthermore, even if the heating temperature is an appropriate value of 900°C, 11h6 has a slow cooling rate of 10°C/S after hot rolling, which is Fe! Precipitation of Zr was observed, and El was poor.

On the other hand, l1h2, 3.4°7, which satisfies the scope of the method of the present invention
．． No. 8, 9, 10, 11, and 12 all had E1≧30% and were good.

〔Effect of the invention〕

As described above, in the present invention, by controlling the hot rolling after blooming, the solution treatment step during or after hot working as in the conventional method and the annealing step after hot working can be achieved. Zr-based alloy sheets for cold working can be manufactured economically without any.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the influence of hot rolling heating temperature on El after hot rolling, and FIG. 2 is a diagram showing the influence of cooling rate after hot rolling on El after hot rolling.

Claims (3)

[Claims] (1) A method for manufacturing a Zr-based alloy sheet for cold working, characterized by hot rolling at a heating temperature of 850 to 950°C and then quenching at a cooling rate of 50°C/sec or more. A method for manufacturing a Zr-based alloy sheet with excellent cold workability. (2) Zr having excellent cold workability according to claim 1, wherein the cold working is cold rolling.
Method for manufacturing base alloy sheet. (3) The method for manufacturing a Zr-based alloy sheet with excellent cold workability according to claim 1, wherein the cold working is cold forming.