JPS6268623A - Manufacture of stub tube - Google Patents

Abstract

PURPOSE:To improve mechanical strength, etc. by drilling a forged round bar in its longitudinal center direction and heat treating the bar after a cold expansion work. CONSTITUTION:An ingot of an inconel alloy, etc. is forged to be formed into a round bar and is drilled in its longitudinal center direction by matching with a lathe or others. Then, an expander is fixed into the center hole of the bar and cold expands the bar. After the above working, the expanded bar is subjected to a heat treatment of a prescribed temperature and time. Crystal grains after manufacturing become smaller and are uniformized because the bar is subjected to the heat treatment after the expansion work. Therefore, this method improves the anti-SCC characteristic and a manufacturing yield as well as the mechanical strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a stub tube, and particularly to a method for manufacturing a stub tube with stable mechanical strength.

[Technical background of the invention and its problems] A stub tube, which is one of the structural members of a nuclear reactor, is used to support control rods, and is particularly required to have corrosion resistance and mechanical strength.

Traditionally, this stub tube has been manufactured by melting a raw material containing a specified metal component in a melting furnace, casting it into an ingot, cutting it to a specified size, and extruding it backwards.B
The inner hole was formed by the ack extrusion method, and then hot working was performed at 1000 to 1100'C.

However, this method has the problem that the crystal grains that are opened after production are relatively large and non-uniform, resulting in variations in the mechanical strength of the resulting products. That is, in order to be able to use a stub tube, it is usually 25
kg/m (in contrast to conventional methods, in some cases the tensile strength is less than 25 kCI/Tl, for example, 23 k (1/m)). It has been desired to develop a method for stably manufacturing a stub tube having a mechanical strength higher than a predetermined value.

[Object of the invention] The present invention was made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method for manufacturing a stub tube with uniform crystal grains and excellent mechanical strength. .

[Summary of the Invention] That is, the method for manufacturing a stub tube of the present invention involves punching a round bar obtained by forging an ingot in the direction of its longitudinal center, and then performing cold extrusion processing (expansion processing). It is characterized by being heat treated.

In the present invention, the material of the stub tube is Inconel 600 (International
Ni-Cr-F manufactured by Al Nicket Company
E-alloy product name> etc. are required. The method of the present invention melts, casts and forges these metals or alloy components into round bars. Next, this sample is cut to a predetermined size as necessary, and then cut to form a perforation in the direction of the longitudinal centerline.
After expansion processing at room temperature, heat treatment is performed.

[Embodiments of the invention] Next, the present invention will be explained by examples.

Example Inconel 600 was cast into an ingot with a diameter of 300 nm+m, then forged into a round bar with a diameter of 210 mm, and this round bar was cut into a length of 300 m'm.

This sample was then perforated using a lathe to a diameter of 120 mT.
After forming the hole 1, attach an expander to this hole (b. Perform expansion processing at room temperature to make the outer diameter 2.
0111Tll, an inner diameter of 138 tm, and a height of 400 m'm. Next, heat treatment was performed at 1015° C. for 1 hour, and cutting was performed to a predetermined size to produce a stub tube.

The stub tubes obtained in this way have grain sizes of No. 6 to No. 7, and all have tensile strengths of 25K (stable above 1/mf, usually 27
28 kg/m2, while the stub tube manufactured by the conventional method had a grain size of No. 3 to No. 6, and the average tensile strength was 26 to 27 k (1/IIl), which was the lowest of the product. 3 of them
~5% did not satisfy the required tensile strength of 25 kg/Tl, and there were variations in mechanical strength.

[Effects of the Invention] As explained above, according to the method of the present invention, it is possible to obtain a stub tube with uniform crystal grains and a small grain size, so that a product having mechanical strength exceeding a predetermined level can be stably produced. At the same time, SCC resistance and manufacturing yield are improved.

Claims (1)

[Claims] (1) A method for producing a stub tube, which comprises perforating a round bar obtained by forging an ingot in the direction of its longitudinal center, cold-expanding it, and then heat-treating it.