JPS6245440A - Local forging method for improving ultrasonic permeability of cast steel material - Google Patents

Abstract

PURPOSE:To improve the ultrasonic permeability by inserting a mandrel into inside of a part to be forged of a cast steel material, executing a pressure forging by using a plunger punch for executing a reciprocating motion in a part positioned at the upper side of the mandrel, rotating the part to be forged, and executing successively the pressure forging to the whole periphery. CONSTITUTION:A mandrel 2 is inserted into the inner surface of a part to be forged 1. Subsequently, a down load is applied to a plunger punch 3 by a press, a part positioned in the upper part of the mandrel 2 is brought to a plastic working and forging is executed. Also, in order to perform this forging in the peripheral direction, the plunger punch 3 is drawn up and the part to be forged 1 is rotated in the peripheral direction, and thereafter, the next part is forged by the plunger punch 3. By repeating this work, the part to be forged 1 is forged uniformly. Thereafter, a solution heat treatment is executed, and the inside and the outside diameters are brought to a machine work. In the part to be forged 1, the casting steel material is brought to a pressure forging, and the crystalline structure is fined, therefore, the ultrasonic permeability is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to stainless steel castings required for in-service inspection (hereinafter referred to as IS work) for valves, elbows, piping, etc. used in nuclear couplants. Concerning local forging of the straight tubular end of.

[Conventional technology]

Austenitic cast stainless steel material has an austenitic two-phase structure containing ferrite, but its crystal structure is coarser than that of forged material, so we conducted ultrasonic flaw detection (hereinafter referred to as UT) as a machining tool. In this case, the attenuation and scattering of sound waves are large and forest-like echoes are generated, making it difficult to identify defective echoes and making it impossible to meet the demands of engineers. This is said to be mainly because the crystal grains of austenitic steel are coarser than those of carbon steel, so that reflected waves from grain boundaries appear as forest echoes.

As a countermeasure to this problem, a method has been proposed in which the material of the cast layer is cold-forged and then recrystallized by heat treatment to make the crystal grain size finer.

In this case, training is extremely difficult depending on the shape of the target product, and the reality is that it has not yet been put into practical use.

For example, when attempting to cold forge a valve weld (a weld between a valve and piping or a valve and a nozzle) in order to improve the UT properties, it is extremely difficult due to its shape. If the UT target is limited to the vicinity of the welded part, local training may be performed, but in reality this is not carried out from the viewpoint of ensuring dimensional accuracy for valves.

[Problem that the invention seeks to solve]

Methods for locally forging the end of a pipe or elbow include applying pressure in the radial direction to plastically deform it into a circular shape, then placing it in a mold to form it into a perfect circle and locally forging it, drawing, and expanding the pipe by pushing in a plug. A method has been proposed in which local forging is performed by adding plastic deformation to the pipe. However, when applied to a thick-walled end such as a valve, there are problems with dimensional accuracy to ensure the function of the valve. It was thought that it would be difficult to apply this method due to problems with the equipment when applying it to locations with higher rigidity than elbows.

[Means for solving problems]

Local training is performed, a core metal is inserted into the inner surface of the area (ring-shaped inner surface), the area is placed on top of the core metal, and pressure is applied with a press. At this time, plastic working is performed uniformly on the entire circumference by sequentially rotating the relevant portions on the core metal in the circumferential direction in small increments.

[Effect]

The cast steel material is pressurized and forged between the push die and the core metal to refine its crystal structure.

〔Example〕

FIG. 4 and FIG. 2 will be explained using the training of the valve end as an example.

As shown in FIGS. 1(a) and 1(b), the core metal 2 is inserted into the inner surface of the portion to be forged 1. Next, a downward load is applied to the push die 3 using a press, and the portion located above the core metal 2 is plastically worked to perform forging. Furthermore, in order to perform this forging in the circumferential direction, the pusher die 3 is pulled up and the object to be forged is rotated in the circumferential direction, after which the next location is forged with the pusher die. By repeating this operation, the part to be trained 1 is uniformly trained. Thereafter, it is subjected to solution treatment, and the inner and outer diameters are machined as necessary to obtain a predetermined dimensional accuracy.

〔Effect of the invention〕

As a measure to improve UT permeability, a method of locally forging only the relevant part has been proposed, but this is difficult to apply to items with shapes such as valve welds (valve and piping, valve and nozzle welds). There was a side. The method of the present invention can be applied to such cases, and can be expected to have great effects in dealing with engineering SI of atomic couplants.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the local forging method for improving the ultrasonic permeability of a cast steel material of the present invention, with FIG. 1(A) being a front view and FIG. 1(B) being a side view. Figure 2 shows a cast steel valve. 1...Part to be forged, 2...Core metal, 3...Press die sub-agent Patent attorney Kaihon Important Literature 2 persons 1 page continuation Akira Kame Atsushi Higashiune Line Wadazaki-cho, Hyogo-ku, Kobe City Company 1 Kobe Shipyard & Machinery Worker Yoshihisa Manabe Yasukura Minami 1, Takarazuka City
-1348-Oakashi Kuniji Inagaki 2-1, Minato-machi, Joetsu City, Akira 1 Tsu Factory, Uchimashita Shiba 1) Kenji, Joetsu City, Minato-cho 2-1, 2-1, Asahi 1 Tsu Factory, Akira Mizuguchi Masaaki, Joetsu City, Minato-cho 2-1-1] Mitsubishi Heavy Industries, Ltd. 6, 1-1 Tsu Factory

Claims (1)

[Claims] A core metal is inserted into the part to be forged of the cast steel material, and the part located above the core metal is pressure-forged by a reciprocating push die.The part to be forged is rotated and the entire circumference of the part to be forged is sequentially pressure-forged. A local forging method for improving the ultrasonic permeability of a cast steel material.