JPS61207514A - Production of cast steel product having excellent ultrasonic flaw detectability - Google Patents

Abstract

PURPOSE:To improve the ultrasonic flaw detectability of a cast steel product and to make possible the inspection of the material for defect during use by casting the tubular end of said product to a projecting polygonal shape, elliptical shape, etc., and pressurizing the projecting part to deform plastically said part to a circular shape having a prescribed size then subjecting the product to a heat treatment for recrystallization. CONSTITUTION:A valve part 1 is cast of an austenitic stainless steel of a 2-phase type having a ferite phase. The end 6 to be welded to the other part is preliminarily cast to a square shape. Such part is grasped by a pair of dies 7 and 7 and is subjected repeatedly to pressurization with a press so that the part is bent and deformed over the entire circumference by the force 8 in the diametral direction to deform plastically the part to the circular section having the prescribed size. The par is thereafter subjected to heating to >=1,000 deg.C recrystallization temp. which serves also as a soln. heat treatment. The heated part is quickly cooled. The finer crystal grains of the structure are formed and the ultrasonic flaw detectability is improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing cast steel products with excellent ultrasonic flaw detection properties, and in particular to pump parts, pulp parts, and straight pipes made of austenitic stainless steel cast steel that are assembled by welding. , relates to a method for manufacturing cast steel products such as piping parts such as curved pipes, which have excellent ultrasonic flaw detection characteristics.

(Prior Art) Austenitic stainless steel cast products are generally made to contain a ferrite phase of several atoms or more to reduce casting defects. Because it contains a ferrite phase, it has superior weldability, intergranular corrosion resistance, and stress corrosion cracking resistance compared to cold-rolled and pressed stainless steels of the same type that do not contain a ferrite phase. Austenitic stainless steel castings are often used as main components for piping systems, pumps, and pulp parts that are used under harsh conditions in nuclear power plants, petrochemical plants, etc. because of their ability to be manufactured into shaped products.

However, the crystal grains of austenitic stainless steel castings become coarse during casting, and the ultrasonic flaw detection (hereinafter referred to as U)
(referred to as T-character). That is, ultrasonic waves are scattered and attenuated at grain boundaries, making it extremely difficult to detect defects in ultrasonic flaw detection tests.

One of the measures to improve UT properties is to apply plastic deformation to a cast steel product, and then heat it to recrystallize it and refine the grain. For example, when plastic deformation is applied to a straight pipe part of a cast steel product that has a straight pipe part with a circular cross section at the end, it is cast in advance to a diameter larger than 10 mm compared to the specified dimensions. There is a method of reducing the diameter by drawing (Tokuko Sho 58-
(See Publication No. 441.27).

That is, as shown in FIG. 8(A), the large diameter portion 2 of the cast steel product 10 is pressurized with a pair of dies 4 to compress the large diameter portion 2 and the tapered adjacent portion 3 into a flat shape. )(a) (Front sectional view)
, deforms into an elliptical cross section as shown in (b) (side sectional view).

A pair of half-split dies 5 each having a semicircular arc-shaped pressure forming surface that matches the diameter of a predetermined cast steel product as shown in FIG. 8(C).
Pressure is applied from the long axis direction of the ellipse through the ellipse until the dies 5 meet as shown in FIG. 8(D), thereby obtaining a cast steel product having a reduced diameter of a predetermined size. In this case, as shown in Fig. 8(E), there is a risk that only the α part will be processed due to the friction of the contact point between the die 5 and the large diameter part 2, and the buckled part will come out to the outside. . In addition, the tapered adjacent portion 3 [Figure (A)]
is easily dented due to pressure. In addition to this technical difficulty, the die 5 is uneconomical due to its versatility, and is not a good idea when the purpose is simply to impart plastic deformation.

Another method of adding plastic deformation is to apply 1
A method has been proposed in which the tube is cast to a small diameter of 0 or more and the tube is expanded by pushing in a plug (see the above-mentioned Japanese Patent Publication No. 5B-4).
4127), however, large-scale equipment is required for thick-walled cast products.

(Problems to be Solved by the Invention) The present invention improves the UT properties of the weld groove and the surrounding area of stainless steel casting products, particularly austenitic stainless steel casting products containing ferrite, and improves the UT properties in actual plants. This paper aims to propose a plastic deformation and recrystallization heat treatment method to facilitate in-use inspection (hereinafter referred to as SI) and to make it possible to grasp the presence or absence of defects and the defect size. The purpose of this paper is to propose an efficient deformation method for applying small-scale processing of 10% or less.

(Another Means to Solve the Problems) The present invention involves casting the tubular end portion of a cast steel product into a convex polygon or ellipse shape having approximately the same dimensions as the pipe circumference of the target product and different from the cross-sectional shape of the target product, and then 1. Concerning a method for manufacturing cast steel products with excellent ultrasonic flaw detection characteristics, which involves pressurizing and plastically deforming steel into a predetermined cross-sectional shape and heating it above the recrystallization temperature;
That is, the features of the present invention are as follows.

(1) A stainless steel cast product having a straight pipe part that becomes a welding groove at the end as a predetermined shape is targeted, and bending deformation is applied as plastic deformation to the core part.

(2) Therefore, the core portion is cast in advance in a shape different from the tubular shape, for example, in a cross-sectional shape of an ellipse or a square, and the circumferential length is set to be approximately the same as the predetermined front dimension.

(3) Bending deformation is applied by compressing the core in a direction perpendicular to its axis using a pair of simple-shaped dies.

(4) Compared to a die that perfectly matches the specified straight pipe dimensions required for drawing, it is more versatile and economical to use a die or mandrel with a simple shape for cast steel products with different dimensions. In addition, due to bending deformation, even thick parts can be handled with small equipment.

Austenitic stainless steel 80819 in the present invention
There are representative examples such as J Engineering S BOSll etc.
□For cast steel and copper products, J Engineering 880813, 80814,
80816.

It can be applied to a method using ferrite-austenite two-phase stainless steel "τ:222:!2:',a maii uA'*.7°.A preferred mode of plastic deformation is cooling of the cast steel product during deformation. In order to prevent temperature rise, a refrigerant is sprayed on the refrigerant, or the refrigerant is immersed in the refrigerant and plastically deformed, or the refrigerant is sufficiently cooled in advance and then deformed immediately after being removed from the refrigerant.

By performing such plastic deformation, it is possible to significantly increase the hardness of the ferrite phase, suppress the deformation of this part, concentrate the deformation in the austenite phase, and transform the austenite phase into austenite with a deformation amount of 10% or less. Desired deformations can be imparted to the phase.

Regarding heating above the recrystallization temperature after deformation, heating to approximately 900°C is sufficient, but if this heating also serves as solution treatment, it is necessary to avoid carbide precipitation at austenite grain boundaries. Heating in a trench above 1000℃ and cooling rapidly.

(Example) Specific Example 1 FIG. 1 shows a predetermined shape of a pulp part 1 as an example of an austenitic stainless steel cast product. The end 6 is the first
As shown in Figure (B), it has a straight tube shape with a circular cross section, and the end face to be machined is welded to other members. FIG. 2 is a diagram showing the shape of a pulp component 1 whose end portion 6 is cast in advance into a shape suitable for plastic deformation by bending (in this case, a square shape as shown in FIG. 2(B)). FIG. 3 shows a pair of dies 7 used for plastic deformation.

As shown in FIG. 4, the plastic deformation is carried out by sandwiching the part 6 of the part previously cast in a shape different from a predetermined shape between a pair of dies 7 and pressurizing it with a press through the dies 7.

#J@The curved portion of the product end 6 and the die 7 come into contact and the pressing force is transmitted to the cast steel product end 6. At this time, if a synthetic resin-based dV lubricant or the like is applied to the outer peripheral surface of the end portion 6 to reduce the friction at the contact portion, the contact portion of the convex portion with the die 7 due to pressurization will have a diametrical force of 8 is added, bending deformation occurs over the entire circumference, and the desired circular cross section is obtained. Depending on the shape of the die 7, it can be formed into a predetermined shape by applying continuous pressure in the axial direction or by rotating the cast steel product 1 to change the position to be machined.

Figure 5 shows a pulp part (austenitic stainless steel cast steel JI8 B0f3) subjected to recrystallization heat treatment after plastic deformation.
13A) Shows the UT property of the end. The end shape of the cast product is a square cross section with a thickness of 80 fins, an inner diameter of the corners of 250 mm, and a diagonal distance between the corners of 1111550 am, and is plastically deformed by being sandwiched between dies to form a circular shape with an inner diameter of 50011 mm and a thickness of 80 mm. It was taken as a cross section. Thereafter, it was heated at 1080° C. for 3 hours and cooled with water. U
The T property was determined by injecting a 2.25 MHz ultrasonic wave from the outer periphery using the longitudinal wave vertical probe method and examining its attenuation. <
Shita. For comparison, Fig. 5 also shows the ultrasonic attenuation constant of the cast product before plastic deformation.

When the circumference is constant, the distortion due to bending deformation is expressed as follows.

Here, e: Distortion on the outer periphery t: Thickness ro: Radius of curvature at the center of the plate thickness before deformation r: Radius of curvature at the center of the plate thickness at the deformed edge The amount of distortion on the outer periphery at this time is approximately 8% near the corner. It was about 6% between corners.

By recrystallizing after applying partial bending deformation, the attenuation of ultrasonic waves is significantly reduced compared to the as-cast state, and the UT properties can be improved.

Concrete Example 2 In Fig. 6, the shape of the cast steel product end 6 is an elliptical cross section,
A case where the cross section is pressurized to a circular cross section as a predetermined shape is shown. By applying pressure through the flat die 9, it can be more easily deformed into a circular cross section.

Specific example 3 Figure 7 (A) (Front view), (B) (Sacral sectional view)
is Ql'' The shape of the part end 6 is a diamond-shaped cross section,
A case is shown in which pressure is applied from two locations on opposing convex portions.

In this case, other convex portions that do not contact the die 9 tend to come out to the outside, and bending deformation of the portion between the convex portions is less likely to occur. To prevent this, a round bar, mandrel, etc. 10 may be installed inside as shown in FIG. The mandrel 10 is preferably of a sliding type, an expanding type, or the like, which can change its outer diameter, since it can follow the deformation of the end portion 6.

The plastic deformation in Examples 1 to 3 above can be performed by either hot working or cold working, and furthermore, as mentioned above, processing at low temperatures by spraying a cooling medium such as oil, water, or liquid nitrogen is also possible. It is.

After plastic deformation, heat treatment is performed at a temperature higher than the recrystallization temperature as described above.

(Effects of the Invention) In the method of the present invention, by adding bending deformation to the end, a deformation amount of up to 10 inches can be easily applied, and
The T property can be improved, and effects such as (1) S machining becomes easier can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of a cast steel product targeted by the present invention, Figure 2 is a diagram showing an example of a cast product used to obtain the target steel product shown in Figure 1, and Figure 3 is a diagram showing an example of a cast product used in the present invention. FIG. 4 is a diagram showing an example of the embodiment of the present invention, FIG. 5 is a chart showing the results when implemented in the embodiment of FIGS. 2 to 4,
FIG. 6.7 is a diagram showing another embodiment of the present invention, and FIG. 8 is a diagram for explaining the prior art. Sub-agent 1) Clearance agent Ryo Hagiwara - Figure 1 (c)' □ Figure 3 Figure 2 (A) Figure 4'

Claims (1)

[Claims] After casting the tubular end of the cast steel product into a convex polygon or ellipse with dimensions that are approximately the same as the circumference of the target product and different from the cross-sectional shape of the target product, the convex portion is pressurized to plastically deform it into a predetermined cross-sectional shape.
A method for manufacturing cast steel products with excellent ultrasonic flaw detection characteristics, which involves heating to a temperature higher than the recrystallization temperature.