JPS63212014A - Manufacture of steel pipe - Google Patents

Abstract

PURPOSE:To contrive grain refining of crystals, diffusion of segregation, and equalization of components, then to improve a whole steel cylinder in quality by passing a core metal having an inner diameter of more than a specified rate through an inner hole of a bent welded cylinder made of hot forged or rolled steel plate so as not to inscribe with each other and forging by interposing a heating weld zone. CONSTITUTION:Through the inner hole of the cylinder 1 bent welded the hot forged or hot rolled steel plate, the core metal 2 having a height or diameter of >=60% of the inner diameter of said hole is passed. Interposing the weld zone 4 to be foged, the cylinder is forged by anvils 3 facing each other on the line of the rolling reduction direction. The heated weld zone 4 is plastic worked both the weld metal and the heat-affected zone of welding are subjected to grain refining by recristallizing the austenitic grains and diffusion of segregation, further the components of the weld metal and the base metal are equalified, moreover as the cold worked parts except the cylinder are not plastic-deformed substantially by the rolling reduction, so the whole steel pipe is made to be excellent in the uniformity and quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing steel pipes used for boilers, low-temperature equipment, and other piping.

[Conventional technology] Recently, there has been a trend in the use of high-temperature, high-pressure glue actors and refining vessels in manufacturing plants aimed at high efficiency, both in the field of new energy development such as nuclear power generation and coal liquefaction, and in the field of traditional petroleum energy. It is in.

Pipes used for piping in these fields have traditionally been so-called seamless pipes without welded parts, whereas welded pipes have little experience of being used due to lack of confidence in the soundness of the welded parts.

The steel that makes up the pipe is JIS 5TPA24.5TB
A24゜A S'r M^3:36-Do22 and AST
MA387-22 (21/4% Cr-1% Mo steel).

ASTM A336-F21 and ASTM A387-21 (
3%Cr-1%Mo steel L JIS STl'A25.
5TBA25. ASTMA336-F5 or ASTMA
387-5 (5% Cr-0.5% MO steel), JIS
5TPA26.5TBA26. A37MA336-do9ya8STMA387-9 (9%Cr-1%Mot
So-called Cr-M such as @).

There are a wide variety of types of steel, such as carbon steel such as IIS ST[l, ASTMA516, other low alloy steel pipes, and high alloy steel pipes such as stainless steel such as 5US304 Tll, but in all steel types, the welded part is either as welded or PWHT ( After welding (stress relief heat treatment), the toughness and
Low ductility.

However, as boilers have recently become more efficient, there has been a demand for sizes that were previously impossible to manufacture as sealed loose tubes, and even among the sizes that can be manufactured, there have been stricter demands for cost-effective sizes. A method of manufacturing steel pipes with the same reliability was desired.

[Problems to be Solved by the Invention] In consideration of the problems of existing welded pipes, the present invention is a manufacturing method in which a welded part consisting of weld metal and a weld heat-affected zone is hot forged. The quality of conventional welded pipes, which were welded or PIJl (T), can be improved by performing temporary processing.

The present invention relates to a method for manufacturing a welded pipe that is as reliable as a seamless steel pipe, without restrictions on the size that can be manufactured, and in a cost-effective manner.

[Means and operations for solving the problems] FIGS. 1 and 2 are diagrams showing a method of hot forging a welded part according to the present invention. The present invention bends one or more hot-forged or hot-rolled steel plates 1 to form a cylinder or a part of a cylinder, welds them to form a cylinder, and partially forms the welded portion 4. When hot forging into a steel pipe, a core metal 2 having a height or diameter d' of 60% or more of the pipe inner diameter d is passed through the pipe.

This method of manufacturing a steel pipe is characterized in that the welded portion 4 to be forged is sandwiched and forged using anvils 3 corresponding to the straight line 1 in the rolling direction.

In a manufacturing method in which a welded part consisting of welded metal and a weld heat-affected zone of a welded pipe is hot forged, the inventors have developed a method for welding through a cored metal having a height or diameter of 60% or more of the inner diameter of the pipe. By rolling down the welded part with opposing anvils arranged in a straight line on the line of force in the stress direction, plastically working the heated welded part, and not applying substantial rolling plastic deformation to other cold parts,
It was discovered that by applying a certain amount of processing deformation along the length of the pipe, it was possible to obtain a forged welded part without uneven thickness.

By heating the welded part after welding and hot forging,
In both the weld metal and the weld heat-affected zone, austenite grains are recrystallized to make them finer and segregation diffused, and the components of the weld metal and the base metal are equalized.

As a means to effectively realize this effect, a certain amount of rolling deformation is applied to the welded part along the length of the pipe,
In order to improve material uniformity and dimensional accuracy, a core metal with a height or diameter of 60% or more of the pipe's inner diameter is inserted into the pipe, and reduction forging is performed with opposing anvils on the same line of force. It becomes possible to apply plastic deformation only to the heated weld zone and its vicinity.

The present invention will be explained in detail below. As shown in Figs. 1 and 2, the steel plate 1 to be formed first is produced by hot forging or hot rolling from a pear-shaped steel ingot, a flat steel ingot, or a continuous cast slab, and is then forged or rolled. There is no particular specification, such as those that have undergone heat treatment or have been further heat treated.

When the steel plate 1 is formed into a cylindrical shape, the thickness of the steel plate 1 is uniform in the circumferential direction, or the thickness of the steel plate 1 is partially thickened at the end to include the reduction for later forging of the part to be welded. . These steel plates 1 are formed into a cylindrical shape and then welded at the end faces to form a pipe. Forming is performed by cold, hot or warm, press forming, bending rollers, etc., but the method is not particularly detailed. Not limited.

Welding methods include welding that uses high energy density such as electron beam welding and laser welding, gas shield welding such as TIG welding, MIG welding, and CO□ welding by creating a bevel on the edge of the steel plate, and submerged arc welding. Any welding method that provides a defect-free welded portion 4 such as coated metal arc welding, electrogas welding, or electroslag welding may be used, and is not particularly limited, but it is necessary to select an appropriate method depending on the type of steel.

The welding materials used, such as welding core wire, welding flux, and welding rods, are not particularly limited, but heat treatments such as quenching, tempering, and normalizing are applied to the welding heat-affected zone and thereafter as necessary. Mechanical properties such as strength, toughness, creep rupture strength, magnetic properties, thermal expansion coefficient, corrosion resistance, hydrogen attack resistance, and other physical and chemical properties are within the tolerance range of the base material depending on the intended use of the pipe. It is necessary that the composition be the same as that of the base material, and it is necessary to select a component that can ensure these properties depending on the hot forging conditions and the subsequent heat treatment conditions, but preferably the base material and tolerances are the same. Use welding materials with the same composition within the range.

Welding requires appropriate preheating and
Conditions such as post-heat, interlayer temperature, current, voltage, and welding speed may be selected and are not particularly limited.

In order to make the thickness of the welded part 4 the same as the thickness of the base metal after forging, it is necessary to make it thicker than the base metal by the amount of reduction in advance, but the amount of reduction in this case is not particularly limited, but 2
0% or more is desirable.

Next, as mentioned above, hot forging after welding reduces micro-segregation in the weld metal and weld zone, including the weld heat-affected zone, by destroying dendrites and refining the austenite grains by recrystallization.
The purpose is to improve mechanical properties, mainly toughness, and to make the chemical composition of the weld metal and base metal uniform, including the base metal. Forging at effectively obtainable temperatures, ie between 800 and 1200°C, particularly preferably between 850 and 1050°C, is preferred.

Forging is carried out by inserting a core metal 2 having a diameter d' with a height of 60% or more of the pipe inner diameter d, but the cross-sectional shape of the core metal 2 is
Any shape suitable for forging is acceptable, and it is not limited to a circular shape. In this case, the height d' of the core metal 2 refers to the cross-sectional height in the pressurizing direction.In the present invention, the height or diameter d of the core metal 2
' shall be 60% or more of the pipe inner diameter d. In the present invention, since the welded portion 4 is partially heated and forged, the welded portion 4
The other parts are not heated.

Therefore, when pressing is performed with the corresponding anvil 3 whose stress line is in a straight line with the forging rolling part with the core metal 2 inserted, if d'/d is 60% or more, the deformation of the entire pipe will be caused by cold. This is because the shape stays in an elliptical shape within the elastic range of the base material in the current state, and when the load is removed, it returns to the light pipe state, that is, a circle.The height or diameter d' of the core metal 2 is made smaller than this This is because it becomes difficult to restore the compressed state when the compressed state is released.

The forging is carried out using corresponding anvils 3 in which the lines of stress applied through the core metal 2 are aligned in a straight line. For example, the forging is carried out using two supports with the protruding portions of the core metal 2 at both ends of the pipe arranged at one end. When the core metal 2 is supported and forged with the upper anvil between the two support stands, the core metal 2 is deflected, and this deflection causes unevenness in the amount of reduction in the longitudinal direction of the pipe in the welded part 4 and the resulting unevenness in the forging effect and nonuniformity in dimensions after forging. However, the purpose of the present invention is to prevent such problems, and this is an essential condition especially when forging the welded portion 4 of a long pipe.

After hot forging, mechanical finishing is performed as necessary to improve roundness, pipe bending, and plate thickness accuracy, and annealing, reheating, and annealing are performed to ensure the mechanical properties of the pipe. Enter/
Heat treatment such as tempering is performed, but this is not particularly specified.

[Example] Next, an example of manufacturing a steel pipe according to the present invention will be described in more detail.

Table 1 shows each steel type, wall thickness, pipe diameter, welding method, and height or diameter of the core metal during forging in which the present invention was implemented. All of the steel plates were rolled thick plates, and a bending roller was used to form them into pipes.

Welding involves submerged arc welding and partial AC M using a combination of wire and flux that result in weld metals with mutually metallic components.
IG welding was used. After welding, the welded portion was heated to 900 to 1050° C. by high-frequency induction heating and forged using a 1500-ton press. After forging, the entire pipe, including the welded parts, was subjected to a prescribed heat treatment.

The trial production results are as shown in Table 2, No. 1 to No. 006 of the present invention material.
Both the co-welded part and the base metal part showed stable but good mechanical properties, and the thickness of the welded part after forging was also uniform in the length direction of the pipe. On the other hand, the 5TS42 pipe shown in the comparison material in Table 1 has a core metal diameter of 200 mm, and the core metal parts protruding from both ends of the pipe are supported by two lower supports, and the welded part is forged by the core metal and upper anvil. However, in this case, the reduction of the m-joint part could not be carried out uniformly in the length direction of the pipe, and as a result, it was not possible to obtain a satisfactory pipe.

[Effects of the Invention] As described above, in the production of steel pipes, the present invention involves forming a steel plate, welding it into a pipe shape, passing it through a core metal whose cross section has a height or diameter of 60% or more of the inner diameter of the pipe, and then forging it. This method is characterized by forging the welded part with anvils that face each other in a straight line in the rolling direction, and provides a method for obtaining a steel pipe with excellent mechanical properties and good dimensions throughout the pipe, and is an industrially popular method. The effect of this is quite large.

[Brief explanation of the drawing]

1 is a cross-sectional view of the method of hot forging a welded part according to the present invention, and FIG. 2 is a perspective view thereof.

Claims (1)

[Claims] One or more hot-forged or hot-rolled steel plates 1 are bent into a cylinder or a part of a cylinder, these are welded to form a cylinder, and the welded part 4 is partially hot-forged. When making a steel pipe, pass the core metal 2 having a height or diameter d' of 60% or more of the pipe inner diameter d through the pipe, sandwich the welded part 4 to be forged, and align it in a straight line in the rolling direction. A method for manufacturing a steel pipe, characterized by forging with an anvil 3.