JPH067942A - Method for welding martensite-based cast steel and product to be welded - Google Patents

Abstract

PURPOSE:To provide a means improving the workability when a pre-heating treatment or a post-heating treatment is executed in the welding site of defective working environment in order to prevent a welding crack or remove an internal stress in the case that a product to be welded consists of a martensite-based cast steel. CONSTITUTION:A built up part 4 consisting of a austenite-based steel is attached at the abutting surface of the product 1 consisting of a martensite-based cast steel in prior to a beveling, after the groove part is formed by removing a part of the built up part 4, and the groove abutting part 2 is formed by executing a heat-treatment in order to remove n internal stress generating at the time attaching the built up part 4. These workings are executed in the excellent working environment different from the welding site.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding martensitic cast steel and a product to be welded, and more specifically, to each abutting surface of the product to be welded made of martensitic cast steel.
After forming the grooved butt part by performing groove processing in advance,
Welding method of martensitic cast steel in which butt welding is performed by forming a weld bead between the butt portions with the groove, and,
The present invention relates to a product to be welded of martensitic cast steel, which is made of a martensitic centrifugal cast steel pipe, and is provided with a grooved butt portion on each butt surface to form a butt portion with a groove.

[0002]

2. Description of the Related Art Martensitic stainless cast steel (for example, cast products such as 13Cr stainless steel) and martensitic heat-resistant cast steel (for example, Cr-Mo heat-resistant steel and Ni-
Products to be welded made of martensitic cast steel such as low alloy steel such as Cr-Mo heat resistant steel) and martensitic carbon cast steel (for example, cast of high carbon steel for structure) (specific examples) For example, in the case of joining a natural gas feed transport pipe constituted by a centrifugally cast steel pipe formed by centrifugally casting 13Cr stainless steel) by the butt welding, the metal structure of the martensitic cast steel is Since it has a cast structure that contains hard and brittle martensite and has coarse crystal grains, weldability such as weld cracking such as toe cracking is likely to occur.
Therefore, conventionally, in order to prevent the occurrence of the weld crack, an appropriate preheat treatment (for example, 100 to 2) is performed at the welding site.
The treatment of preheating to 50 ° C.) was carried out. In addition, a large amount of heat-affected zone is generated in the vicinity of the welded portion of the base metal due to the formation of the weld bead, and a large internal stress (residual stress) is generated. Then, an appropriate post heat treatment (for example, a post heat treatment at 500 to 650 ° C.) is performed. In addition, the groove processing of the product to be welded is
It was usually carried out in advance before shipment of the work piece to the welding site.

[0003]

However, in order to carry out the pre-heat treatment and the post-heat treatment at the welding site, a gas burner for heating the article to be welded is arranged near the article to be welded, or Usually, troublesome work such as winding a heating element that heats the welded product around the welded product, or winding an insulating material around the welded product so that heat does not escape is required without relying on human labor. However, there is a problem that the workability is extremely poor. This problem becomes particularly noticeable when the product to be welded is large. A first object of the present invention is to provide a product to be welded made of martensitic cast steel,
It is an object of the present invention to provide a welding method of martensitic cast steel as a means capable of solving the above-mentioned problem of workability (particularly, the above-mentioned problem that becomes remarkable when the article to be welded is large).

Further, when the product to be welded is a martensitic centrifugal cast steel pipe such as a transport pipe for feeding natural gas, since it is a pipe material, it is more restrained than when the product to be welded is a plate material or the like. Then, the internal stress becomes larger. Therefore, it is necessary to perform the post heat treatment more sufficiently than when the article to be welded is a plate material or the like. Moreover, since the welding site is often an inconvenient place such as a desert or a wilderness, the pre-heat treatment and the post-heat treatment are particularly troublesome. Therefore, when the product to be welded is a martensitic centrifugal cast steel pipe such as a natural gas feeding transport pipe, the workability problem described above has been particularly remarkable. A second object of the present invention is to weld a martensitic cast steel as a means for solving the above problem of workability, which is particularly noticeable when the welded product is a martensitic centrifugal cast steel pipe. To provide.

[0005]

The welding method for martensitic cast steel according to the present invention, which was made in order to achieve the first object, comprises: abutting surfaces of welded articles made of martensitic cast steel; A method of welding martensitic cast steel in which a grooved butt portion is formed in advance to form a grooved butt portion, and then a weld bead is formed between the grooved butt portions to form a butt weld, the welded article being In the butt surface, a padded portion made of austenitic steel is attached prior to the groove processing, and a groove portion is formed by removing a part of the padded portion, and when the padded portion is attached. It is characterized in that a heat treatment for removing the internal stress that occurs is performed to form the butt portion with a groove.

The object to be welded of the martensitic cast steel according to the present invention, which is made in order to achieve the second object, is made of a martensitic centrifugal cast steel pipe, and each butt surface is groove-processed. A welded article of martensitic cast steel in which a butt portion with a groove is formed, wherein the butt portion with a groove is formed by removing a part of a flesh portion made of austenitic steel attached to each butt surface. In addition, it is characterized in that it is formed by heat treatment for removing internal stress at the time of attaching the fleshed portion.

[0007]

According to the method for welding martensitic cast steel according to the present invention, since the work for attaching the beveled portion is carried out prior to the beveling, the beveled portion as well as the beveled portion is processed. It is also possible to carry out the attachment work of (1) in a place with a good working environment before the shipment of the workpiece. Further, the heat treatment for removing the internal stress that occurs when the thickened portion is attached can also be performed before the shipment of the product to be welded in a place with a good working environment. Then, at the welding site, when the weld beads are formed between the butt joints with the groove to perform the butt welding of the workpiece, the weldability is good and the austenitic steel material has a small thermal effect on the base metal. Since the flesh portion is butt-welded, the pre-heat treatment work and the post-heat treatment work at the welding site, which are conventionally required, are unnecessary.

According to the article to be welded of martensitic cast steel according to the present invention, when the article to be welded is a martensitic centrifugal cast steel pipe, as described above, a large internal stress is likely to occur, which causes a problem of workability. Despite being particularly prominent, the heat treatment for removing the internal stress can be sufficiently carried out in a good working environment before shipment of the workpiece to be welded. Can deal with it enough.

[0009]

As described above, according to the method for welding martensitic cast steel according to the present invention, the above-mentioned problem of workability can be solved, and thus the first object of the present invention can be achieved. become.

Further, when the product to be welded is a martensitic centrifugal cast steel pipe, the product to be welded of martensitic cast steel according to the present invention is irrespective of the fact that the problem of workability described above tends to become particularly remarkable. By performing the welding used, the above-mentioned problem of particularly remarkable workability can be solved, and thus,
The second object of the present invention is achieved.

The effect of the present invention is particularly remarkable when the article to be welded is large.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a product to be welded of martensitic cast steel according to the present invention. The figure shows a butt state of a pair of products to be welded.

Reference numeral 1 in the drawing denotes a centrifugal cast steel pipe (for example, outer diameter: 750 mm, inner diameter: 710 mm) produced by centrifugally casting martensitic steel such as 13Cr stainless steel. It is a welded product (specifically, a natural gas delivery transport pipe that is often installed in an inconvenient place such as a desert or a wilderness).
A grooved butt portion 2 is formed by subjecting each of the butt surfaces to groove processing, which will be described in detail later. And
A weld bead 3 is formed between the butt joints 2 with grooves as shown in FIG. 2, so that the articles 1 to be welded are butt-welded together.

In the butt section 2 with groove, after each butt surface is provided with a fleshed portion 4 made of austenitic steel, a part of the fleshed portion 4 is removed by machining to obtain the structure shown in FIG. The U-shaped groove shown in FIG. 2 is formed, and further, heat treatment is performed to remove internal stress generated at the time of attaching the padding portion.

Specifically, the padding portion 4 is, in a factory with a good working environment, overlay welding using a welding rod made of austenitic steel (more specifically, overlay welding by MIG automatic welding). It is attached by carrying out.

Specifically, in the groove processing, in a factory with a good working environment, the groove shape is groove angle θ: 30 °, groove depth d: 18 mm, root radius r: 5 mm. Under such conditions, part of the flesh-filled part 4 is machined and carried out.

The heat treatment for removing the internal stress is carried out at a furnace temperature of about 700 in a state in which several pieces 1 to be welded are put together.
It is carried out by charging it into a heat treatment furnace maintained at ℃ and holding it in the furnace for an appropriate time. When the number of treatments of the article to be welded 1 is particularly large, continuous treatment using a tunnel type continuous furnace may be considered.

In FIG. 2, after the article 1 to be welded having the butt portion 2 with the groove formed on the butt face as described above is conveyed to the welding site, the butt portion 2 with the groove 2 is reciprocated at the welding site. Arc welding using an austenitic welding rod,
The result of butt welding by forming a multi-layered weld bead 3 on that portion is shown. At the welding site,
The pre-heat treatment and post-heat treatment that were conventionally performed are not required.

Next, another embodiment will be described. In the above-mentioned embodiment, the welded article 1 is the centrifugal cast steel pipe made of martensitic stainless cast steel (for example, 13Cr stainless cast steel). The welding method and the article to be welded of the martensitic cast steel according to the present invention are also applicable to the above.

Further, the article to be welded 1 is not made of martensitic stainless cast steel, but may be martensitic heat resistant cast steel (for example, Cr--Mo heat resistant steel or Ni--Cr--M).
o Martensite cast steel such as low alloy steel such as o heat resistant steel) and martensite carbon cast steel (for example, high carbon casting for structure) The welding method of site-based cast steel and the product to be welded are applicable.

Further, in the above-mentioned embodiment, the padding portion 4 is attached by welding the austenitic steel material by welding, but the padding portion 4 is attached to each of the abutting surfaces. On the other hand, it can be attached by various fleshing methods such as spraying an austenitic steel material and welding an austenitic steel piece.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a main part of a product to be welded (centrifugal cast steel pipe) according to the present invention.

FIG. 2 is a longitudinal sectional view showing a result of welding the article to be welded.

[Explanation of symbols]

 1 Welded product 2 Butt with groove 3 Weld bead 4 Filled part

Claims (2)

[Claims] 1. A grooved butt portion (2) is formed by previously forming a groove on each butt surface of a welded article (1) made of martensitic cast steel, and then the grooved butt portion is formed. (2) A welding method for martensitic cast steel, in which weld beads (3) are formed between each other and butt-welded, wherein a butt portion of an austenitic steel material is provided on the butt surface of the workpiece (1) ( 4) is attached prior to the groove processing, a part of the padded portion (4) is removed to form a groove, and then internal stress generated when the padded portion (4) is attached is removed. A heat treatment for forming the grooved butt portion (2)
Welding method of martensitic cast steel for forming slag. 2. A welded article of martensitic cast steel comprising a martensitic centrifugal cast steel pipe, wherein each butted surface is grooved to form a butted portion (2) with a groove. In the grooved butt section (2), a part of the fleshed section (4) made of austenitic steel attached to each butt surface is removed, and the inside of the fleshed section (4) is attached. A martensitic cast steel work piece that is formed by heat treatment to remove stress.