JPS5868480A - Submerged arc welding method for ultralow carbon steel - Google Patents

Abstract

PURPOSE:To prevent the generation of cracking and to obtain good impact toughness in submerged arc welding by adding C which satisfies the specific equation per unit length of a groove. CONSTITUTION:In submerged arc welding to be executed for steel contg. 0.005- 0.06wt% C by using a wire of 0.06-0.14% content of C, a recarburizer is disposed in the bottom part of a groove to add the C satisfying the equation I per unit length of the groove. Here, M is the rate of melting of the metal components in the wire and the recarburizer per unit time, melt sticking speed g/min, and S is a welding speed cm/min.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a submerged arc welding method (hereinafter referred to as submerged arc welding method) for ultra-low carbon steel.

In recent years, there has been a trend toward lower C steel materials, including line pipe materials, in order to improve weldability or reduce costs as well as advances in controlled rolling. The hot cracking susceptibility of these low C steel weld metals has been generally considered to be low.

In other words, in order to improve the hot cracking and cold cracking susceptibility and toughness of the weld metal, it is conventional wisdom to set the C content of the weld metal to a value similar to or lower than that of the base metal. When steel is 0.08% C<, 0.18%, the target value for weld metal is usually 0.07% C<, 0.15%.

However, the inventors' studies have revealed that the weld metal obtained by performing submerged arc welding on ultra-low C steel using conventional welding wires has a rather high high-temperature cracking susceptibility.

That is, it is thought that in the extremely low C region, the dendrite abutting portion undergoes δ solidification, and it was confirmed that an increase in the amount of C, which is a γ stabilizing element, is necessary to reduce cracking.

Therefore, the present invention can prevent hot cracking of bath welded metal of ultra-low C steel.
It has been discovered that there is an appropriate weld metal C content, and a submerged arc welding method for ultra-low C steel is provided to obtain this appropriate range.

That is, the gist of the present invention is to carburize the bottom of the groove in submerged arc welding of steel containing 0.005-0.06% by weight of C using a welding wire with a C content of 0.06-0.14%. By arranging the material, C is added per unit length of the groove.

However, M is the melting amount of the wire and the metal in the carbonized material per unit time, that is, the welding speed (Vz4), and S is the welding speed (--).

The present invention will be explained in detail below.

The target steels of the present invention are ultra-low C steels such as general structural steels and low-alloy steels for low temperature use, which contain 0.06% by weight or less of C and 0.005% or more of C, which is considered to have the strength of steel. Ni
For example, stainless steel and the like containing gamma former elements such as the like are excluded.

It is known that the C content of the welding wire in currently commonly used submerged arc welding is in the range of 0.06 to 0.14%. By the way, according to the studies conducted by the present inventors, when welding a 0.005% C steel plate with a C content wire of 0.06%, the C content in the weld metal is 0.03% or less, and the first layer The weld metal in the eye becomes δ single-phase solidification, and the formation of secondary Punt 9 light is suppressed, so solidification cracks are likely to occur. Therefore, in order to obtain an appropriate amount of C in the weld metal, it is necessary to add at least about 0.04% to 0.14% of C.

Even if a wire with a high C content of 014% is used, the ΩC in the wire will oxidize and become CO gas, so the wire will have a wire content of 1.0%.
Even when 061C steel is used, the weld metal will contain about 0.07% C, and it is necessary to add a small amount of C to ensure a sound weld metal. i.e. at least 0
．． It is necessary to add 0.01% to 0.09% of C.

As mentioned above, when welding steel of 0.005 to 0.064C using normal wire, 0.01
This means that it is necessary to separately supplement C of ~014chi.

According to experiments, in order to achieve the above objective, -a groove unit length is 2.5 X-X 10 (r4) ~ 5
．． Adding C of OX"X10-3S (Ri, 4) is suitable for practical training.

Therefore, in the present invention, a substance containing C, such as cast iron powder, high C cut wire, graphite-containing flux, etc., is placed in the groove during first layer welding.
The amount of these substances to be placed within the groove is considered as follows.

That is, the welding speed and welding speed determined by the submerged arc welding flux and welding conditions applied in the method of the present invention are M 17m and S tB//IiR, respectively.
Then, the amount of welding per unit groove length is M'S (1/
□). Normally, the base metal dilution rate in the first layer of submerged arc welding is about 60 inches, and considering this, the amount of weld metal generated per unit groove length in first layer welding is 2
．． 5XM/S (f/□).

For this weld metal, the above-mentioned C deficiency is 0.01 to 0.014
In order to compensate for this, it is necessary to place C of (r/cyi).

During actual removal, not all of the carbon placed in the groove is added to the weld metal, but a portion reacts with oxygen to become CO gas and dissipate. The amount of consumed C varies depending on the state of addition of C, and according to the study results of the present inventors, it was found that the unit groove length is required.

Although the dilution rate of the base material was set at 60% here, it can be assumed that when a metal object for carburization is placed within the groove, the amount of melting of the base material decreases by that amount. Therefore, even if a metal object for carburization is placed in the groove, the amount of weld metal produced is 2.5
M/S (r/cm').

In the present invention, the following materials are used as the carbonaceous material to be placed in the groove in advance.

High C metal powder: Cast iron powder, high C iron powder, high CFe-Mn, high CFe-Cr Metal carbide' 5i-C% Cr -C High C-containing wire: (In the case of wire, place it horizontally on the groove) High C cut wire: Cut wire is a small diameter wire (1
, 2 to 1.696) shredded into pieces of about 1 to 1.696. The flux C-containing material is granulated by adding a large amount of C. The C-containing material is for adding C to the weld metal, and is usually used. It is necessary to contain a larger amount of C than that of the wire, and at least 0.2 C or more is required. Also, materials that are melted within the groove and contain large amounts of moisture and other substances harmful to the weld metal should be avoided.

The present invention is mainly applied to double-sided single-layer, multi-layer, or single-sided welding, and the S (welding speed) is 20 to 200.
M (welding speed) is approximately 100 to 2000 r/.

The present invention will be explained below with reference to Examples.

Example In welding six types of low C content steels as shown in Table 1, wires and fluxes shown in Table 2 (W1 to W3) and Table 3 (Fl to F3) were used. In Table 3, Fl is a melt-type flux for double-sided welding, and F2.3 is a bond-type flux, where the former is a double-sided welding flux and the latter is a single-sided welding flux.

Twelve types of welding were performed using these materials, and the combinations of steel plates, wires and fluxes and welding procedures are as shown in Table 4. The type and amount of the C-containing substance used to add C are also shown in Table 4.

In the table, A1 to A9 are examples of the present invention, and A1 to A12 are comparative examples for clarifying the effects of the examples of the present invention. Furthermore, the embodiments in which double-sided welding is performed relate to the BP side.

Welding is 2 electrode welding for A3.9, A8 and 12
Single-sided, single-layer welding was performed using three-electrode welding. For others, one-electrode welding is used.

The welding speed shown in the table relates to the first layer in the case of single-sided welding of the BP side layer.

In the case of double-sided multilayer welding, the present invention was applied only to the first layer on the BP side and the EP side, and the second layer was subjected to normal submerged arc welding without disposing any C-containing material.

As a backing method in the case of single-sided welding, a flux-steel backing method was used in which backing flux was spread in a layer on a copper pad and pressed against the back surface of the steel plate. As the back flux, a CaO-MgO-8iOz-based special back flux was used.

As a result of the above welding, based on the effects of the present invention for Yas. 1 to 9, as shown in the welding results in the table, it was possible to obtain the first layer weld metal with an appropriate C content, and no cracking occurred. Also, good impact toughness was obtained.

On the other hand, in Comparative Examples All and No. 12, the C content in the first layer weld metal was too low, and in All and No. 1612, there was too much, so cracks occurred in both cases.

Table 2 51 Chemical components (Chi>---
1 table 3

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are explanatory diagrams of the groove shape. Rod 1 figure Broom 2 figure Procedure amendment (method) 1985 2Jt6 Japan Patent Office Commissioner Island 1) Haruki Tono 1 Indication of case Patent application No. 166340 of 1981 2 Title of invention Submerged arc welding of ultra-low carbon steel Person making Method 3 amendment Relationship to the case Patent applicant Location
2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (66)
5) Nippon Steel Stock Food Coloring Representative Takeshi 1) Yutaka 4th generation Masashi Address 3-3-3 Nihonbashi, Chuo-ku, Tokyo Date of 5th amendment order February n, 1981 (shipment date) 6th amendment increasing number of inventions

Claims (1)

[Claims] In submerged arc welding of steel containing 0.005-0.06% by weight of C using a welding wire with a C content of 0.06-0.14%, the bottom of the groove is pre-formed. A submerged arc welding method for ultra-low carbon steel, characterized in that carbon is added to the groove unit length by arranging a carbon material. However, M is the welding speed (f/m), and S is the welding speed (0V-).