JPS58184091A - Arc welding method with covered electrode of dead soft steel - Google Patents

Abstract

PURPOSE:To prevent solidification cracking by welding thoroughly even in welding at >=30cm/min welding speed, by using a welding rod wherein the content of Ni in the metallic powder in the core wire and covering material in the electrode has the specific relation with the contents of C and org. material in the steel material to be welded and a welding material. CONSTITUTION:An Ni-contg. covered electrode satisfying the equation I where the contents of Ni and C of the core wire of th electrode are designated as Niw%, Cw%, and the contents of the Ni, C and org. material of the metallic powder in the covering material are designated as Nif%, Ca%, Co% is used in the stage of arc welding of a steel material contg. 0.005-0.06% C with a covered electrode at >=30cm/min welding speed. At least the 1st layer is welded. An Ni-contg. covered electrode satisfying the equation II where the content of Ni in the Ni-contg. steel material contg. the above-described content of C is designated as Nip is used in the case of said steel material, and the steel material is welded similarly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coated arc welding of ultra-low carbon steel.

In recent years, with advances in controlled rolling of steel materials, there has been a trend toward lower carbon steel materials, including line pipe materials, in order to improve weldability or reduce costs. Conventionally, it has been thought that the hot cracking susceptibility of weld metals of these low carbon steel materials, particularly their weld solidification cracking susceptibility, is generally low.

However, according to studies conducted by the present inventors, contrary to conventional wisdom, ultra-low carbon steel with a carbon content of 0.06 or less can be used for 30 min/- or more using existing welding materials. We have found that when coated arc welding is performed at a welding speed of As a way to solve welding solidification cracking in metals, the carbon content in the welding rod core wire and coating material is adjusted so that the carbon content in the weld metal does not become too low.
A covered arc welding method that controls the temperature within an appropriate range has previously been proposed (Japanese Patent Application No. 141756/1982).

On the other hand, the present inventors have investigated the effect on weld solidification cracking of low-carbon weld metal that is formed when ultra-low carbon steel materials with C0.06% or less are coated arc welded at a welding speed of 30 crn/Illjm or more. As a result of extensive research into the various factors that affect this process, it was discovered that nickel has a significant effect on preventing weld solidification cracking in low-carbon weld metals.

That is, by making the weld metal contain an appropriate amount of nickel that is equal to or higher than the required nickel content determined in accordance with the carbon content in the low carbon weld metal, 3 Q crn/
It has been found that welding solidification cracking of low carbon weld metals can be completely prevented even when welding is performed at a welding speed of 100% or more.

The present invention was made based on the above findings, and
The gist is (1) Carbon 0.005X0.
When carrying out coated arc welding of steel containing 0.6% at a welding speed of 30 cb or higher, the amount of nickel contained in the core wire of the welding rod kN i jw) h, the amount of gold contained in the coating material
The amount of nickel in the powder is N1 (11%, the amount of carbon in the steel material is “C”)
1p+ ”Amount of carbon contained in the core wire of the welding rod 1kC1w1
9b, the carbon content □ of the metal powder contained in the coating material is c
alb, when the amount of organic matter is expressed as C(.)chi(al), 0.32Ni (W) + 0.14Ni 1f) 2°3 (13,80(p) + 11.3C(2.26)
A method for coated arc welding of ultra-low carbon steel, characterized in that at least the first layer is welded at dawn using a nickel-containing coated arc welding rod that satisfies the formula: C (%+0.015C(ol)). and (2) When nickel-containing steel f containing 0.005 to 0.06% carbon is subjected to covered arc welding at a welding speed of 30 cm/- or more, the amount of nickel contained in the steel is ``(pl'') of the welding rod. The amount of nickel contained in the core wire is t-Ni(w)%, the amount of nickel in the metal powder contained in the coating is N1(1)chi, and the amount of carbon in the steel is Cf1)).
H. The amount of carbon contained in the core wire of the welding rod is C(w)%.

The amount of carbon in the metal powder contained in the coating material is C (a1%.

When the amount of organic matter is expressed as C (01%), 0.55Ni (pH + 0.32N i (w) +
0.14N 1(f) upper 2°3(13,8C(,1+1
1.3 C (season + 2.26 C(a) +0.015
The present invention is directed to a coated arc welding method for ultra-low carbon steel, characterized in that at least the first layer is welded using a nickel-containing coated arc welding rod that satisfies the formula C(ol).

The present invention will be explained in detail below.

In order to improve the cracking resistance and toughness of the weld metal in high and low temperature ranges, it is conventional wisdom that the carbon content of the weld metal should be set to a value similar to or lower than that of the base metal. When low-temperature steel has 0.08% C≦0.18%, the target value for weld metal is usually 0.07≦C<0.15%, and the carbon content further decreases. It was thought that solidification cracking would not occur even if

However, according to the inventors' study, ultra-low carbon steel
The susceptibility to weld solidification cracking of low carbon weld metal obtained by welding using conventionally used coated arc welding rods is as follows:
On the contrary, we found that it actually increased, and obtained Figure 1. In other words, Figure 1 shows the relationship between the carbon content (ts) of the weld metal and the welding speed (cm
/=) and weld solidification cracking, and shows the relationship between carbon content 0.
Using a steel material of 0.01 to 0.1'l, the dimensions and shape (t, (unit capacity): 19.t.

: 1.5. l: 1.5. θ: 300) and the welding test specimen (l, (unit I1
m): 400. J2: 300- Is near 5. J4
:250°15 Near 5. t: l9) T- is prepared, and the carbon content of the core wire of the welding rod is set to 0.04 to 0.12%1. This is obtained when root welding is performed under the welding conditions shown in Table 1 using cellulose welding rods with varying amounts of organic matter in the coating material ranging from 20 to 40%, and the weld metal does not contain nickel. .

As shown in Table 1 and Figure 1, weld solidification cracking occurs in region A where the carbon content is less than 0.09% and welding speed is 30 cy++/- or more, and in region B, weld solidification cracking occurs. We confirmed that this does not occur. That is, the susceptibility to solidification cracking of weld metal is contrary to conventional wisdom, but when the carbon content is below the limit, the susceptibility to solidification cracking of weld metal increases when the welding speed exceeds the limit. The reason for this is thought to be that the lower the carbon content of the weld metal, the more δ phase solidification occurs, which reduces the weld solidification cracking by 0.06.
If the carbon content is less than 0.0%, it is considered to have the strength of steel.
0.005% or more, such as general structural steel and low-alloy steel for low temperature use.

In order to suppress the formation of δ phase in low carbon weld metal, we investigated the effect of nickel, which is a γ phase forming element, by using a welding rod containing nickel only in the coating material and a welding rod containing nickel in both the core wire and coating material. Using the same welding test method as shown in Fig. 1, welding was carried out using a welding rod that had been prepared in the same manner as in Fig. 1, and welding solidification cracking in the root weld metal was investigated in detail, and Fig. 4 was obtained. Table 2 shows the Ni% on the sample side in FIG. 4.

1) By adding nickel to the welding rod shown in Table 2, the upper limit of the carbon content in the weld solidification cracking region shifted to the lower carbon side. This revealed that nickel has a very significant effect on reducing the weld solidification cracking susceptibility of low carbon weld metals. In addition, when welding at a welding speed of less than 30 tyn/-, molten steel continues to flow into the final solidified part of the weld metal (
Since the welding material was supplied with nickel, no weld solidification cracking occurred even with low carbon weld metal that does not contain nickel.

In other words, the weld solidification cracking of low carbon weld metal is 30 cr.
This phenomenon occurred when welding was performed at a welding speed of n/#1 or higher.

Due to metallurgical and mechanical conditions, weld solidification cracking is most likely to occur in the root weld metal. Therefore, if solidification cracking in the root weld metal can be prevented, solidification cracking in low carbon weld metal can be prevented in subsequent welds. Concerns disappear. In order to prevent this welding solidification cracking of the root weld metal, it is necessary to FIG. 4 suggests that it is sufficient to use a welding rod containing more nickel than the upper limit of cracking. Based on FIG. 4, the following equation could be obtained as a relation between c(R) in the welding solidification crack-free region and the amount of nickel in the welding rod.

0.32Ni(w) +0.14Ni (1)≧2.3
25 C(R) (1) On the other hand, the present inventors 3
A number of high-speed covered arc welding tests were carried out at welding speeds of 0 F/N or higher, and the relationship between the carbon content c(R) of the root weld metal and the carbon source of the welding rod was investigated in detail. As a result, it was found that the root weld metal was formed with a contribution rate of 55% on the steel side and 45% on the welding rod side. The carbon source of steel is the carbon content C(p) in the steel, and the carbon source of the welding rod is mainly the carbon content C(wl) of the core wire and the carbon content C(al%) in the metal powder of the coating material. Organic matter amount c(0
It is 1. In addition to this, cot generated by the decomposition of carbon salts may dissociate and become carbon and enter the weld metal, but the amount thereof is extremely small and can be ignored. The contribution rate of the core wire to carbon in the root weld metal is 5 times that of the coating material, and the contribution rate of carbon due to organic matter in the coating material is 1/150 compared to that of metal powder.
Met. Based on these findings, the following formula was obtained as a prediction formula from the accuracy of C(R).

C(R)=0.55 C(p)+0.45 C(,
,)+0.09 C(a)+0.0006 C(o)・
・(2) From equations (1) and (2), in order to prevent weld solidification cracking of low carbon weld metal, if the core wire of the welding rod and the amount of rackel in the coating material satisfy the following equation: It turned out to be good.

0.32Ni (w)+0.14Ni (f)≧2.
3(13,8C(1)+11.3C(w)+2.
260(a1+ 0.015 C(ol)...(3
) Next, ultra-low carbon steel materials may contain nickel for the purpose of ensuring good weld zone toughness. When such nickel-containing ultra-low carbon steel materials are welded, the nickel in the steel material naturally transfers to the weld metal, so the total amount of nickel in the welding rod required to prevent welding solidification cracking must be transferred from the steel material. It is possible to reduce the amount of nickel by an amount corresponding to the amount of nickel that has been used. However, the total amount of nickel in the welding rod is expressed by the following formula.

The total amount of nickel in the welding rod = ,'N 30α/#I The contribution rate to the root weld metal formation when coated arc melting is carried out at a high speed of 30α/#1 or more is, as mentioned above, when the steel material is 55 nickel and the welding rod was 45 N, and since nickel has almost no acid tip loss during welding and transfers from the steel material and welding rod to the weld metal, it is 0.55 N.
It can be considered that + (p) '% of nickel was contained in the welding rod. Therefore, in order to completely prevent weld solidification cracking of the root weld metal when nickel-containing ultra-low carbon steel is subjected to high-speed coated arc welding, it is necessary to It is sufficient that the amount of nickel in it satisfies the following formula.

0.55Ni (p) + 0.32Ni (匍+0.
14Ni(f)≧2.3CI3.8 C(p)+ 11
．． 3 C(w)+ 2.26 C(1)+ 0.015
ICf% as the total nickel content of C(ol) welding rod
In order to contain a certain amount of nickel, it is economical to mix it into the coating material in the form of metallic nickel or nickel metal powder such as ferronickel, and to use mild steel for the core wire. However, if the nickel metal powder in the coating material exceeds 15%, the coating material is likely to be chipped during welding, and the nickel metal powder in the coating material that has migrated to the weld metal may not be uniformly mixed in the molten pool. There is a risk that some parts will be unevenly distributed.

Therefore, if it is necessary to incorporate more than 15% nickel metal powder into the coating, the amount of nickel metal powder in the coating must be 15%.
%, and it is desirable to include the insufficient nickel content in the core wire.

On the other hand, it is of course possible to make the nonylkel wire contain approximately ios of nickel as the total amount of nickel in the welding rod. However, when nickel is contained in the mild steel core wire, the specific electrical resistance of the core wire increases significantly, so if nickel in the core wire exceeds 5%, during welding (stick burning of two welding rods will cause a phenomenon). This will impair welding work and increase the manufacturing cost of the core wire.For this reason, it is desirable to limit the amount of nickel to 5% for nickel-containing core wires, and the amount of nickel supplied from the core wire should be limited to 5%. If the amount of nickel is insufficient, it is preferable to add the missing nickel to the coating material as nickel metal powder.

The effects of the present invention will be illustrated in more detail with reference to Examples below.

Example 1 A welding test specimen shown in FIG. 3 having the groove shape shown in FIG. 2 was prepared using a plate material having the chemical composition shown in Table 3, and a coated arc welding rod shown in Table 4 was used. One-pass welding was performed under the welding conditions shown in Table 5 (2), and solidification cracking of the weld metal was investigated. The test results are shown in Table 6 (C-2).

Within the scope of the present invention, there is no solidification cracking in X-ray transmission tests and weld bead cross-sectional inspections.

Example 2 A steel pipe with the groove shape shown in Fig. 2 and the chemical composition shown in Table 7 (outer diameter 1.219 x 1000 mm) was welded using the coated arc welding rod shown in Table 4 as shown in Table 8. Root welding was performed under the welding conditions. The test results are shown in Table 9.

Those within the scope of the present invention have no solidification cracking in X-ray transmission tests and weld bead cross-sectional inspections.

1111

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between the solidification crack area that occurs in the root weld metal, the carbon content of the weld metal, and the welding speed during shielded arc welding of ultra-low carbon steel, Figure 2 shows the groove shape, and Figure 3 is the dimension of the welded specimen. Figure 4 is a diagram showing the effect of nickel on the solidification cracking susceptibility (2) that occurs in the root weld metal during coated arc welding of ultra-low carbon steel. Yongtou JIC amount (7,) Procedural amendment (spontaneous) 5J1124/1988 Haruki Shimada, Director General of the Japan Patent Office 1 Indication of case 1988 Patent Application No. 67100 3, Person making the amendment Relationship to the case Patent application humanity place
2-6-3 Omitatecho, Chiyoda-ku, Tokyo Name (
665) Nippon Steel Corporation Representative Takeshi 1)
4, Agent Address: 3-3-3-5, Nihonbashi, Chuo-ku, Tokyo Date of amendment order: 1925 Month, day (shipment date) 6. Number of inventions increased by amendment (1) Specification, page 9 2nd line rO,005X O,06
Change "%" to "ro, oos~0.06chi". (2) On page 13, line 1, "acid tip loss" has been changed to "oxidation loss.":; Procedural amendment (voluntary) September 10, 1980 Kazuo Wakasugi, Commissioner of the Japan Patent Office1, Indication of the case Patent Application No. 67100 of 19822, Title of the invention Method for coated arc welding of ultra-low carbon steel3,
Person making the amendment Relationship to the case Patent applicant address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (665)
) Nippon Steel Stock Food Coloring Representative Takeshi 1) Yutaka 4th generation Masaru Address 3-3-3-5 Nihonbashi, Chuo-ku, Tokyo Date of amendment order Showa 1999 Month, day (shipment date) 6, increase due to amendment Number of inventions to be amended 7 Subject of amendment Column 8 of details of the invention in the specification ρ week, contents of amendment 1, Table 2 on page 9 of the specification are amended as follows. Table 2

Claims (1)

[Scope of Claims] 1. A steel material containing 0.005 to 0.06 carbon, 3
When performing coated arc welding at a welding speed of 0d/f or higher, the amount of nickel contained in the core wire of the welding rod is N1(1)chi, and the amount of nickel in the metal powder contained in the coating material is N1(f).
) The carbon content of the steel material is Cfpl' The carbon content contained in the core wire of the welding rod is C(w). The carbon content of the metal powder contained in the coating material is Cfat %. Organic matter amount k C (when expressed as 81%, 0.32Ni
+ 0.14Ni(f1≧2.3(Wl (13,8C(p)+ 11.3C(wl+ 2.26
A coated arc welding method for ultra-low carbon steel, characterized in that at least the first layer is welded using a nickel-containing coated arc welding rod that satisfies the formula: C(a)+0.015C(.)). 2. When welding a nickel-containing steel material containing 0.005 to 0.06% carbon at a welding speed of 30 cm/- or more, the amount of nickel contained in the steel material is
,1%, the amount of nickel contained in the core wire of the welding rod is Ni
(Paulownia%, the amount of nickel in the metal powder contained in the coating material is N
1(f)%, the carbon content of the steel material is C(pl'), the carbon content contained in the core wire of the welding rod is C(w)%, the carbon content of the metal powder contained in the coating material is C(a)%. , organic matter tic(.)%
When displayed as 0.55N 1(p) + 0.32N
i (w) + 0.14N i (1)≧2.3(13
,8C(1)+11.30(Tsukasa+2.26C(a)
+0.015C(o)) A coated arc welding method for ultra-low carbon steel, characterized in that at least the first layer is welded using a nickel-containing coated arc welding rod that satisfies the formula: +0.015C(o)).