JP3115484B2 - Low hydrogen coated arc welding rod and welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is directed to a 490 N / mm ² or higher grade high tensile steel, low hydrogen type covered electrode to improve the low-temperature cracking resistance of the steel weld and welding process using the same It is about.

[0002]

2. Description of the Related Art With the increase in size of ships and buildings, the use of high-tensile steel materials has been increasing in order to reduce the weight of steel materials. Since high strength steel contains a small amount of alloying elements to increase the yield point and tensile strength, when arc welding high strength steel,
It is well known that low-temperature cracking occurs frequently.

[0003] The causes of low-temperature cracking include factors such as the hardness of the weld, the amount of diffusible hydrogen, and the degree of restraint of the welded member. It is known that the effect of the amount of diffusible hydrogen is particularly large. As described above, the low-temperature cracking that occurs when the weld metal contains a large amount of hydrogen is determined by the structure of the weld metal and the amount of hydrogen. Particularly in recent welding of high-strength, high-toughness steel, a coated arc welding rod is used. In order to improve the strength and toughness, a hardenable element is contained, and cracks tend to occur in the welded portion from the heat affected zone of the base material.

[0004] Cracks occurring in the heat-affected zone of the base metal can be improved by employing a method of achieving high strength while securing a low carbon equivalent by a recent controlled rolling control cooling technique. The carbon equivalent is an index for evaluating cold cracking susceptibility, and the lower the carbon equivalent, the higher the cold cracking susceptibility. The idea of this method is to compensate for the decrease in strength due to the low carbon equivalent by the production conditions.However, applying this method directly to improving the low-temperature cracking susceptibility of the weld metal is a low-temperature heating technique, a technology unique to controlled rolling control cooling. This is practically impossible because the rolling process and the accelerated cooling process cannot be applied to the welded joint.

[0005] Several methods have been found as means for preventing or reducing welding cracks. Among them, among them, conventionally, the method is most commonly used and is considered to be the most effective for welding cracks. This is a method of preheating or post-heating the base material. This method has the effect of slowing down the cooling rate of the weld, reducing the generation of martensite in the structure of the weld, and prolonging the release time of diffusible hydrogen in the weld to suppress hydrogen embrittlement. And there is an effect of alleviating generation of residual stress. The preheating temperature for achieving these effects varies depending on the components of the base material, the thickness of the base material, the strength, the composition of the welding material, and the like, but generally about 100 ° C. for welding 590 N / mm ² class high strength steel. It is as high as 200 ° C. Such a high preheating temperature makes the welding operation extremely difficult and, in addition, causes a sharp rise in welding work costs. A coated arc that does not require preheating or has an excellent crack resistance that can reduce the preheating temperature. There is a demand for the development of a welding rod.

As a method of preventing welding cracks without preheating a very thick steel plate, for example, Japanese Patent Publication No. 59-15758 and Japanese Patent Publication No. 60-48280 disclose diffusing hydrogen to a weld portion by performing high temperature firing in a carbon dioxide gas atmosphere. There is a method using a covered arc welding rod in which occurrence of cracks is extremely reduced. This method has shown some effects on steel materials with reduced alloying agents and reduced carbon equivalents that have a negative effect on weld cracking, but it adds to the labor and cost of manufacturing welding rods and lacks versatility. . Also, no matter how much the amount of diffusible hydrogen in the welding rod itself is reduced, water vapor in the atmosphere causes an increase in hydrogen at high temperatures and high humidity.

As a coated arc welding rod containing vanadium, for example, Japanese Unexamined Patent Publication (Kokai) No. 3-285793 discloses a low-hydrogen-based coated arc welding electrode capable of obtaining good fracture toughness for high-tensile steel of 60 kg or more. A stick has been proposed,
Vanadium is added for the purpose of improving the strength, and has not been improved in low-temperature cracking resistance. Japanese Patent Publication No. 60-49993 proposes a low hydrogen coated arc welding rod containing magnesium carbonate and calcium fluoride and having improved pit resistance.
As described above, vanadium is added together with other alloying agents such as Ni, Cr, Mo, Cu, and Nb when the strength of the weld metal is required, and has not been improved in low-temperature cracking resistance.

On the other hand, JP-A-5-161993 and JP-A-2-220797 propose a coated arc welding rod for Cr-Mo based low alloy steel, but the addition of vanadium causes creep characteristics at high temperatures. The purpose is to improve the low temperature cracking resistance. Therefore, these techniques cannot be expected to work without preheating or to reduce the preheating temperature.

Sakai et al. (“Iron and Steel”, Vol. 7) show that the addition of vanadium has an effect of trapping hydrogen.
2 (1986); 9, p. 1375) It is already known. According to this study, the effect is obtained only when vanadium is added in an amount of 0.25% or more, and it is shown that the addition of 0.1% hardly differs from the case where no vanadium is added. As will be described in detail later, the present invention mainly uses vanadium in the range of 0.05 to 0.25% in the weld metal, and a hydrogen trap which is a result of the research by Sakai et al. Can be expected. Does not match range. In addition, the invention described in this research presentation shows that Cr-Mo steel for pressure vessels
This is a technique that prevents the reduction in ductility of steel caused by hydrogen that has entered steel and is an effective technique for the case where hydrogen is constantly supplied from the outside. Is essentially different from the case where
Furthermore, in a weld metal containing several hundred ppm of oxygen and whose microstructure is essentially a solidified structure and is essentially different from the base material, whether vanadium addition has an effect of reducing the preheating temperature to prevent weld cracking. Cannot be clarified from the results of this study.

[0010]

[0008] The present invention was made to solve the problems of the prior art, even when predominantly 490 N / mm ² or higher grade of welding a high strength steel, require preheating It is an object of the present invention to provide a low-hydrogen-based coated arc welding rod and a welding method which are extremely excellent in crack resistance and can reduce the preheating temperature.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is directed to a coated arc welding rod for high-tensile steel of at least 490 N / mm ² class containing at least a metal carbonate and a metal fluoride. A low hydrogen coated arc welding rod characterized in that vanadium is contained in one or both of a core wire and a coating agent so as to satisfy a range based on the following formula (1). 0.05 ≦ Wv + 0.38 Fv ≦ 0.25 (1) where, Wv: the content (% by weight) of vanadium in the core wire with respect to the total mass of the core wire Fv: with respect to the total mass of the coating agent Vanadium content in coatings (% by weight)

The term "vanadium" in the above coating agent refers to alloys and compounds such as metal vanadium and ferrovanadium, as well as mixtures and powders thereof.

Further, the tensile strength is 490 N / mm ²
When the content in the steel is not less than 880 N / mm ² and represented by% by weight and represented by each chemical symbol, the Pcm calculated by the following equation (2) is 0.14 to 0.24%. And a welding method using the low hydrogen-based coated arc welding rod. Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Mo / 15 + V / 10 + 5B (2)

[0014]

The present inventors have conducted research to develop a coated arc welding rod and a welding method that can prevent low-temperature cracking even if the preheating temperature is reduced by a method other than the method of reducing the amount of diffusible hydrogen.
As a result, the present inventors focused on vanadium, which has been conventionally used in Cr-Mo steel welding materials mainly for improving high-temperature strength characteristics, and decided to include a specific amount in the weld metal.
Vanadium reduces carbon in the matrix by producing fine carbides and fixing the carbon in the weld metal,
This has led to the finding that the cracking susceptibility of the weld metal can be reduced, thereby improving the crack resistance of the weld metal and ensuring the strength. Furthermore, by using a steel material in which Pcm represented by the above formula (2) is kept within a predetermined range and a coated arc welding rod in the present invention, cracks in both the weld metal and the HAZ can be prevented even when the preheating temperature is reduced. They came to know that they could do it. The present invention has been made based on such findings, and the operation will be described in detail below.

First, the coated arc welding rod will be described.
In this regard, the present inventors conducted the following tests. That is, in weight%, rutile 2%, carbonated lime 47%, barium carbonate 4%, fluorite 16%, ferrosilicon 10%, ferromanganese 2%, ferromolybdenum 2-5%, ferrovanadium (50% vanadium) 0 1.6%, 8.2% of the dry weight of the binder, 1% of the coating agent, and the coating agent consisting of iron powder with the balance being C: 0.06-0.07%, Si: 0.01%,
Mn: 0.49 to 0.51%, V: 0 to 0.28%,
P: 0.01%, S: 0.01%, N: 0.002%,
The remaining portion was coated with a steel core wire having a Fe diameter of 4.0 mm and a length of 400 mm to a coating outer diameter of 6.4 mm, and then dried and fired to prepare a welding rod.

Using these welding rods, a U-shaped welding crack test (JIS Z3157) for investigating the crack resistance of the weld metal was performed. The steel material is JIS SM590B thickness 30
mm, welding current 170A, welding heat input 17kJ / c
m, the temperature was 30 ° C., and the relative humidity was 80%, and the preheating temperature required for stopping cracking was determined. Table 1 shows the results, and FIG. 1 is a graph showing the relationship between the V amount used in the equation (1) and the crack stop preheating temperature. In the formula (1), the reason why the coefficient of 0.38 is multiplied by vanadium in the coating agent is that it has been found that it becomes equivalent to the content in the cord.

[0017]

[Table 1]

As is clear from Table 1 and FIG. 1, the welding rod No. having a vanadium content of less than 0.05% by weight as defined by the formula (1) added to one or both of the welding rod core and the coating agent. The preheat temperature required to stop cracks 1, 2, 3 and 9 is between 75 ° C and 125 ° C. On the other hand, the welding rod No. having the vanadium content of 0.05 to 0.25% by weight in the formula (1) was used.
4, 5, 6, 10, 11, 13, 14, 16, and 17
The preheating temperature required to stop the cracking of the weld is 50 ° C or less due to the synergistic action of storing hydrogen in the weld metal and fixing the carbon in the weld metal by generating fine carbides, particularly the amount of vanadium in the welding rod. Is about 0.15% by weight of welding rod N
o. 5, 10 and 14 had remarkably excellent crack resistance. However, the welding rod No. with the vanadium amount exceeding 0.25% by weight. For 7, 8, 12, 15, 18 and 19, the formation of fine carbides cannot be expected, and conversely, the strength becomes too high, and the preheating temperature required for stopping cracking is 75 ° C to 125 ° C.

In the case where vanadium is added from one or both of the core wire and the coating agent, vanadium can be selected at any ratio as long as it is within the above range.

Next, the welding rod of the present invention contains a carbonate such as calcium carbonate, barium carbonate, magnesium carbonate and manganese carbonate, calcium fluoride, barium fluoride, magnesium fluoride, manganese fluoride, fluoride fluoride in the coating agent. Fluorine compounds such as lithium and aluminum fluoride can be added. The carbonate is decomposed in the arc, generates CO ₂ gas, shuts off the molten metal from the atmosphere, has the effect of reducing the partial pressure of hydrogen and nitrogen gases in the arc atmosphere and producing basic slag. The range of addition of these carbonates is suitably from 5 to 75% by weight. Any fluorine compound lowers the melting point of the slag to form a slag with good fluidity. In addition, the fluorine decomposed in the arc reacts with the hydrogen of the molten metal or molten slag to lower the hydrogen partial pressure of the weld metal to produce a weld metal having good mechanical performance.
The range of addition of these fluorine compounds is suitably from 5 to 30% by weight.

Further, 1 to 20% by weight of a deoxidizing agent such as manganese, titanium, silicon, aluminum and magnesium, 2 to 20% by weight of an arc stabilizer such as iron powder, alkali metal and rutile, sodium silicate and potassium silicate Can be added in an amount of 10 to 30% by weight. The quality is not limited as long as the target performance can be secured. The production of the welding rod of the present invention is carried out in the same manner as in ordinary means, by dry-mixing the coating materials of the various powders mixed in a predetermined ratio, adding a binder to the mixture, and kneading the coating material. Is coated and coated on a steel core wire by a usual coating machine so that the content becomes 20 to 50% by weight, followed by drying and firing.

Further, the steel core wire referred to herein is JIS G3.
523 can be used, and in order to further improve mechanical performance, 0.01 to 0.04% by weight of carbon, 0.001 to 0.005% by weight of nitrogen, and 0.1 to 0.005% by weight of oxygen.
It also indicates a core wire reduced to 001 to 0.01% by weight.

Next, steel materials will be described. It has been found that the welding heat affected zone (HAZ) low temperature cracking susceptibility of a steel material can be almost evaluated by the carbon equivalent as shown in equation (1).
Therefore, if the value of equation (1) is kept low, HAZ cracking can be prevented even if the preheating temperature is lowered accordingly. In high-strength steels, the welding crack prevention preheating temperature is often determined to prevent weld metal cracking rather than to prevent HAZ cracking. The reason for this is that in high strength steels H
This was due to the fact that the weld metal was more sensitive to cracking than AZ. However, according to the present invention, the low-temperature cracking susceptibility of the weld metal has been dramatically improved. Therefore, from the viewpoint of preventing cracks from occurring in the weld metal, the preheating temperature can be reduced, but HAZ cracking cannot always be prevented at this preheating temperature. Therefore, it was necessary to limit the steel materials in order to prevent HAZ cracking.

The reason for limiting the tensile strength is that the tensile strength is 4
At less than 90 N / mm ^2, it was determined that it was not necessary to use the present invention because preheating was sufficiently reduced only by the conventional techniques of the conventional steel material and the conventional low hydrogen welding rod. In addition, the upper limit of the tensile strength of 880 N / mm ² , if the strength exceeds this, even if the control rolling control cooling technology is used,
This is because it has been determined that it is difficult to obtain good base material toughness while maintaining strength while maintaining the low-temperature cracking resistance of the HAZ.

The reason for limiting Pcm is as follows.
First, the reason why the cold cracking susceptibility of HAZ is almost determined only by the steel material composition and the Pcm calculated therefrom will be described. The HAZ is rapidly quenched by the welding heat, and the structure itself is completely different from that of the steel material before welding. In particular, in the HAZ adjacent to the weld metal, the maximum heating temperature reaches near the melting point of the steel material, so that the austenite grains become coarse, and for this reason, quenching is more likely to occur and the hardness becomes harder than other parts. Such a hardened portion is susceptible to low-temperature cracking and is heated to just below the melting point.
The structure of Z hardly depends on the steel structure before welding.
The reason why the cold cracking susceptibility of the HAZ can be evaluated only by the composition of the steel material and the Pcm calculated from the composition is because of the above background. Therefore, whatever the production process of the steel material, if the Pcm is below a certain value, the HAZ can have the low-temperature cracking resistance.

The upper limit of Pcm of 0.24% by weight was set in order to secure the low-temperature cracking susceptibility of HAZ. Also, P
Even if the cm is limited to 0.24% by weight or less, the strength of the steel material can be reduced by 49% by using a technique such as controlled rolling control cooling.
It is not particularly difficult to set the value in the range from 0 N / mm ^{2 to} 880 N / mm ² using conventional techniques.

The lower limit of Pcm is set mainly from the viewpoint of securing the toughness of the steel material itself. That is, even if Pcm is set to a range lower than that of the present invention, it is possible to increase the strength to 490 N / mm ² or more by using the current steel material manufacturing technology (for example, performing accelerated cooling to room temperature). However, in this case, the toughness of the steel material itself deteriorates. Considering the reliability of the entire welded structure, it is considered that using such a steel material having low toughness is not industrially preferable even if there is an advantage by reducing the preheating temperature. Pcm lower limit 0.14
The weight% was set for the reasons described above.

Next, preferred ranges of the components of the steel material will be described. First, the basic components of steel are described. C and Mn of the steel material are indispensable elements for securing the strength toughness of the base material. However, excessive addition increases the hardenability too much, so the range is 0.03 to 0.03 respectively.
It is desirable that the content be 0.18% by weight and 0.6 to 1.4% by weight.

If the addition amount of Si is too large, the HAZ toughness is deteriorated, but if the addition amount is too small, the deoxidizing effect is lost and there is a risk that inclusions are introduced into the base material. It is desirably 0.011% to 0.6% by weight.

P and S are impurities, but the base material, HA
Since the toughness of Z is deteriorated and S forms sulfide, the upper limits are preferably set to 0.02% by weight and 0.001% by weight, respectively.

Al is used in an amount of 0.01 to 0.06% by weight from the viewpoint of the amount required for deoxidation and the amount that does not deteriorate toughness.
It is desirable to set in the range.

Next, elements which can be selectively added to the steel material, if necessary, alone or in combination of two or more will be described. N
b is an element that can be expected to improve the strength due to the precipitation effect, but also increases the HAZ hardness, so that it is desirable to set b in the range of 0.005 to 0.04% by weight.

[0033] Ti is effective as TiN for refining the base material and HAZ. However, excessive addition of both Ti and N deteriorates the toughness of the base material and HAZ, so that the range is 0.005 to 0.030% by weight of Ti and 0.005% by weight of N.
It is desirable that the content be 6% by weight or less.

Mo improves the strength and toughness of the base material. However, if the added amount is too large, the toughness and weldability are deteriorated. Therefore, the range is preferably 0.05 to 0.5% by weight. .

Although Ni and Cu are effective elements for improving the strength and toughness, excessive addition affects the HAZ toughness. Further, Cu may cause Cu cracks during the production of steel, so that the range is limited. Each 0.1 ~
Desirably, the content is 1.0% by weight.

V contributes to the precipitation effect similarly to Nb, but does not perform as much as Nb, so the range is 0.01 to 0.01%.
It is desirably 0.10% by weight.

B improves hardenability by segregating at the prior austenite grain boundaries. However, excessive addition results in excessive hardenability and deteriorates HAZ toughness and the like. Therefore, the range is preferably 0.0005 to 0.0030% by weight.

Next, desirable welding conditions will be described.
The welding heat input is a factor that affects the HAZ hardness, the weld metal hardness, and the like, and excessive suppression of the heat input is not desirable from the viewpoint of obtaining good joint characteristics. Therefore, within the scope of the present invention, it is desirable to set the heat input to 0.6 kJ / mm or more. However, although adopting a high heat input improves welding work efficiency, it is desirable that the heat input be 4.0 kJ / mm or less from the viewpoint of securing joint toughness.

[0039]

Embodiment 1 First, an embodiment according to claim 1 will be described. Table 2
The core of the welding rod used in the examples (4.0 mm each)
Is shown. Using welding rods having the coating agent chemical components shown in Tables 3 and 4, welding rods having a rod diameter of 4.0 mm, a rod length of 400 mm, and a coating outer diameter of 6.3 mm were produced. In Tables 3 and 4, A-1 to A-20 are welding rods of the present invention, and B-1
B-12 are comparative welding rods.

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

A U-shaped welding crack test (JISZ3157) was conducted to investigate the cracking resistance of the weld metal with these welding rods. Depending on the strength of the welding rod, 590 of JIS standard
N / mm ² primary and 780N / mm ² class thickness 30mm
Was selected. The welding conditions were a welding current of 170 A, a welding heat input of 17 kJ / cm, an air temperature of 30 ° C., and a relative humidity of 80%, and the preheating temperature required for stopping cracking was determined. As a result of crack observation, cracks were found in all the weld metals.

The preheating temperature for stopping welding cracks by the welding rod of the present invention is 590 N since an appropriate amount of vanadium is contained.
/ Mm ² class welding rod is 50 ℃ or less, 780N
/ Mm ² class welding rod has a temperature of 75 ° C. or less.
2, A-3, A-6, A-13, and A-17 have a weld crack stop temperature as low as 30 ° C. and have very good low temperature crack resistance.

The comparative welding rods B-1 and B-12 were ordinary welding rods containing no vanadium in the welding rod, and the welding crack stop preheating temperature was 125 ° C. or higher. B-2, B
-10 is due to too much vanadium in the core,
-3 and B-11 contained too much vanadium in the coating agent, so that the welding crack stop preheating temperature was 75 ° C. or higher.

B-4 and B-9 contain vanadium from the core wire and the coating agent, but since the range was exceeded, the preheating temperature for stopping welding cracks was 75 ° C. or higher. B-5, B
-8 contains vanadium from the coating agent, but the preheating temperature for stopping welding cracking is 75 ° C. because the added amount is too small.
That was all. B-6 and B-7 contain vanadium from the core wire, but the preheating temperature for stopping welding cracking was 100 ° C. or more because the amount of addition was too small.

Embodiment 2 Next, an embodiment according to claim 2 will be described. Table 5 shows the chemical composition of the steel material used in the y-type welding crack test (JIS Z3158) by weight%. Table 6 shows the symbols of the steel materials (corresponding to the symbols in Table 5), the symbols of the low-hydrogen-based coated arc welding rods (corresponding to the symbols in Tables 3 and 4) used in the y-type welding crack test, and the values at that time. It shows the critical preheat temperature for crack arrest. The cracking test was carried out in an atmosphere of 30 ° C. and 80% humidity with a welding current of 170 A and a welding heat input of 17 kJ /
cm, and the steel sheet thickness was 38 mm in all cases. The limit preheating temperature in Table 6 is a temperature at which crack prevention of both the HAZ and the weld metal has become possible.

[0048]

[Table 5]

[0049]

[Table 6]

As shown in Table 6, in the combination of 590 N / mm ² grade steel material and welding rod (Nos. 1, 2, 3, and 4),
Although the Pcm of the steel material is in the range of 0.14 to 0.24% by weight, there is a large difference in the critical preheating temperature depending on the welding rod used. No. 1 of the present invention example. 1 and No. 3
It was possible to prevent cracking by preheating at 50 ° C,
Comparative Example No. 2 and No. In 4, the weld metal crack is 5
It cannot be prevented by preheating at 0 ° C.
It is necessary to preheat at 5 ° C.

In addition, 780 N / mm ² grade steel materials shown in Table 6
In the combination of the welding rods (Nos. 5, 6, 7, 8), No. 5 of the present invention example. No. 5 can be prevented from cracking by preheating at 50 ° C. 6, 7, and 8 need to be preheated to 100 ° C. or more. No. 6: Pcm of steel material is 0.14 ~
Despite being in the range of 0.24% by weight, the preheating temperature is high due to the inadequacy of the vanadium in the welding rod. In addition, No. In No. 7, an A-11 welding rod whose vanadium is appropriate is used.
Since the content is outside the range of the present invention, cracking susceptibility in HAZ is high, and cracking cannot be prevented unless preheating at 100 ° C. That is, in order to lower the preheating and obtain a sound welded joint, it is necessary to appropriately select both the steel material and the welding rod as in the present invention examples (Nos. 1, 3, and 5). .

[0052]

As described above, according to the welding rod and the welding method of the present invention, the low-temperature cracking resistance is remarkably improved as compared with the conventional high-strength steel welding rod and the conventional welding method. It cannot be achieved with high-strength steel welding rods at all, and contributes greatly to the development of various industries.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of vanadium in a welding rod and the preheating temperature for stopping cracking.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-161993 (JP, A) JP-A-61-180695 (JP, A) Edited by the Japan Standards Association, "JIS Handbook Iron and Steel" (1990-4-20) Japan Standards Association p. 1302-1303 (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 9 / 00,35 / 30 B23K 35 / 36,35 / 365 C22C 38/00 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A coated arc welding rod for high-strength steel of at least 490 N / mm ² containing at least a metal carbonate and a metal fluoride, wherein vanadium is formed so as to satisfy a range based on the following formula (1). A low-hydrogen coated arc welding rod characterized in that it is contained in one or both of a wire and a coating agent. 0.05 ≦ Wv + 0.38 Fv ≦ 0.25 (1) where, Wv: the content (% by weight) of vanadium in the core wire with respect to the total mass of the core wire Fv: with respect to the total mass of the coating agent Vanadium content in coatings (% by weight) 2. Tensile strength of 490 N / mm ² or more and 8
A steel material having a Pcm of 0.14 to 0.24%, which is not more than 80 N / mm ² and is represented by the chemical symbol when the content in the steel is represented by% by weight, A welding method using the low hydrogen-based coated arc welding rod according to claim 1. Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Mo / 15 + V / 10 + 5B (2)