KR100709521B1 - Welding joint of large heat input welding and welding method thereof - Google Patents

Abstract

The present invention provides a welded joint obtained by welding a steel sheet by large heat input electrogas welding having a welding heat input of 100 kJ / cm or more and a low temperature toughness of the weld heat affected zone. It is. In the method of the invention, the weld metal of the welded joint is 0.03 to 0.12 mass% of C, 0.10 to 0.80 mass% of Si, 0.80 to 2.50 mass% of Mn, 0.50 to 3.00 mass% of Ni, 0.50 mass% or less of Cr, 0.50 mass% or less Mo, 0.01-0.10 mass% Ti, 0.0010-0.0050 mass% rare earth elements, and content of B [B] (mass%) is f (Q) ≤ [B] ≤0.01 (Q: welding A welded joint and a manufacturing method thereof, which satisfy heat input (kJ / cm) and f (Q): a function of Q, and have a composition in which the balance consists of iron and inevitable impurities.

Description

Welding joint of high heat input welding and its welding method {WELDING JOINT OF LARGE HEAT INPUT WELDING AND WELDING METHOD THEREOF}

1 is a cross-sectional view of an electrogas welded joint and groove,

2 is a view showing a cross section of an electrogas welding part and a Charpy test piece collecting position;

3 is a cross sectional view of a submerged arc welded joint and an improvement;

4 is a view showing a cross section of a submerged arc welding portion and a Charpy test piece collecting position;

5 is a cross sectional view of an electroslag welded joint and an improvement;

It is a figure which shows the cross section of an electroslag welding part, and a Charpy test piece collection position.

The present invention relates to a welded joint obtained by welding a steel sheet by large heat input welding having a welding heat input of 100 kJ / cm or more, and a welding method thereof.                         

In recent years, as the size of steel structures and ships increases, the necessity for increasing the strength and thickening of steel sheets to be used has increased. In order to improve welding efficiency, large heat input welding such as electrogas welding, electroslag welding, submerged arc welding, etc. Are employed. However, when the welding heat input becomes large, the weld metal and the welding heat affected zone are subjected to a high temperature for a long time, resulting in coarsening of the structure and deterioration of the toughness.

In particular, in the shipbuilding field, a technique for performing one pass welding of thick steel sheets having a thickness of 60 mm for sheer strakes by vertical electrogas welding has been put into practice as the container ship is enlarged. In the case of one pass welding of such thick steel sheets with a plate thickness of more than 60 mm by electrogas welding, the welding heat input is increased to about 500 kJ / cm. Therefore, the weld metal and the welding heat affected zone are subjected to high temperature for a long time, resulting in coarse texture. Happens. As a result, the toughness of the weld metal and the weld heat affected zone deteriorates.

In the construction and bridge fields, on the other hand, in submerged arc welding, flux is added with iron in order to increase the amount of welding, and further, multi-electrode welding (so-called tandem welding, three-electrode welding, etc.) of the welding electrode is planned. As a result, welding of large current and large welding becomes possible, and the technique of welding to a plate thickness of about 80 mm in one pass is utilized. Moreover, the technique of welding the steel plate of the plate thickness of about 100 mm is also utilized for the electroslag welding. In the case of one pass welding of such thick steel sheets by submerged arc welding and electroslag welding, the welding heat input exceeds 500 kJ / cm. Therefore, the weld metal and the welding heat affected zone are subjected to high temperature for a long time, resulting in coarsening of the tissue. Happens. As a result, the toughness of the weld metal and the weld heat affected zone deteriorates.

Therefore, in order to prevent the deterioration of the toughness of the weld metal or the weld heat affected zone, TiN is finely dispersed in the steel sheet and used as a nucleus for ferrite transformation, thereby preventing coarsening of the structure by welding heat input and producing fine ferrite. The technique is known. However, in the case of high heat input welding, the weld heat affected zone is subjected to a high temperature for a long time, so that TiN dispersed in the steel sheet is decomposed and N is generated, resulting in deterioration of the toughness of the weld heat affected zone.

Japanese Unexamined Patent Publication No. 6-71447 discloses a method of preventing coarsening of the structure of the weld heat affected zone by heating the vicinity of the weld before and after the welding to control the cooling rate of the weld heat affected zone in the high heat input welding. have. However, when constructing high heat input welding, enormous effort and cost are required to heat the welded portion of a large welded joint, and it is difficult to control the cooling rate by performing such heat treatment at the welding site.

In addition, Japanese Patent Application Laid-open No. Hei 10-109189 or Japanese Patent Laid-Open No. Hei 10-180488 discloses an electrogas arc welding flux that defines the composition of the steel plate shell of the wire and the flux therein to improve the low temperature toughness of the weld metal. Added wires are disclosed. However, in the case of conducting large-gauge electrogas arc welding (i.e., electrogas welding), the weld metal is subjected to a high temperature for a long time, and coarsening of the weld metal structure occurs even when these flux-added wires are used. As a result, the toughness of the weld metal is degraded.

On the other hand, Japanese Unexamined Patent Publication No. 7-328793 and Japanese Unexamined Patent Publication No. 2000-107885 disclose fluxes and solid wires in which a high toughness weld metal is obtained by use for high heat input submerged arc welding. However, in the case of large heat input submerged arc welding with welding heat input of 100 kJ / cm or more, even if these fluxes or solid wires are used, the microstructure and uniformity of the weld metal microstructure are not sufficient, and the effect of preventing the deterioration of the toughness of the weld metal is not sufficient. Not enough

Furthermore, the welding materials disclosed in JP-A-10-109189, JP-A-10-180488, JP-A-7-328793 and JP-A-2000-107885 improve the toughness of the weld metal. It is only intended to prevent the deterioration of the toughness of the weld bond portion and the weld heat affected zone, and therefore prevent the deterioration of the toughness of the entire welded joint.

The present invention solves the above problems and provides a welded joint obtained by welding a steel plate by high heat input welding having a weld heat input of 100 kJ / cm or more and a low temperature toughness of a weld heat affected zone and a welding method thereof. It is purpose.

That is, the present invention is a welded joint obtained by welding a steel plate by a large heat input welding having a weld input heat of 100 kJ / cm or more, and a welding method thereof, wherein the weld metal of the weld joint is 0.03 to 0.12 mass% of C and 0.10 to 0.80 mass of Si. %, Mn 0.80-2.50 mass%, Ni 0.50-3.00 mass%, Cr 0.50 mass% or less, Mo 0.50 mass% or less, Ti 0.01-0.10 mass%, Rare earth element 0.0010-0.050 mass%, Further Content (mass%) of B is following (1) Formula:

f (Q) ≤ [B] ≤0.01 (1)

Here, Q: welding heat input (kJ / cm)

          f (Q): function of Q

          [B]: Content of B (mass%)

And a welded joint having a composition in which the balance is made of iron and unavoidable impurities, and a welding method thereof.

In the above invention, it is preferable that, as a first preferred embodiment, the weld metal of the weld joint contains 0.10% by mass or less of V and 0.10% by mass or less of Nb in addition to the above-mentioned composition.

Further, as a second preferred aspect, the high heat input welding is large heat input electrogas welding, and f (Q) is represented by the following formula (2):

f (Q) = 0.003 x {0.23 x 1n (Q)-0.5} (2)

Where 1n (Q): the natural logarithm of Q

It is preferable that by.

Further, as a third preferred aspect, the high heat input welding is a high heat input submerged arc welding or a high heat input electroslag welding, and f (Q) is represented by the following formula (3):

f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3)                     

It is preferable that by.

MEANS TO SOLVE THE PROBLEM The present inventors improved the low-temperature toughness of the weld metal and welding heat affected part obtained by welding a steel plate by high heat input welding, such as high heat input gas welding of 100 kJ / cm or more, high heat input submerged arc welding, or high heat input electric slag welding. As a result of intensive research on, I have come to the following knowledge.

That is, with respect to the weld metal, in the case of high heat input welding, the cooling rate is slow, so that the time to be maintained at high temperature becomes long, the cornerstone ferrite grows and the low temperature toughness deteriorates. Therefore, in order to improve the low temperature toughness of the weld metal, it is necessary to adjust the addition amount of various alloying elements in the weld metal to improve the hardenability of the weld metal and to remove coarse ferrite structure to make the entire weld metal uniform and fine microstructure. There is.

On the other hand, in the weld heat affected zone, N contained as an unavoidable impurity in the steel sheet or N generated by decomposition of TiN added for the purpose of miniaturization of the structure becomes a cause of deterioration in low temperature toughness. Therefore, in order to improve the low temperature toughness of the weld heat affected zone, it is necessary to combine N present in the weld heat affected zone with other elements and fix it as a nitride.

Therefore, the inventors noted that in the large heat input welding in which the weld metal and the weld heat affected zone are kept at a high temperature for a long time, B diffuses from the weld metal to the weld heat affected zone, and the extent of diffusion depends on the heat input of the weld.

That is, by containing B in the weld metal to improve the hardenability of the weld metal to improve the low temperature toughness of the weld metal. In addition, the low temperature toughness of the weld heat affected zone can be improved by B being fixed to N, which is diffused from the weld metal to the weld heat affected zone and is present in the weld heat affected zone as BN. Further, in the weld heat affected zone, BN becomes a nucleus and microferrite is also produced. Therefore, B is an effective element for improving the low temperature toughness of the weld metal and the weld heat affected zone. The inventors discovered that what is necessary is just to add the amount of B which exhibits the above effect.

In the present invention, the reason for limiting the components of the weld metal of the welded joint obtained by high heat input welding such as high heat input electrogas welding, high heat input submerged arc welding, or high heat input electroslag welding, having a welding heat input of 100 kJ / cm or more, Explain.

C: 0.03-0.12 mass%

C is an element necessary for securing the strength of the weld metal and improving the hardenability. When C content is less than 0.03 mass%, sufficient hardenability is not obtained. On the other hand, when the content exceeds 0.12% by mass, not only hot cracking occurs in the weld metal, but also martensite phase is formed, thereby deteriorating low temperature toughness. Therefore, C needs to satisfy the range of 0.03-0.12 mass%. More preferably, 0.05-0.10 mass% is preferable.

Si: 0.10 to 0.80 mass%

Si is an element which has deoxidation and improves the strength of the weld metal. If the Si content is less than 0.10% by mass, the melt flow of the molten metal is lowered, and welding defects such as a lack of groove fusion are likely to occur, thereby reducing the efficiency of the welding operation. On the other hand, if it exceeds 0.80% by mass, hot cracking occurs in the weld metal. Therefore, Si needs to satisfy | fill the range of 0.10-0.80 mass%. More preferably, it is 0.15-0.50 mass%.

Mn: 0.80-2.50 mass%

Mn is an element which secures the strength of a weld metal and improves hardenability. When Mn content is less than 0.80 mass%, sufficient hardenability is not obtained. On the other hand, if the content exceeds 2.50% by mass, not only hot cracking of the weld metal occurs, but also the upper bainite or martensite phase is generated to deteriorate the low temperature toughness. Therefore, Mn needs to satisfy in the range of 0.80-2.50 mass%. More preferably, they are 1.00-2.00 mass%.

Ni: 0.50-3.00 mass%

Ni is an element that improves the strength and toughness of the weld metal. If Ni content is less than 0.50 mass%, the weld joint of sufficient strength will not be obtained. On the other hand, if the content exceeds 3.00% by mass, not only hot cracking occurs in the weld metal, but also upper bainite or martensite phase is formed to deteriorate low temperature toughness. Therefore, Ni needs to satisfy the range of 0.50-3.00 mass%. More preferably, it is 0.50-2.00 mass%.

Cr: 0.50 mass% or less

Cr is an element that improves the strength and low temperature toughness of the weld metal. In order to acquire the effect, 0.02 mass% or more must be added. When the Cr content exceeds 0.50% by mass, not only hot cracking of the weld metal occurs, but also the upper bainite or martensite phase is formed to deteriorate the low temperature toughness. Therefore, Cr is made into 0.50 mass% or less. Moreover, Preferably it is 0.05-0.40 mass%.

Mo: 0.50 mass% or less

Mo, like V and Nb, is an element that improves the strength of the weld metal in welding with large heat input, and further refines the structure to improve low temperature toughness. In order to acquire the effect, 0.01 mass% or more must be added. If the Mo content exceeds 0.50% by mass, hot cracking of the weld metal occurs. Therefore, Mo is made into 0.50 mass% or less. Moreover, preferably, it is 0.10 to 0.45 mass%.

V: 0.10 mass% or less

V, like Mo and Nb, is an element that improves the strength of the weld metal in welding with large heat input, and further refines the structure to improve low temperature toughness. In order to obtain the effect, it should be added at least 0.005 mass%. If the V content exceeds 0.10 mass%, hot cracking of the weld metal occurs. Therefore, when it contains V, it is preferable to set it as 0.10 mass% or less. More preferably, it is 0.01-0.07 mass%.

Nb: 0.10 mass% or less

Nb, like Mo and V, is an element that improves the strength of the weld metal in welding with large heat input, and further refines the structure to improve low temperature toughness. In order to obtain the effect, it should be added at least 0.005 mass%. If the Nb content exceeds 0.10 mass%, hot cracking of the weld metal occurs. Therefore, when it contains Nb, it is preferable to set it as 0.10 mass% or less. More preferably, it is 0.01-0.07 mass%.

Ti: 0.01-0.10 mass%

Since Ti forms an oxide in the weld metal, and a fine ferrite phase is formed using the oxide as a nucleus, Ti has an effect of improving low temperature toughness of the weld metal. If the Ti content is less than 0.01% by mass, oxides are not sufficiently produced, so that the effect of improving low temperature toughness is not obtained. On the other hand, when it exceeds 0.10 mass%, the weld metal hardens, causing deterioration of low temperature toughness. Therefore, Ti needs to satisfy in the range of 0.01-0.10 mass%. More preferably, 0.02-0.06 mass% is preferable.

Rare Earth Element: 0.0010 to 0.0050 mass%

The rare earth element is a generic term for elements belonging to Group 3 of the periodic table, and is bonded to S in the weld metal to finely deposit and disperse sulfides, thereby preventing the decrease in toughness of the weld metal by S. When the content of the rare earth element is less than 0.0010% by mass, sulfides are not sufficiently produced, and fixation of S is not sufficient, so that low-temperature toughness deteriorates. On the other hand, if it exceeds 0.0050 mass%, the weld metal hardens, causing deterioration of low temperature toughness. Therefore, the rare earth element needs to satisfy the range of 0.0010 to 0.0050 mass%. More preferably, it is 0.0020-0.0040 mass%. In the present invention, the rare earth element is not limited to a specific element, but it is preferable to use a relatively inexpensive and readily available element such as Ce, La, or Nd.

Moreover, content (mass%) of B is about the diffusion distance DB (micrometer) of _B , following formula (1):

f (Q) ≤ [B] ≤0.01 (1)

Here, Q: welding heat input (kJ / cm)

          f (Q): function of Q

          [B]: Content of B (mass%)

It is necessary to satisfy.

B has the effect of improving the strength of the weld metal and the weld heat affected zone and improving the low temperature toughness, and is the most important element constituting the present invention. That is, since B is an element which improves hardenability, the hardenability of a weld metal improves by B which exists in a weld metal, As a result, low-temperature toughness improves. Moreover, since B suppresses the growth of coarse saltpeter ferrite in the weld metal to generate a fine ferrite phase, B also has an effect of further improving the low temperature toughness of the weld metal.

B is also diffused from the weld metal to the weld heat affected zone. In this way, B diffuses from the weld metal into the weld heat affected zone, whereby the hardenability of the weld heat affected zone is improved, and as a result, the low temperature toughness is improved. In addition, N contained as an unavoidable impurity in the steel sheet or TiN added for the purpose of miniaturization of the structure is combined with N generated by welding heat input to form BN, thereby fixing N and preventing deterioration of low temperature toughness. Furthermore, since a fine ferrite phase is produced using BN as a nucleus, there is an effect of further improving the low temperature toughness of the weld heat affected zone.

The main function of B in the present invention is to diffuse from the weld metal to the heat affected zone and to fix the solid solution N as BN in the heat affected zone close to the weld metal. In addition, solid solution N exists as what exists as an unavoidable impurity in steel, and TiN melt | dissolves the precipitate in steel. This function is considered to be necessary to increase the content of B in order to ensure a constant B concentration in the diffusion range if the diffusion distance of B is large regardless of the welding method. Therefore, it can be assumed that the required amount of B in the weld metal is proportional to the diffusion distance D _B (µm) of _B.

The diffusion distance D _B (μm) of _B is determined in accordance with the cooling pattern (ie, the temperature history) at the time of welding. The diffusion of B in the steel is thought to occur immediately after the weld metal solidifies, and therefore, the cooling process from 1500 ° C to 1100 ° C may be considered. That is, when the plate thickness and the improved shape are determined for each welding method, the welding heat input Q (that is, the input heat quantity (kJ / cm) per unit welding length) is almost determined, and the heat influence according to the welding heat input Q (kJ / cm). The negative cooling pattern is changed. Therefore, the temperature can be measured by the actual welding seam by each welding method, the cooling time and cooling rate from 1500 degreeC to 1100 degreeC can be calculated | required, and the diffusion distance DB (micrometer) of _B can be calculated from a diffusion equation. It was found that there is a good correlation between the diffusion distance D ' _B (µm) and weld heat input Q (kJ / cm) of B calculated in this way, and it is expressed by an empirically obtained relational expression. However, if the welding method is different, even though the welding heat input Q (kJ / cm) is the same, the cooling rate from 1500 ° C to 1100 ° C is different, so the calculated diffusion distance D' _B (µm) of _B and welding heat input Q (kJ / cm) are different. The relational expression of needs to be set for each welding method.

That is, in the case of large input heat electrogas welding with a welding heat input of 100 kJ / cm or more, the calculated diffusion distance D ' _B (μm) is expressed by the following equation (4):

D ' _B = 0.23 x 1n (Q)-0.5 (4)

It is expressed as

In the case of large heat input submerged arc welding with a welding heat input of 100 kJ / cm or more, the calculated diffusion distance D ' _B (㎛) is expressed by the following equation (5):

D ' _B = 0.42 x 1n (Q)-1.9 (5)

It is expressed as

Also, in the case of electroslag welding, the thermal cycle during welding is the same as that of the submerged arc welding, so the same relationship as in (5) is established.

Then, a proportional coefficient of 0.003 is empirically obtained from the measured values of the toughness of the heat affected zone of the joint and the diffusion distance of B. That is, the lower limit of content (mass%) of B in a weld metal is given as 0.003 * D' _B .

That is, B content (mass%) is the following (6) formula:

α = 0.003 × D _B (6)

Here, D ' _B : calculation diffusion distance of B (μm)

If it is less than the value of the index α, the effect of improving the low temperature toughness of the weld metal and the weld heat affected zone is not obtained.

On the other hand, when the B content exceeds 0.01% by mass, the hardenability of the weld metal and the weld heat affected zone becomes excessively high, not only hot cracking occurs in the weld metal and the weld heat affected zone, but also a martensite phase is generated to deteriorate low temperature toughness.

Therefore, B content (mass%) is a following (1) Formula:

f (Q) ≤ [B] ≤0.01 (1)

Here, Q: welding heat input (kJ / cm)

          f (Q): function of Q

          [B]: Content of B (mass%)

It is necessary to satisfy.

Here, in the case of large heat input electrogas welding in which the welding heat input is 100 kJ / cm or more, the calculation diffusion distance D' _B (μm) can be calculated with high precision in the above formula (4),

f (Q) = 0.003 x {0.23 x 1n (Q)-0.5} (2)

Becomes

In addition, in the case of large heat input submerged arc welding in which the welding heat input is 100 kJ / cm or more, the calculation diffusion distance D ' _B (μm) can be calculated with high precision according to the above formula (5),

f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3)

Becomes                     

Also in the case of electroslag welding, the same relationship as in (3) is established.

In order to adjust the weld metal to the appropriate range specified above, it is necessary to consider the components of the steel sheet welded by the welding method, and the composition of the welding wire and the welding flux.

The preferable steel material of this invention is demonstrated.

From the standpoint of securing the toughness of the weld heat affected zone, the steel for the high heat input welding is preferably a steel which suppresses the addition of alloying elements. For example, a low carbon equivalent steel using TMCP (Thermo-Mechanical Control Process) (Ceq ≤0.45%, Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 is preferred. For example, the composition of a typical steel plate is C: 0.03-0.15 mass%, Si: 0.05-0.50 mass%, Mn: 0.5-2.5 mass%, P: 0.03 mass% or less, S: 0.006 mass% or less, Al: 0.005-0.06 It is mass% and Ni: 1.5 mass% or less. In addition, in order to prevent the coarsening of a heat-affected zone structure | tissue, application of the steel material which disperse | distributed TiN particle | grains in steel by adding 0.01-0.04 mass% of Ti and 0.003-0.008 mass% of N is assumed. In addition, in the steel sheet used in the present invention, Ni: 3.0% by mass or less, Nb: 0.1% by mass or less, V: 0.2% by mass or less, Cr: 1.0% by mass or less, Cu: 1.5, as necessary to secure the strength of the steel. Mass% or less, Mo: 0.8 mass% or less, B: 0.0003-0.0020 mass% may be added, Ca: 0.0005-0.0040 mass% for the purpose of the coarsening of the structure of a heat-affected zone, Rare earth element (REM): 0.001 Either or both of 0.020 mass% or both may be added, and oxide and sulfide of Ca and REM may be disperse | distributed in steel other than TiN.

Next, the welding wire and the welding flux which are preferable in this invention are demonstrated for every welding method.

In electrogas welding, from the viewpoint of melting efficiency and workability, a thin diameter (approximately 1.6 mm) flux-added wire, that is, a flux cored wire (FCW) is used, and in order to increase the amount of deposition, iron powder in the flux is used. It is preferable to add many alloy powders including these. It is easy to adjust the composition of the weld metal of the electrogas welding mainly by adding an alloy to the flux in the FCW. For example, Ni, Cr, and rare earth elements are powders, and Mn and Nb are iron alloys such as FeMn and FeNb. As the oxide, for example, B ₂ O ₃ is preferably added in the required amount in the flux. In addition, it is necessary to determine the addition amount in consideration of the dilution of the steel sheet with the weld metal.

In submerged arc welding, solid wires with a diameter of 4.0 to 6.4 mm and a BOND type flux are used from the viewpoints of melting efficiency, workability, securing mechanical properties of the weld metal, and the like. In particular, in the one pass high heat input welding, in order to increase the amount of welding, it is preferable to apply multielectrode (so-called tandem welding or three electrode welding) and iron addition flux. In submerged arc welding, the weld metal composition can be adjusted by adding alloy to both wire and flux.However, in the case of wire, it is necessary to select an alloying method in consideration of wire drawing workability and welding workability. desirable. In addition, it is necessary to determine the addition amount in consideration of the dilution of the steel sheet with the weld metal.

In electroslag welding, non-consumable electrode slag welding using a solid wire having a small diameter (about 1.6 mm) and a molten flux has been widely applied in terms of work efficiency and ease of construction. In this non-consumable electroslag welding, the component of the weld metal is mainly adjusted by alloy addition to the solid wire, and it is necessary to determine the addition amount in consideration of dilution of the steel sheet to the weld metal.

In addition, the welding method applied to the present invention can be applied to gas shielded arc welding and the like in addition to electrogas welding, submerged arc welding, and electroslag welding.

However, since the diffusion of B into the weld heat affected zone in the weld metal is used, the effect is large when the toughness deterioration of the weld heat affected zone is remarkable and a slow cooling rate is applied, and the welding heat input is 100 kJ / cm or more. In this case a particularly remarkable effect is obtained.

By appropriately adding B to the weld metal, the low-temperature toughness of the weld metal and the weld heat affected portion of the welded joint obtained by welding the steel sheet by high heat input welding of 100 kJ / cm or more of weld input heat can be improved.

Example 1

The welding heat input of 100 kJ / cm or more was performed by the large heat input electrogas welding, and the welding joint of the steel plate was produced.

The plate thickness and component of a steel plate are as showing in Table 1. In addition, the component of the used fluxing wire for electrogas welding (henceforth a wire) is as showing in Table 2. In addition, content (mass%) of each element shown in Table 2 is a ratio with respect to the gross mass of a wire (that is, the total mass of a steel outer sheath and a flux).

Welding conditions are as showing in Table 3. Moreover, when manufacturing the weld joint of steel plate B (plate 40mm) and steel plate C (plate 60mm), it welds, oscillating wire to a plate thickness direction, in order to prevent a welding defect.

Thus, the steel sheets A-C and the wires 1-31 were variously combined, the electrogas welding was performed by the welding heat input of 100 kJ / cm or more, and the welding joint of the shape shown in FIG. 1 was produced. The weld heat input (kJ / cm) and the component (mass%) of the obtained weld metal at the time of manufacturing each weld joint are as showing in Table 4.

As shown in FIG. 2, after grinding the surface of each welded joint by 1 mm, three test specimens (JIS No. 2 mm-V notched test specimens) were cut out from the weld metal and the weld heat affected zone (bond portion), respectively, and subjected to JIS. The Charpy impact test was conducted in accordance with the provisions of Z 2242. The notch position was set at the center of the weld metal and at the weld heat affected zone where the notched lines intersect with the notch. Charpy absorbed energy _v E- ₄₀ (J) at -40 ° C is the average value of three test pieces, and is shown in Table 4. In addition, (alpha) value in Table 4 is a value computed using (2) Formula.

Hereinafter, Table 4 is demonstrated. Invention Examples 1 to 12 are examples in which the weld heat input (kJ / cm) and the component (mass%) of the weld metal satisfy the scope of the present invention.

Comparative Examples 1-6 are examples with B content out of the range of (1) Formula. In addition, Comparative Examples 7-8 are examples with C content out of the range of this invention, and Comparative Example 9 is an example with Si content out of the range of this invention. In addition, Comparative Examples 10-11 are examples in which Mn content is out of the range of this invention, and Comparative Examples 12-13 are examples in which Ni content is out of the range of this invention. In addition, Comparative Example 14 is an example in which the Cr content is outside the range of the present invention, and Comparative Example 15 is an example in which the Mo content is outside the range of the present invention. In addition, Comparative Example 16 is an example in which the V content is outside the range of the present invention, Comparative Examples 17 to 18 are examples in which the Ti content is outside the range of the present invention, and Comparative Examples 19 to 20 are in which the REM content is outside the range of the present invention. Yes.

In Inventive Examples 1 to 12, the weld metal and the weld heat affected zone had an absorption energy at −40 ° C. of 80 J or more, and a welded joint having excellent low temperature toughness was obtained. On the other hand, in Comparative Examples 1, 3, and 5, since the B content is lower than the lower limit of the range of the formula (1), the suppression of the cornerstone ferrite in the weld metal and the N fixation of the weld heat affected zone become insufficient, and the weld metal and the weld heat affected. Negative low temperature toughness deteriorated.

In Comparative Examples 2 and 4, since the B content exceeded the upper limit of the range of the formula (1), cracks occurred in the weld metal, and a test piece could not be collected. In addition, in Comparative Example 6, since the B content exceeded the upper limit of the range of the formula (1), a martensite phase was generated to deteriorate the low temperature toughness of the weld metal and the weld heat affected zone.

In Comparative Examples 7, 10, 12, 17, and 19, since the contents of C, Mn, Ni, Ti, and REM were less than the lower limit of the range of the present invention, the low-temperature toughness of the weld metal was deteriorated.

In Comparative Examples 8 and 13, since the contents of C and Ni exceeded the upper limit of the present invention, cracks occurred in the weld metal, so that the test piece could not be collected.

In Comparative Examples 9, 11, 14, 15, 16, 18, and 20, since the contents of Si, Mn, Cr, Mo, V, Ti, and REM exceeded the upper limit of the range of the present invention, the low-temperature toughness of the weld metal was Deteriorated.

In short, it has been found that the present invention can improve the low-temperature toughness of the weld metal and the weld heat affected portion of the welded joint obtained by welding the steel sheet by high heat input electrogas welding having a weld input heat of 100 kJ / cm or more.

Example 2

Welding input heat of 100 kJ / cm or more large heat input submerged arc welding was performed, and the welding joint of the steel plate was produced.

The plate thickness and component of a steel plate are as showing in Table 5. For welding, a solid wire with a wire diameter of 6.4 mm and a calcined flux with iron powder (equivalent to FS-BT1 of JIS Z 3352) are used, and submerged arc welding (so-called tandem submerged arc welding) of two electrodes is performed. It was. The welding conditions are as showing in Table 6.

In this way, submerged welding was performed by the welding heat input of 100 kJ / cm or more, and the welding joint of the shape shown in FIG. 3 was produced using steel plates D-F. The welding heat input (kJ / cm) and the component (mass%) of the obtained welding metal at the time of manufacturing each weld joint are as showing in Table 7.

As shown in FIG. 4, after grinding the surface of each welded joint by 1 mm, three test specimens (JIS No. 2 mm-V notched test specimens) were cut out from the weld metal and the welded heat affected zone (bond portion), and then cut into three pieces. The Charpy impact test was conducted in accordance with the provisions of Z 2242. The notch position was set at the center of the weld metal and at the weld heat affected zone (so-called bond section) where the weld line and the notch intersect. Absorption energy _{VE- 40} (J) in _-40 degreeC is an average value of three test pieces, and is as showing in Table 7. In addition, (alpha) value in Table 7 is a value computed using (3) Formula.

Table 7 is demonstrated below. Inventive Examples 13 to 24 are examples in which the welding heat input (kJ / cm) and the component (mass%) of the weld metal satisfy the scope of the present invention.                     

Comparative Examples 21-26 are examples with B content out of the range of (1) Formula. In addition, Comparative Examples 27-28 are examples with C content out of the range of this invention, and Comparative Example 29 is an example with Si content out of the range of this invention. In addition, Comparative Examples 30-31 are examples with Mn content out of the range of this invention, and Comparative Examples 32-33 are examples with Ni content out of the range of this invention. In addition, Comparative Example 34 is an example in which the Cr content is outside the range of the present invention, and Comparative Example 35 is an example in which the Mo content is outside the range of the present invention. In addition, Comparative Example 36 is an example in which the V and Nb content were outside the range of the present invention, Comparative Examples 37 to 38 were examples in which the Ti content was outside the range of the present invention, and Comparative Examples 39 to 40 had a REM content in the range of the present invention. This is an example out of the box.

In the invention examples 13-24, the weld metal and the weld heat-affected part had the absorption energy in -40 degreeC or more at 80J, and the weld seam which has the outstanding low-temperature toughness was obtained.

On the other hand, in Comparative Examples 21, 23, and 25, since the B content was lower than the lower limit of the range of the formula (1), the suppression of the cornerstone ferrite in the weld metal and the N fixation of the weld heat affected zone became insufficient, and the weld metal and the weld heat affected. Negative low temperature toughness deteriorated.

In Comparative Examples 22 and 24, since the B content exceeded the upper limit of the range of the formula (1), cracks occurred in the weld metal, and a test piece could not be collected. In addition, in Comparative Example 26, since the B content exceeded the upper limit of the range of the formula (1), upper bainite and martensite phases were generated, and the low-temperature toughness of the weld metal and the weld heat affected zone deteriorated.

In Comparative Examples 27, 30, 32, 37, and 39, the content of C, Mn, Ni, Ti, and REM was lower than the lower limit of the range of the present invention, respectively, and thus the low-temperature toughness of the weld metal was deteriorated.                     

In Comparative Examples 28 and 33, the content of C and Ni exceeded the upper limit of the range of the present invention, respectively, so that cracks occurred in the weld metal, so that the test piece could not be collected.

In Comparative Examples 29, 31, 34, 35, 36, 38, and 40, since the contents of Si, Mn, Cr, Mo, V, Nb, Ti, and REM exceeded the upper limit of the range of the present invention, the low temperature of the weld metal Toughness deteriorated.

In short, it has been found that the present invention can improve the low-temperature toughness of the weld metal and the weld heat affected zone of the welded joint obtained by welding the steel sheet by high heat input submerged arc welding with a weld heat input of 100 kJ / cm or more.

Example 3

The welding heat input of 100 kJ / cm or more was performed with the high heat input electroslag welding, and the welding joint of the steel plate was produced.

The plate thickness and component of a steel plate are as showing in Table 8. In welding, the non-consumable electrode type electroslag welding was performed using the solid wire of 1.6 mm of wire diameter, and the welding flux equivalent to FS-FG3 of JIS Z 3353. The joint shape was as showing in FIG. 5, and the welding joint was produced on three steel plate combinations and welding conditions shown in Table 9. FIG.

When producing a welded joint, welding was performed while oscillating the wire in the plate thickness direction of the diaphragm so that it melted completely and completely, and a flat bar equivalent to JIS-SN490 was used for the side plate.

The weld heat input (kJ / cm) and the component (mass%) of the obtained weld metal at the time of producing each weld joint are as showing in Table 10.

As shown in Fig. 6, each of the three test specimens (JIS No. 2 mm-V notched test specimens) from the weld metal and the weld heat affected zone (bond) at the site where the weld metal width of each welded joint is maximized. It cut out and carried out the Charpy impact test based on the specification of JISZ2242. The notch position was a heat affected zone (bond section) in contact with the weld metal center section and the weld line on the skin plate side. Absorption energy _{VE- 20} (J) in _-20 degreeC is an average value of each three test pieces, and is as showing in Table 10. In addition, (alpha) value in Table 10 is a value computed using (3) Formula.

Table 10 is demonstrated below. Inventive Examples 1-12 are examples in which the heat input of a weld and the component (mass%) of a weld metal satisfy | fill the range of this invention.

Comparative Examples 1-6 are examples with B content out of the range of (1) Formula. In addition, Comparative Examples 7-8 are examples with C content out of the range of this invention, and Comparative Example 9 is an example with Si content out of the range of this invention. In addition, Comparative Examples 10-11 are examples in which Mn content is out of the range of this invention, and Comparative Examples 12-13 are examples in which Ni content is out of the range of this invention. In addition, Comparative Example 14 is an example in which the Cr content is outside the range of the present invention, and Comparative Example 15 is an example in which the Mo content is outside the range of the present invention. In addition, Comparative Example 16 is an example in which the V content is outside the range of the present invention, Comparative Examples 17 to 18 are examples in which the Ti content is outside the range of the present invention, and Comparative Examples 19 to 20 are in which the REM content is outside the range of the present invention. Yes.                     

In Inventive Examples 1 to 12, both the weld metal and the weld heat affected zone had an absorbed energy at -20 ° C of 80 J or more, and a welded joint having excellent low temperature toughness was obtained.

On the other hand, in Comparative Examples 1, 3, and 5, since the B content is lower than the lower limit of the range of the formula (1), the suppression of the cornerstone ferrite in the weld metal and the N fixation of the weld heat affected zone become insufficient, and the weld metal and the weld heat affected. Negative low temperature toughness deteriorated.

In Comparative Examples 2 and 4, since the B content exceeded the upper limit of the range of the formula (1), B was excessive in the weld metal and the weld heat affected zone to generate upper bainite and martensite phases, resulting in deterioration of toughness.

In Comparative Examples 7, 10, 12, 17, and 19, since the contents of C, Mn, Ni, Ti, and REM were less than the lower limit of the range of the present invention, the low-temperature toughness of the weld metal was deteriorated.

In Comparative Examples 8, 9, 11, 13, 14, 15, 16, 18, and 20, the contents of C, Mn, Cr, Ni, Mo, V, Nb, Ti, and REM exceeded the upper limit of the range of the present invention, respectively. Therefore, the toughness of the weld metal deteriorated.

In the present invention, it is possible to improve the low-temperature toughness of the weld metal and the weld heat affected portion of the welded joint obtained by welding the steel sheet by high heat input welding having a weld heat input of 100 kJ / cm or more.

Claims (10)

In a welded joint obtained by welding a steel plate by large heat input welding having a welding heat input of 100 kJ / cm or more, the weld metal of the weld joint is 0.03 to 0.12 mass% of C and Si 0.10 to 0.80 mass%, Mn 0.80 to 2.50 mass%, Ni 0.50 to 3.00 mass%, Cr 0.50 mass% or less, Mo 0.50 mass% or less, Ti 0.01 to 0.10 mass%, Rare earth element 0.0010 to 0.0050 Mass% and content (mass%) of B are following (1) Formula: f (Q) ≤ [B] ≤0.01 (1) Here, Q: welding heat input (kJ / cm)           f (Q): function of Q           [B]: Content of B (mass%) A welded joint, characterized in that, the balance has a composition consisting of iron and unavoidable impurities. The welded joint according to claim 1, wherein the welded metal of the welded joint contains 0.10 mass% or less of V and 0.10 mass% or less of Nb in addition to the composition. The method of claim 1 or 2, wherein the high heat input welding is a large heat input electrogas welding, wherein f (Q) is represented by the following formula (2): f (Q) = 0.003 x {0.23 x 1n (Q)-0.5} (2) Where 1n (Q): the natural logarithm of Q Welded joint characterized in that by. The method of claim 1 or 2, wherein the high heat input welding is large heat input submerged arc welding, wherein f (Q) is represented by the following formula (3): f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3) Welded joint characterized in that by. The method of claim 1 or 2, wherein the high heat input welding is a large heat input electroslag welding, wherein f (Q) is represented by the following formula (3): f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3) Welded joint characterized in that by. In the method of welding a steel sheet by large heat input welding having a welding heat input of 100 kJ / cm or more, the composition of the weld metal is C: 0.03 to 0.12 mass% and Si: 0.10 to 0.80 mass% , Mn: 0.80 to 2.50 mass%, Ni: 0.50 to 3.00 mass%, Cr: 0.50 mass% or less, Mo: 0.50 mass% or less, Ti: 0.01 to 0.10 mass%, rare earth element: 0.0010 to 0.0050 mass%, and B The content (mass%) of the formula (1) is: f (Q) ≤ [B] ≤0.01 (1) Here, Q: welding heat input (kJ / cm)           f (Q): function of Q           [B]: Content of B (mass%) And the balance is adjusted to be made of iron and unavoidable impurities. The welding method according to claim 6, wherein the composition of the welding metal further contains 0.10% by mass or less of V and 0.10% by mass or less of Nb. The method of claim 6 or 7, wherein the high heat input welding method is a large heat input electrogas welding, wherein f (Q) is represented by the following formula (2): f (Q) = 0.003 x {0.23 x 1n (Q)-0.5} (2) Where 1n (Q): the natural logarithm of Q Welding method characterized by. The method of claim 6 or 7, wherein the high heat input welding is a large heat input submerged arc welding, wherein f (Q) is represented by the following formula (3): f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3) Welding method characterized by. The method of claim 6 or 7, wherein the high heat input welding is a large heat input electroslag welding, wherein f (Q) is represented by the following formula (3): f (Q) = 0.003 x {0.42 x 1n (Q)-1.9} (3) Welding method characterized by.

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