KR20110072608A - High strength submerged arc weld metal joint having excellent low-temperature impact toughness - Google Patents

Abstract

PURPOSE: A high strength submerged arc welding metal part having superior low temperature impact resistance is provided to increase tensile strength of the welding metal part and secure low temperature impact resistance by controlling micro-structure and oxide of the welding metal part. CONSTITUTION: A high strength submerged arc welding metal part having superior low temperature impact resistance includes C of 0.01~0.1%, Si of 0.1~0.5%, Mn of 1.0~3.0%, Ni of 1.5~3.0%, Mo of 0.3~1.0%, Ti of 0.005~0.03%, Nb of 0.005~0.05%, V of 0.005~0.03%, N of 0.002~0.006%, P of less than 0.03%, S of less than 0.03%, residual Fe and other inevitable impurity. The composition satisfies relationships of 0.1<=Ti/O<=0.4, 1.0<=Ti/N<=3.5, 8<=V/N<=12, and 12<=O/B<=25.

Description

High strength submerged arc welding metal part with excellent low temperature impact toughness {HIGH STRENGTH SUBMERGED ARC WELD METAL JOINT HAVING EXCELLENT LOW-TEMPERATURE IMPACT TOUGHNESS}

The present invention relates to a weld metal part formed during submerged arc welding (SAW) used in high strength welded structures such as bridges, construction, ships, offshore structures, steel pipes, and line pipes. More specifically, the present invention relates to a submerged arc welding metal part having high strength by controlling composition and microstructure, and having excellent low temperature impact toughness.

Recently, skyscrapers and ultra long bridges that connect the islands and the inland due to the rise of land prices are being constructed, and the thick steels used are required to have high strength and low temperature impact toughness. In order to secure the stability of such a large welded structure, the impact toughness characteristic of the welding part is most important. In general, in the case of submerged arc welding used for the girder of an ultra long bridge, a heat input amount of approximately 35-100 kJ / cm is used.

In general, the weld metal joint (Weld Metal Joint) formed during welding is formed by melting some of the steel as the welding material is melted to form a molten pool, and then solidifying to form a coarse columnar structure and to form austenite grain boundaries in the coarse grains. Therefore, coarse grain boundary ferrite, Widmanstatten ferrite, martensite and phase martensite (MA, Martensite Austenite constituent) are formed and the impact toughness is the most degraded site.

Therefore, in order to secure the stability of the welded structure, it is necessary to control the microstructure of the welded metal part to secure the impact toughness of the welded metal part. As an example of the technique for securing the impact toughness of such a weld metal part, Unexamined-Japanese-Patent No. 11-170085 is mentioned, The component of a welding material is controlled here. However, the above technique has a problem that it is difficult to obtain sufficient weld metal toughness by controlling only the welding material, not controlling the microstructure, particle size, etc. of the weld metal.

In addition, Japanese Patent Laid-Open Publication No. 2005-171300 discloses C: 0.07% or less, Si: 0.3% or less, Mn: 1.0 to 2.0%, P: 0.02% or less, S 0.1% or less, and sol.Al: 0.04 to 0.1%. , ARM is defined as ARM = 197-1457C-1140sol.Al + 11850N-316 (Pcm-C) in a composition consisting of, N: 0.0020% to 0.01%, Ti: 0.005% to 0.02%, and B: 0.005% to 0.005%. Although a technique for welding high tensile strength steel and a weld metal part is disclosed, it is difficult to secure impact toughness of SAW high heat input weld metal part because there is no limitation of oxygen content in the weld metal part. .

In addition, Japanese Patent Application Laid-open No. Hei 10-180488 describes slag generating agent: 0.5 to 3.0%, C: 0.04 to 0.2%, Si≤0.1%, Mn: 1.2 to 3.5%, Mg: 0.05 to 0.3%, Ni: 0.5 It has good impact toughness, including ~ 4.0%, Mo: 0.05 ~ 1.0%, and B: 0.002 ~ 0.015%. However, since there is no mention of oxygen and nitrogen content in the weld metal part, it is possible to secure impact toughness of high heat input weld metal part. There is a difficult problem.

The present invention is to provide a submerged arc welding metal portion having excellent low-temperature impact toughness and high strength by controlling the composition and the microstructure of the weld metal portion formed during submerged arc welding (SAW).

In the present invention, by weight%, C: 0.01 ~ 0.1%, Si: 0.1 ~ 0.5%, Mn: 1.0 ~ 3.0%, Ni: 1.5 ~ 3.0%, Mo: 0.3 ~ 1.0%, Ti: 0.005 ~ 0.03%, Nb : 0.005 to 0.03%, V: 0.005 to 0.05%, B: 0.0005 to 0.003%, N: 0.002 to 0.006%, P: 0.03% or less, S: 0.03% or less, O: 0.02 to 0.07%, the rest is Fe and Contains inevitable impurities,

The composition is a high strength submerged arc welding metal with excellent impact toughness that satisfies the relationship of 0.1≤Ti / O≤0.4, 1.0≤Ti / N≤3.5, 8≤V / N≤12, and 12≤O / B≤25. Provide wealth.

According to the present invention, in SAW welding having a welding heat input range of 50 to 100 kJ / cm, SAW welding can have high-strength properties of tensile strength of 800 MPa or more and at the same time secure low-temperature impact toughness by controlling the microstructure and oxide of the weld metal part. Metal parts can be provided.

The present inventors investigated the type and size of oxides on the acicular ferrite known to be effective for impact toughness of the weld metal, and accordingly, the amounts of the weld metal grain boundary ferrite and acicular ferrite changed according to TiO and soluble B. It has been found that the impact toughness value of the weld metal portion changes.

Based on these studies, in the present invention,

[1] presenting a technique using TiO- (Ti, V) N composite oxide in SAW welded metals,

[2] improve the toughness by controlling the number of oxides and particle diameter of welded metal parts and transforming them into acicular ferrites of 75% or more;

[3] Soluble boron (Soluble B) has been secured to improve the hardenability and suggest the technology to promote the bed ferrite transformation.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

[1] management of TiO- (Ti, V) N composite oxides

In the present invention, if the ratio of Ti / O, O / B, Ti / N, and V / N is properly maintained in the weld metal part, the number of TiO- (Ti, V) N composite oxides is properly distributed, thereby solidifying the weld metal part during the solidification process. Coarsening of austenite grains is prevented and acicular ferrite transformation is promoted by TiO- (Ti, V) N composite oxide. When the TiO- (Ti, V) N composite oxide is properly distributed in the austenite grains, it becomes a heterogeneous nucleation site of acicular ferrite transformation as the temperature decreases in the austenite grains, which is preferred to the grain boundary ferrites formed at the grain boundaries. By forming a needle-like ferrite, it is possible to significantly improve the impact characteristics of the weld metal.

[2] microstructure, welded metal

In the present invention, the size, amount and distribution of TiO- (Ti, V) N composite oxides are controlled according to the ratio of Ti / O, O / B, Ti / N and V / N. That is, in the present invention, when Ti / O is 0.1 to 0.4, O / B is 12 to 25, and Ti / N is 1.0 to 3.5 V / N of 8 to 12, the fine TiO- (Ti, V having a size of 0.01-0.1 μm It can be seen that N complex oxides are formed at 1.0 × 10 ⁷ / mm ³ or more. When the fine TiO- (Ti, V) N composite oxide is properly distributed in the weld metal part, the needle ferrite transformation is promoted in the crystal grains preferentially rather than the grain boundary during the cooling process of the weld metal part, thereby making the composition ratio of the acicular ferrite of the weld metal part 75%. The above can be secured. In addition, in order to secure a high-strength welded metal part, it was found that high strength and high toughness characteristics can be obtained by controlling the Ni, Mn, Mo, and Nb alloy components to secure a lower bainite structure.

[3] role of soluble B in weld metal

In the present invention, boron, which is dissolved separately from the composite oxide uniformly dispersed in the weld metal part, diffuses into the grain boundary and lowers the energy of the grain boundary, thereby suppressing the grain boundary ferrite transformation at the grain boundary. It plays a role in promoting metamorphosis. In this way, the grain boundary ferrite transformation is suppressed at the grain boundaries, and contributing to the improvement of the impact toughness of the weld metal part is promoted through the promotion of the acicular ferrite transformation in the grains.

Hereinafter, the composition range of the weld metal part of the present invention will be described in detail (hereinafter,% by weight).

It is preferable to make content of carbon (C) into 0.01 to 0.1%.

Carbon (C) is an essential element in order to secure the strength and weld hardness of the weld metal part. However, if the carbon content exceeds 0.1%, the weldability is greatly reduced, there is a problem that the low-temperature cracking is easily generated during welding and the impact toughness of the weld metal is greatly reduced.

The content of silicon (Si) is preferably 0.1 to 0.5%.

When the silicon content is less than 0.1%, the deoxidation effect in the weld metal is insufficient and the fluidity of the weld metal is reduced. When the content of the silicon is more than 0.5%, the low temperature impact is promoted by promoting the transformation of MA constituent in the weld metal part. It is not preferable because it lowers toughness and affects weld cracking susceptibility.

The content of manganese (Mn) is preferably 1.0 to 3.0%.

Mn is an essential element to improve the deoxidation and strength in the weld metal part, and precipitates MnS around TiO- (Ti, V) N composite oxide to promote formation of acicular ferrite, which is beneficial for toughness improvement of the weld metal part. . In addition, Mn forms a solid solution in the matrix structure to strengthen the matrix by solid solution to secure strength and toughness, for this purpose it is preferably contained 1.0% or more. However, if it exceeds 3.0%, it is not preferable because it generates low temperature metamorphic tissue.

The content of titanium (Ti) is preferably set to 0.005 to 0.03%.

Ti is an essential element in the present invention because it combines with O to form a fine Ti oxide, as well as to form a fine TiN precipitate. In order to obtain such a fine TiO oxide and TiN composite precipitate effect, it is preferable to add Ti to 0.005% or more, but when it exceeds 0.03%, coarse TiO oxide and coarse TiN precipitate are formed, which is not preferable.

The content of nickel (Ni) is preferably set to 1.5 to 3.0%.

Ni is an essential element that improves the strength and toughness of the matrix by solid solution strengthening. In order to obtain such an effect, it is preferable to contain Ni content of 1.5% or more, but when it exceeds 3.0%, it is not preferable because it greatly increases the hardenability and there is a possibility of high temperature cracking.

The content of molybdenum (Mo) is preferably 0.3 to 1.0%.

Mo is an element that improves the known strength, but more than 0.3% is required, but when it exceeds 1.0%, the effect is saturated, and the weld hardenability is greatly increased, which promotes martensite transformation, thereby deteriorating weld low temperature crack generation and toughness. Not desirable

The content of boron (boron, B) is preferably set to 0.0005 to 0.003%.

B is an element that improves quenching property and segregates at grain boundaries to suppress grain boundary ferrite transformation. That is, the solid solution B serves to secure the hardenability to improve the strength of the welded metal portion and simultaneously diffuses into the grain boundary to lower the energy of the grain boundary to suppress the grain boundary ferrite transformation to promote the transformation of the acicular ferrite. In order to suppress the grain boundary ferrite transformation, more than 0.0005% is required, but if the content exceeds 0.003%, the effect is saturated, and the welding hardenability is greatly increased, which promotes martensite transformation, thereby lowering the welding low temperature crack generation and toughness. I can't.

The content of niobium (Nb) is preferably 0.005 to 0.03%.

Nb is an essential element for improving the hardenability, and in particular, it is necessary to obtain lower bainite structure because it has an effect of lowering the Ar ₃ temperature and widening the bainite formation range even in a low cooling rate range. In order to expect the effect of improving strength, 0.005% or more is required. However, exceeding 0.03% is undesirable because it promotes the formation of phase martensite in the weld metal part during welding, which adversely affects the toughness of the weld metal part.

The content of vanadium (V) is preferably 0.005 to 0.05%.

V is an element that promotes ferrite transformation by forming VN precipitates on TiO oxides. It requires 0.005% or more, but when it exceeds 0.05%, V forms a hardened phase such as carbide in the weld metal to adversely affect the toughness of the weld metal. It is not desirable because it is crazy.

The content of nitrogen (N) is preferably set to 0.002 to 0.006%.

N is an essential element for forming TiN and VN precipitates and the like, and increases the amount of fine TiN and VN precipitates. In particular, since the TiN and VN precipitates have a significant influence on precipitate size, precipitate spacing, precipitate distribution, complex precipitation frequency with oxide, and high temperature stability of the precipitate itself, the content is preferably set at 0.002% or more. However, if the nitrogen content exceeds 0.006%, the effect is saturated, and the toughness may be reduced due to the increase in the amount of solid solution nitrogen present in the weld metal.

The content of phosphorus (P) is preferably at most 0.030%.

Since P is an impurity element that promotes high temperature cracking during welding, it is desirable to manage P as low as possible. Therefore, in order to improve toughness and reduce cracking, it is preferable to manage at 0.03% or less.

The content of sulfur (S) is preferably 0.030% or less (excluding 0).

S is an element necessary for MnS formation. In order to precipitate the composite precipitate of MnS, it is preferable to be 0.03% or less. If there is more than that, it is not preferable because a low melting point compound such as FeS can be formed to cause high temperature cracking.

The content of oxygen (O) is preferably limited to 0.02 ~ 0.07% or less.

O is an element that reacts with Ti to form Ti oxide during solidification of the weld metal, and Ti oxide promotes the transformation of acicular ferrite in the weld metal. If the O content is less than 0.02%, the Ti oxide is not distributed properly in the weld metal part. If the O content exceeds 0.07%, coarse Ti oxide and other oxides such as FeO are formed, which is not preferable because it affects the impact toughness of the weld metal part.

In the present invention, in order to further improve the mechanical properties, the weld metal formed as described above may further include one or two or more selected from the group of Cu, Al, Cr, W, and Zr.

It is preferable to make content of copper (Cu) into 0.01 to 2.0%.

Cu is a useful element for securing strength and toughness due to solid solution at the base. To this end, the Cu content should be contained 0.01% or more, but when it exceeds 2.0% is not preferable because it increases the hardenability in the weld metal portion to lower the toughness and promote high temperature cracking in the weld metal.

In addition, in the case of complex addition of Cu and Ni, the sum thereof is preferably 3.5% or less. The reason is that when it exceeds 3.5%, the hardenability increases, which adversely affects the toughness and weldability.

 

The content of aluminum (Al) is preferably set to 0.001-0.01%.

Al is an element that reduces the amount of oxygen in the weld metal as a deoxidizer. In addition, in order to form fine AlN precipitates in combination with solid solution nitrogen, the Al content is preferably 0.001% or more. However, if it exceeds 0.01%, coarse Al ₂ O ₃ is formed, which hinders the formation of TiO oxide necessary for toughness improvement.

It is preferable to make chromium (Cr) into 0.05 to 1.0%.

Cr can increase hardenability and can also improve strength. If the content is less than 0.05%, strength cannot be obtained, and if the content exceeds 1.0%, there is a problem that the toughness of the weld metal part is caused.

The tungsten (W) content is preferably made 0.05-0.5%.

W is an effective element for improving high temperature strength and strengthening precipitation. However, less than 0.05% is not preferable because the strength increase effect is weak, and above 0.5% is not preferable because it adversely affects the weld metal part toughness.

The content of zirconium (Zr) is preferably set to 0.005-0.5%.

Since Zr is effective in increasing the strength, it is preferable to add more than 0.005%, and if it exceeds 0.5%, it is not preferable because it adversely affects the toughness of the weld metal.

In addition, in the present invention, one or two kinds of calcium (Ca) and rare earth element (REM) may be further added to suppress grain growth of the austenite.

Ca and REM are elements that stabilize the arc during welding and form oxides in the weld metal portion. In addition, it suppresses austenite grain growth during cooling and promotes ferrite transformation in the mouth, thereby improving the toughness of the weld metal part. To this end, it is preferable to add more than 0.0005% of calcium (Ca) and more than 0.005% of REM. However, when Ca is 0.05% and REM is more than 0.05%, a large oxide may be formed to adversely affect toughness. As REM, 1 type, or 2 or more types, such as Ce, La, Y, and Hf, may be used, and any of the above effects can be obtained.

The rest consists of inevitable impurities and Fe.

Hereinafter, the component relational formula of the present invention will be described in detail.

It is preferable to make ratio of Ti / O into 0.1-0.4.

If the Ti / O ratio is less than 0.1, the number of TiO oxides required for austenite grain growth inhibition and acicular ferrite transformation in the weld metal portion is insufficient, and the Ti ratio contained in the TiO oxide becomes small, thus functioning as a needle-like ferrite nucleation site. As a result, the acicular ferrite phase fraction effective for improving the toughness of the weld heat affected zone is lowered. When the ratio of Ti / O exceeds 0.4, the austenite grain restraining effect in the weld metal portion is saturated, and the proportion of the alloying components contained in the oxide is rather small, thus losing the function of the needle-like ferrite nucleation site.

It is preferable to make ratio of Ti / N into 1.0-3.5.

In the present invention, when the Ti / N ratio is less than 1.0, the amount of TiN precipitates formed in the TiO oxide is reduced, which is not preferable because it adversely affects the needle ferrite transformation, which is effective for improving toughness. It is not preferable because the amount of nitrogen increases and the impact toughness is lowered.

It is preferable to make ratio of V / N into 8-12.

In the present invention, when the V / N ratio is less than 8, the amount of VN precipitates formed in the TiO oxide is reduced, which is not preferable because it adversely affects the needle ferrite transformation, and when it exceeds 12, the effect is saturated and the amount of solid solution is increased. It is not preferable because the impact toughness is lowered.

It is preferable to make ratio of O / B into 12-25.

In the present invention, when the O / B ratio is less than 12, the amount of solid solution B that diffuses to the austenite grain boundary during the cooling process after welding and suppresses grain boundary ferrite transformation is insufficient, and when the O / B ratio exceeds 25, the effect is saturated. It is not preferable because the amount of nitrogen dissolved in solid solution decreases the toughness of the weld heat affected zone.

It is preferable to make ratio of (Ti + 4B) / O into 0.3-0.6.

In the present invention, when the ratio of (Ti + 4B) / O is less than 0.3, the amount of solid solution is increased, which is not effective for improving the toughness of the weld metal part, and when it exceeds 0.6, the number of TiN and BN precipitates is insufficient.

It is preferable that ratio of (Ni + 3Mn + 4Mo + 5Nb) shall be 10-12.

In the present invention, when the ratio of (Ni + 3Mn + 4Mo + 5Nb) is less than 10, since it affects the formation of the lower bainite structure, a high strength welded metal part of 800 MPa or more cannot be secured, and if the ratio exceeds 12, the lower bainite Instead, it is undesirable because the tissue of martensite is formed.

Hereinafter, the microstructure of the weld metal part of the present invention will be described in detail.

In the present invention, the microstructure of the weld metal formed after SAW welding is acicular ferrite and lower bainite, and in order to secure high toughness, the acicular ferrite fraction is preferably 75% or more. The reason is that needle-like ferrite tissue is a tissue that can simultaneously obtain high strength and low temperature impact toughness.

That is, when coarse grained ferrite, Widmanstatten ferrite, and the like, which are not the acicular ferrite structure are mixed, impact toughness is advantageous, but it is difficult to secure high strength, and when martensite tissue is mixed, high strength Although it is possible to secure the low temperature impact toughness it is preferable to have a needle-like ferrite and lower bainite structure in the present invention.

Accordingly, in the present invention, an advantageous optimal microstructure of high strength and high toughness is composed of needle ferrite of 75 to 85% and lower bainite structure of 15 to 25%.

Oxides present in the weld metal portion greatly influence the microstructure transformation of the weld metal portion after welding. That is, the type, size, and number of oxides to be distributed are greatly affected. In particular, the SAW weld metal part has a large amount of welding material that is melted unlike other welding methods, so that grains coarsen in the solidification process and coarse grain boundary ferrite, Widmanstatten ferrite, bainite, etc. The structure is formed and the physical properties of the weld metal part are greatly reduced.

In order to prevent this, it is important that the TiO- (Ti, V) N composite oxide is uniformly dispersed at minute intervals in the weld metal part, and preferably 0.5 μm or less. In addition, it is preferable to limit the particle size and the critical number of the TiO- (Ti, V) N composite oxide to 0.01-0.1 μm and 1.0 × 10 ⁷ or more per 1 mm ³ , respectively.

The reason is that when the particle size of the composite oxide is less than 0.01 µm, it does not promote the transformation of acicular ferrite in the SAW-welded metal part, and when it exceeds 0.1 µm, pinning of the austenite grains is inhibited. This is because it is less effective and behaves like a coarse nonmetallic inclusion, which adversely affects the impact toughness of the high strength welded metal part.

In addition, when the critical number is less than 1.0x10 ⁷ / ㎣, it is not preferable because the number of complex oxides is insufficient to contribute to acicular ferrite nucleation and prevents grain coarsening.

In the present invention, it can also be produced by other welding processes other than SAW. In this case, if the cooling rate of the weld metal part is high, a welding process having a high cooling rate is preferable because the oxide is finely dispersed and the structure is fine. For the same reason, steel cooling and Cu-backing methods are advantageous in order to improve the cooling rate of the weld. However, even if the well-known techniques are applied to the present invention, it is natural that they are interpreted to be substantially within the technical scope of the present invention as a simple change of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following examples.

(Example)

Welded metal parts having a compositional composition as shown in Tables 1 and 2 and the number, size, and microstructure of the composite oxides as shown in Table 3 were manufactured by SAW by applying a welding heat input of 50 to 100 kJ / cm. It shows the composition ratio between sub alloy elements.

The test pieces for evaluating the mechanical properties of the welded metal part as described above were taken from the center part of the welded metal part, and the tensile test piece was used by the KS standard (KS B 0801) No. 4 test piece and the tensile test was the cross head speed. Test at 10 mm / mim. The impact test piece was manufactured and tested in accordance with KS (KS B 0809) No. 3 test piece, and the results are shown in Table 3.

 

The size, number and spacing of oxides, which have a significant effect on the impact toughness of the weld metal, were measured by the point counting method using an image analyzer and an electron microscope. At this time, the test surface was evaluated based on 100 mm ² and the results are shown in Table 3. In addition, the impact toughness evaluation of the SAW welded metal part was processed by the impact test specimen after the SAW welded through Charpy impact test at -20 ℃ and the results are shown in Table 3.

division C Si Mn P S Ni Mo Ti B
(ppm) N
(ppm) Nb V Cu Al Cr Ca REM O
(ppm) Inventive Example
One 0.04 0.35 2.1 0.015 0.005 2.4 0.60 0.005 15 25 0.005 0.025 0.10 - - - - 360 Inventive Example
2 0.07 0.32 2.0 0.010 0.002 2.3 0.65 0.006 14 34 0.007 0.030 0.13 0.006 - - - 340 Inventive Example
3 0.06 0.25 2.2 0.011 0.004 2.5 0.65 0.008 18 35 0.008 0.040 0.15 - 0.11 - - 380 Inventive Example
4 0.08 0.32 2.0 0.018 0.005 1.9 0.72 0.006 20 30 0.007 0.035 0.11 - - - - 320 Inventive Example
5 0.07 0.42 2.2 0.009 0.004 2.5 0.60 0.01 25 33 0.01 0.030 0.14 - - - - 320 Inventive Example
6 0.07 0.38 2.3 0.010 0.003 2.3 0.62 0.008 22 25 0.009 0.027 0.12 0.007 - - - 280 Inventive Example
7 0.09 0.25 2.0 0.011 0.005 2.5 0.65 0.005 19 29 0.008 0.029 0.15 - - - - 260 Inventive Example
8 0.06 0.35 1.9 0.012 0.006 2.6 0.64 0.007 20 30 0.007 0.031 0.12 - 0.10 - - 320 Inventive Example
9 0.06 0.28 1.9 0.010 0.005 2.5 0.50 0.011 15 32 0.008 0.033 0.11 - - 0.001 - 330 Inventive Example
10 0.07 0.38 2.2 0.009 0.003 2.8 0.55 0.008 20 35 0.005 0.035 0.13 - - - 0.005 360 Comparative example
One 0.03 0.06 1.2 0.0414 0.006 1.6 0.19 0.02 19 32 0.02 0.05 - - - - - 450 Comparative example
2 0.05 0.13 1.9 0.013 0.004 1.7 0.20 0.025 69 50 0.04 0.005 0.003 - - - - 415 Comparative example
3 0.06 0.06 1.2 0.018 0.007 1.6 0.01 0.034 41 74 0.07 0.007 0.35 - - - - 450 Comparative example
4 0.04 0.19 2.0 0.018 0.004 3.7 0.55 0.02 105 56 0.05 0.008 0.29 - - - - 460 Comparative example
5 0.06 0.28 1.7 0.013 0.008 2.9 1.14 0.058 58 71 0.001 0.140 0.19 - - - - 170 Comparative example
6 0.06 0.26 1.5 0.012 0.007 3.5 0.16 0.037 52 40 0.002 0.012 0.30 - - - - 640 Comparative example
7 0.05 0.22 2.5 0.015 0.008 1.5 1.12 0.04 92 70 0.008 0.014 0.45 - - - - 160 Comparative example
8 0.07 0.14 1.5 0.011 0.006 2.5 0.51 0.014 42 180 0.032 0.038 0.41 - 0.013 - - 120 Comparative example
9 0.09 0.37 2.7 0.015 0.010 1.4 1.17 0.081 9 100 0.003 0.021 0.33 - - - - 440 Comparative example
10 0.05 0.26 2.6 0.009 0.004 0.05 1.15 0.042 5 80 0.04 0.006 0.55 - - - - 750 Comparative example
11 0.07 0.23 3.7 0.018 0.004 2.3 0.64 0.03 29 60 0.05 0.01 0.8 - - - - 190

division Ti / O Ti / N V / N O / B (Ti + 4B) / O Ni + 3Mn + 4Mo + 5Nb Inventive Example 1 0.1 2.0 10.0 24.0 0.3 11.1 Inventive Example 2 0.2 1.8 8.8 24.3 0.3 10.9 Inventive Example 3 0.2 2.3 11.5 21.1 0.4 11.7 Honorable 4 0.2 2.0 11.7 16.0 0.4 10.8 Inventory 5 0.3 3.0 9.1 12.8 0.6 11.6 Inventory 6 0.3 3.2 10.8 12.7 0.6 11.7 Inventive Example 7 0.2 1.7 10.0 13.7 0.5 11.1 Inventive Example 8 0.2 2.3 10.3 16.0 0.5 10.9 Proposition 9 0.3 3.4 10.3 22.0 0.5 10.2 Inventory 10 0.2 2.3 10.0 18.0 0.4 11.6 Comparative Example 1 0.4 6.3 15.6 23.7 0.6 6.1 Comparative Example 2 0.6 5.0 1.0 6.0 1.3 8.4 Comparative Example 3 0.8 4.6 0.9 10.9 1.1 5.6 Comparative Example 4 0.4 3.6 1.4 4.4 1.4 12.2 Comparative Example 5 3.4 8.2 14.1 2.9 4.8 12.6 Comparative Example 6 0.6 9.3 3.0 12.3 0.9 8.7 Comparative Example 7 2.5 5.7 2.0 1.7 4.8 13.5 Comparative Example 8 1.2 0.8 2.1 2.9 2.6 9.2 Comparative Example 9 1.8 8.1 2.1 48.9 1.9 14.2 Comparative Example 10 0.6 5.3 0.8 150.0 0.6 12.7 Comparative Example 11 1.6 5.0 1.7 6.6 2.2 16.2

division
Welding process and heat input
TiO + VN Composite Oxide
Welding metal parts
acicular ferrite
(%) Welded Metal Part Mechanical Properties
welding
Process Welding heat input
(kJ / cm) Count
(Pcs / mm ³ ) Average size
(Μm) The tensile strength
(MPa) vE _{-20 ℃}
(J) Inventive Example 1 SAW 60 3.1 × 10 ⁸ 0.015 85 832 132 Inventive Example 2 SAW 65 3.6 × 10 ⁸ 0.016 76 843 102 Inventive Example 3 SAW 55 3.7 × 10 ⁸ 0.016 78 828 98 Honorable 4 SAW 80 4.4 × 10 ⁸ 0.018 78 843 128 Inventory 5 SAW 78 5.3 × 10 ⁸ 0.014 76 847 88 Inventory 6 SAW 85 4.8 × 10 ⁸ 0.022 78 835 104 Inventive Example 7 SAW 98 3.6 × 10 ⁸ 0.013 82 824 134 Inventive Example 8 SAW 50 2.3 × 10 ⁸ 0.021 75 852 122 Proposition 9 SAW 55 4.6 × 10 ⁸ 0.025 84 845 135 Inventory 10 SAW 85 4.3 × 10 ⁸ 0.024 85 839 122 Comparative Example 1 SAW 45 2.0 × 10 ⁶ 0.075 36 862 14 Comparative Example 2 SAW 70 1.3 × 10 ⁶ 0.091 32 858 26 Comparative Example 3 SAW 60 2.4 × 10 ⁶ 0.121 24 750 56 Comparative Example 4 SAW 90 2.0 × 10 ⁶ 0.164 45 820 43 Comparative Example 5 SAW 80 1.4 × 10 ⁶ 0.087 37 650 16 Comparative Example 6 SAW 80 1.2 × 10 ⁶ 0.096 42 840 12 Comparative Example 7 SAW 80 2.0 × 10 ⁶ 0.063 44 841 29 Comparative Example 8 SAW 70 2.1 × 10 ⁵ 0.046 32 810 32 Comparative Example 9 SAW 70 1.8 × 10 ⁵ 0.051 29 790 29 Comparative Example 10 SAW 75 1.4 × 10 ⁵ 0.056 22 823 32 Comparative Example 11 SAW 75 1.6 × 10 ⁶ 0.073 41 815 29

As shown in Table 3, the weld metal part of the invention examples 1 to 10 satisfying the composition and the relational expression according to the present invention, while the number of TiO- (Ti, V) N complex oxide is 2X10 ⁸ / mm ³ or more, In the comparative example, the TiO- (Ti, V) N composite oxide showed a range of 2.4x10 ⁶ particles / mm ³ or less, and it was confirmed that the average size was coarse than the invention example.

On the other hand, the microstructure of the present invention is composed of a high fraction of all the acicular ferrite phase fraction of 75% or more. Therefore, the weld metal part of the present invention exhibits high strength and excellent weld metal part impact characteristics of 800 MPa or more.

Claims (9)

By weight%, C: 0.01-0.1%, Si: 0.1-0.5%, Mn: 1.0-3.0%, Ni: 1.5-3.0%, Mo: 0.3-1.0%, Ti: 0.005-0.03%, Nb: 0.005- 0.03%, V: 0.005% to 0.05%, B: 0.0005% to 0.003%, N: 0.002% to 0.006%, P: 0.03% or less, S: 0.03% or less, O: 0.02% to 0.07%, and the rest are Fe and inevitable impurities. Including, The composition is a high strength submerged arc welding metal with excellent impact toughness that satisfies the relationship of 0.1≤Ti / O≤0.4, 1.0≤Ti / N≤3.5, 8≤V / N≤12, and 12≤O / B≤25. part. The method according to claim 1, At least one selected from Al: 0.001-0.05%, Cu: 0.01-2.0%, Cr: 0.05-1.0%, W: 0.05-0.5%, Zr: 0.005-0.5% in the composition. High strength submerged arc welded metal parts with excellent impact toughness. The method according to claim 2, High-strength submerged arc welding metal part having excellent impact toughness when the total of Cu and Ni is less than 3.5% when Cu is added. The method according to claim 1, A high strength submerged arc welded metal portion having excellent impact toughness comprising one or two of Ca: 0.0005 to 0.05% and REM: 0.005 to 0.05% in the composition. The method according to claim 1, The composition is a high strength submerged arc welded metal part excellent in impact toughness that satisfies the relationship of 0.3 ≦ (Ti + 4B) /O≦0.6. The method according to claim 1, The composition is a high strength submerged arc welded metal part excellent in impact toughness that satisfies the relationship of 10≤ (Ni + 3Mn + 4Mo + 5Nb) ≤12. The method according to claim 1, The high-strength submerged arc welding metal portion having excellent impact toughness, wherein the microstructure of the weld metal portion includes an acicular ferrite of 70% or more as the area fraction and the remaining lower bainite. The method according to claim 1, The welded metal portion has an average particle size of 0.01 ~ 0.1㎛ TiO- (Ti, V) N composite oxide is 1.0 × 10 ⁷ gae / ㎣ is distributed over the impact toughness is excellent in high strength sub submerged arc welding metal portion. The method according to claim 8, The high-strength submerged arc welding metal part of the TiO- (Ti, V) N composite oxide having excellent impact toughness dispersed at intervals of 0.5 μm or less.