JP5076658B2 - Steel material for large heat input welding - Google Patents

Steel material for large heat input welding Download PDF

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JP5076658B2
JP5076658B2 JP2007153666A JP2007153666A JP5076658B2 JP 5076658 B2 JP5076658 B2 JP 5076658B2 JP 2007153666 A JP2007153666 A JP 2007153666A JP 2007153666 A JP2007153666 A JP 2007153666A JP 5076658 B2 JP5076658 B2 JP 5076658B2
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JP2008163446A (en
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克行 一宮
伸一 鈴木
伸夫 鹿内
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Jfeスチール株式会社
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Description

The present invention relates to a steel material for welding having a yield strength of 460 N / mm 2 or more and a plate thickness of 40 mm or more, which is used in various structures such as shipbuilding, construction, and civil engineering, and in particular, the welding heat input exceeds 300 kJ / cm. The present invention relates to a material that is excellent in toughness of a heat-affected zone in welding with high heat input welding and that can obtain good CTOD characteristics.

  With increasing strength and thickness of steel materials, high heat input welding with excellent production efficiency such as submerged arc welding, electrogas welding, and electroslag welding has been increasingly applied to welding construction.

  Since the toughness of heat-affected zone welded with high heat input in steel materials decreases, various steels for high heat input welding have been proposed, and TiN is finely dispersed in the steel, resulting in coarsening of austenite grains in the weld heat-affected zone. A technique for suppressing the above-described problem and utilizing it as a ferrite transformation nucleus in a weld heat-affected zone has been put into practical use.

  Further, there is also a technique (Patent Document 2) in which Ti oxide (oxycide) is dispersed in the welding heat-affected zone (Patent Document 1), or the toughness of the weld heat-affected zone is improved by utilizing the ferrite nucleation ability of BN. Proposed.

  Furthermore, in order to improve the toughness of the weld heat affected zone by controlling the form of sulfide (sulfide), it has been proposed to add Ca (Patent Document 3) or REM (Patent Document 4).

  However, when TiN is mainly used, a region heated to a temperature region where TiN dissolves in the heat affected zone is not effective, and the ground structure becomes brittle due to solute Ti and solute N. There was a problem that the toughness was significantly reduced.

  Further, the technology using Ti oxide has a problem that it is difficult to disperse the oxide uniformly and finely. On the other hand, various studies have been made to improve the dispersibility by a method such as oxide compounding. However, in a large heat input welding in which the heat input exceeds 300 kJ / cm, the welding heat affected zone It was difficult to sufficiently suppress the growth of austenite grains.

On the other hand, in Patent Document 5, Ca-based nonmetallic inclusions that promote ferrite transformation in the weld heat-affected zone are dispersed in steel by appropriately controlling the Ca, O, and S contents to improve toughness. Is disclosed.
JP 57-51243 A JP-A-62-170459 JP 60-204863 A Japanese Patent Publication No. 4-14180 Japanese Patent No. 3546308

Recently, the application of high heat input welding to high-strength steels whose yield strength exceeds YP460 N / mm 2 class is increasing. Described in Patent Document 2 and Patent Document 5, the technology yield strength to improve the HAZ toughness by the formation of intragranular ferrite in the 390 N / mm 2 class steels are subject, the yield strength is more than 460N / mm 2 class, Even at a slow cooling rate during high heat input welding, the carbon equivalent is high, so the inside of the grains becomes a mixed structure of ferrite and bainite, and the toughness is not improved.

  Conventionally, the Charpy impact test has been mainly used as a method for evaluating the toughness of a high heat input weld, but in recent years, a CTOD test is sometimes used.

Therefore, the present invention provides a steel material that is excellent in CTOD characteristics of the weld heat affected zone even in large heat input welding with a yield strength of 460 N / mm 2 or more and a plate thickness of 40 mm or more and a welding heat input exceeding 300 kJ / cm. For the purpose.

In order to solve the above problems, the inventors have made various studies and obtained the following knowledge.
1. In order to improve the toughness of the heat-affected zone of high heat input welding, austenite grain coarsening in the high temperature region is suppressed, and in addition to the formation of intragranular ferrite in the subsequent cooling process, the amount of island martensite (MA) in bainite is reduced. It is important to make it happen.
2. Specifically, as a component design guideline, it is important to reduce the amount of P in addition to the amount of C and Si in steel.

The present invention has been made by further studying the obtained knowledge, that is, the present invention,
1. % By mass
C: 0.03-0.10%
Si: 0.09% or less Mn: 0.8-2.0%
P: 0.012% or less S: 0.0005 to 0.0050% or less Al: 0.005 to 0.1%
Ti: 0.004 to 0.03%
Ni: 0.42-2.0%
Nb: 0.03% or less B: 0.0003 to 0.0025%
N: 0.0030 to 0.0070%
Ca: 0.0005 to 0.0030%
O: Less than 0.0040% A steel material for high heat input welding that satisfies the formula (1), and the balance is made of Fe and inevitable impurities.
0 <(Ca− (0.18 + 130 × Ca) × O) /1.25/S <1 (1)
However, Ca, O, and S are the contents (mass%) of each component.
2. As steel composition, V: 0.2% or less, Cu: 1.0% or less in mass% (excluding 0.8% or more)
The steel material for high heat input welding according to 1, which contains one or more of Cr: 0.7% or less, Mo: 0.7% or less, W: 1.5% or less.

According to the present invention, it is suitable for various structures such as shipbuilding, construction, and civil engineering, and has excellent toughness of the weld heat affected zone and good CTOD characteristics even in high heat input welding where the heat input of welding exceeds 300 kJ / cm. Further, a steel material for welding having a yield strength of 460 N / mm 2 or more and a plate thickness of 40 mm or more is obtained, which is extremely useful industrially.

The reason for limiting the chemical components of the present invention will be described. In the description,% is mass%.
C: 0.03-0.10%
C is added in an amount of 0.03% or more in order to obtain the strength required for structural steel. On the other hand, if added over 0.10%, the weld heat affected zone toughness is lowered, so 0.03% to 0.10%, preferably 0.04 to 0.09%.

Si: 0.09% or less If Si is added in excess of 0.09%, island martensite is generated in the heat affected zone of high heat input welding and deteriorates toughness. .

Mn: 0.8 to 2.0%
Mn is added in an amount of 0.8% or more in order to ensure the strength of the base material. On the other hand, if it exceeds 2.0%, the toughness of the welded portion is remarkably deteriorated, so 0.8% to 2.0%, preferably 1.2 to 2.0%.

P: 0.012% or less P is an unavoidable impurity in the present invention. When P is contained in an amount exceeding 0.012%, island martensite is generated in the heat-affected zone of high heat input welding toughness, particularly CTOD characteristics. In order to reduce the content, the content is made 0.012% or less.

S: 0.0005 to 0.0050% or less S is made to be 0.0005% or more in order to generate CaS and MnS. On the other hand, if it exceeds 0.0050%, the toughness of the base material is lowered, so the content is made 0.0005 to 0.0050%.

Ni: 0.42-2.0%
Ni increases strength while maintaining the base material in high toughness, so 0.42% or more is added to obtain the effect. On the other hand, if it exceeds 2.0%, the effect is saturated, so 0.42 to 2.0%.

Nb: 0.03% or less Nb is added in order to ensure the strength, toughness and weld joint strength of the base metal. However, if it exceeds 0.03%, the toughness of the weld heat affected zone decreases, so 0.03% The following.

Ti: 0.004 to 0.03%
Ti forms and precipitates TiN during solidification, suppresses coarsening of austenite grains in the weld heat-affected zone, precipitates ferrite as a ferrite transformation nucleus, and improves toughness, so 0.004% or more Add. On the other hand, if it exceeds 0.03%, the TiN particles become coarse and the toughness is lowered, so the content is made 0.004 to 0.03%.

Al: 0.005 to 0.1%
Al is made 0.005% or more in order to deoxidize steel. On the other hand, if it exceeds 0.1%, the toughness of the base metal is lowered and the toughness of the weld metal is also lowered, so 0.005 to 0.1%, preferably 0.01 to 0.06%.

B: 0.0003 to 0.0025%
B is added in an amount of 0.0003% or more in order to reduce solute N by generating BN in the weld heat affected zone, and to become ferrite transformation nuclei to improve toughness by generating ferrite. On the other hand, if it exceeds 0.0025%, the hardenability increases and the toughness decreases, so the content is made 0.0003 to 0.0025%.

N: 0.0030 to 0.0070%
N forms 0.0030% or more in order to generate TiN. On the other hand, if it exceeds 0.0070%, in the region where TiN is dissolved by the welding heat cycle, the solid solution N increases and the toughness is deteriorated, so the content is made 0.0030 to 0.0070%.

Ca: 0.0005 to 0.0030%
Since Ca fixes S and improves toughness, in order to acquire the effect, it is made 0.0005% or more. On the other hand, if it exceeds 0.0030%, the effect is saturated, so 0.0005 to 0.0030%.

O: Less than 0.0040% O indirectly affects the formation of composite sulfide (sulfide) in which MnS is deposited on CaS, so it is less than 0.0040%, preferably less than 0.0030%.

0 <(Ca− (0.18 + 130 × Ca) × O) /1.25S <1.0
Here, Ca, O, and S are the contents (mass%) of each component.
This parameter formula makes the toughness of the weld heat-affected zone good when large heat input welding is performed on the steel in the above component range. When Ca, O, and S are defined so as to satisfy this formula, the parameter is expressed on CaS. A composite sulfide (sulfide) in which MnS is precipitated is generated and finely dispersed, and the toughness of the weld heat affected zone is improved.

  When it is less than 0, CaS does not crystallize, S precipitates in the form of MnS alone, and extends in the rolling direction during the production of the steel sheet to lower the base metal toughness. Moreover, since MnS is melted in the weld heat affected zone, excellent toughness cannot be obtained.

  On the other hand, if it exceeds 1.0, S is almost fixed by Ca, and MnS that forms ferrite nuclei does not precipitate on CaS. Therefore, ferrite is not generated in the weld heat affected zone, and the effect of improving toughness cannot be obtained.

  The above is the basic component of the present invention, and sufficient effects can be obtained. However, when further improving the characteristics, one or more of V, Cu, Cr, Mo, and W can be added.

V: 0.2% or less V improves the strength and toughness of the base metal, and VN is produced to form ferrite nuclei. However, if it exceeds 0.2%, the toughness is reduced, so when added Is 0.2% or less.

Cu: 1.0% or less Cu has the same effect as Ni. However, if it exceeds 1.0%, hot brittleness is caused and the steel sheet surface properties are deteriorated. The following.

Cr: 0.7% or less Cr is effective in increasing the strength of the base material, but if added in a large amount, the toughness is deteriorated.

Mo: 0.7% or less Mo is effective for increasing the strength of the base material, but if added in a large amount, the toughness is deteriorated.

W: 1.5% or less W is effective for increasing the strength of the base material. However, if added in a large amount, the toughness is deteriorated.

  The steel sheet according to the present invention can be produced by making molten steel by a conventional method, hot rolling, or heat treatment after hot rolling. For example, after hot metal is refined in a converter to form steel, RH degassing is performed, and a steel piece is obtained through a continuous casting or ingot-bundling process.

  Thereafter, the obtained steel slab is reheated and hot-rolled, and accelerated cooling or the like is performed according to desired performance.

  The steel slab adjusted to various components shown in Table 1 was heated, then hot rolled to a thickness of 50 to 80 mm, and then cooled to a temperature range of 450 ° C. or lower by accelerated cooling. Some steel plates were tempered in a temperature range of 450 to 600 ° C.

  The obtained steel sheet was subjected to a tensile test and a Charpy impact test to investigate strength and toughness. In the tensile test, a JIS No. 4 tensile test piece was taken in the rolling width direction from the center of the thickness of each steel plate, and yield strength (YP) and tensile strength (TS) were determined.

  In the Charpy impact test, a JIS No. 4 impact test piece was collected in the rolling width direction from the center of the thickness of each steel plate, and the ductile brittle fracture surface transition temperature (vTrs) was determined.

  Moreover, in order to produce the joint of a V type groove | channel by electrogas arc welding, and to investigate the toughness of a weld bond part, three Charpy impact tests were implemented at test temperature -40 degreeC, and the average value was calculated | required. Furthermore, the CTOD test was performed by notching the bond at the notch position and making it into the entire thickness in the plate thickness direction at a test temperature of −10 ° C.

  Furthermore, a welding heat cycle was given to these steel plates, and the MA fraction was measured. The thermal cycle is to take a test piece of width 80 mm x length 80 mm x thickness 15 mm from a steel plate and heat it to 1400 ° C, then set a cooling rate of 800-500 ° C to 1 ° C / s and a cooling rate of 500-200 ° C. The temperature was 0.5 ° C./s. The MA fraction was quantified by observing with SEM and image processing by revealing MA by two-stage etching.

Table 2 shows the test results. From Table 2, all the steels of the present invention have excellent base metal toughness with yield strength (YP) of 460 N / mm 2 or more and Charpy fracture surface transition temperature (vTrs) of −60 ° C. or less.

  In addition, the steel of the present invention has a Charpy impact value (test temperature of −40 ° C.) of a welded joint of 100 J or more and a CTOD value of −10 ° C. of 0.2 mm or more, and is excellent in weld heat affected zone toughness. The MA fraction is as low as 2.6% or less.

  On the other hand, the steel material of the comparative example has a base material property of yield strength of 460 MPa or less, or vTrs of −40 ° C. or more, or a Charpy impact value (test temperature of −40 ° C.) of a welded joint of 29 J or less, CTOD. The value is 0.08 mm or less, and any one or more of the strength, toughness and weld toughness of the base material is inferior to the steel of the present invention. Moreover, MA fraction is as high as 3.8% or more.

  The CTOD test is performed in accordance with the BS 5762 standard, and the CTOD value is a limit CTOD value.

Claims (2)

  1. % By mass
    C: 0.03-0.10%
    Si: 0.09% or less Mn: 0.8-2.0%
    P: 0.012% or less S: 0.0005 to 0.0050% or less Al: 0.005 to 0.1%
    Ti: 0.004 to 0.03%
    Ni: 0.42-2.0%
    Nb: 0.03% or less B: 0.0003 to 0.0025%
    N: 0.0030 to 0.0070%
    Ca: 0.0005 to 0.0030%
    O: Less than 0.0040% A steel material for high heat input welding that satisfies the formula (1), and the balance is made of Fe and inevitable impurities.
    0 <(Ca− (0.18 + 130 × Ca) × O) /1.25/S <1 (1)
    However, Ca, O, and S are the contents (mass%) of each component.
  2. As steel composition, V: 0.2% or less, Cu: 1.0% or less in mass% (excluding 0.8% or more)
    The steel material for high heat input welding according to claim 1, comprising one or more of Cr: 0.7% or less, Mo: 0.7% or less, W: 1.5% or less.
JP2007153666A 2006-12-06 2007-06-11 Steel material for large heat input welding Active JP5076658B2 (en)

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KR101142185B1 (en) 2007-12-07 2012-05-04 신닛뽄세이테쯔 카부시키카이샤 Steel being excellent in ctod characteristic in welding heat affected zone and a method of producing the same
KR101160790B1 (en) * 2009-05-19 2012-06-27 신닛뽄세이테쯔 카부시키카이샤 Steel material for welding and method for producing same
TWI365915B (en) * 2009-05-21 2012-06-11 Nippon Steel Corp Steel for welded structure and producing method thereof
DK2434027T3 (en) * 2009-05-22 2015-12-07 Jfe Steel Corp Steel materials for welding with high heat input
JP5493557B2 (en) * 2009-07-31 2014-05-14 Jfeスチール株式会社 Steel material for large heat input welding
JP5842314B2 (en) * 2009-09-16 2016-01-13 Jfeスチール株式会社 High heat input welding steel
US9403242B2 (en) 2011-03-24 2016-08-02 Nippon Steel & Sumitomo Metal Corporation Steel for welding
JP5796379B2 (en) * 2011-07-11 2015-10-21 Jfeスチール株式会社 Steel for welded structure excellent in CTOD characteristics of high heat input weld heat affected zone
WO2013128650A1 (en) 2012-03-01 2013-09-06 Jfeスチール株式会社 Steel material for high-heat-input welding
WO2015141203A1 (en) 2014-03-17 2015-09-24 Jfeスチール株式会社 Steel material for welding
JP6036884B2 (en) * 2014-03-25 2016-11-30 Jfeスチール株式会社 A method for producing a non-tempered high-tensile steel sheet with excellent high heat input welding characteristics and ductility.

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JP4432905B2 (en) * 2003-11-27 2010-03-17 住友金属工業株式会社 High-strength steel and offshore structures with excellent weld toughness

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