JP3211046B2 - Method of manufacturing thick steel plate for welded structure excellent in brittle fracture propagation stopping performance of welded joint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in brittle fracture propagation stopping performance (hereinafter referred to as "joint arrest performance") of a welded joint portion of a welded structure. TMCP (Thermo-Mechanica), which also has excellent fracture toughness of the heat affected zone (hereinafter referred to as HAZ).
1 Control Process) a method for producing a steel plate for a welded structure.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for material properties of structural steel sheets used for large-scale welded structures such as marine structures, ships, storage tanks, and the like, particularly tanks and lines for storing LPG and the like. Due to the magnitude of the damage caused by brittle fracture and the magnitude of social unrest caused by the brittle fracture, pipes are required to have improved arrest characteristics.

More specifically, as a base metal arrest characteristic of a tank steel material storing a liquefied gas at −46 ° C., a toughness value measured in a temperature gradient type ESSO test at −50 ° C., Kca (hereinafter referred to as Kca-50 and Kca-50). 400 kgf)
/ Mm ^1.5 or more is required.

In addition, as the demand for ensuring the safety of large-sized welded structures increases, so-called double satisfies both the occurrence of brittle fracture and the cessation of brittle fracture propagation not only in the base metal but also in the welded joint. Integrity assurance is being sought.

[0005] On the other hand, there has conventionally been a proposal focusing on the arrest characteristics of a base material, and Japanese Patent Application Laid-Open No. Sho 62-77419 discloses a method of manufacturing a high-tensile steel having excellent base material arrest characteristics.

[0006] The high strength steel obtained from the manufacturing method disclosed herein has a base material Kca-50 of 440 kgf / mm.
^{1.5 to} 720 kgf / mm ^1.5 , which satisfies the recent demands described above.

However, the joint arrest performance is 9% N
Study on ensuring safety of LNG tank made of i-steel [Reference: Steelmaking Research No. 322 (1986), p. 44-5
1) and research on material selection to ensure the safety of LPG tanks [Reference: Kiyoshi Tanaka / Doctoral dissertation of the University of Tokyo (1988)], but not widely studied and not attracting attention .

[0008] The reason is that in order to ensure the safety of the welded joint against brittle fracture, it is important to prevent the occurrence of brittle fracture, and much research has been concentrated on the prevention of brittle fracture. This is because prevention of brittle fracture propagation is more technically difficult than prevention.

However, the joint arrest performance depends on the Ni content of the steel material, the Ni content of the welding material, and the shape of the welding groove. The effect of steel content Ni on joint arrest performance is 3%
It is known that the above-mentioned amount of Ni appears remarkably.
If the amount is less than 3%, it has been considered that there is no technical expectation to secure joint arrest performance.

At the same time, with the recent increase in demand for large-sized welded structural steel, it has become desirable to increase the supply and reduce the supply price. Excellent steel materials are required.

[0011]

SUMMARY OF THE INVENTION In the present invention, the brittle fracture arresting performance of a welded joint of a steel material is ensured while reducing the Ni element, which causes an increase in cost, as much as possible.
The present invention proposes a method for producing a welded structural steel sheet having excellent low-temperature toughness in a part, and solves the above-mentioned problems.

That is, in this type of application, a steel plate for a welded structure having excellent performance of stopping brittle fracture propagation in a welded joint is provided.
An economical manufacturing method is provided.

[0013]

A first means of the present invention is as follows.
% By weight, C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0.20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, and the balance is Fe and unavoidable components. Carbon equivalent: Ceq = [C ] + ([Si] / 24) +
([Mn] / 6) + ([Ni] / 40): Continuously cast welded structural steel of 0.42% by weight or less, then heated to a temperature of 3 points or more of Ar, and hot rolled with a reduction of 50% or more. Is performed in the austenite non-recrystallization temperature range, and rolling is continuously performed at a reduction ratio of 50% or more in a two-phase region having a temperature lower than the Ar3 point to obtain 65%.
After rolling at 0 ° C. or higher, 5 to
The cooling is performed at a cooling rate of 10 ° C./s to a temperature of 400 ° C. or higher.

The second means of the present invention is as follows: C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al : 0.001 to 0.20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, and the balance is Fe and inevitable Carbon equivalent: Ceq = [C] + ([Si] / 24) +
([Mn] / 6) + ([Ni] / 40): Continuously cast welded structural steel of 0.42% by weight or less, then heated to a temperature of 3 points or more of Ar, and hot rolled with a reduction of 50% or more. Is performed in the austenite non-recrystallization temperature range, and rolling is continuously performed at a reduction ratio of 50% or more in a two-phase region having a temperature lower than the Ar3 point to obtain 65%.
After rolling at 0 ° C. or higher, 5 to
After cooling to a temperature of less than 400 ° C. at a cooling rate of 10 ° C./s, tempering is performed at an Ac 1 point or less.

The third means of the present invention is as follows: C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al : 0.001 to 0.20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, V of 0.1% or less , Zr, Ta, 1.0% or less of Cr,
Any one or more of Mo and Cu are added, and the balance is Fe and unavoidable components. Carbon equivalent: Ceq
= [C] + ([Si] / 24) + ([Mn] / 6) +
([Ni] / 40) + ([Cr] / 5) + ([V] / 1
4) Continuously casting a welded structural steel of 0.42% by weight or less, heating the steel to a temperature of 3 points or more, performing hot rolling at a reduction of 50% or more in the austenite non-recrystallization temperature range, and Rolling is continuously performed at a rolling reduction of 50% or more in a two-phase region having less than 3 points of Ar, and after rolling at 650 ° C. or more,
400 ° C at a cooling rate of 5 to 10 ° C / s from 00 ° C or higher
It is characterized by cooling to the above temperature. In addition,
The fourth means is that in terms of% by weight, C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001. ~0.20%, Ni: 0.3~1.9%, Nb: 0.005~0.030%, Ti: 0.005~0.030%, 0.1% or less of V, Zr, Ta , 1.0% or less of Cr,
Any one or more of Mo and Cu are added and the remaining
Part consists of Fe and unavoidable components, and carbon equivalent: Ceq
= [C] + ([Si] / 24) + ([Mn] / 6) +
([Ni] / 40) + ([Cr] / 5) + ([V] / 1
4) Continuous casting of welded structural steel of 0.42% by weight or less
Then, it is heated to a temperature of 3 points or more of Ar, and the reduction rate is 50% or more.
Hot rolling is performed in the austenite non-recrystallization temperature range, and
In the two-phase region with less than three points of Ar, the rolling reduction is 50% or more.
After rolling at 650 ° C. or higher,
400 ° C at a cooling rate of 5 to 10 ° C / s from 00 ° C or higher
After cooling to a temperature of less than
Features. Further, the fifth means of the present invention comprises the third means.
In the above-mentioned means or the above-mentioned fourth means, 0.1% by weight
% Of Ca, 0.003% or less of B
Is characterized by further adding two types.

The sixth means of the present invention is as follows: C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al : 0.001 to 0.20 %, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030 %, Ti: 0.005 to 0.030%, Ca of 0.1% or less Any of B not more than 0.003%
One or two types are added, and the balance is Fe and inevitable components.
And carbon equivalent: Ceq = [C] + ([Si] /
24) + ([Mn] / 6) + ([Ni] / 40) +
([Cr] / 5) + ([V] / 14) is 0.42% by weight
After continuous casting of the following welded structural steel, the temperature of Ar 3 points or more
Hot rolling with a reduction of 50% or more
Two phases with less than 3 points of Ar
Rolling at a rolling reduction of 50% or more in the
After rolling is completed at a temperature of at least 600 ° C.,
Cool to a temperature of 400 ° C or more at a cooling rate of 0 ° C / s
It is characterized by the following. Further, the seventh means of the present invention is that the weight
%, C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn : 0.5 to 1.6%, Al: 0.001 to 0.20 %, Ni: 0 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, Ca of 0.1% or less, B of 0.003% or less
One or two types are added, and the balance is Fe and inevitable components.
And carbon equivalent: Ceq = [C] + ([Si] /
24) + ([Mn] / 6) + ([Ni] / 40) +
([Cr] / 5) + ([V] / 14) is 0.42% by weight
After continuous casting the following welding structural steel, the temperature on Ar3 Ten以
Hot rolling with a reduction of 50% or more
Two phases with less than 3 points of Ar
Rolling at a rolling reduction of 50% or more in the
After rolling is completed at a temperature of at least 600 ° C.,
After cooling to a temperature of less than 400 ° C. at a cooling rate of 0 ° C./s,
It is characterized in that tempering is performed at an Ac point or less.

[0017]

The structural steels to which the present invention is directed are described in, for example, Japanese Patent Publication No. 58-14849, except for the elements C, Si, Mn, Ni, Nb, and Ti, which are added in limited amounts. As described above, in order to obtain the required material from ordinary structural steel, the effects that have been conventionally confirmed in the field of use in the industry,
The same operation and effect can be obtained by using the type and amount of the additional element determined based on the effect relation in the same manner. Therefore, the present invention includes steels containing these elements as target steels.

The respective elements, the reasons for their addition, and the amounts thereof are as follows.

C is added in an amount of 0.06 % or more as an effective component for improving the strength of steel. If the content is excessively more than 0.20%, island-like martensite precipitates in the weld,
Because significantly degrade the HAZ toughness can not be obtained a joint arrest capability of the target as a result, 0.06%
It is regulated to ~ 0.20%.

Si is necessary as a deoxidizing element of molten steel.
It is effective as a strength increasing element, but if it exceeds 1.0%, the HAZ toughness deteriorates, and if it is less than 0.05%, the deoxidizing effect is insufficient, so the addition amount is restricted to 0.05 to 1.0%. I do.

Mn is added in an amount of 0.5% or more as a component for improving the strength of the steel material. However, excessive addition of Mn causes precipitation of island-like martensite in the welded portion, significantly deteriorating the HAZ toughness, and increasing the target. Since joint arrest performance cannot be obtained, the upper limit is 1.6%.

Since Ni is an extremely important element for improving not only the base material and the joint arrest performance but also the low-temperature toughness, 0.3% of Ni is added, but 1.9% is added.
If it exceeds 1.9%, the hardness of the HAZ portion is increased, and the weldability is degraded.

Nb and Ti are elements that are important for suppressing the coarsening of austenite grains and realizing a fine HAZ structure and ensuring HAZ toughness, and the effect is further enhanced by the combined addition of Nb and Ti. For this purpose, Nb and Ti
Was set at 0.005%. Also, 0.
An excessive addition exceeding 030% deteriorates the HAZ toughness, so the upper limit is specified as 0.030%.

Al is added for the purpose of refining the steel by solid solution and precipitation in the rolling process, in addition to refining the steel by Al nitride, but the effect is manifested when the addition amount is small. Since Al cannot be added and excessive addition deteriorates the toughness of the steel, Al is set to 0.001% to 0.20%.

P and S are preferably each 0.01% or less to ensure the toughness of the base material.

To further improve the strength, 0.1
% Or less of V, Zr, Ta, 1.0% or less of Cr, Mo,
Any one or more of Cu may be added, and when it is desired to further improve toughness, 0.1% or less of Ca,
When it is desired to simultaneously improve both strength and toughness by adding one or two kinds of B of 0.003% or less, V, Zr, Ta of 0.1% or less and Cr of 1.0% or less are used. ,
One or more of Mo and Cu, and 0.1% or less of C
a and / or B of 0.003% or less is added. Even if added more, the effect of improving the strength and toughness is saturated, which is economically disadvantageous.

In addition to the limitation of the amount for each element, the carbon equivalent: Ceq = [C] + ([Si] / 24) + ([Mn]
/ 6) + ([Ni] / 40) + ([Cr] / 5) +
When ([V] / 14) exceeds 0.42% by weight, HAZ
Since the toughness is impaired and the desired joint arrest performance cannot be obtained, the carbon equivalent Ceq is limited to 0.42% by weight or less.

The present inventors have repeatedly conducted various experimental studies using the structural steel described above in order to achieve the object of the present invention, and have obtained the following findings.

FIG. 1 shows C: 0.08%, Si; 0.19
%, Mn 1.44%, Ni; 0.45%, Ti; 0.0
After heating the steel containing 10%, Nb; 0.008% to 1050 ° C., the rolling reduction in the amorphous temperature range and the rolling reduction below the Ar3 point were variously changed from different billet thicknesses to obtain a sheet thickness of 3
Rolled to 8 mm, finished rolling at 650 ° C or higher,
After controlled cooling to 0 ° C, the steel sheet tempered at 530 ° C
The results of a survey on joint arrestability are shown.

As is apparent from FIG. 1, the rolling reduction in the unrecrystallized region is 50% or more and the rolling reduction below Ar3 is 50%.
%, The joint arrestability was improved, and it was found that the target brittle crack propagation distance of 100 mm or less was satisfied. It should be noted that the same effect was obtained with a steel sheet whose rolling was completed at a temperature of 650 ° C. or more and controlled and cooled to a temperature of 400 ° C. or more.

The TIG welding was applied to the test joint in consideration of its use as an LPG land tank, and a γ-based welding material was used as the welding material. Brittle fracture was caused by the welding material. We considered so that there was not. The evaluation of the joint arrest performance was evaluated by a hybrid ESSO test in which a brittle crack was introduced into the fusion line portion of the actual joint.

The test temperature was −50 ° C., and the applied stress was σ = 24.
The test was performed at 5 N / mm ² . The criterion for brittle crack arrest / brittle crack propagation is WES3003 set by the Japan Welding Society.
In accordance with the criteria described above, when the specimen stopped within 100 mm after entering the test joint, it was determined that the brittle crack had stopped, and that the target was satisfied.

As a result of observing the fracture surface of the hybrid ESSO test in detail, when the rolling reduction in the non-recrystallized region is 50% or more and the rolling reduction under Ar3 is 50% or more, the brittle crack which has entered the test joint is found. Has stopped along an uneven path,
This indicated that the brittle crack propagation resistance at the joint fusion line was increased.

On the other hand, when this rolling condition is not satisfied,
The brittle crack that entered the test joint almost went straight through the HAZ, and the fracture surface was flat. It is considered that the brittle crack propagation resistance in the HAZ portion was increased by rolling in the two-phase region less than Ar3 after rolling in the non-recrystallized region having a reduction ratio of 50% or more, thereby satisfying the joint arrestability target. .

Next, preferable cooling conditions for realizing joint arrest characteristics while securing strength and toughness are as follows.
Study was carried out.

2 and 3 show C; 0.06%, S
i; 0.16%, Mn 1.4%, Ni; 0.7%, T
i: 0.010%, Nb; steel containing 0.007%
Drawings showing the results of cooling experiments performed under various cooling conditions after heating to 100 ° C., rolling to a sheet thickness of 25 mm at a reduction rate of 50% in the non-crystalline temperature range, and a reduction rate of less than 3 Ar points of 50%. It is.

As is apparent from FIG. 2, when the cooling is performed at a cooling rate of 600 ° C. or more to 5 ° C./s or more, the strength of the base material,
It was found that the toughness was improved. On the other hand, it was also found that at a water cooling start temperature of less than 600 ° C. or a cooling rate of less than 5 ° C./s, the effect of improving the strength and toughness by water cooling is not substantially exhibited.

Further, as shown in FIG.
If the temperature is lower than 00 ° C., it has been found that the low-temperature transformation products such as island martensite are not tempered, so that the toughness is significantly reduced. However, it has also been found that the above-mentioned problem does not occur when tempering is performed at a temperature equal to or lower than the Acl point even when the temperature is lowered to less than 400 ° C.

As a result of the above-mentioned experimental study, the present inventors have found that
By combining appropriate rolling conditions and controlled cooling after rolling, welded structural steel with a limited composition minimizes the addition of Ni, etc., which increases costs, and therefore impairs weldability and joint toughness altogether. In addition, we established a method that enables stable and smooth production of thick steel plates for welded structures with excellent joint arrest performance.

[0040]

【Example】

(1) As the steel component, except for the limited component of the present invention, any combination may be used as long as it is an element of a general welded structure steel and each element amount. Tables 1 and 2 are shown together with examples.

(2) Rolling conditions are shown in Tables 3 and 4 as manufacturing conditions. Tables 5 and 6 show the material properties and overall evaluation.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

[0048] Table 3 shows test number A14, A16 this onset
Example of the present invention corresponding to the first means of the present invention, test number A15,
A17 is an example of the present invention corresponding to the second means of the present invention, test numbers A5 to A9 and A11 are examples of the present invention corresponding to the third means of the present invention, and test numbers A1 to A4 and A10 are examples of the present invention.
Example Nos. A12 and A13 of the present invention corresponding to means 4
Is an example of the present invention corresponding to the fifth means of the present invention.

In each of the test numbers A1 to A17, both the strength and toughness were sufficient values to satisfy the recent requirements, and the target joint was required at a low temperature of -50 ° C. required for the LPG tank. Arrest performance could be secured.

On the other hand, test numbers B1 to B20 shown in Table 4 are comparative examples. In Comparative Examples B1 to B6, at least one of the unrecrystallization reduction ratio and the two-phase region reduction ratio was not 50% or more, so that the joint arrest performance was low and the target WES3003 required value could not be satisfied. Was.

In Comparative Examples B7 to B14, the joint arrest performance was as good as that of the present invention, but any one of the cooling start temperature, the cooling stop temperature, and the cooling rate did not satisfy the conditions of the present invention. Alternatively, the toughness was further reduced, and could not be used for the intended application.

Comparative Examples B15 and B16 are conventional steels containing a large amount of Ni.
The weldability was clearly inferior to the steel of the present invention. The evaluation criteria for weldability were based on the hardness of the HAZ.
Comparative Examples B17 to B20 were out of the range of the chemical components of the present invention, so that the joint arrest performance was low.

[0053]

As described above, the present invention provides a welded structural steel having a limited composition by combining appropriate rolling conditions and controlled cooling after rolling, thereby minimizing the addition of Ni and the like. It suppresses the increase in cost and improves the base metal toughness and the fracture toughness of the weld heat affected zone in a low temperature use environment, and further the brittle fracture propagation stopping performance, without impairing the weldability and joint toughness. This method establishes a method that enables stable and smooth production of thick steel plates for welded structures with excellent joint arrest performance, and is used in harsh environments such as marine structures, ships, storage tanks, and other large welded structures and pipelines. In the production of the steel sheet originally used, the required material properties are sufficiently satisfied, and the quality and economic effects in this kind of field are extremely large.

[Brief description of the drawings]

FIG. 1 is a drawing showing the relationship between the unrecrystallized region and the rolling reduction below Ar3 and the joint arrest performance.

FIG. 2 is a drawing showing a relationship between a water cooling start temperature, strength, and toughness.

FIG. 3 is a drawing showing the relationship between water cooling stop temperature, strength, and toughness.

Continuation of front page (56) References JP-A-5-9651 (JP, A) JP-A-57-104624 (JP, A) JP-A-5-148539 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) C21D 8/00-8/10 C22C 38/00-38/60

Claims (7)

(57) [Claims] C .: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0. 20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, and the balance is composed of Fe and unavoidable components. Carbon equivalent : Ceq = [C] + ([Si] / 24) +
([Mn] / 6) + ([Ni] / 40): Continuously cast welded structural steel of 0.42% by weight or less, then heated to a temperature of 3 points or more of Ar, and hot rolled with a reduction of 50% or more. Is performed in the austenite non-recrystallization temperature range, and rolling is continuously performed at a reduction ratio of 50% or more in a two-phase region having a temperature lower than the Ar3 point to obtain 65%.
After rolling at 0 ° C. or higher, 5 to
A method for producing a thick steel plate for a welded structure having excellent brittle fracture propagation stopping performance at a weld joint, wherein the steel plate is cooled to a temperature of 400 ° C. or more at a cooling rate of 10 ° C./s. 2. In% by weight, C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0. 20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, and the balance is composed of Fe and unavoidable components. Carbon equivalent : Ceq = [C] + ([Si] / 24) +
([Mn] / 6) + ([Ni] / 40): Continuously cast welded structural steel of 0.42% by weight or less, then heated to a temperature of 3 points or more of Ar, and hot rolled with a reduction of 50% or more. Is performed in the austenite non-recrystallization temperature range, and rolling is continuously performed at a reduction ratio of 50% or more in a two-phase region having a temperature lower than the Ar3 point to obtain 65%.
After rolling at 0 ° C. or higher, 5 to
A method for producing a steel plate for a welded structure having excellent brittle fracture propagation stopping performance at a welded joint portion, wherein after cooling to a temperature of less than 400 ° C. at a cooling rate of 10 ° C./s, tempering is performed at an Ac point or less. 3. In% by weight, C: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0. 20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, V, Zr, Ta of 0.1% or less; 0% or less of Cr,
Any one or more of Mo and Cu are added, and the balance is Fe and unavoidable components. Carbon equivalent: Ceq
= [C] + ([Si] / 24) + ([Mn] / 6) +
([Ni] / 40) + ([Cr] / 5) + ([V] / 1
4) Continuously casting a welded structural steel of 0.42% by weight or less, heating the steel to a temperature of 3 points or more, performing hot rolling at a reduction of 50% or more in the austenite non-recrystallization temperature range, and Rolling is continuously performed at a rolling reduction of 50% or more in a two-phase region having less than 3 points of Ar, and after rolling at 650 ° C. or more,
400 ° C at a cooling rate of 5 to 10 ° C / s from 00 ° C or higher
A method for producing a thick steel plate for a welded structure having excellent brittle fracture propagation stopping performance of a welded joint, characterized by cooling to a temperature as described above. 4. C .: 0.06 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0. 20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, V, Zr, Ta of 0.1% or less; 0% or less of Cr,
Any one or more of Mo and Cu are added, and the balance is Fe and unavoidable components. Carbon equivalent: Ceq
= [C] + ([Si] / 24) + ([Mn] / 6) +
([Ni] / 40) + ([Cr] / 5) + ([V] / 1
4) Continuously casting a welded structural steel of 0.42% by weight or less, heating the steel to a temperature of 3 points or more, performing hot rolling at a reduction of 50% or more in the austenite non-recrystallization temperature range, and Rolling is continuously performed at a rolling reduction of 50% or more in a two-phase region having less than 3 points of Ar, and after rolling at 650 ° C. or more,
400 ° C at a cooling rate of 5 to 10 ° C / s from 00 ° C or higher
A method for producing a steel plate for a welded structure having excellent brittle fracture propagation stopping performance of a welded joint portion, wherein the steel plate is tempered at a temperature of less than or equal to an Ac point after cooling to a temperature of less than. 5. The method according to claim 1, further comprising:
a, add one or two kinds of B of 0.003% or less
The welded joint according to claim 3 or 4, wherein
Of thick steel plates for welded structures with excellent brittle fracture arrest performance
Construction method. 6. In weight percent, C: 0.06 to 0.20%, Si: 0.05-1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0.20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, Any of 0.1% or less of Ca and 0.003% or less of B
One or two types are added, and the balance is Fe and inevitable components.
And carbon equivalent: Ceq = [C] + ([Si] /
24) + ([Mn] / 6) + ([Ni] / 40) +
([Cr] / 5) + ([V] / 14) is 0.42% by weight
After continuous casting of the following welded structural steel, the temperature of Ar 3 points or more
Hot rolling with a reduction of 50% or more
Two phases with less than 3 points of Ar
Rolling at a rolling reduction of 50% or more in the
After rolling is completed at a temperature of at least 600 ° C.,
0 ° C / s Cool to a temperature of 400 ° C or more at a cooling rate of
Characteristic of stopping brittle fracture propagation of welded joints
Excellent method for manufacturing thick steel plates for welded structures. 7. In weight percent, C: 0.06 to 0.20%, Si: 0.05-1.0%, Mn: 0.5 to 1.6%, Al: 0.001 to 0.20%, Ni: 0.3 to 1.9%, Nb: 0.005 to 0.030%, Ti: 0.005 to 0.030%, Any of 0.1% or less of Ca and 0.003% or less of B
One or two types are added, and the balance is Fe and inevitable components.
And carbon equivalent: Ceq = [C] + ([Si] /
24) + ([Mn] / 6) + ([Ni] / 40) +
([Cr] / 5) + ([V] / 14) is 0.42% by weight
After continuous casting of the following welded structural steel, the temperature of Ar 3 points or more
Hot rolling with a reduction of 50% or more
Two phases with less than 3 points of Ar
Rolling at a rolling reduction of 50% or more in the
After rolling is completed at a temperature of at least 600 ° C.,
After cooling to a temperature of less than 400 ° C. at a cooling rate of 0 ° C./s,
Tempering at less than Ac1 point
Manufacture of thick steel plates for welded structures with excellent brittle fracture arrestability
Method.