JP4424484B2 - Welded joints with excellent cold cracking resistance and steel for welding materials - Google Patents

Description

  The present invention relates to a welded joint excellent in low-temperature cracking resistance applied to high-strength steel structures such as building structures, mechanical structures, offshore structures, pressure vessels, tanks, etc., and steel for welding materials for obtaining the joints. About.

One of the important issues when welding steel is prevention of cold cracking. Low temperature cracks are cracks that occur after the temperature of the welded part drops to around room temperature after welding, and are more likely to occur as the strength of the steel being welded increases, and are used when applying high strength steel to welded structures . Sufficient consideration is required for steel materials, welding materials, construction methods, etc.

  It is known that (a) reducing the hardness of the welded portion, (b) reducing diffusible hydrogen, and (c) reducing the degree of restraint (reducing residual stress) are effective in preventing cold cracking. .

  Since the welded part is rapidly cooled from the molten state, most of the alloy components such as an element having a hardenability improving effect and an element having a precipitation hardening action to increase the strength of the steel material have an action of hardening the welded part. However, when the amount thereof increases, the hardness of the welded portion increases and cracking susceptibility increases. On the other hand, in recent years, with the development of the controlled rolling method and the accelerated cooling method, it has become possible to obtain a steel material with higher strength by lowering the content of alloy components.

In addition, for diffusible hydrogen, low-hydrogen and ultra-low hydrogen welding rods have been developed and put to practical use in place of illuminite and cellulosic welding rods that greatly reduce the amount of hydrogen. In TIG welding and MIG welding, further reduction is possible. Furthermore, although the degree of restraint may be changed in the dimensional shape of the welded portion, for example, as in the inventions disclosed in Patent Document 1 and Patent Document 2, residual stress is reduced by utilizing expansion due to transformation of the weld metal. There is a way.

However, even if the above-mentioned means are adopted, preheating of the steel material to be welded is extremely effective for reliably preventing the occurrence of cold cracking, and preheating becomes an essential work if the strength of the steel material increases. come. Preheating for preventing low temperature cracking is effective when the strength is about 50 to 150 ° C. in the high-strength steel with a strength of 600 to 800 MPa, but it is desirable to increase the preheating temperature as the strength increases. . This preheating effect reduces the cooling rate after welding, reduces hardening, promotes the escape of diffusible hydrogen, expands the weld base material in advance, and reduces the amount of shrinkage deformation caused by welding. There are thought to be. The temperature required for preheating can be estimated from the chemical composition of the base material, the amount of diffusible hydrogen, the degree of restraint, etc., as introduced in Non-Patent Document 1 , for example.

JP 2000-17380 A JP 2003-33876 A "Metal Handbook" revised edition, edited by the Japan Institute of Metals, Maruzen Co., Ltd., May 30, 2000, p. 1023-1024

  In order to reliably prevent the occurrence of low temperature cracking during welding of a steel welded joint, it is necessary to preheat the base material, especially when the strength of the steel material is high. However, in this preheating work, when the work to be welded becomes large, a lot of man-hours and time are spent for the preparation work for heating and the heating time, and the welding work efficiency is remarkably lowered.

  By controlling the chemical composition of the weld metal, the present invention provides a welded joint that does not cause cold cracking without performing such preheating, and further provides a steel material for welding material for obtaining the weld metal. Is.

The gist of the present invention is as follows.
(1) When the chemical composition of the weld metal is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.00. 03% or less, S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, the balance being iron and impurities Welded joints with excellent cold cracking resistance.

(2) When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0 0.03% or less, S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, and Cu: 0.1 -1.2%, Ni: 0.1-10.0%, Cr: 0.1-3.0%, Mo: 0.1-3.0%, V: 0.001-0.2%, Contains one or more of Ti: 0.003-0.3%, B: 0.0002-0.008%, and Nb: 0.001-0.05%, with the balance being iron and impurities A welded joint with excellent low-temperature cracking resistance, which is characterized by its existence.

(3) When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0 0.03% or less, S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, and Ca: 0.0003 A welded joint with excellent cold cracking resistance, characterized by containing one or two of ˜0.005% and Mg: 0.0003 to 0.005% , the balance being iron and impurities .

(4) When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0 0.03% or less, S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, and Cu: 0.1 -1.2%, Ni: 0.1-10.0%, Cr: 0.1-3.0%, Mo: 0.1-3.0%, V: 0.001-0.2%, One or more of Ti: 0.003-0.3%, B: 0.0002-0.008% and Nb: 0.001-0.05%, and Ca: 0.0003-0.005 % And Mg: 0.003 to 0.005% of one or two kinds, the balance being iron and impurities, a weld joint with excellent cold cracking resistance.

(5) When the chemical composition is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less , S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, the balance being iron and impurities Steel materials for welding materials.

(6) When the chemical composition is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Cu: 0.1-1. 2%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.0%, Mo: 0.1 to 3.0%, V: 0.001 to 0.2%, Ti: 0 0.001 to 0.3%, B: 0.0002 to 0.008% and Nb: 0.001 to 0.05%, and the balance is iron and impurities. Steel materials for welding materials.

(7) When the chemical composition is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Ca: 0.0003-0. A steel material for welding materials, containing 005% and Mg: 0.0003 to 0.005% or two , the balance being iron and impurities .

(8) When the chemical composition is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Cu: 0.1-1. 2%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.0%, Mo: 0.1 to 3.0%, V: 0.001 to 0.2%, Ti: 0 0.001 to 0.3%, B: 0.0002 to 0.008% and Nb: 0.001 to 0.05%, Ca: 0.0003 to 0.005% and Mg : 0.0003 to 0.005% of one or two kinds, the balance being iron and impurities, the steel material for welding material characterized by the above-mentioned.

  Since the welded joint of the present invention can prevent cold cracking without heating the base steel prior to the welding operation, that is, without preheating, the efficiency of the welding operation can be greatly improved. Moreover, the steel material for welding materials of this invention can form the weld metal of said weld joint easily by producing a covering arc welding rod or a welding wire using it.

  The inventors of the present invention conducted various investigations on measures for suppressing low-temperature cracks generated in a welded joint by an arc welding method in a welded structure using a steel material having higher strength. Although preheating of the base material is extremely effective as a countermeasure against cold cracking, it takes a lot of man-hours to fully implement it, and sometimes it is difficult to implement. Therefore, as a result of examining means for reducing the temperature as much as possible even if preheating is performed, it has been found that the inclusion of Co in the weld metal has a remarkable effect.

  Co is added for the purpose of strengthening the steel material, while the Ms point is generally lowered, while the Ms point is raised, so that the effect of improving the strength is small. In some cases, it is an element that is rarely considered in low-alloy steels that are used by ordinary welding. However, when it is contained in the weld metal, cold cracking can be suppressed, and even if preheating is not performed, an effect equivalent to that obtained by preheating appears.

  The reason why such an effect appears is not necessarily clear, but the dislocation density in the martensite structure generated in the weld metal decreases as the Ms point increases, and the decrease in the dislocation density decreases the hardness and causes deformation. It is thought that the improvement in performance results in the reduction of weld hardness and residual stress as described above, thereby suppressing the occurrence of cracks. Furthermore, since the decrease in the dislocation density decreases the amount of hydrogen occluded in the metal structure, it is presumed that the amount of diffusible hydrogen is decreased.

  Here, the weld metal refers to a portion that has melted and solidified during welding, excluding the heat affected zone, in the weld joint. In addition, the component of the weld metal is analyzed in the vicinity of the center of the weld metal.

In the present invention, the content range represented by mass% of each element in the weld metal is limited as follows.
C: 0.01 to 0.15%
C is 0.01% or more in order to ensure the strength of the weld metal. On the other hand, if the content of C is too large, an excessive hardness increase of the welded portion is caused and the toughness is deteriorated, so the upper limit is made 0.15%. In order to obtain better toughness, it is desirably 0.1% or less, preferably 0.08% or less.

Si: 0.02 to 0.8%
Si is an element that improves the strength of the weld metal and has a deoxidizing effect. In order to acquire the effect, Si content in a weld metal shall be 0.02 mass% or more. However, excessive Si content causes a reduction in the toughness of the weld metal and causes a deterioration in crack resistance, so the upper limit is made 0.8%.

Mn: 0.6 to 3.0%
Mn, like Si, is an element that improves the strength of the weld metal and has a deoxidizing effect. In order to obtain the effect, the lower limit is made 0.6%. However, if it exceeds 3.0%, it causes a decrease in the toughness of the weld metal and causes a deterioration in cracking susceptibility, so the upper limit is made 3.0%. In order to further improve the toughness and crack resistance, it is desirably 2.5% or less, and preferably 1.7%.

P: 0.03% or less P is one of the impurities mixed from the raw material and deteriorates the toughness in the weld metal. Although it is necessary to make it 0.03% or less as a range which does not exert a remarkable influence, the smaller the better. Desirably, it is 0.015% or less.

S: 0.03% or less S is one of the impurities mixed from the raw material, and deteriorates the toughness in the weld metal. Although it is necessary to make it 0.03% or less as a range which does not exert a remarkable influence, the smaller the better. Desirably, it is 0.015% or less.

Al: 0.004 to 0.08%
Al forms an oxide, promotes intragranular ferrite transformation in the weld metal part, and is an important element for improving toughness. In order to exert its effect, the lower limit of the content is 0.004%. To do. On the other hand, excessive Al causes generation of coarse inclusions and formation of a hardened structure, so the upper limit is made 0.08%.

N: 0.015% or less N is mixed as an impurity, but is an effective element for increasing the strength. Further, when Ti is included, toughness is also improved. In order to exhibit this effect, it is preferable to contain 0.0020% or more. On the other hand, if the N content exceeds 0.015%, pores are likely to be generated, resulting in welding defects. Therefore, the upper limit of the N amount needs to be 0.015%.

Co: 0.1-10.0%
Co is an important element for improving the cold cracking resistance of the welded joint of the present invention. In order to obtain such an effect, the weld metal needs to contain 0.1% or more. However, even if the content exceeds 10%, the improvement effect is saturated and the content is wasted. The lower limit of the preferable content that brings about a remarkable effect is 1% or more, and more desirably 2% or more.

Cu: 0.1-1.2%
Cu may not be included. Since Cu contributes to strength improvement by improving hardenability, Cu is contained in the case of high strength. In order to acquire the effect of containing, it is desirable to set it as 0.1% or more, However, If it exceeds 1.2 mass%, it will become easy to generate | occur | produce a weld crack. Good. Further, in order not to adversely affect the cold cracking resistance, 0.8% or less is desirable, and preferably 0.6% or less.

Ni: 0.1 to 10.0%
Ni does not need to be contained. However, if Ni is contained, it has an effect of improving strength, and further has a large effect of increasing toughness. When it is contained, the content is 0.1% or more. In order to obtain a more sufficient effect, it is desirable that the content be 1.0% or more, preferably 1.5% or more. However, if it exceeds 10.0%, the molten metal flow becomes worse at the time of welding, and a weld defect is likely to occur.

Cr: 0.1-3.0%
Although Cr does not need to be contained, it is effective for improving the hardenability, so it is contained when the weld metal is to have higher strength. In order to obtain the effect by being contained, the content is made 0.1% or more. However, in order to obtain a more sufficient effect, the content is preferably made 0.5% or more. However, if it exceeds 3.0%, there is a tendency that low temperature cracking tends to occur.

Mo: 0.1-3.0%
Although Mo may not be contained, it is effective for improving hardenability and precipitation hardening, and is effective for increasing the strength. In order to obtain the effect when it is contained, the content is made 0.1% or more. However, in order to obtain a more sufficient effect, the content is preferably made 0.5% or more. However, if it exceeds 3.0%, low temperature cracking is likely to occur.

V: 0.001 to 0.2%
V may not be included. V improves the hardenability and is effective for increasing the strength, so 0.001% or more is contained when it is desired to increase the strength of the weld metal. However, if it exceeds 0.2%, low temperature cracking is likely to occur.

Ti: 0.003-0.3%
Ti may not be included. Ti binds to N and prevents a very small amount of B from becoming BN, and is effective in securing the hardenability of B and increasing the strength of the weld metal. In order to acquire the effect, the minimum of content shall be 0.003 mass%. On the other hand, excessive Ti causes coarsening of TiN and significantly deteriorates the toughness of the weld metal, so the upper limit is made 0.3%.
B: 0.0002 to 0.008%
B may not be included. A small amount of B significantly increases the hardenability and contributes to increasing the strength of the weld metal. On the other hand, excessive addition of B causes deterioration of cold cracking resistance, so the upper limit is made 0.008%. Furthermore, in order to ensure good weld crack resistance, the content is desirably 0.005% or less, preferably 0.003% or less.

Nb: 0.001 to 0.05%
Nb may not be included. Nb improves the hardenability and is effective for increasing the strength. Therefore, when it is desired to increase the strength of the weld metal, the Nb content is 0.001% or more. However, if it exceeds 0.05%, low temperature cracking is likely to occur.

Ca: 0.0003 to 0.005%
Ca may not be contained, but may be contained for the purpose of improving the drawability when producing a welding material. In order to obtain this effect, the content is made 0.0003% or more, preferably 0.0005% by mass or more. However, if the content exceeds 0.005%, the peelability of the weld slag deteriorates, so the upper limit needs to be 0.005%.

Mg: 0.0003 to 0.005%
Mg does not need to be contained, but it has the same effect as Ca, and is contained when it is desired to improve the drawability when producing the welding material. When contained, it is preferably 0.0003% or more, preferably 0.0005% by mass or more. However, if the content exceeds 0.005%, the peelability of the weld slag deteriorates, so the upper limit needs to be 0.0005%.

  In order to make the chemical composition of the weld metal within the above-mentioned range, particularly a composition containing Co, an appropriate amount of Co is contained in the steel material of the base metal, and a Co component is added to the coating material with a coated arc welding rod. If it is mixed into the weld metal during arc welding, such as by mixing, mixing the Co component in the flux of the flux-cored welding wire, or mixing the Co component in the flux by submerged arc welding. Good.

  However, the most reliable chemical composition range for weld metal is to use steel having the above-mentioned chemical composition as the welding material for arc welding.

  4 mm steel rods were produced from steels having the compositions shown in Table 1, and coated arc welding rods were produced from each. As the base material, a steel plate having a thickness of 40 mm and a tensile strength of 780 MPa class having the composition shown in Table 2 was used. Table 3 shows the characteristics of the specimens taken from the center of the thickness of the base material. From these base materials, based on the U-shaped weld cracking test method of JIS-Z-3157, a test plate having a prescribed shape was produced, and shield metal arc welding (SMAW) was performed under the conditions shown in Table 4. .

  Welding was performed in a room adjusted to room temperature 30 ° C. and humidity 80%, and the test plate was not preheated. With the same combination of steel and welding rod of the test plate, the occurrence of cracking was investigated by repeating three times. The measurement of the crack was carried out by the method specified in the above JIS, and the surface crack ratio and the cross-section crack ratio were determined. Moreover, the No. 4 test piece was extract | collected in the weld metal part, and the impact value in 0 degreeC was calculated | required. The survey results are shown in Table 5. Table 6 shows the chemical composition of the weld metal, and these are the results of analyzing the central part of the bead.

  As can be seen from the comparison between the crack occurrence rate in Table 5 and the weld metal analysis results in Table 6, the test No. in which the composition of the weld metal contains the required Co and other elements are within the range specified in the present invention. . In the case of 1 to 9, cracks do not occur in the U-shaped weld crack test, which is an evaluation test for cold cracks, or even if it occurs, it is 10% or less.

On the other hand, when Co is not included, Test No. 10 to 13 shows a high crack occurrence rate. However, even if the weld metal contain Co, C, Si, Mn, if elements such as exceeds the appropriate amount stipulated boiled present invention, it is cracking rate has is kept low to sufficiently reduce the Can not.

  In addition, the chemical composition of the weld metal is almost the same as that of the steel rod used for the welding material, and it can be seen that it is preferable to use the same welding material steel as that of the intended weld metal composition.

Claims (8)

When the chemical composition of the weld metal is% by mass: C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less , S: 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, the balance being iron and impurities Welded joints with excellent cold cracking resistance. When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Cu: 0.1-1. 2%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.0%, Mo: 0.1 to 3.0%, V: 0.001 to 0.2%, Ti: 0 0.001 to 0.3%, B: 0.0002 to 0.008%, and Nb: 0.001 to 0.05%, and the balance is iron and impurities. A welded joint with excellent cold cracking resistance. When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Ca: 0.0003-0. A welded joint with excellent low temperature cracking resistance, characterized in that it contains one or two of 005% and Mg: 0.0003 to 0.005%, with the balance being iron and impurities . When the chemical composition of the weld metal is% by mass, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% Hereinafter, S: 0.03% or less, Al: 0.004-0.08%, N: 0.015% or less, Co: 0.1-10.0%, and Cu: 0.1-1. 2%, Ni: 0.1 to 10.0%, Cr: 0.1 to 3.0%, Mo: 0.1 to 3.0%, V: 0.001 to 0.2%, Ti: 0 0.001 to 0.3%, B: 0.0002 to 0.008% and Nb: 0.001 to 0.05%, Ca: 0.0003 to 0.005% and Mg : A welded joint having excellent low-temperature cracking resistance, characterized by containing one or two of 0.0003 to 0.005%, with the balance being iron and impurities. When the chemical composition is mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less, S: Welding characterized by 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, the balance being iron and impurities Steel for materials. Chemical composition in mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less, S : 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, Cu: 0.1 to 1.2%, Ni: 0.1-10.0%, Cr: 0.1-3.0%, Mo: 0.1-3.0%, V: 0.001-0.2%, Ti: 0.003- Weld characterized by containing one or more of 0.3%, B: 0.0002-0.008% and Nb: 0.001-0.05%, the balance being iron and impurities Steel for materials. Chemical composition in mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less, S : 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, Ca: 0.0003 to 0.005% and Mg: Steel material for welding material, containing one or two of 0.0003 to 0.005% , the balance being iron and impurities . Chemical composition in mass%, C: 0.01 to 0.15%, Si: 0.02 to 0.8%, Mn: 0.6 to 3.0%, P: 0.03% or less, S : 0.03% or less, Al: 0.004 to 0.08%, N: 0.015% or less, Co: 0.1 to 10.0%, Cu: 0.1 to 1.2%, Ni: 0.1-10.0%, Cr: 0.1-3.0%, Mo: 0.1-3.0%, V: 0.001-0.2%, Ti: 0.003- One or more of 0.3%, B: 0.0002 to 0.008% and Nb: 0.001 to 0.05%; Ca: 0.0003 to 0.005%; A steel material for welding material, comprising one or two of 0003 to 0.005%, the balance being iron and impurities.