TW200538561A - A high-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding - Google Patents

Abstract

The present invention provides a high-strength thick steel plate having a plate thickness of 50 to 80 mm and a tensile strength of 490 to 570 MPa which is able to realize an excellent HAZ toughness even when welding with a heat input of 20 to 100 kJ/mm is conducted and is characterized by containing, by wt%, 0.03-0.14% of C, 0.30% or less of Si, 0.8-2.0% of Mn, 0.02% or less of P, 0.005% or less of S, 0.8-4.0% of Ni, 0.003-0.040% of Nb, 0.001-0.040% of Al, 0.0010-0.0100% of N, and 0.005-0.030% of Ti, where Ni and Mn satisfy equation [1], and the balance of iron and unavoidable impurities: Ni/Mn ≥10×Ceq-3 (0.36 < Ceq < 0.42) [1] where, Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

Description

200538561 IX. Description of the invention: [Technical field #of the invention] Technical Field The present invention relates to a heat affected zone (Heat Affected Zone) used in ships, marine structures, middle and fifth-story buildings, bridges, etc. Hereinafter referred to as HAZ.) High-strength thick steel plates with excellent low-temperature toughness are particularly related to a steel plate having a plate thickness of 5010111 or more, a base material tensile strength of 490 to 570 MPa, and having a weldability of Welding joints that are excellent in welding with heat of 20 to 100kJ / mm. 10 [^^] Background Art In recent years, the demand for material properties of welding steel materials used in large structures such as ships, marine structures, high-rise buildings, and bridges has become more stringent. In particular, in these structures, a steel plate having a plate thickness of more than 50 mm and a tensile strength of 15 base materials of 570 MPa is often used. In addition, in order to promote the efficiency of welding, in the welding of this high-strength thick steel plate, the back welding of the large-scale heat welding method represented by the electric welding method, the electric slag welding method, and the like is reviewed. The toughness of the material is the same, and the requirements on the HAZ toughness are becoming stricter. It is noted that the number of proposals for HAZ toughness of steels to which the large-entry heat welding method can be applied is quite large up to the present. For example, in the Japanese newspaper No. 55-026164 of Yu Yue Ben, the invention of the △ newspaper discloses an invention that reduces the size of AZ Tiantian iron grains of AZ by improving the fine butyl nitride in the steel and improves the cutting edge. Also, Yu Yue

The Japanese Patent Application Laid-Open No. 03-264614 proposes an invention in which a composite precipitate of Ti nitride and MnS is used as a metamorphic nucleus of fertilized iron to improve the toughness of haz 5 200538561. Furthermore, Japanese Patent Application Laid-Open No. 04_143246 proposes an invention in which a composite precipitate of Ti nitride and 作为 is effectively used as a nucleus of grain boundary fertilizer grain iron to improve the HAZ toughness.

However, this Ti nitride almost solid-solves near the junction (hereinafter also referred to as the welded joint) with the weld metal whose maximum HAZ temperature exceeds 1405 ° C, so that there is a problem that the effect of improving toughness is reduced. Therefore, it is difficult for steel materials using the above-mentioned Ti nitrides to meet the stringent requirements for HAZ property in recent years and the characteristics of HAZ mobility necessary for ultra large heat welding. As a method for improving the toughness in the vicinity of the welded joint, a steel containing butyrate is used in various fields such as a thick plate and a shaped steel. For example, in the field of thick steel plates, there are inventions described in Japanese Patent Application Laid-Open No. 61-079745 and Japanese Patent Application Laid-Open No. 61-117245, and the toughness of steels containing butadiene oxide is greatly improved in the toughness of large-input heat-welded parts. Effective, suitable for high tension steel. The principle is to stabilize even the melting point of steel! ^ The oxide is placed as the precipitation position 15 and Ti nitrides, MnS, etc. are deposited on the way after the temperature decreases after welding, and the Ti nitrides, MnS, etc. are used as positions to generate fine ferrous iron, and as a result, coarseness that is harmful to toughness can be suppressed. The formation of fertilizer iron can prevent the deterioration of the duty. 'However, this Ti oxide has a problem of not being able to disperse much in steel. This is due to the coarsening and agglomeration of Ti oxides. If the number of Ti oxides is increased, coarse Ti oxides, which are referred to as inclusions, will increase by 5 // m or more. These inclusions above 5 / zm will be the starting point of structural damage or cause a decline in the edge sharpness. They should be avoided because they are quite harmful. Therefore, in order to achieve the improvement of the HAZ toughness, it is necessary to effectively use the oxide which is not easy to produce coarseness and / or spin mass, and which can be dispersed more finely than Ti oxide. In addition, the method for dispersing the Ti oxide in steel is to add rhenium to a molten steel that does not substantially contain strong deoxygenin such as A1. However, it is difficult to control the number and dispersion of butyl oxide in the steel simply by adding Ti to the molten steel, and it is also difficult to control the number and dispersion of precipitates such as TiN and hafnium in the next five steps. For this reason, in steels in which Ti oxides are dispersed only by Ti deoxidation, there are problems such as an insufficient number of Ti oxides or a change in the thickness direction of a thick plate. In response to this problem, Japanese Unexamined Patent Publication No. 293937 and Japanese Unexamined Patent Publication No. 10-183295 have disclosed a method in which, by adding 10A1 after addition of gadolinium or A1 and Ca at the same time, the Ti- The invention of Al complex oxide or Ti, A and Ca complex oxide. This can greatly improve the initial performance of large-scale heat welding HAZ. C; Wu Mingnei

However, in the above-mentioned conventional method of reducing the grain size of the Vostian iron of HAZ or using a precipitate as a metamorphic nucleation of ferrous iron to produce ferrous iron, the tensile strength for securing a plate thickness of 50 mm or more and a base metal strength of 49 MPa As mentioned above, it is necessary to increase the alloying element. At this time, the hardness of the welding HAZ will increase, and the temple will deteriorate the early edge properties. VIA (Martensite-Austenite constituent) 20 will become obvious, so it cannot be securely secured. For example, it has sufficient HAZ toughness in the E-class (-20 ° C guarantee) in the shipbuilding field. Not to mention that the HAZ toughness required when the strength of the base metal cannot be obtained when the tensile strength is 570 MPa or more. Therefore, an object of the present invention is to provide a high-strength thick steel plate having excellent low-temperature toughness in a welded heat-affected zone under large-entry heat welding. The low-temperature toughness 7 200538561 has an excellent concrete strength thick steel plate having a thickness of 50 to 80 mm, and a base material. A steel sheet with a tensile strength of 49-570 MPa grade can achieve excellent welding ηaz performance even when welding with a welding heat of 20-1000 kJ / mm. The present inventors have found that by specifying the amount of Ni and Ni / Mn, the above problems can be solved advantageously, and the present invention is completed after further review. The gist of the present invention is as follows.

(1) A high-strength thick steel plate with excellent low-temperature toughness in a welded heat-affected zone under large-input heat welding, containing C: 0.03 to 0.14 mass%, Si: 0.30 mass% or less, Mn: 0.8 to 2.0 mass%, P : 〇 · 〇2% by mass or less, 〇S: 0.005% by mass or less, A1: 0.001 ~ 0.040% by mass, N: 0.0010 ~ 0.0100% by mass, Ni ·· 0 · 8 ~ 4.0% by mass, Ti: 0.005 ~ 0.030 mass%, Nb: 0.003 to 0.040 mass%, and Ni and Mη satisfy the following formula [1], that is:

Ni / Mn ^ 10xCeq-3 (0.36 &lt; Ceq &lt; 0.42) [1] 5 However, Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15, and the rest is Iron and inevitable impurities. (2) As described in (1) above, the high-strength thick steel plate having excellent low-temperature toughness in a welded heat-affected zone under large-input heat welding further contains Ca: 0.0003 to 0.0050 mass%, Mg: 0.0003 to 0.0050 mass%, REM: One or two or more of 0.001 to 0.030% by mass, and containing 0.000 to 0.0050% by mass and 100 pieces / mm2 or more of an oxide having a projected area diameter of 0.005 to 0.5 // m. (3) The high-strength thick steel plate having excellent low-temperature toughness in a welded heat-affected zone under large-entry heat welding as described in (1) or (2) above, further containing B: 8 200538561 0.0005 to 0.0050 mass%. (4) The high-strength thick steel plate excellent in low-temperature toughness in a welded heat-affected zone under large-entry heat welding as described in any one of (1) to (3) above, further containing Cr: 0. 1 to 0.5% by mass , 〇: 〇〇1〜〇5 mass%, V ·· 〇〇005〜〇 ″ 〇 mass%, Cu: 0.1 to 1.0 mass% of one or two or more. Brief Description of Drawings Figure 1 shows a welding thermal cycle equivalent to 45 kJ / mm.

10 15

20 Figure 2 shows the relationship between Ni / Mn, Ceq, and reproduced HAZ toughness. Figure 3 is a graph showing the effect of improving the toughness of HAZ by dispersing fine oxides or using b effectively. I: Embodiment 3 Preferred Embodiments of the Invention The present invention will be described in detail below. The method used to improve the HAZ edge-to-edge properties so far is to suppress the growth of Vostian iron grains at high temperatures as described above. One of the most effective methods is to lock the grain boundaries of Vostian iron by dispersing the particles to prevent the grain boundaries from moving. In this method, even when the welding heat input is a large heat input of 20 to 100 kJ / mm, the reheating of the VAZDA iron grains of the HAZ can be extremely fine-grained by locking. However, in order to increase the strength of the base metal, the amount of alloy added is increased, and the carbon equivalent (Ceq) of the steel which shows weldability and hardenability of the chemical composition is 0.36 or higher, because the hardness of the HAZ becomes higher, so When the reheated Vosted iron grains are fine-grained due to locking, a new problem arises in that sufficient HAZ toughness cannot be obtained. Therefore, when the hardness of the HAZ portion becomes high, it is necessary to increase the toughness of the ferrous iron to the south. 9 200538561 Therefore, in order to improve the HAZ toughness when the Ceq required for high-strength thick steel is 0.336 or more and 0.42 or less, the inventors conducted an intensive review of the most suitable ingredient system to improve the toughness of fertilizer iron. . An element for improving the toughness of the base metal is known to be effective. However, this time it is not effective to improve the HAZ toughness with Ceq of 0.36 to 5 and 0.42 or less, and it is unknown whether the composition conditions are effective. Therefore, first, the influence of the amount of Ni added is reviewed. Check

In this case, the premise of adding 0.003% or more can effectively ensure the strength of the base metal. For the evaluation of the HAZ toughness, the ductility and brittleness migration temperature (Charpy) at the time of a 10-stroke test at the time of applying a heat cycle equivalent to electrical welding (heating 45 kJ / mm) as shown in Fig. 1 ( vTrs). After reviewing the influence of the amount of Ni added, it is first understood that the necessary toughness cannot be obtained when it is less than 0.8%. In addition, even when Ni was added in an amount of 0.8% or more, it was found that the HAZ toughness could not be improved, and conversely, the HAZ toughness decreased. Therefore, further intensive review included other added elements or the relationship with Ceq, and the results were found to be 15 when Ceq is 0.36 or more and 0.42 or less. As shown in Figure 2, HAZ toughness is related to Ceq and Ni / Mn. relationship. Fig. 2 is a plot of the reproduced steel material ηΔZ (VTrs) of the steel under review in accordance with the respective Ceq layering types, with Ni / Mn &amp; as the horizontal axis. From Fig. 2, it can be seen that good toughness can be obtained in a steel material where 'v Tr s is -15 ° C or less in the Ni / Mng10xCeq_3 [丨] relationship. The reason why the steel that does not satisfy the formula [i] 20 cannot obtain sufficient HAZ toughness is because the addition of Ni is insufficient, and the high toughness effect of the base material is small, or even if it contains a large amount of Ni, it is caused by excessive addition of Mn. HAZ is formed in Haze, which makes the high toughness effect of jealousy disappear. Furthermore, the steel materials reviewed above were subjected to the same review with a thermal cycle corresponding to a heat input of 100 kJ / mm. As a result, it was confirmed that the steel materials satisfying the relationship of formula [1] even when the heat input was 1001 ^ 111111. Get good reproducibility of HAZ. From the above review, it was found that the HAZ toughness can be improved by satisfying the formula [丨] and adding more than 0.8% Ni, but the inventors reviewed to further improve the HAZ resistance. Review the following three ways to improve the HAZ viability. In the first method, 5 due to the long-term retention at high temperature during large-entry heat welding, the grain size of Vosstian iron is coarsened. This is the cause of the decrease in HAZ toughness. Therefore, the coarsening of Vosstian iron during high-temperature retention is suppressed. In the second method, since the cooling time after the large-scale thermal welding is very long, the ferrous grain iron produced by the Vostian iron grain boundary will coarsen. This coarse grain boundary ferrous grain iron will cause the haz toughness to decrease. 10 Therefore , To suppress the coarsening of grain boundary fertilizer grain iron. The third method is to miniaturize the organization itself.

Regarding the first method for suppressing the coarsening of the Vosted iron grains, for example, the method of dispersing fine oxides described in Patent Document 7 is effective. In Patent Document 7, the dispersion of fine oxides is performed in a deoxidation step to adjust the amount of dissolved oxygen in the dissolved steel in a balanced reaction with Si, and then deoxidizes in the order of Ti and Ab. According to this method, oxides having a particle size of 0.001 to 10 // ιη are dispersed at 5x103 to 1x105 particles / mm2. Therefore, the inventors have eagerly reviewed a method for dispersing 20 fine oxides in a system containing 0.003% Nb and adding 0.8% or more Ni when the Ceq is 0.36 or more and 0.42 or less, to further improve the HAZ toughness. Firstly, a method for dispersing fine oxide was found. This method is based on the system. In the deoxidation step, the dissolved oxygen content of the dissolved steel is adjusted to 0.0010 ~ 0.0050%, and then first deoxidized with Ti, then deoxidized with A1, and further borrowed. By adding one or more of Ca, Mg, and REM, it is possible to disperse micro 11 200538561 fine oxides having a projection area diameter of 0.05 to 0.5 // m at 100 particles / mm2 or more. Further, by dispersing this fine oxide, coarsening of the Vosted iron grains during high-temperature retention during welding can be suppressed, and the HAZ toughness can be further improved. An example of the results compared with the HAZ toughness with the proper addition of Ni is shown in Fig. 3. Furthermore, the more the amount of 5 Ni formed, the finer the number of oxides, and the larger the number of oxides. When the amount of Ni is 1.5% or more, it becomes 1,000 pieces / mm2 or more. This is the discovery. Further, about the

The amount of Si is difficult to form oxides when the amount of Si is large. From this review, it is found that the amount of Si is preferably 0.30% or less, and more preferably 0.20% or less. On the other hand, when the amount of dissolved oxygen before Ti deoxidation exceeds 0.0050% or the order of the deoxidizing elements is not 10, the oxides will coarsen and fine oxides cannot be obtained sufficiently, so the coarsening of the grains of Vostian iron is hardly suppressed The effect. In addition, the number of oxides having a projection area diameter of 0.005 to 0.5 // m is obtained by making an extraction replica from a steel plate of a base material, and observing it with an electron microscope at a magnification of 10,000 times and a field of view of 1,000 or more. (Observation area is 10000 // m2 or more.) For particles less than 15 m from 15 m, the observation rate is increased at an appropriate magnification. Elemental analysis was performed on each particle having a diameter of 0.005 to 0.5 // m observed, and the number of oxides was calculated. Next, the inventors made an intensive review of the second and third methods to improve the haz toughness, that is, to suppress the coarsening of the iron grains in the grain boundary and to make the HAZ group 田 d field. As a result, it was found that when the Ceq is 0.36 or more and 0.42 or less, and 0.8% or more of Ni is added to the system, especially when the large-entry heat welding equivalent to = ~ 1000kJ / mm is performed this time, Adding B is effective. The reason is that, from the point of suppressing coarsening of grain-boundary grain iron, the formation of grain-boundary grain iron can be suppressed by solid solution B in heated Voss load boundary segregation. From the point of miniaturization of the HAZ structure, the cooling rate is slower in this adult thermal welding 12 200538561 5 10

When 'wrongly adding B, nitrides can be contained in Vostian iron grain boundaries and grains of Vostian iron grains', a plurality of micro fertilizer particles with B nitride as the core are formed in the Vostian iron grain boundaries and grains Iron therefore miniaturizes the HA z structure. The ratio of improving the HAZ legibility by adding B to n_az is only appropriate. =, ·. The result is not in Figure 3. It can be understood that by adding boots like fate further, improve. Furthermore, in Fig. 3, in addition to the method for dispersing fine oxides as described above, it is also shown that HAZ at 8 is added, but by dispersing fine oxides and adding B, the sharpness of HAZ can be further improved. The reason for this is that the HAZ structure becomes finer by increasing the amount of oxides that become the deposition sites of BN and increasing the iron content of the fertilized grains with the ^^^^ as the core. From the viewpoints of securing strength and improving rottenness, in addition to the above conditions, the HAZ toughness when CU, Cr, Mo, and V were added was also reviewed. As a result, it was found that when the ranges of 0.1 to 0.4%, 0.1 to 5%, 0.001 to 0.2%, and 0.005 to 0.050% were added to the right, the HAZ toughness did not decrease significantly. Furthermore, the method for producing the steel sheet of the present invention is not particularly limited, and it can be produced by a known method. For example, the molten steel adjusted to the above-mentioned appropriate composition can be pressed into a thick plate by a continuous casting method, then heated to 1000 to 1250 ° C, and subjected to hot rolling. The reason for limiting the component composition of the steel material used in the present invention will be described below. Hereinafter, the mass% of the composition is simply expressed as%. C is a component that effectively increases the strength of steel. The lower limit is 0.03%. When it is added too much, carbides and MA are formed in large quantities, which significantly reduces the HAZ toughness. Therefore, the upper limit is 0.14%.

Si is an essential component to ensure the strength of the base metal and deoxidation, but in order to prevent the decrease in toughness due to HAZ hardening, the upper limit is 0.30%. Furthermore, in order to prevent a decrease in the oxygen concentration in the dissolved steel when using an oxide, the upper limit is preferably 0.20 or less. Mn is a component that effectively ensures the strength and toughness of the base metal, and must be added at 0.8% or more. 'However, the upper limit is 2.0% within the allowable range of the toughness and fracture properties of the welded portion. Further, regarding the upper limit of Μη, the display Ceq,

The relationship [1] between the amount of Mn and the amount of Ni. This is a new finding in this review. The increase in Mη when Ceq is too high is the reason that a large amount of MA is generated in the HAZ structure, and the effect of improving the toughness of ΗΑZ due to Ni disappears. 10 \

Ni / Mn ^ 10xCeq-3 [1] The smaller the content of P, the better. However, reducing it in industry will increase a lot of cost, so the content range is 0.02 or less. The smaller the content of S, the better. However, industrially reducing the content of S will increase a lot of costs, so the content range is 0.005 or less. 15

Ni is an important element in the present invention, and at least 0.8% must be added. Furthermore, "about the lower limit of Ni" must satisfy the formula [1] showing the relationship between the Ceq, the amount of Mη, and the amount of Ni. The upper limit is 40% from the viewpoint of the cost of edge making. Ni / Mn ^ lOxCeq-3 [1]

Nb is used to improve the hardenability and effectively increase the strength of the base metal. Add 0.003% or more. However, when too much Nb is added, it has nothing to do with the Ni / Mn ratio. MA becomes easy to generate in HAZ. When 0.040% or more is added, coarse MA with a complex major diameter of 5 or more is generated in HAZ. Since the performance is greatly reduced, the upper limit of Nb is 0.040%. In addition, in order to obtain the toughest toughness, the Nb content 14 200538561 should be suppressed to 0,02 which does not generate a coarse MA with a long diameter of 5 // m or more under the Ni / Mn ratio satisfying the above formula [1]. 〇% or less. In order to obtain a more stable step-height property, under the valence ratio that satisfies the above formula [1], it is appropriate to suppress the amount of Nb to 0 · 〇ι that hardly generates MA with a long diameter of 3 // m or more. 〇% or less. The lower limit of A1 as an important deoxidizing element is 0.001%. When X and A1 are present in a large amount, the surface quality f of the slab deteriorates, so the upper limit is 0%.

Ti is used to generate Ti nitrides and oxides containing lock wires that are necessary for suppressing the coarsening of the reheated Vosted iron grains. Add 0.005% or more. However, the excessive addition will increase the amount of solid solution Ti and decrease the HAZ toughness. Therefore, the upper limit is 0.30%. N is used to form Ti nitrides and B nitrides in the grain boundaries and grains of Vostian iron during cooling after welding, and the addition amount can be adjusted as required. In order to combine with B to form B-nitride ', it is necessary to add more than tenths. However, the excess addition will increase the amount of solid solution N, which will cause the HAZ cutting edge to decrease, so the upper limit is 15 0.0100%.

Ca is an oxide that is used to generate locked particles that are necessary to suppress the coarsening of the additional Smell grains, and can be added at a level of more than 0. _3% as needed. However, excessive addition will cause coarse inclusions, so the upper limit is 0.0050%. 20 Samarium is used to generate the necessary lock to suppress the reheating of the grains of reheated Vosted iron. The %% oxide is an additive that can be added if necessary. Therefore, the upper limit of the sol is to produce a coarse inclusion of REM. In order to suppress the coarsening of the reheated Vosted iron grains 15 200538561, it is necessary to add REM-based oxides to the REM-based oxides, which can be added by more than 0.001% as needed. However, since the excessive addition generates coarse inclusions, the upper limit is set to 0.030%. The REM-based Ce and La are referred to herein as the total amount of both. The 6 series is used as solid solution B, which is segregated at the Vostian iron grain boundary during cooling after welding to suppress the formation of grain boundary ferrous iron. In addition, in order to generate BN in the Vostian iron grain boundary or grain, it may be added as needed. Above 0.0005%. However, the excessive addition will increase the amount of solid solution B, greatly increase the HAZ hardness, and invite a decrease in HAZ toughness. Therefore, the upper limit is 0.0050%.

Cu is used to improve the strength and corrosion resistance of steel, and it can be added above 0.1% if necessary. The effect is saturated at 1.0%, so the upper limit is 1.0%. However, since MA is easily generated when the content exceeds 0.4%, and the HAZ toughness is reduced, it is preferably 0.4% or less.

Cr is used to improve the corrosion resistance of steel.

15%, but the excessive addition will reduce the HAZ toughness due to the formation of MA, so the upper limit is 0.5%.

Mo is an element used to effectively improve the strength and corrosion resistance of the base material, and may be added by 0.01% or more as necessary. The effect is saturated at 0.5%, so the upper limit is 0.5% '. However, since the addition of extra α causes a decrease in HAZ 20's vigor due to the formation of μα, it is preferably 0.2% or less. V is an element used to effectively increase the strength of the base material. If necessary, 0.005% or more is added. The effect is saturated at 010%, so the upper limit is 0.10%. However, since the addition of aMA will cause a decrease in the toughness of ΗΑZ, it is preferably 0.050% or less. 16 200538561 Example 1

The molten steel with the chemical composition shown in Table 1 was continuously cast to produce a steel sheet. Regarding D23 to D34 and D46 to D49, the dissolved oxygen of dissolved steel was adjusted to 0.0010% to 0.0050% by si before Ti was introduced, and then deoxidation with Ti was followed by deoxidation with A1 5 and Ca, Mg, and REM were added. In either case, deoxidation is performed. After reheating at a temperature of 1100 to 1250 ° C, a steel sheet having a thickness of 50 to 80 mm is manufactured by the following two rolling methods. One is at a surface temperature of 750 ~ 900. (After rolling under the temperature range, the method of cooling the plate surface temperature after water reheating to a temperature range of 2000 ~ 400 ° C (referred to as TMCP in Table 2), the other is 10 after hot rolling and rolling Water-cooled to room temperature, and a tempering method in the range of 500 to 600 ° C (referred to as DQ-T in Table 2). Table 2 shows the steel plate manufacturing conditions, plate thickness, and mechanical properties. Also, D23 ~ D34, D46 ~ D49, the number of fine oxides with a projected area diameter of 0.005 ~ 0.5 // m measured at any place on the steel sheet is also recorded. The number of oxygen 15 compounds is determined by any place on the steel sheet. Make an extraction replica and observe it under an electron microscope at a magnification of 10,000 times and a field of view of 100 or more (observation area is 10000 // m2 or more). For particles less than 0 · 1 // m, increase the observation at an appropriate magnification. 0.005 for observation Elementary analysis of each particle with a diameter of ~ 0.5 / m 'is used to calculate the number of oxides. D23 to D31, j) 46 to D49 are all 20 steel dispersed with a projected area of 1 发明 / mm2 in the scope of the invention. The diameter of the projected area is 0. 01 ~ 〇 · 5 // m fine oxide. Furthermore, when D46, D47, D48, and D49, which have almost the same elements other than Si, are compared, it can be understood that the larger the amount of oxide is, the greater the amount of oxide is. These steel plates are welded by electric welding with a heat input of 20 to 100 kJ / mm. 17 200538561 (EGW) or electric slag welding (ESW), butt the steel plates and perform one-time welding. Then, in the haz located at the center of the plate thickness (t / 2), place a score at two locations HAZ and FL from FLlmm, and perform a Chapel impact test at -4 (rc. Table 2 shows the welding conditions and HAZ toughness. Here, in the Charpy 5 impact test, a full-size test piece using 2mmV nicks of JIS No. 4 was used. In Table 2, the particle size of old Vostian iron between FL and HAZlmm was also recorded. The particle size of the old Vosstian iron grains between FL and HAZlmm described here is included in the grain size of the old Vosstian iron grains including the plane thickness direction 2mm centered on the plate thickness center and the FL to HAZlmm plane The average particle diameter of 10 was measured by a cross-section method. Further, here, the bulk ferrous iron connected in a network shape was measured as a grain boundary of old Vosted iron grains. 15

D1 to D49 are steels of the present invention. Since the chemical composition of the steel is appropriately controlled ', it satisfies the predetermined properties of the base metal, and has a high HAZ toughness at -40 ° C. In addition, after D23 to D34 and D46 to D49 in which fine oxides are dispersed, the old Vosted iron particle size between FL and HAZlmm becomes 200 // m or less, which is lower than other fine grains at -40 ° C. The large-entry heat HAZ toughness is also further raised. In addition, compared with D19, where the addition of B is used to refine the HAZ structure, compared with 〇19, which does not contain B but has the same addition elements as B, D20 has a good HAZ toughness, and the HAZ toughness at -40 ° C is also shown. High value. 20 On the other hand, Comparative Steels C1 to 17 do not contain sufficient Ni or the chemical composition of the steel which satisfies the formula [1], and the chemical composition of the steel is not properly controlled, so the toughness of the HAZ is insufficient. 18 200538561 Table 1

Distinguishing mark C Si Μη Ρ S Νί Nb A) Ti N Ca Mg Invention copper D1 0.04 0.13 1.31 0.008 0.002 1.6 0.006 0.015 0.008 0.0035 02 0.04 0.17 0.81 0.008 0.002 2.8 0.006 0Ό15 0008 0.0035 D3 037 0.17 1.40 αο〇7 0.002 0.9 0.006 0.015 0.007 0.0035 D4 0.07 0.05 0.81 0Ό06 0.002 2.4 0.006 0.014 0.008 0.0035 D5 0.10 0.19 1.11 0.007 0.002 1.1 0.004 0.015 0.007 0.0032 D6 0.13 0.05 0.91 0.007 0.003 1.2; 0.005 丨 0.014 0.006 0.0037 D7 0.06 0.19 1.41 0.007 0.002 1.3 0.005 0.012 0.006 0.0042 D8 0.06 0.22 1,11 0.006 0.003 2.1 0.005 0.014 0.006 0.0035 D9 0.0S 0.15 1.21 0.007 0.003 1.4 0.006 0.015 0.006 0.0035 D10 0.12 0.11 1.01 0.007 αο〇2 1.4 0.005 0.014 0Ό09 0.0035 D11 0.13 0.14 0.91 0.006 0.002 1.5 0.006 0.015 0.008 0.0035 D12 0.06 0.14 1.41 0.007 0.002 1.6 0.005 0.014 0.008 0.0032 D13 0.06 0.22 1.11 0.007 0.002 2.4 0.005 0.014 0Ό07 0.0035 D14 0.09 0.21 1.31 0.008 0.002 1.4; 0.005 0.014 0.0G8 0.0035 D15 0.13 0.19 1.01 0.007 0.002 1.6 0.005 0.014 0.0 07 0.0035 D16 0.12 0.22 0.91 0.007 0.003 2.1 0.006 0.015 0.006 0.0035 D17 0.13 0.17 1.01 0.006 0.002 1.7 0.005 0.014 0.006 0.0032 D18 0.12 0.15 1.11 0.008 0.002 1.5 0.005 0.014 0.006 0.0037 D19 0.06 0J4 1.41 0.007 0.002 1.6 0.005 0.014 0.00 0.0041 020 0.06 0.14 1.40 0.007 0.002 1.6 0.005 0.014 0Ό09 0.0041 D21 0.06 0.10 1.21 0,007 0.002 1.7 0.006 0.015 0.010 0.0035 D22 0.06 0.22 1.11 0.007 0.002 1.8 0.005 0.014 0.008 0.0055 D23 0.06 0.16 1.31 0.008 0.004 1.8 0.005 0.014 0.008 0.0035 0.0018 D24 0.06 0.17 1.40 0.008 0 04 0.008 0.0037 0.0019 D25 0.06 0.12 1.20 0.007 0.002 2.1 0.006 0.0Ϊ5 0.007 0.0033 0.0016 D26 0.06 0.15 1.00 0.007 0.002 2.6 0.005 0.014 0.008 0.0036 D27 0.06 0.11 1.21 0.007 0.002 1.8 0.015 0.015 0.007 0.0035 0.0014 0.002 D28 0.06 0.23 1.00 0Ό07 0.002 1.9 0.005 0: 014 0.006 0.0035 0.0018 D29 0.06 0.17 1,20 0.008 0.004 1.8 0.005 0.014 0.006 0.0035 0.0036 D30 0Ό6 0.12 1.20 0.007 0.002 1.7 0.006 0.015 0.006 0.0035 0.0009 D31 0.06 0.12 1.20 0.007 0.002 1.9 0.006 0.015 0.006 0.0035 0.0016 D32 0.07 0.15 1.21 0.007 0.G03 1.4 0.028 0.014 0.009 0.0032 0.0015 D33 0.08 0.13 1.21 0.00 0.002 1.3 0.013 0.014 0.010 0.0052 0.0017 D34 0.08 0.19 1.21 0.008 0.003 1.5 0.013 0.025 0.008 0.0076 0.0012 0.0012 D35 0.08 0.19 1.21 0.010 0.002 1.2 0.021 0.014 0.008 0.0035

19 200538561 Table 1 of 1

Classification REM 〇8 Cu Cr Mo V Ceq Ni / Mn 10 x Ceq -3 Judgment * 0.37 1.22 0.7 〇0.36 3.46 0.6 〇0.36 0.64 0.6 〇0.37 2.96 0.7 〇0.36 0.99 0.6 〇0.36 1.32 0.6 〇0.38 0.92 0.8 〇0.39 1.89 0.9 〇0.39 1.16 0.9 〇0.38 1.39: 0.8 〇0,38 1.65 0.8 〇0.40 1.13 1.0 〇0.41 2.16 1.1 〇0.40 1.07 1.0 〇0.41 1.58 1.1 〇0.41 2.31 1.1 〇Inventive steel 0.41 1.68 1.1 〇0.41 1.35 1.1 〇0.40 1.13 1.0 〇 0.0012 0.40 1.14 1.0 〇0.4 ΟΛΟ 1.40 1.0 〇0.0023 0.2 0.41 1.62 1.1 〇0.0019 0.40 1.37 1.0 〇0.0019 0.0008 0.40 1.14 1.0 〇0.0017 0.0009 0.40 1.75 1.0 〇0.0220 0.0020 0.0011 0.40 2.60 1.0 〇0.0017 0.3 0.40 1.49 1.0 〇 0.0030 0.0009 0.2 0.017 0.40 1.90 1.0 〇0.0029 0.0009 0,3 0.40 1.50 1.0 ο 0.0028 0.0009 0.2 0.05 0.40 1.42 1 .0 ο 0.0023 0.0009 0.2 0.037 0.41 1.58 1.1 〇 0.0018 0.0012 0.4 0.39 1.16 0.9 〇 0.0020 0.0009 0.3 0.39 1.07 0.9 〇 0.0015 0.0035 0.4 0.41 1.24 1.1 〇 0.36 0.99 I 0.6 〇

20 200538561 Table 1 of 2

Distinguishing symbol c Si Μη Ρ S Ni Nb Al Ti Ν Ca Mg Invention steel D36 0.0S 0.19 1.21 0.010 0.003 1.5 0.015 0.015 0.008 0.0035 D37 0.10 0.19 1.11 0.006 0.002 1.9 0.0151 0.035 0.007 0.0035 D38 0.11 0.14 0.91 0.006 0.003 1.7 0.031 0.014 0.008 0.0035 D39 0.12 0.14 1.11 0.008 0.002 1.8 0.029 0.032 0.007 0.0032 D40 0.10 0.14 1.21 0.009 0.002 1.6 0.030 0.014 0.006 0.0037 D41 0.10 0.24 1.21 0.006 0.002 1.5 0.031 0.028 0.006 0.0042 D42 0.08 0.24 1.31 0.005 0.003 1.6 0.032 0.014 0.006 0.0035 D43 0.03 0.22 1.31 0.008 0.0031 0.0031 2.5 0.035 0.038 0.006 0.0035 D44 0.06 0.24 0.81 0.007 0.003 3,2 0.035 0.014 0.009 0.0035 D45 0.03 0.11 1.51 0.007 0.002 1.8 0.035 0.014 0.010 0.0035 D46 0.07 0.11 1.21 0.007 0.003 1.4 0.028 0.014 0.00 0.0032 0.0015 0.0047 D47 0.07 0.28 1.21 0.007 0.003 1.4 0.028 0.014 0.009 0.0032 0Ό015 D48 0.06 0.11 1.20 0.008 0.004 1.8 0.005 0.014 0.006 0.0035 0.0018 D49 0.06 0.28 1.20 0.008 0.004 1.8 0.005 0.014 0.006 0,0035 0.0017 Compare steel C1 0.04 0.14 1.90 0.0 07 0.002 0.1 0.008 0.012 0.008 0.0032 C2 0.04 α〇9 Κ60 0.006 0.003 0.8 0.009 0.019 0.008 0.0037 C3 0.06 0.09 1.70 0.007 0.003 0.2 0.005 0.012 0.008 0.0042 C4 0.09 0.11 1.60 0.008 0.003 0.0 0.006 0.015 0.007 0.0035 0.005 C5 0.10 0.14 1.30 0.008 0.002 0.7 0.005 0.014 0.008 0.0035 G6 0.13 0.22 1.20 0.007 0.002 0.5 0.003 0.012 0.008 0.0035 C7 0.06 0.11 1.90 0.007 0.002 0.1 0.006 0,015 0.008 0.0035 C8 0.06 0.14 1.60 G.007 0, 004 0.8 0.005 0.014 0Ό07 0.0032 C9 0.09 0.17 1.40 0.008 0.002 0.9 0.005 0.014 0.008 0.0037 C10 0.11 0.23 1.30 0.007 0.002 0.8 0.006 0.015 0.007 0.0042 C11 0.06 0.16 2.00 0.008 0.004 0.1 0.005 0.014 0.006 0.0035 C12 0.06 0.11 1.60 0.007 0.002 1.1 0.006 0.015 0.006 0.0035 C13 0.10 0.25 1.70 0.006 0.003 0.2 0.006 0.015 0.006 0.0035 C14 0.12 0.14 1.40 0.007 0.002 0.7 0,005 0.014 0.006 0.0035 C15 0.09 0.12 1.60 0.008 0.003 0.8 0.015 0.013 0.009 0.0032 C16 0.08 0.24 1.50 0.008 0.003 0.6 0.035 0.013 0.010 0.0037 C17 0.09 0.14 1.20 0.007 0.002 1.4 0.045 0.014 0.008 0.0042

21 200538561 Table 1 of 3 Differentiate REM 〇3 Cu Cr Mo V Ceq Ni / Μπ 10 x Ceq -3 Judgment * Invention steel 0.03 0.40 1.24 1.0 〇0.41 1.71 1.1 0 0.045 0.38 1.87 0.8 〇0.43 1.62 1.3 〇0.2 0.42 1.32 1.2 〇 0.40 1.24 1.0 〇0.41 1.22 1.1 〇0.42 1.91 1.2 〇0.41 3.95 1.1 〇0.40 1.19 1Ό 〇0.0018 0.4 0.39 1.16 0.9 〇0.0018 0.4 0.39 1.16 0.9 〇0.0026 0.0012 0.3 0.40 1.50 1.0 〇0.0026 0.0012 0.3 0.40 1.50 K0 〇Comparative steel 0.36 0.05 0.6 X 0.36 0.50 0.6 X 0.36 0.12 0.6 X 0.36 0.00 0.6 X 0.36 0.54 0.6 X 0.36 0.42 0.6 X 0.38 0.05 0.8 X 0.38 0.50 0.8 X 0.38 0.64 0.8 X 0.38 0.62 0.8 X 0.40 0.05 1.0 X 0.40 0.69 1.0 X 0.40 0.12 1.0 X 0.40 0.50 1.0 X 0.41 0.50 1.1 X 0.37 0.40 0.7 X 0.38 1.17 0.8

* Those who satisfy N i / Μ n g 1 〇 X C e Q — 3 are recorded as 0, those who are not satisfied are recorded as X.

22 200538561 Table 2

Classification Symbol Manufacturing method Plate thickness (mm) Female g 3 (t / 2) u Number of oxides 2) (pieces / mm2) Tensile strength (MPa) Drop stress (Mpa) vE-4. (J) Inventive steel D1 TMCP 60 576 476 231 D2 TMCP 65 565 465 229 D3 DO-T 70 576 456 225 D4 TMCP 60 576 476 231 D5 D〇- T 55 605 485 238 D6 TMCP 65 565 465 229 D7 TMCP 70 560 460 219 D8 TMCP 80 541 441 213 D9 DQ -T 60 601 481 225 D10 TMCP 65 570 470 223 D11 TMCP 75 550 450 216 D12 TMCP 80 545 445 208 D13 TMCP 55 596 496 224 D14 DQ-T 65 595 475 217 D15 TMCP 70 566 466 213 D16 TMCP 65 578 478 214 D17 DQ-T 70 .588 468 211 D18 TMCP 75 556 456 210 D19 TMCP 70 565 465 214 D20 TMCP 70 575 482 214 D21 DQ-T 70 585 465 214 D22 TMCP 70 566 466 213 D23 TMCP 65 575 475 218 900 D24 DQ-T 60 605 485 221 1200 D25 TMCP 70 565 465 214 1300 D26 TMCP 80 545 445 209 1100 D27 TMCP 70 565 465 214 900 D28 TMCP 65 574 474 218 1800 D29 TMCP 60 585 485 221 2100 D30 DOT 65 594 474 218 2400 D31 TMCP 60 587 487 219 1900 D32 TMCP 70 563 463 217 700 D33 TMCP 65 572 472 221 600 D34 DQ-T 80 567 447 207 1400 D35 TMCP 70 555 455 225

23 200538561 Table 1 of 2

Butt] Back welding conditions 3) FL ~ HA21mm 4) Average r particle size (/ im) HAZ toughness 5) Differentiating welding method heat (kJ / mm) FL / vE ^ 0 (J) FL + 1 mm / vE. 40 (J) EGW 39 480 140 128 EGW 42 520 135 124 ESW 85 770 116 106 ESW 73 660 123 113 ESW 67 605 127 117 EGW 42 520 135 124 ESW 85 770 116 106 EGW 51 640 124 114 EGW 39 480 140 128 ESW 79 715 119 109 EGW 48 600 128 117 EGW 51 640 124 114 EGW 35 440 144 132 ESW 79 715 119 109 ESW 85 770 116 106 EGW 42 520 135 124 Invention steel EGW 45 560 131 120 EGW 48 600 128 117 EGW 45 560 131 120 EGW 45 560 171 156 ESW 85 770 116 106 EGW 45 560 184 180 ESW 79 180 207 189 EGW 39 165 214 196 EGW 45 152 221 203 EGW 51 185 204 187 EGW 45 180 207 189 ESW 79 167 213 195 EGW 39 184 205 188 EGW 42 165 214 196 EGW 39 184 205 188 EGW 45 180 207 189 EGW 42 164 214 197 ESW 98 180 196 180 ESW 85 660 123 113

24 200538561 Table 2 of 2

Manufacturing method of distinguishing marks Plate thickness (mm) Female; B (t / 2) &quot; Number of oxides a (piece / mm〇tensile strength (MPa) Drop stress (MPa) vE-4〇 &lt; J) Invention steel D36 DQ-T 70 584 464 215 D37 TMCP 65 578 478 214 D38 TMCP 60 581 481 226 D39 TMCP 70 571 471 208 D40 DQ-T 80 570 450 203 D41 TMCP 70 565 465 214 D42 TMCP 65 576 476 216 D43 TMCP 60 589 489 217 D44 TMCP 65 577 477 215 D45 DQ-T 60 605 485 221 D46 TMCP 70 553 465 217 900 D47 TMCP 70 579 481 217 400 D48 TMCP 60 578 485 221 2300 D49 TMCP 60 592 485 221 1500 Compare steel G1 TMCP 70 556 456 225 C2 DQ-T 60 595 475 233 C3 TMCP 75 544 444 224 C4 TMCP 60 574 474 234 C5 TMCP 60 576 476 232 C6 TMCP 55 586 486 236 C7 DQ-T 60 601 481 226 C8 TMCP 60 580 480 227 C9 TMCP 60 581 481 226 C10 TMCP 60 580 480 227 C11 DQ-T 70 585 465 214 C12 TMCP 60 585 485 221 C13 TMCP 70 564 464 215 C14 TMCP 65 575 475 218 C15 TMCP 55 598 498 222 C16 DQ-T 65 588 468 226 C17 TMCP 60 581 481 226

25 200538561 Table 2-3 Welding conditions for 1 butt joint 3) FL to HAZlmm 4) HAZ toughness 5) Differentiating welding method heat (kJ / mm) average r particle size (ym) FL / vE_40 (J) FL + 1mm / vE_4〇 (J) ESW 85 605 127 117 EGW 42 520 135 124 ESW 73 770 116 106 EGW 45 640 124 114 EGW 51 480 140 128! ESW 85 715 119 109 Invention steel EGW 42 600 128 117 EGW 39 640 124 114 EGW 42 440 144: 132 ESW 73 715 119 109 EGW 45 145 225 206 EGW 45 195 200 183 EGW 39 164 214 236 EGW 39 185 204 225 ESW 85 770 36 25 EGW 39 480 57 40 EGW 48 600 46 32 EGW 39 480 57 40 EGW 39 480 57 40 ESW 67 605 45 32 EGW 39 480 57 40 EGW 39 480 57 40 Comparative steel EGW 39 480 57 40 EGW 39 480 57 40 ESW 85 770 36 25 EGW 39 480 57 40 EGW 45 560 49 34 EGW 42 520 53 37 ESW 67 605 45 32 EGW 42 520 53 37 EGW 39 480 57 40 1) The center position of the plate thickness, YS and TS are the average of 2 test pieces, and the Chabbit absorption energy (vE-40 at -40 ° c) ) Is an average of 3 test pieces.

2) Make an extraction copy from anywhere on the steel plate. Observe 100 fields of view or more with an electron microscope at 10,000 times (observation area is 10000 // m2 or more). However, it is observed that the particles under 0.1 // m increase the appropriate magnification. In elemental analysis of particles having a projected area diameter of 0.005 to 0.5 // m, those containing oxides are calculated and converted to the number per 1 mm2. 3) EGW: electric welding, ESW: electric slag welding, the welding heat is the average value of the total length of the welding, and the same welding material is used in each welding method. 4) The average grain size of old Vostian iron crystal grains included in a plane having a plate thickness direction of 2 mm and a surface of FL to HAZ1 mm centered on the center of the plate thickness. 26 200538561 Measured by section method. The iron grains connected to the network were measured as the grain boundaries of the old Vostian iron grains. 5) FL scoring is to scribe WM and HAZ equally, and vE-40 at each scoring position is a 3-piece test. The average of the slices. 5 Industrial Applicability The present invention provides a thick steel plate that can meet the strict toughness requirements for damage such as ships, marine structures, and high-rise buildings. It has a great effect on the industry and further improves the safety of structures. Considered in the sense of sex, its contribution to society is also considerable. 10 [Brief Description of the Drawings] Figure 1 shows the welding thermal cycle equivalent to 45kJ / mm. Figure 2 is a graph showing the relationship between Ni / Mn, Ceq, and reproduced HAZ toughness. Fig. 3 is a graph showing the effect of improving the reproducibility of HAZ toughness by dispersing fine oxides or using B effectively. 15 [Description of main component symbols]

27

Claims (1)

200538561 5 10 15 20 X. Scope of patent application: 1. A high-strength thick steel plate with excellent low-temperature toughness in a welded heat-affected zone under large-input heat welding, containing the following elements: C: 0.03 ~ 0.14 mass%; Si: 0.30 mass% The following; Mn: 0.8 to 2.0 mass%; P: 0.02 mass% or less; S: 0.005 mass% or less; A1: 0.001 to 0.040 mass%; Ν: 0.0010 to 0.0100 mass%; Ni: 0.8 to 4.0 mass%; Ti: 0.005 to 0.030% by mass; and Nb: 0.003 to 0.040% by mass; and Ni and Mn satisfy the following formula [1], namely: Ni / Mn ^ 10xCeq-3 (0.36 &lt; Ceq &lt; 0.42) [1] However, Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 The rest is iron and inevitable impurities. 2. If the high-strength thick steel plate with excellent low-temperature toughness in the welded heat-affected zone under large-entry heat welding in item 1 of the scope of the patent application, further contains one or more of the following elements, namely: Ca: 0.0003 ~ 0.0050% by mass; Mg: 0.0003 to 0.0050% by mass; and REM: 0.001 to 0.030% by mass; and 〇: 0.0010 to 0.0050% by mass and 100 pieces / mm2 or more cast 28 200538561 10 15 20 An oxide having a shadow area diameter of 0.005 to 0.5 // m. 3. For example, in the welding process under item 1 or 2 of the scope of patent application, the high-strength thick steel plate with excellent low-temperature toughness at the heat-affected zone, further containing B: 0.0005 to 0.0050 mass%. 4. For example, the high-strength thick steel plate with excellent low-temperature toughness in the welded heat-affected zone under large-entry heat welding in item 1 of the scope of the patent application, further contains one or more of the following elements, namely: Cr ·· 0.1 ~ 0.5% by mass; Mo: 0.01 to 0.5% by mass; V ·· 0.005 to 0.10% by mass; and Cu: 0.1 to 1.0% by mass. 5. If the high-strength thick steel plate with excellent low-temperature toughness in the welded heat-affected zone under large-entry heat welding in item 2 of the scope of patent application, further contains one or more of the following elements, namely: Cr: 0.1 to 0.5 % By mass; Mo: 0.01 to 0.5% by mass; V: 0.005 to 0.10% by mass; and Cu: 0.1 to 1.0% by mass. 6. If the high-strength thick steel plate with excellent low-temperature toughness in the welded heat-affected zone under large-entry heat welding in item 3 of the scope of patent application, further contains one or more of the following elements, namely: Cr: 0.1 to 0.5 Mass%; Mo .. 0.01 to 0.5 mass%; V .. 0.005 to 0.10 mass%; and 29 200538561 Cu: 0.1 to 1.0 mass%. 30