TW200827459A - A steel excellent in high toughness at weld heat-affect zone - Google Patents

Abstract

The present invention provides a steel excellent in high toughness at weld heat-affect zone, characterized in that the steel containing; C: 0.02 to 0.06%, Si: 0.05 to 0.30%, Mn: 1.7 to 2.7%, P: less than 0.015%, S: less than 0.010%, Ti: 0.005 to 0.015%, O: 0.0010 to 0.0045%, N: 0.0020 to 0.0060%, and Al, Nb and V are controlled to Al: less than 0.004%, Nb: less than 0.003% and V: less than 0.030% respectively as an impurities amounts, and the balance being Fe and unavoidable impurities, and further satisfying the CeH value formulated in the following expression (A). CeH =C+1/4Si-1/24Mn+1/48Cu+1/32Ni+1/0.4Nb+1/2V …. (A) where the steel components of C, Si, Mn, Cu, Ni, Nb and V are mass%, respectively.

Description

200827459 IX. INSTRUCTIONS: TECHNICAL FIELD OF THE INVENTION The present invention relates to a steel having excellent toughness in a fusion heat affected zone (HAZ) with a small heat input amount welded to a medium heat input amount, and its manufacture law. C Prior Art 3 Background Art The HAZ toughness of low alloy steel is controlled by various factors: (1) crystal grain size; (2) high carbon amount of granita iron (M*), upper toughened steel (Bu) and side plates. 10 pieces of fermented iron (FSP: Ferrite Side Plate) and other hardened phases; (3) precipitation hardening state; (4) presence or absence of grain boundary embrittlement; and (5) microsegregation of elements. We know that the above factors will have a great impact on the edge of the blade, and there are many practical techniques for improving the toughness of the HAZ. The above-mentioned factors of hindrance toughness can be said to be caused by the addition of elements, so that the toughness can be improved by reducing the content of the alloying elements. However, structural steel must be high in strength, so alloying elements must be added. That is, both the required strength and the required toughness are exactly the opposite from the viewpoint of the alloying element content, and therefore a technique for improving the toughness which does not depend on the alloying elements is required. 20 A particularly excellent conventional technique is to use a Ti oxide to refine the microstructure of a steel substantially free of gossip, in addition to adjusting the balance of Ding and N, suppressing the precipitation and reduction of Tic. In the case of precipitation hardening and improvement of toughness (JP-A No. 5-247531). In the above case, the toughness of the fusion heat affected zone will be determined by the influence of the microstructure and the hardening layer containing Μ*, and Fu 5 200827459, in order to solve the toughness of the matrix matrix by Ni, etc. in the prior art. The problem. However, the addition of expensive alloying elements such as Cu and Ni, which are indispensable for realizing this technology, leads to an increase in manufacturing cost, and becomes a high-strength steel excellent in the manufacture of CTOD (Crack Tip Opening Displacement). Obstacles. In the present invention, the steel of the above invention does not substantially contain A1 and Nb. However, in the above invention, the problem that the toughness is deteriorated when the content of c is increased and the content of Μ is increased is not solved. Further, the adverse effects of Nb and V of impurities on toughness are also worrying. In the Japanese Patent Laid-Open No. Hei 5-247531, the use of niobium oxide, addition of Nb, and improvement of the content of Μη are employed. Thereby, the Welstian iron-fertilizer iron metamorphic onset temperature can be reduced, and the production of the nucleation phase can be reduced, and at the same time, a suitable microstructure can be obtained, which can satisfy the characteristics of 〇D. However, the invention of Japanese Laid-Open Patent Publication No. 2003-147484

15 can not meet, the more stringent -40 required for the joint. CTThe following CT0D features. DISCLOSURE OF THE INVENTION The present invention provides a technique for producing high-strength steel having excellent properties in a small to medium input sample at a low cost. By the small ~ joint...the early edge of the shirting area, especially the keynote = the CT0 characteristics of the heat-healing part is extremely good. The steel of the present invention is based on mass % 6 200827459, and the steel contains: C ·· 0·02~〇·〇6%; Si: 0.05~0.30%; Μη: 1.7~2·7%; P: 0.015% or less ;S : 〇·〇ι〇〇/^以下;: 0 005 〜0.015% ; Ο ·· 0.0010~0.0045% ; and N : 〇·0020~0·0060%, and the remainder consists of iron and inevitable impurities In this case, the amount of impurities mixed is limited to Α1: 0.004% or less, Nb: 0.003% or less, and V··0.030% or less, and CeH represented by the following formula (A) is 0.04 or less, CeH. =C+l/4Si-l/24Mn+l/48Cu+l/32Ni+l/0.4Nb+l/2V ··· (A) Again, C, Si, Μη, Cu, Ni, Nb, and V respectively Indicates steel composition (% by mass). 10 (2) Steel having excellent toughness as in the fusion heat affected zone of (1), wherein the aforementioned

CeH is in the range of 0.01 or less. (3) The steel having excellent toughness in the heat-affected zone of the fusion of (1) or (2), in terms of mass%, further contains one or two of Cu: 0.25% or less and Ni: 0.50% or less. (4) A method for producing a steel having excellent toughness in a heat-affected zone, wherein a steel sheet satisfying the steel component of (1) and a steel sheet of CeH is heated to a temperature of ll 〇〇 ° C or less, and then subjected to a processing heat treatment. (5) A method for producing a steel having excellent toughness in a heat-affected zone, wherein the steel component satisfying the steel component of (3) and the steel sheet of ceH are heated to a temperature of 1100 ° C or lower and then subjected to processing heat treatment. Brief Description of the Drawings Figure 1 shows 800 to 5 inches. A diagram of the relationship between cooling time and M* rate. Figure 2 is a graph showing the relationship between CeH and CTOD characteristics. 7 200827459

t EMBODIMENT] J. BEST MODE FOR CARRYING OUT THE INVENTION According to the study of the present inventors, the CTOD characteristics of HAZ at the time of fusion of small to medium heat input (plate thickness 50 mm, 1-5 to 6.0 kJ/mm) (-40 °C has a CT 〇D characteristic at a temperature of 5°), and the toughness of an extremely local region has a great influence. It is extremely important to control the microstructure of this part and to reduce the embrittlement element system. The CTOD characteristic of Lu's is not controlled by the average characteristics of the material, but by the local embrittlement area. Even if only a small part of the steel is the area that causes embrittlement, it will obviously damage the CT〇D of the steel plate. characteristic. 10 Specifically, the local area that has the greatest impact on CTOD characteristics is the hardened phase such as M* and side slab ferrite (FSP). In order to suppress the generation of the hardened phase described above, the conventional technique suppresses the hardenability of steel to a low level, which is a factor that hinders the south strength. The following matters can be known from the features of the present invention, and the present invention can realize a steel having a high HAZ blade. That is: 1) In the small to medium heat input amount welding HAZ, generally the cooling time after refining is within 60 sec, the inventors have found that under the above cooling conditions, if the C content is very low, by appropriately Control of other embrittlement elements, even if Μη is added to about 2.7%, does not produce m 20 * which adversely affects toughness. Figure 1 shows the M* fraction when Μη is changed from 1.73⁄4 to 2.7% with 0.05% C - 0.15% Si. It can be seen that even if the amount of %11 changes, the cooling time of 8〇〇~500 C is Within 6 sec, the M* fraction is extremely small. As a result, it is possible to increase the amount of the ^^^ which cannot be added in a large amount in the past because the toughness is deteriorated. 8 200827459 2) It was found that the A1-free matrix steel can be adjusted to an appropriate steel composition. 3) Undesirable toughness reduction factors can be removed by limiting the impurities Nb, V present in the steel below a certain limit. That is, by using the A1-free matrix steel, Ti crucible can be surely produced to effectively improve the blade edge. By combining the above three points, it is possible to achieve good ctod characteristics under severe temperature conditions of less than _20 C in the HAZ in the small to medium heat input that cannot be achieved in the past. Even in the case where very little M* is generated, it is necessary to control the amount of the embrittlement element 10 such as C, Si, Ni, Nb, V, and the like. Specifically, the value (CeH) of C+l/4Si-1/24Mn+l/48Cu+l/32Ni+l/0.4Nb+l/2V must be controlled within a predetermined range. Fig. 2 is a view showing a steel having a steel composition of 0.05% C-0.15% Si-1.7 to 2·7% Μη in a vacuum melting of 2 〇kg to reproduce a steel plate made of the above-mentioned steel by a heat-cycle 15-ring device. Those who performed the CTOD test on the thermal history of the actual fusion joint.

T5c0.1 (670.9CeH-67.6) is the lowest value of the three CT〇D test values at each test temperature, which shows a temperature of 〇.lmm. It is known that CeH decreases and is slightly straight, and the mo.1 (CTOD characteristic) is more It is getting better. When CeH is reduced to about 20 〇〇1, ΤδοΟ.Ι can reach -6 (Tc. That is, by satisfying the elements of the steel of the present invention and controlling CeH, the required CTOD characteristics can be obtained. In the present invention, The value of CeH required to control the value of CeH is one of the characteristics of the invention. In addition to controlling the value of (10), it is necessary to make other alloying elements contain an appropriate amount in order to achieve both high strength and excellent CTOD characteristics. Steel. The scope and reason for the detailed description are as follows. For the tooth decay to a sufficient strength, the amount of C must be more than 2% of 〇·〇, but if it exceeds 0.06%, the boring property of the refining HAZ will be deteriorated and it will not be satisfied. Good CTOD characteristics, so the upper limit is set to 0. 〇 6%. 5 Since Si hinders HAZ_, it is preferable to obtain a good HAZ edge, but it is preferable to use less. Therefore, in order to remove oxygen, it is necessary to add more than 0.05% of Si. However, when the content exceeds 〇.3〇%, the HAZ toughness is impaired, so 0.30% is the upper limit. The Μη system can effectively adjust the micro-scale weaving. Cheap elements, and can reduce 1〇CeH, adding Μη also does not harm small In order to increase the strength of the steel enthalpy, the amount of Μη is increased. However, if it exceeds 2.7%, segregation of the steel sheet is promoted, and Bu which is harmful to toughness is likely to be generated, so it will contain The upper limit is set to 2.7%, and if it is less than 17%, the effect is small, so the lower limit is set to 1.7%. In addition, from the viewpoint of toughness, it is preferably more than 2%. 15 P, S from the mother From the viewpoint of material toughness and HAZ toughness, it is preferable to use less, but excessive reduction of these contents will also limit industrial productivity, so the upper limit is not 0.015%, 0.010%, respectively. 〇 〇, 〇 005% is more preferable. In the present invention, although the element is not intentionally added, it cannot be prevented from being an impurity and is incorporated into the steel. A1 forms an A1 oxide and hinders the generation of butyl lanthanum oxide 20, so It is preferable to use a small amount, but excessively lowering the content limits industrial productivity, so the upper limit is 0.004%. Although Τι can make the microstructure finer and greatly improve the toughness by producing Τ1 oxide, it is generated when too much yttrium is contained. Tie, which makes the toughness of the crucible worse, so it is appropriate to use 0.005~0.015%. 10 200827459 0 is a necessary element for the formation of a large amount of Ti oxide. If the content is less than 0.0010%, the effect is small. On the other hand, if it is more than 0 0045%, coarse Ti oxide is formed, and the toughness is extremely deteriorated. The content range is set to 0.0010 to 0.0045%. 5 N will form fine Ti nitride and improve the toughness of the base material or HAZ toughness. It is an essential element, but the content is less than 0 002%, the effect is small, and more than 0.006% will be When the steel sheet was produced, surface flaws were generated, so the upper limit was set to 0.006%. Further, 'Nb, V is an embrittlement element in nature, as shown in the formula (A), having a large coefficient of 10, since the presence of such a large increase in CeH, the HAZ toughness is significantly deteriorated, and thus the present invention Not deliberately added. When Nb and V are mixed as impurities in the steel, the amount of Nb must be limited to 0.003% or less in order to ensure the toughness. Further, it is necessary to limit the V content to 0.030% or less, more preferably 0.020% or less. 15 Adding Cu and Ni can prevent HAZ from being deteriorated, and can improve the strength of the base metal, and can effectively improve the characteristics, but it will increase the manufacturing cost. Therefore, when adding, the upper limit of the content is set to Cu: 0.25. %, Ni: 0-50%. Even if the steel component is limited as described above, the right structure is not formed by using the appropriate manufacturing method 20, and the desired effect cannot be achieved. Therefore, manufacturing conditions must also be considered. The steel of the present invention is industrially preferably produced by a continuous casting method. The reason is that the solidification cooling rate of the molten steel is fast, and a large amount of fine Ti oxide and Ti nitride can be formed in the steel sheet. When rolling the sheet steel, it must be reheated to a temperature of 1100 C or less. When the reheating temperature is greater than η (8). In the case of ruthenium, the Ti nitride is coarsened and the base material toughness is deteriorated, and the effect of improving the haz toughness cannot be achieved. Then, the manufacturing method after reheating must use a processing heat treatment. The reason for this is that even if excellent HAZ toughness is obtained, if the base material has poor toughness, it cannot be used as a good steel. The method of processing heat treatment may be as follows: · · · U control rolling; 2) control calendering - accelerated cooling; 3) direct quenching after calendering _ tempering, etc., suitable method is controlled rolling - accelerated cooling method and direct quenching - tempering after rolling law. Further, after the steel is produced, even if it is heated to a temperature lower than the transformation point of Ar3 by the purpose of dehydrogenation or the like, the characteristics of the present invention are not impaired. Further, the above method is an example of the method for producing steel of the present invention, and the method for producing the steel of the present invention is not limited to the above method. Example 15 Thick steel of various steel compositions was produced in a converter_continuous casting-thick plate step

The plate is then subjected to a CT〇D test of the strength of the base metal or the joint. The hybrid system uses the submerged arc _ (SAW) method used for the general test fusion. The non-connected permeation line (FL) produces a K-angle perpendicularly, and the heat input amount of 4·5~5•(4)/face is used. Conduct the test. The CTOD test was carried out by introducing a 50% fatigue crack at the position of FL 20 at a size of t (thickness) x 2t. (Table shows the examples and comparative examples of the present invention.

The steel sheet produced by the present invention (the steel sheet of the present invention) exhibits a drop strength (YS) of 430 N/mm 2 or more, and _2 (rc, _4 (rc, _6 (rC2CT〇D values are all good for 0.27 mm or more). 12 200827459 In contrast, the strength or CTOD of comparative steels 21 to 26 is worse than that of the steel of the present invention, and does not have the necessary characteristics that can be used for steel plates in severe environments. Nb makes the Nb content of the steel plate too much, and increases the CeH value, so its CTOD value is lower. Comparative steel 22 contains too much C, and CeH 5 is too high, so the CTOD value is lower. Compare steel 23 Although the CeH of 24 is low, the content of A1 is too high, so the formation of Ti oxide is insufficient and the microstructure cannot be sufficiently fined. Although the CeH of the comparative steel 25 is the same level as the inventive steel, the C is too small, and the C is too small. Too much, so the strength of the base metal is low, and the CTOD value is also low. However, compared with the excessive amount of impurities Nb in the comparative steel 26, even if CeH 10 is low, the base metal strength and CTOD value are also low. 13 200827459 1 Table steel distinguishes C Si Μ Ρ Ρ S Cu Ni Nb V Ti A1 N 0 CeH Inventive Example 1 0.021 0.13 2.65 0.00 5 0.002 0.24 0.42 < 0.001 < 0.001 0.010 0.003 0.0042 0.0023 -0.039 2 0.023 0.10 2.57 0.006 0.003 0.001 <0.001 0.009 0.004 0.0035 0.0025 -0.057 3 0.025 0.11 2.47 0.004 0.003 0.003 <0.001 0.011 0.003 0.0043 0.0026 -0.043 4 0.025 0.15 2.39 0.005 0.002 0.15 0.24 <0.001 <0.001 0.011 0.002 0.0035 0.0023 -0.026 5 0.031 0.08 2.38 0.005 0.008 0.15 0.30 0.002 <0.001 0.009 0.003 0.0033 0.0031 -0.031 6 0.032 0.09 2.30 0.006 0.002 <0.001 0.020 0.009 0.003 0.0036 0.0027 -0.031 7 0.036 0.11 2.27 0.012 0.003 0.35 0.001 <0.001 0.011 0.004 0.0040 0.0022 -0.018 8 0.037 0.12 2.28 0.005 0.004 0.23 0.001 <0.001 0.009 0.003 0.0044 0.0033 -0.021 9 0.038 0.12 2.16 0.006 0.005 <0.001 <0.001 0.011 0.002 0.0038 0.0018 -0.022 10 0.040 0.15 2.13 0.009 0.003 0.002 0.025 0.011 0.003 0.0041 0.0020 0.006 11 0.040 0.08 2.06 0.005 0.007 <0.001 <0.001 0.012 0.003 0.0043 0.0028 -0.026 12 0.043 0.11 2.03 0.010 0.002 0.002 <0.001 0.010 0.002 0.0033 0.0032 -0.009 13 0.044 0.10 1.94 0.007 0.001 0.003 <0.001 0.013 0.003 0.0035 0.0021 -0.004 14 0.045 0.14 1.99 0.006 0.002 <0.001 0.020 0.008 0.003 0.0025 0.0038 0.007 15 0.048 0.11 1.87 0.004 0.001 0.001 <0.001 0.010 0.004 0.0031 0.0025 0.000 16 0.048 0.09 1.85 0.006 0.002 0.002 <0.001 0.009 0.003 0.0040 0.0024 -0.002 17 0.050 0.12 1.80 0.006 0.003 <0.001 <0.001 0.011 0.002 0.0036 0.0017 0.005 18 0.054 0.11 1.76 0.005 0.008 0.003 0.027 0.010 0.003 0.0030 0.0023 0.029 19 0.057 0.10 1.78 0.006 0.002 0.001 0.015 0.009 0.003 0.0033 0.0026 0.018 20 0.059 0.13 1.73 0.006 0.003 0.13 0.15 <0.001 <0.001 0.010 0.002 0.0042 0.0022 0.027 Comparative Example 21 0.051 0.14 1.85 0.006 0.003 0.042 0.010 0.002 0.0041 0.0030 0.114 22 0.094 0.12 1.88 0.008 0.004 0.026 0.023 0.011 0.003 0.0038 0.0032 0.122 23 0.045 0.16 2.18 0.007 0.004 0.015 0.013 0.024 0.0036 0.0010 0.032 24 0.043 0.11 2.11 0.006 0.002 0.018 0.009 0.031 0.0033 0.0038 0.028 25 0.016 0.13 2.2 0 0.009 0.004 0.017 0.010 0.003 0.0031 0.0008 -0.001 26 0.048 0.14 2.00 0.008 0.004 0.004 0.010 0.003 0.0031 0.0024 0.010 14 200827459 Section 2 Steel Manufacturing Conditions Base Material Properties Molding Joint Toughness, dc (mm) Sheet Steel Reheating Temperature 加工 Processing Heat Treatment Plate thickness (mm) Depth strength (MPa) Tensile strength (MPa) -40 ° C -60 ° C Inventive example 1 1050 ACC 45 531 610 0.83 2 1050 ACC 50 454 543 0.78 3 1100 DO 50 452 543 0.51 4 1100 ACC 65 448 541 0.48 5 1050 ACC 60 493 570 0.56 6 1050 ACC 50 465 553 0.43 7 1100 ACC 50 495 568 0.49 8 1050 ACC 60 471 562 0.58 9 1100 ACC 55 467 559 0.56 10 1100 ACC 60 450 552 0.41 11 1050 ACC 65 442 530 0.46 12 1050 CR 50 451 545 0.31 13 1100 ACC 55 479 565 0.62 14 1050 ACC 60 464 567 0.49 15 1050 ACC 55 495 582 0.53 16 1000 ACC 60 496 594 0.67 17 1050 DO 50 538 619 0.57 18 1100 ACC 60 437 528 0.30 19 1050 ACC 60 455 551 0.35 20 1100 ACC 60 446 547 0.42 Comparative Example 21 1150 ACC 50 463 567 0.04 22 1100 ACC 50 540 646 0 .03 23 1100 ACC 60 435 542 0.06 24 1150 ACC 60 421 513 0.08 25 1100 ACC 60 379 469 0.09 26 1100 ACC 50 433 521 0.06 Machining heat treatment CR Controlled calendering (calendering in the most suitable temperature range for strength and toughness) ACC Accelerated cooling (controlling the water zone after calendering to a temperature of 5 to 600 °C in the temperature zone 5) DQ Direct quenching-tempering after calendering 15 200827459 Industrial use of the steel produced by the present invention, when welded at a high strength The FL part, which is most susceptible to deterioration, exhibits excellent CTOD characteristics and excellent toughness. This makes it possible to manufacture high-strength steels that can be used in harsh environments such as marine structures and earthquake-resistant buildings. [Simple diagram of the drawing 1 Fig. 1 shows a graph showing the relationship between the cooling time of 800 to 500 ° C and the M* fraction. Figure 2 is a graph showing the relationship between CeH and CTOD characteristics. 10 [Main component symbol description] None 0 16

Claims (1)

200827459 X. Patent application scope: 1. A steel with excellent toughness in the heat-affected zone, in terms of mass%, the steel contains ·· C: 0.02~0.06%; Si ·· 0·05~0·30% Mn : 1.7 to 2.7% ; p : 〇.〇15〇/0 or less; S: 〇·〇1〇% or less; Ti: 0·005 5 to 0.015%; 〇: 0·001〇~〇·〇〇 45%; and N: 0·0020 to 0.0060%, and the remainder consists of iron and impurities that are not avoided' and the amount of impurities mixed is limited to A1: 0.004% or less, Nb: 0.003% or less, and V: 0.030 % below, and CeH represented by the following formula (A) is a range of 〇·〇4 or less, 10 CeH=C+l/4Si-l/24Mn+l/48Cu+l/32Ni+l/0.4Nb+l /2V ··· (A) Further, c, Si, Μη, Cu, Ni, Nb, and V represent steel components (mass °/〇), respectively. 2. The 15 steel having excellent toughness in the heat-affected zone of the fusion of the first application of the patent scope, wherein the CeH is in the range of 0.01 or less. 3. A steel having excellent toughness in the heat-affected zone of fusion of the first or second application of the patent application, in terms of mass%, further containing: Cu: 〇·25% or less, and Ni··0.50°/◦ Or two. 4. The method for manufacturing steel with excellent workability in the heat-affected zone is to heat the steel component of the first part of the patent application scope and CeH steel to a temperature below ll ° ° C. Processing heat treatment. 5. A method for producing a steel having excellent toughness in a heat-affected zone, which is a steel sheet satisfying the third component of the patent application and a steel sheet of CeH, which is heated to a temperature of 1100 ° C or less, and then subjected to processing heat treatment. 17