Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

• the present invention relates to a thick high-strength steel sheet excellent in low-temperature toughness of a heat affected zone (hereinafter referred to as HAZ) used for ships, offshore structures, middle-rise buildings, bridges, and the like.
• HAZ heat affected zone
• Japanese Patent Publication No. 55-026164 discloses an invention in which a fine Ti nitride is secured in steel to reduce HAZ austenite grains and improve toughness.
• Japanese Patent Application Laid-Open No. H03-2646414 proposes an invention for improving the toughness of HAZ by utilizing a composite precipitate of Ti nitride and MnS as a transformation nucleus of ferrite.
• a composite precipitate of Ti nitride and BN is used as a precipitation nucleus of grain boundary ferrite to improve HAZ toughness.
• An invention has been proposed.
• the Ti nitride almost completely forms a solid solution in the vicinity of the boundary with the weld metal of the HAZ whose maximum temperature exceeds 140 ° C (hereinafter also referred to as the weld pound).
• the weld pound whose maximum temperature exceeds 140 ° C
• the effect of improving toughness is reduced. For this reason, it is difficult for steel materials using Ti nitride as described above to achieve strict requirements for HAZ toughness in recent years and required properties of HAZ toughness in ultra-high heat input welding.
• steels containing Ti oxide are used in various fields such as thick plates and section steels.
• Ti oxidation The steel containing the material is very effective in improving the toughness of large heat input welds, and its application to high tensile strength steel is promising.
• This principle is based on the assumption that Ti oxides, which are stable even at the melting point of steel, are used as precipitation sites, and Ti nitrides, MnS, etc. precipitate during the temperature drop after welding, and they are then added to the site. As a result, fine ferrite is generated, and as a result, the generation of coarse fly harmful to toughness is suppressed, and deterioration of toughness can be prevented.
• such a Ti oxide has a problem that the number of the Ti oxides dispersed in the steel cannot be sufficiently increased.
• the cause is the coarsening and aggregation of Ti oxides. If the number of Ti oxides is to be increased, coarse Ti oxides of 5 / m or more, so-called inclusions, will occur. It is thought that it would increase. Inclusions of 5 ⁇ m or more should be avoided because they are harmful because they can be a starting point for structural rupture or cause a decrease in toughness. Therefore, in order to achieve further improvement in HAZ toughness, it was necessary to utilize an oxide which is less likely to be coarsened and aggregated and which is more finely dispersed than a Ti oxide.
• H06-293939 / Japanese Patent Application Laid-Open No. Hei 10-1028395 states that A1 addition immediately after Ti addition, Alternatively, there is disclosed an invention utilizing a Ti_A1 composite oxide or a composite oxide of Ti, Al, and Ca produced by adding A1 and Ca composites. According to such an invention, large heat input welding HAZ toughness can be greatly improved. Disclosure of the invention
• the base material strength is increased at a plate thickness of 50 mm or more.
• the base material strength is increased at a plate thickness of 50 mm or more.
• MA Martensite—Austenite constituent
• the base metal strength exceeds 570 MPa in tensile strength, the required HAZ toughness cannot be obtained.
• the present invention is directed to a welding method using a steel plate having a thickness of 50 to 80 mm and a base metal tensile strength of 49 to 570 MPa, and a welding heat input of 20 to 100 kJ / mm. It is an object of the present invention to provide a thick high-strength steel sheet having excellent low-temperature toughness in the heat affected zone by large heat input welding, which can achieve excellent welding HAZ toughness even when welding is performed.
• the present inventors have found that the above problems can be advantageously solved by defining the Ni addition amount and Ni / Mn, and completed the present invention only after further study.
• the gist is as follows.
• N i and Mn are represented by the formula [1] Thick high-strength steel sheet excellent in low-temperature toughness of the heat affected zone by large heat input welding, characterized by satisfying the above conditions, with the balance being iron and inevitable impurities.
• mass. /. And B 0.0005 to 0.0005%, characterized in that the low-temperature toughness of the weld heat-affected zone by the large heat input welding according to the above (1) or (2), Excellent high-strength steel sheet.
• FIG. 1 is a diagram showing a welding heat cycle equivalent to 45 kJ / mm.
• FIG. 2 is a diagram showing the relationship between Ni / Mn, Ceq, and reproduced HAZ toughness.
• Figure 3 shows the effect of improving the reproducible HAZ toughness by dispersing fine oxides or using B.
• the inventors of the present invention need to improve the HAZ toughness when the thickness of the steel, which is required for thick high-strength steel, is as high as 0.36 or more and 0.42 or less.
• the optimal component system to improve toughness was studied diligently. It has been known that Ni is effective as an element that enhances the toughness of the matrix. However, as in this case, C eq is 0.36 or more and 0.42 or less, and it is difficult to know whether it is effective for improving the toughness of HAZ, and if so, what component conditions are effective. Not been. Therefore, first, the effect of the amount of Ni added was examined. In the study, it was assumed that the amount of Nb that is effective for securing the base metal strength was 0.003% or more.
• the HAZ toughness was evaluated by the ductility-brittle transition temperature (vT) in the Charpy impact test when a heat cycle equivalent to the electron gas welding (heat input 45 kJ / mm) shown in Fig. 1 was applied. rs)
• the HAZ toughness can be improved by adding 0.8% or more of Ni, which satisfies the formula [1].
• the improvement of toughness was studied.
• the following three methods were studied to improve the HAZ toughness.
• the cooling time after welding is long, so ferrite generated from austenite grain boundaries becomes coarse, and this coarse grain boundary ferrite may cause a decrease in HAZ toughness. Therefore, it is a method to suppress the grain boundary ferrite from becoming coarse.
• Patent Document 7 a method for dispersing fine oxides is effective.
• the amount of dissolved oxygen in molten steel is adjusted by an equilibrium reaction with Si in a deoxidizing step, and then deoxidizing in the order of Ti, Al, and Ca. Then you are.
• oxides having a particle size of 0.01 to 1.0 ⁇ m are dispersed at 5 ⁇ 10 3 to 1 ⁇ 10 5 particles / mm 2 .
• the present inventors have found that when C eq is as high as 0.36 or more and 0.42 or less, in a system containing 0.003% of Nb and adding 0.8% or more of Ni. Then, a method for dispersing fine oxides and further improving the HAZ toughness was studied diligently. First, a method of dispersing fine oxides. In such a system, the amount of dissolved oxygen in the molten steel is adjusted to 0.010 to 0.050% in the deoxidation step, and thereafter, First, deoxidation is performed at T i, then deoxidation is performed at A 1, and then at least one of Ca, Mg, and REM is added, so that the equivalent circle diameter is 0.0.
• Fig. 3 shows the results of a comparison with the HAZ toughness with only proper addition of Ni. Note that the oxide produced is finer as the amount of N i is large, the number becomes large, the 1 weight 1. In the case of more than 5% 1 0 0 0 or mm 2 or more. This is what we found this time.
• the Si content in the molten steel when the Si content is large, it is difficult to form oxides, so the Si content is ⁇ 0.30% or less, further 0.20% or less. It is clear from this study that I got it.
• the dissolved oxygen content before Ti deoxidation exceeds 0.050% or the order of the deoxidizing elements is different, the oxides become coarse and fine oxides cannot be obtained sufficiently. The effect of suppressing coarsening of austenite grains is hardly obtained.
• the number of oxides with an equivalent circle diameter of 0.005 to 0.5 ⁇ was determined by preparing an extraction replica from a steel sheet as a base metal, and using an electron microscope to increase the number of oxides by 100,000.
• FIG. 3 shows the result of comparing the improvement of HAZ toughness by adding B with the HAZ toughness of only adding Ni properly. It can be seen that the HAZ toughness is further improved by the addition of B. Fig. 3 shows the addition of B The HAZ toughness in the case where the HAZ toughness is shown is shown, but the HAZ toughness is further improved by the fine oxide dispersion and the addition of B. This is probably because the number of oxides serving as BN precipitation sites increased, and the ferrite that nucleated the BN increased, resulting in a finer HAZ structure.
• the HAZ toughness when Cu, Cr, Mo, and V were added in addition to the above conditions was also examined. As a result, respectively, in the range of 0.1 to 0.4%, 0.1 to 0.5%, 0.01 to 0.2%, 0.005 to 0.050% It was found that the addition of HAZ did not significantly reduce the HAZ toughness.
• the method for manufacturing the steel sheet of the present invention is not particularly limited, and may be manufactured according to a known method. For example, after the molten steel adjusted to the above preferable composition is formed into a slab by a continuous forming method, it is heated to 100 to 125 ° C. and then hot-rolled.
• C has a lower limit of 0.03% as an effective component for improving the strength of steel, and an excessive addition generates a large amount of carbides and MA and significantly lowers the HAZ toughness. It was set to 14%.
• S i is a component necessary for securing the strength of the base material and deoxidizing, etc., but the upper limit is set to 0.30% in order to prevent the toughness from being reduced by the hardening of HAZ. Further, when oxides are used, the upper limit is preferably set to 0.20% or less in order to prevent a decrease in the oxygen concentration in the molten steel.
• Mn is required to be added in an amount of 0.8% or more as an effective component for securing the strength and toughness of the base metal, but the upper limit is 2.0 as long as the toughness, cracking, etc. of the weld zone is acceptable. %. Further, regarding the upper limit of Mn, it is necessary to satisfy the equation [1] showing the relationship between Ceq, Mn amount, and Ni amount. This is because of the high C eq that was newly discovered in this study. In this case, the increase in Mn causes the formation of a large amount of MA in the HAZ structure, and the effect of Ni to improve the HAZ toughness is lost.
• N i / M n ⁇ 10 XC eq -3 [1] P is preferably as small as possible, but it costs a lot to reduce it industrially. 0 2 or less.
• the content of S is preferably as small as possible, but it requires a great deal of cost to reduce it industrially. Therefore, the content range of S is set to 0.05 or less.
• Ni is an important element in the present invention, and it is necessary to add at least 0.8%. Further, regarding the lower limit of N i, it is necessary to satisfy the equation [1] showing the relationship between C e q, M n amount, and N i amount. The upper limit was set at 4.0% from the viewpoint of manufacturing costs.
• N b is an element that is effective for improving the strength of the base material by improving the hardenability. Add 3% or more. However, when Nb is added in a large amount, MA is easily generated in HAZ regardless of the Ni / Mn ratio, and when more than 0.040% is added, the major axis in HAZ is 5 ⁇ or more. The upper limit of Nb was set to 0.040% because a large number of coarse MAs may be generated and the HAZ toughness may be significantly reduced. In order to obtain higher toughness, coarse MA with a major axis of 5 ⁇ m or more is hardly generated when the NiZMn ratio satisfies the above equation [1].
• Nb content it is preferable to suppress the Nb content to less than 10%. In order to obtain higher toughness more stably, in the case of the Ni / Mn ratio satisfying the above equation [1], almost no MA with a major axis of 3 ⁇ m or more is generated. It is preferable to suppress the Nb content to 0% or less.
• a 1 is an important deoxidizing element, and the lower limit was set to 0.001%. In addition, when A1 is present in a large amount, the surface quality of the piece is deteriorated. Therefore, the upper limit is set to 0.040%.
• T i is added in an amount of not less than 0.05% in order to generate Ti nitrides and Ti-containing oxides, which are required to suppress coarsening of the reheated austenite grains.
• an excessive addition increases the amount of solid solution Ti and lowers the HAZ toughness. Therefore, the upper limit is 0.030%.
• N is added as necessary to form Ti nitride and B nitride in austenite grain boundaries and in grains during cooling after welding.
• B In order to combine with B to form a B nitride, the addition of 0.010% or more is necessary.However, excessive addition increases the amount of solute N and lowers the HAZ toughness. The upper limit was 0.1%.
• Ca is added in an amount of 0.0003% or more as necessary to generate a Ca-based oxide serving as pinning particles necessary for suppressing coarsening of the reheated austenite grains.
• the upper limit was made 0.050%.
• Mg is added in an amount of 0.0003% or more as necessary to generate Mg-based oxides that become pinning particles necessary for suppressing coarsening of the reheated austenite grains.
• the upper limit was made 0.050%.
• REM is added in an amount of 0.001% or more as necessary to generate a REM-based oxide which becomes a pinning particle necessary for suppressing coarsening of the reheated austenite grains.
• the REMs described here are Ce and La, and the added amount is the total amount of both.
• B is necessary as a solid solution B to segregate at austenite grain boundaries during cooling after welding to suppress generation of grain boundary ferrite, and to form BN at austenite grain boundaries and intragranular. Therefore, add 0.0005% or more.
• excessive addition increases the amount of solute B and greatly increases the HAZ hardness, resulting in a decrease in HAZ toughness. Therefore, the upper limit was set to 0.050%.
• Cu is added in an amount of 0.1% or more as necessary to improve the strength and corrosion resistance of the steel material. Since the effect saturates at 1.0%, the upper limit is set to 1.0.However, if it exceeds 0.4%, MA is likely to be generated and the HAZ toughness is reduced. Is good.
• Mo is an element effective for improving the strength and corrosion resistance of the base material, and is added at 0.01% or more as necessary. Since the effect saturates at 0.5%, the upper limit is set to 0.5%. However, since excessive addition causes reduction in HAZ toughness due to the formation of MA, the upper limit is preferably 0.2% or less.
• V is an element effective for improving the strength of the base material, and is added at 0.05% as necessary. Since the effect saturates at 0.10%, the upper limit is set to 0.10% .However, excessive addition causes reduction in the HAZ toughness due to the formation of MA, so it is preferably 0.050%. The following is good.
• a steel strip was prepared by continuously forming molten steel having the chemical components shown in Table 1.
• Table 1 For D23 to D34 and D46 to D49, before introducing Ti, adjust the dissolved oxygen of the molten steel to 0.010 to 0% to 0.050% by Si, and then First, deoxidation with T i, and then with A 1, then C a, M g, RE Any of M was added for deacidification.
• steel plates with a thickness of 50 to 80 mm were manufactured by the following two rolling methods. One is that after rolling at a surface temperature of 750 to 900 ° C, water cooling is performed until the temperature of the sheet surface after reheating reaches a temperature range of 200 to 400 ° C.
• the other method is hot rolling, water cooling to room temperature, and tempering in the range of 500 to 600 ° C (Table 2).
• Table 2 shows the manufacturing conditions, thickness, and mechanical properties of the steel sheet.
• D23 to D34 and D46 to D49 the number of fine oxides with an equivalent circle diameter of 0.05 to 0.5 m, measured at any point on the steel sheet, is also shown. did.
• an extracted replica was prepared from an arbitrary part of the steel sheet, and it was extracted with an electron microscope at a magnification of 100,000, and a field of view of 100 or more (100,000 ⁇ m in observation area) 2 or more), and particles having a particle size of less than 0.1 ⁇ were observed at an appropriately increased magnification.
• the steel plates were butt-butted and subjected to one-pass welding using electrogas welding (EGW) or electroslag welding (ESW) with a welding heat input of 20 to 100 kJ Zmm. Then, in the HAZ located at the center of the plate thickness (tZ2), notches were inserted at two locations, HAZ and FL, 1 mm away from FL, and a Charby impact test was performed at 140 ° C. . Table 2 shows the welding conditions and HAZ toughness. This In this Charpy impact test, a JIS No. 2 full-size test piece with a 2 mm V notch was used. Table 2 also shows the prior austenite particle size between FL and HA Z l mm.
• the former austenite grain size between FL and HAZ 1 mm described here is 2 mm in the thickness direction centered on the center of the thickness and the former austenite included in the plane containing FL to HAZ 1 mm.
• This is the average particle size of the stenite particles measured by the cross-sectional method.
• the measurement was performed using the massive ferrite connected in a net shape as the grain boundary of the former austenite grains.
• D 1 -D49 is the steel of the present invention. Since the chemical composition of the steel is properly controlled, high heat input HAZ toughness at 140 ° C is satisfactory while satisfying the required base metal performance. D23 to D34 and D46 to D49 in which fine oxides are dispersed have a prior austenite particle size of less than 200 ⁇ between FL and HA It is fine grained, and the high heat input at 140 ° C HA has higher toughness. In addition, D20, to which B was added to reduce the size of the HAZ structure, had better HAZ toughness than D19, which did not contain B and had the same amount of added elements other than B, and Large heat input at-40 ° C HAZ toughness also shows high values.
• the Cl-17 of the comparative steel has a large heat input HAZ toughness because it does not contain enough Ni to satisfy Equation [1] or because the chemical composition of the steel is properly controlled. Is insufficient.
• Table 2 continued 2 Mother: O (t / 2 part) U oxide number 2) Classification a ) "Manufacturing method Plate thickness (mm) Tensile strength (MPa) Yield stress (Mpa) VcL -40 (J) (pcs / mm 2 )
• Sheet thickness center position, Y S and T S are the average values of two test pieces, and the Charpy absorbed energy at 140 ° C (VE _ 40) is the average value of three test pieces.
• E GW Electro-port gas welding
• ESW Electro-slag welding
• welding heat input is the average value of the entire welding length, and common welding materials are used for each welding method.
• the ferrite connected in a net shape is measured as the grain boundary of the former austenite grains.
• the present invention provides a thick steel plate that satisfies the strict toughness requirements for crushing of ships, marine structures, and middle- and high-rise buildings, and has an extremely large effect in this kind of industrial field. Contribution to society is very large in terms of gender.

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• 2005
  • 2005-03-31 JP JP2005102041A patent/JP4660250B2/ja active Active
  • 2005-04-06 KR KR1020067020353A patent/KR100839262B1/ko active IP Right Grant
  • 2005-04-06 WO PCT/JP2005/007109 patent/WO2005098068A1/ja not_active Application Discontinuation
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