WO2009123292A1 - 高張力鋼およびその製造方法 - Google Patents
高張力鋼およびその製造方法 Download PDFInfo
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- WO2009123292A1 WO2009123292A1 PCT/JP2009/056906 JP2009056906W WO2009123292A1 WO 2009123292 A1 WO2009123292 A1 WO 2009123292A1 JP 2009056906 W JP2009056906 W JP 2009056906W WO 2009123292 A1 WO2009123292 A1 WO 2009123292A1
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- 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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C2202/00—Physical properties
Definitions
- the present invention is a ship (ship) and marine structures (marine structure), line pipe (line PIPE), relates to the high tensile steel (high- tensile strength ste els) and a manufacturing method thereof for use in a pressure vessel (pressure vessel) or the like
- the yield stress (YS (yield stress)) is 460 MPa or more, which not only excels in the strength and toughness of the base material (base material) but also the toughness of the weld zone (CTOD ( The present invention relates to a high-strength steel excellent in crack tip opening displacement (characteristic) and a method for producing the same.
- YS yield stress
- COD toughness of the weld zone
- Steel used in ships and offshore structures is usually welded joints and finished in the desired shape. Therefore, from the viewpoint of ensuring the safety of structures, etc., these steels need not be excellent in the strength and toughness of the base metal itself, but also in the welded joint (weld) of the weld joint (weld). It is also required that the toughness of the metal (weld metal) and heat-affected zone is excellent.
- C rack Tip Opening Displacement Test hereinafter abbreviated as “CTOD test”
- C rack Tip Opening Displacement Test hereinafter abbreviated as “CTOD test”
- COD test C rack Tip Opening Displacement Test
- This test involves three-point bending of a specimen with fatigue precrack in the toughness evaluation section and opening the bottom of the crack of the bottom of the crack (bottom of crack). Measure the value of opening displacement (value of plastic deformation) and evaluate the occurrence resistance of brittle fracture.
- multilayer steel multi-pass welding
- the heat affected zone has a complicated thermal history (thermal (History), local embrittlement zone is likely to occur.
- thermal (History) thermal history
- the toughness in the two-phase region of ⁇ and ⁇ is greatly reduced in the second cycle. This is because the pond part is exposed to a high temperature just below the melting point, so that austenite grains are coarsened and are easily transformed into a fragile upper bainitic structure by subsequent cooling. .
- the brittle structure Woodmannstatten structure
- island martensite island martensite, M-A constituent
- the two-phase region reheat zone that is, the region exposed to the high temperature immediately below the melting point in the first welding, the region that becomes the two-phase region of ferrite and austenite by the reheating during the subsequent welding is most brittle.
- the reason for this is that carbon is concentrated in the austenite region due to reheating during the second and subsequent passes, and this forms a fragile paynite structure containing island martensite during cooling, reducing the toughness. Therefore, as a countermeasure, the formation of island martensite is suppressed by reducing C and Si, and Cu is added.
- Discloses a technique for ensuring the strength of the base material see, for example, Japanese Patent Application Laid-Open No. 05-182682).
- the object of the present invention is to solve the above-mentioned problems of the prior art and to improve the strength and toughness of the base metal even in the thick-walled high-strength steel plate, in which the addition amount of the alloy element must be increased.
- the purpose is to propose a high-strength steel excellent in the toughness of the heat-affected zone and its preferred production method. Disclosure of the invention In the present invention, C: 0.03 to 0.10 mass%, Si: 0.30 mass% or less, Mn: 1-60 to 2.30 mass%, P: 0.015 mass% or less, S: 0. 005 ma ss% or less, A 1: 0.
- Nb 0.00 4 to 0.05 ma ss%
- T i 0.005 to 0.02 ma ss%
- N 0.00: !
- Ca 0.0005 to 0.003 ma ss%
- Ca, S and O are represented by the following formula (1):
- the high-tensile steel of the present invention further includes B: 0.0003 to 0.0025 mass%, V: 0.2 mass% or less, Cu: 1 mass% or less, Ni : 2 ma ss% or less, Cr: 0.7 mass% or less and Mo: 0.7 mass% or less selected from 1 type or 2 types or more.
- the present invention includes C: 0.03 to 0.10 mass%, S i: 0.30 mass% or less, Mn: l. 60 to 2.30 mass%, P: 0.015 mass% or less, S : 0.005 ss. /.
- the cumulative reduction in the temperature range of 950 ⁇ or higher is 30% or more and less than 950 From 5 to 45 ° C / s ec from hot rolling finish temperature to 600 to 450 ° C cooling stop temperature
- Pre-stage cooling preferably at 5-20 ° CZ s ec
- High-strength steel characterized in that after-cooling is performed at a temperature of 1 ° C / s ec or more and less than 5 ° CZ s ec from 45 to 50 ° C.
- the production method of the present invention further includes B: 0.03 to 0.025 mass%, V: 0.2 mass% or less, Cu: 1 mass%
- B 0.03 to 0.025 mass%
- V 0.2 mass% or less
- Cu 1 mass%
- B 0.03 to 0.025 mass%
- V 0.2 mass% or less
- Cu 1 mass%
- it is characterized by containing one or more selected from Ni: 2 mass% or less, Cr: 0.7 mass% or less, and Mo: 0.7 mass% or less.
- the production method of the present invention is characterized in that a tempering treatment at 45 to 65 ° C. is performed on the steel after subsequent cooling.
- high-strength copper having a high yield strength of 4600 MPa or more and excellent toughness and excellent toughness (CTOD characteristics) of the heat-affected zone after welding is inexpensive. Can greatly increase the size of ships and offshore structures.
- Fig. 1 is a graph showing the effect of the pre-stage cooling rate after hot rolling (cooling rate from the rolling finish temperature to the cooling stop temperature between 60 ° C and 45 ° C) on the base material properties.
- the inventors diligently studied a method capable of improving the base metal strength and toughness of thick high-strength steel and also improving the toughness of the heat affected zone. As a result, the decrease in toughness in the heat affected zone is due to the formation of embrittlement. To improve the toughness of this heat affected zone, the austenity in the region where high heat is generated during welding. It was found that it is effective to disperse the transformation nuclei uniformly and finely in order to suppress the coarsening of the grains and further promote the ferrite transformation during cooling after welding.
- the first feature of the present invention is that it is added for the purpose of shape control of sulfide in order to improve the toughness of the welded heat affected zone.
- C a S crystallization of the compound
- the crystallization of the compound (C a S) is effectively utilized. Since this C a S crystallizes at a lower temperature than the oxide, it can be uniformly fine dispersed. And by controlling the dissolved oxygen amount in the molten steel at the time of addition of Ca S to the appropriate range, the dissolved S can be dissolved even after C a S crystallization. As a result, M n S force S precipitates on the surface of C a S to form complex sulfide.
- This M n S is known to have a potential for ferrite nucleus, and a M n depleted zone is formed around the deposited M n S. As a result, ferrite transformation is further promoted. The effect of this Mn dilute strip can be expressed more effectively by increasing the amount of Mn added in the steel. Moreover, since ferrite nuclei such as T i N, BN, and A 1 N also precipitate on the precipitated M n S, the ferrite transformation is promoted more often. Also, by increasing the amount of Mn added, the base metal strength can be effectively increased without generating island martensite, which is an embrittled structure, in the weld heat affected zone as much as possible.
- the above technology makes it possible to finely disperse ferrite transformation nuclei that do not melt even at high temperatures, refine the structure of the weld heat-affected zone, and generate island martensite (M-A constituent). Suppression and toughness can be obtained by suppressing as much as possible. Also, in the region where reheating is performed in the two-phase region due to the heat cycle during multi-layer welding (thigh ltilayer welding), the structure of the first weld heat affected zone is refined, so The toughness of the transformation region is improved, and the austenite grains that are retransformed are also refined, so that the degree of reduction in toughness can be kept small.
- the second feature of the present invention is that the cooling after rolling the steel material is divided into two stages, that is, the pre-stage cooling and the post-stage cooling, and the cooling rate of the pre-stage cooling is controlled more greatly than the post-stage cooling. This will be explained based on experimental results.
- Figure 1 shows the effect of the cooling rate of the former stage on the base metal strength and morningity for the above measurement results.
- the cooling rate of the former stage cooling from the rolling end temperature to 500 ° C is shown.
- it has a high strength with a yield stress of 46 OMPa or higher and v E-40 ° C with a strength-toughness balance of 200 J or higher. It can be seen that a steel plate is obtained.
- the steel sheet cooled at the above cooling rate has a structure mainly composed of acicular ferrite.
- the toughness is greatly reduced when a relatively coarse upper benite structure including island-like martensite between laths is obtained. Therefore, in order to achieve both high strength and high toughness, it is necessary to have a fine cashierite structure by devising rolling conditions.
- the inventors divided the cooling after rolling into pre-stage cooling and post-stage cooling, which has a slower cooling rate, and appropriately controlled the respective cooling rates, so that And found that a steel sheet having an excellent balance of strength and toughness can be obtained.
- the present invention has been completed based on the above findings. Next, the component composition that the high-tensile copper according to the present invention should have will be described.
- C is an element that has the greatest influence on the strength of steel. To ensure the strength required for structural steel (Y S ⁇ 46 OMP a), it must be contained by 0.03 m a s s% or more. On the other hand, if the amount is too large, the toughness of the base metal will be lowered and cold cracking will occur during welding. Therefore, the upper limit is set to 0.1 mass%.
- Si is a component added as a deoxidizer and to increase the strength of steel.
- 0.0 lma ss% or more is preferably added. However, if it exceeds 0.3 Oma ss%, the toughness of the base metal and the welded portion is lowered, so that it is necessary to set it to 0.3 Oma ss% or less. Preferably, it is in the range of 0.01 to 0.20 ma ss%.
- Mn is an effective element for ensuring the strength of the base metal.
- the refinement of the structure of the weld heat affected zone is promoted and the formation of the brittle structure is suppressed as much as possible, so that the welding heat effect is reduced.
- it exceeds 2.30 ma s s% the toughness of the base metal and welds will be significantly reduced.
- it is in the range of 1.65 to 2.15 m a s s%.
- P is an impurity that is inevitably mixed, and if it exceeds 0.015 ma s s%, the toughness of the base metal and the welded portion is reduced, so it is limited to 0.015 m s s% or less. Preferably, it is less than 0.01 Oma s s%.
- S is an inevitably mixed impurity, and if it exceeds 0.005 ma ss%, the toughness of the base metal and the weld is reduced, so it is 0.005 m a ss% or less. Preferably, it is not more than 0.0033 ma ss%.
- a 1 is an element added for deoxidation of molten steel, and should be contained in an amount of at least 0.05 mass s s%.
- the toughness of the base metal is reduced and mixed into the weld metal due to dilution by welding to reduce the toughness. Therefore, it is necessary to limit it to 0.06 mass% or less. is there. Preferably, it is 0.0010 to 0.055 ma s s%.
- Nb 0.004 ⁇ 0.05 mass%
- Nb forms a non-recrystallized zone in the low temperature range of austenite.
- the microstructure of the base metal is refined and the toughness is increased. Can be achieved.
- precipitation strengthening can be achieved by rolling and performing tempering after cooling. Therefore, Nb is an important additive element from the viewpoint of strengthening steel. In order to obtain the above effect, it is necessary to add Nb at least 0.004 mass%. However, if it is added excessively exceeding 0.05 mass%, the toughness of the weld will deteriorate, so the upper limit should be 0.05 mass%.
- T i precipitates as Ti N when the molten steel solidifies, suppresses the austenite coarsening in the weld and contributes to the toughness of the weld because it becomes a ferrite transformation nucleus. To do. In order to obtain the effect, it is necessary to add 0.005 mass% or more. However, if the addition is less than 0.005 ma ss%, the effect is small, whereas if it exceeds 0.02 ma ss%, the TiN particles become coarse, and an effect of improving the toughness of the base metal and the weld is obtained. It becomes impossible. Therefore, the amount of Ti added should be in the range of 0.005 to 0.02 mass%.
- N is an element necessary to form TiN that suppresses the coarsening of the weld structure, and is added in an amount of 0. O Olma s s% or more.
- the upper limit is set to 0 ⁇ 005 mass%.
- the range of 0.003 to 0.005 mass% is preferable.
- Ca is an element that improves toughness by fixing S. In order to exert this effect, it is necessary to add at least 0.0005 mass%. But, Even if it contains more than 003 ma ss%, the effect is saturated, so C a is 0.
- C a, S and O can be expressed by the following formula (1):
- (Ca_ (0. 18 + 130 XC a) XO) Z (1. 25 / S) is a value indicating the ratio of the atomic concentrations of Ca and S that is effective in controlling the morphology of sulfides. From this value, it is possible to estimate the form of sulfide (Mochida et al., “Iron and Steel”, Japan Iron and Steel Institute, 66th (1980), No. 3, P. 354-362).
- the high-tensile steel of the present invention further includes one or more selected from B, V, Cu, Ni, Cr and Mo in order to increase strength and toughness. Can contain.
- B segregates at the austenite grain boundaries and has the effect of increasing the strength of the steel by suppressing the ferrite transformation that occurs from the grain boundaries and increasing the fraction of the bainitic structure.
- the effect can be obtained by adding more than 0.0003 mass%. However, if it is added in excess of 0.0025 mass%, the toughness is reduced.
- a more preferable range of B is 0.0 005 to 0.002 ma s s%.
- V 0.2 ma s s% or less
- V is an element effective for improving the strength and toughness of the base metal, and also is an element that precipitates as VN and also serves as a nucleation nucleus. In order to obtain the effect, it is preferable to add 0.01 mass% or more. However, if the amount of added iron exceeds 0.2 m s s%, the toughness will be reduced instead, so it is preferable to add less than 0.2 m s s%. More preferably, it is 0.15 mass% or less.
- Cu is an element that has the effect of improving the strength of steel. In order to obtain the effect, it is preferable to add 0.05 mass% or more. However, if it exceeds 1 m s s%, it causes hot brittleness and deteriorates the surface properties of the steel sheet. Therefore, it is preferable to add it in the range of lma s s% or less. More preferably, it is 0.8 ma s s% or less.
- Ni is an effective element for improving the strength of steel and the C TOD characteristics of the heat affected zone. In order to obtain the effect, 0.05 mass% or more is preferably added. However, since Ni is an expensive element, the upper limit is preferably 2. Oma s s%. When Mn is added at 1.6% or more as in the present application, Ni is more preferably less than 0.3% from the viewpoint of cost reduction.
- C r: 0.7 ma ss% or less Cr is an effective element for increasing the strength of the base material.
- 0.05 mass% or more is preferably added.
- the upper limit is 0.5 ma ss% or less.
- Mo is an effective element for increasing the strength of the base metal.
- 0.05 mass% or more is preferably added.
- the upper limit is preferably set to 0.7 ma s s%. More preferably, it is 0.5 mass% or less.
- the structure of the high-strength steel of the present invention is a structure mainly composed of ashki ferrite, and its preferred area ratio is 60% or more, more preferably 70% or more.
- the area ratio of the fine ferrite is less than 60%, and the coarse upper veinite structure increases, the toughness decreases.
- the upper limit of the area ratio is not particularly limited.
- the basic ferrite structure of the high strength steel of the present invention is a bainetic ferrite having a fine needle-like or lath-like morphology and a high dislocation density in the crystal grains. Polygonal ferrite (polygonal ferrite) and coarse upper bainite are different. Next, the manufacturing method of the high strength steel of this invention is demonstrated.
- the high-strength steel of the present invention is prepared by melting the molten steel adjusted to the component composition suitable for the present invention described above by an ordinary method using a converter, an electric furnace, a vacuum melting furnace, etc. It is preferable to produce a thick high-strength steel by hot rolling the steel material after making it a steel material such as a slab through a normal process such as ingot lump rolling. At this time, the heating temperature of the steel material prior to hot rolling needs to be in the range of 1050 to 1200 ° C. The reason for setting the heating temperature to 1050 ° C or higher is that forging defects existing in the steel material are caused by hot rolling. This is for surely crimping. However, when heated to temperatures exceeding 1 200 ° C, Ti N precipitated during solidification becomes coarse and the toughness of the base metal and welds decreases, so the heating temperature must be regulated to 1 200 ° C or lower. is there.
- the steel material heated to the above temperature is then subjected to hot rolling in which the cumulative rolling reduction in the temperature range of 95 or higher is 30% or higher and the cumulative rolling reduction in the temperature range of 950 ° C or lower is 30 to 70%.
- hot rolling with a cumulative reduction ratio of 30% or higher in the temperature range of 50 ° C or higher is that the austenite grains recrystallize by setting the cumulative reduction ratio in this temperature range to 30% or higher. This is because, when the cumulative reduction ratio that can refine the structure is less than 30%, abnormal coarse grains generated during heating remain, which adversely affects the toughness of the base metal.
- the reason for hot rolling with a cumulative draft of 30 to 70% in the temperature range below 95 is that the austenite grains rolled in this temperature range do not recrystallize sufficiently.
- the austenite grains after rolling are deformed flat and have a high internal strain that contains a large amount of defects such as deformation bands inside.
- This accumulated internal energy acts as a driving force for the subsequent ferrite transformation and promotes the ferrite transformation.
- the rolling reduction is less than 30%, the accumulated internal energy is not sufficient, so ferrite transformation hardly occurs and the base metal toughness deteriorates.
- the rolling reduction exceeds 70% the formation of polygonal ferrite is promoted, the formation of uniaxial ferrite is suppressed, and high strength and high toughness are not compatible.
- Cooling after the end of subsequent hot rolling is divided into pre-stage cooling and post-stage cooling, and the former cooling rate is set to be relatively higher than that of the latter.
- the cooling stop temperature between ° C, preferably from the hot rolling end temperature to the cooling stop temperature between 5 80 and 480 ° C, 5 to 45 ° C Zsec, preferably 5 to 20 ° C / sec.
- cooling is performed at a cooling rate of 6 to 16 ° C Zsec, and in the subsequent post-cooling, from the pre-cooling stop temperature to the post-cooling stop temperature of 450 ° C or lower, preferably from the pre-cooling stop temperature to 400 to Up to 250 ° C cooling stop temperature, It / s ec or more and less than 5 ° C / s ec, more preferably 2 to 4.5. It is necessary to cool at the same cooling rate.
- the pre-cooling stop temperature When the pre-cooling stop temperature is higher than the above temperature range, there is almost no increase in strength, and conversely, when it is lower than the above temperature range, the toughness deteriorates. Further, if the cooling rate of the former stage is less than the lower limit of the above range, it becomes a structure mainly composed of polygonal ferrite, so that the strength cannot be improved. Furthermore, when the cooling stop temperature in the latter stage cooling is higher than the upper limit of the above temperature range, the increase in strength is insufficient. Further, if the subsequent cooling rate is less than the lower limit of the above range, the base material strength is insufficient, and conversely if the upper limit of the above range is exceeded, the toughness of the base material is reduced. If the subsequent cooling rate is too high than the previous cooling rate, island martensite is generated and the toughness of the base metal is deteriorated.
- the steel material after cooling may be tempered in the temperature range of 45 to 50 ° C. for the purpose of reducing the residual internal stress.
- the tempering temperature is less than 45 ° C., the residual stress removal effect is small.
- it exceeds 6500 ° C. various carbonitrides precipitate and precipitate. This is not preferable because it causes strengthening and lowers toughness.
- the base metal becomes a structure mainly composed of ash and ferrite, and a steel material having an excellent balance between strength and toughness can be obtained.
- N is more than 0.030%
- the cooling rate of the former stage cooling is more than 20 to 45 ° CZ sec
- the stop temperature of the former stage cooling is 45 0 to 50
- the steel slabs No. 1 to 31 having the composition shown in Table 1-1 and Table 1-2 are used as raw materials, and hot rolling, pre-cooling and post-cooling are performed under the conditions shown in Table 2-1 and Table 2-2. Cooling was performed to produce a steel plate with a thickness of 25-8 Omm.
- the temperatures listed in Table 2-1 and Table 2-2 are the temperatures of 1/4 part of the plate thickness calculated from the steel plate surface temperature measured with a radiation thermometer. A sample was taken from the thick steel plate thus obtained and subjected to a tensile test and a Charpy impact test. In the tensile test, JIS No.
- a single bevel groove (bevel angle) is applied to a test plate taken from a thick steel plate in which all of the base material properties YS, TS and VE-4 meet the above criteria.
- Carbon dioxide gas arc welding (C0 2 arc welding) with a heat input of 25 k jZcm was made to produce a welded joint, and the straight bond part of the groove was notched from this welded joint.
- Specimens were collected and subjected to a C TOD test at a temperature of 11.
- the test conditions for preparing the C TO D test piece were conducted in accordance with British Standard BS 7448.
- JI S4 impact test specimens with the notch position as the bond part were collected, Charpy impact test was performed at a temperature of _40 ° C, and the absorbed energy (vE-40) was measured.
- the steel sheet of the example of the present invention has a base material with a yield stress (YS) of 46 OMP ai3 ⁇ 4 and a Charpy absorbed energy (VE—40 ° C) of 200 J or more.
- the carbon dioxide arc welded joint has a VE—40 ° C of 200 J or higher and a 000-00 value of 0.10 mm or higher. It can be seen that the toughness of the part is also excellent.
- the steel of the comparative example that is out of the scope of the present invention only a steel sheet inferior in any one or more of the above properties is obtained.
- the CT0D of the weld zone is all superior to 0.45 or more due to the effect of TiN pinning. Yes.
- the N force exceeds 0.303 mass%
- the cooling rate of the pre-cooling after hot rolling exceeds 2 O'C / sec, 45 X / sec or less
- the stop temperature of the pre-cooling Steel plates No. 15 and 16 manufactured under conditions of 450 to 500 ° C both have high strength with a base material yield stress of 55 OMPa or more.
- the high-tensile steel of the present invention can be suitably used not only for ships and offshore structures, line pipes, and pressure vessels, but also for steel structures that are assembled by welding in the fields of construction and civil engineering.
Abstract
Description
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CN2009801118830A CN102124133A (zh) | 2008-03-31 | 2009-03-27 | 高强度钢及其制造方法 |
EP09726619.1A EP2272994B1 (en) | 2008-03-31 | 2009-03-27 | High-tensile strength steel and manufacturing method thereof |
KR1020157021337A KR20150094793A (ko) | 2008-03-31 | 2009-03-27 | 고장력강 및 그 제조 방법 |
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JP (1) | JP5439887B2 (ja) |
KR (3) | KR20130035277A (ja) |
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WO2013099177A1 (ja) * | 2011-12-27 | 2013-07-04 | Jfeスチール株式会社 | 脆性き裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法 |
JPWO2013099177A1 (ja) * | 2011-12-27 | 2015-04-30 | Jfeスチール株式会社 | 脆性き裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法 |
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JP5920542B2 (ja) * | 2014-03-31 | 2016-05-18 | Jfeスチール株式会社 | 溶接継手 |
CN106133165A (zh) * | 2014-03-31 | 2016-11-16 | 杰富意钢铁株式会社 | 焊接接头 |
US10300564B2 (en) | 2014-03-31 | 2019-05-28 | Jfe Steel Corporation | Weld joint |
Also Published As
Publication number | Publication date |
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CN105821313A (zh) | 2016-08-03 |
JP5439887B2 (ja) | 2014-03-12 |
KR20130035277A (ko) | 2013-04-08 |
CN102124133A (zh) | 2011-07-13 |
KR20150094793A (ko) | 2015-08-19 |
KR20100116701A (ko) | 2010-11-01 |
EP2272994A4 (en) | 2014-01-08 |
JP2009263777A (ja) | 2009-11-12 |
EP2272994B1 (en) | 2014-11-12 |
EP2272994A1 (en) | 2011-01-12 |
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