WO2009123195A1 - 高張力厚鋼板の製造方法 - Google Patents
高張力厚鋼板の製造方法 Download PDFInfo
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- WO2009123195A1 WO2009123195A1 PCT/JP2009/056664 JP2009056664W WO2009123195A1 WO 2009123195 A1 WO2009123195 A1 WO 2009123195A1 JP 2009056664 W JP2009056664 W JP 2009056664W WO 2009123195 A1 WO2009123195 A1 WO 2009123195A1
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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
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
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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
- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
-
- 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
- C22C38/02—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
- C22C38/12—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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
- B21B45/0203—Cooling
Definitions
- the present invention requires a high-tensile steel plate with high tensile strength of 780 MPa or more, which is excellent in preheating-free high weldability and low-temperature toughness of the welded joint, without using expensive Ni and requiring reheating and tempering heat treatment after rolling.
- the present invention relates to a method of manufacturing with high productivity and low cost. This application is based on the basic application of Japanese Patent Application No. 2009-061630 filed in Japan on March 13, 2009 and Japanese Patent Application No. 2008-095021 filed in Japan on April 1, 2008. Claim the rights and incorporate their content here.
- Patent Documents 1 to 3 a conventional method of manufacturing a high-tensile steel plate with high weldability of 780 MPa or higher is directly quenched immediately after rolling of the steel plate, and then tempered. There are methods by direct quenching and tempering. With respect to a method for producing a high-tensile thick steel plate of 780 MPa or more in non-tempered condition, for example, Patent Documents 4 to 8 disclose the manufacturing method that is excellent in production period and productivity in that reheating and tempering heat treatment can be omitted. It is.
- Patent Documents 4 to 7 are manufacturing methods by an accelerated cooling-intermediate stopping process in which accelerated cooling after rolling a steel sheet is stopped halfway
- Patent Document 8 is a manufacturing method in which air cooling is performed after rolling to cool to room temperature. is there.
- Japanese Patent Laid-Open No. 03-232923 JP 09-263828 A JP 2000-160281 A JP 2000-319726 A JP 2005-15859 A JP 2004-52063 A JP 2001-226740 A Japanese Patent Laid-Open No. 08-188823
- Patent Documents 1 to 3 require reheating and tempering heat treatment, and there are problems in the manufacturing period, productivity, and manufacturing cost, a so-called non-tempered manufacturing method in which the reheating tempering heat treatment can be omitted.
- the demand for is strong.
- preheating at 50 ° C. or higher is necessary at the time of welding as described in the examples, and high weldability without preheating cannot be satisfied.
- the manufacturing method disclosed in Patent Document 5 requires addition of 0.6% or more of Ni, it is an expensive component system and has a problem in manufacturing cost.
- Patent Document 6 it is possible to manufacture only a plate thickness of 15 mm described in the examples, and it is not possible to satisfy a plate thickness requirement up to a plate thickness of 40 mm. Furthermore, even at a plate thickness of 15 mm, there is a problem that the C content is small and the microstructure of the welded joint becomes coarse, and sufficient welded joint low temperature toughness cannot be obtained. In the manufacturing method disclosed in Patent Document 7, since about 1.0% of Ni addition is necessary as described in the examples, it becomes an expensive component system and has a problem in manufacturing cost. The manufacturing method disclosed in Patent Document 8 can only manufacture up to a plate thickness of 12 mm described in the examples, and cannot satisfy the plate thickness requirement up to a plate thickness of 40 mm.
- rolling is performed at a cumulative reduction ratio of 16 to 30% in the two-phase temperature range of ferrite and austenite, so that the ferrite grains are likely to be coarsened and the strength and toughness are likely to be reduced even in the production of a sheet thickness of 12 mm. There's a problem.
- the high strength and high toughness of the base metal, high weldability, and low temperature toughness of the welded joint are all free of expensive alloy element Ni, and the reheating and tempering heat treatment after rolling cooling is omitted.
- the present situation is that the method for producing a high-tensile thick steel plate that can be satisfied with the present invention has not yet been invented.
- the influence of the plate thickness on making the preheating free is very large. If the thickness is less than 12 mm, preheating-free can be easily achieved. If the thickness is less than 12 mm, the cooling rate of the steel sheet during water cooling can be increased to 100 ° C./sec or more even at the center of the thickness.
- the base material structure can be a bainite or martensite structure with a small alloy element addition amount, and a base material strength of 780 MPa class can be obtained. Since the amount of alloying elements added is small, the hardness of the weld heat affected zone can be kept low without preheating, and weld cracking can be prevented even without preheating.
- the cooling rate during water cooling inevitably decreases.
- the strength of the thick steel plate decreases due to insufficient quenching, and the strength of the 780 MPa class cannot be satisfied.
- the strength reduction is remarkable at the center of the plate thickness (1/2 t portion) where the cooling rate is the smallest.
- the steel plate is thicker than 40 mm and the cooling rate is less than 8 ° C./sec, it is essential to add a large amount of alloying elements to ensure the strength of the base material, and preheating becomes extremely difficult.
- the present invention omits the reheating and tempering heat treatment after rolling and cooling, with all of the high strength and high toughness of the base metal, high weldability, and the low temperature toughness of the welded joint added with no expensive alloy element Ni.
- One object of the present invention is to provide a method for producing a high-tensile thick steel plate having a tensile strength of 780 MPa or more and excellent in weldability and low-temperature toughness.
- the characteristic of the specific steel plate which this invention makes object is as follows.
- the tensile strength is 780 MPa or more, preferably 1000 MPa or less, the yield stress is 685 MPa or more, and the Charpy absorbed energy at ⁇ 80 ° C. is 100 J or more.
- the preheating temperature required for preventing weld cracking at the time of the y-type weld cracking test at room temperature is 25 ° C. or less, or preheating is unnecessary.
- HZ zone weld heat affected zone of submerged arc welding (SAW) joint at welding heat input of 3.0 kJ / mm is 60 J or more at ⁇ 50 ° C.
- the plate thickness is 12 to 40 mm.
- the present inventors have made a number of studies on base materials and welded joints on the premise of manufacturing by direct quenching after rolling with a component system containing no Ni. There are two problems that have been difficult to solve, and one is ensuring low temperature toughness of welded joints without adding Ni. In order to solve this problem, various studies were made on the influence of the additive component on the heat affected zone (HAZ) toughness of the submerged arc welding (SAW) joint at a welding heat input of about 3.0 kJ / mm.
- HZ heat affected zone
- SAW submerged arc welding
- the hardenability of steel that can be evaluated by the hardenability index DI value is strictly controlled to 0.03% or more and 0.055% or less, and the optimum range of 1.00 or more and 2.60 or less.
- cooling was performed at a cooling rate of 8 ° C./sec or more and 80 ° C./sec or less from 700 ° C. to room temperature to 350 ° C.
- a cooling rate 8 ° C./sec or more and 80 ° C./sec or less from 700 ° C. to room temperature to 350 ° C.
- the tensile strength is 780 MPa or more
- the yield stress is 685 MPa or more
- the Charpy absorbed energy at -80 ° C Was newly found to be able to satisfy 100J or more.
- Al 0.002% or more, 0.10% or less
- P 0.01% or less
- S 0.0010% or less
- N 0.0060% or less
- Mo 0.03% or less
- Si 0.09% or less
- V 0.01% or less
- Nb 0.003% or less
- weld crack susceptibility index Pcm value is 0.20.
- a hardenability index DI value of 1.00 to 2.60
- a component composition consisting of the balance Fe and inevitable impurities [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [Al], and [B] are replaced with C and S, respectively.
- a first rolling step in which the cumulative rolling reduction in the temperature range of 850 ° C. or higher is 70 to 90%; and after the one rolling step, in a range of 780 to 830 ° C.
- a second rolling step in which the cumulative rolling reduction is 10 to 40% and is performed at 780 ° C. or higher; and a step of starting accelerated cooling from 700 ° C. or higher to a cooling rate of 8 to 80 ° C./sec after the two rolling steps; And a step of stopping the accelerated cooling at room temperature to 350 ° C .;
- the steel slab or cast slab is further one or two of mass%: Cu: 0.05% or more and 0.20% or less, Cr: 0.05% or more, 1.00% or less.
- the method for producing a high-tensile thick steel plate according to (1) comprising a seed.
- the steel slab or slab further contains one or two of Mg: 0.0005 to 0.01% and Ca: 0.0005 to 0.01% by mass%.
- a structural member of a welded structure such as a construction machine, industrial machine, bridge, building, shipbuilding, etc., which has a strong need for high strength, and has a tensile strength of 780 MPa or more which is excellent in preheating-free weldability.
- a high-tensile steel plate of 12 mm or more and 40 mm or less can be manufactured under high productivity and low cost without using expensive Ni and requiring no reheating and tempering heat treatment after rolling. The effect on the industry is extremely large.
- the steel of the present invention is used in the form of a thick steel plate having a thickness of 12 mm or more and 40 mm or less as a structural member of a welded structure such as a construction machine, an industrial machine, a bridge, a building, or a shipbuilding.
- preheating free means that when JISZ3158 “y-type weld cracking test” is performed at room temperature by welding with a heat input of 2.0 kJ / mm or less using a coated arc, TIG or MIG welding or the like.
- the required preheating temperature for preventing weld cracking is 25 ° C. or lower, or no preheating is required. Below, the reason for limitation of each component and manufacturing method in this invention is demonstrated.
- C is an important element in the present invention. In order to satisfy all of the base material strength / toughness, high weldability, and weld joint low temperature toughness, C must be strictly regulated to 0.030 to 0.055%. . If the amount of C added is less than 0.030%, the transformation temperature during cooling becomes high at the base metal and the weld heat affected zone, and a ferrite structure is generated, so that the base metal strength / toughness and weld joint toughness are lowered. If the amount of addition of C exceeds 0.055%, the required preheating temperature during welding exceeds 25 ° C. and the preheating free cannot be satisfied, and the weld heat affected zone becomes hard, so that the weld joint toughness cannot be satisfied.
- Mn is an important element in the present invention, and it is necessary to add a large amount of 3.0% or more in order to achieve both strength and toughness of the base material. If added over 3.5%, coarse MnS harmful to toughness is generated in the central segregation part, and the base material toughness of the central part of the plate thickness is lowered, so the upper limit is made 3.5%.
- Al should be added in an amount of 0.002% or more as a deoxidizing element. If added over 0.10%, coarse alumina inclusions are produced and the toughness may be lowered, so the upper limit is made 0.10%. In addition, you may restrict
- Mo, Si, V, Ti, and B are elements having particularly important meanings in the present invention. Only when all of these five elements are less than the above upper limit value, Ni is not added and the temperature is ⁇ 50 ° C. Good weld joint toughness is obtained. If one of these five elements exceeds the above upper limit value, a coarse bainite structure containing island martensite that is an embrittled structure in the HAZ part or TiN that is a harmful inclusion is generated.
- Nb is an important element in the present invention, and if added, the strength and toughness of the base material cannot be obtained.
- Nb is effective in obtaining high strength and high toughness through refinement of the structure.
- the distortion during rolling is excessively accumulated by adding Nb, and the ferrite is locally added during rolling and subsequent cooling. Since the structure and a coarse bainite structure including island martensite are generated, the high strength and high toughness of the base material cannot be obtained.
- the upper limit as an impurity element inevitably mixed is 0.003%.
- Cu may be added within the regulation range of the Pcm value and the DI value in order to ensure the strength of the base material. In order to obtain this effect, 0.05% or more must be added. However, if Ni is not added and Cu is added in an amount of 0.20% or more, there is a concern that the manufacturing period, productivity, and manufacturing cost due to the occurrence of surface cracks in steel slabs and steel plates may cause problems, so the upper limit is 0.20%. And Specifically, the content of Cu inevitably mixed is 0.03% or less. Cr may be added within the regulation range of the Pcm value and the DI value in order to ensure the strength of the base material. In order to obtain this effect, 0.05% or more must be added.
- Mg and Ca By adding one or two of Mg and Ca, fine sulfides and oxides can be formed to improve the base metal toughness and weld joint toughness.
- Mg or Ca needs to be added in an amount of 0.0005% or more.
- the addition amount is set to 0.0005% or more and 0.01% or less, respectively.
- limit the upper limit of Ca addition amount to 0.005% or 0.002%.
- Ni is not added.
- Ni is inevitably mixed from scrap raw materials or the like, it is within the scope of the present invention because it is not expensive even if it is contained. Specifically, the content of Ni inevitably mixed is 0.03% or less.
- weld crack sensitivity index Pcm value is not 0.24% or less, preheating during welding cannot be made free, so the upper limit is made 0.24% or less. If the Pcm value is less than 0.20%, the high strength and high toughness of the base material cannot be satisfied, so the lower limit is made 0.20%.
- Pcm [C] + [Si] / 30 + [Mn] / 20 + [Cu] / 20 + [Ni] / 60 + [Cr] / 20 + [Mo] / 15 + [V] / 10 + 5 [B] [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [B] are C, Si, Mn, Cu, Ni, Cr, It means the content expressed by mass% of Mo, V and B.
- the hardenability index DI value When the hardenability index DI value is less than 1.00, the hardenability of the HAZ part becomes insufficient, a coarse bainite structure including island martensite which is an embrittled structure is generated, and the low temperature toughness of the welded joint is lowered. For this reason, 1.00 is set as the lower limit. If the DI value exceeds 2.60, the structure of the HAZ part itself contains a lot of low toughness martensite and the weld joint low temperature toughness decreases, so the upper limit is made 2.60. Note that the upper limit of the DI value may be limited to 2.00, 1.80, or 1.60.
- DI 0.367 ([C] 1/2 ) (1 + 0.7 [Si]) (1 + 3.33 [Mn]) (1 + 0.35 [Cu]) (1 + 0.36 [Ni]) (1 + 2 .16 [Cr]) (1 + 3.0 [Mo]) (1 + 1.75 [V]) (1 + 1.77 [Al])
- [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and [Al] are C, Si, Mn, Cu, and Ni, respectively.
- Cr, Mo, V means the content expressed as mass% of Al.
- the coefficient of each element of the hardenability index DI value is that described in Nippon Steel Technical Report No. 348 (1993), page 11.
- the heating temperature of the steel slab or slab needs to be 950 ° C. or higher required for rolling. When it exceeds 1100 ° C., austenite grains become coarse and toughness decreases. In particular, in the case where Ni is not added according to the present invention, good base material toughness cannot be obtained unless the initial austenite grains during heating are made fine. In the component system in which the C content is low and Nb is not added according to the present invention, the effect of inhibiting the growth of austenite grains by solute C or NbC is small, and the initial austenite grains during heating are likely to be coarsened, so the upper limit of the heating temperature is strict at 1100 ° C. It is necessary to regulate.
- the cumulative rolling reduction in the austenite recrystallization temperature range needs to be 70% or more in order to finely austenite grains isotropically and to obtain high strength and high toughness of the base material.
- the sufficient austenite recrystallization temperature range of the steel of the present invention is 850 ° C. or higher.
- the cumulative rolling reduction at 850 ° C. or higher needs to be 70% or higher.
- the cumulative rolling reduction is a percentage expressed by dividing the total rolling thickness of rolling at 850 ° C. or higher by the rolling start thickness, that is, the steel slab or slab thickness. If the cumulative rolling reduction exceeds 90%, the rolling time becomes long and the productivity decreases, so the upper limit is made 90%.
- the cumulative rolling reduction in the austenite non-recrystallization temperature range needs to be 10% or more in order to obtain the high strength and high toughness of the base material.
- the sufficient austenite non-recrystallization temperature range of the steel of the present invention is 780 to 830 ° C. Therefore, the cumulative rolling reduction at 780 to 830 ° C. needs to be 10% or more.
- the cumulative rolling reduction is expressed as% by dividing the total rolling thickness of rolling at 780 to 830 ° C. by the rolling starting thickness at 780 to 830 ° C. If the cumulative rolling reduction exceeds 40%, the accumulation of excessive rolling strain locally produces a ferrite structure and a coarse bainite structure including island martensite, and the high strength and high toughness of the base material cannot be obtained.
- the upper limit is 40%.
- the rolling temperature is lower than 780 ° C., a ferrite structure and a coarse bainite structure including island martensite are locally generated due to accumulation of excessive rolling strain, and the high strength and high toughness of the base material are obtained. Therefore, the lower limit of the rolling temperature is regulated to 780 ° C.
- the lower limit temperature is 700 ° C.
- the lower limit is 8 ° C./sec.
- the upper limit is 80 ° C./sec, which is a cooling rate that can be stably realized by water cooling.
- the upper limit of the stop temperature is set to 350 ° C.
- the stop temperature at this time is the steel sheet surface temperature when the steel sheet is reheated after the cooling is completed.
- the lower limit of the stop temperature is room temperature, but the more preferable stop temperature is 100 ° C. or higher in terms of dehydrogenation of the steel sheet.
- Table 4 shows the evaluation results of base material strength (base material yield stress, base material tensile strength), base material toughness, weldability (required preheating temperature), and welded joint low temperature toughness (weld heat affected zone toughness) for these steel plates. Shown in ⁇ 7.
- the strength of the base material was measured by taking a No. 1A full thickness tensile test piece or a No. 4 round bar tensile test piece specified in JISZ2201, and measuring it according to the method specified in JISZ2241.
- Tensile test specimens are sampled from No. 1A full-thickness specimens with a thickness of 20 mm or less, and No.
- the weld heat affected zone toughness is obtained by performing SAW welding (current 500A, voltage 30V, speed 30cm / min) with a heat input of 3.0kJ / mm using a V-shaped groove with a root gap and an angle of 20 °.
- JISZ2202 sampled impact test specimen was taken so that the bottom of the notch contained as much melt line (fusion line) as possible from the part (1 / 2t part), and absorbed energy at -50 ° C (vE-50) evaluated.
- the target values for each property are the base material yield stress of 685 MPa or more, the base material tensile strength of 780 MPa or more, the base material toughness (vE-80) of 100 J or more, the required preheating temperature of 25 ° C. or less, and the weld heat affected zone toughness. It was set to 60 J or more at vE-50.
- the base material yield stress is 685 MPa or more
- the base material tensile strength is 780 MPa or more
- the base material toughness (vE-80) is 100 J or more
- the necessary preheating temperature is 25 ° C. or less
- the influence of welding heat The toughness is 60 J or more at vE-50.
- Comparative Example 22 has a small amount of C added
- Comparative Example 25 has a small amount of Mn added
- Comparative Examples 32 and 33 have Nb added thereto
- Comparative Examples 44 and 45 have low Pcm values.
- Comparative Examples 55 and 56 the cumulative rolling reduction at 850 ° C. or higher is lower than 70%
- Comparative Examples 57 and 58 the cumulative rolling reduction at 780 to 830 ° C. is lower than 10%. Since the cumulative rolling reduction at ⁇ 830 ° C.
- Comparative Examples 61, 62 and 69 have a rolling end temperature lower than 780 ° C.
- Comparative Examples 63, 64 and 70 have a water cooling start temperature lower than 700 ° C. Since Comparative Examples 65, 66 and 71 have a cooling rate lower than 8 ° C./sec, and Comparative Examples 67, 68, 72 and 73 have a cooling stop temperature higher than 350 ° C., the yield stress and tensile strength of the base material are low. Run short.
- Comparative Example 26 has a large amount of Mn added
- Comparative Example 27 has a large amount of P added
- Comparative Example 28 has a large amount of S added
- Comparative Example 29 has a large amount of Cr added.
- Nb is added
- Comparative Examples 36 and 37 have Ti added
- Comparative Example 38 has a large Al addition amount. Therefore, Comparative Examples 41, 42, and 43 have Mg, Ca, and N addition amounts, respectively.
- Comparative Examples 44 and 45 have a low Pcm value
- Comparative Examples 53 and 54 have a high heating temperature
- Comparative Examples 55 and 56 have a cumulative reduction ratio of 850 ° C. or higher below 70%.
- Comparative Examples 61, 62, and 69 have a rolling end temperature lower than 780 ° C., so Comparative Examples 63, 64, and 70 are water cooling start temperatures. Comparative Example 65, 6 , 71 because below the cooling rate is 8 ° C. / sec, Comparative Examples 67,68,72,73, since the cooling stop temperature exceeds 350 ° C., the base material toughness is insufficient.
- Comparative Example 23 has a large amount of added C, Comparative Examples 46, 47 and 49 have high Pcm values, so the necessary preheating temperature exceeds 25 ° C. and does not satisfy preheating free.
- the following comparative examples do not satisfy the weld joint low temperature toughness (welding heat affected zone toughness). That is, since Comparative Example 22 has a small amount of C added, Comparative Example 23 has a large amount of C added, and Comparative Example 24 has Si added, so Comparative Examples 27 and 28 have high P and S contents, respectively. Therefore, Comparative Examples 30 and 31 have Mo added, and Comparative Examples 34 and 35 have V added. Since Comparative Examples 36 and 37 have Ti added, Comparative Example 38 has Al added. Since Comparative Examples 39 and 40 are added with B because of the large amount, Comparative Examples 41, 42, and 43 have large amounts of added Mg, Ca, and N, respectively, and Comparative Examples 44 and 45 have low DI values.
- Comparative Examples 48 and 49 have high DI values, and Comparative Examples 50, 51, and 52 contain any of 3 to 4 elements of Mo, V, Si, Ti, and B. Does not satisfy low temperature toughness.
- Comparative Example 49 Cu was added to Ni-free steel in excess of 0.20%, so that a fine crack was produced on the surface of the slab steel piece, and the surface was partially ground by several mm before hot rolling. Productivity has been reduced.
- a structural member of a welded structure such as a construction machine, industrial machine, bridge, building, shipbuilding, etc., which has a strong need for high strength, and has a tensile strength of 780 MPa or more which is excellent in preheating-free weldability.
- a high-tensile steel plate of 12 mm or more and 40 mm or less can be manufactured under high productivity and low cost without using expensive Ni and requiring no reheating and tempering heat treatment after rolling. The effect on the industry is extremely large.
Abstract
Description
本出願は、2009年3月13日に日本に出願された特願2009-061630号と、2008年4月1日に日本に出願された特願2008-095021号とを基礎出願とに基づき優先権を主張し、それらの内容をここに援用する。
非調質での780MPa以上の高張力厚鋼板の製造方法に関しては、例えば、特許文献4~8に開示があり、いずれも再加熱焼戻し熱処理が省略できる点では製造工期、生産性に優れる製造方法である。このうち、特許文献4~7は、鋼板の圧延後の加速冷却を途中で停止する、加速冷却-途中停止プロセスによる製造方法であり、特許文献8は圧延後空冷で室温まで冷却する製造方法である。
一方で、板厚が厚くなると、水冷時の冷却速度は必然的に小さくなる。このため薄手鋼板と同一成分では焼入れ不足から厚手鋼板の強度は低下し、780MPa級の強度を満足できなくなる。特に冷却速度が最も小さくなる板厚中心部(1/2t部)での強度低下が顕著である。冷却速度が8℃/secを下回るような板厚40mmを超える厚手鋼板になると母材強度確保に合金元素の多量添加が必須となり、予熱フリー化は極めて困難となる。
(a)母材の板厚中心部において、引張強さ780MPa以上、好ましくは1000MPa以下、降伏応力685MPa以上、-80℃でのシャルピー吸収エネルギーが100J以上。
(b)室温におけるy形溶接割れ試験時の溶接割れ防止のための必要予熱温度が25℃以下または、予熱不要。
(c)溶接入熱3.0kJ/mmでのサブマージアーク溶接(SAW)継手の溶接熱影響部(HAZ部)のシャルピー吸収エネルギーが-50℃で60J以上
また、本発明が対象とする鋼板の板厚は、12~40mmである。
(1)引張強さ780MPa以上の高張力厚鋼板の製造方法であって、質量%で、C :0.030%以上、0.055%以下、Mn:3.0%以上、3.5%以下、Al:0.002%以上、0.10%以下、P :0.01%以下、S :0.0010%以下、N :0.0060%以下、Mo:0.03%以下、Si:0.09%以下、V :0.01%以下、Ti:0.003%以下、B :0.0003%以下、Nb:0.003%以下を含み、溶接割れ感受性指数Pcm値が0.20~0.24%であり、焼入れ性指数DI値が1.00~2.60であり、残部Feおよび不可避的不純物からなる成分組成を有し、[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[Al]、[B]を、それぞれC、Si、Mn、Cu、Ni、Cr、Mo、V、Al、Bの質量%で表した含有量としたとき、前記Pcm値が以下のように示され、前記DI値が以下のように示される鋼片または鋳片を、
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5[B]
DI=0.367([C]1/2)(1+0.7[Si])(1+3.33[Mn])(1+0.35[Cu])(1+0.36[Ni])(1+2.16[Cr])(1+3.0[Mo])(1+1.75[V])(1+1.77[Al])
950℃~1100℃に加熱する工程と;850℃以上の温度範囲での累積圧下率を70~90%とする第1圧延工程と;前記1圧延工程の後、780~830℃の範囲での累積圧下率を10~40%とし、780℃以上で行う第2圧延工程と;前記2圧延工程の後、700℃以上から冷却速度が8~80℃/secとなる加速冷却を開始する工程と;室温~350℃で前記加速冷却を停止する工程と;を含むことを特徴とする高張力厚鋼板の製造方法。
(3)前記鋼片または鋳片が、さらに、質量%で、Mg:0.0005~0.01%、Ca:0.0005~0.01%の1種または2種を含有することを特徴とする(1)に記載の高張力厚鋼板の製造方法。
(4)板厚12mm以上かつ40mm以下の厚鋼板を製造することを特徴とする(1)に記載の高張力厚鋼板の製造方法。
以下に、本発明における各成分および製造方法の限定理由を説明する。
Cは、本発明において重要な元素であり、母材強度・靭性、高溶接性、溶接継手低温靭性を全て満足するためには、0.030~0.055%に厳格に規制する必要がある。C添加量が0.030%を下回ると、母材および溶接熱影響部にて冷却時の変態温度が高温となりフェライト組織が生成するため母材強度・靭性および溶接継手靭性が低下する。C添加量が0.055%を超えると、溶接時の必要予熱温度が25℃を超えて予熱フリーを満足できず、また、溶接熱影響部が硬くなるため溶接継手靭性も満足できない。
Sは、Mnを多量に添加する本発明方法においては粗大なMnSを生成して母材および溶接継手の靭性を低下させるため、含有しない事が望ましい。本発明では高強度と高靭性の両立に有効な高価なNiを使用しないので、粗大なMnSの有害性は大きく、不可避的に混入する不純物元素としての許容値は0.0010%以下であり、厳格な規制が必要である。
Nは0.0060%を超えて添加すると、母材および溶接継手靭性を低下させるので、その上限を0.0060%とする。
Mo、Si、V、Ti、Bは、本発明において特に重要な意味を持つ元素であり、これら5元素が5元素とも上記上限値未満である場合に限り、Ni無添加で、-50℃で良好な溶接継手靭性が得られる。これら5元素のうち1元素でも上記上限値を超えると、HAZ部に脆化組織である島状マルテンサイトを含む粗大なベイナイト組織、あるいは有害な介在物であるTiNが生成する。これに対し、5元素とも上記上限値未満である場合に限り、島状マルテンサイトを含む粗大なベイナイト組織もTiNもどちらも生成しない事が、溶接継手の低温靭性が良好となる理由と考えられる。本発明では高強度と高靭性の両立に有効な高価なNiを使用しないので、島状マルテンサイトを含む粗大なベイナイト組織やTiNの有害性は大きく、これら5元素は含有しないことが望ましい。
Crは、母材強度の確保のためにPcm値、DI値の規制範囲内で添加しても良い。この効果を得るためには、0.05%以上の添加が必要である。しかしながら、1.00%を超えて添加すると母材及び溶接継手の靭性が低下するので、その上限を1.00%とする。不可避的に混入するCrの含有量は、具体的には0.03%以下である。なお、Cr添加量の上限値を0.50%又は0.30%に制限してもよい。
ここで、Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5[B]であり、[C] 、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[B]は、それぞれC、Si、Mn、Cu、Ni、Cr、Mo、V、Bの質量%で表した含有量を意味する。
ここで、DI=0.367([C]1/2)(1+0.7[Si])(1+3.33[Mn])(1+0.35[Cu])(1+0.36[Ni])(1+2.16[Cr])(1+3.0[Mo])(1+1.75[V])(1+1.77[Al])
ここで、[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[Al]は、それぞれC、Si、Mn、Cu、Ni、Cr、Mo、V、Alの質量%で表した含有量を意味する。焼入れ性指数DI値の各元素の係数は新日鉄技報第348号(1993)、11ページに記載のものである。
鋼片または鋳片の加熱温度は、圧延に必要な950℃以上とする必要がある。1100℃を超えるとオーステナイト粒が粗大化して靭性が低下する。特に、本発明のNi無添加では加熱時の初期オーステナイト粒を細粒にしておかないと、良好な母材靭性が得られない。本発明のC含有量が少なくNbを添加しない成分系では、固溶CやNbCによるオーステナイト粒成長抑制効果が小さく加熱時の初期オーステナイト粒が粗大化しやすいので、加熱温度の上限は1100℃に厳格に規制する必要がある。
同じように、圧延温度が780℃を下回ると過剰な圧延歪の蓄積により局所的にフェライト組織や、島状マルテンサイトを含む粗大なベイナイト組織が生成し、母材の高強度・高靭性が得られないので、圧延温度の下限を780℃に規制する。
加速冷却の冷却速度が8℃/sec未満の場合、局所的にフェライト組織や、島状マルテンサイトを含む粗大なベイナイト組織が生成し、母材の高強度・高靭性が得られないので、その下限値を8℃/secとする。上限は水冷により安定して実現可能な冷却速度である80℃/secとする。
母材強度は、JISZ2201に規定の、1A号全厚引張試験片あるいは4号丸棒引張試験片を採取し、JISZ2241に規定の方法で測定した。引張試験片は板厚20mm以下では1A号全厚引張試験片を採取し、板厚20mm超では4号丸棒引張試験片を板厚の1/4部(1/4t部)と板厚中心部(1/2t部)より採取した。
母材靭性は、板厚中心部から圧延方向に直角な方向にJISZ2202に規定の衝撃試験片を採取し、JISZ2242に規定の方法で-80℃でのシャルピー吸収エネルギー(vE-80)を求めて評価した。
溶接性は、14~16℃にて、JISZ3158に規定の方法で、入熱1.7kJ/mmで被覆アーク溶接を行い、ルート割れ防止に必要な予熱温度を求めて評価した。
溶接熱影響部靭性は、ルートギャップを有する角度20°のV型開先を用いて入熱量3.0kJ/mmのSAW溶接(電流500A、電圧30V、速度30cm/min)を行い、板厚中心部(1/2t部)よりノッチ底が溶融線(フュージョン・ライン)をできるだけ多く含むようにJISZ2202に規定の衝撃試験片を採取して、-50℃での吸収エネルギー(vE-50)にて評価した。
Claims (4)
- 引張強さ780MPa以上の高張力厚鋼板の製造方法であって、
質量%で、
C :0.030%以上、0.055%以下、
Mn:3.0%以上、3.5%以下、
Al:0.002%以上、0.10%以下、
P :0.01%以下、
S :0.0010%以下、
N :0.0060%以下、
Mo:0.03%以下、
Si:0.09%以下、
V :0.01%以下、
Ti:0.003%以下、
B :0.0003%以下、
Nb:0.003%以下
を含み、溶接割れ感受性指数Pcm値が0.20~0.24%であり、焼入れ性指数DI値が1.00~2.60であり、残部Feおよび不可避的不純物からなる成分組成を有し、[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[Al]、[B]を、それぞれC、Si、Mn、Cu、Ni、Cr、Mo、V、Al、Bの質量%で表した含有量としたとき、前記Pcm値が以下のように示され、前記DI値が以下のように示される鋼片または鋳片を、
Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5[B]
DI=0.367([C]1/2)(1+0.7[Si])(1+3.33[Mn])(1+0.35[Cu])(1+0.36[Ni])(1+2.16[Cr])(1+3.0[Mo])(1+1.75[V])(1+1.77[Al])
950℃~1100℃に加熱する工程と;
850℃以上の温度範囲での累積圧下率を70~90%とする第1圧延工程と;
前記1圧延工程の後、780~830℃の範囲での累積圧下率を10~40%とし、780℃以上で行う第2圧延工程と;
前記2圧延工程の後、700℃以上から冷却速度が8~80℃/secとなる加速冷却を開始する工程と;
室温~350℃で前記加速冷却を停止する工程と;を含むことを特徴とする高張力厚鋼板の製造方法。 - 前記鋼片または鋳片が、さらに、質量%で、
Cu:0.05%以上、0.20%以下、
Cr:0.05%以上、1.00%以下、
の1種または2種を含有することを特徴とする請求項1に記載の高張力厚鋼板の製造方法。 - 前記鋼片または鋳片が、さらに、質量%で、
Mg:0.0005%以上、0.01%以下、
Ca:0.0005%以上、0.01%以下
の1種または2種を含有することを特徴とする請求項1に記載の高張力厚鋼板の製造方法。 - 板厚12mm以上かつ40mm以下の厚鋼板を製造することを特徴とする請求項1に記載の高張力厚鋼板の製造方法。
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US20100108202A1 (en) | 2010-05-06 |
CN101680047B (zh) | 2011-06-22 |
EP2258880B1 (en) | 2012-08-08 |
KR101024802B1 (ko) | 2011-03-24 |
US8043447B2 (en) | 2011-10-25 |
CN101680047A (zh) | 2010-03-24 |
JP2009263772A (ja) | 2009-11-12 |
CA2684793A1 (en) | 2009-10-08 |
TW200948986A (en) | 2009-12-01 |
EP2258880A1 (en) | 2010-12-08 |
CA2684793C (en) | 2011-05-24 |
KR20100005214A (ko) | 2010-01-14 |
BRPI0902906A2 (pt) | 2015-06-23 |
TWI340172B (en) | 2011-04-11 |
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