WO2017141714A1 - 鋼板及びその製造方法 - Google Patents
鋼板及びその製造方法 Download PDFInfo
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- WO2017141714A1 WO2017141714A1 PCT/JP2017/003701 JP2017003701W WO2017141714A1 WO 2017141714 A1 WO2017141714 A1 WO 2017141714A1 JP 2017003701 W JP2017003701 W JP 2017003701W WO 2017141714 A1 WO2017141714 A1 WO 2017141714A1
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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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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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
- 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
Definitions
- the present disclosure relates to a steel plate and a method of manufacturing the same.
- HAZ heat affected zone
- This indication is made based on the above situations, and aims at providing a steel plate which is excellent in base material intensity and HAZ toughness, and its manufacturing method.
- the inventors of the present invention found that when the Ti addition amount of the steel plate is increased, fine TiN effective for improving the HAZ toughness is increased, while coarse TiN with a particle diameter of 2.0 ⁇ m or more decreases the HAZ toughness. Also found to increase. Then, the inventors arrived at the present disclosure which can improve the HAZ toughness at the time of high heat input welding by reducing the amount of coarse TiN formed when the amount of added Ti is increased.
- the invention made in order to solve the above-mentioned subject is C: 0.005 mass% or more and 0.07 mass% or less, Si: 0 mass% or more and 0.04 mass% or less, Mn: 1.4 mass% or more 2.0 mass% or less, P: more than 0 mass%, 0.010 mass% or less, S: more than 0 mass%, 0.007 mass% or less, Al: 0.010 mass% or more and 0.040 mass% or less, Ni: 0.1 mass% or more and 1.50 mass% or less, Cu: 0.1 mass% or more and 0.8 mass% or less, Nb: 0.004 mass% or more and 0.025 mass% or less, Ti: 0.010 mass% More than 0.025 mass% or less, N: 0.0040 mass% or more to 0.0080 mass% or less, Ca: 0.0005 mass% or more to 0.0030 mass% or less, and the rest: Fe and compositions which are unavoidable impurities Has acid-insoluble Ti content [mass%] [ins) [
- the steel plate fine TiN is coarsened by adjusting the ratio between the total Ti content and the content of acid-insoluble Ti mainly present as TiN to a value satisfying the above equation (1).
- the brittle fracture due to coarse TiN is suppressed and the HAZ toughness is excellent.
- the said steel plate is excellent also in base material strength by having the said composition.
- the cross-sectional density of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m to 1 ⁇ m and the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m to 1 ⁇ m are in the above range.
- the contents [mass%] of C, Si, Mn, Cu, Ni, Cr, Mo, V and B are respectively [C], [Si], [Mn], [Cu], [Ni], [Cr], In the case of [Mo], [V] and [B], it is preferable to satisfy the following formula (2). ([C] / 10) 0.5 * (1 + 0.7 * [Si]) * (1 + 3.33 * [Mn]) * (1 + 0.35 * [Cu]) * (1 + 0.36 * [Ni]) X (1 + 2.16 x [Cr]) x (1 + 3 x [Mo]) x (1 + 1. 75 x [V]) x (1 + 200 x [B]) x 1.115 0.7 0.72 (2)
- the strength of the base material can be further improved while maintaining the HAZ toughness.
- the content [mass%] of C, Mn, Cu, Ni, Cr, Mo and V is [C], [Mn], [Cu], [Ni], [Cr], [Mo] and [V] respectively It is good to satisfy the following formula (3) when 110 ⁇ [C] + 7 ⁇ [Mn] + 4 ⁇ [Cu] + 5 ⁇ [Ni] + 2.8 ⁇ [Cr] + 5 ⁇ [Mo] + 7.2 ⁇ [V] ⁇ 21.5 (3)
- Another invention made to solve the above problems is C: 0.005% by mass or more and 0.07% by mass or less, Si: 0% by mass or more and 0.04% by mass or less, Mn: 1.4% by mass or more 2.0 mass% or less, P: more than 0 mass%, 0.010 mass% or less, S: more than 0 mass%, 0.007 mass% or less, Al: 0.010 mass% or more and 0.040 mass% or less, Ni: 0.1 mass% or more and 1.50 mass% or less, Cu: 0.1 mass% or more and 0.8 mass% or less, Nb: 0.004 mass% or more and 0.025 mass% or less, Ti: 0.010 mass% More than 0.025 mass% or less, N: 0.0040 mass% or more to 0.0080 mass% or less, Ca: 0.0005 mass% or more to 0.0030 mass% or less, and the rest: Fe and compositions which are unavoidable impurities Casting the molten steel and the casting obtained in the casting step And hot-rolling at
- the method of manufacturing the steel plate is coarse because the fine TiN increases relative to the coarse TiN by the casting process of cooling the molten steel having the above composition from 1,500 ° C. to 1,450 ° C. in less than 300 seconds.
- the brittle fracture resulting from TiN is suppressed, and a steel plate excellent in HAZ toughness can be manufactured.
- the steel plate which is excellent also in base material strength can be obtained by hot-rolling and cooling on the above-mentioned conditions.
- the above-mentioned molten steel is Cr: more than 0 mass% 1.00 mass%, Mo: more than 0 mass% more than 0.50 mass%, V: more than 0 mass% more than 0.50 mass%, B: more than 0 mass% It is preferable to further contain at least one of .0009 mass% or less, rare earth metal: more than 0 mass% and less than 0.0050 mass%, and Zr: more than 0 mass% and less than 0.0050 mass%.
- the base material strength of the obtained steel sheet can be further improved.
- Still another invention made to solve the above problems is C: 0.005% by mass or more and 0.07% by mass or less, Si: 0% by mass or more and 0.04% by mass or less, Mn: 1.4% by mass More than 2.0 mass% or less, P: more than 0 mass% and less than 0.010 mass%, S: more than 0 mass% and less than 0.007 mass%, Al: 0.010 mass% or more and 0.040 mass% or less, Ni 0.1 mass% or more and 1.50 mass% or less, Cu: 0.1 mass% or more and 0.8 mass% or less, Nb: 0.004 mass% or more and 0.025 mass% or less, Ti: 0.010 mass % Or more, 0.025 mass% or less, N: 0.0040 mass% or more, 0.0080 mass% or less, Ca: 0.0005 mass% or more, 0.0030 mass% or less, and the rest: composition containing Fe and unavoidable impurities Content of N based on the entire composition [mass% When the content of [N] and
- the steel plate has a sectional density of TiN-containing precipitates having a [Ti] / [N] equivalent circle diameter of 0.040 ⁇ m to 1 ⁇ m, and a number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m to 1 ⁇ m.
- Still another invention made to solve the above problems is C: 0.005% by mass or more and 0.07% by mass or less, Si: 0% by mass or more and 0.04% by mass or less, Mn: 1.4% by mass More than 2.0 mass% or less, P: more than 0 mass% and less than 0.010 mass%, S: more than 0 mass% and less than 0.007 mass%, Al: 0.010 mass% or more and 0.040 mass% or less, Ni 0.1 mass% or more and 1.50 mass% or less, Cu: 0.1 mass% or more and 0.8 mass% or less, Nb: 0.004 mass% or more and 0.025 mass% or less, Ti: 0.010 mass % Or more, 0.025 mass% or less, N: 0.0040 mass% or more, 0.0080 mass% or less, Ca: 0.0005 mass% or more, 0.0030 mass% or less, and the rest: composition containing Fe and unavoidable impurities
- the ingot before rolling is 1,050 ° C. or more and 1 Steel sheet characterized by holding at 200 ° C. or less for 20 minutes to 5 hours and setting the cumulative rolling reduction at 900 ° C. or higher to 30% or more and the cumulative rolling reduction at 820 ° C. to 900 ° C. to 15% or more Manufacturing method.
- the manufacturing method of the steel plate has a constant melting residue after high heat input welding by a casting step of cooling molten steel having the above composition under the above conditions and a hot rolling step of rolling after holding the temperature of the ingot under the above conditions. Increase the number of TiN of size. Thereby, the coarsening of the prior austenite grain boundary is suppressed, and the formation of the coarse grain boundary ferrite and the coarse grain boundary bainite is suppressed, and therefore, according to the method of manufacturing the steel plate, a steel plate excellent in HAZ toughness is manufactured. Can. Moreover, in the manufacturing method of the said steel plate, the steel plate which is excellent also in base material strength can be obtained by hot-rolling and cooling on the above-mentioned conditions.
- the above-mentioned molten steel is Cr: more than 0 mass% 1.00 mass%, Mo: more than 0 mass% more than 0.50 mass%, V: more than 0 mass% more than 0.50 mass%, B: more than 0 mass% It is preferable to further contain at least one of .0009 mass% or less, rare earth metal: more than 0 mass% and less than 0.0050 mass%, and Zr: more than 0 mass% and less than 0.0050 mass%.
- the base material strength of the obtained steel sheet can be further improved.
- the steel plate of the present disclosure is excellent in base material strength and HAZ toughness, it can be suitably used for a large-sized welded structure. Moreover, the manufacturing method of the steel plate of this indication can obtain the steel plate which is excellent in base material strength and HAZ toughness.
- the said steel plate is C (carbon): 0.005 mass% or more and 0.07 mass% or less, Si (silicon): 0 mass% or more and 0.04 mass% or less, Mn (manganese): 1.4 mass% or more 2 .0 mass% or less, P (phosphorus): more than 0 mass%, 0.010 mass% or less, S (sulfur): more than 0 mass%, 0.007 mass% or less, Al (aluminum): 0.010 mass% or more 0 .040 mass% or less, Ni (nickel): 0.1 mass% or more and 1.50 mass% or less, Cu (copper): 0.1 mass% or more and 0.8 mass% or less, Nb (niobium): 0.004 Mass% or more and 0.025 mass% or less, Ti (titanium): 0.010 mass% or more and 0.025 mass% or less, N (nitrogen): 0.0040 mass% or more and 0.0080 mass% or
- the lower limit of the average thickness of the steel plate is not particularly limited, and is, for example, 50 mm, more preferably 60 mm.
- the upper limit of the average thickness of the steel plate is not particularly limited, and is, for example, 100 mm.
- the average thickness of the said steel plate is smaller than the said minimum, there exists a possibility that it may become unsuitable for uses, such as a ship.
- the average thickness of the steel plate concerned exceeds the above-mentioned upper limit, there is a possibility that processing etc. may become difficult.
- C is an element necessary for securing the strength of the steel sheet.
- the lower limit of the content of C is 0.005% by mass, preferably 0.01% by mass, and more preferably 0.02% by mass.
- the upper limit of the content of C is 0.07% by mass, preferably 0.06% by mass, and more preferably 0.05% by mass.
- the strength of the steel sheet may be insufficient.
- the content of C exceeds the above upper limit, the solidus temperature of the steel sheet is lowered to promote the formation of coarse TiN, and the HAZ toughness may be lowered.
- Si (silicon)] Si is an element useful for deoxidation of the said steel plate.
- the lower limit of the Si content is 0% by mass.
- the upper limit of the content of Si is 0.04% by mass, preferably 0.03% by mass, and more preferably 0.02% by mass.
- Mn is an element necessary for securing the strength of the steel sheet.
- the lower limit of the content of Mn is 1.4% by mass, preferably 1.50% by mass, and more preferably 1.60% by mass.
- the upper limit of the content of Mn is 2.0% by mass, preferably 1.95% by mass, and more preferably 1.92% by mass.
- the content of Mn is smaller than the above lower limit, the strength of the steel sheet may be insufficient.
- the content of Mn exceeds the above upper limit, island martensite is generated in HAZ of high heat input welding, and the hardness may be excessively increased to lower the toughness.
- [P (phosphorus)] P is an element which is unavoidably contained in the steel sheet and which reduces the HAZ toughness.
- the content of P is more than 0% by mass. The smaller the P content, the better, but it is difficult to industrially achieve 0% by mass.
- the upper limit of the content of P is 0.010% by mass, preferably 0.009% by mass, and more preferably 0.008% by mass. When content of P exceeds the above-mentioned upper limit, there is a possibility that HAZ toughness of the steel plate concerned may fall.
- [S (sulfur)] S is an element which is unavoidably contained in the steel sheet and which reduces the HAZ toughness.
- the content of S is more than 0% by mass. The smaller the content of S, the better. However, it is difficult to industrially reduce the content to 0% by mass.
- the upper limit of the content of S is 0.007% by mass, preferably 0.005% by mass, and more preferably 0.003% by mass. If the content of S exceeds the above upper limit, the HAZ toughness of the steel sheet may be reduced.
- Al (Aluminum) is an element necessary for deoxidation of the steel plate.
- the lower limit of the content of Al is 0.010% by mass, preferably 0.015% by mass, and more preferably 0.020% by mass.
- the upper limit of the content of Al is 0.040% by mass, preferably 0.038% by mass, and more preferably 0.036% by mass.
- the content of Al is smaller than the above lower limit, the oxygen concentration in the steel sheet is increased, and there is a possibility that the HAZ toughness may be reduced due to the increase of oxides.
- the content of Al exceeds the above upper limit, coarse oxides may increase and the HAZ toughness may decrease.
- Ni is an element that contributes to the improvement of the strength of the steel sheet.
- the lower limit of the content of Ni is 0.1% by mass, preferably 0.15% by mass, and more preferably 0.20% by mass.
- the upper limit of the content of Ni is 1.50% by mass, preferably 1.00% by mass, and more preferably 0.80% by mass. If the content of Ni is smaller than the above lower limit, the strength of the steel sheet may be reduced. On the other hand, when the content of Ni exceeds the above upper limit, the hardness may be excessively increased to lower the toughness.
- [Cu (copper)] Cu is an element that contributes to the improvement of the strength of the steel sheet.
- the lower limit of the content of Cu is 0.1% by mass, preferably 0.12% by mass, and more preferably 0.15% by mass.
- the upper limit of the content of Cu is 0.8% by mass, preferably 0.60% by mass, and more preferably 0.50% by mass. If the content of Cu is smaller than the above lower limit, the strength of the steel sheet may be reduced. On the contrary, when content of Cu exceeds the above-mentioned upper limit, there is a possibility that hardness may rise too much and toughness may fall.
- Nb (niobium) Nb is an element necessary for securing the strength of the steel sheet.
- the lower limit of the Nb content is 0.004% by mass, preferably 0.006% by mass, and more preferably 0.007% by mass.
- the upper limit of the content of Nb is 0.025% by mass, preferably 0.022% by mass, and more preferably 0.020% by mass. If the content of Nb is smaller than the above lower limit, the strength of the steel sheet may be insufficient. On the other hand, when the content of Nb exceeds the above upper limit, island martensite is generated in HAZ of high heat input welding, and the hardness may be excessively increased to lower the toughness.
- Ti titanium is an element which precipitates as TiN with N, refines the HAZ structure of high heat input welding, and improves the toughness.
- the lower limit of the content of Ti is 0.010% by mass, preferably 0.012% by mass, and more preferably 0.013% by mass.
- the upper limit of the content of Ti is 0.025% by mass, preferably 0.022% by mass, and more preferably 0.020% by mass.
- the content of Ti is smaller than the above lower limit, the absolute amount of fine TiN may be insufficient, and the effect of improving the HAZ toughness may be insufficient.
- solid solution Ti increases in HAZ, and a coarse bainite structure is formed, which may make it impossible to secure HAZ toughness.
- N is an element which precipitates as TiN together with Ti, refines the HAZ structure of high heat input welding, and improves the toughness.
- the lower limit of the content of N is 0.0040% by mass, preferably 0.0045% by mass, and more preferably 0.0050% by mass.
- the upper limit of the content of N is 0.0080% by mass, preferably 0.0075% by mass, and more preferably 0.0070% by mass. If the content of N is smaller than the above lower limit, the effect of improving fine HAZ toughness by TiN may be insufficient. On the contrary, when content of N exceeds the above-mentioned upper limit, there is a possibility that solid solution N in HAZ of large heat input welding may increase, and toughness may fall.
- Ca (calcium) Ca is an element required for the deoxidation of the said steel plate.
- the lower limit of the content of Ca is 0.0005% by mass, preferably 0.0008% by mass, and more preferably 0.0010% by mass.
- the upper limit of the content of Ca is 0.0030% by mass, preferably 0.0025% by mass, and more preferably 0.0022% by mass.
- the content of Ca is less than the above lower limit, the formation of coarse TiN starting from the oxide particles is promoted, and the HAZ toughness may be lowered.
- the content of Ca exceeds the above upper limit, the HAZ toughness may decrease due to the increase of the coarse oxide.
- the steel plate concerned is Cr (chromium): more than 0 mass% 1.00 mass%, Mo (molybdenum): more than 0 mass% 0.50 mass% or less, V (vanadium): 0 mass% More than 0.50 mass% or less, B (boron): more than 0 mass% to less than 0.0009 mass%, rare earth metal: more than 0 mass% to less than 0.0050 mass%, and Zr (zirconium): more than 0 mass%. It is preferable to further contain at least one of 0050% by mass or less.
- [Cr (Chrome)] Cr is an element that contributes to the improvement of the strength of the steel sheet. In order to improve the strength, it is preferable to contain Cr in an amount of 0.01% by mass or more, and more preferably, 0.05% by mass or more. On the other hand, the addition of Cr may excessively increase the HAZ hardness of high heat input welding and reduce the toughness. Therefore, as an upper limit of content of Cr, 1.00 mass% is preferred, 0.50 mass% is more preferable, and 0.10 mass% is more preferable.
- Mo molybdenum
- Mo is an element that contributes to the improvement of the strength of the steel sheet. In order to improve strength, it is preferable to contain Mo 0.01% by mass or more, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more. On the other hand, the addition of Mo may excessively increase the HAZ hardness of high heat input welding and reduce the toughness. Therefore, as an upper limit of content of Mo, 0.50 mass% is preferred, 0.30 mass% is more preferable, and 0.20 mass% is more preferable.
- V vanadium
- V is an element that contributes to the improvement of the strength of the steel sheet.
- V is preferably contained in an amount of 0.003% by mass or more, more preferably 0.02% by mass or more, and still more preferably 0.05% by mass or more.
- an upper limit of content of V 0.50 mass% is preferred, 0.35 mass% is more preferred, and 0.15 mass% is more preferred.
- the content of V exceeds the above upper limit, the HAZ hardness of the high heat input welding may be excessively increased to lower the toughness.
- [B (boron)] B is an element that contributes to the improvement of the strength and HAZ toughness of the steel sheet.
- B is preferably contained in an amount of 0.0002% by mass or more, more preferably 0.0004% by mass or more, and still more preferably 0.0005% by mass or more.
- an upper limit of content of B 0.0009 mass% is preferable, 0.0008 mass% is more preferable, 0.0007 mass% is more preferable.
- the rare earth metal is an element contributing to the deoxidation of the steel sheet, and is preferably contained 0.0003% by mass or more, more preferably 0.0010% by mass or more, and contained 0.0015% by mass or more Is more preferred.
- the upper limit of the content of the rare earth metal is preferably 0.0050% by mass, more preferably 0.0040% by mass, and still more preferably 0.0030% by mass. When the content of the rare earth metal exceeds the above upper limit, the HAZ toughness may be reduced due to the increase of the coarse oxide.
- “rare earth metal” means 15 lanthanoid elements from La (lanthanum) of atomic number 57 to Lu (lutetium) of atomic number 71, and Sc (scandium) and Y (yttrium).
- Zr (zirconium)] Zr is an element contributing to the deoxidation of the steel sheet, and is preferably contained 0.0003% by mass or more, more preferably 0.0008% by mass or more, further preferably 0.0010% by mass or more preferable.
- the upper limit of the content of Zr is preferably 0.005% by mass, more preferably 0.0040% by mass, and still more preferably 0.0030% by mass. If the content of Zr exceeds the above upper limit, the HAZ toughness may be reduced due to the increase of the coarse oxide.
- the said steel plate contains Fe (iron) and an unavoidable impurity as a remainder other than each element mentioned above.
- the unavoidable impurities include Sn (tin), As (arsenic), Pb (lead) and the like.
- the said steel plate contains the content [mass%] of acid insoluble Ti [insol. Ti]
- the content [mass%] of Ti based on the whole composition is set to [Ti]
- the following formula (1) is satisfied.
- the acid-insoluble Ti is Ti in a Ti compound (for example, TiN, Ti oxide, etc.) insoluble in an acid, and is a concept including Ti in so-called precipitates and crystals.
- Ti in the precipitates and the crystals which are not dissolved in the electrolytic solution by the electrolytic extraction method described later is taken as the acid-insoluble Ti.
- the electrolytic extraction method using an electrolytic solution is performed on a test piece collected at a position of 1 ⁇ 4 of the plate thickness in the thickness direction of the steel plate, and the obtained residue is
- the compound is filtered to extract the compound, and the compound is obtained, for example, by measuring the Ti content by ICP emission spectrometry.
- the acid-insoluble Ti in the embodiment of the present invention is mainly present as TiN, those present as other compounds such as Ti oxide are also included.
- the above-mentioned acid-insoluble Ti is mostly a crystallized product generated in molten steel in a casting process described later, it partially contains a precipitate generated in solid iron.
- the lower limit of [Ti] / [N] is preferably 2.0, and more preferably 2.5.
- the upper limit of [Ti] / [N] is preferably 5.0, and more preferably 4.5. If [Ti] / [N] is smaller than the above lower limit, the number of TiN increases, but the size of TiN decreases, and there is a possibility that the cross-sectional density of TiN-containing precipitates having a predetermined equivalent circle diameter will be insufficient. is there. Conversely, if [Ti] / [N] exceeds the above upper limit, Ti diffusion-controlled growth is promoted, the size of TiN increases, and coarse TiN may increase.
- the steel plate is a TiN-containing precipitate having a cross-sectional density of 2.0 ⁇ 10 5 pieces / mm 2 or more and a circle-equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less.
- the proportion of the number of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less is preferably 15% or less.
- the lower limit of the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is more preferably 2.5 ⁇ 10 5 pieces / mm 2 , and 3.0 ⁇ 10 5 pieces / mm 2 preferable. If the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is smaller than the above lower limit, the fine TiN contributing to the suppression of the prior austenite grain size coarsening decreases and the HAZ toughness may be easily lowered. .
- the upper limit of the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is not particularly limited, and is, for example, 1.0 ⁇ 10 6 / mm 2 .
- the lower limit of the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less is not particularly limited, and is substantially 0%.
- the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 to 1 ⁇ m and the number ratio of the TiN-containing precipitate having a circle equivalent diameter of 0.1 to 1 ⁇ m are values measured by the following method. .
- TEM transmission electron microscope
- a precipitate containing Ti is determined by an energy dispersive X-ray spectrometry (EDX) apparatus or the like, and this is used as a TiN-containing precipitate.
- EDX energy dispersive X-ray spectrometry
- the area of each TiN-containing precipitate in the observation field of view is measured by image analysis and converted to an equivalent circle diameter, and the number of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less, and the circle equivalent diameter 0
- the number of TiN-containing precipitates of 1 ⁇ m or more and 1 ⁇ m or less is measured, and the number of particles per 1 mm 2 is calculated to obtain the cross-sectional density, and the number ratio is obtained from the above-mentioned ratio of the numbers.
- the said steel plate is [C], [Si], [Mn], [Cu], [Ni], [C mass of content of C, Si, Mn, Cu, Ni, Cr, Mo, V and B] respectively.
- [Cr], [Mo], [V] and [B] it is preferable to satisfy the following formula (2).
- the said steel plate is excellent in the strength and the HAZ toughness at the time of high heat input welding, it can be suitably used for large-sized welded structures such as ships.
- ⁇ Method of manufacturing steel plate> As a method of manufacturing the steel plate of the first embodiment, for example, a casting process of casting molten steel, a hot rolling process of hot rolling the obtained ingot, and a process of cooling steel materials after hot rolling And the like. Each step will be described below.
- molten steel having the above composition is cast into a slab shape or the like to obtain an ingot.
- the molten steel having the above composition can be obtained by appropriately combining conventionally known methods such as desulfurization treatment, deoxidation treatment, addition of each element, and the like.
- the cooling process in the temperature range of 1,500 ° C. to 1,450 ° C. is performed in a cooling time of less than 300 seconds.
- Coarse TiN is formed in a temperature range (solid-liquid coexistence temperature range) in which steel is partially solidified in the casting process. That is, in the process of solidifying liquid phase iron into solid, Ti is discharged from solid iron to liquid phase iron, and the concentration of Ti in liquid phase iron increases. In liquid phase iron with an increased Ti concentration, TiN is likely to be formed, and in addition, TiN formed in the liquid phase is easily coarsened. Therefore, in order to reduce coarse TiN, it is important to pass quickly through the solid-liquid coexistence temperature range and to suppress the formation and coarsening of TiN.
- the cooling time from 1,500 ° C. to 1,450 ° C. is 300 seconds or more, coarse TiN is formed during casting [insol. Ti] / [Ti] does not satisfy the above equation (1), and the HAZ toughness is reduced.
- the cooling time from 1,500 ° C. to 1,450 ° C. is more preferably less than 285 seconds.
- the cooling temperature is a measurement temperature at a position of t / 4 in the thickness direction from the surface of the ingot.
- a steel plate is obtained by hot-rolling the ingot obtained at the said casting process.
- the final rolling temperature of the ingot during the hot rolling is 750 ° C. or more and 820 ° C. or less. If the final rolling temperature is lower than the above lower limit, the austenite grains become finer and ferrite precipitation in the subsequent cooling step is promoted, so it may be difficult to obtain a predetermined strength. Conversely, if the final rolling temperature exceeds the above upper limit, the toughness of the steel material may be reduced.
- the cooling rate is 5 ° C./second or more. If the cooling rate is less than the above lower limit, ferrite may be precipitated, which may make it difficult to obtain a predetermined strength.
- the said steel plate is C (carbon): 0.005 mass% or more and 0.07 mass% or less, Si (silicon): 0 mass% or more and 0.04 mass% or less, Mn (manganese): 1.4 mass% or more 2 .0 mass% or less, P (phosphorus): more than 0 mass%, 0.010 mass% or less, S (sulfur): more than 0 mass%, 0.007 mass% or less, Al (aluminum): 0.010 mass% or more 0 .040 mass% or less, Ni (nickel): 0.1 mass% or more and 1.50 mass% or less, Cu (copper): 0.1 mass% or more and 0.8 mass% or less, Nb (niobium): 0.004 Mass% or more and 0.025 mass% or less, Ti (titanium): 0.010 mass% or more and 0.025 mass% or less, N (nitrogen): 0.0040 mass% or more and 0.0080 mass% or
- the average thickness of the steel plate can be the same as that of the steel plate of the first embodiment. Moreover, preferable content of C, Si, Mn, P, S, Al, Ni, Cu, Nb, Ti, N and Ca of the said steel plate, and the remainder can be made to be the same as that of the steel plate of said 1st embodiment. .
- the steel plate concerned is Cr (chromium): more than 0 mass% 1.00 mass%, Mo (molybdenum): more than 0 mass% 0.50 mass% or less, V (vanadium): 0 mass% More than 0.50 mass% or less, B (boron): more than 0 mass% to less than 0.0009 mass%, rare earth metal: more than 0 mass% to less than 0.0050 mass%, and Zr (zirconium): more than 0 mass%. It is preferable to further contain at least one of 0050% by mass or less. Moreover, preferable content of these compositions of the said steel plate can be made to be the same as that of the steel plate of said 1st embodiment.
- the lower limit of [Ti] / [N] of the steel plate is 2.0, preferably 2.5.
- the upper limit of [Ti] / [N] is 5.0, preferably 4.5. If [Ti] / [N] is smaller than the above lower limit, the number of TiN increases, but the size of TiN decreases, and the cross-sectional density of TiN-containing precipitates having a certain range of equivalent circle diameter described later tends to be insufficient. . Conversely, when [Ti] / [N] exceeds the above upper limit, Ti diffusion-limited growth is promoted, the size of TiN increases, and coarse TiN tends to increase.
- the steel plate is a TiN-containing precipitate having a cross-sectional density of 2.0 ⁇ 10 5 pieces / mm 2 or more and a circle-equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less.
- the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less is 15% or less.
- the lower limit of the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is preferably 2.5 ⁇ 10 5 pieces / mm 2, and more preferably 3.0 ⁇ 10 5 pieces / mm 2 .
- the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is smaller than the above lower limit, fine TiN contributing to the suppression of the prior austenite grain size decreases and the HAZ toughness tends to be deteriorated.
- the upper limit of the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is not particularly limited, and is, for example, 5.0 ⁇ 10 5 pieces / mm 2 .
- the upper limit of the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m to 1 ⁇ m 10% is preferable, and 6% is more preferable.
- the proportion of the number of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less exceeds the above upper limit, Ostwald growth of TiN at high temperature holding during welding is promoted, and the number of TiN contributing to suppression of the prior austenite grain size is small. As a result, the HAZ toughness tends to decrease.
- the lower limit of the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less is not particularly limited, and is substantially 0%.
- the said steel plate is excellent in the strength and the HAZ toughness at the time of high heat input welding, it can be suitably used for large-sized welded structures such as ships.
- ⁇ Method of manufacturing steel plate> As a method of manufacturing the steel plate of the second embodiment, for example, a casting process of casting molten steel, a hot rolling process of hot rolling the obtained ingot, and a process of cooling steel materials after hot rolling And the like. Each step will be described below.
- molten steel having the above composition is cast into a slab shape or the like to obtain an ingot.
- the molten steel having the above composition can be obtained by appropriately combining conventionally known methods such as desulfurization treatment, deoxidation treatment, addition of each element, and the like.
- the cooling process in the temperature range of 1,500 ° C. to 1,450 ° C. is performed in a cooling time of less than 300 seconds.
- Coarse TiN is formed in a temperature range (solid-liquid coexistence temperature range) in which steel is partially solidified in the casting process. That is, in the process of solidifying liquid phase iron into solid, Ti is discharged from solid iron to liquid phase iron, and the concentration of Ti in liquid phase iron increases. In liquid phase iron with an increased Ti concentration, TiN is likely to be formed, and in addition, TiN formed in the liquid phase is easily coarsened. Therefore, in order to reduce coarse TiN, it is important to pass quickly through the solid-liquid coexistence temperature range and to suppress the formation and coarsening of TiN.
- the cooling time from 1,500 ° C. to 1,450 ° C. is 300 seconds or more, coarse TiN is formed during casting, and the cross-sectional density of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m to 1 ⁇ m is It becomes smaller and hence the HAZ toughness decreases.
- the cooling time from 1,500 ° C. to 1,450 ° C. is more preferably less than 285 seconds.
- the cooling temperature is a measurement temperature at a position of t / 4 in the thickness direction from the surface of the ingot.
- the cooling process in the temperature range of 1,300 ° C. to 1,200 ° C. is performed for 450 seconds or more and 680 seconds or less.
- the lower limit of the cooling treatment time in the above temperature range is preferably 500 seconds, and the upper limit is preferably 600 seconds. If the cooling process time is less than the above lower limit, TiN-containing precipitates with a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less decrease, and the HAZ toughness decreases.
- a steel plate is obtained by hot-rolling the ingot obtained at the said casting process.
- the ingot before rolling is held at 1,050 ° C. or more and 1,200 ° C. or less for 20 minutes or more and 5 hours or less before hot rolling.
- 2 hours are preferable. If the holding temperature or time is less than the above lower limit, minute TiN smaller than 0.040 ⁇ m does not grow, so the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less decreases, and the HAZ toughness decreases.
- the hot rolling step rolling is performed so that the cumulative rolling reduction at 900 ° C. or higher is 30% or more, and the cumulative rolling reduction at 820 ° C. or more and less than 900 ° C. is 15% or more.
- fine TiN grows due to the diffusion of Ti induced from the strain, the number of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m to 1 ⁇ m increases, and the HAZ toughness can be improved.
- the number of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less decreases, and the HAZ toughness decreases.
- the upper limit of the cumulative pressure reduction in each temperature range is not particularly limited, and is, for example, 50%.
- the "cumulative reduction amount” is the sum of the reduction amounts per pass, and the “reduction amount” is a value calculated by the following equation (4).
- Reduction amount (t0-t1) / t0 ⁇ 100 (4)
- t0 is the rolling start thickness [mm] of the billet when the surface temperature is in the rolling temperature range
- t1 is the rolling finish thickness of the billet when the surface temperature is in the rolling temperature range [Mm] is shown respectively.
- the cooling rate is 5 ° C./sec or more, preferably 6 ° C./sec or more. If the cooling rate is less than the above lower limit, ferrite may be precipitated, which may make it difficult to obtain a predetermined strength.
- a molten steel having the composition shown in Table 1 was melted using a 150 kg vacuum induction furnace, and this molten steel was cast to produce a slab.
- the cooling time from 1,500 ° C. to 1,450 ° C. was the time shown in Table 2.
- This slab is held at 1,100 ° C. for 3 hours, hot rolled at a final finishing temperature of 780 ° C., and water-cooled at a cooling rate of 7.5 ° C./sec. 1 to 6 steel plates were obtained.
- yield strength From each steel plate, a rod-like No. 4 test piece prescribed in JIS-Z2241: 2011 was cut out. In this cutting, the axial direction of the test piece coincides with the width direction of the steel plate, and the distance between the central axis of the test piece and one surface of the steel plate is 1/4 of the thickness of the steel plate. Next, a tensile test was performed according to the method described in JIS-Z2241: 2011, and the yield strength YS [MPa] was measured. The yield strength indicates that the larger the value, the better the strength, and it can be judged that “490 MPa or more” is “good”, and “less than 490 MPa” is “not good”.
- [HAZ toughness] A test piece of 12.5 mm (thickness direction) x 32 mm (C direction) x 55 mm (rolling L direction) is cut out from the position of 1 ⁇ 4 of the plate thickness in the thickness direction of each steel plate and held at 1400 ° C for 60 seconds Then, the temperature was controlled to cool so that the cooling time from 800 ° C. to 500 ° C. was 400 seconds. This is a thermal cycle simulating high heat input welding with a heat input of 55 kJ / mm. Next, three Charpy impact test pieces according to JIS-Z2242: 2005 were collected three by three, and the Charpy impact test was performed at -20 ° C. to measure the absorbed energy vE [J]. The HAZ toughness can be determined to be "good” when vE exceeds 100 J and "not good” at 100 J or less.
- the yield strength is a high value of 515 MPa or more, and the yield strength is excellent as compared with Examples 1 and 3 to 5. From this, it is judged that base material strength can be improved while maintaining HAZ toughness by setting the value of Di to 0.72 or more.
- the HAZ toughness is as good as 146 J or more, and the HAZ toughness is superior to Examples 1 and 2. From this, it is judged that the HAZ toughness can be further improved by setting the value of A to 21.5 or less.
- the HAZ toughness is determined in Example 3 under the influence of Cr. It was inferior to ⁇ 5, 9-10.
- Examples 3 to 5 and 10 in which the Cr content is 0.10 mass% or less and the Mo content is 0.20 mass% or less, have a good HAZ toughness of 160 J or more, and Examples 6 to 9 HAZ toughness was superior to. From this, it is judged that the HAZ toughness can be further improved by setting the Cr content to 0.10 mass% or less and the Mo content to 0.20 mass% or less. In Examples 1 and 2, although Cr and Mo are not contained, the value of A exceeds 21.5. Therefore, the HAZ toughness can be obtained in Examples 3 to 5 and 10 under the influence of A. It was inferior compared.
- Example 6 to 9 in which the Cr content is more than 0.10 mass% or the Mo content is more than 0.20 mass%, the yield strength is as high as 527 MPa or more, and Examples 1, 3 and 3 The yield strength was superior to ⁇ 5 and 10. From this, it is judged that the yield strength can be further improved by setting the Cr content to more than 0.10 mass% or the Mo content to more than 0.20 mass%.
- Example 2 although Cr and Mo are not included, since Di is as high as 0.81, the yield strength is higher than in Examples 1, 3 to 5 and 10 due to the influence of Di. The
- Comparative Examples 1 to 4 [insol. Since Ti] / [Ti] is more than 0.8, coarse TiN is large and the HAZ toughness is not good. Moreover, the comparative example 5 is [insol. Although Ti] / [Ti] is 0.8 or less, since the content of Ti is too large, the amount of solid solution Ti increases and the HAZ toughness is not good. Furthermore, also in Comparative Example 6, [insol. Although Ti] / [Ti] is 0.8 or less, since the content of Ti and N is small, the absolute amount of fine TiN is insufficient and the HAZ toughness is not good.
- the test piece was extract
- the axial direction of the test piece was made to coincide with the rolling direction of the steel plate.
- the distance between the central axis of the test piece and one surface of the steel plate was set to be 1 ⁇ 4 of the average thickness of the steel plate.
- one bottom surface of the test piece was made to be a longitudinal cross section of the steel plate.
- a replica TEM test piece was produced from the bottom corresponding to the longitudinal section of the above-mentioned steel plate of this test piece, and it observed with a transmission electron microscope (TEM).
- TEM transmission electron microscope
- observation was performed at a magnification of 15,000 times, an observation field of view of 52.7 ⁇ m 2, and two fields of observation.
- Ti-containing precipitates were identified by an energy dispersive X-ray fluorescence (EDX) apparatus, and the precipitates were regarded as TiN-containing precipitates.
- EDX energy dispersive X-ray fluorescence
- the area of each TiN-containing precipitate in the observation field of view is measured by image analysis and converted to an equivalent circle diameter, and the number of TiN-containing precipitates having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less, and the circle equivalent diameter 0 .
- the number of TiN-containing precipitates of 1 ⁇ m or more and 1 ⁇ m or less is measured, and the cross-sectional density is determined by calculating the number per 1 mm 2 , and the number ratio of TiN-containing precipitates of circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less I asked for.
- the measurement results are shown in Table 4.
- Comparative Examples 7 to 10 either the yield strength or the HAZ toughness is not good because the composition does not satisfy the range of the present invention. Further, in Comparative Examples 11, 13 and 14, the cross-sectional density of the TiN-containing precipitate having a circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less is insufficient, so the HAZ toughness is not good. In Comparative Example 11, the cooling time from 1,500 ° C. to 1,450 ° C. is too long, the cumulative rolling reduction at 900 ° C. or more is too small, and Comparative Example 14 is from 820 ° C. to less than 900 ° C.
- Comparative Example 12 the number ratio of TiN-containing precipitates having a circle equivalent diameter of 0.1 ⁇ m or more and 1 ⁇ m or less is too large, so the HAZ toughness is not good.
- the comparative example 12 is considered to have increased the number ratio because the cooling time from 1,300 ° C. to 1,200 ° C. is too large.
- the disclosure content of the present specification includes the following aspects.
- (Aspect 1) C: 0.005% by mass or more and 0.07% by mass or less, Si: 0% by mass or more and 0.04% by mass or less, Mn: 1.4% by mass or more and 2.0% by mass or less, P: more than 0 mass% and not more than 0.010 mass%, S: more than 0 mass% and not more than 0.007 mass%, Al: 0.010% by mass or more and 0.040% by mass or less, Ni: 0.1% by mass or more and 1.50% by mass or less, Cu: 0.1% by mass or more and 0.8% by mass or less, Nb: 0.004% by mass or more and 0.025% by mass or less, Ti: 0.010% by mass or more and 0.025% by mass or less, N: 0.0040% by mass or more and 0.0080% by mass or less, Ca: 0.0005% by mass or more and 0.0030% by mass or less, and the balance: Fe and a composition that is an unavoidable impurity,
- the above molten steel is Cr: more than 0% by mass and less than 1.00% by mass, Mo: more than 0 mass% and 0.50 mass% or less, V: more than 0 mass% and 0.50 mass% or less, B: more than 0% by mass and not more than 0.0009% by mass
- Circle equivalent diameter 0 for TiN containing precipitates with circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less of TiN containing precipitate of 2.0 ⁇ 10 5 pieces / mm 2 or more and circle equivalent diameter of 0.040 ⁇ m or more and 1 ⁇ m or less Steel sheet in which the number ratio of TiN-containing precipitates of 1 ⁇ m to 1 ⁇ m is 15% or less.
- 1,450 ° C. is performed for less than 300 seconds, and cooling from 1,300 ° C. to 1,200 ° C. for 450 seconds or more and 680 seconds or less. Holding the ingot before rolling at 1,050 ° C. to 1,200 ° C. for 20 minutes to 5 hours, and the cumulative rolling reduction at 900 ° C. or more to 30% or more, cumulative rolling pressure at 820 ° C. to less than 900 ° C.
- the manufacturing method of the steel plate characterized by making amount into 15% or more.
- the above molten steel is Cr: more than 0% by mass and less than 1.00% by mass, Mo: more than 0 mass% and 0.50 mass% or less, V: more than 0 mass% and 0.50 mass% or less, B: more than 0% by mass and not more than 0.0009% by mass Aspect 11.
- the present application is a Japanese patent application whose filing date is February 15, 2016, Japanese Patent Application No. 2016-026380, a Japanese patent application filing date of July 4, 2016, Japanese Patent Application No. 2016-132915. No. and the filing date of which is October 31, 2016, the Japanese Patent Application No. 2016-213579 has priority claims based on Japanese Patent Application No. 2016-213579.
- Japanese Patent Application Nos. 2016-026380, 2016-132915 and 2016-213579 are incorporated herein by reference.
- the steel plate of the present disclosure is excellent in base material strength and HAZ toughness. Moreover, the manufacturing method of the steel plate of this indication can obtain the steel plate which is excellent in base material strength and HAZ toughness.
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Abstract
Description
[insol.Ti]/[Ti]≦0.80 ・・・(1)
([C]/10)0.5×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×(1+200×[B])×1.115≧0.72 ・・・(2)
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3)
まず、本発明の第一実施形態について説明する。
当該鋼板は、C(炭素):0.005質量%以上0.07質量%以下、Si(ケイ素):0質量%以上0.04質量%以下、Mn(マンガン):1.4質量%以上2.0質量%以下、P(リン):0質量%超0.010質量%以下、S(硫黄):0質量%超0.007質量%以下、Al(アルミニウム):0.010質量%以上0.040質量%以下、Ni(ニッケル):0.1質量%以上1.50質量%以下、Cu(銅):0.1質量%以上0.8質量%以下、Nb(ニオブ):0.004質量%以上0.025質量%以下、Ti(チタン):0.010質量%以上0.025質量%以下、N(窒素):0.0040質量%以上0.0080質量%以下、Ca(カルシウム):0.0005質量%以上0.0030質量%以下、並びに残部:Fe(鉄)及び不可避的不純物である組成を有する。
以下、当該鋼板の各成分について説明する。Cは、当該鋼板の強度確保のために必要な元素である。Cの含有量の下限としては、0.005質量%であり、0.01質量%が好ましく、0.02質量%がより好ましい。一方、Cの含有量の上限としては、0.07質量%であり、0.06質量%が好ましく、0.05質量%がより好ましい。Cの含有量が上記下限より小さい場合、当該鋼板の強度が不十分となるおそれがある。逆に、Cの含有量が上記上限を超える場合、当該鋼板の固相線温度が低下することで粗大TiNの生成が助長され、HAZ靭性が低下するおそれがある。
Siは、当該鋼板の脱酸に有用な元素である。Siの含有量の下限としては、0質量%である。一方、Siの含有量の上限としては、0.04質量%であり、0.03質量%が好ましく、0.02質量%がより好ましい。Siの含有量が上記上限を超える場合、Tiの活量が増加することで粗大TiNの生成が助長され、HAZ靭性が低下するおそれがある。
Mnは、当該鋼板の強度確保のために必要な元素である。Mnの含有量の下限としては、1.4質量%であり、1.50質量%が好ましく、1.60質量%がより好ましい。一方、Mnの含有量の上限としては、2.0質量%であり、1.95質量%が好ましく、1.92質量%がより好ましい。Mnの含有量が上記下限より小さい場合、当該鋼板の強度が不十分となるおそれがある。逆に、Mnの含有量が上記上限を超える場合、大入熱溶接のHAZに島状マルテンサイトが生じると共に、硬度が過度に上昇して靭性が低下するおそれがある。
Pは、当該鋼板に不可避的に含まれ、HAZ靭性を低下させる元素である。Pの含有量は、0質量%超である。Pの含有量は小さいほど好ましいが、工業的に0質量%とすることは困難である。一方、Pの含有量の上限としては、0.010質量%であり、0.009質量%が好ましく、0.008質量%がさらに好ましい。Pの含有量が上記上限を超える場合、当該鋼板のHAZ靭性が低下するおそれがある。
Sは、当該鋼板に不可避的に含まれ、HAZ靭性を低下させる元素である。Sの含有量は、0質量%超である。Sの含有量は小さいほど好ましいが、工業的に0質量%とすることは困難である。一方、Sの含有量の上限としては、0.007質量%であり、0.005質量%が好ましく、0.003質量%がより好ましい。Sの含有量が上記上限を超える場合、当該鋼板のHAZ靭性が低下するおそれがある。
Alは、当該鋼板の脱酸に必要な元素である。Alの含有量の下限としては、0.010質量%であり、0.015質量%が好ましく、0.020質量%がより好ましい。一方、Alの含有量の上限としては、0.040質量%であり、0.038質量%が好ましく、0.036質量%がさらに好ましい。Alの含有量が上記下限より小さい場合、当該鋼板中の酸素濃度が上昇し、酸化物の増加によってHAZ靭性が低下するおそれがある。逆に、Alの含有量が上記上限を超える場合、粗大酸化物が増加し、HAZ靭性が低下するおそれがある。
Niは、当該鋼板の強度向上に寄与する元素である。Niの含有量の下限としては、0.1質量%であり、0.15質量%が好ましく、0.20質量%がより好ましい。一方、Niの含有量の上限としては、1.50質量%であり、1.00質量%が好ましく、0.80質量%がより好ましい。Niの含有量が上記下限より小さい場合、当該鋼板の強度が低下するおそれがある。逆に、Niの含有量が上記上限を超える場合、硬度が過度に上昇して靭性が低下するおそれがある。
Cuは、当該鋼板の強度向上に寄与する元素である。Cuの含有量の下限としては、0.1質量%であり、0.12質量%が好ましく、0.15質量%がより好ましい。一方、Cuの含有量の上限としては、0.8質量%であり、0.60質量%が好ましく、0.50質量%がより好ましい。Cuの含有量が上記下限より小さい場合、当該鋼板の強度が低下するおそれがある。逆に、Cuの含有量が上記上限を超える場合、硬度が過度に上昇して靭性が低下するおそれがある。
Nbは、当該鋼板の強度確保に必要な元素である。Nbの含有量の下限としては、0.004質量%であり、0.006質量%が好ましく、0.007質量%がより好ましい。一方、Nbの含有量の上限としては、0.025質量%であり、0.022質量%が好ましく、0.020質量%がより好ましい。Nbの含有量が上記下限より小さい場合、当該鋼板の強度が不十分となるおそれがある。逆に、Nbの含有量が上記上限を超える場合、大入熱溶接のHAZに島状マルテンサイトが生じると共に、硬度が過度に上昇して靭性が低下するおそれがある。
Tiは、Nと共にTiNとして析出し、大入熱溶接のHAZ組織を微細化し、靭性を向上させる元素である。Tiの含有量の下限としては、0.010質量%であり、0.012質量%が好ましく、0.013質量%がより好ましい。一方、Tiの含有量の上限としては、0.025質量%であり、0.022質量%が好ましく、0.020質量%がより好ましい。Tiの含有量が上記下限より小さい場合、微細なTiNの絶対量が不足し、HAZ靭性の向上効果が不十分となるおそれがある。逆に、Tiの含有量が上記上限を超える場合、HAZにおいて固溶Tiが増加し、粗大なベイナイト組織が形成されるようになってHAZ靭性が確保できなくなるおそれがある。
Nは、Tiと共にTiNとして析出し、大入熱溶接のHAZ組織を微細化し、靭性を向上させる元素である。Nの含有量の下限としては、0.0040質量%であり、0.0045質量%が好ましく、0.0050質量%がより好ましい。一方、Nの含有量の上限としては、0.0080質量%であり、0.0075質量%が好ましく、0.0070質量%がより好ましい。Nの含有量が上記下限より小さい場合、微細なTiNによるHAZ靭性の向上効果が不十分となるおそれがある。逆に、Nの含有量が上記上限を超える場合、大入熱溶接のHAZにおける固溶Nが増加し、靭性が低下するおそれがある。
Caは、当該鋼板の脱酸に必要な元素である。Caの含有量の下限としては、0.0005質量%であり、0.0008質量%が好ましく、0.0010質量%がより好ましい。一方、Caの含有量の上限としては、0.0030質量%であり、0.0025質量%が好ましく、0.0022質量%がより好ましい。Caの含有量が上記下限より小さい場合、酸化物粒子を起点とする粗大TiNの生成が助長され、HAZ靭性が低下するおそれがある。逆に、Caの含有量が上記上限を超える場合、粗大酸化物の増加により、HAZ靭性が低下するおそれがある。
Crは、当該鋼板の強度向上に寄与する元素である。強度を向上するためには、Crを0.01質量%以上含有させることが好ましく、0.05質量%以上含有させることがより好ましい。一方、Crの添加により、大入熱溶接のHAZ硬度が過度に上昇して靭性が低下する可能性がある。そのため、Crの含有量の上限としては、1.00質量%が好ましく、0.50質量%がより好ましく、0.10質量%がさらに好ましい。
Moは、当該鋼板の強度向上に寄与する元素である。強度を向上するためには、Moを0.01質量%以上含有させることが好ましく、0.03質量%以上含有させることがより好ましく、0.05質量%以上含有させることがさらに好ましい。一方、Moの添加により、大入熱溶接のHAZ硬度が過度に上昇して靭性が低下する可能性がある。そのため、Moの含有量の上限としては、0.50質量%が好ましく、0.30質量%がより好ましく、0.20質量%がさらに好ましい。
Vは、当該鋼板の強度向上に寄与する元素である。強度を向上するためには、Vを0.003質量%以上含有させることが好ましく、0.02質量%以上含有させることがより好ましく、0.05質量%以上含有させることがさらに好ましい。一方、Vの含有量の上限としては、0.50質量%が好ましく、0.35質量%がより好ましく、0.15質量%がさらに好ましい。Vの含有量が上記上限を超える場合、大入熱溶接のHAZ硬度が過度に上昇して靭性が低下するおそれがある。
Bは、当該鋼板の強度及びHAZ靭性向上に寄与する元素である。強度を向上するためには、Bを0.0002質量%以上含有させることが好ましく、0.0004質量%以上含有させることがより好ましく、0.0005質量%以上含有させることがさらに好ましい。一方、Bの含有量の上限としては、0.0009質量%が好ましく、0.0008質量%がより好ましく、0.0007質量%がさらに好ましい。Bの含有量が上記上限を超える場合、当該鋼板の靭性が不安定となるおそれがある。
希土類金属は、当該鋼板の脱酸に寄与する元素であり、0.0003質量%以上含有させることが好ましく、0.0010質量%以上含有させることがより好ましく、0.0015質量%以上含有させることがさらに好ましい。一方、希土類金属の含有量の上限としては、0.0050質量%が好ましく、0.0040質量%がより好ましく、0.0030質量%がさらに好ましい。希土類金属の含有量が上記上限を超える場合、粗大酸化物の増加により、HAZ靭性が低下するおそれがある。ここで「希土類金属」とは、原子番号57のLa(ランタン)から原子番号71のLu(ルテチウム)までの15のランタノイド元素と、Sc(スカンジウム)及びY(イットリウム)とを意味する。
Zrは当該鋼板の脱酸に寄与する元素であり、0.0003質量%以上含有させることが好ましく、0.0008質量%以上含有させることがより好ましく、0.0010質量%以上含有させることがさらに好ましい。一方、Zrの含有量の上限としては、0.0050質量%が好ましく、0.0040質量%がより好ましく、0.0030質量%がさらに好ましい。Zrの含有量が上記上限を超える場合、粗大酸化物の増加により、HAZ靭性が低下するおそれがある。
当該鋼板は、上述した各元素以外にFe(鉄)及び不可避的不純物を残部として含有する。この不可避的不純物としては、例えばSn(スズ)、As(砒素)、Pb(鉛)等が挙げられる。
[insol.Ti]/[Ti]≦0.80 ・・・(1)
なお、酸不溶性のTiとは、酸に不溶のTi化合物(例えば、TiN、Ti酸化物等)中のTiであり、いわゆる析出物及び晶出物中のTiを含む概念である。本実施形態では、後述する電解抽出法によって電解液に溶解しない析出物及び晶出物中のTiを、酸不溶性のTiとしている。
Di=([C]/10)0.5×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×(1+200×[B])×1.115≧0.72 ・・・(2)
A=110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3)
当該鋼板は、強度及び大入熱溶接時のHAZ靭性に優れるので、船舶等の大型溶接構造物に好適に使用することができる。
第一実施形態の当該鋼板の製造方法としては、例えば溶鋼を鋳造する鋳造工程と、得られた鋳塊を熱間圧延する熱間圧延工程と、熱間圧延後の鋼材を冷却する工程とを備える方法等が挙げられる。以下、各工程について説明する。
本工程では、上記組成を有する溶鋼をスラブ形状等に鋳造し、鋳塊を得る。上記組成を有する溶鋼は、脱硫処理、脱酸処理、各元素の添加等の従来公知の方法を適宜組み合わせることで得ることができる。
本工程では、上記鋳造工程で得られた鋳塊を熱間圧延することで鋼板を得る。この熱間圧延時の鋳塊の最終圧延温度としては、750℃以上820℃以下である。最終圧延温度が上記下限より小さいと、オーステナイト粒が微細化し、続く冷却工程でのフェライト析出が助長されるため、所定の強度を得ることが難しくなるおそれがある。逆に、最終圧延温度が上記上限を超えると、鋼材の靭性が低下するおそれがある。
熱間圧延後には、鋼材の冷却を行う。この冷却速度としては、5℃/秒以上とする。冷却速度が上記下限より小さいと、フェライトが析出し、所定の強度を得ることが難しくなるおそれがある。
次に、本発明の第二実施形態について説明する。
当該鋼板は、C(炭素):0.005質量%以上0.07質量%以下、Si(ケイ素):0質量%以上0.04質量%以下、Mn(マンガン):1.4質量%以上2.0質量%以下、P(リン):0質量%超0.010質量%以下、S(硫黄):0質量%超0.007質量%以下、Al(アルミニウム):0.010質量%以上0.040質量%以下、Ni(ニッケル):0.1質量%以上1.50質量%以下、Cu(銅):0.1質量%以上0.8質量%以下、Nb(ニオブ):0.004質量%以上0.025質量%以下、Ti(チタン):0.010質量%以上0.025質量%以下、N(窒素):0.0040質量%以上0.0080質量%以下、Ca(カルシウム):0.0005質量%以上0.0030質量%以下、並びに残部:Fe(鉄)及び不可避的不純物である組成を有する。
当該鋼板は、強度及び大入熱溶接時のHAZ靭性に優れるので、船舶等の大型溶接構造物に好適に使用することができる。
第二実施形態の当該鋼板の製造方法としては、例えば溶鋼を鋳造する鋳造工程と、得られた鋳塊を熱間圧延する熱間圧延工程と、熱間圧延後の鋼材を冷却する工程とを備える方法等が挙げられる。以下、各工程について説明する。
本工程では、上記組成を有する溶鋼をスラブ形状等に鋳造し、鋳塊を得る。上記組成を有する溶鋼は、脱硫処理、脱酸処理、各元素の添加等の従来公知の方法を適宜組み合わせることで得ることができる。
本工程では、上記鋳造工程で得られた鋳塊を熱間圧延することで鋼板を得る。本工程では、熱間圧延の前に圧延前の鋳塊を1,050℃以上1,200℃以下で20分以上5時間以下保持する。また、上記保持時間の下限としては、2時間が好ましい。保持温度又は時間が上記下限未満であると、0.040μm未満の微小なTiNが成長しないため、円相当径0.040μm以上1μm以下のTiN含有析出物が減少し、HAZ靭性が低下する。一方、保持温度又は時間が上記上限を超えると、オストワルド成長が過剰に進行し円相当径0.040μm以上1μm以下のTiN含有析出物が減少し、HAZ靭性が低下する。
圧下量=(t0 -t1 )/t0 ×100 ・・・(4)
式(4)中、t0 は、表面の温度が圧延温度範囲にあるときの鋼片の圧延開始厚み[mm]、t1 は、表面の温度が圧延温度範囲にあるときの鋼片の圧延終了厚み[mm]をそれぞれ示す。
熱間圧延後には、鋼材の冷却を行う。この冷却速度としては、5℃/秒以上であり、6℃/秒以上が好ましい。冷却速度が上記下限より小さいと、フェライトが析出し、所定の強度を得ることが難しくなるおそれがある。
本開示の鋼板及びその製造方法は、上記実施形態に限定されるものではない。
150kg真空誘導炉を用い、表1に示す組成を有する溶鋼を溶製し、この溶鋼を鋳造することでスラブを作製した。ここで1,500℃から1,450℃までの冷却時間は表2に示す時間とした。このスラブを1,100℃で3時間保持後、最終仕上げ温度780℃で熱間圧延し、冷却速度7.5℃/秒で水冷することにより平均厚さ65mmの実施例1~10及び比較例1~6の鋼板を得た。
得られた鋼板の厚さ方向で板厚の1/4の位置で試験片を採取し、電解液を用いた電解抽出法により上記試験片から抽出した酸不溶性のTiの濃度を測定することで[insol.Ti]の測定を行った。なお、電解液としては、メタノール100cc中に、トリエタノールアミン2ccと、テトラメチルアンモニウムクロライド1gとを含有するものを用いた。測定に際しては、上記電解液での電解抽出により得られた溶液を孔径2.0μmのフィルタでろ過して残渣を得た後、この残渣をICP発光分光分析法によって化学成分を分析し、[insol.Ti]を求めた。なお、上記電解液での電解抽出で不溶であるTiは、本開示で定義する酸不溶性のTiと判断できる。この測定結果を表2に示す。
以下の方法により、各鋼板の降伏強度、及びHAZ靭性を評価した。評価結果を表2に示す。なお、表2中、「Di」は上記(2)式の左辺を示し、「A」は上記(3)式の左辺を示す。
各鋼板から、JIS-Z2241:2011に規定の棒状の4号試験片を切り出した。この切り出しにおいては、試験片の軸方向が鋼板の幅方向と一致し、試験片の中心軸と鋼板の一方の表面との距離が鋼板の板厚の1/4となるようにした。次に、JIS-Z2241:2011に記載の方法で引張り試験を行い、降伏強度YS[MPa]を測定した。降伏強度は、その値が大きいほど強度に優れることを示し、490MPa以上を「良好」、490MPa未満を「良好ではない」と判断できる。
各鋼板の厚さ方向で板厚の1/4の位置から、12.5mm(厚さ方向)×32mm(C方向)×55mm(圧延L方向)の試験片を切り出し、1400℃で60秒間保持した後、800℃から500℃までの冷却時間が400秒となるように速度を制御して冷却した。これは、入熱量が55kJ/mmの大入熱溶接を模擬した熱サイクルである。次に、JIS-Z2242:2005に準拠し、規定のシャルピー衝撃試験片を3本ずつ採取し、-20℃でシャルピー衝撃試験を行い、吸収エネルギーvE[J]を測定した。HAZ靭性は、vEが100Jを超えるものを「良好」、100J以下を「良好ではない」と判断できる。
なお、実施例6~8については、Aの値が21.5以下であるが、Crが0.10質量%を超えて含有されているため、Crの影響により、HAZ靭性は、実施例3~5、9~10に比べると劣っていた。
なお、実施例1~2については、Cr及びMoを含んでいないが、Aの値が21.5を超えているため、当該Aの影響により、HAZ靭性は、実施例3~5、10に比べて劣っていた。
なお、実施例2については、Cr及びMoを含んでいないが、Diが0.81と高いため、当該Diの影響により、降伏強度は、実施例1、3~5、10に比べて高くなった。
次に、150kg真空誘導炉を用い、表3に示す組成を有する溶鋼を溶製し、この溶鋼を鋳造することでスラブを作製した。ここで1,500℃から1,450℃までの冷却時間及び1,300℃から1,200℃までの冷却時間は表4に示す時間とした。このスラブを表4に示す温度及び時間で保持後、900℃以上及び820℃以上900℃未満でそれぞれ表4に示す累積圧下量となるよう熱間圧延し、さらに表4に示す冷却速度で水冷することにより平均厚さ65mmの実施例11~20及び比較例7~15の鋼板を得た。なお、表3の「REM」は、希土類金属(rare earth metal)を示す。
得られた鋼板の厚さ方向で板厚の1/4の位置で試験片を採取し、各鋼板から、柱体状の試験片を切り出した。この切り出しの方法では、試験片の軸方向が鋼板の圧延方向と一致するようにした。また、試験片の中心軸と、鋼板の一方の表面との距離が鋼板の平均厚さの1/4となるようにした。さらに、試験片の一方の底面が鋼板の縦断面となるようにした。次に、この試験片の上記鋼板の縦断面に相当する底面からレプリカTEM試験片を作成し、透過型電子顕微鏡(TEM)で観察した。観察条件は、観察倍率15,000倍、観察視野52.7μm2とし、2視野観察した。観察においては、エネルギー分散型蛍光X線分析(EDX)装置によってTiを含有する析出物を判別し、この析出物をTiN含有析出物とした。次に、画像解析によって観察視野中の各TiN含有析出物の面積を測定して円相当径に換算し、円相当径0.040μm以上1μm以下のTiN含有析出物の個数と、円相当径0.1μm以上1μm以下のTiN含有析出物の個数とを計測し、1mm2あたりの個数を算出することで断面密度を求めると共に、円相当径0.1μm以上1μm以下のTiN含有析出物の個数割合を求めた。測定結果を表4に示す。
上述の方法により、各鋼板の降伏強度、及びHAZ靭性を評価した。評価結果を表4に示す。
(態様1)
C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有し、
酸不溶性のTiの含有量[質量%]を[insol.Ti]、上記組成全体を基準とするTiの含有量[質量%]を[Ti]とした場合に下記式(1)を満たす鋼板。
[insol.Ti]/[Ti]≦0.80 ・・・(1)
(態様2)
Nの含有量[質量%]を[N]とした場合に[Ti]/[N]が2.0以上5.0以下であり、
円相当径0.040μm以上1μm以下のTiN含有析出物の断面密度が2.0×105個/mm2以上、かつ円相当径0.040μm以上1μm以下のTiN含有析出物における円相当径0.1μm以上1μm以下のTiN含有析出物の個数割合が15%以下である態様1に記載の鋼板。
(態様3)
C、Si、Mn、Cu、Ni、Cr、Mo、V及びBの含有量[質量%]をそれぞれ[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]及び[B]とした場合に下記式(2)を満たす態様1又は態様2に記載の鋼板。
([C]/10)0.5×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×(1+200×[B])×1.115≧0.72 ・・・(2)
(態様4)
C、Mn、Cu、Ni、Cr、Mo及びVの含有量[質量%]をそれぞれ[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]及び[V]とした場合に下記式(3)を満たす態様1、態様2又は態様3に記載の鋼板。
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3)
(態様5)
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する態様1から態様4のいずれかに記載の鋼板。
(態様6)
C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有する溶鋼を鋳造する工程と、
上記鋳造工程で得られた鋳塊を750℃以上820℃以下の最終圧延温度で熱間圧延する工程と、
上記熱間圧延工程後の鋼材を5℃/秒以上の冷却速度で冷却する冷却工程とを備え、
上記鋳造工程で1,500℃から1,450℃までの冷却を300秒未満で行うことを特徴とする鋼板の製造方法。
(態様7)
上記溶鋼が、
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する態様6に記載の鋼板の製造方法。
(態様8)
C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有し、
上記組成全体を基準とするNの含有量[質量%]を[N]、Tiの含有量[質量%]を[Ti]とした場合に[Ti]/[N]が2.0以上5.0以下であり、
円相当径0.040μm以上1μm以下のTiN含有析出物の断面密度が2.0×105個/mm2以上、かつ円相当径0.040μm以上1μm以下のTiN含有析出物における円相当径0.1μm以上1μm以下のTiN含有析出物の個数割合が15%以下である鋼板。
(態様9)
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する態様8に記載の鋼板。
(態様10)
C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有する溶鋼を鋳造する工程と、
上記鋳造工程で得られた鋳塊を熱間圧延する工程と、
上記熱間圧延工程後の鋼材を5℃/秒以上の冷却速度で冷却する冷却工程とを備え、
上記鋳造工程で、1,500℃から1,450℃までの冷却を300秒未満、1,300℃から1,200℃までの冷却を450秒以上680秒以下で行い、上記熱間圧延工程で、圧延前の鋳塊を1,050℃以上1,200℃以下で20分以上5時間以下保持し、900℃以上での累積圧下量を30%以上、820℃以上900℃未満での累積圧下量を15%以上とすることを特徴とする鋼板の製造方法。
(態様11)
上記溶鋼が、
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する態様10に記載の鋼板の製造方法。
Claims (15)
- C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有し、
酸不溶性のTiの含有量[質量%]を[insol.Ti]、上記組成全体を基準とするTiの含有量[質量%]を[Ti]とした場合に下記式(1)を満たす鋼板。
[insol.Ti]/[Ti]≦0.80 ・・・(1) - Nの含有量[質量%]を[N]とした場合に[Ti]/[N]が2.0以上5.0以下であり、
円相当径0.040μm以上1μm以下のTiN含有析出物の断面密度が2.0×105個/mm2以上、かつ円相当径0.040μm以上1μm以下のTiN含有析出物における円相当径0.1μm以上1μm以下のTiN含有析出物の個数割合が15%以下である請求項1に記載の鋼板。 - C、Si、Mn、Cu、Ni、Cr、Mo、V及びBの含有量[質量%]をそれぞれ[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]及び[B]とした場合に下記式(2)を満たす請求項1に記載の鋼板。
([C]/10)0.5×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×(1+200×[B])×1.115≧0.72 ・・・(2) - C、Si、Mn、Cu、Ni、Cr、Mo、V及びBの含有量[質量%]をそれぞれ[C]、[Si]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]及び[B]とした場合に下記式(2)を満たす請求項2に記載の鋼板。
([C]/10)0.5×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×(1+200×[B])×1.115≧0.72 ・・・(2) - C、Mn、Cu、Ni、Cr、Mo及びVの含有量[質量%]をそれぞれ[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]及び[V]とした場合に下記式(3)を満たす請求項1に記載の鋼板。
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3) - C、Mn、Cu、Ni、Cr、Mo及びVの含有量[質量%]をそれぞれ[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]及び[V]とした場合に下記式(3)を満たす請求項2に記載の鋼板。
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3) - C、Mn、Cu、Ni、Cr、Mo及びVの含有量[質量%]をそれぞれ[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]及び[V]とした場合に下記式(3)を満たす請求項3に記載の鋼板。
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3) - C、Mn、Cu、Ni、Cr、Mo及びVの含有量[質量%]をそれぞれ[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]及び[V]とした場合に下記式(3)を満たす請求項4に記載の鋼板。
110×[C]+7×[Mn]+4×[Cu]+5×[Ni]+2.8×[Cr]+5×[Mo]+7.2×[V]≦21.5 ・・・(3) - Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する請求項1~8のいずれか1項に記載の鋼板。 - C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有する溶鋼を鋳造する工程と、
上記鋳造工程で得られた鋳塊を750℃以上820℃以下の最終圧延温度で熱間圧延する工程と、
上記熱間圧延工程後の鋼材を5℃/秒以上の冷却速度で冷却する冷却工程とを備え、
上記鋳造工程で1,500℃から1,450℃までの冷却を300秒未満で行うことを特徴とする鋼板の製造方法。 - 上記溶鋼が、
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する請求項10に記載の鋼板の製造方法。 - C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有し、
上記組成全体を基準とするNの含有量[質量%]を[N]、Tiの含有量[質量%]を[Ti]とした場合に[Ti]/[N]が2.0以上5.0以下であり、
円相当径0.040μm以上1μm以下のTiN含有析出物の断面密度が2.0×105個/mm2以上、かつ円相当径0.040μm以上1μm以下のTiN含有析出物における円相当径0.1μm以上1μm以下のTiN含有析出物の個数割合が15%以下である鋼板。 - Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する請求項12に記載の鋼板。 - C:0.005質量%以上0.07質量%以下、
Si:0質量%以上0.04質量%以下、
Mn:1.4質量%以上2.0質量%以下、
P:0質量%超0.010質量%以下、
S:0質量%超0.007質量%以下、
Al:0.010質量%以上0.040質量%以下、
Ni:0.1質量%以上1.50質量%以下、
Cu:0.1質量%以上0.8質量%以下、
Nb:0.004質量%以上0.025質量%以下、
Ti:0.010質量%以上0.025質量%以下、
N:0.0040質量%以上0.0080質量%以下、
Ca:0.0005質量%以上0.0030質量%以下、並びに
残部:Fe及び不可避的不純物
である組成を有する溶鋼を鋳造する工程と、
上記鋳造工程で得られた鋳塊を熱間圧延する工程と、
上記熱間圧延工程後の鋼材を5℃/秒以上の冷却速度で冷却する冷却工程とを備え、
上記鋳造工程で、1,500℃から1,450℃までの冷却を300秒未満、1,300℃から1,200℃までの冷却を450秒以上680秒以下で行い、上記熱間圧延工程で、圧延前の鋳塊を1,050℃以上1,200℃以下で20分以上5時間以下保持し、900℃以上での累積圧下量を30%以上、820℃以上900℃未満での累積圧下量を15%以上とすることを特徴とする鋼板の製造方法。 - 上記溶鋼が、
Cr:0質量%超1.00質量%以下、
Mo:0質量%超0.50質量%以下、
V:0質量%超0.50質量%以下、
B:0質量%超0.0009質量%以下、
希土類金属:0質量%超0.0050質量%以下、及び
Zr:0質量%超0.0050質量%以下
のうち少なくとも1種をさらに含有する請求項14に記載の鋼板の製造方法。
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