WO2011142172A1 - High-strength thick steel plate with excellent drop weight characteristics - Google Patents
High-strength thick steel plate with excellent drop weight characteristics Download PDFInfo
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- WO2011142172A1 WO2011142172A1 PCT/JP2011/056097 JP2011056097W WO2011142172A1 WO 2011142172 A1 WO2011142172 A1 WO 2011142172A1 JP 2011056097 W JP2011056097 W JP 2011056097W WO 2011142172 A1 WO2011142172 A1 WO 2011142172A1
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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
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to a high-strength thick steel plate used as a raw material for a pressure vessel of a nuclear power plant in addition to structural materials such as offshore structures, ships, bridges, etc. It relates to steel plates.
- Thick steel plates used for quenching and tempering have high strength, high toughness and good weldability. It has been widely used as a welded structure for ships and tanks. Such a QT steel sheet tends to be required to have higher strength (for example, yield strength of 415 MPa or more and tensile strength of 620 MPa or more) with the recent increase in size of welded structures.
- Thick steel plates need not only have high strength but also excellent drop weight characteristics, which are indicators of brittle fracture characteristics. However, it is difficult to satisfy these characteristics with increasing strength and thickness.
- NDT non-ductile transition temperature
- Patent Document 2 proposes a technique for generating fine ferrite by performing low temperature rolling to achieve good drop weight characteristics. However, it is difficult to increase the strength with this technique, and it is not possible to ensure a good drop weight characteristic with high strength.
- Patent Document 3 proposes a technology that achieves good drop weight characteristics by generating fine ferrite while suppressing the generation of bainite by roller quench quenching. However, even with this technique, it is difficult to increase the strength, and it is impossible to ensure a good drop weight characteristic with high strength.
- Japanese Unexamined Patent Publication No. 02-93045 Japanese Unexamined Patent Publication No. 55-79828 Japanese Unexamined Patent Publication No. 60-155620
- the present invention has been made in view of such a situation, and the object thereof is to exhibit a good drop weight characteristic with high strength, in addition to structural materials such as marine structures, ships, bridges, etc., as well as nuclear power plants.
- An object of the present invention is to provide a high-strength thick steel plate useful as a material for a pressure vessel or the like.
- the thick steel plate according to the present invention that has solved the above problems is C: 0.03 to 0.150% (meaning “mass%”; the same applies to the chemical composition); Si: 0.5% or less (Including 0%), Mn: 1.0 to 2.0%, P: 0.015% or less (not including 0%), S: 0.01% or less (not including 0%), Al: 0.005 to 0.06%, Cr: 0.10 to 0.5%, Mo: 0.05 to 0.5%, V: 0.10% or less (excluding 0%), N: 0.00.
- the balance is made of iron and inevitable impurities, and the depth t / 4 to t / 2 (t is the surface)
- the area fraction of bainite is 90% or more
- the bainite And the average value of the width is 3.5 ⁇ m or less
- the maximum value of the circle equivalent diameter of bainite islands-like martensite has a gist in that at 3.0 ⁇ m or less.
- the average equivalent circle diameter of the island-shaped martensite is 1.0 ⁇ m or less.
- “equivalent circle diameter” means the diameter when converted to a circle of the same area, focusing on the size of island martensite (hereinafter sometimes abbreviated as “MA”). .
- the thick steel plate of the present invention may further include (a) Cu: 2% or less (not including 0%) and / or Ni: 2% or less (not including 0%), (b) Nb: 0. 05% or less (not including 0%) and / or B: 0.005% or less (not including 0%), (c) Mg: 0.005% or less (not including 0%) and / or Ti: 0.030% or less (not including 0%), (d) Zr: 0.1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%), (e ) Ca: 0.0035% or less (excluding 0%), (f) Co: 2.5% or less (not including 0%) and / or W: 2.5% or less (not including 0%) , (G) rare earth elements: 0.01% or less (not including 0%), etc. are also useful and contain such elements. In Rukoto, characteristics of the steel plate in accordance with the type is further improved.
- the content of Ti is set to 0.005 to 0.030%, and the Ti-based dispersed particles existing in the steel sheet have an average equivalent circle diameter of 40 nm or less.
- the minimum value of the equivalent circle diameter of the particles is preferably 10 nm or more.
- the present invention by appropriately adjusting the chemical component composition and strictly defining the microstructure, it is possible to realize a thick steel plate that can exhibit good drop weight characteristics as well as high strength. In addition to structural materials such as marine structures, ships and bridges, it is extremely useful as a material for pressure vessels in nuclear power plants.
- the present inventors examined from various angles the means for realizing a thick steel plate that can ensure high strength and good drop weight characteristics.
- high strength is ensured by selecting the main structure of bainite (the area fraction of bainite is 90% or more), and the lath width of the bainite (of the bainite formed in a bundle shape) If the average value of (width) is 3.5 ⁇ m or less and the size of MA in bainite (maximum value of equivalent circle diameter) is 3.0 ⁇ m or less, it is effective in improving the drop weight characteristics.
- the headline and the present invention were completed.
- the evaluation position of the above microstructure is t / 4 to t / 2 (t: plate thickness) from the surface, which is representative for evaluating the characteristics of the thick steel sheet.
- the target is chosen as the position.
- the lath width of bainite affects the drop weight characteristic. If the average value is 3.5 ⁇ m or less, the drop weight characteristic can be realized. This can be considered to be because the number of laths that suppress the progress of destruction increases.
- the lath width of bainite is preferably 3 ⁇ m or less, more preferably 2 ⁇ m or less.
- island-shaped martensite is present between the laths of bainite in the form of a plate or particles.
- the maximum value of the equivalent circle diameter affects the drop weight characteristics, and the maximum value (maximum circle) If the equivalent diameter) is 3.0 ⁇ m or less, it will be extremely effective in improving the drop weight characteristics. This can be attributed to the reason that it is difficult to be the starting point of destruction.
- the average value of the MA size is 1.0 ⁇ m or less, and by satisfying these requirements, the drop weight characteristic is further improved because the energy for destruction is improved. Can be made.
- the microstructure is mainly composed of bainite (the area fraction of bainite is 90% or more, preferably 95% or more), and when all are bainite (the total area ratio of bainite is 100%), but part of it (ie, area fraction of 10% or less) is included in another structure (eg, ferrite, Widmanstatten / ferrite, pearlite, martensite, cementite, etc.) Or a plurality of types) may be included.
- bainite the area fraction of bainite is 90% or more, preferably 95% or more
- bainite the total area ratio of bainite is 100%
- part of it ie, area fraction of 10% or less
- another structure eg, ferrite, Widmanstatten / ferrite, pearlite, martensite, cementite, etc.
- a plurality of types may be included.
- the MA size (average equivalent circle diameter) has a correlation with the A value defined by the following formula (1).
- the size of the MA is experimentally determined, and by setting the A value to a value smaller than 1.0 (%), the size of the MA (average circle equivalent diameter) can be controlled to 1.0 ⁇ m or less.
- the following formula (1) includes Si contained if necessary, but when Si is not included, the A value is calculated assuming that there is no item, and when Si is included, the following (1) ) The A value may be calculated from the equation.
- a value 0.34 + 2.2 ⁇ [C] +3.3 [Si] + 6.1 ⁇ [Al] (1)
- [C], [Si], and [Al] indicate the contents (mass%) of C, Si, and Al, respectively.
- the basic component composition in the thick steel plate of the present invention will be described.
- the basic components C, Si, Mn, P, S, Al, Cr, Mo, V, N, and O
- the reasons for limiting the ranges of these components are as follows.
- C is an element necessary for ensuring the strength of the steel sheet, and it is necessary to contain 0.03% or more in order to ensure the desired strength. However, when C is contained excessively, the drop weight characteristic is deteriorated. For these reasons, the upper limit needs to be 0.150%. In addition, the minimum with preferable C content is 0.05%, and a preferable upper limit is 0.13%.
- Si 0.5% or less (including 0%)
- Si is an effective element for securing the strength of the steel sheet, and is contained if necessary. However, if it is contained excessively, the steel material (base material) is coarsened in the form of island martensite (MA) and deteriorates the falling weight characteristics. For these reasons, the upper limit was made 0.5%. In addition, the minimum with preferable Si content is 0.05%, and a preferable upper limit is 0.25%.
- Mn 1.0 to 2.0%
- Mn is an element effective in improving the hardenability and ensuring the strength of the steel sheet. In order to exert such effects, it is necessary to contain Mn in an amount of 1.0% or more. However, if Mn is contained excessively, the drop weight characteristic of the steel sheet deteriorates, so the upper limit is made 2.0%. The minimum with preferable Mn content is 1.2%, and a preferable upper limit is 1.6%.
- P 0.015% or less (excluding 0%)
- P is an impurity inevitably mixed in, and adversely affects the drop weight characteristics of the steel sheet. From such a viewpoint, P is preferably suppressed to 0.015% or less. The upper limit with preferable P content is 0.010%.
- S 0.01% or less (excluding 0%)
- S is an impurity that combines with the alloy elements in the steel sheet to form various inclusions and adversely affects the drop weight characteristics of the steel sheet, so it is preferable that it be as small as possible, taking into account the degree of cleanliness of the practical steel. Therefore, the content should be suppressed to 0.01% or less (preferably 0.005% or less).
- S is an impurity inevitably contained in steel, and it is difficult to make the amount 0% in industrial production.
- Al 0.005 to 0.06%
- Al is an element effective as a deoxidizer and also exhibits an effect of improving the strength of the steel sheet by refining the microstructure of the steel sheet.
- the Al content needs to be 0.005% or more.
- MA island martensite
- the upper limit was made 0.06%.
- the minimum with preferable Al content is 0.01%, and a preferable upper limit is 0.04%.
- Cr 0.10 to 0.5%
- Cr is an element effective in improving the hardenability of the steel sheet and improving the strength.
- the Cr content needs to be 0.10% or more.
- the Cr content needs to be 0.5% or less.
- the minimum with preferable Cr content is 0.2%, and a preferable upper limit is 0.4%.
- Mo 0.05 to 0.5%
- Mo is an element effective in forming fine carbides and improving the strength of the steel sheet.
- the Mo content needs to be 0.05% or more.
- the Mo content needs to be 0.5% or less.
- the minimum with preferable Mo content is 0.15%, and a preferable upper limit is 0.3%.
- V 0.10% or less (excluding 0%)
- V exhibits the effect of improving hardenability and improving the strength of the steel sheet.
- V also has the effect of increasing the temper softening resistance.
- it is preferable to set it to 0.10% or less (more preferably 0.05% or less).
- V content for exhibiting the effect effectively is 0.02% or more.
- N combines with Al and the like, and has the effect of forming nitrides and refining the steel sheet structure to improve the drop weight characteristics. In order to exert such an effect, N needs to be contained by 0.0020% or more. However, if the N content becomes excessive, the drop weight characteristic deteriorates instead, so the content is made 0.010% or less. In addition, the minimum with preferable N content is 0.004%, and a preferable upper limit is 0.008%.
- O 0.010% or less (excluding 0%)
- O is contained as an unavoidable impurity, but exists as an oxide in steel. However, if the content exceeds 0.010%, a coarse oxide is generated and the falling weight characteristic deteriorates. For these reasons, the upper limit of the O content is set to 0.010%. The upper limit with preferable O content is 0.003%.
- the contained elements defined in the present invention are as described above, and the balance is iron and inevitable impurities, and as the inevitable impurities, mixing of elements brought in depending on the situation of raw materials, materials, manufacturing equipment, etc. can be allowed. .
- the thick steel plate of the present invention may further include (a) Cu: 2% or less (not including 0%) and / or Ni: 2% or less (not including 0%), (b) Nb: 0.0.
- Cu and Ni are effective elements for improving the hardenability and improving the strength, and are contained if necessary. However, if the content of these elements is excessive, the drop weight characteristic is lowered, so that it is preferable that both be 2% or less (more preferably 1% or less).
- the preferable lower limit for exhibiting the above effect is 0.2% or more (more preferably 0.3% or more).
- Nb and B exhibit the effect of improving the hardenability and improving the strength of the steel sheet. However, if it is contained in a large amount, the generation of carbides and nitrides increases, and the falling weight characteristic deteriorates. More preferably, Nb is 0.04% or less, and B is 0.002% or less. The contents for effectively exhibiting these effects are 0.01% or more for Nb and 0.0005% or more for B.
- Mg and Ti are contained as necessary because they have the effect of improving the properties of HAZ by forming oxides and nitrides and suppressing the coarsening of austenite grains. However, if these contents are excessive, inclusions become coarse and drop weight characteristics deteriorate, so 0.005% or less (more preferably 0.003% or less) for Mg and 0.030% or less for Ti ( More preferably, it is 0.02% or less.
- the Ti content is 0.005 to 0.030%, and the average size (average circle equivalent diameter) of the Ti-based dispersed particles present in the steel sheet is 40 nm or less.
- the average size of the Ti-based dispersed particles is more preferably 30 nm or less. The smaller the average size, the better the characteristics.
- the minimum size of such Ti-based dispersed particles (minimum circle equivalent diameter) is controlled to be 10 nm or more, the effect of improving the HAZ toughness becomes remarkable, which is more preferable.
- the minimum size of the Ti-based dispersed particles is more preferably 15 nm or more.
- Zr and Hf are effective elements for forming a nitride with N, refining austenite grains, and improving HAZ characteristics. However, if it is excessively contained, the falling weight characteristic is reduced. Therefore, when these elements are contained, Zr is 0.1% or less (more preferably 0.003% or less), and Hf is 0.05% or less (more preferably 0.01% or less).
- Ca 0.0035% or less (excluding 0%)
- Ca is an element that contributes to the improvement of HAZ characteristics by controlling the form of sulfide. However, even if the content exceeds 0.0035%, the falling weight characteristic deteriorates. In addition, the upper limit with more preferable Ca content is 0.0020% or less.
- Co and W are contained as necessary because they have the effect of improving the hardenability and increasing the strength of the steel sheet.
- the upper limit is set to 2.5%.
- the more preferable upper limit of these content is 0.5% or less in all.
- Rare earth elements contribute to improving the toughness of base metal and HAZ by making the shape of inclusions (oxides, sulfides, etc.) inevitably mixed in steel materials finer and spherical. It is an element and is contained if necessary. Such an effect increases as the content thereof increases. However, if the content of REM becomes excessive, inclusions become coarse and drop weight characteristics deteriorate, so it is preferable to suppress the content to 0.01% or less.
- REM means a lanthanoid element (15 elements from La to Lu), Sc (scandium) and Y (yttrium).
- a steel material satisfying the above-mentioned chemical composition is melted by a normal melting method, and this molten steel is cooled to form a slab, for example, after heating in the range of 900 to 1300 ° C.
- Hot rolling is performed, followed by rough rolling so that the rolling reduction in the temperature range from 950 to 850 ° C. becomes 10% or more, and then rolling reduction in the final rolling pass in the temperature range from 800 to 850 ° C.
- finish rolling so as to be 3 to 10%, then directly cool to 400 ° C. at an average cooling rate of 0.1 to 30 ° C./second, and further reheat to a temperature range of 900 to 1000 ° C.
- Quenching is performed and tempering is performed twice or more in a temperature range of 550 to 700 ° C.
- the reason for setting the range of each condition in this method is as follows. The temperature indicated above is controlled by the temperature of the steel sheet surface.
- the reheating temperature needs to be 900 ° C. or higher, but when the reheating temperature exceeds 1000 ° C., coarse austenite is obtained.
- the desired structure structure mainly composed of bainite
- cooling is performed at an average cooling rate of 0.5 to 20 ° C./second. It is necessary to perform quenching.
- tempering is performed. It is important to appropriately control the tempering conditions at this time.
- the tempering conditions affect the lath width and MA size (maximum value) of bainite, and when the tempering temperature is less than 550 ° C. or the number of times of tempering is one, the MA size (maximum value) exceeds the specified value. Become. On the other hand, when the tempering temperature exceeds 700 ° C., the lath width of the bainite exceeds the specified value.
- the method for producing a thick steel sheet according to the present invention is used as follows. It is sufficient to control various conditions.
- the slab heating temperature needs to be 1150 ° C or higher.
- the heating temperature relatively high in this way, Ti-based dispersed particles already present at the time of slab heating can be melted, and the average size can be reduced.
- the temperature relatively high the Ti-based dispersed particles generated in the subsequent process are promoted to some extent, and as a result, the final remaining fine particles can be reduced.
- it is 1200 degreeC or more, and the minimum size can be 10 nm or more by setting it as 1200 degreeC or more.
- the size of the Ti-based dispersed particles is also affected by the content of elements such as C, Si, Mn, Nb, Cu, Ni, Cr, Mo, and V.
- the X value defined by the following formula (2) is 40 (% ) It has been experimentally determined that it is necessary to adjust the content of each additive element so as to achieve the above.
- the X value is preferably 45 (%) or more (more preferably 50 (%) or more), but from the viewpoint of toughness deterioration, it is preferably 150 (%) or less (more preferably). 100 (%) or less).
- the following formula (2) includes elements (Si, Nb, Cu, Ni, etc.) that are included as necessary. When these elements are not included, it is assumed that there is no such item and the X value. When these elements are included, the X value may be calculated from the following equation (2).
- the steel plate which is the object of the present invention basically assumes a thick steel sheet having a thickness of 50 mm or more, it has the same characteristics even in a thickness less than that, and is the object of the present invention. Is included.
- Example 1 Various molten steels having chemical composition shown in Tables 1 and 2 below are melted by a normal melting method, and the molten steel is cooled to form a slab (thickness: 300 mm), and then subjected to the conditions shown in Tables 3 and 4 below. Hot rolling, cooling, and tempering were performed to obtain various steel plates (thickness: 100 mm).
- Tables 1 and 2 below REM was added in the form of a misch metal containing about 50% Ce and about 25% La.
- the “-” column indicates that no element is added.
- No. 25 to 55 are examples that do not meet any of the requirements defined in the present invention, and at least any of the characteristics is inferior.
- the C content is less than the range specified in the present invention, and the drop weight characteristic is good, but the strength is lowered.
- the Si content exceeds the range defined in the present invention (A value is also high), the size of MA (maximum equivalent circle diameter) is increased, and the falling weight characteristic is deteriorated.
- the Mn content is less than the range specified in the present invention, the required strength is not obtained, and the falling weight characteristic is slightly lowered.
- the Mn content exceeds the range specified in the present invention, and the falling weight characteristic is deteriorated.
- the P content exceeds the range specified in the present invention, and although high strength is obtained, the falling weight characteristic is deteriorated.
- the S content exceeds the range defined in the present invention, and although high strength is obtained, the falling weight characteristic is deteriorated.
- the Al content is less than the range specified in the present invention, and the strength is lowered.
- the Al content exceeds the range defined in the present invention, the size of the MA (maximum equivalent circle diameter) is increased, and the falling weight characteristic is deteriorated.
- the content of Cu, which is an optional additive component exceeds the preferable range, the maximum size of the MA is increased, and the falling weight characteristic is deteriorated.
- the content of Ni as an optional additive component exceeds the preferable range, the size of the MA (maximum equivalent circle diameter) is increased, and the falling weight characteristic is deteriorated.
- the Cr content is less than the range defined in the present invention, and the strength is lowered and the falling weight characteristic is slightly lowered.
- the Cr content exceeds the range defined in the present invention, and although high strength is obtained, the falling weight characteristic is deteriorated.
- the Mo content is less than the range defined in the present invention, the strength is lowered, and the falling weight characteristic is slightly lowered.
- the Mo content exceeds the range defined in the present invention, and although high strength is obtained, the falling weight characteristic is deteriorated.
- the V content exceeds the range defined in the present invention, and although high strength is obtained, the falling weight characteristic is deteriorated.
- the content of Nb which is an optional additive component, exceeds the preferable range, and the falling weight characteristic is deteriorated.
- the Ti content as an optional additive component exceeds the preferable range, the strength is lowered, and the falling weight characteristic is deteriorated.
- the B content, which is an optional additive component exceeds the preferable range, and the falling weight characteristic is deteriorated.
- the N content is less than the range defined in the present invention, and the falling weight characteristic is deteriorated.
- the N content exceeds the range defined in the present invention, and the falling weight characteristic is deteriorated.
- the O content exceeds the range specified in the present invention, and the falling weight characteristic is deteriorated.
- the temperature of the final pass is high, the lath width of the bainite becomes large, and the size of the MA (maximum equivalent circle diameter) exceeds the specified value. ing.
- the cooling rate at the time of quenching is not within a predetermined range, the microstructure is not mainly composed of bainite, and satisfies both high strength and good weight loss characteristics. I can't.
- the number of times of tempering is one, the size of the MA (maximum circle equivalent diameter) exceeds the specified value, and the drop weight characteristic is deteriorated.
- the tempering temperature is outside the appropriate temperature range, and either the lath width of bainite or the size of MA (maximum equivalent circle diameter) exceeds the specified value. Has deteriorated.
- Example 2 Various molten steels having chemical composition shown in Table 7 below are melted by a normal melting method, and after this molten steel is cooled to a slab (thickness: 300 mm), hot rolling is performed under the conditions shown in Table 8 below. Cooling and tempering were performed to obtain various steel plates (thickness: 100 mm).
- Tables 7 and 8 the test numbers shown in Tables 1, 3 and 5 are shown for reference. 24 were also shown at the same time.
- HAZ toughness For HAZ toughness, Charpy impact test piece (No. 4 test piece of JIS Z 2201) was taken from the position of t / 4 position (t: thickness) for the obtained thick steel plate, and reproduced HAZ thermal cycle V notch A Charpy test was conducted. The reproduced HAZ heat cycle conditions simulated a heat history of heat input: 100 kJ / mm. For HAZ toughness, the absorbed energy (vE ⁇ 15 ) at ⁇ 15 ° C. was measured for three test pieces, and the average value was obtained.
- No. Nos. 56 to 61 have an average size of Ti-based dispersed particles of 40 nm or less. It can be seen that the HAZ toughness is improved compared to 24 steel plates. In particular, no. In the samples of 60 and 61, the average size of the Ti-based dispersed particles is 40 nm or less, and the minimum size is 10 nm or more, so that it can be seen that good HAZ toughness is exhibited.
- the high-strength thick steel plate of the present invention is useful as a material for a pressure vessel of a nuclear power plant in addition to a structural material such as an offshore structure, a ship, a bridge.
Abstract
Description
A値=0.34+2.2×[C]+3.3[Si]+6.1×[Al]…(1)
但し、[C],[Si]および[Al]は、夫々C,SiおよびAlの含有量(質量%)を示す。 Based on the contents of C, Si and Al, the MA size (average equivalent circle diameter) has a correlation with the A value defined by the following formula (1). The size of the MA is experimentally determined, and by setting the A value to a value smaller than 1.0 (%), the size of the MA (average circle equivalent diameter) can be controlled to 1.0 μm or less. The following formula (1) includes Si contained if necessary, but when Si is not included, the A value is calculated assuming that there is no item, and when Si is included, the following (1) ) The A value may be calculated from the equation.
A value = 0.34 + 2.2 × [C] +3.3 [Si] + 6.1 × [Al] (1)
However, [C], [Si], and [Al] indicate the contents (mass%) of C, Si, and Al, respectively.
Cは鋼板の強度を確保するために必要な元素であり、所望の強度を確保するためには0.03%以上含有させる必要がある。しかしながら、Cを過剰に含有させると、落重特性が却って低下することになる。こうしたことから、その上限は0.150%とする必要がある。尚、C含有量の好ましい下限は0.05%であり、好ましい上限は0.13%である。 [C: 0.03-0.150%]
C is an element necessary for ensuring the strength of the steel sheet, and it is necessary to contain 0.03% or more in order to ensure the desired strength. However, when C is contained excessively, the drop weight characteristic is deteriorated. For these reasons, the upper limit needs to be 0.150%. In addition, the minimum with preferable C content is 0.05%, and a preferable upper limit is 0.13%.
Siは鋼板の強度を確保するために有効な元素であり、必要により含有される。しかしながら、過剰に含有されると鋼材(母材)に島状マルテンサイト(MA)の粗大化を招き落重特性を劣化させる。こうしたことから、その上限を0.5%とした。尚、Si含有量の好ましい下限は0.05%であり、好ましい上限は0.25%である。 [Si: 0.5% or less (including 0%)]
Si is an effective element for securing the strength of the steel sheet, and is contained if necessary. However, if it is contained excessively, the steel material (base material) is coarsened in the form of island martensite (MA) and deteriorates the falling weight characteristics. For these reasons, the upper limit was made 0.5%. In addition, the minimum with preferable Si content is 0.05%, and a preferable upper limit is 0.25%.
Mnは焼入れ性を向上させて鋼板強度を確保する上で有効な元素であり、こうした効果を発揮させるためには、Mnは1.0%以上含有させる必要がある。しかしながらMnを過剰に含有させると、鋼板の落重特性が劣化するので上限を2.0%とする。Mn含有量の好ましい下限は1.2%であり、好ましい上限は1.6%である。 [Mn: 1.0 to 2.0%]
Mn is an element effective in improving the hardenability and ensuring the strength of the steel sheet. In order to exert such effects, it is necessary to contain Mn in an amount of 1.0% or more. However, if Mn is contained excessively, the drop weight characteristic of the steel sheet deteriorates, so the upper limit is made 2.0%. The minimum with preferable Mn content is 1.2%, and a preferable upper limit is 1.6%.
Pは不可避的に混入してくる不純物であり、鋼板の落重特性に悪影響を及ぼすので、できるだけ少ない方が好ましい。こうした観点から、Pは0.015%以下に抑制するのが良い。P含有量の好ましい上限は0.010%である。 [P: 0.015% or less (excluding 0%)]
P is an impurity inevitably mixed in, and adversely affects the drop weight characteristics of the steel sheet. From such a viewpoint, P is preferably suppressed to 0.015% or less. The upper limit with preferable P content is 0.010%.
Sは、鋼板中の合金元素と化合して種々の介在物を形成し、鋼板の落重特性に有害に作用する不純物であるので、できるだけ少ない方が好ましく、実用鋼の清浄度の程度を考慮して0.01%以下(好ましくは0.005%以下)に抑制するのがよい。尚、Sは鋼に不可避的に含まれる不純物であり、その量を0%とすることは工業生産上困難である。 [S: 0.01% or less (excluding 0%)]
S is an impurity that combines with the alloy elements in the steel sheet to form various inclusions and adversely affects the drop weight characteristics of the steel sheet, so it is preferable that it be as small as possible, taking into account the degree of cleanliness of the practical steel. Therefore, the content should be suppressed to 0.01% or less (preferably 0.005% or less). In addition, S is an impurity inevitably contained in steel, and it is difficult to make the amount 0% in industrial production.
Alは脱酸剤として有効な元素であると共に、鋼板のミクロ組織微細化による鋼板強度向上効果も発揮する。こうした効果を発揮させるためには、Al含有量は0.005%以上とする必要がある。しかしながら、過剰に含有されると島状マルテンサイト(MA)の粗大化を招き、落重特性を劣化させる。こうしたことから、その上限を0.06%とした。尚、Al含有量の好ましい下限は0.01%であり、好ましい上限は0.04%である。 [Al: 0.005 to 0.06%]
Al is an element effective as a deoxidizer and also exhibits an effect of improving the strength of the steel sheet by refining the microstructure of the steel sheet. In order to exert such effects, the Al content needs to be 0.005% or more. However, if it is contained excessively, it causes coarsening of island martensite (MA) and deteriorates the falling weight characteristic. For these reasons, the upper limit was made 0.06%. In addition, the minimum with preferable Al content is 0.01%, and a preferable upper limit is 0.04%.
Crは、鋼板の焼入れ性を高めて強度を向上させるのに有効な元素である。こうした効果を発揮させるためには、Cr含有量は0.10%以上とする必要がある。しかしながら、Crの含有量が過剰になると、落重特性を劣化させる。こうしたことから、Cr含有量は0.5%以下とする必要がある。尚、Cr含有量の好ましい下限は0.2%であり、好ましい上限は0.4%である。 [Cr: 0.10 to 0.5%]
Cr is an element effective in improving the hardenability of the steel sheet and improving the strength. In order to exert such effects, the Cr content needs to be 0.10% or more. However, when the Cr content is excessive, the drop weight characteristic is deteriorated. For these reasons, the Cr content needs to be 0.5% or less. In addition, the minimum with preferable Cr content is 0.2%, and a preferable upper limit is 0.4%.
Moは、微細炭化物を形成し、鋼板の強度を向上させる上で有効な元素である。こうした効果を発揮させるためには、Mo含有量は0.05%以上とする必要がある。しかしながら、その含有量が過剰になると、炭化物粗大化が促進され、落重特性が却って低下する。こうしたことから、Mo含有量は0.5%以下にする必要がある。尚、Mo含有量の好ましい下限は0.15%であり、好ましい上限は0.3%である。 [Mo: 0.05 to 0.5%]
Mo is an element effective in forming fine carbides and improving the strength of the steel sheet. In order to exert such effects, the Mo content needs to be 0.05% or more. However, when the content is excessive, the coarsening of the carbide is promoted, and the falling weight characteristic is decreased. For these reasons, the Mo content needs to be 0.5% or less. In addition, the minimum with preferable Mo content is 0.15%, and a preferable upper limit is 0.3%.
Vは焼入れ性を向上させて鋼板の強度を向上させる効果を発揮する。またVは焼戻し軟化抵抗を高くする効果もある。しかしながら、多量に含有されると落重特性が劣化するため、0.10%以下(より好ましくは0.05%以下)とするのが良い。尚、その効果を有効に発揮させるためのV含有量は、0.02%以上である。 [V: 0.10% or less (excluding 0%)]
V exhibits the effect of improving hardenability and improving the strength of the steel sheet. V also has the effect of increasing the temper softening resistance. However, since the falling weight characteristic deteriorates when contained in a large amount, it is preferable to set it to 0.10% or less (more preferably 0.05% or less). In addition, V content for exhibiting the effect effectively is 0.02% or more.
Nは、Al等と結合し、窒化物を形成して鋼板組織を微細化させて落重特性を向上させ
る効果がある。こうした効果を発揮させるには、Nは0.0020%以上含有させる必要がある。しかし、N含有量が過剰になると落重特性が却って劣化するので、0.010%以下とする。尚、N含有量の好ましい下限は0.004%であり、好ましい上限は0.008%である。 [N: 0.0020 to 0.010%]
N combines with Al and the like, and has the effect of forming nitrides and refining the steel sheet structure to improve the drop weight characteristics. In order to exert such an effect, N needs to be contained by 0.0020% or more. However, if the N content becomes excessive, the drop weight characteristic deteriorates instead, so the content is made 0.010% or less. In addition, the minimum with preferable N content is 0.004%, and a preferable upper limit is 0.008%.
Oは、不可避的不純物として含有されるが、鋼中では酸化物として存在する。しかしながら、その含有量が0.010%を超えると粗大な酸化物が生成して落重特性が劣化する。こうしたことから、O含有量の上限を0.010%とする。O含有量の好ましい上限は0.003%である。 [O: 0.010% or less (excluding 0%)]
O is contained as an unavoidable impurity, but exists as an oxide in steel. However, if the content exceeds 0.010%, a coarse oxide is generated and the falling weight characteristic deteriorates. For these reasons, the upper limit of the O content is set to 0.010%. The upper limit with preferable O content is 0.003%.
CuおよびNiは、焼入れ性を高めて強度を向上させるのに有効な元素であり、必要によって含有される。しかしながら、これらの元素の含有量が過剰になると、落重特性が却って低下するので、いずれも2%以下(より好ましくは1%以下)とするのがよい。上記効果を発揮させるための好ましい下限は、いずれも0.2%以上(より好ましくは0.3%以上)である。 [Cu: 2% or less (not including 0%) and / or Ni: 2% or less (not including 0%)]
Cu and Ni are effective elements for improving the hardenability and improving the strength, and are contained if necessary. However, if the content of these elements is excessive, the drop weight characteristic is lowered, so that it is preferable that both be 2% or less (more preferably 1% or less). The preferable lower limit for exhibiting the above effect is 0.2% or more (more preferably 0.3% or more).
NbおよびBは、焼入れ性を向上させて鋼板の強度を向上させる効果を発揮する。しかしながら、多量に含有されると炭化物や窒化物の生成が多くなり落重特性が劣化するため、上記の量までとするのが良い。より好ましくは、Nbで0.04%以下、Bで0.002%以下である。尚、これらの効果を有効に発揮させるための含有量は、Nbで0.01%以上、Bで0.0005%以上である。 [Nb: 0.05% or less (not including 0%) and / or B: 0.005% or less (not including 0%)]
Nb and B exhibit the effect of improving the hardenability and improving the strength of the steel sheet. However, if it is contained in a large amount, the generation of carbides and nitrides increases, and the falling weight characteristic deteriorates. More preferably, Nb is 0.04% or less, and B is 0.002% or less. The contents for effectively exhibiting these effects are 0.01% or more for Nb and 0.0005% or more for B.
MgおよびTiは、酸化物や窒化物を形成し、オーステナイト粒の粗大化を抑制することによって、HAZの特性を向上させる効果を有するため、必要によって含有される。しかしながらこれらの含有量が過剰になると、介在物が粗大化して落重特性が劣化するため、Mgで0.005%以下(より好ましくは0.003%以下)、Tiで0.030%以下(より好ましくは0.02%以下)にするのが良い。 [Mg: 0.005% or less (not including 0%) and / or Ti: 0.030% or less (not including 0%)]
Mg and Ti are contained as necessary because they have the effect of improving the properties of HAZ by forming oxides and nitrides and suppressing the coarsening of austenite grains. However, if these contents are excessive, inclusions become coarse and drop weight characteristics deteriorate, so 0.005% or less (more preferably 0.003% or less) for Mg and 0.030% or less for Ti ( More preferably, it is 0.02% or less.
ZrおよびHfは、Nと窒化物を形成し、オーステナイト粒を微細化し、HAZ特性改善に有効な元素である。しかし、過剰に含有されると落重特性を却って低下させる。このため、これらの元素を含有するときには、Zrは0.1%以下(より好ましくは0.003%以下)、Hfは0.05%以下(より好ましくは0.01%以下)とする。 [Zr: 0.1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%)]
Zr and Hf are effective elements for forming a nitride with N, refining austenite grains, and improving HAZ characteristics. However, if it is excessively contained, the falling weight characteristic is reduced. Therefore, when these elements are contained, Zr is 0.1% or less (more preferably 0.003% or less), and Hf is 0.05% or less (more preferably 0.01% or less).
Caは硫化物の形態を制御してHAZ特性の向上に寄与する元素である。しかし、0.0035%を超えて過剰に含有させても落重特性が却って劣化する。尚、Ca含有量のより好ましい上限は0.0020%以下である。 [Ca: 0.0035% or less (excluding 0%)]
Ca is an element that contributes to the improvement of HAZ characteristics by controlling the form of sulfide. However, even if the content exceeds 0.0035%, the falling weight characteristic deteriorates. In addition, the upper limit with more preferable Ca content is 0.0020% or less.
CoおよびWは、焼入れ性を向上させて鋼板の強度を高める効果を有するので、必要により含有される。しかしながら、過剰に含有するとHAZ靭性が劣化するため、上限をいずれも2.5%とする。尚、これらの含有量のより好ましい上限は、いずれも0.5%以下である。 [Co: 2.5% or less (not including 0%) and / or W: 2.5% or less (not including 0%)]
Co and W are contained as necessary because they have the effect of improving the hardenability and increasing the strength of the steel sheet. However, since HAZ toughness deteriorates when contained excessively, the upper limit is set to 2.5%. In addition, the more preferable upper limit of these content is 0.5% or less in all.
希土類元素(REM)は、鋼材中に不可避的に混入してくる介在物(酸化物や硫化物等)の形状を微細化・球状化することによって、母材やHAZの靭性の向上に寄与する元素であり、必要によって含有される。こうした効果は、その含有量が増加するにつれて増大するが、REMの含有量が過剰になると、介在物が粗大化して落重特性が劣化するため、0.01%以下に抑えることが好ましい。尚、本発明において、REMとは、ランタノイド元素(LaからLuまでの15元素)およびSc(スカンジウム)とY(イットリウム)を含む意味である。 [Rare earth element (REM): 0.01% or less (not including 0%)]
Rare earth elements (REM) contribute to improving the toughness of base metal and HAZ by making the shape of inclusions (oxides, sulfides, etc.) inevitably mixed in steel materials finer and spherical. It is an element and is contained if necessary. Such an effect increases as the content thereof increases. However, if the content of REM becomes excessive, inclusions become coarse and drop weight characteristics deteriorate, so it is preferable to suppress the content to 0.01% or less. In the present invention, REM means a lanthanoid element (15 elements from La to Lu), Sc (scandium) and Y (yttrium).
鋼板の組織を一旦全てオーステナイト化する観点から900℃以上とする必要があるが、加熱温度が1300℃を超えるとオーステナイト粒が粗大化して後の工程で所望の組織を得ることは難しくなる。 [Slab heating temperature: 900-1300 ° C]
Although it is necessary to set it as 900 degreeC or more from a viewpoint which once converts the structure of a steel plate all to austenite, when heating temperature exceeds 1300 degreeC, an austenite grain will coarsen and it will become difficult to obtain a desired structure | tissue in a subsequent process.
この温度範囲での圧下率はベイナイトのラス幅に影響を与え、圧下率を10%以上とすることによって、後の工程との組合せによって、ベイナイトのラス幅の平均値を3.5μm以下にできる。圧下率が10%未満となると、ベイナイトのラス幅の平均値を3.5μm以下にできなくなる。 [Rough rolling is performed so that the rolling reduction in the temperature range from 950 to 850 ° C. is 10% or more]
The rolling reduction in this temperature range affects the lath width of bainite, and by setting the rolling reduction ratio to 10% or more, the average value of the lath width of bainite can be reduced to 3.5 μm or less in combination with the subsequent steps. . When the rolling reduction is less than 10%, the average lath width of bainite cannot be made 3.5 μm or less.
この温度範囲での圧下率はベイナイトのラス幅やMAサイズに影響を与え、温度が850℃を超えたり、圧下率が3%未満となると、ベイナイトのラス幅やMAサイズ(最大値)が規定値を超えることになる。またこのときの圧下率が10%を超えるような圧延は、仕上げ圧延では通常行なわれない。 [Finish rolling is performed in a temperature range of 800 to 850 ° C. so that the rolling reduction in the final rolling pass is 3 to 10%]
The rolling reduction in this temperature range affects the lath width and MA size of bainite. When the temperature exceeds 850 ° C or the rolling reduction is less than 3%, the lath width and MA size (maximum value) of bainite are specified. It will exceed the value. Further, rolling in which the rolling reduction at this time exceeds 10% is not normally performed in finish rolling.
仕上げ圧延を行なった後には、400℃までを0.1~30℃/秒の平均冷却速度で直接冷却する必要がある。冷却時の平均冷却速度が0.1℃/秒未満或は30℃/秒超では、ベイナイト主体とすることができない。このときの冷却を400℃までとするのは、それ以上組織変態を生じないからである。また、直接冷却するのは、焼入れ前の組織を細かくしておくことで、焼入れ後も細かくするという観点からである。 [Cool directly to 400 ° C at an average cooling rate of 0.1 to 30 ° C / second]
After finish rolling, it is necessary to directly cool to 400 ° C. at an average cooling rate of 0.1 to 30 ° C./second. If the average cooling rate during cooling is less than 0.1 ° C./second or more than 30 ° C./second, bainite cannot be the main component. The reason for cooling to 400 ° C. at this time is that no further tissue transformation occurs. Further, the reason for directly cooling is from the viewpoint of making the structure before quenching fine, and making it fine after quenching.
オーステナイト化の観点から、再加熱温度は900℃以上とする必要があるが、再加熱温度が1000℃を超えると粗大オーステナイトとなる。尚、焼入れの効果を発揮させて所望の組織(ベイナイトを主体とする組織)を得るためには、上記の温度範囲に再加熱した後、0.5~20℃/秒の平均冷却速度で冷却を行なって焼入れを行なう必要がある。即ち、焼入れ冷却時の平均冷却速度が0.5℃/秒未満となると、ベイナイト主体の組織とならずフェライト・パーライト主体の組織となり、20℃/秒を超えるような冷却では、マルテンサイトが主体の組織となる。 [Reheating temperature during quenching: 900-1000 ° C]
From the viewpoint of austenitization, the reheating temperature needs to be 900 ° C. or higher, but when the reheating temperature exceeds 1000 ° C., coarse austenite is obtained. In order to obtain the desired structure (structure mainly composed of bainite) by exerting the quenching effect, after reheating to the above temperature range, cooling is performed at an average cooling rate of 0.5 to 20 ° C./second. It is necessary to perform quenching. That is, when the average cooling rate during quenching cooling is less than 0.5 ° C./second, it becomes not a bainite-based structure but a ferrite-pearlite-based structure, and in cooling exceeding 20 ° C./second, martensite is mainly used. Become an organization.
上記のような焼入れを行なった後は、焼戻しを行なうが、このときの焼戻し条件も適切に制御することが重要である。焼戻し条件は、ベイナイトのラス幅やMAサイズ(最大値)に影響を与え、焼戻し温度が550℃未満であったり、焼戻し回数が1回では、MAサイズ(最大値)が規定値を超えることになる。また焼戻し温度が700℃を超えると、ベイナイトのラス幅が規定値を超えることになる。 [Tempering at least twice in the temperature range of 550 to 700 ° C]
After tempering as described above, tempering is performed. It is important to appropriately control the tempering conditions at this time. The tempering conditions affect the lath width and MA size (maximum value) of bainite, and when the tempering temperature is less than 550 ° C. or the number of times of tempering is one, the MA size (maximum value) exceeds the specified value. Become. On the other hand, when the tempering temperature exceeds 700 ° C., the lath width of the bainite exceeds the specified value.
X=500×[C]+32×[Si]+8×[Mn]-9×[Nb]+14×[Cu]+17×[Ni]-5×[Cr]-25×[Mo]-34×[V] …(2)
但し、[C],[Si],[Mn],[Nb],[Cu],[Ni],[Cr],[Mo]および[V]は、夫々C,Si,Mn,Nb,Cu,Ni,Cr,MoおよびVの含有量(質量%)を示す。 The following formula (2) includes elements (Si, Nb, Cu, Ni, etc.) that are included as necessary. When these elements are not included, it is assumed that there is no such item and the X value. When these elements are included, the X value may be calculated from the following equation (2).
X = 500 × [C] + 32 × [Si] + 8 × [Mn] −9 × [Nb] + 14 × [Cu] + 17 × [Ni] −5 × [Cr] −25 × [Mo] −34 × [V ] (2)
However, [C], [Si], [Mn], [Nb], [Cu], [Ni], [Cr], [Mo] and [V] are respectively C, Si, Mn, Nb, Cu, Content (mass%) of Ni, Cr, Mo, and V is shown.
下記表1、2に化学成分組成を示す各種溶鋼を、通常の溶製法によって溶製し、この溶鋼を冷却してスラブ(厚み:300mm)とした後、下記表3、4に示した条件で熱間圧延、冷却および焼戻しを行ない、各種鋼板(厚み:100mm)を得た。尚、下記表1、2において、REMはCeを50%程度とLaを25%程度含有するミッシュメタルの形態で添加した。尚、下記表1、2中「-」の欄は元素を添加していないことを示している。 [Example 1]
Various molten steels having chemical composition shown in Tables 1 and 2 below are melted by a normal melting method, and the molten steel is cooled to form a slab (thickness: 300 mm), and then subjected to the conditions shown in Tables 3 and 4 below. Hot rolling, cooling, and tempering were performed to obtain various steel plates (thickness: 100 mm). In Tables 1 and 2 below, REM was added in the form of a misch metal containing about 50% Ce and about 25% La. In Tables 1 and 2 below, the “-” column indicates that no element is added.
得られた厚鋼板について、t/4(t:板厚)の位置の光学顕微鏡観察を行ない、ベイナイト以外の部位に色を塗り、透明フィルムに映し、その後画像解析装置(Media Cybernetics製:Image-Pro Plus)による画像解析にて色付き部分の面積率を求め、全体100%から差し引いた分をベイナイト面積分率とした。このとき、顕微鏡観察は100倍の3視野で撮影し、その平均値を算出した。 [Measurement of area fraction of bainite]
The obtained thick steel plate was observed with an optical microscope at a position of t / 4 (t: plate thickness), painted on a portion other than bainite and projected on a transparent film, and then an image analysis apparatus (manufactured by Media Cybernetics: Image- The area ratio of the colored portion was determined by image analysis using Pro Plus), and the amount subtracted from the total 100% was defined as the bainite area fraction. At this time, the microscope observation was taken with three fields of view of 100 times, and the average value was calculated.
得られた厚鋼板について、t/4(t:板厚)の位置から採取したサンプルを用いて、倍率:1000倍にて走査型顕微鏡(SEM)観察を行ない、3視野の平均値をその鋼種のラス幅とした。 [Measurement of lath width of bainite]
About the obtained thick steel plate, using the sample extract | collected from the position of t / 4 (t: board thickness), a scanning microscope (SEM) observation is performed by 1000 times of magnification, and the average value of three visual fields is shown for the steel type. The lath width was taken as.
各厚鋼板のt/4(t:板厚)の位置から幅方向にNK U14号試験片を採取し、JIS Z2241に従って引張試験を行うことによって、降伏応力YS(上降伏点YPまたは0.2%耐力σ0.2)および引張強度TSを測定した。合格基準は、3回での平均値で、降伏強度YS:415MPa以上、引張強度TS:620MPa以上である。 [Evaluation of tensile properties of thick steel plate]
An NK U14 test piece is taken in the width direction from the position of t / 4 (t: plate thickness) of each thick steel plate and subjected to a tensile test according to JIS Z2241, thereby yield stress YS (upper yield point YP or 0.2). % Yield strength σ 0.2 ) and tensile strength TS. The acceptance criteria are the average values of three times, yield strength YS: 415 MPa or more, and tensile strength TS: 620 MPa or more.
各厚鋼板のt/4(t:板厚)の位置から採取したサンプルを用いてレペラー腐食し、光学顕微鏡によって組織を観察し、倍率:1000倍、5視野を観察した(白い部分がMAと判断)。画像解析装置(Media Cybernetics製:Image-Pro Plus)による画像解析にて、MAのサイズ(平均円相当直径、最大円相当直径)を測定した。 [Measurement of island-shaped martensite (MA) size (equivalent circle diameter)]
Using a sample taken from the position of t / 4 (t: plate thickness) of each thick steel plate, repeller corrosion was performed, the structure was observed with an optical microscope, magnification: 1000 times, and 5 fields of view were observed (the white part is MA) Judgment). The size of the MA (average circle equivalent diameter, maximum circle equivalent diameter) was measured by image analysis using an image analysis device (Media Cybernetics: Image-Pro Plus).
ASTM E208(2006)に準拠して落重試験を実施し、各厚鋼板の無延性遷移温度NDTを測定した。このとき用いた試験片形状は、P-3タイプとして、厚鋼板のt/4(t:板厚)の位置からC方向(圧延方向に垂直な方向)に沿って採取したものを用いた。また試験片表面に形成するビードは、溶接棒(「NRL-S」 株式会社神戸製鋼所製:直径5mm)を用い、ストレートビードとした。このとき用いた試験片の形状を図1(平均図)に示す(L:50mm、W:130mm)。そして、NDTが-70℃以下を合格とした。 [Evaluation of falling weight characteristics]
A drop weight test was performed according to ASTM E208 (2006), and the non-ductile transition temperature NDT of each thick steel plate was measured. The specimen shape used at this time was a P-3 type sampled from the position of t / 4 (t: plate thickness) of the thick steel plate along the C direction (direction perpendicular to the rolling direction). The bead formed on the surface of the test piece was a straight bead using a welding rod (“NRL-S” manufactured by Kobe Steel, Ltd .: diameter 5 mm). The shape of the test piece used at this time is shown in FIG. 1 (average figure) (L: 50 mm, W: 130 mm). And NDT set to -70 degreeC or less as the pass.
下記表7に化学成分組成を示す各種溶鋼を、通常の溶製法によって溶製し、この溶鋼を冷却してスラブ(厚み:300mm)とした後、下記表8に示した条件で熱間圧延、冷却および焼戻しを行ない、各種鋼板(厚み:100mm)を得た。尚、表7、8には、参考のために前記表1、3、5に示した試験No.24のものも同時に示した。 [Example 2]
Various molten steels having chemical composition shown in Table 7 below are melted by a normal melting method, and after this molten steel is cooled to a slab (thickness: 300 mm), hot rolling is performed under the conditions shown in Table 8 below. Cooling and tempering were performed to obtain various steel plates (thickness: 100 mm). In Tables 7 and 8, the test numbers shown in Tables 1, 3 and 5 are shown for reference. 24 were also shown at the same time.
得られた厚鋼板について、t/4の位置(t:板厚)の位置を、倍率:60000倍にて透過型電子顕微鏡(TEM)観察を行ない、観察視野:2.0×2.0(μm)、観察箇所:5箇所の条件で観察し、その各視野中でのTi系分散粒子の面積を測定して、この面積から各粒子の円相当直径を算出した。またTi系分散粒子であるかどうかは、TEMに付属するEDX(エネルギー分散型X線検出器)によって、各粒子がTiを含むか否かで判別した。また、1nm未満の粒子については測定から除外した。得られた各粒子の円相当直径を算術平均して得られる値を平均サイズ、得られた値で最も小さい値を最小サイズとした。 [Measurement of size of Ti-based dispersed particles]
The obtained thick steel plate was subjected to transmission electron microscope (TEM) observation at a position of t / 4 (t: plate thickness) at a magnification of 60000 times, and an observation field of view: 2.0 × 2.0 ( μm), observation location: Observation was performed under the conditions of 5 locations, the area of the Ti-based dispersed particles in each field of view was measured, and the equivalent circle diameter of each particle was calculated from this area. Whether the particles are Ti-based dispersed particles was determined by whether or not each particle contains Ti by an EDX (energy dispersive X-ray detector) attached to the TEM. Also, particles less than 1 nm were excluded from the measurement. The value obtained by arithmetically averaging the equivalent circle diameters of the obtained particles was the average size, and the smallest value among the obtained values was the minimum size.
HAZ靭性については、得られた厚鋼板について、t/4の位置(t:板厚)の位置からシャルピー衝撃試験片(JIS Z 2201の4号試験片)を採取し、再現HAZ熱サイクルVノッチシャルピー試験を行った。再現HAZ熱サイクル条件は、入熱量:100kJ/mmの熱履歴を模擬した。HAZ靱性については、-15℃での吸収エネルギー(vE-15)を、3本の試験片について測定し、その平均値を求めた。 [Measurement of HAZ toughness]
For HAZ toughness, Charpy impact test piece (No. 4 test piece of JIS Z 2201) was taken from the position of t / 4 position (t: thickness) for the obtained thick steel plate, and reproduced HAZ thermal cycle V notch A Charpy test was conducted. The reproduced HAZ heat cycle conditions simulated a heat history of heat input: 100 kJ / mm. For HAZ toughness, the absorbed energy (vE −15 ) at −15 ° C. was measured for three test pieces, and the average value was obtained.
本出願は、2010年5月12日出願の日本特許出願(特願2010-110509)に基づくものであり、その内容はここに参照として取り込まれる。 Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on May 12, 2010 (Japanese Patent Application No. 2010-110509), the contents of which are incorporated herein by reference.
Claims (11)
- C:0.03~0.150%(「質量%」の意味。化学成分組成について以下同じ)、Si:0.5%以下(0%を含む)、Mn:1.0~2.0%、P:0.015%以下(0%を含まない)、S:0.01%以下(0%を含まない)、Al:0.005~0.06%、Cr:0.10~0.5%、Mo:0.05~0.5%、V:0.10%以下(0%を含まない)、N:0.0020~0.010%およびO:0.010%以下(0%を含まない)を夫々含有し、残部が鉄および不可避的不純物からなり、表面から深さt/4~t/2(tは、板厚を表す、以下同じ)の位置におけるミクロ組織において、ベイナイトの面積分率が90%以上であると共に、ベイナイトのラス幅の平均値が3.5μm以下であり、且つベイナイト中の島状マルテンサイトの円相当直径の最大値が3.0μm以下であることを特徴とする落重特性に優れた高強度厚鋼板。 C: 0.03 to 0.150% (meaning “mass%”; chemical composition is the same hereinafter), Si: 0.5% or less (including 0%), Mn: 1.0 to 2.0% , P: 0.015% or less (not including 0%), S: 0.01% or less (not including 0%), Al: 0.005 to 0.06%, Cr: 0.10 to 0.00. 5%, Mo: 0.05 to 0.5%, V: 0.10% or less (excluding 0%), N: 0.0020 to 0.010% and O: 0.010% or less (0% Bainite in the microstructure at positions t / 4 to t / 2 (t represents the plate thickness, the same shall apply hereinafter) from the surface, the balance being composed of iron and inevitable impurities, respectively. The area fraction of the bainite is 90% or more, the average value of the lath width of the bainite is 3.5 μm or less, and High strength thick steel plate maximum value of the circle equivalent diameter of Jo martensite excellent drop weight characteristic, characterized in that at 3.0μm or less.
- 島状マルテンサイトの平均円相当直径が1.0μm以下である請求項1に記載の高強度厚鋼板。 The high-strength thick steel plate according to claim 1, wherein the average equivalent circle diameter of the island martensite is 1.0 µm or less.
- 更に、Cu:2%以下(0%を含まない)および/またはNi:2%以下(0%を含まない)を含有するものである請求項1または2に記載の高強度厚鋼板。 The high strength thick steel plate according to claim 1 or 2, further comprising Cu: 2% or less (excluding 0%) and / or Ni: 2% or less (not including 0%).
- 更に、Nb:0.05%以下(0%を含まない)および/またはB:0.005%以下(0%を含まない)を含有するものである請求項1~3のいずれかに記載の高強度厚鋼板。 Furthermore, Nb: 0.05% or less (not including 0%) and / or B: 0.005% or less (not including 0%) are contained. High strength thick steel plate.
- 更に、Mg:0.005%以下(0%を含まない)および/またはTi:0.030%以下(0%を含まない)を含有するものである請求項1~4のいずれかに記載の高強度厚鋼板。 Further, Mg: 0.005% or less (not including 0%) and / or Ti: 0.030% or less (not including 0%) High strength thick steel plate.
- 更に、Ti:0.005~0.030%を含有すると共に、鋼板中に存在するTi系分散粒子が平均円相当直径で40nm以下である請求項1~4のいずれかに記載の高強度厚鋼板。 5. The high-strength thickness according to claim 1, further comprising Ti: 0.005 to 0.030%, and Ti-based dispersed particles present in the steel sheet having an average equivalent-circle diameter of 40 nm or less. steel sheet.
- 前記Ti系分散粒子は円相当直径の最小値が10nm以上である請求項6に記載の高強度厚鋼板。 The high-strength thick steel plate according to claim 6, wherein the Ti-based dispersed particles have a minimum equivalent circle diameter of 10 nm or more.
- 更に、Zr:0.1%以下(0%を含まない)および/またはHf:0.05%以下(0%を含まない)を含有するものである請求項1~7のいずれかに記載の高強度厚鋼板。 Furthermore, Zr: 0.1% or less (not including 0%) and / or Hf: 0.05% or less (not including 0%) are contained. High strength thick steel plate.
- 更に、Ca:0.0035%以下(0%を含まない)を含有するものである請求項1~8のいずれかに記載の高強度厚鋼板。 The high-strength thick steel plate according to any one of claims 1 to 8, further comprising Ca: 0.0035% or less (not including 0%).
- 更に、Co:2.5%以下(0%を含まない)および/またはW:2.5%以下(0%を含まない)を含有するものである請求項1~9のいずれかに記載の高強度厚鋼板。 Furthermore, Co: 2.5% or less (not including 0%) and / or W: 2.5% or less (not including 0%) High strength thick steel plate.
- 更に、希土類元素:0.01%以下(0%を含まない)を含有するものである請求項1~10のいずれかに記載の高強度厚鋼板。 The high-strength thick steel plate according to any one of claims 1 to 10, further comprising a rare earth element: 0.01% or less (not including 0%).
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WO2013114519A1 (en) * | 2012-02-02 | 2013-08-08 | Nippon Steel & Sumitomo Metal Corporation | Uoe steel pipe for line pipe |
US10358708B2 (en) | 2012-03-29 | 2019-07-23 | Jfe Steel Corporation | High strength steel plate having low yield ratio excellent in terms of strain ageing resistance, method of manufacturing the same and high strength welded steel pipe made of the same |
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