WO2014148447A1 - Steel material having superior toughness at welding heat affected zone - Google Patents
Steel material having superior toughness at welding heat affected zone Download PDFInfo
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Definitions
- the present invention relates to a thick steel plate suitable for use in welded structures such as shipbuilding, construction, and bridges, and more particularly to a steel material that realizes excellent HAZ toughness even with high heat input welding.
- a weld heat-affected zone (hereinafter also referred to as HAZ) exposed to welding heat regardless of the amount of heat becomes high temperature during welding, and the crystal grains of the steel material are likely to be coarsened.
- HAZ weld heat-affected zone
- the weld heat affected zone becomes higher in temperature and the cooling time becomes longer.
- a high temperature and a long cooling time are conditions that promote the formation of a brittle upper bainite structure in the heat affected zone and the formation of an embrittled structure such as island martensite, and thus reduce the HAZ toughness of the steel material. That is already known.
- Patent Document 1 aims at providing the steel material excellent in the welding heat affected zone toughness (HAZ toughness), and a manufacturing method. Specifically, the manufacturing method disclosed in Patent Document 1 disperses fine sulfides by adding Mg and / or REM in addition to Ca having strong sulfide-forming ability in molten steel to produce fine oxides. The HAZ structure heated to 1400 ° C. or higher is refined and good HAZ toughness is achieved even with high heat input welding of 200 kJ / cm or higher.
- HAZ toughness welding heat affected zone toughness
- Patent Document 2 aims to provide a high-strength welded structural steel with excellent base metal toughness and weld zone HAZ toughness and a method for producing the same.
- the manufacturing method disclosed in Patent Document 2 includes adding one or more of Mg, Ca, and REM after adding Ti, or adding one or more of Ti, Mg, Ca, and REM.
- Patent Document 2 as an effect of these two miniaturizations, high strength welded structural steel having good base metal toughness and welded portion HAZ toughness can be manufactured.
- Patent Document 3 is intended to provide a thick steel plate excellent in welding heat-affected zone toughness of ultra-high heat input welding and a method for producing the same. Specifically, the production method of Patent Document 3 controls the form of dendrites formed in the solidification process in addition to adjusting the particle composition of oxides, sulfides, etc. in the molten steel. As a result, Patent Document 3 disperses dispersed particles in a steel sheet more uniformly and finely than in the past, and refines austenite grains even in HAZ during super-high heat input welding where the heat input is 300 kJ / cm or more. It is said that the HAZ toughness can be significantly improved.
- Patent Document 4 is intended to provide a high-strength steel sheet having API standard X100 or higher having good HAZ toughness. Specifically, in the high-strength steel sheet of Patent Document 4, by limiting the amount of Ti, Mg, REM, Al, S, and N, (1) TiN-based fine precipitation containing Mg-based oxides of 0.1 ⁇ m or less. The inclusion of the material suppresses the coarsening of ⁇ grains even in the vicinity of the melting line. Furthermore, this high-strength steel sheet includes (2) a complex of MnS with an oxide mainly composed of Ti, Mg, and REM of 0.1 ⁇ m or more, and generates IGF from within relatively small ⁇ grains. It is said that the HAZ toughness can be improved by refining the structure throughout the entire HAZ.
- Patent Document 5 aims to propose a non-tempered high-tensile steel material having both good base material toughness and weld heat-affected zone toughness.
- the non-tempered high-tensile steel material of Patent Document 5 has an optimum composition range of an optimum oxide-based inclusion as follows: Ti oxide: 20 to 90% by weight, CaO and REM oxide total: 5 to 50 Weight%, Al 2 O 3 : Controlled to 70% by weight or less.
- non-tempered high-tensile steel can effectively utilize the grain coarsening suppression ability (pinning effect) of inclusions without causing nozzle clogging or generation of harmful inclusion clusters.
- the toughness can be improved, and further, the toughness and strength of the base material can be improved by optimally dispersing TiN or VN.
- Japanese Patent No. 4261968 Japanese Patent No. 4762450 Japanese Patent No. 4039223 Japanese Unexamined Patent Publication No. 11-264048 Japanese Patent No. 4144121
- Patent Documents 1 to 5 discloses that it is possible to cope with a decrease in the HAZ toughness caused by welding heat. It is difficult to improve the HAZ toughness.
- the techniques disclosed in Patent Documents 1 to 3 are intended to refine the HAZ structure by the pinning effect of oxysulfides, but do not mention the structure refinement effect due to intragranular transformation caused by oxides. It cannot be said that it is a technology that can cope with further increase in heat input.
- Patent Document 4 mentions a structural transformation starting from an oxide, but does not show a countermeasure against the coarse oxide and the like, and eliminates the possibility that the HAZ toughness is lowered due to the formation of the coarse oxide. It cannot be said that it is a technology that can cope with further increase in heat input.
- the technique disclosed in Patent Document 5 is a technique for refining the HAZ structure by the pinning effect of oxysulfide, but it is not a technique that takes account of the structure transformation control starting from oxysulfide. It cannot be said that this technology can cope with large heat input.
- the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a steel material having excellent weld heat affected zone toughness (HAZ toughness) during high heat input welding.
- HZ toughness weld heat affected zone toughness
- the present invention has taken the following measures. That is, technical means for solving the problems in the present invention are: C: 0.02 to 0.13% (meaning mass% (mass%); the same applies to the following components); Si: 0.05 to 0.003.
- the balance is a steel material excellent in toughness of the weld heat affected zone consisting of iron and inevitable impurities, the steel material, Including a composite oxide containing REM, Zr, Ti, Al, Ca and S, For oxides, oxides of 3 [mu] m greater is not more than 5.0 per 1 mm 2 equivalent circle diameter, and the composite oxide of the circle equivalent diameter 0.1 ⁇ 3 [mu] m, satisfies the following formula (1) Composite The number of oxides is 100 / mm 2 or more, and the average composition of the composite oxide of 0.1 to
- Nb 0.002 to 0.10%
- V 0.002 to 0.10%
- B 0.0005 to 0.0050% is preferably contained.
- a steel material excellent in the toughness (HAZ toughness) of the weld heat affected zone at the time of high heat input welding can be obtained.
- the steel material according to the present embodiment is a steel material that exhibits excellent toughness in a weld heat affected zone (HAZ, Heat Affected Zone) affected by a very large welding energy, for example, a welding heat input exceeding 60 kJ / mm. is there.
- HAZ weld heat affected zone
- HAZ toughness the toughness in the HAZ
- the steel material according to the present embodiment is a composite oxide (an oxysulfide containing Al, Ti, Zr, REM, Ca, and S) that serves as a nucleus of intragranular transformation, with its size and S concentration being appropriately controlled.
- a composite oxide an oxysulfide containing Al, Ti, Zr, REM, Ca, and S
- the steel material according to the present embodiment can stably exhibit excellent HAZ toughness even when welding is performed with a large heat input.
- the steel material by this embodiment which has the above-mentioned characteristic is obtained by adding each element so that it may become the chemical composition composition explained below in the secondary refining of molten steel, for example.
- the steel material according to the present embodiment (hereinafter simply referred to as the present steel material) has carbon C of 0.02 to 0.13%, silicon Si of 0.05 to 0.5%, and manganese Mn of 1.0 to 2.5%. 0.03% or less of phosphorus P (not including 0%), 0.01% or less of sulfur S (not including 0%), 0.002 to 0.040% of aluminum Al, and 0.02% of titanium Ti.
- the steel material includes a composite oxide containing REM, Zr, Ti, Al, Ca, and S.
- an oxide having an equivalent circle diameter of more than 3 ⁇ m is 5 per mm 2 .
- the number of composite oxides satisfying the following formula (1) is 100 / mm 2 or more.
- the average composition of the composite oxide of 0.1 to 3 ⁇ m satisfying the above formula (1) is 20% or less of Al 2 O 3, 3 to 20% of TiO 2 , 5 to 50% of ZrO 2 , REM oxidation
- the product is 5 to 50%
- CaO is 5 to 50%
- S is 1 to 15%.
- Carbon C 0.02 to 0.13%
- Carbon C is an element indispensable for securing the strength of the steel material (base material). Therefore, 0.02% or more, preferably 0.04% or more is added.
- the content of C exceeds 0.13%, not only does island-like martensite (MA) form in the HAZ, leading to a reduction in the toughness of the HAZ, but also weldability due to the generation of CO gas, etc. It also has an adverse effect. Therefore, the C content is 0.13% or less, preferably 0.1% or less.
- Silicon Si is an element that has a deoxidizing action and contributes to improving the strength of the base material by solid solution strengthening. Therefore, 0.05% or more, preferably 0.07% or more, more preferably 0.1% or more is added. However, if the Si content exceeds 0.5%, the weldability and toughness of the steel material deteriorate, so the upper limit is made 0.5%. In particular, in order to increase the HAZ toughness, it is recommended that the Si content be 0.3% or less. However, as the Si content is reduced, the HAZ toughness is improved, while the strength of the steel material may be reduced. Therefore, the Si content is 0.5% or less, preferably 0.35% or less, more preferably 0.25% or less.
- Manganese Mn is an element that contributes to improving the strength of the base material. However, when the Mn content is less than 1.0%, the strength is lowered. Therefore, 1.0% or more, preferably 1.3% or more is added. However, if the Mn content exceeds 2.5%, the weldability of the base material is degraded. Therefore, the Mn content is set to 2.5% or less, preferably 2.0% or less.
- Phosphorus P is an element that easily segregates, and is an element that segregates at a grain boundary in a steel material and lowers the HAZ toughness.
- P is unavoidably contained in the base material in an amount of about 0.001%, so the content of P is specified to be 0.03% by mass or less. Preferably it is 0.02% or less, More preferably, it is 0.01% or less. However, this embodiment does not include the case where the P content is 0%.
- Sulfur S is an element that combines with Mn to produce sulfide (MnS) and lowers the toughness of the base material and the ductility in the plate thickness direction.
- MnS sulfide
- S is usually unavoidably contained in the base material in an amount of about 0.0005%, so the S content is specified to be 0.01% or less. Preferably it is 0.008% or less, More preferably, it is 0.006% or less.
- this embodiment does not include the case where the S content is 0%.
- Aluminum Al is an element that acts as a deoxidizer. Moreover, when there is little content of Al, molten steel will become easy to be contaminated with oxygen. Therefore, 0.002% or more, preferably 0.004% or more, more preferably 0.005% or more is added. However, when Al is added excessively with respect to the base material, the added Al reduces oxides in the base material to form coarse Al oxide, so that the HAZ toughness decreases. Therefore, the Al content is 0.040% or less, preferably 0.025% or less, and more preferably 0.015% or less.
- Titanium Ti is an element that contributes to the improvement of HAZ toughness by generating a nitride such as TiN or an oxide containing Ti in the base material. Therefore, 0.005% or more, preferably 0.010% or more, more preferably 0.014% or more is added. However, when Ti is excessively added to the base material, the base material itself is hardened by solid solution strengthening of Ti, leading to a decrease in HAZ toughness. Therefore, the Ti content is 0.040% or less, preferably 0.030% or less, and more preferably 0.025% or less.
- Zirconium Zr is an element that contributes to the improvement of HAZ toughness by generating a complex oxide containing Zr. Therefore, 0.0003% or more, preferably 0.0005% or more, more preferably 0.0009% or more is added. However, when Zr is added excessively with respect to the base material, coarse Zr oxide (ZrO 2 ) is generated and HAZ toughness is lowered. Further, the formation of coarse Zr carbide (ZrC) reduces the toughness of the base material itself. Therefore, the Zr content is 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less.
- REM rare earth element
- REM is an element necessary for generation of oxides.
- This finely dispersed oxide serves as a production nucleus for intra-grain ⁇ of HAZ and contributes to improvement of HAZ toughness. Therefore, 0.0003% or more, preferably 0.0005% or more, more preferably 0.0009% or more is added.
- the content of REM is set to 0.020% or less, preferably 0.015% or less, more preferably 0.010% or less.
- REM means an element containing a lanthanoid element (15 elements from La to Ln) and Sc (scandium) and Y (yttrium).
- a lanthanoid element (15 elements from La to Ln) and Sc (scandium) and Y (yttrium).
- Calcium Ca is an element necessary for the production of oxides. Ca also forms nuclei of HAZ in the grains and contributes to the improvement of HAZ toughness. Therefore, it is preferable to contain 0.0003% or more, preferably 0.0005% or more, more preferably 0.0007% or more.
- the Ca content is set to 0.0080% or less, preferably 0.0060% or less, more preferably 0.0030% or less.
- Nitrogen N is an element that precipitates nitrides (eg, ZrN, TiN, etc.). Nitride contributes to the improvement of HAZ toughness by suppressing the austenite grain coarsening during welding by the pinning effect. Since N forms a nitride and promotes refinement of austenite grains as the content increases, it effectively works to improve HAZ toughness. Therefore, 0.0030% or more, preferably 0.0040% or more, more preferably 0.0050% or more is added. However, if the N content exceeds 0.010%, the amount of solute N increases, the toughness of the base metal itself deteriorates, and the HAZ toughness also decreases. Therefore, the N content is 0.010% or less, preferably 0.0090% or less, and more preferably 0.0080% or less.
- Oxygen O is an essential element for the formation of oxides. If the content is less than 0.0003%, a sufficient amount of oxide cannot be obtained in the base material. Preferably it is 0.0010% or more, More preferably, it is 0.0015% or more. However, if the content is more than 0.0050%, the HAZ toughness is lowered due to the coarsening of the oxide. Therefore, the content of O is set to 0.0050% or less, preferably 0.0040% or less, more preferably 0.0035% or less.
- the content of O represents the total amount of oxygen, and means the total amount of O forming an oxide in the base material and free O dissolved in the base material.
- This steel material contains the above-mentioned elements, and the balance consists of iron and inevitable impurities.
- the remaining components other than the above-described elements are iron and inevitable impurities (for example, Mg, As, Se, etc.).
- the present steel material containing the above-mentioned element includes a complex oxide (oxide and / or oxysulfide) containing REM, Zr, Ti, Al, Ca and S.
- the composite oxides contained in this steel are Al, Ti, Zr, REM, and Al / Ti / Zr / REM / Ca / S based composite oxides containing oxides and sulfides of Ca.
- elements such as Mn and Si and other component elements may be included.
- Al, Ti, Zr, REM, and Ca-based oxides have good lattice matching with steel materials, and promote intragranular structure transformation (intragranular transformation) in HAZ, so they are effective in refining the HAZ structure. It is.
- the number of oxides having an equivalent circle diameter of more than 3 ⁇ m in the above-described composite oxide is 5.0 or less per 1 mm 2 in the cross section of the steel material. Since the complex oxide having an equivalent circle diameter exceeding 3 ⁇ m is coarse, in high heat input welding where the heat input reaches 60 kJ / mm, the HAZ toughness is reduced. Therefore, the number of complex oxides exceeding 3 ⁇ m needs to be suppressed to 5.0 / mm 2 or less.
- the above-mentioned composite oxide has a circle equivalent diameter of 0.1 ⁇ m to 3 ⁇ m (hereinafter referred to as 0.1 to 3 ⁇ m), satisfies the following formula (1), and It is contained so that the number thereof is 100 / mm 2 or more in the cross section of the steel material.
- REM and Ca are oxysulfide-forming elements that can form oxides and sulfides. Therefore, if the S concentration (mass% S) with respect to the concentration of the oxysulfide forming elements (REM 2 O 3 and CaO) is too high, excessively generated sulfide inhibits the alignment between the oxide and the matrix. As a result, the ability of the composite oxide to contribute to the structure control (intragranular transformation ability) decreases.
- the 2nd term which considered the conditions considered to influence these intragranular transformation is shown.
- the S concentration (mass% S) with respect to the oxysulfide forming elements (REM 2 O 3 and CaO), and the size of the composite oxide (the equivalent circle diameter d of the composite oxide) ) Has an optimum range for producing strain energy that contributes to intragranular transformation, and it is presumed that an upper limit value and a lower limit value exist in the second term of Equation (1). Therefore, the upper limit value and the lower limit value of the second term of Expression (1) were experimentally obtained.
- a method for obtaining the upper limit value and the lower limit value of the second term of Expression (1) will be described.
- a heat input test simulating welding HAZ with a heat input of 60 kJ / mm was performed on the prototype material.
- the prototype material after the heat input test was mirror-polished and corroded, and the structure was revealed by corrosion to investigate the presence of intragranular transformation caused by the composite oxide.
- the composition and size of the composite oxide in the prototype were measured by EPMA (Electron Probe MicroAnalyzer), and the value of the second term of the formula (1) was calculated for the composite oxide of 0.1 to 3 ⁇ m.
- the presence or absence of intragranular transformation and the calculated value of the second term are summarized as the results shown in Table 1, and the presence or absence of intragranular transformation is indicated by a circle (the value of the second term of the steel material having intragranular transformation). Based on this, the range of the second term was set to 0.008 or more and 0.289 or less.
- the composite oxide having an equivalent circle diameter of 0.1 to 3 ⁇ m is contained in an amount of 100 / mm 2 or more after satisfying the formula (1). Further, the average composition is 20% or less of Al 2 O 3 , TiO 2 is 3% to 20% (3 to 20%), ZrO 2 is 5% to 50% (5 to 50%), REM oxide is 5% to 50% (5 to 50%), CaO is It is necessary to be 5% or more and 50% or less (5 to 50%) and S is 1% or more and 15% or less (1 to 15%).
- the oxide composition affects the lattice matching between the oxide and the steel material in HAZ, so if the oxide composition is not controlled to the content within the above range, a composite oxide having a circle equivalent diameter of 0.1 to 3 ⁇ m. This is because it cannot contribute to the intragranular transformation in HAZ, that is, it cannot contribute to the refinement of the HAZ structure.
- the steel material having the above chemical composition is intended for thick steel plates with a thickness of about 3.0 mm or more. In addition to small to medium heat input welding, the heat input is 50 kJ / mm or more. Since the HAZ toughness can be prevented from being lowered even in thermal welding, it can be used as a material for large structures such as bridges, high-rise buildings, and ships.
- at least one of nickel Ni, copper Cu, chromium Cr, and molybdenum Mo is 0.05% to 1.50% (0.05 to 1.. 50%) may be contained.
- Cu, Ni, Cr, and Mo are all elements that contribute to increasing the toughness and strength of the steel material, and can be added alone or in combination. For example, in order to effectively improve toughness and strength by adding Cu, it is preferable to contain 0.05% or more of Cu.
- the Cu content is specified to be 0.05% or more and 1.50% or less.
- Ni, Cr, and Mo are preferably contained in an amount of 0.05% or more. However, if the content exceeds 1.50%, the strength of the base material is excessively increased and the toughness of the base material is decreased. Therefore, the HAZ toughness is also lowered. Therefore, the contents of Ni, Cr, and Mo are also specified to be 0.05% or more and 1.50% or less.
- Niobium Nb, Vanadium V: 0.002 to 0.10% Further, the steel material according to this embodiment may contain 0.002% or more and 0.10% or less (0.002 to 0.10%) of at least one of niobium Nb and vanadium V. Nb and V are both precipitated as carbonitrides.
- Nb in order to effectively improve the HAZ toughness by adding Nb, it is preferable to contain Nb in an amount of 0.002% or more. However, if the content of Nb exceeds 0.10%, the precipitated carbonitrides are coarsened, and on the contrary, the HAZ toughness is reduced. Therefore, the Nb content is specified to be 0.002% or more and 0.10% or less.
- V is preferably contained in an amount of 0.002% or more. However, if the content of V exceeds 0.10%, the precipitated carbonitrides are coarsened, and on the contrary, the HAZ toughness is lowered. Therefore, the V content is specified to be 0.002% or more and 0.10% or less.
- the steel material according to the present embodiment may contain 0.0005% or more and 0.0050% or less (0.0005 to 0.0050%) of boron B.
- B is an element that suppresses the formation of grain boundary ferrite and improves toughness. Therefore, in order to improve the toughness of the steel material by adding B, it is preferable to contain B in an amount of 0.0005% or more.
- the B content is 0.0050% or less, preferably 0.0040% or less, more preferably 0.0015% or more and 0.0030% or less.
- the steel material according to the present embodiment can be obtained by adding each element so as to have the above-described chemical component composition, for example, in the secondary refining of molten steel.
- the steel manufacturing method (manufacturing conditions) shown, that is, the method of adding each element will be described. In the following description, steel was melted using a vacuum melting furnace (capacity 150 kg), cast into a 150 kg ingot, and cooled to obtain steels shown in examples and comparative examples described later.
- the desulfurization method for adjusting the S concentration is not particularly limited, but a molten steel having a low S concentration may be used in advance.
- the grounds for the dissolved oxygen amount and the S concentration are as follows. First, when the amount of dissolved oxygen exceeds 0.005%, the oxide generated in the molten steel becomes coarse. In addition, when the value of (mass% Of / mass% S) is large, the sulfide necessary for the oxide is not sufficiently generated. Further, when the value of (mass% Of / mass% S) is small, not only the desired oxide cannot be obtained, but also the sulfide is generated to a level that inhibits intragranular transformation because the S concentration is too high. End up.
- Ti was added to the molten steel before REM and Zr. If Ti is added before Al, all Ti oxides are reduced by Al in the subsequent steps. Therefore, Ti must be added after Al is added. After the addition of Ti, the molten steel was held for 2 to 15 minutes without adding other elements.
- the dissolved oxygen amount (mass% Of) is 0.005% or less, and the value of (mass% Of / mass% S) is 0.2 ⁇ mass% Of / mass%.
- S ⁇ 9.6
- the amount of Zr added is 10 ppm to 120 ppm and the amount of REM added is 30 ppm to 150 ppm. This is because if either one of Zr and REM is excessive, a coarse composite oxide having an equivalent circle diameter exceeding 3 ⁇ m is formed, and if either one of the elements is too small, A fine complex oxysulfide having an equivalent diameter of 0.1 to 3 ⁇ m is insufficient. That is, the amount of Zr and REM added affects the particle size distribution of the composite oxide.
- REM has the property of easily forming oxides and sulfides
- Zr has the property of forming oxides but not sulfides. Therefore, in order to optimize the balance between the oxide and the sulfide, it is necessary to add Zr and REM according to mass% Of and mass% S. Therefore, the ratio (add [Zr] / add [REM]) between the Zr addition amount and the REM addition amount is determined so as to satisfy the following expression (2).
- the deoxidizing elements Al, REM, Zr, and Ca are preferably not added all at once to the molten steel, but divided into two or more times or continuously in small amounts.
- REM, Ca, Zr, Ti added to molten steel is not specifically limited,
- REM pure La, pure Ce, and pure Y, pure Ca, pure Zr, pure Ti, and also Fe -Si-La alloy, Fe-Si-Ce alloy, Fe-Si-Ca alloy, Fe-Si-La-Ce alloy, Fe-Ca alloy, Ni-Ca alloy and the like may be added.
- Misch metal is a mixture of rare earth elements, and specifically contains about 40 to 50% of Ce and about 20 to 40% of La.
- misch metal often contains Ca as an impurity, when the misch metal contains Ca, it is necessary to satisfy the range of the Ca content defined in the present embodiment.
- composition (content) of the component elements described so far, the relational expression regarding the content of the component elements, the manufacturing conditions, and the like are referred to as “conditions defined in the present embodiment”.
- “Casting / Rolling” Molten steel whose components were adjusted as described above was cast into an ingot. The cast ingot was processed by hot rolling to produce a thick steel plate having a thickness of 30 mm to 80 mm. In actual operation, the molten steel obtained by adjusting the components may be continuously cast according to a conventional method to form a slab and then hot rolled according to a conventional method.
- Each of these three V-notch specimens is subjected to a Charpy impact test at ⁇ 40 ° C., the absorbed energy (vE-40) is measured, and the average value and minimum value of the measurement results of the three V-notch specimens are measured. The value was determined.
- test piece thin steel plate having an average value of vE-40 exceeding 140 J was evaluated as a steel plate excellent in HAZ toughness.
- Measurement method of composite oxide composition of 0.1 to 3 ⁇ m A test piece is cut out from the surface of the thick steel plate at a depth t / 4 (t: thickness of the thick steel plate) (taken so that the axis of the test piece passes through the position of the depth t / 4), and the rolling direction and A cross section parallel to the plate thickness direction is mirror-polished and 0.1 to 3 ⁇ m using an electron probe microprobe X-ray analyzer (EPMA, trade name JXA-8500F) manufactured by JEOL Datum. The composite oxide composition of was measured.
- EPMA electron probe microprobe X-ray analyzer
- the observation conditions at this time were an acceleration voltage of 20 kV, a sample current of 0.01 ⁇ A, a magnification of 5000 times, an observation area of 0.4 mm 2 or more, and the component composition at the center of the composite oxide with wavelength dispersion of characteristic X-rays Quantitative analysis was performed by spectroscopy.
- the elements to be quantified are Si, Mn, S, Al, Ti, Zr, La, Ce, Ca, and O (oxygen), and the relationship between the X-ray intensity and element concentration of each element using a known substance.
- the amount of elements contained in the composite oxide was quantified based on the X-ray intensity and calibration curve obtained from the composite oxide to be analyzed.
- each element other than S was converted to a single oxide, and the composition of the oxide was calculated.
- S was calculated with a single concentration.
- mass conversion is performed as the single oxide and S single element concentration in this way, and the average of a plurality of composite oxides is used as the composite oxide composition.
- the REM oxide is present in the steel material in the form of M 2 O 3 , M 3 O 5 , MO 2, etc., but all the REM oxide is converted to M 2 O 3 . Converted. Similarly, all Ti was converted to TiO 2 .
- Measurement method of equivalent circle diameter and number of composite oxide In the composition measurement of the composite oxide using the above-described EPMA, the area of the composite oxide was measured and the composite oxide was assumed to be a circle, and the diameter of the circle corresponding to the measured area was calculated as the equivalent circle diameter.
- the magnification is 200 times
- the observation area is 50 mm 2 or more
- other conditions are the number of composite oxides whose equivalent circle diameter is 5 ⁇ m or less. The measurement was performed under the same conditions as in the measurement.
- Table 2 shows steel No. which is an example of the steel according to the present embodiment.
- 1-No. The chemical composition of 31 is shown.
- Steel No. 1-No. All 31 component compositions satisfy the conditions defined in this embodiment.
- Table 3 below shows steel material No. which is an example of this steel material.
- 1-No. 31 production conditions are shown.
- Steel No. 1-No. All the 31 manufacturing conditions also satisfy the conditions defined in this embodiment.
- the selected addition order and addition method are shown in the remarks column.
- Table 4 below shows steel No. which is an example of this steel.
- 1-No. 31 shows the composite oxide particle size and number distribution, the composite oxide average composition, and the HAZ toughness test results.
- the number of composite oxides having a circle equivalent diameter exceeding 3 ⁇ m is 5.0 pieces / mm 2 or less, and the number of composite oxides having a circle equivalent diameter of 0.1 to 3 ⁇ m is 100 pieces / mm 2 or more. It is.
- the steel material No. 1-No. In all cases 31, the average composition of the composite oxide having an equivalent circle diameter of 0.1 to 3 ⁇ m satisfies the conditions defined in this embodiment.
- steel material No. 1-No. All 31 can be evaluated as having a HAZ toughness test result of 140 J or more and exhibiting excellent HAZ toughness.
- Table 5 below shows steel No. as a comparative example that does not satisfy the conditions specified in the present embodiment.
- 32-No. 67 component compositions are shown.
- Steel No. No. 32 does not satisfy the conditions specified by the present embodiment for the Al content.
- Steel No. In 34 and 35 the Ti content does not satisfy the conditions defined in this embodiment.
- Steel No. In 40 and 41 the REM content does not satisfy the conditions defined in the present embodiment.
- Steel No. In Nos. 44 and 45 the Zr content does not satisfy the conditions defined in this embodiment.
- the Ca content does not satisfy the conditions defined in this embodiment.
- the S content does not satisfy the conditions defined in the present embodiment.
- Table 6 below shows steel Nos. That do not satisfy the conditions specified in this embodiment. 32-No. 67 manufacturing conditions are shown. Steel No. In 33, 36, 37, 42, 43, 46, 47, 50, and 51, “addition order of complex oxide forming elements” is marked with “x”, and complex oxide forming elements (Al and Ti) are added. Is added in a different order than the order described above. Steel No. Nos. 38 and 39 indicate that the holding time of the molten steel after addition of Ti does not satisfy the conditions defined in the present embodiment. Steel No. 52 indicates that the value of (mass% Of / mass% S) does not satisfy the condition defined in the present embodiment. Steel No.
- steel material No. 32-No. 67 does not satisfy the conditions defined in the present embodiment in one or both of the component composition shown in Table 5 and the production conditions shown in Table 6.
- Table 7 shows steel No. as a comparative example that does not satisfy the conditions specified in this embodiment.
- 32-No. 67 shows the particle size and number distribution of the composite oxide, the average composition of the composite oxide, and the HAZ toughness test results.
- Steel No. 32-No. 55 the average composition of the composite product does not satisfy the conditions defined in this embodiment.
- Steel No. In 56 and 57 the number of complex oxides having a circle equivalent diameter exceeding 3 ⁇ m exceeds 5.0 / mm 2 .
- Steel No. 58-No. In No. 67 one or both of the number of composite oxides having an equivalent circle diameter exceeding 3 ⁇ m and the number of composite oxides having an equivalent circle diameter of 0.1 to 3 ⁇ m do not satisfy the conditions defined in this embodiment.
- Steel No. 32-No. For each of 55 a condition that is not satisfied among the conditions defined in the present embodiment is shown in “Remarks”.
- FIG. 1 shows the HAZ toughness of the steel material according to the present embodiment shown in Table 4 and the steel material No. of the comparative example shown in Table 7.
- 6 is a graph showing the HAZ toughness of 59, 61-67.
- the number of composite oxides having an equivalent circle diameter of 3 ⁇ m is less than 5.0 / mm 2 .
- Nos. 59, 61 to 67 are examples in which the number of complex oxides with equivalent circle diameters of 0.1 to 3 ⁇ m was less than 100, and in any case, the HAZ toughness test results were much lower than 140J.
- HAZ toughness test result is significantly lower than 140J.
- FIG. 3 shows the HAZ toughness of the steel according to the present embodiment shown in Table 4 and the steel No. of the comparative example shown in Table 7. It is a graph which shows the HAZ toughness of 56,57.
- the number of complex oxides having equivalent circle diameters of 0.1 to 3 ⁇ m is 100 or more.
- 56 and 57 are examples in which the number of composite oxides having an equivalent circle diameter of 3 ⁇ m exceeds 5.0 / mm 2 , and the HAZ toughness test result is significantly lower than 140J in both cases.
- the steel material has a configuration that satisfies the conditions defined in the present embodiment, it can exhibit excellent HAZ toughness even in high heat input welding.
- the embodiment disclosed this time should be considered as illustrative in all points and not restrictive.
- matters that are not explicitly disclosed, for example, operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. Instead, values that can be easily assumed by those skilled in the art are employed.
- the present steel material is manufactured in secondary refining
- a steel material that exhibits the same HAZ toughness can be obtained even if it is manufactured using a converter or an electric furnace. Therefore, the production of the present steel material using a converter or an electric furnace is also included in the technical scope of the present invention.
- the steel sheet of the present invention realizes excellent HAZ toughness even with high heat input welding, and is therefore suitable for use in welded structures such as shipbuilding, construction, and bridges.
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Abstract
Description
ところで、鋼材の溶接効率を向上させるには、同一箇所に対する溶接回数を減らすことが有効であり、小さな熱量(溶接熱)で鋼材に対して溶接を複数回繰り返すよりも、鋼材に対して大きな熱量(溶接熱)を加える大入熱の溶接を行って1回で溶接を完了させる大入熱で高能率の溶接が指向される。 In recent years, structures using steel materials, such as bridges, high-rise buildings, and large ships, have tended to increase in size. To realize such large structures, it is desirable to increase the strength and thickness of steel materials. ing. At the same time, for the purpose of improving the construction efficiency of large structures and reducing the construction cost, there is a demand for improvement in welding efficiency when welding high-strength and thick steel materials.
By the way, in order to improve the welding efficiency of steel materials, it is effective to reduce the number of times of welding to the same location, and a large amount of heat is applied to the steel material rather than repeating the welding to the steel material several times with a small amount of heat (welding heat). High-efficiency welding with high heat input that completes welding at a time by performing welding with high heat input to add (welding heat) is directed.
特許文献1は、溶接熱影響部靭性(HAZ靭性)に優れた鋼材および製造方法を提供することを目的としたものである。具体的に、特許文献1に開示の製造方法は、溶鋼中で強い硫化物生成能を持つCaに加えてMgおよび/またはREMを添加し、微細酸化物を生成させることで微細硫化物を分散させて1400℃以上に加熱されたHAZ組織を細粒化し、200kJ/cm以上の大入熱溶接でも良好なHAZ靭性を実現するとされている。 In order to cope with the reduction in the HAZ toughness due to the welding heat as described above, techniques disclosed in
特許文献1~3に開示の技術は、酸硫化物のピンニング効果によってHAZ組織の微細化を図るものであるが、酸化物起因の粒内変態による組織微細化効果については言及しておらず、更なる大入熱化に対応できる技術であるとはいえない。 As described above, each of
The techniques disclosed in
さらに、特許文献5に開示の技術は、酸硫化物のピン止め効果によってHAZ組織を微細化する技術であるが、酸硫化物を起点とする組織変態制御を考慮した技術ではないので、更なる大入熱化に対応できる技術であるとはいえない。 In addition,
Furthermore, the technique disclosed in
即ち、本発明における課題解決のための技術的手段は、C:0.02~0.13%(質量%(mass%)の意味。以下成分について同じ。)、Si:0.05~0.5%、Mn:1.0~2.5%、P:0.03%以下(0%を含まない)、S:0.01%以下(0%を含まない)、Al:0.002~0.040%、Ti:0.005~0.040%、Zr:0.0003~0.020%、REM:0.0003~0.020%、Ca:0.0003~0.0080%、N:0.0030~0.010%、O:0.0003~0.0050%を含有し、残部が鉄および不可避不純物からなる溶接熱影響部の靭性に優れた鋼材であって、前記鋼材は、REM、Zr、Ti、Al、CaおよびSを含有する複合酸化物を含み、前記鋼材中の複合酸化物について、円相当直径で3μm超の酸化物が1mm2あたり5.0個以下であって、かつ円相当直径が0.1~3μmの複合酸化物について、下記式(1)を満たす複合酸化物個数が100個/mm2以上であって、さらに、下記式(1)を満たす0.1~3μmの複合酸化物の平均組成が、Al2O3:20%以下、TiO2:3~20%、ZrO2:5~50%、REM酸化物:5~50%、CaO:5~50%、S:1~15%であることを特徴とする。 In order to achieve the above object, the present invention has taken the following measures.
That is, technical means for solving the problems in the present invention are: C: 0.02 to 0.13% (meaning mass% (mass%); the same applies to the following components); Si: 0.05 to 0.003. 5%, Mn: 1.0 to 2.5%, P: 0.03% or less (not including 0%), S: 0.01% or less (not including 0%), Al: 0.002 to 0.040%, Ti: 0.005 to 0.040%, Zr: 0.0003 to 0.020%, REM: 0.0003 to 0.020%, Ca: 0.0003 to 0.0080%, N : 0.0030 to 0.010%, O: 0.0003 to 0.0050%, the balance is a steel material excellent in toughness of the weld heat affected zone consisting of iron and inevitable impurities, the steel material, Including a composite oxide containing REM, Zr, Ti, Al, Ca and S, For oxides, oxides of 3 [mu] m greater is not more than 5.0 per 1 mm 2 equivalent circle diameter, and the composite oxide of the circle equivalent diameter 0.1 ~ 3 [mu] m, satisfies the following formula (1) Composite The number of oxides is 100 / mm 2 or more, and the average composition of the composite oxide of 0.1 to 3 μm satisfying the following formula (1) is Al 2 O 3 : 20% or less, TiO 2 : 3 -20%, ZrO 2 : 5 to 50%, REM oxide: 5 to 50%, CaO: 5 to 50%, S: 1 to 15%.
(但し、dは個々の複合酸化物の円相当直径であって、0.1~3μmである)
ここで、Ni:0.05~1.50%、Cu:0.05~1.50%、Cr:0.05~1.50%、Mo:0.05~1.50%のうち、少なくとも1種を含有するとよい。 0.008 ≦ (1 / d) × {mass% S / (mass% CaO + mass% REM 2 O 3 )} ≦ 0.289 (1)
(Where d is the equivalent circle diameter of each composite oxide and is 0.1 to 3 μm)
Here, at least among Ni: 0.05 to 1.50%, Cu: 0.05 to 1.50%, Cr: 0.05 to 1.50%, Mo: 0.05 to 1.50% It is good to contain 1 type.
さらに、B:0.0005~0.0050%を含有するとよい。 Further, it is preferable to contain at least one of Nb: 0.002 to 0.10% and V: 0.002 to 0.10%.
Further, B: 0.0005 to 0.0050% is preferably contained.
本実施形態による鋼材は、例えば溶接入熱量が60kJ/mmを超えるような、非常に大きな溶接エネルギーの影響を受けた溶接熱影響部(HAZ,Heat Affected Zone)において優れた靭性を発揮する鋼材である。以下の説明において、本実施形態による鋼材の溶接熱影響部をHAZと記し、HAZにおける靭性をHAZ靭性と記す。 Hereinafter, a steel material (hereinafter simply referred to as a steel material) excellent in toughness of a weld heat affected zone according to an embodiment of the present invention will be described in detail with reference to the drawings.
The steel material according to the present embodiment is a steel material that exhibits excellent toughness in a weld heat affected zone (HAZ, Heat Affected Zone) affected by a very large welding energy, for example, a welding heat input exceeding 60 kJ / mm. is there. In the following description, the welding heat-affected zone of the steel material according to the present embodiment is denoted as HAZ, and the toughness in the HAZ is denoted as HAZ toughness.
本実施形態による鋼材(以下、単に本鋼材という)は、炭素Cを0.02~0.13%、ケイ素Siを0.05~0.5%、マンガンMnを1.0~2.5%、リンPを0.03%以下(0%を含まない)、硫黄Sを0.01%以下(0%を含まない)、アルミニウムAlを0.002~0.040%、チタンTiを0.005~0.040%、ジルコニウムZrを0.0003~0.020%、希土類金属REMを0.0003~0.020%、カルシウムCaを0.0003~0.0080%、窒素Nを0.0030~0.010%、酸素Oを0.0003~0.0050%を含有し、残部が鉄および不可避不純物からなる。さらに、本鋼材は、REM、Zr、Ti、Al、CaおよびSを含有する複合酸化物を含み、本鋼材中の複合酸化物について、円相当直径で3μm超の酸化物が1mm2あたり5.0個以下であって、かつ円相当直径が0.1~3μmの複合酸化物について、下記式(1)を満たす複合酸化物の個数が100個/mm2以上である。 The steel material by this embodiment which has the above-mentioned characteristic is obtained by adding each element so that it may become the chemical composition composition explained below in the secondary refining of molten steel, for example.
The steel material according to the present embodiment (hereinafter simply referred to as the present steel material) has carbon C of 0.02 to 0.13%, silicon Si of 0.05 to 0.5%, and manganese Mn of 1.0 to 2.5%. 0.03% or less of phosphorus P (not including 0%), 0.01% or less of sulfur S (not including 0%), 0.002 to 0.040% of aluminum Al, and 0.02% of titanium Ti. 005-0.040%, zirconium Zr 0.0003-0.020%, rare earth metal REM 0.0003-0.020%, calcium Ca 0.0003-0.0080%, nitrogen N 0.0030 -0.010%, oxygen O is contained in 0.0003-0.0050%, and the balance consists of iron and inevitable impurities. Further, the steel material includes a composite oxide containing REM, Zr, Ti, Al, Ca, and S. As for the composite oxide in the steel material, an oxide having an equivalent circle diameter of more than 3 μm is 5 per mm 2 . For the composite oxide having 0 or less and an equivalent circle diameter of 0.1 to 3 μm, the number of composite oxides satisfying the following formula (1) is 100 / mm 2 or more.
(但し、dは個々の複合酸化物の円相当直径であって、0.1~3μmである)
さらに、上記式(1)を満たす0.1~3μmの複合酸化物の平均組成は、Al2O3が20%以下、TiO2が3~20%、ZrO2が5~50%、REM酸化物が5~50%、CaOが5~50%、Sが1~15%である。 0.008 ≦ (1 / d) × {mass% S / (mass% CaO + mass% REM 2 O 3 )} ≦ 0.289 (1)
(Where d is the equivalent circle diameter of each composite oxide and is 0.1 to 3 μm)
Further, the average composition of the composite oxide of 0.1 to 3 μm satisfying the above formula (1) is 20% or less of Al 2 O 3, 3 to 20% of TiO 2 , 5 to 50% of ZrO 2 , REM oxidation The product is 5 to 50%, CaO is 5 to 50%, and S is 1 to 15%.
続いて、上述した本鋼材の構成について詳細に説明する。
[炭素C:0.02~0.13%]
炭素Cは、鋼材(母材)の強度を確保するために欠くことのできない元素である。そのため、0.02%以上、好ましくは0.04%以上添加する。しかし、Cの含有量が0.13%を超えると、HAZに島状マルテンサイト(MA)が多く生成してHAZの靱性低下を招くばかりでなく、COガスの発生などに起因して溶接性にも悪影響を及ぼす。そのため、Cの含有量を0.13%以下、好ましくは0.1%以下とする。 In the present embodiment, the contents of elements and components are described simply by using the percentage “%”, but this is a simplified description of the mass percentage “mass%”. Please keep in mind.
Then, the structure of this steel material mentioned above is demonstrated in detail.
[Carbon C: 0.02 to 0.13%]
Carbon C is an element indispensable for securing the strength of the steel material (base material). Therefore, 0.02% or more, preferably 0.04% or more is added. However, if the content of C exceeds 0.13%, not only does island-like martensite (MA) form in the HAZ, leading to a reduction in the toughness of the HAZ, but also weldability due to the generation of CO gas, etc. It also has an adverse effect. Therefore, the C content is 0.13% or less, preferably 0.1% or less.
ケイ素Siは、脱酸作用を有すると共に、固溶強化により母材の強度向上に寄与する元素である。そのため、0.05%以上、好ましくは0.07%以上、より好ましくは0.1%以上添加する。しかし、Siの含有量が0.5%を超えると、鋼材の溶接性や靱性が低下するので、上限を0.5%とする。特にHAZ靱性を高めるには、Siの含有量を0.3%以下とすることが推奨される。但し、Siの含有量を抑えるほどHAZ靱性が向上するが、その一方で鋼材の強度が低下する場合がある。そのため、Siの含有量を0.5%以下、好ましくは0.35%以下、より好ましくは0.25%以下とする。 [Silicon Si: 0.05-0.5%]
Silicon Si is an element that has a deoxidizing action and contributes to improving the strength of the base material by solid solution strengthening. Therefore, 0.05% or more, preferably 0.07% or more, more preferably 0.1% or more is added. However, if the Si content exceeds 0.5%, the weldability and toughness of the steel material deteriorate, so the upper limit is made 0.5%. In particular, in order to increase the HAZ toughness, it is recommended that the Si content be 0.3% or less. However, as the Si content is reduced, the HAZ toughness is improved, while the strength of the steel material may be reduced. Therefore, the Si content is 0.5% or less, preferably 0.35% or less, more preferably 0.25% or less.
マンガンMnは、母材の強度向上に寄与する元素である。しかし、Mnの含有量が1.0%を下回ると強度が低下してしまう。そのため、1.0%以上、好ましくは1.3%以上添加する。しかし、Mnの含有量が2.5%を超えると、母材の溶接性が低下する。そのため、Mnの含有量を2.5%以下、好ましくは2.0%以下とする。 [Manganese Mn: 1.0-2.5%]
Manganese Mn is an element that contributes to improving the strength of the base material. However, when the Mn content is less than 1.0%, the strength is lowered. Therefore, 1.0% or more, preferably 1.3% or more is added. However, if the Mn content exceeds 2.5%, the weldability of the base material is degraded. Therefore, the Mn content is set to 2.5% or less, preferably 2.0% or less.
リンPは、偏析し易い元素であり、特に鋼材中の結晶粒界に偏析してHAZ靱性を低下させる元素である。Pは、通常、母材に不可避的に0.001%程度含有されているので、Pの含有量を0.03質量%以下に規定する。好ましくは0.02%以下、より好ましくは0.01%以下である。但し、本実施形態は、Pの含有量が0%である場合を含まない。 [Phosphorus P: 0.03% or less]
Phosphorus P is an element that easily segregates, and is an element that segregates at a grain boundary in a steel material and lowers the HAZ toughness. Usually, P is unavoidably contained in the base material in an amount of about 0.001%, so the content of P is specified to be 0.03% by mass or less. Preferably it is 0.02% or less, More preferably, it is 0.01% or less. However, this embodiment does not include the case where the P content is 0%.
硫黄Sは、Mnと結合して硫化物(MnS)を生成し、母材の靱性や板厚方向における延性を低下させる元素である。例えば、Sが、ランタンLaやセリウムCeなどのREMと結合してREMの硫化物(例えば、LaSやCeS)を生成すると、REM酸化物の生成が阻害されるため、HAZ靱性が低下する。しかし、Sは、通常、母材に不可避的に0.0005%程度含有されているので、Sの含有量を0.01%以下に規定する。好ましくは0.008%以下、より好ましくは0.006%以下である。但し、本実施形態は、Sの含有量が0%である場合を含まない。 [Sulfur S: 0.01% or less]
Sulfur S is an element that combines with Mn to produce sulfide (MnS) and lowers the toughness of the base material and the ductility in the plate thickness direction. For example, when S is combined with REM such as lanthanum La or cerium Ce to generate a REM sulfide (for example, LaS or CeS), generation of REM oxide is inhibited, so that HAZ toughness is reduced. However, S is usually unavoidably contained in the base material in an amount of about 0.0005%, so the S content is specified to be 0.01% or less. Preferably it is 0.008% or less, More preferably, it is 0.006% or less. However, this embodiment does not include the case where the S content is 0%.
アルミニウムAlは、脱酸剤として作用する元素である。また、Alの含有量が少ないと溶鋼が酸素で汚染されやすくなる。そのため、0.002%以上、好ましくは0.004%以上、より好ましくは0.005%以上添加する。しかし、Alを母材に対して過剰に添加すると、添加されたAlは母材中の酸化物を還元して粗大なAl酸化物を形成するので、HAZ靱性が低下する。そのため、Alの含有量を0.040%以下、好ましくは0.025%以下、より好ましくは0.015%以下とする。 [Aluminum Al: 0.002 to 0.040%]
Aluminum Al is an element that acts as a deoxidizer. Moreover, when there is little content of Al, molten steel will become easy to be contaminated with oxygen. Therefore, 0.002% or more, preferably 0.004% or more, more preferably 0.005% or more is added. However, when Al is added excessively with respect to the base material, the added Al reduces oxides in the base material to form coarse Al oxide, so that the HAZ toughness decreases. Therefore, the Al content is 0.040% or less, preferably 0.025% or less, and more preferably 0.015% or less.
チタンTiは、母材中にTiNなどの窒化物や、Tiを含む酸化物を生成し、HAZ靱性の向上に寄与する元素である。そのため、0.005%以上、好ましくは0.010%以上、より好ましくは0.014%以上添加する。しかし、Tiを母材に対して過剰に添加すると、Tiの固溶強化によって母材自体が硬化しHAZ靱性の低下に繋がる。そのため、Tiの含有量を0.040%以下、好ましくは0.030%以下、より好ましくは0.025%以下とする。 [Titanium Ti: 0.005 to 0.040%]
Titanium Ti is an element that contributes to the improvement of HAZ toughness by generating a nitride such as TiN or an oxide containing Ti in the base material. Therefore, 0.005% or more, preferably 0.010% or more, more preferably 0.014% or more is added. However, when Ti is excessively added to the base material, the base material itself is hardened by solid solution strengthening of Ti, leading to a decrease in HAZ toughness. Therefore, the Ti content is 0.040% or less, preferably 0.030% or less, and more preferably 0.025% or less.
ジルコニウムZrは、Zrを含む複合酸化物を生成してHAZ靱性の向上に寄与する元素である。そのため、0.0003%以上、好ましくは0.0005%以上、よりに好ましくは0.0009%以上添加する。しかし、Zrを母材に対して過剰に添加すると、粗大なZr酸化物(ZrO2)が生成してHAZ靱性が低下する。また、粗大なZr炭化物(ZrC)が生成することで、母材自体の靱性が低下する。そのため、Zrの含有量を0.020%以下、好ましくは0.015%以下、よりに好ましくは0.010%以下とする。 [Zirconium Zr: 0.0003 to 0.020%]
Zirconium Zr is an element that contributes to the improvement of HAZ toughness by generating a complex oxide containing Zr. Therefore, 0.0003% or more, preferably 0.0005% or more, more preferably 0.0009% or more is added. However, when Zr is added excessively with respect to the base material, coarse Zr oxide (ZrO 2 ) is generated and HAZ toughness is lowered. Further, the formation of coarse Zr carbide (ZrC) reduces the toughness of the base material itself. Therefore, the Zr content is 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less.
REM(希土類元素)は、酸化物の生成に必要な元素である。REMによるこれらの酸化物を含有することで、酸化物が鋼材中に微細分散し易くなる。この微細分散した酸化物が、HAZの粒内αの生成核となりHAZ靱性の向上に寄与する。そのため、0.0003%以上、好ましくは0.0005%以上、よりに好ましくは0.0009%以上添加する。しかし、REMを過剰に添加すると、固溶REMが生成して母材内で偏析するので、母材自体の靱性が劣化する。そのため、REMの含有量を0.020%以下、好ましくは0.015%以下、よりに好ましくは0.010%以下とする。 [Rare earth metal REM: 0.0003 to 0.020%]
REM (rare earth element) is an element necessary for generation of oxides. By containing these oxides by REM, the oxides are easily finely dispersed in the steel material. This finely dispersed oxide serves as a production nucleus for intra-grain α of HAZ and contributes to improvement of HAZ toughness. Therefore, 0.0003% or more, preferably 0.0005% or more, more preferably 0.0009% or more is added. However, when REM is added excessively, solid solution REM is generated and segregates in the base material, so that the toughness of the base material itself deteriorates. Therefore, the content of REM is set to 0.020% or less, preferably 0.015% or less, more preferably 0.010% or less.
[カルシウムCa:0.0003~0.0080%]
カルシウムCaは、酸化物の生成に必要な元素である。Caも、HAZの粒内αの生成核となりHAZ靱性の向上に寄与するので、0.0003%以上、好ましくは0.0005%以上、より好ましくは0.0007%以上含有させるとよい。しかし、Caを過剰に添加すると、粗大なCa硫化物が生成して母材の靱性が劣化する。そのため、Caの含有量を0.0080%以下、好ましくは0.0060%以下、より好ましくは0.0030%以下とする。 Specifically, REM means an element containing a lanthanoid element (15 elements from La to Ln) and Sc (scandium) and Y (yttrium). In this embodiment, it is preferable to contain at least one element selected from the group consisting of La, Ce and Y among these elements, and more preferably La and / or Ce.
[Calcium Ca: 0.0003 to 0.0080%]
Calcium Ca is an element necessary for the production of oxides. Ca also forms nuclei of HAZ in the grains and contributes to the improvement of HAZ toughness. Therefore, it is preferable to contain 0.0003% or more, preferably 0.0005% or more, more preferably 0.0007% or more. However, when Ca is added excessively, coarse Ca sulfide is generated and the toughness of the base material is deteriorated. Therefore, the Ca content is set to 0.0080% or less, preferably 0.0060% or less, more preferably 0.0030% or less.
窒素Nは、窒化物(例えば、ZrNやTiNなど)を析出する元素である。窒化物は、ピン止め効果によって溶接時のオーステナイト粒の粗大化を抑制することで、HAZ靱性の向上に寄与する。Nは、含有量が多いほど窒化物を形成してオーステナイト粒の微細化を促進するため、HAZ靱性の向上に有効に作用する。そのため、0.0030%以上、好ましくは0.0040%以上、より好ましくは0.0050%以上添加する。しかし、Nの含有量が0.010%を超えると、固溶Nの量が増大して母材自体の靱性が劣化し、HAZ靱性も低下する。そのため、Nの含有量を0.010%以下、好ましくは0.0090%以下、より好ましくは0.0080%以下とする。 [Nitrogen N: 0.0030 to 0.010%]
Nitrogen N is an element that precipitates nitrides (eg, ZrN, TiN, etc.). Nitride contributes to the improvement of HAZ toughness by suppressing the austenite grain coarsening during welding by the pinning effect. Since N forms a nitride and promotes refinement of austenite grains as the content increases, it effectively works to improve HAZ toughness. Therefore, 0.0030% or more, preferably 0.0040% or more, more preferably 0.0050% or more is added. However, if the N content exceeds 0.010%, the amount of solute N increases, the toughness of the base metal itself deteriorates, and the HAZ toughness also decreases. Therefore, the N content is 0.010% or less, preferably 0.0090% or less, and more preferably 0.0080% or less.
酸素Oは、酸化物の生成に必須の元素であり、含有量が0.0003%より少ないと、母材中に十分な量の酸化物が得られない。好ましくは0.0010%以上、より好ましくは0.0015%以上である。但し、含有量が0.0050%より多いと、酸化物の粗大化によりHAZ靭性の低下を招く。そのため、Oの含有量を0.0050%以下、好ましくは0.0040%以下、より好ましくは0.0035%以下とする。 [Oxygen O: 0.0003 to 0.0050%]
Oxygen O is an essential element for the formation of oxides. If the content is less than 0.0003%, a sufficient amount of oxide cannot be obtained in the base material. Preferably it is 0.0010% or more, More preferably, it is 0.0015% or more. However, if the content is more than 0.0050%, the HAZ toughness is lowered due to the coarsening of the oxide. Therefore, the content of O is set to 0.0050% or less, preferably 0.0040% or less, more preferably 0.0035% or less.
本鋼材は、上述の各元素を含有し、残部が鉄および不可避不純物からなる。
上述の各元素以外の残部の成分は、鉄および不可避不純物(例えば、MgやAs,Seなど)である。 Here, the content of O represents the total amount of oxygen, and means the total amount of O forming an oxide in the base material and free O dissolved in the base material.
This steel material contains the above-mentioned elements, and the balance consists of iron and inevitable impurities.
The remaining components other than the above-described elements are iron and inevitable impurities (for example, Mg, As, Se, etc.).
0.008≦(1/d)×{mass%S/(mass%CaO+mass%REM2O3)}≦0.289 ・・・(1)
(但し、dは個々の複合酸化物の円相当直径であって、0.1~3μmである)
この円相当直径で0.1~3μmの複合酸化物は、HAZにおいて粒内組織変態(粒内変態)を促進してHAZ靭性を向上させるためのものであるため、以下に、円相当直径で0.1~3μmの複合酸化物について検討する。なお、円相当直径で0.1μm未満の複合酸化物は、HAZ靱性の向上に殆ど寄与しないため、上記複合酸化物の個数には含めない。 On the other hand, in the present steel material, the above-mentioned composite oxide has a circle equivalent diameter of 0.1 μm to 3 μm (hereinafter referred to as 0.1 to 3 μm), satisfies the following formula (1), and It is contained so that the number thereof is 100 / mm 2 or more in the cross section of the steel material.
0.008 ≦ (1 / d) × {mass% S / (mass% CaO + mass% REM 2 O 3 )} ≦ 0.289 (1)
(Where d is the equivalent circle diameter of each composite oxide and is 0.1 to 3 μm)
This composite oxide having an equivalent circle diameter of 0.1 to 3 μm is for promoting intragranular structure transformation (intragranular transformation) in HAZ and improving HAZ toughness. Consider a composite oxide of 0.1 to 3 μm. Note that a complex oxide having an equivalent circle diameter of less than 0.1 μm hardly contributes to the improvement of HAZ toughness, and thus is not included in the number of complex oxides.
まず、REMとCaは酸化物も硫化物も形成しうる酸硫化物形成元素である。そこで、酸硫化物形成元素(REM2O3とCaO)の濃度に対するS濃度(mass%S)が高すぎると、過剰に生成される硫化物が、酸化物とマトリックスとの整合を阻害してしまうため、複合酸化物が組織制御に寄与する能力(粒内変態能)が低下する。また、酸硫化物形成元素(REM2O3とCaO)の濃度に対するS濃度(mass%S)が低すぎる場合、硫化物生成に伴うひずみエネルギーが得られず粒内変態にとって不利となるため、粒内変態能が低下する。さらに、複合酸化物そのもののサイズ(複合酸化物の円相当直径d)に起因するひずみエネルギーが粒内変態に影響を与える。 Hereinafter, the reason why a complex oxide having a circle equivalent diameter of 0.1 to 3 μm should satisfy the formula (1) will be described.
First, REM and Ca are oxysulfide-forming elements that can form oxides and sulfides. Therefore, if the S concentration (mass% S) with respect to the concentration of the oxysulfide forming elements (REM 2 O 3 and CaO) is too high, excessively generated sulfide inhibits the alignment between the oxide and the matrix. As a result, the ability of the composite oxide to contribute to the structure control (intragranular transformation ability) decreases. Also, if the S concentration (mass% S) relative to the concentration of oxysulfide forming elements (REM 2 O 3 and CaO) is too low, strain energy associated with sulfide formation cannot be obtained, which is disadvantageous for intragranular transformation. The intragranular transformation ability decreases. Furthermore, the strain energy resulting from the size of the composite oxide itself (equivalent circle diameter d of the composite oxide) affects the intragranular transformation.
まず、試作材に対して入熱量60kJ/mmの溶接のHAZを模擬した入熱試験を実施した。その後、入熱試験後の試作材を鏡面研磨し腐食を行い、腐食により組織を顕にして複合酸化物に起因する粒内変態の有無を調査した。
続いて、EPMA(Electron Probe MicroAnalyzer)にて、試作材における複合酸化物の組成とサイズを測定し、0.1~3μmの複合酸化物について式(1)の第二項の値を算出した。 A method for obtaining the upper limit value and the lower limit value of the second term of Expression (1) will be described.
First, a heat input test simulating welding HAZ with a heat input of 60 kJ / mm was performed on the prototype material. Then, the prototype material after the heat input test was mirror-polished and corroded, and the structure was revealed by corrosion to investigate the presence of intragranular transformation caused by the composite oxide.
Subsequently, the composition and size of the composite oxide in the prototype were measured by EPMA (Electron Probe MicroAnalyzer), and the value of the second term of the formula (1) was calculated for the composite oxide of 0.1 to 3 μm.
以上のような化学成分組成を有する本鋼材は、板厚が約3.0mm以上の厚鋼板などを対象としており、小~中入熱溶接はもとより、入熱量が50kJ/mm以上となる大入熱溶接においてもHAZ靱性の低下を防ぐことができるので、例えば橋梁や高層建造物、船舶などの大型構造物の材料として使用できる。 This is because the oxide composition affects the lattice matching between the oxide and the steel material in HAZ, so if the oxide composition is not controlled to the content within the above range, a composite oxide having a circle equivalent diameter of 0.1 to 3 μm. This is because it cannot contribute to the intragranular transformation in HAZ, that is, it cannot contribute to the refinement of the HAZ structure.
The steel material having the above chemical composition is intended for thick steel plates with a thickness of about 3.0 mm or more. In addition to small to medium heat input welding, the heat input is 50 kJ / mm or more. Since the HAZ toughness can be prevented from being lowered even in thermal welding, it can be used as a material for large structures such as bridges, high-rise buildings, and ships.
本実施形態に係る鋼材は、上述の成分元素に加えて、ニッケルNi、銅Cu、クロムCr、モリブデンMoのうち少なくとも1種を0.05%以上1.50%以下(0.05~1.50%)含有してもよい。
Cu、Ni、Cr、Moは、いずれも本鋼材の靭性と強度を高めるのに寄与する元素であり、各々単独で、あるいは複合して添加できる。例えば、Cuの添加によって靭性と強度を有効に向上させるには、Cuを0.05%以上含有させることが好ましい。しかし、Cuの含有量が1.50%を超えると、母材の強度を高め過ぎて却って母材の靱性を低下させるため、HAZ靱性も低下してしまう。従って、Cuの含有量を0.05%以上1.50%以下に規定する。 [Nickel Ni, Copper Cu, Chromium Cr, Molybdenum Mo: 0.05 to 1.50%]
In the steel material according to the present embodiment, in addition to the above-described component elements, at least one of nickel Ni, copper Cu, chromium Cr, and molybdenum Mo is 0.05% to 1.50% (0.05 to 1.. 50%) may be contained.
Cu, Ni, Cr, and Mo are all elements that contribute to increasing the toughness and strength of the steel material, and can be added alone or in combination. For example, in order to effectively improve toughness and strength by adding Cu, it is preferable to contain 0.05% or more of Cu. However, if the Cu content exceeds 1.50%, the strength of the base material is excessively increased and the toughness of the base material is decreased, so that the HAZ toughness is also decreased. Therefore, the Cu content is specified to be 0.05% or more and 1.50% or less.
[ニオブNb、バナジウムV:0.002~0.10%]
さらに、本実施形態に係る鋼材は、ニオブNb、バナジウムVのうち少なくともいずれか一方を0.002%以上0.10%以下(0.002~0.10%)含有していてもよい。
NbとVは、いずれも炭窒化物として析出する。この炭窒化物はピン止め効果を発揮するので、溶接時におけるオーステナイト粒の粗大化が抑止され、HAZ靱性の向上に寄与する。そこで、Nbの添加によってHAZ靭性を有効に向上させるには、Nbを、0.002%以上含有させるのが好ましい。しかし、Nbの含有量が0.10%を超えると、析出する炭窒化物が粗大化し、却ってHAZ靱性を低下させてしまう。従って、Nbの含有量を0.002%以上0.10%以下に規定する。 Like Cu, Ni, Cr, and Mo are preferably contained in an amount of 0.05% or more. However, if the content exceeds 1.50%, the strength of the base material is excessively increased and the toughness of the base material is decreased. Therefore, the HAZ toughness is also lowered. Therefore, the contents of Ni, Cr, and Mo are also specified to be 0.05% or more and 1.50% or less.
[Niobium Nb, Vanadium V: 0.002 to 0.10%]
Further, the steel material according to this embodiment may contain 0.002% or more and 0.10% or less (0.002 to 0.10%) of at least one of niobium Nb and vanadium V.
Nb and V are both precipitated as carbonitrides. Since this carbonitride exhibits a pinning effect, coarsening of austenite grains at the time of welding is suppressed, contributing to improvement of HAZ toughness. Therefore, in order to effectively improve the HAZ toughness by adding Nb, it is preferable to contain Nb in an amount of 0.002% or more. However, if the content of Nb exceeds 0.10%, the precipitated carbonitrides are coarsened, and on the contrary, the HAZ toughness is reduced. Therefore, the Nb content is specified to be 0.002% or more and 0.10% or less.
[ホウ素B:0.0005~0.0050%]
加えて、本実施形態に係る鋼材は、ホウ素Bを0.0005%以上0.0050%以下(0.0005~0.0050%)含有していてもよい。Bは、粒界フェライトの生成を抑制して靱性を向上させる元素である。そこで、Bの添加によって本鋼材の靭性を向上させるには、Bを0.0005%以上含有させるのが好ましい。より好ましくは0.0010%以上、更に好ましくは0.0015%以上である。しかし、Bの含有量が0.0050%を超えると、オーステナイト粒界にBNとして析出し、靱性の低下を招く。そのため、Bの含有量を0.0050%以下、好ましくは0.0040%以下、より好ましくは0.0015%以上0.0030%以下とする。 V, like Nb, is preferably contained in an amount of 0.002% or more. However, if the content of V exceeds 0.10%, the precipitated carbonitrides are coarsened, and on the contrary, the HAZ toughness is lowered. Therefore, the V content is specified to be 0.002% or more and 0.10% or less.
[Boron B: 0.0005 to 0.0050%]
In addition, the steel material according to the present embodiment may contain 0.0005% or more and 0.0050% or less (0.0005 to 0.0050%) of boron B. B is an element that suppresses the formation of grain boundary ferrite and improves toughness. Therefore, in order to improve the toughness of the steel material by adding B, it is preferable to contain B in an amount of 0.0005% or more. More preferably, it is 0.0010% or more, More preferably, it is 0.0015% or more. However, if the B content exceeds 0.0050%, it precipitates as BN at the austenite grain boundaries, leading to a decrease in toughness. Therefore, the B content is 0.0050% or less, preferably 0.0040% or less, more preferably 0.0015% or more and 0.0030% or less.
本実施形態に係る鋼材は、例えば溶鋼の二次精錬において、上述した化学成分組成となるように各元素を添加することで得られるが、本鋼材の製造方法の一例として、後述する実施例に示す鋼の製造方法(製造条件)、つまり各元素の添加方法について説明する。
以下の説明では、真空溶解炉(容量150kg)を用いて鋼を溶製し、150kgのインゴットに鋳造して冷却することで、後述する実施例および比較例に示す鋼を得た。 [Manufacture of steel materials according to this embodiment]
The steel material according to the present embodiment can be obtained by adding each element so as to have the above-described chemical component composition, for example, in the secondary refining of molten steel. The steel manufacturing method (manufacturing conditions) shown, that is, the method of adding each element will be described.
In the following description, steel was melted using a vacuum melting furnace (capacity 150 kg), cast into a 150 kg ingot, and cooled to obtain steels shown in examples and comparative examples described later.
初めに、真空溶解炉で溶解された溶鋼において、複合酸化物を形成する元素(複合酸化物形成元素)を添加する前に溶存酸素量とS濃度を調整する。
まず、複合酸化物形成元素の添加前における溶存酸素量(mass%Of)を0.005%以下となるように調整した。その後、溶存酸素濃度(mass%Of)と、溶鋼中のS濃度(mass%S)の比(mass%Of/mass%S)が、0.2≦mass%Of/mass%S≦9.6となるようにS濃度(mass%S)を調整した。 [Adjustment of dissolved oxygen content]
First, in a molten steel melted in a vacuum melting furnace, the amount of dissolved oxygen and the S concentration are adjusted before adding an element for forming a complex oxide (a complex oxide forming element).
First, the amount of dissolved oxygen (mass% Of) before addition of the complex oxide forming element was adjusted to 0.005% or less. Thereafter, the ratio of the dissolved oxygen concentration (mass% Of) to the S concentration (mass% S) in the molten steel (mass% Of / mass% S) is 0.2 ≦ mass% Of / mass% S ≦ 9.6. S concentration (mass% S) was adjusted so that
上述の溶存酸素量とS濃度の根拠は次の通りである。まず、溶存酸素量が0.005%を超えると、溶鋼中で生成する酸化物が粗大化してしまう。その上で、(mass%Of/mass%S)の値が大きい場合、酸化物に対して必要な硫化物が十分に生成しない。また(mass%Of/mass%S)の値が小さい場合、所望の酸化物を得ることができないだけでなく、S濃度が高すぎるため粒内変態を阻害する水準にまで硫化物が生成してしまう。 Here, the desulfurization method for adjusting the S concentration (mass% S) is not particularly limited, but a molten steel having a low S concentration may be used in advance.
The grounds for the dissolved oxygen amount and the S concentration are as follows. First, when the amount of dissolved oxygen exceeds 0.005%, the oxide generated in the molten steel becomes coarse. In addition, when the value of (mass% Of / mass% S) is large, the sulfide necessary for the oxide is not sufficiently generated. Further, when the value of (mass% Of / mass% S) is small, not only the desired oxide cannot be obtained, but also the sulfide is generated to a level that inhibits intragranular transformation because the S concentration is too high. End up.
[Alの添加]
次に、Alは酸硫化物構成元素の一つであり、Ti酸化物を確保するために、Tiよりも先に溶鋼に添加した。 Therefore, there is an appropriate balance between mass% Of and mass% S, and an appropriate range exists for the value of (mass% Of / mass% S). The range was experimentally determined, and 0.2 ≦ mass% Of / mass% S ≦ 9.6.
[Addition of Al]
Next, Al is one of oxysulfide constituent elements, and was added to the molten steel before Ti in order to secure Ti oxide.
Alの添加に続いて、REM、Zrよりも先にTiを溶鋼に添加した。TiをAlよりも先に添加すると、その後の工程でTi酸化物が全てAlによって還元されてしまうので、Alを添加した後にTiを添加しなくてはならない。Tiの添加後、2分以上15分以下にわたって、他の元素を添加せずに溶鋼を保持した。 [Addition of Ti]
Following the addition of Al, Ti was added to the molten steel before REM and Zr. If Ti is added before Al, all Ti oxides are reduced by Al in the subsequent steps. Therefore, Ti must be added after Al is added. After the addition of Ti, the molten steel was held for 2 to 15 minutes without adding other elements.
[REM・Zrの添加]
溶鋼を2分~15分間保持した後に、REMおよびZrを添加した。REMとZrの添加順は、特に問わない。つまり、REM→Zrでも良いし、Zr→REMでも良いし、またREMとZrを同時に添加しても良い。 Even if it is added in the order of Al → Ti, if the holding time of the molten steel thereafter is less than 2 minutes, a complex oxide of Al and Ti is not sufficiently formed. This is because the reduction proceeds too much. That is, the order of addition of Al and Ti affects the above formula (1).
[Addition of REM / Zr]
After holding the molten steel for 2 to 15 minutes, REM and Zr were added. The order of addition of REM and Zr is not particularly limited. That is, REM → Zr, Zr → REM, or REM and Zr may be added simultaneously.
そこで、以下の式(2)を満足するように、Zr添加量とREM添加量の比(add[Zr]/add[REM])を決定する。 In addition to this, REM has the property of easily forming oxides and sulfides, while Zr has the property of forming oxides but not sulfides. Therefore, in order to optimize the balance between the oxide and the sulfide, it is necessary to add Zr and REM according to mass% Of and mass% S.
Therefore, the ratio (add [Zr] / add [REM]) between the Zr addition amount and the REM addition amount is determined so as to satisfy the following expression (2).
式(2)に基づいて、(mass%Of/mass%S)の値が大きい、すなわち、オキサイドが生成しやすく硫化物が生成しにくい場合には、ZrをREMより多めに添加する(add[Zr]/add[REM]の値を大きくする)。また、(mass%Of/mass%S)の値が小さい、すなわち、オキサイドよりも硫化物が生成しやすい場合には、REMをZrより多めに添加する(add[Zr]/add[REM]の値を小さくする)。この考え方に立脚し、add[Zr]/add[REM]の値の上限および下限を実験的に求め、式(2)を得た。 0.27 × (mass% Of / mass% S) + 0.21 ≦ add [Zr] / add [REM] ≦ 0.41 × (mass% Of / mass% S) +0.77 (2)
Based on the formula (2), when the value of (mass% Of / mass% S) is large, that is, when oxide is easily generated and sulfide is not easily generated, Zr is added more than REM (add [ Zr] / add [REM] is increased). Further, when the value of (mass% Of / mass% S) is small, that is, when sulfides are more easily generated than oxide, REM is added more than Zr (add [Zr] / add [REM] Decrease the value). Based on this idea, the upper limit and lower limit of the value of add [Zr] / add [REM] were experimentally obtained to obtain Equation (2).
REMおよびZrを添加した後、Caを添加して鋳造した。Caもオキサイドや硫化物を形成するが、それらオキサイドや硫化物の形態は、基本的に既に存在する介在物の形態に依存するので、Caの添加前の介在物の形態に特に留意すべきである。
なお、脱酸元素であるAl,REM,Zr,Caは、全量を一度に溶鋼へ投入するのではなく、2回以上に分割して投入するか、少量ずつ連続的に投入するのが望ましい。 [Ca addition and forging]
After REM and Zr were added, Ca was added and cast. Ca also forms oxides and sulfides. However, since the form of these oxides and sulfides basically depends on the form of inclusions already present, special attention should be paid to the form of inclusions before the addition of Ca. is there.
The deoxidizing elements Al, REM, Zr, and Ca are preferably not added all at once to the molten steel, but divided into two or more times or continuously in small amounts.
[鋳造・圧延]
上述のように成分調整された溶鋼をインゴットに鋳造した。鋳造されたインゴットを熱間圧延して加工し、厚さが30mm~80mmの厚鋼板を製造した。実際の操業においては、成分調整して得られた溶鋼を、常法に従って連続鋳造してスラブとした後、常法に従って熱間圧延すればよい。 The composition (content) of the component elements described so far, the relational expression regarding the content of the component elements, the manufacturing conditions, and the like are referred to as “conditions defined in the present embodiment”.
[Casting / Rolling]
Molten steel whose components were adjusted as described above was cast into an ingot. The cast ingot was processed by hot rolling to produce a thick steel plate having a thickness of 30 mm to 80 mm. In actual operation, the molten steel obtained by adjusting the components may be continuously cast according to a conventional method to form a slab and then hot rolled according to a conventional method.
得られた厚鋼板について、溶接熱の影響を受けたHAZの靱性を評価するために、該厚鋼板から、溶接継手用試験片を採取してV先加工を施した後、大入熱溶接相当の60kJ/mmの入熱量でのエレクトロガスアーク溶接を実施した。この溶接された試験片の表面から深さt/4(t:試験片の板厚)の位置の溶接線(ボンド)近傍のHAZに切欠きを加工したシャルピー衝撃試験片(JIS Z 2202のVノッチ試験片)を3本採取した。これら3本のVノッチ試験片の各々に対して、-40℃でシャルピー衝撃試験を行い、吸収エネルギー(vE-40)を測定し、3本のVノッチ試験片の測定結果の平均値と最小値を求めた。 [Measurement of HAZ toughness value]
In order to evaluate the toughness of the HAZ affected by the welding heat for the obtained thick steel plate, a specimen for a welded joint was sampled from the thick steel plate and subjected to V pre-processing, followed by high heat input welding. Electrogas arc welding was performed at a heat input of 60 kJ / mm. Charpy impact test piece (V of JIS Z 2202) in which a notch is machined in the HAZ near the weld line (bond) at a depth t / 4 (t: thickness of the test piece) from the surface of the welded test piece. Three notch specimens) were collected. Each of these three V-notch specimens is subjected to a Charpy impact test at −40 ° C., the absorbed energy (vE-40) is measured, and the average value and minimum value of the measurement results of the three V-notch specimens are measured. The value was determined.
[0.1~3μmの複合酸化物組成の測定方法]
厚鋼板の表面から深さt/4(t:厚鋼板の板厚)の位置から試験片を切り出し(試験片の軸心が深さt/4の位置を通るように採取)、圧延方向および板厚方向に平行な断面を鏡面研磨し、日本電子データム製の電子線マイクロプローブX線分析計(Electron Probe X-ray Microanalyzer:EPMA,商品名JXA-8500F)を用いて、0.1~3μmの複合酸化物組成を測定した。この時の観察条件は、加速電圧を20kV、試料電流を0.01μA、倍率5000倍、観察面積を0.4mm2以上とし、複合酸化物の中央部での成分組成を特性X線の波長分散分光により定量分析した。 In this measurement result, a test piece (thick steel plate) having an average value of vE-40 exceeding 140 J was evaluated as a steel plate excellent in HAZ toughness.
[Measuring method of composite oxide composition of 0.1 to 3 μm]
A test piece is cut out from the surface of the thick steel plate at a depth t / 4 (t: thickness of the thick steel plate) (taken so that the axis of the test piece passes through the position of the depth t / 4), and the rolling direction and A cross section parallel to the plate thickness direction is mirror-polished and 0.1 to 3 μm using an electron probe microprobe X-ray analyzer (EPMA, trade name JXA-8500F) manufactured by JEOL Datum. The composite oxide composition of was measured. The observation conditions at this time were an acceleration voltage of 20 kV, a sample current of 0.01 μA, a magnification of 5000 times, an observation area of 0.4 mm 2 or more, and the component composition at the center of the composite oxide with wavelength dispersion of characteristic X-rays Quantitative analysis was performed by spectroscopy.
[複合酸化物の円相当直径と個数の測定方法]
上述したEPMAを用いた複合酸化物の組成測定において、複合酸化物の面積を測定すると共に複合酸化物を円と仮定して、測定した面積に対応する円の直径を円相当直径として算出した。円相当直径が5μmを超える複合酸化物の個数を測定する際には、倍率を200倍、観察面積を50mm2以上とし、それ以外の条件を、円相当直径が5μm以下の複合酸化物の個数を測定する場合と同じ条件に揃えて実施した。 In addition, when the REM is represented by the symbol M, the REM oxide is present in the steel material in the form of M 2 O 3 , M 3 O 5 , MO 2, etc., but all the REM oxide is converted to M 2 O 3 . Converted. Similarly, all Ti was converted to TiO 2 .
[Measurement method of equivalent circle diameter and number of composite oxide]
In the composition measurement of the composite oxide using the above-described EPMA, the area of the composite oxide was measured and the composite oxide was assumed to be a circle, and the diameter of the circle corresponding to the measured area was calculated as the equivalent circle diameter. When measuring the number of composite oxides whose equivalent circle diameter exceeds 5 μm, the magnification is 200 times, the observation area is 50 mm 2 or more, and other conditions are the number of composite oxides whose equivalent circle diameter is 5 μm or less. The measurement was performed under the same conditions as in the measurement.
下の表2は、本実施形態による鋼材の実施例である鋼材No.1~No.31の化学成分組成を示している。鋼材No.1~No.31の成分組成は全て、本実施形態で規定する条件を満たしている。 Next, examples of the steel material according to the present embodiment will be specifically described.
Table 2 below shows steel No. which is an example of the steel according to the present embodiment. 1-No. The chemical composition of 31 is shown. Steel No. 1-No. All 31 component compositions satisfy the conditions defined in this embodiment.
図1は、表4に示す本実施形態による鋼材のHAZ靭性と、表7に示す比較例の鋼材No.59,61~67のHAZ靭性を示すグラフである。図1に示す全ての実施例および比較例において、円相当直径3μmを超える複合酸化物の個数は5.0個/mm2未満であるが、比較例の鋼材No.59,61~67は、円相当直径0.1~3μmの複合酸化物の個数が100個に満たなかった例であり、いずれにおいても、HAZ靭性の試験結果が140Jを大きく下回っている。 With reference to FIGS. 1 to 3, the HAZ toughness of the steel material according to this embodiment shown in Table 4 is compared with the HAZ toughness of the comparative example shown in Table 7.
FIG. 1 shows the HAZ toughness of the steel material according to the present embodiment shown in Table 4 and the steel material No. of the comparative example shown in Table 7. 6 is a graph showing the HAZ toughness of 59, 61-67. In all the examples and comparative examples shown in FIG. 1, the number of composite oxides having an equivalent circle diameter of 3 μm is less than 5.0 / mm 2 . Nos. 59, 61 to 67 are examples in which the number of complex oxides with equivalent circle diameters of 0.1 to 3 μm was less than 100, and in any case, the HAZ toughness test results were much lower than 140J.
なお、今回開示された実施形態はすべての点で例示であって制限的なものではないと考えられるべきである。特に、今回開示された実施形態において、明示的に開示されていない事項、例えば、運転条件や操業条件、各種パラメータ、構成物の寸法、重量、体積などは、当業者が通常実施する範囲を逸脱するものではなく、通常の当業者であれば、容易に想定することが可能な値を採用している。 As described above, if the steel material has a configuration that satisfies the conditions defined in the present embodiment, it can exhibit excellent HAZ toughness even in high heat input welding.
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, for example, operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. Instead, values that can be easily assumed by those skilled in the art are employed.
Claims (2)
- C :0.02~0.13%(質量%(mass%)の意味。以下成分について同じ。)、
Si:0.05~0.5%、
Mn:1.0~2.5%、
P :0.03%以下(0%を含まない)、
S :0.01%以下(0%を含まない)、
Al:0.002~0.040%、
Ti:0.005~0.040%、
Zr:0.0003~0.020%、
REM:0.0003~0.020%、
Ca:0.0003~0.0080%、
N :0.0030~0.010%、
O :0.0003~0.0050%を含有し、残部が鉄および不可避不純物からなる鋼材であって、
前記鋼材は、REM、Zr、Ti、Al、CaおよびSを含有する複合酸化物を含み、前記鋼材中の複合酸化物について、
円相当直径で3μm超の酸化物が1mm2あたり5.0個以下であって、
かつ円相当直径が0.1~3μmの複合酸化物について、下記式(1)を満たす複合酸化物個数が100個/mm2以上であって、
さらに、下記式(1)を満たす0.1~3μmの複合酸化物の平均組成が、Al2O3:20%以下、TiO2:3~20%、ZrO2:5~50%、REM酸化物:5~50%、CaO:5~50%、S:1~15%であることを特徴とする溶接熱影響部の靭性に優れた鋼材。
0.008≦(1/d)×{mass%S/(mass%CaO+mass%REM2O3)}≦0.289 ・・・(1)
(但し、dは個々の複合酸化物の円相当直径であって、0.1~3μmである) C: 0.02 to 0.13% (meaning mass%). The same applies to the following components.)
Si: 0.05 to 0.5%,
Mn: 1.0 to 2.5%
P: 0.03% or less (excluding 0%),
S: 0.01% or less (excluding 0%),
Al: 0.002 to 0.040%,
Ti: 0.005 to 0.040%,
Zr: 0.0003 to 0.020%,
REM: 0.0003 to 0.020%,
Ca: 0.0003 to 0.0080%,
N: 0.0030 to 0.010%,
O: a steel material containing 0.0003 to 0.0050%, the balance being iron and inevitable impurities,
The steel material includes a complex oxide containing REM, Zr, Ti, Al, Ca and S, and the complex oxide in the steel material,
The number of oxides with an equivalent circle diameter of more than 3 μm is 5.0 or less per 1 mm 2 ,
In addition, for the complex oxide having an equivalent circle diameter of 0.1 to 3 μm, the number of complex oxides satisfying the following formula (1) is 100 / mm 2 or more,
Further, the average composition of the composite oxide of 0.1 to 3 μm satisfying the following formula (1) is Al 2 O 3 : 20% or less, TiO 2 : 3 to 20%, ZrO 2 : 5 to 50%, REM oxidation Material: 5 to 50%, CaO: 5 to 50%, S: 1 to 15%, steel material excellent in toughness of weld heat affected zone.
0.008 ≦ (1 / d) × {mass% S / (mass% CaO + mass% REM 2 O 3 )} ≦ 0.289 (1)
(Where d is the equivalent circle diameter of each composite oxide and is 0.1 to 3 μm) - Ni:0.05~1.50%、
Cu:0.05~1.50%、
Cr:0.05~1.50%、
Mo:0.05~1.50%、
Nb:0.002~0.10%、
V :0.002~0.10%、
B :0.0005~0.0050%
のうち、少なくとも1種を含有することを特徴とする請求項1に記載の溶接熱影響部の靭性に優れた鋼材。 Ni: 0.05 to 1.50%,
Cu: 0.05 to 1.50%,
Cr: 0.05 to 1.50%,
Mo: 0.05 to 1.50%,
Nb: 0.002 to 0.10%,
V: 0.002 to 0.10%,
B: 0.0005 to 0.0050%
The steel material excellent in toughness of the weld heat affected zone according to claim 1, comprising at least one of them.
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Also Published As
Publication number | Publication date |
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KR101718275B1 (en) | 2017-03-20 |
EP2977479B1 (en) | 2018-04-25 |
EP2977479A4 (en) | 2016-11-30 |
CN105051229B (en) | 2017-03-15 |
JP2014185364A (en) | 2014-10-02 |
CN105051229A (en) | 2015-11-11 |
JP6226542B2 (en) | 2017-11-08 |
KR20150119391A (en) | 2015-10-23 |
EP2977479A1 (en) | 2016-01-27 |
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