WO2014156606A1 - 低温靱性、伸び、および溶接性に優れた高強度鋼板、並びにその製造方法 - Google Patents
低温靱性、伸び、および溶接性に優れた高強度鋼板、並びにその製造方法 Download PDFInfo
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- WO2014156606A1 WO2014156606A1 PCT/JP2014/056272 JP2014056272W WO2014156606A1 WO 2014156606 A1 WO2014156606 A1 WO 2014156606A1 JP 2014056272 W JP2014056272 W JP 2014056272W WO 2014156606 A1 WO2014156606 A1 WO 2014156606A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C—CHEMISTRY; METALLURGY
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
Definitions
- the present invention relates to a high-strength steel plate excellent in low-temperature toughness, elongation, and weldability, and a method for producing the same.
- the high-strength steel sheet according to the present invention includes, for example, penstock (hydraulic iron pipe), construction materials for undamaged buildings, etc .; various construction machines used in construction sites such as excavators, cranes, and scrapers. It is suitably used for applications.
- Steel sheets used for construction materials, construction machinery, and other applications have high strength and good low temperature toughness in the base metal and welded joints, especially workability due to elongation so that they can withstand the harsh environment at the work site. , And excellent weldability is required.
- the strength such as tensile strength and yield point and the elongation are in an inversely proportional relationship, and the elongation decreases when a high strength is to be secured.
- a high preheating temperature is required at the time of welding, and the weldability is lowered. Therefore, until now, only a technique satisfying some of the above characteristics has been provided, and no technique having all the above characteristics has been provided.
- Patent Document 1 discloses a steel sheet in which MA (Martensite-Austenite Constituent) is controlled as a high-strength steel sheet having excellent low-temperature toughness and a tensile strength of 980 MPa or more. .
- MA Martensite-Austenite Constituent
- Ceq carbon equivalent
- solid solution amount of the alloy elements the size of Nb compounds and austenite grains in the steel, etc.
- a steel sheet in which is controlled within a predetermined range is disclosed.
- Patent Document 1 does not intend to improve the elongation.
- Patent Document 2 as a high-strength steel plate having a tensile strength of 980 MPa or more excellent in elongation, Nb and Ti are added to the steel, the prior austenite grain size distribution is refined, and the prior austenite grain size distribution is controlled. A steel plate is disclosed. However, Patent Document 2 does not discuss low temperature toughness or weldability.
- the present invention has been made in view of the above circumstances, and its purpose was excellent in low-temperature toughness, elongation, and weldability despite having high strength such as a tensile strength of 980 MPa or more and a yield point of 960 MPa or more.
- An object of the present invention is to provide a high-strength steel plate and a method for producing the same.
- a high-strength steel sheet having a tensile strength of 980 MPa or more and a yield point of 960 MPa or more excellent in low temperature toughness, elongation, and weldability according to the present invention that can achieve the above-mentioned problems is C: 0.125 to 0.15.
- % (Meaning mass%, the same applies to chemical components), Si: 0.2 to 0.75%, Mn: 0.9 to 1.2%, Al: 0.03 to 0.06%, Cr: 0 .65 to 1%, Mo: 0.2 to 0.7%, V: 0.035 to 0.11%, Nb: more than 0% and 0.11% or less, B: 0.0005 to 0.002%, N: more than 0% and 0.006% or less, the balance is made of iron and inevitable impurities, and the metal structure is a tempered bainite structure, a tempered martensite structure, or a composite structure thereof.
- the parameter shown is 20 or more, and is expressed by the following equation (2). Pcm value and has a gist where it is 0.28 or less.
- the manufacturing method of the high strength steel plate according to the present invention that has achieved the above-mentioned problems and has excellent tensile strength with low temperature toughness, elongation, and weldability of 980 MPa or more and a yield point of 960 MPa or more is C: 0. 125-0.15%, Si: 0.2-0.75%, Mn: 0.9-1.2%, Al: 0.03-0.06%, Cr: 0.65-1%, Mo : 0.2 to 0.7%, V: 0.035 to 0.11%, Nb: over 0% to 0.11% or less, B: 0.0005 to 0.002%, N: over 0%.
- the tensile strength is 980 MPa or more, the yield point. Although it has a high strength of 960 MPa or more, a high-strength steel sheet excellent in low-temperature toughness, elongation, and weldability can be realized.
- the present inventor conducted extensive research in order to provide a high-strength steel sheet having all the above characteristics.
- the parameter of the above formula (1) (0.5 ⁇ [Mo] + 121 ⁇ [V] + 15 ⁇ [Mn] + 0.5 ⁇ [Cr]) composed of the contents of Mo, V, Mn, and Cr ) was controlled to 20 or more, and the tensile strength was 980 MPa or more and the yield point was 960 MPa or more, and the elongation was improved to 13% or more in total elongation.
- the present inventors examined a method for improving the elongation to 13% or more in total elongation while having a high strength with a tensile strength of 980 MPa or more and a yield point of 960 MPa or more.
- the elongation of a steel sheet can be improved by accumulating the amount of dislocation during tension. Therefore, the present inventors have focused particularly on the elements Mo, V, Mn, and Cr from the viewpoint of forming carbides and fine cementite in the steel sheet and improving elongation by pinning dislocations.
- the parameters represented by the above formula (1) are important requirements for realizing a high strength of 980 MPa or more and a yield point of 960 MPa or more and a high elongation of 13% or more in total elongation in the present invention. Therefore, the lower limit is set to 20 or more. A preferable lower limit is 25 or more, and more preferably 29 or more.
- the low temperature toughness was improved by adding no Ti, that is, by making the composition at an impurity level. This is because when Ti nitride is formed by the addition of Ti, the hardenability is lowered due to the pinning effect at the time of quenching (Q time), and the low temperature toughness is lowered.
- the amount of Ti in the present invention is substantially controlled to be approximately 0.005% or less.
- the upper limit of the Pcm value is set to 0.28 or less.
- the preferable upper limit is 0.27 or less, and more preferably 0.26 or less.
- C is an element that generates carbides to pin dislocations and contributes to improvement in elongation. Moreover, the hardenability of a steel plate is improved and it contributes also to strength improvement.
- the lower limit of the C content is set to 0.125% or more.
- the minimum with preferable C content is 0.130% or more, More preferably, it is 0.135% or more.
- the upper limit is made 0.15% or less.
- the upper limit with preferable C content is 0.145% or less.
- Si is an essential element for deoxidation of steel materials.
- the lower limit of the Si content is set to 0.2% or more.
- the minimum with preferable Si content is 0.3% or more.
- the upper limit is made 0.75% or less.
- the upper limit with preferable Si content is 0.7% or less, More preferably, it is 0.6% or less.
- Mn is an element that contributes to improvement in elongation.
- Mn is an element effective in suppressing C diffusion in cementite, and this suppresses coalescence aggregation of cementite, finely precipitates cementite, pins dislocations during tension, and improves elongation.
- the lower limit of the Mn content is set to 0.9% or more.
- the minimum with preferable Mn content is 0.95% or more, More preferably, it is 1.00% or more.
- the upper limit of the Mn content is 1.2% or less.
- the upper limit with preferable Mn content is 1.15% or less, More preferably, it is 1.10% or less.
- Al 0.03-0.06%
- Al is added as a deoxidizer for steel.
- the lower limit of the Al content is set to 0.03% or more.
- the minimum with preferable Al content is 0.035% or more.
- the upper limit is made 0.06% or less.
- the upper limit with preferable Al content is 0.055% or less.
- Cr 0.65 to 1%
- Cr is an element that contributes to improvement in elongation.
- the lower limit of the Cr content is set to 0.65% or more.
- the minimum with preferable Cr content is 0.70% or more.
- the upper limit is made 1% or less.
- the upper limit with preferable Cr content is 0.95% or less, More preferably, it is 0.90% or less.
- Mo is an element contributing to elongation and strength improvement. Specifically, Mo is an element having a good affinity with C, and the amount of dislocations that can be accumulated by pinning dislocations by forming carbides is improved, and the elongation is increased. Further, the strength is improved by precipitation strengthening of Mo.
- the lower limit of the Mo content is set to 0.2% or more.
- a preferable lower limit of the Mo content is 0.23% or more.
- the upper limit is made 0.7% or less.
- the upper limit with preferable Mo content is 0.65% or less, More preferably, it is 0.60% or less.
- V 0.035 to 0.11%
- V is an element that contributes to elongation and strength improvement. Specifically, V increases the amount of dislocations that can be accumulated by forming carbides and pinning the dislocations, thereby improving elongation. Moreover, the strength is improved by precipitation strengthening of V.
- the lower limit of the V content is set to 0.035% or more.
- the minimum with preferable V content is 0.040% or more.
- the upper limit is made 0.11% or less.
- the upper limit with preferable V content is 0.10% or less, More preferably, it is 0.09% or less.
- Nb is an element that contributes to improvement in strength and elongation. Specifically, the strength is increased by precipitation strengthening of Nb. Nb is an element that easily forms nitrides, and forms nitrides in a cluster form. Therefore, although the pinning effect of dislocations is lower than that of carbides such as Mo, the amount of dislocations that can be accumulated is improved and elongation is increased. Improve.
- the preferable lower limit of Nb is set to 0.003% or more. More preferably it is 0.005% or more, and still more preferably 0.010% or more. However, if the Nb content is excessive, the weldability is deteriorated, so the upper limit is made 0.11% or less. The upper limit with preferable Nb content is 0.1% or less, More preferably, it is 0.09% or less.
- B is an element that enhances hardenability and is effective in improving strength.
- the lower limit of the B content is set to 0.0005% or more.
- the minimum with preferable B content is 0.0006% or more.
- the upper limit of the B content is set to 0.002% or less.
- the upper limit with preferable B content is 0.0015% or less.
- N is an element inevitably contained in the steel material. If the amount of N is too large, the base material toughness deteriorates due to the presence of solute N, so the upper limit of the N content is set to 0.006% or less. The upper limit with preferable N content is 0.005% or less. It is extremely difficult to make the N amount substantially zero.
- the contained elements specified in the present invention are as described above, and the balance is iron and inevitable impurities.
- elements such as P, S, Sn, As, and Pb may be allowed to be introduced in addition to the elements introduced depending on the situation of raw materials, materials, manufacturing equipment, and the like.
- P and S are preferably suppressed as follows, for example.
- P more than 0% and 0.02% or less
- P causes temper embrittlement and lowers the toughness, so the amount is preferably as small as possible.
- the upper limit of the P content is preferably suppressed to 0.02% or less, and more preferably 0.015% or less.
- S is an impurity that causes temper embrittlement, and its amount is preferably as small as possible.
- the S content is preferably suppressed to 0.01% or less, and more preferably 0.005% or less.
- steel sheet of the present invention may contain the following selective components as necessary.
- Cu more than 0% and less than 0.5%
- Ni more than 0% and less than 2%
- Cu and Ni are both effective elements for increasing the strength by solid solution strengthening. These may be added alone or in combination.
- the steel sheet of the present invention is composed of tempered bainite, tempered martensite, or a composite structure thereof as a metal structure.
- a predetermined tempering process is performed after quenching, and the tempered structure is formed as described above.
- the steel sheet of the present invention is excellent in all of strength, low temperature toughness, elongation, and weldability.
- the steel sheet of the present invention has a high strength, that is, a tensile strength of 980 MPa or more, preferably 1000 MPa or more. Furthermore, the steel sheet of the present invention has a yield point of 960 MPa or more, preferably 980 MPa or more.
- the steel sheet of the present invention has high elongation (total elongation) despite its high strength as described above.
- the range of elongation varies depending on the plate thickness, the shape of the test piece, and the like.
- the elongation (total elongation) satisfies 13% or more, preferably 15% or more.
- the steel sheet of the present invention is excellent in low temperature toughness. Specifically, when the low-temperature toughness is evaluated by the method described in the examples described later, it satisfies 50 J or more, preferably 60 J or more at ⁇ 20 ° C.
- the steel sheet of the present invention is excellent in weldability.
- the Pcm value represented by the above formula (2) satisfies 0.28 or less, preferably 0.27 or less.
- the steel sheet is obtained by heating and rolling a steel satisfying the above-described composition, then air-cooling to room temperature, further heating to 900 ° C. or higher, and performing a tempering treatment at a temperature of 400 ° C. to 600 ° C. There is a feature.
- the heating temperature (Q temperature) and the tempering temperature (T temperature) during quenching are important to appropriately control the heating temperature (Q temperature) and the tempering temperature (T temperature) during quenching.
- the heating temperature during quenching is 900 ° C. or higher.
- the heating temperature at the time of quenching is lower than 900 ° C., there is a problem that the strength is lowered.
- it is 910 degreeC or more, More preferably, it is 915 degreeC or more.
- Quenching conditions are not particularly limited except that the temperature is controlled within the above temperature range, and further preferably within the above preferable holding temperature. For example, it is recommended to perform the quenching by water quenching.
- a tempering process is performed at a temperature of 400 ° C. to 600 ° C. (T temperature). If the tempering temperature is less than 400 ° C., the tempering effect cannot be obtained.
- a preferable tempering temperature is 430 ° C. or higher, more preferably 450 ° C. or higher. On the other hand, when the tempering temperature exceeds 600 ° C., there is a problem that the strength is lowered.
- a preferable tempering temperature is 580 ° C. or lower, more preferably 560 ° C. or lower.
- the method of the present invention is characterized by quenching treatment and tempering treatment, and other steps are not particularly limited, and a commonly used method can be appropriately adopted so that a desired steel sheet can be obtained.
- the preferred production method recommended in the present invention is as follows.
- steel that satisfies the above components is melted and heated and rolled (hot rolled).
- the hot rolling is preferably performed at a temperature of about 700 to 1100 ° C., for example.
- the sheet thickness after rolling is preferably about 12 to 25 mm.
- the steel After the rolling, the steel is air-cooled to room temperature in the air, and then subjected to the quenching and tempering treatments described above.
- a steel ingot having the composition shown in the following Table 1 (the balance is iron and inevitable impurities, and the unit means mass%) is melted by a normal vacuum melting method, and the steel ingot is heated at 1100 ° C. Hot rolled at a temperature to obtain a hot rolled plate having a thickness of 12 to 25 mm. Next, after reheating and quenching at the Q temperature shown in Table 1, the steel was tempered at the T temperature shown in Table 1, and then air-cooled to room temperature in the atmosphere to produce each steel sheet.
- TS tensile strength
- YP yield point
- EL elongation
- vE -20 (Ave) low temperature toughness
- Tensile strength (TS) is obtained by collecting JIS Z2201 No. 5 test pieces in the direction perpendicular to the rolling direction from t (plate thickness) / 4 part of each steel plate and performing a tensile test in accordance with the procedure of JIS Z2241. , Yield point (YP), and total elongation (EL) were measured. And the thing with a tensile strength (TS) of 980 MPa or more, a yield point (YP) of 960 MPa or more, and an elongation (EL) of 13.0% or more was evaluated as passing as having high strength and high elongation.
- Test pieces were collected from t (plate thickness) / 4 sites of each steel plate, observed at 400 times using an optical microscope, photographed, and image analysis was performed to observe the structure. As a result, only a composite structure of 100% tempered bainite and tempered martensite was recognized in total, and other structures were not recognized.
- No. Nos. 8 to 14 lack any of the requirements defined in the present invention.
- No. 8 is an example where the quenching (Q) temperature is low. As a result, the tensile strength (TS) and the yield point (YP) were lowered.
- No. 9 is an example in which the parameter indicated by the above equation (1) is outside the specified range of the present invention. As a result, although the tensile strength (TS) and the yield point (YP) were secured, the elongation (EL) was low.
- No. 10 is an example in which the parameter indicated by the above formula (1) is within the specified range of the present invention, but the Pcm value indicated by the above formula (2) is outside the specified range of the present invention, that is, the low temperature cracking property is inferior. Is an inferior example.
- No. 11 is an example in which the content of Mn is low, B is not added, and the parameter represented by the above formula (1) is outside the specified range of the present invention.
- the tensile strength (TS) and the yield point (YP) were lowered.
- the strength is low, the elongation (EL) is satisfactory.
- No. No. 12 had a high tempering (T) temperature, so that the tensile strength (TS) and the yield point (YP) were low although other conditions were satisfied.
- No. 13 is an example of simulating the steel sheet described in Patent Document 2. Addition of Ti decreased hardenability and low temperature toughness.
- No. No. 14 is a steel type No. described in Patent Document 1 above.
- Nb was not added, so that high strength was satisfied, but elongation (EL) was low.
Abstract
Description
0.5×[Mo]+121×[V]+15×[Mn]+0.5×[Cr]・・・(1)
Pcm=[C]+([Si]/30)+([Mn]/20)+([Cu]/20)+([Ni]/60)+([Cr]/20)+([Mo]/15)+([V]/10)+5×[B]・・・(2)
式中、[ ]は、鋼中の各成分の含有量(質量%)を意味する。
0.5×[Mo]+121×[V]+15×[Mn]+0.5×[Cr]・・・(1)
Pcm=[C]+([Si]/30)+([Mn]/20)+([Cu]/20)+([Ni]/60)+([Cr]/20)+([Mo]/15)+([V]/10)+5×[B]・・・(2)
式中、[ ]は、鋼中の各成分の含有量(質量%)を意味する。
Cは、炭化物を生成して転位をピン止めし、伸び向上に寄与する元素である。また、鋼板の焼入れ性を向上させ、強度向上にも寄与する。これらの効果を有効に発揮させるため、C含有量の下限を0.125%以上とする。C含有量の好ましい下限は0.130%以上、より好ましくは0.135%以上である。しかしながら、C含有量が過剰になると溶接性が低下するため、その上限を0.15%以下にする。C含有量の好ましい上限は0.145%以下である。
Siは鋼材の脱酸に不可欠の元素である。こうした効果を有効に発揮させるため、Si含有量の下限を0.2%以上とする。Si含有量の好ましい下限は0.3%以上である。しかしながら、Si含有量が過剰になると溶接性が低下するため、その上限を0.75%以下とする。Si含有量の好ましい上限は0.7%以下、より好ましくは0.6%以下である。
Mnは伸び向上に寄与する元素である。詳細にはMnは、セメンタイト中のC拡散抑制に有効な元素であり、これにより、セメンタイトの合体凝集が抑制されてセメンタイトを微細に析出した状態にして引張り時に転位をピン止めし、伸びを向上させる。このような作用を有効に発揮させるためには、Mn含有量の下限は0.9%以上とする。Mn含有量の好ましい下限は0.95%以上、より好ましくは1.00%以上である。しかしながら、Mn含有量が過剰になると、溶接性が低下するため、Mn含有量の上限を1.2%以下とする。Mn含有量の好ましい上限は1.15%以下、より好ましくは1.10%以下である。
Alは鋼材の脱酸剤として添加される。このような作用を有効に発揮させるため、Al含有量の下限を0.03%以上とする。Al含有量の好ましい下限は0.035%以上である。しかし、Al含有量が0.06%を超えて過剰になると鋼板における清浄性を阻害するため、その上限を0.06%以下とする。Al含有量の好ましい上限は0.055%以下である。
CrはMnと同様、伸び向上に寄与する元素である。このような作用を有効に発揮させるため、Cr含有量の下限を0.65%以上とする。Cr含有量の好ましい下限は0.70%以上である。しかしながら、Cr含有量が過剰になると溶接性が損なわれるため、その上限を1%以下とする。Cr含有量の好ましい上限は0.95%以下、より好ましくは0.90%以下である。
Moは、伸びおよび強度向上に寄与する元素である。詳細にはMoは、Cとの親和性が良い元素であり、炭化物を形成して転位をピン止めすることで蓄積できる転位量が向上し、伸びが高くなる。また、Moの析出強化によって強度も向上する。このような効果を有効に発揮させるため、Mo含有量の下限を0.2%以上とする。Mo含有量の好ましい下限は0.23%以上である。しかし、Moを過剰に添加すると溶接性が劣化する原因となるため、その上限を0.7%以下とする。Mo含有量の好ましい上限は0.65%以下、より好ましくは0.60%以下である。
Vも上記Moと同様、伸びおよび強度向上に寄与する元素である。詳細にはVは、炭化物を形成させ、転位をピン止めすることで蓄積できる転位量を向上させ、伸びを向上させる。また、Vの析出強化によって強度も向上する。このような効果を有効に発揮させるため、V含有量の下限を0.035%以上とする。V含有量の好ましい下限は0.040%以上である。しかし、V含有量が過剰になると、溶接性劣化の原因となるため、その上限を0.11%以下とする。V含有量の好ましい上限は0.10%以下、より好ましくは0.09%以下である。
Nbは、強度および伸びの向上に寄与する元素である。詳細にはNbの析出強化により、強度が高められる。また、Nbは窒化物を生成し易い元素であり、クラスター状に窒化物を形成するため、Moなどの炭化物に比べて転位のピン止め効果は低いものの、蓄積できる転位量を向上させ、伸びを向上させる。このような効果を有効に発揮させるためには、Nbの好ましい下限を0.003%以上とする。より好ましくは0.005%以上、更に好ましくは0.010%以上である。しかし、Nb含有量が過剰になると溶接性を劣化させるため、その上限を0.11%以下とする。Nb含有量の好ましい上限は0.1%以下、より好ましくは0.09%以下である。
Bは焼入れ性を高め、強度向上に有効な元素である。このような作用を有効に発揮させるため、B含有量の下限を0.0005%以上とする。B含有量の好ましい下限は0.0006%以上である。しかし、B量が過剰になると溶接性が劣化するため、B含有量の上限を0.002%以下とする。B含有量の好ましい上限は0.0015%以下である。
Nは鋼材中に不可避的に含まれる元素であり、N量が多すぎると固溶Nの存在により母材靱性が劣化するため、N含有量の上限を0.006%以下とする。N含有量の好ましい上限は0.005%以下である。なお、N量を実質的にゼロにすることは極めて困難である。
Pは焼戻し脆化を引き起こし、靱性を低下させるため、その量はできるだけ少ないことが好ましい。特に低温靱性の確保などを考慮すると、P含有量の上限は0.02%以下に抑制することが好ましく、より好ましくは0.015%以下である。しかし、工業的にP含有量を0%にすることは困難である。
Sは、焼戻し脆化を引き起こす不純物であり、その量はできるだけ少ないことが好ましい。特に低温靱性の確保などを考慮すると、S含有量は0.01%以下に抑制することが好ましく、より好ましくは0.005%以下とする。しかし、工業的にS含有量を0%にすることは困難である。
CuおよびNiは、いずれも固溶強化による高強度化に有効な元素である。これらは単独で添加してもよいし、併用してもよい。
各鋼板のt(板厚)/4部位から、圧延方向に対して直角の方向にJIS Z2201の5号試験片を採取し、JIS Z2241の要領で引張試験を行なうことによって、引張強度(TS)、降伏点(YP)、および全伸び(EL)を測定した。そして、引張強度(TS)が980MPa以上、降伏点(YP)が960MPa以上、伸び(EL)が13.0%以上のものを高い強度および高い伸びを有するとして合格と評価した。
各鋼板(母材)のt(板厚)/4部位から、圧延方向に対してJIS Z2242の試験片を採取し、母材の靱性を評価した。JIS Z2242に準拠して、-20℃でシャルピー衝撃試験を行ない、吸収エネルギー(vE-20)を測定した。そして、vE-20の平均値(vE-20(Ave))が50J以上のものを靱性に優れると評価した。
上記(2)式で示されるPcmが0.28以下のものを溶接性に優れると評価した。
各鋼板のt(板厚)/4部位から試験片を採取し、光学顕微鏡を用いて400倍で観察し、写真撮影を行った後、画像解析を行って組織を観察した。その結果、合計で100%の焼戻しベイナイト及び焼戻しマルテンサイトの複合組織のみ認められ、他の組織は認められなかった。
Claims (2)
- C :0.125~0.15%(質量%の意味。化学成分について以下同じ)、
Si:0.2~0.75%、
Mn:0.9~1.2%、
Al:0.03~0.06%、
Cr:0.65~1%、
Mo:0.2~0.7%、
V :0.035~0.11%、
Nb:0%超え0.11%以下、
B :0.0005~0.002%、
N :0%超え0.006%以下を含有し、残部が鉄および不可避的不純物からなり、
金属組織が焼戻しベイナイト組織、焼戻しマルテンサイト組織、またはこれらの複合組織であり、
下記(1)式で示されるパラメータが20以上であり、且つ、
下記(2)式で示されるPcm値が0.28以下であることを特徴とする低温靱性、伸び、および溶接性に優れた引張強度が980MPa以上、且つ降伏点が960MPa以上の高強度鋼板。
0.5×[Mo]+121×[V]+15×[Mn]+0.5×[Cr]・・・(1)
Pcm=[C]+([Si]/30)+([Mn]/20)+([Cu]/20)+([Ni]/60)+([Cr]/20)+([Mo]/15)+([V]/10)+5×[B]・・・(2)
式中、[ ]は、鋼中の各成分の含有量(質量%)を意味する。 - C :0.125~0.15%、
Si:0.2~0.75%、
Mn:0.9~1.2%、
Al:0.03~0.06%、
Cr:0.65~1%、
Mo:0.2~0.7%、
V :0.035~0.11%、
Nb:0%超え0.11%以下、
B :0.0005~0.002%、
N :0%超え0.006%以下を含有し、残部が鉄および不可避的不純物からなり、
下記(1)式で示されるパラメータが20以上、且つ、
下記(2)式で示されるPcm値が0.28以下である鋼を、
加熱圧延した後、室温まで空冷し、さらに900℃以上に加熱して焼入れ処理を行った後、400℃~600℃の温度で焼戻し処理を行うことを特徴とする低温靱性、伸び、および溶接性に優れた引張強度が980MPa以上、且つ降伏点が960MPa以上の高強度鋼板の製造方法。
0.5×[Mo]+121×[V]+15×[Mn]+0.5×[Cr]・・・(1)
Pcm=[C]+([Si]/30)+([Mn]/20)+([Cu]/20)+([Ni]/60)+([Cr]/20)+([Mo]/15)+([V]/10)+5×[B]・・・(2)
式中、[ ]は、鋼中の各成分の含有量(質量%)を意味する。
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JP2011080103A (ja) * | 2009-10-05 | 2011-04-21 | Jfe Steel Corp | 高靭性鋼の製造方法 |
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