JP4792643B2 - Steel material for large heat input welding - Google Patents
Steel material for large heat input welding Download PDFInfo
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- JP4792643B2 JP4792643B2 JP2001066106A JP2001066106A JP4792643B2 JP 4792643 B2 JP4792643 B2 JP 4792643B2 JP 2001066106 A JP2001066106 A JP 2001066106A JP 2001066106 A JP2001066106 A JP 2001066106A JP 4792643 B2 JP4792643 B2 JP 4792643B2
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Description
【0001】
【発明の属する技術分野】
本発明は、溶接構造用鋼材、特に、溶接入熱が200kJ/cmを超えるような大入熱溶接が適用される鋼材に関する。
本発明において、化学成分含有量の単位記号として用いる%は質量百分率を意味する。
【0002】
【従来の技術】
構造物や船舶の大型化が進むにつれて、 使用鋼材の高強度・ 厚肉化が求められ、それらの施工に高能率の溶接が適用されてきた。この施工コスト削減のために、たとえばサブマージアーク溶接、 エレクトロガス溶接およびエレクトロスラグ溶接などの大入熱溶接方法の適用があげられる。一般に溶接入熱が大きくなると溶接熱影響部の組織が粗大化し靭性が低下することが知られており、その対策としてTiN の微細分散によるオーステナイトの粗大化抑制やフェライト変態核としての利用技術が実用化されている。さらに、特開昭60−152626号公報に示されるように、さらに希土類元素(REM )をTiと複合添加することで、鋼中に分散する析出物粒子(TiN とREM(O,S))によりオーステナイトの異常粒成長を防止することにより、溶接部の靭性の向上が図られてきた。
【0003】
【発明が解決しようとする課題】
しかし、近年の溶接技術の進歩に伴い、板厚40mmを超えるような鋼材を200 〜700kJ/cmもの大入熱で1パスで溶接することが可能となった。このような過酷な溶接条件では、熱影響部におけるオーステナイト粒の粗大異常粒成長の抑制は、従来のTi添加では効果が十分ではない。
【0004】
そこで、本発明は、入熱量が200kJ/cm以上に達する過酷な溶接条件下でも熱影響部でのオーステナイト粒粗大化を抑制しうる大入熱溶接用鋼材を提供することを目的とする。
【0005】
【課題を解決するための手段】
上述のように、 溶接熱影響部の靭性向上にはオーステナイト粒の微細化が有効であり、オーステナイト粒の微細化、 すなわちオーステナイト粒の成長抑制にはTiN 粒子によるピン止めが有効である。
しかし、TiN 粒子は温度上昇により溶解する傾向にある。その場合、TiN 粒子の数は減少し、 ピン止めの効果は小さくなる。特に、溶接継手の溶融線近傍の溶接熱影響部は1500℃近くまで加熱されるため、この部位におけるTiN 粒子のほとんどが溶解・ 消失する。したがって、1500℃近くまで加熱されても、溶解しにくいTiN 粒子を析出させる必要がある。
【0006】
本発明者らは、種々のTi、N添加鋼を溶製し、これらの鋼を用い、加熱温度を変化させた熱サイクル試験を行った。そして、熱サイクル後の鋼中のTiN 粒子を観察した。その結果、Ti量:0.015 %以上、N量:0.0045%以上でかつ式:T=13000/(3.28-log[Ti][N])-273 ≧1500、([Ti]:Ti含有量(%)、[N] :N含有量(%))が満たされる場合に限り、TiN 粒子は熱サイクル後も溶解量が少なく、 多数残存することを確認した。ここで、TはTiN の固溶温度 (℃)を示し、この値が大きいほどTiN が溶解しにくいことを示す。
【0007】
さらに、TiとNの量比率すなわち[Ti]/[N] 比が3.5 〜5.0 であれば、 オーステナイト粒は微細、すなわちTiN によるピン止め効果が現れた。
以上の知見に加え、さらに大入熱溶接熱影響部のミクロ組織制御の観点から合金元素添加量の適正化を行った結果、大入熱溶接時の低温靭性の著しい改善が可能となった。
【0008】
すなわち、本発明による大入熱溶接用鋼材は、
C:0.01〜0.15%、Si:0.05〜0.80%、Mn:0.5 〜2.0 %、Al:0.01〜0.08%、かつ、Ti:0.015 〜0.040 %、N:0.0045〜0.0085%を式
3.60≦[Ti]/[N] ≦5.0 、T=13000/(3.28-log[Ti][N])-273 ≧1500
([Ti]:Ti含有量(%)、[N] :N含有量(%))
を満たす範囲で含有し、さらに、Ca:0.0003〜0.0040%、REM :0.0010〜0.0150%の1種または2種を含有し、残部Feおよび不可避的不純物からなることを特徴とする大入熱溶接用鋼材である。本発明では、さらに、Nb:0.020 %以下、V:0.005 〜0.15%の1種または2種を含有してもよい。また、本発明では、さらに、B:0.0003〜0.0025%を含有してもよい。また、本発明では、さらに、Cu:0.1 〜1.0 %、Ni:0.1 〜3.5 %の1種または2種、および/または、Cr:0.1 〜1.0 %、Mo:0.05〜0.5 %の1種または2種を含有してもよい。
【0009】
【発明の実施の形態】
次に各成分の限定理由について説明する。
C:0.01〜0.15%
C量は構造用鋼として必要な強度を得るために下限を0.01%とし、溶接割れの観点から上限を0.15%とした。
【0010】
Si:0.05〜0.80%
Siは製鋼上0.05%以上が必要であり、0.80%を超えると母材の靭性を劣化させる。
Mn:0.5 〜2.0 %
Mnは母材の強度を確保するために0.5 %以上は必要であり、2.0 %を超えると溶接部の靭性を著しく劣化させる。
【0011】
Al:0.01〜0.08%
Alは鋼の脱酸上0.01%以上は必要であり、0.08%を超えて添加すると母材の靭性を低下させると同時に母材から溶接金属部への希釈によって溶接金属部の靭性を劣化させる。
Ti:0.015 〜0.040 %
Tiは凝固時にTiN となって析出し、溶接熱影響部でのオーステナイト粒の粗大化抑制に効果的である。さらにフェライト変態核となって高靭性化に寄与する。既述のとおり0.015 %未満では、TiN は比較的低温で溶解・ 消失し、その量が不足する。その結果、溶接熱影響部の靭性を劣化させる。さらに、0.015 %未満であると、母材強度の確保が困難である。したがって、Tiの下限値は0.015 %とした。一方、0.040 %を超えると母材靭性に悪影響を与えるので、Ti量は0.015 〜0.040 %とした。
【0012】
N:0.0045〜0.0085%
NはTiN の形成に重要な元素であり、0.0045%未満ではTiN が比較的低温で溶解・ 消失し、その量が不足する。また、0.0085%を超えると溶接熱サイクルによってTiN が溶解する領域での固溶N量の増加によって靭性を著しく低下させる。なお、好ましくはN:0.0050%超〜0.0085%である。
【0013】
Ca:0.0003〜0.0040%
Caは、溶接熱影響部において、Ca(O,S) として析出し、微細フェライトの生成を促進し、溶接熱影響部の高靭化に寄与する。この効果は、0.0003%以上で発現する。また、0.0040%超では、この効果が飽和する。
REM :0.0010〜0.0150%
REM は、溶接熱影響部において、REM(O,S)として析出し、オーステナイト粒の粗大化を抑制し、 溶接熱影響部の高靭化に寄与する。この効果は、0.0010%以上で発現する。また、0.0150%超では、この効果が飽和する。
【0014】
Nb:0.020 %以下
Nbは熱間圧延時、または圧延後の冷却過程で炭窒化物を形成し、強度上昇に寄与するが、溶接継手の熱影響部の靭性を劣化させるので、0.020 %を上限とした。
V:0.005 〜0.15%
Vも同じく熱間圧延時、または圧延後の冷却過程で炭窒化物を形成し、強度上昇に寄与するため、母材の強度および継手の強度確保のために添加するが、0.005 %未満ではその効果に乏しく、一方、0.15%を超えると靭性の低下を招くため、0.005 〜0.15%とした。
【0015】
B:0.0003〜0.0025%
Bは、0.0003%を超える添加により、鋼の高強度化に寄与する。また、溶接熱影響部において固溶Nと化合(BNとして析出)することによって、靭性に悪影響を与える固溶Nの量を減少させる働きがある。さらにBNは、オーステナイト粒内から靭性に効果的である微細フェライトの析出を促進させる。この効果は、0.0003%以上で発現する。しかし、0.0025%を超えて添加すると著しく硬化して母材靭性の劣化を招く虞がある。
【0016】
Cu:0.1 〜1.0 %
Cuは0.1 %以上の添加によって、固溶効果による強度上昇が起こるが、1.0 %を超える添加を行った場合、特に大入熱溶接のような冷却の遅い場合に鋼中に単体として析出し、靭性の劣化を起こす場合があるため、上限を1.0 %とする。
Ni:0.1 〜3.5 %
Niは0.1 %以上の添加によって、 母材の高靭性を保ちつつ強度を上昇させるが、高価であるため上限を3.5 %とした。
【0017】
Cr:0.1 〜1.0 %
Mo:0.05〜0.5 %
Cr、Moは母材の高強度化に有効な元素であるが、多量に添加すると靭性に悪影響を与えるために、下限をそれぞれ0.1 %、0.05%とし、また、上限をそれぞれ1.0 %、0.5 %とした。
【0018】
なお、 上記成分以外に、 不可避的不純物が含有される。不可避的不純物の主なものはP、S、Oであり、これらは、それぞれ0.050 %、0.010 %、0.010 %までは許容しうる。
以上のように、本発明によれば、大入熱溶接熱影響部の靭性に優れた鋼材を得ることができる。なお、本発明の鋼材は、銑鉄を転炉で鋼とした後、RHで脱ガスを行い、連続鋳造または造塊- 分塊工程を経て鋼片とし、これを再加熱して熱間圧延し、あるいはさらに、加速冷却、直接焼入れ焼戻し、再加熱焼入れ焼戻し、焼準、焼戻し処理の1つ以上を施して製造する。
【0019】
【実施例】
表1に示す化学組成になる鋼片を加熱、圧延して、板厚50mmの鋼材となし、これらの鋼材について、板厚1/4 部から採取した試験片を用い、引張試験およびシャルピー衝撃試験を行い、母材の強度・ 延性およびシャルピー破面遷移温度(vTrs)を調査した。次に、エレクトロガスアーク溶接(入熱500kJ/cm)にて各鋼材の溶接継手を製作し、継手板厚1/4 部から採取したシャルピー試験片の溶接熱影響部にノッチを導入し、-20 ℃でシャルピー試験を行った。それらの結果を表2に示す。
【0020】
【表1】
【0021】
【表2】
表2に示すとおり、発明鋼(No.1-11) を用いた溶接継手においては、いずれも-20 ℃で200Jを超える高いシャルピー吸収エネルギー(vE -20 ) を得た。一方、比較鋼(No.12-15)では、吸収エネルギーが著しく低い。No.12,13はそれぞれTi, N量が不足し、No.14 では[Ti]/[N]比が5.0 超となっている。また、No.15 ではTi、N量は適正範囲であるが、T値が1500未満となっている。また、比較鋼(No.16)はTi、Nが適正範囲上限を超え、吸収エネルギーが低くなっている。また、比較鋼(No.17-19)は、それぞれC、Si、Mnが適正範囲上限を超え、母材シャルピー破面遷移温度(vTrs)が上昇、 すなわち靭性が劣化し、さらに溶接継手の母材熱影響部(HAZ)のシャルピー吸収エネルギーも著しく低下している。
【0022】
【発明の効果】
以上説明したように、本発明によれば、大入熱溶接を施されても溶接継手熱影響部の靭性の劣化を防ぐことができる。このことにより、船舶や構造物の溶接施工能率を顕著に向上できるという、 産業上格段の効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel material for welded structures, and more particularly, to a steel material to which large heat input welding is applied so that the welding heat input exceeds 200 kJ / cm.
In the present invention,% used as a unit symbol of chemical component content means mass percentage.
[0002]
[Prior art]
As the size of structures and ships has increased, steel materials used have been required to have higher strength and thickness, and high-efficiency welding has been applied to their construction. In order to reduce this construction cost, for example, application of a high heat input welding method such as submerged arc welding, electrogas welding and electroslag welding can be mentioned. In general, it is known that when the heat input increases, the structure of the heat affected zone becomes coarser and the toughness decreases, and as a countermeasure, the austenite coarsening suppression by the fine dispersion of TiN and the application technology as a ferrite transformation nucleus are put into practical use. It has become. Further, as shown in JP-A-60-152626, by adding a rare earth element (REM) in combination with Ti, precipitate particles (TiN and REM (O, S)) dispersed in the steel are added. By preventing abnormal grain growth of austenite, the toughness of the weld has been improved.
[0003]
[Problems to be solved by the invention]
However, with recent advances in welding technology, it has become possible to weld steel with a plate thickness exceeding 40 mm in one pass with a large heat input of 200 to 700 kJ / cm. Under such severe welding conditions, the suppression of the growth of coarse abnormal grains of austenite grains in the heat-affected zone is not sufficiently effective with conventional Ti addition.
[0004]
Therefore, an object of the present invention is to provide a steel material for high heat input welding that can suppress austenite grain coarsening in the heat-affected zone even under severe welding conditions where the heat input reaches 200 kJ / cm or more.
[0005]
[Means for Solving the Problems]
As described above, austenite grain refinement is effective for improving the toughness of the heat affected zone, and pinning with TiN grains is effective for austenite grain refinement, that is, for suppressing growth of austenite grains.
However, TiN particles tend to dissolve with increasing temperature. In that case, the number of TiN particles decreases and the effect of pinning is reduced. In particular, since the weld heat affected zone near the fusion line of the welded joint is heated to nearly 1500 ° C, most of the TiN particles at this site dissolve and disappear. Therefore, it is necessary to deposit TiN particles that are difficult to dissolve even when heated to nearly 1500 ° C.
[0006]
The present inventors melted various Ti and N-added steels and conducted a thermal cycle test in which the heating temperature was changed using these steels. And the TiN particle | grains in the steel after a thermal cycle were observed. As a result, Ti amount: 0.015% or more, N amount: 0.0045% or more, and formula: T = 13000 / (3.28-log [Ti] [N])-273 ≧ 1500, ([Ti]: Ti content (% ), [N]: Only when the N content (%)) is satisfied, it was confirmed that the TiN particles had a small amount of dissolution even after the thermal cycle and remained in large numbers. Here, T indicates the solid solution temperature (° C.) of TiN, and the larger this value is, the more difficult it is to dissolve TiN.
[0007]
Further, when the amount ratio of Ti and N, that is, the [Ti] / [N] ratio is 3.5 to 5.0, the austenite grains are fine, that is, the pinning effect by TiN appears.
In addition to the above knowledge, as a result of optimizing the amount of alloying elements added from the viewpoint of microstructure control of the heat affected zone of high heat input welding, the low temperature toughness during high heat input welding can be significantly improved.
[0008]
That is, the steel material for high heat input welding according to the present invention is:
C: 0.01 to 0.15%, Si: 0.05 to 0.80%, Mn: 0.5 to 2.0%, Al: 0.01 to 0.08%, Ti: 0.015 to 0.040%, N: 0.0045 to 0.0085%
3.60 ≦ [Ti] / [N] ≦ 5.0, T = 13000 / (3.28-log [Ti] [N])-273 ≧ 1500
([Ti]: Ti content (%), [N]: N content (%))
For high heat input welding, characterized by containing one or two of Ca: 0.0003 to 0.0040% and REM: 0.0010 to 0.0150%, the balance being Fe and unavoidable impurities It is a steel material. In this invention, you may contain 1 type or 2 types of Nb: 0.020% or less and V: 0.005-0.15% further. Moreover, in this invention, you may contain B: 0.0003-0.0025% further. In the present invention, Cu: 0.1 to 1.0%, Ni: 0.1 to 3.5%, or 1 type and / or Cr: 0.1 to 1.0%, Mo: 0.05 to 0.5%, 1 type or 2 It may contain seeds.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, the reason for limitation of each component is demonstrated.
C: 0.01-0.15%
In order to obtain the strength required for structural steel, the lower limit is set to 0.01%, and the upper limit is set to 0.15% from the viewpoint of weld cracking.
[0010]
Si: 0.05-0.80%
Si needs to be 0.05% or more in terms of steelmaking, and if it exceeds 0.80%, the toughness of the base metal deteriorates.
Mn: 0.5-2.0%
Mn needs to be 0.5% or more in order to ensure the strength of the base metal, and if it exceeds 2.0%, the toughness of the welded portion will deteriorate significantly.
[0011]
Al: 0.01-0.08%
Al needs to be 0.01% or more in terms of deoxidation of steel, and if added over 0.08%, the toughness of the base metal is lowered and at the same time the toughness of the weld metal part is deteriorated by dilution from the base material to the weld metal part.
Ti: 0.015-0.040%
Ti precipitates as TiN during solidification and is effective in suppressing the coarsening of austenite grains in the heat affected zone. Furthermore, it becomes a ferrite transformation nucleus and contributes to high toughness. As described above, if it is less than 0.015%, TiN dissolves and disappears at a relatively low temperature, and its amount is insufficient. As a result, the toughness of the weld heat affected zone is deteriorated. Furthermore, if it is less than 0.015%, it is difficult to ensure the strength of the base material. Therefore, the lower limit of Ti is set to 0.015%. On the other hand, if it exceeds 0.040%, the toughness of the base metal is adversely affected, so the Ti content is set to 0.015 to 0.040%.
[0012]
N: 0.0045-0.0085%
N is an important element for the formation of TiN. If it is less than 0.0045%, TiN dissolves and disappears at a relatively low temperature, and its amount is insufficient. On the other hand, if it exceeds 0.0085%, the toughness is remarkably lowered by increasing the amount of solute N in the region where TiN is dissolved by the welding heat cycle. In addition, N is preferably more than 0.0050% to 0.0085%.
[0013]
Ca: 0.0003 to 0.0040%
Ca precipitates as Ca (O, S) in the weld heat-affected zone, promotes the formation of fine ferrite, and contributes to increasing the toughness of the weld heat-affected zone. This effect appears at 0.0003% or more. If it exceeds 0.0040%, this effect is saturated.
REM: 0.0010 to 0.0150%
REM precipitates as REM (O, S) in the weld heat affected zone, suppresses the coarsening of austenite grains, and contributes to increasing the toughness of the weld heat affected zone. This effect appears at 0.0010% or more. If it exceeds 0.0150%, this effect is saturated.
[0014]
Nb: 0.020% or less
Nb forms carbonitride during hot rolling or in the cooling process after rolling and contributes to an increase in strength, but deteriorates the toughness of the heat-affected zone of the welded joint, so 0.020% was made the upper limit.
V: 0.005 to 0.15%
V is also added to secure the strength of the base metal and the joint because it forms carbonitride during hot rolling or during the cooling process after rolling and contributes to the strength increase. However, if less than 0.005%, V On the other hand, if it exceeds 0.15%, the toughness is lowered, so 0.005 to 0.15%.
[0015]
B: 0.0003-0.0025%
B contributes to high strength of steel by addition exceeding 0.0003%. In addition, by combining with solute N (precipitating as BN) in the weld heat-affected zone, it acts to reduce the amount of solute N that adversely affects toughness. Furthermore, BN accelerates the precipitation of fine ferrite, which is effective for toughness from within the austenite grains. This effect appears at 0.0003% or more. However, if added over 0.0025%, it may be remarkably cured and the base metal toughness may be deteriorated.
[0016]
Cu: 0.1 to 1.0%
When Cu is added in an amount of 0.1% or more, the strength increases due to a solid solution effect. The upper limit should be 1.0% because toughness may deteriorate.
Ni: 0.1-3.5%
When Ni is added in an amount of 0.1% or more, the strength is increased while maintaining the high toughness of the base metal, but the upper limit is set to 3.5% because it is expensive.
[0017]
Cr: 0.1 to 1.0%
Mo: 0.05-0.5%
Cr and Mo are effective elements for increasing the strength of the base metal, but if added in a large amount, the toughness is adversely affected. Therefore, the lower limits are 0.1% and 0.05%, respectively, and the upper limits are 1.0% and 0.5%, respectively. It was.
[0018]
In addition to the above components, inevitable impurities are contained. The main inevitable impurities are P, S and O, which are acceptable up to 0.050%, 0.010% and 0.010%, respectively.
As mentioned above, according to this invention, the steel material excellent in the toughness of a high heat input welding heat affected zone can be obtained. The steel material of the present invention is made by converting the pig iron into steel in a converter, degassing it with RH, and making it into a slab through a continuous casting or ingot-bundling process, which is reheated and hot rolled. Alternatively, it is manufactured by performing one or more of accelerated cooling, direct quenching and tempering, reheating quenching and tempering, normalizing, and tempering treatment.
[0019]
【Example】
Steel pieces with the chemical composition shown in Table 1 are heated and rolled to form steel materials with a thickness of 50 mm. These steel materials are used for tensile tests and Charpy impact tests using test pieces taken from 1/4 part of the plate thickness. The strength and ductility of the base metal and the Charpy fracture surface transition temperature (vTrs) were investigated. Next, weld joints of each steel material were produced by electrogas arc welding (heat input 500 kJ / cm), and notches were introduced into the weld heat affected zone of Charpy specimens taken from 1/4 thickness of the joint plate. A Charpy test was conducted at ℃. The results are shown in Table 2.
[0020]
[Table 1]
[0021]
[Table 2]
As shown in Table 2, in the welded joints using the inventive steel (No. 1-11), a high Charpy absorbed energy (vE- 20 ) exceeding 200 J was obtained at -20 ° C. On the other hand, the absorbed energy is remarkably low in the comparative steel (No. 12-15). No.12 and 13 have insufficient Ti and N contents respectively, and No.14 has [Ti] / [N] ratio exceeding 5.0. In No. 15, the Ti and N amounts are in the proper range, but the T value is less than 1500. In comparison steel (No. 16), Ti and N exceed the upper limit of the appropriate range, and the absorbed energy is low. In the comparative steel (No. 17-19), C, Si and Mn exceeded the upper limit of the appropriate range, the base metal Charpy fracture surface transition temperature (vTrs) increased, that is, the toughness deteriorated, and the base of the welded joint was further reduced. The Charpy absorbed energy in the material heat affected zone (HAZ) is also significantly reduced.
[0022]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the deterioration of the toughness of the heat-affected zone of a welded joint even when high heat input welding is performed. This has a remarkable industrial effect of significantly improving the welding efficiency of ships and structures.
Claims (4)
記
3.60 ≦[Ti]/[N] ≦5.0 、T=13000/(3.28-log[Ti][N])-273 ≧1500
([Ti]:Ti含有量(%)、[N] :N含有量(%))By mass ratio, C: 0.01 to 0.15%, Si: 0.05 to 0.80%, Mn: 0.5 to 2.0%, Al: 0.01 to 0.08%, Ti: 0.015 to 0.040%, N: 0.0045 to 0.0085% For high heat input welding, characterized by containing one or two of Ca: 0.0003 to 0.0040% and REM: 0.0010 to 0.0150%, the balance being Fe and unavoidable impurities Steel material.
Record
3.60 ≦ [Ti] / [N] ≦ 5.0, T = 13000 / (3.28-log [Ti] [N])-273 ≧ 1500
([Ti]: Ti content (%), [N]: N content (%))
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