WO2016051727A1 - Welded steel pipe, steel plate, and manufacturing method therefor - Google Patents
Welded steel pipe, steel plate, and manufacturing method therefor Download PDFInfo
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- WO2016051727A1 WO2016051727A1 PCT/JP2015/004813 JP2015004813W WO2016051727A1 WO 2016051727 A1 WO2016051727 A1 WO 2016051727A1 JP 2015004813 W JP2015004813 W JP 2015004813W WO 2016051727 A1 WO2016051727 A1 WO 2016051727A1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Definitions
- Oil and natural gas transported by pipelines may contain hydrogen sulfide depending on their properties, and may be laid in an environment where hydrogen sulfide is contained in the seabed or soil.
- HIC hydrogen induced cracking
- SSC hydrogen sulfide stress corrosion cracking
- Fit for Purpose is to perform the HIC test and the SSC test under conditions that consider the severity of the real environment in order to obtain the requirements of the HIC resistance and SSC resistance for the line pipe.
- SSC resistance ISO 15156 classifies environmental severity by pH and H 2 S fraction. Therefore, compared to the conventional conditions where 100% H 2 S is blown into the solution A defined by NACE-TM0288 and NACE-TM0177, the target of HIC resistance and SSC resistance is easily satisfied. Can be set to manufacturing conditions compatible with the above.
- Non-Patent Document 1 evaluates the severity of the HIC test environment by pH and H 2 S fraction, and derives the limit length of MnS generated in the central segregation part.
- the severity of the HIC test environment is evaluated by the pH and H 2 S fraction, and the limit hardness at which HIC occurs is derived.
- the PHIC calculated by the expression (2) described later needs to satisfy the expression (3) described later.
- the P HIC is a parameter obtained by multiplying the thickening degree and carbon equivalent of the alloy elements in the center segregation area, it is possible to quantify the hardness of the center segregation area by P HIC.
- the cumulative rolling reduction is 50% or more, and a formula described later It performs rolling at a rolling start temperature consistent with T s as indicated by (5), it was found that it is necessary to integrate the (211) plane.
- T S ⁇ 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t (5)
- T F ⁇ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t (6)
- T ACS ⁇ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6 t (7)
- T Thickness at the end of rolling (mm)
- test environment for the HIC test in the present invention is 0.5 to 50% in terms of H 2 S fraction.
- N is preferably 0.0010 to 0.0060% and Ti / N (Ti content (mass%) / N content (mass%)) is preferably 1 to 5 from the viewpoint of improving toughness. More preferably, when it is 2 to 4, more excellent toughness is exhibited.
- ACRM 0 or more ACRM is an index for quantifying the morphology control of MnS by Ca.
- ACRM is 0 or more, the generation of MnS due to center segregation is suppressed, and the HIC resistance performance at the center of the plate thickness (tube thickness) is improved. Therefore, it is preferable to set the lower limit of ACRM to 0 and the lower limit to 0.2.
- the ACRM is defined by the following formula (1).
- ACRM ([Ca] ⁇ (1.23 [O] ⁇ 0.000365)) / (1.25 [S]) (1) However, in said formula (1), [Ca], [O], [S] represents content (mass%) of each element.
- V 0.060% or less
- V is an element that increases the strength, and in order to exhibit this effect, the V content is preferably 0.010% or more. However, if the V content exceeds 0.060%, the HAZ toughness and weldability are significantly impaired. Therefore, when adding V, it is preferable to make V amount into 0.060% or less, and it is more preferable that it is 0.050% or less.
- pH pH of the HIC test environment
- P H2S H 2 S fraction of HIC test environment (Vol%)
- the upper limit of the maximum value HV of the micro-Vickers hardness of the hard second phase contained in the center segregation portion and the microstructures of the surface layer and the back layer is set to 400 + 50 (pH-12) (1 + log (P H2S )) / 9.
- the temperature under the production conditions is the surface temperature of the steel material or steel plate.
- the surface temperature of a steel material or a steel plate can be measured by, for example, a radiation thermometer.
- the lower limit temperature of the slab heating temperature is set to 1000 ° C.
- the slab heating temperature is in the range of 1000 to 1200 ° C.
- a method having a two-stage process that is, a main welding process for performing the above-described process is preferable.
- pipe expansion is performed to remove residual welding stress and improve roundness of the steel pipe.
- the pipe expansion ratio ratio of the outer diameter change amount before and after the pipe expansion to the outer diameter of the pipe before the pipe expansion
- the tube expansion rate is preferably in the range of 0.5% to 1.2%.
- a coating treatment can be carried out for the purpose of preventing corrosion.
- the coating treatment for example, after heating to a temperature range of 200 to 300 ° C., a known resin may be applied to the outer surface.
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Abstract
Description
[1]質量%で、C:0.02~0.10%、Si:0.40%以下、Mn:1.00~2.00%、Nb:0.005~0.060%、Ti:0.005~0.025%、Ca:0.0010~0.0040%、N:0.0010~0.0100%を含有し、Ca/Oが2.5以下であり、下記式(1)で示されるACRMが0以上であり、下記式(2)で示されるPHICが下記式(3)を満たし、残部はFeおよび不可避的不純物からなり、
中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVが、下記式(4)を満たし、
表層および裏層のビッカース硬さが248以下であり、
X線回析により得られる管厚中心位置での圧延面の(211)面の集積度が1.6以上であることを特徴とする低硫化水素濃度環境における耐サワー性能に優れた高靱性溶接鋼管。
ACRM=([Ca]-(1.23[O]-0.000365))/(1.25[S])・・・(1)
PHIC=4.46[C]+2.37[Mn]/6+(1.74[Cu]+1.7[Ni])/15+(1.18[Cr]+1.95[Mo]+1.74[V])/5+22.36[P]・・・(2)
PHIC≦1.35+(pH-12)(1+log(PH2S))/60・・・(3)
HV≦400+50(pH-12)(1+log(PH2S))/9・・・(4)
ただし、式(1)~(4)において、
[Ca]、[O]、[S]、[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[P]:各元素の含有量(質量%)であり、含まない場合は0とする
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
とする。
[2]さらに、質量%で、Cu:0.50%以下、Ni:1.00%以下、Cr:0.50%以下、Mo:0.50%以下、V:0.060%以下、B:0.0030%以下から選ばれる1種以上を含有することを特徴とする[1]に記載の低硫化水素濃度環境における耐サワー性能に優れた高靱性溶接鋼管。
[3]質量%で、C:0.02~0.10%、Si:0.40%以下、Mn:1.00~2.00%、Nb:0.005~0.060%、Ti:0.005~0.025%、Ca:0.0010~0.0040%、N:0.0010~0.0100%を含有し、Ca/Oが2.5以下であり、下記式(1)で示されるACRMが0以上であり、下記式(2)で示されるPHICが下記式(3)を満たし、残部はFeおよび不可避的不純物からなり、
中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVが、下記式(4)を満たし、
表層および裏層のビッカース硬さが248以下であり、
X線回析により得られる板厚中心位置での圧延面の(211)面の集積度が1.6以上であることを特徴とする低硫化水素濃度環境における耐サワー性能に優れた高靱性厚鋼板。
ACRM=([Ca]-(1.23[O]-0.000365))/(1.25[S])・・・(1)
PHIC=4.46[C]+2.37[Mn]/6+(1.74[Cu]+1.7[Ni])/15+(1.18[Cr]+1.95[Mo]+1.74[V])/5+22.36[P]・・・(2)
PHIC≦1.35+(pH-12)(1+log(PH2S))/60・・・(3)
HV≦400+50(pH-12)(1+log(PH2S))/9・・・(4)
ただし、式(1)~(4)において、
[Ca]、[O]、[S]、[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[P]:各元素の含有量(質量%)であり、含まない場合は0とする
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
とする。
[4]さらに、質量%で、Cu:0.50%以下、Ni:1.00%以下、Cr:0.50%以下、Mo:0.50%以下、V:0.060%以下、B:0.0030%以下から選ばれる1種以上を含有することを特徴とする[3]に記載の低硫化水素濃度環境における耐サワー性能に優れた高靱性厚鋼板。
[5][3]または[4]に記載の成分組成を有する連続鋳造スラブ鋼素材を、1000~1200℃に加熱し、圧延開始温度TSが下記式(5)を満たすように累積圧下率50%以上で熱間圧延を行い、次いで、圧延終了温度TFが下記式(6)を満たすように熱間圧延を終了し、その後、加速冷却開始温度TACSが下記式(7)を満たすように加速冷却を開始し、冷却停止温度が600℃以下で加速冷却を停止させた後、空冷することを特徴とする低硫化水素濃度環境における耐サワー性能に優れた高靱性厚鋼板の製造方法。
TS≦174log([Nb]([C]+12[N]/14))+1444-1.2t・・・(5)
TF≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(6)
TACS≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(7)
ただし、上記式(5)、(6)、(7)において、
[Nb]、[C]、[N]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]:各元素の含有量(質量%)であり、含まない場合は0とする
t:圧延終了時の板厚(mm)
とする。
[6]前記空冷後、480~720℃に焼戻すことを特徴とする[5]に記載の低硫化水素濃度環境における耐サワー性能に優れた高靱性厚鋼板の製造方法。
[7][5]または[6]の方法で製造した厚鋼板を筒状に冷間加工し、その突合せ部を溶接することで溶接鋼管とすることを特徴とする低硫化水素濃度環境における耐サワー性能に優れた高靱性溶接鋼管の製造方法。 The present invention has been made by further studying the above findings and is as follows.
[1] By mass%, C: 0.02 to 0.10%, Si: 0.40% or less, Mn: 1.00 to 2.00%, Nb: 0.005 to 0.060%, Ti: 0.005 to 0.025%, Ca: 0.0010 to 0.0040%, N: 0.0010 to 0.0100%, Ca / O is 2.5 or less, and the following formula (1) in ACRM shown is not less than 0, P HIC satisfies the following formula (3) represented by the following formula (2), the balance being Fe and unavoidable impurities,
The maximum value HV of the micro Vickers hardness of the hard second phase contained in the microstructure of the center segregation part and the surface layer and the back layer satisfies the following formula (4),
The Vickers hardness of the surface layer and the back layer is 248 or less,
High toughness welding with excellent sour resistance in a low hydrogen sulfide concentration environment characterized in that the degree of integration of the (211) surface of the rolled surface at the tube thickness center position obtained by X-ray diffraction is 1.6 or more Steel pipe.
ACRM = ([Ca] − (1.23 [O] −0.000365)) / (1.25 [S]) (1)
P HIC = 4.46 [C] +2.37 [Mn] / 6 + (1.74 [Cu] +1.7 [Ni]) / 15+ (1.18 [Cr] +1.95 [Mo] +1.74 [ V]) / 5 + 22.36 [P] (2)
P HIC ≦ 1.35 + (pH−12) (1 + log (P H2S )) / 60 (3)
HV ≦ 400 + 50 (pH−12) (1 + log (P H2S )) / 9 (4)
However, in the equations (1) to (4),
[Ca], [O], [S], [C], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [P]: Content of each element ( Mass%), and when not included, pH is 0: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
And
[2] Further, by mass%, Cu: 0.50% or less, Ni: 1.00% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.060% or less, B : A high toughness welded steel pipe excellent in sour resistance performance in a low hydrogen sulfide concentration environment according to [1], comprising at least one selected from 0.0030% or less.
[3] By mass%, C: 0.02 to 0.10%, Si: 0.40% or less, Mn: 1.00 to 2.00%, Nb: 0.005 to 0.060%, Ti: 0.005 to 0.025%, Ca: 0.0010 to 0.0040%, N: 0.0010 to 0.0100%, Ca / O is 2.5 or less, and the following formula (1) in ACRM shown is not less than 0, P HIC satisfies the following formula (3) represented by the following formula (2), the balance being Fe and unavoidable impurities,
The maximum value HV of the micro Vickers hardness of the hard second phase contained in the microstructure of the center segregation part and the surface layer and the back layer satisfies the following formula (4),
The Vickers hardness of the surface layer and the back layer is 248 or less,
High toughness thickness excellent in sour resistance in low hydrogen sulfide concentration environment, characterized in that the degree of integration of the (211) plane of the rolled surface at the thickness center position obtained by X-ray diffraction is 1.6 or more steel sheet.
ACRM = ([Ca] − (1.23 [O] −0.000365)) / (1.25 [S]) (1)
P HIC = 4.46 [C] +2.37 [Mn] / 6 + (1.74 [Cu] +1.7 [Ni]) / 15+ (1.18 [Cr] +1.95 [Mo] +1.74 [ V]) / 5 + 22.36 [P] (2)
P HIC ≦ 1.35 + (pH−12) (1 + log (P H2S )) / 60 (3)
HV ≦ 400 + 50 (pH−12) (1 + log (P H2S )) / 9 (4)
However, in the equations (1) to (4),
[Ca], [O], [S], [C], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [P]: Content of each element ( Mass%), and when not included, pH is 0: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
And
[4] Further, by mass%, Cu: 0.50% or less, Ni: 1.00% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.060% or less, B : A high tough steel plate excellent in sour resistance in a low hydrogen sulfide concentration environment according to [3], containing one or more selected from 0.0030% or less.
[5] [3] or cumulative rolling reduction to the continuously cast slab steel material having a chemical composition, was heated to 1000 ~ 1200 ° C., initial rolling temperature T S satisfies the following formula (5) described in [4] Hot rolling is performed at 50% or more, then the hot rolling is finished so that the rolling end temperature TF satisfies the following formula (6), and then the accelerated cooling start temperature T ACS satisfies the following formula (7). The method for producing a high toughness thick steel plate excellent in sour resistance in a low hydrogen sulfide concentration environment is characterized in that accelerated cooling is started, the accelerated cooling is stopped at a cooling stop temperature of 600 ° C. or less, and then air cooling is performed. .
T S ≦ 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t (5)
T F ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t (6)
T ACS ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6 t (7)
However, in the above formulas (5), (6), (7),
[Nb], [C], [N], [Mn], [Cu], [Ni], [Cr], [Mo]: content (% by mass) of each element, 0 if not included T: Thickness at the end of rolling (mm)
And
[6] The method for producing a high toughness thick steel plate excellent in sour resistance performance in a low hydrogen sulfide concentration environment according to [5], wherein the air cooling is followed by tempering to 480 to 720 ° C.
[7] A thick steel plate produced by the method of [5] or [6] is cold worked into a cylindrical shape, and the butt portion is welded to form a welded steel pipe. A method of manufacturing high toughness welded steel pipes with excellent sour performance.
以下に、本発明に係る溶接鋼管または厚鋼板の成分組成の限定理由を説明する。なお、成分組成を示す単位の%は、全て質量%を意味する。 <Ingredient composition>
Below, the reason for limitation of the component composition of the welded steel pipe or thick steel plate which concerns on this invention is demonstrated. In addition,% of the unit which shows a component composition means the mass% altogether.
Cは加速冷却によって製造される鋼板の強度を高めるために最も有効な元素である。しかしながら、C量(含有量)が0.02%未満では十分な強度を確保できず、0.10%を超えると靭性および耐HIC性が劣化する。従って、C量は0.02%以上、好ましくは0.03%以上とし、0.10%以下、好ましくは0.08%以下とする。 C: 0.02 to 0.10%
C is the most effective element for increasing the strength of the steel sheet produced by accelerated cooling. However, if the C content (content) is less than 0.02%, sufficient strength cannot be secured, and if it exceeds 0.10%, the toughness and HIC resistance deteriorate. Therefore, the C content is 0.02% or more, preferably 0.03% or more, 0.10% or less, preferably 0.08% or less.
Siは脱酸のために添加する。脱酸のためにはSi含有量が0.01%以上が好ましい。しかしながら、Si量が0.40%を超えると靭性や溶接性が劣化する。従って、Si量は0.40%以下の範囲内、好ましくは0.35%以下とする。 Si: 0.40% or less Si is added for deoxidation. For deoxidation, the Si content is preferably 0.01% or more. However, when the Si content exceeds 0.40%, toughness and weldability deteriorate. Therefore, the Si content is within the range of 0.40% or less, preferably 0.35% or less.
Mnは鋼の強度および靭性の向上のため添加する。しかしながら、Mn量が1.00%未満ではその効果が十分ではなく、2.00%を超えると溶接性と耐HIC性が劣化する。従って、Mn量は1.00%以上、好ましくは1.10%以上とし、2.00%以下、好ましくは1.90%以下とする。 Mn: 1.00 to 2.00%
Mn is added to improve the strength and toughness of the steel. However, if the amount of Mn is less than 1.00%, the effect is not sufficient, and if it exceeds 2.00%, weldability and HIC resistance deteriorate. Therefore, the amount of Mn is 1.00% or more, preferably 1.10% or more, 2.00% or less, preferably 1.90% or less.
Nbは固溶Nbとして鋼中に存在すると圧延時の粒成長を抑制し、微細粒化により靭性を向上させる。しかしながら、Nb量が0.005%未満ではその効果がなく、0.060%を超えるとHAZの靭性が劣化するだけでなく、粗大なNb炭窒化物の生成を招き耐HIC性能が劣化する。従って、Nb量は0.005%以上、好ましくは0.010%以上とし、0.060%以下、好ましくは0.040%以下とする。 Nb: 0.005 to 0.060%
When Nb is present in the steel as solute Nb, it suppresses grain growth during rolling and improves toughness by making the particles finer. However, when the Nb content is less than 0.005%, the effect is not obtained. When the Nb content exceeds 0.060%, not only the toughness of the HAZ is degraded, but also the formation of coarse Nb carbonitrides is caused, and the HIC resistance is degraded. Therefore, the Nb content is 0.005% or more, preferably 0.010% or more, 0.060% or less, preferably 0.040% or less.
TiはTiNを形成してスラブ加熱時の粒成長を抑制するだけでなく、HAZの粒成長を抑制し、母材及びHAZの微細粒化により靭性を向上させる。しかしながら、Ti量が0.005%未満ではその効果がなく、0.025%を超えると靭性が劣化する。従って、Ti量は0.005%以上、0.025%以下、好ましくは0.020%以下とする。 Ti: 0.005 to 0.025%
Ti not only suppresses grain growth during slab heating by forming TiN, but also suppresses HAZ grain growth and improves toughness by making the base material and HAZ finer. However, if the amount of Ti is less than 0.005%, there is no effect, and if it exceeds 0.025%, the toughness deteriorates. Therefore, the Ti content is 0.005% or more and 0.025% or less, preferably 0.020% or less.
Caは酸硫化物系介在物の形態を制御し、延性を改善するために有効な元素である。しかしながら、Ca量が0.0010%未満ではその効果がなく、0.0040%を超えても効果が飽和し、むしろ清浄度の低下により靱性が劣化する。従って、Ca量は0.0010%以上、好ましくは0.0015%以上とし、0.0040%以下、好ましくは0.0035%以下とする。 Ca: 0.0010 to 0.0040%
Ca is an effective element for controlling the form of oxysulfide inclusions and improving ductility. However, if the Ca content is less than 0.0010%, the effect is not obtained, and if the Ca content exceeds 0.0040%, the effect is saturated, but rather the toughness deteriorates due to a decrease in cleanliness. Therefore, the Ca content is 0.0010% or more, preferably 0.0015% or more, 0.0040% or less, preferably 0.0035% or less.
NはTiNのピンニング効果により加熱時のオーステナイトの粗大化を抑制し、母材や溶接熱影響部の靱性を改善するために有効な元素である。しかし、N量が0.0010%未満では効果がなく、0.0100%を超える添加はTiNの粗大化や固溶Nの増大により、逆に溶接熱影響部の靱性の劣化を招く。そこで、Nの含有量は、0.0010%以上、好ましくは0.0020%以上とし、0.0100%以下、好ましくは0.0055%以下に規定する。さらに、Nを0.0010~0.0060%にし、Ti/N(Ti含有量(質量%)/N含有量(質量%)))を1~5にすることが、靭性向上の観点から好ましく、いっそう好ましくは2~4とすることで、より優れた靱性を示す。 N: 0.0010 to 0.0100%
N is an element effective for suppressing the austenite coarsening during heating by the pinning effect of TiN and improving the toughness of the base metal and the weld heat affected zone. However, if the amount of N is less than 0.0010%, there is no effect, and the addition exceeding 0.0100% conversely causes the deterioration of the toughness of the weld heat affected zone due to the coarsening of TiN and the increase of solute N. Therefore, the N content is 0.0010% or more, preferably 0.0020% or more, and is specified to be 0.0100% or less, preferably 0.0055% or less. Further, N is preferably 0.0010 to 0.0060% and Ti / N (Ti content (mass%) / N content (mass%)) is preferably 1 to 5 from the viewpoint of improving toughness. More preferably, when it is 2 to 4, more excellent toughness is exhibited.
Oは鋼中に不可避的に含まれる元素であり、通常AlやCaと結合した酸化物として存在している。Oが過剰に含まれると、これらAl、Ca系酸化物の鋼中含有量が多くなりすぎ、クラスタを形成し、耐HIC性能が劣化する。このため、Oの含有量を0.0030%以下とすることが好ましく、0.0025%以下とすることがより好ましい。 O: 0.0030% or less O is an element inevitably contained in the steel, and is usually present as an oxide combined with Al or Ca. When O is excessively contained, the content of these Al and Ca-based oxides in the steel becomes too large to form clusters, and the HIC resistance is deteriorated. For this reason, it is preferable to make content of O into 0.0030% or less, and it is more preferable to set it as 0.0025% or less.
Ca/Oは、CaOクラスタ発生限界を定量化するための指標である。Ca/Oが2.5を超えるとCaクラスタが生成しやすくなり、表層近傍や介在物集積帯での耐HIC性能が劣化する。このため、Ca/Oの上限を2.5とし、上限を2.3とすることが好ましい。 Ca / O: 2.5 or less Ca / O is an index for quantifying the CaO cluster generation limit. When Ca / O exceeds 2.5, Ca clusters are likely to be generated, and the HIC resistance in the vicinity of the surface layer or inclusion inclusion zone deteriorates. For this reason, it is preferable that the upper limit of Ca / O is 2.5 and the upper limit is 2.3.
ACRMは、CaによるMnSの形態制御を定量化するための指標である。ACRMが0以上になると、中心偏析でのMnSの生成が抑制されて板厚(管厚)中心での耐HIC性能が改善する。そこでACRMの下限を0とし、下限を0.2とすることが好ましい。
なお、ACRMは、下記式(1)で定義される。
ACRM=([Ca]-(1.23[O]-0.000365))/(1.25[S])・・・(1)
ただし、上記式(1)において、[Ca]、[O]、[S]は、各元素の含有量(質量%)を表す。 ACRM: 0 or more ACRM is an index for quantifying the morphology control of MnS by Ca. When ACRM is 0 or more, the generation of MnS due to center segregation is suppressed, and the HIC resistance performance at the center of the plate thickness (tube thickness) is improved. Therefore, it is preferable to set the lower limit of ACRM to 0 and the lower limit to 0.2.
The ACRM is defined by the following formula (1).
ACRM = ([Ca] − (1.23 [O] −0.000365)) / (1.25 [S]) (1)
However, in said formula (1), [Ca], [O], [S] represents content (mass%) of each element.
PHICは中心偏析の硬さを定量化するためのパラメータであり、下記式(2)で定義される。
PHIC=4.46[C]+2.37[Mn]/6+(1.74[Cu]+1.7[Ni])/15+(1.18[Cr]+1.95[Mo]+1.74[V])/5+22.36[P]・・・(2)
ただし、上記式(2)において、[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[P]は、各元素の含有量(質量%)であり、含まない場合は0とする。
PHICの値が大きいほど中心偏析の硬さが高くなり、板厚(管厚)中心でのHIC発生を助長する。HICが発生する限界PHICは、HIC試験環境のH2S分率が低く、pHが高いほど高くなる。本発明者らが検討した結果、PHICが、下記式(3)を満たす範囲であれば、耐HIC性能が確保できる。このため、PHICの上限を、1.35+(pH-12)(1+log(PH2S))/60とする。
PHIC≦1.35+(pH-12)(1+log(PH2S))/60・・・(3)
ただし、上記式(3)において、
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
である。 PHIC is 1.35+ (pH-12) (1 + log ( PH2S )) / 60 or less PHIC is a parameter for quantifying the hardness of center segregation and is defined by the following formula (2).
P HIC = 4.46 [C] +2.37 [Mn] / 6 + (1.74 [Cu] +1.7 [Ni]) / 15+ (1.18 [Cr] +1.95 [Mo] +1.74 [ V]) / 5 + 22.36 [P] (2)
However, in the above formula (2), [C], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and [P] are the contents (% by mass) of each element. ) And 0 if not included.
The value of P HIC higher the higher the hardness of the center segregation large, it promotes HIC generation of sheet thickness (wall thickness) center. The limit P HIC at which HIC is generated increases as the H 2 S fraction of the HIC test environment is lower and the pH is higher. The present inventors have studied, P HIC is as long as it satisfies the following expression (3), HIC resistance performance can be ensured. For this reason, the upper limit of P HIC is 1.35+ (pH−12) (1 + log (P H2S )) / 60.
P HIC ≦ 1.35 + (pH−12) (1 + log (P H2S )) / 60 (3)
However, in the above formula (3),
pH: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
It is.
Pは偏析しやすく、中央部に濃化する元素であり、少量含まれるだけでも中央偏析の硬さを顕著に上げ、耐サワー性を劣化させる。このためP量は少なければ少ないほどよい。ただし、P量は0.015%までは許容することができる。より好ましくは、0.010%以下である。 P: 0.015% or less P is an element that easily segregates and concentrates in the central portion, and even if contained in a small amount, the hardness of the central segregation is remarkably increased and sour resistance is deteriorated. For this reason, the smaller the amount of P, the better. However, the amount of P can be tolerated up to 0.015%. More preferably, it is 0.010% or less.
SはMnを結合し、MnSを生成する。また、SはMnを同じく中央偏析に濃化しやすい元素であるためS量が多いとMnSの中央偏析が多数生成し、耐サワー性が著しく劣化する。従って、S量は極力低減することが望ましいが、0.0015%までは許容することができる。より好ましくは、0.0010%以下である。 S: 0.0015% or less S combines with Mn to generate MnS. Further, since S is an element that is also likely to concentrate Mn into central segregation, if the amount of S is large, a large number of central segregation of MnS is generated, and sour resistance is significantly deteriorated. Therefore, it is desirable to reduce the amount of S as much as possible, but it is acceptable up to 0.0015%. More preferably, it is 0.0010% or less.
Cuは、母材靭性の改善と強度の上昇に有効な元素であり、この効果を発揮させるにはCu量は0.10%以上であることが好ましい。しかしながら、Cu量が0.50%を超えると溶接性が劣化する。従って、Cuを添加する場合はCu量を0.50%以下とすることが好ましく、0.30%以下であることがより好ましい。 Cu: 0.50% or less Cu is an element effective for improving the toughness of the base metal and increasing the strength, and the Cu content is preferably 0.10% or more for exhibiting this effect. However, when the amount of Cu exceeds 0.50%, weldability deteriorates. Therefore, when adding Cu, it is preferable to make Cu amount into 0.50% or less, and it is more preferable that it is 0.30% or less.
Niは、母材靭性の改善と強度の上昇に有効な元素であり、この効果を発揮させるにはNi量は0.10%以上であることが好ましい。しかしながら、Ni量が1.00%を超えると溶接性が劣化する。従って、Niを添加する場合は、Ni量を1.00%以下とすることが好ましく、0.50%以下であることがより好ましい。 Ni: 1.00% or less Ni is an element effective for improving the toughness of the base metal and increasing the strength. In order to exhibit this effect, the Ni content is preferably 0.10% or more. However, if the Ni content exceeds 1.00%, the weldability deteriorates. Therefore, when adding Ni, it is preferable to make Ni amount into 1.00% or less, and it is more preferable that it is 0.50% or less.
Crは焼き入れ性を高めることで強度の上昇に有効な元素であり、この効果を発揮させるにはCr量は0.10%以上であることが好ましい。しかしながら、Cr量が0.50%を超えると溶接性が劣化する。従って、Crを添加する場合はCr量を0.50%以下とすることが好ましく、0.30%以下であることがより好ましい。 Cr: 0.50% or less Cr is an element effective for increasing the strength by enhancing the hardenability, and the Cr content is preferably 0.10% or more in order to exhibit this effect. However, if the Cr content exceeds 0.50%, the weldability deteriorates. Therefore, when adding Cr, the Cr content is preferably 0.50% or less, and more preferably 0.30% or less.
Moは母材靭性の改善と強度の上昇に有効な元素であり、この効果を発揮させるにはMo量は0.10%以上であることが好ましい。しかしながら、Mo量が0.50%を超えるとHAZ靭性および溶接性が劣化する。従って、Moを添加する場合はMo量を0.50%以下とすることが好ましく、0.30%以下であることがより好ましい。 Mo: 0.50% or less Mo is an element effective for improving the toughness of the base metal and increasing the strength, and the Mo amount is preferably 0.10% or more in order to exert this effect. However, if the Mo content exceeds 0.50%, the HAZ toughness and weldability deteriorate. Therefore, when adding Mo, it is preferable to make Mo amount into 0.50% or less, and it is more preferable that it is 0.30% or less.
Vは強度を上昇させる元素であり、この効果を発揮させるにはV量は0.010%以上であることが好ましい。しかしながら、V量が0.060%を超えるとHAZ靭性および溶接性を著しく損なう。従って、Vを添加する場合は、V量を0.060%以下とすることが好ましく、0.050%以下であることがより好ましい。 V: 0.060% or less V is an element that increases the strength, and in order to exhibit this effect, the V content is preferably 0.010% or more. However, if the V content exceeds 0.060%, the HAZ toughness and weldability are significantly impaired. Therefore, when adding V, it is preferable to make V amount into 0.060% or less, and it is more preferable that it is 0.050% or less.
Bは強度の上昇に有効な元素であり、この効果を発揮させるにはB量は0.0005%以上であることが好ましい。しかしながら、B量が0.0030%を超えるとHAZ靭性および溶接性が劣化する。従って、Bを添加する場合はB量を0.0030%以下とすることが好ましく、0.0025%以下であることがより好ましい。 B: 0.0030% or less B is an element effective for increasing the strength, and the B content is preferably 0.0005% or more in order to exhibit this effect. However, if the B content exceeds 0.0030%, the HAZ toughness and weldability deteriorate. Therefore, when adding B, the amount of B is preferably 0.0030% or less, and more preferably 0.0025% or less.
中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVが、それぞれ、400+50(pH-12)(1+log(PH2S))/9以下
中心偏析部の硬さ、表層および裏層のミクロ組織に含まれる硬質第二相の硬さが、それぞれ大きいほどHICが発生しやすくなる。本発明者らが検討した結果、それら各々のマイクロビッカース硬さの最大値が、下記式(4)を満たさない場合、HICが発生することがわかった。なお、表層及び裏層とは、表面から板厚方向に5mmまでの領域を指す。
HV≦400+50(pH-12)(1+log(PH2S))/9・・・(4)
ただし、式(4)において、
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
とする。
したがって、本発明では、中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVの上限を、400+50(pH-12)(1+log(PH2S))/9とする。なお、マイクロビッカースの荷重は、硬質第二相の断面寸法に合わせて5~50gの範囲で設定し、測定する硬質第二相から圧痕がはみ出さないように測定する。また、ミクロ組織がほぼ均一(例えば、ベイナイト単相組織など)で、5gを用いても測定できるような大きさの硬質第二相がない場合は、50gで任意の箇所を測定する。また、マイクロビッカース試験は測定ばらつきの大きい試験であるため、中心偏析部、表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値は、5点以上測定した結果の最大値を用いる。 <Hardness>
The central segregation part and the maximum value HV of the micro Vickers hardness of the hard second phase contained in the microstructure of the surface layer and the back layer are 400 + 50 (pH-12) (1 + log (P H2S )) / 9 or less, respectively. HIC is more likely to occur as the hardness of the second layer and the hardness of the hard second phase contained in the microstructures of the surface layer and the back layer increase. As a result of investigations by the present inventors, it has been found that HIC occurs when the maximum value of each micro Vickers hardness does not satisfy the following formula (4). In addition, a surface layer and a back layer refer to the area | region to 5 mm from the surface to a plate | board thickness direction.
HV ≦ 400 + 50 (pH−12) (1 + log (P H2S )) / 9 (4)
However, in Formula (4),
pH: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
And
Accordingly, in the present invention, the upper limit of the maximum value HV of the micro-Vickers hardness of the hard second phase contained in the center segregation portion and the microstructures of the surface layer and the back layer is set to 400 + 50 (pH-12) (1 + log (P H2S )) / 9. The micro Vickers load is set in the range of 5 to 50 g in accordance with the cross-sectional dimension of the hard second phase, and is measured so that no indentation protrudes from the hard second phase to be measured. If the microstructure is almost uniform (for example, a bainite single phase structure) and there is no hard second phase that can be measured even with 5 g, an arbitrary portion is measured with 50 g. In addition, since the micro Vickers test is a test with a large measurement variation, the maximum value of the micro Vickers hardness of the hard second phase contained in the microstructure of the central segregation part, the surface layer and the back layer is a result of measurement of 5 points or more. Use the maximum value.
耐SSC性能を確保するためには、一般にビッカース硬さを248以下に抑える必要があることが知られている。本発明で扱うTMCP(Thermo-Mechanical Control Process)で製造される溶接鋼管および厚鋼板については、表層および裏層が最も硬くなるため、表層および裏層の硬さを248以下に抑える必要がある。なお、ビッカース硬さの荷重は、10kgを用い、測定位置としては、管厚方向断面において表層および裏層から管厚方向に1.5mmの深さの位置で測定することが望ましい。 It is known that the Vickers hardness of the surface layer and the back layer is generally 248 or less. In order to ensure the SSC resistance, it is generally necessary to suppress the Vickers hardness to 248 or less. With respect to the welded steel pipe and the thick steel plate manufactured by TMCP (Thermo-Mechanical Control Process) handled in the present invention, the surface layer and the back layer are the hardest, so it is necessary to suppress the hardness of the surface layer and the back layer to 248 or less. Note that the load of Vickers hardness is 10 kg, and the measurement position is preferably measured at a depth of 1.5 mm in the tube thickness direction from the surface layer and the back layer in the cross section in the tube thickness direction.
X線回析により得られる管厚中心位置または板厚中心位置での圧延面の(211)面の集積度が1.6以上
ラインパイプで要求されるDWTT性能などの母材靭性は、鋼材のミクロ組織や集合組織の影響を受ける。本発明者らは、オーステナイトからベイナイトに変態する際に発達する、管厚中心位置または板厚中心位置での圧延面の(211)面の集積度と母材靭性の間に良好な相関があることを見出した。上記集積度が1.6以上になると母材靭性が良好になるため、集積度の下限を1.6とする。より好ましくは、1.8以上である。なお、ここで(211)面の集積度とは、対象材の(211)結晶面の集積度を表す数値で、対象材の管厚中心位置から鋼板圧延面に平行に採取した板面における(211)反射のX線回折強度(I(211))と、集合組織のないランダムな標準試料の(211)反射のX線回折強度(I0(211))との比(I(211)/I0(211))を指す。 <Group organization>
The accumulation degree of the (211) plane of the rolled surface at the tube thickness center position or the sheet thickness center position obtained by X-ray diffraction is 1.6 or more. Base material toughness such as DWTT performance required for a line pipe is Influenced by microstructure and texture. The present inventors have a good correlation between the degree of integration of the (211) plane of the rolled surface at the tube thickness center position or the sheet thickness center position and the base material toughness that develop when transforming from austenite to bainite. I found out. Since the base material toughness becomes good when the integration degree is 1.6 or more, the lower limit of the integration degree is set to 1.6. More preferably, it is 1.8 or more. Here, the degree of integration of the (211) plane is a numerical value representing the degree of integration of the (211) crystal plane of the target material, and is the value of the plate surface taken in parallel to the steel sheet rolling surface from the tube thickness center position of the target material ( 211) the ratio of the X-ray diffraction intensity of the reflection (I (211)) and, (211) reflection of X-ray diffraction intensity (I 0 (211) without random standard sample of texture) (I (211) / I 0 (211) ).
本発明の製造方法は、上述した成分組成を有する連続鋳造スラブ鋼素材を、1000~1200℃に加熱し、圧延開始温度がTS以下で累積圧下率50%以上で熱間圧延を行い、次いで圧延終了温度がTF以上を満たすように熱間圧延を終了し、その後、冷却停止温度が600℃以下となる加速冷却を行った後、空冷することを特徴とする。 <Production conditions>
Production method of the present invention, a continuous cast slab steel material having the above-mentioned composition of ingredients, and heated to 1000 ~ 1200 ° C., rolling start temperature perform hot rolling at a cumulative rolling reduction of 50% or more below T S, then Hot rolling is terminated so that the rolling end temperature satisfies TF or higher, and then accelerated cooling is performed so that the cooling stop temperature is 600 ° C. or lower, followed by air cooling.
スラブをオーステナイト化しつつ、最低限のNbの固溶量を得るため、スラブ加熱温度の下限温度は1000℃とする。一方、1200℃を超える温度までスラブを加熱すると、NbCおよびTiNによるピンニング効果が弱まり、オーステナイト粒が著しく成長し、母材靭性が劣化する。このため、スラブ加熱温度は1000~1200℃の範囲とする。 Heating temperature: 1000-1200 ° C
In order to obtain a minimum amount of Nb solid solution while austenizing the slab, the lower limit temperature of the slab heating temperature is set to 1000 ° C. On the other hand, when the slab is heated to a temperature exceeding 1200 ° C., the pinning effect by NbC and TiN is weakened, austenite grains grow significantly, and the base material toughness deteriorates. Therefore, the slab heating temperature is in the range of 1000 to 1200 ° C.
母材靭性を向上させるためには、オーステナイト未再結晶温度域低温側で累積圧下率を大きくとる圧延をすることが望ましい。下記式(5)で表されるTSは、鋼の成分と圧延終了時の板厚(mm)に応じて決まり、母材靭性確保のために必要な圧延時の圧延開始温度を示すものである。
TS≦174log([Nb]([C]+12[N]/14))+1444-1.2t・・・(5)
ただし、上記式(5)において、
[Nb]、[C]、[N]:各元素の含有量(質量%)であり、含まない場合は0とする
t:圧延終了時の板厚(mm)
とする。
本発明では、累積圧下率50%以上の圧下を加える際の圧延開始温度が、174log([Nb]([C]+12[N]/14))+1444-1.2tを超える場合、母材靭性が劣化する。このため、圧延開始温度の上限を174log([Nb]([C]+12[N]/14))+1444-1.2tとする。 Rolling start temperature T S : 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t or less when rolling reduction of 50% or more is applied to improve the base metal toughness It is desirable to perform rolling to increase the cumulative rolling reduction at the low temperature side of the austenite non-recrystallization temperature range. T S represented by the following formula (5) is determined in accordance with the composition of steel plate thickness at the completion of rolling (mm), it shows a rolling start temperature during rolling necessary for the base material toughness ensure is there.
T S ≦ 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t (5)
However, in the above formula (5),
[Nb], [C], [N]: content (% by mass) of each element, 0 if not included t: thickness at the end of rolling (mm)
And
In the present invention, when the rolling start temperature at the time of applying the rolling reduction of 50% or more exceeds 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2 t, the base material toughness Deteriorates. Therefore, the upper limit of the rolling start temperature is 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t.
圧延終了温度は低いほど母材靭性が向上する。一方で、圧延終了温度が低いと耐HIC性能が劣化する。圧延終了温度が下記式(6)を満足しない場合には、表面近傍に加工フェライトが生成し、硬質第二相の硬さも高くなり表層近傍の耐HIC性能が劣化する。
TF≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(6)
ただし、上記式(6)において、
[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]:各元素の含有量(質量%)であり、含まない場合は0とする
t:圧延終了時の板厚(mm)
とする。
このため、圧延終了温度TFの下限を910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6tとする。また、圧延終了温度はラインパイプ用途として必要最小限の母材靭性を確保するという理由で950℃以下が好ましい。また、加速冷却開始温度についてもTFを下回ると、中心偏析部近傍にフェライトが生成し、中心偏析近傍の硬質第二相が著しく硬化し、耐HIC性能が劣化する場合があるため、下限をTFとすることが好ましい。 Rolling end temperature T F : 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t or more The lower the rolling end temperature, the base material Toughness is improved. On the other hand, when the rolling end temperature is low, the HIC resistance is deteriorated. When the rolling end temperature does not satisfy the following formula (6), processed ferrite is generated near the surface, the hardness of the hard second phase is increased, and the HIC resistance near the surface layer is deteriorated.
T F ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t (6)
However, in the above formula (6),
[C], [Mn], [Cu], [Ni], [Cr], [Mo]: content (mass%) of each element and 0 when not included t: plate at the end of rolling Thickness (mm)
And
Therefore, the lower limit of the rolling end temperature TF is set to 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6 t. Further, the rolling end temperature is preferably 950 ° C. or lower for the purpose of ensuring the minimum base metal toughness required for line pipe applications. If the lower T F also accelerated cooling start temperature, ferrite is generated in the vicinity of the center segregation area, and hard cured second phase significantly central polarized析近near, since the HIC resistance may deteriorate, the lower limit T F is preferable.
加速冷却開始温度は低いほど母材靭性が向上する。一方で、加速冷却開始温度が低いと耐HIC性能が劣化する。加速冷却開始温度が下記式(7)で表されるTACS未満では、表面近傍に加工フェライトが生成し、硬質第二相の硬さも高くなり表層近傍の耐HIC性能が劣化する。
TACS≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(7)
ただし、上記式(7)において、
[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]:各元素の含有量(質量%)であり、含まない場合は0とする
t:圧延終了時の板厚(mm)
とする。
このため、加速冷却開始温度TACSの下限を910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6tとする。 Accelerated cooling start temperature T ACS: 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] accelerated cooling start temperature or higher -0.6t is as low Base material toughness is improved. On the other hand, when the accelerated cooling start temperature is low, the HIC resistance is deteriorated. If the accelerated cooling start temperature is less than TACS represented by the following formula (7), processed ferrite is generated near the surface, the hardness of the hard second phase is increased, and the HIC resistance near the surface layer is deteriorated.
T ACS ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6 t (7)
However, in the above formula (7),
[C], [Mn], [Cu], [Ni], [Cr], [Mo]: content (mass%) of each element and 0 when not included t: plate at the end of rolling Thickness (mm)
And
Therefore, the lower limit of the accelerated cooling start temperature T ACS and 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t.
圧延終了後、加速冷却を行う。冷却停止温度は低いほど強度が大きくなり、高いほど鋼板の平坦度が良好になる。一方で、耐HIC性能確保の観点から、600℃を超える温度にすると冷却停止後にフェライトおよびパーライト変態が起こり、ミクロ組織が不均一になりHIC性能が劣化する。このため、上限を600℃とする。また、冷却停止温度は必要以上に高強度化することに起因するHIC性能の劣化の抑制という理由で300℃以上が好ましい。なお、加速冷却時の冷却速度は、10℃/s以上が好ましい。 Cooling stop temperature of accelerated cooling is 600 ° C. or less After the rolling, accelerated cooling is performed. The lower the cooling stop temperature, the greater the strength, and the higher the temperature, the better the flatness of the steel sheet. On the other hand, from the viewpoint of securing HIC resistance, if the temperature exceeds 600 ° C., ferrite and pearlite transformation occurs after cooling is stopped, the microstructure becomes non-uniform, and the HIC performance deteriorates. For this reason, an upper limit shall be 600 degreeC. Further, the cooling stop temperature is preferably 300 ° C. or higher for the purpose of suppressing the deterioration of the HIC performance caused by increasing the strength more than necessary. The cooling rate during accelerated cooling is preferably 10 ° C./s or higher.
本発明では、加速冷却後に強度や靭性を調整するために、あるいは応力除去焼鈍時の特性変化を小さくするために、加速冷却後に空冷した後、必要に応じて、焼戻し熱処理を行うことができる。その効果は、焼戻し温度が480℃未満では得られず、720℃を超えるとミクロ組織の一部が逆変態し、HIC性能が劣化する。このため、焼戻し熱処理を行う場合は、焼戻し温度を480~720℃の範囲で行うことが好ましい。 Tempering temperature: 480-720 ° C
In the present invention, in order to adjust the strength and toughness after accelerated cooling, or to reduce the change in characteristics at the time of stress-relieving annealing, after air cooling after accelerated cooling, tempering heat treatment can be performed as necessary. The effect cannot be obtained when the tempering temperature is less than 480 ° C., and when it exceeds 720 ° C., a part of the microstructure is reversely transformed, and the HIC performance is deteriorated. Therefore, when performing the tempering heat treatment, it is preferable to perform the tempering temperature in the range of 480 to 720 ° C.
Claims (7)
- 質量%で、C:0.02~0.10%、Si:0.40%以下、Mn:1.00~2.00%、Nb:0.005~0.060%、Ti:0.005~0.025%、Ca:0.0010~0.0040%、N:0.0010~0.0100%を含有し、Ca/Oが2.5以下であり、下記式(1)で示されるACRMが0以上であり、下記式(2)で示されるPHICが下記式(3)を満たし、残部はFeおよび不可避的不純物からなり、
中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVが、下記式(4)を満たし、
表層および裏層のビッカース硬さが248以下であり、
X線回析により得られる管厚中心位置での圧延面の(211)面の集積度が1.6以上である溶接鋼管。
ACRM=([Ca]-(1.23[O]-0.000365))/(1.25[S])・・・(1)
PHIC=4.46[C]+2.37[Mn]/6+(1.74[Cu]+1.7[Ni])/15+(1.18[Cr]+1.95[Mo]+1.74[V])/5+22.36[P]・・・(2)
PHIC≦1.35+(pH-12)(1+log(PH2S))/60・・・(3)
HV≦400+50(pH-12)(1+log(PH2S))/9・・・(4)
ただし、式(1)~(4)において、
[Ca]、[O]、[S]、[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[P]:各元素の含有量(質量%)であり、含まない場合は0とする
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
とする。 In mass%, C: 0.02 to 0.10%, Si: 0.40% or less, Mn: 1.00 to 2.00%, Nb: 0.005 to 0.060%, Ti: 0.005 -0.025%, Ca: 0.0010-0.0040%, N: 0.0010-0.0100%, Ca / O is 2.5 or less, and is represented by the following formula (1) ACRM is not less than 0, satisfying P HIC has the following formula (3) represented by the following formula (2), the balance being Fe and unavoidable impurities,
The maximum value HV of the micro Vickers hardness of the hard second phase contained in the microstructure of the center segregation part and the surface layer and the back layer satisfies the following formula (4),
The Vickers hardness of the surface layer and the back layer is 248 or less,
A welded steel pipe having an accumulation degree of the (211) plane of the rolled surface at the tube thickness center position obtained by X-ray diffraction of 1.6 or more.
ACRM = ([Ca] − (1.23 [O] −0.000365)) / (1.25 [S]) (1)
P HIC = 4.46 [C] +2.37 [Mn] / 6 + (1.74 [Cu] +1.7 [Ni]) / 15+ (1.18 [Cr] +1.95 [Mo] +1.74 [ V]) / 5 + 22.36 [P] (2)
P HIC ≦ 1.35 + (pH−12) (1 + log (P H2S )) / 60 (3)
HV ≦ 400 + 50 (pH−12) (1 + log (P H2S )) / 9 (4)
However, in the equations (1) to (4),
[Ca], [O], [S], [C], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [P]: Content of each element ( Mass%), and when not included, pH is 0: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
And - さらに、質量%で、Cu:0.50%以下、Ni:1.00%以下、Cr:0.50%以下、Mo:0.50%以下、V:0.060%以下、B:0.0030%以下から選ばれる1種以上を含有する請求項1に記載の溶接鋼管。 Further, in terms of mass%, Cu: 0.50% or less, Ni: 1.00% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.060% or less, B: 0.0. The welded steel pipe according to claim 1, comprising one or more selected from 0030% or less.
- 質量%で、C:0.02~0.10%、Si:0.40%以下、Mn:1.00~2.00%、Nb:0.005~0.060%、Ti:0.005~0.025%、Ca:0.0010~0.0040%、N:0.0010~0.0100%を含有し、Ca/Oが2.5以下であり、下記式(1)で示されるACRMが0以上であり、下記式(2)で示されるPHICが下記式(3)を満たし、残部はFeおよび不可避的不純物からなり、
中心偏析部ならびに表層および裏層のミクロ組織に含まれる硬質第二相のマイクロビッカース硬さの最大値HVが、下記式(4)を満たし、
表層および裏層のビッカース硬さが248以下であり、
X線回析により得られる板厚中心位置での圧延面の(211)面の集積度が1.6以上である厚鋼板。
ACRM=([Ca]-(1.23[O]-0.000365))/(1.25[S])・・・(1)
PHIC=4.46[C]+2.37[Mn]/6+(1.74[Cu]+1.7[Ni])/15+(1.18[Cr]+1.95[Mo]+1.74[V])/5+22.36[P]・・・(2)
PHIC≦1.35+(pH-12)(1+log(PH2S))/60・・・(3)
HV≦400+50(pH-12)(1+log(PH2S))/9・・・(4)
ただし、式(1)~(4)において、
[Ca]、[O]、[S]、[C]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]、[V]、[P]:各元素の含有量(質量%)であり、含まない場合は0とする
pH:HIC試験環境のpH
PH2S:HIC試験環境のH2S分率(Vol%)
とする。 In mass%, C: 0.02 to 0.10%, Si: 0.40% or less, Mn: 1.00 to 2.00%, Nb: 0.005 to 0.060%, Ti: 0.005 -0.025%, Ca: 0.0010-0.0040%, N: 0.0010-0.0100%, Ca / O is 2.5 or less, and is represented by the following formula (1) ACRM is not less than 0, satisfying P HIC has the following formula (3) represented by the following formula (2), the balance being Fe and unavoidable impurities,
The maximum value HV of the micro Vickers hardness of the hard second phase contained in the microstructure of the center segregation part and the surface layer and the back layer satisfies the following formula (4),
The Vickers hardness of the surface layer and the back layer is 248 or less,
A thick steel plate having a degree of integration of the (211) plane of the rolled surface at the plate thickness center position obtained by X-ray diffraction of 1.6 or more.
ACRM = ([Ca] − (1.23 [O] −0.000365)) / (1.25 [S]) (1)
P HIC = 4.46 [C] +2.37 [Mn] / 6 + (1.74 [Cu] +1.7 [Ni]) / 15+ (1.18 [Cr] +1.95 [Mo] +1.74 [ V]) / 5 + 22.36 [P] (2)
P HIC ≦ 1.35 + (pH−12) (1 + log (P H2S )) / 60 (3)
HV ≦ 400 + 50 (pH−12) (1 + log (P H2S )) / 9 (4)
However, in the equations (1) to (4),
[Ca], [O], [S], [C], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [P]: Content of each element ( Mass%), and when not included, pH is 0: pH of the HIC test environment
P H2S: H 2 S fraction of HIC test environment (Vol%)
And - さらに、質量%で、Cu:0.50%以下、Ni:1.00%以下、Cr:0.50%以下、Mo:0.50%以下、V:0.060%以下、B:0.0030%以下から選ばれる1種以上を含有する請求項3に記載の厚鋼板。 Further, in terms of mass%, Cu: 0.50% or less, Ni: 1.00% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.060% or less, B: 0.0. The thick steel plate according to claim 3, containing one or more selected from 0030% or less.
- 請求項3または4に記載の成分組成を有する連続鋳造スラブ鋼素材を、1000~1200℃に加熱し、圧延開始温度TSが下記式(5)を満たすように累積圧下率50%以上で熱間圧延を行い、次いで、圧延終了温度TFが下記式(6)を満たすように熱間圧延を終了し、その後、加速冷却開始温度TACSが下記式(7)を満たすように加速冷却を開始し、冷却停止温度が600℃以下で加速冷却を停止させた後、空冷する厚鋼板の製造方法。
TS≦174log([Nb]([C]+12[N]/14))+1444-1.2t・・・(5)
TF≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(6)
TACS≧910-310[C]-80[Mn]-20[Cu]-55[Ni]-15[Cr]-80[Mo]-0.6t・・・(7)
ただし、上記式(5)、(6)、(7)において、
[Nb]、[C]、[N]、[Mn]、[Cu]、[Ni]、[Cr]、[Mo]:各元素の含有量(質量%)であり、含まない場合は0とする
t:圧延終了時の板厚(mm)
とする。 Heat the continuously cast slab steel material, 1000-1200 was heated to ° C., rolling start temperature T S the following formula (5) to meet as cumulative rolling reduction of 50% or more having a composition as set forth in claim 3 or 4 Then, the hot rolling is finished so that the rolling end temperature TF satisfies the following formula (6), and then the accelerated cooling is performed so that the accelerated cooling start temperature T ACS satisfies the following formula (7). A method for producing a thick steel plate, which is started and air-cooled after stopping cooling at a cooling stop temperature of 600 ° C. or less.
T S ≦ 174 log ([Nb] ([C] +12 [N] / 14)) + 1444-1.2t (5)
T F ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6t (6)
T ACS ≧ 910-310 [C] -80 [Mn] -20 [Cu] -55 [Ni] -15 [Cr] -80 [Mo] -0.6 t (7)
However, in the above formulas (5), (6), (7),
[Nb], [C], [N], [Mn], [Cu], [Ni], [Cr], [Mo]: content (% by mass) of each element, 0 if not included T: Thickness at the end of rolling (mm)
And - 前記空冷後、480~720℃に焼戻す請求項5に記載の厚鋼板の製造方法。 The method for producing a thick steel plate according to claim 5, wherein after the air cooling, the steel plate is tempered to 480 to 720 ° C.
- 請求項5または6の方法で製造した厚鋼板を筒状に冷間加工し、その突合せ部を溶接することで溶接鋼管とする溶接鋼管の製造方法。
A method for producing a welded steel pipe, wherein the thick steel plate produced by the method according to claim 5 or 6 is cold-worked into a cylindrical shape and the butt portion is welded to form a welded steel pipe.
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