JP2002275576A - Low yield ratio steel for low temperature use and production method therefor - Google Patents
Low yield ratio steel for low temperature use and production method thereforInfo
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- JP2002275576A JP2002275576A JP2001072513A JP2001072513A JP2002275576A JP 2002275576 A JP2002275576 A JP 2002275576A JP 2001072513 A JP2001072513 A JP 2001072513A JP 2001072513 A JP2001072513 A JP 2001072513A JP 2002275576 A JP2002275576 A JP 2002275576A
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】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。本発明は、低温用低降伏比鋼材の製造方法に関し、
とくに、降伏応力(YS)355-440MPa、引張強さ(T
S)530-610MPa、破面遷移温度(vTrs)-80 ℃以下の液
体アンモニアと液化天然ガスを混載するタンク等の低温
靭性と低降伏比(低YR)の要求に応えうる低温用低降
伏比鋼材およびその製造方法に関する。なお、鋼材とは
鋼板(厚板)または条鋼を指す。BACKGROUND OF THE INVENTION In the present invention,% used as a unit symbol for the content of a chemical component means percent by mass. The present invention relates to a method for producing a low-yield-ratio steel material for low temperature,
In particular, yield stress (YS) 355-440MPa, tensile strength (T
S) Low yield ratio for low temperature that can meet the demands of low temperature toughness and low yield ratio (low YR) for tanks etc. that mix liquid ammonia and liquefied natural gas with 530-610MPa and fracture surface transition temperature (vTrs) -80 ° C or less The present invention relates to a steel material and a method for manufacturing the same. In addition, a steel material points out a steel plate (thick plate) or a bar steel.
【0002】[0002]
【従来の技術】従来から液体アンモニアを収容するよう
な腐食環境下で使用されるタンク材には、応力腐食割れ
(SCC) 回避のために低いYS(440MPa以下)が要求
される。これはYSを低くして応力集中を防ぐためであ
る。近年、タンクの大型化に伴い鋼材総重量軽減の観点
から鋼材の高強度化のニーズがでてきた。この場合には
TSは高く(530MPa以上)YSは低くという相反する性
質を要求されることになる。さらには液化天然ガス (沸
点-48 ℃)をも収容するため、優れた低温靭性も要求さ
れる。2. Description of the Related Art Conventionally, tank materials used in a corrosive environment containing liquid ammonia include stress corrosion cracking.
(SCC) Low YS (440 MPa or less) is required for avoidance. This is to lower the YS to prevent stress concentration. In recent years, with the increase in size of tanks, there has been a need for higher strength steel materials from the viewpoint of reducing the total weight of steel materials. In this case, the contradictory properties of high TS (530 MPa or more) and low YS are required. In addition, excellent low-temperature toughness is required to accommodate liquefied natural gas (boiling point -48 ° C).
【0003】かかる要求に応える鋼材の製造方法に関す
る従来技術としては、特開平10−130721号公報、特開平
10−168516号公報、特開平11−80832 号公報に開示され
ているように、調質法と総称される、直接焼入れ焼戻し
法、再加熱焼入れ焼戻し法、あるいは焼入れ2相域焼入
れ焼戻し法がある。一方、非調質法で製造する従来技術
としては特開平11−293380号公報所載のものがある。[0003] As a prior art relating to a method for producing a steel material meeting such a demand, there are Japanese Patent Application Laid-Open Nos. 10-130721 and 10-130721.
As disclosed in JP-A-10-168516 and JP-A-11-80832, there is a direct quenching and tempering method, a reheating quenching and tempering method, or a quenching two-phase region quenching and tempering method, which is collectively referred to as a tempering method. . On the other hand, as a conventional technique manufactured by a non-tempering method, there is one disclosed in Japanese Patent Application Laid-Open No. 11-293380.
【0004】[0004]
【発明が解決しようとする課題】前記調質法は安定的に
製造できる反面、製造にかかる時間が非調質法に比べて
長いという短所がある。また、調質法はコストも割高で
ある。また、前記特開平11−293380号公報所載の非調質
法によれば、化学成分と冷却条件を適切に制御すること
で所定の機械的性質を満足する鋼板を製造可能である。
しかし、この製造方法では、水冷の冷却停止温度が150
〜350 ℃と低温の比較的狭い範囲に限定されており、安
定的に鋼板を製造するのは困難と考えられる。なぜなら
ば、このような低い温度範囲では冷却速度が非常に速く
なり冷却が止まらないのである。仮にうまく冷却停止で
きたとしても、板内の材質ばらつきが大きく、やはり安
定した製造が困難と思われる。The tempering method can stably produce, but has a disadvantage that the time required for the production is longer than that of the non-tempering method. The tempering method is also expensive. Further, according to the non-heat treatment method described in JP-A-11-293380, a steel sheet satisfying predetermined mechanical properties can be produced by appropriately controlling the chemical components and cooling conditions.
However, in this manufacturing method, the cooling stop temperature of water cooling is 150
Since the temperature is limited to a relatively narrow range of low temperature of ~ 350 ° C, it is considered difficult to manufacture a steel sheet stably. This is because in such a low temperature range, the cooling rate becomes extremely high and cooling does not stop. Even if the cooling can be stopped successfully, the variation in the material in the plate is large, and it is considered that stable production is also difficult.
【0005】また、強度には第2相の体積率が大きく影
響することは言うまでもないが、今までこの分野で第2
相の体積率の制御まで詳しく示した技術はなく、強度の
適正制御は困難であった。本発明は、これらの困難を克
服し、強度と降伏比を安定させた低温用低降伏比鋼材お
よびその有利な製造方法を提供することを目的とする。It is needless to say that the volume ratio of the second phase greatly affects the strength.
There is no technique showing in detail the control of the volume ratio of the phase, and it is difficult to properly control the strength. An object of the present invention is to provide a low-yield-ratio steel material for low-temperature use in which these difficulties are overcome and the strength and the yield ratio are stabilized, and an advantageous production method thereof.
【0006】[0006]
【課題を解決するための手段】本発明者らは、前記目的
を達成すべく鋭意検討を重ね、その結果、特定の化学組
成の鋼材を、フェライト、ベイナイト、マルテンサイト
の 3相からなりマルテンサイトの体積率が1〜15%にな
る組織に制御することにより、上述の液体アンモニア、
液化天然ガス混載用タンク材で要求される機械的性質を
安定的に満足したものが得られることを見いだした。さ
らに、この組織は、下記式で定義されるMVF が1〜15に
なる圧延ないし冷却条件とすることにより、精度よく形
成させうることを見いだした。Means for Solving the Problems The present inventors have intensively studied to achieve the above object, and as a result, a steel material having a specific chemical composition is composed of three phases of ferrite, bainite and martensite. By controlling the tissue to have a volume ratio of 1 to 15%, the above-described liquid ammonia,
It has been found that the mechanical properties required for the liquefied natural gas mixed tank material can be stably satisfied. Further, it has been found that this structure can be formed with high precision by setting the rolling or cooling conditions so that the MVF defined by the following formula becomes 1 to 15.
【0007】 記 MVF = 0.114・Rnxー 0.00616・Tfin − 0.576・CR
X-500 +8 ただし、Rnx:γ(オーステナイト)未再結晶域での圧
下率(%) Tfin :圧延終了温度(℃) CRX-500 :X 〜500 ℃の冷却速度(℃/s),X=MIN(T
fin ,800) なお、MIN(a,b)はa,b の小さい方(等しい場合は任意の
一方)を意味する。[0007] MVF = 0.114 · R nx -0.00616 · T fin -0.576 · CR
X-500 +8 where R nx : rolling reduction (%) in the γ (austenite) unrecrystallized region T fin : rolling end temperature (° C) CR X-500 : X to 500 ° C cooling rate (° C / s) , X = MIN (T
fin , 800) MIN (a, b) means the smaller of a and b (if equal, any one of them).
【0008】また、前記冷却後に弱い焼戻しを行うこと
で、機械的性質の的中制御精度がさらに向上することも
見いだした。本発明は、これらの知見に基づいてなされ
たものであり、その要旨は以下のとおりである。 (1)C:0.02〜0.16%、Si:0.10〜0.5 %、Mn:0.70
〜1.6 %、Al:0.01〜0.08%を含有し残部Fe及び不可避
的不純物からなる組成と、フェライト、ベイナイト、マ
ルテンサイトの 3相からなりマルテンサイトの体積率が
1〜15%になる組織とを有することを特徴とする低温用
低降伏比鋼材。[0008] It has also been found that by performing weak tempering after the above-mentioned cooling, the accuracy of hit control of mechanical properties is further improved. The present invention has been made based on these findings, and the gist is as follows. (1) C: 0.02 to 0.16%, Si: 0.10 to 0.5%, Mn: 0.70
~ 1.6%, Al: 0.01 ~ 0.08%, the balance consisting of Fe and unavoidable impurities, and the structure consisting of three phases of ferrite, bainite and martensite, and having a martensite volume fraction of 1 ~ 15%. A low-temperature low-yield-ratio steel material characterized by having:
【0009】(2)C:0.02〜0.16%、Si:0.10〜0.5
%、Mn:0.70〜1.6 %、Al:0.01〜0.08%を含有し、さ
らに、下記(a)〜(e)の1つまたは2つ以上を含有
し、残部Fe及び不可避的不純物からなる組成と、フェラ
イト、ベイナイト、マルテンサイトの 3相からなりマル
テンサイトの体積率が1〜15%になる組織とを有するこ
とを特徴とする低温用低降伏比鋼材。(2) C: 0.02 to 0.16%, Si: 0.10 to 0.5
%, Mn: 0.70 to 1.6%, Al: 0.01 to 0.08%, and further contains one or more of the following (a) to (e), with the balance being Fe and inevitable impurities. A low-yield-ratio steel for low temperatures, characterized by having a structure comprising three phases of ferrite, bainite, and martensite, wherein the volume ratio of martensite is 1 to 15%.
【0010】 記 (a)Ni:0.8 %以下 (b)Cr:0.25%以下、Mo:0.08%以下の1種または2
種 (c)Cu:0.35%以下 (d)Nb:0.05%以下、V:0.10%以下、Ti:0.025 %
以下の1種または2種以上 (e)B:0.0025%以下 (3)C:0.02〜0.16%、Si:0.10〜0.5 %、Mn:0.70
〜1.6 %、Al:0.01〜0.08%を含有し、あるいはさら
に、Ni:0.8 %以下、Cr:0.25%以下、Mo:0.08%以
下、Cu:0.35%以下、Nb:0.05%以下、V:0.10%以
下、Ti:0.025 %以下、B:0.0025%以下の1種または
2種以上を含有する鋼素材を950 〜1250℃に加熱後、γ
再結晶域で30%以上の圧下率で圧延し、さらにγ未再結
晶域で30%以上の圧下率で圧延し、850 ℃からAr3点の
間で圧延を終了して鋼材となし、これを圧延終了から50
0 ℃まで20℃/s以下の冷却速度で冷却し、500 ℃から、
450 ℃以下とした冷却停止温度まで10℃/s以上の冷却速
度で冷却する方法であって、下記式で定義されるMVF を
1〜15としたことを特徴とする低温用低降伏比鋼材の製
造方法。(A) Ni: 0.8% or less (b) Cr: 0.25% or less, Mo: 0.08% or less one or two
Species (c) Cu: 0.35% or less (d) Nb: 0.05% or less, V: 0.10% or less, Ti: 0.025%
One or more of the following: (e) B: 0.0025% or less (3) C: 0.02 to 0.16%, Si: 0.10 to 0.5%, Mn: 0.70
1.6%, Al: 0.01-0.08%, or Ni: 0.8% or less, Cr: 0.25% or less, Mo: 0.08% or less, Cu: 0.35% or less, Nb: 0.05% or less, V: 0.10 % Or less, Ti: 0.025% or less, B: 0.0025% or less.
Rolled at a rolling reduction of 30% or more in the recrystallized region, further rolled at a rolling reduction of 30% or more in the γ non-recrystallized region, completed rolling between 850 ° C and three points of Ar to form a steel material. The end of rolling from 50
Cool to 0 ° C at a cooling rate of 20 ° C / s or less.
A method of cooling at a cooling rate of 10 ° C./s or more to a cooling stop temperature of 450 ° C. or less, wherein the MVF defined by the following equation is 1 to 15; Production method.
【0011】記 MVF = 0.114・Rnxー 0.00616・Tfin − 0.576・CR
X-500 +8 ただし、Rnx:γ未再結晶域での圧下率(%) Tfin :圧延終了温度(℃) CRX-500 :X 〜500 ℃の冷却速度(℃/s),X=MIN(T
fin ,800) (4)前記冷却停止後の鋼材を100 〜580 ℃で焼戻しす
ることを特徴とする(3)記載の低温用低降伏比鋼材の
製造方法。MVF = 0.114 · R nx -0.00616 · T fin -0.576 · CR
X-500 +8, where R nx : rolling reduction in γ non-recrystallized region (%) T fin : rolling end temperature (° C) CR X-500 : X to 500 ° C cooling rate (° C / s), X = MIN (T
fin , 800) (4) The method for producing a low-yield-ratio steel material for low-temperature use according to (3), wherein the steel material after the cooling is stopped is tempered at 100 to 580 ° C.
【0012】[0012]
【発明の実施の形態】まず、化学組成の限定理由につい
て説明する。 C:0.02〜0.16% C量は必要な強度を得るためおよび炭化物の析出のため
に下限を0.02%とし、上限は靭性および溶接性の観点か
ら0.16%とした。First, the reasons for limiting the chemical composition will be described. C: 0.02 to 0.16% The lower limit of the C content is set to 0.02% for obtaining necessary strength and for the precipitation of carbide, and the upper limit is set to 0.16% from the viewpoint of toughness and weldability.
【0013】Si:0.10〜0.5 % Siは製鋼上0.10%が必要であり、0.5 %を超えると母材
(溶接前の被溶接鋼材)の靭性を劣化させる。 Mn:0.70〜1.6 % Mnは母材の強度を確保するために0.7 %以上は必要であ
り、1.6 %を超えると溶接部の靭性を著しく劣化させ
る。Si: 0.10 to 0.5% Si is required to be 0.10% in steel making. If it exceeds 0.5%, the toughness of the base metal (steel material to be welded before welding) is deteriorated. Mn: 0.70 to 1.6% Mn is required to be at least 0.7% in order to secure the strength of the base material, and if it exceeds 1.6%, the toughness of the welded portion is significantly deteriorated.
【0014】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ともに母材から
のAlが溶接金属部へ希釈されることにより溶接金属部の
靭性を劣化させる。上記必須成分のほか、必要に応じて
次の(a)〜(e)の1つまたは2つ以上を適宜追加す
ることができる。Al: 0.01 to 0.08% Al is required to be 0.01% or more for deoxidizing steel, and if added in excess of 0.08%, the toughness of the base material is reduced and Al from the base material is diluted into the weld metal. This degrades the toughness of the weld metal. In addition to the above essential components, one or more of the following (a) to (e) can be added as needed.
【0015】(a)Ni:0.8 %以下 Niは母材の高靭性を保ちつつ強度を上昇させるが、0.80
%を超えて添加するとアンモニアによるSCCを発生し
やすくさせる。なお、好ましくは0.1 〜0.8 %である。 (b)Cr:0.25%以下、Mo:0.08%以下の1種または2
種 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ので上限をそれぞれ0.
25%、0.08%とした。なお、好ましくはCr:0.05〜0.25
%、Mo:0.05〜0.08%である。(A) Ni: 0.8% or less Ni increases the strength while maintaining the high toughness of the base material.
%, SCC is easily generated by ammonia. Preferably, the content is 0.1 to 0.8%. (B) One or two of Cr: 0.25% or less and Mo: 0.08% or less
Species Cr and Mo are effective elements for increasing the strength of the base material.However, if added in large amounts, the toughness is adversely affected.
25% and 0.08%. Preferably, Cr: 0.05 to 0.25
%, Mo: 0.05 to 0.08%.
【0016】(c)Cu:0.35%以下 Cuは固溶強化および析出強化による強度上昇に寄与する
が、0.35%を超えて添加すると靭性を劣化させる。な
お、好ましくは0.05〜0.35%である。 (d)Nb:0.05%以下、V:0.10%以下、Ti:0.025 %
以下 Nb、V、TiはそれぞれNb(C,N)、V(C,N)、Ti(C,N)と
して析出し、オーステナイト粒あるいはフェライト粒の
粒成長を抑制する効果がある。またNbにはγ未再結晶域
を拡大する効果もある。しかし、多量に添加すると、Nb
は溶接熱影響部の靭性を劣化させ、Vは母材および溶接
熱影響部の靭性の低下を招き、TiはTi(CN)が粗大化して
前記効果を失うので、上限をそれぞれ0.05%、0.10%、
0.025 %とした。なお、好ましくはNb:0.005 〜0.05
%、V:0.005 〜0.10%、Ti:0.005 〜0.025 %であ
る。(C) Cu: 0.35% or less Cu contributes to an increase in strength due to solid solution strengthening and precipitation strengthening, but when added in excess of 0.35%, toughness is deteriorated. In addition, it is preferably 0.05 to 0.35%. (D) Nb: 0.05% or less, V: 0.10% or less, Ti: 0.025%
Hereinafter, Nb, V, and Ti are precipitated as Nb (C, N), V (C, N), and Ti (C, N), respectively, and have an effect of suppressing grain growth of austenite grains or ferrite grains. Nb also has the effect of expanding the γ-unrecrystallized region. However, when added in large amounts, Nb
Degrades the toughness of the weld heat affected zone, V decreases the toughness of the base metal and the weld heat affected zone, and Ti makes the Ti (CN) coarse and loses the above effects. %,
0.025%. Preferably, Nb: 0.005 to 0.05
%, V: 0.005 to 0.10%, and Ti: 0.005 to 0.025%.
【0017】(e)B:0.0025%以下 Bは、鋼をγ域に加熱したときγ粒界に偏析しフェライ
ト変態を抑制することで、高強度化に寄与するが、0.00
25%を超えて添加すると著しく硬化して靭性の劣化を招
く虞がある。なお、好ましくは0.0002〜0.0025%であ
る。また、本発明では、不可避的不純物は極力低減する
のが望ましいが、それらのうちP,Sはそれぞれ0.04
%、0.01%まで許容できる。(E) B: 0.0025% or less B contributes to high strength by segregating at the γ grain boundary and suppressing ferrite transformation when the steel is heated to the γ region.
If added in excess of 25%, there is a possibility that the composition will be extremely hardened and cause deterioration in toughness. In addition, it is preferably 0.0002 to 0.0025%. In the present invention, it is desirable to reduce unavoidable impurities as much as possible.
%, 0.01% is acceptable.
【0018】次に、本発明鋼材の組織は、フェライト、
ベイナイト、マルテンサイトの 3相からなりマルテンサ
イトの体積率が1〜15%になる組織でなければならな
い。このような組織とすることで、上述の液体アンモニ
ア、液化天然ガス混載用タンク材で要求される機械的性
質を安定的に満足したものが得られる。マルテンサイト
の体積率が1%未満では強度不足となり、15%超では強
度超過となる。なお、マルテンサイトの体積率は好まし
くは3〜15%である。また、ベイナイトの体積率は、強
度オーバー抑止の観点から50%が以下が好ましい。Next, the structure of the steel material of the present invention is ferrite,
The structure must be composed of three phases, bainite and martensite, and the volume ratio of martensite is 1 to 15%. With such a structure, it is possible to obtain a material that stably satisfies the mechanical properties required for the above-described tank material for loading liquid ammonia and liquefied natural gas. If the volume fraction of martensite is less than 1%, the strength will be insufficient, and if it exceeds 15%, the strength will be excessive. The volume ratio of martensite is preferably 3 to 15%. Further, the volume ratio of bainite is preferably 50% or less from the viewpoint of suppressing over strength.
【0019】次に、製造方法の限定理由について説明す
る。鋼素材(スラブ、ブルーム、ビレット等)を950 〜
1250℃に加熱するのは、完全にオーステナイト化しかつ
均一な整細粒組織とするためである。加熱温度が 950℃
未満ではオーステナイト化が不完全であり、1250℃超で
はγ粒が粗大化し、ともに最終的に十分な靭性が得られ
ない。Next, the reasons for limiting the manufacturing method will be described. 950 to steel materials (slabs, blooms, billets, etc.)
The reason for heating to 1250 ° C. is to completely austenitize and obtain a uniform fine-grained structure. Heating temperature is 950 ℃
If it is less than 1, austenitization is incomplete, and if it exceeds 1250 ° C., γ grains are coarsened, and ultimately sufficient toughness cannot be obtained.
【0020】γ再結晶域で30%以上の圧下率で圧延する
のは、オーステナイトを十分に再結晶させて微細化し、
最終的に得られる靭性を良好なものとするためである。
γ未再結晶域で30%以上の圧下率で圧延するのは、この
圧延で歪エネルギーを蓄積し、フェライトの析出を促す
とともに、フェライト中の炭素を未変態オーステナイト
に十分に排出させて、冷却後にこの未変態オーステナイ
トをベイナイト+マルテンサイトにするためである。こ
こでの圧下率が30%未満であると炭素の未変態オーステ
ナイトへの排出が十分でなく、マルテンサイトの体積率
が1%未満となり所望の機械的性質が得られない。Rolling at a rolling reduction of 30% or more in the γ recrystallization region is performed by sufficiently recrystallizing austenite to make it finer.
This is to improve the toughness finally obtained.
Rolling at a rolling reduction of 30% or more in the γ non-recrystallized region is because this rolling accumulates strain energy, promotes the precipitation of ferrite, and sufficiently discharges carbon in ferrite into untransformed austenite to cool. This is because the untransformed austenite is later converted to bainite + martensite. If the rolling reduction is less than 30%, carbon is not sufficiently discharged into untransformed austenite, and the volume ratio of martensite is less than 1%, so that desired mechanical properties cannot be obtained.
【0021】850 ℃からAr3点の間で圧延を終了するの
は、前記歪エネルギーを十分蓄積させ、かつ圧延集合組
織の発達を抑制するためである。圧延終了温度が850 ℃
超では前記歪エネルギーの蓄積が不十分となり、マルテ
ンサイトの体積率が1%未満となって所望の機械的性質
が得られない。一方、圧延終了温度がAr3点未満では圧
延集合組織が発達してシャルピーのシェルフエネルギー
(v Eshelf)が極端に低下する。The reason for terminating the rolling between 850 ° C. and the three Ar points is to sufficiently store the strain energy and suppress the development of the rolling texture. Rolling end temperature is 850 ℃
If it is more than the above, the accumulation of the strain energy becomes insufficient, and the volume ratio of martensite becomes less than 1%, so that desired mechanical properties cannot be obtained. On the other hand, if the rolling end temperature is lower than the Ar 3 point, the rolling texture develops and the Charpy shelf energy ( v Eshelf) is extremely reduced.
【0022】圧延終了から500 ℃までの冷却速度は、フ
ェライトを析出させYSを低くするために20℃/s以下と
する必要がある。これが20℃/s超では組織がベイナイト
+マルテンサイトとなり、強度が高くなりすぎる。さら
に、500 ℃から冷却停止温度までの冷却速度は第2相に
マルテンサイトを形成させるために、10℃/s以上とし、
かつ、冷却停止温度は450 ℃以下としなければならな
い。The cooling rate from the end of rolling to 500 ° C. needs to be 20 ° C./s or less in order to precipitate ferrite and lower YS. If this exceeds 20 ° C./s, the structure becomes bainite + martensite, and the strength becomes too high. Further, the cooling rate from 500 ° C. to the cooling stop temperature is set to 10 ° C./s or more in order to form martensite in the second phase.
In addition, the cooling stop temperature must be 450 ° C or less.
【0023】圧延後の冷却速度条件を上記のように限定
するだけでは、マルテンサイトの体積率を確実に1〜15
%の範囲内に制御するのは難しく、それを達成するには
前述のように、圧延ないし冷却条件を下記式で定義され
るMVF が1〜15となるように調整してやる必要があるの
であり、これによりはじめてマルテンサイトの体積率を
高精度で1〜15%の範囲内に制御できるようになった。If the cooling rate conditions after rolling are limited only as described above, the volume ratio of martensite can be reduced to 1 to 15 without fail.
% Is difficult to control, and as described above, it is necessary to adjust the rolling or cooling conditions so that the MVF defined by the following equation is 1 to 15, As a result, for the first time, the volume ratio of martensite can be controlled within a range of 1 to 15% with high accuracy.
【0024】 記 MVF = 0.114・Rnxー 0.00616・Tfin − 0.576・CR
X-500 +8 ただし、Rnx:γ未再結晶域での圧下率(%) Tfin :圧延終了温度(℃) CRX-500 :X 〜500 ℃の冷却速度(℃/s),X=MIN(T
fin ,800) また、本発明では、前記冷却停止後にYRが低くなりす
ぎた場合、これを焼戻しすることにより、YRを適値に
上昇させることができる。また、意図的に冷却後のYR
が下がるような圧延〜冷却を行い、焼戻しによって適値
に調整することもできる。焼戻しの温度は、100 ℃未満
では強度変化がほとんどなく、580 ℃超ではYRが80%
超と高くなりすぎるから、100 〜580 ℃とするのが好ま
しい。なお、焼戻しは、圧延後の冷却を450 ℃以下で停
止したのち、室温まで放冷した鋼材に対して行ってもよ
く、また、冷却停止から室温まで放冷される途上の鋼材
に対して行ってもよい。MVF = 0.114 · R nx -0.00616 · T fin -0.576 · CR
X-500 +8, where R nx : rolling reduction in γ non-recrystallized region (%) T fin : rolling end temperature (° C) CR X-500 : X to 500 ° C cooling rate (° C / s), X = MIN (T
(fin , 800) Further, in the present invention, when the YR becomes too low after the cooling is stopped, the YR can be raised to an appropriate value by tempering the YR. In addition, YR after intentionally cooling
Can be adjusted to an appropriate value by rolling and cooling such that the temperature decreases. When the tempering temperature is less than 100 ° C, there is almost no change in strength.
The temperature is preferably 100 to 580 ° C. because it is too high when the temperature is too high. Tempering may be performed on steel that has been cooled to 450 ° C or less after cooling after rolling, and then allowed to cool to room temperature. You may.
【0025】[0025]
【実施例】表1に示す化学組成になる鋼スラブを表2に
示す加熱・圧延・冷却条件(冷却停止温度からは室温ま
で放冷)で処理し、製品板厚8〜40mmの鋼板とした。こ
れらの鋼板について板厚中心から採取したJIS14A号
引張およびJIS4号シャルピー試験片を用いて母材の
強度および靭性を調査した。また、板厚中心部の走査型
電子顕微鏡による組織観察像を画像解析し、組織構成相
の体積率を測定した。その結果を表2に示す。表2よ
り、本発明例では組成および組織が本発明要件を満たし
ているので、所望の機械的性質(YS:355-440MPa、T
S:530-610MPa、vTrs:-80 ℃以下)が達成され、比較
例では強度、 靭性のいずれか一方または両方が不十分で
あった。EXAMPLE A steel slab having the chemical composition shown in Table 1 was treated under the heating, rolling, and cooling conditions shown in Table 2 (cooling from the cooling stop temperature to room temperature) to obtain a steel sheet having a product thickness of 8 to 40 mm. . The strength and toughness of the base material of these steel sheets were examined using JIS No. 14A tensile and JIS No. 4 Charpy test pieces collected from the center of the sheet thickness. Further, the image of the structure observation image of the central part of the sheet thickness with a scanning electron microscope was image-analyzed, and the volume fraction of the constituent phases of the structure was measured. Table 2 shows the results. As can be seen from Table 2, since the composition and the structure of the present invention satisfy the requirements of the present invention, the desired mechanical properties (YS: 355-440 MPa, T
S: 530-610 MPa, vTrs: -80 ° C. or less), and in the comparative example, one or both of strength and toughness were insufficient.
【0026】また、YRが低目であったNo. 7,8に対
しそれぞれ表3の温度条件で焼戻しを施した。焼戻し後
の鋼板(No. 7T,8T)について母材と同様に強度お
よび靭性を調査した。その結果、表3に示すように、10
0 〜580 ℃の適正な温度で焼戻しされたNo. 8Tでは良
好な機械的性質が得られ、焼戻し温度が600 ℃と高すぎ
たNo. 7TではTS低下および/またはYS上昇の度が
過ぎてYRが高くなりすぎた。Nos. 7 and 8 having low YR were tempered under the temperature conditions shown in Table 3, respectively. The strength and toughness of the tempered steel sheets (No. 7T, 8T) were examined in the same manner as the base metal. As a result, as shown in Table 3, 10
In No. 8T tempered at an appropriate temperature of 0 to 580 ° C., good mechanical properties were obtained, and in No. 7T, where the tempering temperature was too high as 600 ° C., the degree of TS reduction and / or YS rise was too high. YR was too high.
【0027】[0027]
【表1】 [Table 1]
【0028】[0028]
【表2】 [Table 2]
【0029】[0029]
【表3】 [Table 3]
【0030】[0030]
【発明の効果】かくして本発明によれば、低温用低降伏
比鋼を非調質法で安定製造できるから、液体アンモニ
ア、液化天然ガス収容用タンク材をより安価に供給でき
るようになるという産業上格段の効果を奏する。As described above, according to the present invention, a low-yield-ratio steel for low temperature can be stably produced by a non-refining method, so that a tank material for containing liquid ammonia and liquefied natural gas can be supplied at lower cost. It has a remarkable effect.
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Claims (4)
%、 Mn:0.70〜1.6 %、 Al:0.01〜0.08%を含有し残部
Fe及び不可避的不純物からなる組成と、フェライト、ベ
イナイトと、マルテンサイトの3相からなりマルテンサ
イトの体積率が1〜15%になる組織とを有することを特
徴とする低温用低降伏比鋼材。1. C: 0.02 to 0.16%, Si: 0.10 to 0.5
%, Mn: 0.70-1.6%, Al: 0.01-0.08%
A low-temperature low-yield-ratio steel material characterized by having a composition comprising Fe and unavoidable impurities, a structure comprising three phases of ferrite, bainite, and martensite, wherein the volume ratio of martensite is 1 to 15%.
%、 Mn:0.70〜1.6 %、 Al:0.01〜0.08%を含有し、さ
らに、下記(a)〜(e)の1つまたは2つ以上を含有
し、残部Fe及び不可避的不純物からなる組成と、フェラ
イト、ベイナイト、マルテンサイトの3相からなりマル
テンサイトの体積率が1〜15%になる組織とを有するこ
とを特徴とする低温用低降伏比鋼材。 記 (a)Ni:0.8 %以下 (b)Cr:0.25%以下、Mo:0.08%以下の1種または2
種 (c)Cu:0.35%以下 (d)Nb:0.05%以下、V:0.10%以下、Ti:0.025 %
以下の1種または2種以上 (e)B:0.0025%以下2. C: 0.02 to 0.16%, Si: 0.10 to 0.5
%, Mn: 0.70 to 1.6%, Al: 0.01 to 0.08%, and further contains one or more of the following (a) to (e), with the balance being Fe and unavoidable impurities. A low-yield-ratio steel for low temperatures, characterized by having a structure comprising three phases of ferrite, bainite, and martensite, wherein the volume ratio of martensite is 1 to 15%. (A) Ni: 0.8% or less (b) Cr: 0.25% or less, Mo: 0.08% or less one or two
Species (c) Cu: 0.35% or less (d) Nb: 0.05% or less, V: 0.10% or less, Ti: 0.025%
One or more of the following (e) B: 0.0025% or less
Mn:0.70〜1.6 %、Al:0.01〜0.08%を含有し、あるい
はさらに、Ni:0.8 %以下、Cr:0.25%以下、Mo:0.08
%以下、Cu:0.35%以下、Nb:0.05%以下、V:0.10%
以下、Ti:0.025 %以下、B:0.0025%以下の1種また
は2種以上を含有する鋼素材を950 〜1250℃に加熱後、
γ再結晶域で30%以上の圧下率で圧延し、さらにγ未再
結晶域で30%以上の圧下率で圧延し、850 ℃からAr3点
の間で圧延を終了して鋼材となし、これを圧延終了から
500 ℃まで20℃/s以下の冷却速度で冷却し、500 ℃か
ら、450 ℃以下とした冷却停止温度まで10℃/s以上の冷
却速度で冷却する方法であって、下記式で定義されるMV
F を1〜15としたことを特徴とする低温用低降伏比鋼材
の製造方法。 記 MVF = 0.114・Rnxー 0.00616・Tfin − 0.576・CR
X-500 +8 ただし、Rnx:γ未再結晶域での圧下率(%) Tfin :圧延終了温度(℃) CRX-500 :X 〜500 ℃の冷却速度(℃/s),X=MIN(T
fin ,800)3. C: 0.02 to 0.16%, Si: 0.10 to 0.5%,
Mn: 0.70 to 1.6%, Al: 0.01 to 0.08%, or Ni: 0.8% or less, Cr: 0.25% or less, Mo: 0.08%
%, Cu: 0.35% or less, Nb: 0.05% or less, V: 0.10%
Hereinafter, a steel material containing one or more of Ti: 0.025% or less and B: 0.0025% or less is heated to 950 to 1250 ° C.
Rolled at a rolling reduction of 30% or more in the γ recrystallized region, further rolled at a rolling reduction of 30% or more in the γ non-recrystallized region, completed rolling between 850 ° C. and three points of Ar to form a steel material, From the end of rolling
A method of cooling to 500 ° C at a cooling rate of 20 ° C / s or less, and cooling from 500 ° C to a cooling stop temperature of 450 ° C or less at a cooling rate of 10 ° C / s or more, defined by the following formula MV
A method for producing a low-yield-ratio steel material for low temperature, wherein F is 1 to 15. Note MVF = 0.114 · R nx -0.00616 · T fin -0.576 · CR
X-500 +8, where R nx : rolling reduction (%) in the γ non-recrystallized region T fin : rolling end temperature (° C) CR X-500 : X to 500 ° C cooling rate (° C / s), X = MIN (T
fin , 800)
焼戻しすることを特徴とする請求項3記載の低温用低降
伏比鋼材の製造方法。4. The method according to claim 3, wherein the steel after cooling is tempered at a temperature of 100 to 580 ° C.
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JP2005048289A (en) * | 2003-07-16 | 2005-02-24 | Jfe Steel Kk | Low yield ratio, high strength and high toughness steel sheet, and its production method |
JP2006520431A (en) * | 2003-02-05 | 2006-09-07 | ユジノール | Method for producing cold rolled ferritic / martensitic duplex steel strip and steel strip obtained thereby |
JP2007023328A (en) * | 2005-07-14 | 2007-02-01 | Kobe Steel Ltd | Method for manufacturing steel sheet with low yield ratio, high strength and high toughness |
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JPS62174322A (en) * | 1985-10-15 | 1987-07-31 | Kobe Steel Ltd | Manufacture of low yield ratio high tension steel plate superior in cold workability |
-
2001
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JPS62174322A (en) * | 1985-10-15 | 1987-07-31 | Kobe Steel Ltd | Manufacture of low yield ratio high tension steel plate superior in cold workability |
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