JP3499126B2 - Steel plate for hull excellent in impact energy absorption capacity and method of manufacturing the same - Google Patents
Steel plate for hull excellent in impact energy absorption capacity and method of manufacturing the sameInfo
- Publication number
- JP3499126B2 JP3499126B2 JP06607398A JP6607398A JP3499126B2 JP 3499126 B2 JP3499126 B2 JP 3499126B2 JP 06607398 A JP06607398 A JP 06607398A JP 6607398 A JP6607398 A JP 6607398A JP 3499126 B2 JP3499126 B2 JP 3499126B2
- Authority
- JP
- Japan
- Prior art keywords
- energy absorption
- steel
- impact energy
- steel plate
- residual
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Heat Treatment Of Steel (AREA)
Description
【0001】[0001]
【発明の属する技術分野】本発明は、板厚8mm以上の
船体用鋼板及びその製造方法に関し、特に、タンカーの
衝突による油流出事故に代表されるような船舶の衝突事
故が万一起きた場合でも、船舶の破壊を最小限にくい止
めることができる衝撃エネルギー吸収能に優れた船体用
鋼板及びその製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for a hull having a plate thickness of 8 mm or more and a manufacturing method thereof, and in particular, even if a collision accident of a ship such as an oil spill accident caused by a collision of a tanker should occur. The present invention relates to a steel plate for a hull excellent in impact energy absorption capable of preventing destruction of a ship with minimum difficulty and a manufacturing method thereof.
【0002】[0002]
【従来の技術】近年、タンカーの衝突、座礁等の海難事
故によって油が流出し、海洋汚染を引き起こして社会問
題となっている。2. Description of the Related Art In recent years, oil has been spilled out due to a marine accident such as a collision of a tanker or a grounding, causing marine pollution and becoming a social problem.
【0003】タンカーの海難事故では、特に6万トン以
上のタンカーでの油流出事故の発生率が高くなってお
り、6万トン以下の小型タンカーの海難での油流出事故
は少ない。In the case of marine accidents involving tankers, the incidence of oil spills in tankers of 60,000 tons or more is particularly high, and the number of oil spills in small tankers of 60,000 tons or less is low.
【0004】これは、小型タンカーの衝突事故では、タ
ンカーの大きさが小さいため衝突したタンカーが動いて
衝撃を弱め船体に穴が開く可能性が低いので、大規模な
油流出事故につながらないものと考えられる。一方、6
万トン以上のタンカーの衝突事故では、タンカーの船体
に穴が開き、大規模な油流出事故を起こして、海洋汚染
(環境汚染)を生じるため大きな社会問題となってい
る。In a small tanker collision accident, it is unlikely that a large-scale oil spill accident will occur because it is unlikely that the tanker that collided will move and weaken the impact to open a hole in the hull due to the small size of the tanker. Conceivable. On the other hand, 6
In the case of a collision accident of a tanker of 10,000 tons or more, a hole opens in the hull of the tanker, causing a large-scale oil spill accident, which causes marine pollution (environmental pollution), which is a major social problem.
【0005】そのため、最近の造船分野においては、タ
ンカーの油流出事故による海洋汚染を防止するために、
万一船舶同士が衝突事故を起こしてもその破壊を最小限
にくい止め、タンカーからの油流出や破損部からの浸水
等の被害を最小限にするための技術が検討されている。Therefore, in the recent field of shipbuilding, in order to prevent marine pollution due to oil spill accidents of tankers,
In the unlikely event of a collision between ships, the technology is being studied to minimize damage to the ship and minimize damage such as oil spills from tankers and flooding from damaged parts.
【0006】その一つの技術として、船体用鋼板自体に
エネルギー吸収能を持たせて、船の衝突時に船体の破壊
を防止することが考えられるが、船体に使用される鋼板
自体の特性として、衝突時におけるエネルギー吸収能が
向上した鋼板は、未だ提案されていない。As one of the techniques, it is considered that the hull steel plate itself has an energy absorbing ability to prevent the hull from being destroyed at the time of a collision of a ship. A steel sheet with improved energy absorption capacity has not been proposed yet.
【0007】衝突時の安全性が要求されるのは船以外で
は、自動車の衝突安全性が良く知られていて、自動車の
衝突時のエネルギー吸収メカニズムについては研究さ
れ、衝突時のエネルギーを吸収する自動車の構造、自動
車用鋼板については種々提案されている。しかしなが
ら、従来、タンカー等の船での衝突時のエネルギー吸収
能に関する鋼材面からの検討は、殆どなされていないの
が現状である。Other than ships that require safety at the time of collision, collision safety of automobiles is well known, and energy absorption mechanism at the time of collision of automobiles has been studied to absorb energy at the time of collision. Various proposals have been made for automobile structures and automobile steel plates. However, the present situation is that the steel material has not been studied so far regarding the energy absorption capacity at the time of collision with a ship such as a tanker.
【0008】即ち、自動車の衝突エネルギーの吸収メカ
ニズムは、圧縮荷重下での座屈モードによりエネルギー
を吸収するものであって、具体的には薄鋼板の一ケ所の
座屈でなく、全体が種々の部分を節にしてゆるやかに座
屈し搭乗者を守る座屈モードとなっている。That is, the collision energy absorption mechanism of an automobile absorbs energy by a buckling mode under a compressive load. Specifically, it is not a single buckling of a thin steel plate, but various types as a whole. The buckling mode is designed to protect the passengers by gently buckling with the sections of.
【0009】これに対して、タンカーの衝突エネルギー
吸収メカニズムは、図1(a)〜(c)にタンカー同士
の衝突の1例を模式図に示すと、(a)に示すように、
タンカー側壁部1に他のタンカーの舳先2が衝突した場
合には、まず(b)に示すように、タンカーの舳先2の
全体がタンカー側壁部の平らな鋼板1にめり込んでくる
ので、鋼板1は大きく曲げ変形を受け、次いで(c)に
示すように、鋼板1は、奥に引き伸ばされて大きく引っ
張られる。この衝突過程で鋼板が破壊(破れる)される
と、タンカーの油流出或は海水の浸水事故となる。On the other hand, the collision energy absorption mechanism of a tanker is shown in FIG. 1 (a)-(c), where one example of collision between tankers is shown in FIG.
When the toe 2 of another tank collides with the side wall 1 of the tanker, first, as shown in (b), the entire toe 2 of the tanker fits into the flat steel plate 1 of the side wall of the tanker. Undergoes large bending deformation, and as shown in (c), the steel sheet 1 is stretched deeply and greatly stretched. If the steel plate is broken (broken) during this collision process, an oil spill in the tanker or seawater inundation accident will occur.
【0010】したがって、タンカー同士の衝突時に油流
出等を生じさせないためには、衝突時の初期段階で鋼
板が大きく曲げられた時に、その曲げに耐えられるこ
と、次いで曲がっていない部分が大きく引き伸ばされ
引張り変形を起こすこととなるが、その部分が均一に伸
びて破断しないことが必要である。Therefore, in order to prevent oil outflow or the like when the tankers collide with each other, when the steel sheet is largely bent at the initial stage of collision, the steel sheet can withstand the bending, and then the unbent portion is greatly stretched. Although it causes tensile deformation, it is necessary that the part should stretch uniformly and not break.
【0011】このように、タンカーの衝突の場合は、変
形を起こしてもかまわないが、切れて破れなければ油流
出事故或は浸水事故とはならない。In this way, in the case of a tanker collision, deformation may occur, but if it does not break and break, an oil spill accident or a flood accident will not occur.
【0012】以上述べたように、自動車と船とは、衝突
エネルギーの吸収メカニズムが全く異なっているもので
あり、さらに、船の場合は鋼板を溶接することが必須で
あり、船体の破壊に深刻な影響を及ぼす溶接継手部の強
度も確保されねばならない。[0012] As described above, automobiles and ships have completely different collision energy absorption mechanisms, and in the case of ships, it is essential to weld steel plates, which seriously damages the hull. The strength of the welded joint, which has a negative effect, must be ensured.
【0013】例えば、船舶用厚鋼板の強度は溶接性の観
点から350〜550MPaであるが、自動車の衝突安
全性用部材の薄鋼板の強度は、600〜1000MPa
が一般的であり、高強度のために溶接性が悪いため、ア
ーク溶接を多用する造船では溶接部熱影響部の軟化問題
と溶接割れ問題の両方から使用不可能である。For example, the strength of the thick steel plate for ships is 350 to 550 MPa from the viewpoint of weldability, but the strength of the thin steel plate of the collision safety member for automobiles is 600 to 1000 MPa.
However, because of its high strength and poor weldability, it cannot be used in shipbuilding where arc welding is frequently used due to both the softening problem of the heat affected zone of the weld zone and the weld cracking problem.
【0014】又、自動車の衝突安全性が要求される部材
に適用される鋼板は薄鋼板であるから、この薄鋼板に関
する技術を厚手鋼板に適用しても、冷却速度確保などの
観点から、板厚方向の均一性を保つのが難しい。そのた
め、造船用に使用されている板厚8mm以上のサイズの
もので衝突時の破壊防止を考慮した船体用鋼板は従来存
在していない。Further, since a steel plate applied to a member which is required to have collision safety of an automobile is a thin steel plate, even if the technique relating to this thin steel plate is applied to a thick steel plate, it is necessary to secure a cooling speed and the like. It is difficult to maintain uniformity in the thickness direction. For this reason, there has been no hull steel plate having a plate thickness of 8 mm or more used for shipbuilding and considering the prevention of damage during collision.
【0015】このような理由で、鋼板に要求される特性
が全く異なる自動車用の鋼板をそのまま船体用鋼板とし
て使用することはできないものである。For these reasons, steel sheets for automobiles having completely different properties required for steel sheets cannot be used as they are as steel sheets for hulls.
【0016】[0016]
【発明が解決しようとする課題】本発明は、タンカーの
衝突時に船体の破壊を最小限にすることができる衝撃エ
ネルギー吸収能に優れた船体用鋼板及びその製造方法を
提供することにある。SUMMARY OF THE INVENTION It is an object of the present invention to provide a hull steel sheet excellent in impact energy absorbing ability and capable of minimizing the damage of the hull at the time of collision of a tanker, and a manufacturing method thereof.
【0017】[0017]
【課題を解決するための手段】本発明者は、衝突時の大
きなエネルギーを吸収して船体の破壊を防止する衝撃エ
ネルギー吸収能に優れた船体用鋼板としては、鋼板が下
記の性質を備えていることが必要であることを見い出し
た。
(イ) 曲げ部が加工硬化を充分にして、その後の変形
が平行部に分担されること。
(ロ)特に溶接継手部において主として起り易い曲げ部
が歪みを受けて脆化して、脆性破壊を生じないこと。
(ハ)平行部が伸ばされる際、延性亀裂の発生抵抗が大
きいこと。
(ニ)平行部が伸ばされる際、延性亀裂の伝播抵抗が大
きいこと。
(ホ)平行部が伸ばされる際、高い強度と伸びを有する
こと。
(ヘ)平行部が伸ばされる際、充分な加工硬化をするこ
と。DISCLOSURE OF THE INVENTION The inventors of the present invention have found that a steel plate for a hull excellent in impact energy absorbing ability for absorbing a large amount of energy at the time of collision and preventing the destruction of the hull has the following properties. Found that it was necessary to stay. (B) The bending part should be sufficiently work-hardened and the subsequent deformation should be shared by the parallel part. (B) In particular, in the welded joint portion, the bending portion, which is likely to occur mainly, is not embrittled by being strained to cause brittle fracture. (C) When the parallel part is stretched, the ductile crack initiation resistance is large. (D) The ductile crack has a large propagation resistance when the parallel portion is stretched. (E) When the parallel part is stretched, it has high strength and elongation. (F) Sufficient work hardening when the parallel part is stretched.
【0018】本発明は、上記(イ)〜(ヘ)の性質の
内、特に衝突時のエネルギー吸収能に大きく影響を与え
る(ホ)の特性を向上させた鋼板を得るため、鋼の成分
及び鋼の組織等について研究し、その結果、厚鋼板特有
の現象として、少なくとも鋼板の表裏層のみに残留γを
存在させれば効果的に衝撃エネルギー吸収能が改善でき
ることを知見し本発明を完成した。According to the present invention, in order to obtain a steel sheet having improved characteristics of (e) among the above-mentioned properties (a) to (f), which has a great influence on the energy absorption capacity at the time of collision, the composition of the steel and The present invention was completed by studying the structure of steel and the like, and as a result, as a phenomenon peculiar to thick steel plates, it was found that impact energy absorption capacity can be effectively improved if residual γ is present only in at least the front and back layers of the steel plate. .
【0019】本発明の要旨は、以下の通りである。The gist of the present invention is as follows.
【0020】 (1) 重量%で、
C:0.05〜0.2%、
Si:0.05〜2.0%、
Mn:0.1〜2.0%、
Al:0.001〜0.1%、
を含有し、かつ炭素当量Ceq(=C+Mn/6+(C
u+Ni)/15+(V+Mo+Cr)/5+5B)
(%)が0.42(%)以下であり、残部Feおよび不
可避不純物からなる板厚8mm以上の鋼板であって、該
鋼板の少なくとも板厚の1/8以上の表裏層をフェライ
ト相とし、かつ、そのフェライト相中に、面積率で1.
0〜20%、粒径が5μm以下の残留γを含むことを特
徴とする衝撃エネルギー吸収能に優れた船体用鋼板。(1) In% by weight, C: 0.05 to 0.2%, Si: 0.05 to 2.0%, Mn: 0.1 to 2.0%, Al: 0.001 to 0 0.1%, and the carbon equivalent Ceq (= C + Mn / 6 + (C
u + Ni) / 15 + (V + Mo + Cr) / 5 + 5B)
(%) Is not less 0.42% or less, a thickness less than 8mm steel plates and the balance Fe and unavoidable impurities, ferrite and at least a thickness of 1/8 or more the front and back layers of the steel plate
And an area ratio of 1.
A steel plate for a hull excellent in impact energy absorption, characterized by containing residual γ of 0 to 20% and a particle size of 5 μm or less .
【0021】(2) さらに、重量%で、Nb:0.0
01〜0.1%V:0.001〜0.1%、Ti:0.
001〜0.05%、Ta:0.001〜0.1%、C
r:0.01〜1.0%、Ni:0.01〜1.0%、
Mo:0.01〜1.0%、Cu:0.01〜1.0%
のうちの1種又は2種以上を含有することを特徴とする
前記(1)に記載の衝撃エネルギー吸収能に優れた船体
用鋼板。(2) Further, in% by weight, Nb: 0.0
01-0.1% V: 0.001-0.1%, Ti: 0.
001-0.05%, Ta: 0.001-0.1%, C
r: 0.01 to 1.0%, Ni: 0.01 to 1.0%,
Mo: 0.01-1.0%, Cu: 0.01-1.0%
1 or 2 or more of the above are contained, The hull steel plate excellent in impact energy absorption ability as described in said (1) characterized by the above-mentioned.
【0022】(3) さらに、重量%で、Ca:0.0
001〜0.01%、Mg:0.0001〜0.01
%、REM:0.001〜0.05%
B:0.0001〜0.001%のうちの1種又は2種
以上を含有することを特徴とする前記(1)または
(2)に記載の板厚8mm以上の衝撃エネルギー吸収能
に優れた船体用鋼板。(3) Further, in wt%, Ca: 0.0
001-0.01%, Mg: 0.0001-0.01
%, REM: 0.001 to 0.05% B: 0.0001 to 0.001%, and one or more kinds thereof are contained, (1) or (2) described above. Steel plate for hulls with a plate thickness of 8 mm or more and excellent in absorbing impact energy.
【0023】(4) 重量%で、C:0.05〜0.2
%、Si:0.05〜2.0%、Mn:0.1〜2.0
%、Al:0.001〜0.1%、を含有し、かつ炭素
当量Ceq(=C+Mn/6+(Cu+Ni)/15+
(V+Mo+Cr)/5+5B)(%)が0.42
(%)以下であり、残部Feおよび不可避不純物からな
る鋳片を、直接もしくは加熱後、熱間圧延を行い、Ar
3+100℃〜Ar 3−50℃の温度範囲内で仕上げ圧延
を終了し、その後、Ar3もしくは仕上圧延温度のいず
れか低い方の温度からAr1+100℃〜Ar1℃の温度
まで冷却速度2℃/s以下で冷却し、そして、さらに冷
却速度10℃/s以上で冷却し、250〜450℃の温
度範囲で冷却を停止することを特徴とする衝撃エネルギ
ー吸収能に優れた船体用鋼板の製造方法。(4) C: 0.05 to 0.2 in% by weight
%, Si: 0.05 to 2.0%, Mn: 0.1 to 2.0
%, Al: 0.001-0.1%, and carbon equivalent Ceq (= C + Mn / 6 + (Cu + Ni) / 15 +
(V + Mo + Cr) / 5 + 5B) (%) is 0.42
(%) Or less, and a slab composed of the balance Fe and unavoidable impurities is hot-rolled directly or after heating, Ar
3 + 100 ° C. The finish rolling was terminated at a temperature range of to Ar 3 -50 ° C., then the cooling rate 2 ℃ from any lower temperature of Ar 3 or the finish rolling temperature to a temperature of Ar 1 + 100 ℃ ~Ar 1 ℃ / S or less, and further cooling at a cooling rate of 10 ° C / s or more, and stopping the cooling in the temperature range of 250 to 450 ° C, the production of a steel plate for a hull excellent in impact energy absorption capacity. Method.
【0024】(5) 鋳片が、さらに重量%で、Nb:
0.001〜0.1%
V:0.001〜0.1%、Ti:0.001〜0.0
5%、Ta:0.001〜0.1%、Cr:0.01〜
1.0%、Ni:0.01〜1.0%、Mo:0.01
〜1.0%、Cu:0.01〜1.0%のうちの1種又
は2種以上を含有することを特徴とする前記(4)に記
載の衝撃エネルギー吸収能に優れた船体用鋼板の製造方
法。(5) The slab further contains Nb:
0.001-0.1% V: 0.001-0.1%, Ti: 0.001-0.0
5%, Ta: 0.001 to 0.1%, Cr: 0.01 to
1.0%, Ni: 0.01 to 1.0%, Mo: 0.01
To 1.0%, Cu: 0.01 to 1.0%, and one or more of them are contained, and the steel sheet for a hull excellent in impact energy absorption capacity according to the above (4). Manufacturing method.
【0025】(6) 鋳片が、さらに重量%で、Ca:
0.0001〜0.01%、Mg:0.0001〜0.
01%、REM:0.001〜0.05%
B:0.0001〜0.001%のうちの1種又は2種
以上を含有することを特徴とする前記(4)または
(5)に記載の衝撃エネルギー吸収能に優れた船体用鋼
板の製造方法。(6) The cast slab further contains Ca:
0.0001-0.01%, Mg: 0.0001-0.
01%, REM: 0.001 to 0.05% B: 0.0001 to 0.001%, and 1 or 2 or more of the above (4) or (5) is contained. Method for manufacturing steel plate for hull excellent in impact energy absorption capacity.
【0026】[0026]
【発明の実施の形態】以下本発明について詳細に説明す
る。BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
【0027】本発明者は、船体の衝撃エネルギー吸収能
と鋼材の機械的特性の関係を調査した。The inventor of the present invention investigated the relationship between the impact energy absorption capacity of a ship and the mechanical properties of steel.
【0028】その結果、衝撃エネルギー吸収能(EA)
と鋼材の機械的特性の関係として、鋼材の伸び特性(E
L)と強度特性(YP、TS)の両者が優れていること
が衝撃エネルギー吸収能(EA)を向上させるために必
要であることを見い出した。なお、機械的特性は、日本
海事協会鋼船規則集にあるU1号試験片を用いて評価し
た。As a result, impact energy absorption capacity (EA)
And the mechanical properties of steel, the elongation properties (E
It has been found that both L) and strength properties (YP, TS) are required to be excellent in order to improve impact energy absorption capacity (EA). The mechanical properties were evaluated using the U1 test piece in the Japan Maritime Association Steel Ship Regulations.
【0029】一般に材料が破断するまでのエネルギー吸
収は、正確には、応力をσ、変位をεとすると
∫σdε
で求まるが、これを鋼板に当てはめて、応力としてフロ
ーストレス:(YP+TS)/2、変位として破断伸
び:ELを用いれば、近似的にエネルギー吸収は、
(YP+TS)×EL/2
と表わせる。船体衝突時の船側変形挙動が、部材の引張
特性に支配されることは、T.Ishikawaらが1
5th International Confere
nce on OMAE,1996,Book No.
G00987−1996において破壊の数値シミュレー
ションで示したとおりであり、したがって、上記の指標
は、船体衝突時の船体用鋼板のエネルギー吸収能と対応
関係にあるといえる。したがって、衝撃エネルギー吸収
能EAは、
EA=(YP+TS)/2×EL
で表示できる。Generally, the energy absorption until the material breaks can be accurately calculated by ∫σdε, where σ is the stress and ε is the displacement, but this is applied to the steel plate and the flow stress as the stress: (YP + TS) / 2 If the elongation at break: EL is used as the displacement, the energy absorption can be approximately expressed as (YP + TS) × EL / 2. The fact that the ship-side deformation behavior at the time of a ship collision is governed by the tensile properties of the members is described in T.W. Ishikawa et al. 1
5th International Confere
nce on OMAE, 1996, Book No.
This is as shown in the numerical simulation of fracture in G00987-1996. Therefore, it can be said that the above-mentioned index has a corresponding relationship with the energy absorption capacity of the hull steel sheet during a hull collision. Therefore, the impact energy absorption capacity EA can be expressed as EA = (YP + TS) / 2 × EL.
【0030】現行の一般に用いられている船体用鋼板の
衝撃エネルギー吸収能(EA)を上記式に従って調査し
たところ、EAは100MPa程度であった。本発明の
目標は、この従来の鋼板の衝撃エネルギー吸収能(E
A)よりも少なくとも約20%以上大きい、即ち、衝撃
エネルギー吸収能120MPa以上を有する鋼板を得る
ことである。When the impact energy absorption capacity (EA) of the currently commonly used steel plates for hulls was investigated according to the above formula, the EA was about 100 MPa. The goal of the present invention is to obtain the impact energy absorption capacity (E) of this conventional steel sheet.
It is to obtain a steel sheet having a shock energy absorption capacity of 120 MPa or more, which is at least about 20% larger than that of A).
【0031】衝撃エネルギー吸収能は、前記式から明ら
かなように伸び特性ELが大きな影響を与える。そのた
め本発明においては鋼板の伸びを確保するために、鋼の
組織をフェライト相(α)のマトリックスとした。とこ
ろが、マトリックスがフェライト相(α)の鋼は、強度
特性である降伏点(YP)と引張り強さ(TS)が低い
ため、衝撃エネルギー吸収能を高くすることはできな
い。しかも、強度特性であるYP、TSは、伸び特性E
Lとは相反する性質であって、両者を同時に向上させる
ことは一般に困難とされている。As is clear from the above equation, the elongation characteristic EL has a great influence on the impact energy absorption capacity. Therefore, in the present invention, the structure of the steel is a matrix of the ferrite phase (α) in order to secure the elongation of the steel sheet. However, steel having a ferrite phase (α) as a matrix has a low yield point (YP) and tensile strength (TS), which are strength characteristics, and therefore cannot have high impact energy absorption capability. Moreover, the strength characteristics of YP and TS are
It is a property that is contradictory to L, and it is generally difficult to improve both properties at the same time.
【0032】つまり、マトリックスをフェライト相の鋼
とすることによって、伸び特性が改善されるが、伸びが
向上すれば引張り強さ等の強度特性が低下するので、マ
トリックスをフェライト相の鋼とするだけでは、衝撃エ
ネルギー吸収能の向上に限度がある。That is, when the matrix is a ferrite phase steel, the elongation characteristics are improved, but if the elongation is improved, the strength characteristics such as tensile strength are deteriorated. Therefore, only the ferrite phase steel is used as the matrix. Then, there is a limit to the improvement of impact energy absorption capacity.
【0033】そこで、伸び特性を確保しつつ、強度特性
である降伏点YP+引張強さTSを増加させる手段とし
て、フェライト相中に残留γを微細に分散させることに
着目し、残留γの分散状態等について研究した。Therefore, paying attention to finely dispersing the residual γ in the ferrite phase as a means for increasing the yield point YP + tensile strength TS which is the strength characteristic while securing the elongation characteristic, the dispersion state of the residual γ And so on.
【0034】薄鋼板において強度、伸びバランスを向上
させる技術としては残留γ鋼が知られているが、この技
術を板厚8mm以上の厚手鋼板に適用しても、冷却速度
確保等の観点から板厚方向の均一性を保つことが困難で
あって、薄鋼板についての技術をそのまま適用し得な
い。そこで、本発明では厚手鋼板の特有の問題となる板
厚方向の残留γの存在を制御することにより、伸び特性
を維持したままで強度特性を向上させることについて試
験した。その結果、少なくとも鋼板の表裏層のみに残留
γを存在させれば強度特性が改善できることを知見し
た。Residual γ steel is known as a technique for improving the strength and elongation balance in a thin steel plate, but even if this technique is applied to a thick steel plate having a plate thickness of 8 mm or more, the plate will be cooled from the viewpoint of securing a cooling rate. It is difficult to maintain the uniformity in the thickness direction, and the technique for thin steel sheets cannot be applied as it is. Therefore, in the present invention, by controlling the existence of residual γ in the plate thickness direction, which is a problem peculiar to thick steel plates, tests were conducted to improve the strength properties while maintaining the elongation properties. As a result, it was found that the strength characteristics can be improved if residual γ is present only in at least the front and back layers of the steel sheet.
【0035】本発明では、残留γの存在を特定するため
に、残留γ量(面積率)の測定方法を以下のようにして
行った。In the present invention, in order to identify the presence of residual γ, the method of measuring the amount of residual γ (area ratio) was performed as follows.
【0036】まず、鋼板表面からの距離aの位置のZ断
面を切断或は切削等により形成し、次いで、Z断面をエ
ッチングし、エッチング組織を顕微鏡で観察し、残留γ
が存在していることを確認した。次いで、Z断面の全体
に占める残留γの面積率を測定した。測定は、ポイント
カウンティングやコンピュータによる画像解析などで行
うことができる。First, the Z section at a position a from the surface of the steel sheet is formed by cutting or cutting, and then the Z section is etched and the etched structure is observed with a microscope to find the residual γ.
Was confirmed to exist. Next, the area ratio of residual γ in the entire Z section was measured. The measurement can be performed by point counting or image analysis by a computer.
【0037】上記測定方法に従って、鋼板表面からの距
離aの位置を変更しながら、残留γの面積率を測定する
と図2に示すように、鋼板表面からの距離aと残留γ面
積率Fとの関係の図が得られる。When the area ratio of the residual γ is measured while changing the position of the distance a from the surface of the steel sheet according to the above measuring method, the distance a from the surface of the steel sheet and the residual γ area ratio F are measured as shown in FIG. A diagram of the relationship is obtained.
【0038】このようにして、板厚tが異なる種々の鋼
板について鋼板表面からの距離aと残留γ面積率との関
係を測定した。その測定結果に基づき、距離/板厚(a
/t)と残留γ面積率F(%)との関係を求めると図3
に示すようになった。In this way, the relationship between the distance a from the steel sheet surface and the residual γ area ratio was measured for various steel sheets having different sheet thickness t. Based on the measurement results, distance / plate thickness (a
/ T) and the residual γ area ratio F (%) are calculated as shown in FIG.
It came to be shown in.
【0039】次いで、鋼板の強度特性を改善するには少
なくとも1%の残留γが必要であり、そしてその最大値
は20%が限度であるから、残留γが1〜20%含まれ
る領域の最大厚みをaγとし、最大厚みaγと衝撃エネ
ルギー吸収能EAとの関係を求めた。Next, in order to improve the strength characteristics of the steel sheet, at least 1% of residual γ is necessary, and the maximum value is 20%, so that the maximum of the region containing 1 to 20% of residual γ is required. The thickness was defined as aγ, and the relationship between the maximum thickness aγ and the impact energy absorption capacity EA was determined.
【0040】図4は、最大厚みのaγと衝撃エネルギー
吸収能EAとの関係を示す図である。FIG. 4 is a diagram showing the relationship between the maximum thickness aγ and the impact energy absorption capacity EA.
【0041】図4に示すように、aγが板厚の1/8
(=0.125)以上となると衝撃エネルギー吸収能
が、本発明で目標とする120MPa以上となることを
見い出した。As shown in FIG. 4, aγ is 1/8 of the plate thickness.
It has been found that when (= 0.125) or more, the impact energy absorption capacity is 120 MPa or more, which is the target of the present invention.
【0042】このように、鋼板中に残留γを存在させる
ためには、オーステナイト安定化元素であるCを多く含
有する鋼材を用い、加熱して高温域で安定なγ相を形成
させ、その後これを急冷することにより常温で安定な残
留γとするものである。急冷の限界冷却速度は10℃/
sであって、それ未満では残留γを生成し得ない。As described above, in order to allow the residual γ to exist in the steel sheet, a steel material containing a large amount of austenite stabilizing element C is used and heated to form a stable γ phase in a high temperature region, and thereafter, Is rapidly cooled to a stable residual γ at room temperature. Limiting cooling rate of rapid cooling is 10 ℃ /
s, below which no residual γ can be produced.
【0043】以上の試験結果から明らかなように、鋼成
分を選択し、少なくとも鋼板板厚の1/8以上の表裏層
に面積率で1.0〜20%の残留γを含有させれば、衝
撃エネルギー吸収能の高い鋼板が得られることが確認で
きた。As is clear from the above test results, if the steel components are selected and at least 1/8 or more of the steel plate thickness contains the residual γ in an area ratio of 1.0 to 20%, It was confirmed that a steel plate with high impact energy absorption capacity was obtained.
【0044】また、残留γをフェライトマトリックス中
に微細分散させることにより耐延性破壊性能をも向上さ
せることができる。つまり、一般に鋼材の延性破壊のメ
カニズムは、フェライトマトリックス中に硬い第二相が
存在した鋼材を引き伸ばすと、硬い第二相は変形せずに
第二相の周りが剥がれて、第二相の周りに穴(ボイド)
が生じ、鋼材中に第二相を核として多数のボイドが発生
することとなる。そして、更に引き伸ばすと多数のボイ
ドが合体し、目に見える亀裂となり、次いで、この亀裂
が伝播して延性破壊が生じるというメカニズムが通常で
ある。Further, by finely dispersing the residual γ in the ferrite matrix, the ductile fracture resistance can be improved. That is, generally, the mechanism of ductile fracture of steel materials is that when a steel material in which a hard second phase was present in the ferrite matrix is stretched, the hard second phase does not deform and peels around the second phase, Hole (void)
Occurs, and a large number of voids are generated in the steel material with the second phase as the nucleus. Then, when it is further stretched, a large number of voids are united to form a visible crack, and then the crack propagates to cause ductile fracture.
【0045】ところが、本発明のようにボイドの発生核
となる残留γを小さいコロニ−(固り)として微細に分
散させておくと、ボイドの発生を抑えて良く伸び、切れ
にくくなる。However, when the residual .gamma., Which is a nucleus for generating voids, is finely dispersed as a small colony (hardness) as in the present invention, the generation of voids is suppressed, the elongation is good, and it becomes difficult to cut.
【0046】つまり、微細に分散した残留γの占積率が
大きくなると、延性亀裂発生限界歪を低下させ、また鋼
板が降伏してもα相の変形を拘束し、鋼板の強度を上昇
させる効果がある。That is, when the space factor of the finely dispersed residual γ is increased, the ductile crack initiation critical strain is lowered, and even if the steel plate yields, the deformation of the α phase is restricted and the strength of the steel plate is increased. There is.
【0047】したがって、衝撃エネルギー吸収能を向上
させ、かつ延性破壊を防止するためには、残留γの寸法
を円相当平均粒径で5μm以下、特に3μm以下にする
ことが好ましい。Therefore, in order to improve the impact energy absorption capacity and prevent ductile fracture, the size of the residual γ is preferably 5 μm or less, particularly 3 μm or less in terms of the circle-equivalent mean particle size.
【0048】次に、本発明鋼の成分の限定理由を説明す
る。Next, the reasons for limiting the components of the steel of the present invention will be explained.
【0049】Cは、高温域でのγ相安定化元素であると
共に鋼板の強度を上昇させるのに最も安価かつ有効な元
素であり、残留γ相形成及び強度確保のためには0.0
5%以上が必要であるが、0.2%超となると溶接性、
溶接継手靭性を劣化させるので好ましくない。このた
め、Cは0.05〜0.2%とした。なお、Cは0.0
5〜0.17%とすることが好ましい。C is an element that stabilizes the γ phase in the high temperature range and is the cheapest and most effective element for increasing the strength of the steel sheet, and is 0.0 in order to form the residual γ phase and secure the strength.
5% or more is required, but if it exceeds 0.2%, weldability,
It is not preferable because it deteriorates the toughness of the welded joint. Therefore, C is set to 0.05 to 0.2%. Note that C is 0.0
It is preferably set to 5 to 0.17%.
【0050】Siは、鋼の脱酸及び残留γ相の生成を容
易にする元素として0.05%以上必要であるが、2.
0%を超えると溶接性、溶接継手靭性を劣化させるの
で、0.05〜2.0%とした。Si is required to be 0.05% or more as an element that facilitates deoxidation of steel and formation of residual γ phase.
If it exceeds 0%, the weldability and the weld joint toughness are deteriorated, so the content was made 0.05 to 2.0%.
【0051】Mnは、鋼の靭性を確保し、かつ強度を上
昇させるために0.1%以上必要であるが、2.0%超
となると溶接性を劣化させるので、0.1〜2.0%と
した。Mn is required to be 0.1% or more in order to secure the toughness of steel and to increase the strength, but if it exceeds 2.0%, the weldability is deteriorated, so 0.1-2. It was set to 0%.
【0052】Alは、鋼の脱酸元素として最も重要な元
素であり0.001%以上必要であるが、0.1%超で
溶接性を劣化させるので、0.001〜0.1%とし
た。Al is the most important element as a deoxidizing element of steel and is required to be 0.001% or more, but if it exceeds 0.1%, the weldability is deteriorated, so 0.001 to 0.1% is set. did.
【0053】本発明の第1発明の鋼は以上を基本成分と
するが、現状の製鋼技術で不可避的に含有される不純物
元素であるPは、特に規制する必要はないが、靭性、溶
接性確保の観点から0.04%以下とすることが好まし
く、0.01%以下(0%を含む)であれば更に良い。
また、同様に不純物元素であるS及びNについては、そ
れぞれ靭性、伸び確保の観点から、0.25%以下(0
%を含む)及び0.1%以下(0%を含む)とすること
が好ましい。しかし、これらの不純物元素は衝撃エネル
ギー吸収能の観点からいずれも低い方が望ましい。た
だ、NについてはTi等の元素と共存して溶接性を改善
する場合があり、その場合は、例えば0.002〜0.
006%の範囲に制御されることがある。Although the steel of the first invention of the present invention has the above-mentioned basic components, P, which is an impurity element inevitably contained in the current steelmaking technology, does not have to be particularly restricted, but toughness and weldability are not required. From the viewpoint of securing, it is preferably 0.04% or less, and more preferably 0.01% or less (including 0%).
Similarly, S and N, which are impurity elements, are each 0.25% or less (0
%) And 0.1% or less (including 0%). However, it is desirable that these impurity elements are low in terms of impact energy absorption ability. However, N may coexist with elements such as Ti to improve weldability, and in that case, for example, 0.002 to 0.
It may be controlled in the range of 006%.
【0054】本発明は、上記基本成分に、更に母材の強
化成分である選択元素を1種又は2種以上添加すること
を第2発明とする。A second aspect of the present invention is to add one or more selected elements, which are reinforcing components of the base material, to the above basic components.
【0055】強化成分である選択元素の限定理由につい
て説明する。The reasons for limiting the selection element that is the reinforcing component will be described.
【0056】Nbは、0.001%以上の添加により母
材の強度上昇に有効であるが、0.1%超となると溶接
性を劣化させるので、0.001〜0.1%とした。Addition of 0.001% or more of Nb is effective for increasing the strength of the base material, but if it exceeds 0.1%, the weldability deteriorates, so Nb was made 0.001 to 0.1%.
【0057】Vは、0.001%以上の添加により母材
の強度上昇に有効であるが、0.1%超となると溶接性
を劣化させるので、0.001〜0.1%とした。V is effective in increasing the strength of the base metal when added in an amount of 0.001% or more, but if it exceeds 0.1%, the weldability deteriorates, so V was made 0.001 to 0.1%.
【0058】Tiは、0.001%以上の添加で複合酸
化物、Ti窒化物等を形成して母材の強度上昇に有効で
あるが、0.05%超となるとHAZ靭性の低下を招き
溶接性を劣化させるので、0.001〜0.05%とし
た。When Ti is added in an amount of 0.001% or more, it forms a complex oxide, a Ti nitride, etc. and is effective in increasing the strength of the base material. However, if it exceeds 0.05%, the HAZ toughness deteriorates. Since the weldability is deteriorated, it is set to 0.001 to 0.05%.
【0059】Taは、0.001%以上の添加により母
材の強度上昇に有効であるが、0.1%超となると溶接
性を劣化させるので、0.001〜0.1%とした。Addition of 0.001% or more of Ta is effective for increasing the strength of the base material, but if it exceeds 0.1%, the weldability is deteriorated, so 0.001 to 0.1% was made.
【0060】Crは、0.01%以上の添加で焼入れ性
を向上し母材の強度確保に有効であるが、1.0%超と
なると溶接性を劣化させると共に低温靭性をも劣化させ
るので、0.1〜1.0%とした。When Cr is added in an amount of 0.01% or more, it improves the hardenability and is effective in securing the strength of the base metal. However, if it exceeds 1.0%, it deteriorates the weldability and the low temperature toughness. , 0.1 to 1.0%.
【0061】Niは、0.01%以上の添加で母材の靭
性、強度向上に有効であるが、1.0%超となると溶接
性を劣化させると共にコスト高となるので、0.01〜
1.0%とした。When Ni is added in an amount of 0.01% or more, it is effective in improving the toughness and strength of the base material. However, if it exceeds 1.0%, the weldability is deteriorated and the cost is increased.
It was 1.0%.
【0062】Moは、0.01%以上の添加で、母材の
焼入れ性を向上し強度確保に有効であるが、1.0%超
となると溶接性を劣化させると共に低温靭性を劣化させ
るので、0.01〜1.0%とした。When Mo is added in an amount of 0.01% or more, it is effective in improving the hardenability of the base material and ensuring the strength, but if it exceeds 1.0%, it deteriorates the weldability and the low temperature toughness. , 0.01 to 1.0%.
【0063】Cuは、0.01%以上の添加で母材の強
度上昇に有効であるが、1.0%超で熱間割れが生じや
すくなり、溶接性をも劣化させるので、0.01〜1.
0%とした。Cu is effective for increasing the strength of the base material when added in an amount of 0.01% or more, but if it exceeds 1.0%, hot cracking tends to occur and the weldability is deteriorated. ~ 1.
It was set to 0%.
【0064】また、本発明では、母材の伸び改善のため
に選択元素を1種又は2種以上添加することを第3発明
とする。Further, in the present invention, the third invention is to add one or more selective elements in order to improve the elongation of the base material.
【0065】伸び改善のための選択元素の限定理由につ
いて説明する。The reasons for limiting the selection elements for improving elongation will be described.
【0066】Caは、0.0001%以上の添加で伸び
向上に有害なSを固定し、伸び改善に有効であるが、
0.01%超となると溶接性を劣化するので、0.00
01〜0.01%とした。When Ca is added in an amount of 0.0001% or more, it fixes S, which is harmful to the elongation improvement, and is effective in improving the elongation.
If it exceeds 0.01%, the weldability will deteriorate, so 0.00
It was set to 01 to 0.01%.
【0067】Mgは、0.0001%以上の添加で伸び
向上に有害なSを固定し、伸び改善に有効であるが、
0.01%超となると溶接性を劣化するので、0.00
01〜0.01%とした。When Mg is added in an amount of 0.0001% or more, it fixes S, which is harmful for improving elongation, and is effective in improving elongation.
If it exceeds 0.01%, the weldability will deteriorate, so 0.00
It was set to 01 to 0.01%.
【0068】REM(希土類元素)は、0.001%以
上の添加で伸び向上に有害なSを固定し、伸び改善に有
効であるが、0.05%超で溶接性を劣化し、かつ高価
であるから、0.001〜0.05%とした。REM (rare earth element) fixes 0.001% or more of S to fix S which is detrimental to elongation improvement and is effective for elongation improvement, but if it exceeds 0.05%, weldability deteriorates and it is expensive. Therefore, it was set to 0.001 to 0.05%.
【0069】Bは、焼入性を改善する元素であって、
0.0001%以上で有効であるが、0.001%を超
えると溶接性を劣化するので、0.0001〜0.00
1%とした。B is an element for improving hardenability,
0.0001% or more is effective, but if it exceeds 0.001%, the weldability deteriorates, so 0.0001 to 0.00
It was set to 1%.
【0070】更に、本発明鋼では、下記式に従う炭素当
量(Ceq)は、溶接部の硬化性に及ぼす成分元素の影
響を表わす指標で、高いほど溶接部は硬化しやすく、溶
接時の低温割れ感受性が劣化する。このため上限を0.
42とした。これを超えると、溶接部で割れが発生しや
すく、また、その割れを防止するためには、予熱・後熱
が必要となり、コストの大幅上昇を伴うこととなる。Further, in the steel of the present invention, the carbon equivalent (Ceq) according to the following formula is an index showing the effect of the constituent elements on the hardenability of the weld, and the higher the carbon equivalent, the easier the weld is to harden and the cold cracking during welding. Sensitivity deteriorates. Therefore, the upper limit is set to 0.
42. If it exceeds this, cracks are likely to occur in the welded portion, and preheating and postheating are required to prevent the cracking, resulting in a significant increase in cost.
【0071】Ceq(%)=C+Mn/6+(Cu+N
i)/15+(V+Mo+Cr)/5+5B
また、本発明では鋼板の板厚を8mm以上と限定した
が、これはタンカーの衝突事故により、船体に穴が開い
て油流出事故、或は浸水事故を起こすタンカーの大きさ
が6万トン以上のクラスのタンカーであって、このクラ
スのタンカーの船体用鋼板としては強度確保等の観点で
8mm以上、特に8〜25mmの板厚の鋼板を使用する
必要がある。したがって、本発明においては鋼板の板厚
を8mm以上とした。なお、板厚の上限は船体の大きさ
等に応じて決まるものである。Ceq (%) = C + Mn / 6 + (Cu + N
i) / 15 + (V + Mo + Cr) / 5 + 5B Further, in the present invention, the plate thickness of the steel plate is limited to 8 mm or more, but this may cause an oil spill accident or a flood accident due to a hole in the hull due to a tanker collision accident. The tanker is a tanker of a size of 60,000 tons or more, and as a steel plate for a hull of this class tanker, it is necessary to use a steel plate having a thickness of 8 mm or more, particularly 8 to 25 mm from the viewpoint of ensuring strength. is there. Therefore, in the present invention, the plate thickness of the steel plate is set to 8 mm or more. The upper limit of the plate thickness is determined according to the size of the hull and the like.
【0072】次いで、フェライトマトリックス中に残留
γを微細に分散させる本発明の製造方法について説明す
る。Next, the production method of the present invention in which the residual γ is finely dispersed in the ferrite matrix will be described.
【0073】残留γを微細に分散させるには制御圧延が
有効である。即ち、鋳片を直接又はAc3以上の温度に
加熱後、熱間圧延を行い、かつ圧延終了温度をAr3+
100℃〜Ar3−50℃の温度範囲とする。これによ
ってγ粒が細かくなる。このような温度範囲とするの
は、仕上圧延温度がAr3+100℃超となるとγ粒が
成長してが粗大化し、γ粒の微細化を図ることができな
くなる。またAr3−50℃未満では細粒α生成による
γへのC、Siなどの濃縮が不充分となり、残留γが生
成しなくなるからである。したがって、本発明では、圧
延仕上温度をAr3+100℃〜Ar3−50℃の温度範
囲とした。Controlled rolling is effective for finely dispersing the residual γ. That is, the slab is directly or after being heated to a temperature of Ac 3 or higher, hot rolling is performed, and the rolling end temperature is set to Ar 3 +.
The temperature range of 100 ℃ ~Ar 3 -50 ℃. This makes the γ grains finer. When the finish rolling temperature is higher than Ar 3 + 100 ° C., the γ grains grow and become coarse, and the γ grains cannot be made finer. On the other hand, if Ar 3 is less than -50 ° C, the concentration of C, Si, etc. to γ due to the formation of fine particles α becomes insufficient, and residual γ is not produced. Therefore, in the present invention, the finish rolling temperature to a temperature range of Ar 3 + 100 ℃ ~Ar 3 -50 ℃.
【0074】次いで、圧延後、Ar1+100℃〜Ar1
の温度まで冷却速度2℃/s以下で徐冷或は空冷するこ
とによってαマトリックスの細粒化を促進すると共に、
その後の急冷により残留γが微細に分散した鋼板が得ら
れる。冷却速度を2℃/s以下とするのは、フェライト
(α)を安定的に生成させ、その量の制御が容易にでき
るからである。2℃/s超となると、フェライト(α)
が生成しにくくなり、代わりにベイナイト等の相が生成
するので好ましくない。Then, after rolling, Ar 1 + 100 ° C. to Ar 1
By gradually cooling or air-cooling to a temperature of 2 ° C./s or less, the α-matrix fine-graining is promoted, and
Subsequent rapid cooling gives a steel sheet in which the residual γ is finely dispersed. The cooling rate is set to 2 ° C./s or less because ferrite (α) can be stably generated and the amount thereof can be easily controlled. If it exceeds 2 ° C / s, ferrite (α)
Is less likely to be generated, and instead a phase such as bainite is generated, which is not preferable.
【0075】したがって、鋼の組織中のフェライト占積
率を80〜99%とするためには、Ar1+100℃〜
Ar1の温度範囲まで2℃/s以下の冷却速度で冷却す
る必要がある。Therefore, in order to set the ferrite space factor in the structure of steel to 80 to 99%, Ar 1 + 100 ° C.
It is necessary to cool to the temperature range of Ar 1 at a cooling rate of 2 ° C./s or less.
【0076】そして、徐冷後、さらに冷却速度10℃/
s以上で急冷して安定な残留γとする。つまり、高温で
のαとγの二相の共存域においては、αに固溶するC量
は最大0.02%が限度があり、過剰なCはγ中に移動
した状態となっている。この状態で10℃/s以上の冷
却速度で急冷を施すと残留γが析出することとなる。After the slow cooling, the cooling rate is further 10 ° C /
It is rapidly cooled above s to obtain a stable residual γ. That is, in the coexistence region of two phases of α and γ at high temperature, the maximum amount of C dissolved in α is 0.02%, and excess C is in the state of moving into γ. If rapid cooling is performed at a cooling rate of 10 ° C./s or more in this state, residual γ will be precipitated.
【0077】しかし、10℃/s未満の冷却速度となる
と、ベイナイトを生成し残留γは残らない。また、急冷
の冷却停止温度を250〜450℃の範囲にしてマルテ
ンサイト変態を起こさせないようにしないと、鋼板板厚
の少なくとも1/8以上の表裏層に面積率で1.0〜2
0%の残留γを生成させることができない。即ち、25
0℃未満まで冷却するとマルテンサイト変態を生じ、残
留γが生成しない。また450℃超となると、冷却後の
鋼板内部は、まだ温度が高いので、鋼板の自然復熱によ
り、不安定な状態である残留γは、αと炭化物に分解
し、残留γが消失してしまうからである。However, when the cooling rate is less than 10 ° C./s, bainite is formed and no residual γ remains. Further, unless the quenching cooling temperature is set in the range of 250 to 450 ° C. so as not to cause martensitic transformation, the area ratio is 1.0 to 2 in the front and back layers of at least ⅛ of the steel plate thickness.
It is not possible to produce 0% residual γ. That is, 25
When cooled to below 0 ° C, martensitic transformation occurs and residual γ does not form. If it exceeds 450 ° C., the temperature inside the steel sheet after cooling is still high, so that the residual γ in an unstable state is decomposed into α and carbide due to the natural heat recovery of the steel sheet, and the residual γ disappears. Because it will be.
【0078】[0078]
【実施例】本発明の実施例を比較例と対比して説明す
る。EXAMPLES Examples of the present invention will be described in comparison with comparative examples.
【0079】試験に用いた供試鋼の化学成分を表1に示
す。表1において鋼種A、Bは、第1発明に対応し、鋼
種C〜Eは、第2発明に対応し、そして、鋼種Fは、第
3発明に対応する本発明の鋼成分の規定範囲内のもので
ある。Table 1 shows the chemical composition of the test steel used in the test. In Table 1, steel types A and B correspond to the first invention, steel types C to E correspond to the second invention, and steel type F is within the specified range of the steel composition of the present invention corresponding to the third invention. belongs to.
【0080】表1に示す供試鋼を用いて、熱間圧延によ
り鋼板を製造した。その際の種々の製造条件を表2に示
す。また、得られた鋼板の残留γ面積率及び機械的特性
を表2に併記した。Using the test steels shown in Table 1, steel sheets were manufactured by hot rolling. Table 2 shows various manufacturing conditions at that time. Table 2 also shows the residual γ area ratio and mechanical properties of the obtained steel sheet.
【0081】表2から明らかなように、本発明の規定範
囲内の鋼成分の供試鋼を用いて、本発明で規定する製造
条件で製造した鋼板(実施例No.1〜6)は、いずれ
も、鋼板の少なくとも板厚の1/8以上の表裏層に面積
率で1.3〜14.5%の残留γを含有しており、衝撃
エネルギー吸収値が120MPaを超える120.3〜
161.3MPaであった。特に実施例No.4は、残
留γ面積率が14.5%と高く、衝撃エネルギー吸収値
も161.3MPaと高かった。As is clear from Table 2, the steel sheets (Examples Nos. 1 to 6) manufactured under the manufacturing conditions specified by the present invention using the sample steels having the steel components within the specified range of the present invention, In each case, at least ⅛ of the plate thickness of the front and back layers contains 1.3 to 14.5% of residual γ in area ratio, and the impact energy absorption value exceeds 120 MPa.
It was 161.3 MPa. In particular, Example No. No. 4 had a high residual γ area ratio of 14.5% and a high impact energy absorption value of 161.3 MPa.
【0082】これに対して、本発明で規定する製造条件
外である比較例No.7〜14は、いずれも残留γ面積
率が1%未満であって、衝撃エネルギー吸収値も93.
0〜116.0MPaと低い値しか示さなかった。On the other hand, in Comparative Example No. which is out of the manufacturing conditions specified in the present invention. 7 to 14 all have a residual γ area ratio of less than 1% and an impact energy absorption value of 93.
Only a low value of 0 to 116.0 MPa was shown.
【0083】即ち、比較例No.7は、仕上圧延温度が
高く、また比較例No.8は、仕上圧延温度が低いため
残留γ面積率がそれぞれ0.6%、0.5%と低かっ
た。比較例No.9は徐冷速度が2℃/s以上の2.5
℃/sであるため、残留γ面積率が0.5%と低かっ
た。比較例No.10は、徐冷時の冷却停止温度が高
く、また比較例No.11は、それが低い例であるが、
それぞれ残留γ面積率は0.7%、0.7%と低かっ
た。比較例No.12は、10℃/s以上の冷却速度の
急冷を行わなかったため、残留γ面積率が0.9%と低
かった。そして、比較例No.13は、急冷時の冷却停
止温度が高く、比較例No.14は、それが低い例であ
るが、それぞれ残留γ面積率は0.7%、0.5%と低
かった。That is, Comparative Example No. No. 7 has a high finish rolling temperature, and Comparative Example No. In No. 8, since the finish rolling temperature was low, the residual γ area ratio was as low as 0.6% and 0.5%, respectively. Comparative Example No. 9 is 2.5 with a slow cooling rate of 2 ° C / s or more
Since it was ℃ / s, the residual γ area ratio was as low as 0.5%. Comparative Example No. No. 10 has a high cooling stop temperature during slow cooling, and Comparative Example No. 11 is a low example,
The residual γ area ratio was low at 0.7% and 0.7%, respectively. Comparative Example No. In No. 12, since the rapid cooling at a cooling rate of 10 ° C./s or more was not performed, the residual γ area ratio was as low as 0.9%. Then, in Comparative Example No. No. 13 has a high cooling stop temperature at the time of quenching, and Comparative Example No. No. 14 is an example in which it is low, but the residual γ area ratio was low at 0.7% and 0.5%, respectively.
【0084】以上の試験結果から明らかなように、本発
明で規定する鋼成分及び製造条件を満たす本発明実施例
の鋼板は、いずれも残留γ面積率が1〜20%の範囲と
なっており、衝撃エネルギー吸収能も120MPa以上
の値を示し、衝撃エネルギー吸収能に優れた船体用鋼板
となっていたことが確認できた。As is clear from the above test results, the steel sheets of the examples of the present invention satisfying the steel composition and manufacturing conditions specified in the present invention all have a residual γ area ratio in the range of 1 to 20%. The impact energy absorption capacity also showed a value of 120 MPa or more, and it was confirmed that the steel sheet for ships had excellent impact energy absorption capacity.
【0085】又、本発明で規定する鋼成分を有する鋼板
は、炭素当量(Ceq)が全て0.42以下であるた
め、斜めY型溶接性試験の結果、全て良好なものである
ことが確認できた。Further, the steel sheets having the steel components specified in the present invention all have carbon equivalents (Ceq) of 0.42 or less, and as a result of the oblique Y-type weldability test, it is confirmed that all are good. did it.
【0086】[0086]
【表1】 [Table 1]
【0087】[0087]
【表2】 [Table 2]
【0088】[0088]
【発明の効果】本発明により、120MPa以上の衝撃
エネルギー吸収能の優れた鋼板を提供することが可能で
あり、本発明鋼板をタンカー等の船体に使用することに
より、万一船体同士の衝突事故が起こった場合でも、船
体が破断して穴が開くことを防止或は破断面積を従来の
鋼板の場合よりも減少することができる。Industrial Applicability According to the present invention, it is possible to provide a steel sheet having an impact energy absorption capacity of 120 MPa or more, and by using the steel sheet of the present invention in a hull such as a tanker, a collision between hulls should occur. In the case where the above occurs, the hull can be prevented from breaking and the holes can be prevented or the breaking area can be reduced as compared with the case of the conventional steel plate.
【0089】そのため、タンカーの衝突事故時における
油の流出による海洋汚染、又は衝突損傷部からの浸水量
を低減できる等、環境保護、安全性の点から優れた効果
を奏する。Therefore, the marine pollution due to the oil outflow at the time of the collision accident of the tanker, or the amount of water infiltrated from the collision damaged portion can be reduced, and excellent effects can be obtained from the viewpoint of environmental protection and safety.
【図1】タンカー同士の衝突時のタンカー側面の破壊を
模式的に示す図である。FIG. 1 is a diagram schematically showing destruction of a side surface of a tanker when the tankers collide with each other.
【図2】鋼板表面からの距離aと残留γ面積率Fとの関
係を示す図である。FIG. 2 is a diagram showing a relationship between a distance a from a steel plate surface and a residual γ area ratio F.
【図3】距離/板厚(a/t)と残留γ面積率F(%)
との関係を示す図である。FIG. 3 Distance / plate thickness (a / t) and residual γ area ratio F (%)
It is a figure which shows the relationship with.
【図4】残留γが存在する最大厚みaγと衝撃エネルギ
ー吸収能EAとの関係を示す図である。FIG. 4 is a diagram showing a relationship between a maximum thickness aγ in which residual γ exists and impact energy absorption capacity EA.
1 タンカー側壁部 2 タンカーの舳先 1 Tanker side wall 2 Tanker bow
───────────────────────────────────────────────────── フロントページの続き (72)発明者 石川 忠 大分市大字西ノ洲1番地 新日本製鐵株 式会社 大分製鐵所内 (72)発明者 石田 浩司 大分市大字西ノ洲1番地 新日本製鐵株 式会社 大分製鐵所内 (72)発明者 今井 嗣郎 東京都千代田区大手町二丁目6番3号 新日本製鐵株式会社内 (56)参考文献 特開 平6−287681(JP,A) 特開 平8−283905(JP,A) 特開 平10−17891(JP,A) 特許3434444(JP,B2) 特許3434445(JP,B2) 石川忠ら,表層超細粒鋼の脆性き裂伝 搬停止性能(その2)塑性損傷後の特性 および衝突後のき裂拡大北止への適用, 日本造船学会論文集,日本,1995年12 月,No.178,P.555−563,796− 797 (58)調査した分野(Int.Cl.7,DB名) C22C 38/00 - 38/60 C21D 8/00 - 8/02 B21B 1/00 - 3/02 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Ishikawa 1st Nishinosu, Oita-shi, Nippon Steel Co., Ltd. Inside the Oita Steel Co., Ltd. (72) Koji Ishida 1st Nishinosu, Oita-shi Nippon Steel Co., Ltd. Company Oita Works (72) Inventor Tsuguro Imai 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Co., Ltd. (56) Reference JP-A-6-287681 (JP, A) JP-A 8-283905 (JP, A) JP 10-17891 (JP, A) Patent 3434444 (JP, B2) Patent 3434445 (JP, B2) Tadashi Ishikawa et al. Brittle crack propagation stopping performance of super-fine grain steel (Part 2) Properties after plastic damage and application to crack propagation north stop after collision, Proceedings of the Japan Shipbuilding Society, Japan, December 1995, No. 178, p. 555-563, 796-797 (58) Fields investigated (Int.Cl. 7 , DB name) C22C 38/00-38/60 C21D 8/00-8/02 B21B 1/00-3/02
Claims (6)
u+Ni)/15+(V+Mo+Cr)/5+5B)
(%)が0.42(%)以下であり、残部Feおよび不
可避不純物からなる板厚8mm以上の鋼板であって、該
鋼板の少なくとも板厚の1/8以上の表裏層をフェライ
ト相とし、かつ、そのフェライト相中に、面積率で1.
0〜20%、粒径が5μm以下の残留γを含むことを特
徴とする衝撃エネルギー吸収能に優れた船体用鋼板。1. By weight%, C: 0.05 to 0.2%, Si: 0.05 to 2.0%, Mn: 0.1 to 2.0%, Al: 0.001 to 0. 1%, and the carbon equivalent Ceq (= C + Mn / 6 + (C
u + Ni) / 15 + (V + Mo + Cr) / 5 + 5B)
(%) Is not less 0.42% or less, a thickness less than 8mm steel plates and the balance Fe and unavoidable impurities, ferrite and at least a thickness of 1/8 or more the front and back layers of the steel plate
And an area ratio of 1.
A steel plate for a hull excellent in impact energy absorption, characterized by containing residual γ of 0 to 20% and a particle size of 5 μm or less .
0.1%V:0.001〜0.1%、Ti:0.001
〜0.05%、Ta:0.001〜0.1%、Cr:
0.01〜1.0%、Ni:0.01〜1.0%、M
o:0.01〜1.0%、Cu:0.01〜1.0%の
うちの1種又は2種以上を含有することを特徴とする請
求項1に記載の衝撃エネルギー吸収能に優れた船体用鋼
板。2. Further, in% by weight, Nb: 0.001 to
0.1% V: 0.001-0.1%, Ti: 0.001
~ 0.05%, Ta: 0.001-0.1%, Cr:
0.01-1.0%, Ni: 0.01-1.0%, M
O: 0.01-1.0%, Cu: 0.01-1.0%, 1 type (s) or 2 or more types are contained, It is excellent in the impact energy absorption ability of Claim 1 characterized by the above-mentioned. Steel plate for hull.
〜0.01%、Mg:0.0001〜0.01%、RE
M:0.001〜0.05% B:0.0001〜0.001%のうちの1種又は2種
以上を含有することを特徴とする請求項1または2に記
載の板厚8mm以上の衝撃エネルギー吸収能に優れた船
体用鋼板。3. Further, by weight%, Ca: 0.0001
~ 0.01%, Mg: 0.0001-0.01%, RE
M: 0.001-0.05% B: 0.0001-0.001% of 1 type (s) or 2 or more types, The plate thickness of 8 mm or more of Claim 1 or 2 characterized by the above-mentioned. Steel plate for hulls with excellent impact energy absorption capacity.
i:0.05〜2.0%、Mn:0.1〜2.0%、A
l:0.001〜0.1%、を含有し、かつ炭素当量C
eq(=C+Mn/6+(Cu+Ni)/15+(V+
Mo+Cr)/5+5B)(%)が0.42(%)以下
であり、残部Feおよび不可避不純物からなる鋳片を、
直接もしくは加熱後、熱間圧延を行い、Ar3+100
℃〜Ar3−50℃の温度範囲内で仕上げ圧延を終了
し、その後、Ar3もしくは仕上圧延温度のいずれか低
い方の温度からAr1+100℃〜Ar1℃の温度まで冷
却速度2℃/s以下で冷却し、そして、さらに冷却速度
10℃/s以上で冷却し、250〜450℃の温度範囲
で冷却を停止することを特徴とする衝撃エネルギー吸収
能に優れた船体用鋼板の製造方法。4. By weight%, C: 0.05-0.2%, S
i: 0.05 to 2.0%, Mn: 0.1 to 2.0%, A
1: 0.001 to 0.1%, and carbon equivalent C
eq (= C + Mn / 6 + (Cu + Ni) / 15 + (V +
Mo + Cr) / 5 + 5B) (%) is 0.42 (%) or less, and a slab composed of the balance Fe and unavoidable impurities,
Directly or after heating, hot-rolling Ar 3 +100
° C. to Ar 3 ends the finish rolling within a temperature range of -50 ° C., then, from any lower temperature of Ar 3 or the finish rolling temperature Ar 1 + 100 ℃ ~Ar cooling rate 2 ℃ to a temperature of 1 ° C. / s or less, and further cooling at a cooling rate of 10 ° C./s or more, and stopping cooling in the temperature range of 250 to 450 ° C. .
01〜0.1% V:0.001〜0.1%、Ti:0.001〜0.0
5%、Ta:0.001〜0.1%、Cr:0.01〜
1.0%、Ni:0.01〜1.0%、Mo:0.01
〜1.0%、Cu:0.01〜1.0%のうちの1種又
は2種以上を含有することを特徴とする請求項4に記載
の衝撃エネルギー吸収能に優れた船体用鋼板の製造方
法。5. The cast slab further comprises Nb: 0.0% by weight.
01-0.1% V: 0.001-0.1%, Ti: 0.001-0.0
5%, Ta: 0.001 to 0.1%, Cr: 0.01 to
1.0%, Ni: 0.01 to 1.0%, Mo: 0.01
Of 1.0 to 1.0% and Cu: 0.01 to 1.0% are contained, or at least two of them are contained. Production method.
001〜0.01%、Mg:0.0001〜0.01
%、REM:0.001〜0.05% B:0.0001〜0.001%のうちの1種又は2種
以上を含有することを特徴とする請求項4または5に記
載の衝撃エネルギー吸収能に優れた船体用鋼板の製造方
法。6. The cast slab, in a further weight percentage, is Ca: 0.0.
001-0.01%, Mg: 0.0001-0.01
%, REM: 0.001 to 0.05%, B: 0.0001 to 0.001%, and one or more of them are contained. Impact energy absorption according to claim 4 or 5, A method for manufacturing steel plates for hulls with excellent performance.
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JP06607398A JP3499126B2 (en) | 1998-03-03 | 1998-03-03 | Steel plate for hull excellent in impact energy absorption capacity and method of manufacturing the same |
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JP3499126B2 true JP3499126B2 (en) | 2004-02-23 |
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Cited By (1)
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WO2013080398A1 (en) | 2011-11-30 | 2013-06-06 | Jfeスチール株式会社 | Steel material with excellent crashworthiness and manufacturing process therefor |
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JP4653039B2 (en) * | 2006-08-21 | 2011-03-16 | 株式会社神戸製鋼所 | High tensile steel plate and method for manufacturing the same |
JP4653038B2 (en) * | 2006-08-21 | 2011-03-16 | 株式会社神戸製鋼所 | High tensile steel plate and method for manufacturing the same |
JP4869094B2 (en) * | 2007-02-05 | 2012-02-01 | 株式会社神戸製鋼所 | Impact property prediction method for marine steel |
WO2011024715A1 (en) * | 2009-08-24 | 2011-03-03 | 新日本製鐵株式会社 | Bow structure |
KR101456868B1 (en) * | 2011-11-02 | 2014-11-04 | 삼성중공업 주식회사 | Method for Prediction of Impact thoughness for Cold-Worked Metal |
WO2016013288A1 (en) | 2014-07-25 | 2016-01-28 | 新日鐵住金株式会社 | Ship body structure with excellent crashworthiness, and ship body structure designing method |
CN110536973B (en) | 2018-03-16 | 2020-08-18 | 日本制铁株式会社 | Steel plate for cargo hold of coal/ore transport ship |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3434445B2 (en) | 1997-12-26 | 2003-08-11 | 新日本製鐵株式会社 | Steel plate for hull with excellent shock absorption capacity |
JP3434444B2 (en) | 1997-12-26 | 2003-08-11 | 新日本製鐵株式会社 | Steel plate for hull with excellent shock absorption capacity |
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JP3434445B2 (en) | 1997-12-26 | 2003-08-11 | 新日本製鐵株式会社 | Steel plate for hull with excellent shock absorption capacity |
JP3434444B2 (en) | 1997-12-26 | 2003-08-11 | 新日本製鐵株式会社 | Steel plate for hull with excellent shock absorption capacity |
Non-Patent Citations (1)
Title |
---|
石川忠ら,表層超細粒鋼の脆性き裂伝搬停止性能(その2)塑性損傷後の特性および衝突後のき裂拡大北止への適用,日本造船学会論文集,日本,1995年12月,No.178,P.555−563,796−797 |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2013080398A1 (en) | 2011-11-30 | 2013-06-06 | Jfeスチール株式会社 | Steel material with excellent crashworthiness and manufacturing process therefor |
KR20160104077A (en) | 2011-11-30 | 2016-09-02 | 제이에프이 스틸 가부시키가이샤 | Steel material with excellent crashworthiness and manufacturing process therefor |
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