JPS6410565B2 - - Google Patents
Info
- Publication number
- JPS6410565B2 JPS6410565B2 JP21712684A JP21712684A JPS6410565B2 JP S6410565 B2 JPS6410565 B2 JP S6410565B2 JP 21712684 A JP21712684 A JP 21712684A JP 21712684 A JP21712684 A JP 21712684A JP S6410565 B2 JPS6410565 B2 JP S6410565B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- rolling
- temperature
- cracking resistance
- 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
Links
- 229910000831 Steel Inorganic materials 0.000 claims description 65
- 239000010959 steel Substances 0.000 claims description 65
- 238000005336 cracking Methods 0.000 claims description 44
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 27
- 229910052739 hydrogen Inorganic materials 0.000 claims description 27
- 239000001257 hydrogen Substances 0.000 claims description 27
- 238000005096 rolling process Methods 0.000 claims description 23
- 230000007797 corrosion Effects 0.000 claims description 22
- 238000005260 corrosion Methods 0.000 claims description 22
- 238000001816 cooling Methods 0.000 claims description 15
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 8
- 229910001566 austenite Inorganic materials 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 238000012545 processing Methods 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 238000000034 method Methods 0.000 description 13
- 229910000859 α-Fe Inorganic materials 0.000 description 12
- 229910001567 cementite Inorganic materials 0.000 description 11
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 11
- 230000000694 effects Effects 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 239000000203 mixture Substances 0.000 description 6
- 238000005204 segregation Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 3
- 229910001563 bainite Inorganic materials 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 230000000149 penetrating effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 238000012733 comparative method Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 235000002639 sodium chloride Nutrition 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 125000000101 thioether group Chemical group 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Description
本発明は耐水素誘起割れ性及び耐応力腐食割れ
性にすぐれた高強度高靭性熱延鋼板の製造方法に
関する。
近年、鋼板には高強度、高靭性に加えて、耐水
素誘起割れ性や耐応力腐食割れ性にすぐれた高品
質鋼板が要求されるに至つている。鋼板のこのよ
うな腐食割れに最も大きく影響する因子は、既に
よく知られているように、鋼中のマクロ及びミク
ロ偏析と、非金属介在物の伸長であるため、従
来、上記のような高品質鋼板には、ＳやＰを低減
した焼入れ焼戻し鋼や、調質ベイナイト鋼等の均
質調質鋼からなる鋼板が用いられている。しか
し、このような方法は、生産性と経済性が劣るた
めに、高品質鋼板を安価に量産化し得ない難点が
ある。
このため、近年、特に製鋼技術の進歩を背景と
して、例えば、Ｓ量が0.002％以下、Ｐ量が0.010
％以下のような極低Ｓ低Ｐ鋼の量産化が実現され
るに至り、比較的高い生産性にて非調質ままでこ
れら高品質鋼板を製造する方法が一部で実用化さ
れている。しかし、水素誘起割れや応力腐食割れ
のように、極めて多くの因子が関係する割れにつ
いては、例えば、上記のようにＳ量を0.002％以
下に抑え得たとしても、鋼板表面で発生し、鋼中
に浸入する水素の影響を避けることができない。
このような問題を解決するために、最近におい
ては、鋼の化学成分の観点からは、偏析を抑制す
るためにＣやMn量を低減する、鋼中への水素の
浸入と拡散を抑制するためにCuやCoを添加する、
有効な水素トラツプサイトを確保するためにNb
やTiを添加する、更にはCaやREMを添加する等
の方法が提案されており、一方、金属組織の観点
からは、造塊鋳造組織を良好にすると共に、最終
金属組織をフエライト・パーライト組織から微細
なフエライト・ベイナイト組織やベイナイト組織
に制御することが提案されている。特に、清浄鋼
については、後者の組織制御によつて、鋼材の材
料特性が改善されることが知られている。
しかし、ラインパイプ用鋼材のように、比較的
板厚の厚い鋼材の場合は、ベイナイト組織のよう
な低温変態生成物を均一に得難いため、実際上
は、化学成分を限定すると共に、フエライト・パ
ーライト組織を微細化する方向での研究が主とし
て進められている。即ち、このフエライト・パー
ライト鋼においては、主としてパーライトバンド
であるバンド状組織が鋼材の靭性、耐水素誘起割
れ性及び耐応力腐食割れ性に有害な影響を及ぼす
ので、熱間圧延を制御して極めて微細な組織と
し、パーライト組織を孤立させるものである。し
かし、これらの従来の方法によれば、NACE等
の苛酷な腐食環境下では、鋼板の水素誘起割れや
応力腐食割れの主として伝播を十分に抑制するこ
とができない。
本発明者らは、上記した問題を解決するため
に、鋼板の水素誘起割れ及び応力腐食割れを詳細
且つ広範囲にわたつて研究した結果、清浄鋼の水
素誘起割れ及び応力腐食割れの割れ発生とその伝
播に関しては、粒界に析出する主としてセメンタ
イトからなる炭化物が極めて重要な役割を演じて
おり、この炭化物の析出サイトとその形状を適切
に制御することによつて、耐水素誘起割れ性、耐
応力腐食割れ性のみならず、その他の機械的特性
にもすぐれた熱延鋼板を得ることを見出して、本
発明に至つたものである。
本発明による耐水素誘起割れ性及び耐応力腐食
割れ性にすぐれた熱延鋼板の製造方法は、重量％
で
Ｃ 0.03〜0.3％、
Si 0.01〜1.0％、
Mn 0.5〜2.0％、
Al 0.005〜0.05％、
残部鉄及び不可避的不純物よりなる鋼片を粗圧
延した後、オーステナイト未再結晶域における全
圧下率を30％以上とし、温度900〜800℃にて仕上
圧延した後、平均冷却速度15〜80℃／秒にて温度
750〜650℃まで冷却し、更に、加工率３〜20％に
て軽圧下することを特徴とすし、かかる方法によ
つて、フエライト粒界でのセメンタイトの析出を
抑制しつつ、フエライト粒内に微細に多数析出さ
せることができる。
先ず、本発明の方法において用いる鋼材におけ
る化学成分の限定理由について説明する。
Ｃは、鋼の強度を確保するために必須の元素で
あり、本発明においては少なくとも0.03％を添加
する。しかし、過多に添加するときは鋼の靭性と
溶接性とを阻害し、また、連続鋳造材の場合には
中心偏析の異常発生の原因ともなり、更には、腐
食環境下にカソード反応の促進効果を有するた
め、その添加量の上限を0.3％とする。
Siは、強力な脱酸剤として添加され、また、素
地中に固容して鋼の伸びや延性を改善する効果を
有する。かかる効果を有効に発現させるために
は、少なくとも0.01％の添加を必要とするが、し
かし、過多に添加するときは、溶接性の劣化、清
浄度の悪化、表面スケールの発生等の好ましくな
い問題を生じるため、その添加量の上限を1.0％
とする。
Mnは、本発明において鋼に所要の強度と靭性
を付与するために少なくとも0.5％を添加する。
しかし、余りに多量に添加する場合は、ミクロ偏
析が顕著となつて異常組織が生成し、耐水素誘起
割れ性や靭性を劣化させるので、その上限を2.0
％とする。
Alは、Siと同様に脱酸剤として必要な元素で
あり、少なくとも0.005％を添加するが、過多に
添加するときは、靭性を劣化させ、また、鋳造欠
陥も顕著となるため、上限を0.05％とする。
Ｐは、鋼においてミクロ偏析を生じ、鋼塊中央
部に異常組織の発生を促進し、耐水素誘起割れ性
に有害であるので、本発明においては、その含有
量は好ましくは0.03％以下とする。
また、Ｓは、Mnと結合してＡ系介在物を形成
し、割れ発生の起点となるので有害である。鋼に
Caを添加して、CaSとしてもその含有量が多く
なると、クラスター状になり、割れを誘起する場
合がある。従つて、本発明においては、鋼中のＳ
含有量は好ましくは0.01％以下とする。
本発明においては、鋼板に更に強度が耐食性を
付与するために、必要に応じてCr、Ti、Cu、
Mo、Nb、Ｖ及びNiよりなる群から選ばれる少
なくとも１種の元素を添加することができる。
Crは鋼の強度を高める以外に耐食性を高める
効果を有するが、過多に添加するときは、溶接時
にペネトレータが発生し、溶接性を著しく阻害す
るので、その上限を1.0％とする。
Tiは微細な炭窒化物を析出して、鋼中におい
て水素の有効なトラツプサイトとして作用し、鋼
の耐水素誘起割れ性を更に改善する。しかし、過
多に添加する場合は、前記炭窒化物が粗大化し、
却つて割れ発生を助長するので、その添加量の上
限を0.05％とする。
Cuは鋼中への水素の浸入を防止し、弱酸性の
腐食環境下での耐食性を著しく向上させる。この
ような効果を有効に発現させるためには、少なく
とも0.1％の添加を必要とする。しかし、1.0％を
越えて多量に添加すれば、熱間脆性が生じるの
で、その添加量の上限を1.0％とする。
また、Mo、Nb、Ｖ及びNiは、鋼の強度を上
昇させると共に、その靭性を改善するために添加
されるが、余りに過多に加えても上記効果が飽和
し、更に、経済性を考慮して、その上限をMoに
ついては0.2％、Nbについては0.1％、Ｖについて
は0.1％、Niについては0.2％とする。
更に、本発明においては、鋼にCaを添加する
こともできる。Caは鋼中の硫化物系介在物の形
態と組成を制御するのに効果があり、特に、
Ca／Ｓ≧２を満足する場合に硫化物系介在物が
完全に球状化する結果、すぐれた耐水素誘起割れ
性を付与することができる。しかし、過多に添加
するときは、クラスター状となつて、性能が劣化
するので、上限を0.0050％とする。
本発明の方法によれば、上記のような化学成分
を有する鋼片を粗圧延した後、所定の条件下に処
理することによつて、耐水素誘起割れ性及び耐応
力腐食割れ性にすぐれた高強度高靭性熱延鋼板を
得ることができる。即ち、鋼片をオーステナイト
未再結晶域における全圧力率を30％以上とし、温
度900〜800℃にて仕上圧延した後、平均冷却速度
15〜80℃／秒にて温度750〜650℃まで冷却し、更
に、加工率３〜20％にて軽圧下する。
先ず、本発明の方法においては、鋼片を粗圧延
した後、オーステナイト未再結晶域における全圧
下率を30％以上とする。30％よりも小さい場合
は、微細組織を得ることができず、靭性が劣化す
るからである。仕上圧延温度は900〜800℃の範囲
である。900℃よりも高いときは、オーステナイ
ト未再結晶域における圧下を十分に行なうことが
困難であるので、フエライト粒が粗大化し、靭性
が低下する。一方、800℃よりも低い場合は、析
出フエライトを強化加工することとなり、集合組
織が発達する結果、セパレーシヨンが多発し、板
厚方向の靭性が劣化する。
この仕上圧延後、フエライト中に過飽和に固容
させたＣを析出させるために、直ちに平均冷却速
度15〜80℃／秒にて750〜650℃の範囲の温度まで
急冷する。冷却速度が余りに遅い場合は、冷却途
中で界面にＣが濃縮され、純度の高いフエライト
が析出するため、粒界にセメンタイトが析出しや
すい。冷却速度の上限は特に制限されないが、実
操業上の観点から80℃／秒とする。
この急冷後、本発明の方法においては、セメン
タイトを微細に、且つ、粒内に多く析出させるた
めに、750〜650℃の範囲の温度域にて３〜20％の
加工率にて軽圧下する。この温度域において、フ
エライト中に析出するＣ量が最も多く、この温度
域で軽圧下することによつて、フエライト粒内で
セメンタイトが最も微細に且つ多数析出するから
である。軽圧下温度が上記範囲をはずれる場合に
は、粒界でセメンタイトが多数析出して、所要の
物性を得ることができない。圧下率は、セメンタ
イトを微細に析出させるために、少なくとも３％
を必要とし、一方、20％を越えるときは、析出フ
エライト相を加工することとなり、その結果、集
合組織の発達が顕著となる。
尚、本発明においては、冷却停止温度又は巻取
温度は650℃以下であり、650℃よりも高い場合
は、セメンタイトの粗大成長し、粒界セメンタイ
トの伸長が起こる。
以上のように、所定の化学成分を有する鋼片を
所定の条件に従つて処理することによつて、集合
組織を生成させることなく、微細なフエライト組
織を生成させると共に、セメンタイトを微細に且
つ多数フエライト中に生成させるので、機械的特
性にすぐれるのみならず、耐水素誘起割れ性及び
耐応力腐食割れ性にすぐれた熱延鋼板を得ること
ができる。
以下に実施例を挙げて本発明を説明する。
実施例 １
第１表に示す化学成分を有する鋼片を粗圧延し
た後、第２表に示す条件にてオーステナイト未再
結晶域にて圧延し、所定の温度にて仕上圧延し、
本発明の方法に従つて急冷し、軽圧下し、巻取を
行なつて、厚さ8.8mmの鋼片を得た（発明法）。比
較のために、通常の方法に従つて、第２表に示
The present invention relates to a method for manufacturing a high-strength, high-toughness hot-rolled steel sheet with excellent resistance to hydrogen-induced cracking and stress corrosion cracking. In recent years, there has been a growing demand for high-quality steel plates that have high strength and toughness, as well as excellent resistance to hydrogen-induced cracking and stress corrosion cracking. As is already well known, the factors that most significantly affect corrosion cracking in steel sheets are macro- and micro-segregation in the steel and elongation of non-metallic inclusions. As the quality steel plate, a steel plate made of quenched and tempered steel with reduced S and P content, or homogeneously tempered steel such as tempered bainitic steel is used. However, such a method has a drawback in that high-quality steel sheets cannot be mass-produced at low cost because of poor productivity and economic efficiency. For this reason, in recent years, especially against the background of advances in steelmaking technology, for example, the amount of S is 0.002% or less, the amount of P is 0.010%, etc.
The mass production of ultra-low S and low P steels with temperatures below 20% has been achieved, and some methods have been put into practical use to produce these high-quality steel sheets without heat refining with relatively high productivity. . However, for cracks that are related to an extremely large number of factors, such as hydrogen-induced cracking and stress corrosion cracking, even if the amount of S can be suppressed to 0.002% or less as described above, cracks will occur on the surface of the steel sheet, and the It is impossible to avoid the effects of hydrogen penetrating inside. In order to solve these problems, recently, from the viewpoint of the chemical composition of steel, efforts have been made to reduce the amount of C and Mn to suppress segregation, and to suppress the infiltration and diffusion of hydrogen into the steel. Adding Cu or Co to
Nb to ensure effective hydrogen trap sites.
Methods have been proposed, such as adding Ti, Ca, or REM.On the other hand, from the perspective of metallographic structure, in addition to improving the ingot casting structure, the final metallographic structure is changed to a ferrite/pearlite structure. It has been proposed to control the structure to a fine ferrite-bainite structure or bainite structure. In particular, with respect to clean steel, it is known that the latter microstructural control improves the material properties of the steel material. However, in the case of relatively thick steel materials such as steel materials for line pipes, it is difficult to uniformly obtain low-temperature transformation products such as bainite structure. Research is mainly being carried out in the direction of making the structure finer. In other words, in this ferrite-pearlite steel, the band-like structure, which is mainly a pearlite band, has a detrimental effect on the toughness, hydrogen-induced cracking resistance, and stress corrosion cracking resistance of the steel material, so hot rolling is controlled and extremely It has a fine structure and isolates the pearlite structure. However, these conventional methods cannot sufficiently suppress the propagation of hydrogen-induced cracking and stress corrosion cracking in steel sheets under severe corrosive environments such as NACE. In order to solve the above-mentioned problems, the present inventors conducted a detailed and extensive study on hydrogen-induced cracking and stress corrosion cracking in steel sheets, and as a result, they discovered the occurrence of hydrogen-induced cracking and stress corrosion cracking in clean steel, and their occurrence. Regarding propagation, carbides mainly composed of cementite precipitated at grain boundaries play an extremely important role, and by appropriately controlling the precipitation sites and shapes of these carbides, hydrogen-induced cracking resistance and stress resistance can be improved. The inventors have discovered that it is possible to obtain a hot-rolled steel sheet that is excellent not only in corrosion cracking resistance but also in other mechanical properties, leading to the present invention. The method for producing a hot-rolled steel sheet with excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance according to the present invention is as follows:
After rough rolling a steel billet consisting of C 0.03~0.3%, Si 0.01~1.0%, Mn 0.5~2.0%, Al 0.005~0.05%, balance iron and unavoidable impurities, the total rolling reduction in the austenite non-recrystallized region After finishing rolling at a temperature of 900 to 800℃ with a temperature of 30% or more, the temperature is lowered at an average cooling rate of 15 to 80℃/sec.
It is characterized by cooling to 750 to 650°C and further applying a light reduction at a working rate of 3 to 20%. By this method, precipitation of cementite at the ferrite grain boundaries is suppressed, while the precipitation of cementite is suppressed within the ferrite grains. A large number of fine particles can be precipitated. First, the reason for limiting the chemical composition of the steel used in the method of the present invention will be explained. C is an essential element for ensuring the strength of steel, and in the present invention, at least 0.03% is added. However, when added in excess, it impairs the toughness and weldability of the steel, and in the case of continuously cast materials, it can cause abnormal center segregation, and it also has the effect of promoting cathode reactions in a corrosive environment. Therefore, the upper limit of its addition amount is set at 0.3%. Si is added as a strong deoxidizing agent, and also has the effect of improving the elongation and ductility of steel by solidifying it in the matrix. In order to effectively exhibit this effect, it is necessary to add at least 0.01%, but if too much is added, undesirable problems such as deterioration of weldability, deterioration of cleanliness, and generation of surface scale may occur. Because of this, the upper limit of its addition amount has been set at 1.0%.
shall be. Mn is added in an amount of at least 0.5% in order to impart the required strength and toughness to the steel in the present invention.
However, if too large a quantity is added, micro-segregation becomes noticeable and an abnormal structure is formed, deteriorating the hydrogen-induced cracking resistance and toughness, so the upper limit is set at 2.0.
%. Al, like Si, is an element necessary as a deoxidizing agent, and is added at least 0.005%, but when added in excess, the toughness deteriorates and casting defects become noticeable, so the upper limit is set at 0.05%. %. P causes micro-segregation in steel, promotes the generation of abnormal structures in the center of the steel ingot, and is harmful to hydrogen-induced cracking resistance, so in the present invention, its content is preferably 0.03% or less. . Further, S is harmful because it combines with Mn to form A-based inclusions and becomes a starting point for cracking. to steel
If Ca is added and the content increases even if it is CaS, it may form clusters and induce cracks. Therefore, in the present invention, S in steel
The content is preferably 0.01% or less. In the present invention, in order to further impart strength and corrosion resistance to the steel plate, Cr, Ti, Cu,
At least one element selected from the group consisting of Mo, Nb, V, and Ni can be added. Cr has the effect of increasing corrosion resistance in addition to increasing the strength of steel, but when added in excess, penetrators are generated during welding and significantly impede weldability, so the upper limit is set at 1.0%. Ti precipitates fine carbonitrides and acts as an effective trap site for hydrogen in the steel, further improving the hydrogen-induced cracking resistance of the steel. However, when adding too much, the carbonitrides become coarse and
Since it actually promotes cracking, the upper limit of its addition amount is set at 0.05%. Cu prevents hydrogen from penetrating into steel and significantly improves corrosion resistance in slightly acidic corrosive environments. In order to effectively express such an effect, it is necessary to add at least 0.1%. However, if added in a large amount exceeding 1.0%, hot brittleness will occur, so the upper limit of the amount added is set at 1.0%. In addition, Mo, Nb, V, and Ni are added to increase the strength of steel and improve its toughness, but if they are added in too much, the above effects will be saturated, and furthermore, considering economic efficiency, Therefore, the upper limit is set to 0.2% for Mo, 0.1% for Nb, 0.1% for V, and 0.2% for Ni. Furthermore, in the present invention, Ca can also be added to the steel. Ca is effective in controlling the morphology and composition of sulfide inclusions in steel.
When Ca/S≧2 is satisfied, the sulfide-based inclusions are completely spheroidized, and as a result, excellent hydrogen-induced cracking resistance can be imparted. However, when added in excess, it forms clusters and performance deteriorates, so the upper limit is set at 0.0050%. According to the method of the present invention, by rough rolling a steel billet having the above-mentioned chemical composition and then treating it under predetermined conditions, it has excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance. A hot rolled steel sheet with high strength and high toughness can be obtained. That is, after finish rolling a steel billet at a temperature of 900 to 800°C with a total pressure rate of 30% or more in the austenite non-recrystallized region, the average cooling rate
It is cooled to a temperature of 750 to 650°C at a rate of 15 to 80°C/second, and further reduced lightly at a processing rate of 3 to 20%. First, in the method of the present invention, after rough rolling a steel billet, the total rolling reduction in the austenite non-recrystallized region is set to 30% or more. This is because if it is smaller than 30%, a fine structure cannot be obtained and the toughness deteriorates. Finish rolling temperature ranges from 900 to 800°C. When the temperature is higher than 900°C, it is difficult to sufficiently reduce the austenite non-recrystallized region, so the ferrite grains become coarse and the toughness decreases. On the other hand, if the temperature is lower than 800°C, the precipitated ferrite will be strengthened, and as a result of the development of texture, separation will occur frequently and the toughness in the thickness direction will deteriorate. After this finish rolling, the material is immediately rapidly cooled to a temperature in the range of 750 to 650°C at an average cooling rate of 15 to 80°C/sec in order to precipitate supersaturated solidified C in the ferrite. If the cooling rate is too slow, C is concentrated at the interface during cooling and highly pure ferrite is precipitated, so that cementite is likely to precipitate at the grain boundaries. Although the upper limit of the cooling rate is not particularly limited, it is set to 80°C/sec from the viewpoint of actual operation. After this rapid cooling, in the method of the present invention, light reduction is performed at a working rate of 3 to 20% in a temperature range of 750 to 650°C in order to precipitate cementite finely and in large quantities within the grains. . This is because in this temperature range, the amount of C precipitated in the ferrite is the largest, and by applying a light pressure in this temperature range, cementite is precipitated in the finest form and in the largest number within the ferrite grains. If the light rolling temperature is outside the above range, a large amount of cementite will precipitate at the grain boundaries, making it impossible to obtain the desired physical properties. The reduction rate is at least 3% in order to finely precipitate cementite.
On the other hand, when it exceeds 20%, the precipitated ferrite phase must be processed, and as a result, the development of texture becomes remarkable. In the present invention, the cooling stop temperature or the winding temperature is 650°C or lower, and if it is higher than 650°C, coarse growth of cementite occurs and elongation of grain boundary cementite occurs. As described above, by processing a steel billet having a predetermined chemical composition according to predetermined conditions, a fine ferrite structure is generated without forming a texture, and cementite is finely and in large quantities. Since it is formed in ferrite, it is possible to obtain a hot-rolled steel sheet that not only has excellent mechanical properties but also excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance. The present invention will be explained below with reference to Examples. Example 1 A steel billet having the chemical composition shown in Table 1 was roughly rolled, then rolled in an austenite non-recrystallized area under the conditions shown in Table 2, and finished rolled at a predetermined temperature.
A steel slab with a thickness of 8.8 mm was obtained by quenching, light reduction, and winding according to the method of the present invention (invention method). For comparison, according to the usual method, the results are shown in Table 2.
【表】【table】
【表】
す温度で仕上圧延し、急冷及びその後の軽圧下を
実施することなく、巻取を行なつて、厚さ8.8mm
の鋼片を得た（比較法）。
このようにして得た各鋼片の1/3幅の位置から
引張試験片（JIS 14号Ａ試験片、径６mm、Ｃ方向
切出し）、シヤルピー試験片（５mm厚さ、２mmＶ
ノツチ、Ｃ方向切出し）、水素誘起割れ試験片
（長さ100mm、幅20mm、厚さ５mm、表面仕上）及び
応力腐食割れ性試験片（長さ75mm、幅15mm、厚さ
５mm、表面仕上）を作製し、それぞれの試験に付
した。
水素誘起割れ（耐HIC）試験は、食塩５％と酢
酸0.5％を含み、硫化水素を飽和させた水溶液に
96時間浸漬し、１鋼種について６断面の検査と超
音波探傷器により判定した。評価基準は〇が割れ
なし、△が割れ長さ率が３％未満、×が割れ長さ
率が３％以上とした。ここに、割れ長さ率とは、
Ｗを板幅、ａ亀裂長さとするとき、
Σ6 1Σn 1aij／6Wで規定される。
また、耐応力腐食割れ（耐SCC）性は、降伏強
さの70％応力を付加した条件下に行なつた。試験
終了後、表面を10倍の顕微鏡にて観察して、表面
割れを調べ、評価基準は〇が割れなし、△が割れ
が認められる、×が割れが著しいとした。
第２表に鋼板の機械的性質、衝撃特性、耐水素
誘起割れ性及び耐応力腐食割れ性を示す。本発明
の方法による鋼板は、従来の製造方法による鋼板
に比べて、機械的性質及び衝撃特性がすぐれるの
みならず、耐水素誘起割れ性及び耐応力腐食割れ
性にすぐれていることが明らかである。[Table] After finishing rolling at a temperature of
A steel billet was obtained (comparative method). A tensile test piece (JIS No. 14 A test piece, diameter 6 mm, cut in the C direction) and a sharp python test piece (5 mm thickness, 2 mm V
(notch, cut in C direction), hydrogen-induced cracking test piece (length 100 mm, width 20 mm, thickness 5 mm, surface finish) and stress corrosion cracking test piece (length 75 mm, width 15 mm, thickness 5 mm, surface finish). were prepared and subjected to each test. The hydrogen-induced cracking (HIC) test was performed using an aqueous solution containing 5% common salt and 0.5% acetic acid and saturated with hydrogen sulfide.
After soaking for 96 hours, each steel type was inspected on 6 cross sections and judged using an ultrasonic flaw detector. The evaluation criteria were as follows: ○ indicates no cracking, △ indicates a crack length ratio of less than 3%, and × indicates a crack length ratio of 3% or more. Here, the crack length ratio is
When W is the plate width and a-crack length, it is defined as Σ 6 1 Σ n 1 a ij /6W. In addition, stress corrosion cracking (SCC) resistance was tested under conditions where a stress of 70% of the yield strength was applied. After the test, the surface was observed with a 10x microscope to check for surface cracks, and the evaluation criteria were: ○ means no cracks, Δ means cracks are observed, and × means severe cracks. Table 2 shows the mechanical properties, impact properties, hydrogen-induced cracking resistance, and stress corrosion cracking resistance of the steel sheets. It is clear that the steel plate produced by the method of the present invention not only has superior mechanical properties and impact properties, but also superior hydrogen-induced cracking resistance and stress corrosion cracking resistance compared to steel plates produced by conventional methods. be.
Claims (1)
延した後、オーステナイト未再結晶域における全
圧下率を30％以上とし、温度900〜800℃にて仕上
圧延した後、平均冷却速度15〜80℃／秒にて温度
750〜650℃まで冷却し、加工率３〜20％にて軽圧
下することを特徴とする耐水素誘起割れ性及び耐
応力腐食割れ性にすぐれた高強度高靭性熱延鋼板
の製造方法。 ２ 重量％で (a)Ｃ 0.03〜0.3％、 Si 0.01〜1.0％、 Mn 0.5〜2.0％、 Al 0.005〜0.05％、及び、 (b)Nb 0.1％以下、 Ti 0.05％以下、 Ｖ 0.1％以下、 Cr 1.0％以下、 Cu 1.0％以下、 Mo 0.2％以下、及び、 Ni 0.2％以下よりなる群から選ばれる少なく
とも１種の元素、 残部鉄及び不可避的不純物よりなる鋼片を粗圧
延した後、オーステナイト未再結晶域における全
圧下率を30％以上とし、温度900〜800℃にて仕上
圧延した後、平均冷却速度15〜80℃／秒にて温度
750〜650℃まで冷却し、加工率３〜20％にて軽圧
下することを特徴とする耐水素誘起割れ性及び耐
応力腐食割れ性にすぐれた高強度高靭性熱延鋼板
の製造方法。 ３ 重量％で (a)Ｃ 0.03〜0.3％、 Si 0.01〜1.0％、 Mn 0.5〜2.0％、 Al 0.005〜0.05％、及び、 (b)Nb 0.1％以下、 Ti 0.05％以下、 Ｖ 0.1％以下、 Cr 1.0％以下、 Cu 1.0％以下、 Mo 0.2％以下、及び、 Ni 0.2％以下よりなる群から選ばれる少なく
とも１種の元素、 (c) Ca 0.0050％以下、 残部鉄及び不可避的不純物よりなる鋼片を粗圧
延した後、オーステナイト未再結晶域における全
圧下率を30％以上とし、温度900〜800℃にて仕上
圧延した後、平均冷却速度15〜80℃／秒にて温度
750〜650℃まで冷却し、加工率３〜20％にて軽圧
下することを特徴とする耐水素誘起割れ性及び耐
応力腐食割れ性にすぐれた高強度高靭性熱延鋼板
の製造方法。[Claims] After rough rolling a steel billet consisting of 1% by weight of C 0.03-0.3%, Si 0.01-1.0%, Mn 0.5-2.0%, Al 0.005-0.05%, the balance being iron and unavoidable impurities, After final rolling at a temperature of 900 to 800°C with a total rolling reduction of 30% or more in the austenite non-recrystallized area, the temperature is reduced to an average cooling rate of 15 to 80°C/sec.
A method for producing a high-strength, high-toughness hot-rolled steel sheet with excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance, which comprises cooling to 750 to 650°C and lightly rolling the steel plate at a processing rate of 3 to 20%. 2 Weight%: (a) C 0.03-0.3%, Si 0.01-1.0%, Mn 0.5-2.0%, Al 0.005-0.05%, and (b) Nb 0.1% or less, Ti 0.05% or less, V 0.1% or less After rough rolling a steel billet consisting of at least one element selected from the group consisting of , Cr 1.0% or less, Cu 1.0% or less, Mo 0.2% or less, and Ni 0.2% or less, the balance being iron and unavoidable impurities, After final rolling at a temperature of 900 to 800°C with a total rolling reduction of 30% or more in the austenite non-recrystallized area, the temperature is reduced to an average cooling rate of 15 to 80°C/sec.
A method for producing a high-strength, high-toughness hot-rolled steel sheet with excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance, which comprises cooling to 750 to 650°C and lightly rolling the steel plate at a processing rate of 3 to 20%. 3 Weight% (a) C 0.03-0.3%, Si 0.01-1.0%, Mn 0.5-2.0%, Al 0.005-0.05%, and (b) Nb 0.1% or less, Ti 0.05% or less, V 0.1% or less , at least one element selected from the group consisting of Cr 1.0% or less, Cu 1.0% or less, Mo 0.2% or less, and Ni 0.2% or less, (c) Ca 0.0050% or less, the balance consisting of iron and inevitable impurities. After rough rolling a steel billet, the total rolling reduction in the austenite non-recrystallized region is 30% or more, and after finish rolling at a temperature of 900 to 800°C, the temperature is reduced at an average cooling rate of 15 to 80°C/sec.
A method for producing a high-strength, high-toughness hot-rolled steel sheet with excellent hydrogen-induced cracking resistance and stress corrosion cracking resistance, which comprises cooling to 750 to 650°C and lightly rolling the steel plate at a processing rate of 3 to 20%.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21712684A JPS6196030A (en) | 1984-10-15 | 1984-10-15 | Manufacture of high strength and high toughness hot rolled steel plate having superior resistance to hydrogen induced cracking and stress corrosion cracking |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21712684A JPS6196030A (en) | 1984-10-15 | 1984-10-15 | Manufacture of high strength and high toughness hot rolled steel plate having superior resistance to hydrogen induced cracking and stress corrosion cracking |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6196030A JPS6196030A (en) | 1986-05-14 |
| JPS6410565B2 true JPS6410565B2 (en) | 1989-02-22 |
Family
ID=16699257
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP21712684A Granted JPS6196030A (en) | 1984-10-15 | 1984-10-15 | Manufacture of high strength and high toughness hot rolled steel plate having superior resistance to hydrogen induced cracking and stress corrosion cracking |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6196030A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0813534A (en) * | 1994-07-04 | 1996-01-16 | Shinwa Kogyo Kk | Rolling mechanism of attachment for construction machinery |
| JPH08165676A (en) * | 1994-12-16 | 1996-06-25 | Shinwa Kogyo Kk | Rotary mechanism of attachment to construction machine |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5454883A (en) * | 1993-02-02 | 1995-10-03 | Nippon Steel Corporation | High toughness low yield ratio, high fatigue strength steel plate and process of producing same |
| JP4937222B2 (en) * | 2007-12-25 | 2012-05-23 | 東海ゴム工業株式会社 | Fluid filled anti-vibration connecting rod |
-
1984
- 1984-10-15 JP JP21712684A patent/JPS6196030A/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0813534A (en) * | 1994-07-04 | 1996-01-16 | Shinwa Kogyo Kk | Rolling mechanism of attachment for construction machinery |
| JPH08165676A (en) * | 1994-12-16 | 1996-06-25 | Shinwa Kogyo Kk | Rotary mechanism of attachment to construction machine |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6196030A (en) | 1986-05-14 |
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