JPH0222123B2 - - Google Patents
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- Publication number
- JPH0222123B2 JPH0222123B2 JP56069346A JP6934681A JPH0222123B2 JP H0222123 B2 JPH0222123 B2 JP H0222123B2 JP 56069346 A JP56069346 A JP 56069346A JP 6934681 A JP6934681 A JP 6934681A JP H0222123 B2 JPH0222123 B2 JP H0222123B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- temperature
- transformation point
- hydrogen embrittlement
- 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 - Lifetime
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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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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- 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
本発明は耐水素脆化特性にすぐれた引張強さ
600MPa以上の高張力鋼の製造方法に関するもの
である。
近年、硫化水素をふくむ石油やガスの輸送およ
び貯蔵用の鋼構造物の需要が増大し、それに伴な
い鋼に侵入する水素に起因する鋼の割れ発生およ
び脆化が問題となつている。このような水素脆性
においては、割れの発生は主として硫化物を代表
とする非金属介在物におこり、耐水素脆性を改善
するための従来の方法は硫化物を減少させるか、
あるいは硫化物の形状を球状に近ずけることが主
な手法である。一方水素脆性は一般に鋼の強度が
高くなるほど顕著になるが、鋼の高強度化のため
には鋼の組織をマルテンサイトあるいはベイナイ
トにすることが一般的である。しかしこれらの組
織では、とくに焼もどし脆化を生じた場合に水素
の共存によつて旧オーステナイト粒界で破壊がお
こりやすくなる。
本発明者らは、引張強さで600MPa以上、した
がつて金属組織としてマルテンサイト、あるいは
ベイナイトの鋼で、耐水素脆化特性を改善する方
法を種々研究し、以下にのべる方法で製造された
鋼がいちじるしくすぐれた特性を有することを見
出した。本発明の骨子とするところはＶを含有す
る鋼を比較的低温のオーステナイト域で加工し、
そのまま急速冷却してマルテンサイト、ベイナイ
トあるいはこれらの混合組織とし、さらにそれを
焼もどすことによつて耐水素脆化特性をいちじる
しく向上させることにある。以下に本発明の詳細
と限定理由をのべる。
鋼の成分は重量パーセントでＣ：0.02〜0.40
％、Si：0.01〜1.5％、Mn：0.2〜2.0％、Ｖ：0.03
〜0.50％、Ｎ：0.004％超〜0.03％と、Al：0.05％
以下、Ti：0.08％以下、Nb：0.2％以下の１種ま
たは２種以上を主要成分とする。鋼の板厚に応じ
て焼入性を高め、また耐食性の改善あるいは粒界
割れの防止のために１％以下のMo、２％以下の
Cu、２％以下のCr、３％以下のNi、0.005％以下
のＢなどの１種または２種以上を添加することは
通常の低合金鋼の設計手法として必要に応じて併
用することが出来る。
Ｃの下限を0.02％とした理由はこれ未満ではマ
ルテンサイトあるいはベイナイト組織とすること
が困難で本発明の目的とする600MPa以上の強度
を得ることが困難であり、また上限を0.40％とし
た理由はこれを超えると本発明におけるオーステ
ナイトからの急速冷却の際に割れを発生したり、
また靭性が低下するためである。
Siは鋼の脱酸と強化のために添加されるもので
0.01％未満では脱酸の効果は少なく、また1.5％
超では靭性の低下がいちじるしい。
Mnは脱酸、強化および焼入性のために添加さ
れるものである。そのためには0.2％が下限とし
て必要であり、また２％超では急速冷却の際に残
留オーステナイトが増加し組織の均一化が困難に
なるので２％上限とした。
Ｖは本発明の主要な構成因子である。Ｖは制御
圧延法による圧延のままのフエライト、パーライ
ト組織高張力鋼の強化元素として従来から用いら
れている。本発明はＶ添加鋼を熱間圧延後そのま
ま急速冷却、焼もどしを行うことによつて通常の
熱間加工後、いつたん冷却し再加熱を行う焼入れ
焼もどし処理よりはるかにすぐれた耐水素脆化特
性を与えることが出来ることを見出したものであ
る。その効果は以下にのべるようにAl、Ti、
Nb、Ｎなどの合金元素および熱間圧延条件に依
存するがＶ添加の効果を得るためには0.03％以上
は必要であるが過剰に加えることは高価である上
に靭性の低下をまねくので0.50％を上限とした。
Ｖの作用の機構は必ずしも明確ではないが多量の
Ｖ炭窒化物の微細析出が水素を鋼中に分散し、局
所的な集積を防止する効果を持つと考えられる。
後にのべるようにこの効果を有効にするために熱
間加工後の直接焼入れが成分系とともに必須であ
る。
Al、Ti、Nbは銅の脱酸とともに、加熱時のオ
ーステナイト粒を微粒にするために１種または２
種以上が添加される。そのためにはAl、Ti、Nb
のそれぞれについて0.05％以下、0.08％以下、お
よび0.2％以下で十分であり、過剰にすぎると析
出物の粗大化あるいは溶接部の硬化などで靭性低
下をまねくおそれがあるのでこれらの数値を上限
とした。
さらにＮはＶおよびAl、Ti、Nbの窒化物を形
成させるために必須であり、0.004％超は高強度
を得る下原である。Ｎ量は多いほど析出量も増加
するが、過剰にすぎるととくに溶接部において靭
性低下の原因となり、また添加技術も困難になつ
て実際的でないので0.03％を上限とした。
本発明の特徴は、上記の成分系の鋼に以下の加
工熱履歴を与えることにある。まず加熱温度とし
てはAc3変態点、すなわち鋼を昇温時にフエライ
トからオーステナイト変態が終了する温度以上に
とり、かつ1200℃以下、好ましくは1150℃以下に
する。これはＶの炭窒化物をマトリツクス中に溶
解するとともに、オーステナイト結晶粒が粗大に
すぎないようにするためであり、Al、Ti、Nbな
どの元素の添加および適量のＮの共存によつて達
成されるものである。加熱上下限の温度はこの理
由で定められる。加熱された鋼はオーステナイト
域で圧延または鍛造などの加工が施される。これ
は勿論所定の形状に調整することが一つの目的で
あるが、耐水素脆化特性という観点からも必要な
工程であり、その効果を得るためには鋼片または
鋼片の断面積減少率、すなわち初期断面積と加工
による断面積の減少量の比が50％以上あることが
必要である。加工温度は加熱温度にも依存する
が、1000℃以下の好ましくは900℃以下での加工
量を大きくとることがのぞましい。オーステナイ
ト域での加工を終了した後、鋼はAr3変態点以上
から、すなわちオーステナイトからフエライト変
態が開始される温度以下に自然に冷却されること
なく、熱間加工後オーステナイト域から水、空
気、油あるいはこれらの混合物などを用いてオー
ステナイトからの変態が終了するまで強制冷却さ
れる。本発明の対象は引張強さ600MPa以上の高
張力鋼で組織はマルテンサイト、ベイナイト、あ
るいはこれらの混合組織である。したがつて冷却
時の到達温度はマルテンサイト、あるいはベイナ
イトの変態開始温度以下とする。所要の冷却温度
としては成分系によるがおおむね５℃／秒以上で
あることが必要である。冷却到達温度として200
℃程度が十分なマルテンサイト、あるいはベイナ
イト組織が得られる温度である。鋼はひきつづき
Ac1変態温度、すなわち昇温時にフエライトから
オーステナイトへの変態が開始される温度以上に
焼もどされるが、これは靭性を改良するためとＶ
の炭窒化物を析出させるためである。このために
は焼もどし温度を300℃以上にとることが必要で
ある。
以上のようにして得られた鋼は同一組成の鋼に
通常の焼入れ焼もどし処理をほどこしたものにく
らべてＶの炭窒化物の析出がきわめて微細かつ均
一であり、耐水素脆化特性にきわめてすぐれてい
る。
次に本発明の具体的実施例について説明する。
第１表に用いた鋼材の化学成分を示した。鋼Ａ
〜Ｅは本発明鋼、Ｆは比較鋼である。これらの鋼
を雰囲気を制御した高周波溶解炉を用いて50Kgの
鋼塊に溶製した。熱間加工は圧延によつて行なつ
た。圧延条件および熱処理条件とそれによつて得
られた強度と水素脆化感受性とを第２表に示す。
水素脆化感受性は試料を陰極とする電解溶液の電
気分解で試料に水素を供給しつつ引張試験を行
い、その破断強さで評価した。すなわち試料は直
径７mmの丸棒に円周状に深さ1.5mm、切欠き底半
径0.25mmの切欠きをつけたもので0.02mm／minの
引張速度で引張を行なつた。水素添加を行なつた
ときに生ずる切欠き引張強さの減少量を水素添加
をしないときの切欠き引張強さで除した値を水素
脆化度とした。水素添加の電解条件は電解溶液と
して0.1規定H2SO4に５mg／のAs2O3を加えた
液を用いて、電流密度は10ｍＡ／cm2とした。
第２表の実験番号１、３、５、６、８、10が本
発明による鋼であり、水素脆化度が小さいことが
明らかである。
The present invention has excellent tensile strength and hydrogen embrittlement resistance.
This relates to a method for producing high tensile strength steel of 600 MPa or higher. In recent years, the demand for steel structures for transporting and storing oil and gas containing hydrogen sulfide has increased, and as a result, cracking and embrittlement of steel due to hydrogen penetrating the steel have become problems. In such hydrogen embrittlement, cracks occur mainly in non-metallic inclusions, typically sulfides, and conventional methods to improve hydrogen embrittlement resistance include reducing sulfides or
Alternatively, the main method is to make the shape of the sulfide closer to a spherical shape. On the other hand, hydrogen embrittlement generally becomes more pronounced as the strength of steel increases, and in order to increase the strength of steel, it is common to change the structure of the steel to martensite or bainite. However, in these structures, especially when tempered embrittlement occurs, the coexistence of hydrogen tends to cause fracture at prior austenite grain boundaries. The present inventors have researched various ways to improve the hydrogen embrittlement resistance of steels with a tensile strength of 600 MPa or more and a metal structure of martensite or bainite, and have produced a steel using the method described below. It has been discovered that steel has particularly excellent properties. The gist of the present invention is to process V-containing steel in a relatively low-temperature austenite region,
The purpose is to rapidly cool the material as it is to form martensite, bainite, or a mixed structure thereof, and then further temper it to significantly improve the hydrogen embrittlement resistance. The details of the present invention and the reasons for its limitations will be described below. The composition of steel is C: 0.02 to 0.40 in weight percent.
%, Si: 0.01-1.5%, Mn: 0.2-2.0%, V: 0.03
~0.50%, N: over 0.004% ~0.03%, Al: 0.05%
Hereinafter, the main components are one or more of Ti: 0.08% or less and Nb: 0.2% or less. In order to increase hardenability depending on the thickness of the steel, improve corrosion resistance, or prevent intergranular cracking, Mo content of 1% or less and Mo content of 2% or less are added.
Adding one or more of Cu, 2% or less Cr, 3% or less Ni, 0.005% or less B can be used in combination as necessary as a normal design method for low alloy steel. . The reason why the lower limit of C was set to 0.02% is that if it is less than this, it is difficult to form a martensite or bainite structure and it is difficult to obtain the strength of 600 MPa or more, which is the objective of the present invention, and the reason why the upper limit was set to 0.40%. If it exceeds this, cracks may occur during rapid cooling from austenite in the present invention,
This is also because toughness decreases. Si is added to deoxidize and strengthen steel.
Less than 0.01% has little deoxidizing effect, and 1.5%
In super steel, the decrease in toughness is noticeable. Mn is added for deoxidation, strengthening, and hardenability. For this purpose, 0.2% is required as the lower limit, and since if it exceeds 2%, retained austenite increases during rapid cooling, making it difficult to make the structure uniform, so the upper limit was set at 2%. V is a major component of the present invention. V has been conventionally used as a strengthening element for high-strength steels with ferrite and pearlite structures as rolled by controlled rolling. The present invention rapidly cools and tempers V-added steel as it is after hot rolling, resulting in much better resistance to hydrogen embrittlement than the usual quenching and tempering process, which involves cooling and reheating after hot working. It was discovered that it is possible to impart the properties of oxidation. The effect is as described below for Al, Ti,
Although it depends on alloying elements such as Nb and N and hot rolling conditions, 0.03% or more is necessary to obtain the effect of V addition, but adding too much is expensive and causes a decrease in toughness, so 0.50% or more is required. The upper limit was %.
Although the mechanism of the action of V is not necessarily clear, it is thought that the fine precipitation of a large amount of V carbonitrides disperses hydrogen in the steel and has the effect of preventing local accumulation.
As will be described later, direct quenching after hot working is essential as well as component system in order to make this effect effective. Al, Ti, and Nb are used to deoxidize copper and to make austenite grains finer during heating.
More than one seed is added. For this purpose, Al, Ti, Nb
It is sufficient to use 0.05% or less, 0.08% or less, and 0.2% or less for each of did. Furthermore, N is essential for forming nitrides of V, Al, Ti, and Nb, and more than 0.004% is a base material for obtaining high strength. As the amount of N increases, the amount of precipitation increases, but too much N causes a decrease in toughness, especially in welded parts, and addition techniques become difficult and impractical, so 0.03% is set as the upper limit. The feature of the present invention is to provide the following processing heat history to the steel having the above-mentioned composition system. First, the heating temperature is set to be above the Ac 3 transformation point, that is, the temperature at which the steel undergoes transformation from ferrite to austenite during heating, and below 1200°C, preferably below 1150°C. This is done to dissolve V carbonitrides in the matrix and to prevent austenite crystal grains from being too coarse. This is achieved by adding elements such as Al, Ti, and Nb and coexisting with an appropriate amount of N. It is something that will be done. The upper and lower heating limits are determined for this reason. The heated steel is subjected to processing such as rolling or forging in the austenitic region. Of course, one purpose of this is to adjust it to a predetermined shape, but it is also a necessary process from the perspective of hydrogen embrittlement resistance, and in order to obtain this effect, the cross-sectional area reduction rate of the steel slab or That is, the ratio of the initial cross-sectional area to the amount of reduction in cross-sectional area due to processing must be 50% or more. Although the processing temperature also depends on the heating temperature, it is desirable to increase the processing amount at 1000°C or lower, preferably 900°C or lower. After finishing working in the austenite region, the steel is not cooled naturally from above the Ar3 transformation point, that is, below the temperature at which austenite to ferrite transformation begins, and after hot working, the steel is removed from the austenite region by water, air, etc. Forced cooling is performed using oil or a mixture thereof until the transformation from austenite is completed. The object of the present invention is high-tensile steel having a tensile strength of 600 MPa or more, and the structure is martensite, bainite, or a mixed structure thereof. Therefore, the temperature reached during cooling should be below the transformation start temperature of martensite or bainite. The required cooling temperature depends on the component system, but it needs to be approximately 5° C./second or higher. 200 as the cooling temperature reached
℃ is the temperature at which a sufficient martensite or bainite structure can be obtained. Steel continues
Ac 1 transformation temperature, that is, the temperature at which the transformation from ferrite to austenite starts when the temperature is increased, is tempered, but this is done to improve toughness and V
This is to precipitate carbonitrides. For this purpose, it is necessary to set the tempering temperature to 300°C or higher. The steel obtained as described above has extremely fine and uniform precipitation of V carbonitrides compared to steel of the same composition subjected to ordinary quenching and tempering treatment, and has extremely good hydrogen embrittlement resistance. It is excellent. Next, specific examples of the present invention will be described. Table 1 shows the chemical composition of the steel materials used. Steel A
~E is the invention steel, F is the comparison steel. These steels were melted into 50Kg steel ingots using a high-frequency melting furnace with a controlled atmosphere. Hot working was performed by rolling. Table 2 shows the rolling conditions and heat treatment conditions, as well as the resulting strength and hydrogen embrittlement susceptibility.
Hydrogen embrittlement susceptibility was evaluated by tensile testing while supplying hydrogen to the sample by electrolysis of an electrolytic solution using the sample as a cathode, and by its breaking strength. That is, the sample was a round bar with a diameter of 7 mm with a circumferential notch of 1.5 mm in depth and 0.25 mm in bottom radius, and tension was applied at a tensile rate of 0.02 mm/min. The degree of hydrogen embrittlement was defined as the amount of decrease in notch tensile strength that occurs when hydrogen is added divided by the notch tensile strength when hydrogen is not added. The electrolytic conditions for hydrogenation were as follows: 0.1 N H 2 SO 4 and 5 mg/A of As 2 O 3 were used as the electrolytic solution, and the current density was 10 mA/cm 2 . Experiment numbers 1, 3, 5, 6, 8, and 10 in Table 2 are steels according to the present invention, and it is clear that the degree of hydrogen embrittlement is small.
【表】【table】
【表】【table】
Claims (1)
0.01〜1.5％、Mn：0.2〜2.0％、Ｖ：0.03〜0.50
％、Ｎ：0.004％超〜0.03％とAl：0.05％以下、
Ti：0.08％以下、Nb：0.2％以下の１種または２
種以上を含み、残部実質的にFeからなる鋼を、
1200℃以下のオーステナイト温度域において50％
以上の加工を加えた後に、Ar3変態点以上の温度
から強制的にAr1変態点以下に冷却し、マルテン
サイト、ベイナイトあるいはこれらの混合組織と
し、さらに300℃以上Ac1変態点以下の温度で焼
もどすことを特徴とする耐水素脆化特性にすぐれ
た高張力鋼の製造方法。 ２ 重量パーセントでＣ：0.02〜0.40％、Si：
0.01〜1.5％、Mn：0.2〜2.0％、Ｖ：0.03〜0.50
％、Ｎ：0.004％超〜0.03％とAl：0.05％以下、
Ti：0.08％以下、Nb：0.2％以下の１種または２
種以上に、さらにCr：2.0％以下、Mo：1.0％以
下、Ni：3.0％以下、Cu：2.0％以下、Ｂ：0.005
％以下の１種または２種以上を含み、残部実質的
にFeからなる鋼を、1200℃以下のオーステナイ
ト温度域において50％以上の加工を加えた後に、
Ar3変態点以上の温度から強制的にAr1変態点以
下に冷却し、マルテンサイト、ベイナイトあるい
はこれらの混合組織とし、さらに300℃以上Ac1
変態点以下の温度で焼もどすことを特徴とする耐
水素脆化特性にすぐれた高張力鋼の製造方法。[Claims] 1. C: 0.02 to 0.40%, Si:
0.01~1.5%, Mn: 0.2~2.0%, V: 0.03~0.50
%, N: more than 0.004% to 0.03% and Al: 0.05% or less,
Ti: 0.08% or less, Nb: 0.2% or less type 1 or 2
A steel containing more than
50% in the austenite temperature range below 1200℃
After applying the above processing, it is forcibly cooled from a temperature above the Ar 3 transformation point to below the Ar 1 transformation point to form a martensite, bainite, or a mixed structure of these, and then at a temperature of 300℃ or above and below the Ac 1 transformation point. A method for producing high-strength steel with excellent hydrogen embrittlement resistance, which is characterized by tempering the steel. 2. C: 0.02-0.40%, Si: in weight percent
0.01~1.5%, Mn: 0.2~2.0%, V: 0.03~0.50
%, N: more than 0.004% to 0.03% and Al: 0.05% or less,
Ti: 0.08% or less, Nb: 0.2% or less type 1 or 2
More than species, Cr: 2.0% or less, Mo: 1.0% or less, Ni: 3.0% or less, Cu: 2.0% or less, B: 0.005
After applying 50% or more processing in an austenitic temperature range of 1200℃ or less to a steel containing one or more of
The temperature is forcibly cooled from the Ar 3 transformation point or higher to the Ar 1 transformation point or lower to form martensite, bainite, or a mixture of these, and then the Ac 1
A method for producing high-strength steel with excellent hydrogen embrittlement resistance, which is characterized by tempering at a temperature below the transformation point.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6934681A JPS57185920A (en) | 1981-05-11 | 1981-05-11 | Manufacture of high tensile steel with superior hydrogen embrittlement resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6934681A JPS57185920A (en) | 1981-05-11 | 1981-05-11 | Manufacture of high tensile steel with superior hydrogen embrittlement resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS57185920A JPS57185920A (en) | 1982-11-16 |
| JPH0222123B2 true JPH0222123B2 (en) | 1990-05-17 |
Family
ID=13399887
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6934681A Granted JPS57185920A (en) | 1981-05-11 | 1981-05-11 | Manufacture of high tensile steel with superior hydrogen embrittlement resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS57185920A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH062904B2 (en) * | 1984-12-04 | 1994-01-12 | 新日本製鐵株式会社 | High strength low alloy steel Extra thick steel manufacturing method |
| JPS61166918A (en) * | 1985-01-17 | 1986-07-28 | Nippon Steel Corp | Manufacture of steel with sulfide stress corrosion cracking resistance |
| JP2578598B2 (en) * | 1987-04-08 | 1997-02-05 | 新日本製鐵株式会社 | Manufacturing method of low yield ratio steel with excellent sulfide stress corrosion cracking resistance |
| CN110669990B (en) * | 2019-09-30 | 2021-02-23 | 鞍钢股份有限公司 | A kind of high-performance chromium molybdenum steel plate and production method thereof |
| CN117966046B (en) * | 2024-03-07 | 2025-08-29 | 鞍钢股份有限公司 | Alkali coal water corrosion resistant wear-resistant steel and preparation method thereof |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57158320A (en) * | 1981-03-25 | 1982-09-30 | Sumitomo Metal Ind Ltd | Production of high tensile steel plate of good weldability |
-
1981
- 1981-05-11 JP JP6934681A patent/JPS57185920A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS57185920A (en) | 1982-11-16 |
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