JPH0140091B2 - - Google Patents
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- Publication number
- JPH0140091B2 JPH0140091B2 JP57198439A JP19843982A JPH0140091B2 JP H0140091 B2 JPH0140091 B2 JP H0140091B2 JP 57198439 A JP57198439 A JP 57198439A JP 19843982 A JP19843982 A JP 19843982A JP H0140091 B2 JPH0140091 B2 JP H0140091B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- delayed fracture
- fracture resistance
- temperature
- 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
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- 229910000831 Steel Inorganic materials 0.000 claims description 73
- 239000010959 steel Substances 0.000 claims description 73
- 230000003111 delayed effect Effects 0.000 claims description 31
- 238000005496 tempering Methods 0.000 claims description 25
- 238000010791 quenching Methods 0.000 claims description 16
- 230000000171 quenching effect Effects 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 12
- 238000005098 hot rolling Methods 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 8
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 230000000052 comparative effect Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 10
- 239000000463 material Substances 0.000 description 7
- 238000005452 bending Methods 0.000 description 6
- 238000005204 segregation Methods 0.000 description 5
- 229910000851 Alloy steel Inorganic materials 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229910000746 Structural steel Inorganic materials 0.000 description 2
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 238000003303 reheating Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000712 Boron steel Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910001240 Maraging steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000003009 desulfurizing effect Effects 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 235000013619 trace mineral Nutrition 0.000 description 1
- 239000011573 trace mineral Substances 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
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 Strip Materials And Filament Materials (AREA)
- Heat Treatment Of Steel (AREA)
Description
この発明は、耐遅れ破壊性の優れた強靭鋼の製
造方法に関するものである。
近年、構造物の大型化や、乗用車、トラツク等
の軽量化指向が著しく、これにともなつて機械構
造用部品の強度に対する要求が高まつてきて、高
強度で耐遅れ破壊性の優れた鉄鋼材料の開発が強
く望まれるようになつてきた。
従来、引張強さが100Kgｆ／mm2を超える機械構
造用強靭鋼は、低合金鋼、例えばJISG4105の
SCM435やSNCM431鋼、或いはボロン鋼（0.2％
Ｃ−0.8％Cr−0.002％Ｂに代表される化学成分組
成を有する鋼。なお、以下％は重量％とする）等
の熱延材を焼入れ・焼戻し処理して製造されてい
た。
しかしながら、これらの低合金鋼のうちでも引
張強さが125Kgｆ／mm2を越えるものは、機械構造
用部品として用いた場合、使用中に遅れ破壊を生
じることがあり、自動車や土木建設機械の重要保
安部品としては品質安定性に欠けるという問題点
が指摘されていた。
この遅れ破壊とは、静荷重下におかれた鋼が相
当時間経過した後に、突然、脆性的に破断する現
象として知られており、外部環境から鋼中に侵入
した水素による一種の水素脆性とされているもの
である。
そして、このような遅れ破壊は、特に、高力ボ
ルトやPC鋼棒等の高強度材料で大きな問題とな
つており、それ故に、例えばJIS Ｂ−1186（1979）
「摩擦接合用高力六角ボルト、六角ナツト、平座
金セツト」の項においては、高力ボルトの区分と
して、
F8T（引張強さ：80〜100Kgｆ／mm2）、
F10T（引張強さ：100〜120Kgｆ／mm2）、
F11T（引張強さ：110〜130Kgｆ／mm2）、
の３種類が規定されてはいるものの、F11Tには
括弧付で“なるべく使用しないこと”という指示
までもがなされている。さらにまた、土木建設機
械用として耐摩耗性の要求される鋼板において
も、引張強さが125Kgｆ／mm2を越えるものでは、
使用中の遅れ破壊の問題が認識されるようになつ
てきている。
これに対して、18Niマルエージング鋼（例え
ば、18％Ni−7.5％Co−0.5％Ti−0.1％Al鋼）は、
通常の低合金鋼よりも耐遅れ破壊性が優れてお
り、引張強さ：150Kgｆ／mm2程度まで使用できる
ことが知られているが、これは極めて高価な鋼で
あり、また機械構造用鋼として広く使用されるま
でには至つていないのが現状である。
本発明者等は、上述のような観点から、引張強
さ：125Kgｆ／mm2以上の強度を備え、かつ耐遅れ
破壊性が従来の低合金鋼よりも格段に優れた強靭
鋼を製造すべく研究を行つたところ、
(a) 強靭鋼の耐遅れ破壊性は、旧オーステナイト
粒界に偏析するＰによつて著しく劣化するこ
と、
(b) そこで、高強度を発揮する化学成分組成を有
する鋼に存在するＰの絶対量を抑え、かつＰの
粒界偏析を助長させるMn量をも抑えるととも
に、さらに、熱処理段階でのＰの粒界偏析を極
力防止することを目ざした直接焼入れを施せ
ば、耐遅れ破壊性が格段に改善されること、
(c) しかしながら、このような鋼に対して従来の
ような高温での焼戻しを施すと、強度低下が著
しくなるばかりでなく、耐遅れ破壊性も再び劣
化するようになること、
以上、(a)〜(c)に示す如き知見を得たのである。
この発明は上記知見に基づいてなされたもので
あつて、Ｃ：0.18〜0.28％、Si：0.5％以下、
Mn：0.5％未満、Cr：0.5〜4.0％、Ｐ：0.01％以
下を含むとともに、さらに必要に応じて、Nb：
0.1％以下、Ｖ：0.3％以下、Ｂ：0.003％以下、
Ti：0.05％以下のうちの１種以上含有し、Fe及
び不可避不純物：残り、から成る成分組成の鋼を
熱間圧延後、900℃以上の仕上温度から、直接、
急冷焼入れするか、或いはさらに、これに続いて
450℃以下の温度で焼戻すことによつて、耐遅れ
破壊性の優れた強靭鋼を製造することに特徴を有
するものである。
つぎに、この発明の方法において、鋼組成、熱
延仕上温度、及び焼戻し温度を上述のように限定
した理由を説明する。
(A) 鋼組成
Ｃ
Ｃ成分には、鋼に必要な強度を確保する作
用があるが、その含有量が0.18未満では前記
作用に所望の効果が得られず、一方0.28％を
越えて含有させると、他の合金元素との関連
で靭性を劣化させる恐れがでてくるので、そ
の含有量を0.18〜0.28％と定めた。
Si
Si成分は、鋼の脱酸のために必要な元素で
あるが、その含有量が0.5％を越えると鋼の
脆化が著しくなるので、含有量の上限値を
0.5％と定めた。
Mn
Mn成分は、鋼の脱酸・脱硫のために、通
常の場合、0.5〜1.0％程度添加されるもので
あるが、このように0.5％以上Mnを含有させ
ると、添加されたMnがＰの粒界偏析を助長
して耐遅れ破壊性を著しく損なうようになる
ことから、この発明においては、Mn含有量
を0.5％未満と定めた。
Cr
Cr成分には、鋼に所定の強度と焼入性と
を付与する作用があり、さらに焼戻し軟化抵
抗性を確保する作用もあるが、その含有量が
0.5％未満では前記作用に所望の効果が得ら
れず、一方4.0％を越えて含有させてもそれ
以上の向上効果を得ることができないばかり
か、経済性を損なうことにもなるので、その
含有量を0.5〜4.0％と定めた。
Ｐ
Ｐ分は、鋼の焼戻し脆性を促進する点で有
害な微量元素であることは従来から知られて
おり、前記JIS SCM435やSNCM431におい
てもその含有量を0.030％以下に制限するこ
とが規定されているが、耐遅れ破壊性を考慮
した場合には、通常実施されているような、
Ｐ含有量が0.030％をわずかに下回る程度に
抑える対策では全く効果がなく、特定の条件
での直線焼入れ・焼戻しとの組合せとも絡ん
で、Ｐの含有量を0.01％以下に制限しないと
十分な効果を得ることができないのである。
このようなことから、Ｐの含有量を特に0.01
％以下と定めた。
Nb、及びＶ
これらの成分は、いずれも鋼の細粒化或い
は析出硬化を通じて強度上昇に有効な元素で
あるので、これらの特性をより向上させる場
合に必要に応じて添加されるものであるが、
Nb及びＶの含有量がそれぞれ0.1％及び0.3％
を越えるとそれ以上の向上効果を望めなくな
ることから、それぞれの含有量を、Nb：0.1
％以下、Ｖ：0.3％以下と定めた。
Ｂ
Ｂ成分には、微量の添加で鋼の焼入性を著
しく向上させる作用があり、部品サイズの大
きいものの場合に必要に応じて積極的に添加
して強度確保を図るが、0.003％を越えて含
有させると鋼の靭性を劣化するようになるこ
とから、その含有量を0.003％以下と定めた。
Ti
Ti成分は、Ｂ成分の焼入性向上効果を安
定して発揮させるのに有効な元素であり、特
にこのような特性を必要とする場合に添加さ
れるものであるが、0.05％を越えて含有させ
ると鋼の靭性及び被削性等を劣化するように
なることから、その含有量を0.05％以下と定
めた。
(B) 熱延仕上温度
従来、引張強さ：100Kgｆ／mm2を越える強靭
鋼は、低合金鋼の熱延棒鋼又は熱延鋼板をAc3
点以上に再加熱し、焼入れた後、Ac1点以下で
焼戻すことにより製造されていた。しかし、こ
のような再加熱焼入れ・焼戻し方式の熱処理
は、鋼中のＰの旧オーステナイト粒界偏析を促
進し、強靭鋼の耐遅れ破壊性を劣化させる原因
となつていたのである。そこで、この発明で
は、熱延を900℃以上の温度で終了し、そのま
ま直接焼入れを行つてＰが旧オーステナイト粒
界に偏析するのを抑制して耐遅れ破壊性を向上
させたのである。しかしながら、熱延の仕上温
度が900℃未満になると直接焼入焼戻し後の機
械的性質に異方性が顕著に現われ、また耐遅れ
破壊性も劣化するようになることから、直接焼
入時の温度を900℃以上にすることが極めて重
要であり、従つて熱延仕上温度を900℃以上と
定めた。
(C) 焼戻し温度
この発明において対象となる鋼は、Ｃ：0.18
〜0.28％という低炭素系強靭鋼であるので、焼
入れのままで所定の強度と延性とを備えてお
り、従つて、焼入れのままで十分機械構造用鋼
として使用できるものである。
しかしながら、使用中の応力緩和を防止する
必要のある部分に対しては、焼戻し処理を実施
するのが好ましい。この場合、焼戻し温度が
450℃を越えると、鋼材の強度低下が著しくな
るとともに耐遅れ破壊性も劣化するようになる
ので、焼戻し温度を450℃以下と定めた。
但し、焼戻し温度が300℃以上400℃未満の範
囲では低温焼戻し脆性が生じ、靭性が劣化する
と同時に耐遅れ破壊性も劣化する場合があるの
で、でき得るならば、焼戻し温度を300℃未満、
或いは400〜450℃の範囲に選ぶべきである。
また、この焼戻し温度の限定理由は、第１図
に示される鋼のＰ含有量と焼戻し温度との関係
図からも明らかである。即ち、第１図は、Ｐ含
有量の異る種々の鋼を950℃の仕上温度で加熱
圧延した後、前記仕上温度から直接水冷して焼
入れし、焼入れのまま、或いは焼入れ後種々の
温度で焼戻し処理を行い、この結果得られた鋼
について、耐遅れ破壊性を評価するための定荷
重型片持ち曲げ試験を行つた結果をプロツトし
たものである。
なお、定荷重型片持ち曲げ試験は、第２図に
正面図で示される形状（外径：22mmφ、膨出部
外径：24mmφ、膨出部長さ：60mmφ、全長：
160mm、α：60゜）の丸棒切欠付試験片を用い、
切欠底に公称曲げ応力：260Kgｆ／mm2を付加す
ると共に、切欠部に常温水を滴下して行ない、
この状態を保持しながら、前記試験片が破断に
到るまでの時間（以下t260という）を測定し
た。第１図には、これらの結果を〇印と×印で
示したが、〇印はt260が100時間以上のもの、×
印はt260が100時間未満のものをそれぞれ示す。
第１図に示される結果から、Ｐ含有量が0.01
％以下にして、直接焼入後、焼入れのまま、或
いはさらに450℃以下、好ましくは300℃未満又
は400〜450℃で焼戻した場合に優れた耐遅れ破
壊性を示すことが明らかである。
ついで、この発明を、実施例により比較例と対
比しながら説明する。
実施例 １
通常の溶解法により、それぞれ第１表に示され
る成分組成をもつた鋼を溶製した後、直径：90mm
φ×長さ：1000mmの寸法をもつたビレツトに成形
し、ついで前記ビレツトを温度：1200℃に１時間
保持して加熱した後、仕上温度が950℃となる条
件で熱間圧延を行ない、直径：25mmφ×長さ：
500mmの寸法をもつた棒材とし、引続いて前記仕
上温度から直ちに水冷による焼入れを行い、さら
に、温度：425℃に１時間保持後水冷の焼戻し処
理を行うことによつて、本発明鋼棒１〜11、及び
Mn、Ｐのいずれか一方又は両方がこの発明の範
囲から外れて高い（表中の※印で示す）の比較鋼
棒12〜17をそれぞれ製造した。
The present invention relates to a method for manufacturing strong steel with excellent delayed fracture resistance. In recent years, structures have become larger and there has been a marked trend towards lighter weight passenger cars, trucks, etc., and along with this, the demand for stronger mechanical structural parts has increased. There is a strong desire to develop materials. Conventionally, strong steel for mechanical structures with a tensile strength exceeding 100 Kgf/ mm2 has been made of low alloy steel, such as JIS G4105.
SCM435, SNCM431 steel, or boron steel (0.2%
Steel with a chemical composition represented by C-0.8%Cr-0.002%B. Note that % is hereinafter referred to as % by weight), etc., and was manufactured by quenching and tempering a hot rolled material. However, among these low-alloy steels, those with a tensile strength exceeding 125 Kgf/ mm2 may cause delayed fracture during use when used as mechanical structural parts, making them important for automobiles and civil engineering construction machinery. As a safety part, the problem of lack of quality stability was pointed out. This delayed fracture is known as a phenomenon in which steel under static load suddenly breaks brittle after a considerable period of time, and is a type of hydrogen embrittlement caused by hydrogen penetrating into the steel from the external environment. This is what is being done. This kind of delayed fracture is a big problem, especially with high-strength materials such as high-strength bolts and PC steel bars, and therefore, for example, JIS B-1186 (1979)
In the section ``High-strength hexagonal bolts, hexagonal nuts, and plain washers sets for friction bonding,'' the high-strength bolts are categorized as F8T (tensile strength: 80 to 100 Kgf/mm 2 ), F10T (tensile strength: 100 to Although three types are specified: 120Kgf/mm 2 ) and F11T (tensile strength: 110 to 130Kgf/mm 2 ), there is even a parenthetical instruction for F11T to ``do not use it as much as possible''. There is. Furthermore, even for steel plates for civil engineering and construction machinery that require wear resistance, those with a tensile strength exceeding 125Kgf/ mm2 are
The problem of delayed failure during use is becoming recognized. In contrast, 18Ni maraging steel (e.g., 18%Ni-7.5%Co-0.5%Ti-0.1%Al steel)
It is known that it has better delayed fracture resistance than ordinary low alloy steel and can be used up to a tensile strength of about 150Kgf/ mm2 , but this is an extremely expensive steel and is not suitable for mechanical structural steel. At present, it has not yet reached the point of widespread use. From the above-mentioned viewpoints, the present inventors aimed to produce a strong steel with a tensile strength of 125 Kgf/mm 2 or more and a delayed fracture resistance significantly superior to that of conventional low-alloy steel. Our research revealed that (a) the delayed fracture resistance of high-strength steel is significantly degraded by P segregated at prior austenite grain boundaries; (b) therefore, we found that steel with a chemical composition that exhibits high strength In addition to suppressing the absolute amount of P present in the steel, and also suppressing the amount of Mn that promotes grain boundary segregation of P, direct quenching is performed with the aim of preventing grain boundary segregation of P as much as possible during the heat treatment stage. (c) However, when such steel is tempered at conventional high temperatures, not only does the strength decrease significantly, but the delayed fracture resistance is significantly improved. We have obtained the findings shown in (a) to (c) above, that the material also begins to deteriorate again. This invention was made based on the above findings, and includes C: 0.18 to 0.28%, Si: 0.5% or less,
Contains Mn: less than 0.5%, Cr: 0.5 to 4.0%, P: 0.01% or less, and further contains Nb:
0.1% or less, V: 0.3% or less, B: 0.003% or less,
After hot rolling, a steel containing one or more of Ti: 0.05% or less and the remainder of Fe and unavoidable impurities is directly rolled from a finishing temperature of 900℃ or higher.
Rapid cooling quenching or further, following this
It is characterized by producing strong steel with excellent delayed fracture resistance by tempering at a temperature of 450°C or lower. Next, the reason why the steel composition, hot rolling finishing temperature, and tempering temperature are limited as described above in the method of the present invention will be explained. (A) Steel composition C The C component has the effect of ensuring the strength required for steel, but if its content is less than 0.18%, the desired effect cannot be obtained, and on the other hand, if it is contained in excess of 0.28%. Since there is a risk of deterioration of toughness in relation to other alloying elements, the content was set at 0.18 to 0.28%. Si The Si component is an element necessary for deoxidizing steel, but if its content exceeds 0.5%, the steel will become brittle, so the upper limit of the content should be set.
It was set at 0.5%. Mn The Mn component is normally added in an amount of about 0.5 to 1.0% for deoxidizing and desulfurizing steel, but when Mn is added in this way, 0.5% or more, the added Mn becomes P. In this invention, the Mn content is determined to be less than 0.5% because this promotes grain boundary segregation and significantly impairs delayed fracture resistance. Cr The Cr component has the effect of imparting a certain strength and hardenability to steel, and also has the effect of ensuring temper softening resistance, but its content is
If the content is less than 0.5%, the desired effect cannot be obtained, while if the content exceeds 4.0%, not only will no further improvement effect be obtained, but it will also impair economic efficiency. The amount was determined to be 0.5-4.0%. PP It has long been known that P is a harmful trace element that promotes tempering brittleness in steel, and the aforementioned JIS SCM435 and SNCM431 also stipulate that its content be limited to 0.030% or less. However, when considering delayed fracture resistance,
Measures to suppress the P content to just below 0.030% are completely ineffective, and combined with linear quenching and tempering under specific conditions, it is necessary to limit the P content to 0.01% or less. It cannot be effective.
For this reason, the P content is especially 0.01
% or less. Nb and V These components are elements that are effective in increasing the strength of steel through grain refinement or precipitation hardening, so they are added as necessary to further improve these properties. ,
Nb and V content are 0.1% and 0.3% respectively
If the content exceeds Nb: 0.1, no further improvement effect can be expected.
% or less, V: 0.3% or less. B The B component has the effect of significantly improving the hardenability of steel when added in small amounts, and in the case of large parts, it is actively added as necessary to ensure strength, but if it exceeds 0.003%. Since the toughness of steel deteriorates when it is contained, its content was set at 0.003% or less. Ti Ti component is an effective element to stably exhibit the hardenability improvement effect of component B, and is added especially when such properties are required, but if it exceeds 0.05%. If it is contained, the toughness and machinability of the steel will deteriorate, so the content was set at 0.05% or less. (B) Hot-rolling finishing temperature Conventionally, high-strength steels with tensile strength exceeding 100Kgf/ mm2 are made of low-alloy steel hot-rolled steel bars or hot-rolled steel sheets at Ac 3
It was produced by reheating above the Ac point, quenching, and then tempering below the Ac point . However, such heat treatment using the reheating quenching/tempering method promotes the segregation of P in the steel at the prior austenite grain boundaries, causing a deterioration in the delayed fracture resistance of the tough steel. Therefore, in this invention, hot rolling is completed at a temperature of 900° C. or higher, and direct quenching is performed as it is to suppress segregation of P at prior austenite grain boundaries and improve delayed fracture resistance. However, when the finishing temperature of hot rolling is less than 900℃, anisotropy appears in the mechanical properties after direct quenching and tempering, and delayed fracture resistance also deteriorates. It is extremely important to keep the temperature at 900°C or higher, and therefore the hot rolling finishing temperature was set at 900°C or higher. (C) Tempering temperature The steel targeted by this invention is C: 0.18
Since it is a low-carbon tough steel with a carbon content of ~0.28%, it has a certain level of strength and ductility even after quenching, and therefore can be used as a mechanical structural steel even after quenching. However, it is preferable to perform a tempering treatment on parts where it is necessary to prevent stress relaxation during use. In this case, the tempering temperature is
If the temperature exceeds 450°C, the strength of the steel material will significantly decrease and the delayed fracture resistance will also deteriorate, so the tempering temperature was set at 450°C or less. However, if the tempering temperature is in the range of 300℃ or higher and lower than 400℃, low-temperature tempering brittleness may occur, and the toughness and delayed fracture resistance may deteriorate at the same time, so if possible, the tempering temperature should be lower than 300℃ or lower.
Alternatively, the temperature should be selected within the range of 400 to 450°C. Moreover, the reason for this limitation of the tempering temperature is also clear from the relationship diagram between the P content of the steel and the tempering temperature shown in FIG. That is, Fig. 1 shows that various steels with different P contents are heated and rolled at a finishing temperature of 950°C, then quenched by direct water cooling from the finishing temperature, and then either as quenched or at various temperatures after quenching. This is a plot of the results of a constant load cantilever bending test for evaluating delayed fracture resistance of the steel obtained after tempering. For the constant load cantilever bending test, the shape shown in the front view in Fig. 2 (outer diameter: 22 mmφ, bulge outside diameter: 24 mmφ, bulge length: 60 mmφ, total length:
Using a round bar test piece with a notch of 160mm, α: 60°,
A nominal bending stress of 260Kgf/ mm2 was applied to the bottom of the notch, and room temperature water was dripped into the notch.
While maintaining this state, the time required for the test piece to break (hereinafter referred to as t260 ) was measured. In Figure 1, these results are shown with ○ and × marks, where ○ marks indicate those with t 260 of 100 hours or more, ×
Each mark indicates a t260 of less than 100 hours. From the results shown in Figure 1, the P content is 0.01
% or less, it is clear that excellent delayed fracture resistance is exhibited when directly quenched, as-quenched, or further tempered at 450°C or below, preferably below 300°C, or from 400 to 450°C. Next, the present invention will be explained using Examples and comparing with Comparative Examples. Example 1 After melting steel having the composition shown in Table 1 by a normal melting method, a diameter of 90 mm was produced.
The billet was formed into a billet with dimensions of φ x length: 1000 mm, and then the billet was heated at a temperature of 1200°C for 1 hour, and then hot rolled at a finishing temperature of 950°C. :25mmφ×Length:
The steel rod of the present invention is made into a bar with a size of 500 mm, and then immediately quenched by water cooling from the above finishing temperature, and further tempered by water cooling after being held at a temperature of 425°C for 1 hour. 1 to 11, and
Comparative steel bars 12 to 17 were manufactured, respectively, in which either one or both of Mn and P was high (indicated by * in the table) outside the scope of the present invention.
【表】【table】
【表】
このようにして得られた各種の鋼棒から、平行
部直径：14mmφの引張試験片及び第２図に示され
る上記した寸法の定荷重型片持ち曲げ試験用試験
片を切出し、常温引張強さ及び上記した条件と同
一の条件にて破断時間（t260）を測定した。これ
らの測定結果を第１表に併せて示した。なお、第
１表の破断時間（t260）の欄における〇印は100
時間以上の破断時間であつたことを示し、同×印
は100時間未満の破断時間であつたことを示すも
のである。
第１表に示される結果から、本発明鋼棒１〜11
は、いずれも引張強さ：130Kgｆ／mm2の高強度を
有し、かつt260も100時間以上の優れた耐遅れ破
壊性を示すのに対して、Mn、Ｐのいずれか一方
又は両方がこの発明の範囲から外れた比較鋼棒12
〜16、及びJIS SCM435に相当する比較鋼棒17
は、引張強さ：130Kgｆ／mm2以上の高強度を示す
ものの、耐遅れ破壊性はいずれも劣つたものであ
ることが明らかである。
実施例 ２
成分組成を第２表に示されるようなものとし、
かつ、板材の寸法を、厚さ：25mm×幅：100mm×
長さ：500mmとする以外は、実施例１におけると
同一の条件で本発明鋼板１〜５、及び比較鋼板６
〜７をそれぞれ直接焼入れした。そして、この
後、250℃或いは425℃に１時間保持後水冷の焼戻
処理を行つた。
なお、比較鋼板６及び７は、それぞれＰ及び
Mnの含有量がこの発明の範囲から外れて高い
（表中の※印で示す）組成をもつものである。ま
た、第２表には、実施例１におけると同一の条件
で測定した引張強さ及びt260を示した。
第２表に示される結果からは、比較鋼板６及び
７に見られるように、焼入れ温度及び焼戻し温度
がその発明の範囲内にあつても、Ｐ或いはMn含
有量がこの発明の範囲から外れて高くなると、高
強度は示すものの耐遅れ破壊性の劣つたものにな
るのに対して、本発明鋼板１〜５はいずれも高強
度とともに優れた耐遅れ破壊性をもつことが明ら
かである。[Table] From the various steel bars obtained in this way, tensile test pieces with a parallel part diameter of 14 mmφ and constant load type cantilever bending test pieces with the above dimensions shown in Fig. 2 were cut out and kept at room temperature. Tensile strength and time to break (t 260 ) were measured under the same conditions as described above. These measurement results are also shown in Table 1. In addition, the 〇 mark in the column of rupture time (t 260 ) in Table 1 is 100
The rupture time was more than 100 hours, and the cross mark indicates that the rupture time was less than 100 hours. From the results shown in Table 1, the present invention steel bars 1 to 11
Both have a high tensile strength of 130Kgf/ mm2 , and t260 also exhibits excellent delayed fracture resistance of 100 hours or more, whereas Mn, P, or both have Comparative steel bar 12 outside the scope of this invention
~16, and comparative steel bar 17 equivalent to JIS SCM435
Although they exhibit high tensile strength of 130 Kgf/mm 2 or more, it is clear that they all have poor delayed fracture resistance. Example 2 The component composition was as shown in Table 2,
And the dimensions of the plate material are Thickness: 25mm x Width: 100mm x
Invention steel plates 1 to 5 and comparative steel plate 6 were prepared under the same conditions as in Example 1 except that the length was 500 mm.
~7 were directly quenched, respectively. Thereafter, the material was held at 250°C or 425°C for 1 hour and then water-cooled for tempering. In addition, comparison steel plates 6 and 7 are P and P, respectively.
The composition has a high Mn content (indicated by * in the table) outside the scope of this invention. Table 2 also shows the tensile strength and t260 measured under the same conditions as in Example 1. From the results shown in Table 2, as seen in comparative steel sheets 6 and 7, even if the quenching temperature and tempering temperature are within the range of the invention, the P or Mn content is outside the range of the invention. When the strength increases, the delayed fracture resistance becomes poor although the steel sheets exhibit high strength, whereas it is clear that the steel plates 1 to 5 of the present invention all have high strength and excellent delayed fracture resistance.
【表】
実施例 ３
成分組成を、Ｃ：0.23％、Si：0.20％、Mn：
0.08％、Ｐ：0.004％、Cr：1.76％、Fe及びその
他の不可避不純物：残り、から成るものとし、か
つ熱間圧延後の熱処理条件を第３表に示されるも
のとする以外は、実施例２におけると同一の条件
にて、本発明鋼板９〜11、14〜16、19〜21、並び
に比較鋼板８、12〜13、17〜18、22〜32をそれぞ
れ製造し、さらに、このようにして得られた鋼板
について、実施例１におけると同一の条件にて引
張強さと破断時間（t260）を測定した。これらの
測定結果も第３表に併せて示した。なお、第３表
における※印は、焼入れ条件又は焼戻し条件が本
発明の範囲から外れていることを示すものであ
る。
第３表において、比較鋼板23〜27にみられるよ
うに仕上温度、即ち焼入温度が900℃未満の場合、
同じく比較鋼板28〜32にみられるように仕上温度
が900℃以上であつても熱間圧延後直ちに急冷し
ない場合には、高強度は得られる[Table] Example 3 Component composition: C: 0.23%, Si: 0.20%, Mn:
0.08%, P: 0.004%, Cr: 1.76%, Fe and other unavoidable impurities: the remainder, and the heat treatment conditions after hot rolling were as shown in Table 3. Inventive steel plates 9 to 11, 14 to 16, 19 to 21 and comparative steel plates 8, 12 to 13, 17 to 18, and 22 to 32 were manufactured under the same conditions as in 2, and further, The tensile strength and rupture time (t 260 ) of the obtained steel plate were measured under the same conditions as in Example 1. These measurement results are also shown in Table 3. Note that the * mark in Table 3 indicates that the quenching conditions or tempering conditions are outside the scope of the present invention. In Table 3, when the finishing temperature, that is, the quenching temperature is less than 900°C, as seen in comparative steel sheets 23 to 27,
Similarly, as seen in comparative steel plates 28 to 32, high strength can be obtained even if the finishing temperature is 900°C or higher if the steel is not rapidly cooled immediately after hot rolling.
【表】【table】
【表】
ものの、耐遅れ破壊性の劣つたものになつてい
る。このことは、焼戻し温度がこの発明の範囲か
ら外れた条件で製造された比較鋼板８、12、13、
17、18、及び22においても同様である。これに対
して、本発明鋼板はいずれも高強度と優れた耐遅
れ破壊性を兼ね備えていることが明らかである。
上述のように、この発明の方法によれば、引張
強さ：125Kgｆ／mm2以上の高強度と、定荷重型片
持ち曲げ試験で破断時間が100時間を越える優れ
た耐遅れ破壊性を具備した機械構造用強靭鋼を製
造することができ、高張力ボルト、PC鋼棒、耐
摩耗用高張力鋼板等の製造に適用することで、軽
量で、しかも極めて安全性の高い機械装置、或い
は信頼性の高い大型構造物が実現できるなど、工
業上有用な効果がもたらされるのである。[Table] However, it has poor delayed fracture resistance. This means that comparative steel sheets 8, 12, 13, which were manufactured under conditions where the tempering temperature was outside the range of the present invention,
The same applies to 17, 18, and 22. On the other hand, it is clear that all the steel plates of the present invention have both high strength and excellent delayed fracture resistance. As mentioned above, according to the method of the present invention, it has a high tensile strength of 125 Kgf/mm 2 or more and excellent delayed fracture resistance that takes more than 100 hours to break in a constant load cantilever bending test. By applying it to the production of high-tensile bolts, prestressed steel bars, high-strength steel plates for wear resistance, etc., it is possible to produce strong steel for mechanical structures that are lightweight and extremely safe. This brings about industrially useful effects, such as the ability to create large structures with high performance.
第１図は耐遅れ破壊性に及ぼすＰ含有量と焼戻
し温度との関係を示す図表、第２図は定荷重型片
持ち曲げ試験に用いる丸棒切欠付試験片の形状を
示す説明図である。
Figure 1 is a chart showing the relationship between P content and tempering temperature on delayed fracture resistance, and Figure 2 is an explanatory diagram showing the shape of a round bar test piece with a notch used in a constant load cantilever bending test. .
Claims (1)
後、900℃以上の仕上温度から直接急冷焼入れす
ることを特徴とする耐遅れ破壊性の優れた強靭鋼
の製造方法。 ２ Ｃ：0.18〜0.28％、Si：0.5％以下、 Mn：0.5％未満、Cr：0.5〜4.0％、 Ｐ：0.01％以下、 Fe及び不可避不純物：残り、 から成る成分組成（以下重量％）の鋼を熱間圧延
後、900℃以上の仕上温度から直接急冷焼入れし、
続いて、450℃以下の温度で焼戻すことを特徴と
する耐遅れ破壊性の優れた強靭鋼の製造方法。 ３ Ｃ：0.18〜0.28％、Si：0.5％以下、 Mn：0.5％未満、Cr：0.5〜4.0％、 Ｐ：0.01％以下、 更に、 Nb：0.1％以下、Ｖ：0.3％以下、 Ｂ：0.003％以下、Ti：0.05％以下 のうちの１種以上を含有し、 Fe及び不可避不純物：残り から成る成分組成（以下重量％）の鋼を熱間圧延
後、900℃以上の仕上温度から直接急冷焼入れす
ることを特徴とする耐遅れ破壊性の優れた強靭鋼
の製造方法。 ４ Ｃ：0.18〜0.28％、Si：0.5％以下、 Mn：0.5％未満、Cr：0.5〜4.0％、 Ｐ：0.01％以下、 更に、 Nb：0.1％以下、Ｖ：0.3％以下、
Ｂ：0.003％以下、Ti：0.05％以下、 うちの１種以上を含有し、 Fe及び不可避不純物：残り から成る成分組成（以下重量％）の鋼を熱間圧延
後、900℃以上の仕上温度から直接急冷焼入れし、
続いて、450℃以下の温度で焼戻すことを特徴す
る耐遅れ破壊性の優れた強靭鋼の製造方法。[Claims] 1. A composition consisting of: 1 C: 0.18 to 0.28%, Si: 0.5% or less, Mn: less than 0.5%, Cr: 0.5 to 4.0%, P: 0.01% or less, Fe and unavoidable impurities: the remainder. (hereinafter referred to as weight %) steel is hot-rolled and then directly rapidly quenched from a finishing temperature of 900°C or higher. A method for producing strong steel with excellent delayed fracture resistance. 2 C: 0.18 to 0.28%, Si: 0.5% or less, Mn: less than 0.5%, Cr: 0.5 to 4.0%, P: 0.01% or less, Fe and unavoidable impurities: remainder, of the component composition (hereinafter referred to as weight %) consisting of After hot rolling, the steel is directly quenched and quenched from a finishing temperature of 900℃ or higher.
Next, a method for producing strong steel with excellent delayed fracture resistance, which is characterized by tempering at a temperature of 450°C or lower. 3 C: 0.18 to 0.28%, Si: 0.5% or less, Mn: less than 0.5%, Cr: 0.5 to 4.0%, P: 0.01% or less, furthermore, Nb: 0.1% or less, V: 0.3% or less, B: 0.003 % or less, Ti: 0.05% or less, Fe and unavoidable impurities: After hot rolling steel with a composition (hereinafter referred to as weight %) consisting of the remainder, directly quenching from a finishing temperature of 900°C or more. A method for manufacturing strong steel with excellent delayed fracture resistance, which is characterized by quenching. 4 C: 0.18 to 0.28%, Si: 0.5% or less, Mn: less than 0.5%, Cr: 0.5 to 4.0%, P: 0.01% or less, furthermore, Nb: 0.1% or less, V: 0.3% or less,
B: 0.003% or less, Ti: 0.05% or less, containing one or more of these, Fe and unavoidable impurities: After hot rolling steel with a composition (hereinafter referred to as weight %) consisting of the remainder, the finishing temperature is 900℃ or higher. Rapidly quenched directly from
Next, we developed a method for producing strong steel with excellent delayed fracture resistance, which involves tempering at a temperature of 450°C or lower.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19843982A JPS5989716A (en) | 1982-11-12 | 1982-11-12 | Manufacture of tough steel with superior delayed rupture resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19843982A JPS5989716A (en) | 1982-11-12 | 1982-11-12 | Manufacture of tough steel with superior delayed rupture resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5989716A JPS5989716A (en) | 1984-05-24 |
| JPH0140091B2 true JPH0140091B2 (en) | 1989-08-25 |
Family
ID=16391096
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP19843982A Granted JPS5989716A (en) | 1982-11-12 | 1982-11-12 | Manufacture of tough steel with superior delayed rupture resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5989716A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2578449B2 (en) * | 1987-12-04 | 1997-02-05 | 川崎製鉄株式会社 | Manufacturing method of direct hardened high strength steel with excellent delayed cracking resistance |
| JP5726604B2 (en) * | 2010-06-11 | 2015-06-03 | 株式会社神戸製鋼所 | Steel for high strength bolts |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5395819A (en) * | 1977-02-03 | 1978-08-22 | Nippon Steel Corp | High tensile pc steel wire with uniformly hardened structure and manufacture thereof |
| JPS556102A (en) * | 1978-06-26 | 1980-01-17 | Mo I Himichiesukogo Mashinosut | Contact device for heat exchanging and matter exchanging apparatus |
| JPS5576020A (en) * | 1978-11-30 | 1980-06-07 | Sumitomo Metal Ind Ltd | Production of steel plate stable in strength and toughness by direct hardening and tempering |
| JPS5579856A (en) * | 1978-12-11 | 1980-06-16 | Mitsubishi Heavy Ind Ltd | High toughness, wear resistant steel |
| JPS55131126A (en) * | 1979-03-30 | 1980-10-11 | Sumitomo Metal Ind Ltd | Production of modified by low alloy containing boron high tensile steel plate |
| JPS5633459A (en) * | 1979-08-24 | 1981-04-03 | Kobe Steel Ltd | Al or al alloy annealing method |
-
1982
- 1982-11-12 JP JP19843982A patent/JPS5989716A/en active Granted
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5395819A (en) * | 1977-02-03 | 1978-08-22 | Nippon Steel Corp | High tensile pc steel wire with uniformly hardened structure and manufacture thereof |
| JPS556102A (en) * | 1978-06-26 | 1980-01-17 | Mo I Himichiesukogo Mashinosut | Contact device for heat exchanging and matter exchanging apparatus |
| JPS5576020A (en) * | 1978-11-30 | 1980-06-07 | Sumitomo Metal Ind Ltd | Production of steel plate stable in strength and toughness by direct hardening and tempering |
| JPS5579856A (en) * | 1978-12-11 | 1980-06-16 | Mitsubishi Heavy Ind Ltd | High toughness, wear resistant steel |
| JPS55131126A (en) * | 1979-03-30 | 1980-10-11 | Sumitomo Metal Ind Ltd | Production of modified by low alloy containing boron high tensile steel plate |
| JPS5633459A (en) * | 1979-08-24 | 1981-04-03 | Kobe Steel Ltd | Al or al alloy annealing method |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5989716A (en) | 1984-05-24 |
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