JPS627247B2 - - Google Patents
Info
- Publication number
- JPS627247B2 JPS627247B2 JP57055649A JP5564982A JPS627247B2 JP S627247 B2 JPS627247 B2 JP S627247B2 JP 57055649 A JP57055649 A JP 57055649A JP 5564982 A JP5564982 A JP 5564982A JP S627247 B2 JPS627247 B2 JP S627247B2
- Authority
- JP
- Japan
- Prior art keywords
- steel
- present
- rolling
- less
- cooling
- 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 49
- 239000010959 steel Substances 0.000 claims description 49
- 238000001816 cooling Methods 0.000 claims description 25
- 230000009467 reduction Effects 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 14
- 230000009466 transformation Effects 0.000 claims description 13
- 238000005275 alloying Methods 0.000 claims description 9
- 239000000463 material Substances 0.000 claims description 9
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 238000005096 rolling process Methods 0.000 description 29
- 229910000859 α-Fe Inorganic materials 0.000 description 24
- 230000000694 effects Effects 0.000 description 9
- 229910001562 pearlite Inorganic materials 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 239000013078 crystal Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 229910052750 molybdenum Inorganic materials 0.000 description 3
- 229910052715 tantalum Inorganic materials 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- 230000001186 cumulative effect Effects 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 238000010583 slow cooling Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000000137 annealing Methods 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 238000001192 hot extrusion Methods 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance 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
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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
本発明は熱延まゝで極微細なフエライト結晶組
織を有する延性に優れた細粒組織鋼材の製造方法
に関するものである。
ここで言う細粒フエライト組織は大部分、通常
70〜80℃以上が微細フエライト結晶粒より成り、
所望の機械的性質によつてはフエライト相以外に
他の微細な組織、例えばパーライト、マルテンサ
イト、残留オーステナイト等のうち一つまたは二
つ以上を有しても良いし、カーバイドやナイトラ
イド等の析出物を有しても良い。
本発明で細粒フエライトと呼ぶ組織は、粒の形
の著しい伸長を伴わず、ほぼ等方的であり、また
原側としていわゆる大傾角粒界で囲まれた結晶粒
からなる組織を指し、亜結晶粒界（小傾角粒界）
は粒界として見なしていない。ただし、このよう
な粒の内部に多少の転位密度の増加と亜粒界の形
成はあり得る。
鋼の種々の強化方法のうちで結晶粒の微細化は
強度と共に靭性をも高くする唯一の方法として知
られており、特に熱延ままで使用される鉄鋼材料
の材質向上を計る際には殆んどの場合に先ず考慮
されねばならない重要な技術である。従来の細粒
化技術で工業的に達成されているのは小さくて４
〜６μ程度である。これは通常制御圧延法と呼ば
れる方法で行われており、Nb等の合金元素を含
む鋼を比較的低温域で強い圧延を行う技術であ
る。この場合Nbが圧延まゝで固溶している必要
があるので、圧延前に例えば1200℃以上という高
温で加熱を行つてNbを固溶させ、しかるのちに
仕上圧延は800℃以下という低温域で行うので、
鋼板の温度低下を待つため生産効率が著しく低下
し、また圧延時に変形抵抗が著しく高くなるた
め、圧延機に対する負荷が大であるなど工業的に
欠点がある。この他の低温域で加熱して圧延を行
う方法、あるいは圧延後強制冷却を行う方法など
種々考案されているが、いずれも上記粒径範囲内
に留つており、本発明で云う超微細粒（３〜４μ
以下）を工業的に得るに至つていない。
一方、超微細粒組織を実験的に得る方法が最近
検討されている。例えば、Ni鋼などで、変態点
前後で数回繰り返し焼鈍を行う方法などである。
しかしこのような熱処理は、経済性から見て工業
的に実施することは困難であることは明らかであ
る。
本発明は実際に工業的に得られたこのような画
期的な超細粒鋼に関するものであり、とくに特殊
な合金元素を用いずＣを主成分とする亜共析鋼
で、しかも熱間加工まゝで得られる鋼に関するも
のである。
本発明の要旨とするところは、重量％でC0.3
％以下、Ｃ以下の合金元素含有量が３％以下であ
る鋼を、Ac3変態点以上の温度域から冷却する過
程において熱間加工を行ない、その終段において
（Ar1＋50℃）〜（Ar3＋100℃）の温度域で実質
的に１秒以内の間に１回または２回以上の合計減
面率が50％以上95％以下となる熱間加工を加え、
該熱間加工終了後20℃／Ｓ以上2000℃／Ｓ以下の
冷却速度で600℃以下の温度域まで冷却するよう
にしたことを特徴とするものである。
以下に本発明の限定理由について説明する。
本発明で鋼の化学成分を規定した理由は次の通
りである。
Ｃ0.3％：一般にＣ量が大きくなるとフエラ
イト量が減少し、パーライトが主体の鋼となる。
しかし本発明鋼では同一Ｃ量でも通常の場合より
はるかにフエライト量を増すことができるので、
Ｃ：0.3％まではフエライト主体の組織を得るこ
とができるが、これを超えるとパーライト等の量
が多くなりフエライト主体の鋼を得ることは難し
くなる。
その他の合金元素の合計３％以下：本発明鋼は
原則としてＣ以外の合金元素の有無に拘らず得ら
れるが、熱間加工の最適温度が700〜900℃の間で
あつてしかもAr3変態点に対し、Ar1＋50〜Ar3
＋100℃の間が望ましいという関係があるので、
Ar3変態点を合金元素で調節した方が望ましい場
合が多い。しかし合金元素の合計量が３％を超え
るとAr3が低くなりすぎて細粒が得られにくくな
る。
Nb、Ta、Mo、Ｗを実質的に含有しないこと：
Nb、Ta、Mo、Ｗはいずれも再結晶を遅らせる元
素として知られている。本発明鋼では熱間加工時
に変態・再結晶が起つて細粒化するので、Nb、
Ta、Mo、Ｗ等はこれを阻害する元素であり本発
明鋼には含まれてはならない。
本発明鋼の終段の加工に至る工程にはとくに制
限はない。すなわち通常に溶製された溶鋼は連続
鋳造によつてスラブにされても良いし、造塊−分
塊工程によつてスラブにされても良い。スラブは
高温のまま圧延工程に持ち来たされても良いし、
一旦冷却したものを再加熱しても良い。スラブの
加熱・加工条件としてはスラブが本発明の加工工
程直前にそのオーステナイト粒径が小さい程良く
なるものが一般的に望ましいと言えるが、本発明
の加工工程以前の条件は通常のもので良いので制
限は設けない。
本発明の特徴は該鋼を通常のAr3変態点（鋼が
オーステナイトである温度域から徐冷途中でフエ
ライト変態を開始する温度を指し、以下単にAr3
と言う）とAr1変態点（同様に徐冷途中でパーラ
イト変態を開始する温度を指し、以下単にAr1と
言う）を基準として（Ar1＋50℃）〜（Ar3＋100
℃）の温度域において、短時間内に大圧下を加え
ることである。
本発明者等は従来研究の殆んどなされていなか
つた大圧下加工の熱間加工組織に対する効果を詳
細に研究し、従来全く知られていなかつた新らし
い知見を得た。その結果を模式的に第１図に示
す。この図で減面率50％以下の領域については比
較的よく知られていたし、また大圧下でも比較的
高温域ではオーステナイトが動的再結晶を起すこ
とは最近知られてきた。しかしAr3前後で、大圧
下を加えると加工時に変態が起ることが今回はじ
めて明らかになつた。またこれと一部重複してフ
エライトが圧延時に再結晶することが発見され
た。このような新らしく発見された現象に対応し
て、第２図に示したようにフエライト粒が著しく
細粒化されることを知見した。本発明の熱間加工
条件の範囲は第１図および第２図から明らかに示
されている。即ち、適切な温度域において減面率
が50％を超えると動的変態が生じて、３〜４μ以
下の平均フエライト粒径が得られるようになる
が、減面率をさらに増すと細粒化はさらに著しく
なり、75％程度では恐らくフエライトの動的再結
晶も加わり、２μまたはそれ以下という超微細粒
となり、これ以上では細粒化効果はやゝ飽和す
る。これから減面率は少なくとも50％以上で望ま
しくは75％以上が最適であることがわかる。
ここで減面率の上限は、95％とする。95％以上
の減面率を１秒以内の間に材料に適用すること
は、現在の圧延技術では極めて困難であり、実際
的ではない。
なお、この圧下は１パスで加えるのが最もよい
が、第２図に示したように短時間で多パスで加え
た累積歪でもほぼこれに近い効果があるという知
見を得た。この短時間は通常の圧延においては１
秒程度以内であればよいことも知見した。従つて
上の圧下率は累積された合計の減面率で置き換え
ることができる。
なお、このような短時間の累積圧下は第１図の
上部に示すように線材圧延の仕上段階、ホツトス
トリツプ圧延の後半で実現が可能である。
上記の熱間加工は全体の加工の最終段に行われ
ることが望ましいが、場合により圧延材の形状調
整のための少量の熱間または冷間の変形を与えて
も大きくその特性を損うものではない。
加工後の粒成長を抑制するためには大なる冷却
速度で冷却する事が望ましい。減面率が十分に大
きいときや加工仕上温度が適正な温度域内で低温
側のときは鋼材断面が小さければ放冷しても細粒
が得られるので特に限定する必要はないが、減面
率が下限に近いときや、製品鋼材断面が大なる場
合、また仕上温度の高い場合は加速冷却が必要で
あり、その下限は第３図に示すように20℃／sec
となる。冷却速度の上限を限定する理由は無い
が、冷速が大きくて、少しでも未変態オーステナ
イトが残存する場合はその部分が硬い第二相とな
り、さらに強度を向上する効果がある。このよう
に目的によつては加速冷却で材質、とくに強度を
向上することができる。加速冷却を行なう温度域
については、フエライトの粒成長、あるいは圧延
時に変態しなかつた部分が冷却中にフエライトま
たはパーライトに変態する600℃以上の温度域を
含むべきであるのは当然である。
本発明にあつては、加工誘起された微細なフエ
ライト組織の粒成長を抑えるために、熱間加工後
の材料を20℃／sec以上の冷却速度で冷却する。
ここで前に述べた目的から、熱間加工後の材料
の冷却速度は20℃／sec以上が必要充分条件では
あるが、現在の技術レベルでは2000℃／secが限
界であり、従つて冷却速度の上限を2000℃／sec
とした。
本発明鋼は種々の熱間加工法で提供できる。た
とえば厚板圧延、ホツトストリツプ圧延、線材圧
延などであり、熱間押出あるいは熱間鍛造などの
圧延以外の加工法でも可能である。
次に本発明の効果について述べる。
前述のように細粒化すると強度靭性が向上する
ことはよく知られているが、これまで４μ以下と
いう極細粒でその効果を調べた例はない。第４図
は本発明で得られた細粒鋼（黒丸）のデータを従
来鋼のデータとともに示したものである。従来の
データ（白丸）はいわゆるPetchの関係式により
よく整理できるが、本発明による鋼はこの延長線
からさらに向上する傾向を示している。また、第
５図は本発明鋼の延性を強度に対して示したもの
で本発明鋼は従来鋼と同一強度レベルでより高い
延性が得られることがわかる。そのほかにも２〜
３μ以下の超細粒鋼では600℃以上で著しく延性
が向上する超塑性現象を示すなどの特徴のある特
性を示す。
このように本発明鋼では従来鋼をはるかに上回
る特性を示すので本発明の効果はきわめて莫大
で、非常に低コストで合金元素等を添加せずに高
品質の高張力鋼等を容易に製造できるのである。
実施例 １
第１表に示す転炉溶製鋼、を200mmのスラ
ブに連続鋳造し、1100℃に加熱後ホツトストリツ
プミルで圧延して５mm厚の鋼板とした。
粗圧延では200mmスラブを50mmまで７パスで圧
延し、仕上温度は900〜1000℃であつた。
仕上圧延のパススケジユールを第２表に示す。
Ａは本発明によるもので、１秒以内に行われる
５、６番目のパスで合計58％の圧下を行つた場合
である。Ｂは比較の通常の圧延の例で、最終２圧
下の圧下は合計27％である。
以上の圧延条件の組合せと圧延された鋼板の機
械的性質を第３表に示す。なお本発明の仕上圧延
温度域は第１表の変態温度から計算すると、鋼
は680〜870℃、鋼で660〜890℃である。試番
３、６、10を除いては圧延後の冷却は、ランアウ
トテーブル上でスプレイ冷却で行い、20℃／秒の
本発明冷却速度範囲内で行つた。
機械的性質から本発明の効果は明らかで60Kg／
mm2以上の強度を持ち、20％以上のすぐれた延性を
有している。
第６図にその組織写真の例（試番４）を示す
が、２〜３μの細粒の等軸フエライト粒で殆んど
占められており、前述の本発明鋼の典型的な特徴
を示している。
一方、比較材の試番５は通常の高温での仕上で
あつて急冷の結果強度が上昇するが延性は不良で
ある。この組織は第７図に示すように50％程度焼
きが入つた組織となつており、フエライトも、針
状となつており、急冷途中で変態したことを示
す。また試番６は圧延温度が本発明の範囲より低
い場合で、フエライト粒径が十分細くないため強
度がそれほど上昇しない。試番７および11は圧下
率が小さい場合で、この場合フエライト粒は急冷
でかなり細かくなり、急冷の第２相が多くなるた
め強度が多少上昇するが、本発明鋼には及ばな
い。この場合、第２相（パーライト、ベイナイ
ト）の比率がかなり大きく、このため延性が十分
ではない。
以上から本発明の効果が顕著なことが明らかで
ある。
The present invention relates to a method for producing a hot-rolled fine-grained steel material having an extremely fine ferrite crystal structure and excellent ductility. The fine-grained ferrite structure mentioned here is mostly
The temperature above 70-80℃ consists of fine ferrite crystal grains,
Depending on the desired mechanical properties, in addition to the ferrite phase, one or more of other fine structures such as pearlite, martensite, retained austenite, etc. may be present, or carbide, nitride, etc. may be present. It may contain precipitates. The structure called fine-grained ferrite in the present invention is almost isotropic without significant elongation of the grain shape, and refers to a structure consisting of crystal grains surrounded by so-called high-angle grain boundaries as the original side. Grain boundaries (low angle grain boundaries)
are not considered as grain boundaries. However, there may be some increase in dislocation density and formation of subgrain boundaries inside such grains. Among the various strengthening methods for steel, grain refinement is known to be the only method to increase both strength and toughness, and is most often used to improve the quality of steel materials used as hot-rolled. This is an important technology that must be considered first in most cases. What has been achieved industrially with conventional grain refining technology is as small as 4
It is about ~6μ. This is usually carried out using a method called controlled rolling, which is a technique for strongly rolling steel containing alloying elements such as Nb at relatively low temperatures. In this case, Nb needs to be in solid solution during rolling, so heating is performed at a high temperature of 1200°C or higher before rolling to dissolve Nb in solid solution, and then finish rolling is carried out at a low temperature range of 800°C or lower. Because it is done with
This method has industrial disadvantages, such as waiting for the temperature of the steel plate to drop, resulting in a significant drop in production efficiency, and a significant increase in deformation resistance during rolling, resulting in a heavy load on the rolling mill. Various other methods have been devised, such as heating and rolling in a low-temperature range or forced cooling after rolling, but all of these methods stay within the above grain size range, and the ultrafine grains ( 3~4μ
below) have not yet been obtained industrially. On the other hand, methods for experimentally obtaining ultrafine grain structures have recently been studied. For example, there is a method of repeatedly annealing Ni steel or the like several times before and after the transformation point.
However, it is clear that such heat treatment is difficult to implement industrially from an economic standpoint. The present invention relates to such an epoch-making ultra-fine-grained steel that has actually been obtained industrially, and in particular is a hypo-eutectoid steel whose main component is C without using any special alloying elements. It concerns steel obtained by processing. The gist of the present invention is that C0.3 in weight%
% or less, C or less alloying element content is 3% or less, hot working is carried out in the process of cooling from the temperature range above the Ac 3 transformation point, and at the final stage (Ar 1 + 50 ° C) ~ ( Hot working is carried out once or twice or more in a temperature range of (Ar 3 +100℃) within 1 second, resulting in a total area reduction of 50% or more and 95% or less,
After the hot working is completed, cooling is performed at a cooling rate of 20° C./s or more and 2000° C./s or less to a temperature range of 600° C. or less. The reasons for the limitations of the present invention will be explained below. The reason for specifying the chemical composition of steel in the present invention is as follows. C0.3%: Generally, as the amount of C increases, the amount of ferrite decreases, and the steel becomes pearlite-based.
However, in the steel of the present invention, the amount of ferrite can be increased much more than in the normal case even with the same amount of C.
C: Up to 0.3%, a structure consisting mainly of ferrite can be obtained, but if it exceeds this amount, the amount of pearlite etc. increases and it becomes difficult to obtain a steel consisting mainly of ferrite. 3% or less in total of other alloying elements: In principle, the steel of the present invention can be obtained regardless of the presence or absence of alloying elements other than C, but the optimum temperature for hot working is between 700 and 900°C, and Ar 3 transformation is possible. For the point, Ar1 + 50 ~ Ar3
Since there is a relationship that a temperature between +100℃ is desirable,
It is often desirable to adjust the Ar3 transformation point with alloying elements. However, if the total amount of alloying elements exceeds 3%, Ar3 becomes too low, making it difficult to obtain fine grains. Substantially free of Nb, Ta, Mo, and W:
Nb, Ta, Mo, and W are all known as elements that delay recrystallization. In the steel of the present invention, transformation and recrystallization occur during hot working and the grains become finer, so Nb,
Ta, Mo, W, etc. are elements that inhibit this and must not be included in the steel of the present invention. There are no particular restrictions on the steps leading to the final processing of the steel of the present invention. That is, normally produced molten steel may be made into a slab by continuous casting, or may be made into a slab by an ingot-blending process. The slab may be brought to the rolling process while still at high temperature, or
It may be reheated once cooled. It can be said that it is generally desirable that the heating and processing conditions for the slab be such that the austenite grain size of the slab becomes smaller just before the processing step of the present invention, but normal conditions may be used before the processing step of the present invention. Therefore, there are no restrictions. The feature of the present invention is that the steel is heated to the normal Ar3 transformation point (refers to the temperature at which ferrite transformation begins during slow cooling from the temperature range where the steel is austenite; hereinafter simply referred to as Ar3
) and Ar1 transformation point (also refers to the temperature at which pearlite transformation begins during slow cooling, hereinafter simply referred to as Ar 1 ) as a reference, (Ar1 + 50℃) ~ (Ar3 + 100℃)
The process involves applying a large pressure within a short period of time in a temperature range of (°C). The present inventors conducted a detailed study on the effect of large reduction working on the hot-worked structure, which had not been studied in the past, and obtained new knowledge that was completely unknown in the past. The results are schematically shown in FIG. In this figure, the region where the area reduction rate is less than 50% is relatively well known, and it has recently been known that austenite undergoes dynamic recrystallization at relatively high temperatures even under high pressure. However, it has now been revealed for the first time that transformation occurs during processing when a large pressure is applied around Ar3. It was also discovered that ferrite recrystallizes during rolling, partially overlapping with this. In response to this newly discovered phenomenon, it was found that ferrite grains were significantly refined as shown in FIG. 2. The range of hot working conditions of the present invention is clearly shown in FIGS. 1 and 2. In other words, if the area reduction rate exceeds 50% in an appropriate temperature range, dynamic transformation will occur and an average ferrite grain size of 3 to 4 μm or less will be obtained, but if the area reduction rate is further increased, the grains will become finer. becomes even more remarkable, and at about 75%, dynamic recrystallization of ferrite is probably added, resulting in ultrafine grains of 2μ or less, and above this, the grain refining effect is somewhat saturated. From this, it can be seen that the optimum area reduction rate is at least 50% or more, preferably 75% or more. Here, the upper limit of the area reduction rate is 95%. Applying an area reduction of 95% or more to a material within 1 second is extremely difficult and impractical with current rolling technology. Although it is best to apply this reduction in one pass, it has been found that cumulative strain applied in multiple passes over a short period of time as shown in FIG. 2 has an effect similar to this. This short time is 1 in normal rolling.
It was also found that it is sufficient if the time is within about seconds. Therefore, the above rolling reduction rate can be replaced by the accumulated total area reduction rate. Incidentally, such a short-time cumulative reduction can be realized in the finishing stage of wire rod rolling or in the latter half of hot strip rolling, as shown in the upper part of FIG. It is desirable that the above hot working is carried out at the final stage of the overall working, but in some cases even a small amount of hot or cold deformation to adjust the shape of the rolled material may significantly impair its properties. isn't it. In order to suppress grain growth after processing, it is desirable to cool at a high cooling rate. When the area reduction rate is sufficiently large or when the finishing temperature is within the appropriate temperature range and on the low side, fine grains can be obtained even if the steel cross section is small, so there is no need to limit the area reduction rate. When the temperature is close to the lower limit, when the product steel cross section is large, or when the finishing temperature is high, accelerated cooling is required, and the lower limit is 20℃/sec as shown in Figure 3.
becomes. There is no reason to limit the upper limit of the cooling rate, but if the cooling rate is high and even a small amount of untransformed austenite remains, that part becomes a hard second phase, which has the effect of further improving the strength. As described above, depending on the purpose, accelerated cooling can improve the material quality, especially the strength. It goes without saying that the temperature range in which accelerated cooling is performed should include a temperature range of 600° C. or higher in which ferrite grain growth or portions that are not transformed during rolling transform into ferrite or pearlite during cooling. In the present invention, the material after hot working is cooled at a cooling rate of 20° C./sec or more in order to suppress the grain growth of the fine ferrite structure induced by working. For the purposes stated above, it is necessary and sufficient for the cooling rate of the material after hot working to be 20°C/sec or higher, but at the current technological level, the limit is 2000°C/sec, so the cooling rate is The upper limit of 2000℃/sec
And so. The steel of the invention can be provided by various hot working methods. Examples include thick plate rolling, hot strip rolling, wire rod rolling, etc., and processing methods other than rolling such as hot extrusion or hot forging are also possible. Next, the effects of the present invention will be described. As mentioned above, it is well known that strength and toughness are improved by making the grains finer, but so far there has been no study of this effect using ultrafine grains of 4 μm or less. FIG. 4 shows the data for the fine-grained steel (black circles) obtained by the present invention together with the data for the conventional steel. Conventional data (white circles) can be well organized by the so-called Petch relation, but the steel according to the present invention shows a tendency to further improve from this extension. Furthermore, FIG. 5 shows the ductility of the steel of the present invention relative to its strength, and it can be seen that the steel of the present invention has higher ductility than the conventional steel at the same strength level. In addition, there are 2~
Ultrafine-grained steel with a diameter of 3μ or less exhibits distinctive properties such as a superplastic phenomenon in which ductility increases significantly at temperatures above 600°C. In this way, the steel of the present invention exhibits properties that far exceed those of conventional steel, so the effects of the present invention are extremely large, and it is possible to easily produce high-quality, high-strength steel, etc., at a very low cost and without adding alloying elements. It can be done. Example 1 The converter melted steel shown in Table 1 was continuously cast into a 200 mm slab, heated to 1100°C, and then rolled in a hot strip mill to form a 5 mm thick steel plate. In rough rolling, a 200 mm slab was rolled to 50 mm in 7 passes, and the finishing temperature was 900 to 1000°C. Table 2 shows the pass schedule for finish rolling.
A is based on the present invention and is a case where a total reduction of 58% is performed in the 5th and 6th passes performed within 1 second. B is an example of normal rolling for comparison, and the total reduction in the final two reductions is 27%. Table 3 shows the combinations of the above rolling conditions and the mechanical properties of the rolled steel sheets. Note that the finish rolling temperature range of the present invention is calculated from the transformation temperatures in Table 1, and is 680 to 870°C for steel and 660 to 890°C for steel. With the exception of trial numbers 3, 6, and 10, cooling after rolling was performed by spray cooling on a run-out table within the cooling rate range of the present invention of 20° C./sec. The effect of the present invention is clear from the mechanical properties.
It has a strength of more than mm 2 and excellent ductility of more than 20%. Fig. 6 shows an example of the microstructure photograph (sample number 4), which is mostly occupied by fine equiaxed ferrite grains of 2 to 3μ, showing the typical characteristics of the steel of the present invention mentioned above. ing. On the other hand, comparative material Sample No. 5 was finished at a normal high temperature, and its strength increased as a result of rapid cooling, but its ductility was poor. As shown in FIG. 7, this structure is about 50% burnt, and the ferrite is also needle-shaped, indicating that it was transformed during the rapid cooling. Trial No. 6 is a case where the rolling temperature is lower than the range of the present invention, and the strength does not increase much because the ferrite grain size is not sufficiently small. Trial Nos. 7 and 11 are cases where the rolling reduction is small; in this case, the ferrite grains become considerably finer due to rapid cooling, and the second phase of the rapid cooling increases, so the strength increases somewhat, but it is not as good as the steel of the present invention. In this case, the proportion of the second phase (pearlite, bainite) is quite large, and therefore the ductility is not sufficient. From the above, it is clear that the effects of the present invention are remarkable.
【表】【table】
【表】【table】
【表】【table】
第１図は0.15C−1Mn鋼の熱間加工時の歪量・
温度と加工直後の組織の関係を模式的に示した図
（熱間加工後直ちに急冷した組織で調査したも
の）、第２図は0.15C−1Mn鋼の熱間加工時の歪量
とフエライト粒径の関係を示す図、第３図は加工
終了後の冷速とフエライト粒径の関係を示す図、
第４図は0.1〜0.15％Ｃ−0.5〜1.5Mn鋼のフエラ
イト結晶粒度と降伏応力、靭性の関係を示す図、
第５図は本発明鋼と従来鋼の強度一延性バランス
の比較を示す図、第６図は本発明鋼の光学顕微鏡
による金属組織を示す写真、第７図は本発明より
仕上温度が高い比較鋼の光学顕微鏡による金属組
織を示す写真である。
Figure 1 shows the amount of strain during hot working of 0.15C-1Mn steel.
A diagram schematically showing the relationship between temperature and the structure immediately after working (investigated using a structure that was rapidly cooled immediately after hot working). Figure 2 shows the amount of strain and ferrite grains during hot working of 0.15C-1Mn steel. Figure 3 is a diagram showing the relationship between the diameter and the cooling rate after processing and the ferrite grain size.
Figure 4 is a diagram showing the relationship between ferrite grain size, yield stress, and toughness of 0.1~0.15%C-0.5~1.5Mn steel.
Figure 5 is a diagram showing a comparison of strength-ductility balance between the steel of the present invention and conventional steel, Figure 6 is a photograph showing the metallographic structure of the steel of the present invention taken with an optical microscope, and Figure 7 is a comparison with a higher finishing temperature than that of the present invention. It is a photograph showing the metal structure of steel taken with an optical microscope.
Claims (1)
有量３％以下である鋼を、Ac3変態点以上の温度
域から冷却する過程において、熱間加工を行な
い、その終段において（Ar1＋50℃）〜（Ar3＋
100℃）の温度域で実質的に１秒以内の間に１回
または２回以上の合計減面率が50％以上95％以下
となる熱間加工を加え、該熱間加工終了後20℃／
Ｓ以上2000℃／Ｓ以下の冷却速度で600℃以下の
温度域まで冷却するようにしたことを特徴とする
極細粒高強度熱間加工鋼材の製造法。1 Steel with a C content of 0.3% or less and an alloying element content other than C of 3% or less in weight percent is hot worked during the process of cooling from a temperature range above the Ac 3 transformation point, and in the final stage ( Ar 1 +50℃) ~ (Ar 3 +
100℃) in a temperature range of 1 second or more in which the total area reduction rate is 50% or more and 95% or less, and after the hot working is completed, the temperature is 20℃. /
1. A method for producing ultrafine-grained high-strength hot-worked steel material, characterized by cooling to a temperature range of 600°C or less at a cooling rate of S or more and 2000°C or less.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5564982A JPS58174523A (en) | 1982-04-03 | 1982-04-03 | Manufacture of very fine-grained high-strength hot-worked steel material |
| US06/481,453 US4466842A (en) | 1982-04-03 | 1983-04-01 | Ferritic steel having ultra-fine grains and a method for producing the same |
| FR8305500A FR2524493B1 (en) | 1982-04-03 | 1983-04-05 | FERRITIC STEEL WITH ULTRA-FINE GRAINS AND PROCESS FOR PRODUCING THE SAME |
| DE3312257A DE3312257A1 (en) | 1982-04-03 | 1983-04-05 | FERRITIC STEEL WITH ULTRAFINE GRAIN AND METHOD FOR THE PRODUCTION THEREOF |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5564982A JPS58174523A (en) | 1982-04-03 | 1982-04-03 | Manufacture of very fine-grained high-strength hot-worked steel material |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS58174523A JPS58174523A (en) | 1983-10-13 |
| JPS627247B2 true JPS627247B2 (en) | 1987-02-16 |
Family
ID=13004669
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5564982A Granted JPS58174523A (en) | 1982-04-03 | 1982-04-03 | Manufacture of very fine-grained high-strength hot-worked steel material |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS58174523A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006272441A (en) * | 2005-03-30 | 2006-10-12 | Jfe Steel Kk | Hot rolling method and hot rolling line of steel strip |
| WO2012039270A1 (en) | 2010-09-22 | 2012-03-29 | 三菱日立製鉄機械株式会社 | Cooling system for hot-rolled steel strip |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59107023A (en) * | 1982-12-09 | 1984-06-21 | Nippon Steel Corp | Manufacture of hyperfine-grained hot-rolled steel plate |
| EP1136575A4 (en) * | 1999-08-10 | 2008-04-23 | Jfe Steel Corp | Method of producing cold rolled steel sheet |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54143717A (en) * | 1978-05-01 | 1979-11-09 | Kawasaki Steel Co | Continuous heat treatment of high carbon steel for high processed cold drawing |
| JPS5672127A (en) * | 1979-11-17 | 1981-06-16 | Nippon Steel Corp | Manufacture of low yield ratio complex structure high tension steel having excellent ductility |
| JPS5681620A (en) * | 1979-12-05 | 1981-07-03 | Nippon Steel Corp | Production of tin base low yield ratio composite structure high tensile steel plate |
-
1982
- 1982-04-03 JP JP5564982A patent/JPS58174523A/en active Granted
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54143717A (en) * | 1978-05-01 | 1979-11-09 | Kawasaki Steel Co | Continuous heat treatment of high carbon steel for high processed cold drawing |
| JPS5672127A (en) * | 1979-11-17 | 1981-06-16 | Nippon Steel Corp | Manufacture of low yield ratio complex structure high tension steel having excellent ductility |
| JPS5681620A (en) * | 1979-12-05 | 1981-07-03 | Nippon Steel Corp | Production of tin base low yield ratio composite structure high tensile steel plate |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006272441A (en) * | 2005-03-30 | 2006-10-12 | Jfe Steel Kk | Hot rolling method and hot rolling line of steel strip |
| JP4552731B2 (en) * | 2005-03-30 | 2010-09-29 | Ｊｆｅスチール株式会社 | Hot rolling method for steel strip |
| WO2012039270A1 (en) | 2010-09-22 | 2012-03-29 | 三菱日立製鉄機械株式会社 | Cooling system for hot-rolled steel strip |
| US9039956B2 (en) | 2010-09-22 | 2015-05-26 | Mitsubishi-Hitachi Metals Machinery, Inc. | Cooling system for hot-rolled steel strip |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58174523A (en) | 1983-10-13 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3926687A (en) | Method for producing a killed steel wire rod | |
| JPH0247524B2 (en) | KAKOYONETSUENKOHANNOSEIZOHOHO | |
| JP3113137B2 (en) | Manufacturing method of high toughness rail with pearlite metal structure | |
| JPS58123823A (en) | Manufacture of high strength hot rolled steel sheet of super fine grain | |
| JP3242303B2 (en) | High-strength hot-rolled steel sheet having ultrafine grains and excellent in ductility, toughness, fatigue properties and strength-ductility balance, and method for producing the same | |
| JPS627247B2 (en) | ||
| JPH1171615A (en) | Production of thick steel plate excellent in low temperature toughness | |
| JP3546287B2 (en) | High-strength hot-rolled steel sheet excellent in workability and method for producing the same | |
| JP2756534B2 (en) | Manufacturing method for high ductility steel bars | |
| JP3168665B2 (en) | Hot-rolled high-strength steel sheet with excellent workability and its manufacturing method | |
| JP3261515B2 (en) | Method of manufacturing thick steel plate with excellent low temperature toughness | |
| JP3323737B2 (en) | Method for producing high-strength hot-rolled steel sheet having ultrafine structure | |
| JPS6239231B2 (en) | ||
| JPH0414167B2 (en) | ||
| JPS59205447A (en) | Ultra-fine grain ferrite steel and preparation thereof | |
| JPS6239229B2 (en) | ||
| JPH0525941B2 (en) | ||
| JPH0135048B2 (en) | ||
| JPH05271770A (en) | Manufacture of fine-grained thick steel plate | |
| JPH0369967B2 (en) | ||
| JPS58100663A (en) | Production of rolled material of titanium alloy having good texture | |
| JP2004136321A (en) | Hot-rolled steel sheet manufacturing method | |
| JPS60152627A (en) | Manufacture of rapidly spheroidizable wire rod | |
| JP3212349B2 (en) | Manufacturing method of fine grain high toughness structural steel sheet | |
| KR20040059579A (en) | Method for manufacturing the ultra-fine ferrite by dynamic transformation |