JPH0629480B2 - Hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue characteristics, and method for producing the same - Google Patents
Hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue characteristics, and method for producing the sameInfo
- Publication number
- JPH0629480B2 JPH0629480B2 JP61291555A JP29155586A JPH0629480B2 JP H0629480 B2 JPH0629480 B2 JP H0629480B2 JP 61291555 A JP61291555 A JP 61291555A JP 29155586 A JP29155586 A JP 29155586A JP H0629480 B2 JPH0629480 B2 JP H0629480B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 33
- 239000010959 steel Substances 0.000 title claims description 33
- 238000004519 manufacturing process Methods 0.000 title claims description 13
- 229910000859 α-Fe Inorganic materials 0.000 claims description 28
- 238000001816 cooling Methods 0.000 claims description 12
- 229910052758 niobium Inorganic materials 0.000 claims description 12
- 229910001563 bainite Inorganic materials 0.000 claims description 10
- 229910000734 martensite Inorganic materials 0.000 claims description 10
- 239000002245 particle Substances 0.000 claims description 8
- 238000004804 winding Methods 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 description 18
- 238000005098 hot rolling Methods 0.000 description 13
- 229910001566 austenite Inorganic materials 0.000 description 11
- 238000005096 rolling process Methods 0.000 description 9
- 239000006104 solid solution Substances 0.000 description 5
- 230000006866 deterioration Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229910052750 molybdenum Inorganic materials 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000005256 carbonitriding Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は、強度、延性、靭性及び疲労特性に優れた熱延
高張力鋼板と、その製造方法に関するものである。TECHNICAL FIELD The present invention relates to a hot-rolled high-strength steel sheet excellent in strength, ductility, toughness and fatigue characteristics, and a method for producing the same.
（従来の技術とその問題点） 従来、高強度の熱延鋼板を製造するに際しては、Nb、Ti
等の析出強化型元素を添加し、Nb、Tiの微細な析出物に
よる強化を図っている。しかしながら、Nb、Tiを添加す
ると、鋼の靭性が大きく低下するので好ましくない。こ
のため、高強度で且つ高い靭性を要求される場合におい
ては、特公昭57-49606号公報に記載されているように、
Cr、Ni、Mo等を添加し、鋼の強度と靭性を確保している
が、Ni、Mo等が高価であるために製造コスト面で問題が
ある。(Conventional technology and its problems) Conventionally, when manufacturing high strength hot rolled steel sheet, Nb, Ti
Precipitation-strengthening elements such as Nb and Ti are added to strengthen with fine precipitates of Nb and Ti. However, addition of Nb and Ti is not preferable because the toughness of the steel is significantly reduced. Therefore, when high strength and high toughness are required, as described in JP-B-57-49606,
Although Cr, Ni, Mo, etc. are added to secure the strength and toughness of steel, there is a problem in manufacturing cost because Ni, Mo, etc. are expensive.
本発明の目的は、製造コスト上問題となるCr、Ni、Moの
添加を避けて、微量のNbを添加した鋼の組成成分、スラ
ブ加熱温度、熱間仕上圧延温度、熱間圧延後の冷却速度
および巻取温度を適正な範囲に制御することで、強度、
延性、靭性、更に加えて疲労特性に優れた熱延高張力鋼
板とその製造方法を提供することにある。The object of the present invention is to avoid the addition of Cr, Ni, Mo which is a problem in terms of manufacturing cost, compositional components of steel containing a small amount of Nb, slab heating temperature, hot finish rolling temperature, cooling after hot rolling. By controlling the speed and winding temperature within the proper range, strength,
It is an object of the present invention to provide a hot-rolled high-tensile steel sheet excellent in ductility, toughness, and fatigue characteristics, and a method for manufacturing the same.
（問題点を解決するための手段） 本発明は、重量％で Ｃ：0.01〜0.20％、 Si：1.00％以下、 Mn：2.00％以下、 Al：0.10％以下、 Ｎ：0.0070％以下、 Nb：0.0050〜0.15％、 を含み、残余は不可避不純物を除き実質的にFeの組成か
らなり、フェライトの平均粒径が２〜３μｍの微細フェ
ライトが面積率で70％以上、ベイナイトとマルテンサイ
トを含む組織を面積率が20％以下で、残部の面積率が平
均粒径１０μｍ以下のフェライトの混合組織からなる強
度、延性、靭性及び疲労特性に優れた熱延高張力鋼板
と、 Ｃ：0.01〜0.20％、 Si：1.00％以下、 Mn：2.00％以下、 Ｎ：0.0070％以下、 Al：0.10％以下、 Nb：0.005 〜0.15％、 に加えて、Ti：0.005〜0.050 ％、Ｖ：0.01〜0.200 ％
のうち一種又は二種を含み、残余は不可避不純物を除き
実質的にFeの組成からなり、フェライトの平均粒径が２
〜３μｍの微細フェライトが面積率で70％以上、ベイナ
イトとマルテンサイトを含む組織の面積率が20％以下
で、残部の面積率が平均粒径１０μｍ以下のの混合組織
からなる強度、延性、靭性及び疲労特性に優れた熱延高
張力鋼板、及び、 Ｃ：0.01〜0.20％、 Si：1.00％以下、 Mn：2.00％以下、 Al：0.10％以下、 Ｎ：0.0070％以下、 Nb：0.005 〜0.15％を含み、残余は不可避不純物からな
る鋼塊又はスラブを下記式で決まる温度Tc以下に加熱
し、850 〜Ar３−50℃の温度範囲で熱間圧延後、冷却速
度30℃／秒以上で冷却した後、450 ℃〜150 ℃の温度範
囲で巻取ることを特徴とする強度、延性、靭性及び疲労
特性に優れた熱延高張力鋼板の製造方法、 Nb≦0.015 ％の場合、 Tc＝850 ＋ 139000 ×〔Nb重量％〕 ×〔Ｃ重量％＋12/14 Ｎ重量％〕 Nb＞0.015 ％の場合、 Tc＝961 ＋ 51000×〔Nb重量％〕 ×〔Ｃ重量％＋12/14 Ｎ重量％〕 とすることにより、前述した問題点を解決した。また、 Ｃ：0.01〜0.20％、 Si：1.00％以下、 Al：0.10％以下、 Ｎ：0.0070％以下、 Nb：0.005 〜0.15％に加えて、 Ti：0.005 〜0.050 ％、Ｖ：0.01〜0.200 ％のうち一種
又は二種を含み、残余は不可避不純物を除き実質的にFe
の組成からなる鋼塊又はスラブの場合も、下記式で決ま
る温度Tc以下に加熱し、850〜Ar３〜−50℃の温度範囲
で熱間圧延後、冷却速度30℃／秒以上で冷却した後、45
0 ℃〜150 ℃の温度範囲で巻取ることにより強度、延
性、靭性及び疲労特性に優れた熱延鋼板を製造すること
ができる。なお、式はNb≦0.015 ％の場合、 Tc＝850 ＋ 139000 ×〔Nb重量％〕 ×〔Ｃ重量％＋12/14 Ｎ重量％〕 Nb＞0.015 ％の場合、 Tc＝961 ＋ 51000×〔Nb重量％〕 ×〔Ｃ重量％＋12/14 Ｎ重量％〕 とする。(Means for Solving Problems) In the present invention, C: 0.01 to 0.20%, Si: 1.00% or less, Mn: 2.00% or less, Al: 0.10% or less, N: 0.0070% or less, Nb: 0.0050 to 0.15%, and the balance is essentially Fe composition excluding unavoidable impurities. Fine ferrite having an average grain size of ferrite of 2 to 3 μm is 70% or more in area ratio, and a structure containing bainite and martensite. A hot-rolled high-strength steel sheet having an area ratio of 20% or less and a balance area ratio of ferrite having a mean grain size of 10 μm or less, which is excellent in strength, ductility, toughness, and fatigue properties, and C: 0.01 to 0.20%. , Si: 1.00% or less, Mn: 2.00% or less, N: 0.0070% or less, Al: 0.10% or less, Nb: 0.005 to 0.15%, Ti: 0.005 to 0.050%, V: 0.01 to 0.200%
One or two of them are included, and the balance is essentially Fe composition excluding unavoidable impurities, and the average grain size of ferrite is 2
The strength, ductility, and toughness consist of a mixed structure in which the area ratio of fine ferrite of ~ 3 μm is 70% or more, the area ratio of the structure containing bainite and martensite is 20% or less, and the area ratio of the balance is 10 μm or less in average grain size. And hot-rolled high-tensile steel sheet with excellent fatigue properties, and C: 0.01 to 0.20%, Si: 1.00% or less, Mn: 2.00% or less, Al: 0.10% or less, N: 0.0070% or less, Nb: 0.005 to 0.15. %, With the balance being unavoidable impurities, the steel ingot or slab is heated to a temperature Tc or lower determined by the following formula, and hot-rolled in a temperature range of 850 to Ar 3 −50 ° C., then at a cooling rate of 30 ° C./sec or more. After cooling, it is wound in the temperature range of 450 ℃ ~ 150 ℃, the manufacturing method of hot-rolled high-strength steel sheet excellent in strength, ductility, toughness and fatigue characteristics, and when Nb ≤ 0.015%, Tc = 850 +139000 x [Nb wt%] x [C wt% +12/14 N wt%] If Nb> 0.015%, Tc = 961 + 51 By setting 000 × [Nb wt%] × [C wt% + 12/14 N wt%], the above-mentioned problems were solved. In addition to C: 0.01 to 0.20%, Si: 1.00% or less, Al: 0.10% or less, N: 0.0070% or less, Nb: 0.005 to 0.15%, Ti: 0.005 to 0.050%, V: 0.01 to 0.200% One or two of them, and the balance is essentially Fe except for inevitable impurities.
Also in the case of a steel ingot or a slab having the composition of No. 1 , it is heated to a temperature Tc or less determined by the following formula, hot-rolled in a temperature range of 850 to Ar 3 to −50 ° C., and then cooled at a cooling rate of 30 ° C./sec or more. After 45
By rolling in a temperature range of 0 ° C to 150 ° C, a hot rolled steel sheet excellent in strength, ductility, toughness and fatigue characteristics can be manufactured. If Nb ≤ 0.015%, Tc = 850 + 139000 x [Nb wt%] x [C wt% + 12/14 N wt%] Nb> 0.015%, Tc = 961 + 51000 x [Nb wt %] × [C wt% + 12/14 N wt%].
（作 用） 以下に本発明の成分、製造条件の限定理由について述べ
る。(Operation) The components of the present invention and the reasons for limiting the production conditions will be described below.
Ｃ：Ｃは多いほど強度を向上するうえで有効であるが、
0.20重量％を超えると熱間圧延後の組織中に占めるパー
ライトの面積率が増加して靭性が劣化する。更に、熱間
圧延中、或いは熱間圧延後の冷却中にNbの炭窒化物（(N
b(C,N)）の析出物が生じ易く、巻取り前の固溶Nbを所定
量確保することが困難となるので、上限は0.08重量％と
する。また、熱間圧延後のフェライト組織が粗大になる
ことと、Ar３点が高くなり比較的低い熱間圧延温度を確
保できなくなるので、その含有量の下限は、0.01重量％
とする。C: The more C, the more effective it is in improving the strength.
If it exceeds 0.20% by weight, the area ratio of pearlite in the microstructure after hot rolling increases and the toughness deteriorates. Furthermore, during hot rolling or during cooling after hot rolling, Nb carbonitride ((N
b (C, N)) precipitates easily and it becomes difficult to secure a predetermined amount of solid solution Nb before winding, so the upper limit is made 0.08% by weight. In addition, since the ferrite structure after hot rolling becomes coarse and the Ar 3 point becomes high and a relatively low hot rolling temperature cannot be secured, the lower limit of its content is 0.01% by weight.
And
Si：Siは、冷却中のポリゴナルフェライトの生成を促進
し、さらにそれを固溶強化するため、延性の大きな劣化
を伴わずに高強度化できることで望ましい元素である。
しかし、1.00重量％を越えて添加されると溶接が困難に
なることや、表面性状の劣化強化効果の飽和などの問題
となるので上限を1.00重量％とした。Si: Si is a desirable element because it promotes the formation of polygonal ferrite during cooling and further strengthens it by solid solution, so that it can be strengthened without significant deterioration in ductility.
However, if it is added in an amount of more than 1.00% by weight, welding becomes difficult and there is a problem such as saturation of the deterioration enhancing effect of the surface texture. Therefore, the upper limit was made 1.00% by weight.
Mn：Mnは、引張強さを確保すると共に熱間加工性を確保
するうえで重要な元素であり、熱間圧延時における低融
点のFeS の形成を防止する元素である。しかし、その添
加量が2.0 重量％を超えると、スラブの中心偏析部に異
常硬化組織が生じ易く、また溶接時の割れの原因となる
ので、その添加量を2.0 重量％以下とする。Mn: Mn is an element that is important for ensuring tensile strength and hot workability, and is an element that prevents the formation of FeS with a low melting point during hot rolling. However, if the added amount exceeds 2.0% by weight, an abnormally hardened structure is likely to occur in the central segregated portion of the slab and it may cause cracking during welding. Therefore, the added amount is set to 2.0% by weight or less.
Al：Alは、鋼を脱酸するために添加するが、その添加量
が0.10重量％を超えると、置換型固溶原子状態にあるAl
が溶接時に酸素と結びついてペネトレーターと呼ばれる
介在物となり易く、更に鋼板の表面性状を劣化させる原
因となるので、Alの添加量の上限は0.10重量％とする。Al: Al is added to deoxidize steel, but if the amount added exceeds 0.10% by weight, Al in the substitutional solid solution atomic state will be present.
Is likely to become an inclusion called a penetrator by being combined with oxygen during welding and further deteriorating the surface properties of the steel sheet. Therefore, the upper limit of the amount of Al added is 0.10% by weight.
Ｎ：Ｎの含有量が0.0070重量％を超えると、熱間圧延後
に低温で巻取った場合に固溶状態でＮが存在するように
なり、靭性が劣化するので、その含有量は0.0070重量％
以下とする。N: If the content of N exceeds 0.0070% by weight, N will exist in a solid solution state when wound at a low temperature after hot rolling and the toughness deteriorates. Therefore, the content is 0.0070% by weight.
Below.
Ｓ：Ｓは特にMnが多量に添加されている場合には、靭性
に有害な介在物を形成して靭性が劣化するので、その含
有量は0.0100重量％以下とする。S: S, especially when a large amount of Mn is added, forms inclusions harmful to the toughness and deteriorates the toughness, so the content is made 0.0100% by weight or less.
Nb：Nbは、スラブ加熱時のオーステナイトの細粒化を促
進する作用があるが、その含有量が0.005 重量％未満で
あるとスラブ加熱時のオーステナイトの細粒化効果が得
られない。また、その含有量が増加するにつれてオース
テナイトの細粒化は進むが、0.150 重量％を超えると飽
和するので、0.005 〜0.15重量％の範囲とする。Nb: Nb has an action of promoting austenite refining during heating of the slab, but if the content thereof is less than 0.005% by weight, the austenite refining effect during heating of the slab cannot be obtained. Further, as the content thereof increases, austenite becomes finer, but when it exceeds 0.150% by weight, it is saturated, so the content is made 0.005 to 0.15% by weight.
Ti及びV は、靭性の大きな劣化をともなわずに高強度化
を進める元素である。Ti and V are elements that promote high strength without significant deterioration in toughness.
Ti：Tiは、スラグ加熱時のオーステナイト粒を細粒化す
る作用があるので、0.005 重量％以上添加する必要があ
るが、０．０５０重量％を超えて添加すると鋼板表面性
状を劣化させるので、0.005 〜0.050 重量％の範囲とす
る。Ti: Ti has the effect of refining the austenite grains during slag heating, so it is necessary to add 0.005% by weight or more, but if added in excess of 0.050% by weight, the surface properties of the steel sheet deteriorate, so The range is 0.005 to 0.050% by weight.
Ｖ：Ｖは、0.01重量％以上添加することで、強度と延性
を向上させるが、0.20重量％を超えて添加しても効果が
飽和するので、0.01〜0.20重量％の範囲とする。V: V improves strength and ductility when added in an amount of 0.01% by weight or more, but the effect saturates even when added in an amount of more than 0.20% by weight, so the amount is made 0.01 to 0.20% by weight.
次いで、スラブ加熱温度範囲、熱間圧延温度、熱間圧延
後から巻取りまでの冷却速度及び巻取温度についての限
定理由について述べる。Next, the reasons for limiting the slab heating temperature range, hot rolling temperature, cooling rate from hot rolling to winding and the winding temperature will be described.
スラブの加熱温度は概して低くすることで、加熱時の初
期オーステナイト粒径が小さくなり、 最終的なオーステナイト粒径を小さくできると共に、ス
ラブ加熱時に溶け残ったNb(C,N) のような炭窒化物粒子
がオーステナイトの細粒化にも寄与する。本発明におい
ては、スラブ加熱時において既に析出物として存在して
いるNbは強化元素として利用できないために、添加した
Ｃ，Ｎ，Nbの量に応じて最適なスラブ加熱温度が決めら
れる。即ち、Nbの含有量が0.015 重量％以下の場合のス
ラブ加熱温度の上限Tc（℃）は、 Tc＝850 ＋ 139000 ×〔Nb〕 ×〔Ｃ＋12/14 Ｎ〕 …(1) Nbの含有量が0.015 重量％を超えるとスラブ加熱温度の
上限Tc（℃）は、 Tc＝961 ＋ 51000×〔Nb〕 ×〔Ｃ＋12/14 Ｎ〕 …(2) となる。本発明者等は、0.08％Ｃ−1.21％Mn−0.04％Al
− 0.004％Ｎ− 0.035％Nb鋼について、スラブ加熱温度
を変化させ、熱間仕上圧延温度を一定とし、巻取温度を
300 ℃として、引張強さ、靭性等について調査した結果
を第１図に示す。同図からも判るように、(2)式で決ま
るTc、即ちTo＝1109℃より低いスラブ加熱温度にするこ
とで、引張強さ及び降伏点は多少減少するが、靭性を示
すvTrsは顕著に低下しており、靭性が改善されているこ
とが確認できた。更に本発明においては、1120℃以下の
スラブ再加熱温度にすれば充分な靭性が得られる。ま
た、スラブ加熱温度の下限は、熱間仕上圧延温度が確保
できる温度とすることで、スラブ加熱時に固溶するNb
(C,N)が減少し、靭性に有害な最終な熱延鋼板中に析出
する微細なNb(C,N)による析出強化を減少させることが
できる。By generally lowering the heating temperature of the slab, the initial austenite grain size during heating can be reduced, the final austenite grain size can be reduced, and carbonitriding such as Nb (C, N) left unmelted during slab heating can be achieved. The material particles also contribute to the fine graining of austenite. In the present invention, Nb, which is already present as a precipitate during slab heating, cannot be used as a strengthening element, so the optimum slab heating temperature is determined according to the amounts of added C, N, and Nb. That is, when the Nb content is 0.015% by weight or less, the upper limit Tc (° C) of the slab heating temperature is Tc = 850 + 139000 x [Nb] x [C + 12/14 N] (1) The Nb content is When it exceeds 0.015% by weight, the upper limit Tc (° C) of the slab heating temperature becomes Tc = 961 + 51000 × [Nb] × [C + 12/14 N] (2). The present inventors have found that 0.08% C-1.21% Mn-0.04% Al
-0.004% N-0.035% Nb For steel, change the slab heating temperature to keep the hot finish rolling temperature constant and the winding temperature
Figure 1 shows the results of an examination of tensile strength, toughness, etc. at 300 ° C. As can be seen from the figure, when the slab heating temperature lower than Tc determined by the equation (2), that is, To = 1109 ° C, the tensile strength and the yield point are slightly decreased, but the vTrs indicating the toughness is significantly increased. It was confirmed that the toughness was improved and the toughness was improved. Further, in the present invention, if the slab reheating temperature is 1120 ° C. or less, sufficient toughness can be obtained. Also, the lower limit of the slab heating temperature is set to a temperature at which the hot finish rolling temperature can be secured, so that the Nb dissolved during slab heating becomes solid solution.
(C, N) is reduced, and precipitation strengthening due to fine Nb (C, N) precipitated in the final hot-rolled steel sheet, which is harmful to toughness, can be reduced.
次に、熱間圧延温度は、オーステナイトの細粒化のため
には比較的低温であることが望ましい。熱間圧延温度が
850 ℃を超えると、オーステナイトの微細化が充分に達
成できず、最終の熱延鋼板の組織を微細化できない。一
方、熱間仕上圧延温度の下限をAr３−50℃とした理由
は、熱間仕上圧延をオーステナイトとフェライトの２相
領域で行った場合、ある範囲までは靭性を損わずに高強
度化できるが、その範囲を超えると著しい靭性の劣化が
生じ、その温度がAr３−50℃であるので、熱間仕上圧延
温度は 850℃〜Ar３−50℃とする。Next, it is desirable that the hot rolling temperature is relatively low in order to refine the austenite grains. Hot rolling temperature is
If the temperature exceeds 850 ° C, the austenite cannot be sufficiently refined and the final hot-rolled steel sheet cannot be refined. On the other hand, the reason for setting the lower limit of the hot finish rolling temperature to Ar 3 −50 ° C. is that when hot finish rolling is performed in the two-phase region of austenite and ferrite, the strength is increased up to a certain range without impairing the toughness. possible, beyond which range is remarkable toughness deterioration occurs, its temperature because it is Ar 3 -50 ° C., the hot finish rolling temperature is set to 850 ℃ ~Ar 3 -50 ℃.
次に、熱間仕上圧延後より巻取りまでの冷却速度は、冷
却中にNb(C,N)が析出することを抑えると共に固溶Nbの
オーステナイト安定化効果を利用して第２相をベイナイ
ト、マルテンサイトとし強度を増し、更に超微細粒を含
む母相のフェライトを細粒化するためには、30℃／秒以
上の冷却速度にしなければならない。Next, the cooling rate from hot finish rolling to winding is such that the precipitation of Nb (C, N) during cooling is suppressed and the austenite stabilizing effect of solute Nb is used to make the second phase bainite. In order to increase the strength of martensite and to further refine the ferrite of the matrix phase containing ultrafine grains, the cooling rate must be 30 ° C / sec or more.
また、巻取り温度は、微細に析出するNb(C,N)による析
出強化を抑えて、母相のフェライトを細粒化すると共に
第２相をベイナイト、マルテンサイト等の変態相とする
ことで強度を増すためには、450 ℃が上限である。一
方、巻取り温度が150 ℃未満であると、固溶Ｃ，Ｎが多
く残留して、靭性の面で極めて有害であるので、その温
度を150 ℃以上とした。The coiling temperature is controlled by suppressing precipitation strengthening by finely precipitated Nb (C, N), making the ferrite of the matrix phase finer, and making the second phase a transformation phase such as bainite or martensite. 450 ° C is the upper limit for increasing strength. On the other hand, if the coiling temperature is lower than 150 ° C, a large amount of solute C and N remains, which is extremely harmful in terms of toughness, so the temperature was set to 150 ° C or higher.
上述の工程で製造される鋼は、フェライト粒径が２〜３
μｍの超微細のフェライトが面積率で70％以上、ベイナ
イト・マルテンサイトを含む組織の面積率が20％以下、
残部の面積率が平均粒径10μｍ以下のフェライトからな
る組織となる。上記フェライト粒径２〜３μｍの超微細
フェライトは面積率で70％以上ないと、靭性および疲労
特性が向上しないので、粒径２〜３μｍの超微細フェラ
イトの面積率は70％以上である必要がある。このフェラ
イトの性状は、比較的低温で熱間圧延した場合に生じ
る、謂ゆるサブグレインと呼ばれるものでなく、等軸粒
で、比較的相対方位差の大きいフェライトである必要が
ある。また、ベイナイト、マルテンサイトの低温変態相
の面積率が20％を超えると、強度は向上するが靭性の面
で問題が生じて好ましくないので、ベイナイト、マルテ
ンサイトを含む組織の面積率は20％以下とする。更に、
残部の面積率中のフェライトの平均粒径が10μｍ以上と
なると、高靭性、良好な疲労特性という優れた特性が失
われるので、残部の面積率中のフェライトは平均粒径10
μｍ以下のフェライトである。The steel produced in the above process has a ferrite grain size of 2 to 3
The area ratio of ultra-fine ferrite of 70 μm or more is 70% or more, and the area ratio of the structure containing bainite / martensite is 20% or less,
The area ratio of the rest is a structure composed of ferrite having an average grain size of 10 μm or less. If the area ratio of the ultrafine ferrite particles having a ferrite particle size of 2 to 3 μm is 70% or more, the toughness and fatigue properties are not improved. Therefore, the area ratio of the ultrafine ferrite particles having a particle size of 2 to 3 μm needs to be 70% or more. is there. The property of this ferrite is not what is called a so-called subgrain that occurs when hot-rolling at a relatively low temperature, but it is necessary that the ferrite be equiaxed grains and have a relatively large relative orientation difference. Further, if the area ratio of the low temperature transformation phase of bainite and martensite exceeds 20%, the strength is improved but a problem occurs in terms of toughness, which is not preferable. Therefore, the area ratio of the structure containing bainite and martensite is 20%. Below. Furthermore,
If the average grain size of ferrite in the balance of area ratio is 10 μm or more, the excellent properties such as high toughness and good fatigue properties are lost, so ferrite in the balance of percentage of area ratio has an average grain size of 10 μm.
It is ferrite with a size of μm or less.
本発明の鋼が高靭性で優れた疲労特性を示す理由は明確
でないが、極めて微細なフェライトの粒界が脆性亀裂或
いは疲労亀裂の伝播に対して大きな抵抗となるためと推
定される。The reason why the steel of the present invention exhibits high toughness and excellent fatigue properties is not clear, but it is presumed that the extremely fine grain boundaries of ferrite have a large resistance to the propagation of brittle cracks or fatigue cracks.
また、本発明の鋼は、高強度、高靭性、高延性の特性が
要求される用途に適用可能であり、例えば一般構造用、
パイプ素材用、自動車部品用等に適用可能である。Further, the steel of the present invention is applicable to applications requiring high strength, high toughness, and high ductility characteristics, for example, for general structures,
It is applicable to pipe materials, automobile parts, etc.
（実施例） 実施例１ 第１表に示す組成の鋼を転炉で溶製して、連鋳スラブに
した。次に、各スラブを第２表に示す製造条件、即ちス
ラブ加熱温度（ＳＲＴ）、熱間仕上圧延温度（ＦＤ
Ｔ）、冷却速度（ＣＲＴ）及び巻取温度（ＣＴ）で、仕
上板厚4.5 mm、6.0 mmにして、降伏点（ＹＰ）、引張強
さ（ＴＳ）、伸び（Ｅｌ）、衝撃値 vTrs について調査
した結果を第２表に示す。なお、衝撃値 vTrs は、板厚
は元厚のままで２mmＶノッチを機械加工して、衝撃試験
により求めた。(Example) Example 1 Steel having the composition shown in Table 1 was melted in a converter to form a continuous cast slab. Next, the manufacturing conditions shown in Table 2 for each slab, that is, slab heating temperature (SRT), hot finish rolling temperature (FD
T), cooling rate (CRT) and coiling temperature (CT), finish plate thickness 4.5 mm, 6.0 mm, yield point (YP), tensile strength (TS), elongation (El), impact value vTrs The results of the investigation are shown in Table 2. The impact value vTrs was obtained by an impact test by machining a 2 mm V notch with the plate thickness being the original thickness.
また、本発明で規定する製造条件を満足する鋼の組織
は、平均粒径２〜３μｍの超微細フェライト粒の面積率
が70％以上、面積率が20％以下のベイナイト及びマルテ
ンサイトであり、残部の面積率は平均粒径10μｍ以下の
フェライト粒であった。本発明法による鋼板はvTrsで示
す靭性が良好であり、引張強さ、伸びも低下していな
い。Further, the structure of steel satisfying the manufacturing conditions specified in the present invention is bainite and martensite in which the area ratio of the ultrafine ferrite grains having an average particle diameter of 2 to 3 μm is 70% or more and the area ratio is 20% or less, The area ratio of the balance was ferrite grains having an average grain size of 10 μm or less. The steel sheet produced by the method of the present invention has good toughness as indicated by vTrs, and tensile strength and elongation are not reduced.
実施例２ Ｃ：0.08重量％、Si：0.20重量％、Mn：1.30重量％、N
b： 0.030重量％、Al： 0.040重量％、Ｎ：0.0040重量
％の鋼を転炉で溶製し、連鋳スラブとした後、第３表で
示す製造条件で熱延鋼板とし、疲労強度（なお、σ10 5
は10５くり返し変形時の疲れ強さである。）を調査した
結果も同表中に示す。Example 2 C: 0.08% by weight, Si: 0.20% by weight, Mn: 1.30% by weight, N
b: 0.030% by weight, Al: 0.040% by weight, N: 0.0040% by weight was melted in a converter to form a continuous cast slab, and then hot rolled steel sheet was manufactured under the manufacturing conditions shown in Table 3 and fatigue strength ( Note that σ 10 5
Is the fatigue strength at 10 5 repeated deformation. The results of the investigation of () are also shown in the table.
同表からも判るように、本発明の製造条件を満足する鋼
は、引張強さ、伸びが低下せずに、疲労特性が良くなっ
ていることが判る。As can be seen from the table, it is understood that the steel satisfying the manufacturing conditions of the present invention has improved fatigue properties without lowering tensile strength and elongation.
（発明の効果） 以上説明したように本発明によれば、コスト面で問題と
なるCr，Ni，Mo等の添加を避けられ、強度、延性を損な
わないで、靭性、疲労特性の優れた熱延高張力綱板が得
られる。 (Effect of the invention) As described above, according to the present invention, it is possible to avoid addition of Cr, Ni, Mo, etc., which is a problem in terms of cost, and to improve the toughness and fatigue characteristics without impairing the strength and ductility. A high tensile strength steel plate is obtained.
第１図は、0.08％Ｃ−1.21％Mn−0.04％Al−0.0040％Ｎ
−0.035Nb 鋼の引張特性、衝撃特性、伸びに及ぼすスラ
ブ加熱温度の影響を示す図である。Fig. 1 shows 0.08% C-1.21% Mn-0.04% Al-0.0040% N
It is a figure which shows the influence of the slab heating temperature which acts on the tensile property, impact property, and elongation of -0.035Nb steel.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 岡野 忍 千葉県千葉市川崎町１番地 川崎製鉄株式 会社技術研究本部内 (56)参考文献 特開 昭58−130221（ＪＰ，Ａ) ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinobu Okano 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (56) References JP-A-58-130221 (JP, A)
Claims (3)
らなり、フェライトの平均粒径が２〜３μｍの微細フェ
ライトが面積率で70％以上、ベイナイトとマルテンサイ
トを含む組織の面積率が20％以下で、残部の面積率が平
均粒径１０μｍ以下のフェライトの混合組織からなる強
度、延性、靭性及び疲労特性に優れた熱延高張力鋼板。1. C: 0.01 to 0.20 wt%, Si: 1.00 wt% or less, Mn: 2.00 wt% or less, Al: 0.10 wt% or less, N: 0.0070 wt% or less, Nb: 0.0050 to 0.15 wt%, Included, the balance is essentially Fe composition except unavoidable impurities, fine ferrite having an average grain size of 2-3 μm is 70% or more in area ratio, and the area ratio of structure including bainite and martensite is 20%. Below, a hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue properties, which is composed of a mixed structure of ferrite having an area ratio of the balance of 10 μm or less in average.
残余は不可避不純物を除き実質的にFeの組成からなり、
フェライトの平均粒径が２〜３μｍの微細フェライトが
面積率で70％以上、ベイナイトとマルテンサイトを含む
組織の面積率が20％以下で、残部の面積率が平均粒径１
０μｍ以下のフェライトの混合組織からなる強度、延
性、靭性及び疲労特性に優れた熱延高張力鋼板。2. C: 0.01 to 0.20% by weight, Si: 1.00% by weight or less, Mn: 2.00% by weight or less, Al: 0.10% by weight or less, N: 0.0070% by weight or less, Nb: 0.005 to 0.15% by weight, In addition, one or two of Ti: 0.005 to 0.050 wt% and V: 0.01 to 0.200 wt% are included,
The balance consists essentially of Fe composition except for inevitable impurities,
The area ratio of fine ferrite having an average particle size of ferrite of 2 to 3 μm is 70% or more, the area ratio of the structure containing bainite and martensite is 20% or less, and the area ratio of the rest is an average particle size of 1
A hot-rolled high-tensile steel sheet having a mixed structure of ferrite of 0 μm or less and having excellent strength, ductility, toughness, and fatigue characteristics.
で決まるTc以下に加熱し、850 〜Ar３−50℃の温度範囲
で熱間圧延後、冷却速度30℃／秒以上で冷却した後、45
0℃〜150℃の温度範囲で巻取ることを特徴とする強度、
延性、靭性及び疲労特性に優れた熱延高張力鋼板の製造
方法。 Nb≦0.015 重量％の場合、 Nb＞0.015 重量％の場合、 3. C: 0.01 to 0.20 wt%, Si: 1.00 wt% or less, Mn: 2.00 wt% or less, Al: 0.10 wt% or less, N: 0.0070 wt% or less, Nb: 0.005 to 0.15 wt% The steel ingot or slab is heated to Tc or less determined by the following formula, hot-rolled in a temperature range of 850 to Ar 3 −50 ° C., and then cooled at a cooling rate of 30 ° C./sec or more, and then 45
Strength characterized by winding in the temperature range of 0 ℃ ~ 150 ℃,
A method for producing a hot-rolled high-tensile steel sheet having excellent ductility, toughness, and fatigue characteristics. If Nb ≤ 0.015% by weight, When Nb> 0.015% by weight,
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61291555A JPH0629480B2 (en) | 1986-12-09 | 1986-12-09 | Hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue characteristics, and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61291555A JPH0629480B2 (en) | 1986-12-09 | 1986-12-09 | Hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue characteristics, and method for producing the same |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9162418A Division JP2807453B2 (en) | 1997-06-19 | 1997-06-19 | Hot-rolled high-strength steel sheet with excellent strength, ductility, toughness and fatigue properties |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS63145745A JPS63145745A (en) | 1988-06-17 |
| JPH0629480B2 true JPH0629480B2 (en) | 1994-04-20 |
Family
ID=17770431
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP61291555A Expired - Fee Related JPH0629480B2 (en) | 1986-12-09 | 1986-12-09 | Hot-rolled high-strength steel sheet excellent in strength, ductility, toughness, and fatigue characteristics, and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0629480B2 (en) |
Cited By (1)
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| WO2019103121A1 (en) | 2017-11-24 | 2019-05-31 | 日本製鉄株式会社 | Hot-rolled steel sheet and manufacturing method therefor |
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|---|---|---|---|---|
| JP2803891B2 (en) * | 1990-04-20 | 1998-09-24 | 新日本製鐵株式会社 | Manufacturing method of hot rolled steel sheet with excellent fatigue properties |
| JP2785643B2 (en) * | 1993-05-11 | 1998-08-13 | 住友金属工業株式会社 | Steel plate for tanker with excellent fatigue crack growth resistance in wet hydrogen sulfide environment |
| JP4501699B2 (en) * | 2004-02-18 | 2010-07-14 | Ｊｆｅスチール株式会社 | High-strength steel sheet excellent in deep drawability and stretch flangeability and method for producing the same |
| JP5029748B2 (en) | 2010-09-17 | 2012-09-19 | Ｊｆｅスチール株式会社 | High strength hot rolled steel sheet with excellent toughness and method for producing the same |
| JP5842515B2 (en) * | 2011-09-29 | 2016-01-13 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet and manufacturing method thereof |
| US10718040B2 (en) | 2015-04-22 | 2020-07-21 | Nippon Steel Corporation | Hot-rolled steel sheet, steel material, and method for producing hot-rolled steel sheet |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58130221A (en) * | 1982-01-29 | 1983-08-03 | Sumitomo Metal Ind Ltd | Manufacture of hot rolling high tension steel plate for working |
| JPS58167750A (en) * | 1982-03-29 | 1983-10-04 | Kobe Steel Ltd | High strength steel plate excellent in elongation flange property |
| JPS60184628A (en) * | 1984-02-29 | 1985-09-20 | Nippon Steel Corp | Manufacture of hot-rolled high-tension steel sheet having superior workability |
| JPS60184631A (en) * | 1984-02-29 | 1985-09-20 | Nippon Steel Corp | Manufacture of hot-rolled high-tension steel sheet having superior workability |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2019103121A1 (en) | 2017-11-24 | 2019-05-31 | 日本製鉄株式会社 | Hot-rolled steel sheet and manufacturing method therefor |
| US11512359B2 (en) | 2017-11-24 | 2022-11-29 | Nippon Steel Corporation | Hot rolled steel sheet and method for producing same |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63145745A (en) | 1988-06-17 |
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