JPS582571B2 - Manufacturing method of Tin-based low yield ratio composite structure high tensile strength steel plate - Google Patents

Description

【発明の詳細な説明】 本発明は延性の優れた低降伏比高張力鋼を低コストで製
造する方法に関するものである。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing low yield ratio high tensile strength steel with excellent ductility at low cost.

近年、フエライト〜マルテンサイトからなる複合組織鋼
が商業ベースで生産され、軽量化が必要な自動車等の部
品として使用される傾向にある。In recent years, composite structure steels consisting of ferrite to martensite have been produced on a commercial basis, and there is a tendency for them to be used as parts for automobiles and the like that require weight reduction.

そして、このような複合組織鋼を生産する方法には熱間
圧延後オフラインで熱処理する方法、あるいはＣｒ，Ｓ
ｉ，Ｍｏ等の高価な元素を多量に添加して５００〜６０
０℃で捲取る圧延ままで得る方法、あるいは又、Ｃ，Ｓ
ｉ，Ｍｎ，Ｃｒ等の比較的低廉な成分系を極めて低い捲
取温度で捲取ることにより低降伏比高張力鋼板を得る方
法が開示されている。Methods for producing such composite structure steel include offline heat treatment after hot rolling, or Cr, S
500 to 60 by adding large amounts of expensive elements such as i and Mo.
A method of obtaining as-rolled material by winding it at 0°C, or a method of obtaining C, S
A method for obtaining a high tensile strength steel sheet with a low yield ratio by rolling a relatively inexpensive component system such as i, Mn, and Cr at an extremely low winding temperature is disclosed.

しかし、オフラインで熱処理する方法はプロセスコスト
が高くなる欠点があり、また、高価な元素を添加する方
法は合金コストが高くなる欠点がある。However, the off-line heat treatment method has the disadvantage of increasing process cost, and the method of adding expensive elements has the disadvantage of increasing alloy cost.

さらに、比較的低廉な元素のみからなる鋼を超低温で捲
取る方法は、厳しいユーザーの要求に適合する十分な延
性が得られ難い欠点があった。Furthermore, the method of rolling steel made only of relatively inexpensive elements at ultra-low temperatures has the disadvantage that it is difficult to obtain sufficient ductility to meet the strict requirements of users.

本発明者らはこれらの問題点を解決するため比較的低廉
な成分の鋼を超低温で捲取る方法を案出し、その改良を
図って来た。In order to solve these problems, the present inventors have devised a method for rolling steel of relatively inexpensive components at an ultra-low temperature, and have endeavored to improve the method.

さらに、本発明者らは微細なＴｉＮを利用して、通常加
熱条件で優れた強度〜延性バランスを有する複合組織鋼
を製造する方法をここに発明するに至った。Furthermore, the present inventors have now invented a method of manufacturing a composite structure steel having an excellent strength-ductility balance under normal heating conditions by using fine TiN.

即ち、本発明の要旨とするところはＣ０．０５〜０．１
５％、Ｓｉ≦２％、Ｍｎ０．５〜２．０％、Ａｌ残余は
鉄および不町避不純物からなる鋼をＡｒ３点以上、全圧
下率９０％以上で圧延し、圧延後は１０〜１００℃／秒
で冷却し、３００℃以下で捲取るＴｉＮ系高張力鋼板の
製造方法である。That is, the gist of the present invention is that C0.05 to 0.1
5%, Si≦2%, Mn 0.5-2.0%, Al residual is 10-100% by rolling steel consisting of iron and fumachi impurities at 3 points or more of Ar and a total reduction rate of 90% or more. This is a method for manufacturing a TiN-based high-strength steel sheet, which is cooled at a rate of °C/second and rolled at a temperature of 300 °C or less.

本発明の、さらに改良された発明はＣ０．０５〜０．１
５％、Ｓｉ≦２％、Ｍｎ０．５〜２．０％、Ａｌ≦０．
１０．０１５％からなり、さらにＺｒを２≦Ｚｒ／Ｓ≦
１０、または希土類元素（ＲＥＭ）を１．３≦ＲＥＭ／
Ｓ≦５、もしくはＣａを０．５≦Ｃａ／Ｓ≦１．５含有
し、残余は鉄および不町避不純物からなる鋼をＡｒ３点
以上、全圧下率９０％以上で圧延し、圧延後は１０〜１
００℃／秒で冷却し、３００℃以下で捲取るＴｉＮ系高
張力鋼板の製造方法で、厳しい曲げ加工、バーリング加
工などの用途にも十分耐え得る。The further improved invention of the present invention is C0.05 to 0.1
5%, Si≦2%, Mn0.5-2.0%, Al≦0.
10.015%, and further Zr is 2≦Zr/S≦
10, or rare earth elements (REM) 1.3≦REM/
A steel containing S≦5 or Ca of 0.5≦Ca/S≦1.5, with the remainder consisting of iron and impurities, is rolled at 3 points or more of Ar and a total reduction rate of 90% or more, and after rolling. 10-1
This is a method for manufacturing TiN-based high-strength steel sheets that is cooled at 00°C/second and rolled at 300°C or less, and can withstand severe bending, burring, and other applications.

以下本発明の成分の限定理由についてのべる。The reasons for limiting the components of the present invention will be described below.

Ｃは硬質なマルテンサイトを生成し、強度を上げるのに
有効であるが、Ｃが高くなり過ぎると延性の低下が大き
くなり、溶接性も低下するので０．１５％以下とした。C is effective in producing hard martensite and increasing strength, but if the C content becomes too high, the ductility decreases significantly and the weldability also decreases, so the content was set to 0.15% or less.

また、低くなり過ぎても強度が低下し複合組織鋼の特徴
が失なわれ、低降伏比高延性とならないので下限を０．
０５％とした。In addition, if it becomes too low, the strength will decrease and the characteristics of composite structure steel will be lost, and the low yield ratio and high ductility will not be achieved, so the lower limit should be set to 0.
05%.

Ｍｎは固溶強化およびフエライトの細粒化のために必要
な元素であるが、０．５％未満ではその効果が小さく、
２％を超えると溶接性が劣化するので０．５〜２．０％
の範囲とした。Mn is a necessary element for solid solution strengthening and grain refinement of ferrite, but if it is less than 0.5%, its effect is small;
If it exceeds 2%, weldability deteriorates, so 0.5 to 2.0%.
The range of

Ｓｉは延性を損うことなく、固溶強化によって強度を増
すことができるので高いほうがよいが２％を超えると溶
接性が劣化するので２％以下とした。Since Si can increase strength through solid solution strengthening without impairing ductility, it is better to have a higher content, but if it exceeds 2%, weldability deteriorates, so it is set to 2% or less.

Ａｌはフエライトの細粒化を助長する効果があるが、０
．１％をこえるとその効果は飽和するので０．１％以下
とした。Al has the effect of promoting fine graining of ferrite, but 0
．． If it exceeds 1%, the effect is saturated, so it was set to 0.1% or less.

また、ＴｉＮの作用のみでも細粒化ははかれるので、Ａ
ｌ量の下限は特に設けない。In addition, since grain refinement can be achieved only by the action of TiN,
There is no particular lower limit for the amount.

Ｔｉはオーステナイトの粒成長を抑制できる程度の微細
なＴｉＮが生成される範囲でよく、これは０．００５〜
０．０３％である。Ti may be in a range that produces fine TiN that can suppress austenite grain growth, and this range is 0.005 to 0.005.
It is 0.03%.

ＮはＴｉＮを形成するに必要な化学当量よりも過剰に添
加することが微細なＴｉＮを生成するに１図は１２５０
℃で１時間加熱した時のＴｉおよびＮ量とγ粒度の関係
をＣ０．１０％、Ｓｉ０．２５％、Ｍｎ１．５％、Ａｌ
０．０３％のベース成分の鋼す直線、丸内の数字は各Ｔ
ｉ、Ｎ量でのオーステり少ないとγ粒径が著しく粗大化
することが明確である。Figure 1 shows that adding N in excess of the chemical equivalent required to form TiN produces fine TiN.
The relationship between Ti and N amounts and γ particle size when heated at ℃ for 1 hour is shown for C0.10%, Si0.25%, Mn1.5%, Al
0.03% base component steel straight line, numbers in circles are each T
It is clear that the γ grain size becomes significantly coarser when there is less austening in the amount of i and N.

さらに、曲げ性、伸びフランジ性など圧延方向に延伸し
た介在物の影響を受ける特性を改善した鋼板の製造方法
としてＳを制限するのは圧延により延伸するＭｎＳ系の
介在物を減少させるＺｒ、ＲＥＭ、Ｃａの添加量を少く
するためで上限を０．０１５％とする。Furthermore, as a manufacturing method for steel sheets with improved properties affected by inclusions stretched in the rolling direction, such as bendability and stretch flangeability, S is limited by Zr and REM, which reduce MnS-based inclusions stretched during rolling. , the upper limit is set to 0.015% in order to reduce the amount of Ca added.

硫化物形状制御元素であるＺｒ、ＲＥＭ、ＣａのＳ量に
対する添加範囲はこれらの元素のＯ、Ｎなどとの結合力
により異なるので、２≦Ｚｒ／Ｓ≦１０、１．３≦ＲＥ
Ｍ／Ｓ≦５、０．５≦Ｃａ／Ｓ≦１．５が適当である。The addition range of Zr, REM, and Ca, which are sulfide shape control elements, to the amount of S varies depending on the bond strength of these elements with O, N, etc., so 2≦Zr/S≦10, 1.3≦RE.
It is appropriate that M/S≦5 and 0.5≦Ca/S≦1.5.

この下限はいずれもＭｎＳを熱間で塑性加工が容易でな
い硫化物組成に変えるのに必要な量であり、上限は各元
素の硫化物形状改善効果が飽和し、それ以上の添加は酸
化物系の介在物が増加し加工性を逆に低下させるために
制限を受ける。These lower limits are the amount necessary to change MnS into a sulfide composition that is not easy to plastically work under hot conditions, and the upper limit is the amount at which the sulfide shape improvement effect of each element is saturated, and further addition is required for oxide-based The number of inclusions increases and the processability is adversely affected.

以上の成分の鋼の製造は通常の製鋼法によって良く、鋼
片の製造は造塊一分塊圧延、連続鋳造のいずれによるも
差支えないが、連続鋳造がより望ましい。Steel having the above components may be manufactured by a normal steel manufacturing method, and the steel billets may be manufactured by either ingot rolling or continuous casting, but continuous casting is more preferable.

次に、加熱、圧延、冷却条件の限定理由についてのべる 第２図は第１図と同じベース成分の鋼のＴｉ、Ｎ量を種
々変化させた鋼を１２５０℃で加熱後Ａｒ３以上、全圧
下率９０％以上で圧延し、３００℃以下まで１０〜１０
０℃／秒の冷速で冷却したときの強度〜延性バランスを
示す。Next, Figure 2, which describes the reasons for limiting the heating, rolling, and cooling conditions, shows steels with the same base composition as in Figure 1 with various amounts of Ti and N.After heating at 1250℃, the total rolling reduction was Rolled at 90% or higher, 10 to 10 to 300℃ or lower
It shows the balance between strength and ductility when cooled at a cooling rate of 0°C/sec.

ここで巨大なγ粒が生ずるため、圧延で再結晶させても
変態前のγが大きく、このため変態後粗大な低温変態相
が生成し延性が劣化する。Since huge γ grains are generated here, even if recrystallized by rolling, γ is large before transformation, and therefore, after transformation, a coarse low-temperature transformed phase is generated and ductility deteriorates.

これより、加熱温度には特に制限は必要でなく、通常の
加熱温度であれば良いことは明らかである。From this, it is clear that there is no particular restriction on the heating temperature, and any normal heating temperature may be sufficient.

しかしながら、加熱温度が低くなり過ぎると能率的な熱
間圧延が困難となるので、加熱温度は１０００℃以上が
望ましい。However, if the heating temperature becomes too low, efficient hot rolling becomes difficult, so the heating temperature is preferably 1000° C. or higher.

熱間圧延はＡｒ３点より低い温度まで圧延すると延性が
低下するのでＡｒ３点以上で圧延する。Hot rolling is performed at an Ar point of 3 or higher, since ductility decreases if the steel is rolled to a temperature lower than the Ar point of 3.

また、全圧下率は９０％未満では微細なマルテンサイト
とならず延性が低下するので、９０％以上とする。Further, if the total rolling reduction ratio is less than 90%, fine martensite will not be formed and ductility will decrease, so the total rolling reduction ratio is set to 90% or more.

また、全圧下率の上限は加熱温度〜Ａｒ３間の圧延を行
うと自ずと規制されるので特に設定しない。Further, the upper limit of the total rolling reduction is not particularly set because it is naturally regulated when rolling is performed between the heating temperature and Ar3.

圧延後は１０〜１００℃／秒で急冷し、３００℃以下で
捲取る。After rolling, it is rapidly cooled at 10 to 100°C/second and rolled up at 300°C or less.

冷速か１０℃／秒未満であればパーライトが出現し強度
〜延性バランスが悪化し、１００℃／秒を超えるとマル
テンサイト、ペイナイトなどが急増し、良好な延性が得
られないばかりか、降伏比も高くなる。If the cooling rate is less than 10°C/sec, pearlite will appear and the balance between strength and ductility will deteriorate; if the cooling rate exceeds 100°C/sec, martensite, paynite, etc. will rapidly increase, and not only will good ductility not be obtained, but it will also lead to yielding. The ratio also increases.

また、捲取温度が３００℃を超えると低温変態相による
強化作用が十分でなく、降伏比が高くなるので捲取温度
は３００℃以下とする。Further, if the winding temperature exceeds 300°C, the reinforcing effect by the low-temperature transformed phase will not be sufficient and the yield ratio will increase, so the winding temperature should be 300°C or less.

次に実施例を示す。Next, examples will be shown.

第１表はホットストリップミルで仕上板厚３．２ｍｍに
圧延したときの鋼種、成分、圧延条件を示す。Table 1 shows the steel type, components, and rolling conditions when rolled to a finished plate thickness of 3.2 mm using a hot strip mill.

第２表は得られた製品の機下しており、Ｂ鋼は捲取温度
が高いため、引張強さが低くなり、降伏比が高くなって
いる。Table 2 shows the obtained product after being unloaded from the machine. Steel B has a high coiling temperature, so its tensile strength is low and its yield ratio is high.

Ｃ鋼は本発明鋼であり、従来よりもよい延性が得られて
いる。Steel C is a steel of the present invention, and has better ductility than conventional steel.

Ｄ，Ｅ，Ｆ鋼はＲＥＭ、Ｚｒ、Ｃａなどの添加によって
さらに加工性も改善されている。D, E, and F steels have further improved workability by adding REM, Zr, Ca, etc.

このように本発明では、微細なＴｉＮを利用することに
より、従来と同じ加熱条件でも強度〜延性バランスの優
れた鋼が得られ、高品質の高張力鋼を低コストで製造で
きる優れた方法である。In this way, in the present invention, by using fine TiN, steel with an excellent balance of strength and ductility can be obtained even under the same heating conditions as conventional methods, and is an excellent method for manufacturing high-quality, high-strength steel at low cost. be.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は１２５０℃加熱時のＴｉ，Ｎ量とオーステナイ
ト粒度番号の関係を示す図であり、第２図は強度と全伸
びの関係を示す図である。FIG. 1 is a diagram showing the relationship between Ti and N contents and austenite grain size number when heated at 1250° C., and FIG. 2 is a diagram showing the relationship between strength and total elongation.

Claims (1)

【特許請求の範囲】 １ Ｃ０．０５〜０．１５％、Ｓｉ≦２％、Ｍｎ０．５
〜２．０％、Ａｌ≦０．１％、Ｔｉ０．００５〜０．０
３なる鋼をＡｒ３ 点以上、全圧下率９０％以上で圧延
し、圧延後は１０〜１００℃／秒で冷却し、３００℃以
下で捲取ることを特徴とするＴｉＮ系低降伏比複合組織
高張力鋼板の製造方法。 ２ Ｃ０．０５〜０．１５％、Ｓｉ≦２％、Ｍｎ０．５
〜２．０％、Ａｌ≦０．１％、Ｔｉ０．００５〜０．０
３Ｚｒを２≦Ｚｒ／Ｓ≦１０、または希土類元素（ＲＥ
Ｍ）を１．３≦ＲＥＭ／Ｓ≦５、もしくはＣａを０．５
≦Ｃａ／Ｓ≦１．５含有し、残余は鉄および不可避不純
物からなる鋼をＡｒ３点以上、全圧下率９０％以上で圧
延し、圧延後は１０〜１００℃／秒で冷却し、３００℃
以下で捲取ることを特徴とするＴｉＮ系低降伏比複合組
織高張力鋼板の製造方法。[Claims] 1 C0.05-0.15%, Si≦2%, Mn0.5
~2.0%, Al≦0.1%, Ti0.005~0.0
A TiN-based low yield ratio composite structure characterized by rolling steel No. 3 at an Ar3 point or higher and a total reduction rate of 90% or higher, cooling at 10 to 100°C/sec after rolling, and rolling at 300°C or lower. Method of manufacturing tensile steel plate. 2 C0.05-0.15%, Si≦2%, Mn0.5
~2.0%, Al≦0.1%, Ti0.005~0.0
3Zr with 2≦Zr/S≦10, or rare earth elements (RE
M) is 1.3≦REM/S≦5, or Ca is 0.5
Steel containing ≦Ca/S≦1.5 with the remainder consisting of iron and unavoidable impurities is rolled at 3 or more Ar points and a total reduction rate of 90% or more, and after rolling, it is cooled at 10 to 100°C/sec and heated to 300°C.
A method for producing a TiN-based low yield ratio composite structure high-strength steel sheet, which comprises rolling it as follows.