JP2008274393A

JP2008274393A - Manufacturing method of high-strength, high-toughness ferrite/pearlite non-heat-treated steel forging part

Info

Publication number: JP2008274393A
Application number: JP2007208340A
Authority: JP
Inventors: Hiroaki Yoshida; 広明吉田; Juichi Ito; 樹一伊藤
Original assignee: Daido Steel Co Ltd
Current assignee: Daido Steel Co Ltd
Priority date: 2007-03-30
Filing date: 2007-08-09
Publication date: 2008-11-13

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a ferrite and pearlite non-heat-treated steel forging part, capable of easily realizing a fine ferrite and pearlite structure through freezing and hardening of crystal grains, by using a ferrite and pearlite non-heat-treated steel containing V and suppressing process heat immediately after forging. <P>SOLUTION: In the manufacturing method of the high-strength, high-toughness ferrite and pearlite non-heat-treated steel forging part, the ferrite and pearlite non-heat-treated steel containing by mass, 0.05-0.50% V and comprising ≥90% of ferrite and pearlite structure is heated to a solution temperature of a V carbide, subsequently cooled to 700-950°C, subjected to forging at this temperature range so that the compression forming rate reaches ≥30% and the contact time with a die reaches ≥0.20 sec, and subsequently cooled so as to induce ferrite and pearlite transformation to obtain the forging part having a pearlite grain size of ≤18 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、例えば自動車エンジンに使用されるコンロッドなどの高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法に関する。 The present invention relates to a method for producing a high-strength and high-toughness ferrite + pearlite type non-tempered steel forged member such as a connecting rod used in an automobile engine, for example.

この種のフェライト＋パーライト型非調質鋼鍛造部材の製造方法として、例えば下記特許文献１に記載されているように、Ｖを含む鋼材をＶ系炭化物であるＶＣの固溶温度以上に加熱した後、７５０℃〜１０５０℃で鍛造加工することによって、ＶＣによる加工誘起析出硬化を得ながら、同時にピンニング効果により再結晶粒の粒成長を抑制しつつ再結晶粒を細粒化して、フェライト＋パーライト組織の微細化を図るようにしたものが知られている。この製造方法によれば、高い降伏強度と靭性を備えたフェライト＋パーライト型非調質鋼鍛造部材を製造することができる。
特開平１０−２３５４４７号公報 As a manufacturing method of this type of ferrite + pearlite type non-heat treated steel forged member, for example, as described in Patent Document 1 below, a steel material containing V is heated to a solid solution temperature or higher of VC which is a V-based carbide. After that, by forging at 750 ° C. to 1050 ° C., while obtaining work-induced precipitation hardening by VC, simultaneously refining the recrystallized grains while suppressing the grain growth of the recrystallized grains by the pinning effect, ferrite + pearlite Those designed to refine the structure are known. According to this manufacturing method, it is possible to manufacture a ferrite + pearlite type non-heat treated steel forged member having high yield strength and toughness.
Japanese Patent Laid-Open No. 10-235447

しかしながら、上記特許文献１に記載されたフェライト＋パーライト型非調質鋼鍛造部材の製造方法では、鍛造加工した後、その鍛造部材を単に衝風冷却や空冷などにより室温まで冷却するにすぎないため、鍛造加工時の加工発熱や残熱によって結晶粒の粗大化を引き起こし易く、特に鍛造部材が肉厚製品である場合においてその結晶粒の微細化が困難であった。 However, in the method for producing a ferrite + pearlite non-tempered steel forged member described in Patent Document 1, after forging, the forged member is simply cooled to room temperature by blast cooling or air cooling. Further, it is easy to cause coarsening of crystal grains due to processing heat generation and residual heat during forging, and particularly when the forged member is a thick product, it is difficult to refine the crystal grains.

本発明の課題は、Ｖを含有するフェライト＋パーライト型非調質鋼を用いつつ、鍛造直後の加工発熱を抑制することで、結晶粒の凍結効果によりフェライト＋パーライト組織の微細化を容易に実現することが可能なフェライト＋パーライト型非調質鋼鍛造部材の製造方法を提供することにある。 The object of the present invention is to easily reduce the size of the ferrite + pearlite structure by the freezing effect of the crystal grains by suppressing the heat generated by processing immediately after forging while using ferrite containing V + pearlite type non-heat treated steel. An object of the present invention is to provide a method for producing a forged ferrite + pearlite type non-heat treated steel member.

課題を解決するための手段及び作用・効果Means and actions / effects for solving the problems

上記の課題を解決するために、本発明の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法は、質量％で０．０５〜０．５０％のＶを含み、フェライト＋パーライト組織が９０％以上となるフェライト＋パーライト型非調質鋼を、Ｖ系炭化物の固溶温度以上に加熱した後、７００℃〜９５０℃に降温させてその温度域で圧縮加工率が３０％以上、かつ金型との接触時間が０．２０秒以上となるように鍛造加工を行い、その後冷却を行ってフェライト＋パーライト変態させ、パーライト粒径が１８μｍ以下である鍛造部材を得ることを特徴とする。 In order to solve the above problems, the method for producing a high-strength and high-toughness ferrite + pearlite-type non-tempered steel forged member of the present invention includes 0.05% to 0.50% V in mass%, Ferrite + pearlite type non-heat treated steel with a pearlite structure of 90% or higher is heated to a temperature higher than the solid solution temperature of V-based carbides, then cooled to 700 ° C to 950 ° C, and the compression rate is 30% at that temperature As described above, forging is performed so that the contact time with the mold is 0.20 seconds or more, and then cooling is performed to transform the ferrite and pearlite, thereby obtaining a forged member having a pearlite particle size of 18 μm or less. And

本発明では、金型との接触時間が０．２０秒以上となるように鍛造加工を行う。このように金型の抜熱を利用することによって、鍛造直後の加工発熱が抑制されるので、７００℃〜９５０℃の低温オーステナイト域での鍛造加工により生じる極めて微細かつ成長速度の速い動的再結晶粒の凍結効果が良好に向上する。また、加工誘起効果によって変態が促進される微細なフェライト＋パーライト組織の凍結効果も良好に向上する。しかし、金型との接触時間が１０秒を超えて保持しても、冷却の効果は飽和し、作業性を悪くするだけなので、接触時間の上限を１０秒とした。ここで、金型との接触時間が０．２０秒以上となるように鍛造加工を行うには、例えばクランクモーションプレスを用いる場合、約３０回／分よりも遅い成形速度で鍛造加工すればよく、また、例えば油圧プレスを用いる場合には、下死点保持時間が０．２０秒以上となるようにすればよい。 In the present invention, forging is performed so that the contact time with the mold is 0.20 seconds or longer. By utilizing the heat removal from the die in this way, the heat generation immediately after forging is suppressed, so that the dynamic re-generation caused by forging in the low-temperature austenite region at 700 ° C. to 950 ° C. is very fine. The freezing effect of crystal grains is improved satisfactorily. Moreover, the freezing effect of the fine ferrite + pearlite structure whose transformation is promoted by the processing inducing effect is also improved satisfactorily. However, even if the contact time with the mold exceeds 10 seconds, the cooling effect is saturated and only the workability is deteriorated, so the upper limit of the contact time is set to 10 seconds. Here, in order to perform the forging process so that the contact time with the mold is 0.20 seconds or more, for example, when using a crank motion press, the forging process may be performed at a molding speed slower than about 30 times / minute. For example, when using a hydraulic press, the bottom dead center retention time may be 0.20 seconds or longer.

また、本発明では、圧縮加工率が３０％以上となるように鍛造加工を行う。ここで、圧縮加工率とは、鍛造加工の程度を表す量を意味し、最初の鋼材の直径をＤ１、加工後の鋼材の高さ（厚さ）をＤ２とすると、次式（１）で定義される。
{（Ｄ１−Ｄ２）／Ｄ１}×１００（％） …（１）
圧縮加工率が３０％以上となるように鍛造加工を行うことにより、動的再結晶粒の凍結効果がより一層良好となり、パーライトをほぼ確実に微細化することができる。一方、８５％以上の圧縮加工率で鍛造加工すると、鍛造部材の内部で加工による発熱が発生し、冷却の効果が得られなくなるので、圧縮加工率の上限値を８５％とする。 In the present invention, forging is performed so that the compression rate is 30% or more. Here, the compression processing rate means an amount representing the degree of forging, and when the diameter of the first steel material is D1 and the height (thickness) of the steel material after processing is D2, the following equation (1) is satisfied. Defined.
{(D1-D2) / D1} × 100 (%) (1)
By performing forging so that the compression rate becomes 30% or more, the effect of freezing dynamic recrystallized grains can be further improved, and pearlite can be refined almost certainly. On the other hand, if forging is performed at a compression rate of 85% or more, heat is generated by processing inside the forged member, and the cooling effect cannot be obtained. Therefore, the upper limit value of the compression rate is set to 85%.

パーライト粒径が１８μｍ以下、好ましくは１０μｍ以下であることが望ましい。これにより、高強度と高靭性を兼ね備えたフェライト＋パーライト型非調質鋼鍛造部材を得ることができる。 The pearlite particle size is 18 μm or less, preferably 10 μm or less. Thereby, the ferrite + pearlite type non-heat treated steel forging member which has both high strength and high toughness can be obtained.

また、本発明の実施に際して、前記７００℃〜９５０℃の温度域で鍛造加工を行う前に、前記フェライト＋パーライト型非調質鋼をＶ系炭化物の固溶温度以上に加熱した後、９００℃〜１０５０℃の温度域で鍛造加工を行うようにするとよい。これによれば、粗大化したオーステナイト粒が高温オーステナイト域での鍛造加工により細粒化されるので、この細粒化した状態の結晶粒を更に低温オーステナイト域で鍛造加工することで、より一段と微細化されたパーライト組織を得ることができる。 In carrying out the present invention, before forging in the temperature range of 700 ° C. to 950 ° C., after heating the ferrite + pearlite type non-heat treated steel to a temperature higher than the solid solution temperature of the V-based carbide, 900 ° C. Forging may be performed in a temperature range of 1050 ° C. According to this, the coarsened austenite grains are refined by forging in the high-temperature austenite region, so that by further forging the crystal grains in the refined state in the low-temperature austenite region, the finer grain becomes even finer. A perlite structure can be obtained.

また、本発明の適用対象としては、前記高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材がコンロッドであるとよい。これによれば、自動車用等の高負荷環境で使用されるコンロッドを、疲労強度等に格段に優れた製品とすることができる。 In addition, as an application target of the present invention, the high-strength and high-toughness ferrite + pearlite type non-heat treated steel forged member may be a connecting rod. According to this, the connecting rod used in a high load environment such as for automobiles can be a product that is remarkably excellent in fatigue strength.

また、本発明の実施に際して、フェライト＋パーライト型非調質鋼の具体的な組成は、質量％で、Ｃ：０．２〜０．５％、Ｓｉ：０．２〜２．０％、Ｍｎ：０．３〜２．０％、Ｐ：０．０１〜０．０８％、Ｓ：０．０１〜０．０５％、Ｖ：０．０５〜０．５０％を含有し、残部がＦｅ及び不可避不純物からなるものにするとよい。この場合、例えば、Ｃｕ：０．０５〜０．３０％、Ｎｉ：０．０５〜０．３０％、及びＣｒ：０．０５〜０．３０％のうちの１種又は２種以上を含有させるようにするとよい。また、これに加えて、例えば、Ｎｂ：０．０２〜０．１０％、Ｔｉ：０．０２〜０．１０％、及びＡｌ：０．００３〜０．０４０％のうちの１種又は２種以上、Ｎ：０．００４〜０．０３０％を含有させるようにするとよく、さらに、例えば、Ｃａ：０．０００１〜０．０１００％を含有させるようにするとよい。 Further, in the practice of the present invention, the specific composition of the ferrite + pearlite type non-heat treated steel is mass%, C: 0.2 to 0.5%, Si: 0.2 to 2.0%, Mn : 0.3 to 2.0%, P: 0.01 to 0.08%, S: 0.01 to 0.05%, V: 0.05 to 0.50%, the balance being Fe and It should be made of inevitable impurities. In this case, for example, one or more of Cu: 0.05 to 0.30%, Ni: 0.05 to 0.30%, and Cr: 0.05 to 0.30% are contained. It is good to do so. In addition, for example, one or two of Nb: 0.02-0.10%, Ti: 0.02-0.10%, and Al: 0.003-0.040% As mentioned above, it is good to make it contain N: 0.004-0.030%, and it is good to contain Ca: 0.0001-0.0100% further, for example.

組成限定理由は以下の通りである。
（１）Ｃ：０．２〜０．５％
Ｃは強度を確保するために必要な元素であり、Ｖ系炭化物の必須元素である。このため、０．２質量％以上の添加が必要である。一方、０．５質量％を超えて添加すると鍛造加工後の硬さが過剰となり、被削性が低下するので０．５質量％以下にする必要がある。 The reasons for limiting the composition are as follows.
(1) C: 0.2 to 0.5%
C is an element necessary for ensuring strength and is an essential element of V-based carbide. For this reason, addition of 0.2% by mass or more is necessary. On the other hand, if added over 0.5% by mass, the hardness after forging becomes excessive and the machinability deteriorates, so it is necessary to make it 0.5% by mass or less.

（２）Ｓｉ：０．２〜２．０％
Ｓｉは鋼溶製時において脱酸作用を有し、軟質相であるフェライトの強度を高めて、耐力や疲労強度を向上させる。このような効果を得るためにＳｉは０．２質量％以上含有させることが必要である。しかし、含有量が多すぎると不必要に硬さを増加させ被削性を劣化させるので２．０質量％以下にすることが必要となる。 (2) Si: 0.2-2.0%
Si has a deoxidizing action when steel is melted, and increases the strength of ferrite, which is a soft phase, thereby improving the yield strength and fatigue strength. In order to obtain such an effect, it is necessary to contain Si by 0.2% by mass or more. However, if the content is too large, the hardness is unnecessarily increased and the machinability is deteriorated.

（３）Ｍｎ：０．３〜２．０％
Ｍｎは鍛造部材の強度を高めるとともに焼入れ性を向上させる。しかし、多量に添加すると鍛造後にベイナイトが生成し、硬さが著しく増加して被削性を低下させるため０．３〜２．０質量％とした。 (3) Mn: 0.3 to 2.0%
Mn increases the strength of the forged member and improves the hardenability. However, when added in a large amount, bainite is formed after forging, the hardness is remarkably increased and the machinability is lowered, so that the content is set to 0.3 to 2.0% by mass.

（４）Ｐ：０．０１〜０．０８％
Ｐは不可避な不純物で、粒界への偏析により靭性を低下させる元素としてできるだけ低く抑えられるのが一般的である。しかし、ＰはＳｉと同様にフェライト中に固溶しフェライトの強度を向上させるため耐力や疲労強度の向上に有効である。ただし、多量に添加してもその効果が飽和したり、鍛造加工性を阻害するために、添加量は０．０８質量％以下に留める。 (4) P: 0.01 to 0.08%
P is an unavoidable impurity and is generally kept as low as possible as an element that lowers toughness due to segregation at grain boundaries. However, P is effective in improving the yield strength and fatigue strength because it dissolves in the ferrite and improves the strength of the ferrite as with Si. However, even if it is added in a large amount, the effect is saturated or the forging workability is hindered, so the addition amount is limited to 0.08% by mass or less.

（５）Ｓ：０．０１〜０．０５％
Ｓは被削性を向上させるのに有効な元素である。しかし、添加量が多すぎると、強度や鍛造加工性を低下させるので、０．０１〜０．０５質量％とした。 (5) S: 0.01 to 0.05%
S is an element effective for improving machinability. However, if the addition amount is too large, the strength and forging processability are lowered, so the content was set to 0.01 to 0.05% by mass.

（６）Ｖ：０．０５〜０．５０％
ＶはＣと微細な炭化物を生成し、鍛造後の強度を高める元素である。特に耐力、疲労強度の向上には有効である。このような効果を得るためにも０．０５質量％以上の添加が必要である。しかしながら０．５０質量％以上添加しても高強度化の効果は飽和し、さらに被削性を低下させるので上限を０．５０質量％にした。 (6) V: 0.05 to 0.50%
V is an element that generates fine carbides with C and increases the strength after forging. This is particularly effective for improving the proof stress and fatigue strength. In order to obtain such an effect, addition of 0.05% by mass or more is necessary. However, even if 0.50% by mass or more is added, the effect of increasing the strength is saturated and further the machinability is lowered, so the upper limit was made 0.50% by mass.

（７）Ｃｕ及びＮｉ：０．０５〜０．３０％
Ｃｕ、Ｎｉは不可避な不純物であり、０．０５質量％以下にすることは多大な努力を必要とし経済的に不利である。一方、Ｍｎ、Ｃｒと同様に強度を高めるためには有効な元素であるが多量の添加も同様に経済的に不利となるためその上限を０．３０質量％以下にする。
（８）Ｃｒ：０．０５〜０．３０％
ＣｒはＭｎと同様に鍛造部材の強度を高める。しかし、多量に添加すると鍛造後にベイナイトが生成し、硬さを著しく増大させるので、０．０５〜０．３０質量％とした。 (7) Cu and Ni: 0.05 to 0.30%
Cu and Ni are unavoidable impurities, and 0.05% by mass or less requires great efforts and is economically disadvantageous. On the other hand, although it is an element effective for increasing the strength as with Mn and Cr, addition of a large amount is also economically disadvantageous, so the upper limit is made 0.30% by mass or less.
(8) Cr: 0.05-0.30%
Cr, like Mn, increases the strength of the forged member. However, if added in a large amount, bainite is formed after forging and the hardness is remarkably increased, so the content was set to 0.05 to 0.30% by mass.

（９）Ｎｂ：０．０２〜０．１０％、Ｔｉ：０．０２〜０．１０％、及びＡｌ：０．００３〜０．０４０％
Ｎｂ，ＴｉおよびＡｌは、窒化物および炭窒化物を生成し、鍛造後の結晶粒を微細化して強度を向上させるが、多量に添加すると、逆に強度が低下する。適切な添加量はＮｂ，Ｔｉは、０．０２〜０．１０％であり、Ａｌは０．００３〜０．０４０％である。
（１０）Ｎ：０．００４〜０．０３０％
Ｎは、Ｖ，Ａｌ，Ｔｉ，Ｎｂなどと窒化物や炭窒化物を生成して、結晶粒を微細化させ、結果として耐力を向上させる点で有用である。この効果を得るためには、０．００４％以上のＮが必要である。多量に添加しようとすると、ブローホールが発生して健全な鋼塊が得られないおそれがあるから、その上限を０．０３０％とした。
（１１）Ｃａ：０．０００１〜０．０１００％
Ｃａは、ＭｎＳ介在物の形態を制御する作用があり、それによって工具磨耗を抑制し、被削性を改善する効果がある。この効果を得るためには、０．０００１％以上が必要である。多量に添加すると、熱間加工性を低くするので、上限を０．０１００％とした。 (9) Nb: 0.02-0.10%, Ti: 0.02-0.10%, and Al: 0.003-0.040%
Nb, Ti, and Al generate nitrides and carbonitrides and refine the crystal grains after forging to improve the strength. However, when added in a large amount, the strength decreases conversely. Appropriate amounts of addition are 0.02 to 0.10% for Nb and Ti and 0.003 to 0.040% for Al.
(10) N: 0.004 to 0.030%
N is useful in that it produces nitrides or carbonitrides with V, Al, Ti, Nb, etc., thereby refining the crystal grains and consequently improving the yield strength. In order to obtain this effect, N of 0.004% or more is necessary. If an attempt is made to add a large amount, blow holes may occur and a healthy steel ingot may not be obtained, so the upper limit was made 0.030%.
(11) Ca: 0.0001 to 0.0100%
Ca has the effect | action which controls the form of a MnS inclusion, and there exists an effect which suppresses tool wear and improves machinability by it. In order to obtain this effect, 0.0001% or more is necessary. If added in a large amount, the hot workability is lowered, so the upper limit was made 0.0100%.

ａ．第１実施例
以下、本発明の効果を確認するために行なった試験結果について説明する。表１のＡに示す化学組成のφ３０ｍｍの丸棒を、高周波加熱装置にて、１２００℃、２分間の加熱後、図１に示すように直径方向に圧縮加工率５０％の鍛造加工を行い、底部から３／４の高さの横断面のパーライト粒径を測定した。このとき、横断面を研磨してナイタール腐食後に組織写真を撮影し、フェライト＋パーライト組織以外の部位に色を塗ってフェライト＋パーライト組織の面積率を求めた。フェライト＋パーライト組織は何れも９０％以上であった。図２に鍛造温度をパラメータとしたときの、丸棒と金型（パンチ）との接触時間と、パーライト粒径との関係を示す。また、表２の上欄に、図２に示した試験データのうち圧縮加工率を５０％、接触時間を０．８０秒とした実施例１〜６と、圧縮加工率を５０％、接触時間を０．８０秒として鍛造温度をそれぞれ６５０℃，１０００℃とした比較例１，２を示す。 a. First Example Hereinafter, the results of tests conducted to confirm the effects of the present invention will be described. A round bar of φ30 mm having a chemical composition shown in A of Table 1 is heated at 1200 ° C. for 2 minutes with a high-frequency heating device, and then forged with a compression rate of 50% in the diameter direction as shown in FIG. The pearlite particle size of a cross section 3/4 height from the bottom was measured. At this time, the cross section was polished, and a structure photograph was taken after nital corrosion, and the area other than the ferrite + pearlite structure was painted to obtain the area ratio of the ferrite + pearlite structure. The ferrite + pearlite structure was 90% or more. FIG. 2 shows the relationship between the contact time between the round bar and the die (punch) and the pearlite particle size when the forging temperature is used as a parameter. Further, in the upper column of Table 2, Examples 1 to 6 in which the compression rate is 50% and the contact time is 0.80 seconds among the test data shown in FIG. 2, the compression rate is 50%, and the contact time. Comparative Examples 1 and 2 in which the forging temperatures were 650 ° C. and 1000 ° C., respectively, for 0.80 seconds.

表２から明らかなように、比較例１では、鍛造部材に割れが発生した。また、比較例２では、パーライト粒径が１８μｍを超えた（１８．９μｍ）。これに対して、実施例１〜６では、何れもパーライト粒径が１０μｍ以下となった。また、図２から明らかなように、金型との接触時間が０．２０秒以上であるときパーライト粒径が１８μｍ以下となり、金型との接触時間が０．８０秒以上であるときパーライト粒径が１０μｍ以下となることがわかる。 As is clear from Table 2, in Comparative Example 1, cracks occurred in the forged member. In Comparative Example 2, the pearlite particle size exceeded 18 μm (18.9 μm). On the other hand, in Examples 1-6, the pearlite particle size became 10 micrometers or less in any case. As is clear from FIG. 2, the pearlite particle size is 18 μm or less when the contact time with the mold is 0.20 seconds or more, and the pearlite particles when the contact time with the mold is 0.80 seconds or more. It can be seen that the diameter is 10 μm or less.

図３に鍛造温度を７５０℃として金型との接触時間をパラメータ（０．２５秒，０．８０秒）としたときの、圧縮加工率とパーライト粒径との関係を示す。また、表２に、鍛造温度を何れも７５０℃とした上で、接触時間を０．８０秒、圧縮加工率をそれぞれ３０％，４０％，５０％とした実施例７，８，２と、圧縮加工率を５０％、接触時間をそれぞれ０．２０秒，１．５０秒とした実施例９，１０を示す。併せて、圧縮加工率を２０％、接触時間を０．８０秒とした比較例３と、圧縮加工率を５０％、接触時間を０．１０秒とした比較例４を示す。 FIG. 3 shows the relationship between the compression rate and the pearlite particle size when the forging temperature is 750 ° C. and the contact time with the mold is a parameter (0.25 seconds, 0.80 seconds). In Table 2, Examples 7, 8, and 2 in which the forging temperature was 750 ° C., the contact time was 0.80 seconds, and the compression rate was 30%, 40%, and 50%, respectively. Examples 9 and 10 in which the compression rate is 50% and the contact times are 0.20 seconds and 1.50 seconds, respectively are shown. In addition, Comparative Example 3 in which the compression rate is 20% and the contact time is 0.80 seconds and Comparative Example 4 in which the compression rate is 50% and the contact time is 0.10 seconds are shown.

表２から明らかなように、比較例３，４では、何れもパーライト粒径が１８μｍを超えた（１８．５μｍ，２２．０μｍ）。これに対して、実施例２，７〜１０では、何れもパーライト粒径が１８μｍ以下となった。また、図３から明らかなように、圧縮加工率が３０％以上であるときパーライト粒径が１８μｍ以下となることがわかる。図４に微細化されたパーライトの有効範囲を模式的に示す。 As is clear from Table 2, in Comparative Examples 3 and 4, the pearlite particle size exceeded 18 μm (18.5 μm, 22.0 μm). On the other hand, in Examples 2 and 7 to 10, the pearlite particle size was 18 μm or less in all cases. Further, as is apparent from FIG. 3, it is understood that the pearlite particle size is 18 μm or less when the compression rate is 30% or more. FIG. 4 schematically shows the effective range of the refined pearlite.

ｂ．第２実施例
この第２実施例では、表１のＢ〜Ｇに示す化学組成のφ３０ｍｍの丸棒を、上記第１実施例と同様、高周波加熱装置にて、１２００℃、２分間の加熱後、図１に示すように直径方向に鍛造加工を行い、底部から３／４の高さの横断面のパーライト粒径を測定した。この場合、鍛造温度を７００℃、圧縮加工率を５０％、金型との接触時間を０．８０秒とした。試験結果を表３に示す。表３から明らかなように、実施例１１〜１６のパーライト粒径は、何れも１０μｍ以下となった。 b. Second Example In this second example, a φ30 mm round bar having the chemical composition shown in Tables B to G in Table 1 was heated at 1200 ° C. for 2 minutes using a high-frequency heating apparatus, as in the first example. As shown in FIG. 1, forging was performed in the diameter direction, and the pearlite particle size of a cross section 3/4 height from the bottom was measured. In this case, the forging temperature was 700 ° C., the compression rate was 50%, and the contact time with the mold was 0.80 seconds. The test results are shown in Table 3. As apparent from Table 3, the pearlite particle sizes of Examples 11 to 16 were all 10 μm or less.

ｃ．第３実施例
この第３実施例では、表１のＡに示す化学組成のφ３０ｍｍの丸棒を、高周波加熱装置にて、１２００℃、２分間の加熱後、合計２回の圧縮加工率が５０％となるように、１回目は９５０℃にて圧縮加工率２０％の鍛造加工を行い、２回目は鍛造温度をパラメータとして圧縮加工率３７．５％の鍛造加工を行って、底部から３／４の高さの横断面のパーライト粒径を測定した。この第３実施例においても、上記第１および第２実施例と同様にして、フェライト＋パーライト組織の面積率を求めた。フェライト＋パーライト組織は何れも９０％以上であった。図５に鍛造温度をパラメータとしたときの、丸棒と金型（パンチ）との接触時間（２回目の鍛造加工時における金型との接触時間）と、パーライト粒径との関係を示す。表４に、図５に示した試験データのうち接触時間を０．８０秒とした実施例１７〜２２と、２回目の鍛造温度７５０℃にて接触時間をそれぞれ０．２０秒，１．５０秒とした実施例２３，２４を示す。また、比較例として、２回目の鍛造温度を６５０℃（接触時間０．８０秒）とした比較例５、１回目と２回目の鍛造温度を何れも１０００℃（接触時間０．８０秒）とした比較例６、９５０℃にて圧縮加工率２０％の鍛造加工を行い、その後鍛造加工を行わずに７５０℃にて接触時間を０．８０秒とした比較例７、および２回目の鍛造温度７５０℃にて接触時間を０．１０秒とした比較例８を示す。 c. Third Example In this third example, a round bar having a chemical composition shown in A of Table 1 with a diameter of 30 mm was heated at 1200 ° C. for 2 minutes with a high-frequency heating apparatus, and the compression rate of the total two times was 50. %, The first time forging with a compression rate of 20% at 950 ° C., and the second time forging with a compression rate of 37.5% with the forging temperature as a parameter, The pearlite particle size of a 4 cross section was measured. Also in the third example, the area ratio of the ferrite + pearlite structure was obtained in the same manner as in the first and second examples. The ferrite + pearlite structure was 90% or more. FIG. 5 shows the relationship between the contact time between the round bar and the die (punch) (contact time with the die during the second forging process) and the pearlite particle size when the forging temperature is used as a parameter. Table 4 shows Examples 17 to 22 in which the contact time is 0.80 seconds in the test data shown in FIG. 5 and the contact times are 0.20 seconds and 1.50 at the second forging temperature of 750 ° C., respectively. Examples 23 and 24 in seconds are shown. Further, as a comparative example, Comparative Example 5 in which the second forging temperature was 650 ° C. (contact time 0.80 seconds), and the first and second forging temperatures were both 1000 ° C. (contact time 0.80 seconds). Comparative Example 6, Comparative Example 7 in which a forging process at a compression rate of 20% was performed at 950 ° C., and then the contact time was 0.80 seconds at 750 ° C. without performing the forging process, and the second forging temperature The comparative example 8 which made contact time 0.10 second at 750 degreeC is shown.

表４および図５から明らかなように、第３実施例における各実施例１７〜２４は、対応する第１実施例における各実施例１〜６，９，１０に比して、何れもパーライト粒径がより一段と微細化していることがわかる。これに対して、２回目の鍛造温度が７００℃よりも低い比較例５では割れが発生し、２回目の鍛造温度が９５０℃よりも高い比較例６、合計の圧縮加工率が３０％よりも小さい比較例７、および接触時間が０．２０秒に満たない比較例８では、何れもパーライト粒径が１８μｍを超えた（１８．５μｍ，１８．２μｍ，２０．９μｍ）。 As is clear from Table 4 and FIG. 5, each of Examples 17 to 24 in the third example is pearlite grains as compared with Examples 1 to 6, 9, and 10 in the corresponding first example. It can be seen that the diameter is further refined. On the other hand, in Comparative Example 5 in which the second forging temperature is lower than 700 ° C., cracks occur, and in Comparative Example 6 in which the second forging temperature is higher than 950 ° C., the total compression ratio is less than 30%. In the small comparative example 7 and the comparative example 8 in which the contact time was less than 0.20 seconds, the pearlite particle size exceeded 18 μm (18.5 μm, 18.2 μm, 20.9 μm).

ｄ．第４実施例
この第４実施例では、表１のＢ〜Ｇに示す化学組成のφ３０ｍｍの丸棒を、上記第３実施例と同様、高周波加熱装置にて、１２００℃、２分間の加熱後、合計２回の圧縮加工率が５０％となるように、１回目は９５０℃にて圧縮加工率２０％の鍛造加工を行い、２回目は７００℃にて圧縮加工率３７．５％の鍛造加工を行って、底部から３／４の高さの横断面のパーライト粒径を測定した。この場合、７００℃にて金型との接触時間を０．８０秒とした。試験結果を表５に示す。表５から明らかなように、第４実施例における各実施例２５〜３０は、対応する第２実施例における各実施例１１〜１６に比して、何れもパーライト粒径がより一段と微細化していることがわかる。 d. Fourth Example In this fourth example, a round bar of φ30 mm having the chemical composition shown in Tables B to G in Table 1 was heated at 1200 ° C. for 2 minutes with a high-frequency heating apparatus, as in the third example. Forging with a compression rate of 20% at 950 ° C. for the first time and forging with a compression rate of 37.5% at 700 ° C. for the second time so that the compression rate of the total two times becomes 50%. Processing was performed to measure the pearlite particle size of a cross section 3/4 height from the bottom. In this case, the contact time with the mold at 700 ° C. was set to 0.80 seconds. The test results are shown in Table 5. As is clear from Table 5, each of the Examples 25-30 in the fourth example has a finer pearlite particle size than the corresponding Examples 11-16 in the second Example. I understand that.

試験片を示す説明図。Explanatory drawing which shows a test piece. 本発明の第１実施例に係り、鍛造温度をパラメータとしたときの、丸棒と金型との接触時間と、パーライト粒径との関係を示す説明図。Explanatory drawing which concerns on 1st Example of this invention, and shows the relationship between the contact time of a round bar and a metal mold | die when a forging temperature is used as a parameter, and a pearlite particle size. 本発明の第１実施例に係り、鍛造温度を７５０℃として金型との接触時間をパラメータとしたときの圧縮加工率とパーライト粒径との関係を示す説明図。Explanatory drawing which concerns on 1st Example of this invention and shows the relationship between a compression processing rate and a pearlite particle size when forging temperature is 750 degreeC and the contact time with a metal mold | die is used as a parameter. 微細化されたパーライトの有効範囲を示す模式図。The schematic diagram which shows the effective range of refined pearlite. 本発明の第３実施例に係り、２回目の鍛造温度をパラメータとしたときの、丸棒と金型との接触時間と、パーライト粒径との関係を示す説明図。Explanatory drawing which concerns on 3rd Example of this invention, and shows the relationship between the contact time of a round bar and a metal mold | die when a 2nd forge temperature is used as a parameter, and a pearlite particle size.

Claims

質量％で０．０５〜０．５０％のＶを含み、フェライト＋パーライト組織が９０％以上となるフェライト＋パーライト型非調質鋼を、Ｖ系炭化物の固溶温度以上に加熱した後、７００℃〜９５０℃に降温させてその温度域で圧縮加工率が３０％以上、かつ金型との接触時間が０．２０秒以上となるように鍛造加工を行い、その後冷却を行ってフェライト＋パーライト変態させ、パーライト粒径が１８μｍ以下である鍛造部材を得ることを特徴とする高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 After heating the ferrite + pearlite type non-refined steel containing 0.05 to 0.50% by mass of V and having a ferrite + pearlite structure of 90% or more above the solid solution temperature of the V-based carbide, 700 The temperature is lowered to 950 ° C. to 950 ° C., the forging process is performed so that the compression processing rate is 30% or more and the contact time with the mold is 0.20 seconds or more in that temperature range, and then cooling is performed, and ferrite + pearlite A method for producing a high-strength and high-toughness ferrite + pearlite-type non-tempered steel forged member obtained by transforming to obtain a forged member having a pearlite particle size of 18 μm or less.

前記７００℃〜９５０℃の温度域で鍛造加工を行う前に、前記フェライト＋パーライト型非調質鋼をＶ系炭化物の固溶温度以上に加熱した後、９００℃〜１０５０℃の温度域で鍛造加工を行う請求項１に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 Before forging in the temperature range of 700 ° C. to 950 ° C., the ferrite + pearlite type non-heat treated steel is heated to a temperature higher than the solid solution temperature of the V-based carbide, and then forged in the temperature range of 900 ° C. to 1050 ° C. The manufacturing method of the high strength and high toughness ferrite + pearlite type non-heat treated steel forging member according to claim 1 which processes.

質量％で、Ｃ：０．２〜０．５％、Ｓｉ：０．２〜２．０％、Ｍｎ：０．３〜２．０％、Ｐ：０．０１〜０．０８％、Ｓ：０．０１〜０．０５％、Ｖ：０．０５〜０．５０％を含有し、残部がＦｅ及び不可避不純物からなるフェライト＋パーライト型非調質鋼が用いられる請求項１または２に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 In mass%, C: 0.2 to 0.5%, Si: 0.2 to 2.0%, Mn: 0.3 to 2.0%, P: 0.01 to 0.08%, S: The ferrite + pearlite type non-tempered steel containing 0.01 to 0.05%, V: 0.05 to 0.50%, the balance being Fe and inevitable impurities is used. Manufacturing method of high strength and high toughness ferrite + pearlite type non-tempered steel forged member.

Ｃｕ：０．０５〜０．３０％、Ｎｉ：０．０５〜０．３０％、及びＣｒ：０．０５〜０．３０％のうちの１種又は２種以上を含有する請求項３に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 It contains 1 type (s) or 2 or more types in Cu: 0.05-0.30%, Ni: 0.05-0.30%, and Cr: 0.05-0.30%. Of high strength and high toughness ferrite + pearlite type non-tempered steel forged member.

Ｎｂ：０．０２〜０．１０％、Ｔｉ：０．０２〜０．１０％、及びＡｌ：０．００３〜０．０４０％のうちの１種又は２種以上、Ｎ：０．００４〜０．０３０％を含有する請求項４に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 One or more of Nb: 0.02-0.10%, Ti: 0.02-0.10%, and Al: 0.003-0.040%, N: 0.004-0 The manufacturing method of the high strength and toughness ferrite + pearlite type non-tempered steel forged member of Claim 4 containing 0.030%.

Ｃａ：０．０００１〜０．０１００％を含有する請求項５に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 The manufacturing method of the high strength and toughness ferrite + pearlite type non-tempered steel forged member of Claim 5 containing Ca: 0.0001-0.0100%.

前記高強度フェライト＋パーライト型非調質鋼鍛造部材は、コンロッドである請求項１〜６のいずれか１項に記載の高強度及び高靭性フェライト＋パーライト型非調質鋼鍛造部材の製造方法。 The method for producing a high-strength and high-toughness ferrite + pearlite-type non-heat treated steel forged member according to any one of claims 1 to 6, wherein the high-strength ferrite + pearlite-type non-heat treated steel forged member is a connecting rod.