JPH0617186A - Spheroidal graphite cast iron member and manufacture thereof - Google Patents
Spheroidal graphite cast iron member and manufacture thereofInfo
- Publication number
- JPH0617186A JPH0617186A JP5773193A JP5773193A JPH0617186A JP H0617186 A JPH0617186 A JP H0617186A JP 5773193 A JP5773193 A JP 5773193A JP 5773193 A JP5773193 A JP 5773193A JP H0617186 A JPH0617186 A JP H0617186A
- Authority
- JP
- Japan
- Prior art keywords
- surface layer
- cast iron
- spheroidal graphite
- graphite cast
- rate
- 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.)
- Pending
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は優れた機械的強度を有す
る球状黒鉛鋳鉄部材及びその製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spheroidal graphite cast iron member having excellent mechanical strength and a method for producing the same.
【０００２】[0002]
【従来の技術及び発明が解決しようとする課題】球状黒
鉛鋳鉄は高い機械的強度及び伸びを有するため、種々の
機械や自動車の部品として広く使用されている。特に、
機械的強度を必要とする部品には、ＪＩＳＧ５５０２の
５種（ＦＣＤ７００）及び６種（ＦＣＤ８００）等が使
用され、また伸びを必要とする部品には０種（ＦＣＤ３
７０）及び１種（ＦＣＤ４００）等が使用されている。
なかでも自動車の懸架装置等の重要な部品は引張強さ、
伸び、疲労強度、衝撃強度等が良好であることが要求さ
れているので、それを構成する球状黒鉛鋳鉄部材は上記
強度の要求レベルを十分にクリアするものでなければな
らない。ところが、鋳造品の表面の黒皮には砂噛みやノ
ロ噛み等により微細な凹凸があり、その凹部が切り欠き
の作用をして破壊の起点となることがある。そのために
球状黒鉛鋳鉄部材は本来の強度を十分に発揮することが
できないという問題があることがわかった。BACKGROUND OF THE INVENTION Since spheroidal graphite cast iron has high mechanical strength and elongation, it is widely used as parts of various machines and automobiles. In particular,
JIS G5502 5 types (FCD700) and 6 types (FCD800) are used for parts that require mechanical strength, and 0 type (FCD3) for parts that require elongation.
70) and 1 type (FCD400).
Above all, important parts such as automobile suspension systems are tensile strength,
Since it is required to have good elongation, fatigue strength, impact strength, etc., the spheroidal graphite cast iron member constituting the member must sufficiently satisfy the above-mentioned required level of strength. However, the black skin on the surface of the cast product has fine irregularities due to sand biting, slag biting, and the like, and the concave portion may act as a notch and become a starting point of fracture. Therefore, it has been found that the spheroidal graphite cast iron member has a problem that the original strength cannot be sufficiently exhibited.
【０００３】以上の状況において、本発明者等は、特に
薄肉の球状黒鉛鋳鉄部材であって、良好な機械的強度を
有するものを提案した（特開平２−２９０９４３号）。
具体的には、この薄肉強靭球状黒鉛鋳鉄部材は、パーラ
イトが面積率で10％以下のフェライト基地中に黒鉛粒子
が分散したもので、前記黒鉛粒子と前記フェライト基地
との間に微細な空隙が実質的に存在しないことを特徴と
する。また、この薄肉強靭球状黒鉛鋳鉄部材は、球状黒
鉛鋳鉄組成を有する溶湯を鋳型に注入し、前記溶湯の凝
固完了後鋳造品のほぼ全体がまだＡ3 変態点以上の状態
にあるときに型バラシを行い、得られた鋳造品を直ちに
Ａ3 変態点以上の温度に保持された連続炉の均熱域に入
れ、そこで基地中のセメンタイトを分解するために前記
鋳造品を30分以下保持し、次いで前記鋳造品を前記連続
炉の冷却域に移送して、前記基地のフェライト化を達成
する冷却速度で、前記鋳造品を冷却することにより製造
することができる。Under the above circumstances, the present inventors have proposed a particularly thin spheroidal graphite cast iron member having good mechanical strength (Japanese Patent Laid-Open No. 2-290943).
Specifically, this thin-walled tough spheroidal graphite cast iron member is one in which graphite particles are dispersed in a ferrite matrix having an area ratio of 10% or less, and fine voids are present between the graphite particles and the ferrite matrix. It is characterized by being substantially absent. Further, this thin-walled, tough spheroidal graphite cast iron member is prepared by pouring a molten metal having a spheroidal graphite cast iron composition into a mold, and after the completion of solidification of the molten metal, almost all of the cast product is still in a state of A 3 transformation point or higher. The obtained cast product was immediately put in a soaking zone of a continuous furnace maintained at a temperature of A 3 transformation point or higher, and the cast product was held for 30 minutes or less in order to decompose cementite in the base therein, Then, the cast product can be manufactured by transferring the cast product to the cooling zone of the continuous furnace and cooling the cast product at a cooling rate that achieves ferritic conversion of the matrix.
【０００４】しかしながら、薄肉球状黒鉛鋳鉄部材の場
合と異なり、より高い機械的強度が要求される部品に使
用するために比較的厚肉にした球状黒鉛鋳鉄部材の場
合、パーライト組織を残して引張強さ等を保持したま
ま、曲げ強度を向上する必要がある。そのためには、球
状黒鉛鋳鉄部材の全体又は大部分がフェライト化するよ
うな熱処理では良くないことが分かった。However, unlike the case of the thin-walled spheroidal graphite cast iron member, in the case of the spheroidal graphite cast iron member having a relatively thick wall for use in a component requiring higher mechanical strength, the pearlite structure remains and the tensile strength remains. It is necessary to improve the bending strength while maintaining the bending strength. For that purpose, it has been found that heat treatment in which the whole or most of the spheroidal graphite cast iron member is made into ferrite is not good.
【０００５】従って、本発明の目的は、表面の黒皮層に
おける切り欠き感受性を鈍化させ、機械的性質、特に伸
びに優れた球状黒鉛鋳鉄部材を提供することである。[0005] Therefore, an object of the present invention is to provide a spheroidal graphite cast iron member which has a blunted cutout sensitivity in the surface black skin layer and which is excellent in mechanical properties, particularly elongation.
【０００６】本発明のもう１つの目的は、かかる球状黒
鉛鋳鉄部材を製造する方法を提供することである。Another object of the present invention is to provide a method of manufacturing such a spheroidal graphite cast iron member.
【０００７】[0007]
【課題を解決するための手段】上記目的に鑑み鋭意研究
の結果、本発明者らは、鋳造されたままの球状黒鉛鋳鉄
部材は非常に凹凸の激しい表層部を有するために、表面
の凹凸が破壊の起点となることを発見し、また、曲げ応
力等による破壊を防止するためには、内部のパーライト
組織が実質的に不変のままで表層部の硬度を幾分低下さ
せる（表層部のフェライト化率を向上させる）ような熱
処理を施せばよいことを発見し、本発明に想到した。As a result of earnest research in view of the above object, the inventors of the present invention have found that the as-cast spheroidal graphite cast iron member has a surface layer portion with extremely large irregularities, so that the surface irregularities are In order to discover that it becomes the starting point of fracture, and to prevent fracture due to bending stress, etc., the hardness of the surface layer part is reduced somewhat while the internal pearlite structure remains substantially unchanged (ferrite in the surface layer part). The present invention was conceived by discovering that a heat treatment for improving the conversion rate should be performed.
【０００８】すなわち、本発明の球状黒鉛鋳鉄部材は、
大部分がフェライト相からなる少なくとも１ｍｍの厚さ
の表層部と、パーライト相及びフェライト相からなる内
部とを有し前記表層部のフェライト化率は７０％以上で
あり、前記内部のフェライト化率より少なくとも約１５
％高いことを特徴とする。That is, the spheroidal graphite cast iron member of the present invention is
Most of the surface layer portion is composed of a ferrite phase and has a thickness of at least 1 mm, and the interior is composed of a pearlite phase and a ferrite phase. The surface layer portion has a ferritization rate of 70% or more. At least about 15
% High.
【０００９】本発明の球状黒鉛鋳鉄部材を製造する第一
の方法は、球状黒鉛鋳鉄組成を有する溶湯を鋳型に注入
し、前記溶湯の凝固完了後鋳造品のほぼ全体がまだＡ1
変態点以上の状態にあるときに型バラシを行い、得られ
た鋳造品の表層部と内部との温度差が４０〜６０℃にな
ったときに、前記鋳造品を７５０〜９００℃に保持され
た均熱炉に入れ、前記表層部のフェライト化率が７０％
以上でかつ前記内部のフェライト化率より少なくとも１
５％高くなる時間だけ前記均熱炉内に保持し、次いで前
記鋳造品を冷却炉に移送して、１５〜１００℃／分の冷
却速度で冷却することを特徴とする。The first method for producing the spheroidal graphite cast iron member of the present invention is to inject a molten metal having a spheroidal graphite cast iron composition into a mold, and after completion of solidification of the molten metal, almost all of the cast product is still A 1
When the temperature difference between the surface layer and the inside of the obtained cast product is 40 to 60 ° C., the cast product is held at 750 to 900 ° C. Put in a soaking furnace, and the rate of ferritization of the surface layer is 70%
At least 1 from the above-mentioned internal ferrite ratio
It is characterized in that it is held in the soaking furnace for a time period which increases by 5%, then the cast product is transferred to a cooling furnace and cooled at a cooling rate of 15 to 100 ° C./min.
【００１０】本発明の球状黒鉛鋳鉄部材を製造する第二
の方法は、パーライト化された球状黒鉛鋳鉄部材を７８
０〜８７０℃に保持された均熱炉に入れ、前記表層部の
フェライト化率が７０％以上でかつ前記内部のフェライ
ト化率より少なくとも１５％高くなる時間だけ前記均熱
炉内に保持し、次いで前記鋳造品を冷却炉に移送して、
１５〜１００℃／分の冷却速度で冷却することを特徴と
する。The second method for producing the spheroidal graphite cast iron member of the present invention is to prepare a pearlitic spheroidal graphite cast iron member.
It is placed in a soaking furnace maintained at 0 to 870 ° C., and is kept in the soaking furnace for a time at which the ferritization rate of the surface layer portion is 70% or more and is at least 15% higher than the internal ferritization rate, Then transfer the casting to a cooling furnace,
It is characterized by cooling at a cooling rate of 15 to 100 ° C./min.
【００１１】以下、本発明を詳細に説明する。 〔Ａ〕球状黒鉛鋳鉄の組成The present invention will be described in detail below. [A] Composition of spheroidal graphite cast iron
【００１２】本発明の球状黒鉛鋳鉄部材は、一般に以下
の化学成分を含有し、 Ｃ：3.40〜3.90重量％ Si: 1.9 〜2.5 重量％ Mn: 0.5 重量％以下 Ｐ：0.05重量％以下 Ｓ：0.02重量％以下 Mg: 0.02〜0.06重量％ Cu: 0.8 重量％以下 残部は実質的にFe及び不可避的不純物からなる組成を有
する。The spheroidal graphite cast iron member of the present invention generally contains the following chemical components: C: 3.40 to 3.90 wt% Si: 1.9 to 2.5 wt% Mn: 0.5 wt% or less P: 0.05 wt% or less S: 0.02 % By weight Mg: 0.02 to 0.06% by weight Cu: 0.8% by weight or less The balance has a composition consisting essentially of Fe and inevitable impurities.
【００１３】(1) Ｃ：3.40〜3.90重量％ Ｃの含有量が3.40重量％未満、あるいは3.90重量％を越
えると鋳造性が低下する。(1) C: 3.40 to 3.90% by weight If the content of C is less than 3.40% by weight or exceeds 3.90% by weight, the castability is deteriorated.
【００１４】(2) Si: 1.9 〜2.5 重量％ Ｓｉの含有量が1.9 重量％未満であると、炭化物生成傾
向が増大し、2.5 重量％を越えるとパーライト量の制御
が困難になり、均一なパーライトを得ることが難しくな
る。(2) Si: 1.9 to 2.5% by weight If the Si content is less than 1.9% by weight, the tendency to form carbides increases, and if it exceeds 2.5% by weight, it becomes difficult to control the amount of pearlite and the content of pearlite becomes uniform. It becomes difficult to obtain perlite.
【００１５】(3) Mn: 0.5 重量％以下 Ｍｎはパーライト安定化元素であるとともに、炭化物生
成元素である。Ｍｎの含有量が0.5 重量％を越えるとこ
れらの作用が低下する。(3) Mn: 0.5% by weight or less Mn is a pearlite stabilizing element and a carbide forming element. If the Mn content exceeds 0.5% by weight, these effects are reduced.
【００１６】(4) Ｐ：0.05重量％以下 Ｐは球状化阻害元素材であり、その含有量は0.05重量％
を越えるべきでない。(4) P: 0.05% by weight or less P is a raw material for inhibiting spheroidization, and its content is 0.05% by weight.
Should not be exceeded.
【００１７】(5) Ｓ：0.02重量％以下 Ｓは球状化阻害元素材であり、その含有量は0.02重量％
を越えるべきでない。(5) S: 0.02% by weight or less S is a spheroidization inhibiting material, and its content is 0.02% by weight.
Should not be exceeded.
【００１８】(6) Mg: 0.02〜0.06重量％ Ｍｇの含有量が0.02重量％未満であると、球状黒鉛鋳鉄
を得る歩留りが低下する。一方、0.06重量％を越えると
チル発生の要因となる。(6) Mg: 0.02 to 0.06% by weight When the content of Mg is less than 0.02% by weight, the yield for obtaining spheroidal graphite cast iron decreases. On the other hand, if it exceeds 0.06% by weight, chilling may occur.
【００１９】(7) Cu: 0.8 重量％以下 Ｃｕは炭化物生成傾向を持たないパーライト安定化元素
であり、組織中のパーライトを均一にする。しかし、Ｃ
ｕの含有量が0.8 重量％を越えてもその効果の一層の増
大は期待できない。(7) Cu: 0.8% by weight or less Cu is a pearlite stabilizing element having no tendency to form carbides, and makes pearlite in the structure uniform. But C
Even if the content of u exceeds 0.8% by weight, its effect cannot be expected to be further increased.
【００２０】好ましい球状黒鉛鋳鉄部材の組成は、 Ｃ：3.60〜3.80重量％ Si: 2.0 〜2.5 重量％ Mn: 0.4 重量％以下 Ｐ：0.05重量％以下 Ｓ：0.015 重量％以下 Mg: 0.02〜0.05重量％ Cu: 0.7 重量％以下 残部は実質的にFe及び不可避的不純物である。The preferred composition of the spheroidal graphite cast iron member is C: 3.60 to 3.80% by weight Si: 2.0 to 2.5% by weight Mn: 0.4% by weight or less P: 0.05% by weight or less S: 0.015% by weight or less Mg: 0.02 to 0.05% by weight % Cu: 0.7 wt% or less The balance is essentially Fe and unavoidable impurities.
【００２１】〔Ｂ〕球状黒鉛鋳鉄部材の層構造 （１）表層部 表層部の金属組織は、フェライト化率が７０％以上であ
る必要がある。ここで「フェライト化率」とは、基地中
のフェライト相の割合をいう。フェライト化率が７０％
未満であると、表層部の硬度が十分に低下しておらず、
破壊防止の作用が不十分である。好ましいフェライト化
率は８０％以上である。なお、表層部の基地の残部はほ
とんどパーライト相である。[B] Layer structure of spheroidal graphite cast iron member (1) Surface layer part The metallographic structure of the surface layer part needs to have a ferrite rate of 70% or more. Here, the "ferritization rate" refers to the rate of the ferrite phase in the matrix. Ferritization rate is 70%
If it is less than, the hardness of the surface layer is not sufficiently reduced,
The action of preventing destruction is insufficient. A preferable ferritic conversion rate is 80% or more. The rest of the base in the surface layer is mostly pearlite phase.
【００２２】表層部は９３未満のロックウェル硬度ＨＲ
Ｂを有する。ロックウェル硬度ＨＲＢが９３以上である
と、その凹凸が破壊の起点になるおそれが大きくなる。The surface layer has a Rockwell hardness HR of less than 93.
Have B. When the Rockwell hardness HRB is 93 or more, there is a high possibility that the unevenness will be the starting point of the fracture.
【００２３】表層部の厚さは、少なくとも１ｍｍであ
る。表層部が１ｍｍ未満であると、破壊防止の効果が十
分に得られない。なお、厚さの上限は球状黒鉛鋳鉄部材
全体の厚さに依存するが、一般に全厚の１０％以下であ
る。表層部の厚さが全厚の１０％を越えると、球状黒鉛
鋳鉄部材の機械的強度は低下する。The surface layer has a thickness of at least 1 mm. If the surface layer portion is less than 1 mm, the effect of preventing breakage cannot be sufficiently obtained. The upper limit of the thickness depends on the total thickness of the spheroidal graphite cast iron member, but is generally 10% or less of the total thickness. If the thickness of the surface layer portion exceeds 10% of the total thickness, the mechanical strength of the spheroidal graphite cast iron member decreases.
【００２４】（２）内部 内部の金属組織は、パーライト相とフェライト相とから
なる。内部のフェライト相の割合（フェライト化率）は
表層部より少なくとも約１５％低い。内部のフェライト
化率が表層部より少なくとも約１５％低くないと（パー
ライト相の割合が約４５％未満であると）、球状黒鉛鋳
鉄部材全体の機械的強度が不十分である。表層部のフェ
ライト化率にもよるが、一般に内部のフェライト化率は
０〜４５％程度が好ましい。(2) Inside The metal structure inside is composed of a pearlite phase and a ferrite phase. The ratio of the internal ferrite phase (ferritization ratio) is lower than that of the surface layer portion by at least about 15%. The mechanical strength of the entire spheroidal graphite cast iron member is insufficient unless the internal ferrite ratio is at least about 15% lower than that of the surface layer portion (the ratio of the pearlite phase is less than about 45%). Although it depends on the ferriticity of the surface layer, the internal ferriticity is generally preferably about 0 to 45%.
【００２５】以上の構造のために、内部は表層部より高
いロックウェル硬度ＨＲＢを有する。一般に、内部のロ
ックウェル硬度ＨＲＢは表層部より１０程度高いのが好
ましい。Due to the above structure, the inside has a higher Rockwell hardness HRB than the surface layer portion. Generally, it is preferable that the internal Rockwell hardness HRB is higher than the surface layer portion by about 10.
【００２６】以上のような二重構造を有する球状黒鉛鋳
鉄部材は、少なくとも１ｍｍの表層部を有するので比較
的厚肉である。具体的には、１２ｍｍ以上、好ましくは
１５ｍｍ以上の肉厚を有する場合に効果が大きい。The spheroidal graphite cast iron member having the double structure as described above has a surface layer portion of at least 1 mm, and is therefore relatively thick. Specifically, the effect is great when the wall thickness is 12 mm or more, preferably 15 mm or more.
【００２７】〔Ｃ〕球状黒鉛鋳鉄部材の製造方法 （１）第一の方法[C] Method for producing spheroidal graphite cast iron member (1) First method
【００２８】このような層構造を有する球状黒鉛鋳鉄部
材を製造する第一の方法は、型バラシ後短時間のうちに
鋳造品に対して、均熱炉及び冷却炉で熱処理を施すもの
である。好ましくは、均熱域及び冷却域を有する連続炉
を使用する。第一の方法において、球状黒鉛鋳鉄組成を
有する溶湯を鋳型に注入し、前記溶湯の凝固完了後鋳造
品のほぼ全体がまだＡ1 変態点以上の状態にあるときに
型バラシを行い、得られた鋳造品の表層部と内部との温
度差が４０〜６０℃になったときに、前記鋳造品を７５
０〜９００℃に保持された均熱炉に入れ、前記表層部の
フェライト化率が７０％以上でかつ前記内部のフェライ
ト化率より少なくとも１５％高くなる時間だけ前記均熱
炉内に保持し、次いで前記鋳造品を前記冷却炉に移送し
て、１５〜１００℃／分の冷却速度で冷却することによ
り、表層部の方をよりフェライト化するものである。The first method for producing the spheroidal graphite cast iron member having such a layered structure is to subject the cast product to heat treatment in a soaking furnace and a cooling furnace within a short time after the mold is separated. . A continuous furnace having a soaking zone and a cooling zone is preferably used. In the first method, a molten metal having a spheroidal graphite cast iron composition is injected into a mold, and after completion of solidification of the molten metal, mold casting is performed when almost all of the cast product is still in a state of A 1 transformation point or higher, When the temperature difference between the surface layer and the inside of the cast product reached 40 to 60 ° C,
It is placed in a soaking furnace maintained at 0 to 900 ° C., and kept in the soaking furnace for a time at which the ferritization rate of the surface layer portion is 70% or more and is at least 15% higher than the internal ferritization rate, Next, the cast product is transferred to the cooling furnace and cooled at a cooling rate of 15 to 100 ° C./min to make the surface layer portion more ferrite.
【００２９】第一の方法を図１〜図２を参照して詳細に
説明する。The first method will be described in detail with reference to FIGS.
【００３０】まず、鋳造後温度Ｔ1 （点Ａ）で型バラシ
を行う。型バラシ温度Ｔ1 はＡ1 変態点（約７２０℃）
以上である必要がある。温度Ｔ1 がＡ1 変態点より低い
と、以後の加熱保持時間が長くなるだけでなく、長時間
加熱により内外層の温度差が小さくなり、その結果二重
構造が得られなくなる。具体的には、温度Ｔ1 を８００
〜９００℃にするのが好ましい。First, mold casting is performed at a temperature T 1 (point A) after casting. Mold separation temperature T 1 is A 1 transformation point (about 720 ° C)
It must be above. When the temperature T 1 is lower than the A 1 transformation point, not only the heating and holding time thereafter becomes long, but also the temperature difference between the inner and outer layers becomes small due to long-time heating, and as a result, the double structure cannot be obtained. Specifically, the temperature T 1 is set to 800
It is preferable to set the temperature to 900 ° C.
【００３１】型バラシ後鋳造品を大気中に短時間放置す
る。点Ｂまで冷却する間に、内部より表層部の方が温度
低下が大きいので、温度差ΔＴが生じる。この温度差Δ
Ｔは４０〜６０℃である必要がある。４０℃未満である
と、十分な二重構造が得られない。また、６０℃を超え
るようだと、表層部の温度が低くなりすぎる。ただし、
表層部の温度は鋳造品の表面温度であり、内部の温度は
鋳造品の中心部の温度である。また、上記温度差ΔＴが
得られのに要する時間ｔ1 は、鋳造品の肉厚にもよる
が、通常２〜３０分である。好ましい保持時間は５〜20
分である。After separating the mold, the cast product is left in the atmosphere for a short time. During the cooling to the point B, the temperature difference in the surface layer portion is larger than that in the inside, so that the temperature difference ΔT occurs. This temperature difference Δ
T needs to be 40-60 degreeC. If it is lower than 40 ° C, a sufficient double structure cannot be obtained. On the other hand, if it exceeds 60 ° C., the temperature of the surface layer portion becomes too low. However,
The surface temperature is the surface temperature of the cast product, and the internal temperature is the temperature of the central part of the cast product. The time t 1 required for obtaining the temperature difference ΔT depends on the wall thickness of the cast product, but is usually 2 to 30 minutes. The preferred holding time is 5 to 20
Minutes.
【００３２】この温度差ΔＴが得られた鋳造品を均熱炉
に導入する。均熱炉の温度Ｔ2 は７５０〜９００℃に保
持されている。均熱炉の温度が７５０℃未満であると、
鋳造品の温度が低下しすぎ、再加熱が必要になる。ま
た、９００℃を超えると、エネルギーの損失が大とな
る。好ましい加熱保持温度Ｔ2 は７８０〜８５０℃であ
る。The cast product obtained with this temperature difference ΔT is introduced into a soaking furnace. The temperature T 2 of the soaking furnace is maintained at 750 to 900 ° C. When the temperature of the soaking furnace is less than 750 ° C,
The temperature of the casting is too low and needs to be reheated. Further, when the temperature exceeds 900 ° C, the energy loss becomes large. The preferable heating and holding temperature T 2 is 780 to 850 ° C.
【００３３】上記温度の均熱炉内では、表層部は直ちに
加熱保持温度Ｔ2 に到達するが（点Ｃ）、内部の温度は
それより低い温度のままである。In the soaking furnace at the above temperature, the surface layer portion immediately reaches the heating and holding temperature T 2 (point C), but the internal temperature remains lower than that.
【００３４】均熱炉内に鋳造品を保持する時間ｔ2 は、
表層部のフェライト化率が７０％以上でかつ内部のフェ
ライト化率より少なくとも１５％高くなる時間である。
この理由は以下の通りである。The time t 2 for holding the cast product in the soaking furnace is
This is the time when the ferritic conversion rate of the surface layer portion is 70% or more and is higher than the internal ferritic conversion rate by at least 15%.
The reason for this is as follows.
【００３５】図２(a) に示す通り、表層部は比較的急速
に冷却されるので、黒鉛粒子は微細化しており、かつ基
地はγ相になっている。このような組織の表層部が温度
Ｔ2に加熱保持されると、基地中の炭素が黒鉛粒子内に
吸収され、基地の炭素含有量は低下する。このため、以
後の徐冷により基地はフェライト化される。As shown in FIG. 2 (a), since the surface layer portion is cooled relatively rapidly, the graphite particles are miniaturized and the matrix is in the γ phase. When the surface layer portion of such a structure is heated and held at the temperature T 2 , carbon in the matrix is absorbed in the graphite particles, and the carbon content of the matrix decreases. Therefore, the matrix is ferriticized by the subsequent slow cooling.
【００３６】一方、内部は、表層部に比較して緩やかに
冷却されるので、図２(b) に示す通り、黒鉛粒子は成長
する。また、基地は表層部と同様にγ相である。このよ
うな組織の内部が表層部より低い温度に加熱されると、
黒鉛粒子内に吸収される基地中の炭素量は相対的に少な
く、黒鉛粒子の周囲の領域だけ炭素含有量が低下した相
ができる。この低炭素相が、以後の徐冷工程によりフェ
ライト化する。ところが、低炭素化していない相はパー
ライト化する。そのため、内部の基地はフェライト相と
パーライト相との混合物になる。On the other hand, since the inside is cooled more slowly than the surface layer, graphite particles grow as shown in FIG. 2 (b). Further, the base is in the γ phase, like the surface layer. When the inside of such tissue is heated to a temperature lower than the surface layer,
The amount of carbon in the matrix absorbed in the graphite particles is relatively small, and a phase in which the carbon content is reduced is formed only in the area around the graphite particles. This low carbon phase becomes ferritic in the subsequent slow cooling step. However, the phase that has not been reduced to carbon becomes pearlite. Therefore, the internal matrix is a mixture of ferrite phase and pearlite phase.
【００３７】加熱保持後、鋳造品を冷却域に移送して、
１５〜１００℃／分の冷却速度で徐冷する（点Ｄ）。冷
却速度が１５℃／分未満であると、内部のパーライト化
率が低下する。一方、１００℃／分を超えると、パーラ
イトが基地中に残留する傾向を示し、表層部の軟化がで
きなくなる。好ましい冷却速度は２０〜４０℃／分であ
る。この徐冷により表層部及び内部の基地にフェライト
化が起こるが、上記の通り表層部と内部との組織の差が
あるので、表層部のフェライト化率の方が高くなる。な
お、徐冷は室温まで行う必要がなく、少なくとも約６５
０℃（温度Ｔ3）まで行えばよい（点Ｅ）。温度Ｔ3 よ
り低いと、基地の相変化は起こらない。After heating and holding, the cast product was transferred to the cooling zone,
Gradually cool at a cooling rate of 15 to 100 ° C./minute (point D). If the cooling rate is less than 15 ° C./minute, the rate of internal pearlite decreases. On the other hand, if it exceeds 100 ° C./min, pearlite tends to remain in the matrix and the surface layer cannot be softened. A preferable cooling rate is 20 to 40 ° C / minute. This gradual cooling causes ferrite formation in the surface layer portion and the matrix in the inside, but since there is a difference in the structure between the surface layer portion and the inside as described above, the rate of ferrite formation in the surface layer portion becomes higher. In addition, it is not necessary to perform gradual cooling to room temperature, and at least about 65
It may be performed up to 0 ° C. (temperature T 3 ) (point E). Below the temperature T 3 , no phase change of the matrix occurs.
【００３８】以上の熱処理により、球状黒鉛鋳鉄部材の
表層部のみがフェライト化して、高硬度の内部と低硬度
の表層部とからなる二重構造を有する鋳造品が得られ
る。By the above heat treatment, only the surface layer of the spheroidal graphite cast iron member is transformed into ferrite, and a cast product having a double structure composed of a high hardness inside and a low hardness surface layer is obtained.
【００３９】（２）第二の方法 本発明の球状黒鉛鋳鉄部材を製造する第二の方法は、パ
ーライト化された球状黒鉛鋳鉄部材を７８０〜８７０℃
に保持された均熱炉に入れ、前記表層部のフェライト化
率が７０％以上でかつ前記内部のフェライト化率より少
なくとも１５％高くなる時間だけ前記均熱域内に保持
し、次いで前記鋳造品を前記連続炉の冷却域に移送し
て、１５〜１００℃／分の冷却速度で冷却することによ
り、表層部の方をよりフェライト化するものである。(2) Second Method The second method for producing the spheroidal graphite cast iron member of the present invention is a method of producing a pearlitic spheroidal graphite cast iron member at 780 to 870 ° C.
In the soaking furnace held in the above step, and holding in the soaking zone for a time such that the ferritization rate of the surface layer portion is 70% or more and at least 15% higher than the internal ferritization rate, and then the cast product is By transferring to the cooling zone of the continuous furnace and cooling at a cooling rate of 15 to 100 ° C./min, the surface layer portion is made more ferrite.
【００４０】出発材料である球状黒鉛鋳鉄部材は、パー
ライト化されたものである。具体的には、３０％以上の
パーライト面積率を有する球状黒鉛鋳鉄部材を用いるの
が好ましい。このようなパーライト化された球状黒鉛鋳
鉄部材は、上記組成を有する球状黒鉛鋳鉄に公知のパー
ライト化処理を施すことにより製造することができる。
パーライト化処理を施された球状黒鉛鋳鉄部材も、表層
部では黒鉛粒子が微細化しており、内部では比較的粗大
に成長している。The spheroidal graphite cast iron member which is the starting material is pearlite. Specifically, it is preferable to use a spheroidal graphite cast iron member having a pearlite area ratio of 30% or more. Such a pearlitic spheroidal graphite cast iron member can be produced by subjecting spheroidal graphite cast iron having the above composition to a known pearlite treatment.
Also in the spheroidal graphite cast iron member that has been subjected to the pearlite treatment, the graphite particles are finely divided in the surface layer portion, and the graphite particles are relatively coarsely grown inside.
【００４１】第二の方法を図３を参照して詳細に説明す
る。まず、パーライト化された球状黒鉛鋳鉄部材を、７
８０〜８７０℃に保持された均熱炉に入れ（点Ｂ）、前
記表層部のフェライト化率が７０％以上でかつ前記内部
のフェライト化率より少なくとも１５％高くなる時間だ
け、前記均熱炉内に保持する。加熱保持温度が７８０℃
未満であると、基地中のＣの拡散による組織の均一化が
困難であり、一方、８７０℃より高いと、内部まで熱処
理の影響を受け、二重構造組織に制御するのが困難であ
る。好ましい加熱保持温度は８００〜８５０℃である。The second method will be described in detail with reference to FIG. First, the pearlitic spheroidal graphite cast iron member was
The soaking furnace is placed in a soaking furnace maintained at 80 to 870 ° C. (point B), and the soaking furnace is kept for a period of time at which the ferritization rate of the surface layer portion is 70% or more and at least 15% higher than the internal ferritization rate. Hold in. Heating temperature is 780 ℃
If it is less than the above, it is difficult to make the structure uniform by diffusion of C in the matrix. On the other hand, if it is higher than 870 ° C., it is difficult to control the structure to have a double structure because the inside is affected by heat treatment. A preferable heating and holding temperature is 800 to 850 ° C.
【００４２】上記均熱域内での保持時間ｔ2 は、表層部
のフェライト化率が７０％以上でかつ内部のフェライト
化率より少なくとも１５％高くなる時間である。この
間、表層部は比較的急速に加熱されるので、内部よりΔ
Ｔだけ温度が高くなる。このため、表層部の基地中の炭
素は黒鉛粒子内に吸収され、基地の炭素含有量は低下す
る。The holding time t 2 in the soaking zone is the time during which the ferritic conversion rate of the surface layer portion is 70% or more and at least 15% higher than the internal ferritic conversion rate. During this time, the surface layer is heated relatively quickly, so
The temperature rises by T. Therefore, the carbon in the matrix of the surface layer portion is absorbed in the graphite particles, and the carbon content of the matrix decreases.
【００４３】一方、内部は、表層部に比較して緩やかに
加熱されるので、黒鉛粒子内に吸収される基地中の炭素
量は相対的に少なく、黒鉛粒子の周囲の領域だけ炭素含
有量が低下した相ができる。この低炭素相が、以後の徐
冷工程によりフェライト化する。ところが、低炭素化し
ていない相はパーライト化する。そのため、内部の基地
はフェライト相とパーライト相との混合物になる。On the other hand, since the inside is heated more gently than the surface layer portion, the amount of carbon in the matrix absorbed in the graphite particles is relatively small, and the carbon content in the region around the graphite particles is relatively small. There is a degraded phase. This low carbon phase becomes ferritic in the subsequent slow cooling step. However, the phase that has not been reduced to carbon becomes pearlite. Therefore, the internal matrix is a mixture of ferrite phase and pearlite phase.
【００４４】鋳造品の加熱保持時間ｔ2 は、鋳造品の肉
厚にもよるが、通常２〜３０分、好ましくは５〜20分で
ある。The heating and holding time t 2 of the cast product depends on the wall thickness of the cast product, but is usually 2 to 30 minutes, preferably 5 to 20 minutes.
【００４５】加熱保持後、鋳造品を冷却域に移送して、
１５〜１００℃／分の冷却速度で徐冷する（点Ｄ）。冷
却速度の限定理由は上記と同じである。徐冷は室温まで
行う必要がなく、少なくとも約６５０℃（温度Ｔ3 ）ま
で行えばよい（点Ｅ）。After heating and holding, the cast product was transferred to the cooling zone,
Gradually cool at a cooling rate of 15 to 100 ° C./minute (point D). The reason for limiting the cooling rate is the same as above. The slow cooling does not have to be performed to room temperature, and may be performed to at least about 650 ° C. (temperature T 3 ) (point E).
【００４６】以上の熱処理により、第一の方法と同様
に、球状黒鉛鋳鉄部材の表層部がよりフェライト化し
て、高硬度の内部と低硬度の表層部とからなる二重構造
を有する鋳造品が得られる。By the above heat treatment, as in the first method, the surface layer of the spheroidal graphite cast iron member becomes more ferrite, and a cast product having a double structure consisting of a high hardness inside and a low hardness surface is obtained. can get.
【００４７】図４は、第二の方法をパーライト化処理に
続いて行う場合の温度パターンを示す。パーライト化処
理では、工程Ｇ−Ｈで８４０〜８６０℃、０．５〜２時
間のオーステナイト処理を行い、工程Ｉ−Ｊで７８０〜
８２０℃、０．５〜１時間の均熱化処理を行い、次いで
強制冷却を行う。FIG. 4 shows a temperature pattern when the second method is performed subsequent to the pearlite treatment. In the pearlite treatment, austenite treatment at 840 to 860 ° C. for 0.5 to 2 hours is performed in step G-H, and 780 to 780 in step I-J.
A soaking treatment at 820 ° C. for 0.5 to 1 hour is performed, and then forced cooling is performed.
【００４８】本発明を以下の実施例により詳細に説明す
る。The present invention is explained in detail by the following examples.
【００４９】実施例１、比較例１及び２ (1) 組 成 鉄、不可避的不純物及び以下の表１の例１に示す成分か
らなる組成を有する球状黒鉛鋳鉄材料を用いて、図５乃
至図７に示す形状の試験片を作成した。 Example 1, Comparative Examples 1 and 2 (1) Composition Using spheroidal graphite cast iron material having a composition consisting of iron, unavoidable impurities and components shown in Example 1 of Table 1 below, FIGS. A test piece having the shape shown in FIG.
【００５０】 表１ 重量％ 例No. Ｃ Ｓｉ Ｍｎ Ｐ Ｓ Ｍｇ Ｃｕ １(1) 3.68 2.26 0.31 0.035 0.011 0.037 0.56 ２(2) 3.71 2.40 0.21 0.021 0.007 0.035 0.18 ３(3) 3.60 2.40 0.30 0.022 0.008 0.031 0.52 注：（１）実施例１。 （２）ＦＣＤ４５。 （３）ＦＣＤ６０。Table 1 Weight% Example No. C Si Mn P S Mg Mg Cu 1 (1) 3.68 2.26 0.31 0.035 0.011 0.037 0.56 2 (2) 3.71 2.40 0.21 0.021 0.007 0.035 0.18 3 (3) 3.60 2.40 0.30 0.022 0.008 0.031 0.52 Note: (1) Example 1. (2) FCD45. (3) FCD60.
【００５１】(2) 熱処理 上記組成を有する球状黒鉛鋳鉄溶湯を1410℃で鋳型に注
入し、得られた試験片状の鋳造品の表面温度がまだＡ1
変態点（約７２０℃）以上にある時に、型バラシをし
た。表層部と内部との温度差ΔＴが５０℃になる時間
（５分間）経過後に、鋳造品を８３０℃に加熱保持した
連続炉の均熱域に入れ、１５分間保持した。次いで、鋳
造品を冷却域に移送し、そこで５５℃／分の冷却速度で
６５０℃まで冷却し、連続炉から取り出した。(2) Heat treatment The spheroidal graphite cast iron melt having the above composition was poured into the mold at 1410 ° C., and the surface temperature of the obtained test piece-shaped cast product was still A 1
When the temperature was above the transformation point (about 720 ° C.), the mold was removed. After the time (5 minutes) when the temperature difference ΔT between the surface layer portion and the inside reached 50 ° C., the cast product was put into a soaking zone of a continuous furnace heated and held at 830 ° C. and held for 15 minutes. The cast was then transferred to a cooling zone where it was cooled to 650 ° C at a cooling rate of 55 ° C / min and removed from the continuous furnace.
【００５２】上記熱処理により得られた実施例１の鋳造
品（図６に示す形状）について、顕微鏡写真観察を行っ
た。図８(a) に表層部の顕微鏡写真（×１００）を示
し、図８(b) に内部の顕微鏡写真（×１００）を示す。
各顕微鏡写真から表層部及び内部のフェライト化率を求
めた。The cast product of Example 1 (shape shown in FIG. 6) obtained by the above heat treatment was observed with a micrograph. FIG. 8 (a) shows a photomicrograph (× 100) of the surface layer portion, and FIG. 8 (b) shows a photomicrograph (× 100) of the inside.
From each micrograph, the ferritic conversion rate of the surface layer and the inside was obtained.
【００５３】また、表１の例２及び３に示す組成の球状
黒鉛鋳鉄から、実施例１と同じ試験片を作製したが（比
較例２、３）、比較例２、３の球状黒鉛鋳鉄部材には従
来のパーライト化処理（条件：８５０℃×１時間＋７８
０〜８２０℃の均熱化＋強制冷却）だけを施した。Further, the same test pieces as in Example 1 were prepared from the spheroidal graphite cast iron having the compositions shown in Examples 2 and 3 of Table 1 (Comparative Examples 2 and 3), but the spheroidal graphite cast iron members of Comparative Examples 2 and 3 were manufactured. Conventional pearlite treatment (conditions: 850 ° C x 1 hour +78
Only soaking at 0 to 820 ° C + forced cooling) was performed.
【００５４】(3) 強度試験 図５に示す曲げ引張試験片（測定部分は黒皮のままに
し、その他の部分を機械加工した）を用いて、引張強さ
（σＢ）及び耐力（σ0.2 ）及び伸び（δ）を測定し
た。(3) Strength test Using a bending tensile test piece shown in FIG. 5 (measuring portion was left as black skin and other portion was machined), tensile strength (σB) and proof stress (σ 0.2 ) were used. And elongation (δ) were measured.
【００５５】図６に示す曲げ試験片（全体を黒皮のまま
にした）を支点間距離３００ｍｍで支承して、荷重を加
え、曲げ荷重と曲げ変位との関係を求めた。The bending test piece shown in FIG. 6 (whole body was left as a black skin) was supported at a fulcrum distance of 300 mm, and a load was applied to determine the relationship between the bending load and the bending displacement.
【００５６】また、図６に示す曲げ衝撃試験片を支点間
距離１００ｍｍで支承して、５０ｋｇの重りを１０ｃｍ
の高さから落下させた。この条件で、試験片に亀裂が発
生するまで１０ｃｍづづ落下位置を高くし、亀裂が発生
した時の落下高さから曲げ衝撃強度を求めた。Further, the bending impact test piece shown in FIG. 6 was supported at a distance between fulcrums of 100 mm, and a weight of 50 kg was 10 cm.
Dropped from the height of. Under these conditions, the drop position was raised by 10 cm until a crack was generated in the test piece, and the bending impact strength was determined from the drop height when the crack was generated.
【００５７】さらに、図７に示す回転曲げ疲労試験片
（測定部分は黒皮のままにし、その他の部分を機械加工
した）を用いて、小野式回転曲げ疲労試験機により疲労
限（条件：室温、定荷重、空気中で回転数３６００rpm
）を測定した。疲労限は、１０7 回の繰り返しで破損
しない応力限度（亀裂が発生しないか、発生しても進展
しない応力限度）により表す。以上の測定の結果を表４
に示す。Further, using the rotary bending fatigue test piece shown in FIG. 7 (the measurement portion was left as a black skin and the other portion was machined), the fatigue limit (condition: room temperature) was measured by an Ono type rotary bending fatigue tester. , Constant load, rotation speed 3600rpm in air
) Was measured. The fatigue limit is expressed by a stress limit that does not damage after repeated 10 7 times (a stress limit in which a crack does not occur or does not propagate even if a crack occurs). The results of the above measurements are shown in Table 4.
Shown in.
【００５８】実施例２ (1) 組 成 鉄、不可避的不純物及び以下の表２に示す成分からなる
組成を有する球状黒鉛鋳鉄材料を用いて、実施例１と同
じ試験片を作成した。 Example 2 (1) Composition The same test piece as in Example 1 was prepared using a spheroidal graphite cast iron material having a composition consisting of iron, unavoidable impurities and the components shown in Table 2 below.
【００５９】 表２ 重量％ 実施例No. Ｃ Ｓｉ Ｍｎ Ｐ Ｓ Ｍｇ Ｃｕ ２ 3.73 2.24 0.35 0.020 0.009 0.033 0.45 Table 2 wt% Example No. C Si Mn P S Mg Mg Cu 2 3.73 2.24 0.35 0.020 0.009 0.033 0.45
【００６０】(2) 熱処理 上記組成を有する球状黒鉛鋳鉄溶湯を1420℃で鋳型に注
入し、型バラシし後パーライト化処理して試験片状の鋳
造品を得た。室温まで冷却した後、８００℃に加熱保持
した均熱炉に入れ、５分間保持した。次に鋳造品を冷却
炉に入れ、２０℃／分の速度で冷却し、２００℃で取り
出した。(2) Heat Treatment A spheroidal graphite cast iron melt having the above composition was poured into a mold at 1420 ° C., the mold was separated, and then pearlite treatment was performed to obtain a test piece-shaped cast product. After cooling to room temperature, it was placed in a soaking furnace heated to 800 ° C. and held for 5 minutes. Next, the cast product was placed in a cooling furnace, cooled at a rate of 20 ° C./min, and taken out at 200 ° C.
【００６１】上記熱処理により得られた鋳造品（図６に
示す形状）について、顕微鏡写真観察を行った。図９
(a) に表層部の顕微鏡写真（×１００）を示し、図９
(b) に内部の顕微鏡写真（×１００）を示す。各顕微鏡
写真から表層部及び内部のフェライト化率を求めた。ま
た、実施例１と同様に機械的強度試験を行った。結果を
表４に示す。The cast product (shape shown in FIG. 6) obtained by the above heat treatment was observed with a micrograph. Figure 9
A micrograph (× 100) of the surface layer is shown in FIG.
An internal micrograph (× 100) is shown in (b). From each micrograph, the ferritic conversion rate of the surface layer and the inside was obtained. Further, a mechanical strength test was conducted in the same manner as in Example 1. The results are shown in Table 4.
【００６２】実施例３ (1) 組 成 鉄、不可避的不純物及び以下の表３に示す成分からなる
組成を有する球状黒鉛鋳鉄材料を用いて、実施例１と同
じ試験片を作成した。 Example 3 (1) Composition A spheroidal graphite cast iron material having a composition consisting of iron, unavoidable impurities and the components shown in Table 3 below was used to prepare the same test piece as in Example 1.
【００６３】 表３ 重量％ 実施例No. Ｃ Ｓｉ Ｍｎ Ｐ Ｓ Ｍｇ Ｃｕ ３ 3.70 2.21 0.30 0.021 0.008 0.038 0.08 Table 3 wt% Example No. C Si Mn P S Mg Mg Cu 3 3.70 2.21 0.30 0.021 0.008 0.038 0.08
【００６４】(2) 熱処理 上記組成を有する球状黒鉛鋳鉄溶湯を1415℃で鋳型に注
入し、型バラシし後室温まで冷却した。次いで、８５０
℃に加熱保持した熱処理炉に入れて６０分間保持し、次
いで８１０℃の炉に１時間保持した。炉から取り出した
後、強制空冷を行い、パーライト化処理をした。得られ
た各鋳造品を、８１０℃に加熱保持した均熱炉に入れ、
５分間保持した。次に鋳造品を冷却炉に入れ、２０℃／
分の速度で冷却し、２００℃で取り出した。(2) Heat Treatment The molten spheroidal graphite cast iron having the above composition was poured into a mold at 1415 ° C., the mold was separated, and then cooled to room temperature. Then 850
It was placed in a heat treatment furnace heated and maintained at 0 ° C. and maintained for 60 minutes, and then maintained at 810 ° C. for 1 hour. After taking out from the furnace, forced air cooling was performed to perform pearlite treatment. Each of the obtained castings was placed in a soaking furnace heated and held at 810 ° C,
Hold for 5 minutes. Next, put the cast product in a cooling furnace, and
It was cooled at a rate of minutes and taken out at 200 ° C.
【００６５】上記熱処理により得られた鋳造品（図６に
示す形状）について、顕微鏡写真観察を行った。図１０
(a) に表層部の顕微鏡写真（×１００）を示し、図１０
(b)に内部の顕微鏡写真（×１００）を示す。各顕微鏡
写真から表層部及び内部のフェライト化率を求めた。ま
た、実施例１と同様に機械的強度試験を行った。結果を
表４に示す。The cast product (shape shown in FIG. 6) obtained by the above heat treatment was observed with a micrograph. Figure 10
A micrograph (× 100) of the surface layer portion is shown in FIG.
An internal micrograph (× 100) is shown in (b). From each micrograph, the ferritic conversion rate of the surface layer and the inside was obtained. Further, a mechanical strength test was conducted in the same manner as in Example 1. The results are shown in Table 4.
【００６６】 表４ 引張試験 フェライト化率 (1) σＢ σ0.2 δ 表層部 内部 試料 （kg/mm 2 ) （kg/mm 2 ) （％） （％） （％） 実施例１ １ 64.8 43.6 6.6 ８２ ４７ ２ 64.0 42.4 5.7 ３ 67.7 43.8 7.5 実施例２ １ 65.5 43.8 7.2 ９０ ７５ ２ 64.1 42.9 6.5 ３ 63.7 44.2 5.9 実施例３ １ 60.5 42.5 7.3 ８７ ６８ ２ 59.3 41.8 6.9 ３ 61.4 39.6 7.6 比較例１ １ 54.9 41.0 4.8 ７３ ７６ ２ 53.0 40.7 4.9 ３ 52.7 39.9 4.2 比較例２ １ 62.7 44.1 2.2 ４２ ４０ ２ 63.5 43.8 3.4 ３ 62.7 43.6 2.8 Table 4 Tensile Test Ferritization Rate (1) σB σ 0.2 δ Surface Layer Internal Sample (kg / mm 2 ) (kg / mm 2 ) (%) (%) (%) Example 1 1 64.8 43.6 6.6 82 47 2 64.0 42.4 5.7 3 67.7 43.8 7.5 Example 2 1 65.5 43.8 7.2 90 75 2 64.1 42.9 6.5 3 63.7 44.2 5.9 Example 3 1 60.5 42.5 7.3 87 68 2 59.3 41.8 6.9 3 61.4 39.6 7.6 Comparative Example 1 1 54.9 41.0 4.8 73 76 2 53.0 40.7 4.9 3 52.7 39.9 4.2 Comparative Example 2 1 62.7 44.1 2.2 42 40 2 63.5 43.8 3.4 3 62.7 43.6 2.8
【００６７】 表４（続き） 曲げ試験 回転曲げ疲労試験 曲げ荷重 曲げ変位 曲げ衝撃強度 疲労限(1) 試料 (kg) (mm) （kgf-m) （kg/mm 2 ) 実施例１ １ 1295 65 30 19 ２ 1300 60 30 ３ 1290 62 30 実施例２ １ 1320 64 30 18 ２ 1310 61 30 ３ 1280 62 25 実施例３ １ 1300 61 25 16 ２ 1310 62 30 ３ 1300 65 25 比較例１ １ 1150 22 20 16 ２ 1100 20 20 ３ 1150 23 25 比較例２ １ 1360 15 20 17 ２ 1300 15 15 ３ 1330 12 20 注：（１）３つの試験片のデータの平均値。Table 4 (continued) Bending test Rotating bending fatigue test Bending load Bending displacement Bending impact strength Fatigue limit (1) Sample (kg) (mm) (kgf-m) (kg / mm 2 ) Example 1 1 1295 65 30 19 2 1300 60 30 3 1290 62 30 Example 2 1 1320 64 30 18 2 1310 61 30 3 3 1280 62 25 Example 3 1 1300 61 25 16 2 1310 62 30 3 1300 65 25 Comparative Example 1 1 1150 22 20 16 2 1100 20 20 3 1150 23 25 Comparative example 2 1 1360 15 20 17 2 1300 15 15 3 1330 12 20 Note: (1) Average value of data of three test pieces.
【００６８】表４の結果から明らかなように、ＦＣＤ４
５（比較例１）及びＦＣＤ６０（比較例２）に比べて、
本発明の球状黒鉛鋳鉄部材（実施例１〜３）は、引張強
さ、伸び、曲げ強度、曲げ衝撃強度及び疲労限のいずれ
においても優れている。As is clear from the results shown in Table 4, FCD4
5 (Comparative Example 1) and FCD60 (Comparative Example 2),
The spheroidal graphite cast iron members of the present invention (Examples 1 to 3) are excellent in any of tensile strength, elongation, bending strength, bending impact strength and fatigue limit.
【００６９】実施例１〜３の試験片（図６に示す）につ
いて、表面からの各深さにおいてロックウェル硬度ＨＲ
Ｂを測定した。表面からの深さとロックウェル硬度ＨＲ
Ｂとの関係を図１１に示す。図１１から明らかなよう
に、深さ約２．５ｍｍまでロックウェル硬度ＨＲＢが次
第に増大しているので、表層部が約２．５ｍｍの厚さに
形成されていることがわかる。With respect to the test pieces of Examples 1 to 3 (shown in FIG. 6), Rockwell hardness HR was measured at each depth from the surface.
B was measured. Depth from the surface and Rockwell hardness HR
The relationship with B is shown in FIG. As is clear from FIG. 11, since the Rockwell hardness HRB gradually increases up to a depth of about 2.5 mm, it can be seen that the surface layer portion is formed with a thickness of about 2.5 mm.
【００７０】[0070]
【発明の効果】以上詳述したように、本発明の球状黒鉛
鋳鉄部材は、硬度が幾分低下して伸びが改善された表層
部を有するので、全体的に優れた機械的強度を発揮す
る。このような高強度の球状黒鉛鋳鉄部材は、特に靭性
と強度が要求されるとともに黒皮面が多い鋳造品（例え
ば、自動車の懸架装置用部品、鉄筋接続用接手、建築物
の柱脚を固定するための接合用金物等）として使用する
のに適している。As described above in detail, since the spheroidal graphite cast iron member of the present invention has the surface layer portion whose hardness is somewhat lowered and elongation is improved, it exhibits excellent mechanical strength as a whole. . Such a high-strength spheroidal graphite cast iron member is a cast product that requires particularly toughness and strength and has a lot of black surface (for example, parts for automobile suspension systems, joints for connecting reinforcing bars, fixing column bases of buildings. It is suitable for use as a metal fitting for joining).
【図１】本発明の第一の方法を示すグラフである。FIG. 1 is a graph showing a first method of the present invention.
【図２】球状黒鉛鋳鉄部材の金属組織が本発明の第一の
方法により変化する様子を示す概略図であり、(a) は表
層部を示し、(b) は内部を示す。FIG. 2 is a schematic view showing how the metallic structure of a spheroidal graphite cast iron member is changed by the first method of the present invention, (a) showing a surface layer portion, and (b) showing the inside.
【図３】本発明の第二の方法を示すグラフである。FIG. 3 is a graph showing a second method of the present invention.
【図４】前段にパーライト化処理工程を有する本発明の
第二の方法を示すグラフである。FIG. 4 is a graph showing a second method of the present invention having a pearlite treatment step in the first stage.
【図５】引張強さ試験をするための球状黒鉛鋳鉄の試験
片を示す側面図である。FIG. 5 is a side view showing a test piece of spheroidal graphite cast iron for performing a tensile strength test.
【図６】曲げ試験及び曲げ衝撃試験をするための球状黒
鉛鋳鉄の試験片を示す一部破断側面図である。FIG. 6 is a partially cutaway side view showing a test piece of spheroidal graphite cast iron for a bending test and a bending impact test.
【図７】回転曲げ疲労試験をするための球状黒鉛鋳鉄の
試験片を示す側面図である。FIG. 7 is a side view showing a test piece of spheroidal graphite cast iron for a rotary bending fatigue test.
【図８】実施例１で作成した試験片の金属組織を示す顕
微鏡写真（×100)であり、(a)は表層部を示し、(b) は
内部を示す。FIG. 8 is a micrograph (× 100) showing the metal structure of the test piece prepared in Example 1, where (a) shows the surface layer portion and (b) shows the inside.
【図９】実施例２で作成した試験片の金属組織を示す顕
微鏡写真（×100)であり、(a)は表層部を示し、(b) は
内部を示す。9 is a micrograph (× 100) showing the metal structure of the test piece prepared in Example 2, where (a) shows the surface layer portion and (b) shows the inside.
【図１０】実施例３で作成した試験片の金属組織を示す
顕微鏡写真（×100)であり、(a)は表層部を示し、(b)
は内部を示す。FIG. 10 is a micrograph (× 100) showing the metal structure of the test piece prepared in Example 3, where (a) shows the surface layer portion and (b).
Indicates the inside.
【図１１】実施例１〜３で作成した試験片について、表
面からの深さとロックウェル硬度ＨＲＢとの関係を示す
グラフである。FIG. 11 is a graph showing the relationship between the depth from the surface and the Rockwell hardness HRB for the test pieces prepared in Examples 1 to 3.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 末原 清 福岡県京都郡苅田町長浜町35番地 日立金 属株式会社九州工場内 (72)発明者 吉田 敏樹 栃木県真岡市鬼怒ヶ丘11番地 日立金属株 式会社素材研究所内 (72)発明者 今西 幸平 福岡県京都郡苅田町長浜町35番地 日立金 属株式会社九州工場内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kiyoshi Suehara Kiyoshi Suehara 35 Nagahama-cho, Kanda-cho, Kyoto-gun, Fukuoka Kyushu Plant, Hitachi Metals, Ltd. (72) Toshiki Yoshida 11 Kinugaoka, Moka-shi, Tochigi Hitachi Metals (72) Inventor Kouhei Imanishi 35, Nagahama-cho, Kanda-cho, Kyoto-gun, Fukuoka Kyushu Plant, Hitachi Metals, Ltd.
Claims (6)
１ｍｍの厚さの表層部と、パーライト相及びフェライト
相からなる内部とを有する球状黒鉛鋳鉄部材であって、
前記表層部のフェライト化率は７０％以上であり、前記
内部のフェライト化率より少なくとも約１５％高いこと
を特徴とする球状黒鉛鋳鉄部材。1. A spheroidal graphite cast iron member having a surface layer portion having a thickness of at least 1 mm, which is mostly composed of a ferrite phase, and an interior composed of a pearlite phase and a ferrite phase,
The spheroidal graphite cast iron member is characterized in that the surface layer has a ferritization rate of 70% or more, which is at least about 15% higher than the internal ferritization rate.
て、前記表層部の硬さがロックウェル硬度ＨＲＢで９３
以下であり、前記内部の硬さより低いことを特徴とする
球状黒鉛鋳鉄部材。2. The spheroidal graphite cast iron member according to claim 1, wherein the surface layer has a Rockwell hardness of HRB of 93.
The spheroidal graphite cast iron member is characterized in that the hardness is lower than the internal hardness.
において、前記球状黒鉛鋳鉄が、重量比で、3.40〜3.90
％のＣ、1.9 〜2.5 ％のSi、0.5 ％以下のMn、0.05％以
下のＰ、0.02％以下のＳ、0.02〜0.06％のMg、0.8 ％以
下のCu及び残部実質的にFe及び不可避的不純物からなる
組成を有することを特徴とする球状黒鉛鋳鉄部材。3. The spheroidal graphite cast iron member according to claim 1, wherein the spheroidal graphite cast iron has a weight ratio of 3.40 to 3.90.
% C, 1.9 to 2.5% Si, 0.5% or less Mn, 0.05% or less P, 0.02% or less S, 0.02 to 0.06% Mg, 0.8% or less Cu and the balance substantially Fe and unavoidable. A spheroidal graphite cast iron member having a composition of impurities.
１ｍｍの厚さの表層部と、パーライト相及びフェライト
相からなる内部とを有し、前記表層部のフェライト化率
は７０％以上であって、前記内部のフェライト化率より
少なくとも約１５％高い球状黒鉛鋳鉄部材を製造する方
法において、球状黒鉛鋳鉄組成を有する溶湯を鋳型に注
入し、前記溶湯の凝固完了後鋳造品のほぼ全体がまだＡ
1 変態点以上の状態にあるときに型バラシを行い、得ら
れた鋳造品の表層部と内部との温度差が４０〜６０℃に
なったときに、前記鋳造品を７５０〜９００℃に保持さ
れた均熱炉に入れ、前記表層部のフェライト化率が７０
％以上でかつ前記内部のフェライト化率より少なくとも
１５％高くなる時間だけ前記均熱炉内に保持し、次いで
前記鋳造品を冷却炉に移送して、１５〜１００℃／分の
冷却速度で冷却することを特徴とする方法。4. A surface layer part having a thickness of at least 1 mm, which is mostly composed of a ferrite phase, and an interior composed of a pearlite phase and a ferrite phase, and the ferrite conversion rate of the surface layer part is 70% or more, In the method of manufacturing a spheroidal graphite cast iron member having a ferritic conversion rate higher than the internal ferrite content by at least about 15%, a molten metal having a spheroidal graphite cast iron composition is poured into a mold, and after completion of solidification of the molten metal, almost all of the cast product is
Mold casting is performed when it is in a state of 1 transformation point or more, and when the temperature difference between the surface layer portion and the inside of the obtained cast product is 40 to 60 ° C, the cast product is held at 750 to 900 ° C. Put into a soaking furnace, and the ferrite rate of the surface layer is 70
% Or more and at least 15% higher than the internal ferritic rate, held in the soaking furnace, and then transferring the cast product to a cooling furnace to cool at a cooling rate of 15 to 100 ° C./min. A method characterized by:
１ｍｍの厚さの表層部と、パーライト相及びフェライト
相からなる内部とを有し、前記表層部のフェライト化率
は７０％以上であり、前記内部のフェライト化率より少
なくとも約１５％高い球状黒鉛鋳鉄部材を製造する方法
において、パーライト化された球状黒鉛鋳鉄部材を７８
０〜８７０℃に保持された均熱炉に入れ、前記表層部の
フェライト化率が７０％以上でかつ前記内部のフェライ
ト化率より少なくとも１５％高くなる時間だけ前記均熱
炉内に保持し、次いで前記鋳造品を冷却炉に移送して、
１５〜１００℃／分の冷却速度で冷却することを特徴と
する方法。5. A surface layer part having a thickness of at least 1 mm, which is mostly composed of a ferrite phase, and an interior composed of a pearlite phase and a ferrite phase, wherein the surface layer part has a ferritization ratio of 70% or more, A method for producing a spheroidal graphite cast iron member having a ferritic conversion rate of at least about 15% higher than that of the internal ferrite is provided.
It is placed in a soaking furnace maintained at 0 to 870 ° C., and is kept in the soaking furnace for a time at which the ferritization rate of the surface layer portion is 70% or more and is at least 15% higher than the internal ferritization rate, Then transfer the casting to a cooling furnace,
A method comprising cooling at a cooling rate of 15 to 100 ° C./min.
の製造方法において、前記球状黒鉛鋳鉄として、重量比
で、3.40〜3.90％のＣ、1.9 〜2.5 ％のSi、0.5％以下
のMn、0.05％以下のＰ、0.02％以下のＳ、0.02〜0.06％
のMg、0.8 ％以下のCu及び残部実質的にFe及び不可避的
不純物からなる組成を有するものを使用することを特徴
とする方法。6. The method for manufacturing a spheroidal graphite cast iron member according to claim 4 or 5, wherein the spheroidal graphite cast iron is in a weight ratio of 3.40 to 3.90% C, 1.9 to 2.5% Si, and 0.5% or less. Mn, P less than 0.05%, S less than 0.02%, 0.02-0.06%
Of Mg, 0.8% or less of Cu and the balance substantially Fe and inevitable impurities are used.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5773193A JPH0617186A (en) | 1992-02-27 | 1993-02-23 | Spheroidal graphite cast iron member and manufacture thereof |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4-76299 | 1992-02-27 | ||
| JP7629992 | 1992-02-27 | ||
| JP5773193A JPH0617186A (en) | 1992-02-27 | 1993-02-23 | Spheroidal graphite cast iron member and manufacture thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH0617186A true JPH0617186A (en) | 1994-01-25 |
Family
ID=26398799
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5773193A Pending JPH0617186A (en) | 1992-02-27 | 1993-02-23 | Spheroidal graphite cast iron member and manufacture thereof |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0617186A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012040614A (en) * | 2004-06-02 | 2012-03-01 | Consolidated Engineering Co Inc | Integrated metal processing facility |
| WO2017160782A1 (en) * | 2016-03-15 | 2017-09-21 | Federal-Mogul Llc | High strength cast iron for cylinder liners |
| KR101883290B1 (en) * | 2017-05-10 | 2018-07-31 | 우경금속주식회사 | Method for manufacturing for austempered ductile cast iron |
| KR20200005821A (en) * | 2018-07-09 | 2020-01-17 | 한국기계연구원 | Spheroidal graphite cast iron with excellent tensile property and preparation method thereof |
| CN111411207A (en) * | 2019-01-07 | 2020-07-14 | 现代自动车株式会社 | Method for heat-treating uppermost surface of nodular cast iron and nodular cast iron heat-treated thereby |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02173240A (en) * | 1988-12-26 | 1990-07-04 | Hitachi Metals Ltd | High-speed rotating member and its production |
-
1993
- 1993-02-23 JP JP5773193A patent/JPH0617186A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02173240A (en) * | 1988-12-26 | 1990-07-04 | Hitachi Metals Ltd | High-speed rotating member and its production |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012040614A (en) * | 2004-06-02 | 2012-03-01 | Consolidated Engineering Co Inc | Integrated metal processing facility |
| WO2017160782A1 (en) * | 2016-03-15 | 2017-09-21 | Federal-Mogul Llc | High strength cast iron for cylinder liners |
| US9873928B2 (en) | 2016-03-15 | 2018-01-23 | Federal-Mogul | High strength cast iron for cylinder liners |
| KR101883290B1 (en) * | 2017-05-10 | 2018-07-31 | 우경금속주식회사 | Method for manufacturing for austempered ductile cast iron |
| KR20200005821A (en) * | 2018-07-09 | 2020-01-17 | 한국기계연구원 | Spheroidal graphite cast iron with excellent tensile property and preparation method thereof |
| CN111411207A (en) * | 2019-01-07 | 2020-07-14 | 现代自动车株式会社 | Method for heat-treating uppermost surface of nodular cast iron and nodular cast iron heat-treated thereby |
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