【発明の詳細な説明】[Detailed description of the invention]
本発明は連続鋳造材を素材としてステンレス
鋼、超合金等の管、丸棒、形材等を熱間押出加工
する方法に関するものである。
金属加工法には大別して熱間加工法と冷間加工
法とが一般に適用されている。加工力を小さくす
る方法として熱間加工法が広く採用されており、
その中には圧延、押出、鍛造等が挙げられる。１
回の加工で大きい加工率がとれ、且つダイスの変
換のみで種々の形状の製品が容易に得られかつ圧
縮加工のため難加工金属も欠陥なしに加工出来る
という点で熱間押出法が特に有利である。
熱間押出加工に供する素材は、一般には溶製―
造塊―熱間分塊圧延工程により、円形断面形状に
仕上げられている（以下この工程による素材を熱
延素材と称する）。しかし、連続鋳造技術の発達
した現状では円形断面の連続鋳造鋳片の製造が可
能となり熱間分塊圧延工程を省略した溶製―連続
鋳造工程により熱間押出加工用素材が製造可能な
段階に達している（以下この工程による素材を連
鋳素材と称する）。
連続鋳造技術の発達は、ステンレス鋼、超合金
等においても例外ではなく、上記工程省略の利益
を享受出来る段階に達しており、連鋳素材を熱間
押出加工に適用することで大幅な歩留向上が期待
出来る。しかし、連鋳素材を熱間押出加工する場
合に、加熱・冷却時に組織変態を生じない材料で
は、押出材表面に、押出方向にスジ状欠陥が多発
して、商品価値を著しく損うという欠点がある。
このため、従来、ステンレス鋼、超合金等におい
ては連鋳素材を熱間押出加工して管、丸棒、形材
等の熱間押出材を製造することが出来なかつた。
なお、このスジ状欠陥は、熱延素材を用いた場合
には、殆んど見られない。
ステンレス鋼の連鋳素材を鋳造組織のままで熱
間押出する研究は古くから行なわれている。しか
しR.CoxがJournal of the Iron and Steel
Institute Vol.202（1964）P.246〜260に述べてい
るように、鋳造組織の粗大結晶粒に起因するスジ
状欠陥（R.Coxはscore marksと呼んでいる）が
発生するために、対策が必要であつた。R.Cox
は、押出機のコンテナ内で32％までの加工率のア
ツプセツト加工を行い引き続き押出加工を試みた
が、鋳造組織の粗大結晶粒の微細化を得ることは
出来ずスジ状欠陥防止策とはならなかつた。ま
た、ダイス形状にも着目して、コニカルダイスと
平ダイスの比較検討も行つたが、表面品質の改善
には至らなかつた。その他杉谷らは鉄と鋼Vol65
（1979）P.S244において、連鋳素材を直接押出す
るに際し“押拡げ加工等で結晶粒の微細化を行う
ことにより、良好な表面の鋼管が得られた“と述
べている。しかし、本発明者の検討の結果、押拡
げ等の加工のみでは結晶粒の微細化は得られな
い。
本発明の目的は、熱間押出温度への加熱・冷却
時に組織変態を生じないステンレス鋼や超合金等
の熱間押出材を製造するに当り、連鋳素材を用い
て熱延素材を用いた場合と同等以上の押出材表面
品質を得ることにある。
連鋳素材は、方向性の強い鋳造組織を有してい
るのに対して熱延素材は熱間分塊圧延工程で、こ
のような鋳造組織が破壊されて微細結晶組織とな
り、その方向性がランダム化されていることから
本発明者は、熱間押出加工以前に連鋳素材の組織
を微細化する方法について種々実験検討した結
果、本発明を完成した。
以下連鋳素材によるスジ状欠陥のない押出製品
を得るための製造工程について述べる。
円形断面の連鋳素材は、第１図に示すフローチ
ヤートに従つて加工される。即ち、押出製品の欠
陥となるようなブルーム表面の疵除去あるいはブ
ルーム偏心是正、場合によつてはスケール皮除去
のためのピーリング等を行い、所定の長さに切断
して、ビレツトを調整する。以下の工程について
は、押出製品の形状によつて若干の相違がある。
押出製品が管状材等中空の場合にはビレツト中
心を穿孔し次に加熱して、エクスパンシヨン加工
を行う。エクスパンシヨン加工の概略を第２図に
示す。全面潤滑処理をした中空ビレツト１はコン
テナ２とダイス３およびダイホルダ４からなる容
器内にセツトされる。ビレツト１後端からビレツ
ト１内径より大なるコーンノーズ５を有するマン
ドレル６を押し込み、ビレツト全長にわたつてコ
ーンノーズ５を通過させる。この加工により、ビ
レツト１の内径は大きくなり、外径と内径の差は
小さくなるためビレツト１後端はコーンノーズ５
の進行方向とは逆方向へ移動する。即ちビレツト
は全長にわたつて加工を受ける。このエクスパン
シヨン加工によりビレツト１外表面近傍へ加工歪
を付与してやる。しかしこの状態では、ビレツト
１外表面近傍ではスジ状欠陥防止に必要な微細組
織は期待出来ない。第３図に示すように粗大鋳造
組織を微細化するための再結晶組織を得るために
は十分な加工歪と十分な熱量の供給が必要であ
る。即ち、エクスパンシヨン工程では、ビレツト
外表面近傍への加工歪は十分大きいものが付与さ
れるが、加工中のビレツト表面温度低下により、
外表面近傍では十分な熱量が確保されない。従つ
てエクスパンシヨンままではスジ状欠陥の発生し
やすい外表面近傍では再結晶組織は得られ難い。
外表面近傍で再結晶組織を得るためには、第１図
に示す如くエクスパンシヨン後に再加熱すること
が必要である。
押出材形状が形材等中実の場合には穿孔工程は
なく加熱―アツプセツト工程となる。アツプセツ
ト工程の概略を第４図に示す。全面潤滑処理をし
た中実ビレツト１０はコンテナ２、孔のないダイ
ス３、ダイホルダー４によつて形成される空間内
に置かれる。この時ビレツト１０の径はコンテナ
２内径より小さくなる。ビレツト１０の後端にダ
ミーブロツク１１を押当てて、これにステム１２
から力が加わりダミーブロツク１１をビレツト１
０方向へ押しやる。この工程により第５図のよう
にビレツト１０の横断面はコンテナ横断面と同じ
になるまで加工を受ける。この際ビレツト外表面
近傍に加工歪が付与される。この場合もエクスパ
ンシヨン工程の場合と同じ理由で、押出前に再加
熱工程が必要である。
以上のビレツト前処理によりビレツト外表面近
傍を再結晶微細化することで押出製品の大部分の
スジ状欠陥は防止出来る。しかしエクスパンシヨ
ン、アツプセツト時にガラス潤滑剤層の不均一又
はビレツト加工の不適当等のために十分な加工歪
が付与出来ない部分が生じる場合がある。これら
の事態に対処するため、押出工程において第６図
ロに示すようなビレツトに接するダイス前面の全
面にわたりダイス孔型に向けて高くなるテーパー
を設けたダイス（逆テーパーダイス）を用いてス
ジ状欠陥の発生を完全に防止する。通常使用され
ているダイスと逆テーパーダイスの概略を第６図
に示す。通常使用されているダイス１３では矢印
の押出方向に対して角度αをもち、凹形状を呈し
ている。これに対して逆テーパダイス１４は押出
方向に対して角度β（αを正とすればβは負の値
となる）で凸形状を呈するものである。連鋳素材
で、エクスパンシヨン、アツプセツト処理なしの
場合の押出材円周方向表面粗さの大なるもの10個
の平均値とダイス形状との関係を第７図に示す。
図中△印は熱延素材による表面粗さを示す。第７
図から、押出前工程で、部分的に微細組織が得ら
れない場合が生じてもβ≧10度の逆テーパーダイ
スを使用することにより従来の熱延素材によるも
の以上の表面性状の得られることが示される。
次に実施例により本発明の詳細を説明する。熱
間加工工程は、中空ビレツトの場合はエキスパン
シヨン、中実ビレツトではアツプセツト加工を行
い以下にその時の条件を記す。
The present invention relates to a method for hot extruding stainless steel, superalloy, etc. tubes, round bars, shapes, etc. using continuous casting materials as raw materials. Metal working methods are generally divided into hot working methods and cold working methods. Hot processing is widely used as a method to reduce processing force.
These include rolling, extrusion, forging, etc. 1
The hot extrusion method is particularly advantageous in that it can achieve a high processing rate in one process, easily produce products of various shapes by simply changing the die, and can process difficult-to-process metals without defects due to compression processing. It is. Materials subjected to hot extrusion are generally melt-produced.
The ingot is finished into a circular cross-sectional shape by the hot blooming and rolling process (hereinafter, the material produced by this process will be referred to as a hot-rolled material). However, with the current state of development of continuous casting technology, it is now possible to manufacture continuously cast slabs with a circular cross section, and we have reached the stage where it is now possible to manufacture materials for hot extrusion using the ingot-continuous casting process that eliminates the hot blooming and rolling process. (Hereinafter, the material produced through this process will be referred to as continuous casting material.) The development of continuous casting technology, including stainless steel and superalloys, has reached a stage where it is possible to enjoy the benefits of omitting the above steps, and by applying continuous casting materials to hot extrusion processing, yields can be significantly increased. We can expect improvement. However, when hot extruding continuously cast materials, materials that do not undergo structural transformation during heating and cooling have the disadvantage that streak-like defects occur frequently on the extruded material surface in the extrusion direction, significantly reducing commercial value. There is.
For this reason, conventionally, it has not been possible to hot extrude continuously cast materials such as stainless steels and superalloys to produce hot extruded materials such as pipes, round bars, shapes, and the like.
Note that this streak-like defect is hardly seen when a hot-rolled material is used. Research on hot extrusion of continuously cast stainless steel materials in their cast structure has been carried out for a long time. However, R. Cox published the Journal of the Iron and Steel.
As stated in Institute Vol. 202 (1964) P. 246-260, since streak defects (referred to by R. Cox as score marks) occur due to coarse grains in the casting structure, countermeasures must be taken. was necessary. R.Cox
attempted upset processing at a processing rate of up to 32% in the extruder container and continued extrusion processing, but it was not possible to refine the coarse grains of the cast structure, and this was not a measure to prevent streak-like defects. Nakatsuta. We also focused on the die shape and compared conical dies and flat dies, but this did not lead to an improvement in surface quality. Others Sugitani and others Tetsu to Hagane Vol65
(1979) P.S. 244 states that when directly extruding continuously cast material, ``a steel pipe with a good surface was obtained by refining the crystal grains through extrusion processing, etc.''. However, as a result of studies by the present inventors, grain refinement cannot be achieved only by processing such as pressing and expanding. The purpose of the present invention is to produce hot-extruded materials such as stainless steel and superalloys that do not undergo structural transformation when heated to hot-extrusion temperatures and cooled, by using continuously cast materials and hot-rolled materials. The objective is to obtain a surface quality of the extruded material that is equal to or better than that of the conventional method. Continuously cast materials have a cast structure with strong directionality, while hot-rolled materials have such a cast structure destroyed during the hot blooming process and become a microcrystalline structure, which causes the directionality to change. Because of the randomization, the present inventor completed the present invention as a result of various experimental studies on methods for refining the structure of the continuously cast material before hot extrusion processing. The manufacturing process for obtaining extruded products free of streak-like defects using continuously cast materials will be described below. A continuously cast material having a circular cross section is processed according to the flowchart shown in FIG. That is, the billet is adjusted by removing defects on the surface of the bloom or correcting the eccentricity of the bloom, which may cause defects in the extruded product, and in some cases, peeling to remove scale, and cutting to a predetermined length. There are some differences in the following steps depending on the shape of the extruded product. If the extruded product is hollow, such as a tubular material, the center of the billet is perforated and then heated to perform expansion processing. Figure 2 shows an outline of the expansion process. The hollow billet 1, which has been completely lubricated, is set in a container consisting of a container 2, a die 3, and a die holder 4. A mandrel 6 having a cone nose 5 larger than the inside diameter of the billet 1 is pushed in from the rear end of the billet 1, and the cone nose 5 is passed over the entire length of the billet. By this processing, the inner diameter of billet 1 becomes larger and the difference between the outer diameter and inner diameter becomes smaller, so the rear end of billet 1 becomes cone nose 5.
move in the opposite direction to the direction of travel. That is, the billet is processed over its entire length. This expansion process imparts processing strain to the vicinity of the outer surface of the billet 1. However, in this state, the fine structure necessary for preventing streak-like defects cannot be expected near the outer surface of the billet 1. As shown in FIG. 3, in order to obtain a recrystallized structure for refining a coarse cast structure, it is necessary to supply sufficient working strain and a sufficient amount of heat. That is, in the expansion process, a sufficiently large processing strain is applied to the vicinity of the outer surface of the billet, but due to a decrease in the billet surface temperature during processing,
Sufficient amount of heat is not secured near the outer surface. Therefore, in the expanded state, it is difficult to obtain a recrystallized structure in the vicinity of the outer surface where streak defects are likely to occur.
In order to obtain a recrystallized structure near the outer surface, it is necessary to reheat after expansion as shown in FIG. If the shape of the extruded material is solid, such as a shaped material, there is no perforation step and a heating-upsetting step is performed. FIG. 4 shows an outline of the upsetting process. A solid billet 10, which has been fully lubricated, is placed in a space formed by a container 2, a solid die 3, and a die holder 4. At this time, the diameter of the billet 10 becomes smaller than the inner diameter of the container 2. Press the dummy block 11 against the rear end of the billet 10, and attach the stem 12 to it.
Force is applied from dummy block 11 to billet 1
Push it in the 0 direction. Through this process, the cross section of the billet 10 is processed until it becomes the same as the cross section of the container, as shown in FIG. At this time, machining strain is applied near the outer surface of the billet. In this case as well, a reheating step is required before extrusion for the same reason as in the expansion step. By recrystallizing the vicinity of the outer surface of the billet to make it finer through the billet pretreatment described above, most of the streak-like defects in extruded products can be prevented. However, during expansion or upsetting, there may be some areas where sufficient processing strain cannot be applied due to non-uniformity of the glass lubricant layer or inappropriate billet processing. To deal with these situations, during the extrusion process, a die (reverse tapered die) is used that has a taper that increases toward the die hole shape over the entire front surface of the die in contact with the billet, as shown in Figure 6 (b). Completely prevent defects from occurring. FIG. 6 shows an outline of a commonly used die and a reverse tapered die. A commonly used die 13 has an angle α with respect to the extrusion direction indicated by the arrow, and has a concave shape. On the other hand, the reverse taper die 14 has a convex shape at an angle β (if α is positive, β is a negative value) with respect to the extrusion direction. Figure 7 shows the relationship between the die shape and the average value of the 10 largest circumferential surface roughness values of the extruded material in the case of continuous casting material without expansion or upsetting treatment.
In the figure, the mark △ indicates the surface roughness due to the hot-rolled material. 7th
The figure shows that even if the microstructure cannot be obtained in some areas during the pre-extrusion process, by using a reverse taper die with β≧10 degrees, it is possible to obtain a surface texture that is better than that obtained with conventional hot-rolled materials. is shown. Next, the details of the present invention will be explained with reference to Examples. In the hot working process, expansion is performed for hollow billets, and upset processing is performed for solid billets, and the conditions at that time are described below.
【表】
ス成分
上記条件による押出製品では表面のスジ状欠陥
は殆んど見られなかつた。
本発明に従い連鋳素材の押出加工に際して押出
前にエクスパンシヨン又はアツプセツト加工をし
押出直前に再加熱して逆テーパーダイスによる押
出工程を適用することにより、従来の熱延素材に
よる押出品以上に良好な表面性状の押出製品が得
られる。
ここで押出前の熱間加工の好ましい条件は種々
の実験結果から次のように整理される。[Table] Screw component In the extruded products under the above conditions, almost no streak-like defects were observed on the surface. According to the present invention, when extruding a continuously cast material, by performing expansion or upset processing before extrusion, reheating immediately before extrusion, and applying an extrusion process using an inverted tapered die, it is possible to produce a product that is superior to extruded products made of conventional hot rolled materials. Extruded products with good surface properties can be obtained. Here, preferable conditions for hot working before extrusion are summarized as follows based on various experimental results.
【表】【table】
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は連鋳素材から押出製品を得る場合のフ
ローチヤート、第２図はエクスパンシヨン加工の
概略説明図、第３図は粗大鋳造組織を微細化する
ための再結晶組織を得るための工程を示す図、第
４図はアツプセツト工程の概略を示す図、第５図
はダミーブロツクをビレツト方向へ押した際のビ
レツトの横断面形状を示す図、第６図イは通常使
用されているダイス、第６図ロは逆テーパーダイ
スの概略を夫々示す図、第７図は連鋳素材でエク
スパンシヨン、アツプセツト処理なしの場合の押
出材円周方向表面粗さの大なるもの10個の平均値
とダイス形状との関係を示す図である。
Figure 1 is a flow chart for obtaining an extruded product from continuously cast material, Figure 2 is a schematic explanatory diagram of expansion processing, and Figure 3 is for obtaining a recrystallized structure to refine a coarse cast structure. Figure 4 is a diagram showing the outline of the upsetting process, Figure 5 is a diagram showing the cross-sectional shape of the billet when the dummy block is pushed in the direction of the billet, and Figure 6 A is the diagram that is normally used. Figure 6 (b) is a diagram showing the outline of a reverse taper die, and Figure 7 shows the 10 pieces with the highest surface roughness in the circumferential direction of extruded materials in the case of continuous casting materials without expansion or upset treatment. It is a figure showing the relationship between an average value and die shape.