JP7283271B2 - Free-cutting ferritic stainless steel and method for producing the same - Google Patents

Free-cutting ferritic stainless steel and method for producing the same Download PDF

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JP7283271B2
JP7283271B2 JP2019122390A JP2019122390A JP7283271B2 JP 7283271 B2 JP7283271 B2 JP 7283271B2 JP 2019122390 A JP2019122390 A JP 2019122390A JP 2019122390 A JP2019122390 A JP 2019122390A JP 7283271 B2 JP7283271 B2 JP 7283271B2
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千紘 古庄
宏之 高林
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Daido Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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Description

本発明は、切削性に優れたフェライト系快削ステンレス鋼及びその鋼材の製造方法に関し、特に、冷間で切断加工されて供される製品に適したフェライト系快削ステンレス鋼及びその鋼材の製造方法に関する。 TECHNICAL FIELD The present invention relates to a ferritic free-cutting stainless steel with excellent machinability and a method for producing the steel material thereof, and in particular, the production of a ferritic free-cutting stainless steel suitable for cold-cutting products and the steel material thereof. Regarding the method.

ＳＵＳ４３０Ｆに代表されるフェライト系快削ステンレス鋼は、被削性を向上させる目的でＳ（硫黄）のような、いわゆる「快削元素」を添加された成分組成を有している。また、更なる被削性の向上のため、Ｓｅ（セレン），Ｐｂ（鉛），Ｂｉ（ビスマス），Ｔｅ（テルル）などの成分元素を適宜、複合添加することも提案されている。 Ferritic free-cutting stainless steel represented by SUS430F has a chemical composition to which a so-called "free-cutting element" such as S (sulfur) is added for the purpose of improving machinability. Further, in order to further improve machinability, it has been proposed to appropriately add component elements such as Se (selenium), Pb (lead), Bi (bismuth), and Te (tellurium).

ここで、孔径が２ｍｍ以下といった細径ドリル加工において、特に、孔深さが孔径の２倍以上の細径ドリル加工を施そうとした場合、工具寿命、加工面粗度、及び切り屑破砕性に対する要求がよりシビアとなる。そこで、上記したような快削元素の添加量を増やした快削鋼が検討され得るが、一方で、かかる快削元素を添加することで、素材の供給工程における熱間加工性が低下し素材の供給工程での製造性に欠けるといった問題を指摘された。 Here, in small-diameter drilling with a hole diameter of 2 mm or less, especially when trying to perform small-diameter drilling with a hole depth of at least twice the hole diameter, tool life, machined surface roughness, and chip crushability requirements become more severe. Therefore, a free-cutting steel with an increased amount of free-cutting elements as described above can be considered. It was pointed out that the problem of lack of manufacturability in the supply process of

例えば、特許文献１では、細径ドリルに対する被削性及び素材の供給工程における熱間加工性に優れるフェライト系快削ステンレス鋼として、フェライト安定化元素であるＡｌの含有量を高めてフェライトの相安定性を高めた快削鋼を開示している。詳細には、質量％で、Ｃ：０．０１５％以下、Ｓｉ：０．０２～０．６０％、Ｍｎ：０．２～２．０％、Ｐ：０．０５０％以下、Ｃｕ：１．５％以下、Ｎｉ：１．５％以下、Ｃｒ:１０．０～２５．０％、Ｍｏ：２．０％以下、Ａl:０．３０～２．５０％、Ｏ：０．００３０～０．０４００％、Ｎ：０．０３５％以下、Ｓ：０．１０～０．４５％を含むとともに、更に、Ｐｂ：０．０３～０．４０％、Ｂｉ：０．０３～０．４０％、及び、Ｔｅ：０．０１～０．１０％から選択される２種以上を含み、元素Ｍの質量％を［Ｍ］とすると、９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］≦３００を満たす合金組成を有し、フェライト断面積率を９５％以上とした合金であるとしている。ここで、元素Ｍの式は、固溶化元素によるマトリクス強度を示す式としているように、特許文献１の合金では、フェライト単相を維持しつつ、マトリクス強度を低減させ、切削性と熱間加工性の両立を図っている。 For example, in Patent Document 1, as a ferritic free-cutting stainless steel that is excellent in machinability for small-diameter drills and hot workability in the material supply process, the content of Al, which is a ferrite stabilizing element, is increased to form a ferrite phase. It discloses a free-cutting steel with enhanced stability. Specifically, in mass %, C: 0.015% or less, Si: 0.02 to 0.60%, Mn: 0.2 to 2.0%, P: 0.050% or less, Cu: 1.0%. 5% or less, Ni: 1.5% or less, Cr: 10.0-25.0%, Mo: 2.0% or less, Al: 0.30-2.50%, O: 0.0030-0. 0400%, N: 0.035% or less, S: 0.10 to 0.45%, and further Pb: 0.03 to 0.40%, Bi: 0.03 to 0.40%, and , Te: 900 ([C] + [N]) + 170 [Si] + 12 [Cr ]+30[Mo]+10[Al]≦300 and has a ferrite cross-sectional area ratio of 95% or more. Here, as the formula of the element M is a formula showing the matrix strength by the solution element, in the alloy of Patent Document 1, the matrix strength is reduced while maintaining the ferrite single phase, machinability and hot workability We are striving for compatibility between genders.

特開２０１７－１１０２８５号公報JP 2017-110285 A

フェライト系快削ステンレス鋼を用いて、ボールペンのペン先のような精密加工をする場合、冷間切断後に細径ドリル加工を行い、その開口を利用したいとの要望がある。ここで、特許文献１のように、マトリクス強度を低減させた合金の場合、冷間切断による切断部に加工変質層が残存することがあり、続く細径ドリル加工において、十分な加工精度を得ることができない場合があった。 When using ferritic free-cutting stainless steel for precision machining such as the tip of a ball-point pen, there is a demand to perform small-diameter drilling after cold cutting and to utilize the opening. Here, as in Patent Document 1, in the case of an alloy with reduced matrix strength, a work-affected layer may remain in the cut portion by cold cutting, and sufficient processing accuracy is obtained in the subsequent small-diameter drilling. Sometimes it was not possible.

本発明はかかる状況に鑑みてなされたものであって、その目的とするところは、細径ドリルに対する被削性及び熱間加工性に優れ、冷間で切断加工されて供される製品に適したフェライト系快削ステンレス鋼及びその鋼材の製造方法を提供することにある。 The present invention has been made in view of such circumstances, and its object is to provide a product that is excellent in machinability with a small-diameter drill and hot workability, and is suitable for products that are cold-cut and provided. It is another object of the present invention to provide a ferritic free-cutting stainless steel and a method for producing the steel material.

本発明によるフェライト系快削ステンレス鋼は、フェライト系快削ステンレス鋼であって、質量％で、Ｃ：０．０１５％以下、Ｓｉ：０．０２～０．６０％、Ｍｎ：０．１～２．０％、Ｐ：０．０５０％を超え０．３００％以下、Ｃｕ：１．５％以下、Ｎｉ：１．５％以下、Ｃｒ:１０．０～２５．０％、Ｍｏ：２．０％以下、Ａl:０．３０～２．００％、Ｏ：０．０４００％以下、Ｎ：０．０３５％以下、Ｓ：０．１０～０．４５％を含むとともに、更に、Ｐｂ：０．０３～０．４０％、Ｂｉ：０．０３～０．４０％、及び、Ｔｅ：０．０１～０．１０％から選択される２種以上を含み、且つ、元素Ｍの質量％を［Ｍ］とすると、９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋４５０［Ｐ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］≦３４０、及び、（［Ｃｒ］＋［Ｍｏ］＋１．５［Ｓｉ］＋４［Ａｌ］）／（［Ｎｉ］＋０．５［Ｍｎ］＋３０［Ｃ］＋３０［Ｎ］）≧７、を満たし、残部をＦｅ及び不可避的不純物とする成分組成からなることを特徴とする。 The ferritic free-cutting stainless steel according to the present invention is a ferritic free-cutting stainless steel, in terms of % by mass, C: 0.015% or less, Si: 0.02-0.60%, Mn: 0.1- 2.0%, P: more than 0.050% and 0.300% or less, Cu: 1.5% or less, Ni: 1.5% or less, Cr: 10.0 to 25.0%, Mo: 2.0%. 0% or less, Al: 0.30 to 2.00%, O: 0.0400% or less, N: 0.035% or less, S: 0.10 to 0.45%, and further Pb: 0 .03 to 0.40%, Bi: 0.03 to 0.40%, and Te: 0.01 to 0.10%. M], 900([C]+[N])+170[Si]+450[P]+12[Cr]+30[Mo]+10[Al]≦340, and ([Cr]+[Mo]+1. 5 [Si] + 4 [Al]) / ([Ni] + 0.5 [Mn] + 30 [C] + 30 [N]) ≥ 7, and the balance is Fe and unavoidable impurities. Characterized by

かかる発明によれば、細径ドリルに対する被削性及び素材の供給工程における熱間加工性に優れるとともに、冷間で切断加工されて供される製品に適するのである。 According to this invention, the machinability for a small-diameter drill and the hot workability in the supply process of the raw material are excellent, and it is suitable for products that are provided by cold cutting.

上記した発明において、前記成分組成は、Ｂ：０．０００１～０．００８０％、Ｍｇ：０．０００５～０．０１００％、及び、Ｃａ：０．０００５～０．０１００％から選択される１種又は２種以上を更に含むことを特徴としてもよい。かかる発明によれば、熱間加工性に更に優れ、高い製造性を有するのである。 In the above invention, the component composition is B: 0.0001 to 0.0080%, Mg: 0.0005 to 0.0100%, and Ca: one selected from 0.0005 to 0.0100% Alternatively, it may be characterized by further including two or more kinds. According to this invention, the hot workability is further improved and the productivity is high.

また、本発明によるフェライト系快削ステンレス鋼材の製造方法は、フェライト系快削ステンレス鋼の製造方法であって、質量％で、Ｃ：０．０１５％以下、Ｓｉ：０．０２～０．６０％、Ｍｎ：０．１～２．０％、Ｐ：０．０５０％を超え０．３００％以下、Ｃｕ：１．５％以下、Ｎｉ：１．５％以下、Ｃｒ:１０．０～２５．０％、Ｍｏ：２．０％以下、Ａl:０．３０～２．００％、Ｏ：０．０４００％以下、Ｎ：０．０３５％以下、Ｓ：０．１０～０．４５％を含むとともに、更に、Ｐｂ：０．０３～０．４０％、Ｂｉ：０．０３～０．４０％、及び、Ｔｅ：０．０１～０．１０％から選択される２種以上を含み、且つ、元素Ｍの質量％を［Ｍ］とすると、９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋４５０［Ｐ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］≦３４０、及び、（［Ｃｒ］＋［Ｍｏ］＋１．５［Ｓｉ］＋４［Ａｌ］）／（［Ｎｉ］＋０．５［Ｍｎ］＋３０［Ｃ］＋３０［Ｎ］）≧７を満たし、残部をＦｅ及び不可避的不純物とする成分組成からなるフェライト単相合金を鍛造し、９００～１２００℃における絞り量が５０パーセント以上とする鋼塊を得た上で、焼き鈍し熱処理を施されて供されることを特徴とする。 Further, a method for producing a ferritic free-cutting stainless steel material according to the present invention is a method for producing a ferritic free-cutting stainless steel, in which, in mass%, C: 0.015% or less, Si: 0.02 to 0.60 %, Mn: 0.1 to 2.0%, P: more than 0.050% and 0.300% or less, Cu: 1.5% or less, Ni: 1.5% or less, Cr: 10.0 to 25 .0%, Mo: 2.0% or less, Al: 0.30 to 2.00%, O: 0.0400% or less, N: 0.035% or less, S: 0.10 to 0.45% In addition, Pb: 0.03 to 0.40%, Bi: 0.03 to 0.40%, and Te: 0.01 to 0.10%. , where [M] is the mass% of the element M, 900 ([C] + [N]) + 170 [Si] + 450 [P] + 12 [Cr] + 30 [Mo] + 10 [Al] ≤ 340, and ([ Cr] + [Mo] + 1.5 [Si] + 4 [Al]) / ([Ni] + 0.5 [Mn] + 30 [C] + 30 [N]) ≥ 7, and the balance is Fe and unavoidable impurities A steel ingot having a drawing amount of 50% or more at 900 to 1200° C. is obtained by forging a ferrite single-phase alloy having a chemical composition of 900 to 1200° C., and then subjected to annealing and heat treatment.

かかる発明によれば、細径ドリルに対する被削性及び素材の供給工程における熱間加工性に優れるとともに、冷間で切断加工されて供される製品に適したフェライト系快削ステンレス鋼材を製造できる。 According to this invention, it is possible to manufacture a ferritic free-cutting stainless steel material that is excellent in machinability with a small-diameter drill and hot workability in the material supply process, and is suitable for products that are cold-cut and served. .

上記した発明において、前記成分組成は、Ｂ：０．０００１～０．００８０％、Ｍｇ：０．０００５～０．０１００％、及び、Ｃａ：０．０００５～０．０１００％から選択される１種又は２種以上を更に含むことを特徴としてもよい。かかる発明によれば、熱間加工性に優れ製造性を高め得るのである。 In the above invention, the component composition is B: 0.0001 to 0.0080%, Mg: 0.0005 to 0.0100%, and Ca: one selected from 0.0005 to 0.0100% Alternatively, it may be characterized by further including two or more kinds. According to this invention, the hot workability is excellent and the manufacturability can be improved.

上記した発明において、前記焼き鈍し熱処理後の硬さが１９０ＨＶ以下であることを特徴としてもよい。かかる発明によれば、さらに細径ドリルに対する被削性に優れる。 In the above invention, the hardness after the annealing heat treatment may be 190 HV or less. According to this invention, the machinability for a small-diameter drill is further improved.

フェライト系快削ステンレス鋼の製造方法の例を示すフロー図である。FIG. 2 is a flow chart showing an example of a method for manufacturing ferritic free-cutting stainless steel; 実施例及び比較例の成分組成を示す図である。It is a figure which shows the component composition of an Example and a comparative example. 実施例及び比較例の成分組成を示す図である。It is a figure which shows the component composition of an Example and a comparative example. 実施例及び比較例の評価試験の結果を示す図である。It is a figure which shows the result of the evaluation test of an Example and a comparative example.

本発明者は、細径ドリルでの加工に対する被削性に優れるとともに、冷間で切断加工されて供される製品に適した加工性を有するフェライト系快削ステンレス鋼の成分組成について検討した。 The present inventors have studied the chemical composition of ferritic free-cutting stainless steel that has excellent machinability with a small-diameter drill and that has machinability suitable for cold-cut products.

細径ドリルでの加工に対する被削性としては、鋼のマトリクス強度を低下させることで細径ドリルでの高速切削におけるスラスト値を低く安定させて、工具摩耗を抑制する。 As for the machinability for machining with a small-diameter drill, the thrust value in high-speed cutting with a small-diameter drill is stabilized at a low level by reducing the matrix strength of the steel, thereby suppressing tool wear.

他方、冷間切断性としては、例えば、冷間で部材を剪断し切断加工したときに変形の少ない切断面を得られるよう、鋼の脆性を高める。特に、延性脆性遷移温度（ＤＢＴＴ）を高く保ち、材料の切断面にバリなどの原因となる塑性歪みを発生しづらくすることで、最終製品の形状を安定させる。 On the other hand, as for cold cutability, for example, the brittleness of steel is increased so that a cut surface with little deformation can be obtained when a member is cold sheared and cut. In particular, by keeping the ductile brittle transition temperature (DBTT) high and making it difficult for plastic strain, which causes burrs and the like, to occur on the cut surface of the material, the shape of the final product is stabilized.

ところで、フェライト系ステンレス鋼においては、一般的にマトリクス強度を低下させるとＤＢＴＴを低下させる傾向にある。ＤＢＴＴの低下は、鋼の延性を増大させて冷間切断性の低下を生じさせる。つまり、細径ドリル加工に対する被削性と冷間切断性とは単純には両立しない。 By the way, in ferritic stainless steel, generally, when the matrix strength is lowered, the DBTT tends to be lowered. A decrease in DBTT increases the ductility of the steel resulting in a decrease in cold cutability. In other words, machinability and cold cutability for small-diameter drilling are simply incompatible.

そこで、本発明者はＰの添加による影響に着目した。例えば、ＰはＡｌとともにマトリクス強度を上昇させる元素であるとともに、延性脆性遷移温度を上昇させる元素でもある。ところが、ＰはＡｌに比べて延性脆性遷移温度を上昇させる効果が大きく、マトリクス強度の上昇を抑えつつ延性脆性遷移温度を上昇させるよう含有させることが可能である。 Therefore, the present inventor focused on the influence of the addition of P. For example, P is an element that raises the matrix strength together with Al, and is also an element that raises the ductile-brittle transition temperature. However, P has a greater effect of raising the ductile-brittle transition temperature than Al, and can be contained so as to raise the ductile-brittle transition temperature while suppressing an increase in matrix strength.

そして、Ｓｉ、Ｃｒ、ＭｏやＡｌなどの固溶強化元素の添加量を減少させてＰの含有量を高めた複数の成分組成のフェライト系快削ステンレス鋼において、マトリクス強度及びフェライト相の相安定性を予測する以下の式１及び式２の値を算出し、熱間加工性に併せ、被削性や冷間加工性の評価を行った。また、その結果に基づいて、熱間加工性を維持しつつ細径ドリル加工に対する被削性及び冷間切断性を向上させ得るＰ及びその他の元素の含有量の範囲、及び式１の値（ＭＳ値）及び式２の値（ＦＳ値）の範囲を見出した。 Then, in ferritic free-cutting stainless steel with a plurality of chemical compositions in which the amount of addition of solid-solution strengthening elements such as Si, Cr, Mo and Al is reduced and the content of P is increased, matrix strength and phase stability of the ferrite phase The values of the following formulas 1 and 2 for predicting the workability were calculated, and the machinability and cold workability were evaluated along with the hot workability. Also, based on the results, the range of the content of P and other elements that can improve the machinability and cold cutability for small-diameter drilling while maintaining hot workability, and the value of formula 1 ( MS values) and a range of values for Equation 2 (FS values) were found.

なお、式１及び式２については、元素Ｍの質量％を［Ｍ］とし、以下の通りである。

式１：ＭＳ＝９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋４５０［Ｐ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］

式２：ＦＳ＝（［Ｃｒ］＋［Ｍｏ］＋１．５［Ｓｉ］＋４［Ａｌ］）／（［Ｎｉ］＋０．５［Ｍｎ］＋３０［Ｃ］＋３０［Ｎ］）

ここで、式１はマトリクス強度を予測するための式であり固溶強化元素によるものである。また、式２は熱間鍛造温度域でのフェライト相の相安定性を予測するための式であり、分子がフェライト安定化元素、分母がオーステナイト安定化元素の寄与を示すものである。 In addition, regarding Formula 1 and Formula 2, the mass % of the element M is set to [M], and is as follows.

Formula 1: MS = 900 ([C] + [N]) + 170 [Si] + 450 [P] + 12 [Cr] + 30 [Mo] + 10 [Al]

Formula 2: FS = ([Cr] + [Mo] + 1.5 [Si] + 4 [Al]) / ([Ni] + 0.5 [Mn] + 30 [C] + 30 [N])

Here, Formula 1 is a formula for predicting matrix strength and is based on solid solution strengthening elements. Formula 2 is a formula for predicting the phase stability of the ferrite phase in the hot forging temperature range.

上記を踏まえて、図１に沿って本実施例におけるフェライト系ステンレス鋼材の製造方法について説明する。 Based on the above, the manufacturing method of the ferritic stainless steel material in this embodiment will be described along FIG.

図１に示すように、まず、所定の成分組成のフェライト系ステンレス鋼によって、フェライト単相合金の鋼塊を鍛造する（Ｓ１）。 As shown in FIG. 1, first, a steel ingot of a ferritic single-phase alloy is forged with a ferritic stainless steel having a predetermined chemical composition (S1).

ここで、所定の成分組成としては、質量％で、Ｃ：０．０１５％以下、Ｓｉ：０．０２～０．６０％、Ｍｎ：０．１～２．０％、Ｐ：０．０５０％を超え０．３００％以下、Ｃｕ：１．５％以下、Ｎｉ：１．５％以下、Ｃｒ:１０．０～２５．０％、Ｍｏ：２．０％以下、Ａl:０．３０～２．００％、Ｏ：０．０４００％以下、Ｎ：０．０３５％以下、Ｓ：０．１０～０．４５％を含むとともに、更に、Ｐｂ：０．０３～０．４０％、Ｂｉ：０．０３～０．４０％、及び、Ｔｅ：０．０１～０．１０％から選択される２種以上を含むものとする。さらに、上記した式１及び式２において、ＭＳ≦３４０、ＦＳ≧７を満たすものとする。 Here, as a predetermined component composition, in mass%, C: 0.015% or less, Si: 0.02 to 0.60%, Mn: 0.1 to 2.0%, P: 0.050% 0.300% or less, Cu: 1.5% or less, Ni: 1.5% or less, Cr: 10.0 to 25.0%, Mo: 2.0% or less, Al: 0.30 to 2 .00%, O: 0.0400% or less, N: 0.035% or less, S: 0.10 to 0.45%, and further Pb: 0.03 to 0.40%, Bi: 0 .03 to 0.40% and Te: 0.01 to 0.10%. Furthermore, in the above formulas 1 and 2, it is assumed that MS≦340 and FS≧7 are satisfied.

さらに、この鋼塊は、鍛造ままの状態で９００～１２００℃のいずれの温度においても絞り量を５０パーセント以上とするようにされる。 Furthermore, this steel ingot is made to have a drawing amount of 50% or more at any temperature of 900 to 1200° C. in the as-forged state.

次いで、この鋼塊に焼き鈍し熱処理を施すことで製品としてのフェライト系ステンレス鋼材が得られる（Ｓ２）。焼き鈍し熱処理としては、例えば、７４０～８００℃の間で適宜設定される保持温度において４時間保持する熱処理とし得る。 Then, the steel ingot is annealed and heat-treated to obtain a ferritic stainless steel material as a product (S2). The annealing heat treatment may be, for example, a heat treatment in which the temperature is appropriately set between 740 and 800° C. and held for 4 hours.

以上によって、細径ドリル加工に対する被削性に優れるとともに、冷間切断性に優れる快削ステンレス鋼材を得ることができる。 As described above, it is possible to obtain a free-cutting stainless steel material having excellent machinability for small-diameter drilling and excellent cold-cutting properties.

＜評価試験＞
このような快削ステンレス鋼や、これに類似するステンレス鋼を用いた評価試験について、図２～図４を用いて説明する。 <Evaluation test>
Evaluation tests using such free-cutting stainless steel and similar stainless steel will be described with reference to FIGS. 2 to 4. FIG.

評価試験では、図２及び図３の実施例１乃至２５及び比較例１乃至１５に示す成分組成の鋼塊１５０ｋｇをそれぞれ溶製し、熱間鍛造した後、一部を熱間鍛造まま材として後述する試験に供し、残りを熱間圧延して直径２０ｍｍの丸棒及び６０ｍｍ角の角材とした。さらに、焼鈍処理として、７５０℃の温度で４時間保持して空冷した。得られた丸棒及び角材からなる焼鈍材等を用いて、適宜、下記試験片を切り出してそれぞれ試験し結果を評価した。 In the evaluation test, 150 kg of steel ingots having the chemical compositions shown in Examples 1 to 25 and Comparative Examples 1 to 15 in FIGS. It was subjected to a test described later, and the remainder was hot-rolled into a round bar with a diameter of 20 mm and a square bar of 60 mm square. Further, as an annealing treatment, the steel sheet was held at a temperature of 750° C. for 4 hours and air-cooled. Using the obtained annealed materials such as round bars and rectangular bars, the following test pieces were cut out as appropriate, and the results were evaluated by testing.

［ビッカース硬さ］
焼鈍材から、溶製後の鋼塊時に「ｍｉｄｄｌｅ部」に相当する箇所において、ビッカース硬さを測定した。測定は５点で行い、その平均値を記録し、図４に示した。 [Vickers hardness]
From the annealed material, the Vickers hardness was measured at a portion corresponding to the "middle portion" when the steel ingot was produced after melting. The measurement was performed at 5 points and the average value was recorded and shown in FIG.

［熱間加工性］
上記した熱間鍛造まま材からグリーブル試験片を採取して、高温での高速引張試験を行った。試験片の平行部はφ４．５ｍｍ×２０ｍｍＬ、つかみ部はＭ６×１０ｍｍＬとした。試験片は、１００秒で１１００℃まで昇温して６０秒保持後、それぞれ試験温度まで１０℃／ｓで変化させて６０秒保持し、５０．８ｍｍ／ｓの速度で引っ張り、破断させた。試験温度は９００℃から５０℃刻みで１２００℃までの７点とする。破断後、破断位置での絞り量を測定し、９００～１２００℃での熱間加工性として、７点の試験温度の全てにおいて絞り量５０％以上となった場合を良好と評価して「Ａ」を、７点の試験温度のうちいずれかにおいて絞り量５０％未満となった場合を不良と評価して「Ｃ」をそれぞれ記録し、図４に示した。 [Hot workability]
A Gleeble test piece was taken from the hot forged material as described above, and a high-speed tensile test was performed at a high temperature. The parallel portion of the test piece was φ4.5 mm×20 mmL, and the grip portion was M6×10 mmL. The test piece was heated to 1100° C. in 100 seconds, held for 60 seconds, changed to the test temperature at 10° C./s, held for 60 seconds, and pulled at a speed of 50.8 mm/s to break. The test temperature shall be 7 points from 900°C to 1200°C in increments of 50°C. After breaking, the amount of reduction at the fracture position was measured, and as hot workability at 900 to 1200 ° C., a case where the amount of reduction was 50% or more at all seven test temperatures was evaluated as good, and "A ” was evaluated as defective when the reduction amount was less than 50% at any of the seven test temperatures, and “C” was recorded, as shown in FIG. 4 .

［熱間オーステナイト量］
上記した熱間鍛造まま材より、１５ｍｍ角×２ｍｍＴの板状試料を採取し、表面を鏡面研磨してエッチングし、２５℃においてミクロ組織観察を行った。熱間で生じたオーステナイトは冷却によってマルテンサイトに変態するため、かかるミクロ組織観察においては、組織中にマルテンサイトが含まれるかを観察し、熱間でのオーステナイト発生の有無を調査した。組織中にマルテンサイトが含まれない場合に熱間でオーステナイトが生じていないと評価して「Ａ」を、マルテンサイトが含まれる場合に熱間でオーステナイトが生じたものと評価して「Ｃ」をそれぞれ記録し、図４に示した。すなわち、鋼塊溶製後の製造工程で最も高温度となる熱間鍛造時にフェライト－オーステナイトの２相状態を生じると熱間加工性に悪影響を与えると評価しているのである。 [Amount of hot austenite]
A plate-shaped sample of 15 mm square x 2 mm T was taken from the hot forged material as described above, the surface was mirror-polished and etched, and the microstructure was observed at 25°C. Since hot austenite transforms into martensite upon cooling, the presence or absence of hot austenite generation was investigated by observing whether martensite was contained in the microstructure. When no martensite is included in the structure, it is evaluated as "A" when hot austenite is not generated, and when martensite is included, it is evaluated as "C" when hot austenite is generated. were respectively recorded and shown in FIG. In other words, it is evaluated that if a two-phase state of ferrite and austenite is generated during hot forging, which is the highest temperature in the manufacturing process after ingot melting, hot workability is adversely affected.

［冷間切断性］
冷間切断性については、ＤＢＴＴ（延性脆性遷移温度）で評価した。焼鈍材を用いた衝撃試験を行い、ＤＢＴＴを求めた。シャルピー吸収エネルギーの温度依存データを取得し、脆性破面率５０％となる温度をＤＢＴＴと規定した。ＤＢＴＴが５℃以上のときを冷間切断性が良好なものと評価して「Ａ」を、－２０℃を超えて５℃未満のときを可と評価して「Ｂ」を、－２０℃以下のときを不良と評価して「Ｃ」をそれぞれ記録し、図４に示した。 [Cold cutability]
Cold cuttability was evaluated by DBTT (Ductile Brittle Transition Temperature). An impact test using an annealed material was performed to obtain DBTT. Temperature dependent data of Charpy absorbed energy was obtained, and the temperature at which the brittle fracture rate was 50% was defined as DBTT. When the DBTT is 5 ° C. or higher, the cold cutting property is evaluated as "A", and when the DBTT is over -20 ° C. and less than 5 ° C., it is evaluated as "B" and -20 ° C. The following cases were evaluated as bad and recorded with "C", respectively, and are shown in FIG.

［細径ドリル被削性］
細径ドリルに対する被削性を評価するため、ドリル工具寿命及び切屑破砕性を評価した。詳細には、焼鈍材に対して、φ１ｍｍのハイスドリルを用いて、送り０．０３ｍｍ／ｒｅｖ、切削速度７０ｍ／ｍｉｎとし、潤滑剤を用いずに穿孔を行ってドリル工具寿命及び切屑破砕性を評価した。ドリルの折損なく４０００ｍｍを超えて穿孔の可能な場合を良好と評価して「Ａ」を、２０００～４０００ｍｍの穿孔の可能な場合を可と評価して「Ｂ」を、２０００ｍｍ未満の場合を不良と評価して「Ｃ」を記録し、それぞれ図４に示した。また、切屑破砕性は、切り屑を観察して８０％以上の切り屑が１又は２カール以内で分断されていれば良好と評価して「Ａ」を、３～５カールで分断されていれば可と評価して「Ｂ」を、６カール以上連続していれば不良と評価して「Ｃ」をそれぞれ記録し、図４に示した。 [Machinability for small diameter drills]
In order to evaluate machinability for small-diameter drills, drill tool life and chip crushability were evaluated. Specifically, drilling is performed on an annealed material using a φ1 mm high-speed steel drill at a feed rate of 0.03 mm / rev and a cutting speed of 70 m / min without using a lubricant to evaluate the drill tool life and chip crushability. bottom. If it is possible to drill over 4000 mm without breakage of the drill, it is evaluated as "A", if it is possible to drill 2000 to 4000 mm, it is evaluated as "B", and if it is less than 2000 mm, it is poor. and recorded "C", respectively shown in FIG. In addition, the chip crushability is evaluated as good if 80% or more of the chips are divided within 1 or 2 curls by observing the chips, and "A" is evaluated if the chips are divided by 3 to 5 curls. It was evaluated as good and recorded as "B", and if it continued for 6 curls or more, it was evaluated as defective and recorded as "C", as shown in FIG.

次に、上記した実施例１乃至２５及び比較例１乃至１５のビッカース硬さ、熱間加工性、フェライト量、ドリル工具寿命、切屑破砕性のそれぞれの結果について、図４に基づいて説明する。 Next, the Vickers hardness, hot workability, ferrite content, drill tool life, and chip crushability of Examples 1 to 25 and Comparative Examples 1 to 15 will be described with reference to FIG.

実施例１乃至２５は、ビッカース硬さが１２４～１８９ＨＶの範囲内であり、いずれの実施例においてもマトリクス強度を低下せしめ、被削性の向上に寄与していると考えられる。また、ドリル工具寿命及び切屑破砕性のいずれにおいても良好（Ａ）又は可（Ｂ）の評価を得ている。また、熱間オーステナイト量の評価はいずれも良好（Ａ）であり、熱間鍛造においてフェライト単相を維持できたと考えられる。併せて、熱間加工性の評価においていずれも良好（Ａ）であった通り、この試験温度において高い熱間加工性を維持できている。さらに、ＤＢＴＴによって評価した冷間切断性も「Ａ」又は「Ｂ」であり、優れた冷間切断性を有するものと考えられる。すなわち、実施例１乃至２５によれば熱間加工性を維持しつつ、細径ドリル加工に対する被削性に優れるとともに、冷間切断性に優れる快削ステンレス鋼材とし得ることが判った。なお、マトリクス強度を予測する式１の値（ＭＳ値）は２１９～３３２であった。さらに、熱間鍛造温度域でのフェライト相の相安定性を予測する式２の値（ＦＳ値）は１０．３～２９．５であった。 Examples 1 to 25 have a Vickers hardness within the range of 124 to 189 HV, which is considered to contribute to the improvement of machinability by lowering the matrix strength in any of the examples. In addition, both the drill tool life and chip crushability are evaluated as good (A) or fair (B). In addition, the evaluation of the amount of hot austenite was good (A), and it is considered that the ferrite single phase was maintained in the hot forging. In addition, high hot workability can be maintained at this test temperature, as all of them were good (A) in the evaluation of hot workability. Furthermore, the cold cutability evaluated by DBTT was also "A" or "B", and it is considered to have excellent cold cutability. That is, according to Examples 1 to 25, it was found that a free-cutting stainless steel material having excellent cold cutability as well as excellent machinability for small-diameter drilling can be obtained while maintaining hot workability. The value (MS value) of Equation 1 for predicting the matrix intensity was 219-332. Furthermore, the value (FS value) of Formula 2 for predicting the phase stability of the ferrite phase in the hot forging temperature range was 10.3 to 29.5.

一方、比較例１は、実施例に比べてＣの含有量が多く、熱間加工性及び熱間オーステナイト量において不良の評価であり、熱間鍛造できなかった。熱間でオーステナイトが生成されたためと考えられる。 On the other hand, Comparative Example 1 had a higher C content than in Examples, was evaluated as poor in hot workability and hot austenite content, and could not be hot forged. It is thought that this is because austenite was generated in hot conditions.

比較例２は、実施例に比べてＳｉの含有量が多く、ドリル工具寿命で不良の評価であった。ＭＳ値が大きかったことからも、マトリクス強度を高くして、ドリル切削時のスラストを大きくしてしまったものと考えられる。 Comparative Example 2 had a higher Si content than in Examples, and was evaluated as poor in terms of drill tool life. From the fact that the MS value was large, it is considered that the matrix strength was increased to increase the thrust during drill cutting.

比較例３は、実施例に比べて快削元素であるＳの含有量が低く、冷間切断性、ドリル工具寿命、切屑破砕性において不良の評価であった。 Comparative Example 3 had a lower content of S, which is a free-cutting element, than in Examples, and was evaluated as poor in cold cutting properties, drill tool life, and chip crushability.

比較例４は、実施例に比べてＳの含有量が多く、熱間加工性において不良の評価であり、熱間鍛造できなかった。 In Comparative Example 4, the S content was higher than in Examples, and the hot workability was evaluated as poor, and hot forging could not be performed.

比較例５は、実施例に比べてＮｉの含有量が多く、熱間加工性、熱間オーステナイト量において不良の評価であり、熱間鍛造できなかった。ＦＳ値が実施例に比べて小さかったこともあり、熱間でオーステナイトが生成されたものと考えられる。 Comparative Example 5 had a higher Ni content than in Examples, was evaluated as poor in terms of hot workability and hot austenite content, and could not be hot forged. Partly because the FS value was smaller than in the examples, it is believed that austenite was generated during hot working.

比較例６は、実施例に比べてＭｏの含有量が多く、ドリル工具寿命において不良の評価であった。ＭＳ値は３４０以下ではあるものの比較的大きく、マトリクス強度を高くして、ドリル切削時のスラストを大きくしてしまったものと考えられる。 Comparative Example 6 had a higher Mo content than in Examples, and was evaluated as poor in terms of drill tool life. Although the MS value was 340 or less, it was relatively large, and it is considered that the matrix strength was increased to increase the thrust during drill cutting.

比較例７は、実施例に比べてＡｌの含有量が少なく、熱間加工性において不良の評価であり、熱間鍛造できなかった。熱間オーステナイト量も不良の評価であり、ＦＳ値が低かったことからも、熱間でオーステナイトが生成されたものと考えられる。 Comparative Example 7 had a smaller Al content than in Examples, was evaluated as poor in hot workability, and could not be hot forged. The amount of hot austenite was also evaluated as unsatisfactory, and the FS value was low.

比較例８は、実施例に比べてＣｒの含有量が少なく、Ｐｂの含有量が多く、熱間加工性において不良の評価であり、熱間鍛造できなかった。 Comparative Example 8 had a lower Cr content and a higher Pb content than those of Examples, was evaluated as poor in hot workability, and could not be hot forged.

比較例９は、実施例に比べてＢｉの含有量が多く、熱間加工性において不良の評価であり、熱間鍛造できなかった。 In Comparative Example 9, the content of Bi was larger than that in Examples, and the hot workability was evaluated as poor, and hot forging could not be performed.

比較例１０、比較例１１、及び、比較例１２は、実施例に比べてＡｌの含有量が少なく、代わりにそれぞれＮｂ、Ｔｉ、及び、Ｖが添加されており、冷間切断性、ドリル工具寿命、切屑破砕性において不良の評価であった。Ｎｂ、Ｔｉ、又は、Ｖの含有によってフェライト相を安定させて熱間でオーステナイトを生成させず熱間加工性には優れるものの、炭窒化物の微細分散による結晶粒の微細化や固溶強化によってマトリクス強度を高くしてしまい、ドリル加工時のスラストを大きくしてしまったものと考えられる。また、Ｎｂ、Ｔｉ、及び、Ｖそれぞれの脆化作用はＡｌに劣り、そのため冷間切断性や切屑破砕性の評価を低下させたものと考えられる。 Comparative Examples 10, 11, and 12 have a lower Al content than those of Examples, and instead, Nb, Ti, and V are added, respectively, and cold cutting properties and drill tools are improved. It was evaluated as poor in terms of life and chip crushability. The inclusion of Nb, Ti, or V stabilizes the ferrite phase and does not generate austenite in hot working, and is excellent in hot workability. It is thought that the matrix strength was increased and the thrust during drilling was increased. In addition, the embrittlement action of Nb, Ti, and V is inferior to that of Al, which is considered to have lowered the evaluation of cold cutability and chip crushability.

比較例１３は、冷間切断性、ドリル工具寿命において不良の評価であった。ＭＳ値が実施例に比べて大きく３４０を超えたことからも、マトリクス強度を高くして、ドリル切削時のスラストを大きくしてしまったものと考えられる。 Comparative Example 13 was evaluated as poor in cold cutability and drill tool life. From the fact that the MS value exceeded 340, which is much higher than that of the example, it is considered that the matrix strength was increased to increase the thrust during drill cutting.

比較例１４は、実施例に比べてＦＳ値が小さく、熱間加工性、熱間オーステナイト量において不良の評価であり、熱間鍛造できなかった。熱間でオーステナイトが生成されたものと考えられる。 Comparative Example 14 had a smaller FS value than those of Examples, was evaluated as poor in hot workability and hot austenite content, and could not be hot forged. It is believed that austenite was generated during hot work.

比較例１５は、Ｐの含有量が少ない以外、実施例と同等の成分組成を有していたが、冷間切断性において不良の評価であった。Ｐの不足によってＤＢＴＴを低くしてしまったものと考えられる。 Comparative Example 15 had a component composition similar to that of Examples except that the P content was small, but was evaluated as poor in cold cutability. It is believed that the lack of P caused the DBTT to be low.

以上の結果と他のいくつかの同様の試験結果に基づき、上記した実施例と同等の成分組成の鋼において、必要とされる細径ドリル被削性と冷間切断性を得るためのマトリクス強度を予測する式１の値（ＭＳ値）を３４０以下と定めた。なお、ＭＳ値は上記したドリル被削性の評価などから、好ましくは１００～３４０の範囲内であり、より好ましくは１５０～３２０の範囲内である。 Based on the above results and some other similar test results, the matrix strength to obtain the required small diameter drill machinability and cold cutability in the steel with the same chemical composition as the above example. The value (MS value) of Formula 1 that predicts is set to 340 or less. The MS value is preferably in the range of 100 to 340, more preferably in the range of 150 to 320, based on the above evaluation of drill machinability.

また、熱間加工性を維持するためには、上記したように、フェライト単相領域で熱間鍛造を行うことを必要とする。そのためにフェライト相の好ましい相安定性とするための式２の値（ＦＳ値）を７以上と定めた。すなわち、ＦＳ値を７以上とすることで、フェライト相の相安定性を高めてフェライト単相温度領域の上限温度を上昇させ、フェライト単相温度領域での鍛造を容易とするのである。 Further, in order to maintain hot workability, it is necessary to perform hot forging in the ferrite single-phase region, as described above. For this reason, the value (FS value) of Equation 2 for obtaining preferable phase stability of the ferrite phase is set to 7 or more. That is, by setting the FS value to 7 or more, the phase stability of the ferrite phase is enhanced, the upper limit temperature of the ferrite single phase temperature range is increased, and forging in the ferrite single phase temperature range is facilitated.

ところで、上記した評価試験とほぼ同等の熱間加工性、被削性及び冷間切断性を与え得る合金の組成範囲は以下のように定められる。 By the way, the compositional range of the alloy that can provide almost the same hot workability, machinability and cold cutability as in the above evaluation test is determined as follows.

Ｃは、代表的な固溶強化元素であり、マトリクス強度を上昇させるとともに、アブレシブ粒子となる硬質な炭化物を形成し、ドリル被削性を低下させ得る。そこで、Ｃは、質量％で、０．０１５％以下であり、好ましくは０．０１２％以下である。 C is a typical solid-solution strengthening element, increases matrix strength, forms hard carbides that become abrasive particles, and can reduce drill machinability. Therefore, C is 0.015% or less, preferably 0.012% or less in mass %.

Ｓｉは、脱酸剤として有効な元素である。一方、Ｓｉは代表的な固溶強化元素でもあり、過剰に添加するとマトリクス強度を上昇させドリル被削性を低下させる可能性がある。そこで、Ｓｉは、質量％で、０．０２～０．６０％の範囲内、好ましくは０．０２～０．４０％の範囲内である。 Si is an element effective as a deoxidizing agent. On the other hand, Si is also a representative solid-solution strengthening element, and if added excessively, it may increase matrix strength and reduce drill machinability. Therefore, Si is in the range of 0.02 to 0.60%, preferably in the range of 0.02 to 0.40% by mass.

Ｍｎは、Ｓと化合物を生成し、ドリル被削性の向上に寄与する元素である。また、Ｓの粒界偏析を抑制し熱間加工性を向上させる。一方、Ｍｎはオーステナイト安定化元素であり、過剰に添加すると熱間鍛造温度域でフェライト相を不安定にする。そこで、Ｍｎは、質量％で、０．２～２．０％の範囲内である。 Mn is an element that forms a compound with S and contributes to the improvement of drill machinability. Also, it suppresses grain boundary segregation of S and improves hot workability. On the other hand, Mn is an austenite stabilizing element, and when added excessively, it destabilizes the ferrite phase in the hot forging temperature range. Therefore, Mn is in the range of 0.2 to 2.0% by mass.

Ｐは、ＤＢＴＴを大きく上昇させて冷間切断性を向上させ得る。一方、Ｐは固溶強化元素であり、マトリクス強度を上昇させドリル被削性を低下させる可能性がある。そこで、Ｐは、質量％で、０．０５０％を超え、０．３００％以下であり、好ましくは０．２００％以下である。 P can greatly increase DBTT and improve cold cutability. On the other hand, P is a solid-solution strengthening element and may increase matrix strength and reduce drill machinability. Therefore, P is more than 0.050% and not more than 0.300%, preferably not more than 0.200% by mass.

Ｃｕは、オーステナイト安定化元素であり、熱間鍛造温度域でフェライト相を不安定にする。そこで、Ｃｕは、質量％で、１．５％以下である。 Cu is an austenite stabilizing element and destabilizes the ferrite phase in the hot forging temperature range. Therefore, Cu is 1.5% or less in mass %.

Ｎｉは、オーステナイト安定化元素であり、熱間鍛造温度域でフェライト相を不安定にする。そこで、Ｎｉは、質量％で、１．５％以下である。 Ni is an austenite stabilizing element and destabilizes the ferrite phase in the hot forging temperature range. Therefore, Ni is 1.5% or less in mass %.

Ｃｒは、耐食性の向上に寄与する元素である。一方、Ｃｒは過剰に添加するとマトリクス強度を上昇させ、ドリル被削性を低下させる可能性がある。そこで、Ｃｒは、質量％で、１０．０～２５．０％の範囲内、好ましくは１０．０～１７．０％の範囲内である。 Cr is an element that contributes to the improvement of corrosion resistance. On the other hand, when Cr is added excessively, it may increase matrix strength and degrade drill machinability. Therefore, Cr is in the range of 10.0 to 25.0%, preferably in the range of 10.0 to 17.0% by mass.

Ｍｏは、耐食性の向上に寄与する元素であり必要に応じて添加し得るが、代表的な固溶強化元素でもあり、マトリクス強度を上昇させ、被削性を低下させる可能性がある。そこで、Ｍｏは、質量％で、２．０％以下である。 Mo is an element that contributes to the improvement of corrosion resistance and can be added as necessary, but it is also a typical solid solution strengthening element, and may increase matrix strength and reduce machinability. Therefore, Mo is 2.0% or less in mass %.

Ａｌは、延性脆性遷移温度を高温側にシフトさせ、マトリクスの脆化を促し切屑破砕性の向上に寄与する元素である。また、鍛造温度域における強力なフェライト相の安定化元素であり、熱間加工性の確保のために必要である。一方、Ａｌは過剰に添加すると鋼塊の冷却割れの要因となり製造性に悪影響を及ぼす可能性がある。そこで、Ａｌは、質量％で、０．３０～２．００％の範囲内、好ましくは０．３０～１．８０％の範囲内、さらに好ましくは０．３５～１．５０％の範囲内である。 Al is an element that shifts the ductile embrittlement transition temperature to the high temperature side, promotes embrittlement of the matrix, and contributes to improvement of chip crushability. In addition, it is a strong ferrite phase stabilizing element in the forging temperature range, and is necessary for ensuring hot workability. On the other hand, excessive addition of Al may cause cooling cracks in steel ingots and adversely affect manufacturability. Therefore, Al is in the range of 0.30 to 2.00% by mass, preferably in the range of 0.30 to 1.80%, more preferably in the range of 0.35 to 1.50% be.

Ｏは、アブレシブ粒子となる硬質の酸化物の生成を促し、ドリル被削性を低下させる可能性がある。そこで、Ｏは、質量％で、０．０４００％以下の範囲内である。 O promotes the formation of hard oxides that become abrasive particles, possibly degrading drill machinability. Therefore, O is within the range of 0.0400% or less in mass %.

Ｎは、代表的な固溶強化元素でありマトリクス強度を上昇させ、また、硬質な窒化物を生成してドリル被削性を低下させてしまう可能性がある。そこで、Ｎは、質量％で、０．０３５％以下であり、好ましくは０．０２５％以下である。 N is a representative solid-solution strengthening element, increases matrix strength, and may form hard nitrides to reduce drill machinability. Therefore, N is 0.035% or less, preferably 0.025% or less in mass %.

Ｓは、硫化物を生成しドリル被削性の向上に寄与する元素である。一方、Ｓは過剰に添加すると熱間加工性を著しく悪化させてしまう。そこで、Ｓは、質量％で、０．１０～０．４５％の範囲内、好ましくは０．１０～０．４０％の範囲内である。 S is an element that forms sulfides and contributes to improving drill machinability. On the other hand, when S is added excessively, the hot workability is remarkably deteriorated. Therefore, S is in the range of 0.10 to 0.45%, preferably in the range of 0.10 to 0.40% by mass.

Ｐｂは、切削加工中の熱による溶融脆化作用によりドリル被削性の向上に寄与する元素である。一方、Ｐｂは過剰に添加すると熱間加工性を著しく悪化させてしまう。そこで、Ｐｂは、質量％で、０．０３～０．４０％の範囲内であり、好ましくは０．０３～０．３０％の範囲内である。 Pb is an element that contributes to the improvement of drill machinability due to melting embrittlement caused by heat during cutting. On the other hand, if Pb is added excessively, the hot workability is remarkably deteriorated. Therefore, Pb is in the range of 0.03 to 0.40%, preferably in the range of 0.03 to 0.30% by mass.

Ｂｉは、切削加工中の熱による溶融脆化作用によりドリル被削性の向上に寄与する元素である。一方、Ｂｉは過剰に添加すると熱間加工性を著しく悪化させてしまう。そこで、Ｂｉは、質量％で、０．０３～０．４０％の範囲内であり、好ましくは０．０３～０．３０％の範囲内である。 Bi is an element that contributes to the improvement of drill machinability due to melting embrittlement caused by heat during cutting. On the other hand, if Bi is added excessively, the hot workability is remarkably deteriorated. Therefore, Bi is in the range of 0.03 to 0.40% by mass, preferably in the range of 0.03 to 0.30%.

Ｔｅは、切削加工中の熱による溶融脆化作用と硫化物の針状比低下による異方性の緩和作用とによりドリル被削性の向上に寄与する元素である。一方、Ｔｅは過剰に添加すると熱間加工性を著しく悪化させてしまう。そこで、Ｔｅは、質量％で、０．０１～０．１０％の範囲内であり、好ましくは０．０１～０．０８％の範囲内である。 Te is an element that contributes to the improvement of drill machinability by the melting embrittlement effect due to heat during cutting and the anisotropic relaxation effect due to the decrease in the acicular ratio of sulfides. On the other hand, when Te is added excessively, the hot workability is remarkably deteriorated. Therefore, Te is in the range of 0.01 to 0.10% by mass, preferably in the range of 0.01 to 0.08%.

なお、上記したＰｂ、Ｂｉ、Ｔｅは３種のうち２種以上を添加すればよい。また、以下では選択的に添加してもよい元素について説明する。 Two or more of the three types of Pb, Bi, and Te described above may be added. Elements that may be selectively added are described below.

Ｂは、熱間加工性の確保に有効な元素である。一方、Ｂは過剰に添加すると却って熱間加工性を悪化させてしまう。そこで、Ｂは、質量％で、０．０００１～０．００８０％の範囲内、好ましくは０．０００３～０．００６０％の範囲内で含有させ得る。 B is an element effective for ensuring hot workability. On the other hand, if B is added excessively, it rather deteriorates the hot workability. Therefore, B can be contained within the range of 0.0001 to 0.0080%, preferably within the range of 0.0003 to 0.0060% by mass.

Ｍｇは、熱間加工性の確保に有効な元素である。一方、Ｍｇは過剰に添加すると熱間加工性を向上させる効果を飽和させてしまう。そこで、Ｍｇは、質量％で、０．０００５～０．０１００％の範囲内、好ましくは０．００１０～０．０１００％の範囲内で含有させ得る。 Mg is an effective element for ensuring hot workability. On the other hand, excessive addition of Mg saturates the effect of improving hot workability. Therefore, Mg can be contained within the range of 0.0005 to 0.0100%, preferably within the range of 0.0010 to 0.0100% by mass.

Ｃａは、熱間加工性の確保に有効な元素である。一方、Ｃａは過剰に添加すると熱間加工性を向上させる効果を飽和させてしまう。そこで、Ｃａは、質量％で、０．０００５～０．０１００％の範囲内、好ましくは０．００１０～０．０１００％の範囲内で含有させ得る。 Ca is an element effective for ensuring hot workability. On the other hand, excessive addition of Ca saturates the effect of improving hot workability. Therefore, Ca can be contained within the range of 0.0005 to 0.0100%, preferably within the range of 0.0010 to 0.0100% by mass.

以上、本発明の代表的な実施例を説明したが、本発明は必ずしもこれらに限定されるものではなく、当業者であれば、本発明の主旨又は添付した特許請求の範囲を逸脱することなく、種々の代替実施例及び改変例を見出すことができるであろう。 Although representative embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to make modifications without departing from the spirit of the present invention or the scope of the appended claims. , one may find various alternatives and modifications.

Claims (5)

フェライト系快削ステンレス鋼であって、
質量％で、
Ｃ：０．０１５％以下、
Ｓｉ：０．０２～０．６０％、
Ｍｎ：０．１～２．０％、
Ｐ：０．０５０％を超え０．３００％以下、
Ｃｕ：１．５％以下、
Ｎｉ：１．５％以下、
Ｃｒ:１０．０～２５．０％、
Ｍｏ：２．０％以下、
Ａl:０．３０～２．００％、
Ｏ：０．０４００％以下、
Ｎ：０．０３５％以下、
Ｓ：０．１０～０．４５％を含むとともに、
更に、
Ｐｂ：０．０３～０．４０％、
Ｂｉ：０．０３～０．４０％、及び、
Ｔｅ：０．０１～０．１０％から選択される２種以上を含み、且つ、
元素Ｍの質量％を［Ｍ］とすると、
９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋４５０［Ｐ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］≦３４０、及び、
（［Ｃｒ］＋［Ｍｏ］＋１．５［Ｓｉ］＋４［Ａｌ］）／（［Ｎｉ］＋０．５［Ｍｎ］＋３０［Ｃ］＋３０［Ｎ］）≧７
を満たし、残部をＦｅ及び不可避的不純物とする成分組成からなることを特徴とするフェライト系快削ステンレス鋼。 Ferritic free-cutting stainless steel,
in % by mass,
C: 0.015% or less,
Si: 0.02 to 0.60%,
Mn: 0.1 to 2.0%,
P: more than 0.050% and 0.300% or less,
Cu: 1.5% or less,
Ni: 1.5% or less,
Cr: 10.0 to 25.0%,
Mo: 2.0% or less,
Al: 0.30-2.00%,
O: 0.0400% or less,
N: 0.035% or less,
S: containing 0.10 to 0.45%,
Furthermore,
Pb: 0.03 to 0.40%,
Bi: 0.03 to 0.40%, and
Te: contains two or more selected from 0.01 to 0.10%, and
If the mass% of the element M is [M],
900 ([C] + [N]) + 170 [Si] + 450 [P] + 12 [Cr] + 30 [Mo] + 10 [Al] ≤ 340, and
([Cr] + [Mo] + 1.5 [Si] + 4 [Al]) / ([Ni] + 0.5 [Mn] + 30 [C] + 30 [N]) ≥ 7
and the balance being Fe and inevitable impurities. 前記成分組成は、
Ｂ：０．０００１～０．００８０％、
Ｍｇ：０．０００５～０．０１００％、及び、
Ｃａ：０．０００５～０．０１００％
から選択される１種又は２種以上を更に含むことを特徴とする請求項１記載のフェライト系快削ステンレス鋼。 The component composition is
B: 0.0001 to 0.0080%,
Mg: 0.0005 to 0.0100%, and
Ca: 0.0005-0.0100%
The free-cutting ferritic stainless steel according to claim 1, further comprising one or more selected from: フェライト系快削ステンレス鋼材の製造方法であって、
質量％で、
Ｃ：０．０１５％以下、
Ｓｉ：０．０２～０．６０％、
Ｍｎ：０．１～２．０％、
Ｐ：０．０５０％を超え０．３００％以下、
Ｃｕ：１．５％以下、
Ｎｉ：１．５％以下、
Ｃｒ:１０．０～２５．０％、
Ｍｏ：２．０％以下、
Ａl:０．３０～２．００％、
Ｏ：０．０４００％以下、
Ｎ：０．０３５％以下、
Ｓ：０．１０～０．４５％を含むとともに、
更に、
Ｐｂ：０．０３～０．４０％、
Ｂｉ：０．０３～０．４０％、及び、
Ｔｅ：０．０１～０．１０％から選択される２種以上を含み、且つ、
元素Ｍの質量％を［Ｍ］とすると、
９００（［Ｃ］＋［Ｎ］）＋１７０［Ｓｉ］＋４５０［Ｐ］＋１２［Ｃｒ］＋３０［Ｍｏ］＋１０［Ａｌ］≦３４０、及び、
（［Ｃｒ］＋［Ｍｏ］＋１．５［Ｓｉ］＋４［Ａｌ］）／（［Ｎｉ］＋０．５［Ｍｎ］＋３０［Ｃ］＋３０［Ｎ］）≧７
を満たし、残部をＦｅ及び不可避的不純物とする成分組成からなるフェライト単相合金を鍛造し、９００～１２００℃における絞り量が５０パーセント以上とする鋼塊を得た上で、焼き鈍し熱処理を施されて供されることを特徴とするフェライト系快削ステンレス鋼材の製造方法。 A method for producing a ferritic free-cutting stainless steel material, comprising:
in % by mass,
C: 0.015% or less,
Si: 0.02 to 0.60%,
Mn: 0.1 to 2.0%,
P: more than 0.050% and 0.300% or less,
Cu: 1.5% or less,
Ni: 1.5% or less,
Cr: 10.0 to 25.0%,
Mo: 2.0% or less,
Al: 0.30-2.00%,
O: 0.0400% or less,
N: 0.035% or less,
S: containing 0.10 to 0.45%,
Furthermore,
Pb: 0.03 to 0.40%,
Bi: 0.03 to 0.40%, and
Te: contains two or more selected from 0.01 to 0.10%, and
If the mass% of the element M is [M],
900 ([C] + [N]) + 170 [Si] + 450 [P] + 12 [Cr] + 30 [Mo] + 10 [Al] ≤ 340, and
([Cr] + [Mo] + 1.5 [Si] + 4 [Al]) / ([Ni] + 0.5 [Mn] + 30 [C] + 30 [N]) ≥ 7
and the balance being Fe and unavoidable impurities to obtain a steel ingot with a reduction of 50% or more at 900 to 1200 ° C., and then subjected to annealing heat treatment. A method for producing a ferritic free-cutting stainless steel material, characterized in that it is provided by 前記成分組成は、
Ｂ：０．０００１～０．００８０％、
Ｍｇ：０．０００５～０．０１００％、及び、
Ｃａ：０．０００５～０．０１００％
から選択される１種又は２種以上を更に含むことを特徴とする請求項３記載のフェライト系快削ステンレス鋼材の製造方法。 The component composition is
B: 0.0001 to 0.0080%,
Mg: 0.0005 to 0.0100%, and
Ca: 0.0005-0.0100%
4. The method for producing a ferritic free-cutting stainless steel material according to claim 3, further comprising one or more selected from: 前記焼き鈍し熱処理後の硬さが１９０ＨＶ以下であることを特徴とする請求項３又は４に記載のフェライト系快削ステンレス鋼材の製造方法。
5. The method for producing a ferritic free-cutting stainless steel material according to claim 3, wherein the hardness after the annealing heat treatment is 190 HV or less.
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