JP4949100B2 - Austenitic stainless free-cutting steel with excellent cold forgeability and machinability - Google Patents
Austenitic stainless free-cutting steel with excellent cold forgeability and machinability Download PDFInfo
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- JP4949100B2 JP4949100B2 JP2007081146A JP2007081146A JP4949100B2 JP 4949100 B2 JP4949100 B2 JP 4949100B2 JP 2007081146 A JP2007081146 A JP 2007081146A JP 2007081146 A JP2007081146 A JP 2007081146A JP 4949100 B2 JP4949100 B2 JP 4949100B2
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- 229910000915 Free machining steel Inorganic materials 0.000 title claims description 11
- 229910000831 Steel Inorganic materials 0.000 claims description 15
- 239000010959 steel Substances 0.000 claims description 15
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 238000005520 cutting process Methods 0.000 description 15
- 239000000463 material Substances 0.000 description 14
- 238000005260 corrosion Methods 0.000 description 13
- 230000007797 corrosion Effects 0.000 description 13
- 230000000694 effects Effects 0.000 description 9
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 8
- 229910052791 calcium Inorganic materials 0.000 description 6
- 238000010273 cold forging Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 150000003568 thioethers Chemical class 0.000 description 6
- 229910052726 zirconium Inorganic materials 0.000 description 6
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 5
- 239000006185 dispersion Substances 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229910052717 sulfur Inorganic materials 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000012669 compression test Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 229910052745 lead Inorganic materials 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052714 tellurium Inorganic materials 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
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Description
本発明は、冷間鍛造性と被削性に優れた環境にやさしいオーステナイト系ステンレス鋼に関するものであり、例えば、複雑な形状を有しこれまで、切削加工のみで加工を行っている精密部品などを冷間鍛造加工と切削加工をあわせて行うことにより、材料歩留よく加工することが可能なオーステナイト系ステンレス鋼に関するものである。 The present invention relates to an environment-friendly austenitic stainless steel having excellent cold forgeability and machinability, such as a precision part that has a complicated shape and has been processed only by cutting so far. The present invention relates to an austenitic stainless steel that can be processed with high material yield by performing cold forging and cutting together.
オーステナイト系ステンレス鋼は加工性、耐食性などに優れた性質を有することから、様々な分野において広く使用されている。ネジ、ボルトなどの各種機器部品は一般に冷間鍛造によって成形加工して製造されることが多い。この冷間鍛造による方法は加工能率、歩留が高い利点を有するが、精密な加工精度に劣る。一方、複雑な形状を有する部品では、すべて切削加工で製造されている。切削加工による方法では複雑な形状への加工が可能であり、非常に精密な寸法精度を満足することができる利点があるものの、太い線径の材料から加工されるため材料歩留が悪いという欠点がある。 Austenitic stainless steel is widely used in various fields because it has excellent properties such as workability and corrosion resistance. In general, various equipment parts such as screws and bolts are generally manufactured by cold forging. This cold forging method has the advantage of high processing efficiency and yield, but is inferior in precise processing accuracy. On the other hand, all parts having complicated shapes are manufactured by cutting. The cutting method allows processing into complex shapes and has the advantage of satisfying very precise dimensional accuracy, but has the disadvantage of poor material yield because it is processed from a material with a large wire diameter. There is.
従来、冷間鍛造性を求められる製造方法ではＳＵＳＸＭ７（１７％Ｃｒ−９％Ｎｉ−３％Ｃｕ−低Ｃ、Ｎ系）が、被削性を求められる製造方法ではＳＵＳ３０３（１８％Ｃｒ−９％Ｎｉ−０．３％Ｓ）などが用いられてきた。 Conventionally, SUSXM7 (17% Cr-9% Ni-3% Cu-low C, N-based) is used in manufacturing methods that require cold forgeability, while SUS303 (18% Cr-9 is used in manufacturing methods that require machinability. % Ni-0.3% S) has been used.
冷間鍛造性に優れたＳＵＳＸＭ７は被削性が悪く、被削性の優れたＳＵＳ３０３は冷間鍛造性が悪いという相反する特徴を有している。従って、複雑な形状を有する部品では材料歩留が悪くても被削性の高い鋼を使用し、切削加工にて製造しているのが通常であった。 SUSXM7, which has excellent cold forgeability, has a conflicting characteristic that machinability is poor and SUS303, which has excellent machinability, has poor cold forgeability. Therefore, parts having a complicated shape are usually manufactured by cutting using steel having high machinability even if the material yield is low.
しかしながら、近年、複雑な形状を有する部品を歩留・生産性よく製造するために、冷間鍛造性と被削性を兼備したオーステナイト系ステンレス鋼が提案されている（特許文献１〜６）。一方最近、脱酸による介在物の形態を変えることで特性を改善することも提案されている（特許文献６〜８）。 However, in recent years, austenitic stainless steels having both cold forgeability and machinability have been proposed in order to manufacture parts having complicated shapes with high yield and productivity (Patent Documents 1 to 6). On the other hand, recently, it has also been proposed to improve characteristics by changing the form of inclusions by deoxidation (Patent Documents 6 to 8).
特許文献１に記載された発明は高い耐食性と強度を有しかつ塑性加工（冷温間鍛造加工）性を付与すると同時に被削性を向上させた発明であり、被削性を向上させるためにＳ（０．０５〜０．１５％）を添加させることを特徴としているが、その塑性加工性はＳＵＳＸＭ７には及ばない。 The invention described in Patent Document 1 is an invention having high corrosion resistance and strength, and imparting plastic working (cold forging), and at the same time improving machinability. In order to improve machinability, S (0.05 to 0.15%) is added, but its plastic workability does not reach SUSXM7.
特許文献２、４、５に記載された発明はＰｂ、Ｂｉ、Ｓｅ、Ｔｅといった低融点金属を添加することによって被削性、冷間圧造性を向上させることを特徴としたものである。 The inventions described in Patent Documents 2, 4, and 5 are characterized in that machinability and cold heading are improved by adding a low melting point metal such as Pb, Bi, Se, and Te.
特許文献３に記載された文献は被削性を向上させる元素であるＳｅの添加に加えて、介在物の大きさを規定することにより、被削性、冷間鍛造性を向上させたことを特徴とするものである。 In addition to the addition of Se, which is an element that improves machinability, the document described in Patent Document 3 has improved machinability and cold forgeability by defining the size of inclusions. It is a feature.
特許文献６に記載された発明は耐食性を劣化させることなく被削性を向上させるために、耐食性の低下が少ないとされているＣａを添加し、また硬質な介在物であるＡｌ2Ｏ3の生成を可能な限り抑制し、鋼中の介在物をＣａＯ・ＳｉＯ２とＭｎＯ・ＳｉＯ２の複合体とすることで被削性、冷間加工性を向上させることを特徴とするものである。 In the invention described in Patent Document 6, in order to improve machinability without deteriorating the corrosion resistance, Ca, which is considered to have a small decrease in corrosion resistance, is added, and Al 2 O 3 which is a hard inclusion is added. The production is suppressed as much as possible, and the inclusion in the steel is made of a composite of CaO · SiO 2 and MnO · SiO 2 to improve machinability and cold workability.
特許文献７に記載された発明は高Ｓ含有材にてＣａ、Ｚｒを添加することによる硫化物の形態を制御（粒状化）し、熱間加工性等を向上させることを特徴とするものである。 The invention described in Patent Document 7 is characterized in that the form of sulfide is controlled (granulated) by adding Ca and Zr with a high S content material, and hot workability is improved. is there.
特許文献８に記載された発明は硫化物が発銹や孔食の起点となり耐食性を悪化させることから、これらの硫化物を用いないで、被削性改善に有効なアノーサイト（ＣａＯ・Ａｌ２Ｏ３・２ＳｉＯ２）系の酸化物を生成させ被削性を改善し、また多量のＺｒなどを添加することにより炭化物を生成し、耐食性を改善したことを特徴とするものである。 In the invention described in Patent Document 8, since sulfides are the starting point of rusting and pitting corrosion and deteriorate corrosion resistance, anorsite (CaO · Al 2) effective for improving machinability without using these sulfides. It is characterized by improving the corrosion resistance by generating an O 3 .2SiO 2 ) -based oxide to improve machinability and adding a large amount of Zr or the like to generate carbides.
しかしながら、これまで、被削性と冷間鍛造性の両特性をバランスよく付与した環境にやさしいオーステナイト系ステンレス鋼は提案されていない。
本発明の目的は、環境に悪影響を与える重金属（Ｐｂ、Ｂｉ、Ｓｅ、Ｔｅ）を使用しないで、冷間鍛造性と被削性を併せ持つオーステナイト系ステンレス快削鋼を提供することで、これまで切削加工のみで行われてきた部品加工の歩留を向上させることにある。 The object of the present invention is to provide an austenitic stainless free-cutting steel having both cold forgeability and machinability without using heavy metals (Pb, Bi, Se, Te) that adversely affect the environment. The purpose is to improve the yield of parts processing that has been performed only by cutting.
本発明は前記課題を解決するためになされたもので、種々検討した結果、冷間鍛造性に優れるＳＵＳＸＭ７（１７％Ｃｒ−９％Ｎｉ−３％Ｃｕ−低Ｃ、Ｎ系）を基本成分として、微量Ｓと極微量のＡｌ、Ｚｒ、Ｃａの複合添加量を制御することで、硫化物系を中心とした介在物を著しく微細分散化でき、かつ引張強さを５２０ＭＰａ以下に軟質化することで、冷間鍛造性と被削性の両特性をバランスよく付与することを見出した。 The present invention has been made to solve the above-mentioned problems. As a result of various studies, SUSXM7 (17% Cr-9% Ni-3% Cu-low C, N-based) having excellent cold forgeability is a basic component. By controlling the combined amount of trace S and trace amounts of Al, Zr, and Ca, inclusions centering on sulfides can be remarkably finely dispersed, and the tensile strength can be softened to 520 MPa or less. Thus, it has been found that both cold forgeability and machinability are imparted in a well-balanced manner.
すなわち、本発明の要旨とするところは以下の通りである。
（１）質量％で、Ｃ≦０．０３％、Ｓｉ：０．１〜２．０％、Ｍｎ０．１〜３．０％、Ｐ≦０．０５％、Ｓ：０．０１〜０．０４％、Ｎｉ：８．０〜１２．０％、Ｃｒ：１７．０〜２０．０％、Ｃｕ：１．０〜４．０％、Ｎ≦０．０３％、Ａｌ：０．００２〜０．０１％、Ｃａ：０．００１〜０．０１％、Ｚｒ：０．０００１〜０．０１％を含有し残部Ｆｅおよび不可避的不純物からなる鋼であって、冷間鍛造性と被削性に優れたオーステナイト系ステンレス快削鋼。
（２）さらに、質量％で、Ｂ≦０．０１％を含有することを特徴とする（１）に記載の冷間鍛造性と被削性に優れたオーステナイト系ステンレス快削鋼。
（３）さらに、質量％で、質量％でＭｏ≦３．０％を含有することを特徴とする（１）または（２）に記載の冷間鍛造性と被削性に優れたオーステナイト系ステンレス快削鋼。
（４）前記鋼の引張強度（ＴＳ）が５２０ＭＰａ以下であることを特徴とする（１）乃至（３）のいずれか一項に記載の冷間鍛造性と被削性に優れたオーステナイト系ステンレス快削鋼。
That is, the gist of the present invention is as follows.
(1) By mass%, C ≦ 0.03%, Si: 0.1-2.0%, Mn 0.1-3.0%, P ≦ 0.05%, S: 0.01-0.04 %, Ni: 8.0-12.0%, Cr: 17.0-20.0%, Cu: 1.0-4.0%, N ≦ 0.03%, Al: 0.002-0. 01%, Ca: 0.001-0.01%, Zr: 0.0001-0.01% steel with balance Fe and inevitable impurities, excellent in cold forgeability and machinability Austenitic stainless free-cutting steel.
(2) The austenitic stainless free-cutting steel excellent in cold forgeability and machinability according to (1), further comprising B ≦ 0.01% by mass.
(3) Further, the austenitic stainless steel having excellent cold forgeability and machinability according to (1) or (2), characterized by containing, by mass%, Mo ≦ 3.0% by mass%. Free-cutting steel.
(4) The austenitic stainless steel excellent in cold forgeability and machinability according to any one of (1) to (3), wherein the steel has a tensile strength (TS) of 520 MPa or less. Free-cutting steel.
本発明による冷間鍛造性と被削性を併せ持つオーステナイト系ステンレス快削鋼は冷間鍛造性と切削加工で効率よく部品加工が可能となり、部品加工の低コスト化の効果を発揮する。 The austenitic stainless free-cutting steel having both cold forgeability and machinability according to the present invention can efficiently process parts by cold forgeability and cutting, and exhibits an effect of reducing the cost of parts processing.
以下に、先ず、本発明の請求項１記載の限定理由について説明する。
＜Ｃ：０．０３％以下＞
Ｃはオーステナイト安定化元素であるが多量に含有させると耐食性、冷間鍛造性、耐工具磨耗性が劣化するため上限を０．０３％とした。また、Ｃは鋼の強度を確保するために０.００３％以上は必要である。好ましくは０．００５〜０．０１５％である。
＜Ｓｉ：０．１〜２．０％＞
Ｓｉは脱酸剤として作用し、耐酸化性を向上させるにも有効な元素であるので０．１％以上含有させるが、必要以上の含有は冷間鍛造性、耐工具磨耗性を劣化させるため２．０％を上限とした。好ましくは０．１〜０．４％である。
＜Ｍｎ：０．１〜３．０％＞
本発明ではＭｎはＭｎＳとして被削性を向上させる効果があるため。０．１％以上含有させるが、過剰な含有は耐食性や靭性を低下させるためその上限を３．０％とした。好ましくは１．０〜２．５％である。
＜Ｐ：０．０５％以下＞
Ｐは含有量が多いと熱間加工性を低下させるため０．０５％を上限とした。好ましくは０．０４％以下である。
＜Ｓ：０．０１〜０．０４％＞
Ｓは被削性を改善する元素であるため０．０１％以上含有させるが、大量に含有させると硫化物を中心とした介在物が粗大化し、冷間鍛造性が劣化する。そのため微量Ａｌ、Ｚｒ、Ｃａを添加（制御）して、被削性と冷間鍛造性を兼備させるためには０．０１〜０．０４％の範囲とした。好ましくは０．０２〜０．０４％である。
Below, the reason for limitation of Claim 1 of this invention is demonstrated first.
<C: 0.03% or less>
C is an austenite stabilizing element, but if contained in a large amount, the corrosion resistance, cold forgeability, and tool wear resistance deteriorate, so the upper limit was made 0.03%. Further, C is required to be 0.003% or more in order to ensure the strength of the steel. Preferably it is 0.005 to 0.015%.
<Si: 0.1 to 2.0%>
Si acts as a deoxidizer and is an effective element for improving oxidation resistance. Therefore, Si is contained in an amount of 0.1% or more. However, excessive inclusion deteriorates cold forgeability and tool wear resistance. The upper limit was 2.0%. Preferably it is 0.1 to 0.4%.
<Mn: 0.1 to 3.0%>
In the present invention, Mn has the effect of improving machinability as MnS. Although the content is 0.1% or more, an excessive content lowers the corrosion resistance and toughness, so the upper limit was made 3.0%. Preferably it is 1.0 to 2.5%.
<P: 0.05% or less>
When P content is large, the hot workability is lowered, so 0.05% was made the upper limit. Preferably it is 0.04% or less.
<S: 0.01-0.04%>
Since S is an element that improves machinability, it is contained in an amount of 0.01% or more. However, if it is contained in a large amount, inclusions centering on sulfides become coarse and cold forgeability deteriorates. Therefore, in order to add (control) trace amounts of Al, Zr, and Ca to combine both machinability and cold forgeability, the range is set to 0.01 to 0.04%. Preferably it is 0.02 to 0.04%.
図１に引張強度を約480〜510MPaとした材料の限界据込率に及ぼすＳ量の影響を示す。限界据込率の測定方法は実施例の項で述べる。一般に限界据込率が８０％以上あればヘッダー加工など冷間鍛造において良好な作業性・生産性を示すことが知られている。図１から被削性を向上させる元素であるＳ量の増加によって冷間鍛造性が低下していることが分かる。また、０．０３％のＳ量の鋼にＺｒ、Ｃａ添加すると約８０％の限界据込率を示した。しかし、０．１５％のＳを含有した鋼ではＺｒ、Ｃａ添加による限界据込率の上昇は確認できなかった。この試験結果より、冷間鍛造性を高く保つためにはＳ量を制限する必要がある。従ってＳの上限を０．０４％とした。
＜Ｎｉ：８．０〜１２．０％＞
Ｎｉは耐食性を向上させるとともに、冷間加工性を改善させる元素である。そのため下限を８．０％とした。また、Ｎｉは高価な元素であるためにその上限を１２．０％とした。好ましくは９．０〜１１．０％である。
＜Ｃr：１７．０〜２０．０％＞
Ｃｒは耐食性向上に有効な元素である。１７．０％以下では耐食性が悪くなり、多いとオーステナイト相が不安定となるため上限を２０．０％とした。好ましくは１７．０〜１９．０％である。
＜Ｃｕ：１．０〜４．０％＞
Ｃｕはオーステナイト安定元素であり、冷間鍛造性を改善させる重要な元素である。そのためには少なくとも１．０％以上の添加が必要であるが、４．０％を超えて含有すると熱間加工性が悪化することから上限を４．０％とした。好ましくは２．０〜４．０％である。
＜Ｎ：０．０３％以下＞
Ｎは固溶作用によって冷間鍛造性を低下させる元素であるため、できる限り低下させることが望ましく、上限を０．０３％とした。しかしながら低Ｎ量化は製造コストを増加させるため０．０１％以上は必要である。好ましくは０．０１〜０．０１５％である。
＜Ａｌ：０．００２〜０．０１％＞
Ａｌは脱酸剤として介在物の微細分散の形態制御に必要な元素であるが、多量に含有すると硬質な粗大非金属介在物として存在するために冷間鍛造性を低下させる。そこで、その範囲を０．００２〜０．０１％とした。好ましくは０．００２〜０．００８％である。
＜Ｃａ：０．００１〜０．０１＞
Ｃａは被削性を改善するのに有効な元素である。また、Ｃａは単体の添加によってもＣa系の酸化物となり、硫化物の析出サイトになることによって比較的微細に分散することに有効である。これらの効果を得るためには少なくとも０．００１％以上の添加が必要である。また図１に示すようにＺｒと複合添加することによって硫化物の微細分散化が向上し、冷間鍛造性向上につながる。また、Ｃａ添加は硫化物の形態制御の役割だけでなく、被削性の向上効果もある。しかし、多量に含有させると、これらの効果が得られなくなることに加え、製造性も低下することから、その上限を０．０１％とした。好ましくは０．００１〜０．００５％である。
＜Zr：０．０００１〜０．０１％＞
Zrは本発明鋼において最も重要な元素である。Ｚｒは酸化物の析出サイトとして働き、硫化物の析出サイトとなる酸化物を微細に分散させることにより硫化物の微細分散化に有効な元素である。またこの硫化物の微細分散化は微量Ｓ含有材にＣａと複合添加することにより効果が著しく向上する。しかし、多量に含有すると介在物として存在し、冷間鍛造性を低下させるため上限を０．０１％とした。好ましくは０．００１〜０．００５％である。
本発明の請求項２記載の限定理由について述べる。
＜B：≦０．０1％＞
Bは熱間加工性や軟質化を改善するために添加される元素であり、０．００２％以上の添加により安定した効果が得られる。しかし過剰に添加するとBの化合物が析出し、熱間加工性を劣化させるので、その上限を０．０１％とした。好ましくは０．００２〜０．００４％である。
FIG. 1 shows the influence of the amount of S on the limit upsetting rate of a material having a tensile strength of about 480 to 510 MPa. The method for measuring the limit upsetting rate will be described in the section of Examples. In general, it is known that if the limit upsetting rate is 80% or more, good workability and productivity are exhibited in cold forging such as header processing. It can be seen from FIG. 1 that the cold forgeability is reduced by increasing the amount of S, which is an element that improves machinability. Moreover, when Zr and Ca were added to 0.03% S steel, a limit upsetting rate of about 80% was exhibited. However, in steel containing 0.15% S, the increase in the limit upsetting rate due to the addition of Zr and Ca could not be confirmed. From this test result, it is necessary to limit the amount of S in order to keep the cold forgeability high. Therefore, the upper limit of S is set to 0.04%.
<Ni: 8.0 to 12.0%>
Ni is an element that improves corrosion resistance and cold workability. Therefore, the lower limit is set to 8.0%. Moreover, since Ni is an expensive element, the upper limit was made 12.0%. Preferably it is 9.0 to 11.0%.
<Cr: 17.0 to 20.0%>
Cr is an element effective for improving corrosion resistance. If it is 17.0% or less, the corrosion resistance deteriorates. If it is too much, the austenite phase becomes unstable, so the upper limit was made 20.0%. Preferably it is 17.0 to 19.0%.
<Cu: 1.0-4.0%>
Cu is an austenite stable element and is an important element for improving cold forgeability. For that purpose, addition of at least 1.0% is necessary, but if the content exceeds 4.0%, the hot workability deteriorates, so the upper limit was made 4.0%. Preferably it is 2.0 to 4.0%.
<N: 0.03% or less>
Since N is an element that lowers the cold forgeability by a solid solution action, it is desirable to reduce it as much as possible, and the upper limit was made 0.03%. However, a reduction in N content increases the manufacturing cost, so 0.01% or more is necessary. Preferably it is 0.01 to 0.015%.
<Al: 0.002-0.01%>
Al is an element necessary for controlling the form of fine dispersion of inclusions as a deoxidizer, but if contained in a large amount, Al exists as hard coarse non-metallic inclusions, so that cold forgeability is lowered. Therefore, the range was made 0.002 to 0.01%. Preferably it is 0.002 to 0.008%.
<Ca: 0.001-0.01>
Ca is an element effective for improving machinability. Further, Ca is effective to form a Ca-based oxide by addition of a simple substance and to disperse relatively finely by forming a sulfide precipitation site. In order to obtain these effects, addition of at least 0.001% is necessary. Further, as shown in FIG. 1, the composite addition of Zr improves the fine dispersion of sulfides, leading to an improvement in cold forgeability. Moreover, addition of Ca has an effect of improving machinability as well as a role of controlling the form of sulfide. However, if contained in a large amount, these effects cannot be obtained, and the manufacturability also decreases. Therefore, the upper limit was made 0.01%. Preferably it is 0.001 to 0.005%.
<Zr: 0.0001 to 0.01%>
Zr is the most important element in the steel of the present invention. Zr acts as an oxide precipitation site and is an element effective for fine dispersion of sulfides by finely dispersing oxides that form sulfide precipitation sites. Further, the effect of the fine dispersion of the sulfide is remarkably improved by adding Ca to the trace S-containing material. However, when it is contained in a large amount, it exists as an inclusion, and the upper limit is made 0.01% in order to reduce the cold forgeability. Preferably it is 0.001 to 0.005%.
The reason for limitation according to claim 2 of the present invention will be described.
<B: ≦ 0.01%>
B is an element added to improve hot workability and softening, and a stable effect can be obtained by adding 0.002% or more. However, if added in excess, the B compound precipitates and degrades hot workability, so the upper limit was made 0.01%. Preferably it is 0.002 to 0.004%.
本発明の請求項３記載の限定理由について述べる。
＜Ｍｏ：≦３．０％＞
ＭｏはＣｒと同様に耐食性を向上させるのに有効な元素であり０．１％以上の添加により安定した効果が得られる。しかし、多量に添加させると熱間加工性が低下するために上限を３．０％とした。好ましくは０．１〜２．５％である。
The reason for limitation according to claim 3 of the present invention will be described.
<Mo: ≦ 3.0%>
Mo is an element effective for improving the corrosion resistance like Cr, and a stable effect can be obtained by addition of 0.1% or more. However, the hot workability is lowered when a large amount is added, so the upper limit was made 3.0%. Preferably it is 0.1 to 2.5%.
本発明の請求項4記載の限定理由について述べる。
＜引張強度≦５２０ＭＰａ＞
図２にＳ量を約０．０３％とした材料の限界据込率に及ぼす引張強度の影響を示す。図２から引張強度（ＴＳ）の上昇によって冷間鍛造性が低下していることが分かる。この試験結果より、冷間鍛造性を高く保つためには引張強度を制限する必要がある。従って引張強度の上限を５２０ＭＰａとした。
The reason for limitation according to claim 4 of the present invention will be described.
<Tensile strength ≦ 520 MPa>
FIG. 2 shows the effect of tensile strength on the limit upsetting rate of a material having an S content of about 0.03%. It can be seen from FIG. 2 that the cold forgeability is lowered due to the increase in tensile strength (TS). From this test result, it is necessary to limit the tensile strength in order to keep the cold forgeability high. Therefore, the upper limit of the tensile strength was set to 520 MPa.
以下に本発明の実施例について説明する。 Examples of the present invention will be described below.
表1、２に本発明の実施例の化学成分と冷間鍛造性、被削性（切屑処理性、耐工具磨耗性）および引張強度の評価結果を示す。 Tables 1 and 2 show the evaluation results of the chemical components, cold forgeability, machinability (chip treatability, tool wear resistance) and tensile strength of the examples of the present invention.
冷間鍛造性は圧縮試験によって得られる限界据込率によって評価した。圧縮試験は直径１１ｍｍの線材から高さ１２ｍｍ、直径８ｍｍの円柱状の試験片を作製して供試材とし、同心円状の溝をもつ拘束型ダイスでの圧縮試験により評価した。試験片の初期の高さをH０、割れが発生した圧縮後の高さをHとし以下の式で求めた値を限界据込率とした。
（1−H／H０）×１００（％）
圧縮試験機によって一定速度で試験片を圧縮し、試験片側面の割れの有無を目視で判定し、限界据込率によって大小で評価した。
本発明鋼は限界据込率が８０％以上であった。
Cold forgeability was evaluated by the limit upsetting rate obtained by the compression test. In the compression test, a cylindrical test piece having a height of 12 mm and a diameter of 8 mm was prepared from a wire material having a diameter of 11 mm and used as a test material. The initial height of the test piece was H 0 , the height after compression at which cracking occurred was H, and the value obtained by the following formula was defined as the limit upsetting rate.
(1−H / H 0 ) × 100 (%)
The test piece was compressed at a constant speed with a compression tester, the presence or absence of cracks on the side of the test piece was visually judged, and the size was evaluated based on the limit upsetting rate.
The steel of the present invention had a limit upsetting rate of 80% or more.
切削試験は直径２２ｍｍに熱間鍛伸した棒鋼を供試材として、超硬工具（Ｐ２０種）を用いて、切削速度（５０〜２００ｍ／ｍｉｎ）、切込み（０．１〜１．０ｍｍ）、送り速度（０．０１〜０．１ｍｍ／ｒｅｖ）で外周切削をおこなった。被削性の評価は切屑処理性、耐工具磨耗性にて評価した。 The cutting test uses a steel bar hot forged to a diameter of 22 mm as a test material, using a carbide tool (P20 type), cutting speed (50 to 200 m / min), cutting (0.1 to 1.0 mm), Peripheral cutting was performed at a feed rate (0.01 to 0.1 mm / rev). The machinability was evaluated based on chip disposal and tool wear resistance.
切屑処理性の評価は短く破損しているものおよび規則的ならせん状のものを○、無規則で長く繋がったものを×とした。これは、短く破損した切屑を排出するものは切削中に表面に疵をつける可能性が低いが、無規則で長く繋がった切屑は表面に疵をつけたり、工具に絡まったりするためである。本発明鋼は短く破損したものと規則的ならせん状の切屑が観察された。 In the evaluation of the chip disposability, the short-damaged and regular spiral-shaped ones were marked with ◯, and the ones that were irregularly connected for a long time were marked with ×. This is because chips that discharge short and broken chips are less likely to wrinkle the surface during cutting, but chips that are irregularly connected for a long time are wrinkled on the surface or entangled with the tool. The steel of the present invention was observed to be short and broken and regular spiral chips.
耐工具磨耗は約4000ｍ切削時の工具を観察して評価した。工具磨耗がないものは○、局所的に大きな工具磨耗が観察されるものを×とした。本発明鋼は一部微量の工具磨耗が観察されるものもあるが、大きな工具磨耗は観察されなかった。 Tool wear resistance was evaluated by observing the tool when cutting about 4000 m. The case where there was no tool wear was rated as ◯, and the case where large tool wear was observed locally was marked as x. Some of the steels of the present invention have a small amount of tool wear observed, but no significant tool wear was observed.
引張強度はＪＩＳ９号Ａ（Ｇ．Ｌ１００ｍｍ）を用いて試験を行い、引張強度を測定した。本発明鋼の引張強度は５２０ＭＰａ以下であった。 The tensile strength was tested using JIS No. 9A (G.L100 mm), and the tensile strength was measured. The tensile strength of the steel of the present invention was 520 MPa or less.
一方、比較例Ｎｏ．１４〜３０は本発明に比べ、冷間鍛造性、被削性（切屑処理性、耐工具磨耗性）、引張強度のいずれかが劣っていた。 On the other hand, Comparative Example No. 14 to 30 were inferior in cold forgeability, machinability (chip disposability, tool wear resistance), or tensile strength as compared with the present invention.
以上の実施例から分かるように本発明例に優位性は明らかである。 As can be seen from the above embodiments, the advantages of the present invention are obvious.
以上の実施例から明らかなように、本発明により冷間鍛造性と被削性に優れたオーステナイト系ステンレス鋼の提供が可能であり、これまで切削加工のみで複雑な形状を製造していた部品を冷間鍛造と切削加工によって、材料歩留まり、生産性よく製造する上で極めて有用である。 As is clear from the above examples, the present invention can provide austenitic stainless steel excellent in cold forgeability and machinability by the present invention, and has so far produced a complicated shape only by cutting. Is extremely useful for producing materials with high yield and productivity by cold forging and cutting.
Claims (4)
Ｃ≦０．０３％、
Ｓｉ：０．１〜２．０％、
Ｍｎ０．１〜３．０％、
Ｐ≦０．０５％、
Ｓ：０．０１〜０．０４％、
Ｎｉ：８．０〜１２．０％、
Ｃｒ：１７．０〜２０．０％、
Ｃｕ：１．０〜４．０％、
Ｎ≦０．０３％、
Ａｌ：０．００２〜０．０１％、
Ｃａ：０．００１〜０．０１％、
Ｚｒ：０．０００１〜０．０１％を含有し残部Ｆｅおよび不可避的不純物からなる鋼であって、冷間鍛造性と被削性に優れたオーステナイト系ステンレス快削鋼。 % By mass
C ≦ 0.03%,
Si: 0.1 to 2.0%,
Mn 0.1-3.0%,
P ≦ 0.05%,
S: 0.01-0.04%,
Ni: 8.0 to 12.0%,
Cr: 17.0 to 20.0%,
Cu: 1.0-4.0%,
N ≦ 0.03%,
Al: 0.002 to 0.01%
Ca: 0.001 to 0.01%,
An austenitic stainless free-cutting steel that contains Zr: 0.0001 to 0.01% and consists of the remainder Fe and inevitable impurities, and is excellent in cold forgeability and machinability.
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