【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
本発明はオーステナイト系ステンレス鋼に係り、より詳
細には、特定の含有成分を規制することにより優れた熱
間加工性を付与せしめた新規なオーステナイト系ステン
レス鋼に関する。
（従来の技術及びその問題点）
周知のとうり、Ｎｉ及びＣｒを必須の主要添加成分とし
て含み、他にＭＯ１Ｃｕ等々の任意添加成分を含むオー
ステナイト系ステンレス鋼は、反応容器などの各種構造
材からシャフト、ネジ等の部品材に至るまで、様々な用
途の材料として使用されている。
このように多種多様の用途に供されるオーステナイト系
ステンレス鋼は、通常、溶製後にインテ ・ット或い
は鋳片となし、熱間圧延を経て、冷間圧延、引抜き等々
の２次加工により帯、板、棒線材などの形状で製品仕上
げ加工に供されている。
しかし、オーステナイト系ステンレス鋼は一般に加工性
が良好でなく、これらの製造工程でも、熱間圧延工程で
は、インゴット或いは鋳片の分塊圧延乃至粗圧延前に疵
取り工程をおき、以降工程における表面欠陥の発生防止
を図ると共に、以降の工程においても疵等が発生しない
よう細心の注意が払われている。
例えば、オーステナイト系ステンレス鋼の代表的鋼種で
ある５ＵＳ３０１．３０２は、 １７〜１９％Ｃｒ−８
〜１０％Ｎｉの所謂１８−８系ステンレス鋼として知ら
れており、これを材料とする場合には、インゴット乃至
鋳片の疵取り後、加熱し、粗圧延、仕上げ圧延を行い、
２次加工が行われるが、この圧延段階においてコーナー
割れ、ヘゲ疵等々の表面欠陥が往々にして発生する。そ
のため、余分の手入れを必要とし、材料の歩留まり低下
の問題があった。
この問題は、特にＮｉを高レベルで含む５ＵＳ３１０（
Ｎｉ：２４〜２６％（重量割合、以下同じ）などの高Ｎ
ｕオーステナイト系ステンレス鋼や。
シャフト、ネジなどの切削加工を受ける部品用として１
８−８系ステンレス鋼にＳを添加して快削性の向上を図
った鋼種５ＵＳ３０３において著しく、例えば、後者の
ような快削Ｎｉ系ステンレス鋼線材の熱間圧延では、粗
圧延時にコナー割れが発生し、圧延線材にヘゲ疵などの
外観疵が生じ、皮削り工程を追加することが余儀なくさ
れている。
このように、オーステナイト系ステンレス鋼は、熱間圧
延前に疵取りを行っても、熱間圧延工程、特に粗圧延で
表面欠陥が生じ、更には以降の圧延工程でも外観疵が発
生する等、熱間加工性に劣る欠点があった。
（発明の目的）
本発明は、前述の従来のオーステナイト系ステンレス鋼
が加工性の点で問題が多く、特に熱間加工性が良好でな
いことに鑑み、その成分組成を厳格に規制することによ
って熱間加工性を大幅に改善し、以って各種用途に供さ
れる素材を歩留まりよく、かつ能率的に熱間加工を実現
でき、２次加工においても表面性状の良好な製品を製造
できる新規なオーステナイト系ステンレス鋼を提供する
ことを目的とするものである。
（発明の構成）
かへる目的達成のため、本発明に係るオーステナイト系
ステンレス鋼は、その含有成分のうち。
ＳｉとＮの量を次の関係式（第４図参照）Ｓｉ％≦−１
，４５ＸＮ％＋０．４４
を満足させるように規制するものである。
以下に本発明の詳細な説明する。
まず、前述のオーステナイト系ステンレス鋼の３１錆種
のうち、熱間加工性が特に問題となっている鋼種５ＵＳ
３０３は、線材圧延後の外観疵のために皮削り工程を追
加する率が高いので、疵発生の原因究明のため基礎実験
を行った。５ＵＳ３０３は第１表に示す化学成分を有し
ており、１８−８系ステンレス鋼にＳを０．１５％以上
添加して快削性を向上させ、主として自動盤で切削加工
されるネジ、シャフト等の部品に供される快削Ｎｉ系ス
テンレス鋼であり、快削成分Ｓを多量に含むために熱間
加工性に悪影響を及ぼすものと考えられていた。
第１表５ＵＳ３０３の化学成分（ｖｔ％）実験は、上記
化学成分を有する５ＵＳ３０３を溶製後、連続鋳造鋳片
となし、疵取り工程で鋳片の全面研削を実施して疵皆無
の鋳片を粗圧延に供し、粗圧延後に外観検査を行い、コ
ーナー割れの有無を調べた０次いで仕上げ圧延を行った
後、外観疵の有無を調べた。その結果、線材圧延後の外
観疵は、圧倒的にヘゲ疵が多く、全体の約９２％を占め
ており、しかもこのヘゲ疵は鋳片コーナー相当部にのみ
発生していることが判明した（第３図参照）。
そこで、粗圧延時にコーナー相当部に割れが発生したも
のについて仕上げ圧延を行った圧延線材を調べたところ
、１００％の割合でヘゲ疵が発生しており、これらの事
実よりヘゲ疵は粗圧延時に発生するコーナー割れがその
後の鍛錬により形態変化したものであることが明らかと
なった。このため、粗圧延時のコーナー割れ発生防止策
として圧延条件を変化させて改善を試みたが、効果は得
られなかった。
次いで、コーナー割れと化学成分との関係を明らかにす
べく全化学成分（添加元素、不純物元素）の含有量を変
化させて熱間加工性を調査した。なお、熱間加工性はグ
リ−プルテスト（熱間引張試験）を行い、絞り（％）に
て評価した。また、化学成分のうち、Ｃは引張り強さを
確保する元素であるが高目にすると炭化物析出が起こり
耐食性が低下し、ＭｎはＭｎ／Ｓの関係から高目にする
必要があり、Ｐはスクラップから混入する不純物でコン
トロールが困難であるため、これらの３成分は調査対象
から除外した。
調査結果は、第１図に示すように、Ｓｉが熱間加工性に
最も影響を及ぼしており、ＳＬ含有量を低目に規制する
ことが極めて効果的である（同図中、傾斜度合が急峻）
。次いでＮ、Ｓが影響を及ぼしており、Ｎ、Ｓも低目の
方がよいことが判明した。なお、Ｓはこの種の鋼種では
快削成分として添加しているため、コーナー割れ防止の
ためのみで余り低目にすることはできない。
更に、上記の快削Ｎｉ系ステンレス鋼についての基礎実
験の結果を踏まえて、Ｓ含有量が０．０３０％以下の他
の１８−８系ステンレス鋼の他。
Ｐｂ、Ｓｅ等の他の快削成分を添加したオーステナイト
系ステンレス鋼や、高Ｎｉ含有のオーステナイト系ステ
ンレス鋼などの鋼種についても実験を行い、またインゴ
ットの熱間圧延による場合についても調査したところ、
いずれも同様の傾向が見られた。
以上の諸知見に基づき、本発明に係るオーステナイト系
ステンレス鋼の特徴とするところは、含有成分のうち、
ＳｉとＮの含有量を
Ｓｉ％≦−１，，４’５ＸＮ％＋０．４４の関係式を満
足する範囲に規制したものである。
なお、オーステナイト系ステンレス鋼に含まれる他の添
加成分（必須元素、任意添加元素）並びに不純物元素の
含有量は、オーステナイト系としての通常の範囲でよく
、特に更に制限しなくとも本発明により熱間加工性の大
幅な改善が得られる。
したがって、各種適用鋼種の化学成分を考慮のうえ、Ｓ
ｉ及びＮ以外の成分の可能な含有量を例示するならば、
次のとうりである。
Ｃは強度を確保するために必要とする元素であり、しか
し多量に含むと炭化物析出により耐食性が低下するので
、０．１５％以下にするのが好ましい。
Ｍｎは特別な鋼種（ＳＵＳ２０１．２０２など）を除き
、通常は２．５０％以下にしてオーステナイト組織の安
定性等を確保するが、５ＵＳ３０３の如く快削性向上を
期する等の場合には高目にする方が熱間加工性の面で好
ましい。
Ｎｉ及びＣｒは必須の添加成分であり、安定したオース
テナイト組織を得て、優れた耐食性、機械的性質などを
確保すべく最大添加範囲はＮｉ：３．５〜２２．０％、
Ｃｒ：１６〜２６％である。
不純物元素であるＰは、製鋼工程でスクラップより必然
的に混入するが、可能な限り少ない方がよく、０．２０
％以下、通常は０．０４５％以下にする。
任意添加元素としては、Ｍｏ、 Ｃｕ、 Ｔｉ、 Ｎｂ
、Ｐｂ等々を適当量を添加することができる。
なお、ＳｉとＮについての前記関係式を満足する範囲内
においても更にＳｉ Ｏ，３５％未満、ＮＯ，１０％未
満においては、特に優れた熱間加工性を示すものである
。
（実施例）
第２表に示す化学成分を有するオーステナイト系ステン
レス鋼の３ｇＲ種について、溶製後、インゴット及び連
続鋳造法により鋳片を得、各々に疵取りを行った後、加
熱して粗圧延、仕上げ圧延の熱間圧延（加熱温度約１２
７０〜１３２０’Ｃ）を行い、圧延材についてグリ−プ
ルテストを実施した。
その結果を第２表に併記する。(Industrial Application Field) The present invention relates to austenitic stainless steel, and more particularly to a novel austenitic stainless steel that has excellent hot workability by regulating specific components. (Prior art and its problems) As is well known, austenitic stainless steel, which contains Ni and Cr as essential main additive components and also contains optional additive components such as MO1Cu, can be used for various structural materials such as reaction vessels. It is used as a material for a variety of purposes, including parts such as shafts and screws. Austenitic stainless steel, which is used for a wide variety of purposes, is usually made into ingots or slabs after melting, hot rolling, and then into strips through secondary processing such as cold rolling and drawing. It is used for product finishing in shapes such as plates, rods, and wire rods. However, austenitic stainless steel generally does not have good workability, and even in these manufacturing processes, a flaw removal process is performed in the hot rolling process before the ingot or slab is bloomed or rough rolled, and the surface in subsequent processes is In addition to preventing the occurrence of defects, great care is taken to prevent scratches and the like from occurring in subsequent steps as well. For example, 5US301.302, a typical austenitic stainless steel, has 17-19% Cr-8
It is known as the so-called 18-8 stainless steel with ~10% Ni, and when using this as a material, after removing defects from the ingot or slab, it is heated, rough rolled, and finished rolled.
Secondary processing is performed, but surface defects such as corner cracks and scabs often occur during this rolling stage. Therefore, extra care was required and there was a problem of a decrease in material yield. This problem is especially true for 5US310 (5US310), which contains high levels of Ni.
Ni: High N such as 24-26% (weight percentage, same below)
uAustenitic stainless steel. 1 for parts that undergo cutting processing such as shafts and screws
In steel type 5US303, which is made by adding S to 8-8 stainless steel to improve its free machinability, for example, during hot rolling of free-cutting Ni-based stainless steel wire rods such as the latter, conner cracking occurs during rough rolling. This causes appearance defects such as sludge marks on the rolled wire rod, making it necessary to add a peeling process. In this way, even if austenitic stainless steel is removed from defects before hot rolling, surface defects occur during the hot rolling process, especially during rough rolling, and furthermore, appearance defects occur during subsequent rolling processes. It had the disadvantage of poor hot workability. (Objective of the Invention) In view of the fact that the conventional austenitic stainless steel mentioned above has many problems in terms of workability, and in particular does not have good hot workability, the present invention aims to improve heat workability by strictly regulating its component composition. A new product that significantly improves machining properties and enables efficient hot working of materials used in various applications with high yields, as well as the ability to produce products with good surface quality even during secondary processing. The purpose is to provide an austenitic stainless steel. (Structure of the Invention) In order to achieve the purpose of improving energy saving, the austenitic stainless steel according to the present invention includes: The amounts of Si and N are determined by the following relational expression (see Figure 4): Si%≦-1
, 45XN% + 0.44. The present invention will be explained in detail below. First, among the 31 rust types of austenitic stainless steel mentioned above, 5 US steel types have particularly problematic hot workability.
Since No. 303 has a high rate of additional skin scraping process due to appearance defects after wire rolling, basic experiments were conducted to investigate the cause of the occurrence of defects. 5US303 has the chemical composition shown in Table 1, and is made by adding 0.15% or more of S to 18-8 stainless steel to improve free machinability, and is mainly used for screws and shafts that are machined with automatic lathes. It is a free-cutting Ni-based stainless steel that is used for parts such as, and was thought to have a negative effect on hot workability because it contains a large amount of free-cutting component S. Chemical composition (vt%) of 5US303 in Table 1 In the experiment, 5US303 having the above chemical composition was melted and made into a continuously cast slab, and the slab was completely ground in the flaw removal process to produce a slab with no defects. The material was subjected to rough rolling, and after the rough rolling, an external appearance was inspected to check for the presence of corner cracks.Then, after finish rolling, the presence or absence of external defects was examined. As a result, it was found that the overwhelming majority of the appearance defects after wire rolling were sludge defects, accounting for approximately 92% of the total, and that these sludge defects only occurred in the areas corresponding to the corners of the slab. (See Figure 3). Therefore, when we examined rolled wire rods that had undergone finish rolling with cracks occurring at the corners during rough rolling, we found that sludge defects occurred in 100% of the cases, and these facts indicate that sludge defects are caused by rough rolling. It has become clear that the corner cracks that occur during rolling have changed shape due to subsequent forging. Therefore, an attempt was made to improve the rolling conditions by changing the rolling conditions as a measure to prevent the occurrence of corner cracks during rough rolling, but no results were obtained. Next, in order to clarify the relationship between corner cracking and chemical components, hot workability was investigated by varying the content of all chemical components (additional elements, impurity elements). Note that hot workability was evaluated by performing a grieple test (hot tensile test) and evaluating the area of area (%). In addition, among the chemical components, C is an element that ensures tensile strength, but if it is set too high, carbide precipitation occurs and corrosion resistance decreases, Mn needs to be set high because of the Mn/S relationship, and P is an element that ensures tensile strength. These three components were excluded from the survey because they are impurities mixed in from scrap and difficult to control. As shown in Figure 1, the survey results show that Si has the greatest effect on hot workability, and that regulating the SL content to a low level is extremely effective (in the figure, the degree of slope is steep)
. Next, N and S have an influence, and it was found that lower N and S are also better. Note that since S is added as a free-cutting component in this type of steel, it is only used to prevent corner cracks and cannot be made too low. Furthermore, based on the results of the basic experiments on the above-mentioned free-cutting Ni-based stainless steels, other 18-8-based stainless steels with an S content of 0.030% or less. Experiments were also conducted on steel types such as austenitic stainless steel to which other free-cutting components such as Pb and Se were added, and austenitic stainless steel with high Ni content, and the case of hot rolling of ingots was also investigated.
Similar trends were observed in both cases. Based on the above findings, the austenitic stainless steel according to the present invention is characterized by:
The contents of Si and N are regulated within a range that satisfies the relational expression: Si%≦-1, 4'5XN%+0.44. The contents of other additive components (essential elements, optionally added elements) and impurity elements contained in the austenitic stainless steel may be within the normal range for the austenitic stainless steel, and the present invention does not require any further restrictions on the content of other additive components (essential elements, optional addition elements) and impurity elements. Significant improvement in workability can be obtained. Therefore, after considering the chemical composition of various applicable steel types, S
To illustrate possible contents of components other than i and N,
The following is true. C is an element required to ensure strength, but if it is included in a large amount, corrosion resistance will be reduced due to carbide precipitation, so it is preferably kept at 0.15% or less. Except for special steel types (such as SUS201.202), Mn is normally kept at 2.50% or less to ensure the stability of the austenite structure, but in cases such as 5US303 where free machinability is to be improved, it is increased. It is preferable to see it from the viewpoint of hot workability. Ni and Cr are essential additive components, and in order to obtain a stable austenite structure and ensure excellent corrosion resistance and mechanical properties, the maximum addition range is Ni: 3.5 to 22.0%.
Cr: 16-26%. P, which is an impurity element, is inevitably mixed in from scrap during the steelmaking process, but it is better to have as little as possible, and 0.20
% or less, usually 0.045% or less. Optional addition elements include Mo, Cu, Ti, and Nb.
, Pb, etc. can be added in appropriate amounts. Note that even within the range that satisfies the above relational expressions for Si and N, particularly excellent hot workability is exhibited when SiO is less than 35% and NO is less than 10%. (Example) For the 3gR type of austenitic stainless steel having the chemical composition shown in Table 2, after melting, slabs were obtained by ingot and continuous casting methods, and after removing defects, they were heated and roughened. Hot rolling for rolling and finish rolling (heating temperature approx. 12
70 to 1320'C), and a Greeple test was conducted on the rolled material. The results are also listed in Table 2.
【以下余白】[Left below]
同表より明らかなように、従来のようにＳｉ及びＮの含
有量が高目の比較鋼＆７〜９はいずれもグリ−プル絞り
（％）が極めて低く、熱間加工性が不良で、粗圧延後に
手入れ作業が必要とすることを示し、そのまＮ圧延を行
った場合にはヘゲ疵等の外観疵が全圧延材に発生した。
これに対し、Ｓｉ、Ｎを規制した本発明ｌｌＮα１〜６
は、グリ−プル絞り（％）が５０以上で良好な熱間加工
性を示し、この中でも更にＳｉ及びＮの双方を低く規制
した本発明鋼虱１，３．５は、いずれの鋼種でも一層熱
間加工性が改善されている（第４図参照）。このように
本発明鋼は熱間加工性が大幅に改善されたので、粗圧延
後の手入れ作業が不要となり、圧延材でのヘゲ疵などの
外観疵が発生しなかった（第２図参照）。
なお、本発明鋼の場合、インゴット鋳造よりも連続鋳造
による方がより熱間加工性が良好であることが判明した
。
（発明の効果）
以上詳述したように１本発明によれば、各種のオーステ
ナイト系ステンレス鋼でＳｉ或いはＳｉ及びＮの含有量
を規制することにより、熱間加工性を大幅に改善するこ
とができ、従来熱間圧延で実施を余儀なくされていた疵
取り作業の追加を省略でき、しかも圧延材の外観疵の発
生も実質皆無にでき、材料歩留まりの向上、コストダウ
ンに寄与するところが大である。As is clear from the table, comparative steels &7 to 9, which have high Si and N contents, have extremely low greasy area of area (%), poor hot workability, and roughness. This indicates that maintenance work is required after rolling, and when N rolling was performed as it was, appearance defects such as sludge defects occurred in all rolled materials. On the other hand, the present invention in which Si and N are regulated
shows good hot workability with a Grieple reduction (%) of 50 or more, and among these, steels of the present invention No. 1 and 3.5, in which both Si and N are regulated low, have even better hot workability than any other steel type. Hot workability is improved (see Figure 4). As described above, the hot workability of the steel of the present invention was greatly improved, so there was no need for maintenance work after rough rolling, and appearance defects such as sludge marks did not occur in the rolled material (see Figure 2). ). In the case of the steel of the present invention, it has been found that continuous casting has better hot workability than ingot casting. (Effects of the Invention) As detailed above, according to the present invention, hot workability can be significantly improved by regulating the content of Si or Si and N in various austenitic stainless steels. This makes it possible to omit the additional work of removing defects, which was traditionally required in hot rolling, and virtually eliminates appearance defects on rolled materials, which greatly contributes to improving material yield and reducing costs. .
【図面の簡単な説明】[Brief explanation of drawings]
第１図はオーステナイト系ステンレス鋼における化学成
分とグリ−プル絞り（％）との関係を示す図。
第２図及び第３図は圧延材の外観検査の結果を示す拡大
組織写真で、第２図は本発明鋼の場合。
第３図は従来鋼の場合を示し、
第４図はＳｉ、Ｎの含有量と熱間加工性に関する実験結
果を示す図である。
特許出願人 大同特殊鋼株式会社
代理人弁通土 中 村 尚
第１図
グ
（ＮＪ ＣＣｕ］（５１ｒａｉｌ （Ｓｉ
ｌ ＥＣｐｌ ［Ｍｏ１）へｉ 分 （ｗ
ｔ％ン
第 ２ 口
算 ３ 国FIG. 1 is a diagram showing the relationship between chemical components and Greeple area (%) in austenitic stainless steel. Figures 2 and 3 are enlarged microstructure photographs showing the results of appearance inspection of rolled materials, and Figure 2 is for the steel of the present invention. FIG. 3 shows the case of conventional steel, and FIG. 4 shows experimental results regarding Si and N contents and hot workability. Patent Applicant: Daido Steel Co., Ltd. Agent: Hisashi Nakamura (NJ CCu) (51rail (Si)
l ECpl [Mo1) i minutes (w
t%n 2nd account 3 countries