JP5406686B2 - Non-magnetic steel - Google Patents

Non-magnetic steel Download PDF

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JP5406686B2
JP5406686B2 JP2009271806A JP2009271806A JP5406686B2 JP 5406686 B2 JP5406686 B2 JP 5406686B2 JP 2009271806 A JP2009271806 A JP 2009271806A JP 2009271806 A JP2009271806 A JP 2009271806A JP 5406686 B2 JP5406686 B2 JP 5406686B2
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政道 千葉
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Kobe Steel Ltd
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Description

本発明は、強磁界に晒されるリニアモーターカーや発電・送電設備の構造部材、微弱磁界が問題となる医療設備の構造部材、または電磁制御部品の非磁性部を構成する材料等に関するものである。   The present invention relates to a structural member of a linear motor car or power generation / transmission facility exposed to a strong magnetic field, a structural member of a medical facility in which a weak magnetic field is a problem, or a material constituting a nonmagnetic part of an electromagnetic control component. .

磁界環境に晒される構造部材などにおいて、設備本体の性能への悪影響が許されないものには、通常、外部磁界によって磁化を有さない非磁性材料が用いられる。   For structural members that are exposed to a magnetic field environment, a non-magnetic material that is not magnetized by an external magnetic field is generally used for those that do not allow adverse effects on the performance of the equipment body.

代表的な非磁性材料としては、従来からSUS304やSUS316等のオーステナイト系ステンレスが知られている。しかし、オーステナイト系ステンレスはNiやCrといった希少金属を多く含有するため部材の製造コスト増加を招くという問題がある。さらに、加工歪みが付与されるとオーステナイト組織が誘起マルテンサイト組織に変態して磁性を示すため、加工歪みの増加に伴って透磁率が増加し、非磁性材料としての特性が低下するという問題もあった。   As a typical nonmagnetic material, austenitic stainless steel such as SUS304 and SUS316 has been conventionally known. However, since austenitic stainless steel contains a large amount of rare metals such as Ni and Cr, there is a problem that the manufacturing cost of the member is increased. In addition, when processing strain is applied, the austenite structure transforms into an induced martensite structure and exhibits magnetism, so that the magnetic permeability increases with an increase in processing strain and the characteristics as a nonmagnetic material deteriorate. there were.

一方、オーステナイト系ステンレス以外の非磁性材料として、従来からオーステナイト組織を安定化させるC、Mnを増量した高Mn非磁性鋼が開発されてきたが、近年要求されている高強度化には十分に対応できておらず、未だ改善の余地があった。そこで、高Mn非磁性鋼の高強度化技術として、例えば特許文献1には、Mo、Nb、Vなどの合金元素を添加したものが開示されている。しかし、いずれも非磁性材料としての特性が不十分であった。   On the other hand, as a nonmagnetic material other than austenitic stainless steel, a high Mn nonmagnetic steel with an increased amount of C and Mn that stabilizes the austenite structure has been developed. However, it is sufficient for increasing the strength required in recent years. There was no room for improvement. Therefore, as a technique for increasing the strength of high-Mn nonmagnetic steel, for example, Patent Document 1 discloses a technique in which an alloy element such as Mo, Nb, or V is added. However, all of them have insufficient characteristics as nonmagnetic materials.

特開昭62−202023号公報Japanese Unexamined Patent Publication No. 62-202023

本発明は上記事情に鑑みてなされたものであり、その目的は圧延材および加工歪み付与後における非磁性特性に優れた非磁性鋼を提供することにある。   This invention is made | formed in view of the said situation, The objective is to provide the nonmagnetic steel excellent in the nonmagnetic characteristic after rolling material and processing distortion provision.

上記課題を解決した本発明の非磁性鋼は、C:0.5〜0.8%(質量%の意味。以下、同じ。)、Si:0.5〜1.0%、Mn:8〜14.6%、P:0.030%以下(0%を含まない)、S:0.030%以下(0%を含まない)、Cu:0.1%以下(0%を含まない)、Ni:0.1%以下(0%を含まない)、Cr:1.8〜3.0%、Al:0.005〜0.1%、N:0.004〜0.1%を含有し、下記式(1)〜(3)を満たすとともに、残部が鉄および不可避不純物であり、ミクロ組織がオーステナイト組織であり、透磁率が1.030以下であることを特徴とする。
[Mn]+34×[C]≦40 ・・・(1)
FB≧−0.78×FA+27 ・・・(2)
FB≧1.2×FA−9.6 ・・・(3)
(但し、FA=[Cr]+1.5×[Si]、FB=[Ni]+30×[C]+0.5×[Mn]であり、[ ]は各元素の含有量(質量%)を表す。)
The nonmagnetic steel of the present invention that has solved the above problems is C: 0.5 to 0.8% (meaning mass%, hereinafter the same), Si: 0.5 to 1.0%, Mn: 8 to 14.6%, P: 0.030% or less (not including 0%), S: 0.030% or less (not including 0%), Cu: 0.1% or less (not including 0%), Ni: 0.1% or less (excluding 0%), Cr: 1.8-3.0%, Al: 0.005-0.1%, N: 0.004-0.1% The following formulas (1) to (3) are satisfied, the balance is iron and inevitable impurities, the microstructure is an austenite structure, and the magnetic permeability is 1.030 or less.
[Mn] + 34 × [C] ≦ 40 (1)
FB ≧ −0.78 × FA + 27 (2)
FB ≧ 1.2 × FA-9.6 (3)
(However, FA = [Cr] + 1.5 × [Si], FB = [Ni] + 30 × [C] + 0.5 × [Mn], and [] represents the content (mass%) of each element. .)

本発明の非磁性鋼は、減面率30%で伸線加工した後の透磁率が1.030以下であることが好ましい。また、オーステナイト結晶粒度が6.0以上であり、且つ、引張強度が850MPa以上であることも好ましい。   The nonmagnetic steel of the present invention preferably has a magnetic permeability of 1.030 or less after being drawn at a surface reduction rate of 30%. It is also preferable that the austenite crystal grain size is 6.0 or more and the tensile strength is 850 MPa or more.

本発明によれば、合金元素が適切に制御されているため、ミクロ組織を安定したオーステナイトとすることができるとともに、CとMnの含有量が適切に制御されているため生成する炭化物等を粒界に偏析させることなく微細に分散させることができ、優れた非磁性特性(透磁率が1.030以下)を実現することができる。また、オーステナイト系ステンレスに比べてNi、Crが減量されているため、加工歪み付与後の非磁性特性にも優れている。更に、微細分散した上記炭化物等により高強度化できるため、部材強度と非磁性特性の両立が必要な構造部材(鉄筋材料など)や磁気回路の非磁性部品において、非磁性特性の向上と製造コストの低減が可能となる他、軽量化効果等に伴うCO2削減にも大きく寄与することができる。 According to the present invention, since the alloy elements are appropriately controlled, the microstructure can be made stable austenite, and the generated carbides and the like are produced because the contents of C and Mn are appropriately controlled. It can be finely dispersed without being segregated in the field, and excellent nonmagnetic properties (permeability is 1.030 or less) can be realized. Moreover, since Ni and Cr are reduced as compared with austenitic stainless steel, the nonmagnetic properties after application of processing strain are also excellent. Furthermore, since the strength can be increased by the finely dispersed carbides, etc., improvement in nonmagnetic properties and manufacturing costs in structural members (rebar materials, etc.) and nonmagnetic parts of magnetic circuits that require both strength and nonmagnetic properties. In addition to the reduction of CO 2, it can greatly contribute to the reduction of CO 2 due to the weight reduction effect.

図1は、実施例における鋼種D−1を用い、熱間圧延後の冷却速度を0.5℃/秒として製造した鋼のミクロ組織を示す光学顕微鏡写真である。FIG. 1 is an optical micrograph showing the microstructure of steel produced using steel type D-1 in the Examples and having a cooling rate after hot rolling of 0.5 ° C./second.

ミクロ組織を安定したオーステナイト組織とするためには、C、Mn等の合金元素を増量させればよいことが一般に知られており、より詳細にはシェフラーの組織図においてCr当量(=[Cr]+[Mo]+1.5×[Si]+0.5×[Nb])とNi当量(=[Ni]+30×[C]+0.5×[Mn])を最適に制御することによって安定したオーステナイト組織が得られることが知られている。一方、上記のような合金元素の添加量が多くなると、生成した炭化物等が磁束線および磁壁をトラップして残留磁化が増加して非磁性特性が低下するという問題がある。そこで、本発明者らが検討した結果、合金元素の中でもNi、Crは減量して(i)特にC、Mnを多く含有させるとともに、(ii)Cr当量およびNi当量を、シェフラーの組織図においてオーステナイトが安定する領域に制御することによって、オーステナイト組織を安定化させた上で、(iii)C量とMn量を相互に制御して炭化物等が粒界に偏析することなく微細分散するようにすれば、優れた非磁性特性を実現できることを見出し、本発明を完成した。上記(i)〜(iii)について、以下に説明する。なお、以下では[ ]は各元素の含有量(質量%)を表すものとする。   In order to make the microstructure a stable austenite structure, it is generally known that the amount of alloy elements such as C and Mn may be increased. More specifically, in the Schaeffler structure diagram, Cr equivalent (= [Cr] + [Mo] + 1.5 × [Si] + 0.5 × [Nb]) and Ni equivalent (= [Ni] + 30 × [C] + 0.5 × [Mn]) are optimally controlled to stabilize austenite It is known that an organization can be obtained. On the other hand, when the addition amount of the alloy element as described above is increased, there is a problem that the generated carbide or the like traps the magnetic flux lines and the domain wall to increase the residual magnetization and deteriorate the nonmagnetic characteristics. Therefore, as a result of the study by the present inventors, the amount of Ni and Cr in the alloy elements is reduced to (i) particularly contain a large amount of C and Mn, and (ii) the Cr equivalent and the Ni equivalent in the Schaeffler structure chart. By controlling the austenite to a stable region, the austenite structure is stabilized, and (iii) the amount of C and the amount of Mn are mutually controlled so that carbides and the like are finely dispersed without segregating at the grain boundaries. As a result, it was found that excellent nonmagnetic characteristics can be realized, and the present invention has been completed. The above (i) to (iii) will be described below. In the following, [] represents the content (mass%) of each element.

(i)CとMnを多く含有させる点について
C:0.5〜0.8%
Cは、非磁性相であるオーステナイト相の安定化に有効な元素である。また、強度向上に寄与するCrの微細炭窒化物を得るために必要な元素である。そこでC量を0.5%以上と定めた。C量は好ましくは0.55%以上であり、より好ましくは0.60%以上である。一方、C量が過剰になるとオーステナイト地の加工硬化性を増大させ、鍛造性や被削性が大幅に低下するとともに、粗大な炭窒化物が生成することによって非磁性特性と靭性の劣化を招く。そこでC量は0.8%以下と定めた。C量は好ましくは0.75%以下であり、より好ましくは0.70%以下である。
(I) About containing a large amount of C and Mn C: 0.5 to 0.8%
C is an element effective for stabilizing the austenite phase, which is a nonmagnetic phase. Further, it is an element necessary for obtaining a fine carbonitride of Cr that contributes to strength improvement. Therefore, the C amount is set to 0.5% or more. The amount of C is preferably 0.55% or more, more preferably 0.60% or more. On the other hand, if the amount of C is excessive, the work hardenability of austenite is increased, and the forgeability and machinability are greatly reduced, and the formation of coarse carbonitrides causes the deterioration of nonmagnetic properties and toughness. . Therefore, the C amount is set to 0.8% or less. The amount of C is preferably 0.75% or less, more preferably 0.70% or less.

Mn:8〜14.6%
Mnは、Cと同様にオーステナイト相の安定化に有効な元素である。上記したC量の範囲でオーステナイト相を安定化させるため、Mn量は8%以上とする。Mn量は好ましくは9%以上であり、より好ましくは10%以上である。一方、Mn量が過剰になると熱間加工性が著しく低下し、鋼材の製造性の悪化を招く。そこでMn量は14.6%以下と定めた。Mn量は好ましくは14.55%以下、より好ましくは14.5%以下である。
Mn: 8 to 14.6%
Mn, like C, is an element effective for stabilizing the austenite phase. In order to stabilize the austenite phase in the range of the above C amount, the Mn amount is 8% or more. The amount of Mn is preferably 9% or more, more preferably 10% or more. On the other hand, when the amount of Mn becomes excessive, the hot workability is remarkably lowered, and the productivity of the steel material is deteriorated. Therefore, the amount of Mn is determined to be 14.6% or less. The amount of Mn is preferably 14.55% or less, more preferably 14.5% or less.

(ii)シェフラーの組織図におけるオーステナイト安定化領域について
シェフラーの組織図において、オーステナイト安定領域は、
(Ni当量)≧−0.78×(Cr当量)+27 ・・・(2a)
(Ni当量)≧1.2×(Cr当量)−9.6 ・・・(3a)
と表される。ここで、Ni当量=[Ni]+30×[C]+0.5×[Mn]であり、Cr当量=[Cr]+[Mo]+1.5×[Si]+0.5×[Nb]であるから、本発明の成分系において上記(2a)式、および(3a)式は、下記(2b)式、および(3b)式と表すことができる。
FB≧−0.78×FA+27 ・・・(2b)
FB≧1.2×FA−9.6 ・・・(3b)
(但し、FA=[Cr]+1.5×[Si]、FB=[Ni]+30×[C]+0.5×[Mn]を表す。)
(Ii) About the austenite stabilization region in the Schaeffler organization chart In the Schaeffler organization diagram, the austenite stabilization region is
(Ni equivalent) ≧ −0.78 × (Cr equivalent) +27 (2a)
(Ni equivalent) ≧ 1.2 × (Cr equivalent) −9.6 (3a)
It is expressed. Here, Ni equivalent = [Ni] + 30 × [C] + 0.5 × [Mn], and Cr equivalent = [Cr] + [Mo] + 1.5 × [Si] + 0.5 × [Nb]. From the above, in the component system of the present invention, the above formulas (2a) and (3a) can be expressed as the following formulas (2b) and (3b).
FB ≧ −0.78 × FA + 27 (2b)
FB ≧ 1.2 × FA−9.6 (3b)
(However, FA = [Cr] + 1.5 × [Si], FB = [Ni] + 30 × [C] + 0.5 × [Mn]).

(iii)C量とMn量を相互に制御する点について
本発明では、CおよびMnを多く含有しているが、C量とMn量を下記(1)式を満たすように制御しているため、炭化物等を粒界に偏析することなく微細に分散させることができる。
[Mn]+34×[C]≦40 ・・・(1)
(Iii) About the point which controls C amount and Mn amount mutually In this invention, since it contains many C and Mn, since C amount and Mn amount are controlled so that the following (1) Formula may be satisfy | filled. Further, carbides and the like can be finely dispersed without segregating at the grain boundaries.
[Mn] + 34 × [C] ≦ 40 (1)

上記(1)式の右辺の値は、好ましくは39であり、より好ましくは38である。   The value on the right side of the formula (1) is preferably 39, more preferably 38.

なお、上述した特許文献1では上記(2a)式を満たさないためオーステナイト安定化領域を外れる例か、または上記(1)式を満たさないため炭化物等が粒界に偏析する例が開示されるのみであり、いずれも非磁性特性が不十分である。   In addition, the above-mentioned Patent Document 1 only discloses an example that does not satisfy the above equation (2a) and thus deviates from the austenite stabilization region, or an example in which carbide or the like segregates at grain boundaries because the above equation (1) is not satisfied. In any case, the nonmagnetic properties are insufficient.

本発明に係る非磁性鋼は、上記したC、Mn以外にSi、P、S、Cu、Ni、Cr、Al、Nを含有する。以下、各成分について説明する。   The nonmagnetic steel according to the present invention contains Si, P, S, Cu, Ni, Cr, Al, and N in addition to the above-described C and Mn. Hereinafter, each component will be described.

Si:0.5〜1.0%
Siは、鋼の溶製時に脱酸剤として作用する他、オーステナイト相を安定化させるのに有効な元素である。また強度の向上にも有効である。そこでSi量を0.5%以上と定めた。Si量は好ましくは0.55%以上であり、より好ましくは0.6%以上である。一方、Si量が過剰になると熱間加工性を損ない、鋼材の製造性が大幅に低下する。そこでSi量は1.0%以下と定めた。Si量は好ましくは0.9%以下であり、より好ましくは0.8%以下である。
Si: 0.5 to 1.0%
Si is an effective element for stabilizing the austenite phase, as well as acting as a deoxidizer during the melting of steel. It is also effective in improving strength. Therefore, the amount of Si is set to 0.5% or more. The amount of Si is preferably 0.55% or more, and more preferably 0.6% or more. On the other hand, when the amount of Si is excessive, hot workability is impaired, and the productivity of the steel material is greatly reduced. Therefore, the Si amount is determined to be 1.0% or less. The amount of Si is preferably 0.9% or less, and more preferably 0.8% or less.

P:0.030%以下(0%を含まない)
Pは、熱間加工性および溶接性を損なう元素であり、また冷間鍛造性を低下させるため、極力低減することが好ましい。しかし、鋼材の製造コストの増加を招くため0%とすることは難しく、経済性を考慮して0.030%以下と定めた。P量は好ましくは0.020%以下である。
P: 0.030% or less (excluding 0%)
P is an element that impairs hot workability and weldability, and it is preferable to reduce P as much as possible in order to reduce cold forgeability. However, since it causes an increase in the manufacturing cost of the steel material, it is difficult to make it 0%, and it is set to 0.030% or less in consideration of economy. The amount of P is preferably 0.020% or less.

S:0.030%以下(0%を含まない)
Sは、被削性の改善には有効な元素であるが、熱間加工性および溶接性を損なう元素であるため、極力低減することが好ましい。しかしPと同様、鋼材の製造コストの増加を招くため0%とすることは難しく、経済性を考慮して0.030%以下と定めた。S量は好ましくは0.025%以下である。
S: 0.030% or less (excluding 0%)
S is an element effective for improving machinability, but is an element that impairs hot workability and weldability, and therefore it is preferably reduced as much as possible. However, like P, it causes an increase in the manufacturing cost of the steel material, so it is difficult to set it to 0%, and it is set to 0.030% or less in consideration of economy. The amount of S is preferably 0.025% or less.

Cu:0.1%以下(0%を含まない)
Cuは、オーステナイトの安定化と靭性向上に有効な元素である。このような効果を有効に発揮させるため、Cu量は0.01%以上とすることが好ましく、より好ましくは0.02%以上である。一方、Cu量が過剰になるとオーステナイト地の加工硬化を大きくし、冷間鍛造性や被削性を損なうとともに、経済性も損なう。そこでCu量は0.1%以下とする。Cu量は好ましくは、0.08%以下であり、より好ましくは0.06%以下である。
Cu: 0.1% or less (excluding 0%)
Cu is an element effective for stabilizing austenite and improving toughness. In order to effectively exhibit such effects, the Cu content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, when the amount of Cu is excessive, work hardening of austenite is increased, and cold forgeability and machinability are impaired, and economic efficiency is also impaired. Therefore, the Cu content is 0.1% or less. The amount of Cu is preferably 0.08% or less, more preferably 0.06% or less.

Ni:0.1%以下(0%を含まない)
Niは、Cuと同様に、オーステナイトの安定化と靭性の向上に有効な元素である。このような効果を有効に発揮させるため、Ni量は0.01%以上とすることが好ましく、より好ましくは0.02%以上である。一方、Ni量が過剰になるとオーステナイト地の加工硬化を大きくし、冷間鍛造性や被削性を損なうとともに、経済性も損なう。そこでNi量は0.1%以下とする。Ni量は好ましくは、0.08%以下であり、より好ましくは0.06%以下である。
Ni: 0.1% or less (excluding 0%)
Ni, like Cu, is an element effective in stabilizing austenite and improving toughness. In order to effectively exhibit such an effect, the Ni content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, when the amount of Ni is excessive, work hardening of austenite is increased, and cold forgeability and machinability are impaired, and economical efficiency is also impaired. Therefore, the Ni content is 0.1% or less. The amount of Ni is preferably 0.08% or less, and more preferably 0.06% or less.

Cr:1.8〜3.0%
Crは、オーステナイト相の安定化に有効な元素であり、また特にCrの微細な炭窒化物を形成することにより高強度化に寄与する元素である。そこでCr量は1.8%以上と定めた。Cr量は好ましくは2.0%以上であり、より好ましくは2.2%以上である。一方、Cr量が過剰になるとδフェライト相が生成しやすくなるとともに、Cr炭化物が結晶粒界上に析出しやすくなり、非磁性特性と靭性を損なう。そこでCr量は3.0%以下と定めた。Cr量は好ましくは2.8%以下であり、より好ましくは2.6%以下である。
Cr: 1.8-3.0%
Cr is an element effective for stabilizing the austenite phase, and is an element that contributes to increasing the strength by forming fine carbonitride of Cr in particular. Therefore, the Cr content is determined to be 1.8% or more. The amount of Cr is preferably 2.0% or more, and more preferably 2.2% or more. On the other hand, when the amount of Cr is excessive, a δ ferrite phase is easily generated, and Cr carbides are likely to precipitate on the grain boundaries, thereby deteriorating nonmagnetic properties and toughness. Therefore, the Cr content is determined to be 3.0% or less. The amount of Cr is preferably 2.8% or less, and more preferably 2.6% or less.

Al:0.005〜0.1%
Alは強度の向上に寄与する元素である。そこでAl量は0.005%以上とする。Al量は好ましくは0.01%以上であり、より好ましくは0.03%以上である。一方、Al量が過剰になると鋼材の靭性が低下する。そこでAl量は0.1%以下と定めた。Al量は好ましくは0.09%以下であり、より好ましくは0.085%以下である。
Al: 0.005 to 0.1%
Al is an element that contributes to improving the strength. Therefore, the Al content is 0.005% or more. The amount of Al is preferably 0.01% or more, and more preferably 0.03% or more. On the other hand, when the amount of Al becomes excessive, the toughness of the steel material decreases. Therefore, the Al content is determined to be 0.1% or less. The amount of Al is preferably 0.09% or less, and more preferably 0.085% or less.

N:0.004〜0.1%
Nは、Cと同様にオーステナイト相の安定化に有効な元素であり、また特にCrの微細な炭窒化物を形成することによって高強度化に寄与する元素である。そこで、N量は0.004%以上と定めた。N量は好ましくは0.005%以上であり、より好ましくは0.006%以上である。一方、N量が過剰になると、オーステナイト相の加工硬化を増大させ、冷間鍛造性や被削性が大幅に低下する。また、Cr炭窒化物の量が過剰になると、非磁性特性や靭性の劣化を招く。そこでN量は0.1%以下と定めた。N量は好ましくは0.08%以下であり、より好ましくは0.05%以下である。
N: 0.004 to 0.1%
N is an element that is effective for stabilizing the austenite phase, as is the case with C, and is an element that contributes to high strength by forming fine carbonitrides of Cr in particular. Therefore, the N amount is determined to be 0.004% or more. The N amount is preferably 0.005% or more, and more preferably 0.006% or more. On the other hand, when the amount of N is excessive, work hardening of the austenite phase is increased, and cold forgeability and machinability are significantly reduced. Moreover, when the amount of Cr carbonitride is excessive, nonmagnetic properties and toughness are deteriorated. Therefore, the N amount is determined to be 0.1% or less. The N amount is preferably 0.08% or less, more preferably 0.05% or less.

本発明に係る非磁性鋼の成分組成は上記の通りであり、残部は実質的に鉄である。但し、原料、資材、製造設備等の状況によって持ち込まれる不可避不純物が、各成分元素の作用効果や部品の特性を阻害しない範囲で鋼中に含まれることは当然に許容される。   The component composition of the nonmagnetic steel according to the present invention is as described above, and the balance is substantially iron. However, it is naturally allowed that unavoidable impurities brought in depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel as long as they do not impair the effects of the component elements and the characteristics of the parts.

本発明に係る非磁性鋼のミクロ組織は、上記のように成分組成を最適に調整することにより、室温においても安定したオーステナイト組織とすることができる。またオーステナイト結晶粒度は6.0以上とすることが好ましく、その結果引張強度を850MPa以上とすることができる。オーステナイト結晶粒度は、好ましくは7.0以上である。   The microstructure of the nonmagnetic steel according to the present invention can be a stable austenite structure even at room temperature by optimally adjusting the component composition as described above. The austenite grain size is preferably 6.0 or more, and as a result, the tensile strength can be 850 MPa or more. The austenite grain size is preferably 7.0 or more.

本発明に係る非磁性鋼において、炭化物等を微細に分散析出させて非磁性特性を良好にし、また好ましくはオーステナイト結晶粒の粗大化を抑制するためには、化学成分組成を上記のように適切に制御した鋼を、溶製し、鋳造した後、熱間圧延するという一連の製造工程において、特に熱間圧延条件(加熱温度、圧延終了温度、圧延後の冷却速度)を適切に制御することが好ましい。具体的には、熱間圧延前の加熱温度を一定以上として合金成分を母相に完全に固溶させ、かつ、熱間圧延前の加熱温度および圧延終了温度を高くしすぎないことによって結晶粒の粗大化を抑制することができる。   In the nonmagnetic steel according to the present invention, in order to finely disperse and precipitate carbides and the like to improve the nonmagnetic characteristics, and preferably to suppress the coarsening of the austenite crystal grains, the chemical composition is appropriately set as described above. In a series of manufacturing processes in which steel is controlled to be melted, cast, and then hot rolled, in particular, the hot rolling conditions (heating temperature, rolling end temperature, cooling rate after rolling) should be appropriately controlled. Is preferred. Specifically, the crystal grains are obtained by setting the heating temperature before hot rolling to a certain level or more so that the alloy components are completely dissolved in the matrix and not increasing the heating temperature before hot rolling and the rolling end temperature too much. Can be suppressed.

合金成分を母相に完全に固溶させて、熱間圧延後の冷却過程において炭化物等を微細に析出させるため、熱間圧延前の加熱はできるだけ高温であることが好ましい。熱間圧延前の加熱温度は1000℃以上が好ましく、より好ましくは1050℃以上である。一方、加熱温度が1200℃を超えると加熱コストが増加し経済性が低下する上、オーステナイト結晶粒が粗大化し、熱間脆性の兆候が現れることに加えて、高温加熱によって鋼材の表層部が脱炭すると透磁率の増加を招くため、加熱温度は1200℃以下とすることが好ましい。   In order to completely dissolve the alloy components in the matrix and precipitate carbides and the like in the cooling process after hot rolling, heating before hot rolling is preferably as high as possible. The heating temperature before hot rolling is preferably 1000 ° C. or higher, more preferably 1050 ° C. or higher. On the other hand, if the heating temperature exceeds 1200 ° C., the heating cost increases and the economic efficiency decreases, and the austenite crystal grains become coarse and signs of hot brittleness appear. In addition, the surface layer of the steel material is removed by high-temperature heating. Since charcoal increases the magnetic permeability, the heating temperature is preferably 1200 ° C. or lower.

熱間圧延終了温度は高くなりすぎると、オーステナイト結晶粒が粗大化し、部材強度と表面状態の両面で品質低下を招く。そこで、圧延終了温度は1050℃以下とすることが好ましく、より好ましくは1000℃以下である。一方、圧延終了温度が低すぎると、圧延時のロール負荷の増大を招き、製造コストが増加する。よって、圧延終了温度は800℃以上とすることが好ましい。   If the hot rolling finish temperature is too high, the austenite crystal grains become coarse, and the quality of both the member strength and the surface state is deteriorated. Therefore, the rolling end temperature is preferably 1050 ° C. or lower, more preferably 1000 ° C. or lower. On the other hand, when the rolling end temperature is too low, the roll load during rolling is increased, and the production cost is increased. Therefore, the rolling end temperature is preferably 800 ° C. or higher.

熱間圧延後の冷却速度は、通常行われる範囲から適宜設定することが可能であるが、800〜600℃における冷却速度を0.5℃/秒超2℃/秒以下の範囲とすることが好ましい。図1は後述する実施例における鋼種D−1を用い、熱間圧延前加熱温度:1050℃、熱間圧延終了温度:800℃、熱間圧延後の800〜600℃における冷却速度:0.5℃/秒の条件で製造した鋼のミクロ組織を示す光学顕微鏡写真である。図1では、結晶粒界が黒く観察されている。すなわち、800〜600℃の温度範囲は、炭化物等の析出に影響を与える温度であり、該温度範囲での冷却速度が遅すぎると、結晶粒界に析出する炭化物等が増加する傾向があるものと考えられる。一方、冷却速度が速すぎると、鋼材表面と中心部とで組織の均一性が損なわれる可能性が大きくなる。そこで、上記のような不具合を避けるため、800〜600℃における冷却速度は0.5℃/秒超2℃/秒以下の範囲とすることが好ましい。   Although the cooling rate after hot rolling can be appropriately set from the range usually performed, the cooling rate at 800 to 600 ° C. may be in the range of more than 0.5 ° C./second and 2 ° C./second or less. preferable. FIG. 1 uses steel type D-1 in the examples described later, heating temperature before hot rolling: 1050 ° C., end temperature of hot rolling: 800 ° C., cooling rate at 800 to 600 ° C. after hot rolling: 0.5 It is an optical micrograph which shows the microstructure of the steel manufactured on the conditions of (degreeC / sec). In FIG. 1, the crystal grain boundary is observed to be black. That is, the temperature range of 800 to 600 ° C. is a temperature that affects the precipitation of carbides and the like, and if the cooling rate in the temperature range is too slow, the carbides and the like that precipitate at the grain boundaries tend to increase. it is conceivable that. On the other hand, when the cooling rate is too high, the possibility of the uniformity of the structure being impaired between the steel material surface and the central portion increases. Therefore, in order to avoid the above problems, the cooling rate at 800 to 600 ° C. is preferably in the range of more than 0.5 ° C./second and 2 ° C./second or less.

本発明の非磁性鋼は、上記のように化学成分組成・製造条件を適切に制御することによって、室温でも安定したオーステナイト組織が得られるとともに、炭化物等を粒界に偏析させることなく微細に分散して析出させることができ、その結果、鋼材の透磁率を1.030以下とすることができる。鋼材の透磁率は好ましくは1.02以下であり、より好ましくは1.01以下である。   As described above, the nonmagnetic steel of the present invention can obtain a stable austenite structure even at room temperature by appropriately controlling the chemical composition and production conditions as described above, and can be finely dispersed without segregating carbides and the like at grain boundaries. As a result, the permeability of the steel material can be made 1.030 or less. The magnetic permeability of the steel material is preferably 1.02 or less, more preferably 1.01 or less.

さらに、本発明の非磁性鋼は、加工歪み付与後の非磁性特性にも優れ、減面率30%で伸線加工する場合に相当する歪みを与えた後の透磁率が1.030以下であることが好ましい。上記歪み付与後の透磁率は好ましくは1.025以下であり、より好ましくは1.02以下である。   Furthermore, the nonmagnetic steel of the present invention is excellent in nonmagnetic properties after imparting a working strain, and has a magnetic permeability of 1.030 or less after imparting a strain equivalent to the case of wire drawing with a surface reduction of 30%. Preferably there is. The permeability after applying the strain is preferably 1.025 or less, and more preferably 1.02 or less.

以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。   EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

表1に示す化学成分組成の鋼を20ton電気炉または150kg真空炉で溶製し、鋳造して鋼塊を得、鋼塊を155mm×155mm角に鍛造加工した後、表2に示す圧延条件で熱間圧延することにより、φ30mmの圧延材を得た。熱間圧延後の800〜600℃における冷却速度は、いずれも1〜2℃/秒とした。なお、150kg真空炉溶製材については、上記鍛造加工後、1100℃で1時間均熱処理を施し、ダミービレットに溶接したものを熱間圧延した。   Steel having the chemical composition shown in Table 1 is melted in a 20 ton electric furnace or 150 kg vacuum furnace, cast to obtain a steel ingot, the steel ingot is forged into a 155 mm × 155 mm square, and then rolled under the conditions shown in Table 2. A rolled material having a diameter of 30 mm was obtained by hot rolling. The cooling rate at 800 to 600 ° C. after hot rolling was 1 to 2 ° C./second. In addition, about the 150kg vacuum furnace melted material, the soaking process was performed at 1100 degreeC for 1 hour after the said forge processing, and what was welded to the dummy billet was hot-rolled.

(1)ミクロ組織の同定、結晶粒度および混粒の有無の測定
上記圧延材を、軸心に垂直な断面で切断して支持基材内に埋め込み、表面を研磨した後、光学顕微鏡によって圧延材の表層部、D/4位置(Dは直径)、D/2位置のミクロ組織を観察した(倍率100倍、および400倍)。なお、上記研磨は、5%のピクリン酸アルコール液に15〜30秒浸漬することによって行った。
(1) Identification of microstructure, measurement of crystal grain size and presence / absence of mixed grains The above rolled material is cut in a cross section perpendicular to the axis, embedded in a supporting base material, the surface is polished, and then rolled with an optical microscope. The microstructure of the surface layer portion, D / 4 position (D is diameter), and D / 2 position were observed (magnification 100 times and 400 times). The polishing was performed by immersing in a 5% picric acid alcohol solution for 15 to 30 seconds.

またオーステナイト粒度は、D/4位置の任意の0.039mm2(0.175mm×0.225mm)の領域を光学顕微鏡で観察し(倍率:400倍)、JIS G0551に従って結晶粒度番号、混粒の有無を測定した。測定は4視野について行った。オーステナイト結晶粒度は、これら4視野の平均値をオーステナイト結晶粒度とし、混粒の有無については4視野のいずれにも混粒が発生していない場合を混粒「無」とし、1視野でも混粒の発生が確認された場合を混粒「有」とした。 As for the austenite grain size, an arbitrary 0.039 mm 2 (0.175 mm × 0.225 mm) region at the D / 4 position was observed with an optical microscope (magnification: 400 times), and the grain size number and the mixed grain size were determined according to JIS G0551. The presence or absence was measured. The measurement was performed for 4 fields of view. As for the austenite grain size, the average value of these four fields of view is the austenite grain size, and the presence or absence of mixed grains is defined as “no” when no grains are present in any of the four fields of view. The case where the occurrence of water was confirmed was regarded as “mixed” “present”.

(2)引張強度の測定
上記圧延材から、圧延方向が試験片の長手方向となるように、JIS4号試験片を採取し、JIS Z2241に従って、引張強度(TS)を測定した。
(2) Measurement of tensile strength From the rolled material, a JIS No. 4 test piece was collected so that the rolling direction was the longitudinal direction of the test piece, and the tensile strength (TS) was measured according to JIS Z2241.

(3)磁気特性の測定
上記圧延材、および圧延材を減面率30%で伸線加工した伸線加工材から、外径24mm×内径16mm×高さ4mmのリング状試料を作製し、JIS C2504に従って透磁率を測定した。
(3) Measurement of magnetic properties A ring-shaped sample having an outer diameter of 24 mm, an inner diameter of 16 mm, and a height of 4 mm was prepared from the rolled material and the drawn material obtained by drawing the rolled material at a reduction in area of 30%. The magnetic permeability was measured according to C2504.

結果を表2に示す。   The results are shown in Table 2.

実験No.3、4は、成分組成および製造条件が適切に制御されているため、ミクロ組織をオーステナイト組織とすることができ、圧延材および伸線材の透磁率を共に1.030以下とすることができ、さらに引張強度が850MPa以上の高強度となった。   Experiment No. 3 and 4, since the component composition and production conditions are appropriately controlled, the microstructure can be an austenite structure, and the magnetic permeability of both the rolled material and the wire drawing material can be 1.030 or less, Furthermore, the tensile strength became high strength of 850 MPa or more.

一方、実験No.1〜2、5〜23は、製造条件が好ましい範囲を外れたか、または化学成分組成が適切でなかったため、引張強度または透磁率のいずれかが劣化した。   On the other hand, Experiment No. For 1-2 and 5-23, the manufacturing conditions were outside the preferred range, or the chemical composition was not appropriate, so either the tensile strength or the magnetic permeability deteriorated.

実験No.1、2は圧延前加熱温度または圧延終了温度が高かったため、オーステナイト結晶粒が粗大化し、引張強度が不十分となった。   Experiment No. In Nos. 1 and 2, the heating temperature before rolling or the rolling finishing temperature was high, so the austenite crystal grains became coarse and the tensile strength became insufficient.

実験No.5〜8は、C量、Mn量の少なくともいずれかが多かった例であり、多量に生成した炭化物等が粒界に偏析したため、圧延材に内部割れが発生し、引張強度が不十分となるとともに、伸線材の透磁率が大きくなった。なお、炭化物が多量に偏析した部位では母相のC量が低下することによってオーステナイト相が不安定となる結果、冷間加工した場合にオーステナイト相の一部が加工誘起マルテンサイト変態することとなり、このことが伸線材の透磁率が大きくなった原因であると考えられる。   Experiment No. Nos. 5 to 8 are examples in which at least one of the amount of C and the amount of Mn was large. Since a large amount of carbides and the like were segregated at the grain boundaries, internal cracks occurred in the rolled material and the tensile strength was insufficient. At the same time, the permeability of the wire drawing material increased. In addition, as a result of the austenite phase becoming unstable due to a decrease in the amount of C in the parent phase at a site where a large amount of carbides segregated, a part of the austenite phase undergoes work-induced martensitic transformation when cold worked, This is considered to be the cause of the increase in the magnetic permeability of the wire drawing material.

実験No.9、10は、C量を減量し、Mn、Ni、Crといったオーステナイト安定化元素を増量した例であるが、ミクロ組織はオーステナイト組織とすることができたものの、C量を減量した影響で引張強度が不十分なものとなった。   Experiment No. Nos. 9 and 10 are examples in which the amount of C is reduced and the amount of austenite stabilizing elements such as Mn, Ni, and Cr is increased. The strength was insufficient.

実験No.11〜13は、Si量を減量し、Ni量を増量した例である。これらは引張強度が850MPa以上となり、圧延材の透磁率も1.030以下とすることができたが、Ni量の増量の影響で、加工誘起マルテンサイトが生成し、伸線材における透磁率が大きくなった。   Experiment No. 11 to 13 are examples in which the Si amount was decreased and the Ni amount was increased. These had a tensile strength of 850 MPa or more and the permeability of the rolled material could be 1.030 or less, but due to the increase in the amount of Ni, work-induced martensite was generated, and the permeability in the wire drawing material was large. became.

実験No.14は、Si量が少なかった例であり、引張強度が不十分となった。   Experiment No. No. 14 was an example in which the amount of Si was small, and the tensile strength was insufficient.

実験No.15、16からMn量の影響をみることができる。Mn量が少ない場合は、ミクロ組織の一部に強磁性であるフェライト相が析出し、圧延材および伸線材ともに透磁率が増大する。一方、Mn量が多い場合は多量に生成した炭化物等が結晶粒界に偏析したことによって鋼材の熱間延性が低下し、圧延材に微小クラックが発生する結果、引張強度が不十分となり、圧延材および伸線材ともに透磁率が増大した。   Experiment No. From 15 and 16, the influence of the amount of Mn can be seen. When the amount of Mn is small, a ferromagnetic ferrite phase precipitates in a part of the microstructure, and the magnetic permeability increases in both the rolled material and the wire drawing material. On the other hand, when the amount of Mn is large, the hot ductility of the steel material is reduced due to segregation of a large amount of carbide, etc. generated at the grain boundaries, resulting in microcracks in the rolled material, resulting in insufficient tensile strength and rolling. The permeability increased for both the wire and the wire drawing material.

実験No.17はCu量が多かった例であり、鋼材の熱間延性が低下し、圧延材に微小クラックが発生する結果、引張強度の低下と透磁率の増加を招く結果となった。   Experiment No. No. 17 is an example in which the amount of Cu is large. As a result of the hot ductility of the steel material being reduced and microcracks being generated in the rolled material, this resulted in a decrease in tensile strength and an increase in magnetic permeability.

実験No.18はNi量が多かった例であり、伸線加工による歪みでオーステナイトの一部が加工誘起マルテンサイトに変態したため、伸線材の透磁率の増加を招く結果となった。   Experiment No. No. 18 was an example in which the amount of Ni was large, and a part of austenite was transformed into work-induced martensite due to strain caused by wire drawing, resulting in an increase in the magnetic permeability of the wire drawing material.

実験No.19はCrが過剰であった例であり、Cr炭化物が析出した結果、母相のC量が減少してミクロ組織の一部に強磁性のフェライトが混在するため、圧延材および伸線材ともに透磁率が増大した。   Experiment No. No. 19 is an example in which Cr is excessive. As a result of precipitation of Cr carbide, the amount of C in the parent phase is reduced and ferromagnetic ferrite is mixed in a part of the microstructure. Magnetic susceptibility increased.

実験No.20はAlが過剰であった例である。Alは強度の上昇に有効な元素であるが、0.1%を超える多量添加では靭性が低下するため、伸線加工材においては微小のクラックが局所的に発生し、伸線材の透磁率が増加する結果となった。   Experiment No. 20 is an example in which Al was excessive. Al is an element effective in increasing the strength, but if added in a large amount exceeding 0.1%, the toughness is lowered, so that a fine crack is locally generated in the drawn material, and the permeability of the drawn material is low. Increased results.

実験No.21はNが過剰であった例であり、靭性が低下するため伸線加工材では微小クラックが発生したと考えられ、伸線材の透磁率が増加する結果となった。   Experiment No. No. 21 is an example in which N was excessive, and it was considered that microcracks were generated in the drawn wire material because the toughness was lowered, resulting in an increase in the magnetic permeability of the drawn wire material.

実験No.22は、C量とMn量が少ない例であり、ミクロ組織がフェライト+パーライト組織となるため、引張強度が不十分であるとともに、圧延材および伸線材ともに透磁率が増大した。   Experiment No. No. 22 is an example in which the amount of C and the amount of Mn are small, and since the microstructure is a ferrite + pearlite structure, the tensile strength is insufficient, and the permeability of both the rolled material and the wire drawing material is increased.

実験No.23は、[Mn]+34×[C]の値が40を超えていたため、結晶粒界に炭化物の生成が見られ、圧延材および伸線材ともに透磁率が増加した。   Experiment No. In No. 23, since the value of [Mn] + 34 × [C] exceeded 40, generation of carbides was observed at the crystal grain boundaries, and both the rolling material and the wire drawing material had increased magnetic permeability.

Claims (3)

C :0.5〜0.8%(質量%の意味。以下、同じ。)、
Si:0.50.9%、
Mn:8〜14.6%、
P :0.030%以下(0%を含まない)、
S :0.030%以下(0%を含まない)、
Cu:0.1%以下(0%を含まない)、
Ni:0.1%以下(0%を含まない)、
Cr:1.8〜3.0%、
Al:0.005〜0.1%、
N :0.004〜0.1%を含有し、下記式(1)〜(3)を満たすとともに、残部が鉄および不可避不純物であり、
ミクロ組織がオーステナイト組織であり、
透磁率が1.030以下であることを特徴とする非磁性鋼。
[Mn]+34×[C]≦40 ・・・(1)
FB≧−0.78×FA+27 ・・・(2)
FB≧1.2×FA−9.6 ・・・(3)
(但し、FA=[Cr]+1.5×[Si]、FB=[Ni]+30×[C]+0.5×[Mn]であり、[ ]は各元素の含有量(質量%)を表す。)
C: 0.5 to 0.8% (meaning mass%, hereinafter the same),
Si: 0.5 5 ~ 0.9%,
Mn: 8 to 14.6%
P: 0.030% or less (excluding 0%),
S: 0.030% or less (excluding 0%),
Cu: 0.1% or less (excluding 0%),
Ni: 0.1% or less (excluding 0%),
Cr: 1.8-3.0%,
Al: 0.005 to 0.1%,
N: 0.004 to 0.1% is contained, the following formulas (1) to (3) are satisfied, and the balance is iron and inevitable impurities,
The microstructure is an austenite structure,
A nonmagnetic steel having a magnetic permeability of 1.030 or less.
[Mn] + 34 × [C] ≦ 40 (1)
FB ≧ −0.78 × FA + 27 (2)
FB ≧ 1.2 × FA-9.6 (3)
(However, FA = [Cr] + 1.5 × [Si], FB = [Ni] + 30 × [C] + 0.5 × [Mn], and [] represents the content (mass%) of each element. .)
減面率30%で伸線加工した後の透磁率が1.030以下である請求項1に記載の非磁性鋼。   The nonmagnetic steel according to claim 1, wherein the magnetic permeability after drawing at a surface reduction rate of 30% is 1.030 or less. オーステナイト結晶粒度が6.0以上であり、且つ、引張強度が850MPa以上である請求項1または2に記載の非磁性鋼。   The nonmagnetic steel according to claim 1 or 2, wherein the austenite grain size is 6.0 or more and the tensile strength is 850 MPa or more.
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