JP3682881B2 - Method for producing maraging steel and maraging steel - Google Patents
Method for producing maraging steel and maraging steel Download PDFInfo
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- JP3682881B2 JP3682881B2 JP2003409822A JP2003409822A JP3682881B2 JP 3682881 B2 JP3682881 B2 JP 3682881B2 JP 2003409822 A JP2003409822 A JP 2003409822A JP 2003409822 A JP2003409822 A JP 2003409822A JP 3682881 B2 JP3682881 B2 JP 3682881B2
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- 229910001240 Maraging steel Inorganic materials 0.000 title claims description 80
- 238000004519 manufacturing process Methods 0.000 title claims description 29
- 150000004767 nitrides Chemical class 0.000 claims description 40
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 26
- 229910052760 oxygen Inorganic materials 0.000 claims description 16
- 229910052757 nitrogen Inorganic materials 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 14
- 239000001301 oxygen Substances 0.000 claims description 14
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 13
- 229910052719 titanium Inorganic materials 0.000 claims description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 8
- 238000002844 melting Methods 0.000 claims description 7
- 230000008018 melting Effects 0.000 claims description 7
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 238000010313 vacuum arc remelting Methods 0.000 claims description 6
- 230000006698 induction Effects 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 230000003647 oxidation Effects 0.000 claims 1
- 238000007254 oxidation reaction Methods 0.000 claims 1
- 229910000831 Steel Inorganic materials 0.000 description 31
- 239000010959 steel Substances 0.000 description 31
- 239000010936 titanium Substances 0.000 description 23
- 230000000694 effects Effects 0.000 description 19
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 16
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 15
- 239000002994 raw material Substances 0.000 description 12
- 229910052596 spinel Inorganic materials 0.000 description 10
- 239000011029 spinel Substances 0.000 description 10
- 230000005540 biological transmission Effects 0.000 description 9
- 238000011282 treatment Methods 0.000 description 9
- 229910000765 intermetallic Inorganic materials 0.000 description 7
- 230000032683 aging Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 238000005728 strengthening Methods 0.000 description 6
- MODGUXHMLLXODK-UHFFFAOYSA-N [Br].CO Chemical compound [Br].CO MODGUXHMLLXODK-UHFFFAOYSA-N 0.000 description 5
- 239000002253 acid Substances 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 238000000635 electron micrograph Methods 0.000 description 5
- 238000009661 fatigue test Methods 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 238000000265 homogenisation Methods 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 238000005204 segregation Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 230000002411 adverse Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 238000005097 cold rolling Methods 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000005242 forging Methods 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 229910000861 Mg alloy Inorganic materials 0.000 description 2
- 229910018505 Ni—Mg Inorganic materials 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 238000004453 electron probe microanalysis Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910019092 Mg-O Inorganic materials 0.000 description 1
- 229910019395 Mg—O Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000001364 causal effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- -1 nitrogen carbides Chemical class 0.000 description 1
- 229910052755 nonmetal Inorganic materials 0.000 description 1
- 150000002843 nonmetals Chemical class 0.000 description 1
- 150000002926 oxygen Chemical class 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000004451 qualitative analysis Methods 0.000 description 1
- 238000003908 quality control method Methods 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
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- 229910052717 sulfur Inorganic materials 0.000 description 1
- 238000010301 surface-oxidation reaction Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
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- Manufacture And Refinement Of Metals (AREA)
- Treatment Of Steel In Its Molten State (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、マルエージング鋼の製造方法及びマルエージング鋼に関するものである。 The present invention relates to a method for producing maraging steel and maraging steel.
マルエージング鋼は、2000MPa前後の非常に高い引張強さをもつため、高強度が要求される部材、例えば、ロケット用部品、遠心分離機部品、航空機部品、自動車エンジンの無段変速機用部品、金型、等種々の用途に使用されている。
このマルエージング鋼は、通常、強化元素として、Mo、Ti、を適量含んでおり、時効処理を行うことによって、Ni3Mo、Ni3Ti、Fe2Mo等の金属間化合物を析出させて高強度を得ることのできる鋼である。このMoやTiを含んだマルエージング鋼の代表的な組成としては、質量%で18%Ni−8%Co−5%Mo−0.45%Ti−0.1%Al−bal.Feが挙げられる。
Since maraging steel has a very high tensile strength of around 2000 MPa, members that require high strength, such as rocket parts, centrifuge parts, aircraft parts, automobile engine continuously variable transmission parts, It is used for various applications such as molds.
This maraging steel usually contains appropriate amounts of Mo and Ti as strengthening elements, and by performing an aging treatment, intermetallic compounds such as Ni 3 Mo, Ni 3 Ti, and Fe 2 Mo are precipitated. Steel that can provide strength. A typical composition of this maraging steel containing Mo and Ti is 18% Ni-8% Co-5% Mo-0.45% Ti-0.1% Al-bal. Fe.
しかし、マルエージング鋼は、非常に高い引張強度が得られる一方、疲労強度に関しては必ずしも高くない。この疲労強度を劣化させる最大の要因に、TiNやTiCN等といった窒化物や炭窒化物の非金属介在物があり、この非金属介在物が鋼中で大きく成長してしまうと、介在物を起点として疲労破壊を生じることになる。
そのため、一般的に鋼中に存在する非金属介在物を少なくするために、真空アーク再溶解(以下、VARと記す)法が用いられている。
However, while maraging steel can obtain very high tensile strength, fatigue strength is not necessarily high. Non-metallic inclusions such as nitrides and carbonitrides such as TiN and TiCN are the biggest factors that degrade this fatigue strength. If these non-metallic inclusions grow greatly in steel, the inclusions originate from the inclusions. Will cause fatigue failure.
Therefore, a vacuum arc remelting (hereinafter referred to as VAR) method is generally used to reduce nonmetallic inclusions present in steel.
このVAR法で製造されるマルエージング鋼は、均質(成分偏析が少ない)でしかも、非金属介在物の量が少なくなると言った利点を有するものである。
しかしながら、VAR法で製造するマルエージング鋼にも、比較的大きなTiNやTiCN等の窒化物や炭窒化物の非金属介在物が残留し、残留した大きな非金属介在物は、VAR後に行う熱間鍛造、熱処理、熱間圧延、冷間圧延を行った後の素材中にもそのまま残留し、残留する大きな非金属介在物を起点とした疲労破壊を生じる原因となっていた。
この問題に対しては種々の提案がなされており、例えば特開2001−214212号(特許文献1参照)に、TiN系介在物を含まない含Ti鋼用原材料を真空誘導炉で溶解し、鋳造して製造した含Ti鋼材を電極として真空アーク溶解法で再溶解するTiN系介在物を微細にする含Ti鋼の製造方法がある。
The maraging steel produced by this VAR method has the advantage that it is homogeneous (small component segregation) and the amount of non-metallic inclusions is reduced.
However, relatively large non-metallic inclusions such as TiN and TiCN nitrides and carbonitrides remain in the maraging steel produced by the VAR method, and the remaining large non-metallic inclusions are heated after VAR. It remains in the raw material after forging, heat treatment, hot rolling, and cold rolling, and causes fatigue failure starting from the remaining large non-metallic inclusions.
Various proposals have been made for this problem. For example, in Japanese Patent Laid-Open No. 2001-214212 (see Patent Document 1), a raw material for Ti-containing steel that does not contain TiN inclusions is melted in a vacuum induction furnace, and cast. There is a method for producing a Ti-containing steel in which TiN-based inclusions are re-melted by a vacuum arc melting method using the Ti-containing steel material produced in this manner as an electrode.
本発者等は、マルエージング鋼の清浄度を更に向上させる検討を行った。
上記の特開2001−214212号では、TiNやTiCNと言った窒化物系非金属介在物を含まない含Ti鋼用原材料を用いることでTiN系窒化物を微細にできることを特徴としている。このような原料自体の品質の管理は窒化物系非金属介在物を低減する一つの手段であるが、高品位な原料は必然的に高価な原料でありコストが大きいという問題がある。
また、TiN系非金属介在物が発生するのは溶解条件等にも依存するため原料の管理だけでは十分な問題解決とはなっていない。
The present inventors studied to further improve the cleanliness of maraging steel.
The above Japanese Patent Application Laid-Open No. 2001-214212 is characterized in that the TiN-based nitride can be made fine by using a raw material for Ti-containing steel that does not contain nitride-based non-metallic inclusions such as TiN and TiCN. Such quality control of the raw material itself is one means for reducing nitride-based nonmetallic inclusions. However, a high-quality raw material is inevitably an expensive raw material and has a problem of high cost.
Further, since the occurrence of TiN-based nonmetallic inclusions depends on the dissolution conditions and the like, the management of the raw materials alone does not sufficiently solve the problem.
また実際にはマルエージング鋼中には窒化物系非金属介在物の他にも、酸化物系非金属介在物も確認されている。酸化物系非金属介在物は存在個数は少ないものの、比較的サイズの大きいもの、例えば直径で20μmを超えるものが確認される場合がある。
このような大きな酸化物系非金属介在物の存在は、TiN等の窒化物系非金属介在物と同様に材料の疲労強度等の機械特性に悪影響を及ぼすことが懸念される。
この非金属介在物による疲労破壊は、非金属介在物の大きさにより決定付けられるものであり、マルエージング鋼の用途が薄い帯材の場合であれば、非金属介在物の種類の存在自身が107回を超える高疲労領域での使用には大きな問題となる。
In fact, oxide-based nonmetallic inclusions have been confirmed in the maraging steel in addition to nitride-based nonmetallic inclusions. Although the number of oxide-based nonmetallic inclusions is small, a relatively large size, for example, a diameter exceeding 20 μm may be confirmed.
The presence of such large oxide-based non-metallic inclusions is likely to have an adverse effect on mechanical properties such as fatigue strength of the material as in the case of nitride-based non-metallic inclusions such as TiN.
This fatigue failure due to non-metallic inclusions is determined by the size of non-metallic inclusions. If the application of maraging steel is a thin strip, the existence of the type of non-metallic inclusions It becomes a big problem when used in a high fatigue region exceeding 10 7 times.
窒化物や酸化物といったガス成分に起因する非金属介在物を低減する手法としてVAR等の真空再溶解法があるが、上述したようにVARの適用だけでは窒化物系や酸化物系の非金属介在物の大きさの低減には限界があった。そのため、マルエージング鋼の非金属介在物の大きさの低減に対して飛躍的に効果がある新しいブレークスルー技術の開発が切望されている。
本発明の目的は、上記課題に鑑みマルエージング鋼中に残留する、非金属介在物の大きさを飛躍的に低減できるマルエージング鋼の製造方法と、これによって得られる新規のマルエージング鋼を提供することである。
As a technique for reducing nonmetallic inclusions caused by gas components such as nitrides and oxides, there is a vacuum remelting method such as VAR, but as described above, nitride-based or oxide-based nonmetals can be obtained only by applying VAR. There was a limit to reducing the size of inclusions. Therefore, the development of a new breakthrough technology that has a dramatic effect on reducing the size of non-metallic inclusions in maraging steel is eagerly desired.
An object of the present invention is to provide a maraging steel manufacturing method capable of dramatically reducing the size of non-metallic inclusions remaining in the maraging steel in view of the above problems, and a novel maraging steel obtained thereby. It is to be.
本発明者等は、マルエージング鋼中のガス成分に起因する非金属介在物の溶解工程、精錬工程、再溶解工程での発生挙動と溶解成分中に存在する元素との因果関係を探求し、上記非金属介在物に対する、真空再溶解に使用する消耗電極中に存在させたMgの優れた非金属介在物の低減と微細化の効果を見いだし、本発明に到達した。 The present inventors have explored the causal relationship between the generation behavior in the melting process, refining process, and remelting process of non-metallic inclusions caused by the gas component in maraging steel and the elements present in the dissolved component, The present inventors have found the excellent effect of reducing and miniaturizing nonmetallic inclusions of Mg present in a consumable electrode used for vacuum remelting with respect to the nonmetallic inclusions, and have reached the present invention.
即ち本発明は、真空再溶解用の消耗電極を製造し、該消耗電極を用いて、真空再溶解を行うTiを含有するマルエージング鋼の製造方法において、前記消耗電極にあらかじめMgを5ppm以上含有させるマルエージング鋼の製造方法である。
好ましくは、真空再溶解用の消耗電極は、真空誘導溶解法で製造するマルエージング鋼の製造方法である。
更に好ましくは、真空再溶解法は真空アーク再溶解法であるマルエージング鋼の製造方法である。
また本発明は、上述した真空再溶解した後、塑性加工により厚さ0.5mm以下の薄帯とするマルエージング鋼の製造方法である。
That is, the present invention produces a consumable electrode for vacuum remelting, and uses the consumable electrode to produce Ti maraging steel containing Ti for vacuum remelting. The consumable electrode contains 5 ppm or more of Mg in advance. This is a method for producing maraging steel.
Preferably, the consumable electrode for vacuum remelting is a method for producing maraging steel produced by a vacuum induction melting method.
More preferably, the vacuum remelting method is a method for producing maraging steel which is a vacuum arc remelting method.
Moreover, this invention is a manufacturing method of the maraging steel made into the thin strip of thickness 0.5mm or less by plastic working, after melt | dissolving in the vacuum mentioned above.
また本発明は、少なくとも質量%で、Mg:10ppm未満(0は含まず)、酸素:10ppm未満、窒素:15ppm未満、Ti:2.0%以下を含有したマルエージング鋼であって、組織中の10μm以上の酸化物系非金属介在物の総個数に対して、前記酸化物系非金属介在物中の金属元素のうち、Alを85mass%以上含む10μm以上の酸化物系非金属介在物(以下、Alを85mass%以上含む酸化物系非金属介在物をアルミナ系の介在物と言う)が70%未満であるマルエージング鋼である。
好ましくは、上述したマルエージング鋼は、酸化物系非金属介在物の最大長さが20μm以下であるマルエージング鋼である。
更に好ましくは、上述のマルエージング鋼は、窒化物系非金属介在物の最大長さが10μm以下であるマルエージング鋼である。
また上述した本発明のマルエージング鋼の好ましい化学組成は、質量%でMg:15ppm未満(0は含まず)、酸素:10ppm未満、窒素:15ppm未満の化学組成に加えて、質量%で、C:0.01%以下、Ni:8.0〜22.0%、Co:5.0〜20.0%、Mo:2.0〜9.0%、Ti:2.0%以下(0は含まず)、Al:1.7%以下、残部は実質的にFeからなるマルエージング鋼である。
また上述した本発明のマルエージング鋼は、厚さが0.5mm以下の薄帯であるマルエージング鋼である。
The present invention also relates to a maraging steel containing at least mass%, Mg: less than 10 ppm (excluding 0), oxygen: less than 10 ppm, nitrogen: less than 15 ppm, and Ti: 2.0% or less. 10 μm or more of oxide-based nonmetallic inclusions containing 10 μm or more of oxide-based nonmetallic inclusions containing 85 mass% or more of Al among the metal elements in the oxide-based nonmetallic inclusions ( Hereinafter, the maraging steel has an oxide-based non-metallic inclusion containing 85 mass% or more of Al (referred to as an alumina-based inclusion) of less than 70%.
Preferably, the above-described maraging steel is maraging steel in which the maximum length of oxide-based nonmetallic inclusions is 20 μm or less.
More preferably, the above-mentioned maraging steel is maraging steel in which the maximum length of nitride-based nonmetallic inclusions is 10 μm or less.
Further, the preferred chemical composition of the above-described maraging steel of the present invention is, in addition to the chemical composition of Mg: less than 15 ppm (excluding 0), oxygen: less than 10 ppm, nitrogen: less than 15 ppm, : 0.01% or less, Ni: 8.0 to 22.0%, Co: 5.0 to 20.0%, Mo: 2.0 to 9.0%, Ti: 2.0% or less (0 is Not including), Al: 1.7% or less, the balance being maraging steel substantially consisting of Fe.
The maraging steel of the present invention described above is a maraging steel that is a ribbon having a thickness of 0.5 mm or less.
本発明のマルエージング鋼は酸化物系非金属介在物を小さくすることができ、更に、TiNやTiCN等の窒化物系非金属介在物の大きさも小さくすることが可能であり、大きな非金属介在物を少なくすることができるため、優れた疲労強度を有するものとなる。
本発明のマルエージング鋼の薄帯は、自動車エンジンの無段変速機用部品として最適である。
The maraging steel of the present invention can reduce oxide-based non-metallic inclusions, and can further reduce the size of nitride-based non-metallic inclusions such as TiN and TiCN. Since the number of objects can be reduced, it has excellent fatigue strength.
The maraging steel ribbon of the present invention is optimal as a component for a continuously variable transmission of an automobile engine.
本発明の最大の特徴は、VARや真空ESR等の真空再溶解に用いる消耗電極中に特定量のMgを添加したことにある。これらの消耗電極中にMgを添加することによる非金属介在物の低減あるいは微細化の効果は、以下に基づくものと推定している。
Mgを適量添加すると、消耗電極製造過程で溶解中に存在する酸素は、典型的な非金属介在物であるアルミナの起源となるAlよりも親和力の高いMgと結びついてMgOを主体とするMgO系非金属介在物を多く生成する。
そして、このMgO系非金属介在物の凝集性はアルミナより弱いため、電極中には極端に大きな酸化物系非金属介在物は少なくなる。なお、実際の酸化物系非金属介在物の形態としては、Al−Mg−O系(MgO・Al2O3系)のスピネル系の介在物となることもある。
また、凝集性の弱いMgOが多数形成することに伴い、MgOを核として窒化物や炭窒化物が生成することで消耗電極中における窒化物や炭窒化物が微細化する。
The greatest feature of the present invention is that a specific amount of Mg is added to a consumable electrode used for vacuum remelting such as VAR and vacuum ESR. The effect of reducing or miniaturizing non-metallic inclusions by adding Mg to these consumable electrodes is presumed to be based on the following.
When an appropriate amount of Mg is added, the oxygen present during dissolution in the consumable electrode manufacturing process is combined with Mg, which has a higher affinity than Al, which is the origin of alumina, which is a typical non-metallic inclusion, and is based on MgO. Many non-metallic inclusions are produced.
And since the aggregation property of this MgO-based nonmetallic inclusion is weaker than that of alumina, extremely large oxide-based nonmetallic inclusions are reduced in the electrode. In addition, as an actual form of oxide-based non-metallic inclusions, an Al—Mg—O-based (MgO · Al 2 O 3 -based) spinel-based inclusion may be used.
In addition, with the formation of a large number of MgO having weak cohesion, nitrides and carbonitrides in the consumable electrode are refined by forming nitrides and carbonitrides using MgO as a nucleus.
このような消耗電極に対して真空再溶解を適用すると、高温領で揮発性元素であるMgの蒸発が起こり、MgOやスピネル系の非金属介在物が分解され、酸素の気相および液相への拡散が起こる。つまり、MgOの分解により、酸化物の低減は促進されることになる。一部液相に拡散する酸素もあるが、この酸素によって新たに発生する酸化物系非金属介在物は多くなく結果として酸化物系非金属介在物は微細なものとなる。
一方、TiNやTiCNといった窒化物系非金属介在物もMgOを核として消耗電極中に存在するため、再溶解中に窒化物系非金属介在物の熱分解が促進され、結果として窒化物系非金属介在物の微細化が達成される。
When vacuum remelting is applied to such a consumable electrode, Mg, which is a volatile element, evaporates in a high temperature region, and MgO and spinel-based non-metallic inclusions are decomposed into oxygen gas phase and liquid phase. Diffusion occurs. That is, the reduction of the oxide is promoted by the decomposition of MgO. Although some oxygen diffuses into the liquid phase, there are not many oxide-based nonmetallic inclusions newly generated by this oxygen, and as a result, the oxide-based nonmetallic inclusions are fine.
On the other hand, nitride-based nonmetallic inclusions such as TiN and TiCN are also present in the consumable electrode with MgO as a nucleus, so that the thermal decomposition of the nitride-based nonmetallic inclusions is promoted during remelting. Miniaturization of metal inclusions is achieved.
以上の推定される作用により、従来技術により得られたマルエージング鋼よりも著しく非金属介在物が低減かつ微細化されたマルエージング鋼を提供することが可能になる。
マルエージング鋼においては、TiやAlといった時効処理により微細な金属間化合物を形成し、析出することによって強化に寄与する元素を必要とする一方で、これらの元素は、非金属介在物を形成するという避けられない問題を抱えていた。
本発明により見いだされた、Mgを利用した製造技術の開発は、窒化物系及び酸化物系の両方に対する低減効果と微細化効果が両立できるという、極めて有効なブレークスルー技術である。
By the above estimated action, it is possible to provide a maraging steel in which nonmetallic inclusions are remarkably reduced and refined compared to the maraging steel obtained by the prior art.
In maraging steel, fine intermetallic compounds such as Ti and Al are formed, and elements contributing to strengthening by precipitation are required, while these elements form non-metallic inclusions. I had an inevitable problem.
The development of a manufacturing technology using Mg found by the present invention is a very effective breakthrough technology that can achieve both a reduction effect and a miniaturization effect for both nitride and oxide systems.
なお、TiNやTiCN等の窒化物系の非金属介在物が及ぼす悪影響を考慮して、Tiを意図的に無添加としたり、0.2%未満の範囲に制限したようなマルエージング鋼もあるが、本発明の製造方法の効果によって、TiNやTiCN等の窒化物系の非金属介在物が及ぼす悪影響を排除することができるため、Tiを積極的に添加させ、Tiによる強化の効果を最大限発揮させることができる。
よって、本発明の製造方法は、Tiを0.3%以上含有するマルエージング鋼に対して、特に有効である。
なお、本発明で真空再溶解とは真空排気を行いながら、再溶解を行うものである。
In consideration of the adverse effects of nitride-based non-metallic inclusions such as TiN and TiCN, there are also maraging steels in which Ti is intentionally not added or limited to a range of less than 0.2%. However, since the adverse effects exerted by nitride-based non-metallic inclusions such as TiN and TiCN can be eliminated by the effect of the manufacturing method of the present invention, Ti is actively added, and the effect of strengthening by Ti is maximized. It can be made to the limit.
Therefore, the production method of the present invention is particularly effective for maraging steel containing 0.3% or more of Ti.
In the present invention, vacuum remelting refers to remelting while evacuating.
本発明の製造方法において、消耗電極中にMgを5ppm以上含有させると規定した。これは、Mgが5ppm未満ではMg添加による非金属介在物の低減と微細化の効果が顕著に現れないためである。
望ましい消耗電極でのMg濃度の上限は、再溶解後の鋼塊または製品の靭性を考慮すると300ppm以下であり、5〜250ppmであれば上記の効果がより確実に得られるので上限は250ppmとするのが好ましい。
但し、揮発性の強いMgの添加は歩留が低く経済的でなく、またMgは真空再溶解で激しく蒸発し、操業を害するだけでなく鋼塊肌を悪くする場合があることからMg濃度の好ましい上限は200ppmとすると良い。より好ましい範囲は10〜150ppmの範囲である。
In the production method of the present invention, it is defined that 5 ppm or more of Mg is contained in the consumable electrode. This is because when Mg is less than 5 ppm, the effects of reduction and refinement of nonmetallic inclusions due to the addition of Mg do not appear remarkably.
The upper limit of the Mg concentration at the desired consumable electrode is 300 ppm or less in consideration of the toughness of the steel ingot or product after remelting, and the upper limit is 250 ppm because the above effect can be obtained more reliably if it is 5 to 250 ppm. Is preferred.
However, the addition of Mg, which is highly volatile, is low in yield and is not economical, and Mg evaporates violently by vacuum remelting, which not only harms the operation but also worsens the steel ingot skin. A preferable upper limit is 200 ppm. A more preferred range is from 10 to 150 ppm.
本発明において、消耗電極の製造は真空誘導溶解法(以下、VIMと記す)の適用が望ましい。これは、ルツボ内の溶解原料を真空中で溶解するため、大気中の酸素、窒素と溶鋼との反応による鋼中の酸化物、窒炭化物の増加を避けられる点、酸素と活性なMgを安定して溶鋼中に添加するのに有利である点、原料から不可避的に混入する酸素、窒素を除去できる機能を有している点を有しているからである。
特に、マルエージング鋼の場合では、活性なTiを含有しているため、溶湯と大気との接触はできる限り避けた方がよく、大気と遮断された環境中でから消耗電極を製造可能なVIMの適用は最適である。
なお、同様の機能すなわち大気による溶鋼の汚染を防止でき、Mgを添加できる機能を有している溶解設備であればVIMの代わりとすることもできる。
In the present invention, it is desirable to apply a vacuum induction melting method (hereinafter referred to as VIM) for the production of the consumable electrode. This is because the melting raw material in the crucible is melted in vacuum, so that the increase of oxygen in the atmosphere, oxides in the steel due to the reaction between nitrogen and molten steel, and nitrogen carbides can be avoided, and oxygen and active Mg are stabilized. This is because it has the function of being able to remove oxygen and nitrogen that are inevitably mixed from the raw material.
In particular, in the case of maraging steel, since it contains active Ti, it is better to avoid contact between the molten metal and the atmosphere as much as possible, and a VIM that can produce a consumable electrode in an environment cut off from the atmosphere. The application of is optimal.
It should be noted that a melting facility having the same function, that is, contamination of molten steel by the atmosphere and capable of adding Mg, can be used in place of VIM.
真空再溶解法には真空アーク再溶解法の他に、電子ビーム再溶解法があるが、電子ビーム再溶解法はランニングコストが高いこと、高真空下でビームが照射される溶鋼表面温度が高く元素の選択的蒸発が起こり成分制御が難しいことがある。また真空エレクトロスラグ再溶解法は真空アーク再溶解法同様にMg添加の効果は得られるが、スラグによりMgの蒸発現象が抑制されるため、Mg添加効果が低減されることから、本発明において真空再溶解には真空アーク再溶解法が好ましい。 The vacuum remelting method includes the electron beam remelting method in addition to the vacuum arc remelting method, but the electron beam remelting method has a high running cost and the surface temperature of the molten steel irradiated with the beam under high vacuum is high. Selective evaporation of elements may occur and component control may be difficult. In addition, the vacuum electroslag remelting method has the effect of adding Mg as in the vacuum arc remelting method, but since the Mg evaporation phenomenon is suppressed by the slag, the effect of adding Mg is reduced. A vacuum arc remelting method is preferred for remelting.
上述した方法により製造されたマルエージング鋼を、自動車エンジンの無段変速機用部品に適用する場合、熱間圧延や冷間圧延等の塑性加工により、0.5mm以下の薄帯とする。
この塑性加工によって、酸化物系の非金属介在物は真空再溶解後に行う塑性加工等によって、破砕されたり伸展されさらには引き千切られた状態となって更に微細なものとすることが可能となる。例えば、Mg添加によって生成されたMgOや、真空再溶解時で生成するスピネル系の介在物凝集体も、熱間や冷間での塑性加工により分断し、微細化していく。
この塑性加工を組み合わせることで、高疲労強度を有する無段変速機用部品用マルエージング鋼薄帯として特に好適となる。
When the maraging steel produced by the above-described method is applied to a continuously variable transmission part of an automobile engine, a strip of 0.5 mm or less is formed by plastic working such as hot rolling or cold rolling.
Owing to this plastic working, oxide-based non-metallic inclusions can be crushed or stretched and further shredded and further refined by plastic working performed after vacuum remelting. . For example, MgO produced by the addition of Mg and spinel inclusion aggregates produced during vacuum remelting are divided and refined by hot or cold plastic working.
Combining this plastic working is particularly suitable as a maraging steel ribbon for continuously variable transmission parts having high fatigue strength.
なお、より無段変速機用部品用マルエージング鋼薄帯に好適とするためには、真空再溶解後の鋼塊状態または熱間鍛造後の何れか若しくは両方で、1000〜1300℃で少なくとも5時間以上の保持を行い、成分の偏析を軽減する均質化熱処理を適用すると良い。
均質化熱処理を施すと、成分偏析を更に低減できる。均質化熱処理の温度は、高温で長時間行うとより成分偏析は少なくなるが、保持温度が1300℃を超えると表面酸化が過度に促進してしまう。逆に1000℃より低いとその効果は低くいため、1000℃〜1300℃の範囲で行うと良い。
In order to make it more suitable for a maraging steel ribbon for parts for continuously variable transmissions, at least 5 at 1000 to 1300 ° C., either in a steel ingot state after vacuum remelting or after hot forging, or both. It is preferable to apply a homogenization heat treatment that keeps for more than a time and reduces segregation of components.
When the homogenization heat treatment is performed, component segregation can be further reduced. When the homogenization heat treatment is performed at a high temperature for a long time, the segregation of components is reduced. However, when the holding temperature exceeds 1300 ° C., surface oxidation is excessively promoted. Conversely, when the temperature is lower than 1000 ° C., the effect is low.
また、均質化熱処理の保持時間が5時間より短いと均質化の効果が低いため、保持時間は少なくとも5時間以上が良く、この均質化熱処理を施すと、特に成分偏析を起こし易いTi及びMoの成分偏析を、EPMAにて線分析した時、TiとMoそれぞれの最大値と最小値とを測定して、その比(最大値/最小値)を算出して1.3以下の範囲とすることができる。 Further, if the holding time of the homogenization heat treatment is shorter than 5 hours, the effect of the homogenization is low. Therefore, the holding time is preferably at least 5 hours or more. When component segregation is linearly analyzed with EPMA, the maximum and minimum values of Ti and Mo are measured, and the ratio (maximum value / minimum value) is calculated to be within 1.3 or less. Can do.
上述したように、Mgを適量添加することで窒化物系非金属介在物を小さくすることが可能となる。この効果をより確実に得るには以下の方法が有効である。
(1)電極鋼塊製造時の凝固速度を高めること、
(2)電極鋼塊の窒素濃度を下げること、
(3)電極中に存在する窒化物や炭窒化物の非金属介在物の大きさを、最大で10μm以下に調整すること、
以上のような製造方法を単独若しくは幾つかを組合せて適用することが有効である。
As described above, the addition of an appropriate amount of Mg makes it possible to reduce nitride-based nonmetallic inclusions. The following method is effective for obtaining this effect more reliably.
(1) Increasing the solidification rate at the time of manufacturing the electrode ingot,
(2) reducing the nitrogen concentration of the electrode steel ingot,
(3) adjusting the size of the non-metallic inclusions of nitrides and carbonitrides present in the electrode to a maximum of 10 μm or less,
It is effective to apply the above manufacturing methods singly or in combination.
上述した製造方法を適用したマルエージング鋼では、Mgの積極添加により、従来のマルエージング鋼では見られない特徴的な酸化物系非金属介在物の形態となり、窒化物や炭窒化物等の窒化物系非金属介在物も微細化される。
具体的には、非常に僅かではあり例えば電子顕微鏡観察でも容易に発見することはできないが、MgO単独の非金属介在物が存在したり、10μm以上の酸化物系非金属介在物の総個数に対して、10μm以上のアルミナ系の介在物が70%未満である。
In the maraging steel to which the manufacturing method described above is applied, the active addition of Mg results in the form of characteristic oxide-based non-metallic inclusions not found in conventional maraging steel, and nitrides such as nitrides and carbonitrides. Physical non-metallic inclusions are also refined.
Specifically, for example, it is very small and cannot be easily found even by observation with an electron microscope, but there is a non-metallic inclusion of MgO alone or the total number of oxide-based non-metallic inclusions of 10 μm or more. On the other hand, alumina inclusions of 10 μm or more are less than 70%.
これは、消耗電極製造時にMgを積極添加しないものでは、アルミナ系の介在物が約80%程度の確認できるが、本発明の製造方法を適用すると10μm以上の酸化物系非金属介在物の総個数に対して、10μm以上のアルミナ系の介在物が70%未満である点で、非常に特徴的である。より好ましい範囲は10μm以上のアルミナ系の介在物が50%未満の範囲であり、更に好ましくは30%未満の範囲である。
なお、10μm以上の酸化物系非金属介在物としているのは、この範囲が疲労強度に特に影響を及ぼす可能性のある大きさの非金属介在物であることと、余りにも小さな非金属介在物は正確に個数の確認のするのが困難であるためである。
This is because alumina inclusions can be confirmed to be about 80% in the case where Mg is not actively added at the time of consumable electrode production, but when the production method of the present invention is applied, the total of oxide-based nonmetallic inclusions of 10 μm or more is confirmed. This is very characteristic in that the number of alumina inclusions of 10 μm or more is less than 70% with respect to the number. A more preferred range is a range of less than 50% of alumina inclusions of 10 μm or more, and a further preferred range is less than 30%.
Note that the oxide-based non-metallic inclusions of 10 μm or more are the non-metallic inclusions having a size that may particularly affect the fatigue strength, and the non-metallic inclusions that are too small. This is because it is difficult to confirm the number accurately.
なお、本発明で言うアルミナ系の介在物とは、組織中の非金属介在物を例えばEDX(エネルギー分散型エックス線分析装置)で定性/定量分析を行った時、例えば図3、4に示すように非金属介在物を構成するガス成分のうち、O(酸素)ピークが主体となって検出され、O以外の検出された元素のうち、Alが85mass%以上となる非金属介在物を言う。
また、スピネル系の介在物とは、例えば図1、2に示すように、非金属介在物を構成するガス成分のうち、O(酸素)ピークが主体となって検出され、O以外の検出された元素のうち、Alが85mass%未満であり、Mgが検出される非金属介在物を言う。
なお、非金属介在物を分析する際には、例えば金属ブロック状の試験片を用いる場合には、マトリックス(基地)の影響が大きく、マルエージング鋼の主成分が検出されるため、できることなら非金属介在物を抽出して分析するのが良い。但し、図1、3に示すように酸化物系介在物は球状のものが多いため、ポイント分析するより、ある程度の範囲をもってエリア分析するのが良い。
The alumina-based inclusions referred to in the present invention are, for example, as shown in FIGS. 3 and 4 when non-metallic inclusions in the structure are subjected to qualitative / quantitative analysis using, for example, EDX (energy dispersive X-ray analyzer). Among the gas components constituting non-metallic inclusions, the non-metallic inclusions are mainly detected by the O (oxygen) peak, and among the detected elements other than O, Al is 85 mass% or more.
In addition, as shown in FIGS. 1 and 2, for example, spinel inclusions are detected mainly by O (oxygen) peaks in gas components constituting nonmetallic inclusions, and are detected except for O. Among these elements, Al is less than 85 mass%, and refers to non-metallic inclusions in which Mg is detected.
When analyzing non-metallic inclusions, for example, when using a metal block-shaped test piece, the influence of the matrix (base) is large and the main component of maraging steel is detected. It is better to extract and analyze metal inclusions. However, as shown in FIGS. 1 and 3, since oxide inclusions are mostly spherical, it is better to perform area analysis with a certain range rather than point analysis.
また、上述の酸化物系非金属介在物の総個数に対するアルミナ系の介在物の割合に加えて、本発明の製造方法を適用したものでは、Mg添加量の調整や電極鋼塊の製造条件の調整に加えて、VIM、VAR等を組合せることで酸化物系非金属介在物の最大長さを20μm以下、窒化物系非金属介在物の最大長さが10μm以下とすることができる。
酸化物系非金属介在物の最大長さが20μm以下とすると、疲労破壊の起点となる危険性も低減でき、高疲労強度を有する無段変速機用部品用マルエージング鋼薄帯として特に好適となる。
In addition to the above-mentioned ratio of alumina inclusions to the total number of oxide-based nonmetallic inclusions, in the case where the production method of the present invention is applied, the adjustment of the Mg addition amount and the production conditions of the electrode steel ingot In addition to adjustment, by combining VIM, VAR, etc., the maximum length of the oxide-based nonmetallic inclusions can be 20 μm or less, and the maximum length of the nitride-based nonmetallic inclusions can be 10 μm or less.
When the maximum length of oxide-based nonmetallic inclusions is 20 μm or less, the risk of starting fatigue failure can be reduced, and it is particularly suitable as a maraging steel ribbon for continuously variable transmission parts having high fatigue strength. Become.
窒化物系非金属介在物の最大長さも10μm以下とすると、更に疲労破壊の起点となる危険性も低減でき、高疲労強度を有する無段変速機用部品用マルエージング鋼薄帯として特に好適となる。なお、適正なMg添加、上述した電極鋼塊製造条件等を調整すれば、窒化物系非金属介在物の最大長さを8μm以下にすることもできる。
また、本発明で言う最大長さとは、非金属介在物が酸化物系である場合、非金属介在物に外接する円の直径で評価し、この外接する円の直径を非金属介在物の最大の長さと定義する。但し、窒化物系非金属介在物は矩形形状であるため、長辺aと短辺bを測定し、面積a×bに相当する円の直径をその最大長さとする。
If the maximum length of nitride-based nonmetallic inclusions is also 10 μm or less, the risk of starting fatigue failure can be further reduced, and it is particularly suitable as a maraging steel ribbon for continuously variable transmission parts having high fatigue strength. Become. It should be noted that the maximum length of the nitride-based nonmetallic inclusions can be reduced to 8 μm or less by adjusting the appropriate Mg addition, the above-described electrode ingot manufacturing conditions, and the like.
In addition, the maximum length referred to in the present invention means that when the nonmetallic inclusion is an oxide, it is evaluated by the diameter of a circle circumscribing the nonmetallic inclusion, and the diameter of the circumscribed circle is the maximum of the nonmetallic inclusion. Is defined as the length of However, since the nitride-based nonmetallic inclusion has a rectangular shape, the long side a and the short side b are measured, and the diameter of a circle corresponding to the area a × b is set as the maximum length.
次に、本発明のマルエージング鋼の組成範囲の限定理由について述べる。特に指定がない限り、質量%として示す。
先ずは、必須で規定するMg、O(酸素)、N(窒素)及びTiの限定理由から述べる。
Mgは、本発明で電極製造時に必須で添加されるもので、真空再溶解後のマルエージング鋼とした時にも必須成分として残留する。しかしながら、Mgが15ppm以上残留すると、製品としてのマルエージング鋼や塑性加工を行う素材としてのマルエージング鋼として、Mgの過度の残留は靭性の点から好ましくなく、本発明の真空再溶解を適用してMgを15ppm未満まで低減させるのが良い。
そのためには、上述のように消耗電極中のMgの上限を250ppm以下に制御するのが良く、真空再溶解後のマルエージング鋼とした時に15ppm未満とすることが必要である。
Next, the reason for limiting the composition range of the maraging steel of the present invention will be described. Unless otherwise specified, it is expressed as mass%.
First, the reasons for limiting Mg, O (oxygen), N (nitrogen), and Ti, which are essential, will be described.
Mg is essential and added during the production of the electrode in the present invention, and remains as an essential component even when maraging steel is obtained after vacuum remelting. However, if Mg remains at 15 ppm or more, excessive residual Mg is not preferable in terms of toughness as maraging steel as a product or maraging steel as a material for plastic working, and the vacuum remelting of the present invention is applied. Therefore, it is preferable to reduce Mg to less than 15 ppm.
For that purpose, it is good to control the upper limit of Mg in the consumable electrode to 250 ppm or less as mentioned above, and it is necessary to make it less than 15 ppm when it is set as the maraging steel after vacuum remelting.
O(酸素)は、酸化物系非金属介在物を形成するため、10ppm未満に制限する。Oが10ppm以上含有すると疲労強度が著しく低下するため、その含有量を10ppm未満にした。
N(窒素)は、窒化物や炭窒化物系非金属介在物を形成するため、15ppm未満に制限する。Nが15ppm以上含有すると疲労強度が著しく低下するため、その含有量を15ppm未満にした。
Tiは、時効処理により微細な金属間化合物を形成し、析出することによって強化に寄与する必要不可欠な元素であるが、その含有量が2.0%を越えて含有させると延性、靱性が劣化するため、Tiの含有量を2.0%以下(0は含まず)とした。
O (oxygen) is limited to less than 10 ppm because it forms oxide-based nonmetallic inclusions. When O is contained in an amount of 10 ppm or more, the fatigue strength is remarkably lowered, so the content was made less than 10 ppm.
N (nitrogen) is limited to less than 15 ppm in order to form nitrides and carbonitride nonmetallic inclusions. When N is contained in an amount of 15 ppm or more, the fatigue strength is remarkably lowered, so the content was made less than 15 ppm.
Ti is an indispensable element that contributes to strengthening by forming and precipitating fine intermetallic compounds by aging treatment, but if its content exceeds 2.0%, ductility and toughness deteriorate. Therefore, the Ti content is set to 2.0% or less (0 is not included).
次に、上記の化学組成に加えて、好ましい範囲として規定した成分限定理由について述べる。
Cは炭化物を形成し、金属間化合物の析出量を減少させて疲労強度を低下させるため本発明ではCの上限を0.01%以下とした。
Niは靱性の高い母相組織を形成させるためには不可欠の元素であるが、8.0%未満では靱性が劣化する。一方、22%を越えるとオーステナイトが安定化し、マルテンサイト組織を形成し難くなることから、Niは8.0〜22.0%とした。
Next, in addition to the above chemical composition, the reasons for limiting the components defined as a preferred range will be described.
Since C forms carbides and decreases the precipitation amount of intermetallic compounds to reduce fatigue strength, the upper limit of C is set to 0.01% or less in the present invention.
Ni is an indispensable element for forming a matrix structure with high toughness, but if it is less than 8.0%, the toughness deteriorates. On the other hand, if it exceeds 22%, austenite is stabilized and it becomes difficult to form a martensite structure. Therefore, Ni is set to 8.0 to 22.0%.
Coは、マトリックスであるマルテンサイト組織を安定性に大きく影響することなく、Moの固溶度を低下させることによってMoが微細な金属間化合物を形成して析出するのを促進することによって析出強化に寄与するが、その含有量が5.0%未満では必ずしも十分効果が得られず、また20.0%を越えると脆化する傾向がみられることから、Coの含有量は5.0〜20.0%にした。
Moは時効処理により、微細な金属間化合物を形成し、マトリックスに析出することによって強化に寄与する元素であるが、その含有量が2.0%未満の場合その効果が少なく、また9.0%を越えて含有すると延性、靱性を劣化させるFe、Moを主要元素とする粗大析出物を形成しやすくなるため、Moの含有量を2.0〜9.0%とした。
Alは、時効析出した強化に寄与するだけでなく、脱酸作用を持っているが、1.7%を越えて含有させると靱性が劣化することから、その含有量を1.7%以下とした。
Co does not greatly affect the stability of the martensite structure that is the matrix, but strengthens the precipitation by reducing the solid solubility of Mo and promoting the precipitation of Mo by forming fine intermetallic compounds. However, if the content is less than 5.0%, a sufficient effect is not necessarily obtained, and if it exceeds 20.0%, embrittlement tends to occur, so the Co content is 5.0 to 20.0%.
Mo is an element that contributes to strengthening by forming a fine intermetallic compound by aging treatment and precipitating in the matrix. However, when its content is less than 2.0%, its effect is small, and 9.0 If the content exceeds 50%, it becomes easy to form coarse precipitates containing Fe and Mo as main elements which deteriorate ductility and toughness. Therefore, the Mo content is set to 2.0 to 9.0%.
Al not only contributes to strengthening by aging precipitation, but also has a deoxidizing action, but if it exceeds 1.7%, toughness deteriorates, so its content is 1.7% or less. did.
なお、本発明ではこれら規定する元素以外は実質的にFeとしているが、例えばBは結晶粒を微細化するのに有効な元素でるため、靱性が劣化させない程度の0.01%以下の範囲で含有させても良い。
また、不可避的に含有する不純物元素は含有されるものである。このうち、Si、Mnは脆化をもたらす粗大な金属間化合物の析出を促進して延性、靭性を低下させたり、非金属介在物を形成して疲労強度を低下させるので、Si、Mn共に0.1%以下に、望ましくは0.05%以下とすれば良く、また、P、Sも粒界脆化させたり、非金属介在物を形成して疲労強度を低下させるので、0.01%以下とすると良い。
In the present invention, elements other than these specified elements are substantially Fe. However, for example, B is an element effective for refining crystal grains, so that the toughness is not deteriorated within a range of 0.01% or less. It may be included.
Moreover, the impurity element contained unavoidable is contained. Among these, Si and Mn promote precipitation of coarse intermetallic compounds that cause embrittlement, thereby reducing ductility and toughness, and forming non-metallic inclusions to reduce fatigue strength. .1% or less, preferably 0.05% or less, and P and S also cause grain boundary embrittlement or non-metallic inclusions to reduce fatigue strength. The following should be used.
以下、実施例として更に詳しく本発明を説明する。
マルエージング鋼の代表成分に、Mg含有量を6通りに変化させたVAR溶解用の消耗電極をVIMで製造した。また比較材としてVIMでMg無添加の条件で製造した消耗電極も製造した。消耗電極にはそれぞれ鋳型寸法鋳型比は同一のものを使用した。(No.1〜6)
VIMでは原料を精選し真空精錬を行ない、酸化物系非金属介在物と同様マルエージング鋼の疲労特性に有害な影響を及ぼすTiCN,TiNといったチタンの炭窒化物系非金属介在物の大きさを10μm以下に制御した。
制御の方法は、電極製造時の鋳型比は2.5とし、鋳造後鋳型の衝風冷却によって凝固速度を高めた。なお、原料は窒素含有量が15ppmといった窒素含有量の低い原料を用いた。
Hereinafter, the present invention will be described in more detail as examples.
As a representative component of maraging steel, a consumable electrode for VAR melting, in which the Mg content was changed in six ways, was manufactured by VIM. In addition, a consumable electrode manufactured by VIM under the condition of no addition of Mg was also manufactured as a comparative material. Consumable electrodes having the same mold size and mold ratio were used. (No. 1-6)
In VIM, raw materials are carefully selected and vacuum refining is performed, and the size of titanium carbonitride nonmetallic inclusions such as TiCN and TiN, which have a detrimental effect on the fatigue properties of maraging steel, as well as oxide nonmetallic inclusions. It controlled to 10 micrometers or less.
In the control method, the mold ratio at the time of electrode production was 2.5, and the solidification rate was increased by blast cooling of the mold after casting. As the raw material, a raw material having a low nitrogen content such as a nitrogen content of 15 ppm was used.
これら炭窒化物のための処置に加えNi−Mg合金によるMgの添加を行ないVAR造塊に供する電極を製造した。
Mgの添加については、Ni−Mg,Fe−MgをはじめとするMg合金や金属Mgを溶鋼へ直接添加する方法があるが、今回は取り扱いが容易で、Mgの成分調整が容易なことからNi−Mg合金による添加を行った。
さらに、Mg添加による窒化物や炭窒化物への影響を明確にするため、窒素濃度を5ppmと10ppmに調整した消耗電極を6本(No.7〜12)製造し、真空再溶解を行なった。
In addition to these treatments for carbonitride, Mg was added by a Ni—Mg alloy to produce an electrode for VAR ingot formation.
Regarding the addition of Mg, there is a method of directly adding Mg alloys such as Ni-Mg and Fe-Mg or metal Mg to molten steel, but this time it is easy to handle and Ni components can be easily adjusted. -Addition with Mg alloy was performed.
Furthermore, in order to clarify the influence of the addition of Mg on nitrides and carbonitrides, six consumable electrodes (No. 7 to 12) whose nitrogen concentrations were adjusted to 5 ppm and 10 ppm were manufactured, and vacuum remelting was performed. .
これらVIMで製造した電極を同一条件の下でVARを用いて再溶解し、鋼塊を製造した。VARの鋳型はそれぞれ同一のものを用い、真空度は1.3Pa、投入電流は鋼塊の定常部で6.5KAで溶解した。
VIMで製造した消耗電極及びその電極をVARにて真空再溶解して得られた鋼塊の化学組成を表1に示す。No7〜No12がMg添加による窒化物や炭窒化物への影響を見たものである。なお、消耗電極は「電極」として、VAR後のものは「鋼塊」として示した。
These VIM-made electrodes were remelted using VAR under the same conditions to produce steel ingots. The same VAR molds were used, the degree of vacuum was 1.3 Pa, and the input current was melted at 6.5 KA in the stationary part of the steel ingot.
Table 1 shows the chemical composition of the consumable electrode manufactured by VIM and the steel ingot obtained by vacuum remelting the electrode with VAR. No. 7 to No. 12 look at the influence on the nitrides and carbonitrides due to the addition of Mg. The consumable electrode is indicated as “electrode”, and the post-VAR electrode is indicated as “steel ingot”.
得られたVAR後の鋼塊を1250℃×20時間のソーキングを行なった後、熱間鍛造を行なって熱間鍛造品とした。
次に、これら材料に熱間圧延、820℃×1時間の溶体化処理、冷間圧延、820℃×1時間の溶体化処理と480℃×5時間の時効処理を行ない、厚み0.5mmのマルエージング鋼帯を製造した。
The obtained steel ingot after VAR was soaked at 1250 ° C. for 20 hours, and then hot forged to obtain a hot forged product.
Next, hot rolling, solution treatment at 820 ° C. × 1 hour, cold rolling, solution treatment at 820 ° C. × 1 hour and aging treatment at 480 ° C. × 5 hours are performed on these materials, and the thickness is 0.5 mm. A maraging steel strip was produced.
先ず、No.1〜No.6のマルエージングの「鋼塊」から100g採取し、混酸溶液または臭素メタノール溶液等で溶解後、フィルターでろ過し、フィルター上の酸化物からなる残渣をSEM(走査型電子顕微鏡)とEDXを用いて観察・分析を行ない、10μm以上の酸化物系非金属介在物の組成及びサイズを測定した。測定結果を表2に示す。
また、No.1〜No.6のマルエージングの鋼帯の両端部から横断試料を100g採取し、混酸溶液または臭素メタノール溶液等で溶解後、フィルターでろ過し、フィルター上の酸化物からなる残渣をSEMで観察を行ない、10μm以上の酸化物系非金属介在物の組成及びサイズを測定した。
これらの非金属介在物のサイズ測定にあたっては非金属介在物に外接する円の直径を非金属介在物の最大長さとした。この結果を表3に示す。
First, no. 1-No. 100 g from the “steel ingot” of No. 6 maraging, dissolved in a mixed acid solution or bromine-methanol solution, etc., filtered through a filter, and the residue consisting of oxides on the filter was analyzed using SEM (scanning electron microscope) and EDX Observation and analysis were performed, and the composition and size of oxide-based nonmetallic inclusions of 10 μm or more were measured. The measurement results are shown in Table 2.
No. 1-No. 100 g of a transverse sample was taken from both ends of the maraging steel strip of No. 6, dissolved in a mixed acid solution or bromine-methanol solution, filtered through a filter, and the residue made of oxide on the filter was observed by SEM, and 10 μm The composition and size of the above oxide-based nonmetallic inclusions were measured.
In measuring the sizes of these nonmetallic inclusions, the diameter of the circle circumscribing the nonmetallic inclusions was taken as the maximum length of the nonmetallic inclusions. The results are shown in Table 3.
表2及び3から、消耗電極Mgの値が5ppm以上のものではマルエージング鋼中には20μmを越える大きな酸化物系非金属介在物がなくなり、電極Mg含有量が多くなるに従いその大きさが小さくなる傾向が伺える。
また、「鋼塊」から鋼帯に塑性加工を加えることで、No.1〜No.6の酸化物系非金属介在物の大きさが小さくなっていることも分かる。これは、非金属介在物が塑性加工による分解(破砕)が進行したものと考えられる。
また、今回の評価で観察された酸化物系非金属介在物の組成は本発明によるものではスピネル系の介在物とMgOが主体となっており、表1及び2中の10μm以上のアルミナ系の介在物以外の酸化物系非金属介在物は、殆どが前述のスピネル系の介在物、MgOであった。比較例のものではアルミナ系の介在物を主体とするものであった。
なお、0.5mmの薄帯の化学組成は表1に「鋼塊」として示したものと同じであり、TiNやTiCNの介在物の最大長さは、何れのものも15μm以下となっていたことをSEM観察により確認した。
図1にNo.1のマルエージング鋼塊中に見られたスピネル系の介在物の電子顕微鏡写真と、化学組成ピークを図2として示し、図3にNo.5のマルエージング鋼塊中に見られたアルミナ系の介在物の電子顕微鏡写真と、化学組成ピークを図4として示す。両者の間では、非金属介在物の種類や大きさが異なるのが良く分かる。
From Tables 2 and 3, when the value of the consumable electrode Mg is 5 ppm or more, there is no large oxide-based nonmetallic inclusion exceeding 20 μm in the maraging steel, and the size decreases as the electrode Mg content increases. I can see a tendency to become.
In addition, by applying plastic working from “steel ingot” to steel strip, No. 1-No. It can also be seen that the size of the oxide-based non-metallic inclusion of 6 is small. This is considered that the decomposition (crushing) of the non-metallic inclusions by plastic working has progressed.
The composition of oxide-based nonmetallic inclusions observed in this evaluation is mainly composed of spinel inclusions and MgO according to the present invention. Most of the oxide-based nonmetallic inclusions other than the inclusions were the above-mentioned spinel inclusions, MgO. The comparative example was mainly composed of alumina inclusions.
The chemical composition of the 0.5 mm ribbon was the same as that shown in Table 1 as “steel ingots”, and the maximum length of inclusions of TiN and TiCN was 15 μm or less in any case. This was confirmed by SEM observation.
In FIG. 1 shows an electron micrograph and a chemical composition peak of the spinel inclusions found in the maraging steel ingot No. 1 in FIG. FIG. 4 shows an electron micrograph of an alumina-based inclusion and a chemical composition peak as seen in No. 5 maraging steel ingot. It can be clearly seen that the type and size of non-metallic inclusions are different between the two.
次に、No.7〜No.12のマルエージングの「鋼塊」から100g採取し、混酸溶液または臭素メタノール溶液等で溶解後、フィルターでろ過し、フィルター上の酸化物からなる残渣をSEMとEDXを用いて観察・分析を行ない、10μm以上の酸化物系非金属介在物の組成及びサイズを測定した。測定結果を表4に示す。
また、No.7〜No.12のマルエージングの鋼帯マルエージング鋼帯の両端部から横断試料を100g採取し、混酸溶液または臭素メタノール溶液等で溶解後、フィルターでろ過し、フィルター上の酸化物物からなる残渣をSEMで観察を行ない、10μm以上の酸化物系非金属介在物のサイズを測定した。
さらに、窒化物や炭窒化物を詳細に評価するため10g採取して、混酸溶液または臭素メタノール溶液等で溶解後、フィルターのろ過面積を小さくして窒化物や炭窒化物の密集度をあげ、SEMで10000個の窒化物や炭窒化物を観察し最大のサイズを測定した。
窒化物等は矩形形状であるため、長辺aと短辺bを測定し、面積a×bに相当する円の直径をその最大長さとした。なお、酸化物系非金属介在物は、上記同様に非金属介在物に外接する円の直径を非金属介在物の最大長さとした。測定結果を表5に示す。
Next, no. 7-No. 100 g from 12 maraging “steel ingots” was collected, dissolved in a mixed acid solution or bromine-methanol solution, etc., filtered through a filter, and the oxide residue on the filter was observed and analyzed using SEM and EDX. The composition and size of oxide-based nonmetallic inclusions of 10 μm or more were measured. Table 4 shows the measurement results.
No. 7-No. 100 g of a cross-sampling sample was collected from both ends of a 12 maraging steel strip, dissolved in a mixed acid solution or bromine-methanol solution, etc., filtered through a filter, and the residue consisting of oxides on the filter was removed by SEM. Observation was performed, and the size of oxide-based nonmetallic inclusions of 10 μm or more was measured.
Furthermore, in order to evaluate nitrides and carbonitrides in detail, 10 g was collected, dissolved in a mixed acid solution or bromine-methanol solution, etc., and the filter area of the filter was reduced to increase the density of nitrides and carbonitrides. The maximum size was measured by observing 10,000 nitrides and carbonitrides with SEM.
Since nitride or the like has a rectangular shape, the long side a and the short side b were measured, and the diameter of a circle corresponding to the area a × b was set as the maximum length. Note that the oxide-based non-metallic inclusions had the maximum length of the non-metallic inclusions as the diameter of the circle circumscribing the non-metallic inclusions as described above. Table 5 shows the measurement results.
表4及び5から、酸化物に関しては、No.1〜No.6の調査結果同様に消耗電極Mgの値が5ppm以上のものではマルエージング鋼帯中には20μmを越える酸化物系非金属介在物がなくなっていることがわかる。また、表4及び5中の10μm以上のアルミナ系の介在物以外の酸化物系非金属介在物は、殆どが前述のスピネル系の介在物、MgOであった。比較例のものではアルミナ系の介在物を主体とするものであった。
また、「鋼塊」から鋼帯に塑性加工を加えることで、No.7〜No.12の酸化物系非金属介在物の大きさが小さくなっていることも分かる。これは、非金属介在物が塑性加工による分解(破砕)が進行したものと考えられる。
From Tables 4 and 5, regarding the oxide, No. 1-No. Similarly to the investigation result of No. 6, it is understood that when the value of the consumable electrode Mg is 5 ppm or more, oxide-based nonmetallic inclusions exceeding 20 μm are eliminated in the maraging steel strip. In Tables 4 and 5, most of the oxide-based non-metallic inclusions other than the alumina-based inclusions of 10 μm or more were the above-mentioned spinel-based inclusions, MgO. The comparative example was mainly composed of alumina inclusions.
In addition, by applying plastic working from “steel ingot” to steel strip, No. 7-No. It can also be seen that the size of 12 oxide-based nonmetallic inclusions is reduced. This is considered that the decomposition (crushing) of the non-metallic inclusions by plastic working has progressed.
窒化物等の最大長さについては、電極窒素濃度5ppmのとき、Mg添加により窒化物等のサイズは2〜3μm微細になり、電極窒素濃度10ppmのとき、Mg添加により窒化物等のサイズは3〜4μm微細になっていることがわかる。
本発明No.8の断面をSEMで観察し、断面中に見られた非金属介在物を図5に示す。この非金属介在物は窒化物系非金属介在物であり、非常に微細であることが分かる。
なお、No.7〜12のマルエージング鋼帯の断面をEPMAにてTiとMoそれぞれの最大値と最小値とを線分析し、その比(最大値/最小値)を算出したところ、全ての試料で偏析比が1.3以下となっていたのを確認した。
With respect to the maximum length of nitride, etc., when the electrode nitrogen concentration is 5 ppm, the size of the nitride etc. becomes 2 to 3 μm fine by adding Mg, and when the electrode nitrogen concentration is 10 ppm, the size of the nitride etc. is 3 by adding Mg. It can be seen that the fineness is ˜4 μm.
This invention No. The cross section of 8 was observed with SEM, and the nonmetallic inclusions observed in the cross section are shown in FIG. It can be seen that this non-metallic inclusion is a nitride-based non-metallic inclusion and is very fine.
In addition, No. The cross section of 7-12 maraging steel strip was analyzed by EPMA for the maximum and minimum values of Ti and Mo, and the ratio (maximum / minimum) was calculated. Was 1.3 or less.
次に、上記の「鋼塊」から疲労試験用のサンプルを採取した。
サンプルは、本発明No.7と比較例試料No.11の試験片を1250℃×20時間のソーキングを行なった後、熱間鍛造を行なって、直径15mmの棒材とした。次に、棒材を820℃×0.5時間の溶体化処理後、480℃×3時間の時効処理を行い、試料No.7と比較材No.11の各々10本の超音波疲労試験片を作製した。
この超音波疲労試験片を、超音波疲労試験機にて、応力振幅400Mpaで疲労試験を行った。疲労試験は、20kHzの振動速度の運転期間が80ms、冷却のための停止が190msとなるように行い、試験片が破断するまで繰返した。
破断した試験片の破断起点部を観察した結果、試験片は介在物を起点に疲労亀裂が進展し、破断に至ったことが確認され、本発明No.7では、平均破断寿命は108回以上と長寿命であったが、比較例No.11では、平均破断寿命は107回であった。
Next, a sample for a fatigue test was taken from the above “steel ingot”.
The sample is a sample of the present invention. 7 and Comparative Sample No. After 11 specimens were soaked at 1250 ° C. for 20 hours, hot forging was performed to obtain a bar having a diameter of 15 mm. Next, the bar was subjected to a solution treatment at 820 ° C. for 0.5 hour, and then an aging treatment at 480 ° C. for 3 hours. 7 and comparative material no. 11 ultrasonic fatigue test pieces of 11 were prepared.
The ultrasonic fatigue test piece was subjected to a fatigue test with a stress amplitude of 400 Mpa using an ultrasonic fatigue tester. The fatigue test was performed so that the operation period at a vibration speed of 20 kHz was 80 ms and the cooling stop was 190 ms, and was repeated until the test piece broke.
As a result of observing the fracture starting portion of the fractured test piece, it was confirmed that the test piece had fatigue cracks starting from the inclusions, leading to fracture. In Example 7, the average rupture life was as long as 10 8 times or longer. 11, the average rupture life was 10 7 times.
以上の結果から、本発明のマルエージング鋼は酸化物系非金属介在物を小さく、少なくすることができ、更に、TiNやTiCN等の窒化物系非金属介在物の大きさも小さくすることが可能であることも分かり、優れた疲労強度を有するものとなっていることが分かる。
本発明のマルエージング鋼の薄帯は、自動車エンジンの無段変速機用部品として最適である。
From the above results, the maraging steel of the present invention can reduce and reduce the number of oxide-based nonmetallic inclusions, and can further reduce the size of nitride-based nonmetallic inclusions such as TiN and TiCN. It can also be seen that it has excellent fatigue strength.
The maraging steel ribbon of the present invention is optimal as a component for a continuously variable transmission of an automobile engine.
本発明のマルエージング鋼の製造方法を適用すれば、酸化物系非金属介在物を小さく、更に、TiNやTiCN等の窒化物系非金属介在物の大きさも小さくすることが可能であり、大きな非金属介在物を少なくすることができるため、厳しい疲労強度を要求されるような用途に最適である。代表的な用途しては、例えば自動車エンジンの無段変速機用部品として最適となる。 By applying the maraging steel manufacturing method of the present invention, it is possible to reduce the size of oxide-based non-metallic inclusions, and further reduce the size of nitride-based non-metallic inclusions such as TiN and TiCN. Since non-metallic inclusions can be reduced, it is optimal for applications that require severe fatigue strength. As a typical application, for example, it is optimal as a component for a continuously variable transmission of an automobile engine.
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