JP6116286B2 - Ferritic stainless steel with less heat generation - Google Patents

Ferritic stainless steel with less heat generation Download PDF

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JP6116286B2
JP6116286B2 JP2013034547A JP2013034547A JP6116286B2 JP 6116286 B2 JP6116286 B2 JP 6116286B2 JP 2013034547 A JP2013034547 A JP 2013034547A JP 2013034547 A JP2013034547 A JP 2013034547A JP 6116286 B2 JP6116286 B2 JP 6116286B2
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stainless steel
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成雄 福元
成雄 福元
石丸 詠一朗
詠一朗 石丸
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Nippon Steel and Sumikin Stainless Steel Corp
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本発明は、発銹起点となるCaSなど水溶性の硫化物系非金属介在物の生成を抑制したフェライト系ステンレス鋼に関するものである。   The present invention relates to a ferritic stainless steel that suppresses the formation of water-soluble sulfide-based non-metallic inclusions such as CaS, which is a starting point.

フェライト系ステンレス鋼をはじめとする鉄鋼材料では、CaSなどの水溶性の硫化物系非金属介在物を起点とした発銹が問題となる。このCaSなどによる発銹を抑制する方法としては、溶製条件により行う方法が知られている。   In steel materials such as ferritic stainless steel, there is a problem of starting from water-soluble sulfide-based non-metallic inclusions such as CaS. As a method for suppressing the occurrence of wrinkling due to CaS or the like, a method performed under melting conditions is known.

例えば特許文献1では、CaSの生成を抑制するために、鋼中のCa量を10ppm未満とすることを提案している。この方法では、酸化物の組成が高CaOとなった場合には、その周囲に水溶性硫化物系非金属介在物のCaSが生成し発銹起点となる。
しかしながら、鋼中の酸化物は脱酸元素や精錬スラグの懸濁にも影響されるため、[Ca]濃度の管理のみでは不十分である。CaS生成を抑制するためには[Ca]濃度だけではなく、他の鋼中成分や酸化物系介在物組成の制御も重要なことが明らかになってきている。
For example, Patent Document 1 proposes that the amount of Ca in steel be less than 10 ppm in order to suppress the formation of CaS. In this method, when the composition of the oxide becomes high CaO, CaS of water-soluble sulfide-based nonmetallic inclusions is generated around it and becomes a starting point.
However, since the oxides in steel are affected by deoxidation elements and refining slag suspension, it is not sufficient to manage the [Ca] concentration alone. In order to suppress the formation of CaS, it has become clear that not only the [Ca] concentration but also the control of other steel components and oxide inclusions are important.

特許文献2に示されるような酸化物系非金属介在物の組成と非金属介在物中の平衡S溶解量を0.03%以下に制御することで水溶性硫化物系非金属介在物CaSの析出を抑制する方法がある。この方法は、溶製・鋳造工程における非金属介在物組成を制御することを対象としており、スラブ加熱時に介在物と鋼材が反応してCaSが生成することまでは考慮しておらず、発銹を完全に防止できないことが問題であった。   By controlling the composition of oxide-based non-metallic inclusions as shown in Patent Document 2 and the equilibrium S dissolution amount in non-metallic inclusions to 0.03% or less, water-soluble sulfide-based non-metallic inclusions CaS There is a method for suppressing precipitation. This method is intended to control the composition of non-metallic inclusions in the smelting / casting process, and does not take into account that the inclusions and the steel material react to generate CaS during slab heating. It was a problem that could not be completely prevented.

また、本発明者らは、特許文献3にて、S濃度の低減と酸化物系介在物の平均組成を制御することによって、フェライト系ステンレス鋼板の発銹を低減する手法を開示している。特許文献3の手法は、X値で表される介在物平均組成の関係式において0.50以下の範囲で非常に有用なものであった。ただ、実機製造を考慮すると、制御すべき酸化物系介在物組成範囲を広げることが求められており、更なる改善が要求されていた。   In addition, in the patent document 3, the present inventors have disclosed a technique for reducing the occurrence of ferritic stainless steel sheet by controlling the reduction of S concentration and the average composition of oxide inclusions. The method of Patent Document 3 was very useful in the range of 0.50 or less in the relational expression of inclusion average composition represented by the X value. However, considering the production of the actual machine, it is required to expand the composition range of oxide inclusions to be controlled, and further improvement is required.

特開平06−000599号公報Japanese Patent Laid-Open No. 06-0000599 特開2001−107178号公報JP 2001-107178 A 特開2012−184494号公報JP 2012-184494 A

ステンレス鋼板の発銹を低減する製造方法では、前述のような非金属介在物組成を制御するために、溶製工程での脱酸剤の投入時期やスラグ精錬方法など厳しい工程管理が必要とされている。しかしながら、溶製時に生成した非金属介在物と鋼材の組成によっては、その後のスラブ加熱工程において酸化物周囲に硫化物が析出・成長し、発銹の起点となる場合がある。本発明はスラブ加熱時の硫化物生成までを考慮して、鋼中成分と非金属介在物組成を制御し、最終製品の発銹を改善することを目的とする。   In manufacturing methods that reduce the occurrence of stainless steel sheet flaws, strict process control is required, such as the timing of deoxidizing agents and the slag refining method, in order to control the composition of non-metallic inclusions as described above. ing. However, depending on the composition of the non-metallic inclusions and steel material produced during melting, sulfides may precipitate and grow around the oxide in the subsequent slab heating process, which may be the starting point for igniting. An object of the present invention is to control the composition of steel and non-metallic inclusions in consideration of the formation of sulfide during slab heating, and to improve the formation of the final product.

上記課題を解決する本発明は、下記のフェライト系ステンレス鋼からなる。
[1]酸化物系介在物を含むフェライト系ステンレス鋼であって、該フェライト系ステンレス鋼は、質量%で、C:0.070%以下、N:0.020%以下、Si:0.05〜0.60%、Mn:0.04〜0.50%、P:0.050%以下、Cr:13〜21%、Ni:0.60%以下(0を含む)、S:0.0002〜0.0030%、Al:0.004〜0.030%、Ca:0.0030%以下、T.O:0.007%以下を含有するとともに、下記(1)式を満足し、残部がFeおよび不可避不純物からなり、前記酸化物系介在物はCaO、及びAl23を含有するとともに、最大径2μm以上の平均組成が下記(2)、(3)式を満足することを特徴とする発銹の少ないフェライト系ステンレス鋼。
[Ca]×[S]×10≦2.4−0.18×[Al]/T.[O] ・・・(1)
0.50<[(CaO)+(MgO)]/[(Al23)+(SiO2)]≦1.3
・・・(2)
(FeO)≦1.0 ・・・(3)
但し、式中の[元素名]は、当該元素の質量%を、(化合物名)は、当該化合物の含有質量%を意味する。
The present invention for solving the above-mentioned problems comprises the following ferritic stainless steel.
[1] Ferritic stainless steel containing oxide inclusions, and the ferritic stainless steel is in mass%, C: 0.070% or less, N: 0.020% or less, Si: 0.05 ˜0.60%, Mn: 0.04 to 0.50%, P: 0.050% or less, Cr: 13 to 21%, Ni: 0.60% or less (including 0), S: 0.0002 -0.0030%, Al: 0.004-0.030%, Ca: 0.0030% or less, T.I. O: 0.007% or less is satisfied, the following formula (1) is satisfied, the balance consists of Fe and inevitable impurities, and the oxide inclusions contain CaO and Al 2 O 3 A ferritic stainless steel with less wrinkling, characterized in that an average composition having a diameter of 2 μm or more satisfies the following formulas (2) and (3).
[Ca] × [S] × 10 6 ≦ 2.4-0.18 × [Al] / T. [O] (1)
0.50 < [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 )] ≦ 1.3
... (2)
(FeO) ≦ 1.0 (3)
However, [element name] in the formula means mass% of the element, and (compound name) means content mass% of the compound.

[2]前記フェライト系ステンレス鋼が、更に、質量%でTi:0.35%以下を含有し、前記酸化物系介在物はCaO、及びAl23を含有するとともに、最大径2μm以上の平均組成が下記(4)式を満足することを特徴とする前記[1]に記載の発銹の少ないフェライト系ステンレス鋼。
0.50<[(CaO)+(MgO)]/[(Al23)+(SiO2)+(TiO2)]≦1.30
・・・(4)
前記フェライト系ステンレス鋼が、更に、質量%で、Cu:0.1〜0.5%、Mo:0.1〜2.0%、Nb:0.1〜0.7%、B:0.001%以下、Sn:0.3%以下の1種又は2種以上を含有することを特徴とする前記[1]又は[2]に記載の発銹の少ないフェライト系ステンレス鋼。
[2] The ferritic stainless steel further contains Ti: 0.35% or less by mass%, the oxide inclusions contain CaO and Al 2 O 3 and have a maximum diameter of 2 μm or more. The ferritic stainless steel with less glazing as described in [1] above, wherein the average composition satisfies the following formula (4):
0.50 < [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] ≦ 1.30
... (4)
[ 3 ] The ferritic stainless steel is further, in mass%, Cu: 0.1 to 0.5%, Mo: 0.1 to 2.0%, Nb: 0.1 to 0.7%, B : Ferritic stainless steel with less glazing as described in [ 1] or [2 ] above, containing one or more of 0.001% or less and Sn: 0.3% or less.

本発明は、ステンレス鋼板の表面に存在する非金属介在物に関して、スラブ加熱工程における水溶性CaSなど硫化物系非金属介在物の生成を防止し、発銹を大幅に抑制することを可能とするものである。   The present invention makes it possible to prevent the formation of sulfide-based non-metallic inclusions such as water-soluble CaS in the slab heating process and to significantly suppress the occurrence of non-metallic inclusions existing on the surface of the stainless steel plate. Is.

鋼片および熱処理後の介在物の組成分布を示す図である。It is a figure which shows the composition distribution of the inclusion after a steel piece and heat processing. 鋼材成分とSST発銹発生の関係を示す図である。It is a figure which shows the relationship between a steel material component and SST generation | occurrence | production. X値とSST発銹発生の関係を示す図である。It is a figure which shows the relationship between X value and SST occurrence. (FeO)濃度とSST発銹発生の関係を示す図である。It is a figure which shows the relationship between (FeO) density | concentration and SST generation | occurrence | production.

以下に本発明を詳細に説明する。なお、本発明において、特に指定しない限り、%は質量%を意味する。また、[元素名]濃度は、当該元素の質量%を、(化合物名)濃度は、当該化合物の含有質量%を意味する。   The present invention is described in detail below. In the present invention, unless otherwise specified,% means mass%. The [element name] concentration means mass% of the element, and the (compound name) concentration means content mass% of the compound.

まず、本発明の基礎となった知見が得られた試験について説明する。
Ar雰囲気の高周波溶解炉にて、C:0.003〜0.065wt%、Mn:0.10〜0.53wt%、P:0.011〜0.030wt%、S:0.0002〜0.0040wt%、Cr:13〜21wt%、のフェライト系ステンレス鋼となるよう原料を溶解し、Si脱酸後、Al脱酸した後、Ca添加またはフラックス(67%CaO−23%Al−10%CaF)添加を施して、酸化物組成をCaO−Al−SiOを主に含有する酸化物に制御した。この際、脱酸元素であるSi、Al、Caの濃度をそれぞれSi添加量:0.10〜0.50%、Al添加量:0.01〜0.07%、Ca:0.0002〜0.005%と変化させ、また、フラックス添加量を溶鋼1kg当り0.05〜0.10kg、処理時間を5〜30minの範囲で変えることによって、鋼中のメタル成分と酸化物組成を変更した。また、高周波溶解時の撹拌力などを変更することで介在物個数を変更させるようにした。
First, a description will be given of a test in which knowledge that is the basis of the present invention was obtained.
In a high-frequency melting furnace in an Ar atmosphere, C: 0.003 to 0.065 wt%, Mn: 0.10 to 0.53 wt%, P: 0.011 to 0.030 wt%, S: 0.0002 to 0. 0. The raw material is dissolved so that it becomes a ferritic stainless steel of 0040 wt%, Cr: 13 to 21 wt%, Si is deoxidized, Al is deoxidized, and then Ca is added or flux (67% CaO-23% Al 2 O 3 − 10% CaF 2 ) was added to control the oxide composition to an oxide mainly containing CaO—Al 2 O 3 —SiO 2 . At this time, the concentrations of Si, Al, and Ca, which are deoxidizing elements, are respectively set to Si addition amount: 0.10 to 0.50%, Al addition amount: 0.01 to 0.07%, Ca: 0.0002 to 0 The metal component and the oxide composition in the steel were changed by changing the amount of flux to 0.005% and changing the flux addition amount in the range of 0.05 to 0.10 kg / kg of molten steel and the treatment time in the range of 5 to 30 min. In addition, the number of inclusions was changed by changing the stirring force during high-frequency dissolution.

この溶鋼を鋳造し、1200℃で1時間保持する熱処理を行った後に鋳片C断面の表層から5〜20mmの任意の位置において、最大径が2μm以上の介在物を10個選んで、その組成および形態をEPMAによって調査し、CaSの生成有無を確認した。なお、ここで介在物の最大径を限定した理由は、最大径2μm未満の微細な介在物は発銹の起点にはなり難いためである。また、この鋳片を圧延した薄鋼板から試験片を採取し、この試験片について、塩水噴霧試験−JIS−Z−2371(以下、SST)を実施した。さらに、SST試験を行った試験片についても、SEM−EDXにて調査し、CaSによる発銹を確認した。   After casting this molten steel and carrying out a heat treatment for 1 hour at 1200 ° C., 10 inclusions having a maximum diameter of 2 μm or more are selected at an arbitrary position of 5 to 20 mm from the surface layer of the slab C cross section, and the composition And the form was investigated by EPMA, and the presence or absence of the production | generation of CaS was confirmed. The reason why the maximum diameter of the inclusions is limited here is that fine inclusions having a maximum diameter of less than 2 μm are unlikely to be the starting point of the generation. Moreover, the test piece was extract | collected from the thin steel plate which rolled this cast piece, and the salt spray test-JIS-Z-2371 (henceforth, SST) was implemented about this test piece. Furthermore, about the test piece which performed the SST test, it investigated by SEM-EDX, and confirmed the generation | occurrence | production by CaS.

図1に、鋳片の熱処理前および熱処理後(1200℃×1hr)の介在物のEPMA測定結果を示す。熱処理後にはCaO−Al主体の酸化物の周囲にCaSが析出している様子が確認された。また、酸化物中にCaSの析出している鋼片から得られた薄鋼板では、SST発銹量が多く、しかも酸化物の周囲のCaSを起点として錆が生成していることが判明した。 FIG. 1 shows the EPMA measurement results of inclusions before and after heat treatment of a slab (1200 ° C. × 1 hr). After heat treatment, it was confirmed that CaS was precipitated around the CaO—Al 2 O 3 based oxide. Further, it was found that the thin steel plate obtained from the steel piece in which CaS is precipitated in the oxide has a large amount of SST cracking and rust is generated starting from CaS around the oxide.

酸化物周囲におけるCaS生成反応は下記の(A)式のように考えられ、介在物組成以外に鋼中の[S]濃度や[Al]濃度の影響が挙げられる。
3(CaO)+3[S]+2[Al]→ 3(CaS)+(Al23) ・・・(A)
また、従来知見のような、介在物中の(CaO)濃度を、[Ca]濃度やT.[O]濃度から推定するだけでは十分でなく、鋼材成分の制御が重要であることを見出した。
The CaS formation reaction around the oxide is considered as shown in the following formula (A), and there are effects of [S] concentration and [Al] concentration in the steel in addition to the inclusion composition.
3 (CaO) +3 [S] +2 [Al] → 3 (CaS) + (Al 2 O 3 ) (A)
Moreover, it was found that it is not sufficient to estimate the (CaO) concentration in inclusions from the [Ca] concentration and T. [O] concentration as in the conventional knowledge, and it is important to control the steel material components. .

そこで、鋼材成分とCaSの析出状態および発銹状況からさらに検討を重ねた結果、[Ca]、[Al]、T.[O]濃度が高いほど、また[S]濃度が低いほど、酸化物の周囲にCaSが析出し、発銹の起点となることが判明した。これらは、(A)式の反応の進行に対応するものと考えられる。   Accordingly, as a result of further examination from the precipitation state and the occurrence state of the steel component and CaS, the higher the [Ca], [Al], T. [O] concentration and the lower the [S] concentration, the more the oxide. It was found that CaS was deposited around, and became the starting point of wrinkling. These are considered to correspond to the progress of the reaction of the formula (A).

続いて、上述した元素の含有量割合をどのように制御するかについて検討した。
まず、上記のように作成した、[Ca]、[S]、[Al]、T.[O]濃度の異なるフェライト系ステンレス鋼材であって、他は本発明の要件を満たす鋼材を多数準備して、それらの濃度とSST発銹発生との関係を調べた。
CaS生成は非金属介在物を含めた鋼材中の[Ca]濃度と[S]濃度に大きく影響される。また、(A)式の反応のように、CaOとCaSの置換反応が起きるが、放出されたOはAlで固定される。さらに、その挙動が鋼材中のT.[O]濃度の影響も受けることも考慮して実験データを統計処理した結果、〔(2.4−0.18×[Al]/T.[O])−[Ca]×[S]×10〕の値をパラメータとして実験結果を整理することとした。
Then, it examined about how to control the content rate of the element mentioned above.
First, a large number of ferritic stainless steel materials having different [Ca], [S], [Al], and T. [O] concentrations prepared as described above and satisfying the requirements of the present invention are prepared. Then, the relationship between these concentrations and the occurrence of SST occurrence was examined.
The formation of CaS is greatly affected by the [Ca] concentration and [S] concentration in the steel material including non-metallic inclusions. Further, a substitution reaction of CaO and CaS occurs as in the reaction of the formula (A), but the released O is fixed with Al. Furthermore, its behavior is the same as that of T. As a result of statistical processing of experimental data in consideration of the influence of [O] concentration, [(2.4-0.18 × [Al] / T. [O]) − [Ca] × [S] × It was decided to arrange the experimental results using the value of 10 6 ] as a parameter.

図2に、鋼材中の[Ca]、[S]、[Al]、T.[O]濃度に基づく上記パラメータの値とSST発銹の個数との関係を示す。図中、発銹個数が5個/100cm以下のものを○印で、6個/100cm以上を×印で示した。
この結果から、上記パラメータの値が0以上、すなわち、下式(1)を満足する範囲では発銹が抑制できることが分かった。なお、発銹個数が6個/100cm以上の場合は目視観察で発銹が目立つため、今回は5個/100cm以下をしきい値として設定した。
[Ca]×[S]×10≦2.4−0.18×[Al]/T.[O]・・・(1)
FIG. 2 shows the relationship between the values of the above parameters based on the [Ca], [S], [Al], and T. [O] concentrations in the steel material and the number of SST firings. In the figure, those having a number of sprout of 5 pieces / 100 cm 2 or less are indicated by ◯, and those having 6 pieces / 100 cm 2 or more are indicated by × marks.
From this result, it has been found that the occurrence of wrinkles can be suppressed when the value of the parameter is 0 or more, that is, in a range satisfying the following expression (1). Since when calling銹個number six / 100 cm 2 or more rust noticeable by visual observation, this time was set five / 100 cm 2 or less as the threshold.
[Ca] × [S] × 10 6 ≦ 2.4-0.18 × [Al] / T. [O] (1)

さらに、酸化物組成についても数多く調査し、酸化物組成とCaSの析出状態および発銹状況から検討を重ねた。
本発明者らは、特許文献3で、(CaO)、(MgO)、(Al23)、(SiO2)、(TiO2)濃度を制御することを提案したが、鋼材成分の濃度を上記式(1)を満たすようにすれば、これらの酸化物の濃度を制御する幅を広げることが可能であることが判明した。なお、MgOは耐火物の溶損に起因して混入するものである。
Furthermore, many oxide compositions were investigated, and examination was repeated from the oxide composition, the precipitation state of CaS, and the starting state.
In the patent document 3, the present inventors have proposed controlling the concentrations of (CaO), (MgO), (Al 2 O 3 ), (SiO 2 ), and (TiO 2 ). It has been found that if the above formula (1) is satisfied, the range for controlling the concentration of these oxides can be expanded. Note that MgO is mixed due to the refractory melt.

まず、上記のように作成したフェライト系ステンレス鋼材であって、介在物の組成以外は本発明範囲内に制御したフェライト系ステンレス鋼材を用いて、鋼材中に存在するCaO、及びAl23を含有する酸化物系介在物であって、最大径2μm以上の介在物の平均組成とSST発銹個数の関係を調べた。
図3に、その介在物中の(CaO)、(MgO)、(Al23)、(SiO2)濃度について、X値=[(CaO)+(MgO)]/[(Al23)+(SiO2)]とSST発銹個数の関係を調べた結果を示す。なお、〇と×の内訳は図2と同様である。
図3の結果から、X値が1.3の範囲まで、すなわち下記の(2)式を満たす範囲で、発銹を抑えることが可能であることが分かった。なお、X値の好ましい下限は、0.50超である。
[(CaO)+(MgO)]/[(Al23)+(SiO2)]≦1.3 ・・・(2)
なお、特許請求の範囲では、(2)式の下限を好ましい値の0.50超とした。
First, a ferritic stainless steel material prepared as described above, and using a ferritic stainless steel material controlled within the scope of the present invention except for the composition of inclusions, CaO and Al 2 O 3 present in the steel material are The relationship between the average composition of inclusions containing oxide inclusions having a maximum diameter of 2 μm or more and the number of SST occurrences was examined.
FIG. 3 shows the X value = [(CaO) + (MgO)] / [(Al 2 O 3 ) for the (CaO), (MgO), (Al 2 O 3 ), and (SiO 2 ) concentrations in the inclusions. ) + (SiO 2 )] and the number of SST generations. The breakdown of ○ and × is the same as in FIG.
From the results shown in FIG. 3, it was found that it is possible to suppress the wrinkling until the X value is in the range of 1.3, that is, in the range satisfying the following expression (2). The preferred lower limit of the X value is more than 0.50.
[(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 )] ≦ 1.3 (2)
In the claims, the lower limit of the expression (2) is set to a preferable value exceeding 0.50.

ここで、制御する対象をCaO、及びAl23を含有する酸化物系介在物であって、最大径2μm以上の介在物としたのは、前述のようにCaO−Al主体の介在物の周囲にCaSが析出して発銹の起点となるが、最大径2μm未満の微細な介在物は発銹の起点にはなり難いためである。 Here, the object to be controlled is an oxide-based inclusion containing CaO and Al 2 O 3 , and the inclusion having a maximum diameter of 2 μm or more is mainly composed of CaO—Al 2 O 3 as described above. This is because CaS precipitates around the inclusions and becomes the starting point of the cracking, but fine inclusions having a maximum diameter of less than 2 μm are unlikely to be the starting point of the cracking.

このX値の制御は、式を構成する各化合物量を調整することによって行うが、これらの含有量は脱酸元素やフラックスとして意図的に添加する以外にも溶鋼中に懸濁するスラグの量、耐火物からの混入、溶製・鋳造工程における介在物の浮上分離除去量、など、使用している設備や操業条件で異なってくる要因が大きく影響する。したがって、これら設備・操業要因を考慮して脱酸元素やフラックスの添加量、処理時間を適宜調整することで制御することができる。   This X value is controlled by adjusting the amount of each compound constituting the formula, but these contents are not only intentionally added as a deoxidizing element or flux, but the amount of slag suspended in the molten steel. Factors that vary depending on the equipment and operating conditions used, such as contamination from refractories and the amount of inclusions floating and removed in the smelting / casting process, are greatly affected. Therefore, it can be controlled by appropriately adjusting the addition amount of deoxidizing element and flux and the processing time in consideration of these equipment / operation factors.

さらに、鋼材中に存在するCaO、及びAl23を含有する酸化物系介在物であって、最大径2μm以上の介在物について、(CaO)、(MgO)、(Al23)、(SiO2)、(TiO2)濃度以外の他の酸化物の影響を調べた結果、(FeO)濃度がSST発銹発生と関係があることを見出した。
図4に介在物中の(FeO)濃度とSST発銹個数の関係を示す。なお、(FeO)濃度以外は本発明範囲内に制御した鋼材を用いている。図4の結果から、(FeO)濃度が、下記(3)式で表されるように1.0%を越えるとCaS生成が促進され、発銹しやすくなることが分かった。
(FeO)≦1.0 ・・・(3)
Furthermore, it is an oxide-based inclusion containing CaO and Al 2 O 3 present in the steel material, and for inclusions having a maximum diameter of 2 μm or more, (CaO), (MgO), (Al 2 O 3 ), As a result of examining the influence of oxides other than (SiO 2 ) and (TiO 2 ) concentrations, it was found that the (FeO) concentration is related to the occurrence of SST generation.
FIG. 4 shows the relationship between the (FeO) concentration in inclusions and the number of SST generations. In addition, the steel materials controlled within the scope of the present invention other than the (FeO) concentration are used. From the results shown in FIG. 4, it was found that when the (FeO) concentration exceeds 1.0% as represented by the following formula (3), CaS generation is promoted and it is easy to generate rust.
(FeO) ≦ 1.0 (3)

(FeO)濃度が高い場合には、熱処理時において介在物中にCaO−Al23−FeO系の液相がわずかながら存在するため、(A)式の反応が容易に起こると考えられる。なお、(FeO)濃度は脱酸元素が多い場合やフラックス量、処理時間が多い場合に低い傾向がある。(FeO)の制御についても、上記介在物中の(CaO)等の制御同様、設備や操業要因を考慮し、脱酸元素やフラックスの添加量、処理時間を適宜調整することで適正な範囲にすることができる。 When the (FeO) concentration is high, a slight amount of CaO—Al 2 O 3 —FeO-based liquid phase is present in the inclusions during the heat treatment, and therefore the reaction of formula (A) is considered to occur easily. The (FeO) concentration tends to be low when the amount of deoxidizing element is large, the amount of flux, and the processing time are large. Regarding the control of (FeO), in the same manner as the control of (CaO) and the like in the inclusions, considering the equipment and operating factors, the addition amount of deoxidizing element and flux and the processing time are appropriately adjusted to within an appropriate range. can do.

以上説明した要件を兼ね備えることによって、本発明の効果を得ることが可能となるが、さらに、S、Al、Ca、T.[O]については、上記(1)式を満たすとともに、下記に示す範囲を満たすことが必要になる。以下、その範囲と限定理由について説明する。   By combining the requirements described above, the effects of the present invention can be obtained. Regarding [O], it is necessary to satisfy the above formula (1) and to satisfy the following range. Hereinafter, the range and the reason for limitation will be described.

Sは発銹を防止するため、0.0002〜0.0030%に制御する。好ましくは、0.0020%以下である。
Alは、強力な脱酸および脱硫元素として有用な元素である。しかしながら、過剰に添加すると製造時に表面疵を生じやすくなる。また、Alが低い場合には脱酸および脱硫ができなくなる。このため、0.004〜0.030%とする。好ましくは、0.020%以下である。
S is controlled to be 0.0002 to 0.0030% in order to prevent generation. Preferably, it is 0.0020% or less.
Al is an element useful as a powerful deoxidation and desulfurization element. However, excessive addition tends to cause surface defects during production. Moreover, when Al is low, deoxidation and desulfurization cannot be performed. For this reason, it is set as 0.004 to 0.030%. Preferably, it is 0.020% or less.

Caを添加されない場合も、精錬スラグの懸濁に起因したCaO主体の介在物が生成し、温度降下に伴う脱酸反応によりCaO−Al−SiO主体の介在物が形成される。[Ca]濃度が0.0010%未満でも上記のような介在物が主体になり、脱硫などの溶製条件や二次精錬における介在物除去などの影響も大きく受ける。
Caが0.0030%を越える場合は鋳片段階でCaSの生成が確認され、発銹の原因になるため、Caを0.0030%以下に下げる必要がある。好ましくは、0.0020%以下であり、更に好ましくは0.0012%以下である。
Even when Ca is not added, inclusions mainly composed of CaO due to suspension of the refining slag are generated, and inclusions mainly composed of CaO—Al 2 O 3 —SiO 2 are formed by a deoxidation reaction accompanying a temperature drop. Even when the [Ca] concentration is less than 0.0010%, the inclusions as described above are mainly used, and are greatly affected by melting conditions such as desulfurization and inclusion removal in secondary refining.
When Ca exceeds 0.0030%, the formation of CaS is confirmed at the slab stage, which causes rusting. Therefore, it is necessary to lower Ca to 0.0030% or less. Preferably, it is 0.0020% or less, More preferably, it is 0.0012% or less.

T.[O]濃度は、主に脱酸材の添加や精錬条件に左右される。T.[O]濃度が高い場合には脱硫が困難になり、CaS生成を抑制できなくなるという問題があり、0.007%以下であることが必要である。過度の低減による製造コストアップも考慮した好ましい範囲は、0.0050%以下である。   T. T. The [O] concentration mainly depends on the addition of the deoxidizer and the refining conditions. T. T. When the [O] concentration is high, desulfurization becomes difficult, and there is a problem that CaS generation cannot be suppressed, and it is necessary that the concentration be 0.007% or less. A preferable range considering the manufacturing cost increase due to excessive reduction is 0.0050% or less.

また、Tiは、フェライト系ステンレス鋼におけるC、N安定化に効果があり、脱酸にも寄与するため、Tiを必要に応じて含有させる場合がある。
しかしながらTiの添加量が多すぎると、製造時に表面疵を生じやすくなり、耐食性および溶接部の強度を下げる。また、本発明はCaO−SiO2−Al23系介在物を対象としており、Ti添加量が多い場合には脱酸生成物中にTi酸化物が含有されてしまうため、添加する場合の望ましい範囲は、0.03〜0.35%である。
なお、Ti酸化物もCaSの生成に影響を及ぼすため、Tiを含有させる場合、上述したX値は、()式に替えて下式(4)を満たすことが必要となる。
[(CaO)+(MgO)]/[(Al23)+(SiO2)+(TiO2)]≦1.3
・・・(4)
なお、特許請求の範囲では、(2)式と同様に(4)式の下限を0.50超とした。
Further, Ti is effective in stabilizing C and N in ferritic stainless steel and contributes to deoxidation, so Ti may be included as necessary.
However, when there is too much addition amount of Ti, it will become easy to produce a surface flaw at the time of manufacture, and corrosion resistance and the intensity | strength of a welding part will be reduced. Further, the present invention is directed to CaO—SiO 2 —Al 2 O 3 inclusions, and when the amount of Ti added is large, Ti oxide is contained in the deoxidation product. A desirable range is 0.03 to 0.35%.
In addition, since Ti oxide also influences the production | generation of CaS, when Ti is contained, it is necessary for the X value mentioned above to satisfy the following formula (4) instead of the formula ( 2 ).
[(CaO) + (MgO) ] / [(Al 2 O 3) + (SiO 2) + (TiO 2)] ≦ 1.3 0
... (4)
In the claims, the lower limit of the expression (4) is set to be more than 0.50 as in the expression (2).

本発明は、上述した通り、脱酸および介在物組成制御に関するものであり、一般的に製造されている全てのフェライト系ステンレス鋼に適用可能なものである。以下に好適に用いることが出来る成分範囲を示すが、それらに限定されるものではない。   As described above, the present invention relates to deoxidation and inclusion composition control, and can be applied to all commonly manufactured ferritic stainless steels. Although the component range which can be used suitably is shown below, it is not limited to them.

Cは、析出物の影響で耐食性を劣化させるため、0.070%以下にすることが好ましい。また、過度に低減することは製造コストの増加につながるため、更に好ましくは0.05%以下である。
Nは、靭性劣化のため、0.020%以下にすることが好ましい。更に好ましくは、0.01%以下である。
Since C deteriorates the corrosion resistance due to the influence of precipitates, it is preferable to make it 0.070% or less. Moreover, since excessive reduction leads to an increase in manufacturing cost, it is more preferably 0.05% or less.
N is preferably 0.020% or less because of toughness deterioration. More preferably, it is 0.01% or less.

Siは、脱酸元素として有用であり、耐食性にも有効な元素である。しかし、多すぎると加工性が低下するために、0.05〜0.60%含有させることが好ましい。更に好ましい範囲は0.10〜0.50%である。また、SiはTiとの相互作用が大きく、溶鋼中のTiの活量を大きくする効果があるために、Ti添加の有効活用も考慮して添加量が選択される。   Si is useful as a deoxidizing element and is also an element effective for corrosion resistance. However, since processability will fall when there is too much, it is preferable to make it contain 0.05 to 0.60%. A more preferable range is 0.10 to 0.50%. Further, since Si has a large interaction with Ti and has an effect of increasing the activity of Ti in the molten steel, the addition amount is selected in consideration of effective utilization of Ti addition.

Mnは脱酸剤として機能するとともに、熱間加工性を向上させる元素である。また、SをMnSとして固定して、FeSの生成による赤熱脆性の発生を防止する元素である。これらの添加効果を得るため、0.04〜0.50%にすることが好ましい。   Mn is an element that functions as a deoxidizer and improves hot workability. It is an element that fixes S as MnS and prevents the occurrence of red heat embrittlement due to the formation of FeS. In order to acquire these addition effects, it is preferable to make it 0.04 to 0.50%.

Pは、製鋼工程では不純物である。0.05%を超えると、熱間加工性が低下するので、0.05%以下とした。好ましくは0.03%以下である。
Crは耐食性改善のため、13〜21%含有させることが好ましい。更にこのましくは、16〜20%である。
Niは耐食性改善の効果があるが、高価であり、0.60%以下(0を含む)にすることが好ましい。
P is an impurity in the steel making process. If it exceeds 0.05%, the hot workability deteriorates, so the content was made 0.05% or less. Preferably it is 0.03% or less.
It is preferable to contain 13 to 21% of Cr for improving corrosion resistance. Further preferably, it is 16 to 20%.
Ni has an effect of improving corrosion resistance, but is expensive and is preferably made 0.60% or less (including 0).

また、上記成分組成をベースとして考える場合は、必要に応じてCu、Mo、Nb、B、Snから1種以上を更に含有させることが出来る。   Moreover, when considering it based on the said component composition, 1 or more types can further be contained from Cu, Mo, Nb, B, and Sn as needed.

Cuは耐食性改善のために添加されるが、過剰の添加では鋳造および圧延時の割れが発生するため、0.1〜0.5%にすることが好ましい。
Moは耐食性改善のために添加されるが、高価であり、0.1〜2.0%にすることが好ましい。
NbはCやNの固定、高強度化、耐熱性改善のため、0.1〜0.7%にすることが好ましい。更に好ましくは0.2〜0.6%である。
Cu is added to improve corrosion resistance, but excessive addition causes cracking during casting and rolling, so 0.1 to 0.5% is preferable.
Mo is added to improve corrosion resistance, but is expensive and is preferably 0.1 to 2.0%.
Nb is preferably 0.1 to 0.7% in order to fix C and N, increase strength, and improve heat resistance. More preferably, it is 0.2 to 0.6%.

Bは二次加工割れ防止の目的で添加されるが、過剰の添加は耐食性を劣化させるため、0.0010%以下にすることが好ましい。なお、Bの効果を得るには0.0005%以上とするのが好ましい。
Snは耐食性改善のため添加されるが、過剰の添加では鋳造および圧延時の割れが発生するため0.3%以下にすることが好ましい。なお、Snの効果を得るには0.05%以上が好ましい。
また、記載した以外の元素についても、本発明の効果を損なわない範囲において適宜含有させることが可能である。
B is added for the purpose of preventing secondary work cracking, but excessive addition deteriorates the corrosion resistance, so 0.0010% or less is preferable. In order to obtain the effect of B, the content is preferably 0.0005% or more.
Sn is added to improve corrosion resistance, but if added excessively, cracks occur during casting and rolling, so it is preferably made 0.3% or less. In order to obtain the effect of Sn, 0.05% or more is preferable.
Further, elements other than those described can be appropriately contained within a range not impairing the effects of the present invention.

本発明の実施例を以下に記す。なお、実施例は、本発明の実施可能性や効果を示すための一例であって、これに限定されるものではない。
表1に記す成分組成のフェライト系ステンレス鋼を前述のようにAr雰囲気の高周波溶解炉で溶製、鋳造した。これを熱間圧延、熱延板焼鈍・酸洗、冷延、冷延板焼鈍・酸洗を実施し、1.0mmの冷延板を作製した。なお冷延板焼鈍の温度は、各々の鋼材の再結晶温度に基づき950〜1050℃の間で調整した。なお、表1の空欄は、添加していないため測定していないことを表す。
Examples of the present invention will be described below. In addition, an Example is an example for showing the feasibility and effect of this invention, Comprising: It is not limited to this.
Ferritic stainless steel having the composition shown in Table 1 was melted and cast in a high-frequency melting furnace in an Ar atmosphere as described above. This was subjected to hot rolling, hot rolled sheet annealing / pickling, cold rolling, cold rolled sheet annealing / pickling to produce a 1.0 mm cold rolled sheet. In addition, the temperature of cold-rolled sheet annealing was adjusted between 950-1050 degreeC based on the recrystallization temperature of each steel material. In addition, the blank of Table 1 represents not measuring because it was not added.

また、鋳造後の鋳片を1200℃で1時間熱処理し、空冷したサンプルについて、上述した方法で2μm以上の介在物の組成、及び個数密度を調査した。また、塩水噴霧試験−JIS−Z−2371に準拠して、5%NaCl溶液を用いて、35℃−4時間の連続噴霧試験を行い、これらの結果を表2に記載した。なお、冷延板についても同様に調査したが、介在物組成は変化していなかった。   Moreover, about the sample which heat-processed the slab after casting for 1 hour at 1200 degreeC, and air-cooled, the composition of the inclusion of 2 micrometers or more and the number density were investigated by the method mentioned above. Moreover, based on the salt spray test-JIS-Z-2371, a continuous spray test at 35 ° C. for 4 hours was performed using a 5% NaCl solution, and the results are shown in Table 2. In addition, although it investigated similarly about the cold-rolled sheet, the inclusion composition did not change.

本発明鋼であるNo.1〜10の鋼ではSST発銹個数が5個/100cm以下であり、良好な耐食性を示した。一方、本発明の鋼成分範囲を外されたNo.11〜13ではSST発銹個数が6個/100cm以上と多く、耐食性に劣ることを確認した。また、鋼成分は満たすものの、(1)式の範囲が外れているNo.14〜16も、SST発銹個数が多く、耐食性に劣っていた。 In the steels of Nos. 1 to 10, which are the steels of the present invention, the number of SST firing was 5/100 cm 2 or less, and good corrosion resistance was exhibited. On the other hand, in No.11-13 which remove | excluded the steel component range of this invention, the number of SST firing was as many as 6 pieces / 100cm < 2 > or more, and it confirmed that it was inferior to corrosion resistance. Moreover, although steel component is satisfy | filled, the range of (1) Formula is out of No. 14 to 16 also had a large number of SST cracks and were inferior in corrosion resistance.

本発明の範囲を外されたNo.17ではCa添加の代わりにフラックス添加(67%CaO−23%Al−10%CaF、0.05kg/kg−steel)を施して、30min処理したが、[Al]濃度が低かったために、T.[O」が高く、また十分な脱硫も得られず、SST発銹個数が多く、耐食性に劣ることを確認した。
また、No.18、No.19では、鋼成分組成や(1)式を満たすものの、FeO濃度、又は、X値が範囲外となっており、SST発銹個数が多く、耐食性に劣っていた。
In No. 17 outside the scope of the present invention, flux addition (67% CaO-23% Al 2 O 3 -10% CaF 2 , 0.05 kg / kg-steel) was applied instead of Ca addition, and treatment was performed for 30 min. However, since the [Al] concentration was low, T.W. It was confirmed that [O] was high, sufficient desulfurization could not be obtained, the number of SST generations was large, and the corrosion resistance was poor.
No. 18, no. In No. 19, although the steel composition and the formula (1) were satisfied, the FeO concentration or the X value was out of the range, the number of SST firing was large, and the corrosion resistance was inferior.

Claims (3)

酸化物系介在物を含むフェライト系ステンレス鋼であって、
該フェライト系ステンレス鋼は、質量%で、
C:0.070%以下、
N:0.020%以下、
Si:0.05〜0.60%、
Mn:0.04〜0.50%、
P:0.050%以下、
Cr:13〜21%、
Ni:0.60%以下(0を含む)、
S:0.0002〜0.0030%、
Al:0.004〜0.030%、
Ca:0.0030%以下、
T.O:0.007%以下
を含有するとともに、下記(1)式を満足し、残部がFeおよび不可避不純物からなり、
前記酸化物系介在物はCaO、及びAl23を含有するとともに、最大径2μm以上の平均組成が下記(2)、(3)式を満足することを特徴とする発銹の少ないフェライト系ステンレス鋼。
[Ca]×[S]×10≦2.4−0.18×[Al]/T.[O] ・・・(1)
0.50<[(CaO)+(MgO)]/[(Al23)+(SiO2)]≦1.3
・・・(2)
(FeO)≦1.0 ・・・(3)
但し、式中の[元素名]は、当該元素の質量%を、(化合物名)は、当該化合物の含有質量%を意味する。
Ferritic stainless steel containing oxide inclusions,
The ferritic stainless steel is in mass%,
C: 0.070% or less,
N: 0.020% or less,
Si: 0.05 to 0.60%,
Mn: 0.04 to 0.50%
P: 0.050% or less,
Cr: 13-21%,
Ni: 0.60% or less (including 0),
S: 0.0002 to 0.0030%,
Al: 0.004 to 0.030%,
Ca: 0.0030% or less,
T.A. O: with containing 0.007% or less, satisfying the following formula (1), the balance being Fe and unavoidable impurities,
The oxide inclusions contain CaO and Al 2 O 3 , and an average composition having a maximum diameter of 2 μm or more satisfies the following formulas (2) and (3): Stainless steel.
[Ca] × [S] × 10 6 ≦ 2.4-0.18 × [Al] / T. [O] (1)
0.50 < [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 )] ≦ 1.3
... (2)
(FeO) ≦ 1.0 (3)
However, [element name] in the formula means mass% of the element, and (compound name) means content mass% of the compound.
前記フェライト系ステンレス鋼が、更に、質量%でTi:0.35%以下を含有し、前記酸化物系介在物はCaO、及びAl23を含有するとともに、最大径2μm以上の平均組成が下記(4)式を満足することを特徴とする請求項1に記載の発銹の少ないフェライト系ステンレス鋼。
0.50<[(CaO)+(MgO)]/[(Al23)+(SiO2)+(TiO2)]≦1.30
・・・(4)
The ferritic stainless steel further contains, by mass%, Ti: 0.35% or less, the oxide inclusions contain CaO and Al 2 O 3 and have an average composition with a maximum diameter of 2 μm or more. 2. The ferritic stainless steel with less cracking according to claim 1, wherein the following formula (4) is satisfied.
0.50 < [(CaO) + (MgO)] / [(Al 2 O 3 ) + (SiO 2 ) + (TiO 2 )] ≦ 1.30
... (4)
前記フェライト系ステンレス鋼が、更に、質量%で、
Cu:0.1〜0.5%、
Mo:0.1〜2.0%、
Nb:0.1〜0.7%、
B:0.001%以下、
Sn:0.3%以下
の1種又は2種以上を含有することを特徴とする請求項1又は2に記載の発銹の少ないフェライト系ステンレス鋼。
The ferritic stainless steel is further in mass%,
Cu: 0.1 to 0.5%,
Mo: 0.1 to 2.0%,
Nb: 0.1-0.7%
B: 0.001% or less,
Sn: Ferritic stainless steel with less cracking according to claim 1 or 2 , characterized in that it contains one or more of 0.3% or less.
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