JP3772530B2 - Austenitic stainless steel with good surface properties and excellent corrosion resistance - Google Patents

Description

【００４６】
【表２】

【００４７】
表２に示したとおり、この発明に従うオーステナイト系ステンレス鋼は、その溶製後の連続鋳造時においてノズル閉塞が全く生じず、また製品板においても、表面欠陥が全くなく、しかも優れた耐食性を有していた。
【００４８】
【発明の効果】
かくして、この発明によれば、酸化物系介在物に起因した表面欠陥がなく、また耐食性にも優れたオーステナイト系ステンレス鋼を安定して得ることができる。
さらに、この発明のオーステナイト系ステンレス鋼は、その製造過程の連続鋳造時においてノズル閉塞が生じることもない。
【図面の簡単な説明】
【図１】 鋼中のAl量と熱延焼鈍板の表面欠陥個数との関係を示したグラフである。
【図２】 酸化物系介在物中の Al₂O₃濃度とヘゲ状表面欠陥個数との関係を示したグラフである。
【図３】 酸化物系介在物中のTi酸化物濃度とノズル閉塞率および発錆個数との関係を示したグラフである。
【図４】 酸化物系介在物中のCaＯ濃度とノズル閉塞率および発錆個数との関係を示したグラフである。
【図５】 耐食性に及ぼすＳ量とCa量の影響を、２つの Al₂O₃水準で比較して示したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an austenitic stainless steel having good surface properties and excellent corrosion resistance, and is intended to advantageously improve various properties by modifying the composition of oxide inclusions contained in the steel. .
[0002]
[Prior art]
Austenitic stainless steel has high strength at high temperatures, poor hot ductility, and inferior oxidation resistance compared to ferritic stainless steel, so grain boundary oxidation occurs during slab heating in the hot rolling process. There was a problem in that it was easy to crack at the time of hot working.
[0003]
It is known that positive addition of an element having a large chemical affinity with oxygen such as Al and Ti is effective for the above problem. In general, Ti addition to molten steel is performed by deoxidizing with Al in advance for the purpose of improving the yield.
However, when Al or Ti is positively added, there has been a serious problem in production in which clogging occurs because oxides of these elements adhere to the inner wall of the immersion nozzle during continuous casting after melting.
[0004]
Accordingly, various proposals have been made for measures for preventing the clogging of the immersion nozzle. For example, Japanese Patent Application Laid-Open Nos. 8-144021 and 8-260106 disclose oxide inclusions as Al ₂ O _3. A technique for preventing nozzle clogging by using a —TiO ₂ —CaO system and lowering the melting point is disclosed.
However, in this technique, CaS is easily generated as inclusions, and since this CaS is the starting point and rust is likely to be generated, there is a problem that the corrosion resistance is deteriorated, and low S is required.
Moreover, since it is basically an Al deoxidation technique, there remains a fundamental problem that cold-rolled plates cannot avoid the shaved surface defects.
[0005]
In addition, Al ₂ O ₃ which is a deoxidation product is agglomerated and clustered in the melting stage, so if it is contained in the molten steel, it not only causes nozzle clogging as described above, but also the surface of the product plate. However, there is a problem that dent defects along the rolling direction occur.
In response to this problem, Japanese Patent Application Laid-Open No. 4-99151 discloses that in ferritic stainless steel to which Ti is added, cooling is caused by severe restrictions on Al content (≦ 0.002 mass%) and oxygen contents (≦ 0.005 mass%). We are proposing a technique to improve the surface quality of the sheet.
According to this technology, the amount of oxygen is restricted and the formation of Al ₂ O ₃ is suppressed, so that the surface defects caused by aggregation and clustering of Al ₂ O ₃ are remarkably reduced, but TiO ₂ There was a problem that the resulting bald defects occurred.
[0006]
[Problems to be solved by the invention]
The present invention has been developed in view of the above circumstances, and an object thereof is to propose an austenitic stainless steel having excellent surface properties and excellent corrosion resistance, which has solved all the conventional problems as described above.
That is, the problems in the present invention are as follows.
(1) No clogging of nozzles during continuous casting during production, and good manufacturability.
(2) Excellent surface properties with no shaved surface defects.
(3) There should be no bald defects associated with cracking during hot rolling.
(4) Excellent corrosion resistance.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventors have appropriately adjusted the composition of steel components and appropriately modified the composition of oxide inclusions contained in the steel. In order to stably improve the oxide inclusions to the desired composition, the order of addition of the components acting as a deoxidizer among the steel components is very effective in achieving the intended purpose. The knowledge that is very important.
The present invention is based on the above findings.
[0008]
That is, the gist configuration of the present invention is as follows.
1. C: 0.15 wt% or less, Si: 1.0 wt% or less, Mn: 2.0 wt% or less,
Cr: 15-30 wt%, Ni: 5-30 wt%, P: 0.05 wt% or less,
S: 0.015 wt% or less, N: 0.15 wt% or less, Al: 0.005 wt% or less,
O: 0.01 wt% or less, Ti: 0.015-0.4 wt%, Ca: 0.0005-0.0050 wt%
The balance is Fe and inevitable impurities , and the composition of oxide inclusions due to deoxidation products in the steel is Ti oxide: 20 to 90 wt%, Al ₂ O ₃ : 50 wt % Austenitic stainless steel with good surface properties and excellent corrosion resistance, characterized by satisfying the following range:
[0009]
2. In the above 1, the steel composition is further
Mo: 0.05-6.0 mass %
Good corrosion resistance surface properties characterized by comprising a composition containing an excellent austenitic stainless steel.
[0010]
3. In the above 1 or 2, the steel composition is further
Nb: 0.01 to 0.08 mass%, V: 0.01 to 0.1 mass%, B: 0.0002 to 0.0030 mass%
An austenitic stainless steel with excellent surface properties and excellent corrosion resistance, characterized in that it has a composition containing one or more selected from among them.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the experimental results that are the basis of the present invention will be described.
Experiment 1
C: 0.022 to 0.091 mass%, Si: 0.45 to 0.86 mass%, Mn: 0.66 to 1.22 mass%, Cr: 18.2 to 18.6 mass%, Ni: 8.3 to 8.8 mass%, P: 0.021 to 0.037 mass%, S: 0.003 to 0.011 mass%, N: 0.025 to 0.041 mass%, O: 0.0037 to 0.0076 mass%, Ti: 0.021 to 0.041 mass%, Ca: 0.0006 to 0.0022 mass%, Al content from 0.0007 mass% to 0.021 Steel changed to mass% was melted, and after continuous casting (slab size: 200 mm thickness x 1240 mm width), it was hot rolled without taking care of the slab. In hot rolling, slab heating conditions: 1230 ° C-50 minutes, rough rolling 7 passes, rough rolling finishing temperature: 1060-1120 ° C, rough rolling finish thickness: 28mm, finishing (7 stands) rolling mill delivery temperature: 900- 1060 ° C., finishing thickness: 3 mm, coil winding temperature: 590 to 1000 ° C.
[0012]
Next, the hot-rolled coil was continuously annealed at 1100 ° C. and then pickled, and then the surface was observed over the entire length of the coil to determine the average number of barbed defects per unit area.
The obtained results are shown in FIG. 1 in relation to the amount of Al in steel. In addition, all of the observed bald defects had a width of about 0.4 to 3.0 mm and a length of about 30 to 500 mm.
As can be seen from FIG. 1, when the Al content exceeds 0.005 mass%, a barbed defect starts to appear.
Analysis of these shaved defects revealed Al ₂ O ₃ . Therefore, it is considered that such a stub-like defect was formed by agglomeration of Al ₂ O ₃ which is a deoxidation product generated at the time of casting and division in the rolling direction at the time of hot rolling.
[0013]
Experiment 2
C: 0.022 to 0.091 mass%, Si: 0.45 to 0.86 mass%, Mn: 0.66 to 1.22 mass%, Cr: 18.2 to 18.6 mass%, Ni: 8.3 to 8.7 mass%, P: 0.021 to 0.037 mass%, S: 0.003 to 0.011 mass%, N: 0.025 to 0.041 mass%, O: 0.0037 to 0.0076 mass%, Ti: 0.021 to 0.041 mass%, Ca: 0.0006 to 0.0022 mass%, Al content from 0.0007 mass% to 0.021 Steel changed to mass% was melted, and after continuous casting (slab size: 200 mm thickness x 1240 mm width), it was hot-rolled without taking care of the slab. For hot rolling, slab heating conditions: 1260 ° C-50 minutes, rough rolling 7 passes, rough rolling finishing temperature: 1060-1120 ° C, rough rolling finish thickness: 28mm, finishing (7 stands) rolling mill delivery temperature: 900- 1060 ° C., finishing thickness: 3 mm, coil winding temperature: 590 to 1000 ° C.
The obtained hot-rolled coil is continuously annealed at 1100 ° C, pickled, and finished to a thickness of 0.8 mm by cold rolling, then continuously annealed at 1080-1130 ° C, pickled, and then cold-rolled annealed. A board was used.
[0014]
The surface of the cold-rolled annealed plate thus obtained was observed over the entire length, and the average number of barbed defects per unit area was determined.
In addition, the oxide inclusions present in the obtained cold-rolled annealed sheet were quantified by the brom method.
The obtained results are shown in FIG. 2 organized by the amount of Al ₂ O ₃ in the inclusions.
As shown in the figure, it can be seen that when the amount of Al ₂ O ₃ in the oxide inclusion exceeds 50 mass%, the bald defects begin to occur rapidly.
On the other hand, when the Al ₂ O ₃ content is 50 mass% or less, the occurrence of scab-like defects is small. Especially when the Al ₂ O ₃ content is 20 mass% or less, almost no scab-like defects are observed. . In addition, all the observed bald defects had a width of about 0.2 to 2.0 mm and a length of about 80 to 1000 mm.
[0015]
Experiment 3
C: 0.022 to 0.091 mass%, Si: 0.45 to 0.86 mass%, Mn: 0.66 to 1.22 mass%, Cr: 18.2 to 18.6 mass%, Ni: 8.3 to 8.8 mass%, P: 0.021 to 0.037 mass%, S: 0.003 to 0.011 mass%, N: 0.025 to 0.041 mass%, O: 0.0037 to 0.0083 mass%, Ti: 0.015 to 0.27 mass%, Ca: 0.0006 to 0.0022 mass%, Al content from 0.0007 mass% to 0.0044 Steel changed to mass% was melted, and after continuous casting (slab size: 200 mm thickness x 1240 mm width), it was hot-rolled without taking care of the slab. For hot rolling, slab heating conditions: 1260 ° C-50 minutes, rough rolling 7 passes, rough rolling finishing temperature: 1060-1120 ° C, rough rolling finish thickness: 28mm, finishing (7 stands) rolling mill delivery temperature: 900- 1060 ° C., finishing thickness: 3 mm, coil winding temperature: 700 to 1000 ° C.
Next, the obtained hot-rolled coil was continuously annealed at 1100 ° C, pickled, finished to a thickness of 0.8 mm by cold rolling, then continuously annealed at 1080-1130 ° C, pickled, and cold-rolled. An annealing plate was used.
[0016]
The surface of the test piece of the cold-rolled annealed plate thus obtained was emery # 600 polished, a salt spray test (based on JIS-Z-2371) was performed at 50 ° C. for 4 hours, and the number of rusts was counted. Moreover, the immersion nozzle after continuous casting was collect | recovered and the nozzle obstruction | occlusion rate was measured. Furthermore, the oxide inclusions present in the cold-rolled annealed plate were quantified by the brom method.
The obtained results are shown in FIG. 3 organized by the amount of Ti oxide in the oxide inclusions.
As can be seen from the figure, when the amount of Ti oxide in the inclusion is in the range of 20 to 90 mass%, it can be seen that there is no nozzle blockage during continuous casting and that the corrosion resistance is also good.
[0017]
Experiment 4
C: 0.022 to 0.091 mass%, Si: 0.45 to 0.86 mass%, Mn: 0.66 to 1.22 mass%, Cr: 18.2 to 18.6 mass%, Ni: 8.3 to 9.5 mass%, P: 0.021 to 0.037 mass%, S: 0.003 to 0.011 mass%, N: 0.025 to 0.041 mass%, O: 0.0037 to 0.0083 mass%, Ti: 0.026 to 0.033 mass%, Al: 0.0002 to 0.0033 mass%, Ca content from 0.0002 mass% to 0.0059 Steel changed to mass% was melted, and after continuous casting (slab size: 200 mm thickness x 1240 mm width), it was hot-rolled without taking care of the slab. For hot rolling, slab heating conditions: 1260 ° C-50 minutes, rough rolling 7 passes, rough rolling finishing temperature: 1060-1120 ° C, rough rolling finish thickness: 28mm, finishing (7 stands) rolling mill delivery temperature: 900- 1060 ° C., finishing thickness: 3 mm, coil winding temperature: 700 to 1000 ° C.
Next, the obtained hot-rolled coil was continuously annealed at 1100 ° C, pickled, finished to a thickness of 0.8 mm by cold rolling, then continuously annealed at 1080-1130 ° C, pickled, and cold-rolled. An annealing plate was used.
[0018]
The surface of the test piece of the cold-rolled annealed plate thus obtained was emery # 600 polished, a salt spray test (based on JIS-Z-2371) was performed at 50 ° C. for 4 hours, and the number of rusts was counted. Moreover, the immersion nozzle after continuous casting was collect | recovered and the nozzle obstruction | occlusion rate was measured. Furthermore, the oxide inclusions present in the cold-rolled annealed plate were quantified by the brom method.
The obtained results are shown in FIG. 4 organized by the amount of CaO in the oxide inclusions.
As can be seen from the figure, when the CaO content in the inclusions is in the range of 5 to 50 mass%, the nozzle is not blocked during continuous casting, and the corrosion resistance is good.
[0019]
Experiment 5
C: 0.022 to 0.091 mass%, Si: 0.45 to 0.86 mass%, Mn: 0.66 to 1.22 mass%, Cr: 18.2 to 18.6 mass%, Ni: 8.3 to 9.5 mass%, P: 0.021 to 0.037 mass%, S: 0.001 to 0.021 mass%, N: 0.025 to 0.041 mass%, O: 0.0037 to 0.0083 mass%, Ti: 0.026 to 0.038 mass%, Al: 0.0018 to 0.0033 mass%, and in oxide inclusions For _two levels of Al ₂ O ₃ content of 5-20 mass% and 55-65 mass%, steel with varying Ca content in the range of 0.0002-0.0058 mass% was melted and continuously cast (slab (Size: 200mm thickness x 1240mm width) and hot rolled without slab care. For hot rolling, slab heating conditions: 1260 ° C-50 minutes, rough rolling 7 passes, rough rolling finishing temperature: 1060-1120 ° C, rough rolling finish thickness: 28mm, finishing (7 stands) rolling mill delivery temperature: 900- 1060 ° C., finishing thickness: 3 mm, coil winding temperature: 700 to 1000 ° C.
Next, the obtained hot-rolled coil was continuously annealed at 1100 ° C, pickled, finished to a thickness of 0.8 mm by cold rolling, then continuously annealed at 1080-1130 ° C, pickled, and cold-rolled. An annealing plate was used.
[0020]
The surface of the test piece of the cold-rolled annealed plate thus obtained was emery # 600 polished, a salt spray test (based on JIS-Z-2371) was performed at 50 ° C. for 4 hours, and the number of rusts was counted. Here, the case where the number of rusting is 5 or less per dm ² is OK, and the case where it is 20 or more is NG.
FIG. 5 shows the corrosion resistance evaluation results performed for each of the Al ₂ O ₃ levels, organized by S content and Ca content.
As shown in the figure, when the amount of Al ₂ O ₃ in the oxide inclusions is 50 mass% or less, the S and Ca ranges with good corrosion resistance are wide, whereas the amount of Al ₂ O ₃ is 55 It can be seen that at a level of ˜65 mass%, the range is very narrow, and low S is indispensable in terms of corrosion resistance.
[0021]
As described above, in order to achieve the intended purpose of the present invention, the amount of Al in the steel is suppressed to 0.005 mass% or less, and the composition of oxide inclusions is Al ₂ O ₃ : 50 mass% or less. It is important to limit the range to Ti oxide: 20 to 90 mass% and CaO: 5 to 50 mass%.
However, it is not easy to control the composition of the oxide inclusions in the above range, and even if the steel composition is adjusted so that the inclusion composition is in the above range, the inclusion composition varies greatly. It has been found that it does not necessarily fall within the desired composition range.
[0022]
Therefore, as a result of further research on this point, the inventors have studied the deoxidizer components Al, Ti, and Ca in order to stably control the composition of oxide inclusions within the above range. It was found that the order in which these components are added is extremely important.
That is, first, after preliminary deoxidation by adding a small amount of Al or Si, if Ti is deoxidized by adding a relatively large amount of Ti, Al ₂ O ₃ or Si generated by Al deoxidation is removed. The SiO ₂ produced by the acid becomes a Ti oxide in such a form that the Ti oxide wraps, and when an appropriate amount of Ca is added after making such a form of Ti oxide, an oxide inclusion of the desired composition is formed. It was determined that it could be obtained stably.
Here, since the oxide inclusions obtained as described above have a low melting point, nozzle clogging does not occur during continuous casting, and the size is only about 5 to 20 μm. In this case, surface defects due to cluster inclusions are not generated. Moreover, since no CaS is generated around the oxide inclusions, there is no risk of rusting.
[0023]
In this regard, when steel is melted, the addition order of the deoxidizer components is not particularly considered, and when the alloy components are added simultaneously, particularly when a relatively large amount of Al is added as in the conventional case, Al ₂ Since oxides mainly composed of O ₃ are likely to be formed, it is not an inclusion having a composition as expected in the present invention, and as a result, it is considered that a desired effect was not obtained.
In addition, in the present invention, the strong agitation using a VOD furnace or the like is used in the steel melting stage, but conventionally, such a melting means has not been properly taken. It is thought that this was one of the reasons why
[0024]
C: 0.15 mass% or less C is an austenite stabilizing element and an element necessary for stably forming an austenite phase. However, when the content is too large, the ductility is lowered or the corrosion resistance is deteriorated, so the content is limited to 0.15 mass% or less.
[0025]
Si: 1.0 mass% or less
Si is a useful element for deoxidation, but is also a strong ferrite stabilizing element. Therefore, excessive addition destabilizes the austenite phase and also causes a decrease in ductility. Therefore, in this invention, it was made to contain at 1.0 mass% or less.
[0026]
Mn: 2.0 mass% or less
Mn is an element effective for deoxidation and is also an austenite stabilizing element. However, excessive addition causes a decrease in oxidation resistance and corrosion resistance, so it was limited to 2.0 mass% or less.
[0027]
Cr: 15-30mass%
Cr is an indispensable element for ensuring corrosion resistance, and is a main alloy element of austenitic stainless steel. Considering the corrosion resistance under various environments, sufficient corrosion resistance can be obtained at 15 mass% or more, so the lower limit was limited to 15 mass%. On the other hand, if it exceeds 30 mass%, the hot workability is significantly lowered, so the upper limit is set to 30 mass%.
[0028]
P: 0.05 mass% or less P is an element that is harmful to corrosion resistance, particularly intergranular corrosion resistance. When the content exceeds 0.05 mass%, the adverse effect becomes significant, so it is limited to 0.05 mass%.
[0029]
S: 0.015 mass% or less As described above, S is an element that lowers the corrosion resistance. In particular, when Ca is added as in the present invention, water-soluble CaS is likely to occur.
Although depending on the amount of Ca to be added, even if the oxide inclusion composition which is the main object of the present invention is controlled, if the S amount exceeds 0.015 mass%, the corrosion resistance tends to deteriorate, so the S amount is 0.015. Restricted to less than mass%.
[0030]
N: 0.15 mass% or less N, like C, is an austenite stabilizing element, and is an element necessary for stably obtaining an austenite phase. However, if contained in a large amount, the ductility is lowered and the corrosion resistance is deteriorated, so the upper limit was set to 0.15 mass%.
[0031]
Al: 0.005 mass% or less As is clear from the results of Experiment 1, it is necessary to make the content 0.005 mass% or less from the viewpoint of the surface quality of the cold rolled sheet. That is, when the content exceeds 0.005 mass%, a barbed defect caused by aggregation of Al ₂ O ₃ occurs on the surface.
[0032]
O: 0.01 mass% or less Oxygen does not dissolve at all in steel but exists as an oxide. Such inclusions tend to be the starting point of rust and breakage, and particularly when the oxygen content exceeds 0.01 mass%, the influence becomes significant. Therefore, the O content is limited to 0.01 mass% or less.
[0033]
Ti: 0.015-0.4 mass%
Ti is an element that is not only useful for deoxidation, but also effective for preventing grain boundary oxidation during slab heating in the hot rolling process and suppressing defects caused by hot rolling cracks. However, if the content is less than 0.015 mass%, the effect of addition is poor. On the other hand, if it exceeds 0.4 mass%, the ductility starts to decrease, so Ti is contained in the range of 0.015 to 0.4 mass%.
[0034]
Ca: 0.0005 to 0.0050 mass%
Ca is an extremely effective element for effectively reducing the melting point of the oxide inclusions according to the present invention and preventing nozzle clogging during continuous casting, and the effect is significant at 0.0005 mass% or more. Therefore, the lower limit was set to 0.0005 mass%. On the other hand, addition of a large amount causes deterioration of corrosion resistance even if the deoxidation product composition is controlled. If the content exceeds 0.0050 mass%, the risk becomes significant, so the upper limit was set to 0.0050 mass%.
[0035]
The basic components have been described above. In the present invention, the following elements can be appropriately added as necessary.
Mo: 0.05-6.0 mass%
Mo is a very effective element for improving the corrosion resistance, and the effect becomes remarkable at 0.05 mass% or more, so the lower limit was set to 0.05 mass%. On the other hand, the corrosion resistance improves as Mo is added, but it is not only a strong ferrite stabilizing element, but if it exceeds 6.0 mass%, it generates a brittle intermetallic compound at high temperature and deteriorates toughness. The upper limit was 6.0 mass%.
[0036]
Nb: 0.01 to 0.08 mass%, V: 0.01 to 0.1 mass%, B: 0.0002 to 0.0030 mass%
Nb, V, and B are all extremely useful elements for preventing the occurrence of striped patterns that are likely to be generated on the surface of a cold-rolled annealed plate due to the nonuniformity of the crystal grain size. The effect is observed when Nb: 0.01 mass% or more, V: 0.01 mass% or more, and B: 0.0002% or more alone or in combination, so the lower limits were limited to 0.01 mass%, 0.01 mass%, and 0.0002 mass%, respectively. . However, when Nb exceeds 0.08 mass%, the elongation begins to decrease, and when V exceeds 0.1 mass%, the ductility begins to decrease, and when B exceeds 0.0030 mass%, intergranular corrosion resistance decreases. Therefore, the upper limit was limited to 0.08 mass%, 0.1 mass%, and 0.0030 mass%, respectively.
[0037]
Next, the reason why the range of the oxide inclusion composition is limited in the present invention will be described.
Ti oxide amount: 20 to 90 mass%, Al ₂ O ₃ : 50 mass% or less, CaO: 5 to 50 mass%
The main technique of the present invention is to make the composition of the oxide inclusions in the above range.
As previously shown in Experiments 2, 3, 4, and 5, the amount of Al ₂ O ₃ is set to 50 mass% or less, more preferably 20 mass% or less, thereby preventing the bald surface defects generated in the cold-rolled sheet Further, by setting the amount of Ti oxide to 20 to 90 mass% and the amount of CaO to 5 to 50 mass%, nozzle clogging during continuous casting can be prevented, and corrosion resistance does not deteriorate. Therefore, in the present invention, the composition of oxide inclusions resulting from the deoxidation product is limited to the range of Ti oxide: 20 to 90 mass%, Al ₂ O ₃ : 50 mass% or less, CaO: 5 to 50 mass%. It was.
[0038]
In the present invention, it is not necessary that all the inclusions in the steel be a composite oxide having the above composition, but at least 50%, preferably 70% or more of Al ₂ O ₃ —Ti oxide— Any CaO-based complex oxide may be used.
Other oxides produced here include SiO ₂ , MnO, FeO _X and MgO.
[0039]
Next, the preferred manufacturing method of the present invention will be described.
In the present invention, as described above, the order of adding the deoxidizer components in the melting stage is important.
That is, first, a small amount of Al or Si is added to perform preliminary deoxidation, and then a relatively large amount of Ti is added to perform Ti deoxidation. In this way, Al ₂ O ₃ or SiO ₂ produced by deoxidation of Al or Si becomes a Ti oxide in the form of being wrapped with Ti oxide, but the size of such a form of Ti oxide Is about 5 to 20 μm, it is possible to advantageously prevent surface defects caused by huge cluster-like inclusions in the product plate.
However, since such Ti oxide is a solid phase in the molten steel, if it remains as it is, it may adhere to and deposit on the inner surface of the nozzle of the tundish in a form in which the steel is taken in during continuous casting, and the nozzle may be clogged.
However, if an appropriate amount of Ca is added thereafter, a low melting point oxide is formed, and therefore nozzle clogging during continuous casting is advantageously avoided.
Moreover, since CaS is not generated around the oxide inclusions, rusting can be prevented as described above.
[0040]
The molten steel adjusted to the desired steel composition and inclusion composition as described above is subjected to casting, hot rolling, cold rolling and annealing treatments to obtain a product according to a conventional method.
Here, suitable hot rolling conditions, cold rolling conditions and annealing conditions are as follows.
Hot rolling conditions Slab heating temperature: 1050 to 1260 ° C, rough rolling temperature: 900 to 1180 ° C, rough rolling total rolling reduction: 80 to 93%, finishing rolling temperature: 750 to 1000 ° C, finishing rolling exit thickness: 1.5 to 7 mm, winding temperature: 400-850 ° C.
Cold rolling conditions Cold rolling can be performed by a tandem mill, a cluster mill or a Sendzimir mill. The total rolling reduction is preferably about 45 to 95%. Cold rolling-annealing-cold rolling may be repeated.
Annealing conditions Finish annealing temperature: Select within the range of 1000-1180 ° C according to the target material. Target temperature holding time: Select from the range of 0 to 1800 s according to the target material.
Further, surface finish includes 2D, 2B, BA, and polishing.
[0041]
【Example】
Molten steel having the composition shown in Table 1 was produced as follows.
That is, for the chromium-containing molten steel after the decarburization treatment, a predetermined amount of Al was first added to the chromium-containing molten steel while stirring the molten steel, followed by preliminary deoxidation, and then Ti was added to perform Ti deoxidation. After that, the components were adjusted and Ca was added after the molten steel was transferred to the atmosphere.
Subsequently, it was cast to a thickness of 200 mm and a width of 1000 mm by a continuous casting method. The obtained slab was hot rolled under the following conditions without care.
Slab heating temperature: 1170-1260 ° C, heating time: 30-90 minutes, rough 7 passes, rough finish thickness: 25mm, rough rolling finish temperature: 990-1120 ° C, finish (7-step mill), finish thickness: 3mm, FDT : 800-1080 ° C, CT: 700-1030 ° C.
[0042]
The obtained hot-rolled coil is continuously annealed at 1090 to 1140 ° C, pickled and finished to a thickness of 0.6 mm by cold rolling, then continuously annealed at 1070 to 1140 ° C, then pickled and cold rolled. An annealing plate was used.
With respect to the cold-rolled annealed sheet thus obtained, Table 2 shows the results of examining the composition of oxide inclusions, the nozzle clogging rate after continuous casting, the number of bald defects on the surface of the cold-rolled annealed sheet, and the occurrence of striped patterns. Shown in
In addition, the table shows the number of rusting and the rusting area ratio after emery # 600 polishing of the surface of cold-rolled annealed plate and conducting salt spray test (SST) and salt dry and wet combined cycle corrosion test (CCT). The results are also shown.
The surface properties were evaluated by the number of surface defects and striped patterns on the cold-rolled sheet, and the corrosion resistance was evaluated by the number of rusting and the rusting area ratio in the salt spray test and the salt dry / wet combined cycle corrosion test, respectively. did.
[0043]
In addition, each characteristic evaluation method is as follows.
・ Analysis of oxide inclusions in cold-rolled annealed plates Samples were taken from the cold-rolled annealed plates and electrolyzed in a bromine-methanol solution. Chemical analysis was conducted after dissolving in
・ Measurement method of nozzle clogging rate
Initial diameter after 160-ton continuous casting: Collect 60mm nozzle, cut the cross section and measure the minimum diameter, ((initial diameter-minimum diameter after casting) / initial diameter) x 100 (%) It was.
[0044]
・ Salt spray test (SST)
The surface of the cold-rolled annealed sheet was emery # 600 polished, degreased, and subjected to a salt spray test for 4 hours under conditions (50 ° C.) in accordance with JIS Z 2371, and the number of rusting was counted.
・ Salt dry and wet combined cycle corrosion test (CCT)
After emery # 600 polishing finish on cold-rolled annealed sheet surface, degrease, spray 3.5% NaCl at 35 ° C for 0.5 hour, dry for 1 h (60 ° C) and wet for 1 h (40 ° C, relative humidity: 95% or more) A composite corrosion test with one cycle was performed for 30 cycles, and the rust area ratio was measured.
[0045]
[Table 1]

[0046]
[Table 2]

[0047]
As shown in Table 2, the austenitic stainless steel according to the present invention has no nozzle clogging at the time of continuous casting after melting, and there is no surface defect on the product plate, and it has excellent corrosion resistance. Was.
[0048]
【The invention's effect】
Thus, according to the present invention, it is possible to stably obtain an austenitic stainless steel free from surface defects due to oxide inclusions and having excellent corrosion resistance.
Further, the austenitic stainless steel of the present invention does not cause nozzle clogging during continuous casting during the production process.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of Al in steel and the number of surface defects on a hot-rolled annealed plate.
FIG. 2 is a graph showing the relationship between the Al ₂ O ₃ concentration in oxide inclusions and the number of bald surface defects.
FIG. 3 is a graph showing the relationship between the Ti oxide concentration in oxide inclusions, the nozzle clogging rate, and the number of rusting.
FIG. 4 is a graph showing the relationship between the CaO concentration in oxide inclusions, the nozzle clogging rate, and the number of rusting.
FIG. 5 is a graph showing the effects of the amount of S and Ca on corrosion resistance in comparison with two Al ₂ O ₃ levels.

Claims (3)

C: 0.15 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less,
Cr: 15-30 mass%, Ni: 5-30 mass%, P: 0.05 mass% or less,
S: 0.015 mass% or less, N: 0.15 mass% or less, Al: 0.005 mass% or less,
O: 0.01 mass% or less, Ti: 0.015-0.4 mass%, Ca: 0.0005-0.0050 mass%
The balance is Fe and inevitable impurities , and the composition of oxide inclusions due to deoxidation products in the steel is Ti oxide: 20 to 90 mass%, Al ₂ O ₃ : 50 mass % Austenitic stainless steel with good surface properties and excellent corrosion resistance, characterized by satisfying a range of not more than% and a range of CaO: 5 to 50 mass%. The steel composition according to claim 1, further comprising:
Mo: 0.05-6.0 mass %
Good corrosion resistance surface properties characterized by comprising a composition containing an excellent austenitic stainless steel. The steel composition according to claim 1 or 2, further comprising:
Nb: 0.01 to 0.08 mass%, V: 0.01 to 0.1 mass%, B: 0.0002 to 0.0030 mass%
An austenitic stainless steel with excellent surface properties and excellent corrosion resistance, characterized in that it has a composition containing one or more selected from among them.

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