JP2005290449A - Fine inclusion-containing stainless steel and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide austenitic stainless steel whose workability in etching working, mechanical working such as deep drawing, further, welding working or the like is improved by controlling inclusions. <P>SOLUTION: The inclusions in the stainless steel are composed of CaO-SiO<SB>2</SB>-MgO-Al<SB>2</SB>O<SB>3</SB>-MnO-Cr<SB>2</SB>O<SB>3</SB>. The average composition thereof is allowed to satisfy 1 to 55% Cr<SB>2</SB>O<SB>3</SB>, ≤50% Al<SB>2</SB>O<SB>3</SB>, and ≤15% MgO, and also, the maximum diameter of the equivalent circle in the inclusions is controlled to the fine one of ≤20 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to stainless steel, in particular, stainless steel in which the size and composition of inclusions are defined, and a method for producing the same.
The stainless steel according to the present invention can be used for many applications. To name a few, a stainless steel plate suitable for etching used for molding metal precision parts used in electronic equipment and precision equipment. As a stainless steel plate that is most suitable for sinks, bathtubs, flexible pipes, etc. formed by deep drawing, overhanging, bending, etc., as well as medical injection needles with excellent surface properties and corrosion resistance, in trains and stairs, etc. It can be used as a stainless steel plate suitable for a decorative pipe used as a handrail, or a welded pipe used for piping in a wide range of applications such as chemical equipment and food equipment.

Stainless steel used for these applications is generally manufactured as follows. One example will be described below.
For example, each component raw material is melted to produce a desired composition in an electric furnace to produce crude molten steel, then transferred to, for example, a VOD furnace, and decarburized and refined with vacuum argon-oxygen gas to achieve a target [C] concentration. Adjust to the value. Thereafter, in order to recover [Cr] that inevitably oxidized and transferred to slag, reduction refining is performed by adding Si or Al. At this time, adjustment of components such as Si and Mn is also performed. Thereafter, the molten steel is cast by continuous casting, and the obtained slab is hot-rolled and cold-rolled to obtain a plate material having a desired thickness, and then used for each application.

In the melting process, various non-metallic oxide inclusions (hereinafter simply referred to as inclusions) are inevitably generated in the molten steel. For example, when Si is used as the reducing agent during the reductive refining, SiO ₂ inclusions are generated, and when Al is used, Al ₂ O ₃ inclusions are generated. In addition, Mn and Cr in the raw material components are partially MnO and Cr ₂ O ₃ inclusions.

  Inclusions included in the stainless steel plate are, for example, a factor that hinders etching processing, and are desirably as small and fine as possible. In particular, in recent years, with the miniaturization and high performance of equipment, the parts used there have been required to be processed with higher precision than before, and it has become necessary to further refine the inclusions than before. It was.

 Here, the etching process is a process method that utilizes the phenomenon of metal corrosion and dissolution. First, a thin metal plate to be processed is degreased and cleaned, and a photosensitive photoresist is coated on the surface. Next, the desired product shape is exposed and baked on the photoresist and developed to form a photoresist pattern. Next, an etching solution is sprayed to dissolve unnecessary metal exposed portions so as to be processed into a desired product shape, and finally the photoresist film is peeled to obtain a target product.

On the other hand, in austenitic stainless steel, there are large hard inclusions such as CaO-SiO ₂ -MgO inclusions containing a large amount of MgO or inclusions of Al ₂ O ₃ alone. When a large amount is present in the slab, such inclusions are difficult to plastically deform, resulting in a material with poor formability. Therefore, efforts have also been made to reduce the amount of hard inclusions produced during melting and control the composition of inclusions so that the inclusions become soft inclusions in the steel sheet used for forming.

  In addition, a lot of welded pipes made of SUS304 or SUS316 stainless steel sheet are used for injection needles and decorative pipes. Due to this problem, the surface finish was applied to the mirror surface after welding. However, even in such applications, if there are coarse inclusions in the steel sheet, and inclusions float on the surface of the melted part during welding or in the vicinity thereof, there will be defects such as holes and whiskers during surface finishing in grinding and polishing. There was a problem that occurred. There was also a problem of early corrosion (rust generation) starting from inclusions. Moreover, since the injection needle, the cosmetic pipe, and the like are products that are applied to or touched by an unspecified number of people, it is necessary to have high reliability for reducing the occurrence rate of those problems as much as possible.

  Even in the past, because of the various problems as described above, for inclusions, particularly inclusions in austenitic stainless steel, many proposals have been made in relation to the reduction means or control means, The prior art will be summarized below.

  In Patent Document 1, the contents of S and O are regulated to ppmS <42-0.094 (ppmO), and the generation of etching pits is prevented by suppressing the generation of S-based or O-based inclusions. Martensitic stainless steel is disclosed.

Patent Document 2 discloses an Fe—Ni alloy for etching processing in which the C content <0.01% and the cross-sectional cleanliness <0.017% are regulated. The cross-sectional cleanliness is defined by JIS G 0555.
In Patent Document 3, a stainless foil having a thickness of 25 μm or less is accompanied by cracks during etching by restricting the average number of inclusions having a maximum diameter of 5 μm or more to 3 or less per 1 mm ^{2 in the} rolling direction cross section. A method for preventing tunnel-like local corrosion is disclosed. In general, a plate thickness exceeding 25 μm is often used as an etching material, and this is intended to be an ultra-thin material to make it thinner.

On the other hand, for forming stainless steel, for example, as described in Patent Document 4, the ratio of length (ι) to width (d) is L / d ≦ 5 in the L section of the rolled steel material. average composition SiO ₂ 20 to 60% of small non-metallic inclusions, 10~80% MnO, CaO 50% or less, Ano consisting of 15% MgO - high cleanliness steel is known as a main component site .

Further, as described in Patent Document 5, the average composition of inclusions with small stretchability having a ratio of length (ι) to width (d) of ι / d ≦ 5 in the L cross section of the rolled steel material is SiO _2. A high cleanliness steel mainly composed of spesite composed of 35 to 75%, Al ₂ O ₃ 30% or less, CaO 50% or less, and MgO 25% or less is known.

However, in the case of stainless steel, the inclusions shown in these prior arts contain a large amount of Cr in the steel composition. Therefore, in actual production, the inclusions are coarse and hard with a large amount of Cr ₂ O _3. It becomes a composite inclusion containing inclusions, and a sufficient effect cannot be obtained.

  Furthermore, since the size of inclusions has a critical effect as the thickness of the material decreases as a result of strong processing, efforts have been made to soften the inclusions remaining in steel materials. The relationship between the size and cold workability has not been fully elucidated.

  In addition, for injection needles, decorative pipes, etc., recently, in Patent Literature 6, Patent Literature 7, Patent Literature 8, and Patent Literature 9, elements such as C, P, and S are adjusted to improve weldability and corrosion resistance at the welded portion. Many stainless steels have been reported that improve the above.

Regarding the influence of inclusions, a report such as Patent Document 10 is also seen.
JP 60-92449 A JP-A-61-84356 Japanese Unexamined Patent Publication No. 2000-273586 Japanese Patent Publication No. 6-74485 Japanese Examined Patent Publication No. 6-74484 JP 05-17852 A Japanese Patent Laid-Open No. 10-81940 JP 2000-178697 JP 2003-64453 A Japanese Unexamined Patent Publication No. 08-246105

   In order to solve the above-mentioned problems, the present invention proposes an austenitic stainless steel having improved workability including etching, deep drawing, and other machinability, as well as welding, by controlling inclusions. .

The present inventors investigated the composition and form in more detail than before by introducing a method of analyzing and observing the base material after removing and extracting the corrosion with respect to the inclusion investigation.
Here, as a result of intensive investigations aimed at preventing etching defects starting from inclusions and breakage during product use, the present inventors have made extensive investigations on stainless steel, particularly stainless steel sheets used for etching. It has been found that the maximum equivalent circle diameter of an object may be 20 μm or less.

By limiting to such fine inclusions, it has now been found that general workability, as well as corrosion resistance and appearance, particularly surface properties and corrosion resistance of welds, are significantly improved.
Furthermore, as a result of the study, the following points were found for a method for miniaturizing such inclusions to a critical size.

  That is, in the manufacturing method of the material, during melting, (1) strengthen the floating separation due to the difference in specific gravity of coarse inclusions that have a particularly adverse effect on fatigue properties by holding molten steel, (2) by controlling the slag composition in secondary refining By adjusting the oxide-based non-metallic inclusions to a soft composition and, if necessary, taking the double measures of crushing in subsequent processing, the coarse inclusions disappear, ensuring excellent processing characteristics and ensuring reliability. It has been found that austenitic stainless steel having high workability and high workability can be provided.

According to the present invention, inclusions can be miniaturized, so that various characteristics inherent to stainless steel can be sufficiently exhibited. For example, a material suitable for the following specific application can be obtained.
By using the stainless steel plate according to the present invention, it becomes possible to manufacture high-definition etching products used in electronic equipment and precision machines.

By the stable control of inclusions in the present invention, highly reliable austenitic stainless steel that can stably obtain excellent formability can be provided industrially at low cost.
Through stable control of inclusions in the present invention, it is possible to provide stainless steel sheets and products made of the same steel sheets (injection needles, decorative pipes, etc.) with excellent surface properties and corrosion resistance of welds and at low cost and stably industrially. it can.

The reasons for limiting the composition and shape of the inclusions in the stainless steel according to the present invention are as follows.
The size of inclusions is greatly affected by the degree of extension and division during rolling, but the degree of extension and division was found to be related to the Cr ₂ O ₃ content of nonmetallic inclusions in stainless steel. Is. More precisely, according to the present invention, by increasing the amount of Cr ₂ O _{3, the} content of Al ₂ O ₃ and MgO that form hard inclusions can be suppressed and refined. .

  On the other hand, the processing characteristics depend on the size of the inclusions, not the composition of inclusions, and are improved by miniaturization. The critical circle diameter is 20 μm or less at the maximum equivalent circle diameter, and cracks starting from inclusions are not seen. The behavior was confirmed.

Therefore, in the present invention, the maximum equivalent circle diameter of the nonmetallic inclusion is specified to be 20 μm or less. Furthermore, it is preferably 15 μm or less.
The reason for limiting the inclusion composition is as follows. In the present specification, “%” is “% by mass” unless otherwise specified.

Control of Cr ₂ O ₃ is to suppress the formation of Al ₂ O _3, the hard inclusions of MgO and Cr ₂ O _3, to allow efficient miniaturization due to processing. For this reason, the content of inclusions composed of CaO—SiO ₂ —MgO—Al ₂ O ₃ —MnO—Cr ₂ O ₃ is determined to be 1% or more and 55% or less, based on the results of the average composition.

Al ₂ O ₃ and MgO generate hard inclusions, and it is considered difficult to refine them efficiently by processing. From this result, the average composition of inclusions composed of CaO—SiO ₂ —MgO—Al ₂ O ₃ —MnO—Cr ₂ O ₃ was determined to be 50% or less and 15% or less, respectively. The other alloy components were ignored because of their low content.

In this specification, the inclusion composition was converted as CaO—SiO ₂ —MgO—Al ₂ O ₃ —MnO—Cr ₂ O ₃ from the composition analysis result (alloy element amount).
Said composition is a composition in the cold rolled steel plate which is a final product raw material. That is, if fine inclusions having the above composition remain, inclusions exceeding 20 μm, which is a critical nonmetallic inclusion diameter, usually do not exist.

  The stainless steel targeted by the present invention is not particularly limited in its components. For example, it is applicable to all materials used for etching, such as austenitic stainless steel represented by SUS304 and ferritic stainless steel represented by SUS430. Is possible. The form is a thin plate having a thickness of 0.5 mm or less by cold rolling.

However, the preferred composition of the stainless steel according to the present invention is as follows.
The composition of the stainless steel matrix is preferably a metastable γ-based stainless steel having the following composition for the following reasons, mainly from the viewpoint of maintaining high strength and workability.

  C is an interstitial solid solution strengthening element and is the most effective element that strengthens the material together with N. However, when it is added excessively, chromium carbide is generated, and therefore, the corrosion resistance necessary for stainless steel cannot be obtained, and when it is coarse, the processing characteristics are deteriorated. For this reason, it was set to 0.01% or more and 0.15% or less. Preferably, it is 0.01 to 0.12%.

  Si is a solid solution strengthening element and is an effective element for strengthening the material. As a lower limit, it is an indispensable element as a mixing and deoxidizing agent. However, when it contains excessively, workability will deteriorate. For this reason, it was set to 0.1% or more and 3.0% or less. Furthermore, it is preferably 0.2% or more and 2.6% or less.

  Mn is a gamma stabilizing element. In consideration of the balance with other elements, 0.1% or more is added. However, when excessively added, the amount of processing-induced α ′ phase may decrease and the strength may be insufficient. However, there is an aspect in which the solid solution amount of N can be increased and the material can be strengthened. As a lower limit, it is an indispensable element for ensuring mixing and hot workability. For this reason, the upper limit was made 4.0% or less. Furthermore, it is preferably 0.2% or more and 2.5% or less.

P is preferably as small as possible since it impairs hot workability and weldability, and is set to 0.050% or less. Furthermore, it is preferably 0.040% or less.
S is less desirable because it impairs hot workability and corrosion resistance, and is set to 0.020% or less. Furthermore, it is preferably 0.015% or less.

   Cr is a basic element of stainless steel, and is added at 10.0% or more. However, Cr is also a ferrite stabilizing element, and when added in a large amount, the ferrite phase remains in the steel. On the other hand, Cr can increase the solid solution amount of N and strengthen the material. For this reason, it was set at 25.0% or less. Furthermore, it is preferably 14.0% or more and 24.0% or less.

  Ni is one of the most powerful austenite stabilizing elements among the alloy elements, and is essential for obtaining an austenite phase structure at room temperature. The effective range is considered to be a lower limit of 3.0% and an upper limit of 22.0%. Furthermore, it is preferably 4.4% or more and 12.0% or less.

N is an interstitial solid solution strengthening element and is the most effective element that strengthens the material together with C. Although some adjustment is possible depending on the amount of addition of Mn, Cr, etc., when it is added excessively, coarse nitrogen compounds are generated, resulting in problems such as deterioration in processing characteristics. For this reason, it was made 0.01% or more and 0.30% or less. Furthermore, it is preferably 0.02% or more and 0.24% or less.
For Ti, Nb, V
Ti, Nb, V precipitates fine carbon and nitride (may include other alloying elements such as Cr) during welding to suppress grain growth, and balance between strength and workability due to refinement of weld grain Improvement in corrosion resistance is expected. Moreover, precipitation of chromium carbide which causes corrosion resistance deterioration is suppressed by these. In order to obtain the same effect, at least one of each is added in an amount of 0.01% or more. However, when excessively added, coarse precipitates are generated, which may cause problems such as deterioration of the productivity of the plate. Moreover, it is an expensive element, and when it is added in a large amount, the material becomes expensive. For this reason, the upper limit was 0.5% respectively. Furthermore, it is preferably 0.04% or more and 0.46% or less, respectively.

The balance of the steel composition consists of Fe and inevitable impurity elements.
In addition to the above components, Mo and Cu may be added in an amount of 0.5% or less, if desired, for adjusting γ stability. Additive elements from the industrial side, such as Al, Ca or REM (rare earth elements) used as a deoxidizer during melting, B, etc., where improvement in hot workability is expected, are 0.05% or less as required. It may be contained. In addition, Mg, which is one of the main elements forming inclusions, is not particularly added, but mainly penetrates with Al, Ca, etc. from heat-resistant materials used in various parts during melting, 0.02 % Or less may be contained.

The melting of the stainless steel having such a steel composition can be performed, for example, under the following conditions.
(1) Holding time ≧ 1hr, molten steel stirring power ≦ 40W / ton, for strengthening floating separation of coarse inclusions in holding molten steel,
(2) For efficient refinement of inclusions in subsequent processing, the basic slag composition in secondary refining is basic CaO / SiO ₂ 1.4 to 1.8, Al ₂ O ₃ ≦ 2%, MgO ≦ 10% And
It can be realized by the following method. However, the method is not limited to this method.

  The above condition (1) is for strengthening the floating separation of coarse inclusions, and the condition (2) is for producing ductile inclusions that can be broken and crushed in processing. Condition (2) is an empirically determined value from the analysis of molten steel, taking into account the change in inclusion components due to repeated solidification, hot rolling and cold rolling, and annealing.

  From these, it was considered that the implementation of the same step was effective when producing the steel of the present invention, and the production method (same step) at the time of melting was also limited in the present invention. The other conditions are not particularly different from general melting of stainless steel.

  Subsequently, a steel sheet having a thickness of about t1 mm was manufactured by repeating hot and cold rolling and annealing. It is desirable that the rolling ratio is 60 or more in total including the temper rolling in the next step, and particularly the hot rolling ratio is 35 or more. Intermediate and final annealing may be held at 900 to 1200 ° C for about 60 seconds per 1 mm thickness.

Next, a thin plate having a thickness of t0.4 mm is manufactured by repeating hot and cold rolling and annealing. The rolling ratio is preferably 75 or more including the temper rolling in the next step, and particularly the hot rolling ratio is preferably 35 or more.
Here, taking the etching process as an example, the present invention will be described more specifically as follows.

  Inclusions contained in the stainless steel sheet do not melt directly into the etching solution, but remain undissolved at the etching end face, or fall off during the etching and cause etching defects such as the unintended part of the peripheral part melting and the shape being damaged. Will cause the yield to deteriorate.

  Furthermore, when bending is performed after etching, cracks may occur starting from etching defects. Alternatively, there is a risk of causing a serious defect such as damage starting from an etching defect when used in an environment where a repetitive stress such as a gimbal spring is applied. According to the present invention, such a problem can be solved by setting the maximum equivalent circle diameter of inclusions to 20 μm or less.

  Conventionally, the minimum width of a resist pattern in etching processing has conventionally been about 50 μm, but recently, the resist resin and the exposure / development apparatus have been improved, and resolution has become possible even with a width of 30 μm or less. As the resist pattern increases in definition, the effect of the size of inclusions increases, and according to the present invention, the size of the inclusions is at least 1/2 or less of the minimum width of the resist pattern, that is, the maximum equivalent circle diameter. Therefore, it is possible to perform high-definition etching with a high yield by restricting the thickness to 15 μm or less, more preferably to 10 μm or less.

When used for etching processing in the present invention, it is preferable to use a material melted by the following method.
(1) Secondary refining slag composition Al ₂ O ₃ ≦ 2%, T.CaO / SiO ₂ 1.4-1.8, MgO 10%
(2) The inclusion is generated while maintaining the ratio of the amorphous layer and the low melting point inclusion.

(3) Molten steel stirring power in ladle ≤ 40 W / ton, molten steel holding time ≥ 2.0 hrs
(4) Take a rolling ratio of 75 or more (hot rolling ratio> 30)
As a result of investigating the composition and shape of the inclusions in the thin plate produced in the above process, etching defects starting from the inclusions are hardly seen at the maximum equivalent circle diameter of 15 μm or less.

   Next, the function and effect of the present invention will be described more specifically by way of examples.

Stainless steel having the composition shown in Table 1 was melted by an electric furnace → VOD → LF → CCM, and the basicity of the slag composition was controlled by the amounts of CaO / SiO ₂ , AlO ₃ and MgO. In No. 1 to No. 12, the molten steel was held at LF at a constant temperature for 4 hours and stirred with a power of 40 W / ton or less. The comparative steels No. 13 and No. 14 were cast from the VOD and immediately cast by CCM without holding the molten steel at LF.

The steel strip obtained by hot rolling the slab obtained by the above-described method to a thickness of 4 mm was further subjected to cold rolling and annealing to finally obtain a stainless steel plate having a thickness of 0.10 mm.
The survey was conducted as follows.

  First, after removing the base material part from a 5g sample by corrosive removal with 10% bromine-methanol, it is extracted through a specified filter, and the shape is investigated using a scanning electron microscope (SEM), and energy dispersive X-rays are obtained. Composition analysis was performed using a detector (EDX: Energy-Dispersive X-Ray Spectrometer).

The shape of the inclusion was calculated from the following equivalent circle diameter, and the maximum value (maximum equivalent circle diameter) of them was displayed.
d = (dmax × dmin) ^1/2
d: equivalent circle diameter (μm), dmax, dmin: major axis and minor axis of inclusion (μm)
The composition was converted from the analysis result (alloy element amount) as CaO—SiO ₂ —MgO—Al ₂ O ₃ —MnO—Cr ₂ O ₃ .

  The stainless steel plate manufactured by the above-mentioned method was pretreated (alkali degreasing cleaning), and then an acrylic resin-based photoresist was applied and dried by a dip coating method to a dry film thickness of 10 μm.

  The dot pattern shown in FIG. 1 (front surface φ0.1 mm, back surface φ0.03 mm, dot pitch 0.3 mm) was exposed and baked. FIG. 2A is a cross-sectional view after the resist phenomenon, and FIG. 2B is a cross-sectional view after the etching process.

An etching solution (47 Baume ferric chloride solution, 50 ° C.) was sprayed from both sides to penetrate, and finally the resist film was peeled off.
The etching processability was evaluated by observing 50 dot views of the dot pattern with an optical microscope (400x magnification), and drilling holes with defective roundness of the dots or missing shapes on the wall surface due to inclusions missing or remaining inclusions. Counted as a defect.

If the hole defect is 1 field or less out of 50 visual fields, the etching processability is good (marked with ◯).
Examples No. 1 to No. 7 are inclusion compositions defined in the present invention, the maximum equivalent circle diameter of inclusions is 15 μm or less, and these have a hole defect of one field of view or less, and etching processability Were determined to be good.

Comparative steels No. 8 and No. 10 have a large amount of MgO with respect to the inclusion composition specified in the present invention, and No. 9 and No. 11 have a large amount of Al ₂ O ₃ as well. Since these were all hard inclusions, there was a coarse inclusion with a maximum equivalent circle diameter exceeding 15 μm without breaking during rolling.

The comparative steels No. 12 and No. 13 had coarse inclusions with a maximum equivalent circle diameter exceeding 15 μm due to insufficient floating separation of inclusions in the molten steel.
In any of these cases, the hole defects due to coarse inclusions exceeded two fields of view, and it was determined that the etching property was inferior.

FIG. 3 shows the influence of the equivalent circle diameter of the inclusions and the processing crack in the annealed material tempered and rolled to a thickness of about 0.4 mm in this example. There are no processing cracks when the equivalent circle diameter of inclusions is 20 μm or less.
Table 2 shows the influence of the composition of inclusions and the maximum equivalent circle diameter on the processing characteristics of the temper-rolled annealed material with a thickness of about 0.4 mm. Inclusions are refined by increasing Cr ₂ O ₃ content and decreasing Al ₂ O ₃ and MgO content. Further, the processing characteristics do not depend on the inclusion composition, but are improved by miniaturization. As a result, there was no work cracking in the material whose inclusions were refined by holding the molten steel and controlling the composition.

The sample material was manufactured by repeating Example 1.
In addition, the molten steel was held at a constant temperature in LF. The stirring power of the molten steel being held was 40 W / ton or less. The thickness t0.4 mm was obtained by repeating hot and cold rolling and annealing. The processing rate in each rolling in the same process was the same.

Inclusion investigation was carried out in the same manner as in Example 1.
In the processing test, multistage deep drawing with a drawing ratio of 3 was performed to investigate the occurrence of processing cracks. The evaluation was made in three stages: no cracking in the processed part, cracking and opening.

Table 3 shows the influence of the inclusion composition and the maximum equivalent circle diameter on the grindability and corrosion resistance of the weld.
The inclusions of the inventive materials No. 1 to No. 7 satisfy the composition defined in the present invention, and the maximum equivalent circle diameter (maximum diameter) is 18 μm or less. In addition, the results show excellent grindability and corrosion resistance.

On the other hand, Comparative Materials No. 8 to No. 18 have a maximum inclusion diameter of 22 μm or more, and are inferior in corrosion resistance. The No. 12, No. 14, and No. 18 materials with a maximum diameter of 30μ or more also had poor weld grindability. This is because the No. 12 and No. 13 materials did not hold molten steel, the No. 17 material contained a large amount of Al ₂ O ₃ and MgO, and crushing and miniaturization during rolling were insufficient, which was coarse. It is presumed that this is due to the remaining inclusions. Note that these are obtained by multiplying the plate surface after grinding and corrosion resistance by a defect starting from coarse inclusions.

From these, it is confirmed that there is no problem in the material in which inclusions are refined by holding molten steel × (composition control + crushing by rolling).
Hereinafter, the above test method will be described supplementarily.

The sample was a thin plate of about t1 mm manufactured in the same process using a hot rolled plate of t4 mm manufactured from an actual melted material and a small ingot at the laboratory level. Note that actual melting electric furnace → VOD (Vacuum-Oxygen Decarburization furnace ) → LF (Ladle Furnace) → CCM (Continuous Casting machine) were melted by, basicity CaO / Si0 ₂ the slag composition, Al ₂ O ₃ amount The amount of MgO was controlled. In LF, the molten steel was kept at a constant temperature and stirred with a power of 40 W / ton or less. On the other hand, the small ingot was manufactured at around 17 kg using a vacuum melting furnace. And after hot rolling and annealing to t4mm with actual equipment or laboratory level equipment, cold rolling → annealing was repeated once or twice with laboratory level equipment to make a thin sheet of t1mm. Then, TIG welding was performed to investigate the grindability and corrosion resistance of the weld. TIG welding was carried out with a bead-on plate using an electric current of 80 A, a speed of 0.5 M / min., Ar (10 L / min.) As a sealing gas. Welding was performed three times in the vicinity of the center of the plate width in parallel with the rolling direction so that the beads were separated by about 15 mm in the width direction.

Thereafter, a test piece having a predetermined size including three bead portions was collected, and the following tests were performed.
The inclusion investigation was conducted according to Example 1.
Grindability of welds:
Take a W20mm × L20mm test piece from the annealed material after welding so that a bead is included in the center of the plate width, and use a wet polishing machine in the order of # 400, # 800, # 1000, # 1200 abrasive paper. Polished. Then, the surface was observed using SEM, and the presence or absence of a hole or a crest-like defect starting from inclusions was confirmed. In the case of no evaluation, the evaluation was ○, and the evaluation was ×.

Corrosion resistance of welds:
A specimen with a 100 mm square was taken from the annealed material so that it contained three beads at the center of the plate width, and was immersed in a 0.1% NaCl aqueous solution maintained at 60 ° C. for 100 hr. Then, the surface was observed using SEM and the presence or absence of rusting from the inclusion was confirmed. In the case of no evaluation, the evaluation was ○, and the evaluation was ×.

It is a plane schematic diagram of a dot pattern. 2A is a schematic cross-sectional view after developing the resist pattern, and FIG. 2B is a schematic cross-sectional view after etching. It is a graph which shows the influence of the circle equivalent diameter of an inclusion, and a processing crack.

Claims (4)

In the stainless steel containing inclusions, the inclusions are composed of CaO—SiO ₂ —MgO—Al ₂ O ₃ —MnO—Cr ₂ O ₃ , and the average composition of the nonmetallic inclusions is
Cr ₂ O ₃ : 1% to 55%,
Al ₂ O ₃ : 50% or less,
Stainless steel characterized in that MgO: 15% or less, and the maximum equivalent circle diameter of the inclusions is 20 μm or less. The steel composition of the stainless steel is mass%,
C: 0.01% to 0.15%, Si: 0.1% to 3.0%
Mn: 0.1% to 4.0%, P: 0.050% or less S: 0.020% or less, Cr: 10.0% or more, 25.0% or less
Ni: 3.0% or more and 22.0% or less, N: 0.01% or more and 0.30% or less The balance is substantially Fe
The stainless steel according to claim 1, wherein: The steel composition is mass%, and
The stainless steel according to claim 2, comprising at least one of Ti: 0.01% to 0.5%, Nb: 0.01% to 0.5%, and V: 0.01% to 0.5%. Retention time at the time of melting: 1hr above, molten steel stirring power: holding the molten steel below 40W / ton, secondary refining slag composition at basicity CaO / Si0 _2: 1.4 to 1.8, Al ₂ O _{3: 2%} The method for producing stainless steel according to claim 1, further comprising a step of making MgO: 10% or less.

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