JP3373078B2 - Method of producing austenitic stainless steel ribbon-shaped slab with excellent cold-rolled surface quality and slab - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an austenitic stainless steel ribbon having excellent surface quality in a synchronous continuous casting process such as a so-called twin roll method in which there is no relative speed difference between a cast slab and a mold inner wall surface. The present invention relates to a method for manufacturing a slab and a cold rolled strip steel sheet thereof.

[0002]

2. Description of the Related Art Synchronous continuous casting processes include twin roll method, twin belt method, such as those introduced in the article featured in "Iron and Steel"'85 -A197-A256.
It is a synchronous continuous casting process such as a single roll method in which there is no relative speed difference between the slab and the inner wall surface of the mold. The twin-roll continuous casting method, which is one of these synchronous continuous casting processes, is a continuous casting mold composed of a pair of parallel or inclined cooling drums of the same or different diameter and side dams that seal both end surfaces of the cooling drums. Molten steel is poured into the inside of the two cooling drums to form solidified shells on the circumferential surfaces of the two cooling drums, and the solidified shells are combined near the closest position (so-called “kissing point”) of the rotating cooling drums to form an integrated body. It is a continuous casting method for forming thin strip-shaped cast pieces.

For example, a thin strip slab cast by a twin roll type continuous casting method has a thickness of several mm (usually about 2 to 5 mm), and is cold-rolled without the conventional hot rolling. Thin sheet products can be manufactured. Therefore, the conventional manufacturing method (slab casting-hot rolling process) in which a hot-rolling slab having a thickness of more than 100 mm is cast by continuous casting using a vibration mold or the like, hot-rolled and then cold-rolled Compared to,
The production efficiency and cost will be significantly improved.

However, various surface defects may occur in a product obtained by cold-rolling a thin strip-shaped slab cast by a twin roll type continuous casting method or the like without hot rolling. For example,
As described in JP-A-2-19426,
After cold rolling, roping (rough surface) caused by coarse crystal grains of the slab occurs. Further, a product manufactured by a twin roll type continuous casting method or the like in which dimples are formed on the peripheral surface of the cooling drum in order to stably prevent casting cracks and the like, is described in JP-A-4-158957. like,
Coarse-grained and fine-grained structures after the final annealing corresponding to unevenness of δ-ferrite in the cast structure may cause uneven gloss, which may cause uneven color tone.

Among these problems, as a countermeasure against roping, in Japanese Patent Laid-Open No. 19426/1990, the cooling rate immediately after casting is enhanced to suppress the crystal grain growth of the slab, and the cold rolling is performed twice to obtain an average grain size. It has been proposed to have a recrystallized structure with a diameter of 50 μm or less. In the above invention, instead of omitting the hot rolling, it is necessary to add the cold rolling / annealing process once more, which not only reduces the original purpose of the process omission but also leads to a decrease in productivity. , Was not the preferred method.

As a measure against uneven gloss, Japanese Patent Laid-Open No. 4-1 is used.
In Japanese Patent No. 58957, by setting the adjoining intervals of all the dimples provided on the wall surface of the cooling drum to be 0.35 mm or less, uneven cooling corresponding to the dimple unevenness is alleviated and the solidified structure is made uniform, and δ-Fe _cal. (%) 5-9%
A method of reducing the sensitivity to unevenness of coagulation tissue by adjusting the amount to 1 has been proposed. However, the method for processing the predetermined dimples is limited to the expensive photo-etching method and the like, and the inexpensive processing methods such as shot blasting cannot be used, and there are many spares for the cooling drum in case of unexpected trouble. Is necessary, and it is not economical and δ-F in terms of quality.
It was not possible to obtain a stable coagulated tissue according to the component definition of e _cal . As described above, the prior art does not disclose any means for solving the problems of roping and uneven gloss at the same time economically and without reducing productivity.

[0007]

DISCLOSURE OF THE INVENTION The present invention, in a so-called synchronous continuous casting process such as a twin roll method in which dimples are formed on the peripheral surface of a cooling drum, is carried out by rolling / heat treatment in-line with specific components and casting, or by casting. An object of the present invention is to provide an austenitic stainless steel thin strip slab excellent in cold rolling surface quality in which roping and uneven gloss are improved by heat treatment by in-line rolling and winding and reheating, and a method for producing the same.

[0008]

In order to solve the above problems, the present invention comprises the following means. By a continuous casting machine in which the slab moves in synchronization with the peripheral surface of the cooling drum in which a large number of random dimples are scattered by the shot blasting method, in the manufacturing method of casting a strip-shaped strip of austenitic stainless steel, in mass% , Cr + Mo +
Cr equivalent defined by 1.5Si and Ni + 30 (C +
Ni equivalent defined by N) +0.5 (Mn + Cu) is
Austenite as a component composition that satisfies the following formula (1)
Cast into thin strip of stainless steel series,
The rolling rate R _d shown in the following formula (2) is 20% or more and 30% or more.
Rolling as less than 1 and then 1 defined by the following formula (3)
A cold rolling table in which heat treatment is carried out under the condition that the equivalent heat treatment time t _{a at} 100 ° C. satisfies the following expression (4), followed by winding at 600 ° C. or lower.
Austenitic stainless steel thin strip casting with excellent surface quality
Piece manufacturing method. Alternatively, 2. this slab is then rolled at a rolling rate R _d defined by the following formula (2) of 30% or more, and subsequently, at 1100 ° C. equivalent heat treatment time t _a defined by the following formula (3). heat treating the at least four seconds, followed by taking up in 600 ° C. or less Hiyanobehyo
Austenitic stainless steel thin strip casting with excellent surface quality
It is a method of manufacturing a piece . Alternatively, 3. Subsequently this slab, the following (2) rolling a rolling reduction ratio R _d, defined as 20% or more and less than 30% by the formula, followed by wound below immediately water-cooled to 600 ° C., followed by (3) below the cold rolled surface 1100 ° C. equivalent heat treatment time t _a which is defined by the equation is a heat treatment under conditions satisfying the following equation (4) quality
Of excellent austenitic stainless steel thin strip casting . Or 4. Then , this slab is rolled at a rolling ratio R _d defined by the following formula (2) of 30% or more, immediately followed by water cooling and winding at 600 ° C. or less, and then the following (3 1100 ° C. equivalent heat treatment time t _a of 4 seconds or more, the austenitic stainless steel excellent in cold-rolled surface quality is used.
It is a method for manufacturing a stainless steel strip-shaped slab . And an austenitic stainless steel thin strip slab having excellent cold-rolled surface quality, which is produced by any of the above methods (1) and has a recrystallized structure having a sphere-reduced particle diameter D _ave of 70 μm or less defined by the following formula (5) is there. here,

[Equation 6] However, P: rolling load (ton), W: slab width (mm), T ₁ : rolling inlet temperature (° C), T ₂ : rolling outlet temperature (° C), T _i : rolling to winding Each temperature (° C) obtained by dividing the heat pattern in 0.1 second steps, Q: activation energy (365
KJ · mol ⁻¹ ) R: Gas constant (8.314 J · mol ⁻¹ · K ⁻¹ ) S: Total area of particle size measurement, S _i : i-th particle area.

[0009]

The inventors have made a detailed analysis of the roping phenomenon that occurs when a slab obtained by casting austenitic stainless steel by twin roll casting or the like is directly cold-rolled with a rapidly solidified structure. As a result, it was found that the degree of roping depends on the size of the crystal grain size before cold rolling. For the evaluation of the crystal grain size, D _n (= Σ2 × (3 × S _i / 2π / n) ^1/2 is defined as an expected value of the number frequency of crystal grains which is conventionally used for convenience.
However, in the rapidly solidified structure and the recrystallized structure obtained by rolling-heat treatment, it cannot be used as an index value representing the mixed grain state, and the area ratio of crystal grains (actually, it is necessary to consider the volume ratio). However, it is impossible to actually measure the volume, and for the sake of convenience, the area ratio is the volume ratio), which is the expected value D _ave (= Σ2 × (3 × S _i / 2π))
^½ × S _i / S) was defined as a new index value. The relationship is shown in FIGS. 1 and 2. As a matter of course, since the conventional index D _n is the expected value of the number frequency of crystal grains, the average value appears on the fine grain side in the mixed grain structure. However, the roping phenomenon is understood to be a phenomenon in which the sum of deformation differences in the plate thickness direction due to the presence of individual crystal grains or coarse and fine grain colonies (groups) appears on the surface. The more the grains, the more the accumulated deformation difference in the plate thickness direction is averaged, and the better the roping is. Therefore, the definition of the average crystal grain size in a mixed grain structure with a very large difference in grain size is expressed by D _ave , which is the expected value for the area ratio, and is an index that represents the actual state of the structure. In fact, the inventors
The recrystallized structure after hot rolling at a rolling rate of -40% is not an equiaxed grain like the current CC slab-hot rolled material, the surface layer is fine grain and the central part tends to be coarse grain, and further, Coarse grains that are far apart from adjacent crystal grains may appear, and such coarse grains are larger than the adjacent grains even if recrystallized, or in extreme cases, it becomes a mixed grain structure that remains as unrecrystallized grains. We have observed that the improvement in roping is insufficient. From the above, the inventors of the present invention have a value close to D _n in the case of equiaxed grains, and a large deviation from D _n in accordance with the degree in the case of mixed grains, and the influence of coarse grains harmful to roping. The average particle size D _ave was defined as an intermediate index that can be reflected. If the recrystallized grain size D _ave defined by this definition is secured to 70 μm or less, the roping rank (sensory evaluation of 1 to 5 ranks) can be a pass level of 2 or less (see Table 2).

In order to prevent roping, it is necessary to make the solidified structure equiaxed and fine-grained as much as possible.
Utilizing recrystallization by heat treatment is an effective method. In the present invention, hot rolling is performed by a hot rolling mill directly connected to a casting machine, a method of subsequently performing heat treatment to complete recrystallization, a method of winding after hot rolling, and a method of heat treatment by reheating are disclosed. However, if the recrystallization time is long depending on the steel type, it is possible to combine recrystallization in a heat treatment furnace following rolling and complete recrystallization in the solution treatment (annealing) before cold rolling. It has no effect on productivity. This is because pickling for scale removal is necessary regardless of recrystallization, and this treatment is performed in a continuous annealing / pickling line.

The main factors affecting recrystallization are as follows. (1) Initial particle size: The smaller the size, the faster the recrystallization. (2) Strain rate (= rolling rate): Recrystallization is promoted as the strain rate increases. (3) Processing temperature (= rolling temperature): The lower the temperature, the faster the recrystallization. (4) Strain amount (= rolling rate): The larger the strain, the more the recrystallization is promoted. (5) heat history (= heat treatment condition) after processing: more recrystallization to stay at a high temperature accelerated. Generally, in order to reduce the initial particle size, it is necessary to increase the solidification cooling rate. In twin roll casting, if the cooling drum structure and the casting temperature are constant, the solidification cold speed is almost determined by the casting speed according to the casting thickness, so there is a limit in controlling the initial grain size by the solidification cold speed. However, in the present invention, the initial grain size D _{ave is set} to 2 by adjusting the molten steel composition of the austenitic stainless steel to a specific range regardless of the casting speed.
It can be controlled to 50 μm or less (the maximum value is about 500 μm or less). This is because the solidification structure after casting is an acicular δ structure (a predominantly acicular δ structure and some pseudo-laceic δ exists, but it is a solidification form called “F mode solidification” in the weld metal). Judging from the above, it is considered that the columnar crystals are divided by the δ solidification → δ / γ transformation and the pinning effect by δ ferrite. The components of the present invention are Cr + Mo + 1.5S in mass%.
Cr equivalent defined by i and Ni + 30 (C + N) +
In the relation of Ni equivalent defined by 0.5 (Mn + Cu), F mode solidification is surely achieved by limiting to a range that satisfies Ni equivalent ≦ 0.63 × Cr equivalent−1.29, and The initial particle size can be controlled stably.

In order to improve roping, it is effective to use an equiaxed grain refinement structure that utilizes recrystallization. In the present invention, hot rolling is performed by a hot rolling mill directly connected to the casting machine, and subsequently heat treatment is performed. Alternatively, or by appropriately adjusting the condition of heat treatment after rewinding after winding, a predetermined recrystallized grain size can be economically obtained. Here, as a result of examination by the present inventors, the influence of the strain rate (= rolling speed) was found to be small, and is not taken into consideration in the present invention. Further, the rolling ratio R _d depends on the deformation resistance of the material at the rolling temperature, but is 17 to 2 of the Low-C, N system.
As a result of investigating the change in strength of each of the 0Cr-6 to 11Ni-0 to 2Mo-0 to 3Cu steels at each temperature in advance, it was clarified that the deformation resistances of those materials did not have a large difference. Do not consider. From the above assumptions,
The present inventors have found that the average rolling temperature (T ₁ + T ₂ ) / 2 calculated from the rolling inlet temperature T ₁ and the rolling outlet temperature T ₂ , the rolling load P of the hot rolling mill, the slab width W and rolling. Based on the relationship of the rate R _d , 40.6 × P / W + 0.04 × (T ₁ + T ₂ ).
It has been found that the rolling ratio R _d is almost determined by the relational expression of /2-42.1. Next, the rolling rate and heat treatment conditions will be described. As shown in FIG. 3, the rolling ratio R _d is 20% or more 3
If it is less than 0%, the equivalent heat treatment time t of 1100 ° C.
_It is necessary to secure a. When the rolling ratio R _d is less than 20%, the surface layer is sufficiently recrystallized, but unrecrystallized grains remain in the 1 / 4t layer to the central layer, and sufficient strain cannot be applied to the entire plate thickness. Rolling ratio more than 30% R _d at 1100 ° C. equivalent heat treatment time t _a is the thickness throughout at least 4sec almost completely recrystallized. Further, when the rolling ratio R _d is increased to 40%, the recrystallized grain size becomes finer, but the effect of improving the roping is saturated. In addition, 1100 ° C equivalent heat treatment time is 10
Almost no change in recrystallized grain size and roping was observed by 0 seconds. Even if the heat treatment time is longer than that, D _ave is 70 μm
There is no problem if the following is secured, but grain growth occurs due to heat treatment for a long time (particularly, a tendency that the crystal grains in the surface layer are coarsened is recognized), and conversely there is a risk that the roping is lowered. In addition, in order to secure a heat treatment time of 100 seconds or more, a realistic heat treatment furnace length cannot be obtained from the viewpoint of the casting speed (20 to 100 m / min).

Here, the equivalent heat treatment time t _a will be described. As in the present invention, if a line configuration for performing hot rolling-heat treatment subsequent to casting is used, although the temperature is lowered at a certain cooling rate between the hot rolling mill outlet and the heat treatment furnace inlet, if it is air cooling, A temperature of 900 ° C. or higher, which is the recrystallization temperature of austenitic stainless steel, is reliably ensured, and the heat treatment furnace should have the ability to raise the temperature from this temperature. That is, the thermal energy required for recrystallization is applied from the hot rolling mill and thereafter, and this zone can also be regarded as the effective heat treatment furnace length. Further, the industrial heat treatment furnace has a limit in temperature rising ability, and it takes some time to reach a predetermined temperature, but this temperature rising process is also a recrystallization phenomenon in a temperature range of 900 ° C. or higher. This is effective thermal energy for the heat treatment, and when directly heat-treating from casting to hot rolling, the furnace length can be significantly shortened as compared with heat treatment by reheating. Therefore, the equivalent heat treatment time t _a shown in the formula (3) is defined as the heat energy equivalent to the constant temperature / holding at the arbitrary temperature (1100 ° C. in the present invention) for the heat pattern in which the temperature rising / falling is repeated. This is also effective in designing an economical heat treatment furnace. In addition, 1100 ° C. defined in the present invention
Equivalent heat treatment time t _a, the cooling pattern from the hot rolling mill exit to the heat treatment furnace inlet, heating-retention pattern in the heat treatment furnace (heating-retention pattern distinction), more winding from the heat treatment furnace outlet (the In the present invention, the average temperature rise / fall rate up to the temperature drop pattern (in the invention is 600 ° C.) (the temperature rise in the heat treatment furnace is the average rate every 10 seconds), and in reheating, the temperature is raised from room temperature, retained and The average temperature rise / fall rate every 10 seconds of the temperature drop pattern up to 600 ° C is represented as
It shows the time when the total amount of heat accumulated in 0.1 second time intervals becomes equivalent to the amount of heat kept constant at 1100 ° C. Equivalent temperature can be displayed at any temperature without any problem, and even if the heat pattern is finely divided into less than 0.1 seconds, the calculation accuracy will increase, but in view of the variation in the rate of temperature rise / fall that can be industrially controlled. has no meaning.

Next, uneven gloss will be described. In the continuous casting method such as the twin roll method, the purpose of randomly distributing the dimples on the peripheral surface of the cooling drum is to directly cool the part (dimple center part) which is still cooled by the air gap and has low rigidity. The thermal stress generated by surrounding a highly rigid part (dimple edge part) that is sufficiently cooled by contacting is reduced by dimple dispersion, and cracks due to shrinkage of the solidified shell are spread over multiple reduced rigidity parts. It is to prevent it from occurring. However, the uneven cooling caused by the formation of the dimples adversely affects the uniformity of the solidified structure of the surface layer, and unevenness of the residual δ ferrite corresponding to the dimple unevenness occurs. The occurrence of the residual δ-ferrite unevenness is a phenomenon peculiar to austenitic stainless steel.

The inventors of the present invention adjusted various components from a twin roll casting machine in which dimples having random arrangement were formed on the peripheral surface of the cooling drum without regulating the dimple interval, size, etc. by the shot blast method. The austenitic stainless steel was cast, and the solidification structure of the slab and the uneven gloss after cold rolling were evaluated. The result is shown in FIG. In weight%, in the relationship between the Cr equivalent defined by Cr + Mo + 1.5Si and the Ni equivalent defined by Ni + 30 (C + N) +0.5 (Mn + Cu), Ni equivalent < 0.63C
Due to the limitation of the components satisfying r equivalent weight-1.29, the solidified morphology of the slab became F-mode solidification, and no gloss unevenness due to residual δ-ferrite was generated in the cold rolled sheet. This is the same condition range as the above-mentioned control of the initial particle size, and F
It means that the initial grain size and the residual δ ferrite unevenness can be controlled at the same time by mode solidification. The inventors of the present invention have found that the uneven glossiness due to δ-ferrite is an ash-like δ that occurs when it is completely solidified in the δ single phase and transformed into γ rather than the vermicular δ that occurs in the eutectic structure of the δ + γ phase during solidification. Has found that the residual ferrite unevenness of the solidified structure is reduced by observing the solidified structure of many twin-roll cast materials, but it was necessary to reduce the dimple spacing from the conventional knowledge. However, in the case of shot dimples, it became clear that the dimple spacing is not always a necessary and sufficient condition. The reason for this is as shown in FIG.
It can be considered as follows.

Since the dimple edge of the photoetching process is almost right angle, the molten steel does not enter the central part of the dimple due to the surface tension and the air gap layer in that part becomes thick, whereas the dimple formed by the shot process does not. Since the slope of the edge is gentle, the molten steel enters the dimple center along the slope of the edge, resulting in a thin air gap layer and reducing the difference in solidification cold speed between the dimple center and between the dimples. . Further, in the shot dimple, small dimples are present in large dimples, and the effect of direct contact with the cooling drum changing from surface to point disperses the solidification cold speed difference in each part of the dimple. It is considered that these effects notably replace the action of narrowing the dimple spacing, which is called photoetching dimples, and that the uneven glossiness of the product is substantially improved only by limiting the specific components.

The reason why the winding temperature is limited to 600 ° C. or lower is that the microgrooves (corrosion grooves along the grain boundaries) during pickling due to sensitization remain as a mesh pattern after cold rolling and cold rolling. This is to prevent the gloss of the plate surface from decreasing. However, there is no problem if mechanical grinding such as a coil grinder is performed, but in order to omit this step,
It is necessary to prevent sensitization during casting or intermediate annealing.

According to the present invention, the dimple formation of the cooling drum is performed by the shot blasting method, which facilitates the dimple processing and the repair, not by the photoetching method, and the initial particle size and Stabilize the solidification structure and perform hot rolling with a hot rolling mill directly connected to the casting machine, and then perform heat treatment to complete recrystallization, or perform heat treatment by reheating after winding. By optimizing it, an austenitic stainless steel sheet with excellent surface quality without roping or uneven gloss can be economically produced.

[0019]

EXAMPLES Austenitic stainless steels shown in Tables 1 and 2 were cast at a casting thickness of 3 to 5 mm by a twin roll casting machine using a cooling drum in which dimples having random arrangement were formed by a shot blasting method, and cast to about 1000 mm. ~ 1200
42% or less of one-pass rolling was performed by a 2Hi hot rolling mill disposed on the rear surface of the casting machine in a temperature range of ℃, immediately water-cooled, wound at 600 ℃ or less, and heat-treated by reheating.

[Table 1]

[Table 2] In addition, a part of a simple heat treatment furnace was installed to perform the post-rolling heat treatment, and then water cooling was performed to produce a strip-shaped cast piece wound at 600 ° C. or less. Rolling achieved the above rolling ratio by a combination of changing the mill rolling force on the way and adjusting the heat insulating cover between the cooling drum and the rolling mill in advance to change the rolling temperature in relation to the casting speed. . Since the rolling temperature is less affected by the rolling rate, the average value between charges is used. Then, if necessary, annealing, pickling, cold rolling,
Final annealing / pickling finish and bright annealing finish. As a quality evaluation, the initial grain size D _{ave of the} unpressed lower part of the slab, the solidification mode,
The recrystallized grain size D _ave after rolling and heat treatment was investigated as an intermediate index, and the roping and final annealing of the bright annealed material and the gloss unevenness of the pickled material were sensory evaluated. The results are shown in Tables 3 and 4.

[Table 3]

[Table 4]

The manufacturing method according to the present invention (No. 1 to No.
31) has a roping rank of 2
Below the roping passed. Moreover, uneven gloss was not generated at all, and good surface quality was exhibited. These were compositions having Ni equivalents satisfying the values on the right side of the formula (1) shown in Tables 1 and 2, the solidification mode was F, and the recrystallization D _ave was 70 μm or less. On the other hand, Comparative Example No. Three
2, 33 and No. Nos. 40 to 49 had a solidification mode of F and had good gloss unevenness of the cold rolled sheet, but the rolling ratio and 1100 ° C.
Since the combination of equivalent heat treatment times is out of the range of the present invention, the roping rank was 3 or more, and the test failed. In particular, Comparative Example No. In Nos. 48 and 49, although the rolling rate was 30% or more, the roping was not improved because the heat treatment time was insufficient. Further, Comparative Example No. 34-
In No. 39, since the solidification mode was FA, uneven gloss was generated on the cold-rolled sheet, the surface quality was poor, and the recrystallization conditions were also insufficient, so roping also failed.

[0021]

As described above, according to the present invention,
An austenitic stainless steel thin strip cold-rolled steel sheet having a surface quality equivalent to that of the conventional production method by the slab casting-hot rolling process can be manufactured at low cost and in a short delivery time.

[Brief description of drawings]

FIG. 1 is a diagram comparing the distribution of the recrystallized grain size with the initial grain size in the as-cast state with the conventional index and the index of the present invention.

FIG. 2 is a diagram comparing the distribution of recrystallized grain sizes after rolling-heat treatment with a conventional index and an index of the present invention.

FIG. 3 is a diagram showing a relationship between a rolling rate and a 1100 ° C. equivalent heat treatment time which pass / fail roping.

[Fig. 4] Cr equivalent and Ni depending on the occurrence of uneven gloss
It is a figure showing a relation of equivalent.

FIG. 5 is a schematic view showing a molten steel intrusion state by photoetching and shot dimple shape.

Front page continuation (51) Int.Cl. ⁷ Identification code FI B22D 11/12 B22D 11/12 Z B24C 1/06 B24C 1/06 C21D 8/02 D C21D 8/02 9/46 Q 9/46 C22C 38 / 00 302Z C22C 38/00 302 38/44 38/44 B21B 37/00 132A (72) Inventor Tetsuro Takeshita 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Co., Ltd. (56) References JP-A-3-66460 (JP, A) JP-A-4-200801 (JP, A) JP-A-2-133528 (JP, A) JP-A-63-421 (JP, A) JP-A-3-204146 (JP, A) JP 4-232208 (JP, A) JP 3-254336 (JP, A) JP 4-158957 (JP, A) JP 2-19426 (JP, A) 58) Fields examined (Int.Cl. ⁷ , DB name) B22D 11/06 330 B21B 1/46 B21B 3/02 B21B 37/76 B22D 11/00 B22D 11/12 B24C 1/06 C21D 8/02 C21D 9 / 46 C22C 38/00 302 C22C 38/44

Claims (5)

(57) [Claims] 1. A method of casting a strip of austenitic stainless steel by a continuous casting machine in which a slab moves in synchronism with the peripheral surface of a cooling drum in which a large number of random dimples are scattered by a shot blasting method. ,
In mass%, the Cr equivalent defined by Cr + Mo + 1.5Si and the Ni equivalent defined by Ni + 30 (C + N) +0.5 (Mn + Cu) are thin composition of austenitic stainless steel as component compositions satisfying the following formula (1). For strip slabs
After casting, the cast slab is rolled at a rolling rate R _d defined by the following formula (2) of 20% or more and less than 30%, and subsequently at 1100 ° C. equivalent heat treatment time defined by the following formula (3). t _a is a heat treatment under conditions satisfying the following equation (4), followed by cold rolled surface quality, characterized by winding at 600 ° C. or less good austenitic stainless steel thin strip cast piece manufacturing method. [Equation 1] However, P: rolling load (ton), W: slab width (mm), T ₁ : rolling inlet temperature (° C), T ₂ : rolling outlet temperature (° C), T _i : rolling to winding Each temperature (° C) obtained by dividing the heat pattern in 0.1 second steps, Q: activation energy (365
KJ · mol ⁻¹ ) R: Gas constant (8.314 J · mol ⁻¹ · K ⁻¹ ). 2. A method for casting a strip-shaped cast piece of austenitic stainless steel by a continuous casting machine in which the cast piece moves in synchronization with the peripheral surface of a cooling drum in which a large number of random dimples are scattered by the shot blasting method. ,
In mass%, the Cr equivalent defined by Cr + Mo + 1.5Si and the Ni equivalent defined by Ni + 30 (C + N) +0.5 (Mn + Cu) are thin composition of austenitic stainless steel as component compositions satisfying the following formula (1). For strip slabs
After casting, the cast slab is rolled at a rolling rate R _d defined by the following formula (2) of 30% or more, and subsequently a 1100 ° C. equivalent heat treatment time t _a defined by the following formula (3) is performed. A method for producing an austenitic stainless steel thin strip slab having excellent cold-rolled surface quality, which comprises heat-treating for 4 seconds or more and then winding at 600 ° C. or less. [Equation 2] However, P: rolling load (ton), W: slab width (mm), T ₁ : rolling inlet temperature (° C), T ₂ : rolling outlet temperature (° C), T _i : rolling to winding Each temperature (° C) obtained by dividing the heat pattern in 0.1 second steps, Q: activation energy (365
KJ · mol ⁻¹ ) R: Gas constant (8.314 J · mol ⁻¹ · K ⁻¹ ). 3. A manufacturing method for casting thin strip-shaped cast pieces of austenitic stainless steel by a continuous casting machine in which the cast pieces move in synchronization with the peripheral surface of a cooling drum in which a large number of random dimples are scattered by the shot blasting method. In % by mass, C defined as Cr + Mo + 1.5Si
r equivalent and Ni + 30 (C + N) +0.5 (Mn + C
Ni equivalent defined in u) is a strip of austenitic stainless steel having a composition that satisfies the formula (1) below.
Casting into a slab, then rolling the slab with a rolling ratio R _d defined by the following formula (2) at 20% or more and less than 30%, followed by immediate water cooling and winding at 600 ° C. or less, cast followed by the following (3) austenitic stainless steel thin strip 1100 ° C. equivalent heat treatment time t _a which is defined with excellent cold rolled surface quality, characterized by a heat treatment under conditions satisfying the following equation (4) by the formula Piece manufacturing method. [Equation 3] However, P: rolling load (ton), W: slab width (mm), T ₁ : rolling inlet temperature (° C), T ₂ : rolling outlet temperature (° C), T _i : rolling to winding Each temperature (° C) obtained by dividing the heat pattern in 0.1 second steps, Q: activation energy (365
KJ · mol ⁻¹ ) R: Gas constant (8.314 J · mol ⁻¹ · K ⁻¹ ). 4. A method for producing a strip-shaped cast piece of austenitic stainless steel by a continuous casting machine in which the cast piece moves in synchronization with the peripheral surface of a cooling drum in which a large number of random dimples are scattered by a shot blasting method. In % by mass, C defined as Cr + Mo + 1.5Si
r equivalent and Ni + 30 (C + N) +0.5 (Mn + C
Ni equivalent defined in u) is a strip of austenitic stainless steel having a composition that satisfies the formula (1) below.
It is cast into a slab, and then the slab is rolled at a rolling ratio R _d defined by the following formula (2) of 30% or more, immediately followed by water cooling and winding at 600 ° C. or less, and then the following. (3) defined by 1100 ° C. equivalent heat treatment time t _a cold surface excellent austenitic stainless steel thin strip cast piece manufacturing method of quality, characterized in that heat treatment of the four or more seconds equation. [Equation 4] However, P: rolling load (ton), W: slab width (mm), T ₁ : rolling inlet temperature (° C), T ₂ : rolling outlet temperature (° C), T _i : rolling to winding Each temperature (° C) obtained by dividing the heat pattern in 0.1 second steps, Q: activation energy (365
KJ · mol ⁻¹ ) R: Gas constant (8.314 J · mol ⁻¹ · K ⁻¹ ). 5. A shot blasting cast in synchronism with the peripheral surface of the cooling drum interspersed many random dimples by piece is cast by a continuous casting machine that moves, mass%
And Cr equivalent defined by Cr + Mo + 1.5Si,
Ni equivalent defined by Ni + 30 (C + N) +0.5 (Mn + Cu) is an austenitic stainless steel having a composition satisfying the following formula (1), and has a crystal structure (5)
Austenitic stainless steel thin strip with excellent cold-rolled surface quality, characterized by having a recrystallized structure with a sphere-reduced particle diameter D _ave defined by the formula of 70 μm or less. [Equation 5] However, S: total area of particle size measurement, S _i : i-th particle area