JPH08281385A - Production of austenitic stainless steel thin cast strip excellent in cold-rolled surface quality and cast strip - Google Patents

Abstract

PURPOSE: To produce an austenitic stainless steel thin strip excellent in cold- rolled surface quality improved in roping and uneven glossiness by specifying component composition of Cr equivalent and Ni equivalent, rolling condition and heat treatment condition. CONSTITUTION: The component composition of this austenitic stainless steel satisfys the inequality I with respect to the Cr equivalent defined with, by wt.%, Cr+Mo+1.5 Si, and the Ni equivalent defined with Ni+30(C+N)+0.5 (Mn+Cu). Rolling is executed at 20% to <30% rolling ratio Rd, which is defined with the equation II. Successively, the heat treatment is executed in a condition that the heat treatment equivalent time at 1100 deg.C defined with the equation III satisfys the inequality IV and successively, this strip is coiled at <=600 deg.C. Wherein, in the inequalities and the equations, P is rolling load, W is the width of cast strip, T<1> is a temp. at the inlet side of rolling, T2 is a temp. at the outlet side of rolling, Ti is each temp. of respective patterns obtd. by dividing a heat pattern during a process between the rolling and the cooling by 0.1sec interval steps. Q is activated energy and R is the gas constant.

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 slab of austenitic stainless steel, , Cr + Mo +
Cr equivalent defined by 1.5Si and Ni + 30 (C +
N) +0.5 (Mn + Cu) defined as Ni composition equivalent to the following formula (1), and then rolled with rolling ratio R _d shown in the following formula (2) being 20% or more and less than 30%. followed by the following (3) 1100 ° C. equivalent heat treatment time defined by the equation t _a is heat treated as a condition satisfying the following equation (4), which is followed by taking up production process at 600 ° C. or less. Alternatively, subsequently, rolling is performed by setting the rolling rate R _d shown in the following formula (2) to 30% or more, and then 110 defined by the following formula (3) is used.
0 ℃ heat treatment equivalent heat treatment time t _a as more than 4 seconds, followed by taking up production process at 600 ° C. or less. Alternatively, subsequently, rolling is performed by setting the rolling rate R _d shown in the following formula (2) to 20% or more and less than 30%, followed by immediate water cooling to 600
Wind up below ℃, then 1 specified by the following formula (3)
100 ° C. equivalent heat treatment time t _a is a manufacturing method for heat treating a condition satisfying the following equation (4). Alternatively, subsequently, the rolling rate R _d shown in the following formula (2) is rolled to 30% or more, immediately followed by water cooling and winding at 600 ° C. or lower, and subsequently 1100 ° C. equivalent heat treatment defined by the following formula (3). This is a manufacturing method in which the heat treatment is performed for _a time ta of 4 seconds or more. And an austenitic stainless steel thin slab excellent in cold-rolled surface quality having a recrystallized structure having a sphere-reduced particle diameter D _ave defined by the following formula (5), which is 70 μm or less, manufactured by the above methods. . 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 : temperature between rolling and winding, or each temperature (° C) obtained by dividing the reheating 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 present 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. Regarding the evaluation of the crystal grain size, D _n (= Σ2 × SQR (3 × S _i / 2π) / n), which is conventionally used for convenience and is defined as the expected value of the number frequency of crystal grains, is rapidly cooled. It was found that the solidified structure and the recrystallized structure obtained by rolling and heat treating it cannot be the index value representing the mixed grain state, and it is necessary to consider 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, an area ratio is an expected value for D _ave (= Σ2 × SQR (3 × S _i / 2)
π) × 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 an expected value of the number frequency of crystal grains, an 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, very definition of an average crystal grain size in a large mixed grain structure of grain diameter difference can be represented by D _{av e} is the expected value for the area ratio is an index representing the actual conditions of tissue. 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 if extremely large, it becomes a mixed grain structure that remains as unrecrystallized, We observe inadequate improvements in roping. 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 the case of mixed grains depending on the degree thereof, and the influence of coarse grains harmful to roping. The average particle diameter D _ave was defined as an intermediate index that can be reflected. The recrystallized grain size D _ave defined by this definition is 70 μm
If secured below, 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 grain size: Smaller promotes recrystallization (2) Strain rate (= rolling speed): Larger promotes recrystallization (3) Processing temperature (= rolling temperature): Lower promotes recrystallization (4) Strain amount (= rolling rate): Larger promotes recrystallization (5) Thermal history after processing (= heat treatment condition): Recrystallization is promoted as it stays at higher temperature Generally, solidification is required to reduce the initial grain size. It is necessary to increase the cold speed. In twin roll casting and the like, 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 a solidification structure in which the solidification structure after casting is an ash-like δ structure (a predominantly ash-like δ structure and a part of lacy-like δ exists, but is called “F mode solidification” in the weld metal. Therefore, it is considered that the columnar crystals are divided by the δ solidification → δ / γ transformation, the pinning effect by δ ferrite, and the like. The components of the present invention are, by weight%, Cr + Mo + 1.
Cr equivalent defined by 5Si and Ni + 30 (C + N) +
In the relationship of Ni equivalent defined by 0.5 (Mn + Cu), F mode solidification is reliably achieved by limiting the Ni equivalent < 0.63Cr equivalent-1.29 to the range satisfying the initial grain size during casting. The diameter 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. meaningless.

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. FIG. 4 shows the results. 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.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B22D 11/04 311 B22D 11/12 A 11/12 Z B24C 1/06 B24C 1/06 9270-4K C21D 8 / 02 D C21D 8/02 9/46 Q 9/46 C22C 38/00 302Z C22C 38/00 302 38/44 38/44 8315-4E B21B 37/00 132A (72) Inventor Tetsuro Takeshita 20 Shintomi, Futtsu, Chiba Prefecture -1 Inside Nippon Steel Co., Ltd. Technology Development Division

Claims (5)

[Claims] 1. Random by shot blasting method
Synchronized with the peripheral surface of the cooling drum with many dimples
By a continuous casting machine in which the slab moves
A manufacturing method for casting thin strips of stainless steel
C, defined as Cr + Mo + 1.5Si in wt%
r equivalent and Ni + 30 (C + N) +0.5 (Mn + Cu)
A component set whose Ni equivalent defined by
Rolling rate R defined by the following formula (2)_d20%
Roll it as less than 30%, and then use the formula (3) below.
1100 ° C equivalent heat treatment time t_aIs the following formula (4)
Heat treatment under the conditions that satisfy
Austener with excellent cold-rolled surface quality characterized by taking
Method for producing Ito-based stainless steel thin strip slab. [Equation 1]However, P: rolling load (ton), W: slab width (mm),
T₁: Rolling inlet temperature (℃), T₂: Rolling outlet temperature
(℃), T_i: Heat pattern between rolling and winding
Each temperature (℃) divided by 0.1 second step, Q: Activation
Energy (365 KJ · mol ^-1), R: gas constant (8.
314 J · mol^-1・ K^-1). 2. Random by shot blasting method
Synchronized with the peripheral surface of the cooling drum with many dimples
By a continuous casting machine in which the slab moves
A manufacturing method for casting thin strips of stainless steel
C, defined as Cr + Mo + 1.5Si in wt%
r equivalent and Ni + 30 (C + N) +0.5 (Mn + Cu)
A component set whose Ni equivalent defined by
Rolling rate R defined by the following formula (2)_d30%
Rolled as above, then 1 defined by the following equation (3)
100 ° C equivalent heat treatment time t_aHeat treatment for 4 seconds or more
And then wound up at 600 ° C or lower
Austenitic stainless steel ribbon with excellent rolled surface quality
Of manufacturing a cast slab. [Equation 2]However, P: rolling load (ton), W: slab width (mm),
T₁: Rolling inlet temperature (℃), T₂: Rolling outlet temperature
(℃), T_i: Heat pattern between rolling and winding
Each temperature (℃) divided by 0.1 second step, 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 weight, C defined as Cr + Mo + 1.5Si
r equivalent and Ni + 30 (C + N) +0.5 (Mn + Cu)
The Ni equivalent defined by is a composition that satisfies the following formula (1), and the rolling ratio R _d defined by the following formula (2) is 20%.
Roll less than 30% and then immediately water-cool 6
00 ° C. wound below followed by the following (3) 1100 ° C. equivalent heat treatment time t _a which is defined by the equation below (4) that is excellent in cold-rolled surface quality, wherein a heat treatment under conditions satisfying the A method for producing an austenitic stainless steel thin strip slab. (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 : Each temperature (° C.) obtained by dividing the reheating heat pattern in 0.1 second steps, Q: Activation energy ( Three
65 KJ · mol ⁻¹ ), R: Gas constant (8.314 J · mol)
⁻¹ · K ⁻¹ ). 4. A manufacturing method for casting thin strip-shaped slabs of austenitic stainless steel by a continuous casting machine in which the slabs 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 weight, C defined as Cr + Mo + 1.5Si
r equivalent and Ni + 30 (C + N) +0.5 (Mn + Cu)
The Ni equivalent defined by the formula (1) is a composition that satisfies the following formula (1), and the rolling ratio R _d defined by the following formula (2) is 30%.
After rolling as above, immediately followed by water cooling and winding at 600 ° C. or lower, and subsequently 1100 defined by the following formula (3)
A method for producing an austenitic stainless steel thin strip slab having excellent cold-rolled surface quality, which is characterized by performing a heat treatment at _a temperature equivalent heat treatment time of ta of 4 seconds or more. [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 : Each temperature (° C.) obtained by dividing the reheating heat pattern in 0.1 second steps, Q: Activation energy ( Three
65 KJ · mol ⁻¹ ), R: Gas constant (8.314 J · mol)
⁻¹ · K ⁻¹ ). 5. A continuous casting machine in which a slab moves in synchronism with a peripheral surface of a cooling drum in which a large number of random dimples are scattered by a shot blast method, and is cast by the weight%
And Cr equivalent and N defined by Cr + Mo + 1.5Si
i + 30 (C + N) +0.5 (Mn + Cu) Ni equivalent defined by the following composition (1) is an austenitic stainless steel with a composition that satisfies the following formula (5) An austenitic stainless steel thin slab having excellent cold-rolled surface quality, which has a recrystallized structure of D _ave of 70 μm or less. (Equation 5) Where S: total area of particle size measurement, S _i : i-th particle area