JP2718642B2 - Method for producing austenitic stainless steel thin slab - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin cast slab for cold-rolled steel sheet having good surface properties by casting molten austenitic stainless steel into a thin cast slab, followed by hot rolling.

[0002]

2. Description of the Related Art FIG. 1 shows an outline of a twin-drum continuous casting apparatus as an example of an apparatus for continuously casting thin cast pieces. This device comprises a pair of cooling drums 1, 1 having a built-in cooling mechanism.
And a pair of side weirs 2 and 2 pressed against both end surfaces of the cooling drums 1 and 1 as main constituent members. The molten metal M supplied to the pool 3 formed by the cooling drums 1 and the side weirs 2 and 2 solidifies on the peripheral surface of the cooling drums 1 and 1 rotating in the direction of the arrow, and With a gap of 1, a thin slab S having a thickness of 1 to 10 mm is formed. The thin slab S is sent downward and is driven to rotate and rotate.
Is sent to the winder 5 and wound up. A rolling mill, a cooling device, and the like may be provided between the pinch rolls 4 and 4 and the winder 5 in some cases.

[0003] Thin cast slabs produced by such a continuous casting apparatus using a cooling drum are liable to crack due to shrinkage stress when solidified on the peripheral surface of the cooling drum. In order to prevent this, the peripheral surface of the cooling drum is often provided with a number of depressions or subjected to shot blasting to roughen the surface to an average surface roughness of about 40 to 120 μm. Irregularities having a height of about 30 to 100 μm are formed on the surface of a thin slab manufactured using such a cooling drum. Due to these irregularities, there has been a problem that the surface gloss of the cold-rolled steel sheet after cold rolling deteriorates, and that scale remains on the concave portions and scale flaws are generated on the surface of the cold-rolled steel sheet. In addition, the continuously cast thin slab is annealed as necessary in the same manner as a conventional hot rolled sheet, followed by pickling and cold rolling to a cold rolled steel sheet. The steel sheet has a problem that roping occurs because the crystal grain size is larger than that of a cold-rolled steel sheet manufactured from a hot-rolled sheet.

Conventionally, as a method of reducing the grain size of a hot-rolled steel sheet, in hot rolling of austenitic stainless steel slabs, a hot rolling temperature of about 1000 to 1 is set.
A method of obtaining a recrystallized structure by setting the temperature to 200 ° C. and the rolling reduction to about 15 to 55% is disclosed in, for example, JP-A-58-341.
No. 39 is known. However, when rolling was performed under such conditions, the occurrence of roping could be solved, but the occurrence of poor surface gloss and scale flaws could not be solved.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to produce a cold-rolled steel sheet free from poor surface gloss, scale flaws and roping from continuously cast austenitic stainless steel thin slabs.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a molten austenitic stainless steel is cast into a thin slab, and then the thin slab is cast in a temperature range of 1150 ° C. to 1300 ° C. and a rolling reduction of 5% or more. Is characterized in that surface smoothing rolling is performed. Following the surface smoothing rolling, the thin slab was 900
In the temperature range of not less than 1150 ° C and a rolling reduction of 10
% Or more. After the surface smoothing rolling or the recrystallization rolling, annealing, pickling, cold rolling, and the like are performed under the conditions for producing a normal cold-rolled steel sheet to produce a cold-rolled steel sheet. The rolling reduction in the present invention is defined by the following equation (1).

[0007]

In the present invention, the reason why the rolling temperature and the rolling reduction in the hot rolling of the austenitic stainless steel thin slab are limited as described above will be described. FIG. 4 shows an example of an apparatus for implementing the present invention. In the figure, a thin slab S cast by a pair of cooling drums 1 and 1 is sent by pinch rolls 4 and 4 in the direction of the arrow to smooth the thin slab surface and a crystal structure of the slab. Is hot-rolled by a subsequent rolling mill 7 for recrystallization, and then wound up by a winder 5. A looper is provided between support rolls 8, 8 provided behind the former rolling mill 6 by a dancer roll 10 having a weight 9 suspended therefrom, and a thinner between the former rolling mill 6 and the latter rolling mill 7 is provided. A tension is applied to the slab S.

FIG. 2 shows a SUS304 austenitic stainless steel thin slab having a sheet thickness of 4.0 mm using the twin-drum continuous casting apparatus shown in FIG. The graph shows the relationship between the rolling temperature and rolling reduction in the pre-rolling mill 6 and the surface roughness (Rmax) of the pickled hot-rolled steel sheet in the case where the hot-rolled steel sheet is subjected to smoothing rolling.

FIG. 2 shows that the surface roughness (Rma)
In order to set x) to 20 μm or less at which the surface gloss and scale flaws do not pose a problem in the cold-rolled steel sheet, the rolling temperature should be in a temperature range of 1150 ° C. to 1300 ° C., and the rolling reduction should be 5% or more. is necessary. Note that, even if the rolling reduction is increased beyond 15%, the improvement in surface smoothing is extremely small, so the upper limit of the rolling reduction is desirably 15% or less.

FIG. 3 shows a SUS304 stainless steel thin slab cast using the twin-drum type continuous casting apparatus shown in FIG. 4 and a rolling temperature of 1150.degree. Rolling in the latter rolling mill 7 in the case of performing surface smoothing rolling with a draft of 5% in a temperature range of 1300 ° C. or less and subsequently performing recrystallization rolling using the latter rolling mill 7 to obtain a hot-rolled steel sheet. 4 shows the relationship between temperature and rolling reduction and the average crystal grain size of a hot-rolled steel sheet after annealing. From FIG. 3, in order to set the average crystal grain size of the hot-rolled steel sheet to 50 μm or less in which roping generated in the cold-rolled steel sheet does not pose a problem, the rolling temperature is set to a temperature range of 900 ° C. to less than 1150 ° C. Needs to be 10% or more. Note that, even if the rolling reduction exceeds 35%, the improvement in crystal grain refinement is extremely small, so the upper limit of the rolling reduction is desirably 35% or less.

According to the present invention, a continuously cast austenitic stainless steel thin slab is cast at a rolling temperature of 1 after casting.
5% reduction in temperature range from 150 ° C to 1300 ° C
When the above-described surface smoothing rolling is performed, the slab surface is easily deformed plastically because of its high temperature. Therefore, the irregularities on the surface of the thin slab caused by the irregularities around the cooling drum are easily smoothed. At this time, if the rolling temperature is lower than 1150 ° C., plastic deformation of the irregularities becomes difficult, and the required draft decreases rapidly, so that the irregularities on the surface of the thin slab cannot be sufficiently smoothed. As a result, poor surface gloss occurs in the cold-rolled sheet, and scale remains in the concave portions, resulting in surface defects. On the other hand, when the rolling temperature exceeds 1300 ° C., a seizure phenomenon occurs between the thin slab and the rolling roll, and streaks are generated on both sides.

Following the surface smoothing rolling, the rolling temperature is 9
10% reduction in the temperature range between 00 ° C and 1150 ° C
By performing the recrystallization rolling described above, strain energy is accumulated in the crystal grains inside the thin slab, and the crystal grains are recrystallized and refined by the strain energy. At this time, if the rolling temperature is 1150 ° C. or more, or less than 900 ° C., even if the rolling reduction is 10% or more, the strain energy is hardly accumulated in the crystal grains, so that recrystallization is difficult.

By using both the first-stage rolling mill 6 and the second-stage rolling mill 7 shown in FIG. 4 at the same time, it is possible to simultaneously perform the process of smoothing the irregularities on the surface of the thin slab and the refinement of the crystal grains. . This makes it possible to manufacture a cold-rolled steel sheet in which poor surface gloss, scale flaws and roping are prevented.

[0014]

EXAMPLE A SUS304 austenitic stainless steel molten steel was cast into a thin slab having a thickness of 4.0 mm using the apparatus shown in FIG. 4, and after casting, a plate was formed using a pre-rolling mill 6 and a post-rolling mill 7. It was hot-rolled to a thickness of 2.4 to 3.4 mm. After hot rolling, annealed, pickled and cold rolled to a thickness of 0.7 mm
Was manufactured. Table 1 shows the hot rolling conditions and the quality of the hot-rolled steel sheet and the cold-rolled steel sheet of the present invention and comparative examples.

[0015]

[Table 1]

No. 1 of the present invention example Nos. 1 to 8 are examples in which surface smoothing rolling was performed by a first-stage rolling mill 6 and then recrystallization rolling was performed by a second-stage rolling mill 7. was gotten. On the other hand, No. of the comparative example. Nos. 9 to 20 are examples in which surface smoothing rolling and recrystallization rolling were performed. However, in Nos. 9 and 10, the temperature in surface smoothing rolling was low, and in Nos. 11 and 12, the rolling reduction was low. For,
In both cases, a cold-rolled steel sheet of satisfactory quality with respect to surface gloss and scale flaws was not obtained. Further, in No. 13, since the temperature in the surface smoothing rolling was too high, seizure flaws occurred on the drum and the slab. Nos. 14 and 15 have low temperatures in recrystallization rolling, and Nos. 16 and 17 have low rolling reductions in recrystallization rolling.
In the case of No. 20, since the temperature in recrystallization rolling was too high, a cold-rolled steel sheet having a quality sufficient for roping could not be obtained.

[0017]

According to the present invention, a continuously cast austenitic stainless steel thin slab is subjected to surface smoothing rolling after casting to smooth the unevenness on the surface of the thin slab, thereby cooling due to unevenness. It is possible to prevent surface defects such as poor surface gloss and scale flaws of the rolled sheet. Further, by performing recrystallization rolling following surface smoothing rolling to refine crystal grains, it is possible to prevent occurrence of roping in a cold rolled sheet.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of a twin-drum continuous casting apparatus.

FIG. 2 is a diagram showing a relationship between a rolling temperature and a rolling reduction in surface smoothing rolling.

FIG. 3 is a diagram showing a relationship between a rolling temperature and a rolling reduction in recrystallization rolling.

FIG. 4 is a front view showing an outline of an example of an apparatus for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 2 ... Side weir 3 ... Pool part 4 ... Pinch roll 5 ... Winding machine 6 ... Pre-rolling mill 7 ... Post-rolling mill 8 ... Support roll 9 ... Weight 10 ... Dancer roll M ... Molten metal S ... Thin Slab

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B22D 11/20 B22D 11/20 C

Claims (1)

(57) [Claims] 1. A molten austenitic stainless steel is cast into a thin slab, and then the thin slab is cast at a temperature of 1150 ° C. to 130 ° C.
Surface smoothing rolling is performed in a temperature range of 0 ° C. or less and a draft of 5% or more.
A method for producing an austenitic stainless steel thin slab, wherein recrystallization rolling is performed at a temperature range of less than 50 ° C. and a rolling reduction of 10% or more.