JPH082450B2 - Method for manufacturing austenitic stainless thin plate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an austenitic stainless steel thin plate, and particularly by a so-called synchronous continuous casting process in which there is no relative speed difference between a slab and a mold inner wall surface. The present invention relates to a method for producing an austenitic stainless steel thin plate by cold rolling a cast piece having a thickness close to that of a cast product.

[Conventional technology]

The conventional method of producing a stainless steel thin plate using the continuous casting method is to make the thickness of 100 mm while vibrating the mold in the casting direction.
Casting to the above slab, performing surface maintenance of the obtained slab, after heating to 1000 ℃ or more in a heating furnace, hot rolling is performed by a hot strip mill consisting of a rough rolling machine and a finishing rolling mill train. A hot strip with a thickness of several mm,
Further, after annealing as required, descaling and cold rolling were performed for final annealing.

Thus, in the conventional process, in order to hot-roll a slab with a thickness of 100 mm or more, a long hot strip mill is required, and a problem of using a large amount of energy for heating and rolling the slab was there.

For this problem, research on a process for producing a slab having a thickness equal to or close to that of a hot strip by continuous casting is under way. For example, the twin-roll method, the twin-belt method, etc., such as those introduced in the articles on "Iron and Steel"'85 -A197 to '85 -A256, are used to determine the relative velocity difference There is no synchronous continuous casting process.

Japanese Unexamined Patent Publication (Kokai) No. 62-21443 discloses a thin plate continuous casting apparatus using a twin roll method.

However, there have been unsolved problems in producing stainless steel sheet products through these synchronous continuous casting processes.

[Problems to be Solved by the Invention]

When a stainless steel thin plate is produced by continuous casting such as the twin roll method or the twin belt method, the steps from the conventional casting to the production are largely omitted and shortened. occured.

That is, the present inventors cast molten steel of SUS304, which is a typical austenitic stainless steel, into a thin strip-shaped slab having a plate thickness of 1 to 5 mm by casting with a twin roll continuous casting machine of an internal water cooling system, and cold casting it. After rolling (reduction rate about 50-85%),
Part was annealed and pickled to give a 2B product, and part was bright annealed to give a BA product. Further, a continuously cast slab having a thickness of 100 mm or more was hot-rolled and then cold-rolled to manufacture 2B products and BA products. As a result of a detailed comparison of the surface quality properties of these products, the product when using a twin roll continuous casting machine has a characteristic fine crease-like undulation (roping) with a height of about 0.5 to 0.6 μm. It was This roping cannot be removed by buffing, which is a problem as a product.

Therefore, the present inventors have studied the post-treatment of the cold rolling step, cold rolling, after performing the final annealing, the elongation rate of 0.
It was found that roping disappeared by temper rolling with adjusting to 5% to 2.5% (Japanese Patent Application No. 1-59781).
However, if the roping generated in the cold rolled sheet is eliminated by this method, the elongation rate is large (eg 2.5%).
In temper rolling, there were cases where the mechanical properties of the product sheet deteriorated, such as 44%. There was also a case where roping that could not be eliminated was observed in temper rolling with an elongation of 0.5 to 2.5%.

Compared with the conventional hot-rolled material, the twin-drum ribbon-shaped slab has a large amount of δ-ferrite remaining and tends to suppress grain growth in the final annealing after cold rolling. Therefore, under normal annealing conditions (1080 ° C x 20 sec), a fine-grained structure with GSN> 9 is obtained, so that good mechanical properties may not be ensured when the elongation percentage of temper rolling is increased.

The present invention, after cold rolling a thin strip-shaped slab obtained by synchronous continuous casting in which the slab moves in synchronization with the mold inner wall surface such as the twin roll method, final annealing, and then temper rolling In the method for producing an austenitic stainless steel thin plate, the object is to eliminate the roping which is a surface property defect of the thin plate and to obtain a thin plate product having good mechanical properties.

[Means for solving the problem]

According to the present invention, according to the present invention, austenitic stainless steel is cast into a thin strip slab by a continuous casting machine in which the mold wall surface moves in synchronization with the slab, and cold-rolled after descaling, and finally. After performing the annealing, in the method for producing an austenitic stainless thin plate including a step of temper rolling, the final annealing is performed at a temperature of 1025 to 1200 ° C. for 60 seconds or less, and the grain size of the thin plate is 6.0. To 9.0, and the temper rolling is performed at an elongation rate of more than 2.5% and 4.0% or less, which is solved by the method for producing an austenitic stainless steel sheet.

[Action]

In the present invention, in forming a thin strip product obtained by twin roll casting or the like into a thin plate product, the final annealing and temper rolling conditions after cold rolling are combined in an appropriate range to improve the surface texture (roping). , Which has good mechanical properties and does not cause rough skin due to processing.

That is, in the present invention, the final annealing is performed at a temperature of 1025 to 1200 ° C.
The grain size (GSN) of the cold-rolled thin strip is controlled to 6.0 to 9.0 by performing the treatment for 60 seconds or less. If the GSN is coarser than 6.0, roughening occurs when the product after temper rolling is processed, and if it is more than 9.0, the mechanical properties of the product that has lost roping due to temper rolling deteriorates. Is out of the management standard. The lower limit of the annealing temperature of 1025 ° C. is to secure a completely recrystallized structure, while the upper limit of 1200 ° C. is limited to GSN 6.0 or more. The upper limit of holding time was limited to GSN of 6.0 or more. However, the holding time may be 0 seconds because the GSN can be 9.0 or less even if it is cooled immediately after reaching the temperature range. In temper rolling, the elongation is over 2.5%.
Control below 4.0%. The lower limit of more than 2.5% stably reduces roping, and the upper limit of 4.0% is limited to ensure good mechanical properties.

In the present invention, the twin roll method is most preferably used, but as described above, the twin belt method, the inner ring method, the roll belt method and the like can also be used. The target steel type is SUS30.
Austenitic stainless steel such as 4, SUS316, SUS321, SUS347, SUS310 is used.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to tables and drawings.

SUS304 of test material A consisting of the components shown in Table 1 was cast into a strip-shaped slab with a thickness of 3.3 mm by a vertical twin roll continuous casting machine with an internal water cooling system, descaled by pickling, and then cold-worked. It was rolled to produce a sheet product. Table 2 shows the final annealing conditions (temperature, time) after cold rolling and the grain size (GSN) after final annealing of thin plate products produced by variously changing the elongation (%) of temper rolling after the final annealing. ), The roping height (μm) of the product, the mechanical properties and the rough skin condition after deep drawing are shown by the results obtained by the method of the present invention and the comparative method.

In Table 2, the roping height is the height of the waviness of the product after temper rolling, measured with a roughness meter. Of the mechanical properties, the in-plane anisotropy of elongation is represented by ΔEl shown in the following equation.

ΔEl = (El _L + El _c −2 El ₄₅ ) / 2 The above El _L , El _c and El ₄₅ are respectively El _L : elongation in rolling direction (%) El _c : elongation in perpendicular direction (%) El ₄₅ : 45 ° The elongation (%) in the direction is shown.

According to Table 2, No. 2 and No. 4 using the method of the present invention are
Any roping caused by cold rolling disappeared (0.
If it is 2 μm or less, it is not judged as roping and there is no problem as a product). In addition, the mechanical properties were all good values within the control standards, especially the proof stress and tensile strength were excellent, and the in-plane anisotropy was smaller than that of the conventional method. Furthermore, the rough surface after deep drawing did not occur.

In this example, the grain size (GSN) after final annealing was changed in the range of 5.0 to 10.0, and the elongation percentage of temper rolling was changed in the range of 0.3 to 4.5%. In Comparative Examples No. 1, 3, and 4, the roping disappeared, but the elongation of the temper rolling was in the range of 0.5 to 2.5, and thus roping that did not disappear could be unstable and unstable. Although the internal elongation was improved, the yield strength and tensile strength were lower than those of the method of the present invention. Comparative example
No. 6 has a large crystal grain size (GSN = 5.0), so roughening becomes apparent after deep drawing, and No. 7 has a small crystal grain size (GSN = 10.0), so high elongation temper rolling Although the roping could be improved by, the mechanical properties were out of the control standards, and there was a problem with the product material.

FIG. 1 shows the relationship between the elongation rate (%) of temper rolling and the roping height (μm) after temper rolling among the data in Table 2.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain an austenitic stainless steel thin plate which is free from the occurrence of roping and has good mechanical properties by using continuous casting by the twin roll method or the like.

[Brief description of drawings]

FIG. 1 shows the relationship between the elongation rate (%) of temper rolling and the roping height (μm) after temper rolling.

Claims (1)

[Claims] 1. An austenitic stainless steel is cast into a strip-shaped ingot by a continuous casting machine in which the wall surface of the die moves in synchronization with the ingot, and after descaling, cold rolling and final annealing are performed. In the method for producing an austenitic stainless steel thin plate including a step of temper rolling, the final annealing is performed at a temperature of 1025 to 1200 ° C. for 60 seconds or less, and the grain size of the thin plate is set to 6.0 to 9.0. A method for producing an austenitic stainless steel, characterized by performing temper rolling at an elongation of more than 2.5% and not more than 4.0%.