JPS6327407B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing stainless steel plates and steel wires, and in particular to a method for winding continuously cast slabs into coils and warm rolling them to obtain thin steel plates or steel wires. Conventionally, many proposals have been made regarding methods for directly manufacturing thin plates from molten metal. For example, there are methods for manufacturing amorphous alloys into foil-like strips with a thickness of several micrometers by a casting process in which molten alloys containing Fe, Ni, Cr, etc. and other alloy components such as C, P, etc. are ultra-quenched. From castings with a thickness of 12.5 mm or less, as disclosed in Publication No. 38-22703,
A method of manufacturing a non-oriented electrical steel sheet through processing steps such as hot rolling and cold rolling has been proposed. The present invention overcomes the above-mentioned conventional techniques, such as the process of ultra-quenching molten alloy in the manufacturing process of amorphous alloy and the process of manufacturing non-oriented electrical steel sheets, which adopt complicated steps. The purpose of this work is to provide a method that can produce stainless steel sheets or wires using an extremely simple process. The feature of the present invention is that a steel strip with a thickness of 10 mm or less or a steel wire with a diameter of 20 mm or less is heated at 700℃/
A steel slab continuously cast at a cooling rate of min or more is wound up to form a coil, warm rolled in a temperature range of 100 to 700°C, and then recrystallized and annealed. A steel slab continuously cast at a cooling rate of 700℃/min or more is wound around a strip or a steel wire with a diameter of 20 mm or less to form a coil, and the coil is placed in a recuperation furnace to complete the coil. After being uniformly maintained at a temperature of 100 to 700 °C, warm rolling in a temperature range of 100 to 700 °C, and then recrystallization annealing.
A steel slab continuously cast at a cooling rate of 700℃/min or more is wound around a steel strip with a thickness of 10 mm or less or a steel wire with a diameter of 20 mm or less to form a coil.
The purpose is to perform warm rolling in a temperature range of 100 to 700°C with intervening intermediate annealing in a temperature range of 800 to 1150°C, followed by recrystallization annealing. The present invention will be explained in detail below. When carrying out the present invention, for example, an apparatus shown in FIG. 1 is used. That is, molten steel 1 is stored in a refractory container 2, passes through a slit 4 made of refractory material 3 provided at the lower part of the refractory container 2, passes through a slit 5 provided at the lower part of the slit 4, and reaches the surface of the roll 6. is extruded. The surface of the roll 6 is cooled by a cooling device 7, and when the molten steel 1 is extracted from the slit 5 and comes into contact with the surface of the roll 6, it is rapidly cooled and solidified to become a strip-shaped slab 8. The strip-shaped slab 8 is rolled by the roll 6
It is wound up by a winding machine 9 installed near the coil to form a strip coil. When obtaining a strip coil from the molten steel 1 by casting, a space B ₁ , where the molten steel is extracted from the slit 5 onto the surface of the roll 6 shown in FIG.
A shielding device 10 is provided to shield B ₂ from the atmosphere. Furthermore, if necessary, extraction of molten steel 1, casting,
A shielding device 11 is provided to shield the space C in which winding is performed from the atmosphere, and the space C is placed under vacuum or under an inert atmosphere such as Ar. 12 is a pinch roll. When obtaining a wire coil from molten steel 1 by casting, the same apparatus as described above is used. The cast and wound strip coil or wire coil is either warm-rolled at a temperature range of 100 to 700°C, or placed in a recuperation furnace to process the entire coil using the sensible heat of the coil. After being reheated to a uniform temperature, it is warm rolled in a temperature range of 100 to 700°C. When uniformly heating the coil in the recuperation furnace, an external heating means may also be used. The soaking temperature of the coil is
Equal to the warm rolling start temperature. Coils that have been wound up and soaked after casting (hereinafter, the explanation will be based on the case of strips as the metallurgy is the same for both strips and wires) must be warm-rolled. Instead, it is warm rolled at a temperature of 700°C or less, preferably 200 to 600°C, and then recrystallized and annealed to produce a product. Next, the characteristics of the product manufactured by the process of the present invention and the process conditions in the process will be explained. Although the present invention is applied to the manufacture of stainless steel strip, when such a process is used, the uniform distribution of the constituent elements may be difficult to achieve if two or more phases crystallize within the cast structure, as for example in SUS430. This is difficult to achieve because the distribution of alloy components or impurity elements is different between the phase and the crystallized phase. Incidentally, in the case of SUS430, the matrix is α phase and the crystallized phase is γ phase. Because of this, when the grains of the crystallized phase are large and the distance between the crystallized grains is large (as in the slab obtained by the current continuous casting process,
Suitable for cases where the thickness of the slab is large and the cooling rate during the casting process is low. ), as shown in FIG. 2, non-uniform portions a occur in the structure of the material treated by the warm rolling-recrystallization annealing process. Figure 2 shows the structure of a 4 mm thick cut piece taken from a continuously cast SUS430 steel slab (190 mm thick), warm rolled and recrystallized annealed. A coagulation structure corresponding to the structure shown in FIG. 2 is shown in FIG. From Figure 3, it can be seen that γ is present in the α phase matrix.
It can be seen that the phase is crystallized. Shown in Figure 3
γ in the cast structure of SUS430 steel (190mm thickness)
The phase corresponds to part a in the structure of the material after warm rolling and recrystallization annealing shown in FIG. When a material having such a structure is subjected to a tensile test, it breaks at part a and exhibits a low elongation value. On the other hand, when the grains of the crystallized phase are small and the distance between the crystallized grains is small, the structure of the material after warm rolling and recrystallization annealing becomes a uniform structure, as shown in Figure 4, and the tensile strength The test results also show good elongation properties. Figure 4 shows the structure of SUS430 steel that has been rapidly solidified and then recrystallized and annealed.
(a) is the recrystallization annealing temperature: 950°C, and (b) is the recrystallization annealing temperature: 1100°C. The distribution of the second phase, that is, the distribution of alloy components shown in Figure 3, is determined by the solidification rate, and the structure of the material (product) after warm rolling and recrystallization annealing corresponds to the distribution of the second phase. changes as shown in FIG. 2 or 4. As mentioned earlier, the elongation of the product corresponds to the structure of the material (product) after warm rolling and recrystallization annealing, so the conditions during solidification of molten steel can be defined using the product properties. can. Figure 5 shows the cooling rate during solidification of molten steel (the molten steel temperature is 50°C higher than the freezing point, and is defined as the average cooling rate from this temperature to 1000°C),
Regarding the elongation relationship of the product, SUS430 steel slab, 300
A product obtained by warm rolling at ℃ and then recrystallization annealing is shown. As is clear from FIG. 5, the average cooling rate during solidification of molten steel needs to be 700° C./min or more. However, through the process of solidification, warm rolling, and recrystallization annealing, if the material has a single phase structure, for example, austenitic stainless steel with a single phase of austenite or ferritic stainless steel with a single phase of ferrite, Since there is no change in material quality due to the formation of the second phase as described above, there is no limit to the cooling rate of the cast metal during casting in relation to the dispersion of the second phase. Next, it will be explained that crystal grains can be refined by directly performing warm rolling-recrystallization annealing of a material with a rapidly solidified structure (high cooling rate). FIG. 6 shows the relationship between the cooling rate during casting of molten steel and the grain size of the product after warm rolling and recrystallization annealing. Figure 6 shows the largest recrystallized grain in a 0.1 mm x 0.1 mm square of recrystallized grains obtained by recrystallization annealing at the lowest possible recrystallization temperature. The average value of 10 values, a: Normally cold rolled SUS430 steel, b: Rapid solidification - warm rolling - recrystallization annealing of SUS304 steel, c: Rapid solidification - warm rolling - recrystallization annealing of SUS430 steel. It is a crystal annealed material. As is clear from Figure 6, in order for the cooling rate of the slab during casting to affect the crystal grain size of the product, approximately
A cooling rate of 400° C./min or higher is required, preferably 700° C./min or higher, so that the effect on the grain size of the product becomes significant. This effect is achieved by SUS304 steel,
This is common to both SUS430 steels. The cooling rate of the slab during casting is preferably 700
The higher the temperature is, the better. However, if the temperature is too high, cracks will occur in the slab, so the temperature should be set at 1500℃/min.
is the upper limit. As is well known, the yield strength of steel is
There is a dependence on the grain size of the product as shown by the Ha11-Petch relationship. On the other hand, the strength changes with changes in the crystal grain size of the product, and also changes depending on the presence or absence of rapid solidification and its degree. This is made clear by Table 1.

[Table] In Table 1, the comparative materials are materials manufactured under normal conditions, and the inventive materials are manufactured under 800 to 1000
A 3 mm thick slab solidified at a cooling rate of ℃/min is warm rolled in a temperature range of 300 to 500 ℃ to 1.2 mm.
This is a material (product) that has been recrystallized and annealed at various temperatures after being made into a strip of different thickness. As is clear from Table 1, it is possible to control the mechanical properties of the product in the process of warm rolling and recrystallization annealing of slabs obtained by rapid solidification casting. In particular, products of various strength levels can be obtained, including high strength steel sheets (strips) or high strength steel wires (wires). In the process according to the present invention, a slab is obtained by casting molten steel by rapidly cooling and solidifying it, which is then directly warm rolled and then recrystallized and annealed. In the process of the present invention, if the thickness or diameter of the slab exceeds a certain limit, the slab will crack. That is, there is a limit thickness or diameter of a slab, which is determined by the cooling rate during solidification of the slab, and a limit temperature during warm rolling. To further explain this point, firstly, when casting molten steel, if the thickness or diameter of the slab is increased, the amount of heat required to be removed to solidify the molten steel increases, and the cooling rate decreases. descend. Therefore, in order to obtain a cooling rate above a certain level, it is necessary to reduce the thickness or diameter of the slab to below a certain level. Second, when molten steel is rapidly solidified, cracks occur in the slab due to thermal stress generated during solidification.
The thermal stress increases as the thickness or diameter of the slab increases and as the cooling rate increases. Therefore, from this point as well, the thickness or diameter of the slab is limited. The first condition mentioned above is, as explained later,
It can be included in the second condition. Figure 7 shows the relationship between the thickness or diameter of the slab and the cooling rate of the slab, which affects the occurrence of cracks in the slab, i.e., when molten steel is rapidly solidified by changing the thickness or diameter of the slab. shows the critical cooling rate at which solidification cracking occurs. As is clear from Figure 7, in order to solidify molten steel at a cooling rate of 700°C/min or more, which is required in the process of the present invention, the thickness of the strip must be 10 mm or less. Also,
If the slab is made of wire, its diameter shall not exceed 20 mm. Figure 8 shows the relationship between strip thickness and cracking limit rolling temperature for SUS430 steel. As is clear from Fig. 8, when warm rolling the slab, the rolling temperature is 100°C or higher, preferably 200°C or higher.
℃ or higher. On the other hand, when the slab is directly warm-rolled after casting molten steel, if carbide precipitates in the material, this will lead to a) non-uniform distribution of component elements and) cracking of the slab during rolling. Therefore, in order to prevent carbide from precipitating when the coil is charged into a recuperation furnace and soaked after molten steel is cast and coiled, the temperature at the center in the thickness direction of the slab at the time of coiling must be set at 700°C. It is necessary that the temperature is below ℃. Based on these conditions, the material temperature during warm rolling is 100 to 700℃, preferably 200 to 700℃.
Limited to 600℃. (Example) SUS430 steel (No. 1, 2) shown in Table 2, SUS304
A steel (No. 3) slab was processed under the conditions shown in Table 2 to produce a product. A photo of the structure of this product (100x magnification)
It is shown in FIGS. 4, 9 and 10. Sample No. 1 in Table 2 is shown in Figure 4, and No. 2 is shown in Figure 9.
Figure No. 3 corresponds to FIG. 10, respectively. Sample No. 1 in Table 2 is obtained by changing the recrystallization annealing temperature, and the low-temperature annealed material a has a refined crystal structure as shown in Figure 4 a, and is 100 kg/mm It showed an intensity of ² . Further, high temperature annealed material b showed the same crystal structure as the normal material, and the strength level was also the same as that of the normal material (55 kg/mm ² ). As is clear from Figures 9 and 10, the samples obtained by processing under conditions No. 2 and No. 3 in Table 2 have the same crystal structure and strength as ordinary materials with the same composition. It shows. Recrystallization annealing is performed in a temperature range of 800 to 1150°C. Further, also in the warm rolling process, intermediate annealing in the above temperature range can be inserted.

[Table] Since the present invention is configured and operated as described above, stainless steel strips or stainless steel wires having various mechanical properties can be manufactured with an extremely simple process. Industrially useful.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the method of the present invention, Figure 2 is SUS430
Figure 3 is a micrograph of the structure after recrystallization annealing.
Figure 4 is a micrograph of the cast structure of SUS430.
Micrograph of the structure of SUS430 after recrystallization annealing, Figure 5 is a graph of cooling rate during solidification and elongation of warm rolled plate, Figure 6 is a graph of cooling rate and grain size, Figure 7 is solidification of slab. Figure 8 is a graph of the relationship between warm rolling temperature and slab thickness, and Figure 9 is a graph of the relationship between the slab thickness (wire diameter) and cooling rate on the occurrence of cracking during 17Cr-Ti.
FIG. 10 is a micrograph of the structure of SUS304 after recrystallization annealing. 1: Molten steel, 3: Refractory, 4, 5: Slit,
6: Roll, 7: Roll cooling device, 8: Platy slab, 9: Winding machine, 10, 11: Shielding device, 12:
Pinch roll.

Claims (1)

[Claims] 1. A steel slab continuously cast at a cooling rate of 700°C/min or more is wound around a steel strip with a thickness of 10 mm or less or a steel wire with a diameter of 20 mm or less to form a coil, A method for manufacturing stainless steel sheets and steel wires, which comprises warm rolling the coil in a temperature range of 100 to 700°C and then recrystallizing it. 2. A steel slab continuously cast at a cooling rate of 700°C/min or more is wound around a steel strip with a thickness of 10 mm or less or a steel wire with a diameter of 20 mm or less to form a coil, and the coil is placed in a recuperator. Manufacture of stainless steel sheets and steel wires, which are characterized by charging the coil into a coil, holding the whole coil at a uniform temperature of 100 to 700 degrees Celsius, then warm rolling in a temperature range of 100 to 700 degrees Celsius, and then recrystallization annealing. Method. 3. A steel slab continuously cast at a cooling rate of 700°C/min or more is wound around a steel strip with a thickness of 10 mm or less or a steel wire with a diameter of 20 mm or less to form a coil, and the coil is In the temperature range of ℃, 800~1150℃
1. A method for producing stainless steel sheets and steel wires, which comprises performing warm rolling with intervening intermediate annealing in a temperature range of 10 to 10, followed by recrystallization annealing.