KR100771832B1 - Method for producing ferritic stainless steel sheets having excellent ridging property - Google Patents

Abstract

The present invention relates to a method for producing a ferritic stainless steel that improves ridging by eliminating hot rolling after hot rolling and controlling cold rolling and annealing conditions. : Less than 1.0%, P: Less than 0.040%, S: Less than 0.030%, Cr: 15.0 to 20.0%, Al: Less than 0.2% and N: less than 0.05%, ferrite composed of the remaining Fe and other unavoidable impurities In the manufacturing method of the stainless steel, the step of hot rolling the ferritic stainless steel slab formed as described above, the step of cold rolling in a continuous cold rolling machine without annealing the hot rolled plate, and the cold rolled plate at a temperature of 800 ~ 900 ℃ After annealing by maintaining for 1 hour to 10 hours or by heating to 850 ~ 1000 ℃ temperature for 10 seconds to 5 minutes, followed by quenching and continuous annealing, cold rolling annealing plate again cold pressure in 20 stage cold rolling mill A step, and a cold-rolled sheet, which comprises a step of continuous annealing for 5-3 seconds at a temperature of 800 ~ 900 ℃. In addition, the austenitic maximum fraction ( _max ) of the ferritic stainless steel slab is preferably 15 to 40%.

Stainless steel, ferritic, ridging, continuous annealing

Description

Method for producing ferritic stainless steel with improved ridging property {Method for producing ferritic stainless steel sheets having excellent ridging property}             

1 is a block diagram illustrating a method of manufacturing a ferritic stainless steel according to an embodiment of the present invention.

Figure 2 is a graph comparing the result of the ridging height of the specimen prepared by the conventional method of manufacturing ferritic stainless steel of the present invention.

The present invention relates to a method for producing a ferritic stainless steel, and in particular, after hot rolling, hot rolling annealing is omitted, followed by cold rolling in a continuous cold rolling mill, annealing or continuous annealing, followed by continuous annealing after cold rolling in a 20 stage cold rolling mill. It relates to a method for producing ferritic stainless steel with improved properties.

Ferritic stainless steel cold rolled products are widely used in various kitchen utensils and automobile parts by molding processing such as deep drawing, and this ferritic stainless steel has streaked ridding defects during press molding. I have a problem. Such ridging defects not only deteriorate the appearance of the product, but also have a problem in that the manufacturing cost increases because the grinding process is added after molding if the ridging occurs badly.

The cause of such leasing has not been clarified yet, but it is usually known as follows. That is, in the final cold-rolled annealing plate, irregularities appear on the surface by plastic anisotropy of a site having a different texture. In particular, it is known that the formation of coarse grain groups having a {001} <110> crystal orientation present in the hot rolled sheet due to the coarse cast structure.

Conventional countermeasures for improving such ridging are generally classified into three types based on the above-mentioned estimation mechanism. That is, (1) miniaturization of coagulated grains, the origin of coarse grain groups, (2) disorder of aggregates of coarse grain groups (randomization), and (3) decomposition of coarse grain groups.

In the case of (1), for example, as described in Japanese Patent Application Laid-open No. 50-123294, electron stirring for columnar crystallization, introduction of solidification crystal nuclei for miniaturization of solidification grains, and reduction of casting temperature It is proposed as a concrete countermeasure against rapid solidification.

For the above (2), as shown in Japanese Patent Application Laid-Open No. 57-70234, it is appropriate to optimize the hot rolling temperature (heating temperature, finishing temperature, winding temperature, etc.), rolling reduction rate, annealing temperature, etc. to promote recrystallization during the manufacturing process. And the addition of an intermediate annealing process during cold rolling to increase the number of re-crystallizations of cold rolling, the addition of stretching deformation during hot rolling, the addition of widthwise deformation, the use of intragranular precipitates and austenite phases, and the optimization of hot rolling lubrication.

In the case of (3), as described in Japanese Patent Application Laid-Open No. Hei 6-81036, a component change intended for introduction of transformation and a special heat treatment step have been proposed. Most of these prior arts are aimed at increasing the effect by a combination of several techniques, rather than performing each individually.

In general, stainless 430 steel undergoes a hot rolled annealing process, and performs box annealing for heat treatment at a relatively low temperature (800 to 850 ° C.) for a long time (35 to 50 hours). The purpose of hot-rolled sheet annealing is to eliminate the leasing that occurs during forming by satisfying two metallurgical factors that destroy the hot-rolled texture by recrystallization and decompose the austenite phase (martensite phase at room temperature) into ferrite + carbide. It is for reducing, improving moldability, and improving cold rolling property. However, such annealing process not only has a large energy consumption, but also causes a problem of lowering productivity due to prolonged heat treatment.

Therefore, in recent years, research and technology development on the improvement of productivity through sequencing of the hot-rolling annealing process or omission of the hot-rolling annealing process suitable for mass production systems as well as improving the ridging property and the formability have been concentrated.

The above technique is described in a number of patent publications. Among them, Japanese Patent Publication No. 59-43977 and Japanese Patent Publication No. 59-43978 (1984.10.25) show that Al is 0.1 to 430 in stainless steel. A method for producing a hot-rolled hot rolled sheet, which is added at 0.15% and increases the isoaxial crystallization rate of the slab during continuous casting, and which is hot-rolled under relatively low temperature heating and high pressure, is described.

However, there is a problem in that recrystallization does not occur well regardless of hot rolling annealing conditions because the internal strain energy accumulated in the hot rolled sheet is small when hot rolling.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, when the hot rolled plate is cold rolled in a continuous cold rolling mill to accumulate internal strain energy to sufficiently recrystallize when the annealing to coarse grain group It is an object of the present invention to provide a method for producing ferritic stainless steel that improves ridging by breaking and annealing again after cold rolling.

According to the present invention for achieving the above object, by weight% C: 0.10% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Cr: 15.0 ~ 20.0 In the manufacturing method of ferritic stainless steel containing%, Al: 0.2% or less and N: 0.05% or less, and the remaining Fe and other inevitable impurities,

Hot rolling the ferritic stainless steel slab formed as described above, cold rolling in a continuous cold rolling machine without annealing the hot rolled plate, and maintaining the cold rolled plate at a temperature of 800 to 900 ° C. for 1 hour to 10 hours. 10 seconds to 5 minutes by dull or heated to a temperature of 850 ~ 1000 ℃, followed by quenching and continuous annealing, cold rolling annealing again in a 20-stage cold rolling mill, and cold rolling 800 to 900 Continuous annealing for 5 seconds to 3 minutes at a temperature ℃.

_max)은 15 ~ 40% 인 것이 바람직하다.
Further, according to the present invention, the maximum fraction of austenite of the ferritic stainless steel slab (

_max ) is preferably 15 to 40%.

Hereinafter, the present invention will be described in detail.

Ferritic stainless steel of the present invention is a known component system in terms of weight% C: 0.10% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Cr : 15.0 ~ 20.0%, Al: 0.2% or less and N: 0.05% or less, and the rest of Fe and other inevitable impurities.

_max)이 15 ~ 40% 가 되도록 조정한다. 왜냐하면, 오스테나이트 최대 분율이 15%미만인 경우에는 열연소둔 후 잔존하는 오스테나이트상(냉각시 마르텐사이트상)에 의한 결정립 미세화효과가 적어서 리징성 개선이 크지 않고, 40%를 넘게 되면 열연소둔 후 잔존하는 오스테나이트상이 너무 많아서 마르텐사이트상에 의한 취화현상이 나타나기 때문이다. 이런 오스테나이트 최대 분율(

_max)은 수학식 1에 의해 구해진다. In the alloy component system as described above, the maximum fraction of austenite (

_max ) is adjusted to 15 ~ 40%. Because, when the maximum fraction of austenite is less than 15%, the grain refining effect of the austenite phase (martensite phase) remaining after hot annealing is small and the leaching property is not improved. This is because there is too much austenite phase and embrittlement phenomenon by martensite phase appears. This austenitic maximum fraction (

_max ) is obtained by the equation (1).

오스테나이트 최대 분율( _max) = 420(%C) + 470(%N) + 23(%Ni) + 9(%Cu) + 10(%Mn) + 180 - 11.5(%Cr) - 11.5(%Si) - 12(%Mo) - 52(%Al)

Austenitic maximum fraction ( _max ) = 420 (% C) + 470 (% N) + 23 (% Ni) + 9 (% Cu) + 10 (% Mn) + 180-11.5 (% Cr)-11.5 (% Si )-12 (% Mo)-52 (% Al)

Next, a preferred embodiment of a method for manufacturing ferritic stainless steel according to the present invention will be described in detail with reference to the drawings.

1 is a block diagram illustrating a method of manufacturing a ferritic stainless steel according to an embodiment of the present invention.

As shown in Figure 1, after the hot-rolled ferritic stainless steel slab composition as described above (S1), it is cold rolled in a continuous cold rolling machine (S2) without annealing the hot rolled plate. Working in such a condition is to compensate for less recrystallization due to the small amount of strain energy accumulated in the hot-rolled sheet and because the productivity can be increased by cold rolling in a continuous cold rolling mill.

Subsequently, the cold rolled sheet is maintained at 800 to 900 ° C. for 1 hour to 10 hours, or annealed, or heated to 850 to 1000 ° C. for 10 seconds to 5 minutes, and then quenched and continuously annealed (S3). This is because, when annealing the cold rolled sheet, the recrystallization does not sufficiently occur at less than 800 ° C, and if it exceeds 900 ° C, the austenite phase remains and the moldability deteriorates. This is because the recrystallization does not occur sufficiently within 1 hour, and the longer the retention time, the easier the carbonitride precipitates, which is advantageous in moldability.

In addition, when the cold rolled sheet is continuously annealed at a temperature of less than 850 ° C. for a short time, recrystallization does not occur sufficiently to obtain a grain refining effect. Because there is. Within 10 seconds of continuous annealing, recrystallization does not occur sufficiently, and the longer the retention time is, the more advantageous it is.

Then, cold rolling is performed in a 20 stage cold rolling mill (S4). After cold rolling, continuous annealing for 5 seconds to 3 minutes at a temperature of 800 ~ 900 ℃ (S5). The reason for working under such conditions is that recrystallization does not occur sufficiently below 800 ° C, and when it exceeds 900 ° C, the austenite phase remains and moldability deteriorates.

That is, as described above, the ferritic stainless steel manufacturing method of the present invention does not anneal the hot rolled sheet but accumulates internal strain energy as it is cold rolled in a continuous cold rolling mill to sufficiently recrystallize when annealed to destroy coarse grain groups. In addition, by re-annealing after cold rolling, the ridging property can be improved by destroying the coarse texture.

The following describes the present invention in detail by way of examples.

Hot-rolling was performed by the method of the present invention as shown in Table 2 using ferritic stainless steel (Inventive steels A, B and C) ingot specimens having the composition shown in Table 1. At this time, as the hot rolling conditions, the reheating temperature was 1250 ° C, the finish rolling temperature was 850-900 ° C, and the winding temperature was 700 ° C. Subsequently, the hot rolled sheet was rolled in a continuous cold rolling mill, followed by annealing for 5 hours at 800 to 900 ° C., or cold rolling and annealing for 1 minute at 850 to 1000 ° C., followed by cold rolling and annealing. A test specimen was prepared, and the ridging height was measured by a tensile test. Here, the ridging property is measured by measuring the surface roughness after the tensile test to the ridging height, the lower the ridging height is advantageous.

On the other hand, the comparative steel (D) was manufactured under the conditions of the conventional methods (I, II) of Table 2 and measured the ridging height.

Classification (w%) C Si Mn Cr Al N

_max

_max Remarks  Invention steel A 0.052 0.39 0.38 16.23 0.003 0.03 31.1 P: trace S: trace B 0.047 0.40 0.25 16.34 0.002 0.0114 18.4 C 0.052 0.42 0.25 16.38 0.134 0.025 18.4 Comparative steel D 0.044 0.40 0.23 16.50 0.063 0.011 11.4

Conventional Method (Ⅰ)  Hot Rolled → Upper Annealed → Cold Rolled → Continuous Annealed Conventional Method (Ⅱ)  Hot Rolled → Continuous Annealed → Cold Rolled → Continuous Annealed Invention method  Hot rolling → cold rolling (continuous cold rolling mill) → normal annealing or continuous annealing → cold rolling (20 stage cold rolling mill) → continuous annealing

The measurement results of the ridging height of the specimens prepared by the conventional method and the present invention of A, B, C, and D steel of the chemical components of Table 1 are shown in FIG. 2.

Figure 2 is a graph comparing the measurement results of the ridging height of the specimen prepared by the prior art and the method of manufacturing ferritic stainless steel of the present invention. As shown in Fig. 2, the steel produced by the ordinary annealing of the conventional method (I) shows a higher level of ridging height except the A steel than the conventional method (II), and also the conventional method in the comparative steel (D). Compared to (I, II), the ridging height of the specimen prepared by the present invention showed a lower level.

Therefore, the present invention shows that the leaching height is very low than the conventional method, it can be seen that the leaching property is remarkably improved when the ferritic stainless steel is manufactured by the manufacturing method of the present invention.

_max)을 적절히 조절한 슬라브를 열간압연 후 열연판을 소둔하지 않고 연속냉간압연기에서 냉간압연한 다음 소둔하고 나서 다시 냉연 후 소둔함에 따라 리징성을 현저하게 향상시키는 효과를 얻을 수 있으며, 이에 따라 성형 가공 후에 미려한 표면을 얻을 수 있을 뿐만 아니라 최종제품의 연마공정 생략에 의한 제조원가 절감효과를 기대할 수 있다. As described in detail above, the method of manufacturing the ferritic stainless steel of the present invention has a maximum fraction of austenite (

_max ) slab suitably adjusted after hot rolling is cold rolled in a continuous cold rolling machine without annealing after annealing, then annealing and then annealing again after cold rolling, thereby remarkably improving the ridging property. Not only can a beautiful surface be obtained after processing, but also manufacturing cost reduction effect can be expected by eliminating the polishing process of the final product.

Although the technical idea of the method for manufacturing the ferritic stainless steel of the present invention has been described with the accompanying drawings, this is illustrative of the best embodiment of the present invention and is not intended to limit the present invention.

In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (2)

By weight% C: 0.10% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Cr: 15.0 ~ 20.0%, Al: 0.2% or less and N: 0.05% In the method of manufacturing a ferritic stainless steel containing the following Fe and other inevitable impurities, hot rolling of the ferritic stainless steel slab formed as above, and continuous cold rolling without annealing the hot rolled sheet. Cold rolling step, and the cold rolled sheet is maintained at 800 ~ 900 ℃ temperature for 1 hour to 10 hours or annealing or heated to 850 ~ 1000 ℃ temperature for 10 seconds to 5 minutes and then quenched continuously annealing And, the cold rolled annealing plate again cold-rolled in a 20-stage cold rolling mill, and the step of continuously annealing the cold rolled sheet at 800 ~ 900 ℃ temperature for 5 seconds to 3 minutes characterized in that the leasing properties improved ferrite system Made of stainless steel Way. The method of claim 1, wherein the maximum fraction of austenite of the ferritic stainless steel slab (

_max ) is 15 to 40% manufacturing method of ferritic stainless steel with improved ridging property.

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