JPH0250806B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention eliminates the annealing step of the steel plate or steel strip after hot rolling in the manufacturing process of austenitic stainless steel plates or steel strips, and is equivalent to or better than conventional annealing. The present invention relates to a method of manufacturing a thin plate product having characteristics such as processability, particularly small internal anisotropy. (Prior art) In general, in the manufacturing method of austenitic stainless steel thin sheets mainly made of 18% Cr-8% Ni, hot rolling is performed after melting and composition adjustment in an electric furnace or converter. to produce hot-rolled steel sheets or steel strips (hereinafter collectively referred to as hot-rolled sheets),
After that, the hot-rolled sheet is heat treated at a high temperature of 1010℃ or higher, and after mechanical descaling such as shot blasting and chemical descaling such as pickling,
Cold rolled steel plates or steel strips (hereinafter collectively referred to as sheet products) were manufactured through cold rolling and final annealing. The main purposes of heat treatment of hot-rolled sheets are to recrystallize and soften them and to make the mechanical properties uniform, and to solidify the carbides produced during the cooling process after hot rolling, so that they can be used for pickling in the post-process. The object of the present invention is to prevent roughening of the surface due to intergranular corrosion and obtain a thin plate product with excellent surface gloss. However, the recrystallization temperature of austenitic stainless steel is significantly higher than that of ordinary steel sheets, and high-temperature heat treatment is required in the hot-rolled sheet annealing process. Therefore, if the hot-rolled plate annealing process can be omitted, significant improvements in energy savings and productivity are expected. With the development of cold rolling technology, it has become possible to cold roll a hot rolled sheet to the thickness of a thin sheet product without annealing it. However, simply omitting the annealing step causes the following problems. That is, increasing the in-plane anisotropy of the mechanical properties of thin sheet products. High anisotropy refers to a large difference in properties within the rolling plane in the rolling direction, perpendicular direction, and 45° direction from the rolling direction.For example, when such a thin plate product is deep drawn into a cylinder, In this case, large earrings occur, which causes a decrease in material yield. In the past, there have been many reports on the omission of hot-rolled sheet annealing, but all of them ignore the fact that in-plane anisotropy increases in thin sheet products. That is, JP-A-51-77523
The invention described in the publication attempts to eliminate susceptibility to intergranular corrosion by rapid cooling in the temperature range of 800 to 500°C after hot rolling, but does not take into account the mechanical properties of the thin sheet product. JP-A No. 52-28424 discloses that the r value in the 45° direction with respect to the rolling direction can be improved by cold rolling without hot-rolled sheet annealing. The purpose is to increase the in-plane anisotropy of the product sheet for use as a drawing material. The invention described in JP-A-53-100124 improves press workability by omitting hot-rolled sheet annealing and rolling the sheet to the product thickness in one cold rolling without intermediate annealing. However, in-plane anisotropy is not taken into consideration. The invention described in JP-A-55-70404 is
Recrystallization and solution treatment are carried out by limiting the hot rolling finish rolling conditions and the cooling conditions after hot rolling. Although taste pickling has been disclosed, none of them take into account the mechanical properties of the sheet products. (Object of the Invention) The present invention aims to omit the annealing process of hot-rolled sheets in the production of austenitic stainless steel sheets or steel strips, and to achieve mechanical properties equivalent to or higher than those of thin plate products manufactured through the conventional annealing process. The aim is to obtain products with small in-plane anisotropy. (Structure of the Invention) The present invention omit annealing of a hot-rolled austenitic stainless steel sheet, and after descaling, the steel sheet surface temperature is reduced to 160°C or less using a cold rolling mill or rolling mill group having large diameter rolls of 200 mmφ or more. A method of manufacturing small austenitic stainless steel plates or steel strips with small earrings by cold rolling, which involves cold rolling with large diameter rolls at a cumulative reduction rate of 30% or more, and then cold rolling with small diameter rolls. After cold rolling with diameter rolls, intermediate annealing at 800℃~1150℃ and
This includes a method of pickling and then cold rolling with small diameter rolls. The present invention will be explained in detail below. The inventor believes that earrings occur due to the development of a strong texture unique to austenitic stainless steel, and that in order to make earrings smaller, it is necessary to reduce this unique texture, or to reverse the orientation of the earrings. We believe that this can be prevented if randomization of the texture is achieved, such as by preferentially developing secondary orientations that have an effect. Based on the above concept, we investigated the texture of various austenitic stainless steel sheets in detail, and found that the formation of texture is strongly influenced by the temperature of the steel sheet during cold rolling, especially when the rolling temperature is low. It has been found that the cold-rolled texture and recrystallized texture in this case are significantly different from the texture obtained from conventional rolling methods. The present inventor focused on the temperature of the steel plate when cold rolling austenitic stainless steel, and performed careful cold rolling by controlling the biting temperature at a constant temperature in each pass using a reverse cold rolling mill. After ivy,
The texture of the product was examined after normal annealing and pickling. Figure 1 shows a typical example of the texture obtained with SUS304. When the biting temperature is high (approximately 80℃), the preferred orientation is (211) [111], but when the biting temperature is low (0℃)
In the case of , (110) [111] increases. (211) [111]
An increase in the orientation produces earring peaks at a position inclined at 45° to the rolling direction, and an increase in the (110) [001] orientation produces earring peaks in the rolling direction and in a direction perpendicular to it. Therefore, it was predicted that if cold rolling is performed at a rolling temperature at which both textures are appropriately mixed, the positions of the peaks and valleys of the earring will be averaged and the anisotropy will be reduced. Therefore, the steel plate temperature during rolling,
The relationship between product anisotropy was investigated. By the way, conventional cold rolling of austenitic stainless steel sheets is usually carried out using a Sendzimir mill.
The target thickness was obtained by performing 12-pass multi-pass rolling. At this time, the biting temperature in the initial pass of multiple passes of cold rolling is often the same as the temperature (room temperature) where the material was placed, but the biting temperature in the second and subsequent passes is 50 under the influence of machining heat in the initial pass
It is common for the temperature to rise to around 200℃. In multi-pass rolling, as this phenomenon is repeated, the temperature of the plate rises further, and generally, even in cold rolling, the temperature rises to about 200°C, meaning that rolling is repeated in a considerably high temperature range. The inventors have determined that rolling in this high temperature range causes an increase in internal anisotropy of the material. The causes of this temperature increase are thought to be that the Sendzimir mill uses small diameter rolls and uses only mineral oil lubricating oil with low cooling ability. As a method for suppressing the rise in steel plate temperature and reducing anisotropy during cold rolling of stainless steel, the present inventors have developed a method for continuous cold rolling of large diameters, which has been conventionally used for cold rolling of ordinary steel sheets. I paid attention to the machine. Compared to the Sendzimier mill, the temperature rise is not as great during cold rolling as it uses a water-soluble cold rolling lubricant with excellent cooling ability and cold rolling with large diameter rolls, at a maximum of around 160°C. It was estimated that Therefore, the present inventors developed a hot-rolled SUS304 coil (2.5
mm thickness), hot-rolled sheet annealing was omitted, and after simply descaling, a cold rolling mill with large diameter rolls of 400 mm was used, and reverse rolling was performed while keeping the rolling temperature constant for all passes. . In both cases, the total reduction rate is
It is 72%. These cold-rolled sheets were annealed at 1100°C for 10 seconds and then air-cooled, and then the anisotropy was examined by an earring test. For the earring test, a blank with a diameter of 80.0 mm was cut from a cold-rolled annealed plate, deep drawn using a punch with a diameter of 40.0 mm, and the earring ratio was determined from the unevenness of the cup end. The earring rate used here is defined by the following equation. h _e = h ₁ - h ₂ / (h ₁ + h ₂ ) / 2 x 100 (%)... (1) h ₁ indicates the height from the bottom of the cup to the top of the mountain at the edge of the cup, h ₂ indicates the height of the cup edge to the valley. The results are shown in FIG. Figure 2 shows the cold rolling temperature (°C) (temperature of the steel plate maintained during rolling) on the horizontal axis and the earring ratio (%) on the vertical axis. Earring rate when applied and rolled in a Sendzimir mill (approximately 7
%) is obtained at a rolling temperature of approximately 160°C.
It can be seen that it is. From this result, we found that SUS304 without hot-rolled plate annealing
It has become clear that the anisotropy of product sheets, which is a drawback of austenitic steels, can be prevented by suppressing the rise in steel sheet temperature during cold rolling, and it is desirable that the steel sheet temperature be 160℃ or less. There was found. In this way, in order to suppress the temperature rise during cold rolling and keep it below the specified temperature, rolling is carried out using a cold rolling mill with large rolls with a diameter of 200 mm or more, and water-soluble lubrication with excellent cooling ability is used. The combination of oils was found to be extremely effective. In this way, in the manufacturing process of austenitic stainless steel thin sheets, in order to omit the hot-rolled sheet annealing step and still obtain a product with small in-plane anisotropy, it is necessary to cold-roll the hot-rolled sheets (hot strips). It is primarily important to lower the temperature of the steel plate (strip) during rolling to below 160°C. As mentioned above, the inventors have found that by maintaining the steel plate temperature at 160°C or lower when cold rolling a hot-rolled plate, the in-plane anisotropy in the product can be reduced. is most suitable for cold rolling using a tandem mill consisting of a cold rolling mill with work rolls having a diameter of 200 mm or more. From the viewpoint of maintaining the temperature of the steel plate during cold rolling as low as possible below 160°C, a water-soluble lubricant with a large cooling capacity is suitable for the lubricant applied to the steel plate during rolling. The temperature of a steel plate (strip) during cold rolling increases due to heat generated during processing. As in the conventional process, cluster type mills, e.g.
When reverse rolling is performed using a Sendzimir mill with 80 mm diameter work rolls, the material is wound into strip coils with each pass.
Heat transfer is difficult and the temperature of the steel plate reaches 200-400℃. Therefore, as a preferred embodiment of the present invention,
Cold rolling is carried out using a rolling mill with work rolls with a diameter of 200 mm or more under the application of a water-soluble lubricant with a large cooling capacity. Considering productivity as well, it is preferable to perform cold rolling using a tandem mill while applying a cooling medium between the stands. Here, the reason why the work roll diameter of the rolling mill when cold rolling a hot rolled sheet is limited to 200 mm or more will be explained. First, it is cold rolled by a rolling mill with large diameter work rolls under the application of water-soluble lubricating oil, rather than by reverse rolling by a cluster mill, such as a Sendzimier mill with a work roll diameter of 50-80 mm. As mentioned above, the steel plate temperature can be reliably suppressed to 160°C or less. Preferably, the strip is cold rolled in a tandem mill with a cooling medium applied to the strip between stands. The work roll diameter of current tandem cold rolling mills for rolling ordinary steel is 300 to 600 mm. As for tandem cold rolling mills, tandem mills are being developed that have work rolls with a diameter of about 200 mm and are capable of applying high rolling reductions. However, cold rolling in rolling mills with work rolls having a diameter of less than 200 mm makes it extremely difficult to produce austenitic stainless steel sheets with high productivity, which is one of the objectives of the present invention. Furthermore, if the work roll diameter is less than 200 mm, the rolled product is likely to suffer from poor shape (flatness) due to roll deformation. Furthermore, when the work roll diameter is less than 200 mm, a cluster type must be used to avoid the above-mentioned problems, and the mill becomes complicated. Therefore, even if continuous rolling is performed by arranging, for example, four rolling mills having large diameter work rolls of 200 mm or more in diameter, the rolling temperature of each stand is maintained at 160° C. or lower. In addition, for earring product sheets, it is important to control the temperature of the steel sheet at the initial stage of cold rolling, so if the rolling reduction is 30% or more with large diameter rolls (200 mm or more in diameter), then the next step is to use small diameter rolls such as a Sendzimir mill. Even if the earrings are cold-rolled in a rolling mill, the earrings do not deteriorate, and the surface properties can be improved. As mentioned above, the problem of in-plane anisotropy in austenitic stainless steel sheets and, by extension, earrings is caused by the texture of the steel. Therefore, controlling the texture of the steel is the key to improving the in-plane anisotropy in the austenitic stainless steel thin plate and suppressing the formation of earrings during press forming. In low-temperature cold rolling, which the inventors focused on,
During cold rolling, the γ phase of the steel transforms into martensite, and this effect changes the texture during final annealing, improving the anisotropy of the product. Therefore, the greater the amount of transformation from the γ phase to martensite, the greater the anisotropy of the product and the greater the effect of improving the earrings. Since this improvement is based on this mechanism, it is applicable to all austenitic stainless steels that undergo deformation-induced transformation. Four steel types were selected from the sample materials shown in Table 2, and the influence of martensitic transformation during cold rolling was investigated.
Md ₃₀ (°C) is an index indicating the ease with which steel becomes martensite during processing, and is given by the following formula. Md ₃₀ (℃)=497−462(C+N)−9.2Si−8.1Mn−
13.7Cr−20 (Ni+Cu) These test materials (hot-rolled sheets) were rolled into small-diameter work rolls (60 mm diameter), medium-diameter work rolls (240 mm diameter),
Cold rolling was carried out in a rolling mill each having large diameter work rolls (400 mm diameter). In cold rolling using a rolling mill with small diameter work rolls (60 mm diameter), neat oil was applied to the steel plate as a lubricant and reverse rolling was performed. In cold rolling using rolling mills each having relay work rolls and large diameter work rolls,
Tandem cold rolling was carried out under the application of water-soluble lubricating oil. When we measured the surface temperature of a steel plate (strip) immediately after cold rolling, we found that the surface temperature of a steel plate reverse rolled by a rolling mill with small diameter work rolls was
The surface temperature of the steel plate was 120°C, which was subjected to tandem cold rolling at 180°C using a rolling mill having medium-diameter work rolls and large-diameter work rolls.
The thickness of the material is 3.0mm, and the thickness of the cold rolled product is 0.7mm (cold rolling rate: 77%), which is common to all three products. Table 3 shows the results of measuring the earring ratio of these product boards. From Table 3, it can be seen that the earring ratio is more influenced by the temperature of the steel sheet during cold rolling than by the diameter of the work roll. On the other hand, in terms of the influence of steel components, martensite is more likely to occur during cold rolling, that is, steel types with larger Md ₃₀ (℃) are more susceptible to the influence of cold rolling conditions, especially the steel plate temperature during cold rolling. , the earring improvement effect of low-temperature cold rolling is greater for steel types that are more likely to become martensitic. Therefore, the effect of the present invention is large on austenitic stainless steels that tend to produce deformation-induced martensite. After cold rolling in a cold rolling mill with large diameter rolls, intermediate annealing at 800 to 1150°C and pickling are performed.
Then, by cold rolling in a cold rolling mill with small diameter rolls, the earrings are very small and the surface properties are significantly improved. The above manufacturing method of the present invention is applicable not only to SUS304 but also to any austenitic stainless steel with deformation-induced martensitic transformation. Table 4 shows the cold rolling rate when SUS304b steel (hot rolled plate) is tandem cold rolled using a rolling mill with a large diameter work roll (400 mm diameter) and the rolling rate with a small diameter work roll (60 mm diameter). When followed by reverse cold rolling by a machine, and
This figure shows the change in the earring ratio of the product when intermediate annealing is interposed between tandem cold rolling and reverse cold rolling. From Table 4, it can be seen that when the cold rolling rate in tandem cold rolling using a rolling mill with large diameter work rolls is 30% or more, the improvement effect on the earrings is remarkable. Additionally, subjecting the material to an intermediate annealing between tandem cold rolling and reverse cold rolling significantly improves the earrings. However, the effect of this intermediate annealing is not due to randomization of the texture due to martensitic formation described above, but is due to recrystallization. (Example) Examples of the present invention will be described below. Hot-rolled SUS304 coils (3.0 mm) are processed by omitting hot-rolled plate annealing, subjected to mechanical descaling by shot blasting, and then pickled, and then processed into a 4-stand tandem cold rolling machine with a roll diameter of 300φ to 400φ. The diameter was 1.5mm through the hole. The cold rolling lubricating oil was the usual tandem cold rolling lubricant, and as a supplement, the steel plate was cooled with 10% neat oil. The maximum surface temperature of the steel plate was 90°C. Then, it was cold rolled from 1.5 mm to 0.7 mm using the tandem mill described above. After tandem cold rolling, the sheet was rolled to 0.7 mm in 5 passes using a Sendzimire cold rolling machine with small diameter rolls (60φ) from a 1.5 mm plate. Furthermore, after tandem cold rolling, the 1.5 mm plate was intermediately annealed at 1050°C for 10 seconds, and after pickling, it was rolled to 0.7 mm in 5 passes using a Sendzimir cold rolling mill with small diameter rolls (60φ) in reverse mode. After that, it was subjected to final annealing at 1100°C for 10 seconds and pickling as usual, and after skin pass, it was made into a JIS 2B product. Table 1 shows the results of comparing these with the product characteristics obtained only by the conventional small-diameter Sendzimir mill method. As is clear from these results, it is clear that the tandem cold rolling method according to the present invention, which uses large-diameter rolls and has good cooling ability, has smaller anisotropy than the conventional small-diameter Sendzimir mill method. Summer. Furthermore, roughness is shown as a surface property, but cold rolling with a tandem of large-diameter rolls is disadvantageous in this respect, but by cold-rolling the latter half with a small-diameter Sendzimir, good surface properties can be obtained. It became clear that this could be achieved. The tandem mill used in the method of the present invention shown in Table 1 consists of four stands, and the work roll diameter from the first stand to the third stand is 300 mm.
φ, the work roll diameter of the fourth stand is 400 mmφ. Also, the work roll diameter of the Sendzimir mill is
It is 60mmφ.

【table】

【table】

【table】

[Table] (Effects) As described above, by applying the present invention, it is possible to significantly reduce earrings generated during deep drawing, reduce the amount of cut-off after pressing, and reduce the required blank size before deep drawing. It brings about many effects. Furthermore, by utilizing the tandem cold rolling method using large-diameter rolls, the effect of lowering costs and increasing production pressure is extremely large.

[Brief explanation of drawings]

Figure 1 shows the (100) pole figure (a
Fig. 2 is a diagram showing the relationship between the steel plate temperature and the product earring during reverse cold rolling of SUS304 with large diameter rolls, omitting hot-rolled plate annealing.

Claims (1)

[Claims] 1 A material obtained by hot rolling austenitic stainless steel is subjected to mechanical or chemical descaling without annealing the hot rolled sheet, and then the diameter
An austenitic stainless steel plate or steel strip characterized in that cold rolling is carried out using a rolling mill with work rolls of 200 mm or more, maintaining the steel plate surface temperature at 160°C or less and applying a cumulative reduction rate of at least 30%. manufacturing method. 2. After applying mechanical or chemical descaling to the material obtained by hot rolling austenitic stainless steel without annealing the hot rolled sheet, the diameter
After performing cold rolling using a rolling mill with work rolls of 200 mm or more to maintain the surface temperature of the steel plate at 160°C or less and achieving a cumulative reduction rate of at least 30%,
1. A method for producing an austenitic stainless steel plate or steel strip, which comprises cold rolling to a final thickness using a cold rolling mill with work rolls having a diameter of less than 200 mm. 3 The material obtained by hot rolling austenitic stainless steel is subjected to mechanical or chemical descaling without annealing the hot rolled sheet, and then the diameter
After performing cold rolling using a rolling mill with work rolls of 200 mm or more to maintain the surface temperature of the steel plate at 160°C or less and achieving a cumulative reduction rate of at least 30%,
An austenitic stainless steel plate or steel characterized in that the material is intermediately sintered in a temperature range of 800 to 1150°C, and then cold rolled to the final thickness by a cold rolling mill with work rolls of less than 200 mm in diameter. How to make obi.