JPS60262921A - Manufacture of sheet or strip of austenitic stainless steel - Google Patents

Abstract

PURPOSE:To obtain an austenitic stainless steel sheet having low anisotropy in the surface by specifying the hot rough rolling condition of a steel slab, descaling after finishing rolling, cold rolling in two steps then annealing finally said material. CONSTITUTION:The slab of austenitic stainless steel is heated to 1,200-1,300 deg.C, and hot rolled. Thereat, said slab is roughly rolled by one pass or more under >=25%/pass reduction ratio, hot rolled with finishing at >=1,050 deg.C, then said material is wound at <=650 deg.C. Next, descaling is performed without annealing the hot rolled plate. Successively, said plate is cold rolled by >=30% cumulative reduction ratio by using large diameter working roll having >=200mm. diameter. Next, cold rolling is performed by >=30% reduction by using small diameter working roll having <200mm. diameter. Thereafter, final annealing and skin pass rolling are performed to obtain the steel sheet or strip being the final product.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an austenitic stainless steel sheet or copper strip manufacturing process that eliminates the annealing step of the steel sheet or steel strip after hot rolling and the subsequent cooling process. The present invention relates to a method for producing a thin plate product having workability equivalent to or better than that obtained by conventional annealing by appropriately combining roll diameters during inter-rolling, and in particular, having characteristics of small in-plane anisotropy.

(Prior art) In general, in the manufacturing method of austenitic stainless steel thin sheets mainly made of 184Cr-8N1 series, conventionally, after adjusting the composition of melted steel in an electric furnace, hot rolling is carried out. A steel plate or a copper strip (hereinafter collectively referred to as a hot-rolled plate) is formed, and then the hot-rolled plate is heat treated at a high temperature of 1010°C or higher, and mechanical descaling by shot blasting etc. and chemical descaling by pickling etc. are performed. After that, cold rolled steel sheets or copper 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 can be expected.

With the development of cold rolling technology, hot rolled sheets can be rolled without annealing.
It has become possible to cold-roll sheets to the thickness of thin sheet products.

However, simply omitting the annealing step causes the following problems. That is, the in-plane anisotropy of the mechanical properties of the thin sheet product increases. Large anisotropy refers to a large difference in properties in the rolling plane, in the rolling direction, in the perpendicular direction, and in the 45° direction from the rolling direction. 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. In other words, the invention described in JP-A-51-77523 attempts to eliminate susceptibility to intergranular corrosion by rapid cooling in the temperature range of 800 to 500°C after hot rolling, but the mechanical properties of the thin sheet product are Not considered. Japanese Patent Publication No. 52-284
Publication No. 24 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. For use,
The aim is to increase the in-plane anisotropy of the product plate.

The invention described in JP-A-53-100124 improves press workability by omitting hot-rolled sheet annealing and rolling the sheet to the product sheet thickness in one cold rolling without intermediate annealing. , in-plane anisotropy is not considered. The invention described in JP-A No. 55-70404 performs recrystallization and solution treatment by limiting hot-rolling finish rolling conditions and cooling conditions after hot rolling, and JP-A No. 56-158819. The publication discloses that the hot-rolled sheet annealing is omitted and the sheet is pickled with only hydrochloric acid, but neither of them takes into account the mechanical properties of the thin sheet product.

The present inventors have proposed a method for manufacturing thin sheet products with in-plane anisotropy of mechanical properties equivalent to or higher than that of hot-rolled sheet annealed materials even if hot-rolled sheet annealing is omitted. rolling 15
It is proposed to carry out the finish rolling in the indicated range of ~55%/pass and outlet temperature of 990 to 1200°C, and to perform finish rolling in the indicated range of lθ to 55%/nox and biting temperature of 820 to 1040°C. Publication No. 58-34139). Subsequently, the present inventor discovered that it is possible to produce a thin plate product with small in-plane anisotropy of mechanical properties even if the hot rolling conditions are not particularly within this range.

(Problems to be Solved by the Invention) The present invention eliminates the annealing process of hot-pressed plates in the production of austenitic stainless steel plates or copper strips, and provides mechanical strength equivalent to or higher than that of thin plate products manufactured through the conventional annealing process. nature,
In particular, the purpose is to obtain products with small in-plane anisotropy.

(Means for solving problems) The present invention is characterized by passing through the following steps.

A.1200 austenitic stainless steel slab
Heat to a temperature range of 1300°C or higher.

B. In the rough rolling of hot rolling, perform one or more passes of 25%/no rolling (1) or more (25- or more rolling with a gusset) and finish the rough rolling at a temperature of 1050°C or higher. . The finishing rolling conditions of hot rolling are not limited.

Coiling at a temperature of 650°C or less at the C0 hot rolling edge.

D. Descaling the hot rolled sheet.

E. Cold rolling is performed at a cumulative reduction rate of 930% or more using a cold rolling mill that uses large diameter rolls of 200 m or more as work rolls.

F. Cold rolling using a cold rolling mill using small diameter rolls of less than 200 fi as work rolls and J) 30 inch or more cumulative lateral rolling.

G. Final annealing.

The austenitic stainless steel targeted by the present invention is S
Usual components such as U8304 may be used, but as proposed by the present inventors and disclosed in Japanese Patent Application Laid-Open No. 58-22328, CO,07
0% or less, 811.0% or less, Mn 3. Q % or less, P 0.040% or less, 80.03 (1 or less, C
r16.0-19.0%, Ni 6.0-9.0%,
In austenitic stainless steel containing NO, 2% or less, the relationship between the amounts of C and Ni added is 102X (C)
+4X (Regulating N1 to 39.5%) is effective.

In step B, finish rolling may be performed immediately after the completion of rough rolling, but as proposed by the present inventors and disclosed in Japanese Patent Application Laid-Open No. 58-34139, the material after rough rolling may be placed on temporary standby. It is more effective to reduce the biting temperature during finish rolling to 970°C or less.

In step C, the hot-rolled copper strip is cooled by water cooling or forced air cooling and then rolled. After winding, it may be left to cool.

In the D process, shotplast, high pressure slurry spraying,
Descaling can be performed by a combination of mechanical means such as repeated bending or light reduction rolling with pickling, or by mechanical means alone such as polishing with high-pressure slurry or grinding with a grinding belt or bristle brush.

In step E, reciprocating rolling using a 4-high rolling mill, a 6-high rolling mill, etc., or tandem rolling using a group of these rolling mills can be performed, and it is desirable that the surface ITJ temperature of the steel plate is 200° C. or lower.

In step F, a multi-high rolling mill such as a Sendzimir rolling mill can be used. Note that annealing may be performed between the E step and the F step, if necessary.

In step C, annealing and descaling can be performed through an annealing pickling line (AP line)'f, or only annealing can be performed through a bright annealing line (BA line).

(Function) The present inventor believes that the formation of earrings is due to the development of a strong texture unique to austenitic stainless steel, and that in order to make earrings smaller, this unique texture should be reduced. We believe that this problem can be prevented if randomization of the texture is achieved, such as by preferentially developing sub-orientations that have the opposite effect to this orientation.

Based on the above concept, we investigated the texture of various austenitic stainless steel sheets in detail, and found that the formation of the texture depends on the rough rolling conditions during hot rolling, the combination of rolls during cold rolling, and the steel sheet. It was found that the temperature has a strong influence.

That is, as recrystallization and grain growth progress during rough rolling during hot rolling and the crystal grains become coarser, the texture in the product sheet tends to become more random and the anisotropy becomes smaller. For this reason, rough rolling is preferably performed at high temperature and with large reduction.
In order to finish above ℃, the slab heating temperature must be 1200℃.
It must be more than that. However, if the temperature exceeds 1300°C, delta-ferrite increases rapidly and impedes hot workability, so the upper limit of slab heating was set at 1300°C. Recrystallization during rough rolling is affected by the rolling temperature and reduction ratio, but in order to obtain a uniform recrystallization state in the thickness direction, at least 25%/-
It is necessary to perform one pass or more of rolling of 4 passes or more, and to finish rough rolling at a temperature of 1050° C. or higher. If the rolling reduction per nox is lower than this, the accumulation of strain will be insufficient)) Recrystallization will proceed only partially.

The material that has become a recrystallized structure of coarse grains at the end of hot rough rolling becomes an expanded worked structure in the subsequent hot finish rolling, and a part of the material becomes a recrystallized structure at the end of p1 finish rolling. If this hot-rolled sheet with a smooth structure is cold-rolled under the above conditions without annealing and finally annealed, a thin sheet product with small in-plane anisotropy of mechanical properties can be obtained. Here, the more elongated grains there are at the end of hot finish rolling, the better for reducing the in-plane anisotropy of the thin sheet product.
The following is most effective.

In cold rolling, the texture of a thin sheet product changes markedly depending on the rolling temperature, and FIG. 1 shows a typical example of the texture obtained from SUS 304. Cold rolling biting temperature is high (approximately 8
(0°C), the preferred orientation is (211) [11], but in the case of low-temperature biting (0°C), (110) [001] increases. (211) [111] An increase in the orientation produces a mountain of earrings at a position tilted by 45° to the rolling direction, and (110)
An increase in the (001) orientation produces earring ridges in the rolling direction and in a direction perpendicular thereto. Therefore, it was predicted that if cold rolling was performed at a rolling temperature at which both textures were appropriately mixed, the positions of the peaks and valleys of the earrings would be averaged and the anisotropy would be reduced.

By the way, in the conventional cold rolling of austenitic stainless steel sheets, a target thickness is usually obtained by performing multi-pass rolling of 4 to 12 steps using a Sendzimir rolling mill. At this time, the biting temperature of the initial part of the cold-rolled material is often the same as the temperature (room temperature) where the material was placed, but the biting temperature of the second and subsequent rolls is The temperature generally rises to about 50 to 230°C under the influence of processing heat in the initial pass. Many/? In steel rolling, this phenomenon occurs because the temperature of the plate rises even further due to the rolling process being rolled repeatedly in a high temperature range (generally speaking, even in cold rolling, the temperature only rises to about 230°C). Become.

The inventors have determined that rolling in this high temperature range causes an increase in the in-plane anisotropy of the material.

The cause of this temperature rise is thought to be the small diameter work rolls of the Sendzimir rolling mill and the use of mineral oil-only lubricating oil with low cooling capacity.・The temperature of the steel plate during cold rolling of stainless steel As a method for suppressing the rise and reducing anisotropy, the present inventor, Misaki, focused on a large-diameter continuous cold rolling mill that has conventionally been used for cold rolling ordinary steel thin plates. Compared to the Sendzimir rolling mill, the temperature rise during cold rolling is not so large because water-soluble cold rolling lubricating oil with excellent cooling ability is used and cold rolling is performed with large diameter work rolls. , the maximum temperature was estimated to be around 200°C.

Therefore, the present inventors developed Bus 304 (C: 0.04
blood.

81: 0.6%, Mn: 1.2%, Ni: 8.3%
, Cr: 18.2%, N: 0.035%) was heated to 1260°C, and then the final rough rolling was performed at a rolling reduction of 3mm and a finishing temperature of 1080°C. No4
A hot-rolled steel plate with a thickness of 4 mm was manufactured by finishing rolling the steel sheet.

Subsequently, hot-rolled sheet annealing was omitted, and after simply descaling, rolling was carried out using a cold rolling mill using a large-diameter roll of 4005 m in diameter as a work roll, and keeping the rolling temperature of all passes at a constant degree. In both cases, the total pressure is $d80%. These cold-rolled sheets were annealed at 1100°C for 10 seconds with air cooling.
The anisotropy was examined by i+shi and then earring tests. Earring test wire A cold-rolled annealed plate was cut out from an aso, o-φ 2-ink, and deep-drawn using a 40.0 mm φ inch, and the earring ratio was determined from the force and unevenness of the f end. .

The earring rate used here is defined by the following equation.

h, H force, indicates the height measured from the bottom of the cup to the top of the peak at the edge of the cup, and h2 indicates the height to the valley at the edge of the cup.

The results are shown in Figure 2. In Figure 2, the horizontal axis shows the cold rolling temperature (°C) (the steel plate temperature maintained during rolling), and the vertical axis shows the earring ratio (%). It can be seen that the rolling temperature at which an earring ratio (approximately 7 inches) can be obtained is approximately 200° C. in the conventional technique, that is, when hot-rolled sheets are annealed and rolled using a Sendzimir rolling mill.

These results indicate that the anisotropy of the product sheet, which is a drawback of austenitic steels such as 9SUB 304, can be prevented by omitting hot-rolled sheet annealing and suppressing the rise in steel sheet temperature during cold rolling. It is clear that the steel plate temperature is 200℃
The following was found to be desirable.

In this way, in order to suppress the temperature rise during cold rolling and keep it below a predetermined temperature, it is necessary to roll with a cold rolling mill that has large diameter work rolls with a diameter of 200 mm or more. It has been confirmed that the combination of water-soluble lubricating oils is extremely effective.

Therefore, even if continuous rolling is performed by arranging, for example, four rolling mills having large work rolls with a diameter of 200° or more, the rolling temperature of each stand is maintained at 200° C. or lower.

In addition, it is important to control the temperature of the steel sheet during the early stage of cold rolling, and the earrings of the product sheet are rolled at a reduction rate of 30 inches or more using a large-diameter work roll ([
If the earrings are cold-rolled with a diameter of 200 mm or more, the earrings will not deteriorate even if they are subsequently cold-rolled in a rolling mill with a small-diameter working hole, such as a Sendzimir mill.

However, the surface of the steel plate when rolled with large-diameter work rolls is rougher and less glossy than when rolled with small-diameter work rolls. In order to maintain the surface quality at the same level as the latter, cold rolling using small-diameter work rolls may be performed at a reduction rate of 30% or more.

Incidentally, in the method of the present invention, it is essential to rapidly cool the piezoelectric sheet after hot piezoelectricity and to coil it at a temperature of 650° C. or lower, and this is intended to prevent precipitation of oxycarbide and to prevent surface roughness after pickling of the hot-rolled sheet. 650
If the surface of the hot-rolled sheet pickled after being coiled at a temperature exceeding .degree. C. is removed, it may be removed using a coil eaves removal machine, but this is not preferable because it increases manufacturing costs.

Further, annealing is not necessary between cold rolling using large diameter work rolls and cold opening rolling using small diameter work rolls. However, the capabilities of cold rolling mills, especially when manufacturing thin products,
Annealing may be performed depending on the shape of the cold ivy plate.

The above manufacturing method of the present invention is applicable not only to 8U83Q4 but also to any austenitic stainless steel with deformation-induced martensitic transformation.

(Example) Hereinafter, the present invention will be explained in detail according to an example.・C:0
．． 035%, Si: 0.6%, Mn: 0.9%,
P: 0.027i8: 0.004%, Ni: 8.4%,
A slab of austenitic stainless steel containing Cr: 1B, 2%, N: 0.036%, and other inevitable impurities was heated to 1200°C or higher, then hot rough rolled and finish rolled to a thickness of 3. ~4 After forming a hot-rolled sheet, it was water-cooled on a runout table and wound up. Table 1 shows various conditions at this time.

The inventive example has a higher slab heating temperature than the comparative example, and also has a higher maximum rolling reduction rate in the ∆ stroke of the rough pressure vine. Therefore, the microstructure observation results in both cases indicate coarse recrystallized grains.

Furthermore, since the winding temperature is as low as 650° C. or less, precipitation of carbides is prevented.

The above hot-rolled sheets omit the hot-rolled sheet annealing, and after being mechanically and chemically scaled, the
The plate was passed through a four-stand tandem cold rolling machine having a work roll diameter of φ to a thickness of 1.5 wm. The lubricating oil for cold rolling is for normal tandem cold rolling, with a supplement of 10%.
The steel plate was cooled with neat oil. Maximum steel plate surface temperature is 90℃
Met. Next, the material was cold rolled in a reverse manner using a Sendzimir cold rolling mill having a work roll diameter of 60 mm to give a plate thickness of 0.6 mm. After that, Ordinary Hotsutsu, j), 110
After final annealing at 0° C. for 10 seconds, skin pass rolling was performed to obtain a thin plate product. In addition, as a comparative example, cold rolling was performed using only a Zenji mill and cold rolling using only a tandem rolling mill. These results are shown in Table 2.

All of the examples of the present invention have a low earring ratio, small surface roughness, and are excellent in both in-plane anisotropy of mechanical properties and surface texture. On the other hand, Comparative Examples 45, 6, and 7 all had a low slab heating temperature, a low rolling reduction in hot rough rolling, and a low end temperature, so the earring ratio of the products was high. Furthermore, since the hot-rolling and winding temperature of Comparative Example Flat 5 is high, the surface roughness occurs during pickling, and the surface properties are not improved even when the whole steel is cold-rolled using a Sendzimir rolling mill.

I66 has a low winding temperature, so there is a risk of rough skin during pickling.
Furthermore, the surface quality is very good because all of the slabs are cold-open rolled using a Sendzimir rolling mill, but the conditions for slab heating and hot rough rolling are not met, and the cold rolling using large-diameter work rolls is not enough. The earring rate is high because the earrings are not carried out. A7 has different conditions for slab heating and hot rough rolling, but all cold opening rolling is done in a tandem rolling mill with large diameter work rolls, so the earrings are slightly improved compared to A5. However, since cold open rolling is performed only with large-diameter work rolls, the surface quality is poor.

(Effects) By applying the present invention to V5, it is possible to significantly reduce earrings that occur during deep drawing of thin sheet products manufactured by omitting hot-rolled sheet annealing completely, and to reduce the number of earrings that occur during deep drawing. This brings about great effects such as a reduction in the amount of paper and the blank size required before deep drawing.

Furthermore, by utilizing the tandem cold rolling method using one large-diameter collecting roll, the effect of reducing costs and increasing productivity is extremely large.

[Brief explanation of the drawing]

Figure 11 shows the change in the cold rolling temperature on the texture of SUS 304 cold rolled annealed plate. The diagram shows thermoelectric #
It is a figure which shows the relationship between the steel plate temperature and the earring of a product plate at the time of cold rolling by the large-diameter work roll of 5Us304 which omitted Ii annealing. Figure 2 Oki M Rinnobe Atsushi (6c) Procedural Amendment (Voluntary) June 15, 1980 Kazuo Wakasugi, Commissioner of the Patent Office 2 Title of Invention Method for manufacturing austenitic stainless steel plate or steel strip 3 Relationship with the case of the person making the amendment Patent applicant 5, date of amendment order 1920, month, day 6, amend the scope of the patent claims to be amended as follows. Heated to a temperature range of
Finish rolling at a temperature of 0°C or higher, perform hot finish rolling,
After being coiled at a temperature of 650°C or less and desk-ringed without annealing, the hot-rolled sheet is rolled at a cumulative reduction rate of 30% or more using a cold rolling machine using a large diameter roll of 200 mm or more as the work roll. An austenitic stainless steel sheet characterized by cold rolling, then cold rolling in a cold rolling machine using small diameter rolls of less than 200 wg as work rolls at a cumulative reduction rate of 30 inches or more, and final annealing. Method of manufacturing copper strips.

Claims (1)

[Claims] A slab of austenitic stainless steel is heated to a temperature range of 1200°C or higher and 1300°C or lower, and then subjected to one or more passes of 254727 or higher in hot rough rolling to 1050°C.
The rolling is finished at the above temperature, hot finish rolling is carried out, and 65
After being coiled at a temperature below 0°C and descaling without annealing the hot-rolled sheet, it is transferred to a cold rolling machine using a large diameter roll of 200 m in diameter as a work roll at a cumulative reduction rate of 30 cm or more. An austenitic stainless steel sheet or copper strip characterized by cold rolling, then cold rolling at a cumulative reduction rate of 9304 or more using a cold rolling mill using small diameter rolls of less than 200 m in diameter as work rolls, and final annealing. manufacturing method.