JPS59129731A - Production of austenitic stainless steel plate or strip - Google Patents

Abstract

PURPOSE:To enable production of a sheet of a stainless steel having excellent characteristics while omiting an annealing stage by regulating the content of C, N, Mn, Ni and P of an austenitic stainless steel to specific values and controlling the draft and gnawing temp. in the stage of hot rolling then cold rolling the steel. CONSTITUTION:An austenitic stainless steel slab contg. 0.005-0.07% C, <1.0% Si, <3.0% Mn, 16-20% Cr, 6-11.5% Ni, 0.005-0.2% N, <0.040% P, and <0.010% S, and having the compsn. of the 1st points A, BP, CP, D (where the values of BP, CP change respectively with the content of P) with respect to C, N, Mn, Ni, and P is subjected to hot rough rolling to a plate material. The hot finish rolling thereof is accomplished at the draft and gnawing temp. at least in the 2nd range enclosed by P, Q, R, ST and thereafter the plate material is pickled with the mixed solution of nitric acid and hydrochloric acid added with ferric salt and is finished by cold rolling without annealing to a steel strip which is then annealed. Even if the annealing after the hot rolling is omitted, the steel sheet having small in-plane anisotropy of mechanical properties and less surface roughnening is produced.

Description

Detailed Description of the Invention The present invention eliminates the step of annealing the steel plate or copper strip after hot rolling in the manufacturing process of an austenitic stainless steel plate or copper strip, thereby producing an austenitic stainless steel plate or copper strip that is equivalent to or better than conventional annealing. The present invention relates to a method for manufacturing a thin plate product having processability and surface texture of .

In general, in the manufacturing method of austenitic stainless steel thin plate mainly based on 18%Cr -8%l'Ji system,
Conventionally, after melting and adjusting the composition in an electric furnace or converter, hot rolling is performed to make a hot rolled steel sheet or copper strip (hereinafter collectively referred to as hot rolled sheet), and then the hot rolled sheet is rolled into a 1010
After heat treatment at a high temperature of ℃ or higher, mechanical descaling using shot gelatin, etc., and chemical descaling using pickling, etc., cold rolling □ and final annealing are performed to produce cold rolled steel sheets or copper strips (hereinafter collectively referred to as copper strips). The company manufactured thin sheet products).

The main purposes of heat treatment of hot-rolled sheets are to recrystallize them to soften them and to homogenize their mechanical properties, as well as to dissolve the carbides produced during the cooling process after hot-rolling and reduce the acidity of the post-rolled culm. Washing prevents surface roughness due to intergranular corrosion and produces thin plate products 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 two problems. The first problem is that the in-plane anisotropy of the mechanical properties of sheet products 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 some cases, large earrings occur, causing a decrease in material yield. The second problem is that when a hot rolled sheet is pickled without being annealed, significant roughness occurs on the surface, which remains in the thin sheet product.

In hot-rolled sheets hot-rolled using the conventional method, grain boundary KCr carbides precipitate during the cooling process after hot rolling, and there are regions around them with low Cr content, so this was pickled. In conventional pickling, a mixed acid of hydrofluoric acid and nitric acid is generally used, so the roughening of the surface due to intergranular corrosion is significant. In this case, traces remain even after cold rolling and annealing, making it impossible to obtain a thin sheet product with good surface gloss. Carbides in hot-rolled sheets can be prevented by water-cooling after finishing hot-rolling, and by winding at a low temperature of 550°C or less, but it tends to cause shape defects during cooling, and in the case of copper strips, defects occur during winding. Easy to occur.

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 omitting hot-rolled plate annealing and performing cold rolling. ,
This is intended 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 to the product sheet thickness in one cold rolling without intermediate annealing. In-plane anisotropy is not considered. Japanese Patent Application Publication No. 5
The invention described in JP-A No. 5-70404 performs recrystallization and solution treatment by limiting hot-rolling finish rolling conditions and post-hot-rolling cooling conditions.
Although it has been disclosed that hot-rolled sheet annealing is omitted and pickling is performed with only hydrochloric acid, the mechanical properties of the thin sheet product are not taken into consideration in any of these methods. In addition, Japanese Patent Application Publication No. 1983. = Grain boundary corrosion does not occur if pickling is carried out with only hydrochloric acid as in the method described in Publication No. 158819, but pickling takes a long time and is not practical. Increasing the shot gelatinization will increase the roughness of the surface.

The present invention aims to omit the annealing process of hot-rolled sheets in the production of austenitic stainless steel sheets or copper strips, and to achieve surface properties and mechanical properties that are equal to or better than those of thin sheet products manufactured through the conventional annealing process, especially in terms of their surface properties. The purpose is to obtain a product with small internal anisotropy.

The method of the present invention limits the composition of austenitic stainless steel, controls the rolling reduction rate and biting temperature in hot finish rolling, and pickles the hot rolled sheet using a solution with an appropriate composition. The manufacturing method involves cold rolling and annealing.

The composition of the austenitic stainless steel used in the method of the present invention is co, oos ~ 0.07 cm, 81: 1.0% or less, Po, 0.40 cm or less, SO, 0% by weight.
10% or less, Mn 3.0% or less, Ni 6. 'O~1
1.5%Cr 16~20%, NO,005~
0.2%, Mo 4% or less, Cu
4% or less of one or both, and 2C and N
+ Points A, B, in Figure 1 depending on Nl and P content
, C, and D (where p indicates the P content X10 q6, and points B, , C, are each determined by the P content), and the remainder consists of Fe and unavoidably mixed impurities. After hot rough rolling a slab of austenitic stainless steel having such a composition, at least one pass, preferably each pass, is performed at points A, B, C, and D in Fig. 2 in hot finishing rolling. , l13 at a rolling reduction rate and biting temperature to form a hot rolled steel sheet or copper strip.

without annealing the hot-rolled steel sheet or copper strip with (after mechanical descaling if necessary) (20 as N03)
~130 g/13 as nitric acid and HCl 50-300
Pickling is carried out using solution # in which a ferric salt is added to a nitrate aqueous solution containing 1 liter of hydrochloric acid so as to contain 3 to 90 Ve as FeS+ ions.

The pickled hot rolled steel sheet or copper strip is cold rolled and annealed by a known method to produce a thin sheet product.

According to the research of the present inventor, the first problem, the increase in in-plane anisotropy of austenitic stainless steel thin sheet products, is due to the development of a strong mixed structure unique to stainless steel thin sheet products. Chemical components, especially C1N・Mn r Ni r P, make a large contribution to the randomization of the texture. In addition to these, the rolling reduction and biting temperature during hot finish rolling also have a large effect on the anisotropy.

First, the contribution of the composition of austenitic stainless steel and the reasons for limitations in the present invention will be explained.

C: C is the factor that has the greatest influence on the anisotropy improvement of austenitic stainless steel thin plate products for which hot rolled plate annealing is omitted, and its effect is exhibited at 0.07% or less, and lower values are desirable.

However, it is industrially difficult to keep it below 0.005%.
, if you dare to implement it, the price will be high, so set the lower limit to 0.00
It was set as 5.

st: st is a strong deoxidizing agent and is effective in removing oxygen harmful to workability, but if it becomes too high, it inhibits hot workability, so it is set to 1.0 or less.

Mn: Mn Fi shows the same effect as Ni with respect to anisotropy, and the lower the value, the better the anisotropy. The effect is 3.
The upper limit was set at 3.0% because it becomes noticeable below 0%.

Cr: Cr does not have a significant effect on anisotropy and workability, but 16 or more Cr is required to maintain corrosion resistance. However, when it exceeds 20 inches, ferrite t increases and hot workability deteriorates. For this reason, the range of Cr was limited to 16 to 20%.

Ni: Ni is an element that affects anisotropy, and the lower the Ni, the better the anisotropy, but the higher the elongation, the better. Therefore, if it is too low, it will inhibit the workability, and if it is too high, it will increase the anisotropy.
+N and P. In the present invention, N1 is set to 6.0 to 11.5% in relation to the above components.

N: N is also preferably lower for anisotropy, 0.2%
The following values are good, and from an industrial and economic point of view, it is desirable that it be as low as possible. However, it is industrially difficult to reduce the N content to less than 0.005%, so the range of N is set to 0.005 to 0.2%.

P: Similarly to Cr Mn r Ni + N, the anisotropy is improved when P is lower. The improvement in anisotropy due to lower P expands the allowable range of these components within the range shown in Figure 1 in relation to Mn+Ni and 2C+N, and has an advantageous effect on elongation and improvement of the Erichsen value. do. Therefore, it is desirable to have a lower value, but it is set to 0,040 or less, which can be reduced industrially and economically.

S: Reducing S improves various corrosion resistances of thin sheet products manufactured by a process that omits hot-rolled sheet annealing. The effect becomes noticeable at 0.010% or less, and the lower the content, the more desirable it is.

Furthermore, in the present invention, as a result of experimental testing of a large number of samples, in addition to the above-mentioned addition range, each component is particularly C + N +
For Mn + Ni r P, point A in Figure 1.

B, , C,,,D (I mark p is P content x 10
In order to improve the in-plane anisotropy and processability of thin sheet products, it is essential to set the range surrounded by the points B, , and Cp, each of which is determined by the P content salary. It was confirmed that the conditions and conditions were as follows.

In FIG. 1, lines A, B, and C are the limits where anisotropy is restricted, and in the range above these, the earring rate increases rapidly and the quality of fI4 board products deteriorates. In the figure, the line Bo
Co'+B1 (4,'++B2C2+Bs,C3
+B4 C4 has P views of 0%, 0.01%, and 0.02 respectively.
%, 0.03%.

This is the limit line for the case of 0.04%.

The line AD indicates the lower limit of the amount of Mn + Ni,
If the Mn + Ni ratio is lower than this, the austenite phase becomes too unstable and elongation deteriorates. Lines C and D are 2
This indicates the lower limit of the amount of C+N, and if the amount of 2C+N is lower than this, the manufacturing cost will increase rapidly and it will be less economical. Therefore, Ch
N + Mn r Ni * Let's not talk about P.
All of them must satisfy the range surrounded by points A, B, , C, and D in Figure 1.

Further, one or both of the above chemical components 11, Mo 4% or less and Cu 4% or less are added as necessary. Mo
+Cu is usually contained as an impurity in an amount of about 0.2 to 0.3%, but in the present invention, it is added in an amount exceeding this amount if necessary.

Mo: Mo is an effective component for improving corrosion resistance, and is added at an upper limit of 4% especially when it is necessary to improve the corrosion resistance of hot-rolled sheets or cold-rolled sheets.

Cu: Cu exhibits the same behavior as Ni as an austenite-forming element. Therefore, by adding Cu, it is possible to reduce the amount of Ni corresponding to the amount of Ni, and the manufacturing cost can be reduced, so it is added when necessary.

However, when Cu exceeds 4%, hot workability is significantly impaired.
Edge cracking occurs during hot rolling. Therefore, the upper limit of Cu was set at 4%.

In addition to the above-mentioned chemical components, hot rolling and finish rolling have a large influence on the reduction of anisotropy, and act additively to the effects of the above-mentioned components.

Normally, hot rolling is divided into rough rolling and finish rolling, but since rough rolling is finished at a high temperature of 1050° C. or higher, the structure after rolling becomes phase crystal grains that have completed recrystallization. However, when several passes of finish rolling are subsequently performed, recrystallization occurs during rolling, and the If4 weave of the hot rolled sheet has extremely small crystal grains. When a hot-rolled sheet with such a fine-grained structure is annealed, it becomes difficult to annealing the sheet. 211) The <111> component increases extremely and the anisotropy becomes significant. On the other hand, when a steel plate after rough rolling is left on a runout table for a few seconds to lower the temperature and finish rolling is started, the structure of the hot rolled sheet is such that the coarse grain boundaries generated during rough rolling extend in the rolling direction. This results in a so-called elongated grain state, and the area of grain boundaries becomes significantly smaller than under the above conditions. Even if such a hot-rolled sheet is cold-rolled without annealing, the texture of the thin sheet product after final annealing becomes random and the anisotropy is improved. That is, if the biting temperature during hot-rolling finish rolling is lowered to make the hot-rolled sheet structure into elongated grains, the anisotropy of the thin sheet product will be improved and the earring ratio will be reduced even if annealing of the hot-rolled sheet is omitted.

As a result of numerous experiments, the inventors of the present invention have found that in order to achieve the object of the present invention, after normal rough rolling is performed using a continuous hot rolling mill, hot finishing rolling is performed for at least one pass or more. It was confirmed that it was necessary to carry out each step at a reduction rate and a biting temperature within the range of PQR8T P shown in Fig. 2.

The conditions in the range of PQR8TP in Figure 2 are such that recrystallization does not occur.
That is, the rolling conditions are such that the crystal grains after rough rolling are simply expanded into grains and the grain boundary area can be kept to a minimum.

In FIG. 2, the upper limit of the biting temperature is regulated by line PQ and line QR, but if finish rolling is started at a higher temperature than this, recrystallization will occur during finish rolling and the structure will become fine grained. Furthermore, when the biting temperature decreases (sTJ, #), the deformation resistance increases, and surface flaws rapidly increase, impeding productivity. The rolling reduction rate is line R
When it is larger than 8, surface flaws increase and at the same time, edge cracks begin to occur. If the rolling reduction rate is lower than the line TP, the finished plate thickness will become extremely thick or the number of passes will increase, resulting in a decrease in rolling efficiency.

Therefore, the finish rolling conditions are PQR8TP shown in Figure 2,
The rolling reduction rate and biting temperature must be within the shaded range.

Next, regarding the second problem of surface quality, if the hot rolled sheet is descaled using a nitric acid solution containing ferric ions, the surface will become rough regardless of the winding conditions during hot rolling. A good surface skin with no blemishes can be obtained in a short time. When descaling hot-rolled sheets, using the pickling solution adjusted to an appropriate concentration significantly improves descaling properties, making it possible not only to remove scale with a short immersion, but also to improve cooling after hot-rolling. It has been found that even in a hot-rolled sheet where the descaling speed is slow and some carbides are precipitated at the grain boundaries, intergranular corrosion is less likely to occur, resulting in an extremely beautiful surface finish after descaling.

The reasons for limiting the component composition of the descaling solution will be explained below.

HNO3 coexists with HCt and Fe5 ions to strengthen the pickling action and remove the potential range where intergranular corrosion occurs.
Therefore, even if carbides are precipitated at the grain boundaries, the pickling action prevents the skin from becoming rough. For this action, 201//
ll ~1301//e, preferably 30 Vi ~
1001//i is required.

HCl strengthens the pickling action in place of conventional HF in the coexistence of HNO and Fe5+ ions, and
Coexists with e3+ ions, removes the potential range where intergranular corrosion occurs, and prevents pickling surface roughness even if carbides are precipitated at grain boundaries.1o For this action, HCl, HNO3, and F
e The balance of ions is important, and as HCt, Ha5
0g/l~300g/e hope 1oooy/l~2o
oVl is required and is 6. Fe ions are extremely effective for descaling stainless steel, and HNO and HC
It coexists with t, strengthens its descaling effect, and removes the potential range where intergranular corrosion tends to occur, so that even if carbides are precipitated at grain boundaries, pickling does not cause roughness. For this effect, Fe ion is 3~9011/13, preferably 10~
70 f//e is required. To add Fe'+ ions, FeCl31 pe2(so4)3. Pa(
Ferric salts such as No. 5) 3 can be used.

In addition, in descaling the hot rolled sheet, mechanical descaling is performed as necessary before pickling.

In the method of the present invention, the hot-rolled sheet is not annealed, and the hot-rolled finish rolling temperature is lower than that in the conventional method, so the scale is thinner than in the conventional method. Therefore, scale can be removed only by pickling under the above conditions without performing mechanical descaling such as shot shirasu, which has been conventionally generally performed. However, mechanical descaling is preferable because it reduces the load of pickling.

The descaled hot-rolled sheet is cold-rolled and annealed by a known method to produce a thin sheet product. Cold rolling can be performed in one step up to the thickness of a thin sheet product without any intermediate annealing process without causing any material quality problems. If the thickness of the product is particularly thin and it cannot be cold-rolled in one step, it may be annealed and pickled in the middle and then cold-rolled.

EXAMPLES The present invention will be specifically explained below using examples.

Austenitic stainless steel having the components shown in Table 1 was melted using an electric furnace-AOD method to obtain a continuously cast slab with a thickness of 160 mm. After that, it was heated to 1250° C. in a heating furnace to perform phase hot rolling, and then finish hot rolling was performed under the conditions shown in Table 2. The coils after finish hot rolling were wound up in an air-cooled state.These hot rolled sheets were not subjected to solution heat treatment, and after mechanical descaling by shot blasting, HNO5-HCt-F'eCt3 with the concentration shown in Table 3 was obtained. Pickling was performed by immersing the sample in the solution for 50 seconds. Cold rolling was carried out using a Zen-shimia mill to give a final plate thickness of 0.7 mm. Final annealing is 1100
A product plate was obtained by quenching at 55 seconds in the oven and pickling.

After observing the surface gloss of the product board, a scale test was conducted. Material tests were conducted for 0.2% yield strength, tensile strength, elongation, and earring percentage.

The earring ratio (he) was calculated using the following formula.

Here, indicates the height from the bottom of the cup to the top of the peak at the edge of the cup, and h2 indicates the height from the bottom to the trough.The hot-rolled plate descaling of the comparative material is the same as above. After performing all shot blasting under the same conditions, the specimens were immersed in a )LNO,-)IF bath solution for 50 seconds, washed, and subjected to cold rolling.

Table 3 shows the material tests and test results after cold rolling and annealing.

The chemical composition and hot rolling conditions satisfy the conditions shown in Figures 1 and 2, respectively, and the pickling of the hot rolled coil is carried out using HNO-HCt.
The austenitic stainless steel copper plate produced under the manufacturing conditions of -Fe C1-5 solution has excellent surface quality even if hot-rolled plate annealing is omitted, and at the same time has a small earring ratio and improved anisotropy. It can be seen that the elongation is large and the workability is excellent. Good results were also obtained regarding various types of corrosion resistance of the product plate.

Table 2 Hot rolling conditions of Examples Table 4 Tensile properties, earring ratio and surface conditions of Examples The present invention can omit hot rolled plate annealing in the production of austenitic stainless steel plates or copper strips, reducing production costs. . The obtained thin sheet products have excellent surface quality similar to products manufactured through conventional manufacturing processes, and have low earrings generated by deep drawing. It is possible to reduce the blank size, reduce dust, and greatly improve yield.

[Brief explanation of the drawing]

~IJ1 diagram is a diagram showing the relationship between Mn+Ni first, 2C+N amount, and pg- of the starting steel slab defined according to the present invention. B and C9 are determined by the P content, and the coordinates of each point are Bo (10,010,3), Bl (9,5,0,3)
, B2 (9,0,0,3). B3 (&5+0.3), R4 (8,0,0,,3) and Co (13,5,0,02). C'+ (13,0,,0,02), Cz (12
,5,0,02),C3(12,0,0,02). C4 (11,5,0,02). FIG. 2 is a diagram showing the relationship between the biting degree and the rolling reduction ratio of the pass during finishing hot rolling in the method of the present invention.

Claims (1)

[Claims] (In weight%, C: 0.005 to 007%, Si: 1.0% or less Mn
: 3.0% or less, Cr: 16-20%N
i: 6.0~11.5chi jN: 0.005
~0.2%P: 0.040% or less, S:
0.010 chi or less, and 2C0N is Mn + N
Points A, Bp, C in Figure 1 depending on i and P content
p, D (where p indicates P content x 10 pieces, and point B
p, C, are respectively determined by the P content), and after hot rough rolling a slab of austenitic stainless steel consisting of the remainder Fe and unavoidable impurities, at least Hot-rolled steel sheets or copper strips manufactured by performing one or more passes at the reduction rate and biting temperature in the ranges surrounded by points P, Q, R, S, and T in Figure 2 can be processed as needed without annealing. After mechanical descaling, 20-130Ii/13 of nitric acid and HNO,
Pickling is performed using a solution prepared by adding ferric salt to a nitric acid aqueous solution containing 50 to 30011/l of hydrochloric acid as Cl so as to contain 3 to 901/l of Fe ions, and then cold rolling and annealing. A method for producing an austenitic stainless steel plate or a copper strip, characterized by: (2) In terms of weight, C: 0.005 to 0.07%, St: 1.0 or less, Mn: 3. 0% or less, Cr: 16-201N
i: 6.0-11.5%, N: 0.005-0
．． 2%P: 0.040% or less, S: 0.010%
Points A, B, , C, D in Figure 1 (where p indicates the P content 4: X 10-''%, and point B
, , C, are respectively determined by the P content), and furthermore, Mo: 496 or less r Cu
: After hot rough rolling a slab of austenitic stainless steel containing 4% or less of one or both, the balance being Fe and unavoidable impurities, at least one pass or more is applied to point p in FIG. 2 in hot finishing rolling. After mechanical descaling as necessary without annealing the hot-rolled steel sheet or copper strip produced by rolling reduction and biting temperature in the ranges enclosed by Q, R, S, and T, 20% HNO3 ~130g/
50 to 3001/(1) as nitric acid and HO2 (3 to 90 g as Fe io/to a nitric acid aqueous solution containing 1)
1. A method for producing an austenitic stainless steel sheet or a copper strip, which comprises pickling using a solution containing a ferric salt such that the austenitic stainless steel sheet or copper strip contains 1/1, followed by cold rolling and annealing.