DE1231279B - Process for the production of steel strip - Google Patents

Description

FEDERAL SAE PUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C21c

German class: 18 c-9/52

Number: 1 231279

File number: U 12033 VI a / 18 c

Filing date: September 14, 1965

Opening day: December 29, 1966

The invention relates to a method for the production of steel strip, in particular for Processing to tinplate is suitable, made of non-killed steel with a maximum of 0.05% carbon and maximum 0.15% manganese through cold working.

At present, steel strip is either in a ductile, annealed state with a recrystallized structure (which can also have been rolled for the purpose of tempering) or as high-strength, not annealed Material available with a cold worked metallurgical structure. When using steel tape a compromise with respect to ductility has to be made at a desired high strength or the other way around. Considerable amounts of steel strip are used in manufacture as tinplate used by cans and containers. If this involves significant deformation and machining is, such as B. in the manufacture of containers, the steel belt must be so ductile that it at does not tear during the molding process. However, the containers themselves must have great strength.

The present invention provides a method of making a steel strip having a novel metallurgical structure which causes the strip to have improved ductility upon deformation while maintaining great strength. The novel structure is created by starting with a non-killed steel, the maximum carbon and manganese content of which is 0.05 and 0.15% and cold-reducing the steel to a desired thickness. The cold-reduced strip is then annealed at 425 to 620 ° C. until the edge zone essentially recrystallizes, but the core essentially does not recrystallize. Another inventive method is characterized in that the strip is annealed by batch in 16 to 24 hours at a temperature in the range of about 468-496 ⁰ C. According to another embodiment of the method, the strip is continuously annealed 10 to 30 seconds at a temperature in the range of about 565-593 ⁰ C.

It is possible to improve the ductility of high strength strip material, i.e. H. of partially or completely hardened strip material, to be improved by annealing. However, it is becoming more common, partially or completely hardened steel annealed, then the recrystallization takes place arbitrarily in the whole band, with with the result that the strength is substantially reduced. Annealed "black plate" is an example for soft steel strip material with good deformation properties but relatively low strength. »Black sheet« is a cold-reduced product process for the production of steel strip

Applicant:

United States Steel Corporation,

Pittsburgh, Pa. (V. St. A.)

Representative:

Dipl.-Ing. M. Licht, Dr. R. Schmidt,

Dipl.-Wirtsch.-Ing. A. Hansmann

and Dipl.-Phys. S. Herrmann, patent attorneys,

Munich 2, Theresienstr. 33

Named as inventor:

Andrew Lesney, Tarentum, Pa. (V. St. A.)

Claimed priority:
V. St. v. America September 15, 1964
(396 765)

0.3581 mm thick or less that is not actually black and used to make tinplate and sheet metal or plate material used for other purposes. On the other hand, a steel can can be made of high strength even in very small thicknesses, however a steel band is made of such a material is generally so hard that it will crack if it is severely deformed. Unannealed, cold-reduced black plate and so-called »fine« - Sheet metal are examples of such a material. "Fine" tinplate is made by using a double cold reduction, which not only significantly reduces its thickness (to approximately 0.111 mm), but also considerably increases its hardness and tensile strength.

The present invention describes a method for producing steel strip, the one has recrystallized surface, which gives the tape greater ductility than unannealed high-strength tape material, and a fibrous, d. H. cold worked core that gives the tape a tensile strength greater than that of conventional annealed strip material. It has been found that it can be achieved by using an unquieted Steel with a maximum carbon content of 0.05% and a maximum manganese content of 0.15% and a controlled heat treatment

609 749/292

3 4

is possible, the cold-reduced band with such a steel band usually for the purpose of tempering Composition to anneal so that the surface rolled to favor its surface finish recrystallizes while the core is in better shape to flatten the tape and its mecha-essential not recrystallized. To improve the surface of the niche properties. That for the purpose cold-reduced, unkilled steel is recrystallized 5 tempering rolled strip is pickled and can sized by being hot-dip tinned or galvanically tinned at a temperature in the range, is annealed from about 420 to 625 ° C for so long. When hot-dip tinning, the strip is bathed until the cold-reduced edge zone of the strip is passed in the molten tin, where there is an over-essential is recrystallized, but does not receive as much tension as the metal, which solidifies on cooling, long that the cold-reduced core of the strip noticeably io Electrolytic tinning can be done either in lent is recrystallized. acid or alkaline electrolytes The term used here "unkilled steel" is used in which the tape is connected as a cathode refers to a steel that is in a mold and metallic tin on the surface of the strip was made to freeze, that the difference will be made.

On the surface of the cast block, an edge zone of purer 15 doubly reduced tinplate material is made of metal than is present in the core. Such a steel is made by tapping the cold-reduced steel after one is usually tapped without the intermediate deoxidizing annealing, which is usually added to the furnace at about 675 ° C, so that sufficient oxygen is available to completely recrystallize the steel to be allowed to act with a second cold reduction from the carbon present in the steel, 20 is set. The second cold reduction is when the steel is poured into a mold. the thickness of the strip is reduced by about 40%. The carbon-oxygen reaction increases the gas and the strength as well as the hardness considerably, develops it and, as the metal begins to solidify in the mold, increases the evolution of gas in the steel strip material in the same way as along the surface of the mold wall. On the basis of the above described, but with no gas evolution, an outer shell or calm steel is used which no longer contains as the edge zone of the ingot of relatively pure 0.05% carbon and 0.15% manganese, as well as metal . Because the solidification of the metal is carried out by a controlled heat treatment of a layer of relatively pure, liquid. The cast block made of unkilled steel runs out of metal, consists of the entire solidified edge zone 3 ° rolled into blocks and then at over 76O ⁰ C, ahead of iron, which has a relatively low proportion, preferably between 760 and 870 ° C, to the usual amount of residues and alloy components hot-rolled to "hot strip thickness" and then whipped. Becomes entangled after solidification of the restless. The rolled up, unkilled steel is rolled as a cast steel block, for example into strips, then cold-reduced to the desired thickness, after which the edge zone remains on the surface. 35 it is annealed at a temperature in the range of approximately the relatively pure metal in the edge zone 425 to 620 ° C for so long that although this brings about an excellent quality of the rolled, cold-reduced, unsmoothed surface of the strip surface, which recrystallizes characteristic of the production, but not the tape core, which retains its fibrous metal structure, which is cold-reduced from objects made of unevenly cast blocks. It is. For the production of tinplate material, a 40 is important, the annealing temperature range, in particular steel strip, is created in that blocks whose origin - the upper limit, i.e. 620 ° C., is precisely adhered to, the thickness is about 101.60 to 177.80 mm, becomes higher Temperatures applied, then takes place at about 815 ° C to a single continuous - not the preferred recrystallization of the strip, borrowed strip of "hot strip thickness", ie of an arbitrary but an arbitrary recrystallization of its approximately 2.032 mm thickness are hot rolled, which after 45 structure. If temperatures below about descaling are used for further processing up to 425 ° C, then the annealing requires rolls to be wound up. Of course, the surface crystallization depends on an unduly long time, particular thicknesses and procedures on which it is desirable that 100% of the edge zone of the end product be used. In order to produce the tape recrystallized by the annealing treatment, the usual, commercially available tape should be recrystallized, while the core is intended to recrystallize as little material as possible, ie black plate that is tinned. However, the tape rolls can also be continuously pickled and a tape which is satisfactory for many purposes is produced and then cold-reduced to its final thickness. Become, the surface of which is only 50% recrystallized, becomes homely, the tape has been cold-reduced by 80 to 90%; recrystallization of the core and in preparation for annealing and tinning 55 can also be tolerated to a lesser extent. The degree cleaned. The cold-reduced black plate is quite the recrystallization allowed in the core, and must be hard, for most uses, generally less than 30% depending on being softened by annealing. The annealing of the strength of the desired end product can be carried out intermittently, through the so-called box, since the strength anneals with increasing recrystallization, or it can be carried out continuously. 60 decreases. In any case, when performing the box annealing of steel strips, which are required for the production of the method according to the invention, that the position of tinplate is determined, the surface or edge zone in a thicker strip is usually recrystallized in the wound state 4 to the extent that the core . Heated the upper 12 hours at approximately 620 to 675 ° C. The surface recrystallization of the strip from unquenched continuous annealing can occur at high speeds. B. 305 to 700 m / min, by continuous box annealing, in which the band ratio-heat treatment of non-wound strip material is kept moderately long at the annealing temperature, are carried out. After the glow, lower temperatures can be used,

whereas higher temperatures are required with continuous annealing, since only a short treatment time is possible with continuous work. So z. B. recrystallize a band of unkilled steel by box annealing at a temperature of about 455 to 510 ° C in 4 to 30 hours on the surface in the preferred manner, while this in the case of continuous annealing at a temperature of 565 to 62O ⁰ C only in 10 to 30 seconds takes place. ίο

Preferred surface recrystallization of the steel strip can only be achieved with an unkilled steel can be achieved, the carbon and manganese content is limited to 0.05 and 0.15% and the was annealed in the manner described above. Steels whose compositions have these limits exceed, recrystallize randomly and not preferentially on the surface. Table 1 shows the Results of a series of tests carried out with two cold-reduced, non-killed steels. Sample "1" contained 0.03% carbon and 0.08% manganese, while sample "2" contained 0.04% carbon and contained 0.18% manganese. The steel samples were of different lengths at different temperatures annealed, and the degree of recrystallization in percent both in the edge zone and in the core was found at all time and temperature conditions. It can be seen that the recrystallization of steel sample "2" containing 0.18% manganese was not preferentially made on the surface. A Similar behavior was found with a carbon content of over 0.05%. Table 1 follows.

Table 1 Glow Glow time Template " 1 «(0.03% C, 3.08 ° / ₀ Mn) core Sample »2« (0.04% C, 0.18% Mn) % Recrystallization 0 temperature Hardness* % Recrystallization 0 Hardness* Edge I core 0 ⁰ C 0 R30-T edge 0 R30-T 0 0 comparison 1 hour 77.9 0 0 79.0 0 0 426 8 hours 74.8 0 0 77.5 0 0 16 hours 74.5 0 0 76.5 0 0 24 hours 74.5 0 0 76.0 0 30th 1 hour 74.2 0 0 75.8 0 75 482 8 hours 74.2 5 0 74.8 30th 85 16 hours 70.7 20th 0 69.0 75 0 24 hours 69.3 100 0 63.2 85 5 0.33 minutes 69.3 100 0 62.8 0 80 537 1 minute 74.8 0 0 76.0 5 90 5 minutes 74.0 10 0 74.2 80 95 10 mins 69.7 75 0 65.0 90 100 15 minutes 70.0 75 0 59.8 95 100 30 minutes 69.0 100 20th 59.2 100 100 0.33 minutes 68.7 100 30th 57.5 100 100 593 1 minute 69.0 100 50 59.5 100 100 3 minutes 66.5 100 70 58.5 100 5 minutes 64.0 100 57.2 100 63.2 100 56.7

* Each hardness value is the average of five measurements.

The steel samples used in the experiments given in Table 1 were small samples (2.54 x 5.08 cm) made from a strip of 90% cold reduced (fully hard) black plate 1.676 mm thick. The samples were submerged in molten salt heat treated according to the time and temperature conditions given in Table 1 and then in air chilled. Rockwell hardness tests and metallographic studies were performed to determine the hardness and determine the percentage of recrystallization. The steel patterns "1" and "2" had the following Composition:

Pattern "1" Pattern "2" C 0.03 C 0.04 Mn 0.08 Mn 0.18 P 0.010 P 0.010 S 0.025 S 0.023 Si 0.008 Si 0.007 Cu 0.02 Cu 0.02 Ni 0.01 Ni 0.01 Cr 0.02 Cr 0.02 Mo 0.01 Mo 0.01 Fe rest Fe rest

The in F i g. 1 and 2 show pictures in 250x magnification of preferably recrystallized Plates of unkilled steel after etching with a mixture of nitric acid and Alcohol, in which the recrystallized grains on the surface and the cold-worked fiber structure lie in the middle. After the preferred surface recrystallization, the steel strip contains one fibrous cold-worked core approximately 0.127mm thick sandwiched between two surface layers of 0.0254 mm thick of fully recrystallized ferrite is sandwiched. The tape, its cuts in Fig. 1 and 2 had the same composition as sample "1" of Table 1. That Sample according to FIG. 1 was simulated for 20 hours at a temperature of approximately 468 ° C Box annealing and the pattern according to FIG. 2 of a simulated box anneal lasting 20 seconds exposed at a temperature of approximately 579 ° C.

When carrying out a series of tests as shown in Table 1 ao is shown, it was found that under optimal box annealing conditions, the annealing temperatures 468 to about 496 ° C and the annealing times from 16 to 24 hours. It was found that the optimal conditions for continuous annealing at a temperature of about 565 to 593 ° C reached over a period of at least 10 seconds, preferably 20 to 30 seconds will. Table 2 below provides a summary of a series of tests in which the recrystallization was found in short (20 seconds) annealing processes. With these The tests were carried out on steels with the same compositions as sample "1" and sample "2" in Table 1 used. It can be seen that the pattern with the limited carbon and manganese content (Pattern »1«) was preferentially recrystallized on the surface, while a recrystallization of the core only take place when the edge zone is essentially completely recrystallized. In contrast to there was no preferential surface recrystallization with pattern "2", but instead an arbitrary one Recrystallization to the same extent in the core as in the edge zone.

Table 2

Pattern "1" 2, 0.08% Mn) core Pattern »2 2, 0.18% Mn) core Glow (0.03% < Recrystalli 0 (0.04% < Recrystalli 0 temperature ¹ ) hardness sation 0 hardness sation 5 R30-T edge 0 R30-T edge 70 ° C 0 50 0 100 comparison 77.9 5 50 79.0 0 100 537 75.0 25th 70 76.0 70 100 565 73.0 100 90 66.0 100 100 593 70.0 100 95 59.7 100 100 621 65.0 100 58.5 100 648 59.5 100 57.0 100 676 58.8 100 56.3 100 704 56.3 55.3

^x ) The samples were exposed to the temperature for 20 seconds.

Unkilled steel consists in that there is increased ductility at the expense of only a minimal decrease which has tensile strength. The improved ductility can be seen from Table 3, which is the number which indicates bends of 180 ° that patterns of different types of tape could withstand the showed the first signs of breakage. The steel sample A, which was in the completely hard state, became produced by cold rolling without subsequent annealing. Samples B and C were made according to Invention subjected to a simulated box or continuous anneal, and sample D is a double-reduced tinplate that is placed between the first and the second cold reduction one was subjected to the usual intermediate annealing.

Table 3

number Cross tensile strenght
kg / mm ² Q ** Stretch
border
kg / mm ² of the bends bend 74.62 template by 180 °
until the first
Signs 3 61.60 a break 16 L * 56.00 L * Along 19th 74.34 72.38 73.57 bend 8th 56.28 54.95 A. 19th 52.92 52.50 B. 29 66.29 66.29 C. 37 D. 25th

A = Completely hard (unannealed condition).

B = simulated box annealing at 468 ° C,
Duration 20 hours.

C = simulated continuous annealing at 579 ° C,
Duration 20 seconds.

D = Usual double-reduced tinplate.
* Longitudinal direction.
** Cross direction.

45 Table 3 also shows that the tensile strength of the is preferred at the surface recrystallized ribbon remains satisfactorily high despite annealing to improve ductility.

The tensile strength of the usual, annealed black plate (not included in Table 3) is only 42.00 to 45.50 kg / mm ² , while the tensile strength of the strip crystallized on the surface is over 52.50 kg / mm ² and even 61, 60 kg / mm ² can reach.

The steel strip produced according to the invention is particularly suitable for the production of tinplate. A tin coating can be applied to the tape using conventional techniques.

60

Claims (3)

Claims: A great advantage of the surface recrystallized tape produced according to the invention 1. Process for the production of steel strip, in particular for processing into tinplate suitable is made of unskilled steel with a maximum of 0.05% carbon and a maximum of 0.15% manganese by cold deformation, thus marked characterized in that the strip is annealed at 425 to 62O ⁰ C until the rim is substantially recrystallized, but the core is not substantially re-crystallized. 2. The method according to claim 1, characterized in that the tape 16 to 24 hours at is annealed in batches at a temperature in the range of about 468 to 496 ° C. 3. The method according to claim 1, characterized in that the strip is annealed continuously ^{at a temperature in the range of approximately 565 to 593 0 C for 10 to 30 seconds.} 1 sheet of drawings 609 749/292 12.66 © Bundesdruckerei Berlin