EP1238727B1 - Process for manufacturing metallic strip having differing material properties through their section - Google Patents

Abstract

Production of metallic strips (B) having sections of different material properties comprises: (i) melting a low alloyed or micro-alloyed steel; (ii) casting the steel in the casting gap (2) formed between walls of a casting machine (1); and (iii) cooling the cast strip. The force (G1, G2) exerted on the strip in the casting gap and measured over the width of the strip is more than 100 kN/m. Preferred Features: The steel contains (in wt.%) 0.01-0.80 C, 0.30-5.00 Mn, ≤ 0.50 Cr, ≤ 0.10 Al, ≤ 0.80 Si, ≤ 0.05 Ti, ≤ 0.05 Nb, ≤ 0.05 Nb, ≤ 0.01 N, ≤ 0.02 S, ≤ 0.02 P, ≤ 0.2 Ni, ≤ 0.1 Mo, ≤ 0.1 W and a balance iron and unavoidable impurities. The casting machine is a two roller casting machine. The force exerted on the strip in the casting gap and measured over the width of the strip is at least 200 kN/m.

Description

For the production of cast tapes and from them obtained blanks are usually two-roll casting machines, so-called "double roller" casting machines, used. These casting machines are parallel with two Casting rollers arranged to each other, between which a casting gap is formed. When pouring the In rotating rolls, the strip melts from above placed in this gap. The melt solidifies on the Surfaces of the rolls to two shells, which are in the casting gap to be compressed into the band. Because the thickness of the Band is set, is the effective in the casting gap Force depends on the thickness of the tape pressed, solidified bowls on the rollers.

In addition to "double roller" casting machines are others Casting machines in testing or in development. What these machines have in common is that at least a wall of the casting gap is moved during casting and the tape by continuously pressing Shells of solidified molten metal is produced.

An essential goal in the manufacture of cast In practice, tape is a high quality To produce tape material, its material properties are homogeneous over its length and cross section. On such an even distribution of its properties having band can be used both during the Pour the following rolling steps as well as during forming in the intended component shape well and with Process repeatable success.

From Ulrich Rudolphi "Contribution to the assessment of quality of directly cast steel strips, manufactured according to the Two-roll strip casting process ", Shaker Verlag, Aachen 1998, it is known that for the production of a cast tape with a homogeneous Distribution of properties on the one hand in the casting gap the band exerted forces and on the other hand the Temperatures at which the strip leaves the casting gap, direct influence on its material properties to have. According to the known method, a low-alloy or micro-alloyed steel melt melted and one in between moving walls Casting machine formed casting gap to a cast Shed tape, with the casting gap on the tape applied force measured across the width of the belt is more than 100 kN / m. Then that will cast tape cooled in a known manner. to Setting of a uniform structure, It is therefore easy to process cast strip required to keep the tape at a high temperature Exiting the pouring gap to watch out and reduce the emergence of segregations and to avoid a non-uniform temperature distribution on the Avoid excessive belt surface forces in the casting gap. There may also be active post-cooling of the cast tape.

Especially in the field of automobile body construction the demand has been made to use materials for To have available at a reduced weight the manufacture and practical use of Motor vehicles to meet the requirements are. This requirement is met by so-called "tailored blanks" been fulfilled. Such sheets are concerned are boards that are made by combining having different properties Sheet metal blanks are made. That way you can Tailored blanks, for example, in each of the areas be trained particularly resilient, in which they as Body components during practical use or are subject to special requirements during production, while less stressful in everyone else Areas optimal in terms of their weight have reduced thickness.

The production of tailored blanks is technical consuming. Such boards are therefore currently in the Usually only used to manufacture products that have a high added value.

The task is to create a process which is the inexpensive manufacture of metal strip, steel strip in particular, enables one with regard to its later use optimized distribution of its Has material properties.

• Erschmelzen eines niedriglegierten oder mikrolegierten Stahls,
• Vergießen des Stahls im zwischen bewegten Wänden einer Gießmaschine ausgebildeten Gießspalt zu einem gegossenen Band, wobei die im Gießspalt auf das Band ausgeübte, über die Breite des Bandes gemessene Kraft mehr als 100 kN/m beträgt,
• Abkühlen des gegossenen Bandes,

wobei erfindungsgemäß die auf das Band im Gießspalt wirkenden Kräfte gezielt eingestellt werden und benachbarte Streifenbereiche des Bandes gezielt mit unterschiedlichen Abkühlgeschwindigkeiten abgekühlt werden, so daß das erhaltene Band zwischen den unterschiedlich gekühlten-Streifenbereichen und / oder zwischen Streifenbereichen und Kernbereich des Bandes voneinander unterschiedliche Materialeigenschaften, wie Festigkeit, Dehnung oder Abriebfestigkeit besitzt.This object is achieved by a method for producing strips with sections of different material properties, which comprises the following steps:

• Melting of a low-alloy or micro-alloyed steel,
• Casting the steel into a cast strip in the casting gap formed between moving walls of a casting machine, the force exerted on the strip in the casting gap and measured over the width of the strip being more than 100 kN / m,
• Cooling the cast strip,

According to the invention, the forces acting on the strip in the casting gap are adjusted in a targeted manner and adjacent strip areas of the strip are specifically cooled at different cooling speeds, so that the strip obtained between the differently cooled strip areas and / or between the strip areas and the core area of the strip have different material properties, such as Has strength, stretch or abrasion resistance.

When using the procedure according to the invention receive cast strips and blanks made from them, comparable to "tailored blanks", locally have clearly specified certain properties. This can be achieved specifically, if a different cooling different Adjacent areas of the cast tape performed becomes. Sheets with such a distribution and Setting the properties are particularly suitable for Manufacture of automotive body components, at which certain zones are special in practical use Exposed to other zones special requirements with regard to their deformability be put. Likewise generated are according to the invention Tapes for the manufacture of for scaffolding certain components, such as pipes, clamps and similar fasteners determined in which in a certain direction a particular strength, Dimensional stability or comparable is required. The distribution of properties can also be done Adjust the tapes produced according to the invention so that they to manufacture wear-stressed Use components such as channels for bulk goods leave the tapes a wear-resistant, hard Surface with a sufficiently stretchable at the same time Should have core area.

Tapes produced according to the invention and, if appropriate, from them obtained boards show already when leaving the Pouring a distribution of their composition on that is adapted to their respective purpose. This is on the one hand by a suitable dimensioning of the Casting gap effective forces and on the other hand by a targeted cooling of the belt achieved. The invention makes use of the knowledge that through a Control of the forces acting in the casting gap direct influence on the structure of the structure can be taken over which the cast tape has its cross section. That way it can cast tape so influenced already during casting be that it's his for construction materials meaningful properties such as strength, elongation, Abrasion resistance and the like already in the cast state has.

Due to the high level, especially in the case of forced cooling Solidification speed, which occurs during thin strip casting is typical of the process, the Diffusion compensation of the steel accompanying elements largely suppressed. This also applies to interstitially resolved ones Atoms with high diffusion speeds. Both high band forming forces provided according to the invention there is a depletion of steel elements in the strip core on. This "segregation" or "depletion" is all the more larger, the stronger the respective element for segregation inclines. To achieve this effect are specific Belt forming forces of over 100 kN per meter of belt width required, preferably 200 kN / m and more be provided to ensure the desired result to reach.

In the casting gap they are placed on the casting gap bounding walls solidifying band shells compressed. This creates a forming zone from which between the solidified dendritic proportions of the Shells existing, not yet solidified interdendritic melt due to the across the width of the band acting high forces back in the still liquid part of the over the pouring gap Melt pools is squeezed. The remaining Dendrites are iron-rich and poorer Steel accompanying elements as the flowable residual melt between the dendrites.

Because of the high casting forces continuous backflow of the with Melt-enriched steel is created in a central zone of dendrites and Dendritenfragmenten. This way, despite one homogeneously composed melt a tape with over cross-section of inhomogeneous composition, the band core contains fewer alloy elements than the rest of the band. After the original and reshaping of the Due to the small thickness, the tape is quick Cooling down from the pouring heat. As a result, the Band core different properties than the outer areas a tape cast according to the invention. In this way can be inexpensive, for example, by a targeted adjustment of the belt in the casting gap produce a cast tape in which the required strength through its inner core zone is guaranteed, while its outer shells a low wear resistance with better formability possess.For the implementation of the invention Process can be low alloyed or use microalloyed steel alloys, which typically 0.01 - 0.80% by weight C, 0.30 - 5.00% by weight Mn, ≤ 0.50 wt% Cr, ≤ 0.10 wt% Al, ≤ 0.80 wt% Si and the balance iron and unavoidable impurities contain. If a steel with 0.01 - 0.20% by weight of C and 0.30-1.00% by weight of Mn, see above can be created a tape that in the core area higher elasticity and in its outer areas has a high strength. On the other hand, should be a tape generated, which in its inner core area higher strength and greater elasticity on the outside has, this can be done by using a Reach steel alloy, the 0.10 - 0.8 wt .-% C and 1.00 - 5.00 wt .-% Mn contains, this alloy preferably in addition to iron and impurities other than chromium preferably in concentrations of up to 0.5% by weight no further alloying elements are added. In addition, the steel according to the invention can be up to 0.05 % By weight Ti, up to 0.05% Nb, up to 0.01% N, up to 0.02 % By weight S, up to 0.02% by weight P, up to 0.2% by weight Ni, to 0.1% by weight of Mo and up to 0.1% by weight of W. The Origin of the respective areas of the cast tape can by the targeted cooling of the cast tape supported after its exit from the casting gap become.

Has to carry out the method according to the invention a two-roll casting machine has proven itself. Such Casting machine makes it easy to put on the tape exerted force in the casting gap vary that the speed is varied at which the walls bounding the pouring gap move, which in the case of the two-roll casting machine by the Circumferential surfaces of the rollers delimiting the casting gap be formed. The diameter of the rolls is preferably 200 mm to 2000 mm.

By changing the speed at which the walls that delimit the pouring gap become the on them solidifying melt more or less time for building a more or less thick shell given. This is how a two-roll casting machine performs Reduce the speed of the rollers to one Increasing the thickness of the shells. Because at the same time Thickness of the tape to be produced and thus the measure of narrowest point of the casting gap is set to rise the forces acting in the casting gap. The opposite Effect is increased by increasing the speed of the Casting rolls causes.

Alternatively or in addition to a variation of the Speed of the walls delimiting the casting gap the forces in the casting gap can also be Change in those taking place over the walls in question Cooling of the melt solidifying on them affected become. So a larger cooling causes a stronger one Increasing the thickness of the solidified shells and thus higher forces in the casting gap, while by a low Cooling on the walls of the casting gap the thickness of the solidified shells and consequently the casting forces can be reduced.

Is of particular importance in the implementation of the inventive method also following the Exit from the casting gap cooling of the cast band. The achieved Cooling speeds should be at least until Reaching certain limit temperatures of at least 30 K / s be. This can cool the cast strip in at least two successive stages with different cooling rates, where the cooling rate is from the casting heat outgoing temperature range up to 800 ° C should be at least 30 K / s while in the of Temperature range from 800 ° C to 300 ° C preferably at least 10 K / s but at most 500 K / s is. The cooling can be done with splash water as well also done with gases. When cooling takes place due to the small amount made possible by strip casting Strip thicknesses from 0.5 mm to 4 mm in contrast to continuous casting cooling not only close to the surface, but almost at the same time over the entire cross-section of the belt. The in the casting gap due to the effect of the band forming forces generated non-uniform structural state is due to this Way frozen, so that an adjustment of the Characteristics of the individual areas different Compositions due to an otherwise occurring Temperature compensation is prevented.

One with regard to the diversity of the Products that can be produced according to the method of the invention is a particularly advantageous embodiment of the invention characterized in that adjacent portions of the cast tape with different Cooling rates are cooled. The different cooling in the different areas of the cast tape, in cooperation with the inhomogeneous distribution of the alloy elements that a different transformation in the areas is achieved. In this way you can cast Create tapes where not only the core area and the adjacent outdoor areas a have different characteristics, but it zones can also be used in the external areas create their properties for example as a result a specifically reduced cooling the properties of the Core area adapted or as a result of a special strong cooling are clearly different from the Properties of the adjacent area.

The differently cooled sections can in the longitudinal or transverse direction of the cast tape extend. It is also conceivable to only use certain closely delimited sections of the cast tape to cool so that the properties desired there locally narrowly trained, while the remaining band is cooled less, so that this less refrigerated areas other properties mint.

Fig. 1

eine Zweirollen-Gießmaschine in einem Ausschnitt in seitlicher Ansicht;

Fig. 2

einen Ausschnitt eines in der Zweirollen-Gießmaschine gegossenen Bandes in Aufsicht;

Fig. 3

das gegossene Band gemäß Fig. 2 in einem Querschnitt entlang der in Fig. 2 eingezeichneten Linie X-X;

Fig. 4-6

verschiedene Bauelemente im Querschnitt.

Further advantageous refinements of the invention are specified in the dependent claims and are explained in more detail in connection with the exemplary embodiment described below with reference to a drawing. They show schematically:

Fig. 1

a two-roll casting machine in a cutout in a side view;

Fig. 2

a section of a strip cast in the two-roll casting machine in supervision;

Fig. 3

2 in a cross section along the line XX drawn in FIG. 2;

Fig. 4-6

different components in cross section.

The two-roll casting machine 1 has two axially parallel arranged to each other, a casting gap 2 along its Longitudinal bounding casters 3.4 on a Not shown, adjustable cooling device from the inside be cooled with cooling water. The roles 3.4 consist preferably made of a copper alloy and can with a Nickel coating.

The center distance of the casting rolls 3.4 is fixed set that the depth of the casting gap 2 of predetermined thickness D of the cast strip to be produced B corresponds. Are via a controller, not shown the speeds of the opposite direction in the conveying direction F of Band B in the casting gap 2 conveying casting rolls 3.4 adjustable.

The cast strip B is in the vertical conveying direction F conveyed downwards from the casting gap 2. In Delivery direction F extends behind the casting gap 2 below the casting rolls 3.4 across the width of the belt B a cooling device 5.6. Every single one of the nozzles of the Cooling devices 5,6 is also not one Control device shown controllable, so that in nozzles arranged in certain rows or columns apply cooling fluid K, such as water, together as a group, while none of the others at that time Cooling fluid K emerges.

To cast a strip B, melt S is in the Pouring gap 2 poured so that it is above the casting gap 2 forms a melt pool 7. The melt S solidifies thereby on the rotating casting rolls 3, 4 to shells N1, N2, from the casting rolls 3, 4 into the casting gap 2 be promoted. The thickness of the shells N1, N2 at Entry into the casting gap 2 depends on it Dwell time on the casting rolls 3, 4, i.e. the time that passes until they arrive in the casting gap 2.

The shells N1, N2 meet in the casting gap 2 and are squeezed together between the casting rolls 3, 4. The due to the firm attitude of Center distance of the casting rolls 3.4 over the width of the Band B acting, essentially normal to Casting forces acting on the belt surface G1, G2 at least 200 kN / m. As a result of these high casting forces G1, G2 forms a core area in the cast strip B. C, which has properties other than those of it adjacent outer areas A1, A2 of the cast strip B.

The cast strip B then passes through the Cooling devices 5.6. In the example explained here are two in the longitudinal direction L of the tape B extending, distributed over the width of the band B. Stripe areas S2, S4 of a particularly intense, through direct application of cooling fluid K brings about cooling subjected, while in the side of each Strip areas S2, S4 or arranged between them Strip areas S1, S3, S5 direct cooling omitted. This way, in the outer Areas A1, A2 with the stripe areas S1 - S5 in essentially matching zones of different Material properties trained.

Starting from a molten steel, which is 0.01 - 0.2 % By weight C, 0.3-1.0% by weight Mn, up to 0.5% by weight Cr, to contains 0.1% by weight of Al and up to 0.8% by weight of Si, Cast tape produced shows when leaving the Casting gap 2 in the strip core 0.04 wt .-% carbon and the surface of the outer areas A1, A2 0.08% by weight Carbon on. By a far above 30 K / s horizontal, strong cooling in the cooling devices 5,6 the austenite in the core area C in ferrite and pearlite converted. In the direct and therefore special intensely cooled strip areas S2, S4 of the outer Areas A1, A2, on the other hand, develop bainite during it in the not directly cooled strip areas S1, S3, S5 no bainite or martensite is formed. Despite the differences in their chemical composition (e.g. higher carbon content) correspond to the Material properties of these strip areas S1, S3, S5 therefore essentially those of the core area C. According to The belt exits from the cooling devices 5, 6 Area of the band core C and the not directly cooled Strip areas S1, S3, S5 soften ferritic phases, while in the directly cooled strip area S2, S4 in the outer areas A1, A2 of volume B hard phases available.

Assuming a steel melt, the 0.1 - 0.8 % By weight C, 1.0 - 5.0% by weight Mn (in the specific example 1.5 wt .-% Mn) and up to 0.5 wt .-% Cr, so remains in the due to the high cooling rate directly cooled strip areas S2, S4 of the areas A1, A2 near the surface predominantly get austenitic structure, which has a high Has elasticity. Here, manganese acts as Austenite former, the carbon remains in the Austenite in solution. In contrast, arises in the core area C and the not directly cooled strip areas S1, S3, S5 a pearlitic or martensitic phase that has a higher hardness with reduced toughness.

In the examples shown in FIGS. 4 to 6 point the zones Zh, in which the components in question 8,9,10 subjected to high loads in practical use are particularly high strengths, while the other zones Zg, in which the manufacture of the Components 8,9,10 a particularly large deformation takes place, are soft and stretchy. On this way, the components 8,9,10 in a simple manner are manufactured in a material-saving and cost-effective manner can nevertheless be used as carriers for high loads.

REFERENCE NUMBERS

1

Two-roll casting machine

2

casting gap

3.4

casting rolls

5.6

cooling device

7

melt pool

8-10

components

A1, A2

outer areas

B

cast tape

C

core area

D

thickness

F

Delivery direction F

G1, G2

Gießkräfte

K

Cooling fluid K

L

Longitudinal direction of the tape B

N1, N2

from solidified melt S on the casting rolls 3.4 formed shells

S

melt

S1-S5

strip areas

Zh

High stress zones

zg

Less stressed zones

Claims (17)

1. Process for manufacturing metallic strips (B) having sections (S1 - S5) of different material properties which comprises the following steps:

   melting a low alloyed or micro-alloyed steel,

   casting the steel in the casting gap (2) formed between moved walls of a casting machine (1) to a cast strip (B), whereby the force (G1, G2) exerted on the strip (B) in the casting gap (2), measured over the width of the strip (B) amounts to more than 100 kN/m,

   cooling the cast strip (B),

   characterised in that the forces exerted on the strip in the casting gap are purposefully adjusted and adjacent laminar sections (S1 - S5) of the strip (B) are specifically cooled down at different cooling rates, so that between the differingly cooled laminar sections and/or between laminar sections and core section (C) of the strip, the strip produced (B) possesses material properties, such as tenacity, ductility or abrasion resistance which differ from one another.
2. Process according to Claim 1, characterised in that the steel contains (in wt. %) C 0.01 - 0.80 %, Mn 0.30 - 5.00 %, Cr ≤ 0.50 %, Al ≤ 0.10 %, Si ≤ 0.80 %, Ti ≤ 0.05 %, Nb ≤ 0.05 %, N ≤ 0.01 %, S ≤ 0.02 % P ≤ 0.02 % Ni ≤ 0.2 % Mo ≤ 0.1 % W ≤ 0.1 % a balance iron and unavoidable impurities.
3. Process according to Claim 2, characterised in that the steel contains in wt. % 0.01 - 0.20 carbon and 0.30 - 1.00 manganese.
4. Process according to Claim 2, characterised in that the steel contains in wt. % 0.10 - 0.8 carbon and 1.00 - 5.00 manganese.
5. Process according to any one of the above claims, characterised in that the casting machine (1) is a double roller casting machine.
6. Process according to any one of the above claims, characterised in that the force (G1, G2) exerted on the strip (B) in the casting gap (2) amounts to at least 200 kN/m.
7. Process according to any one of the above claims, characterised in that for adjusting the force (G1, G2) exerted on the strip (B) in the casting gap (2) the rate at which the walls delimiting the casting gap (2) move is varied.
8. Process according to any one of the above claims, characterised in that the differingly cooled sections (S1 - S5) in their laminar-form extend in longitudinal direction (L) of the cast strip (B).
9. Process according to any one of the above claims, characterised in that the differingly cooled sections in their laminar-form extend in transverse direction of the cast strip (B).
10. Process according to any one of the above claims, characterised in that the cast strip (B) is cooled down at a cooling rate amounting to at least 30 K/s.
11. Process according to any one of the above claims, characterised in that the cast strip (B) is cooled in at least two stages subsequent to one another at differing cooling rates.
12. Process according to Claim 11, characterised in that the cooling rate in the temperature range starting from the casting heat and reaching up to 800°C amounts to at least 30 K/s.
13. Process according to either of Claims 11 or 12, characterised in that the cooling rate in the temperature range from 800°C to 300°C amounts to at least 10 K/s, however at the most 500 K/s.
14. Use of a strip produced according to a process claimed in any one of Claims 1 to 13 for producing automotive body components (8-10).
15. Use of a strip produced according to a process claimed in any one of Claims 1 to 13 for producing components (8-10) intended for scaffolding construction.
16. Use of a strip produced according to a process claimed in any one of Claims 1 to 13 as pre-material for flexible rolling.
17. Use of a strip produced according to a process claimed in any one of Claims 1 to 13 for producing wear-resistant components.

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