Method for producing a metal product

Abstract

A method for producing a metal product, wherein in a strand casting system, liquid metal is output as a slab from a mold vertically downward in a conveying direction, is guided along a strand guide, and is deflected into the horizontal, wherein the slab is heated in a furnace or inductively downstream of the stand casting system.

Claims

1. A method for producing a steel product, for which liquid metal is discharged from a mold in a strand casting system as a slab vertically downwards in a conveying direction, guided along a strand guide and diverted into a horizontal direction, the slab being heated in a furnace downstream from strand casting system, wherein the method comprises the steps of: a) her the conveying direction behind the mold in a first cooling zone: cooling of the slab takes place in such a way, that a structural conversion from austenite to ferrite occurs near a surface of the slab; b) downstream from the first cooling zone in the conveying direction in a first heating zone: reheating the slab in such a way that a structure conversion from ferrite into austenite takes place near the surface of the slab, the reheating of the slab takes place due to heat equalization in the slab by permitting heat to flow from the interior of the slab to the surface of the slab; c) in the conveying direction behind the first heating zone in a second cooling zone: cooling of the slab in such a way, that a structural conversion of austenite into ferrite takes place near the surface of the slab; wherein the steps a) to c) are carried out while the slab is still oriented in the vertical direction, and d) downstream from the second cooling zone in the conveying direction, in a second heating zone: reheating of the slab in such a way, that structural conversion from ferrite into austenite takes place near the surface of the slab, the slab being heated in the furnace or by inductive heating, wherein, if the slab is heated by inductive heating in the second heating zone, the slab is heated in the furnace in a subsequent heating zone further downstream; wherein at least one further cooling of the slab is carried out after the implementation of step d) in such a way, that a structural transformation of austenite into ferrite occurs near the surface of the slab, wherein, after the implementation of the at least one further cooling of the slab, there is at least one further heating of the slab in such a manner, that the ferrite structure is converted into the austenite structure near the surface of the slab, and wherein chilled beams for cooling are disposed before after the second heating zone and are configured to effect a conversion of austenite to ferrite.

2. The method of claim 1, wherein the surface of the slab is cooled in steps a) and c) of claim 1, to a temperature below the Ac1 temperature.

3. The method of claim 1, wherein the surface of the slab is heated in steps b) and d) of claim 1 to a temperature above the Ac3 temperature.

4. The method of claim 1, wherein the at least one further cooling of the slab takes place as soon as the slab is diverted into the horizontal direction.

Description

(1) Examples of the invention are shown in the drawings, which show the following:

(2) FIG. 1 shows the evaluation of the result of the copper hot shortness of a steel strip over the width of the hot strip for different degrees of intensity of the cooling,

(3) FIG. 2 shows a diagram indicating continuous casting installation with an illustration of a first embodiment of the invention,

(4) FIG. 3 shows a diagram indicating continuous casting installation with an illustration of a second embodiment of the invention and

(5) FIG. 4 shows a diagram of a representation of the structure formation in an edge zone of a slab near the surface during an inventive method.

(6) The present invention relates to a method that is carried out in a continuous casting installation for steel. Conventional slabs, thin slabs or slabs with a medium thickness can be produced.

(7) A first example of the invention can be seen in FIG. 2. The strand casting system 1 has a mold 3, below which is disposed a strand guide 4. The cast slab 2 is deflected by the vertical guide V into the horizontal plane H by means of the strand guide 4 or the downstream rollers. The slab 2 is thereby conveyed in a feed direction F. After the slab 2 is deflected into the horizontal direction H, it is conveyed into a furnace 5.

(8) It is essential that intensive cooling of the slab 2 takes place behind the mold 3 in the conveying direction F (that is, directly below the mold 3), in a first cooling zone 6. For this purpose, an appropriate volume of water is sprayed onto the surface of the slab. The cooling takes place at such an intensity that the structure of austenite is converted into that of ferrite in the edge zone of the slab 2 near the surface.

(9) The slab subsequently reaches a first heating zone 6, which, in the conveying direction, is disposed behind the first cooling zone 6. Reheating of the slab 2 takes place in such a way that a conversion of the structure of the ferrite back into the structure of austenite takes place in the edge zone of the slab 2 near the surface. In the heating zone 7, there is normal or weak cooling, so that the said structural conversion can take place.

(10) In the conveying direction F of the first heating zone 7, there is a second cooling zone 8. Once again an intensive cooling of the slab 2 takes place in such a way that a structural conversion of austenite to ferrite takes place in the edge zone of the slab 2 near the surface.

(11) Finally, downstream from the second cooling zone 8 in the conveying direction F, a second heating zone 9 follows in which the slab 2 is reheated in such a way that a structural conversion of ferrite into austenite takes place in the edge zone of the slab 2 near the surface.

(12) The reference numeral 11 indicates that alternative positions for additional chilled beams for intensive cooling are disposed here in order to effect a conversion of austenite to ferrite

(13) In addition, it should still be mentioned in connection with furnace 5 that a conversion of ferrite to austenite may take place also here, if appropriate warming takes place.

(14) FIG. 2 shows that the strand casting system 1 is designed as a perpendicular bending installation, wherein the bending of the slab from the vertical into the horizontal position takes place in the case of a solid slab core.

(15) As shown in FIG. 3, an alternative embodiment of the invention provides that a strand casting system 1 is used as the vertical bending installation, wherein the bending is carried out with a liquid slab core.

(16) The indicated reference symbols correspond to those of FIG. 2. The first heating zone 7 lies precisely where the slab leaves the vertical V and it is bent around. The furnace 5 is provided as a second heating zone 9.

(17) The diagram indicated in FIG. 4 shows how the structure is changed when the respective changes from austenite to ferrite and back take place.

(18) The slab surface 10 is indicated and the structure in the area of the slab near the surface is sketched. The respective grain diameters are shown diagrammatically here and placed in relation to one another. The last letters for the grain diameters D for three adjacent regions 1, 2 and 3 over the width of the slab indicate the respective status after the corresponding structural conversions.

(19) It can be seen that, from phase conversion to phase conversion, the grain size not only becomes smaller, but also uniform.

(20) In the case of slabs, the grain diameters are in accordance with the ASTM grain size Table of ASTM Nos. 3 to 0.

(21) The following grain sizes are achieved by the conversion:

(22) D 1, 2, 3a: ASTM No. 0 through 2,

(23) D 1, 2, 3b: ASTM No. 2 through 4,

(24) D 1, 2, 3c: ASTM No. 4 through 6,

(25) D 1, 2, 3d: ASTM No. 6 through 7.

(26) ASTM: American Society for Testing and Material

LIST OF REFERENCE SYMBOLS

(27) 1 strand casting system

(28) 2 slab

(29) 3 mold

(30) 4 strand guide

(31) 5 furnace/inductive heating

(32) 6 first cooling zone

(33) 7 first heating zone

(34) 8 second cooling zone

(35) 9 second heating zone

(36) 10 slab surface

(37) 11 chilled beam

(38) V vertical position

(39) H horizontal position

(40) F conveying direction