AT507475B1 - METHOD AND DEVICE FOR PRODUCING HOT-ROLLED SILICON STEEL ROLLING MATERIAL - Google Patents

Abstract

The invention relates to a method and an apparatus for producing hot rolled strip of silicon alloyed steels for further processing into grain oriented electrical steel. The object of the invention is to provide a method and a cast-rolling composite system (1), with which high-quality hot-rolled strip can be produced cost-effectively for further processing into grain-oriented electrical steel. This object is achieved by a method in which the following method steps are carried out in the stated sequence on a cast-rolling composite installation: a) melting a steel having a chemical composition in weight% of Si 2 to 7%, C 0.01 to 0.1%, Mn <0.3%, Cu 0.1 to 0.7%, Sn <0.2%, S <0.05%, Al <0.09%, Cr <0.3%, N <0.02%, P <0.1%, remainder Fe and impurities b) casting a strand (3) with a thickness of 25 to 150 mm on a continuous casting line (2) c) rolling into a strip (4 ) in up to 4 rolling passes immediately after casting the strand, wherein at least one rolling pass is a degree of deformation> 30% or the total degree of deformation of all passes> 50%, d) heating the strip to a final temperature of 1050 to 1250 ° C, preferably 1100 to 1180 ° C; e) finish rolling the strip in a second rolling line (8), then f) cooling and reeling the strip.

Description

Austrian Patent Office AT 507 475 B1 2010-08-15

Description: The present invention relates to a method and an apparatus for producing hot rolled strip of silicon-alloyed steels for further processing into grain-oriented electrical steel strip. The further processing of the hot strip is not the subject of this application; it is done by heat treatments and cold rolling.

Grain-oriented electrical steel, for example, for subsequent processing to laminated electrical steel for transformers or electrical machines, is characterized by low specific Ummagnetisierungsverluste and high magnetic permeability. As the consumption of electrical energy increases and ever higher demands are made on the efficiencies of electrical machines, there is a high demand for high-quality and low-priced electrical sheets.

The production of electrical steel strip can be divided into the following process steps: steel, hot strip and cold strip production, heat treatment and coil coating (see leaflet 401 "electrical steel and sheet", Steel Information Center, Dusseldorf, 2005 edition).

The person skilled in the art is familiar with cast-rolling composite plants for particularly economical production of high-quality hot strips, for example for subsequent processing into automotive panels (see, for example, EP 1662011 A1).

WO 98/46802 A1 discloses a method for the production of grain-oriented electrical steel sheets, where either [0006] a) a specific steel alloy is melted and from this a thin strand is cast in a continuous casting plant, then the strand is cut, the slabs annealed, finish rolled, cooled and rolled up the hot strip; or [0007] b) melting a specific steel alloy and casting a thin strand in a continuous casting plant, then the strand is finish-rolled, cooled and the hot-rolled strip is wound up.

Following the steps according to a) or b), the hot strip is substantially annealed, rolled in a cold rolling mill to the final thickness, decarburized and subjected to a targeted secondary recrystallization. The molten steel alloy contains so-called. Growth inhibitors, namely sulfides, carbides or nitrides of the elements Mn, Cu and Al, which prevent the grain growth of the present after finish rolling structure. Depending on the temperature, these precipitates also act on the recrystallization during the deformation and immediately thereafter in such a way that a microstructure can be formed which is subsequently suitable for the production of a material having the desired grain properties.

The method of the prior art for the production of hot strip rolling is either very energy consuming, or results in quality losses of further processed grain-oriented electrical steel sheets. The compensation ovens used for the annealing of the slabs are also not very compact, which in turn increases the investment costs of the entire system.

The object of the invention is to provide a method and a casting-rolling composite system of the type mentioned, with which high-quality hot strip rolling for further processing grain-oriented electrical steel can be produced inexpensively with excellent magnetic, electrical and geometric properties. A high-quality hot strip rolling stock of this type is understood to mean a hot strip in which the growth inhibitors are finely dispersed and homogeneously distributed in the hot strip.

This object is achieved by a method in which the following method steps are carried out in the order mentioned on a cast-rolling composite system: a) melting a steel having a chemical composition in weight% of

Si is 2 to 7%, C is 0.01 to 0.1%, Mn &lt; 0.3%, Cu 0.1 to 0.7%, Sn &lt; 0.2%, S &lt; 0.05%, 1/7 Austrian Patent Office AT 507 475 B1 2010-08-15 AI &lt; 0.09%, Cr &lt; 0.3%, N &lt; 0.02%, P &lt; 0.1%, remainder Fe and impurities; B) casting a strand having a thickness of 25 to 150 mm on a continuous casting plant; C) rolling into a strip in up to 4 rolling passes immediately after casting

Strand, wherein at least one rolling pass a degree of deformation &gt; 30% or the total degree of deformation of all stitches &gt;50%; D) heating the tape to a final temperature of 1050 to 1250 ° C, preferably 1100 to 1180 ° C; E) finish rolling the strip in a second rolling mill, then f) cooling and coiling the strip.

In this production process, the formation of homogeneously distributed and finely dispersed growth inhibitors, namely sulfides, nitrides and carbides of the elements Mn, Cu, Al but also Cr, by the melting of a specific steel alloy (step a) and the casting of a thin Strand (step b) immediately following rolls of a belt with high degrees of deformation (step c) promoted on a first rolling mill. The degree of deformation φ is defined as _ \ where h0 indicates the thickness before the forming and h ×, the ψ ~ K '[0019] strip or strand thickness after one or more forming steps; the degree of deformation is specified in this application in percent. The heating of the tape (step d) causes the further excretion of growth inhibitors is stopped and already formed precipitates are given at a given kinetics again. If the temperature is lowered again during finish rolling on a second rolling line (step e) and the subsequent cooling of the strip (step f), further homogeneously distributed and finely dispersed growth inhibitors are formed. The manufacturing process can either fully continuous, ie. based on a strand or an undivided band, or in non-continuous batch mode, i. based on slabs.

In an advantageous embodiment of the manufacturing method, the final temperature after heating the tape for a duration t, for which applies t &gt; 15 s, preferably t &gt; 60 s, maintained. By this measure, a higher proportion of possibly present in the band in coarse clusters excretions is resolved. Maintaining the temperature for a time t, t &gt; 90 s, does not make sense, because after this time already all excretions are resolved.

In full-continuous operation, the final temperature of the strip is advantageously maintained in a continuous furnace, which is designed, for example, as a gas-fired furnace or as an induction furnace. As a result, the temperature of the belt in fully continuous operation can be maintained in a particularly compact manner.

In the non-continuous batch mode, the end temperature of the strip is advantageously maintained by winding and unwinding in a coiler oven. As a result, the temperature of the belt in non-continuous operation can be maintained in a particularly compact manner.

In an advantageous embodiment of the method according to the invention, the strip is finish-rolled on a second rolling train in 2 to 6, preferably in 3 to 5, rolling passes. As a result, common thicknesses can be produced in a particularly economical manner.

When finish rolling, it is advantageous if the strip after finish rolling has a final rolling temperature of 900 to 1050 ° C. This will ensure that the strip is finish rolled in a favorable temperature range.

A further advantageous embodiment is that the band within max. 10 s, preferably within max. 6 s, after the finish rolling on a reel temperature is cooled from 300 to 600 ° C by means of an intensive cooling step 2/7 Austrian Patent Office AT 507 475 B1 2010-08-15.

A further advantageous embodiment of the method according to the invention is that the band is cooled at the beginning of the intensive cooling step with a twice, preferably three times, as high a cooling rate as at the end of the cooling step. By means of this temperature control, it is ensured that the structure present after finish rolling is "frozen" as quickly as possible for the subsequent steps. becomes.

With regard to the formation of growth inhibitors, it is preferable that in the molten steel, the sum of the alloying elements Cu + Mn &gt; 0.35% by weight, preferably &gt; 0.55% by weight. To form a sufficiently high number of growth inhibitors, it is advantageous that in the molten steel the sum of the alloying elements S + N &gt; 100 ppm, preferably &gt; 200 ppm. A sufficient amount of Cu, Mn, S and N in the molten steel is advantageous in order to be able to excrete sufficient amount of growth inhibitors into the hot strip.

Advantageously, in the molten steel, the quotient of the alloying elements Cu / Mn &gt; 2.5, preferably &gt; 3.5. Since Cu sulfides have a smaller size and precipitation temperature than Mn sulfides and are therefore preferable, it is preferable that the molten steel contains more Cu than Mn. However, since Mn is more affine to S than Cu, an "oversupply &quot; be present at Cu to quantitatively more Cu sulfides than Mn sulfides can form.

An advantageous implementation of the method according to the invention, which solves the problem underlying the invention, for the continuous operation is that the first rolling mill of the continuous casting plant is immediately downstream and between the heating device and the second rolling mill a continuous furnace for heat input and / or maintaining the temperature of the hot strip. This configuration of the plant makes it possible to carry out the inventive process with high product quality particularly economically, i. high production capacity (fully continuous operation), low energy costs (amount of energy for heating the hot strip is minimized) and low investment costs (compact plant).

An advantageous embodiment of the casting-rolling composite plant is to run the continuous casting plant as a thin slab continuous casting plant. Another embodiment is that the first rolling mill comprises up to four rolling mills. A further embodiment consists in that the second rolling train comprises 2 to 6, preferably 3 to 5, rolling stands. Through these measures, the investment costs for the first rolling mill and the second rolling mill are kept low (common hot strip thicknesses can be produced on a few rolling stands).

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following figures, which show: Fig. 1 is a schematic representation of a non-continuous cast-rolling composite plant Production of Hot Rolled Rolled Material for Further Processing into Grain-Oriented Sheet Metal [0033] FIG. 2 A schematic representation of a cast-rolled composite plant for the fully continuous production of hot strip rolling stock for further processing into grain-oriented sheets. EXEMPLARY EMBODIMENT 1

In Fig. 1, a casting-rolling compound plant 1 for the production of hot rolled strip of silicon-alloyed steels is shown; the system parts for further processing of the hot strip to a grain-oriented electrical steel are not shown. The states, i. the temperatures and thicknesses of the strand or strip in the individual process steps are given in Tab. I; the states are referred to as P1 to P15. In a continuous casting plant 2 for the production of thin slabs is made of a specific steel alloy, in weight% consisting of Si 3.2%, C 0.08%, Mn 0.1%, Cu 0.3%, Sn 0.08%, S 0.01%, Al 0.03%, Cr 0.1%, N 3/7 Austrian Patent Office AT 507 475 B1 2010-08-15 0.012%, P 0.05%, remainder Fe and impurities, one strand 3 with a thickness of 90 mm poured. Immediately after the solidification (temperature of the strand 1174 ° C, state P1), the strand 3 is subjected to a first rolling step consisting of 2 rolling passes on a first rolling line 5. The individual degrees of deformation are 53% and 52%, respectively. a strip 42 mm thick (state P2) and then a 20 mm thick strip (state P3) are rolled first. The temperature of the strip after the first pass is 1171 ° C, after the second pass 1086 ° C. This first rolling step promotes the formation of homogeneously distributed and finely dispersed clusters of growth inhibitors, namely sulfides, nitrides and carbides of the elements Cu, Al, Mn and Cr, in the ribbon, thereby inhibiting further grain growth. Following the first rolling step, the belt 4 is transported by means of a roller table to a heating device 6, designed as an induction furnace, in which the incoming, cooled to 944 ° C (state P4), strip to a final temperature of 1150 ° C (state P5 ) is heated. Subsequently, the temperature of the strip in a coiler oven 7 (temperature at the entrance of the coiler furnace 1134 ° C, state P6) is maintained for at least 30 s. The residence time of a band area, the so-called local residence time, varies depending on the band position. Due to the winding and unwinding of the tape, e.g. the - existing before winding - tape head longer in the coiler oven than the end of the tape; In this sense, the existing before winding tape head to the end of the tape and vice versa. By heating the belt 4, growth inhibitor precipitation is prevented until finish rolling of the belt in a second rolling line 8; by maintaining the temperature for a time t, coarse clusters of growth inhibitors are dissolved, which are re-formed in a finely divided manner upon renewed temperature reduction during finish rolling. After winding and unwinding the leader in the coiler oven 7, the strip is freed from scale by a descaling unit 12, whereby the temperature of the strip falls from 1101 ° C to 1070 ° C (temperatures before and after descaling, states P7 and P8). The strip is then subjected to four rolling passes on a second rolling line 8 (individual degrees of deformation 55, 53, 28 and 16%, ie strip thicknesses of 9.1, 4.3, 3.1 and 2.6 mm, states P9 to P12). finished to a final hot-rolled strip thickness of 2.6 mm. In these rolling passes, the strip of 1043, 1012 and 984 cools to a final rolling temperature of 955 ° C after the last pass. After finish rolling, the strip is cooled on a cooling section 9 within 3 s after the last pass in the second rolling mill 8 from 932 ° C (inlet cooling path, state P13) to a temperature of 560 ° C at the exit of the cooling section (state P14) , Upon finish rolling and cooling of the ribbon, the cluster of growth inhibitors present in the strand become finely dispersed, i. with a typical cluster size &lt; 60 nm, excreted. After cutting off the hot strip by means of a pair of scissors 10, the tape is wound up in a take-up device 11; the winding temperature is 540 ° C (state P15). In further, not shown. Manufacturing steps, the present hot strip is annealed, rolled in a cold rolling mill to the final thickness, decarburized and subjected to a targeted secondary recrystallization. EXEMPLARY EMBODIMENT 2 FIG. 2 shows another cast-rolled composite plant 1 for the fully continuous production of hot-rolled strip made of silicon-alloyed steels; the plant parts for further processing of the hot strip to a grain-oriented electrical steel are again not shown. The states P1 to P5 and P7 to P15 of the strand or strip in the individual process steps are given in Tab. In this case, in turn, a specific steel alloy (chemical composition see Embodiment 1) is melted and cast in a continuous casting plant 2 a strand 3 (state P1). Immediately after the solidification, the strand is subjected to a first rolling step consisting of 2 rolling passes on a first rolling line 5 (states P2 and P3). Subsequently, the belt 4 is heated in a heating device 6, which is designed as an induction furnace (states P4 and P5). The essential difference from the embodiment 1 consists in the fact that the temperature of the belt 4 is maintained after heating in a continuous furnace 13, designed as a gas-fired furnace, for at least 15 s; the local residence time in the continuous furnace is 4/7 for all belt areas

Claims (15)

Austrian Patent Office AT 507 475 B1 2010-08-15 (band head, band foot) constant. The further process steps (descaling P7 to P8, finish rolling P9 to P12, cooling P13 to P14 and coiling P15) are shown in the embodiment 1. REFERENCE LIST 1 Continuous Casting Unit 2 Continuous Casting Unit 3 Strand 4 Belt 5 First Rolling Line 6 Heater 7 Coiler 8 Second Rolling Line 9 Cooling Section 10 Scissors 11 Winder 12 Descaling Unit 13 Continuous Furnace Patent Claims Location Thickness [mm] Temp. [° C] P1 End Casting Roll -Verbundanlage 90 1174 P2 After 1st pass in first rolling mill 42 1171 P3 After 2nd pass in first rolling mill 20 1086 P4 input heating device 20 944 P5 output heating device 20 1150 P6 input coiler 20 1134 P7 input descaling unit 20 1101 P8 descaling unit 20 1070 P9 After 1st pass in second rolling mill 9.1 1043 P10 After 2nd pass in second rolling mill 4.3 1012 P11 After 3rd pass in second rolling mill 3.1 984 P12 After 4th pass in second rolling mill 2.6 955 P13 Cooling section 2.6 932 P14 Cooling section 2.6 560 P15 In rewinder 2.6 540 Tab. I 1. Process for the production of hot rolled strip silicon-alloyed steels on a cast-rolled composite plant for further processing into grain-oriented electrical steel, comprising the following process steps in the order named: a) melting a steel having a chemical composition in weight% of Si 2 to 7%, C 0.01 to 0, 1%, Mn &lt; 0.3%, Cu 0.1 to 0.7%, Sn &lt; 0.2%, S &lt; 0.05%, Al &lt; 0.09%, Cr &lt; 0.3%, N &lt; 0.02%, P &lt; 0.1%, remainder Fe and impurities; b) casting a strand having a thickness of 25 to 150 mm on a continuous caster; c) rolling a strip in up to 4 rolling passes immediately after the casting of the strand, at least in one rolling pass a degree of deformation &gt; 30% or the total degree of transformation of all stitches &gt;50%; D) heating the tape to a final temperature of 1050 to 1250 ° C, preferably 1100 to 1180 ° C; e) finish rolling the strip in a second rolling mill, then f) cooling and reeling the strip. 2. The method according to claim 1, characterized in that the final temperature after heating the tape for a duration, t &gt; 15 s, preferably &gt; 60 s, is maintained. 3. The method according to claim 2, characterized in that the final temperature of the belt is maintained in a continuous furnace. 4. The method according to claim 2, characterized in that the final temperature of the belt is maintained during winding and subsequent unwinding in a coiler oven. 5. The method according to any one of the preceding claims, characterized in that the strip is finish-rolled in the second rolling mill in 2 to 6, preferably 3 to 5, rolling passes. 6. The method according to any one of the preceding claims, characterized in that the strip after finish rolling has a final rolling temperature of 900 to 1050 ° C. 7. The method according to any one of the preceding claims, characterized in that the strip is cooled within 10 s, preferably within 6 s, after the finish rolling to a reel temperature of 300 to 600 ° C by means of an intensive cooling step. 8. The method according to claim 7, characterized in that the band is cooled at the beginning of the intensive cooling step with a double, preferably three times, as high a cooling rate as at the end of the cooling step. 9. The method according to claim 1, characterized in that in the molten steel, the sum of the alloying elements Cu + Mn &gt; 0.35% by weight, preferably &gt; 0.55% by weight. 10. The method according to claim 1, characterized in that in the molten steel, the sum of the alloying elements S + N &gt; 100 ppm, preferably &gt; 200 ppm. 11. The method according to claim 1, characterized in that in the molten steel, the quotient of the alloying elements Cu / Mn &gt; 2.5, preferably &gt; 3.5, is. 12. Cast-rolling composite plant (1) for the production of hot strip rolling stock of silicon-alloyed steels for further processing into grain-oriented electrical steel, comprising a continuous casting plant (2), a first rolling train (5), a heating device (6), a second rolling train (8 ), a cooling section (9) and a winding device (11), characterized in that the first rolling train (5) of the continuous casting plant (2) is located immediately downstream and between the heating device (6) and the second rolling train (8) a coiler furnace ( 7) or a continuous furnace (13) for introducing heat and / or maintaining the temperature of the hot strip. 13. Plant according to claim 12, characterized in that the continuous casting plant (2) is designed as a thin slab continuous casting plant. 14. Plant according to claim 12, characterized in that the first rolling train (5) comprises up to four rolling mills. 15. Plant according to claim 12, characterized in that the second rolling train (8) comprises 2 to 6, preferably 3 to 5, rolling mills. For this 1 sheet drawings 6/7