PLANT TO PRODUCE STEEL, AND CORRESPONDING METHOD

Abstract

Steel production plant to obtain long products such as rods, bars or sections, with overall productivity comprised between 0.7-3.0 Mton/year, preferably between 1.0 and 3.0 Mton/year, comprising at least two co-rolling lines (11a, 11b).

Claims

1. A steel, Steel production plant to obtain long products such as rods, bars or sections, with overall productivity comprised between 0.7-3.0 Mton/year, preferably between 1.0 and 3.0 Mton/year, comprising at least two co-rolling lines, wherein it provides a single high-capacity melting furnace and at least two ladles to receive the liquid steel from said melting furnace and feed said co-rolling lines, wherein the total useful capacity of the at least two ladles expressed in tons does not exceed the capacity in tons of the liquid steel tapped from said melting furnace.

2. The steel production plant as in claim 1, wherein the at least two ladles have the same useful capacity and substantially equal, together, to the capacity in tons of tapped steel of the single melting furnace.

3. The steel production plant as in claim 1, wherein the at least two ladles have different useful capacities and substantially equal, together, to the capacity in tons of tapped steel of the single melting furnace.

4. The steel production plant as in claim 1, comprising at least two secondary metallurgy stations for executing refining and/or thermal or other treatments.

5. The steel production plant as in claim 1, comprising hoppers to add alloy elements directly to the ladle during the step of tapping from the melting furnace.

6. The steel production plant as in claim 1, wherein the furnace is of the tiltable type.

7. The steel production plant as in claim 6, wherein the furnace is of the type with pouring spout.

8. The steel production plant as in claim 6, wherein the furnace is of the type with a tapping hole which can be selectively closed by means of closing means.

9. The steel production plant as in claim 1, wherein the furnace is of the type with siphon tapping with tapping chamber.

10. The steel production plant as in claim 1, wherein the furnace is of the non-tiltable type and with double lateral tapping duct.

11. The steel production plant as in claim 1, wherein the furnace is of the tiltable type with double tapping hole.

12. A method to produce steel to obtain long products such as rods, bars or sections, with productivity comprised between 0.7-3.0 Mton/year, preferably between 1.0 and 3.0 Mton/year, comprising the following steps: melting the steel in a single high-capacity melting furnace; pouring the molten steel from the single melting furnace into at least two ladles whose total useful capacity expressed in tons does not exceed the capacity in tons of liquid steel tapped from said single melting furnace; feeding with each of said at least two ladles a respective co-rolling line of a multiple co-rolling apparatus.

13. The method as in claim 12, wherein the liquid steel contained in said two ladles is diversified by type.

14. The method as in claim 13, wherein the diversification of the type of liquid steel occurs in the tapping step.

15. The method as in claim 13, wherein the diversification of the type of liquid steel occurs inside the ladles in at least two secondary metallurgy stations.

16. The method as in claim 12, wherein the co-rolling lines are equal to two, and one or both co-rolling lines work in endless mode.

17. The method as in claim 12, wherein the co-rolling lines are equal to two, and one or both co-rolling lines work in billet-to-billet or semi-endless mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0045] FIG. 1 is a schematic representation of a steel production plant in accordance with some embodiments described here;

[0046] FIG. 2 is a schematic representation of a possible example multi-line co-rolling apparatus used in the plant of FIG. 1;

[0047] FIGS. 3-6 schematically show different modes for tapping the steel into two ladles, with corresponding different types of EAF, which can be implemented in the present invention;

[0048] FIGS. 7a-7e show a tapping sequence in a first embodiment of the invention;

[0049] FIGS. 8a-8e show a tapping sequence in a second embodiment of the invention.

[0050] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0051] Some embodiments, described by way of example by means of FIGS. 1-2, concern a steel production plant 10 that uses a multiple co-rolling apparatus 50 configured to simultaneously produce, along respective co-rolling lines 11a, 11b, two steel products that are the same or different, having the same or a different steel grade. The solution shown by way of example provides two co-rolling lines 11a, 11b and uses two ladles 14 to feed them, as described below, although the teaching of the invention is applied in a similar manner to a larger number of co-rolling lines and/or a larger number of ladles 14.

[0052] The product made on one line can be made of steel with a steel grade known as “GB/T 1499.2-2018 Grade HRB400/HRBF400”, poor in manganese and without vanadium, while the product made on the other line can be enriched with alloy elements and the steel grades are known as “GB/T 1499.2-2018 Grade HRB400E/HRBF400E”, “GB/T 1499.2-2018 Grade HRB500”, “GB/T 1499.2-2018 Grade HRB500E/HRBF500E”, which have progressively higher carbon, manganese, silicon and vanadium contents.

[0053] The two co-rolling lines 11a, 11b can function in endless mode, but also in billet-to-billet or semi-endless mode, in any case at high casting speed, for example greater than 6.5 m/min.

[0054] In some embodiments, each casting line 11a, 11b of the multi-line casting apparatus 50 can comprise, downstream of the tundish 17, a casting machine 18 (schematically shown in FIGS. 1 and 2), an extractor unit 21, a cutting unit 22, usable in the case of billet-to-billet mode, an induction furnace 20 and a rolling train comprising rolling stands 12.

[0055] The sequence of rolling stands 12 can define a roughing train 24, an intermediate train 25 and a finishing train 26.

[0056] As can be seen in the drawings, neither of the two co-rolling lines 11a, 11b provides the presence of a fossil fuel (typically natural gas) furnace for heating the billets.

[0057] The heating inductor 20 is positioned upstream of the rolling train and advantageously consists of modular units.

[0058] The heating power of the inductor 20 is between 2 and 6 MW (from 20 to 60 kWh/t depending on the maximum ΔT to be compensated) in order to manage temperature increases between 30° C. and 200° C. For high productivities and large ΔT (e.g. billets of 130 mm at 180 t/h with a thermal integration of 350° C.) it is possible to have an inductor power of up to 12-14 MW. The two co-rolling lines 11a, 11b can have a number of rolling stands 12 that depends on the final product.

[0059] To produce rod, between 26 and 30 total rolling steps can be considered, for bars between 20 and 24 total rolling steps, while for sections/profiles approximately 20 total stands.

[0060] As can be seen in FIG. 1, the plant 10 provides a single high-capacity melting furnace 13 to feed the two co-rolling lines.

[0061] The high-capacity furnace 13 is suitable to distribute the quantity of liquid steel produced into two respective ladles 14 with a smaller capacity. The total useful capacity of the two ladles 14, defined in terms of quantity of steel, expressed in tons, which the ladles 14 receive at each tapping cycle of the furnace 13 does not exceed the capacity of the furnace 13, so that for each melting cycle the two ladles 14 are filled with the quantity of molten steel from the single furnace 13.

[0062] In accordance with the invention, the two ladles 14 can have the same capacities and, as a whole, substantially equal to the capacity of the single EAF 13. In one variant, the two ladles 14 have different capacities, for example, but not only, in relation to the absorption capacity of the two respective casting machines downstream, that is, their productivity, which in turn depends on the type of finished product. In fact, as can be seen in FIG. 1, the two lines 11a, 11b can simultaneously produce different types of product, for example bars 27 to be unloaded into plate 28, or rod 29 to be wound in reel 39.

[0063] The present plant 10 can be used effectively to manage significantly different productivities on the two lines 11a, 11b, for example 75 ton/h on line 11b to produce rod and 150 ton/h on line 11a to produce bars, using ladles 14 of different capacities.

[0064] The furnace 13 can be advantageously, although not necessarily, of the tiltable electric arc (EAF) type. In FIG. 1, the furnace 13 is shown as non-tiltable and with a double lateral tapping duct 15, so that the two ladles 14 can be filled simultaneously and continue in parallel in the subsequent operating steps.

[0065] The tiltable furnace, during the melting step, is kept in a horizontal position; during the slagging step, that is, when the slag layer covering the steel is at least partly evacuated from the furnace, the furnace is tilted on one side (for example by 2°-3°), while during the tapping step it is tilted on the opposite side (for example from 5° to 12° between the beginning and end of the tapping).

[0066] The tapping device through which the outflow of liquid steel occurs can be of various types.

[0067] In particular, the furnace 13 can be of the type with a tapping hole 32 located on the bottom of the furnace 13 and associated with selective closing means, in this specific case of the movable slide 30 type (FIG. 3), with which there can possibly be associated a buffer rod 41, equipped with a respective movement mean 40. The buffer rod 41 can be used not only to close the tapping hole 32 once the filling of the ladles 14 has been completed, but also to regulate the flow of steel through the respective tapping hole 32, closing it only in part by partly introducing its end. In FIG. 3, the buffer rod 41 is shown in a partly lowered position ready to close the tapping hole 32. On the opposite side of the tapping hole 32 the furnace 13 has a slag door 42.

[0068] In an alternative solution, the furnace 13 can be of the type with a tapping spout 38 (FIG. 4). Again, it can be of the siphon type, with a tapping chamber 35 connected to a passage channel 37 that communicates with the inside of the furnace 13 (FIG. 5). In this case, associated with the tapping chamber 35 there can be pumping means 43 to create the depression that draws the steel into the tapping chamber 35.

[0069] Finally, the furnace 13 can be of the type with double tapping hole 32. In this variant, shown in FIG. 6, the tapping device consists of two tapping holes 32 adjacent to each other, which can be selectively closed with suitable and respective closing means 30 of the movable slide type (shown in dashed lines). Each tapping hole 32 is suitable to cooperate with a respective ladle 14 and the center to center distance between the tapping holes 32 is advantageously such as to be able to cooperate with a substantially central position of the underlying ladles 14 (also shown in dashed lines). This solution allows to fill both ladles 14 with a single tapping cycle, by tilting the furnace 13 according to the modes described for the solution of FIG. 3. Also in this case, with each tapping hole 32 there can be associated a corresponding buffer rod 41 for the possible regulation of the flow of steel at exit.

[0070] The types of furnace of FIGS. 5 and 3 have been shown in the example tapping sequence of FIGS. 7a-7e and 8a-8e respectively. It is obvious that these sequences can also be applied to the other types of furnace 13 shown in FIGS. 4 and 6, or also to other types not shown here.

[0071] FIGS. 7a-7e show a siphon tapping device consisting of a tapping chamber 35, equipped with a tapping duct 36, in which the liquid steel 31 located on the bottom of the furnace 13 can be drawn through the channel 37. The suction of the steel through the siphon can be carried out in different ways: for example by tilting the furnace on the side of the tapping chamber 35, so as to use the principle of communicating tanks to induce the exit of the steel, or by means of the pumping means 43 that create a depression in the tapping chamber 35 so as to draw the liquid steel inside. According to one variant, the two modes described above (inclination and depression) can be used in combination.

[0072] Once the first tapping cycle has been performed, for example with a first ladle 14 (FIG. 7b), the inclination or suction can be interrupted and then resumed once the ladle change has been performed. As can be seen in FIG. 7c, the furnace 13 can be taken into an inclined position in the opposite direction in which the remaining steel 31 remains below the channel 37, until the second ladle 14 is ready for the filling cycle to be repeated (FIG. 7d).

[0073] Once the filling of the second ladle 14 is also completed, the furnace 13 returns to a horizontal position (FIG. 7e), with the liquid steel pool 31 inside it, for a new melting cycle.

[0074] In the example shown in FIGS. 8a-8e the furnace 13 is provided on the bottom with a selective closing device (for example of the movable slide type 30) to pour the liquid steel produced into two ladles 14 in succession.

[0075] To proceed with filling the first ladle 14, the furnace 13 is tilted on the side where the opening/closing device is located (FIG. 8b), the tapping hole 32 is opened by moving the movable slide device 30 and the filling of the first ladle 14 begins.

[0076] Once the first ladle 14 has been filled, the furnace 13 is tilted in the opposite direction, taking the liquid steel 31 to a position outside the tapping hole 32 (FIG. 8c) in order to stop the outflow through the hole. The first ladle 14 is then evacuated from the tapping area and the second ladle 14 to be filled is introduced (FIG. 8d). The furnace 13 is again tilted for the tapping and the filling of the second ladle 14 begins.

[0077] Once the second ladle 14 has also been filled, possibly keeping a volume of molten steel inside the shell of the furnace 13 as a liquid pool, in order to facilitate subsequent melting, the tapping hole 32 is closed with the movable slide device 30 (FIG. 8e) and the furnace 13 is then returned to a horizontal position in order to prepare a new melting cycle. In this step, an introducer device 33 can be driven to discharge inert material 34, for example sand, in order to fill and close the tapping hole 32, until the next tapping cycle starts.

[0078] A similar method is also adopted when the tapping device consists of a casting spout 38 or channel located on a lateral wall of the furnace, as in the solution shown in FIG. 4.

[0079] The ladles 14, in a first solution, can both have a capacity exactly equal to half the capacity of the furnace 13, so that for each melting cycle of the furnace 13 the two ladles 14 are both filled with a same quantity of steel.

[0080] In an alternative solution, not shown, the two ladles 14 have different capacities, in particular if the absorption capacity of the two respective casting machines downstream is different, that is, their productivity, which in turn depends on the type of finished product (e.g. rod or bars) is different.

[0081] The differentiation of the steel grade of the steel between one ladle 14 and the other, or in any case of at least one ladle 14, can occur both in the step of tapping from the electric furnace, and also in the secondary metallurgy station 16 in the ladle furnace.

[0082] In the first case, in the tapping step, it is possible to use elements, for example hoppers not shown here, for introducing alloy elements to chemically differentiate the metal materials independently and autonomously between the two ladles 14.

[0083] In the ladle furnace, on the other hand, the steel can be subjected to enrichment treatments with precise dosages of the various alloy elements (ferroalloys) in order to obtain the desired metallurgical quality.

[0084] The ladle furnace consists of a liftable vault, through which, in the secondary metallurgy station 16, electrodes can be inserted which are necessary for maintaining the bath at temperature.

[0085] For producing special steels and stainless steels, the secondary metallurgy treatment can provide, downstream of the ladle furnace LF, an additional vacuum degassing treatment stage (VD or VOD) for the removal of unwanted gases, such as nitrogen and hydrogen, and for decarburization.

[0086] From the respective ladles 14 the steel can be poured into a respective tundish 17 which feeds the respective continuous casting machine 18. As mentioned, each of the co-rolling lines 11a, 11b has its own tundish 17 which operates independently of the tundish 17 of the other line.

[0087] The two continuous casting machines 18 form part of the co-rolling lines 11a, 11b.

[0088] The present plant 10 as described above is suitable for always exploiting the productivity of the steel plant (EAF) to the maximum, even when one line 11a or 11b has a reduced productivity because of the product to be made, for example rod which dictates a maximum productivity of 75 ton/h.

[0089] With this plant configuration, the invention provides the possibility of transferring billets from line 11a to line 11b, for example by means of a transverse transferer of a known type, if the two lines produce products with the same steel grade.

[0090] The transfer of billets between the two lines can be carried out in case of emergency, for example in the event a rolling train is blocked due to accidents or jamming.

[0091] The transfer of billets from one line to another can also be carried out when, for example, there is a desire to increase the productivity of one of the two lines for a certain period (for example 1 month), for example line 11a. In this case, line 11a would function in billet-to-billet mode. This option can be provided in the design stage of the plant by adequately sizing the rolling train of line 11a. In the design stage it is also possible to provide special diverter means, shown only schematically in dashed lines in FIGS. 1 and 2, to send the rolled product at exit from the roughing train 24 or from the intermediate train 25 of one line, to the intermediate train 25 or to the finishing train 26 of the other line, when one of the lines is idle for maintenance or other.

[0092] As stated, the two co-rolling lines 11a and 11b can be complete lines, as shown in FIG. 2, or one of the two can be without the rolling mill and produce a semi-finished product (billets) intended for sale.

[0093] It is clear that modifications and/or additions of parts or steps may be made to the plant 10 and to the method as described heretofore, without departing from the field and scope of the present invention as defined by the claims.