DE10164610C1 - Producing a steel melt comprises melting a process material into a melt, deoxidizing the melt with aluminum, adding manganese and silicon to the deoxidized melt, and treating the melt - Google Patents

Abstract

Production of a steel melt containing up to 30 weight % silicon and up to 1 weight % carbon comprises melting a process material into a melt; deoxidizing the melt with aluminum so that oxygen fixing by aluminum during the whole melting duration takes place; adding manganese and silicon to the deoxidized melt; and treating the melt. The temperature of the melt is held at a constant melt bath temperature lying just above its liquidus temperature within a tolerance region. Preferred Features: The manganese and silicon are added at the same time, either in portions or continuously. The manganese is added as electrolytic manganese and the silicon as ferrosilicon. During addition of the manganese and silicon, the melt bath temperature is held at a maximum deviation of 20 degrees C by 50 degrees C above each actual liquidus temperature of the melt.

Description

The invention relates to a method for producing a steel melt containing up to 30% by mass of manganese, silicon and up to 1% by mass of carbon. Such steels, which are also referred to in the technical field by the abbreviation "L-IP" (Light Steel with Induced Plasticity), are used, for example, for the production of flat products. They are characterized by high formability combined with high hardness (R _m ≈ 700 MPa, A ₈₀ ≈ 50%).

The chemical target composition of L-IP steels is largely based on a typical one Basic composition of 1 to 25% by mass of manganese, approx. 3 Mass% silicon and approx. 3 mass% aluminum. there carbon contents of 0.6 mass% and more tolerated. In addition, the steels P, Cr, Ni, N or H included.

In the production of manganese-iron alloys the fundamental problem that such alloys in Comparison to the infinitely thinned iron alloys of the usual quality steels an increased vapor pressure have. As a result, it happens at the Melt treatment for the increased development of  so-called "brown smoke". Such brown smoke arises by the evaporation of Fe and Mn with subsequent partial oxidation.

The lowering of the total pressure and thus an increased evaporation of iron and manganese occurs especially in plants in which the melt is treated at reduced pressure (VOD plants, RH plants, vacuum induction furnaces) as a result of flushing the melt with gases such as N ₂ or Ar and when CO or N ₂ bubbles are formed during the solidification of the melt.

Recent studies assume that the brown Smoke mainly from melt drops caused by CO bubbles and are atomized into fine particles (EGKS 7210- CC / 123/124 "Control of Ejections Caused by Bubble Bursting in Secondary Steelmaking Processes ", 1996-1999). The CO bubbles are created in the melt by reaction of carbon with oxygen, which over the Gas phase, refractory material or through alloying materials get into the melt.

When alloying, manganese is usually in the form of fine, free-flowing material with a Grain fraction from 3 to 20 mm from a bunker on the Melted bath or poured into a sink given. However, since the manganese is lighter than that Is molten steel, it floats and forms on the Melt a so-called "pillow" from manganese flakes, which are in a sintering process due to the Melt emitted heat from the granular  Form the manganese material before the manganese is melted is. This pillow dissolves only slowly because it is sufficient only at the contact area with the molten steel warms, melts and dissolves. Is inside the pillow the heat transfer through numerous cavities is disturbed. in the Area of the manganese / air / molten steel contact zone brown smoke is created by evaporation and CO Gas formation.

Another problem with alloying one Melting steel consists of larger amounts of manganese in that it is due to the withdrawal of the for Melting the manganese requires heat energy to a Lowering the melt bath temperature comes. This Temperature loss can occur until the melt freezes to lead.

In addition to the prior art explained above it is known for example from US 3,059,326 for Manufacture of an iron product an iron aluminum To melt and then melt this melt to shed a body. The melt can additional contents of (in% by weight) up to 0.5% C, each up to 5% Si and Ti, up to 25% Cr, each up to to 30% Mn and Ni, each up to 10% Mo, W and V, to up to 7% Nb, up to 20% Co, up to 3% Cu and up to 5% Zr included. It remains open how the melt is melted when they have high manganese contents should.

The object of the invention is a method for the production of steel melts with a manganese content of up to 30% by mass, at which the manganese addition  be carried out quickly and largely smoke-free can.

This call is generated by a method for generating a up to 30 mass% manganese, silicon and up to 1 mass% Carbon-containing molten steel dissolved, in which melted a feed into a melt is, in which the melt with aluminum such is deoxidized that the oxygen release during the total melting time by aluminum, in which manganese and silicon are added to the deoxidized melt be, the temperature of the melt within a Tolerance range on a constant, just above  their respective liquidus temperature Melt bath temperature is maintained, and at which the Melt is then treated.

According to the invention, the molten iron is initially with Deoxidized aluminum. This is an aluminum buffer built up, which ensures that during the whole Oxygen binding over aluminum melts he follows. In this way the oxygen content of the Melt kept so low that even when present of carbon in the melt the formation of CO bubbles is avoided.

The melt thus deoxidized with aluminum then added manganese and silicon. Doing so the melt bath temperature is continuously related to that changing with the addition of alloy additives Adjusted liquidus temperature of the melt. Aim this Measure is the one for the alloying process required overheating of the melt on a to keep the lowest possible level to an increased Avoid oxygen intake. The result of Oxygen absorption when the melt temperature is too high Existing danger of smoke formation is reduced in this way bypassed safely.

As a result, with the invention Procedure large amounts of manganese in the Introduce molten steel, the smoke formation almost completely avoided and the total alloy duration compared to conventional procedures is reduced.  

It is advantageous to use manganese and silicon at the same time Melt added. In this way, the one with the Adding manganese accompanying heat loss at least partly due to the dissolution of silicon in the Relatively high heat released be compensated. It is particularly cheap in this Context when manganese and silicon are mixed be added so that when loosening the silicon the resulting heat acts directly on the manganese can. Through this direct action when loosening the Silicon released heat will melt and Dissolve the manganese in the molten steel additionally accelerated. A transfer of the released Intensive mixing of the heat that favors heat Manganese and silicon formed mixture can simple way to ensure that manganese and silicon can be added as a free-flowing material.

Another related to the addition of manganese and silicon particularly advantageous aspect of the invention is that these alloy elements below the Surface of the melt pool are added. This can for example, that manganese and silicon by means of a submersible probe below the Melt surface are introduced into the melt.

Basically, it is convenient if the required Amount of manganese and silicon over a given Period is distributed into the melt. To this In this way, a uniform melting and loosening of the Alloy components are guaranteed. It can the addition of manganese and silicon in portions or done continuously.  

When adding a mixture of silicon and Manganese is released when the silicon is dissolved Use released heat particularly effectively. This can the manganese-silicon mixture for example in a Melt, although open, but defined defined space be placed in the melt below the bath level. The effect is within this clearly defined space the heat released when the silicon is released onto the with manganese contained in the room in question concentrated. After melting and releasing the The mixture formed from silicon and manganese is distributed the resulting highly concentrated manganese-silicon solution then in the iron and put it on.

In practice, it has been related to the portionwise introduction has proven to be favorable if the for the introduction of the manganese-silicon mixture the immersion probe used is shaped like a bell, whose opening area preferably on their from Side mirror facing away from the bathroom mirror is formed. alternative However, it is also possible to combine manganese and silicon closed tube or in appropriately dimensioned Put barrels into the melt.

Regardless of their respective shape, the Submersible probe be made of a steel material that melts itself during the melt treatment ("lost immersion probe"). Should the immersion probe against it can be used multiple times, it can also be used be made of a refractory material. You can also Diving bells are used several times, made with one Refractory coated steel material made are.  

For the continuous addition of manganese and silicon a cored wire can be used in a conventional manner become. It is also conceivable to add manganese and silicon inflate the melt.

Ferromanganese can contain considerable amounts of Carbon also occur in phosphorus and lead Steels of the type produced according to the invention have a disruptive effect. The entry of these disturbing can be avoided Components in that the manganese as electrolyte manganese is used. The silicon is preferred as Ferrosilicon added.

Another advantageous embodiment of the invention provides that together with manganese and silicon Aluminum is introduced into the melt. Similar to when the silicon is loosened, when the Aluminum free heat, which leads to the heat balance of the Melt contributes positively during alloying. The ones from Aluminum can also be supplied with additional heat use particularly effectively when the aluminum is liquid is alloyed. In the case of liquid aluminum added up to otherwise to warm up solid aluminum to Melting temperature as well as the enthalpy of fusion and a part the necessary superheat no longer Steel melt can be withdrawn.

The generation of flue gas as a result of an increased oxygen uptake by the melt during the alloy treatment is minimized according to the invention by limiting the superheating temperature. For this purpose, the melt bath temperature during the addition of manganese and silicon can be controlled according to the following conditions:

T _melt [° C] = T _LS - 5% Mn - 8% Si + DT _UE

With
T _melt : current melt bath temperature,
T _LS : liquidus temperature of the melt before the addition of Mn and Si,
DT _Ue : temperature _amount by which the T _{melt is kept} above the current liquidus temperature,
% Mn: current Mn content,
% Si: Current Si content.

Preferably, the amount of temperature by which the Melt temperature above the current one Liquidus temperature is so limited that the Melt temperature with a maximum deviation of 20 ° C at most 50 ° C above the current one Liquidus temperature of the melt is maintained.

The method according to the invention is preferably suitable for Production of molten steel, which is up to 0.85 mass%, preferably contains up to 0.6% by mass of carbon.

The aluminum buffer set during deoxidation is preferably such that it is at least 0.02% by mass over the amount for oxygen depletion lies.

Melts according to the invention can typically be up to 3 mass% silicon and up to 3 mass% aluminum be added. However, it is also possible  Silicon contents of up to 5% by mass or 6% by mass provided. If larger amounts of aluminum are added, it may be necessary to remove the resulting clay to remove the melt.

The invention is based on a Exemplary embodiment drawing closer explained. The figure shows schematically a diving bell for introducing a fine-grained manganese-silicon Mix in a molten steel.

In the first step, the production of a block cast from an L-IP steel melt

feedstock is melted with coal. Subsequently, the melt S obtained in this way 0.8% by mass Al deoxidized.

The deoxidized melt is then a mixture formed from free-flowing fine-grained electrolyte-manganese and ferrosilicon (high purity) in the ratio of approx. [15% by mass Mn] / [3% by mass Si] by means of the immersion bell 1 shown in the figure in portions added a total of ten steps.

For this purpose, the diving bell 1 has a bell body 3 held on a tubular lance 2 . The bell body 3 has the shape of a cylindrical disk, the peripheral wall 4 of which surrounds an interior 5 . The lance 2 is attached at one end to the outside of the roof 6 of the bell body 3 , the bell body 3 and lance 2 being aligned coaxially with the longitudinal axis L of the diving bell 1 .

In the area of the connection between the lance 2 and the bell body 3 , a centrally arranged ventilation opening 7 is formed in the roof 6 of the bell body 3 , the inside diameter of which corresponds essentially to the inside diameter of the lance 2 . In this way, gas which forms in the interior 5 of the bell body 3 can be discharged through the tubular lance 2 .

On the side opposite the roof 6 , the bell body 3 has an opening into which a perforated plate 8 is placed. The perforated plate 8 has the task of holding material contained in the interior 5 of the diving bell 1 until the diving bell 1 is immersed in the melt S. The temperature prevailing in the interior 5 of the diving bell 1 can be tapped via a temperature probe 9 .

In order to introduce the manganese and the silicon into the melt S, the interior 5 of the diving bell is filled with a portion P of the intensely mixed manganese-silicon mixture. Subsequently, the diving bell 1 is immersed in the melt S to such an extent that it is arranged at a safe distance A below the surface O of the melt S.

As a result of the heat given off by the melt S, the melting and dissolving process of the manganese and silicon contained in the diving bell 1 now begins. The heat released by the silicon acts directly on the manganese within the tightly delimited interior space 5 , so that a rapid, uniform melting of the manganese is achieved. The Mn-Si solution formed in this way emerges from the opening of the diving bell 1 and mixes with the melt S.

The portionwise addition of the manganese-silicon mixture is repeated until the required Mn and Si content is reached. It is during the addition of Batch portions the melt bath temperature in each case set that they are a maximum of 50 ° C above the current, by the respective content of Mn and Si significantly determined liquidus temperature of the melt S lies.

After alloying with Mn and Si, the melt S first by adding FeP, Cr and Ni and then alloyed by adding Al. Then the temperature the melt S to the casting temperature of 1550 ° C. brought and cast the melt S into a block.

The table below shows the alloy contents of the melt S which arise during the course of production and treatment until the casting, the respective liquidus temperature T _LS and the target temperature T _{target of} the melt S for each of the work steps explained here.

REFERENCE NUMBERS

1

diving bell

2

lance

3

bell body

4

Circumferential wall of the bell body

3

5

Interior of the bell body

3

6

Roof of the bell body

3

L Longitudinal axis of the diving bell

1

7

vent

8th

perforated sheet

9

temperature probe
A distance
O surface of the melt S
S melt

Claims (21)

1. Process for producing a steel melt containing up to 30% by mass of manganese, silicon and up to 1% by mass of carbon,
in which a feed material is melted into a melt,
in which the melt is deoxidized with aluminum in such a way that the oxygen removal takes place through aluminum during the entire duration of the melt,
where manganese and silicon are added to the deoxidized melt
the temperature of the melt being kept within a tolerance range at a constant melt bath temperature just above its respective liquidus temperature, and
in which the melt is subsequently treated. 2. The method according to claim 1, characterized characterized that the manganese and the silicon simultaneously added to the melt become.   3. The method according to claim 2, characterized characterized that manganese and Silicon can be added as a batch. 4. The method according to any one of the preceding claims, characterized in that Manganese and silicon as a free-flowing material be added. 5. The method according to any one of the preceding claims, characterized in that the manganese as electrolyte manganese and the silicon as Ferrosilicon can be added. 6. The method according to any one of the preceding claims, characterized in that the required amount of manganese and silicon over distributed in the melt for a certain period of time is given. 7. The method according to claim 6, characterized characterized in that the addition of Manganese and silicon are done in portions. 8. The method according to claim 6, characterized characterized in that the addition of Manganese and silicon are carried out continuously.   9. The method according to any one of the preceding claims, characterized in that while adding manganese and silicon the Melt bath temperature with a maximum deviation from 20 ° C to a maximum of 50 ° C above each current liquidus temperature of the melt kept becomes. 10. The method according to any one of the preceding claims, characterized in that the melt bath temperature is adjusted as follows during the addition of manganese and silicon:
T _melt [° C] = T _LS - 5% Mn - 8% Si + DT _UE
With
T _melt : current melt bath temperature,
T _LS : liquidus temperature of the melt before the addition of Mn and Si,
DT _Ue : temperature _amount by which the T _{melt is kept} above the current liquidus temperature,
% Mn: current Mn content,
% Si: Current Si content. 11. The method according to any one of the preceding claims, characterized in that Manganese and silicon below the melt surface be introduced into the melt. 12. The method according to any one of claims 1 to 9, characterized in that  Manganese and silicon using a cored wire in the Melt are introduced. 13. The method according to any one of claims 1 to 10, characterized in that Manganese and silicon are inflated onto the melt become. 14. The method according to any one of claims 1 to 10, characterized in that the manganese and silicon in barrels in the melt be introduced. 15. The method according to any one of the preceding claims, characterized in that together with manganese and silicon aluminum in the Melt is introduced. 16. The method according to any one of the preceding claims, characterized in that the completely alloyed steel melt up to 0.85 mass% Contains carbon. 17. The method according to claim 16, characterized characterized that the finished Alloyed steel melt up to 0.6 mass% carbon contains. 18. The method according to any one of the preceding claims, characterized in that  when deoxidizing the melt a lot of Aluminum is added by at least 0.02% by mass above that for oxygen binding lying amount. 19. The method according to any one of the preceding claims, characterized in that up to 3% by mass of silicon was added to the melt become. 20. The method according to any one of the preceding claims, characterized in that up to 3% by mass of aluminum were added to the melt become. 21. The method according to any one of the preceding claims, characterized in that the aluminum in the molten form of the melt is added.