JP2013227673A - Method for smelting low-carbon high-manganese steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for smelting low-carbon high-manganese steel including ≥0.02 mass% and <0.10 mass% C and ≥0.5 mass% Mn, at a high Mn yield rate.SOLUTION: A method for smelting low-carbon high-manganese steel includes performing vacuum degassing process for molten steel taken from a convertor to a ladle. During the time from the discharging of the molten steel from the converter to the start of the vacuum degassing process, among the total Mn source to be charged to the molten steel, an Mn source of less than 50 mass% in terms of metal Mn is charged. In a succeeding vacuum degassing, a rimmed treatment is performed without feeding oxygen from a top-blown lance, and after deoxidization using a deoxidizing agent, a killed treatment is performed, as well as an Mn source containing at least C within a range of 0.5 to 10 mass% is charged as the residual Mn source, whereby the concentration of each of C and Mn is adjusted to a desired range.

Description

  The present invention relates to a method for producing low-carbon high-manganese steel by vacuum degassing of molten steel discharged from a converter. Specifically, even if inexpensive FeMn is used as a Mn source, Mn is produced with a high yield. It is related with the melting method of the low carbon high manganese steel which can add.

  Low carbon high manganese steel is used in large quantities for steel pipe materials for line pipes and high strength steel plates for automobiles. Here, the low carbon high manganese steel in the present invention refers to a steel having a C content of 0.02 mass% or more and a Mn content of 0.5 mass% or more.

  Addition of Mn to steel is generally performed by decarburizing the molten steel from the converter to the ladle and using the vacuum degassing equipment such as RH vacuum degassing equipment. And is performed during secondary refining to adjust the composition of alloying elements. As Mn raw materials used for the addition of Mn, metal manganese (Met-Mn, metal Mn), low C ferromanganese (LCFeMn) having a low C concentration, and high C ferromanganese having a high C concentration (shown in Table 1 below) Three types of HCFeMn) are mainly used. Hereinafter, the above three types are also referred to as “Mn source”, and the two types of LCFeMn and HCFeMn are also referred to as “FeMn” or “Mn alloy iron”.

  Since Mn is an element that has a high vapor pressure and is easily lost, high-Mn steel needs to be melted while minimizing loss due to evaporation of Mn. Then, when melting high Mn steel using a vacuum degassing apparatus, in order to shorten the decarburization time, metal Mn or LCFeMn having a low C content is used as a Mn source. However, metal Mn has a problem that the raw material cost is higher than that of Mn alloy iron such as LCFeMn and HCFeMn. In addition, FeMn is produced domestically by importing Mn ore, but metal Mn largely depends on import, and stable supply is considered uneasy.

Accordingly, attempts have been made to increase the use ratio of LCFeMn or HCFeMn Mn alloy iron, which is inexpensive and can be supplied relatively stably, instead of metal Mn. For example, in Patent Document 1, in the production of a high Mn ultra-low carbon steel having an Mn amount of 1 mass% or more, about 20 kg of HCFeMn / molten steel t is charged at the time of steel leaving the converter, and oxygen is discharged from the top blow lance during RH treatment. And an inert gas are mixed and sent to decarburize without losing Mn, thereby reducing the amount of metal Mn used in the killing process and reducing the cost. Here, the above-mentioned killing treatment includes vacuum degassing treatment of molten steel deoxidized with Al or Si, etc. to adjust the alloy components, reduce dissolved gas components, and promote flotation separation of deoxidized products (inclusions). This refers to the refining operation.
Further, in Patent Document 2, 19.0 kg / t of HCFeMn is introduced into the ladle during the steel output from the converter, and then from the upper blowing lance in a vacuum suction state against the molten steel surface in the ladle in the vacuum degassing tank. In the melting method of high Mn steel that blows oxygen and vacuum decarburization of molten steel, while adding Al to the molten steel in the ladle during the converter steel, it suppresses the temperature drop of the molten steel in the ladle. A technique for suppressing Mn loss by mixing water with oxygen blown from an upper blowing lance and vacuum decarburizing while adjusting the degree of vacuum in the degassing tank is disclosed.

JP 05-195046 A JP 2003-221613 A

  However, in a low carbon steel having a C content of 0.02 mass% or more, the amount of oxygen in the molten steel required for the decarburization reaction is small, and the decarburization rate is slow. In this respect, in each of the above prior arts, in order to ensure the amount of oxygen necessary for decarburization, the rim vacuum treatment is performed while the acid is fed from the top blowing lance with the RH vacuum degassing apparatus. Here, the rimdo treatment refers to a refining operation in which undeoxidized or semi-deoxidized molten steel is vacuum degassed to remove C in the molten steel as CO gas. However, the oxygen sent from the top blow lance not only reacts with C in the molten steel to decarburize, but also reacts with Mn, so that Mn is lost due to feeding and the Mn yield decreases. There is.

  The present invention has been made in view of the above-described problems of the prior art, and the purpose thereof is steel having a C content of 0.02 mass% or more and less than 0.10 mass% and a Mn content of 0.5 mass% or more. Another object of the present invention is to propose an advantageous method for producing low carbon high manganese steel that can be produced with a high Mn yield.

  The inventors have intensively studied to solve the above problems. As a result, the molten steel blown in the converter is put into less than 50 mass% in terms of metal Mn out of all the Mn sources added to the molten steel before the start of vacuum degassing from the steel output. The amount of oxygen necessary for decarburization is ensured as non-deoxidation without deoxidation or addition of any deoxidizer, and then the vacuum degassing treatment in which de-C is advanced over de-Mn, Rim treatment without dehydration without blowing acid from the blow lance, decarburization of the C pick-up allowance, and by introducing the remaining Mn source, Mn source of inexpensive Mn alloy iron The inventors have found that the use ratio can be increased and the Mn yield can be improved, and the present invention has been completed.

  That is, the present invention provides a low carbon high manganese steel with C: 0.02 mass% or more and less than 0.10 mass% and Mn: 0.5 mass% or more by vacuum degassing of the molten steel discharged from the converter to the ladle. In the method of melting, the Mn source to be introduced from the converter steel to the start of vacuum degassing is less than 50 mass% in terms of metal Mn out of the total Mn sources to be introduced into the molten steel, followed by vacuum degassing. In the gas treatment, after performing the rimd treatment without performing the acid supply from the top blowing lance, the deoxidizer is added and killed, and at least C is in the range of 0.5 to 10 mass% as the remaining Mn source. A method for melting low-carbon, high-manganese steel is proposed in which the Mn source contained in the above is introduced into the vacuum degassing process and the concentrations of C and Mn are adjusted within a target range.

  The melting method of the low carbon high manganese steel of the present invention is characterized in that a deoxidizer and a Mn source are not added to the molten steel before the vacuum degassing treatment is started from the converter steel. .

  Further, in the above-described vacuum degassing process, the low carbon high manganese steel melting method of the present invention is deoxidized by introducing a deoxidizing agent, and the C concentration in the molten steel at the time of starting the killing process is the target component range. The Mn source containing C in the range of 0.5 to 10 mass% is introduced during the killing process.

Further, the melting method of the low carbon high manganese steel of the present invention is based on the assumption that the yield of C and Mn of the Mn source is 100% when the Mn source is introduced during the rimd process of the vacuum degassing process. The concentration of C and Mn in the molten steel after the Mn source is charged is represented by the following formula (1):
P ≦ (C / Mn) × 10 ^{(12.759-13890 / T)} (1)
However, the pressure in the vacuum degassing tank immediately after the P: Mn source is charged (Pa)
C: C concentration (mass%) of the average composition of molten steel immediately after Mn source input
Mn: Mn concentration (mass%) of the average composition of molten steel immediately after the Mn source is charged
T: Molten steel temperature (K) immediately after Mn source is charged
It is characterized in that a Mn source is introduced so as to satisfy the above.

  Moreover, the melting method of the low carbon high manganese steel of this invention is 30 mass% or more in conversion of metal Mn among the total Mn sources thrown into molten steel, when melting steel of C: less than 0.05 mass%. FeMn is introduced at a stage before the deoxidizer is introduced by vacuum degassing.

  Moreover, the melting method of the low carbon high manganese steel of this invention is 50 mass% or more in conversion of metal Mn among all the Mn sources thrown into the molten steel taken out from the converter, and C is 0.5-10 mass%. FeMn contained in a range is used.

  According to the present invention, the pick-up allowable amount of C can be increased by decarburizing by degassing the molten steel that has sufficiently secured the amount of dissolved oxygen as non-deoxidized or semi-deoxidized. It is possible to increase the use ratio of inexpensive Mn alloy iron (FeMn) as a source, and to add Mn source to the molten steel mainly during vacuum degassing treatment, so that Mn can be added at a high yield. Therefore, the basic unit of Mn alloy iron can be greatly reduced.

It is Mn alloy iron injection | throwing-in flowchart of the invention example 1 in an Example. It is a Mn alloy iron injection | throwing-in flowchart of the invention example 2 in an Example. It is a Mn alloy iron injection | throwing-in flowchart of the comparative example 2 in an Example. It is a Mn alloy iron injection | throwing-in flowchart of the comparative example 5 in an Example.

  The method for melting low-carbon high-manganese steel according to the present invention is obtained by secondary refining of molten steel discharged from a converter to a ladle by vacuum degassing using an RH vacuum degassing apparatus or the like. : 0.02 mass% or more and less than 0.10 mass%, Mn: 0.5 mass% or more of low carbon high manganese steel is melted. Its basic technical idea is semi-desorption of molten steel blown in a converter. The amount of oxygen necessary for decarburization is secured as acid or non-deoxidized, and in the subsequent vacuum degassing treatment, decarburization is performed without rimming without sending acid from the top blowing lance, and the allowable amount of pickup of C By adding a Mn source with a margin, the ratio of inexpensive Mn alloy iron (HCFeMn, LCFeMn) used as a Mn source is increased, Mn loss is reduced, and the yield of Mn is increased. There is a place to improve. This will be specifically described below.

  First, the melting method of the present invention is applied to a low carbon high manganese steel having target components of C: 0.02 mass% or more and less than 0.10 mass% and Mn: 0.5 mass% or more. If the target C concentration is less than 0.02 mass%, if an inexpensive Mn alloy iron containing a large amount of C is used as the Mn source, the desired C concentration may not be achieved due to C pickup. On the other hand, if C exceeds 0.10 mass%, inexpensive Mn alloy iron containing a large amount of C can be used without applying the present invention.

  In addition, when applying the melting method of this invention, it is preferable that C concentration of the steel which comes out from a converter is below the upper limit of the target C concentration after secondary refining. If the upper limit of the target C concentration is exceeded, if the target C concentration is low, even if decarburization is performed in the subsequent vacuum degassing process, the upper limit value of the target C concentration is set for pickup using C-containing Mn alloy iron. It is because there is a risk of exceeding.

  Next, in the melting method of the present invention, the Mn source of less than 50 mass% in terms of metal Mn is included among all the Mn sources to be introduced into the molten steel before the vacuum degassing process starts from the converter steel. In a semi-deoxidized state, or in a non-deoxidized state without adding any deoxidizer during the above, in the subsequent vacuum degassing treatment, at least C is 0.5 to It is important to adjust the concentration of C and Mn within the target range by introducing a Mn source contained in the range of 10 mass%. This is because Mn and C contained in the Mn source are weak deoxidizing elements, and therefore, before starting the vacuum degassing treatment, among all the Mn sources to be introduced into the molten steel, 50 mass% in terms of metal Mn. If the above is added, the oxygen in the molten steel will be reduced too much, and in the “rimmed process” in the vacuum degassing process of the next step described later, the [C] + [O] → CO (g) reaction will desorb. This is because it becomes difficult to charcoal and the oxidation loss of Mn added increases.

  However, when steel with C of less than 0.05 mass% is melted, in the vacuum degassing treatment, before introducing the deoxidizer, out of all Mn sources to be introduced into the molten steel, in terms of metal Mn. It is preferable to add FeMn at 30 mass% or more. This is because when FeMn is added, the C concentration in the molten steel increases due to the pick-up of C, but in the killing treatment after Al deoxidation, the amount of oxygen necessary for decarburization is small, and therefore decarburization cannot be performed. Therefore, when melting steel with C less than 0.05 mass%, it is necessary to use expensive metal Mn as a Mn source unless FeMn is added before adding a deoxidizer. Because.

  Subsequently, the semi-deoxidized or non-deoxidized molten steel produced from the converter is subjected to a rimmed process for decarburization under vacuum using a vacuum degassing facility such as an RH vacuum degassing apparatus, It is necessary to perform a vacuum degassing process consisting of a series of steps in which a deoxidizer is added to perform deoxidation and kill processing. Here, the reason why the vacuum degassing treatment is performed is that, in the above “rimmed treatment”, the higher the degree of vacuum, the more the reaction [C] + [O] → the reaction of [Mn] + [O] → (MnO). This is because the reaction of CO (g) occurs preferentially, so that decarburization can be performed with less Mn oxidation loss. For this purpose, it is desirable to control the degree of vacuum at the time of charging the Mn source during the rimming process to a range of 0.5 to 20 torr (67 to 2667 Pa). When the degree of vacuum exceeds 20 torr, the effect of reducing Mn loss is reduced. On the other hand, from the viewpoint of enhancing the above effect, it is preferable that the degree of vacuum is high, but not only a huge exhaust facility is required to raise the vacuum to less than 0.5 torr, but also the above effect is saturated. The “killing process” is also preferably performed under reduced pressure. This is because the higher the degree of vacuum, the greater the agitation force, which can promote the agglomeration / separation of inclusions, which is advantageous for melting high cleanliness steel.

  Moreover, in the rimd process in the said vacuum degassing process, it is necessary not to carry out the oxygen blowing (acid delivery) from the top blowing lance to the molten steel. The acid sent from the top blow lance increases the oxygen concentration in the molten steel and advances the [C] + [O] → CO (g) reaction, and is effective in promoting decarburization. This is because the Mn loss due to the progress of the Mn evaporation at the fire point formed on the surface of the molten steel or the progress of the [Mn] + [O] → (MnO) reaction due to the decrease in the degree of vacuum increases.

  In the vacuum degassing process, among all the Mn sources to be charged into the molten steel, the remaining Mn source that has not been charged until the vacuum degassing process is started from the converter steel is at least C of 0. It is necessary to input using a Mn source contained in a range of 5 to 10 mass%. The reason for this is that a Mn source containing C in a range of 0.5 to 10 mass% is less expensive than metal Mn. By using this, the amount of metal Mn used can be reduced, and the iron alloy cost can be reduced. This is because it can be reduced.

In addition, when the Mn source is charged in the vacuum degassing process during the rimming process, the C of the Mn source to be charged and the C in the molten steel after the Mn source is charged when the yield of Mn is assumed to be 100%. And the concentration of Mn is the following formula (1):
P ≦ (C / Mn) × 10 ^{(12.759-13890 / T)} (1)
However, the pressure in the vacuum degassing tank immediately after the P: Mn source is charged (Pa)
C: C concentration (mass%) of the average composition of molten steel immediately after Mn source input
Mn: Mn concentration (mass%) of the average composition of molten steel immediately after the Mn source is charged
T: Molten steel temperature (K) immediately after Mn source is charged
It is preferable to introduce a Mn source so as to satisfy the above.

  Here, the above equation (1) is an equation representing which of C and Mn is preferentially oxidized, and C is given priority over Mn by introducing a Mn source so as to satisfy the above equation (1). This is because it becomes possible to suppress oxidation loss of Mn.

  On the other hand, when the Mn source in the vacuum degassing process is performed during the killing process after the deoxidizing agent is added and deoxidized, the C concentration in the molten steel at the start of the killing process is set to the target component range. It is preferable to use a Mn source containing C in a range of 0.5 to 10 mass%. The reason for this is that the Mn source containing C in the range of 0.5 to 10 mass% is less expensive than metal Mn. By using this, the amount of metal Mn used can be reduced, and the alloy iron cost can be reduced. However, if this is used during the killing process, the C concentration increases, and accordingly, the C concentration in the molten steel at the start of the killing process is lowered below the upper limit of the target component range. It is necessary to keep it.

  In the present invention, FeMn containing C in the range of 0.5 to 10 mass% is used for 50 mass% or more in terms of metal Mn among all Mn sources to be introduced into the molten steel discharged from the converter. preferable. Thereby, the usage-amount of metal Mn can be reduced and alloy iron cost can be reduced effectively.

  By using the above melting method of the present invention, low carbon high manganese steel can be efficiently melted with a high Mn yield even if FeMn is used at low cost without using expensive metal Mn.

  A series of processes in which the molten steel discharged from the converter to the ladle is rimmed and decarburized using an RH vacuum degassing apparatus, and an Al-based deoxidizer is added and deoxidized and then killed. The secondary refining which performed the vacuum degassing process which consists of this, and melted | dissolved the low carbon high manganese steel of 2 types of component system A and B which are different in C and Mn content shown in Table 2.

It should be noted that the molten steel from the converter to the ladle includes undeoxidized steel (No. 1, 3, 7, 8 and 10) to which no deoxidizer is added, HCFeMn which is a weak deoxidizer, and Three levels of semi-deoxidized steel (No. 2, 4 to 6 and 9) to which LCFeMn is added and deoxidized steel (No. 11) to which a metal Al-based deoxidizer is added are used.
Further, as the Mn source to be added to the molten steel, three types of metals Mn, HCFeMn, and LCFeMn having different C contents shown in Table 1 described above were used. As shown in Table 1 and Table 3-2, before starting vacuum degassing from the converter steel, it was divided into three stages: rimmed in vacuum degassing and killed after Al deoxidation. It was.
When the Mn source is added during the rimming process (Nos. 1-3, 5, and 7-9), the molten steel temperature immediately before the Mn source input and the measured values of the components and the input amount of the input Mn source, Table 3-1 also shows the C concentration, Mn concentration and temperature of the molten steel, which is calculated from the composition and specific heat, etc., and becomes uniform immediately after the Mn source is charged, and the value on the right side of equation (1) calculated from these. It was shown to.
Further, the degree of vacuum in the degassing tank before and after the Mn source was charged during the rim treatment was controlled to be 5 to 20 torr (667 to 2667 Pa). However, the degree of vacuum when sending the acid from the top blowing lance decreased to 50 torr (6666 Pa) due to the capacity of the exhaust equipment because of the high CO gas generation rate.
As a reference, FIGS. The charging flow of Mn alloy iron from 1, 2, 5, and 11 converter steels to the end of vacuum degassing is shown.

  From the steel composition obtained in the converter, the molten steel composition after the RH treatment, and the input amounts of the three types of Mn sources, the Mn yield (%) and the decarburization amount by vacuum degassing (kg / molten steel t) are calculated. The calculation was made and the results are shown in Tables 3-1 and 3-2.

From Table 3-1 and Table 3-2, No. 1 satisfying the conditions of the present invention is obtained. In each of the invention examples of 1-3, 7, 8, and 10, a Mn yield of 82% or more was obtained, and in particular, No. 1 in which the Mn addition ratio during RH treatment was 80 mass% or more. 1,3, No. In Examples 7, 8, and 10, the Mn yield is 85% or more.
However, no. In Example 10 of the invention, although the M content of the target component is as low as 0.03 mass%, the Mn source is added in the killing treatment after the Al deoxidation, so the metal Mn is added to a part of the Mn source. It was necessary to use and limit the pickup of C.

On the other hand, No. 1 which sent acid during the rim treatment with RH. In Comparative Example 5, although the amount of decarburization is large, the Mn yield is the lowest due to Mn oxidation loss.
In addition, No. 1 containing a large amount of Mn source before the start of RH treatment. In the comparative examples of 4, 6 and 9, all have a Mn yield of less than 80%. In particular, no. Although the comparative example of No. 9 had a low C content of the target component of 0.03 mass%, the amount of Mn source added before the start of the RH treatment was large, so metal Mn had to be used in the RH treatment. The raw material cost is high.
In addition, No. 1 was deoxidized when the molten steel was discharged from the converter. In Comparative Example 11, although the Mn yield was as high as 86%, decarburization was not performed by the rimmed process, so a large amount of metal Mn had to be used in the RH process due to the C concentration limitation, and the raw material cost was high. It has become.
From the above results, it can be seen that by applying the present invention, a low carbon high manganese steel can be efficiently melted with a high Mn yield.

Claims (6)

In the method of vacuum degassing the molten steel discharged from the converter to the ladle and melting low carbon high manganese steel with C: 0.02 mass% or more and less than 0.10 mass%, Mn: 0.5 mass% or more,
The total Mn source to be introduced from the converter steel to the start of vacuum degassing treatment is less than 50 mass% in terms of metal Mn among all the Mn sources to be introduced into the molten steel.
In the subsequent vacuum degassing treatment, after performing the rimd treatment without performing the acid sending from the top blowing lance, the deoxidizer is added and the killed treatment is performed.
As the remaining Mn source, a Mn source containing at least C in the range of 0.5 to 10 mass% is introduced during the vacuum degassing process, and the concentrations of C and Mn are adjusted within the target range. Melting method of low carbon high manganese steel. 2. The low-carbon high-manganese steel according to claim 1, wherein no deoxidizer and Mn source are added to the molten steel before the vacuum degassing process is started from the converter steel. Method. In the vacuum degassing treatment, a deoxidizing agent is added to perform deoxidation, and the C concentration in the molten steel at the time of starting the killing treatment is set to be less than the upper limit value of the target component range. The method for melting low carbon high manganese steel according to claim 1 or 2, wherein a Mn source contained in a range of 10 mass% to 10 mass% is added. When the Mn source is charged during the rimd process of the vacuum degassing process, the C and Mn concentrations in the molten steel after the Mn source is charged when the C and Mn yield of the Mn source is assumed to be 100% are as follows. The method for melting low-carbon high-manganese steel according to any one of claims 1 to 3, wherein a Mn source is added so as to satisfy the formula (1).
P ≦ (C / Mn) × 10 ^{(12.759-13890 / T)} (1)
However, the pressure in the vacuum degassing tank immediately after the P: Mn source is charged (Pa)
C: C concentration (mass%) of the average composition of molten steel immediately after Mn source input
Mn: Mn concentration (mass%) of the average composition of molten steel immediately after the Mn source is charged
T: Molten steel temperature (K) immediately after Mn source is charged C: When melting steel of less than 0.05 mass%, among all Mn sources to be introduced into the molten steel, FeMn of 30 mass% or more in terms of metal Mn, before introducing the deoxidizer by vacuum degassing treatment The method for melting low-carbon high-manganese steel according to any one of claims 1 to 4, wherein the melting is performed in stages. The FeMn containing C in a range of 0.5 to 10 mass% is used for 50 mass% or more in terms of metal Mn among all Mn sources to be introduced into molten steel produced from a converter. The method for melting low carbon high manganese steel according to any one of 5.

Images