JPS61243111A - Method for controlling end point concentration of nitrogen in top and bottom blown converter - Google Patents

Abstract

PURPOSE:To control exactly the content of N2 in a molten steel to a target value by calculating the gaseous N2 to be blown from the target content of N2 and the concn. of N2 prior to blowing of the gaseous N2 in accordance with the actual amt. of the gaseous N2 to be blown into the molten steel and the pick up amt. of the molten steel and blowing a required amt. of the gaseous N2 into the molten steel from a nozzle. CONSTITUTION:The content of N2 Nc in the molten iron which is the raw material is estimated from the concn. of Ti having a correlation therewith and the molten iron is charged into a converter where the molten iron is refined to a steel by oxygen top blown refining. The concn. DELTA(N) of N to pickup the difference between the target concn. (N)0 and (N)c of N2 in the steel of the final product is calculated. The weight R of the N2 to be picked up into the molten steel is calculated from such concn. of N and the amt. of the molten steel. The amt. of the gaseous N2 S to be blown into the molten steel upon lapse of the prescribed time t0 from the start of converter blowing is determined from the yield of the N2 blown. The time (t) for blowing N2 is determined from the amt. of the gaseous N2 passing through a lance for blowing gaseous N2 and the gaseous N2 is blown to the molten iron for the determined time, by which the molten steel having the intended concn. of N2 is produced.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention provides an end point in a top-bottom blowing converter that can reduce the nitrogen concentration [N] of molten steel to 1 lJlll with high accuracy in top-bottom blowing converter blowing. This invention relates to a nitrogen concentration control method.

[Prior Art] The applicant of the present application noticed that there is a certain relationship between the titanium concentration [T1] of hot metal and its nitrogen concentration [N],
Estimate [N] from [T1] of the hot metal, inject the required amount of nitrogen gas found from the target value at the end point of the converter and this estimate [N] into the molten steel, and set the nitrogen concentration [N] at the end point of the converter to the target value. ill
proposed a nitrogen control method for molten steel that
-50548).

[Problems to be solved by the invention] However, depending on the tapping conditions such as deoxidized tapped steel, semi-deoxidized tapped steel, or non-deoxidized tapped steel, and the hot metal content ratio in the converter charge, [N] Due to variations in the estimated value and the amount of N picked up in molten steel, when operating conditions are diversifying as in recent years, in conventional molten steel nitrogen concentration control methods,
There is a problem that the control accuracy of the converter end point [N] is low.

[Means for Solving the Problems] The present invention has been made in view of the above circumstances, and has a high control accuracy of the converter end point [N], and enables highly accurate converter conversion despite fluctuations in operating conditions. It is an object of the present invention to provide a method for controlling the nitrogen concentration at the end point of a top-bottom blowing converter, which can control the nitrogen concentration of molten steel at the furnace end point to its target value.

The end-point nitrogen concentration control method in a top-bottom blowing converter according to the present invention is such that the relationship between the amount of nitrogen gas blown in from the nozzle provided at the bottom of the converter and the amount of nitrogen picked up by WJ8 is determined in advance, and the blowing The required pick-up concentration of nitrogen to be added to the molten metal in the converter is calculated from the initial R8 nitrogen concentration and the final target nitrogen concentration, and the required pick-up concentration of nitrogen is calculated based on the relationship between the nitrogen gas layer and the nitrogen pick-up amount. Determine the required amount of nitrogen gas to be injected into the molten steel from this, determine the required nitrogen gas blowing time from this required nitrogen gas amount and the gas flow rate at the nozzle, and inject nitrogen gas into the molten steel in the converter for the required blowing time. It is characterized by

[Examples] Examples of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a flowchart showing an end point nitrogen concentration control method according to an embodiment of the present invention.

First, the component composition in the hot metal is analyzed (step 1), and the nitrogen concentration [N
] is estimated (step 2). Figures 2 and 3 are
In a converter, the nitrogen concentration [N] of molten steel after a certain period of time has passed after oxygen gas ignites is expressed as the titanium concentration [T
i] is a graph plotted against

There are usually four (sometimes one) nozzles installed at the bottom of the converter, and through these nozzles gas can be injected into the molten steel inside the converter. ing.

Each nozzle has a plurality of holes formed along two concentrically arranged circles, and the first group of holes along the inner circle of each nozzle is connected to the first piping system. A second hole group along the outer circle is connected to a second piping system.

Figure 2 shows that when there is one nozzle installed at the bottom of the converter, the third
The figure shows the case where the nozzles are 2 to 411I.

In each figure, the solid line is when the hot metal ratio is 96% or more, the broken line is when the hot metal ratio is less than 96% and 88% or more, and the dashed line is when the hot metal ratio is less than 88%. In this way, there is a clear relationship between the titanium concentration [Ti] in hot metal and the nitrogen concentration [N] in molten steel after a certain period of time has passed after the start of converter blowing. Based on the determined titanium concentration [T1], the nitrogen concentration IN of the molten steel at a certain time during converter blowing can be estimated.

A target value [N]a of the nitrogen concentration at the end point of the converter is set for each charge (step 3), and from the estimated value [N]c of the nitrogen concentration of molten steel and the target value [N]a of the end point, the converter In,
The required nitrogen pickup amount Δ[N] to be added to the molten steel is calculated according to the following equation (1) (step 4).

Δ[N] = [N]O−[N]c” (1)
As mentioned above, a converter is equipped with a plurality of nozzles at its bottom. Oxygen gas is blown onto the molten steel from a lance inserted into the converter to oxygen-blow the molten steel. Carbon dioxide (CO2>gas or argon (
Ar> gas can be blown into the molten steel in the converter to stir the molten steel, or nitrogen (N2) gas can be blown into the molten steel to add nitrogen to the molten steel. Figure 4 shows the flow of nitrogen gas blown into the molten steel from the nozzle at the bottom of the converter.
(Nm3/ton) and nitrogen pickup amount (pom)
It is a graph showing the relationship between. As is clear from this figure, there is a close relationship between the amount of nitrogen gas blown into the molten steel and the amount of nitrogen picked up by the molten steel. The amount of nitrogen gas blown R (Nm
'/ton) can be calculated.

There are usually two types of nitrogen addition patterns to molten steel. The first addition pattern is a pattern in which nitrogen gas is blown into the molten steel through both the first and second hole groups after a predetermined time period of 1nto has elapsed after the start of converter blowing (after ignition of oxygen gas). . On the other hand, in the second addition pattern, after the start of converter blowing, nitrogen gas is introduced into the molten steel from the second hole group to add nitrogen to the molten steel, and CO2 is added from the first hole group. Gas or Ar gas is injected into the molten steel to stir the molten steel, and the molten steel is stirred for a predetermined time 1. After the lapse of time, nitrogen gas is blown into the molten steel from both the first and second hole groups to add nitrogen to III.

Predetermined time after the start of converter blowing 1. After the lapse of time, the nitrogen gas Is (Nm3/ton) to be blown into the molten steel is calculated according to the following formula (Step 6).

5-R-P...(2) However, P is the amount of nitrogen gas (Nm3/ton) already blown into the molten steel from the second hole group connected to the second piping system. Note that in the first addition pattern, P is 0.

Next, based on the required blowing amount S, the required blowing time 1t of nitrogen gas is calculated. Ql (Nm
3/ton・sec), and the flow rate of the gas injected into the molten steel from the second hole group connected to the second piping system is 02 (Nm”/second).
tons/second), the required nitrogen gas! The injection time t (seconds) required to inject S into the molten steel is calculated using the following equation (3).

t-8/ (Ql +Q2) ...(
3) As a result, the control system that controls the type and supply time of gas to be supplied to the first and second piping systems is instructed to The supply time of nitrogen gas to the first and second piping systems is t
Set to .

Next, after starting to blow nitrogen gas into the molten steel from the nozzle at the bottom of the converter, the flow rate of the gas being blown into the molten steel from the nozzle is measured (step 8).

Actual measurement value Q of gas flow rate in this first and second piping system
1* and Q2*, the required nitrogen gas blowing time t* is calculated again according to the following formula (step 9).

t*-8/ (Ql *102*) ...(
4) Then, change the setting of the nitrogen gas supply time in the gas blowing control system and correct the nitrogen gas addition time from t to t*.

After a certain period of time has elapsed since the start of converter blowing, nitrogen gas is blown into the molten steel through the first and second hole groups for a required time t. Therefore, the nitrogen gas injection pattern is as shown in Figures 5 and 6, and when adding nitrogen to molten steel in the first pattern (Figure 5), the first and second holes are Nitrogen gas is blown into the molten steel for t* seconds after a certain period of time to has elapsed after the start of converter blowing, and in the second addition pattern (Fig. 6), nitrogen gas is Nitrogen gas is injected into the molten steel for tl + t * time from the start of converter blowing, and from the first hole group for a fixed time 1. After the elapse of time, nitrogen gas is blown into the molten steel for a time t*.

After blowing the required amount of nitrogen gas into the molten steel, CO is added to the molten steel.
Continue stirring the molten steel by blowing 2 gas or Ar gas,
After the required time of oxygen blowing is completed, the discharge of oxygen gas from the lance is stopped and the molten steel is tapped.

In the end-point nitrogen concentration control method configured as described above, the nitrogen concentration [N] of the molten steel at a certain time to has elapsed after the start of converter blowing is estimated from the titanium 1 degree [Til] of the hot metal. 2). Then, from the nitrogen concentration target 111 [N]a at the end point of the converter and this estimated fll[N]c, the required nitrogen pickup amount Δ[N] during converter blowing is determined.
) is determined (Step 4), and the required amount of nitrogen gas to be injected into the molten steel in the converter is determined from the predetermined relationship between the nitrogen gas injection fog and the amount of nitrogen pickup (Fig. 4) (Step 5). ).

In the first addition pattern, after charging hot metal into a converter, oxygen gas is blown onto the hot metal through a lance to start oxygen blowing. After a predetermined time te has elapsed, nitrogen gas is blown into the molten steel through the first and second hole groups. The required addition time mt is determined from the required nitrogen gas blowing Is after the constant time 1111 (-R step 6) according to the above equation (3), and this addition time t is set in the converter gas blowing control system. Then, after 30 seconds have elapsed, the flow rate of the gas being blown into the molten steel from the first and second hole groups is measured, and based on this measured gas flow rate, the required blowing time is determined according to equation (4) above. Calculate mt* and correct the nitrogen gas blowing time into the control system from t to t*. After 1+1*times have elapsed after the start of converter blowing, the injection of nitrogen gas into WIm is stopped.

In the second addition pattern, after the start of oxygen blowing, the second
Nitrogen gas is blown into the molten steel through the first hole group, and GO2 gas or Ar gas is blown into the molten steel through the first hole group. After the predetermined time to has elapsed, the gas injected from the first hole group is switched to nitrogen gas, and the nitrogen gas is injected into the molten steel through both the first and second hole groups. The required addition time t is the required nitrogen gas injection amount 5 (-
RP, step 6), is determined according to (3) above, and this addition time t is set in the converter gas injection control system. Then, after 30 seconds have elapsed, *m of the gas being blown into the molten steel from the first and twelfth nozzle groups is measured, and based on this measured gas flow rate, the required blowing time is calculated according to the above equation (4). Calculate t* and correct the nitrogen gas blowing time into the control system from t to t*. After 1+1* has passed after the start of converter blowing, the blowing of nitrogen gas into the molten steel is stopped.

[Effects of the Invention] According to the present invention, the nitrogen concentration of molten steel in the converter can be estimated from the predetermined relationship between the amount of nitrogen gas injected from the nozzle provided at the bottom of the converter and the amount of nitrogen picked up in the molten steel. Based on the value, the amount of nitrogen gas to be injected into the molten steel in the converter is determined, and this amount of nitrogen gas is injected into the molten steel, making it possible to match the nitrogen concentration of the molten steel at the end point of the converter with high accuracy to the target value. . In addition, the required amount of nitrogen gas injection can be appropriately set in response to fluctuations in operating conditions such as the hot metal ratio, so even in the current situation where operating conditions are diversifying, the end point [N] of the converter can be adjusted. I11 has high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the end point nitrogen concentration control method according to an embodiment of the present invention, FIGS. 2 and 3 are graphs showing the relationship between titanium concentration [Til] and nitrogen concentration [N] in hot metal; FIG. 4 is a graph showing the relationship between the nitrogen gas blowing amount and nitrogen pickup, and FIGS. 5 and 6 are schematic diagrams showing the nitrogen gas blowing pattern. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 3 digit〉Sida (v+) (Kishi 4E Is Is, 7-) Figure 4 N2 force p lack ton) 5th
Figure 6 Human O→ti

Claims (5)

[Claims] (1) The relationship between the amount of nitrogen gas blown in from the nozzle installed at the bottom of the converter and the amount of nitrogen picked up in the molten metal is determined in advance, and the relationship between the nitrogen concentration in the molten metal at the initial stage of blowing and the target nitrogen concentration at the end point is determined in advance. Calculate the required pickup concentration of nitrogen to be added to the molten metal, calculate the required amount of nitrogen gas to be blown into the molten steel from the required pickup concentration of nitrogen based on the relationship between the nitrogen gas amount and the nitrogen pickup amount, and calculate the required amount of nitrogen gas to be blown into the molten steel. End point nitrogen concentration control in a top-bottom blowing converter, characterized in that the required blowing time of nitrogen gas is determined from the amount of nitrogen gas and the gas flow rate in the nozzle, and nitrogen gas is injected into molten steel in the converter for the required blowing time. Method. (2) The nozzle has first and second hole groups each consisting of a plurality of gas discharge holes, and after a predetermined period of time has passed after the start of converter blowing, the nozzle A method for controlling the end point nitrogen concentration in a top-bottom blowing converter according to claim 1, which comprises blowing nitrogen gas into molten steel. (3) The nozzle has first and second hole groups each consisting of a plurality of gas discharge holes, and after the start of converter blowing, nitrogen gas is blown into the molten steel through the second hole group. After the elapse of time, the required gas injection amount is changed to a second amount through the first and second hole groups.
A top-bottom blowing converter according to claim 1, characterized in that nitrogen gas is injected into the molten steel for the required blowing time determined from the amount obtained by subtracting the amount of gas injected through the hole group. End point nitrogen concentration control method. (4) After the start of converter blowing, measure the gas flow rate being blown into the molten steel from the first and second hole groups, calculate the required blowing time from the required blowing amount and the measured gas flow rate, and Claim 2, characterized in that the blowing time is modified.
A method for controlling the end point nitrogen concentration in a top-bottom blowing converter according to item 1 or 3. (5) The end point nitrogen concentration control method in a top-bottom blowing converter according to claim 1, wherein the nitrogen concentration of the molten metal at the initial stage of blowing is estimated from the titanium concentration of the molten steel.