JPS589913A - Controlling method for content of nitrogen in steel - Google Patents

Abstract

PURPOSE:To improve the accuracy in hitting of the content of nitrogen in steel and to eliminate influence upon the controlling of other components such as Mn by estimating the content of nitrogen during tapping of steel from a converter from the content of free oxygen detected when the converter is blown out, and adding a specific nitrogen source at proper timings. CONSTITUTION:Steel is beforehand refined in a converter at the content of nitrogen therein slightly lower than a desired content, and when the converter is blown out, the content of free oxygen in molten steel is directly detected. The relation between the content of free oxygen and the content of nitrogen in such molten steel is as shown in the figure, from which the content of nitrogen of the molten steel in the blowing-out time can be estimated. The difference from a required content of nitrogen is determined from the estimated value, and a required amt. of a nitrogen source is added into a ladle during tapping. The basic flux consisting essentially of >=20% CaO and 10-50% N2 (generally called lime nitrogen) is used for the nitrogen source. Such flux is added during the time since tapping until the steel is received in the ladle to 1/2 its capacity. If it is added later than this time, the flux is difficult to be included in the molten metal and is extremely unstable because the nitrogen source is light, thus affecting the yield of nitrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the amount of nitrogen in steel during steel tapping in a converter.

The nitrogen content in steel affects the aging properties of steel, and
Significant impact on product quality. In addition, depending on the type of steel, for example, low carbon aluminum killed steel, there are strict limits on the upper and lower limits of nitrogen content, and in order to satisfy this, the amount of nitrogen must be It is necessary to adjust the amount of nitrogen added to reach the desired amount of nitrogen.

Conventionally, these processes have involved detecting the amount of carbon blow-up during tapping, estimating the amount of free oxygen based on this, and determining the amount of nitrogen. Next, by comparing this amount of nitrogen with a desired amount of nitrogen, a required nitrogen-containing ferroalloy, for example, N2-Fe-Mn, is added to the ladle in the receiving steel.

This conventional method for detecting the blowout carbon content has poor accuracy because it cannot quantify the effects of blowdown temperature, slag composition, and especially the total amount of FeO.

Furthermore, since Mn is included in the adjustment additive, and the amount of addition is determined based on nitrogen, on the other hand, the adjustment of Mn is disrupted, causing a contradiction. Furthermore, if the Mn value at the time of blow-off is high, the addition of N2-Fe-Mn may cause the MnO steel composition standard value to be exceeded. However, the cost of these additives is high.The present invention was made to solve these problems all at once. Perform refining in a furnace, directly detect the free oxygen content in the molten steel at the time of blow-off, estimate the nitrogen content of the molten steel at the time of blow-off from the value of the free oxygen content, and calculate the required amount of nitrogen to be added 1'' 2 is determined, and the amount of nitrogen in the form of a flux whose main components are Oak: 20% or more and N2: 10 to 50% is added to the ladle after tapping from the converter until the amount of steel received is %. In addition to increasing the accuracy of determining the amount of nitrogen in steel, it is possible to improve the level of operation by separating each additive source without affecting the adjustment of other components such as Mn, and to reduce the cost of additives. This provides a way to lower the

The details are described below.

In converter refining, the amount of nitrogen in the steel is set to be lower than a desired value in advance, and then adjusted to the desired value by adding a nitrogen source during tapping. 6 Therefore, when determining the nitrogen content of molten steel at the time of blow-off, the method of the present invention directly detects the free oxygen content in the molten steel. According to experiments conducted by the present inventors, the relationship between the amount of free oxygen and the nitrogen content in the molten steel is as shown in Figure 1, and from this it is possible to estimate the nitrogen content of the molten steel at the time of blow-out. . The difference between the nitrogen content of the molten steel and the required nitrogen content can be calculated from this estimated value, and the necessary amount of nitrogen source is added to the ladle at the time of tapping.

As the nitrogen source, a basic flux whose main components are +:aO: 20% or more and N2: 10 to 50% is used. This is generally called lime nitrogen, and has the advantage of being inexpensively available.

Next, the timing and timing of injecting this nitrogen source into the molten steel in the ladle is also critical, and this affects the nitrogen yield as shown in Figure 2. In other words, if the nitrogen source is added after the molten steel has been received in the tapping ladle, it is flux-like and light, so it is difficult to be uniformly rolled into the molten steel, which is indicated by the (x) mark in the figure. This results in a very unstable situation.

However, if it is added early before the assisted steel production reaches %, the state becomes stable as shown by the mark (・) in the figure. This has important implications for the estimation accuracy of nitrogen content.

Therefore, the timing of adding the nitrogen source should be until the amount of steel received in the tapping ladle reaches %0. It is.

An example of implementation according to the method of the present invention will be shown.

The steel type used in the example is low carbon aluminum guild and the standard value of nitrogen is 40~
In case of 50PPM.

The internal oxygen content of the molten steel at the time of blow-out was measured by the following method. That is, a commercially available oxygen probe was attached to the sublance, and after the blowing was stopped, the free oxygen concentration was measured at a point 500 mm below the hot water surface.

From the measured value of the amount of free oxygen, FIG. 1 and FIG.

The amount of nitrogen in the molten steel at the time of blow-out was determined based on the estimation standard of free oxygen amount → nitrogen amount prepared in advance as shown in Figure 2.

The value was compared with the standard value of 40 to 60 PPM, and the necessary additional amount of the tank was determined to meet the standard, and the nitrogen source was lime nitrogen (IJ-N): 21.07%.

Free C! ao: 22.5%, free c:lo,
s%, bulk ratio blood: 2.29) to 1.219 per ton of molten steel
1 minute after the start of tapping, the entire amount was poured into the ladle.

At the end of the addition, the molten steel receiver lid in the ladle was at a level of about 100 ml.

As a result, the nitrogen content of the sampled steel was 52 PPM, which was similar to the value of the preliminary test.

As described above, the present invention makes it easy to control the desired amount of nitrogen, vD, and the influence on other components can be completely ignored and only the nitrogen adjustment can be operated independently. The cost can also be reduced, and the effect is large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of free oxygen and the amount of nitrogen in molten steel at the time of blow-off, and FIG. 2 is a diagram similarly showing the relationship between the free oxygen cap and the nitrogen yield. Applicant Nippon Steel Corporation 1111 oyS yo white rb smell, (2rh) Totoi mountain i side fat (rPr-q)

Claims (1)

[Claims] Refining is performed in a converter in advance so that the nitrogen content in the steel is lower than the desired amount, and the free oxygen content in the molten steel is detected at the time of blow-off, and the nitrogen content of the molten steel at the time of blow-off is determined from the value of the free oxygen content lid. Estimate the required amount of nitrogen to be added, Car: 2
0% or more, N2: 10 to 50% as the main component of a nitrogen source in the form of a flux is added to the ladle after tapping from the converter until the amount of received steel reaches %. How to adjust the amount of nitrogen.