JPH0686614B2 - Method for producing high nitrogen content steel in bottom blown or top blown converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a bottom blowing or top bottom blowing steelmaking converter of 60 ppm.
The present invention relates to the method for producing nitrogen-containing steel described above.

<Prior Art> Generally, as a method for producing nitrogen-containing steel in a steelmaking refining furnace,
JP-A-53-128520, JP-A-54-125113, JP-A-55-50415, JP-A-58-167708, JP-A-61-
As disclosed in Japanese Patent No. 243111, etc., a method of blowing a required amount of nitrogen gas to obtain a target nitrogen concentration from a furnace opening or a tapping hole during blowing, or blowing it into molten steel from a bottom blowing nozzle. Is being done.

Therefore, the present applicant has proposed a method for producing nitrogen-containing steel by adding coke at the time when C reaches 1.0 to 0.3% during refining, as Japanese Patent Application No. 63-234846. Incidentally, FIG. 1 shows the relationship between the input coke amount and the steel output nitrogen content at that time.

However, in the method of introducing coke during refining, the problem that S (usually 0.4-0.8% content) in the coke enters the molten steel and the S concentration increases, as can be seen from FIG. However, there was a problem that it was difficult to obtain N concentration of 60 ppm or more only by adding coke.

<Problems to be Solved by the Invention> An object of the present invention is to propose a method capable of stably and economically obtaining a high-nitrogen steel having a target concentration of 60 ppm or more in a bottom-blown or top-blown converter. Is.

However, the method of blowing nitrogen gas into the molten steel from the top or bottom has a problem that the nitrogen yield is low and unstable, and the target end point nitrogen concentration cannot be accurately controlled.

Further, in particular, in the method disclosed in Japanese Patent Laid-Open No. 55-50415, since nitrogen blowing is carried out once oxygen blowing is stopped, refining time is extended, molten steel temperature is lowered, and furnace refractory melting loss is increased. There was a problem of inviting.

<Means for Solving the Problem> The present invention has a C content of 1.0 to 0.3 wt% when producing nitrogen-containing steel of 60 ppm or more in a bottom-blown or top-blown steelmaking converter.
At that time, coke was charged into the molten steel of 6 to 8 kg / ch · t, and then when the converter unburned exhaust gas recovery was completed, an amount of N ₂ gas according to the amount of burnt lime used for refining was added to the bottom. A method for producing high nitrogen content steel in a bottom-blown or top-blown converter, which is characterized in that it is blown from the tuyere.

<Operation> First, the reason why the coke is added to the steel when the C content becomes 1.0 to 0.3 wt% during refining in the converter will be described.

Nitrogenation by coke is about 1% N contained in coke
However, when molten steel is at the peak of decarburization,
Since N in steel is trapped in the generated CO gas and denitrified, it is necessary to add coke at the final stage of blowing, when decarburization is reduced, in order to efficiently perform nitrification by coke. Fig. 2 shows the experimental results showing the yield of N in the coke when a certain amount of coke was added at various C contents, but when C was 1.0 to 0.3 wt%, It was found that the yield of N was high.

Next, the reason why the amount of coke charged is limited to 6 to 8 kg / ch · t will be described.

As can be seen from Fig. 1, the tapping nitrogen linearly rises up to the amount of coke input of 8 kg / ch · t, but above that, the variation becomes large and the tapping nitrogen levels off. Therefore, the upper limit of the amount of coke input was set to 8 kg / ch · t. Further, the lower limit of the amount of coke charged was set to 6 kg / ch · t in order to stabilize the yield and obtain the maximum N concentration in it.

Then when the converter unburned gas recovery is completed, the reason for blowing N ₂ gas, N ₂ in the coke after turning BOF gas recovery
This is because if the gas is blown in, the decarburization reaction is temporarily interrupted, and the exhaust gas recovery must be stopped, which causes energy recovery loss. Therefore, in the present invention, N ₂ gas is blown at a time when the converter exhaust gas recovery is not affected and C is the highest (corresponding to the completion of the converter exhaust gas recovery).

Next, the reason why the amount of N ₂ gas is blown according to the amount of calcined lime used for refining will be described.

There was a problem that nitrogen yield was not stable if only N ₂ gas was blown in. As a result of various studies, it was discovered that the nitrogen yield varies depending on the amount of burnt lime used, as shown in FIG.

The present invention is based on this finding, and the blowing amount of N ₂ gas may be determined from FIG. 3 depending on the target N content and the amount of calcined lime used for refining.

Next, the present invention will be described in more detail based on examples.

<Example> Coke of 7 to 6 kg / ch · t is added at C of 0.6 to 0.8 wt% in steel, and OG gas recovery is interrupted at C of 0.2 to 0.3 wt% of steel. At the same time, N ₂ gas corresponding to the amount of calcined lime used up to that time is blown from the bottom blowing tuyere, blowing stop C is 0.03 to 0.05%, and blowing stop temperature is 1590 to 1610 ° C.

Fig. 4 shows a histograph of nitrogen concentration when the target was N85ppm for tapping. It was possible to produce 85ppm high nitrogen steel which could not be obtained by the coke charging method alone.

Note that the relationship between the amount of lime used and the amount of N ₂ gas blown when the target nitrogen was 85 ppm and the coke amount was 7 kg / ch · t was as shown in Table 1.

<Effects of the Invention> Conventionally, steel with N60 ppm or more used Mn alloy iron nitride, but according to the present invention, stable high nitrogen steel can be economically manufactured without using Mn alloy iron nitride. Became.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of coke input and steel output nitrogen, and FIG. 2 is a graph showing the relationship between C in steel and nitrogen yield.
FIG. 3 is a graph showing the relationship between the amount of burnt lime used and the yield of nitrogen, and FIG. 4 is a histograph showing the frequency of discharged steel nitrogen.

Claims (1)

[Claims] 1. When producing a nitrogen-containing steel of 60 ppm or more in a bottom-blown or top-blown steelmaking converter, when the C content reaches 1.0 to 0.3% by weight, the coke content is 6 to 8 kg / ch. t Bottom blowing or top blowing characterized by blowing N ₂ gas into the molten steel from the tuyere of the bottom according to the amount of burnt lime used for refining when the converter unburned exhaust gas recovery is completed. Method for producing high nitrogen content steel in bottom blowing converter.