JPS5819422A - Manufacture of steel with converter - Google Patents

Abstract

PURPOSE:To easily refine low P steel in the manufacture of steel with a converter by carrying out primary blowing using a premolten flux as a slag making agent so as to regulate the carbon concn. of molten metal, the basicity of slag and the temp. of the molten metal after finishing the blowing to prescribed ranges. CONSTITUTION:Primary blowing is carried out using a premolten CaO-CaF2-SiO2 flux or the like as a part or all of a slag making agent so as to regulate the C concn. of molten metal after finishing the blowing to 3.0-3.5%, the basicity (CaO/SiO2) of slag to >=2.0 and the temp. of the molten metal to 1,400-1,450 deg.C. Thus, the P concn. of the molten metal after the blowing can be restricted to a low value, and by carrying out secondary blowing, steel with <=0.005% P concn. can be discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a converter steel manufacturing method, and an object of the present invention is to melt low phosphorus steel in a container in accordance with 4C) of the converter steel manufacturing method in which primary blowing and secondary blowing are performed in step 41. shall be.

As is well known in the normal line of converter steel manufacturing, the main raw materials, pig iron and scrap, are charged into a converter vessel, and then oxygen gas is introduced while sub-raw materials such as scale, burnt lime, and dolomite are charged. Through the top-blowing lance and tuyeres provided in the belly or bottom of the furnace, desulfurization, decarburization, dephosphorization, and desulfurization reactions are carried out to obtain molten steel at the desired temperature and composition. It is a steel manufacturing method.

At this time, it is necessary to adjust the temperature! During blowing, iron ore or quicklime is continuously fed into the furnace (according to the furnace opening). In this type of converter steel manufacturing method, unless pig iron that has been reduced in phosphorus according to the hot metal precipitate theory is used, there is no phosphorus in the normal main raw material pig iron.
As approximately 0.090-0.110 tatami mats have been counterfeited, it is extremely difficult for the country to produce low-phosphorus steel, and under normal operation, (96P] = 0.010 to 0.0151 copper is melted. .

It was a big guy.

The ninth double slug method and two-time blowing method were considered, and achieved a similar result, (*P) = o, oos ~ 0.0
It has become possible to obtain low phosphorus steel of about 10%.The double slug method involves two blowing steps: primary and secondary.
The slag produced during the first blowing is allowed to overflow naturally from the furnace mouth, and the slag is manually removed.In the double blowing method, the slag is poured out after the first blowing, and the slag is poured out after the first blowing. After slag removal,
There is a difference in the method of removing the slag from the primary blowing between the methods of recharging the converter, performing secondary blowing, and then tapping the steel. (due to the imperfection of the slag, and the latter due to the disadvantage of temperature drop due to the reidle),
Stable ultra-low cast steel ((IIP)≦0 by converter blowing only)
．． 005) has not yet reached S1s.

The ninth ultra-low cast steel, 1llllJl, is either smelted in a converter using pig iron that has been made low in phosphorus through hot metal dephosphorization treatment, or removed from molten steel in a later process (by ladle 7 arness, powder injection, etc.). Currently, it is manufactured using phosphorous.The present invention was made in view of the above points, and it is a double
By carrying out the primary blowing in a predetermined method such as the double blowing method during the slag method, it is possible to easily obtain a low phosphorus steel.

That is, in the converter steel manufacturing method of the present invention, pre-melt flux is used as part or all of the slag-forming agent in the primary blowing, and the carbon concentration of the molten metal after the primary blowing is 3. O~3.5, slag basicity ((CaO)/(
810m) ): 10 or more, molten metal temperature: 1400~
Perform the first blowing to a temperature of 1450℃ (this)
It is possible to keep the molten phosphorus concentration low after the first blowing)
Then, if secondary blowing is performed, the raw steel phosphorus becomes 11 degrees [IGPI≦
It is possible to tap steel of 0.005.

Primelt 7lux includes Ca0-C, F,
-B IO, system or CaOCaFt re, o, s
io.

The carbon concentration after primary blowing is set to [%C)-S, O~1s because the carbon concentration after primary blowing is set at this concentration. This is because by the time 81 oxidation combustion has finished and the dephosphorization efficiency has reached its maximum,
This is because if the carbon degree is outside the above range, it will be disadvantageous for dephosphorization.

Furthermore, since it is more advantageous for dephosphorization to set the slag basicity above the limit filO for using pre-melt flux, this is set as the lower limit. The upper limit may be determined as appropriate depending on the composition and usage amount of Primelt 7lux.

The lower the fluidity of the slag, the better the molten metal temperature for dephosphorization, but in order to remove the slag from the primary blowing slag, it is preferably 1400 to 1450°C, and the temperature is limited to this range. do.

Next, examples will be shown.

A method of the present invention was carried out using a 250 ton pure oxygen top-blowing converter by the double slug method as follows. That is, in the primary blowing, hot metal with a phosphorus concentration of 011B is pre-melted.
Flux used in 25 of all flypx, CaO/81
0. =4.3, blowstop (c)-a, is, temperature 142
The temperature was lowered to [嗟P] = o, oos t, and then the slag was discharged from the furnace mouth, followed by subsequent blowing. As a result, extremely low cast steel with a steel phosphorus concentration of 3% was produced.

The results are shown in the table below.

Although a top blowing converter was used in the above embodiments, the present invention is not limited to this, and can also be applied to composite blowing using a top and bottom converter.

Claims (1)

[Claims] In a converter steel manufacturing method that performs primary blowing and tertiary blowing,
Pre-melt flux was used as an itch agent, and the molten carbon 11 [: 10 - Slag basicity [(CaO) / (810 J)]: 10 or more, molten metal temperature *: 1400-14 after the first blowing was completed. A converter steel manufacturing method characterized by carrying out primary blowing at $0°C.