JPS5852004B2 - Low-hydrogen steel melting process in pure oxygen bottom-blown converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the blowing method of a pure oxygen bottom-blown converter, and particularly to a method for producing low hydrogen steel in the converter.

Pure oxygen bottom-blown converters inherently have a high concentration of hydrogen, which is caused by a steel bath of hydrocarbons such as propane gas being fed around the tuyere to protect the tuyere for pure oxygen blowing. It was thought that this was due to the generation of hydrogen gas by decomposition in

In fact, when operating in the normal blowing method, the hydrogen concentration in the steel at the time of the converter's blow-off is approximately 5 to 6 Wml, compared to 1.5 to 3.0 pIlffl for LD converter steel. It is much higher and about the same level as open hearth steel.

As a result, for example, in structural killed steel for thick plates, it is necessary to slowly cool the hydrogen during the rolling process to release the hydrogen, or to increase the blowing stop temperature and then re-injecting Ar gas such as Ar gas after the blow stop. It was necessary to carry out dehydrogenation treatment, which resulted in disadvantages in terms of productivity and cost.

After gaining experience in operating a pure oxygen bottom-blown converter, the inventors conducted various studies regarding the fact that the absorbed hydrogen concentration in this case is higher than expected from the amount of propane gas blown into the reactor. As a result, the cause of this problem is particularly the absorption of hydrogen produced by the decomposition of water-containing fluxes, such as burnt lime and dephosphorized fluxes, which are continuously added to the steel bath during the whole blowing period, and which usually contain 3 to 4% water. It has been determined that this is added to the hydrogen absorption resulting from the propane gas injection.

Therefore, as a countermeasure for this point, in the blowing process, during the lowest decarburization period, there is a large amount of dilution with CO + CO2 gas generated in the steel bath, so there is virtually no effect, but the decarburization efficiency is The blowing time during which the temperature decreased, especially during the time when the converter stopped blowing, the amount of oxygen supplied per unit weight of molten steel was approximately 5 N m/
During the period after leaving the cht, Co + C in a steel bath.
Since the amount of o2 gas generated becomes extremely small, the hydrogen gas concentration in the bubbles floating in the molten steel becomes relatively high.As a result, according to Sievert's law, the hydrogen concentration in the molten steel increases, and in fact, blowing From the results of the investigation using continuous sampling, the relationship between the absorbed hydrogen concentration and the amount of oxygen supplied (elapsed blowing time) as shown in Figure 1 was determined.Based on the results of such experiments and investigations, this invention The amount of oxygen supplied per unit weight of molten steel is at least 5 N m/cht until the converter stops blowing up.
In order to prevent the hydrogen concentration from increasing, the injection of the above-mentioned hydrated flux such as burnt lime is completed, and subsequent blowing operations are performed without injecting such hydrated flux. Thus, it has become possible to melt low-hydrogen steel in a bottom-blown converter without reducing productivity or affecting costs.

Further, in this invention, in addition to suppressing the rise in the hydrogen gas concentration described above, as a means to more effectively promote active dehydrogenation, the present invention has been developed to or scale and/or
The effectiveness of adding or blowing limestone was investigated through numerous experiments, and as a result of this, it was found that low hydrogen steel, which absorbs even less hydrogen, could be melted in a pure oxygen bottom-blowing converter without hindering productivity. This was achieved without any increase in costs.

Here, in a pure oxygen bottom-blown converter, for example, the oxygen feeding rate is 70ON.
The H2 concentration is when rrt1 minute and the propane blowing rate is 28N77+3/minute, but if, for example, burnt lime with a moisture content of 4% is injected at 1 ton/minute, the H2 concentration increases to is up to 40%.

The injection of burnt lime was carried out at 2 N immediately before the converter stopped blowing.
rrt/cht (oxygen supply remaining amount) and the first half of converter blowing, that is, 2ON7713/c
ht (remaining oxygen supply amount),
Histograms of the hydrogen content of blow-stopped molten steel for each category are shown in Figures 2a and 2b.

In the latter example according to this invention (first invention), the blowstop hydrogen content is on average 4.4 pI), whereas in the former case the average is 5.15, and the effect of this invention is obvious. .

Next, as the dehydrogenation forcing means described above, iron ore C is introduced by the reaction, and scale is introduced by the reaction FeO+ C-) Fe + CO↑ 2 FeO+ C→2 Fe + CO2↑, and further limestone The injection or blowing of these gases causes a reaction and the generation of these CO or CO2 gases dilutes the hydrogen gas from the decomposition of propane and promotes its release from the steel bath.

For pure oxygen bottom blowing, if iron ore is injected at 1 ton/min under the same conditions as described above, the hydrogen concentration will be 7.4%, which was calculated earlier when no burnt lime is injected. Even the hydrogen concentration decreased by 22%.
The effect is obvious.

An example of the effect of adding these dehydrogenation forcing agents at the final stage of blowing is shown in Figure 3, which effectively reduces the hydrogen content of blow-stopping molten steel, and particularly reduces the collapse of ferrite, scale, and limestone. 4, 0 kg/cht or more8
．． It can be seen that there is a significant difference in the time it takes to reach 0 kg/cht.

Next, an example of this invention (second invention) will be described.

Operation example 1 Amount of charging bath steel: 250.7 tons Blowing time: i5.1 min Oxidation amount 11048 ON” Burnt lime injection: Iron ore input: Blow-off H: Operation example 2 Amount of charged molten steel: Blowing time: Sintering Lime injection: (41,8NR/cht) Blow 7.2 tons (28,7kicht) 19,8
Nrr? /cht before blowing 8.3 tons (33,1k
g/cht) was added before the blow-off 10.2 Nm/cht 3.7 ppm 250.81-15.3 minutes Oxygen supply amount 1056 ON? 71” (42, I
Nrrl/cht) 9.1 tons all 20.9 Nrt? /cht (
Injecting iron ore into the blow stop (21.2 Nm'/cht): total amount 5.0 tons (19.9 kicht)
Of these, 3. The O tonneau (12,0 kicht) was put in before the blowstop was 17.7N, and the 2.0 ton (7,9ky/cht) was put in before the blowstop was 3.8N.
Nrrl/ch before - 0.6 Nm'/ch before blow-off H: 3. Opym operation example 3 Charged molten steel amount: 239.6 tons Blowing time: 15.0 minutes Oxygen feeding amount 1041040ON 3
．． 4NrrVCht) Burnt lime injection: 80 tons all stopped 19.6Nm'/c
Injection of iron ore by ht: 4.41-n (18.4 kg/cht)
Of these, 30 tons (12.5 kg/cht) were put in at the blow stop of 14.5 Nrrl/ch, and 1.4 tons (5,81 y/ch t) were put in at the blow stop of 3.6 Nrrl/ch.
Blow-off H before NrrVcht: 2.4 ppm Operation example 4 Amount of molten steel charged: 253. Ohn blowing time: 15.8 minutes Oxygen supply amount 1121ONm' (4
4,3N hot) Burnt lime injection: 9.81-ton (38,7kg/cht)
Iron ore injection: 3.01-tons (11.9 kycht) was injected before the blow stop of 20.2 Nrn'1ch. Limestone injection: 1.6 tons ( 6.3kg/cht)
, Blow stop H between before 5Nrrtlcht and stop stop.
: 2.5p door operation example 5 Charged molten steel amount: 251.31-ton blowing time: 15.6 minutes Oxygen feeding amount 11053ON" (41
, 9Nm'/cht ) Burnt lime injection: 8.6 tons (34.2 tons/ht) was injected until 18.3 Nm/cht before the blow-off. Iron ore injection: 4.2 tons (t 6.7 kg/cht )
13.3 N? Input scale before rVcht: 1.51-ton (6.0kg/cht)
1.5 Nrt? Blow-off H: 2.9 pI) m As mentioned in the introduction, molten steel obtained in a pure oxygen bottom-blown converter, that is, Q-BOP steel, has a considerably high hydrogen concentration, and therefore is generally low in hydrogen. For steel types that require high dehydrogenation, the dehydrogenation treatment may be performed by increasing the concentration of dehydrogenation, followed by additional dehydrogenation treatment such as by injecting expensive Ar gas again, or During the rolling process, it is necessary to perform slow cooling to release hydrogen.
Both of these methods lead to an increase in cost and a decrease in productivity, which is undesirable.However, in the present invention, as described above, no special auxiliary raw materials or gases are used, and no extra processing is required. It is possible to melt steel in a pure oxygen bottom-blown converter, which has a hydrogen concentration as low as that in an LD converter, without any need for it and without any productivity impediment in the rolling process.

[Brief explanation of the drawing]

Figure 1 is a diagram showing how the molten steel H concentration changes during the blowing process, Figures 2 a and b are comparison charts showing the blow-stop H distribution caused by the timing restrictions on the addition of burnt lime, and Figure 3 The figure is a graph showing the relationship between the blowstop H and the amount of iron ore, scale, and limestone added or blown at the final stage of blowing.

Claims (1)

[Claims] 1. When blowing low-hydrogen steel in a pure oxygen bottom-blowing converter, blowing a hydrous flux component added into the steel bath during blowing until the converter stops blowing. A low hydrogen steel melting process in a pure oxygen bottom-blowing converter, characterized in that the process is terminated until at least 5 Nm'/cht remains in the oxygen flow rate per unit weight of molten steel. 2. When blowing low-hydrogen steel in a pure oxygen bottom-blowing converter, the amount of water-containing flux added to the steel bath during blowing is blown per unit weight of molten steel until the converter stops blowing. The process should be completed until at least 5 Nm''/cht remains in terms of oxygen supply, and after this end, one or more types of iron ore, scale, and limestone should be added or blown in at least 41q/cht. A low hydrogen steel melting method in a pure oxygen bottom-blown converter, which is characterized by: