STEEL

D E O X I D A T t O N A N D A L L O Y I N G

(UDC 669.183.4)

V . A. G e i z e n b l a z a n d D.

Dnepropetrovsk Plant for Presses Translated from Metallurg, No. 8,

pp. 17-18, August, 1965

OF C A R B O N S T E E L S

A. G o r e l i k

In the 30-ton open-hear th furnaces of the s tee l -cas t ing mi l l of our p lant ,k i l led s teel is deoxidized and a l loyed for shaped castings according to a technology ensuring the necessary m e t a l quality. This technology was adopted as

a result of testing three variants.

According to the first variant when a carbon content in the m e t a l 0.01-0.02% below the average given content for the given s teel was reached, 12%-ferrosilicon was added to the bath es t imated at 12.2 k g / t o n of s teel and then

after 3-5 rain ferromanganese was added in an amount which depended on the residual manganese content of the

me ta l and the tonnage of the heat. Within 7-10 rain after,this the heat was tapped. Final deoxidat ion was conducted in the ladle with 45% -ferrosi l icon (7.2 k g / t o n of mol ten steel) and a luminum 1 kg / ton of mol ten steel).

With this method of deoxidation there were instances of tapping heats containing phosphorus 0.002-0.005% higher than the permissible level; this led to scrap. The act ive reduction of phosphorus from the slag was caused by

the minor drop in slag basiei ty due to addit ion of 12%-ferrosihcon to the bath and superheating of the meta l . In this case even the addi t ion of l ime to the ladle in the amount 5 k g / t o n of steei did not always yield the required phos-

phorus content in the finished steel.

In 1960 after conducting test heats and obtaining positive results there was a switch to tapping heats of carbon steels without prel iminary deoxidat ion of the m e t a l with blast-furnace ferrosflicon. When deoxidiz ing and al loying

the m e t a l with ferromanganese a lone, the bath remains act ive almost right up to tapping.

According to the second variant when the upper l imi t of carbon content was reached ferromanganese was added to the furnace in an amount es t imated to give a manganese content in the s teel at the lower l imit ; then after 5-Train

the remaining ferromanganese is added to the bath, and in 3-5 rain the heat is tapped. The sequence of final deoxi-

dation of m e t a l in the ladle was as before. With this method of deoxidation factors which tend to reduce phosphorus from the slag are absent, but no improvement in the quality of the m e t a l is observed (Table t).

Correct ly-conducted polishing makes it possible to reduce the length of a heat in spite of the fact that the master must a r t i f ic ia l ly slow down the oxidat ion of carbon in order to obtain steel with the necessary carbon content.

This is corroborated by the following da ta :

Number Deoxidation

of heats variant

35 I

45 II

Average heat Fuel Weight duration, h consumption, of heat,

k g / t o n ton

5.44 292.1 28.0 5.36 290.0 28.0

In 1963-1964 projects were conducted on deoxidat ion and al loying of s teel with ferromanganese in the ladle (third variant). The m e t a l was tapped when the average given carbon content was reached. When the ladle was 1/4 f i l led with mol ten meta l , ferromanganese was fed under the stream of meta l , followed by si l icon and then a lum- inum. The amount of 45~ remained as in the I and II variants. The deoxidizers are added in chunks with a size up to 50 mm in cross section; in addit ion, fine (even dust-size) tails of ferromanganese are used which is impossible when deoxidizing in the furnace.

In order to determine the effect of the ferromanganese added to the ladle on the temperature of the mol ten s teel its temperature was measured with a tungsten-molybdenum thermocouple immersed in the furnace before

448

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TABLE 2. The Effect of fne Deoxidizer

on the Tern era ture of the Metal

Meta l temperature ,

Deoxida- Weight Number ~ of heat ,

t ionvar ian t of heats I in the in the ton ! furnace ladie

In the

furn a c e . . tn the ladle . . .

28.0

28.0

8

Ii

I 1590 1530

f

i 1610 1540

tapping (Table 2). When deoxidizing me ta l with ferro- manganese in the ladle it is necessary to tap the m e t a l with a temperature 10 ~ C higher than when deoxidizing

in the furnace.

During the tests of the character of distribution of chemica l e lements when deoxidiz ing in the ladle ,32 heats

were tapped. During teeming,96 samples of the me ta l

were taken (at the start, in the midd le , and at the end) to determine the content of manganese , carbon, and s i l i -

con. Samples for mechan ica l testing were taken

s imukaneously.

In a l l tests conducted, the difference in the manga- nese content wkh respect to the sample taken in the mid - die of t eeming amounted to + 0.02% when the holding

period of m e t a l in the ladle before the start of t eeming

was more than 10 min; this is evidence of the comple te

ass imilat ion of ferromanganese by the m e t a l by the start of teeming. The results of the me c ha n i c a l tests of s tee l when deoxidized in the furnace and in the ladle are prac- t i ca l ly ident ical .

The opinion exhts that deoxidat ion of s tee l in the

ladle increases the contaminat ion of the m e t a l with non-

m e t a l l i c inclusions, since the temperature of the s teel

during the t ime of tapping drops by 70 ~ C due to ass imi- lat ion of heat by the ladle and addit ion of cold ferroalloys.

However, it must be considered that when deoxidizing in

the ladle the loss of deoxidizers is considerably reduced as is evident from the data given below:

Deoxida- Consumption Consumption t ionvar ian t o f l 2 % - f e r r o - of 4g%-fer ro-

si l icon,kg/ton s i l icon,kg/ ton

Ferroman-

ganese con-

sumption,

k g / t o n

11.4

12.4

8.7

I 12.2 7.20

II -- 7.22

Ill - 7.20

The contamination of cast steel with nonmetallic

inclusions of sulfide and oxide type when deoxidizing and

al loying s teel in the furnace and in the ladle is p rac t i ca l ly the same. The surface quality of the casts is somewhat better with deoxidation in the ladle.

449

The positive results with respect to metal quality and saving of deoxidizers (a reduction in the cost of one ton of molten steel of 30.6 kopecks) made it possible to adopt the technology of producing carbon steels for shaped casting whereby they are deoxidized and alloyed with ferromanganese in the ladle.

450