O X Y G E N IN S P O N G E I R O N A N D I R O N P O W D E R S

E . A . K a p u s t i n , V. A . M a s l o v , A . M. K u l a k o v , A . S. Y u r e n k o , a n d G. M. S a d o v s k i i

UDC 621.762 : 669.141.17

One of the undes i rab le e lements p resen t in sponge iron and iron powder, which can be r emoved f rom these m a t e r i a l s by reduct ion annealing, is oxygen [1]. To per fo rm reduction annealing effect ively, it is im- por tant to know not only the total concentra t ion of oxygen in the sponge iron or iron powder to be t r ea t ed , but a l so the form in whieh it occurs and its d is t r ibut ion . These p rob lems have up to now rece ived in- suff ic ient at tent ion.

The iron powders being manufactured by the Sulinsk Meta l lu rg ica l Plant contain 0.7-1.5% of oxygen. The p r e s e n c e of oxygen in these powders is a t t r ibu tab le pa r t ly to incomplete reduet ion of the raw m a t e r i a l used, mi l l sca le , and pa r t ly to s econda ry oxidat ion of the sponge iron produced.

O x y g e n in S p o n g e I r o n

Sulinsk sponge iron contains oxygen in the form of unreduced iron oxides and oxides formed as a r e - sul t of s eeonda ry oxidation. According to [2, 3], the unredueed oxides a r e usual ly wiist i te, and the products of s econda ry oxidation, magnet i te .

Chemica l ana lys i s can only de te rmine the total oxygen content of sponge iron. r e obtain informat ion on the form and d is t r ibu t ion of the oxygen in sponge iron, it is n e c e s s a r y to combine chemica l ana lys i s with me ta l log raph ic examinat ion. In the p resen t work, four spec imens , each measur ing 70 x 15 x 10 mm, were cut f rom a sponge. Two of these spec imens were cut f rom the more s e v e r e l y oxidized par t s (top and bottom of the sponge) and two f rom the cen t ra l , l e ss s e v e r e l y oxidized pa r t (Fig. 1). F r o m these s p e c i - mens, s amp le s for chemica l ana lyses we re obtained at s ix points. The spec imens were then embedded by

/ :f2.~Y

Specimen 1 Specimen 2 Specimen 3 Specimen 4

l

i t �9 ~. E -J k~'

Fig. 1. Diagram of location of spec imens and samples for chemi- cal ana lys i s (all d imensions in m i l l i m e t e r s ) .

Zhdanovsk Meta l lu rg ica l Inst i tute. Sulinsk Meta l lu rg ica l Plant. T r a ns l a t e d from Poroshkovaya Meta l lu rg iya , No. 6 (138), pp. 17-21, June, 1974. Original a r t i c l e submit ted December 2 7 , 1972.

� 9 Consultants llureau, a a'ivi,~ion o.f Plenum Publishtng Corl)or,tion , 2.-:7 Ilest 17t]~ 5tr,.,~:!, \ t :u }'or.I., \ . }. lOOll. \o [~art o f this pulJicahon ma) t;e :'eprodn:'ed. sto~cd in a retriet c:[ ,~).st~::,,i, or tr~msmit'cd, ir~ ~lt!~ :})r,'n o ~ ~ ~:n~ m~'a:l.~, electronic, mechat~ica[, photocopying, micro.filmi,zg, recor:':ir~g or othc:'ui.~c, I~i:hout written pt~rmission og th~' ?n;,l',sher. ::op~ o ! t h i s article is aT:ailab!e ,from the publis/zcr [or 515.00.

4,t 7

32

28

24 r

2O o

t2

0

F i g . 2.

\

"'k

S 2 4 6 b'

e.--f

X - -2

2,;o

2,25

f,8O

1,35 ,.= o

Field No.

Distribution of iron oxides and pores over sponge thickness: I) porosity, %; 2} iron oxides, %.

2,o

2 ~

0 2 S 4 5 5

No. of field along sponge length

F i g . 3. D i s t r i b u t i o n of p r i m a r y ( l ) , s e c o n d a r y (2), and to t a l (3) oxygen con ten t s in i r on sponge .

F ig . 4. P r i m a r y o x i d e s in i ron powder p a r t i c l e s , • 500.

c a s t i n g S t y r a c r y l round t hem in molds and holding them in a i r fo r 5 h, a f t e r which they w e r e g round and p o l i s h e d by the usua l p r o c e d u r e . M e t a l l o g r a p h i e e x a m i n a t i o n s w e r e c a r r i e d out wi th an MIM-8M m i c r o s c o p e .

M e t a l l o g r a p h i c e x a m i n a t i o n s of c r o s s - s e c t i o n a l sponge i ron s p e c i m e n s r e v e a l e d tha t the u n r c d u c e d o x i d e s , o r p r i m a r y oxygen , w e r e in the f o r m of n o n m e t a l l i c i nc lu s ions , the amoun t of which was a m i n i m u m at the p e r i p h e r y and a m a x i m u m in the c e n t e r of the i ron sponge . The p r o d u c t s of s e c o n d a r y ox ida t ion

44.8

"FABLE 1. Ana lyses of I ron Powders

Powder {Total Fe. Total C, trotal [O],{ Prim. [0]0 �9 grade [ % % / % ] % %, PZh 4K 98,04 0,175 1.14 0,44 0,70 61,0 PZh 3K 98,40 0,135 0,95 0,46 0,49 51,5 PZh 4S 98,00 0,190 1,00 0,30 0,70 70,0 PZh 4M 98,04 0,200 I,II 0,02 1,09 98,0

. 98,00 0,200 I,I0 0,30 0,80 72,6 . 98,10 0,195 0,90 0,15 0,75 83.4

PZh 5M 98,00 0,310 1,00 0,32 0,68 68,00 PZh 40M 96,64 0,160 1,60 0,31 1,29 80,0

( s econda ry oxygen) w e r e brought out v e r y fa in t ly by meta l lograph ic means , and it was only o c c a s i o n a l l y that the th ickness of s e c o n d a r y oxidation f i lms , which s o m e t i m e s did not exceed 3 ~, could be de te rmined .

Quant i ta t ive me ta l log raph ic ana lys i s was p e r f o r m e d by the Glagolev point technique [4]. A sponge m i c r o s e c t i o n was divided into 18 equal f ie lds . F r o m each th ree pa r t s , a gene ra l s ample was obtained for chemica l ana lys i s . In each of the 18 f ie lds , using an ocu la r g r id with 289 points, counts w e r e taken in 15 point f ie lds . The total n u m b e r of points in a s ingle sponge m i c r o s e c t i o n was 78,030. Meta l lograph ic ana lys i s y ie lds data on comtmsi t ion by vo lume o r weight. In the c a s e of ana lyses of sponge iron, however , the method has the d i sadvantage that, because of the lack of data on s e c o n d a r y oxidation, it is imposs ib le to d e t e r m i n e full phase compos i t ions with its aid.

F o r s impl ic i ty , it was a s s u m e d that the sponge cons i s t ed of Fe which conta ined all impur i t i e s , FeO, Fe304, and pores . The sponge po ros i t y was de te rmined as the ra t io of the pore volume to the total vo lume. In the de t e rmina t ions of f r ac t ions of Fe and FeO, the i r sum was taken as 100~. The r e su l t s obtained (Fig. 2) show that the po ros i t y of the sponge s tead i ly d e c r e a s e d on pass ing f rom the ou te r (blue edge) to the inner s u r f a c e . In the cen t r a l pa r t of the iron sponge, t he re was an incomple te ly r educed zone.

To de t e rmine the f r ac t ion of the s e c o n d a r y oxygen (oxygen in the products of s e c o n d a r y oxidation), a method was developed based on the s imul taneous use of data y ie lded by chemica l and me ta l log raph ic ana ly - ses . The pr inc ip le of the method is as fol lows. F i r s t , the amounts of Fe and FeO phases a r e d e t e r m i n e d in the sponge iron o r iron powder being ana lyzed . F r o m a c o m p a r i s o n of oxygen contents d e t e r m i n e d c h e m i c a l l y and me ta l log raph ica l ly , it follows that

VF~" 7Fe [ % O] -]- VF,. o . 7FeO [ % O] -- 22.2VFe o �9 7F~O VF~'~ = 27.6" 7F~,O, -b [ %0] (?v~ - - 7,:e,o,) ' (1)

where VFc3Q is tile volume of the oxides produced by secondary oxidation (%), VFe is the volume of the iron (~), VFe O is the volume of the unreduced oxides (~,c), YFe, VFcO, and YFe304 are the densities, re- spectively, of Fe, FeO, and Fc304 (g/cm3), [~ O] is the oxygen in the sponge iron (%), and 22.2 and 27.6 are the fractions of oxygen, respectively, in FeO and Fe304 ~).

In accordance with Eq. (1)

[%O]F~O ' = 27.6

[ %OIF~ o = 22,2

VFe,O4 "'~Fe,O,

(VF~ - - V,:~,o,) '7w -b VF~O �9 7F~O + VF~O, '7,:~o,

VF~o" YF~O (VFe - - VI-%o,) 7Fe "}" YFeo "7FeO -]-' VFe,O, 'YFe,O,

; (2)

(3)

where {% O]Fe304 iS the oxygen in the oxides produced by secondary oxidation C~) and [% O]FeO is the oxy- gen in the unreduced oxides (~).

The distribution of oxygen be~veen the primary and secondary oxides can also be ca]culated with the following, simpler formulas, which, however, arc less accurate:

YFeo" YF~,O [ % O]F~ o = 22.2 ; (4)

VF~O'7F~O § VF~" 7F~

449

0! 1% O]ee,o. ~ 1% O}tot. -- [ ~00]~e o. (5)

Examinat ion of Eqs. (2)-(5) shows that calculat ions with Eqs. (4) and (5) involve an e r r o r of not m o r e than 4%. Thus, in calculat ions of this type the complex equations (2) and (3) can be success fu l ly rep laced by the somewhat less accu ra t e but s i m p l e r equations (4) and (5).

The above fo rmulas we re employed to de te rmine the distr ibution of oxygen in the sponge iron invest i- gated (Fig. 3). The exper imenta l data obtained demons t r a t e that the concentrat ion of the secondary oxygen exceeded that of the p r i m a r y oxygen, espec ia l ly in the oxidized par t of the iron sponge. The lowest sec - ondary oxygen concentra t ion was obse rved in the cen t ra l pa r t of the sponge, which was due to diffusional impediments to the oxidation p r o c e s s . The inner pa r t s of the iron sponge contained more secondary oxygen than did the cen t ra l par t .

O x y g e n in I r o n P o w d e r

An iron powder produced by milling sponge iron would be expected to contain, like the la t ter , both p r i m a r y and secondary oxygen. To de te rmine the p r i m a r y and secondary oxygen contents of iron powders , chemica l and meta l lographic ana lyses we re pe r fo rmed . For meta l lographic analys is , spec imens were p repa red as follows. Each iron powder was mixed with P r o t a c r y l powder in the propor t ion of 1 : 3 . To the powder mix tu re was added a solvent , af ter which the resu l t an t m a s s was poured into molds, where it was left for 5 h to solidify. The solidified spec imens were ground and polished by the usual method.

Metal lographic examinat ions revea led the p re sence of p r i m a r y oxides in some par t i c les of the iron powders (Fig. 4). F r o m the r e su l t s of the chemica l and meta l lographic ana lyses (Table 1), it can be seen that the oxygen in the iron powders was mainly in the fo rm of secondary oxides, i .e., was p re sen t on the par t i c le su r faces .

On passing f rom PZhK to PZhS, PZhM, and, finally, PZhOM,* the rat io between the secondary and p r i m a r y oxygen oontents of these powders i nc reases . The r ea son for this is that the higher the degree of mill ing of a powder, the g r e a t e r is the amount of unrcduced oxides exposed, which a r e subsequently r e - moved during magnet ic separa t ion .

1 .

2. 3.

4.

L I T E R A T U R E C I T E D

M. Petrdl ik , Contaminants and Additions in Sintered Metals [Russian t ranslat ion] , Metal lurgiya, Moscow (1971). V. F. Knyazev and E. A. Krasheninnikov, Izv. Akad. Nauk SSSR, Metally, No. 1, 18 (1967). E. A. Krasheninnikov, M. I. Kononov, and Yu. M. Mishkin, Powder Metal lurgy [in Russian], Sb. Tr . TsNIIChM, No. 72, Metal lurgiya, Moscow (1970), p. 32. S. A. Saltykov, S t e r eome t r i c Meta l lography [in Russian], Metal lurgiya , Moscow (1970).

* PZhK, PZhS, PZhM, and PZhOM are , r e spec t ive ly , coa r se , medium, fine, and ve ry fine reduced iron powders . The f igures 3, 4, and 5 in such powder designations denote iron contents of not less than 98, 96, and 94%, r e spec t i ve ly - T r a n s l a t o r .

450