METALLURGICAL CONSIDERATIONS REGARDING OPEN-HEARTH STEEL FOR CASTINGS

R eferen ce to th e c a rb o n -co n ten t in th e charge, th o u g h t to be im p o rta n t, was m ade in p receding p a ra g ra p h s ex p la in in g th e p ig -iro n ch arg es in basic an d acid m eltin g . O th er fa c to rs ju s tify special, if b rief, m en tio n .

Proportion of Foundry Scrap Charged.

M ost o p en -h e a rth fo u n d ry m en believe i t is wise to estab lish a m axim um p ro p o rtio n of th e scrap produced in th e fo u n d ry , to th e to ta l a m o u n t of scrap m ak in g u p th e fu rn a c e charge. The a u th o r’s experience h as in d ic a te d th e a d v isa b ility of p re ­ scribing a m axim um p e rcen tag e for such fo u n d ry scrap as used in acid a n d basic o p en -h e a rth o p e ra ­ tio n s ; an d h a s stro n g ly suggested a relatio n sh ip betw een o b jectio n ab le red -sh o rtn ess an d a very la rg e p e rc e n ta g e of fo u n d ry scrap ch arg ed . The w rite r does n o t know of a n y conclusive (research in to th is problem t h a t has been m ade. T ests of th e k in d necessary to establish definite d a ta re g a rd in g th is problem a re seldom u n d e rta k e n because of possible very costly resu lts if i t m ig h t be shown t h a t m any very u n sa tisfa c to ry steel castin g s a re produced when excessive q u a n titie s of fo u n d ry scrap a r e used. T he steel fo u n d ry m an , who generally has a m ost p ra c tic a l m ind, is a p t to assum e th e possibility of tro u b le , when by so doing he is p lay in g safe as re g a rd s q u a lity , an d is n o t app reciab ly ad d in g to h is m eltin g o r o th e r costs in his re g u la r p ra c tic e . So fa r as th e a u th o r knows, th e r e is no g en eral a g reem en t of opinion as to th e m axim um p ercen tag e of fo u n d ry scrap advisable to ch a rg e in o p e n -h e a rth p ra c tic e . Each fo u n d ry m an has re g u la te d i t according to his own ju d g m e n t, which is influenced by th e n a tu r e of th e w ork he o rd in a rily produces. Some p la n ts have established th e m axim um lim it a t 45 p e r cen t, of th e to ta l m e ta l charge, which, in th e opinion of th e a u th o r, is reasonable.

Oxidation.

I n A m erica i t is th e opinion of m any acid and o p e n -h e a rth meltens, sh a re d by e m in e n t m e ta l­

s' 3

lu rg ists, t h a t i t is d esirab le to use iro n ore- in reasonable q u a n ti ty to secure a good boil in th e b a th . T he b eh av io u r o f th e h e a t a f t e r a m o d e ra te ore a d d itio n , a n d th e q u a lity of th e re s u ltin g m etal as show n u n d e r physical te s t, seem to su s ta in th e belief re fe rre d to. I t is g en e ra lly th o u g h t th a t o x id a tio n should n o t p ro g ress to th e p o in t w here a re la tiv e ly la rg e a m o u n t of som e recairb u riser such as a n th r a c ite coal o r coke is n eeded in th e ladle.

E x p erie n ce of th o m e lte r w ith th e p a r tic u la r f u r ­ nace u n d e r h is c o n tro l is u su ally th e b e st g u id e as to th e e x a c t m axim um p ro p o rtio n o f such re c a r- b u rise r t h a t can be safely em ployed fo r th e p r o ­ d u ctio n of first-class steel. Tho ore used fo r a c c e le ra tin g o x id a tio n in A m erican o p e n -h e a rth fu rn aces is h ig h g ra d e , a n d is fre q u e n tly p u rc h a s e d to come w ith in th e follow ing re q u ir e m e n ts :— I r o n , n o t less th a n 55.0 ; silica, n o t m ore th a n 1 0 .0 ; phosphorus, n o t m o re th a n 0.500; a n d su lp h u r, n o t m ore th a n 0.250 p e r c e n t.

De-oxidation by Means of Manganese and Silicon.

E x c e p tin g th e slig h tly in creased p e rc e n ta g e s of m anganese a n d silicon co nsidered b e st to p ro v id e for finished basic o p e n -h e a rth ste e l as c o m p ared w ith th e acid m e ta l, th e r e is no e ss e n tia l d ifference in A m erican p ra c tic e re g a r d in g t h e m a n n e r of in tro d u c in g th e alloys c o n ta in in g th e se tw o im p o rta n t d eo xidising ag en ts.

T h e ferro -m an g an ese is g e n e ra lly p u rc h a s e d o n specifications callin g fo r th e fo llo w in g :— M a n ­ ganese, n o t less th a n 78.0; p h o sp h o ru s, n o t m ore th a n 0.200; an d su lp h u r, n o t m ore th a n 0.050 p e r cent. A t th is w ritin g th e re is u n f o r tu n a te ly co n ­ sid erab le v a ria tio n in th e m an g an e se c o n te n t of ferro-m anganese, re s u ltin g som etim es in m an y d e te rm in a tio n s an d g r e a t c a re on th e p a r t of th e fo u n d ry m an to s o r t o u t sh ip m en ts c o n ta in in g v a ry in g a m o u n ts of th e p r in c ip a l e le m e n t.

T h e m an g an ese alloy is added in th e b a th o r in th e lad le according to th e ju d g m e n t o f th e con­

tro llin g m e ta llu rg ist. P ro b ab ly in m ost A m erican steel fo u n d ries m anganese a d d itio n s a re m a d e cold in th e ladle, w ith th e re s u ltin g m in im u m loss by o x id atio n of th is elem ent. T h ere a re som e who believe t h a t b e tte r d is trib u tio n of th e m an g an e se in th e steel follows a b a th a d d itio n . T h e re is in th e in a ju an p n proved conviction to th is effect,

as the controlling element of practice in some plants; and an established fact regarding the lesser quantity of manganese needed for ladle additions, as the regulating factor in other foundries. Investi­

gations are in progress in certain foundries with which the author has close contact, to ascertain definitely the various factors, such as relative oxidation loss, uniform ity of distribution, and deoxidising influence of manganese additions made to steel before and after tapping from the furnace.

The in tro d u c tio n of silicon in A m erican open- h e a rth fo u n d rie s fo r purposes of d eo x id atio n , is n early alw ays m ad e by m ean s of “ 50 p e r cen t, ferro-silicon,” in tro d u c e d cold in th e la d le ju s t before ta p p in g . T his alloy is fre q u e n tly p urchased to conform w ith th e follow ing analysis : silicon, betw een 48 p e r c en t, an d 55 p e r c e n t., w ith no sh ip m en t to v a ry m ore th a n 2 p e r cen t. No lim ita ­ tions a re im posed for phosphorus an d su lp h u r.

O p en -h earth fo u n d ries som etim es use a n alloy c o n ta in in g ap p ro x im a te ly 1 2 p e r c en t, of silicon in tro d u ced in p ig form an d c o n ta in in g a la rg e iro n co n ten t. I t is gen erally specified t h a t th is alloy shall c o n ta in n o t m ore th a n 0 .1 0 0 p e r c e n t, phos­

phorus o r m ore th a n 0.050 p e r c en t, su lp h u r. T his pig silicon alloy w hen used, is g e n e ra lly fo r th e purpose of ad d in g carbon o r te m p e ra tu re , o r b o th : and its influence on th e final silicon c o n te n t is very slig h t, because of considerable tim e re q u ire d to m elt it, d u rin g w hich p erio d o x id a tio n of th e silicon occurs, and indeed, is gen erally desired.

Effect of Aluminium.

A mong th e im p o rta n t fa c to rs in o p en -h earth and o th er steels is th e influence of alu m in iu m , probablv used in every A m erican steel fo u n d ry as a final deoxidiser, to su p p lem en t th e useful service p e r­

form ed by m anganese an d silicon. T he a u th o r 's sources of in fo rm atio n in d ic a te t h a t in m ost cases an a m o u n t of alu m in iu m is added to th e steel in fo u n d ry p ra c tic e in th e S ta te s, v a ry in g from 4 to 16 oz. p e r n e t to n of m e ta l ch arg ed . The use of th is elem ent h as been p ro p erly re g a rd e d w ith sus­

picion. No published d a ta have come to th e a tte n tio n of th e w rite r, show ing conclusively th e influence on physical p ro p e rtie s in steel castings, of alu m in iu m a d d itio n s in th e steel. Tests m ade w ith which th e a u th o r is fa m ilia r, a p p a re n tly

134

in d ic a te little , if any, bad re s u lts on physical p ro ­ p e rtie s when alu m in iu m a d d itio n s re p r e s e n t less th a n 4 ozs. p e r to n of ch arg e. H e believes th e effect of an a lu m in iu m a d d itio n a m o u n tin g to as m uch as 1 2 ozs. p e r to n is d is tin c tly h a rm fu l in th e influence on d u c tility . I t seems a lto g e th e r probable t h a t in v e s tig a tio n s now in pro g ress w ill show little or no bad influence of th e v ery sm all q u a n tity of alu m in iu m ad v isab le to use as a final p re c a u tio n w hen p o u rin g steel in to sand m oulds;

an d t h a t i t will also be a sc e rta in e d t h a t a d e fin ite low lim it in q u a n tity p er to n should be e stab lish ed for d aily p ra c tic e , beyond w hich i t m ay safely assum e a m ark ed d ecrease in th e p e rc e n ta g e of red u ctio n of a re a , an a p p reciab le lessen in g of th e p e rcen tag e of elo n g atio n , an d a slig h t, h a rm fu l influence on th e yield p o in t a n d u ltim a te s tr e n g th of th e specim en used fo r te n s ile te s tin g . I n v e s ti­

g atio n s w hich p o in t in th e d ire c tio n s in d ic a te d a re being conducted by several com panies w ith w hich th e a u th o r is associated.

Conceding in a g e n e ra l w ay th e p ro b ab le bad influence of a lu m in iu m a d d itio n s of a p p re c ia b le am o u n t, m any A m erican steel fo u n d rie s h a v e ex p erim en ted w ith th e use of o th e r elem en ts th a n alu m in iu m , a n d com pounds c o n ta in in g e lem en ts h a v in g an affinity fo r oxygen— all fo r th e p u rp o se of red u cin g or e lim in a tin g th e c u sto m ary alu m in iu m a d d itio n . E x p e rim e n ta l s u b s titu tio n s h a v e n o t been g en erally successful. A few fo u n d rie s believe th e y secure b e tte r re s u lts by th e use of som e com­

pounds (generally c o n ta in in g silicon) sim u lta n e ­ ously w ith th e a d d itio n of a very sm all a m o u n t of alum inium . T here is a g r e a t d eal o f k now ledge y e t to be g ain ed re g a rd in g th is im p o r ta n t d e ta il of A m erican steel fo u n d ry p ra c tic e . N a tu r a lly it has m ore significance fo r basic th a n fo r acid founders. N a tu ra lly , too, th is fa c to r is of p a r ­ tic u la r im p o rtan ce to o p e n -h e a rth p ra c tic e as com pared w ith elec tric p ra c tic e , becau se of th e g re a te r o p p o rtu n ity in th e o p e n -h e a rth fo r o x id a ­ tio n . W h ate v er th e process em ployed, i t m ay be conceded t h a t th e in d u s try as a whole h a s n o t been able to b rin g a b o u t all th e d e o x id a tio n d esired by th e use of g en erally useful elem ents such as m a n ­ ganese and silicon, im p o rta n t as th e y a r e in such reactions,

In o p en -h earth p ra c tic e th e alum inium is in tro ­ duced in several ways. R arely is it added in th e b a th . G enerally i t is placed in th e bottom of th e lad le as i t receives th e m etal from th e fu rn a c e sp out. W hen th is is done th e alu m in iu m m ay be in p ig form or in th e form of “ sh o t ” of irre g u la r p ro p o rtio n s. S u p p lem en tin g th e in tro d u c tio n of th e alu m in iu m e ith e r in th e b a th o r in th e ladle, i t is common p ra c tic e in o p e n -h e a rth foundries reg u larly or periodically to feed alum inium -w ire, usually a b o u t §-in. d ia ., in to th e stre a m of m etal as it e n te rs th e m ould. Some o p en -h earth foundries m ake th is su p p lem en tary alu m in iu m a d d itio n only when th e m etal in d icates a ten d en c y tow ard

“ w ildness.” I n c e rta in basic o p en -h e a rth foundries th e use of th e alum inium -w 'ire h as been re so rte d to in v ariab ly n e a r th e end of th e p o u rin g op eratio n , when by reason of th e closer c o n ta c t of th e m etal being poured, w ith th e o verlying slag in th e ladle, th e reduced percen tag es of m anganese an d silicon in th e steel of th e la s t p a r t of th e h e a t can be safely assum ed.*