DEFECTS IN STEEL CASTINGS

U n d er th is h ead th e a u th o r does n o t c o n sid er i t possible in th e scope of such a P a p e r as th is , to deal w ith all th e ills to w hich a steel c a s tin g is h e ir , a n d consequently proposes only to d eal w ith one o r tw o of th e m ore p ro m in e n tly o c c u rrin g ones.

Blowholes.

T his d efect is th e m ost comm only o c c u rrin g o n e in steel castin g s, an d m ay be d u e to a v a rie ty of in itia l causes, several b ein g connected d ire c tly w ith th e m etal used, a n d o th e rs b e in g d u e to th e

in-■s ft .*3 _{a s}

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fluence on th e m e ta l d u rin g c a stin g , of fa c to rs in tro d u c e d in th e m a k in g of th e m ould o r cores.

This p o in t h as been, in m any cases, w here co n tro l of m etal a n d m oulding is u n d e r d iffe re n t heads, th e su b je c t of discussion w hich m ig h t som etim es easily be te rm e d acrim onious.

F ro m th e m etal s ta n d p o in t th e presence of blow ­ holes is due to th e m e ta l b ein g c a st in such a con­

d itio n as to c o n ta in a c tiv e oxides, w hich, re a c tin g w ith th e c arb o n p re s e n t, p ro d u ce a g as w hich is evolved d u rin g solidification.

O r, a g a in , th e m etal m ay c o n ta in o th e r dissolved gases which a re evolved fro m so lu tio n as th e m a te ria l cry stallises fro m th e fluid c o n d itio n . I n th e g re a t b u lk of such cases th e a n a ly sis o f th e steel for th e common steel-m ak in g c o n s titu e n ts will alm ost alw ays lead to a d e fe c t in th e m e ltin g p r a c ­ tice, which is c o m p a ra tiv e ly easy to c o rre c t. Blow­

holes in cases w here m e ta l a n a ly sis is sa tis fa c to ry , how ever, c a n n o t alw ays be so d efin itely assig n ed to a single cause. E xcessive q u a n titie s of m o istu re , lack of efficient v e n tin g of th e m ould o r core, th e use of too fine a san d e ith e r as fa c in g o r b a c k in g , th e closing of a p a rtia lly d rie d m ould w h ilst w arm , w ith th e co n seq u en t fo rm a tio n of steam in th e mould, an d th e use of chills, in te r n a l o r e x te rn a l, in an u n fit co n d itio n , a re all w ell-know n cau ses

Ta b l e IV .— Analyses of Samples.

Series. C.C. Si. Mn. S. P.

A 0.16 0.23 0.56 0 .0 12 0.027

B 0.23 0.31 0.82 0.008 0.032

C. 0.30 0.38 0.75 0 .0 10 0.026

which a t once occur to m in d . I t is only, th e r e fo re , by a process of elim in atio n ap p lied to one a f t e r th e o th e r of th e possible causes, t h a t th e r e a l reaso n for a case of such unsoundness can be d efin itely a sc e rta in e d an d a rem edy ap p lied . Blow holes in c astin g s occur in tw o very d is tin c t form s, o n e in which th e y a r e sc a tte re d m ore o r less ev en ly as sm all holes th ro u g h o u t th e e n tir e c a stin g , an d one in which th e y ex ist as la rg e r cav ities, u su a lly to be found in or n e a r th ic k e r p o rtio n s or in a ra d iu s In th e first form i t is probable t h a t th e m e ta l is a t fa u lt, b u t as excessive m o istu re in th e san d causes d efects v e ry sim ilar in a p p e a ra n c e , ju d g m e n t on

th e m a tte r c a n n o t be too im petuous. In th e second form described th ese holes a re very o ften described as “ draw s ” an d th e m etal defined as

“ h u n g ry ,” o r as possessing excessive liq u id con­

tra c tio n which h as caused holes to occur w here norm ally such a ctio n does n o t occur.

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F i g . 15.— C.2 x 50 b i a s .

In m any in tr ic a te types of c a stin g , how ever, th e a u th o r h as noticed t h a t th is second ty p e of defect occurs o fte n e r w ith a low c a stin g te m p e ra tu re , th a n when th e steel is very h o t and fluid. H e assumes, th e re fo re , t h a t v ery o ften cav ities described as “ d raw s ” a re in r e a l i t y -“ blow s,” and a re due to th e period d u rin g which th e steel is

liquid in th e m ould, b ein g too sh o rt to allow of th e escape of c e rta in gases blow ing in to th e m etal from (usually) p ro je c tio n s in th e m ould o r cores.

Contraction Cracks.

These m ay be due e ith e r to (1) a m e ta l so im p u re as to be excessively w eak im m ed iately a f t e r solidi­

fication an d consequently u n a b le to overcom e th e resistan ce offered to its c o n tra c tio n by ev en th e best m ade m ould o r core, o r (2) sufficient th o u g h t n o t being given d u rin g th e m a n u fa c tu re o f m ould or cores, to th e need fo r th e le a s t possible re s is t­

ance to th e c o n tra c tio n of th e cooling metal.^

In th e first case th e m ost likely enem y is su l­

p h u r, w hich if p re s e n t in larg e q u a n titie s (p a r­

tic u la rly if m an g an e se p e rc e n ta g e is on th e low side) causes a definite s t a te of red -sh o rtn ess.

I n th e second case (1) to o fine a g ra d e of sa n d o r too h ig h a p e rc e n ta g e of bo n d in g m a te ria l c au s­

in g th e m ould o r core to ra m too h a r d a n d close, an d consequently if d rie d to b a k e lik e a b ric k ; (2) th e fa ilu re to p ro v id e b ra c k e ts or chills o n p o r­

tio n s su b jected to u n d u e c o n c e n tra tio n of stresses due to ir re g u la r d e s ig n ; (3) th e use of such stay s in th e m o u ld in g box as w ill p re v e n t th e fre e co n ­ tr a c tio n m ovem ents of risers, e t c . ; (4) th e n e g le c t in c e rta in cases to release th e to p s as q u ick ly as possible a f t e r c a stin g . T hese a r e all p o in ts fo r co n ­ sid e ra tio n w hen a tte m p tin g to e lu c id a te th e cau ses of such cracks.

Draws or Contraction Cavities.

These are in ev itab ly d u e to lack of p ro p e r fe e d ­ ing, e ith e r ow ing to th e m o u ld e r’s sh o rtco m in g s or to such com plication of design t h a t p o rtio n s r e ­ q u irin g feed in g a re inaccessible. I n th e fo rm e r case th e rem edy is obvious, b u t th e la t t e r , in th e a u th o r ’s opinion, occurs w ith m uch g r e a te r f r e ­ quency th a n it should, an d calls fo r s till closer co-operation of th e d esig n er an d fo u n d ry .

The Need for Research.

D u rin g a considerable p e rio d dev o ted to th e co n sid eratio n of d efects in steel c a stin g s, th e a u th o r h as been im pressed w ith th e g e n e ra l a p p e a r­

ance of a m b ig u ity w here th e i r in itia l causes w ere concerned. D efects of one an d th e sam e k in d

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a p p e a r to h av e arisen , possibly from an y one of a v a rie ty of ca u se s; w hich s ta te of affairs h as been som ew hat fo stered by th e m ore o r less g en eral p ra c tic e of s e p a ra te control of m ould and m etal p ro d u ctio n . Scientific research applied to th e problem s associated w ith th e p ro d u ctio n of th e v ario u s form s of w orked steels, h as resu lted to a larg e e x te n t in th e e lim in atio n of th is am biguity w here everyday d efects a re concerned, an d in most cases they can be definitely allo tted a cause. The

F i g . 16.— C.3 x 100 d i a s .

problems of th e fo u n d ry , how ever, probably ow ing to th e g re a t n u m b e r of v ariab les which e n te r in to th e p ro d u ctio n of a c a stin g , do n o t a p p e a r to h ave had, u p to th e p re s e n t tim e , th e sam e scientific in v e stig a tio n , an d a re consequently v ery o ften assigned to some cause or o th e r on a m ere visual ap p earan ce, w hich m ay be grossly m isleading.

A prolonged scientifically-controlled in v e s tig a ­ tio n in to th e b e h av io u r of m ild steels in sand moulds, an d th e influence of th e v ario u s elem ents

on such b e h av io u r, could n o t help b u t be of assist­

ance to th e steel fo u n d er.

V ery few steel fo u n d ries, how ever, a re in such a p o sitio n as to be able to afford a full scien tific con­

tro l an d th e necessary e x h a u stiv e in v e s tig a tio n s.

T h e ir only hope, th e re fo re , is in som e form o f com ­ m u n a l re se a rc h o rg a n is a tio n , o r in o n e such as th e B ritis h C a st-Iro n R esearch A ssociation, w hich, it is safe to say, is now d e a lin g w ith th e so lu tio n of problem s in a n o rg an ised scientific m a n n e r, w hich h av e e x isted d u rin g th e whole h is to ry of c a s t iro n , an d h av e o fte n been d e a lt w ith p rev io u sly b y ru le of th u m b , o r h a p h a z a rd assu m p tio n .

The a u th o r believes he is c o rre c t in s t a ti n g t h a t no such o rg a n isa tio n e x is ts w here steel c a s tin g s a re concerned, an d w ould su g g est t h a t its fo r m a ­ tio n , or th e possible f u t u r e ex ten sio n o f th e scope of th e above A ssociation to in clu d e steel c a stin g s, would prove a g r e a t boon to th e sm aller steel fo u n d ers, who, w ith every d esire to im p ro v e th e i r pro d u ct, a re u n a b le to a v a il th em selv es o f th e necessary know ledge a n d a p p lia n c e s to b rin g science to th e ir assistance.

The a u th o r acknow ledges w ith th a n k s th e fa c ili­

tie s g ra n te d by th e D ire c to rs o f h is C o m p an y , th e B r a in tre e C astin g s C om pany, a n d also p a r tic u la r ly th e in v alu ab le assistan ce w ith th e m icro -p h o to ­ g ra p h s of M r. J . H . G. M onypenny, c h ie f m e ta l­

lu rg ist, M essrs. B row n B a y le y ’s S te e l W o rk s, L im ited , Sheffield.

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THE MANUFACTURE OF STEEL CASTINGS IN