coiistrriit progrcss lirib bccn inude nut1 iiintcrinls nre rcyuircd with propert ies wry iniicli supcrior to t#liosc 111 ci~git~ccrii~g p*:icr,icc litis iiicrct:iscd tlic stntic, dgnnniic, tint1 tlicriiiiil conditions wliicli miterials Iiiivc lind to wit1lst;ind. Strcsscs. both tcnsilc rind Intiguc, Iinvc becn incrcriscd. IYcigl~t Iiris lirrtl to tic roduccd in order to iiicrcusc spectl nnd to ccoiiomise spice, wit11 tlie result that fnctors of safety hive iilso been rctlucetl consiclcrnbly. This has involved thc production mid usc of niorc rcliiiblc. t i Inore rigid cstriiiiii:itioir niitl iiispectioii in t,hc clioicc iilitl sclcct ion of sricli miitcriiils.
Corrosioii is also ti problciil wliicli hiis pluyctl : i n iiiiportniit ptirt, in tlie tlcvclopinent of new iilloys. I n 1111 brunclies of i n d u s t r ~, corrosion is, untl htis bccii, :I coiisiilcrriblc source of troublc nnd cspcnsc to till uscrs of mctnls. Tt lias rniscd inii~iy scrious qucstions, which Iinve Iititl to be tlciilt wit,h by the. clicniicnl citgiiicer ill tlic dcvclopiiicnt of new INJ-CC'SSCS, i i i l t l t l ~c striictttriil cngiticcr 1 1 1 1 ~ nlso hritl to give it scrious consitlcriition. Ihriiig the Inst t~vt*tit.y yc:irs :I c ~~~i s i ~I ~~r : i i ~i ~ iinioittit nf cspcrirnentnl rcsciirch \.Orli liris been untlcriukcin, with 11 vicw to solving iiinny of tlic tliflicultics wliicll linvc occurrrtl ns thc result of corrosion, nntl, us 11 result o f sucli worli, the nciturc of the phcnomcnn of corrosion liils been better untlcrstoorl nnd n sntisfnctory tlicory of corrosion-the clcctrochcniicnl t.licoryclevclopcd. This bcttcr undcrstnnding of the nnturc of corrosion lins lcrl l o tho de~clopmcnt of nl10j.s siiitnblc to witlistniitl it; nntl to rediico it in Innny ciiscs to 11 niinimum.
\VitIi the dcvclopilic.iit of 1icw i l i h l s tint1 nlloys JJI'Oblcn1S nrisc, unooniicclctl witli thc scrricc of sucli rrititcriiils but vcry cssciitinl to tlicir usc. Tlicsc nrcb probleiiis invol\ul iti tlicir tniicliinitig owiiig to ttlicir incrcnsed strcngtli, Iiiirtlnc!ss, ntltl tougltticss, nntl to tlie inorcnsctl spcctls of ~notlci*n production. The result liiis bccn the iitlvcnt of nc\v rind iiuprovcd cutting mntcrit~ls, h i wit11 IiigIi spcctl tool stccls, :ind then \villi litirtl ~illtr~s, t l i c 1 I)rtsis of wliicli is tungsten, cliroiiiiuiii, or cobnlt.
'l'lic new iniitcririls. wliicli hiirc~ been cvol~cd l o mcct hlie ueiv tlciiiiiiitlr; fnr streiighli, hnrtliiess, ftitiguu, rcsistnilcc tb corrosion, nntl ciit,tiiig niuterinls, hnve bccn foiitid both i n ferrous nntl.-ilonferrous nllogs. Tlie p~inc*ipal nlloys, Iio\vcvcr,~ hnvc bcoti ferrous nlloyvfi, or cillogs rrf metels closely irsctl fn~*nit:rly. 1 1 J IIC. progress whicli Iiiis I)een nindc ulctllls :111tl nlloys, botl1 ferrous :lilt1 non-ferrous, iltld relntcd to iron, such :IS chromiuni, nickel, or tuugstcn, nnd these alloys hnvc given rise to viirioiis types nf stccl, both ordinary nnd al1o.y.