439 vs 444 Stainless hlau: Ferritic Corrosion-Resistant Alloys

 

Cov tshuaj muaj pes tsawg leeg, cov yam ntxwv sib koom, thiab kev siv 439 thiab 444 yog dab tsi?
Ob leeg yog chromium-raws li (439: 17-19% Cr, 444: 17-20% Cr), titanium{13}}stabilized, thiab npib tsib xee{14}}dawb, muab lawv zoo tiv thaiv kev ntxhov siab corrosion cracking. Lawv yog cov hlau nplaum, muaj zog nruab nrab, thiab zoo thermal conductivity. Qib 439 yog cov khoom siv rau kev siv lub tshuab hluav taws xob thiab cov khoom siv hluav taws xob. Qib 444, nrog nws cov molybdenum ntxiv, yog hloov kho dua tshiab rau kev siv hauv cov tso tsheb hlau luam dej kub, lub hnub ci thermal tshuab, cov twj tso kua mis tso cua sov, thiab kev siv vaj tsev nyob hauv thaj chaw ntug dej hiav txwv. Lawv qhov zoo tshaj plaws yog cov nqi-zoo piv rau cov qib nickel-muaj austenitic.

Yuav ua li cas molybdenum hloov cov corrosion kuj ntawm 444 piv rau 439?
Molybdenum yog ib qho muaj zog alloying ntsiab uas tshwj xeeb txhim khu kev tiv thaiv hauv zos corrosion. Nws koom ua ke rau hauv cov txheej txheem chromium oxide passive, ua rau nws ruaj khov thiab tiv taus kev tawg los ntawm chlorides. Hauv kev xyaum, qhov no txhais tau hais tias 444 tuaj yeem tiv taus tsis tu ncua lossis qeeb - txav chloride- muaj cov dej (xws li hauv cov dej kub hauv tsev) zoo dua li 439. Thaum 439 tuaj yeem pom cov pitting nyob rau hauv ib puag ncig zoo li lub sij hawm, 444 muab lub sij hawm ntev -kev ncaj ncees, ua tau zoo bridging 3 ferritics tshwj xeeb ntawm cov hlau tsis sib haum thiab cov qauv kev ua tau zoo. daim ntawv thov.

Thaum twg nws yog qhov tseem ceeb los qhia qhov kim tshaj 444 tshaj tus qauv 439?
Qhia meej 444 thaum cov khoom sib txuas txuas ntxiv nrog cov tshuaj chloride-muaj dej, tshwj xeeb tshaj yog tias cov dej kub. Qhov no suav nrog cov dej kub hauv tsev thiab kev lag luam, cov kav dej rhaub dej, thiab cov kav dej hnub ci thermal. Nws tseem yog ib qho tseem ceeb rau cov vaj tse vaj tse thiab cov khoom siv hauv cov chaw ntug dej hiav txwv nrog cov ntsev txau. Rau cov pa hluav taws xob hauv tsheb, qhov twg chlorides tsis yog qhov kev txhawj xeeb tseem ceeb, lossis rau cov ntawv thov sab hauv qhuav, 439 tseem muaj peev xwm txaus thiab tus nqi ntau dua - siv tau.

Puas yog 439 thiab 444 muaj qhov sib txawv ntawm kev tsim khoom lossis kev siv vuam?
Lawv fabrication thiab vuam yam ntxwv zoo sib xws vim lawv sib koom ferritic qauv thiab titanium stabilization. Ob leeg yuav tsum tau ceev faj tus qauv rau ferritic steels: tswj cov cua sov tawm tswv yim thaum lub sij hawm vuam kom tsis txhob muaj qoob loo ntau dhau lawm, thiab siv cov roj shielding kom zoo. Lub molybdenum nyob rau hauv 444 tsis nyuaj vuam. Txawm li cas los xij, cov neeg tsim khoom yuav tsum ua kom huv si, nplai -dawb qhov chaw ua ntej vuam kom ua tiav qhov zoo tshaj plaws corrosion nyob rau hauv lub rooj sib dhos tiav.

Dab tsi yog qhov kawg, txoj cai xaiv tswv yim rau engineers thiab designers?
Ua raws li cov tshuaj chloride no-thiab- txoj cai ntsuas kub: Yog tias daim ntawv thov muaj cov dej kub uas muaj cov ntsiab lus chloride, lossis tsis tu ncua rau cov huab cua ntawm ntug dej hiav txwv, xaiv 444. Yog tias daim ntawv thov muaj cov roj cua kub (kua pa), cua sov qhuav, lossis dej tshiab yam tsis muaj cov tshuaj chloride, xaiv 439. Txoj cai no ua kom cov khoom siv tau zoo dua qub {{4}. Nco ntsoov xyuas cov dej chemistry (chloride qib, pH) thiab ib puag ncig tej yam kev mob thaum lub sij hawm tsim qauv kom paub qhov kev xaiv.