Vim li cas 316 Stainless Hlau Sheath Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob Hluav Taws Xob hauv Kub-Dip Galvanizing Baths Fail los ntawm Intergranular Corrosion ntawm 450-480℃Txawm tias tsis muaj chloride ntsiab lus?

Ib puag ncig ntawm molten zinc galvanizing da dej yog qhov ua siab phem heev rau cov hluav taws xob hluav taws xob cua sov thiab cov kev sib tw cov ntsiab lus ntawm kev tiv thaiv corrosion ntawm 316 stainless hlau. Lub da dej kub ntawm 450-480 degree, qis dua qhov ntsuas kub ib txwm muaj ntawm 450-850℃rau chromium carbide nag lossis daus, zoo li muaj kev nyab xeeb rau austenitic stainless hlau. Ntawm qhov tod tes, kev ua haujlwm tsis zoo los ntawm cov nroj tsuag galvanizing tsis tu ncua qhia qhov sib txawv ntawm kev xeb thiab tawg ntawm 316 stainless hlau sheaths tom qab 3-9 lub hlis ntawm kev pabcuam, thaum tsis muaj chlorides thiab muaj cov zinc molten, uas tsis yog inherently corrosive rau stainless hlau nyob rau hauv cov tsoos electrochemical kev nkag siab. Metallurgical txoj kev tshawb fawb ntawm cov tsis ua tiav sheaths qhia tau hais tias tus txheej txheem sib txawv, piv txwv li kua hlau embrittlement (LME) tshwm sim los ntawm zinc nkag mus rau hauv cov ciam teb, txuam nrog nag lossis daus ntawm sigma (σ) theem - ib qho nyuaj thiab nkig intermetallic ua ke ntawm hlau thiab chromium (FeCr). Ntev -lub sij hawm tshav kub kub ntawm 450-480 degree, uas yog nyob rau hauv qhov ntau ntawm carbides rhiab heev, yog nyob rau hauv lub kub tseem ceeb heev rau sigma theem kev loj hlob nyob rau hauv molybdenum-cov kabmob austenitic stainless steels xws li 316. Ntawm qhov kub thiab txias, sigma theem tshwm sim los ntawm fertainer fertainer strain-induced martensite) tom qab 1000-3000 teev. Qhov no siv chromium los ntawm cov nplej nyob ze austenite thiab tsim cov chromium-depleted aav uas ua rau cov zinc intergranular nkag mus. Daim ntawv no ntsuas lub kinetics ntawm lub sigma theem kev loj hlob ntawm galvanizing kub thiab muab cov ntaub ntawv rau alloy xaiv ntawm cov cua sov nyob rau hauv molten zinc kev pab cuam.

Metallurgical Hloov hauv 316 Stainless Hlau ntawm Galvanizing Kub
Standard 316 stainless hlau muaj 2-3% molybdenum kom tiv thaiv pitting nyob rau hauv chloride tej yam kev mob. Txawm li cas los xij, molybdenum zoo siab rau txoj kev loj hlob ntawm sigma theem nyob rau hauv qhov kub ntawm 450-900℃nrog rau nag lossis daus kinetics sai tshaj plaws txog 600 degree. Ntawm galvanizing da dej kub ntawm 450-480℃sigma theem tsim yog qeeb dua, tab sis tseem mus txog qhov txaus ntshai ntim feem ntau tom qab ntev raug. Electron backscatter diffraction (EBSD) txoj kev kawm ntawm 316 stainless hlau raj tshem tawm los ntawm kev pabcuam hauv galvanizing tom qab 6 lub hlis (~ 4320 h ntawm 465 degree) qhia tau hais tias sigma theem ntim feem ntawm 3-8% nyob ze ntawm qhov chaw. Sigma hais (feem ntau yog 0.5-5 µm nyob rau hauv txoj kab uas hla) txhua precipitate ntawm yav tas los ferrite qhov chaw los yog nyob rau hauv lub grain ciam teb, depleting lub puag ncig matrix ntawm chromium. Qhov chaw chromium-depleted nyob ib sab ntawm sigma hais tuaj yeem poob los ntawm nominal 16-18% chromium mus rau 10-12% chromium, uas tsis txaus los lav qhov kev tawm tsam tiv thaiv zinc.

Zinc ib puag ncig muab ib txoj kev thib ob. Zinc yog molten ntawm 450℃thiab ntub stainless hlau zoo. Zinc atoms migrate interstitially raws cov ciam teb, tshwj xeeb tshaj yog cov degraded los ntawm sigma theem los yog chromium depletion. Lub diffusion coefficient ntawm zinc raws cov ciam teb nyob rau hauv austenitic stainless hlau ntawm 465℃yog nyob ib ncig ntawm 2 × 10⁻¹⁰ cm² / s, uas yog txaus nkag mus rau 100-200 mm rau hauv lub raj phab ntsa hauv 6 lub hlis. Cov kua hlau embrittlement yog tshwm sim los ntawm kev nce siab ntawm zinc ntawm cov qoob loo ciam teb dhau ib theem pib. Lub brittle intergranular cracking tuaj yeem tshwm sim txawm tias nyob rau hauv nruab nrab tensile loads vim qhov tsis sib haum ntawm thermal expansion ntawm sheath thiab cov cua sov sab hauv. Cracking txuas ntxiv mus txog thaum lub sheath poob siab ncaj ncees thiab molten zinc hu rau sab hauv NiCr cua sov hlau. NiCr yaj sai sai hauv cov kua zinc thiab lub rhaub tsis ua haujlwm tam sim ntawd.

Quantitative Relation Ntawm Lub Sijhawm Tshaj Tawm thiab Sigma Phase Tsim
Kev ua kom nrawm ntawm kev laus ntawm cov qauv raj ntawm 316 stainless hlau (phab ntsa tuab 1.5 hli, OD 12 hli) ntawm qhov kub thiab txias hauv qhov galvanizing ntau tuaj yeem kwv yees qhov kev nce qib ntawm sigma thiab qhov seem ductility. Cov qauv raug kho cua sov hauv huab cua rau lub sijhawm muab, ntu rau kev tshuaj xyuas metallographic thiab plaub taw qhia khoov kuaj los txiav txim qhov seem ductility. Qhov kub ntawm 465℃tau xaiv los sawv cev rau ib txwm molten zinc da dej ua haujlwm.

Lub Sijhawm Tshaj Tawm ntawm 465℃(teev) Sigma Phase Volume Fraction (%)Grain Boundary Chromium (wt%, ntawm STEM-EDS) Khoov Ductility (elongation thaum lub sij hawm tawg, % ntawm thawj) Failure Mode in Zinc Exposure Test 0 (raws li tau txais, tshuaj annealed)<0.5 17.2 100% No cracking after 500 hours 500 0.8 16.8 97% Surface wetting only, no penetration 1000 1.5 16.1 92% Shallow intergranular zinc penetration (20-30 µm) 2000 3.0 15.2 83% Zinc penetration depth 80-120 µm 3000 4.5 14.5 71% Intergranular cracks at 40-60% wall thickness 4000 6.5 13.8 58% Complete perforation or cracking within 100-200 hours
6000 9.0 12.5 42% Kev ua tsis tiav sai thaum tso dej (2-10 teev)
Qhov tseem ceeb tshaj plaws rau kev pabcuam galvanizing yog nyob ntawm sigma theem ntim feem ntau> 3% (~ 2000 teev ntawm 465 degree). Yog tias cov ciam teb muaj cov chromium txaus los tiv thaiv kev nkag mus ntawm zinc, ces qhov pib yuav tsis ua tiav. Tshaj li 3% sigma qhov kev nkag mus ntawm intergranular ntawm zinc nrawm tsis yog -linearly thiab txhua yam kev ncaj ncees ntawm cov sheath yog degraded los ntawm embrittlement thiab localized corrosion.

Microstructural rhiab heev rau yav dhau los Cold Work thiab Initial Ferrite ntsiab lus
Txawv 316 stainless hlau raj tsis ua tib yam ntawm galvanizing kub. Lub kinetics ntawm sigma theem kev loj hlob muaj kev cuam tshuam los ntawm peb cov khoom sib txawv: thawj delta -ferrite cov ntsiab lus ntawm cov as- cov raj xa khoom, cov nyiaj ua haujlwm txias vim lub raj kos duab, thiab cov ntsiab lus carbon (316 vs 316L). Delta-ferrite yog lub cev nruab nrab lub cubic theem uas yog tsim thaum lub sij hawm solidification ntawm austenitic stainless hlau weldments thiab castings tab sis kuj tseem muaj nyob rau hauv wrought khoom ntawm 1-10% qib nyob ntawm seb muaj pes tsawg leeg tswj. Sigma theem nucleates nyiam tshaj plaws ntawm ferrite. Ib lub raj nrog 5% raws li -muab delta-ferrite yuav siv sijhawm 2500 teev ntawm 465C kom ncav cuag 5% sigma ntim feem ntau thaum lub raj nrog<1% delta-ferrite will need 5000–6000 hours to reach the same sigma level.

Kev ua haujlwm txias kuj nce tus nqi ntawm sigma ntau lawm. Dislocations yog qhia los ntawm kev kos duab ntawm 316 stainless hlau raj mus rau qhov kawg qhov ntev thiab me me ntawm strain induced martensite kuj tseem raug tsim, ob qho tib si yog qhov chaw nucleation rau theem sigma. Cov raj tau kos nrog 15-20% txo qis hauv cross-sectional cheeb tsam muaj cov qauv tsim cov sigma kwv yees li 1.5 npaug sai dua li cov hlab ntim tag nrho ntawm tib qhov muaj pes tsawg leeg. Rau kev pab cuam galvanizing, qhov siab tshaj plaws tiv thaiv rau sigma nag lossis daus yog ua tiav los ntawm kev qhia txog kev daws teeb meem -cov hlab ntim nrog delta-ferrite concentration hauv qab 1% (qhov siab tshaj 2% ua haujlwm txias thiab cov qauv siv tag nrho recrystallised).

Khoom Siv Lub Sijhawm Delta Ferrite Cov Ntsiab Lus (vol %) Kev Ua Haujlwm Txias (%) Lub Sijhawm mus rau 3% Sigma ntawm 465℃(teev) Kwv yees Kev Pabcuam Lub Neej hauv Galvanizing Bath 316L, tshuaj annealed, qis ferrite<1 <5 4000 – 5000 12 – 18 months 316, solution annealed, standard ferrite 3 – 5 <5 2500 – 3500 8 – 12 months 316, as-drawn (20% reduction), standard ferrite 3 – 5 15 – 20 1500 – 2000 4 – 8 months 316L, as-drawn, low ferrite <1 15 – 20 2500 – 3500 8 – 12 months
316H (high carbon), tov annealed 2 - 4<5 1800 – 2500 6 – 9 months
Cov ntsiab lus carbon (316H - 0.04-0.10% C; 316L - Tsawg dua lossis sib npaug li 0.03% C) muaj kev cuam tshuam me ntsis ntawm sigma ntau lawm tab sis muaj txiaj ntsig zoo rau chromium carbide nag lossis daus. Qhov kub ntawm galvanizing yog nyob ze ntawm qhov txwv ntawm carbide nag lossis daus ntau thiab yog li 316L raug xaiv kom tsis txhob muaj kev cuam tshuam ntawm carbide.

Galvanizing Bath Service Life Extention Alternative Alloys
Thaum lub sij hawm kwv yees lub neej ntawm lub tshuab cua sov siab tshaj 12 lub hlis hauv kev pabcuam galvanizing txuas ntxiv peb lub peev xwm sheath cov ntaub ntawv muab kev ua tau zoo dua li 316 stainless hlau nrog qhov zoo sib txawv thiab cov nqi lag luam -offs. Cov nram qab no xaiv matrix pab xaiv cov khoom siv los txiav txim siab txog qhov ntsuas kub ntawm da dej thiab qhov kev pab cuam lub sijhawm.

Sheath Material Max Service Temp (degree) Sigma Phase Susceptibility kwv yees lub neej ntawm 465℃kwv tij nqi (piv rau 316) Cov ntawv thov Galvanizing
316 stainless hlau 500High (molybdenum accelerates sigma) 6 - 12 lub hlis 1.0x da dej me me, ua haujlwm tsis tu ncua, txhua xyoo kaw
310 Stainless Hlau (25% Cr, 20% Ni) 1000 Tsawg (tsis muaj molybdenum, siab dua Ni stabilizes austenite) 24 - 36 lub hlis 1.8x Nruam galvanizing nruab nrab rau da dej loj
Incoloy 800 (32% Ni, 21% Cr) 1000 Tsawg heev (siab Ni suppresses sigma kiag li) 36 - 60 lub hlis 2.5x Cov kab muaj kev ntseeg siab, kev saib xyuas tsawg tsawg
Sanicro 28 (27% Cr, 31% Ni, 3.5% Mo) 500 Nruab Nrab (Moderate Mo, siab Ni stabilizes) 24 - 30 lub hlis 3.5x Aggressive flux- pab kev pabcuam nrog cov chlorides seem
Titanium Qib 2 300 Tsis siv tau (sigma theem tsis tsim) Tsis tau - oxidises tshaj 350℃2.0x Tsawg kub zinc alloys (<350°C only)
310 stainless hlau yog qhov zoo tshaj plaws kev cuam tshuam ntawm tus nqi thiab kev tiv thaiv corrosion rau feem ntau txuas ntxiv galvanizing da dej. Cov ntsiab lus npib tsib xee ntxiv (20% es tsis txhob 10% hauv 316) stabilizes austenitic qauv tiv thaiv sigma tsim txawm tias tom qab xyoo ntawm 450-480℃. Cov ntaub ntawv pov thawj los ntawm lub Hoobkas galvanizing uas hloov 316 nrog 310 sheaths qhia qhov nruab nrab lub neej kev pabcuam tau nce los ntawm 7 lub hlis mus rau 28 lub hlis, nrog rau qee lub tshuab cua sov ua haujlwm tshaj 36 lub hlis tsis ua haujlwm. Incoloy 800 muaj lub neej ntev dua tab sis qhov kev nce qib siab tshaj 310 yuav tsis tsim nyog rau 40% tus nqi siab dua tshwj tsis yog tias chav da dej kub ze li 500℃lossis qhov chaw npaj kho lub sijhawm ntau dua ob xyoos.

Cov tswv yim pom zoo rau qhov tshwj xeeb ntawm cov cua sov rau Galvanizing da dej
Cov lus qhia hauv qab no rau kev tsim hluav taws xob cua sov raj rau molten zinc galvanizing da dej yog ua raws li kev paub dhau los thiab cov ntaub ntawv kuaj. Tsis txhob siv 316 stainless hlau nyob rau hauv ib qho kev nruam galvanizing tshaj 4000 teev / xyoo. Yog tias siv 316 vim nws muaj lossis tsis tshua kim, qhia txog kev daws teeb meem -annealed 316L nrog cov ntaub ntawv delta-ferrite cov ntsiab lus tsawg dua 1% thiab siab tshaj 5% ua haujlwm txias, thiab npaj rau kev hloov cov ntaub qhwv txhua 6-12 lub hlis. Rau ib txwm galvanizing ntawm 450 mus rau 465℃nrog zinc da dej ntau tshaj 10 tonnes muab 310 stainless hlau sheaths nrog phab ntsa thickness ntawm 2.0 mus rau 2.5 hli (ntau tshaj 1.2 mus rau 1.5 mm thickness ib txwm siv rau aqueous kev pab cuam) tso cai rau corrosion ntxiv nyiaj. Rau cov da dej uas muaj zinc-aluminium alloys los yog aggressive flux residues, xav txog kev siv Incoloy 800 los yog txhua lub lim tiam sheath thickness ntsuas siv ultrasonic kuaj xyuas tus nqi ntawm corrosion. Cov ntsiab lus tshwj xeeb tseem ceeb tshaj plaws yog xav kom tus neeg muag khoom siv lub tshuab cua sov kom lees paub qhov kev daws teeb meem -annealed mob thiab cov ntsiab lus siab tshaj plaws ferrite. Standard zeb annealed 316 tej zaum yuav muaj txaus delta -ferrite ua rau ua tsis taus ntxov ntxov txawm hais tias cov kev cai muaj pes tsawg leeg nominal. Txij li thaum lub tshuab tsis ua hauj lwm yog sigma theem embrittlement nrog cov kua hlau nkag mus, thiab tsis raug aqueous corrosion, cov engineers tuaj yeem xaiv cov ntaub ntawv tsim nyog uas txuas lub cua sov lub neej los ntawm lub hlis mus rau xyoo nyob rau hauv qhov kub kub tsis zoo no - aqueous daim ntawv thov.