Ib daim ntawv duplex stainless hlau raj uas tau pom ntev kev pab cuam ntawm qhov kub siab yuav zoo zoo, tab sis ib qho yooj yim kais nrog rauj tuaj yeem tawg nws. Qhov no yog qhov txaus ntshai ntawm sigma theem embrittlement-kev hloov pauv ntawm metallurgical uas hloov cov tawv tawv, ductile alloy rau hauv cov khoom siv ceramic tsis hloov nws cov tsos. Kev soj ntsuamsigma theem embrittlement duplex stainless hlau exchangerCheebtsam thaum ntxov yog ib qho tseem ceeb, vim hais tias ib zaug sigma cov ntaub ntawv, tsis muaj nyob rau hauv-situ kho yog ua tau. Qhov cuam tshuam yuav tsum tau hloov.
Sigma Phase Embrittlement yog dab tsi?
Duplex stainless hlau (xws li, 2205, 2507) muaj qhov sib npaug microstructure ntawm kwv yees li qhov sib npaug austenite thiab ferrite. Qhov no dual-theem qauv muab lub zog siab, zoo ductility, thiab zoo heev corrosion kuj. Txawm li cas los xij, thaum cov hlau duplex raug rau qhov kub thiab txias hauv thaj tsam li ntawm 600-900℃rau lub sijhawm ntev, kev hloov pauv tshwm sim. Cov theem ferrite pib decompose, tsim ib theem tshiab intermetallic hu ua sigma (σ). Sigma yog ib qho hlau-chromium-molybdenum compound nrog tetragonal siv lead ua qauv. Nws yog ib qho nyuaj heev, nkig heev, thiab nplua nuj nyob rau hauv chromium thiab molybdenum.
Kev tsim ntawm sigma yog nyob ntawm lub sijhawm thiab qhov kub thiab txias. Ntawm 750-850 degree, kev hloov pauv sai tshaj plaws; tseem ceeb embrittlement tuaj yeem tshwm sim hauv tsawg li ob peb teev. Thaum qhov kub thiab txias (600-700 degree), nws yuav siv sij hawm ntau pua lossis ntau txhiab teev. Thaum sigma precipitates- feem ntau yog me me, nyias daim hlau raws li cov ciam teb thiab hauv cov nplej ferrite- nws tsis tuaj yeem thim rov qab los ntawm kev kho cua sov hauv qhov chaw. Cov khoom ua nkig thiab poob nws qhov cuam tshuam toughness yuav luag tag.
Common Ua hauv Cov Cua Txias Txias Txias
Sigma theem embrittlement feem ntau ntsib hauv cov xwm txheej hauv qab no:
Welds tsis muaj cov tshuaj tom qab vuam annealing- Lub tshav kub cuam tshuam (HAZ) uas nyob ib sab ntawm lub vuam tuaj yeem nyob hauv qhov kub thiab txias ntev ntev yog tias txias qeeb. Cov ntu loj, tuab yog qhov tshwj xeeb. Yog hais tias qhov kev tivthaiv tsis yog tom qab cov tshuaj annealed (rhuab mus rau 1040-1100℃thiab sai quenched), sigma tseem nyob rau hauv HAZ.
Kev pabcuam ntev ntawm qhov kub siab- Cov khoom siv hluav taws xob kub uas ua haujlwm nrog cov hlau kub tsis tu ncua nyob rau hauv 600-900℃ntau, txawm tias tsis xav tau, tuaj yeem maj mam embrittle. Qhov no tej zaum yuav tshwm sim nyob rau hauv ib tug khib nyiab rov qab unit los yog ib tug tsis zoo cooled exchanger.
Hluav taws kub- Ib tsob nroj hluav taws kub uas ua rau ib feem ntawm qhov sib hloov pauv mus rau hauv qhov sib txawv ntawm sigma, txawm tias lub sijhawm luv luv, tuaj yeem ua rau embrittlement hauv thaj tsam cuam tshuam.
Fabrication yuam kev- Kev kho cua sov tsis raug thaum lub sijhawm tsim khoom (xws li, txias txias los ntawm qhov kub thiab txias) tuaj yeem txhawb nqa sigma.
Qhov chaw muaj kev phom sij tshaj plaws yog cov ntaub ntawv raj, cov flanges tuab dua, thiab cov cheeb tsam uas cuam tshuam rau cov cua sov. Cov raj nyias nyias txias sai dua thiab tsis tshua muaj kev tsim cov sigma, tab sis lawv tsis muaj kev tiv thaiv yog tias qhov kev pabcuam kub kub tshwj xeeb.
Visual thiab Mechanical Indicators
Sigma theem embrittlement tsis hloov qhov tsos ntawm cov hlau. Ib qho kev tivthaiv yuav zoo ib yam li qub- tsis muaj xim, tsis pom tawg -tab sis yuav nkig kiag li. Txawm li cas los xij, ua tib zoo tshuaj xyuas thiab kev sim tuaj yeem qhia tau tias nws muaj.
Qhov tshwm sim ntawm Fracture Surfaces
Yog hais tias ib qho khoom ua tsis tiav los yog txhob txwm ua txhaum, qhov tawg ntawm lub sigma-embrittled duplex steel yuav tshwm ci ntsa iab, granular, thiab crystalline, tsis muaj ductile tearing lossis shear di ncauj. Qhov no contrasts sharply nrog dull, fibrous tsos ntawm ib txwm ductile puas. Sigma tawm hauv cov hlau nrog lub zog ntawm cov qhob noom xim kasfes: ib qho me me cuam tshuam nws ntau dua li deforming nws.
Impact Toughness Test
Qhov kev xeem kom muaj nuj nqis rau sigma embrittlement yog Charpy V-notch (CVN) cuam tshuam kuaj. Duplex 2205 nyob rau hauv cov kev daws teeb meem-annealed kom raug feem ntau pom muaj kev cuam tshuam toughness ntawm 100-200 J ntawm chav tsev kub. Thaum sigma tam sim no, qhov nyuaj yuav poob qis dua 20 J, thiab feem ntau rau ib daim duab. Rau cov khoom me me lossis daim coupon xeem txiav los ntawm ib daim ntawv raj, qhov kev sim no muab pov thawj tseeb.
Metallographic Examination: Qhov Tsaus Etch Spots
Lub ntsiab lus ntawm sigma theem embrittlement yog qhia nyob rau hauv lub tshuab tsom iav tom qab etching. Cov qauv polished yog etched nrog ib tug haum reagent, xws li electrolytic etching nyob rau hauv 10% oxalic acid los yog ib tug sib tov ntawm HCl thiab HNO₃ (Aqua Regia) los yog KOH (rau duplex). Nyob rau hauv ib txwm duplex microstructure, lub austenite thiab ferrite tshwm raws li ob theem sib txawv -feem ntau austenite li lub teeb los yog me ntsis etched, ferrite li darker. Thaum lub sij hawm sigma tau tsim, nws zoo nkaus li tsaus nti, feem ntau blocky los yog phaj-zoo li lub network nyob rau hauv lub ferrite nplej thiab raws li cov ciam teb. Raws li kev nthuav dav dua, cov sigma hais lawv tus kheej tuaj yeem pom tau tias yog ib qho kev sib cais, tsaus ntuj heev. Cov yam ntxwv "dub etch me ntsis" los yog txuas ntxiv tsaus nti yog qhov qhia tau zoo.
Field metallographic replication (raws li tau piav qhia hauv cov ntawv dhau los) tuaj yeem siv rau ntawm qhov chaw coj mus rau qhov chaw replica ntawm etched nto, uas yog tom qab kuaj xyuas nyob rau hauv lub tshuab nqus tsev portable. Qhov no tsis yog kev puas tsuaj (lossis tsawg kawg nkaus) cov txheej txheem tso cai rau kev kuaj pom yam tsis tau txiav cov qauv los ntawm kev sib pauv loj.
ASTM A923: Txoj Kev Ntsuas Tus Qauv
ASTM A923, "Standard Test Methods for Detecting Detrimental Intermetallic Phases in Duplex Austenitic/Ferritic Stainless Steels," muab peb txoj kev lees paub rau kev kuaj xyuas sigma thiab lwm yam intermetallic theem (xws li chi):
Txoj Kev A(Sodium hydroxide etch test) - Cov qauv polished yog etched hauv cov tshuaj kub 40% NaOH. Lub xub ntiag ntawm sigma lossis chi theem yog qhia los ntawm cov lus teb tsaus nti. Qhov no yog qhov kev xeem dhau / tsis ua haujlwm.
Txoj kev B(Charpy impact test) – Impact toughness yog ntsuas. Qhov tsawg kawg nkaus qhov nruab nrab absorbed zog (piv txwv li, 54 J rau 2205) yog yuav tsum tau txais.
Txoj kev C(Kev ntsuas cov ntsiab lus ferrite) - Ib qho ferritescope ntsuas qhov feem pua ferrite. Sigma tsim txo cov ntsiab lus ferrite loj. Txawm li cas los xij, txoj kev no tsis tshua ncaj qha thiab tuaj yeem cuam tshuam los ntawm lwm yam.
Rau kev ua haujlwm hauv thaj chaw, Txoj Kev A (etch test) ntawm thaj chaw me me lossis ntawm ib qho kev hloov pauv yog qhov ua tau zoo tshaj plaws.
Irreversibility: Tsis Muaj Kev Kho Hauv Qhov Chaw
Lub ntsiab lus tseem ceeb rau cov kws tsim khoom cog: tsis muaj kev kho cua sov uas tuaj yeem siv rau qhov loj, sib sau ua ke cua sov kom tshem tawm cov theem sigma. Txhawm rau rov ua kom cov sigma rov qab, tag nrho cov khoom yuav tsum tau ua kom sov rau 1040-1100℃thiab tom qab ntawd nrawm nrawm (dej lossis quab yuam roj). Qhov no yog tsis yooj yim sua rau ib tug nyob rau hauv-kev pab cuam exchanger nrog hlab, gaskets, thiab txuas piping. Txawm hais tias lub plhaub tuaj yeem ua kom sov, cov khoom hauv lub raj yuav nthuav dav thiab cuam tshuam, thiab qhov txias ceev yuav ua rau thermal shock. Yog li ntawd, ib zaug sigma embrittlement raug lees paub nyob rau hauv ib qho tseem ceeb tivthaiv (xws li, ib tug tubesheet los yog ib tug tuab flange), cov khoom yuav tsum tau hloov. Rau cov hlua khi, tshem tawm thiab hloov pauv yog tib txoj kev xaiv.
Yog li kev kuaj xyuas yog qhov tseem ceeb rau kev tiv thaiv kev puas tsuaj loj. Yog hais tias ib tug xav tias lub tshav kub exchanger yog ua los ntawm embrittled qhov chaw, ib tug thermal lossis mechanical shock (xws li, lub siab surge, ib tug rauj tshuab, los yog txawm ib txwm vibration) yuav ua rau sai li sai tau.
Cov kauj ruam qhia txog qhov chaw ua haujlwm
Thaum sigma theem embrittlement yog xav tias nyob rau hauv ib tug laus duplex stainless hlau tshav kub exchanger, cov nram qab no cov kauj ruam yuav tsum tau ua:
Tshawb xyuas keeb kwm kev pabcuam- Puas yog lub exchanger tau raug kub siab tshaj 600 degree? Tshawb xyuas cov ntaub ntawv ua haujlwm, cov ntawv ceeb toom xwm txheej hluav taws, lossis cov txheej txheem tsis zoo. Vuam cov ntaub ntawv: puas tau tom qab weld tov anneals ua rau tuab seem?
Ua qhov ntsuas tsis muaj kev puas tsuaj ferrite- Kev nyeem ntawv ferritescope ntawm qhov huv, hauv av tuaj yeem pom cov ntsiab lus ferrite txo qis (ib txwm yog li 40-60%; sigma tuaj yeem poob qis dua 30%). Txawm li cas los xij, qhov no ib leeg tsis yog qhov tseeb.
Siv ib tug metallographic replica- Ib cheeb tsam me me (piv txwv li, ntawm lub ntsej muag lub raj lossis lub flange tuab) yog hauv av du, polished, thiab etched nrog ASTM A923 Method A tov. Ib qho acetate replica yog coj thiab tshuaj xyuas ntawm 200-500 × magnification. Lub xub ntiag ntawm qhov tsaus ntuj, blocky sigma theem tes hauj lwm lees paub embrittlement.
Yog ua tau, muab daim coupon me me- Ib lub raj me me lossis ib qho ntawm cov khoom seem ntawm qhov chaw tsis tseem ceeb tuaj yeem raug tshem tawm mus rau chav kuaj Charpy cuam tshuam. Kev ntsuas qhov cuam tshuam lub zog qis dua 20 J rau 2205 (lossis qis dua qhov tshwj xeeb) qhia tias muaj qhov hnyav heev.
Ntsuas qhov ceev- Yog tias pom sigma, qhov cuam tshuam cuam tshuam yuav tsum tau teem sijhawm rau hloov. Nyob rau hauv ib ntus, lub exchanger yuav tsum tau ua ntawm txo thermal thiab mechanical loads, thiab tej qhov chaw vibration yuav tsum tau dampened.
Kev Tiv Thaiv: Kev kho cua sov kom zoo thiab kev txwv kev pabcuam
Txoj hauv kev zoo tshaj los tswj sigma embrittlement yog los tiv thaiv nws:
Ib txwm daws anneal duplex weldments- Rau cov ntu tuab (ntau dua 6 hli), kev daws teeb meem tom qab vuam annealing ua kom nrawm nrawm yog qhov yuav tsum tau ua. Rau cov ntu nyias, cov txheej txheem vuam tsim nyog (tsawg tshav kub tawm, kev tswj qhov kub thiab txias) feem ntau tuaj yeem zam sigma, tab sis annealing muaj kev nyab xeeb dua.
Tsis txhob siv sijhawm ntev tshaj 600 degree – If a duplex exchanger is needed for a high‑temperature application (e.g., >500 degree) rau ncua sij hawm, yuav tsum xav txog ib qho sib txawv alloy (xws li, npib tsib xee-based superalloy) yuav tsum tau txiav txim siab.
Tswj cua txias tom qab muaj cua sov- Yog tias muaj hluav taws kub lossis kub kub tshwm sim, qhov sib pauv yuav tsum tau txias kom sai li qhov ua tau zoo (piv txwv li, los ntawm dej nyab nrog dej) kom txo tau lub sij hawm ntawm 600-900 degree.
Xaus
Sigma theem embrittlement yog ib qho irreversible, kev puas tsuaj loj heev uas tuaj yeem tswj tau los ntawm kev kho cua sov kom raug thiab tsis txhob raug ncua ntev rau nws qhov kub thiab txias. Cov cim ntawmsigma theem embrittlement duplex stainless hlau exchangerCheebtsam suav nrog kev poob qis hauv qhov cuam tshuam hnyav, qhov ci ntsa iab tawg, thiab cov tsos ntawm cov pob zeb tsaus nti lossis cov tes hauj lwm hauv kev kuaj xyuas metallographic. ASTM A923 muab cov qauv kev sim rau kev kuaj pom. Thaum paub meej, cov khoom cuam tshuam tsis tuaj yeem kho thiab yuav tsum tau hloov. Lub neej ntawm cov hlau tuaj yeem tsis sau los ntawm cua sov-thiab nyob rau hauv cov ntaub ntawv ntawm duplex stainless hlau, zaj dab neeg uas tsis tau sau yog sigma embrittlement. Kev tshuaj xyuas tsis tu ncua, kev paub txog kev ua haujlwm kub hauv keeb kwm, thiab kev xaiv cov khoom tsim nyog tsuas yog tiv thaiv tus yeeb ncuab uas ntsiag to, ua rau tawg.
