Ntawm Qhov Kev Sib Txuas Tshwj Xeeb ntawm Kev Ua Haujlwm Txias Ua Ntej (15% vs 25%) thiab Peak Sensitization Temperature (650℃vs 700 degree) Puas yog 316L Heater Sheath Tsim Nruam Cov Nroj Tsuag Nroj Tsuag Cr₂₃C₆ Carbides Tom qab 1,000 Teev Kev Ua Haujlwm Zoo Tshaj Plaws

Sijhawm-Tsuas Kub-Cold Work Interaction for Initiation of Sensitization in Low-Carbon 316L

Lub sijhawm los tsim cov qoob loo txuas ntxiv chromium carbides (Cr2 3}C 6) uas tsim cov kev sib xyaw ua ke (IGC) hauv ASTM A262 Practice E test (copper-copper sulfate-}sulfuric acid) yog nyob ntawm qhov ua haujlwm txias ua ntej feem pua thiab qhov kub siab tshaj plaws rau 316L pos huab cua kub stainless hlau sheathed (600-750 degree) thaum lub sijhawm ua haujlwm lossis kev tsim khoom (vuam ntawm cov flanges tuab, kev ua haujlwm brazing lossis txheej txheem kev mus ncig ua si). 316L muaj cov pa roj carbon tsawg (<0.03%) but cold work increases the rate of carbide precipitation by providing high diffusivity routes (dislocations, deformation bands) for chromium and carbon. For fully annealed 316L (0% cold work), it takes >2,000 teev los tsim cov carbides tas li ntawm qhov kub siab tshaj ntawm 700 degree. Nruam carbides yog tsim los ntawm 600-1,000 teev (borderline rau 1,000-teev kev pabcuam) nrog 15% ua haujlwm txias. Ntawm 25% kev ua haujlwm txias, txuas ntxiv carbides tshwm sim ntawm 200-1,000 teev ua rau ASTM A262 Practice E tsis ua haujlwm ua ntej 1,000 teev. Kev ua haujlwm txias tseem ceeb los tsim 1,000 teev rhiab heev ntawm 650℃yog li 20-25%. Daim ntawv no qhia txog qhov ua haujlwm txias-kub sib xyaw ua ke uas ua rau ASTM A262 Practice E tsis ua haujlwm li ntawm 1,000 teev.

Mechanism of Sensitization Accelerated los ntawm Kev Ua Haujlwm Txias

Dislocations yog tsim los ntawm kev ua haujlwm txias (10¹¹-10¹² cm⁻² rau 25% ua haujlwm txias piv rau 10⁸ cm⁻² hauv cov khoom siv annealed). Dislocations ua haujlwm raws li txoj hauv kev nrawm nrawm rau cov pa roj carbon thiab chromium, ua rau 10-100 npaug ntawm diffusivity ntawm 600-750 degree. Cov pa roj carbon atoms tsiv mus sai dua rau cov ciam teb, xws li chromium atoms uas tsim Cr 23 C 6 carbides. Kev ua tsis tiav hauv ASTM A262 Practice E yog qhov kev txhim kho txuas ntxiv lossis nyob ze txuas ntxiv ntawm cov carbides ntawm cov ciam teb uas ua rau cov cheeb tsam sib tshooj chromium-depleted (Cr 12%).

Quantified Txias Ua Haujlwm - Kub - Lub Sijhawm Ua Haujlwm

Lub sij hawm los kuaj pom thawj zaug (nruam carbides) tau txiav txim siab rau kev tswj kev laus ntawm 316L tubing (0.022% C, 0.07% N, 2.2% Mo) nrog rau kev ua haujlwm txias ua ntej ntawm 0, 15 thiab 25% ntawm 650 thiab 700℃tom qab los ntawm ASTM A262 Kev Ntsuas 40 teev (21 teev) kev ntsuas E.

Ua Haujlwm Txias Ua Ntej (%) Peak Temp (C) Nruam Grain Ciam Teb Carbides (hrs) ASTM A262 Practice E Failure (kawg ntawm khoov) (hrs) Zoo rau 1,000-teev Lub Luag Haujlwm?
0 (annealed) 650 >10,000 >10,000 Yog 0 700 2,500-3,500 2,500-3,500 Yog
15 650 2,000-3,000 2,500-4,000 Yog (marginal)
15 700 600-1,000 800-1,200 Borderline (mob txaus ntshai) 25 650 800-1,200 1,000-1,500 Borderline (saib) 25 700 200-400 250-500 Tsis yog (ua tsis tau ua ntej 1,000h)
Kev sib xyaw tseem ceeb rau 1000 Teev Tsis Ua Haujlwm

Qhov sib xyaw ua ke ua rau ASTM A262 Xyaum E tsis ua haujlwm hauv 1,000 teev ntawm kev laus yog qhia hauv cov lus hauv qab no.

Ua ntej Cold Work (%) Peak Temperature (degree) Ua Tsis Tau ASTM A262 Xyaum E Hauv 1,000 Teev?Lub Sijhawm Ua Tsis Taus (nruab nrab, teev) Cov Lus Qhia Ua Haujlwm
15 650 No >3,000 Txais tau 15 675 Tsis muaj (borderline) 1,500-2,500 Txais nrog kev saib xyuas 15 700 Yog (borderline) 800-1,200Tsis pom zoo rau 1,000h 20 650 Tsis muaj 1500-2500 Marginal
20 675 Yog (borderline) 900-1,500 Tsis pom zoo
20 700 Yog 400-700 Tsis yog
25 625 Tsis muaj 1,500-2,500 Txais
25 650 Yog (borderline) 1,000-1,500 Tsis pom zoo 25 675 Yog 500-800 Tsis yog 25 700 Yog 250-500 Tsis yog
30 600 Tsis yog 1,500-2,500 Marginal 30 625 Yog 800-1,200 Tsis yog
650 Yog 400–700 No 30
Cov tswv yim pom zoo rau 316L welds lossis kub cuam tshuam

Rau 316L encased heaters nrog 1,000 teev cumulative exposure ntawm 650-700℃(xws li nyob rau hauv kev pab cuam los yog thaum lub sij hawm ntau weld kho) cov nram qab no ua hauj lwm txias txwv siv los tiv thaiv ASTM A262 xyaum E tsis ua hauj lwm.

Lub Sijhawm Tag Nrho Tag Nrho Tag Nrho ntawm 650-700℃(hr)% Max Ua Ntej Ua Haujlwm Txias rau Kev Ruaj Ntseg -Kev Pabcuam Pub DawbPost-Exposure Verification Pom Zoo<500 3020 ASTM A262 500 to 1,000 Practice A (etching with oxalic acid)
500-1,000 25-30 (not advised)Practice E 1,000-2,000 15 Practice E recommended 2,000-5,000 10 Practice E at 2,000 h >5,000 0 (annealed) Xyaum E ntawm 5,000 teev
Sensitization Verification Post Service

Yav dhau los 650-700℃kev pabcuam nrog kev ua haujlwm txias dhau los: ASTM A262 Xyaum A (oxalic acid etch) yog kev tshuaj xyuas sai. Tsis muaj rhiab heev nyob rau hauv ib 'kauj ruam' qauv (zoo li ib thaj tsam ntawm nplej). Ib tug "ditch" qauv (etched pits ntawm grain ciam teb) implies tas mus li carbides thiab kwv yees kev xyaum E tsis ua hauj lwm. Xyaum E (tooj liab- tooj liab sulfate-sulfuric acid, 24h, khoov kuaj) yog qhov tseeb rau cov ntawv thov tseem ceeb.

Xaus: Lub 1,000-teev Sensitization Zone

Rau 316L stainless hlau rhaub sheaths nyob rau hauv 700℃kev pab cuam rau 1000 teev, 15% txias ua hauj lwm nyob rau hauv ciam teb rhiab heev (800-1200 teev tsis ua hauj lwm), hos 25% txias ua hauj lwm ua rau tsis ua hauj lwm nyob rau hauv 250-500 teev . 650℃, 25% txias 100 xuab moos ua hauj lwm, ciam teb 10. Ua ntej ua haujlwm txias rau kev pabcuam lossis tsim cov 316L sheaths xav tau 1,000 teev ntawm 650-700℃yuav tsum tau txwv rau 15-20% kom tsis txhob ua tsis tiav ntawm ASTM A262 Practice E. Yog tias ua haujlwm txias yog> 20-25%, kev daws teebmeem anneal yog xav tau tom qab tsim (1,040℃rectification) thiab tshem tawm cov txheej txheem dej. muaj peev xwm ntawm rhiab heev. Lub moj khaum uas tau nthuav tawm ntawm no cuam tshuam txog kev ua haujlwm txias ua ntej feem pua ​​thiab qhov kub siab tshaj plaws rau lub sijhawm rau cov carbides tas li thiab ASTM A262 Kev Xyaum E tsis ua haujlwm, tso cai rau cov neeg yuav khoom kom paub meej txog kev ua haujlwm txias thiab kev kho cua sov tom qab uas ua kom muaj kev cuam tshuam kev cuam tshuam rau 1,000-teev kev pabcuam ntawm qhov kub siab.