Yuav Ua Li Cas Ua Ntej Txias Ua Haujlwm Feem Xyuam los ntawm Tube Drawing ntawm 316 Heater Sheath Tswj tus nqi ntawm kev ntxhov siab thiab kev sib haum xeeb thaum ua haujlwm ntawm 550 degree

Kev sib tw kinetics ntawm kev rov qab los thiab nag lossis daus ntawm carbides

Rau 316 stainless hlau sheathed hluav taws xob cua sov raj ntawm qhov kub thiab txias (550 degree, feem ntau rau cov cua kub los yog roj cua sov daim ntaub ntawv) qhov kev ua haujlwm txias dhau los ntawm cov raj kos duab tswj ob qhov kev tsis sib haum xeeb ntawm cov txheej txheem metallurgical: kev ntxhov siab (txoj kev rov qab los, uas txo cov kev ntxhov siab seem thiab ua kom nkag siab ntxiv) thiab rhiab heev (chrompitates) ntawm cov hmoov nplej tsis kam. Hnyav txias txias ntawm lub raj (25-}35% txo) ntawm 550℃so sai sai (50-80% kev ntxhov siab txo hauv 100-500 teev) tab sis tsim cov nplej tas li carbides (sensitisation) nyob rau tib lub sij hawm vim qhov siab dislocation ceev ceev chromium diffusion. Lub tshuab ua haujlwm txias txias (5 mus rau 15 feem pua ​​​​txo) txo qis dua (50 feem pua ​​​​txo kev ntxhov siab yuav siv sij hawm 1000 mus rau 5000 h) tab sis tsis hnov ​​​​tsw vim qhov txo qis dislocation density tsim tsawg qhov chaw nucleation rau carbides. Daim ntawv no qhia txog qhov sib txheeb ntawm kev ua haujlwm txias ua ntej, kev ntxhov siab so kinetics thiab pib rhiab ntawm 550 $^{\\circ}$C.

Mechanism ntawm rhiab heev thiab kev sib tw rov qab

316 stainless hlau tsim cov dislocations thiab, nyob ntawm qhov kev siv, strain-induced martensite nyob rau hauv txias kos duab. Ntawm 550℃rov qab mechanisms (dislocation annihilation thiab rearrangement) txo qis residual stress thiab hardness. Tus nqi rov qab yog Arrhenius thiab nrawm dua hauv cov khoom ua haujlwm txias dua vim tias lub zog khaws cia muaj lub zog thawb. nyob rau tib lub sijhawm, chromium carbide (Cr 23 C 6 ) precipitates raws li ib thaj tsam ntawm cov nplej thiab ntawm qhov tsis sib xws. Tus nqi ntawm nucleation ntawm carbides yog proportional rau lub dislocation ceev, vim dislocations muab ceev diffusion txoj kev rau chromium thiab carbon. Nyob rau hauv qhov txias heev- cov khoom ua haujlwm (siab dislocation ceev) carbides nucleate sai, tsim ib qho kev sib txuas ua ke txuas ntxiv hauv 100-500 teev ntawm 550℃. Carbide nucleation qeeb hauv cov khoom kho mob me me thiab txawm tias tom qab 5,000 teev carbides muaj tsawg thiab tsis txuas ntxiv.

Kev sib raug zoo ntawm kev ua haujlwm txias, kev ntxhov siab thiab kev xav ntawm 550 degree

Cov kev sib raug zoo hauv qab no yog tsim los ntawm kev tswj hwm isothermal aging ntawm 316 tubing nrog ntau feem pua ​​​​ntawm kev ua haujlwm txias ntawm 550 degree, ntsuas qhov kev ntxhov siab seem (los ntawm X-ray diffraction) thiab rhiab heev (los ntawm ASTM A262 Practice A).

Cold Work (%) Initial Residual Stress (MPa) Time Required for 50% Relaxation of Residual Stress at 550 C (hours)Time to Continuous Grain Boundary Carbides (sensitisation) at 550°C (hours) ASTM A262 Practice A Result after 1,000 hours Recommended for 550°C Service >1,000 teev 0 (annealed)<30 N/A (no stress) >10,000 (tsis muaj qhov hnov ​​​​qab) Cov kauj ruam yog Tau 5-10 100-150 2,000-5,000 5,000-10,000 Kauj Ruam (tau txais) Tau 10-15 150-200 1,000-2,000 2,000-5,000 Kauj Ruam kom pov tseg txoj kev hloov mus rau 2,000 xuab moos
15-20 200-250 500-1,000 1,000-2,000 Ditch (sensitised) after 1,500 Not recommended >1,000 teev
20-25 250-300 200-500 500-1,000 Ditch (sensitised) tom qab 500 teev Tsis muaj 25-30 300-350 100-200 200-500 ditch hnyav tsis txaus
30-35 350-400 50-100 100-200 Severe ditch + grain dropping Unacceptable35 >400 <50 <100 Full sensitization Unacceptable
Qhov cuam tshuam ntawm kev pabcuam kub ntawm cov nqi sib tw

Lub sij hawm rau rhiab heev txo nrog nce kub, nro so accelerates. Qhov zoo tshaj plaws txias- ua haujlwm ntau rau qhov muab kev pabcuam kub yog qhov cuam tshuam ntawm cov kev hloov pauv no.

Kev Pabcuam Kub (degree ) Pom Zoo Ua Haujlwm Txias Ntau Yam rau 10,000-teev Kev Pabcuam (%) Kev ntxhov siab so tau tiav (%) Kev puas tsuaj rau cov khoom nyiam 450 15-25 50-70% tom qab 10,000h Tsawg (carbides qeeb) 316 (txhua yam) 500 10-20 60-800redrate 1h 1h 525 5-15 70-85% tom qab 10,000h Nruab Nrab-High 316L yuav tsum tau 550 0-10 80-90% tom qab 10,000h Siab (rhiab heev yuav) 316L nrog stabilization 575 0-5 (annealed) N/A (tsis muaj kev ntxhov siab) Siab (tag nrho sensitize) Hloov mus rau 3 3
600 0 (tsuas yog annealed) N/A Severe 316 tsis tau
Cov tswv yim pom zoo txog kev tsim khoom siv cua sov

Cov hauv qab no tau pom zoo ua haujlwm txias thiab tom qab- tsim cov qauv kev kho mob rau 316 sheathed heaters rau 550℃lub luag haujlwm.

Kev Ua Haujlwm Txias Siab Tshaj Plaws hauv Cov Khaub Ncaws Ua tiav (%) Cov Kev Pabcuam Lub Neej ntawm 550℃(teev) Pom Zoo Tshaj Tawm-Kev Ua Kev Kho Mob Kev Ntsuas Kev Ntsuas Yuav Tsum Muaj Lwm Yam Alloy<1,000 (intermittent) 20 None None 316 acceptable 1,000-2,500 15 Stress relief 400°C, 1h ASTM A262 Practice A (step) 316L 2,500-5,000 10 Stress relief 450°C, 2h ASTM A262 Practice E (pass) 316L 5,000-10,000 5 (annealed)Full solution anneal ASTM A262 Practice A (step) 316L or 347 >10, 000 0 (ua tiav recrystallized) Tag nrho cov tshuaj anneal + stabilization (850 degree, 4h) ASTM A262 Xyaum C (<0.3 mm/year) 347 or 310
Field Detection of Service Sensitization at Elevated Temperatures

If a 316 heater that has been in service at 550°C for >1,000 teev ua tsis tiav nyob rau hauv ib puag ncig corrosive (xws li thaum lub sij hawm tu lub voj voog los yog tom qab kaw) rhiab heev thaum lub sij hawm kev pab cuam yuav tsum tau txiav txim siab. Metallographic xeem (ASTM A262 Xyaum A etch) yuav nthuav tawm "ditch" qauv ntawm cov ciam teb. Lub hardness yuav raug txo los ntawm qhov raws li - kos tus nqi (xws li . 300 HV rau 200 HV) vim rov qab los. Qhov no yuav qhia tau tias cov khoom nyob ntawm qhov kub thiab txias. Cracking lossis intergranular corrosion yuav yog hom tsis ua haujlwm. Rau cov kev ua tsis tiav no, kev kho rau yav tom ntej yuav yog los qhia tag nrho annealed (recrystallised) tubing uas tsis tshua muaj kev ntxhov siab, lossis hloov mus rau qib ruaj khov xws li 347 (columbium stabilized) lossis 310 stainless hlau, uas tsis hnov ​​​​tsw ntawm 550 degree.

Xaus: 550℃kev lag luam-tawm ntawm kev txo kev ntxhov siab thiab kev xav

Rau 316 stainless hlau encased heaters khiav ntawm 550℃tus nqi ntawm kev ua haujlwm txias ua ntej tswj cov kinetics ntawm ob txoj kev tsis sib haum xeeb, kev ntxhov siab (zoo) thiab rhiab heev (tsis zoo). Kev ua haujlwm txias siab tshaj 15-20% ua rau muaj kev kub ntxhov ceev (tej nag lossis daus ntawm carbides hauv 500-1,500 teev), uas ua rau muaj kev cuam tshuam rau intergranular corrosion. Kev ua haujlwm txias<10% is slow to relax but stays unsensitized for >5,000 hours. For operation at 550 °C, engineers specifying 316 sheaths must limit preceding cold work to < 10 - 15 % with fully annealed (recrystallised) tubing required for prolonged life (>5,000 teev). Qhov chaw ua haujlwm txias tsis tuaj yeem zam tau, kev daws teeb meem anneal tom qab tsim yog tsim nyog los recrystallise cov qauv thiab txo qhov seem ntawm kev ntxhov siab nrog rau qhov muaj peev xwm ntawm rhiab heev.