Ntawm Qhov Kev Sib Txuas Tshwj Xeeb ntawm Kev Ua Haujlwm Txias Ua Ntej (5% vs 15% vs 25%) thiab Lub Sijhawm Kev Laus ntawm 700℃(1,000 vs 5,000 vs 10,000 Teev) Puas 316L Lub Rhaub Sheath Hloov ntawm Transgranular mus rau Intergranular Creep Cracking Under 60 MPa Hoop

Txias ua hauj lwm-Induced Creep Mode Transition in Low-Carbon Austenitic Stainless Steel

Hom kev creep cracking (transgranular vs. intergranular) nyob rau hauv 316L stainless hlau sheathed hluav taws xob cua sov hlab ua hauj lwm ntawm 700℃nyob rau hauv 60 MPa hoop kev nyuaj siab, xws li kub kub rauv cua sov, superheater txhawb los yog tshuaj txheej txheem heaters, yog ib tug muaj nuj nqi ntawm ob qho tib si ua ntej txias ua hauj lwm feem pua ​​thiab lub sij hawm laus. Cov khoom siv ua kom tiav tag nrho (5% lossis tsawg dua ua haujlwm txias) qhia tau tias muaj cov kab mob sib kis (los ntawm cov nplej) nrog cov ductility zoo thiab lub neej ntev rupture mus txog 10, 000+ teev. Ntawm 15% ua ntej ua haujlwm txias, cov khoom hloov pauv los ntawm transgranular mus rau intergranular cracking (raws li cov ciam teb) tom qab 1,000-5,000 teev ntawm kev laus, nrog rau kev txo qis hauv lub neej tawg. Ntawm 25 feem pua ​​​​ntawm kev ua haujlwm txias ua ntej kev sib tsoo yog pom nyob rau hauv 1,000 teev. Qhov kev hloov pauv no cuam tshuam rau kev nrawm nrawm ntawm M{sub 2} {sub 3} C{sub 6} carbides ntawm cov ciam teb nplej uas ua raws li qhov chaw nucleation rau cavitation. Kab lus no suav cov kev sib txuas tshwj xeeb ntawm kev ua haujlwm txias thiab lub sijhawm laus uas ua rau kev hloov pauv ntawm transgranular mus rau intergranular creep cracking ntawm 700℃thiab 60 MPa hoop stress.

Mechanism ntawm Creep Mode Transition Induced by Cold Work

Thaum 700 C creep deformation tshwm sim los ntawm dislocation nce thiab grain ciam swb. Cov txheej txheem intragranular dislocation yeej muaj nyob rau hauv cov khoom siv annealed (tsawg dislocation ceev) thiab pom cov pob txha tawg. The previous cold work leads to a high dislocation density and favours the fast precipitation of fine M₂₃C₆ carbides at the grain boundaries. Cov carbides pin lis ciam teb tiv thaiv zawv zawg tab sis kuj yog qhov chaw rau kab noj hniav nucleation. Thaum tsim, cov kab noj hniav interconnect raws ciam teb ua rau intergranular cracking. Qhov ceev ntawm carbide nag lossis daus thiab sai dua qhov hloov mus rau intergranular cracking, qhov ua haujlwm txias dua.

Quantitative Relationship ntawm Kev Ua Haujlwm Txias, Lub Sijhawm Laus thiab Creep Cracking Hom

Kev ntsuam xyuas creep ntawm 316L tubing (0.022% C, 2.2% Mo) nrog kev ua haujlwm txias ua ntej ntawm 5%, 15% thiab 25% ntawm 700℃hauv qab 60 MPa hoop kev ntxhov siab tau tsim cov kev hloov pauv hauv qab no thiab tawg mus txog 10,000 teev.

Yav dhau los Kev Ua Haujlwm Txias (%) Lub Sijhawm Hnub nyoog ntawm 700oC (h) M23C6 Carbide Spacing ntawm Grain Boundaries (nm) Creep Cracking Mode Creep Repture Life at 700oC, 60 MPa (h) Rupture Elongation (%) Pom zoo rau kev pabcuam ntawm 700℃rau 10,000 h
5 0 (raws li -annealed) N/A (tsis muaj carbides) Transgranular 12,000-15,000 18-22 Yog
5 1,000 >500 (sparse) Transgranular 11,000-14, 000 17-21 Yog
5 5,000 200-300 Transgranular (mixed) 10,000-13,000 15-19 Yog
5 10,000 150-200 Transgranular (predominant) 9,000-12,000 14-18 Tau
15 0 N/A Transgranular 11,000-14, 000 17-21 Yog
15 1,000 100-150 Mixed (trans + inter) 7,000-9,000 10-14 Marginal
15 5,000 60-80 Intergranular (dominant) 4,000-6,000 6-10 Tsis pom zoo.
15 10,000 50-60 Intergranular (mob) 3000-4500 4-8N/A 25 0 NoMixed (qee inter) 8,000-11,000 12-16 Marginal 25 1,000 50-80 Intergranular 3,500-5,500 5-9 25 5,{{ranular (severg) 2,500-4,000 3-6Tsis yog 25 10,000 40-50 Intergranular (hnyav heev) 2,000-3,500 2-5 Tsis yog
1,000 Teev, 5,000 Teev Sijhawm thiab 10,000 Teev Cov Kev Hloov Kho Tshwj Xeeb

Cov lus hauv qab no qhia txog qhov ua haujlwm txias txias uas ua rau hloov pauv ntawm transgranular mus rau feem ntau intergranular tawg ntawm txhua lub sijhawm.

Ageing Time (hr) at 700°CCold Work (%) 50% Intergranular Cracking ModeCold Work Intergranular Cracking Mode (%) >80% Pom Zoo Ua Haujlwm Txias Siab Tshaj Plaws rau Transgranular Hom 1, 000 15-18 22-25 12 % 5, 000 10-12 15-18 8 % 10, 000 7-9 10-12 5 % (ua kom tiav)
Cov lus pom zoo rau kev pabcuam ntawm 700 degree

Rau 316L encased heaters tsim los rau 700℃kev khiav hauj lwm ntawm 60 MPa hoop kev nyuaj siab, cov nram qab no ua hauj lwm txias kev txwv yuav tsum tau ua raws li los xyuas kom meej transgranular (zoo dua ductility, ntev lub neej) creep cracking tom qab teev cov kev pab cuam ntev.

Lub Hom Phiaj Kev Pabcuam Lub Neej ntawm 700℃(teev) Qhov siab tshaj plaws Ua Ntej Ua Haujlwm Txias Ua Haujlwm rau Transgranular Dominant Cracking (%) tau qhia ua ntej-Kev Pabcuam Kev Pabcuam Xav Tau Lub Neej (teev) 5,000 15 7,000-10,000 Raws li- tsis tau,{8} kev pabcuam 3,500-5,500 Post-draw anneal tsim nyog 10,000 8 8,000-11,000 Teeb kos lossis annealed
10,000 12 (marginal) 6,000-8,000 Anneal pom zoo 15,000 5 10,000-13,000 Fully annealed (0-5% CW)
V. Kev txheeb xyuas ntawm Creep Cracking Hom Tom Qab Kev Pabcuam

Txoj kev tawg yog qhia los ntawm kev tshawb nrhiav metallographic ntawm txoj kab ntev -section tom qab etching rau cov cua sov ua haujlwm ntawm 700℃. Transgranular fractures nkag mus rau hauv cov nplej (ncaj, mob, nquag tsis muaj ceg). Intergranular kab nrib pleb raws li cov ciam teb (jagged, branching) Ua ntej txias ua hauj lwm ntsuas yuav txiav txim los ntawm hardness (tag nrho annealed 316L ~ 150-170 HV; 15% CW ~ 200-230 HV; 25% CW ~ 250-280 HV).

Cov ntsiab lus: Kev Tswj Xyuas Kev Ua Haujlwm Txias Ua Ntej kom tswj tau Transgranular Creep rau 10,000 hr Kev Pabcuam ntawm 700 degree

Transgranular creep cracking (ntau dua ductility, 9,000-12, 000+ teev rupture life) nyob rau 10,000 teev nyob rau hauv 316L stainless hlau rhaub sheaths ntawm 700℃nyob rau hauv 60 MPa hoop stress nrog 5% los yog tsawg dua ua ntej txias ua hauj lwm. Kev ua haujlwm txias ua ntej ntawm 15% ua rau cov khoom ua kom tawg tuaj yeem ua rau hauv 1000-5000 xuab moos, txiav lub neej tawg mus rau 4000-6000 xuab moos. 25% ua haujlwm txias ua ntej raug cuam tshuam hauv kev sib tsoo hauv 1000 hr thiab rupture lub neej tsawg dua 4000 hr. Cov neeg tsim qauv qhia txog 316L sheaths rau 10,000 teev ua haujlwm ntawm 700℃yuav tsum muab cov haujlwm txias ua ntej ntawm<8-10% and, for sensitive applications, specify totally annealed tubing (0-5% cold work). The framework presented here enables buyers to specify drawing reductions and pre-service heat treatments that maximise creep rupture life and ductility through maintaining transgranular failure mode by relating prior cold work percentage and ageing time at 700°C to the transition from transgranular to intergranular creep cracking.