321 vs 347 Stainless Steel Stabilized Grade Sib piv rau Siab -Tsev Kev Pabcuam

Thaum austenitic stainless hlau (xws li 304 lossis 316) raug rau qhov kub thiab txias ntawm425℃thiab 870 degreerau ncua sij hawm, chromium carbides precipitate ntawm grain ciam teb - ib tug tshwm sim hu uakev xav. Qhov no depletes lub grain-txheej cheeb tsam ntawm chromium, rhuav tshem corrosion kuj.

Cov qhab nia ruaj khov daws qhov teeb meem nolos ntawm kev ntxiv cov khoom muaj zog carbide-forming (titanium hauv 321, niobium hauv 347) uas "locks" carbon ua ntej chromium carbides tuaj yeem tsim. Qhov tshwm sim: cov khoom khaws cia nws cov kev tiv thaiv corrosion txawm tias tom qab vuam los yog ntev-kub raug.

Xav txog nws zoo li no: yog 304 yog ib qho yooj yim xauv, 321 thiab 347 yog xauv nrog ib qho ntxiv deadbolt uas yuav tsis jam txawm tias tom qab siv xyoo.

321 vs 347 Stainless Steel

Vim li cas piv 321 thiab 347 tshwj xeeb?Ob leeg yog austenitic stabilized qib teev tseg nyob rau hauv ASME Tshooj VIII, ASTM A240, thiab EN 10088. Lawv yog ob qho kev xaiv ntau tshaj plaws rau cov kev pabcuam kub kub hauv refineries, petrochemical nroj tsuag, chaw nres tsheb fais fab, thiab lub dav hlau tso pa. Txawm li cas los xij lawv txawv hauv kev hloov maj mam tab sis tseem ceeb uas cuam tshuam rau tus nqi ntawm cov khoom siv, kev ntseeg tau ntawm vuam, thiab kev ncaj ncees mus ntev.

Cov kab hauv qab -Yog tias koj cov cuab yeej ua haujlwm siab tshaj 500℃thiab yuav raug welded hauv qhov chaw, qhov kev xaiv ntawm 321 thiab 347 yog ib qho kev txiav txim siab ntawm cov khoom siv feem ntau koj yuav ua.

Ob qib yog tsim los ntawm tib 18-Cr / 10-Ni puag li 304. Qhov sib txawv tseem ceeb yogstabilization keeb: 321 siv titanium (Ti); 347 siv niobium (Nb, kuj hu ua columbium).

Rooj:Table 1 - Kev sib piv tshuaj muaj pes tsawg leeg (Source: ASTM A240 / A240M-24)

Element (wt.%)	321/321H (UNS S32100)	347/347H (UNS S34700)	Qhov tseem ceeb
Cov pa roj carbon (C)	Tsawg dua lossis sib npaug rau 0.08 (H: 0.04–0.10)	Tsawg dua lossis sib npaug rau 0.08 (H: 0.04–0.10)	Siab dua C=siab dua creep zog
Chromium (Cr)	17.0–19.0	17.0–19.0	Corrosion + oxidation tsis kam
Nickel (Ni)	9.0–12.0	9.0–13.0	Austenite stability + toughness
Titanium (Ti)	Ntau dua lossis sib npaug rau 5 × C (min 0.20)	-	Stabilizer (321 nkaus xwb)
Niobium (Nb)	-	Ntau dua lossis sib npaug rau 10 × C (min 0.32)	Stabilizer (347 nkaus xwb)
Manganese (Mn)	Tsawg dua lossis sib npaug li 2.00	Tsawg dua lossis sib npaug li 2.00	Deoxidizer
Silicon (Si)	Tsawg dua lossis sib npaug li 0.75	Tsawg dua lossis sib npaug li 0.75	Siab kub. oxidation
Phosphorus (P)	Tsawg dua lossis sib npaug li 0.045	Tsawg dua lossis sib npaug li 0.045	Impurity (kom qis)
Sulfur (S)	Tsawg dua lossis sib npaug li 0.030	Tsawg dua lossis sib npaug li 0.030	Impurity (kom qis)
Nitrogen (N)	Tsawg dua lossis sib npaug li 0.10	Tsawg dua lossis sib npaug li 0.10	Txhim kho, tab sis kho C

Tau qhov twg los: ASTM A240 / A240M-24: Standard Specification rau Chromium thiab Chromium-Nickel Stainless Hlau Phaj, Sheet, thiab Sawb rau Siab Vessels thiab rau General Applications.

Vim li cas Ti los yog Nb - thiab tsis yog "tsawg carbon"?

You might ask: "Why not just use 304L (extra‑low carbon)?" The answer: at high temperatures (>500 degree), txawm tias 304L thaum kawg yuav hnov qab thaum lub sijhawm ua haujlwm ntev.Stabilization yog ruaj khov.Ti thiab Nb daim ntawv carbides uas ruaj khov dua li chromium carbides, yog li cov pa roj carbon monoxide yeej tsis muaj los cuam tshuam nrog chromium.

Titanium vs Niobium

Titanium (hauv 321)yog pheej yig duathiab me ntsis yooj yim rau tshuab. Niobium (hauv 347)yog ruaj khov nyob rau hauv lub weld arc(nws tsis "kub tawm"), thiab tsim ntau qhov kub thiab ruaj khov carbides uas tiv taus "kev laus dhau" thaum lub sijhawm ua haujlwm ntev.

Key takeaway -Nb nyob rau hauv 347 daim ntawv NbC (niobium carbide), uas tseem zoo dispersed mus txog ~ 900 degree. TiC hauv 321 tuaj yeem yaj thiab rov ua dua li chromium carbide yog tias kub dhau - qhov tsis yooj yim tab sis muaj kev pheej hmoo tiag tiag hauv kev pabcuam ntev tshaj 650 degree.

Chav ntsuas kub ntawm 321 thiab 347 yog tib yam vim tias lawv lub hauv paus matrix yog tib yam 18-Cr / 10-Ni austenite. Cov ntsiab lus stabilization (Ti, Nb) muaj qhov cuam tshuam tsawg heev ntawm qhov kub thiab txias.

Rooj:Table 2 - Chav ntsuas kub ntsuas (Source: ASTM A240-24; Outokumpu 2024)

Khoom	321 (Ntawv qhia zaub mov)	347 (Ntawv qhia zaub mov)	Test Standard
Tensile zog (MPa)	515–730	515–655	ASTM A 240 Cov Lus Qhia
Yield zog @ 0.2% (MPa)	Ntau dua lossis sib npaug li 205	Ntau dua lossis sib npaug li 205	ASTM A 240 Cov Lus Qhia
Elongation hauv 50 mm (%)	Ntau dua lossis sib npaug li 40	Ntau dua lossis sib npaug li 40	ASTM A 240 Cov Lus Qhia
Hardness (Brinell, HB)	Tsawg dua lossis sib npaug li 217	Tsawg dua lossis sib npaug li 217	ASTM A 240 Cov Lus Qhia
Hardness (Rockwell B)	Tsawg dua los yog sib npaug li 95	Tsawg dua los yog sib npaug li 95	ASTM E18
Impact Toughness @ -196℃(J)	Ntau dua lossis sib npaug li 32	Ntau dua lossis sib npaug li 32	ASTM A 370 Cov Lus Qhia Tshwj Xeeb
Elastic Modulus (GPa)	193	193	-
Poisson tus ratio	0.29	0.29	-

Tau qhov twg los: Outokumpu: Stainless Hlau Phau Ntawv - Cov Khoom Ntawm Qhov Kub Kub (2024).

Qhov no txhais li cas rau kev tsim:Rau ambient-temperature piping lossis khoom siv, 321 thiab 347 yog qhov sib hloov tau. Qhov kev xaiv tsuas yog qhov tseem ceeb thaum kub tshaj ~ 400 degree, los yog vuam yuav tsum tau.

Qhov no yog qhov tseem ceeb tshaj plaws ntawm kab lus no.Ua tib zoo nyeem nws ua ntej xaiv cov khoom siv rau txhua daim ntawv thov kub.

Ob qib tsim kev tiv thaiv Cr₂O₃ ntsuas txog ~ 870℃hauv huab cua. Nyob rau hauv tas li ntawd, lub scale spills thiab oxidation accelerates.347 muaj ib tug me ntsis ntugvim tias Nb-stabilized microstructure yog ntau resistant rau grain-txheej oxidation tom qab ntev raug.

Rooj:Table 3 - Kev taw qhia kub-kub oxidation (Source: Nickel Institute Publication 9004; ATI 321/347 Datasheet 2025)

Kub (degree)	321 - Oxidation Rate	347 - Oxidation Rate	Kev pom zoo
Tsawg dua los yog sib npaug li 650	Tsis tsim nyog	Tsis tsim nyog	Qib twg
650–800	< 0.1 mm/year	< 0.1 mm/year	Qib twg
800–900	0.1-0.5 hli / xyoo	0.08-0.4 hli / xyoo	347 preferred for >10 xyoo lub neej
900–950	>0.5 hli / xyoo (localized)	0.4-0.6 hli / xyoo	347 xwb; txwv rau<5 years
> 950	Tsis pom zoo	Tsis pom zoo	Siv 310S lossis RA253MA

Tau qhov twg los: Nickel Institute: High-Temperature Yam ntxwv ntawm Stainless Steels (Pub luam 9004, 2023). ATI (Allegheny Technologies) 321/347/348 Technical Datasheet (2025).

Creep yog tusntsiag to killerntawm cov khoom siv kub kub: ib lub yeeb nkab uas ua haujlwm tsuas yog 40% ntawm nws chav tsev kub qhov tawm los lub zog tseem tuaj yeem tawg tom qab 100,000 teev (≈11.4 xyoo) vim yog nkag.

Kev sib piv rau cov tub ntxhais kawm theem siab: nkag mus zoo li tus pas yas sab laug khoov ntawm lub rooj thaum hmo ntuj - nws tsis snap, tab sis nws yeej tsis rov qab ncaj. Thaum kub kub, hlau ua tib yam, tab sis nyob rau hauv load.

Rooj:Table 4 - ASME tso cai rau kev ntxhov siab thiab kwv yees li 100,000-h creep-rupture zog (Source: ASME Section II-D 2023; tubingchina.com creep data 2024)

Temp.	Tsim Kev Nyuaj Siab (321)	Tsim Nyog (347)	100,000-h Rupture Stress (321)	100,000-h Rupture Stress (347)
500℃(932℃F)	117 MPa	117 MPa	~ 95 MPa	~ 100 MPa
550℃(1022℃F)	105 MPa	107 MPa	~ 65 MPa	~ 72 MPa
600℃(1112℃F)	52 MPa ua	55 MPa ua	~ 38 MPa	~ 44 MPa
650℃(1202℃F)	32 MPa	35 MPa	~ 20 MPa	~ 25 MPa
700℃(1292℃F)	18 MPa	21 MPa	~ 10 MPa	~ 13 MPa
750℃(1382℃F)	10 MPa	12 MPa	~ 5 MPa	~ 7 MPa

Source: ASME Boiler & Pressure Vessel Code, Tshooj II-D (2023 tsab). Creep rupture curves: TubingChina.com - TP321/347 Mechanical Properties (2024).

Cov ntsiab lus nkag siab -Ntawm 600-700 degree,347 steel muab 10-20% siab dua tso cai rau 321 raws li ASME code. Rau lub qhov cub tshiab convection seem tsim los rau lub neej 20 xyoo, qhov no tuaj yeem txo cov phab ntsa ntawm phab ntsa los ntawm ~ 1-2 hli - txuag qhov hnyav thiab nqi.

Ntev raug ntawm austenitic stainless hlau rau 500-850℃tuaj yeem ua rau nag.sigma theem(ib qho nyuaj, brittle intermetallic) . 321 feem ntau yogtsawg raugto sigma formation because Ti restricts chromium mobility. 347, with higher Cr and Nb, has a slightly higher risk - but this is only a concern for very long exposures (>50,000 h) siab tshaj 650 degree.

Rooj:Table 5 - Kev sib piv kev pheej hmoo rau kev laus (Source: NACE MR0103; ASM Handbook Vol. 13C 2023)

Risk Factor	321	347	Kev txo qis
Sigma theem (650 degree, 10,000 h)	Tsawg	Nruab nrab	Tswj %Ni < 11; siv 321h
Carbide coarsening (>700 degree)	Nruab nrab	Tsawg	Siv stabilized H-qib
Impact toughness tom qab kev laus	Zoo khaws cia	Tsawg me ntsis	Qhia Charpy kuaj

Source: NACE MR0103/ISO 15156 - Cov hlau siv rau hauv H₂S-muaj ib puag ncig. ASM Phau Ntawv Phau Ntawv Vol. 13C: Corrosion in Specific Industries (2023).

Yog tias koj nco qab ib yam ntawm kab lus no, nco ntsoov qhov no:321 yog ib qho nyuaj rau vuam zoo dua 347 - tsis yog vim lub hauv paus hlau yog nyuaj, tab sis vim hais tias covtitanium tsis hloov hla lub vuam arc.

Qhov teeb meem ntawm Titanium Burn-Off

Thaum koj txuas 321 nrog Ti-bearing muab tub lim (ER321), txog li 50-70% ntawm titanium poob rau hauv arc.Qhov tshwm sim:qhov kev tso nyiaj ntawm cov khoom siv vuam tsis tau ruaj khov lawm, thiab qhov chaw muaj kev kub ntxhov (HAZ) tuaj yeem hnov qab thaum ua haujlwm.

Kev sib piv: nws zoo li sim pleev xim rau lub laj kab thaum muaj cua daj cua dub - titanium "tshem tawm" ua ntej nws tuaj yeem ua nws txoj haujlwm.

Vuam zoo tshaj plaws -Txawm tias thaum lub hauv paus hlau yog 321, feem ntau FABRICATORS siv ER347 (niobium-bearing) FILLER METAL. Nb nyob rau hauv ER347 stabilizes 321 thiab 347 puag hlau zoo kawg nkaus. API 582 thiab ASME BPVC Tshooj IX ob leeg pom zoo qhov kev coj ua no.

Vuam Consumable Summary

Rooj:Table 6 - Welding consumable selection (Source: AWS A5.4 / A5.9; API 582 2024)

Base Hlau	Recommended Filler (SMAW)	Recommended Filler (GTAW/GMAW)	Vim li cas
321	E347-XX	TIAB SA 347	Ti hlawv; Nb stabilizes weld
321H	E347-XX	TIAB SA 347	Tib yam vim li cas; H-qib rau creep
347	E347-XX	TIAB SA 347	Nb hloov zoo kawg nkaus
347H	E347-XX	TIAB SA 347	H-qib rau high-temperature. zog
321 welded rau 347	E347-XX	TIAB SA 347	Common denominator=Nb

Kev kho cua sov tom qab Weld (PWHT)

Tsis yog 321 lossis 347xav tau PWHT to restore corrosion resistance (that's the whole point of stabilization). However, stress‑relief PWHT may still be needed for: • Thick‑walled pressure vessels (ASME requires it >38 hli nrog qee qhov kev zam) • Cov khoom siv hauv cov khoom siv caustic lossis polythionic-acid kev pabcuam • Cryogenic kev pabcuam (kom ua kom tawv tawv)

Rooj:Table 7 - PWHT cov lus qhia (Source: ASME BPVC Section VIII Div.1 UCS-56)

Qhov xwm txheej	321 PAB	347 PAB	Nco tseg
Tom qab vuam (thaj chaw)	Tsis xav tau	Tsis xav tau	Stabilized qib
Kev ntxhov siab (ASME VIII)	600-700 degree, 1 h / hauv	600-700 degree, 1 h / hauv	Kev xaiv rau corrosion
Sensitization txaus ntshai los ntawm PWHT	Tsawg	qis	347 zam txim ntxiv

321 thiab 347 muaj ze li ntawm lub cev zoo tib yam vim tias lawv cov qauv hauv paus yog tib yam. Qhov sib txawv me me los ntawm Ti vs. Nb atomic hnyav.

Rooj:Table 8 - Kev sib piv ntawm lub cev (Source: ASM Phau Ntawv Qhia Vol. 1; Outokumpu 2024)

Khoom	321	347	Vim Li Cas Nws Tseem Ceeb
Qhov ceev (kg / m³)	7930	7960	Kev xam qhov hnyav
Thermal expansion (μm / m· degree, 0-500 degree)	16.5	16.5	Tube kev nyuaj siab los ntawm thermal loj hlob
Thermal conductivity (W / m · K, 100 degree)	16.3	16.3	Cov khoom siv hluav taws xob hloov hluav taws xob
Thermal conductivity (W / m · K, 500 degree)	21.5	21.5	-
Hluav taws xob tiv taus (μΩ·m, 20 degree)	0.72	0.73	-
Sib nqus?	Tsis yog (austenitic)	Tsis yog (austenitic)	PM tracer xyuas
Melting ntau (degree)	1400–1425	1400–1425	Vuam preheat

Ob qib tiv thaiv cov xov xwm corrosive feem ntau nrog rau 304. Qhov kev ruaj ntseg feem ntau tiv thaivintergranular corrosion(IGC) tom qab vuam. Ntawm no yog li cas lawv sib piv hauv ib puag ncig tshwj xeeb.

Rooj:Table 9 - Corrosion resistance nyob rau hauv ib puag ncig xaiv (Source: NACE MR0103; Outokumpu Corrosion Tables 2024)

Ib puag ncig	321	347	Yeej
Intergranular corrosion (welded)	Zoo (Ti)	Zoo dua (Nb)	347
Polythionic acid (lub refinery kaw)	Txais tau	Zoo heev	347 (API 571)
Chloride SCC (tsawg dua lossis sib npaug li 60 degree)	Tawm tsam	Tawm tsam	Ob leeg (ib yam li 304)
Chloride SCC (>60 degree)	pluag	pluag	Siv 2205 duplex
Nitric acid (HNO ₃)	Zoo heev	Zoo heev	Ob leeg
Sulfuric acid (H₂SO₄, dilute)	Ncaj ncees	Ncaj ncees	Siv Alloy 20
Caustic (NaOH, <50%)	Zoo rau 250 degree	Zoo rau 250 degree	Ob leeg
Atmospheric corrosion	Zoo	Zoo	Ob leeg

Polythionic Acid Stress Corrosion Cracking (PASCC)

Thaum lub refinery hydroprocessor raug kaw thiab raug rau huab cua, sulfur compounds ntawm steel nto reacts nrog ya raws rau daim ntawv.polythionic acid(H₂S₄O₆). Cov kua qaub no ua rau nrawm intergranular cracking hauv sensitized stainless hlau.

API 571 (Kev puas tsuaj Mechanisms)pom zoo 347 (tsis yog 321) rau qhov kev pabcuam no. Nb stabilization muab kev ntseeg tau ntau dua rau PASCC thaum lub sijhawm kaw.

Cov lus pom zoo rau kev ua kom zoo dua -Yog tias koj cov cuab yeej yuav pom hydroprocessing, hloov kho, lossis kev pabcuam hydrocracking - SPECIFY 347 (los yog 347H). Siv 321 ntawm no yog qhov kev lees paub tab sis muaj kev pheej hmoo siab dua.

Rooj:Table 12 - Tus nqi sib piv (2025 kev lag luam siv, ex-China zeb qhov chaw) (Source: JN Alloy tus nqi nruab nrab 2025; Sandmeyer Steel price list 2025)

Nqi Element	321	347	Qhov txawv
Cov khoom siv hauv paus (phaj, $ / kg)	$3.20–3.80	$3.50–4.20	347 +9–10%
Seamless yeeb nkab 4 "Sch 40 ($ / m)	$85–105	$95–120	347 +12%
Welded yeeb nkab ($/m)	$55–70	$62–78	347 +10%
Welding Consumable ($/kg)	ER347: $18–22	ER347: $18–22	Tib yam (siv ER347)
Machining nqi (Index)	100 (lub hauv paus)	105–110	347 me ntsis nyuaj
Installation ua haujlwm	Ib yam	Ib yam	-
Cia siab rau lub neej txuas ntxiv (xyoo)	-	+3 mus rau +8 xyoo	Siab kub. kev pabcuam
Unplanned shutdown txaus ntshai	Nruab nrab	Tsawg	347 txo kev pheej hmoo

Lub Neej-Cycle Cost (LCC) Kev Pom Zoo

Rau qhov project refinery rhaub (500 m ntawm 6 "pipe, 650 degree): •321 khoomtus nqi: ~ $ 68,000 • 347 tus nqi khoom siv: ~ $ 76,000 (+$ 8,000) • Kev pheej hmoo ntawm kev kaw tsis tau npaj tseg nrog 321: kwv yees $ 2–5M rau ib qho kev tshwm sim • Qhov yuav txo tau nrog 347: ~ 60–80% →Kev cia siab tus nqi ntawm kev siv 347=$8,000 peev piv rau $1.2–4M kev pheej hmoo txo.

Tus nqi txiav txim -Cov khoom siv tus nqi them nqi rau 347 yog qhov tsis txaus ntseeg piv rau kev pheej hmoo nyiaj txiag ntawm kev ua tsis tiav. Rau txhua qhov haujlwm uas tus nqi poob qis tshaj $ 100k, 347 yog qhov kev xaiv nyiaj txiag muaj txiaj ntsig - tsis yog 321.

A: Rau ambient-temperature, tsis-welded daim ntawv thov - yog.Rau txhua qhov kub-kub lossis welded daim ntawv thov - tsis yog . 347 muab kev nkag siab zoo dua thiab kev ruaj ntseg weld-HAZ. Nco ntsoov sab laj ASME B31.3 lossis Tshooj VIII rau qhov tshwj xeeb tsim kub.

Q2: Vim li cas cov neeg tsim khoom ib txwm pom zoo ER347 muab tub lim txawm rau 321?

A: Vim tias titanium tsis hloov kev ntseeg siab hla lub vuam arc.Ti burns tawm, tawm hauv weld un-stabilized. ER347 (niobium-bearing) hloov zoo kawg nkaus thiab ruaj khov ntawm 321 thiab 347 hauv paus hlau. This is industries standard practice (AWS A5.4).

Q3: Qhov kev pabcuam siab tshaj plaws rau 321 thiab 347 yog dab tsi?

A: Kev pabcuam cuam tshuam:mus txog 870℃(321) / 900℃(347).Kev pabcuam txuas ntxiv:limit to 750°C for long design life (>20 xyoo). Tshaj 800 degree, xav txog kev siv 310S lossis RA253MA (high-temperature alloys).

Q4: Puas yog 347 ib txwm zoo dua 321 rau kev pabcuam kub kub?

A: Tsis muaj.Rau aviation tso pa (cyclic 400-750 degree, kev co- qaug zog-driven), 321 feem ntau nyiam vim nws yooj yim rau kev tsim, tshuab, thiab yog ~ 0.4% sib dua. Rau refinery / petrochemical (kuj 600-800 degree), 347 zoo dua.

Q5: Qib "H" (321H / 347H) txhais li cas?

A: "H"=Cov pa roj carbon ntau(0.04–0.10%, vs. Tsawg dua lossis sib npaug li 0.08% rau qib tsis H). Cov pa roj carbon ntau dua ua rau muaj kev kub ntxhov siab ntxiv. Rau txhua qhov kev pabcuam siab tshaj 550 degree,ib txwm qhia H-qib(321H lossis 347H).

Q6: 321 lossis 347 puas tuaj yeem siv rau hauv qhov chaw uas muaj cov tshuaj chloride thaum kub kub?

A: Tsis muaj.Zoo li tag nrho 300-series austenitic steels, 321 thiab 347 muaj kev cuam tshuam rau chloride stress-corrosion cracking (Cl-SCC) saum toj no ~ 60 degree. Rau chloride-muaj cov kev pabcuam kub kub, siv duplex 2205 lossis super-austenitic 254 SMO.

Q7: Puas yog 347 tau txais los ntawm ASME rau kev tsim cov hlab ntsha siab?

A: Yog lawm.347 thiab 347H tau teev nyob rau hauv ASME Tshooj II-D nrog kev tso cai rau kev ntxhov siab txog 900℃F (482 degree) thiab, nrog kev ntxiv, mus txog ~ 1200℃F (650 degree). Tshooj VIII Div.1 cov qauv tsim muaj xws li ob qib.

Q8: Kuv yuav txheeb xyuas li cas seb ib daim yeeb nkab yog 321 lossis 347 hauv daim teb?

A: PMI (Positive Material Identification)siv X-ray fluorescence (XRF) yog tib txoj kev txhim khu kev qha. Ti (titanium) yog pom tseeb los ntawm XRF. Nb (niobium) kuj tuaj yeem kuaj tau tab sis yuav xav tau cov cuab yeej rhiab dua. Kev txheeb xyuas qhov pom tsis yooj yim - ob qib zoo ib yam.