600 daraja haroratda 20 000 soatdan so‘ng 347 isitish moslamasi qobig‘idagi G-faza (Ni₁₆Nb₆Si₇) yog‘ingarchilik hajmining ulushi xona haroratining Charpy ta’sir energiyasini post-xizmat tashish va demontaj qilish uchun qanday nazorat qiladi

Niobiyning murakkab silitsid fazasi va mo'rtlashtiruvchi ta'siri-stabillangan zanglamaydigan po'lat

Precipitation of G-phase (Ni 16 Nb 6 Si 7 ), a complex nickel-niobium-silicide intermetallic phase, can cause significant embrittlement, as measured by room temperature Charpy V-notch impact energy, for 347 stainless steel (Nb-stabilized) sheathed electric heating tubes operating at 600 C for extended periods (20,000+ hours)-such as in long-term industrial furnace heaters, petrochemical reformer tubes or superheater supports. The G-phase is formed at lower temperatures (550-650°C) during very lengthy ageing times (10,000-30,000 hours) while chi (χ) and Laves phases form at higher temperatures (650-750°C). G-phase is brittle with face centred cubic (FCC) structure and is mostly formed at the grain boundaries. G-phase at volume fractions as low as 0.2-0.5% reduces impact energy from >200 J (ductile) to 100-150 J (acceptable). At 1.0-1.5 vol% the impact energy is reduced only to 50-80 J. Impact energy drops to below 40 J (brittle) at >2,0-2,5%, xizmatdan keyingi demontaj, ishlov berish va jo‘natish vaqtida yorilish xavfi tug‘diradi. Ushbu maqola 600 C da 20 000 soatdan keyin Charpy ta'siriga chidamliligi va G fazasi hajmi o'rtasidagi bog'liqlikni aniqlaydi.

G-fazali mo'rtlashuv mexanizmi

G-fazasi (Ni₁₆Nb₆Si₇) ogʻirligiga ~50-60% Ni, 20-25% Nb va 10-15% Si ni oʻz ichiga oladi. U 550-650 daraja uzoq qarigandan so'ng don chegaralarida cho'kadi, asosan niobiy stabillashgan zanglamaydigan po'latlarda (347, 348). Faza qattiq (400-600 VV) va mo'rt. Xona haroratining ta'siri sinovi shuni ko'rsatadiki, yoriqlar G-faza zarralarida yadro hosil qiladi va kichik plastik deformatsiyalar bilan don chegaralari bo'ylab harakatlanadi. Mo'rtlashuv juda nozik: qattiqlik biroz yaxshilanishi mumkin (160-180 HV dan 190-220 V gacha), zarba chidamliligi esa sezilarli darajada kamayadi. G-faza odatda e'tiborga olinmaydi, chunki qarishning uzoq davom etishi (10,000+ soat) va maxsus niobiy-kremniy juftligi.

G-faza hajmining ulushi va Charpi ta'sir energiyasi o'rtasidagi miqdoriy bog'liqlik

600° haroratda 25 000 soatgacha boʻlgan 347 ta trubaning (0.45% Nb, 0.50% Si, 0.08% C) moʻrtlashuv jarayoni SEM/EDS yordamida G-faza miqdorini aniqlash va 25Â darajali Charpy V{8}}chogʻlik zarbasi sinovi bilan aniqlanadi.

Qarish vaqti 600 daraja (soat) G-Faza hajmi ulushi (%)G-Faza zarralari hajmi (nm) Yogʻingarchilikning joylashuvi Charpy taʼsir energiyasi 25 daraja (J) Sinishi koʻrinishi Postdan keyin tavsiya etiladi-Xizmat koʻrsatish (demontaj, tashish)
0 (tavlangan) 0 Yo'q Yo'q 200-240 Egiluvchan (100% kesish) Ha 5,000 0.05<20 Intragranular (sparse) 190-220 DuctileYes 10,000 0.05-0.10 20-40 Grain boundaries (few) 160-190 DuctileYes 12,000 0.10-0.20 30-50 Grain boundaries (scattered) 130-160Mixed (some cleavage) Yes 14,000 0.20-0.35 40-60 Partial grain borders 100-130 Mixed Acceptable 16,000 0.35-0.50 50-70 Near-continuous grain boundaries 80-100 Mixed-brittle Marginal 18,000 0.50-0.70 60-80 Continuous grain boundaries 60-80 Brittle (cleavage)Not recommended 20,000 0.70-1.00 70-10045-65 Brittle continuous netNo (high risk when handled)
22,000 1.00-1.30 80-120 Uzluksiz + dona ichidagi 30-50 Juda mo'rt Yo'q 25,000 1.30-1.70 100-150 Keng, birlashtirilgan 20-35 Juda mo'rt Yo'q
Kremniy va niobiyning G-fazali yog'ingarchilikka ta'siri

G-faza niobiy va kremniyga muhtoj. Kamroq kremniy va kamroq niobiy G-fazali yog'ingarchilikni sekinlashtiradi.

Silicon (wt%) Niobium (wt%) Time to 0.7% G-Phase at 600°C (h) Charpy Impact after 20,000h at 600°C (J)Recommended for 20,000h Service with Post Service Handling 0.20 0.40 >25,000 120-160 Ha 0.35 0.45 15,000-20,000 70-100 Qabul qilinadi (monitor) 0.50 0.45 10,000-15,000 45-65 Tavsiya etilmaydi 0.65 0.50 8,000-12,000 35-55 Yoʻq 0.80 0.55 6,000-10,{13}}Rektorlik kurslari uchun Post xizmati bilan ishlash bilan 600 daraja

Quyidagi G-faza cheklovlari va material parametrlari 600 daraja haroratda 20 000 soatdan keyin olib tashlanadigan, qismlarga ajratiladigan, tashiladigan yoki tashlab yuboriladigan 347 ta qoplamali isitgich uchun yorilishning oldini olish uchun tegishli mustahkamlikni taʼminlaydi.

Xizmatdan keyingi faollik Xavfsiz ishlov berish uchun minimal Charpy ta'siri (J) Ruxsat etilgan maksimal G-faza (%) Maks. Kremniy (wt%) Maksimal niobiy (wt%} Tavsiya etilgan xizmat muddati chegarasi (soat)
Removal and disposal (no impact loading) >30 1.3 0.50 0.45 25000
Removal with crane lifting >50 0.9 0.45 0.45 18000
Dismantling (cutting, welding) >70 0,6 0,40 0,40 15 000
Re-use or Refurbishment >100 0.3 0.35 0.40 12,000
Critical handling (people nearby) >120 0.2 0.30 0.40 10 000
G-Faza mo'rtlashuvini tasdiqlash

Three approaches are used to evaluate G-phase embrittlement for heaters retired after long-term service at 600°C. The first is Charpy impact testing on a deleted sample (if available). Acceptance: >Xavfsiz ishlov berish uchun 50 J Ikkinchisi qattiqlik sinovi: G-faza qattiqlikni 160-180 HV dan 190-220 HV (o'rtacha) ga oshiradi. Uchinchisi, G-fazasini aniqlash uchun metallografik tekshirish (SEM/EDS) (Ni-Nb-Si tarkibiga ega boʻlgan don chegaralaridagi yorqin, blokli zarralar). Oddiy dala testi kichik kuponni egishdir. Agar u 10 mm radius bo'ylab 90 daraja egilganida bo'linib ketsa, mo'rtlashish jiddiydir.

Xulosa: Xizmatdan foydalanish vaqtida G-fazali mo'rtlashuvning oldini olish uchun Past Si + Low Nb dan foydalaning{2}}

For 347 stainless steel heater sheaths after 20,000 h at 600°C, G-phase (Ni16Nb6Si7) precipitation at volume fractions as low as 0.7-1.0% decreases room temperature Charpy impact energy from >200 J dan 45-65 J gacha (mo'rt) demontaj qilish, kranni ko'tarish yoki tashish paytida yorilish xavfi yuqori. Belgilangan 347 ta qobiqni o'z ichiga olishi kerak<0.35% silicon and <0.40% niobium to reduce G-phase to <0.5% after 20,000 hours for the recommended 20,000 hour service at 600°C with expected post-service handling. For service beyond 15,000-18,000 hours, it is recommended to upgrade to 310 stainless steel (which does not create G-phase) or Inconnel 600. The current system allows the buyers to define 347 chemical limits to avoid brittle failure during retirement and handling of long-service heater sheaths, by correlating G-phase volume fraction after 20,000 hours at 600°C to Charpy impact energy reduction.