Niobiy-Stabillangan zanglamaydigan po'latdagi silitsidning murakkab fazasi va uning mo'rtlashtiruvchi ta'siri
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 precipitation of G-phase (Ni₁₆Nb₆Si₇), a complex nickel-niobium-silicide intermetallic phase, can cause significant embrittlement as measured by room temperature Charpy V-notch impact energy. Unlike chi (χ) and Laves phases which form at higher temperatures (650-750°C), G-phase precipitates at lower temperatures (550-650°C) after very long aging times (10,000-30,000 hours). G-phase has a face-centered cubic (FCC) structure but is brittle and forms primarily at grain boundaries. At volume fractions as low as 0.2-0.5%, G-phase reduces impact energy from >200 J (ductile) to 100-150 J (acceptable). At 1.0-1.5% volume fraction, impact energy drops to 50-80 J (marginal). At >2,0{2}}2,5%, zarba energiyasi 40 J (moʻrt) dan past boʻladi, bu -xizmatni demontaj qilish, qayta ishlash va tashish vaqtida yorilish xavfini yaratadi. Ushbu maqola 600 gradusda 20 000 soatdan keyin G-fazali hajm ulushi va Charpy zarbasining mustahkamligi o'rtasidagi bog'liqlikni aniqlaydi.
G-fazali mo'rtlanish mexanizmi
G-faza (Ni₁₆Nb₆Si₇) vazniga koʻra taxminan 50-60% Ni, 20-25% Nb va 10-15% Si ni oʻz ichiga oladi. U 550{20}}650 daraja uzoq vaqt qarigandan so'ng don chegaralarida cho'kadi, birinchi navbatda niobiy bilan barqarorlashtirilgan zanglamaydigan po'latlarda (347, 348). Faza qattiq (400-600 VV) va mo'rt. Xona haroratiga ta'sir qilish sinovi paytida G-faza zarralarida yoriqlar boshlanadi va kichik plastik deformatsiyalar bilan don chegaralari bo'ylab tarqaladi. Mo'rtlashuv juda nozik: qattiqlik faqat o'rtacha darajada oshishi mumkin (160-180 HV dan 190-220 HV gacha), ammo zarbaga chidamlilik keskin pasayadi. G-faza ko'pincha e'tibordan chetda qoladi, chunki u uzoq qarish vaqtlarini (10,{19}} soat) va maxsus niobiy-kremniy birikmalarini talab qiladi.
G-faza hajmining ulushi va Charpi ta'sir energiyasi o'rtasidagi miqdoriy bog'liqlik
347 trubaning (0,45% Nb, 0,50% Si, 0,08% C) 600 daraja haroratda 25 000 soatgacha nazorat ostida qarishi, SEM/EDS tomonidan G-faza miqdorini aniqlash va 25 daraja Charpy V-cho'ntak ta'siri sinovi bilan quyidagi natijalar qayd etildi.
| Qarish vaqti 600 daraja (soat) | G-Faza hajmi ulushi (%) | G-Faza zarrachalari hajmi (nm) | Yog'ingarchilik joyi | Charpy ta'sir energiyasi 25 daraja (J) | Singan ko'rinishi | Postdan keyin{0}}xizmat ko‘rsatish (demontaj, tashish) uchun tavsiya etiladi |
|---|---|---|---|---|---|---|
| 0 (tavlangan) | 0 | N/A | Yo'q | 200-240 | Egiluvchan (100% kesish) | Ha |
| 5,000 | <0.05 | <20 | Intragranular (siyrak) | 190-220 | Egiluvchan | Ha |
| 10,000 | 0.05-0.10 | 20-40 | Don chegaralari (siyrak) | 160-190 | Egiluvchan | Ha |
| 12,000 | 0.10-0.20 | 30-50 | Don chegaralari (tarqalgan) | 130-160 | Aralash (ba'zi dekolte) | Ha |
| 14,000 | 0.20-0.35 | 40-60 | Don chegaralari (qisman) | 100-130 | Aralash | Qabul qilinadi |
| 16,000 | 0.35-0.50 | 50-70 | Don chegaralari (uzluksiz-yaqin) | 80-100 | Aralash{0}}mo'rt | Marginal |
| 18,000 | 0.50-0.70 | 60-80 | Don chegaralari (uzluksiz) | 60-80 | Mo'rt (yorilish) | Tavsiya etilmaydi |
| 20,000 | 0.70-1.00 | 70-100 | Uzluksiz tarmoq | 45-65 | Mo'rt | Yo'q (qo'llash paytida yuqori xavf) |
| 22,000 | 1.00-1.30 | 80-120 | Uzluksiz + intragranular | 30-50 | Juda mo'rt | Yo'q |
| 25,000 | 1.30-1.70 | 100-150 | Keng qamrovli, birlashgan | 20-35 | Juda mo'rt | Yo'q |
Kremniy va niobiyning G-faza shakllanishiga ta'siri
G-faza niobiy va kremniyni talab qiladi. Pastki kremniy va past niobiy G-fazali yog'ingarchilikni sekinlashtiradi.
| Kremniy (og'irligi%) | Niobiy (og'irlik%) | 0,7% G-fazaga 600 daraja (soat) vaqti | Charpy Impact 20 000 soatdan keyin 600 daraja (J) | 20 000 soatlik xizmat uchun-Post xizmat koʻrsatish uchun tavsiya etiladi |
|---|---|---|---|---|
| 0.20 | 0.40 | >25,000 | 120-160 | Ha |
| 0.35 | 0.45 | 15,000-20,000 | 70-100 | Qabul qilinadi (monitoring) |
| 0.50 | 0.45 | 10,000-15,000 | 45-65 | Tavsiya etilmaydi |
| 0.65 | 0.50 | 8,000-12,000 | 35-55 | Yo'q |
| 0.80 | 0.55 | 6,000-10,000 | 25-40 | Yo'q |
600 gradusda 347 ta isitish moslamalari uchun amaliy tavsiyalar-Xizmatdan foydalanish
20 000 soatdan keyin 600 daraja haroratda olib tashlanadigan, demontaj qilinadigan, tashiladigan yoki utilizatsiya qilinadigan 347 ta qoplamali isitgichlar uchun quyidagi G-faza chegaralari va materiallarning texnik xususiyatlari ishlov berish natijasida yuzaga keladigan yorilish-ning oldini olish uchun yetarli darajada mustahkamlikni ta'minlaydi.
| Kerakli post-xizmat faoliyati | Xavfsiz ishlov berish uchun minimal Charpy ta'siri (J) | Ruxsat etilgan maksimal G-faza (%) | Maksimal kremniy (og'irlik%) | Maksimal niobiy (og'irlik%) | Tavsiya etilgan xizmat muddati chegarasi (soat) |
|---|---|---|---|---|---|
| Olib tashlash va yo'q qilish (zarba yuklamaydi) | >30 | 1.3 | 0.50 | 0.45 | 25,000 |
| Kranni ko'tarish bilan olib tashlash | >50 | 0.9 | 0.45 | 0.45 | 18,000 |
| Demontaj (kesish, payvandlash) | >70 | 0.6 | 0.40 | 0.40 | 15,000 |
| Qayta{0}}foydalanish yoki qayta tiklash | >100 | 0.3 | 0.35 | 0.40 | 12,000 |
| Muhim ishlov berish (yaqin-atrofdagi xodimlar) | >120 | 0.2 | 0.30 | 0.40 | 10,000 |
G-fazali mo'rtlashuvni tekshirish
For heaters retired after long-term 600°C service, three methods assess G-phase embrittlement. The first is Charpy impact testing of a removed sample (if available). Acceptance: >Xavfsiz ishlov berish uchun 50 J. Ikkinchisi - qattiqlik sinovi: G-faza qattiqlikni 160-180 HV dan 190-220 HV (kamtar) ga oshiradi. Uchinchisi, G-fazasini aniqlash uchun metallografik tekshirish (SEM/EDS) (Ni-Nb-Si tarkibiga ega boʻlgan don chegaralaridagi yorqin, blokli zarralar). Soddalashtirilgan dala usuli - bukish sinovi: kichik kupon, agar u 10 mm radiusda 90 daraja egilganida yorilib ketsa, mo'rtlashuv kuchli bo'ladi.
Xulosa: G-Post{2}}xizmat bilan ishlashda mo'rtlashuv fazasining oldini olish uchun Past Si + Past Nb ni belgilash
For 347 stainless steel heater sheaths after 20,000 hours at 600°C, G-phase (Ni₁₆Nb₆Si₇) precipitation at volume fractions as low as 0.7-1.0% reduces room temperature Charpy impact energy from >200 J dan 45-65 J gacha (mo‘rt) bo‘lib, xizmatdan keyingi demontaj, kranni ko‘tarish yoki tashishda-yorilish xavfi yuqori. 600 daraja haroratda 20 000 soatlik xizmat ko'rsatish uchun 347 ta g'ilofni belgilovchi muhandislar, xizmatdan keyingi ishlov berish uchun silikonni cheklashlari kerak.<0.35% and niobium to <0.40% to keep G-phase <0.5% after 20,000 hours. For service exceeding 15,000-18,000 hours, upgrading to 310 stainless steel (which does not form G-phase) or Inconel 600 is recommended. By linking G-phase volume fraction after 20,000 hours at 600°C to Charpy impact energy reduction, the framework presented here enables buyers to specify 347 chemistry limits that prevent brittle failure during the retirement and handling of long-service heater sheaths.
