Ön Isıtma M270M Gr.345S — H4, High HI, ≤ 20 mm: 100°F

M270M Gr.345S / M270 Gr.50S

AASHTO M270M Gr.345S (M270 Gr.50S) is the structural shape variant of Gr.345, intended for rolled W-shapes and channels used in bridge framing. The "S" suffix indicates the shape-specific chemistry and mechanical property requirements. Used in cross-frame angles, diaphragm members, and built-up sections where rolled shapes are specified rather than plate. Preheat requirements match Gr.345 — Table 6.3 Group 1 for NFC, Tables 12.4/12.5 for FC applications.

M270M Gr.345S / M270 Gr.50S için FC Ön Isıtmayı Anlama

Shape-grade 345 MPa (50 ksi) steel for rolled bridge members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 100°F minimum preheat at ≤ 20 mm (3/4 in). Lower hydrogen levels (H4 < H8 < H16) allow lower preheat because less hydrogen enters the weld deposit. Similarly, higher heat input reduces preheat requirements because slower cooling rates give hydrogen more time to diffuse out.

M270M Gr.345S / M270 Gr.50S Nerede Kullanılır

Used as rolled W-shapes and channels in bridge cross-frames, diaphragm members, and built-up sections. The "S" shape designation indicates procurement under AASHTO M270 with shape-specific chemistry and mandatory CVN testing. Common applications include WT sections for cross-frame members, MC channels for diaphragms, and W-shapes for floor beams on shorter spans. Weld details are primarily fillet welds at gusset connections and clip angles.

M270M Gr.345S / M270 Gr.50S için H4 Hidrojen Kontrolü

Shape-grade Gr.345S (50S) benefits from H4 at gusset-to-shape connections where access for torch preheat is limited by flanges and stiffeners. The lower preheat achievable with H4 reduces the thermal management complexity in tight spaces typical of cross-frame subassemblies.

≤ 20 mm (3/4 in)'de Ön Isıtma Neden Önemlidir

Material up to 20 mm (3/4 in) covers most cross-frame angles, stiffener clips, lateral bracing members, and light bridge plate. At this thickness, hydrogen diffusion is efficient and preheat requirements are the lowest in Table 6.3 — 10°C (50°F) for both groups. In FC service, this thickness tier also carries the lowest preheat in Tables 12.4–12.7, starting at 40°C (100°F) for H4 consumables.

≤ 20 mm (3/4 in)'de M270M Gr.345S / M270 Gr.50S

Gr.345S (50S) shapes under 20 mm flange thickness include WT sections for K-frame cross-frames and MC channels for diaphragms. The rolled section geometry concentrates stress at the flange-to-web fillet, making proper preheat at gusset connections critical for fatigue performance. SMAW E7018 is the typical process for shape-to-plate connections in bridge subassemblies because of limited access around shape flanges.

FC Köprü Kaynağı için H4 Sertifikalı Sarf Malzemeleri

H4 ek tanımlaması, sarf malzemenin 100g yığılan metal başına en fazla 4 mL difüze edilebilir hidrojen bıraktığını sertifikalandırır. Kırılma kritik M270M Gr.345S / M270 Gr.50S için ≤ 20 mm (3/4 in) kalınlıkta > 2.8 kJ/mm ısı girdisi ile H4 sarf malzemeleri FC tablolarında en düşük ön ısıtma olan 100°F (40°C)'yi sağlar.

H4 > 2.8 kJ/mm · ≤ 20 mm (3/4 in)'de Diğer Köprü Çelikleri

H4 > 2.8 kJ/mm'de M270M Gr.345S / M270 Gr.50S

Farklı Kombinasyonları Dene

Herhangi bir AASHTO M270 çelik, hidrojen seviyesi ve ısı girdisi kombinasyonunu aramak için D1.5 Köprü Ön Isıtma Hesap Makinesini kullanın. Yapısal çelik için D1.1 Ön Isıtma Hesap Makinesine de bakın.

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