Preheat M270M Gr.345S — H8, Low HI, 40–60 mm: 225°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.

Memahami Preheat FC untuk M270M Gr.345S / M270 Gr.50S

Shape-grade 345 MPa (50 ksi) steel for rolled bridge members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H8 hydrogen designation and this heat input band requires 225°F minimum preheat at 40–60 mm (1½–2½ 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.

Di Mana M270M Gr.345S / M270 Gr.50S Digunakan

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.

Kontrol Hidrogen H8 untuk M270M Gr.345S / M270 Gr.50S

For Gr.345S (50S) rolled shapes, H8 is adequate for most connection details where the weld length is short and access allows proper preheat application. Cross-frame gusset connections rarely justify the cost premium of H4 consumables when H8 meets the FC preheat budget.

Mengapa Preheat Penting pada 40–60 mm (1½–2½ in)

Material from 40 to 65 mm (1-1/2 to 2-1/2 in) covers heavy girder flanges, thick splice plates, and main member plate. This is the critical thickness range for bridge fabrication — preheat reaches 65°C (150°F) for Group 1 and 80°C (175°F) for Group 2. FC preheat at this thickness can exceed 200°C (400°F) depending on hydrogen level and heat input.

M270M Gr.345S / M270 Gr.50S pada 40–60 mm (1½–2½ in)

Gr.345S (50S) shapes at 40–65 mm flange thickness are heavy built-up members — typically W14×426 or similar jumbo sections used as pier cap beams or transfer girders. The thick flanges of these shapes require full preheat per the heavy-section tier. Welding on thick rolled sections is complicated by residual stresses from rolling — preheat helps mitigate the cumulative effect of rolling residual stress plus welding shrinkage stress.

Baja Jembatan Lain pada H8 1.2–2.0 kJ/mm · 40–60 mm (1½–2½ in)

M270M Gr.345S / M270 Gr.50S pada H8 1.2–2.0 kJ/mm

Coba Kombinasi Berbeda

Gunakan Kalkulator Preheat Jembatan D1.5 untuk mencari baja AASHTO M270, tingkat hidrogen, dan kombinasi masukan panas. Lihat juga Kalkulator Preheat D1.1 untuk baja struktural.

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