M270M Gr.345S予熱 — H4、Low 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のFC予熱を理解する

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の使用箇所

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におけるH4水素管理

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)で予熱が重要な理由

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)での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.

橋梁FC溶接用H4認定溶接材料

H4補足記号は、溶接材料が溶着金属100gあたり4mL以下の拡散性水素しか溶着しないことを証明します。1.2–2.0 kJ/mm入熱での≤ 20 mm (3/4 in)板厚における破壊臨界M270M Gr.345S / M270 Gr.50Sにおいて、H4溶接材料はFCテーブルで最低予熱100°F (40°C)を達成します。予熱低減が優先される場合、これが推奨される水素レベルです。

H4 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)における他の橋梁鋼材

H4 1.2–2.0 kJ/mmでのM270M Gr.345S / M270 Gr.50S

別の組み合わせを試す

D1.5橋梁予熱計算機を使用して、AASHTO M270鋼材の水素レベルと入熱の任意の組み合わせを検索できます。構造用鋼にはD1.1予熱計算機もご覧ください。

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