M270M Gr.345S予熱 — H4、Low HI、20–40 mm: 150°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 150°F minimum preheat at 20–40 mm (3/4–1½ 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.

20–40 mm (3/4–1½ in)で予熱が重要な理由

Material from 20 to 40 mm (3/4 to 1-1/2 in) includes many girder web plates, splice plates, and bearing stiffener plates. Preheat increases to 20°C (70°F) for Group 1 and 50°C (125°F) for Group 2 under Table 6.3. The thicker section slows hydrogen diffusion, requiring higher preheat to maintain safe cooling rates.

20–40 mm (3/4–1½ in)でのM270M Gr.345S / M270 Gr.50S

At 20–40 mm flange thickness, Gr.345S (50S) W-shapes serve as floor beams on shorter spans and as bracing members in steel box girders. Connection details include moment connections to girder webs requiring CJP flange welds with backing bars. Preheat is applied to the thicker element at the connection — when a 25 mm shape connects to a 50 mm plate, preheat must meet the requirement for the 50 mm thickness tier.

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20–40 mm (3/4–1½ 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150°F (70°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 · 20–40 mm (3/4–1½ 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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