M270M Gr.345予熱 — H4、Low HI、40–60 mm: 200°F

M270M Gr.345 / M270 Gr.50

AASHTO M270M Gr.345 (M270 Gr.50) is the standard bridge plate and shape grade with 345 MPa (50 ksi) minimum yield, corresponding to ASTM A709 Gr.50. It is the baseline strength for modern highway bridge design per AASHTO LRFD. Used for plate girder flanges, webs, floor beams, cross-frames, and splice plates. Flanges on large plate girders routinely reach 50–75 mm (2–3 in) thick, making preheat compliance at upper thickness tiers a significant production consideration. NFC preheat per Table 6.3 Group 1; FC per Tables 12.4/12.5.

M270M Gr.345 / M270 Gr.50のFC予熱を理解する

Standard 345 MPa (50 ksi) bridge plate for girders and floor beams. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 200°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.

M270M Gr.345 / M270 Gr.50の使用箇所

Standard for highway bridge plate girder flanges, box girder webs, cross-frame angles, bearing sole plates, and splice plates in bolted-welded connections. Gr.345 (50) is the baseline strength for modern AASHTO LRFD bridge design. Flange butt splices, web-to-flange continuous fillet welds, and bearing stiffener clips are the dominant weld types in girder fabrication. Girder flanges typically range from 20 to 75 mm (3/4 to 3 in) thick with widths from 300 to 750 mm (12 to 30 in), requiring extended preheat soak times on thicker flange splices.

M270M Gr.345 / M270 Gr.50におけるH4水素管理

Gr.345 (50) with H4 consumables achieves the lowest FC preheat requirements available for the workhorse bridge grade. On girder fabrication lines producing 50–100 meters of flange-to-web fillet weld per shift, the reduced preheat from H4 translates directly to faster welding speed and lower fuel costs for preheat maintenance.

40–60 mm (1½–2½ in)で予熱が重要な理由

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.

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

Gr.345 (50) at 40–65 mm includes the main flange plates on medium-span highway bridges. Flange width typically runs 400–600 mm (16–24 in), requiring multi-pass CJP butt splices that accumulate 40–60 passes. Interpass temperature must stay above preheat minimum between passes and below the Table 6.4 maximum — this dual constraint makes temperature monitoring continuous during flange splice welding. Magnetic particle examination of each completed splice adds to the production schedule.

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40–60 mm (1½–2½ in)板厚における破壊臨界M270M Gr.345 / M270 Gr.50において、H4溶接材料はFCテーブルで最低予熱200°F (90°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 · 40–60 mm (1½–2½ in)における他の橋梁鋼材

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

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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