M270M Gr.345予熱 — H16、Mid HI、20–40 mm: 175°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 H16 hydrogen designation and this heat input band requires 175°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.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H16水素管理

Gr.345 (50) at H16 requires the highest FC preheat in the standard grade range. The elevated preheat compensates for the substantial hydrogen potential but adds significant production cost on thick girder flanges. Most fabricators avoid H16 for shop work, reserving it only for field processes where lower-hydrogen alternatives are not feasible.

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.345 / M270 Gr.50

At 20–40 mm, Gr.345 (50) serves splice plates, web plates, and bearing sole plates in standard highway bridge girders. CJP butt welds at flange splices are the most critical joint at this thickness — full-penetration ultrasonically-inspected joints that must pass D1.5 acceptance criteria. Preheat compliance is production-critical: 70°F minimum means heated fabrication bays in northern climates during winter bridge contracts.

H16指定での高い予熱

H16溶接材料は100gあたり最大16mLの拡散性水素を許容します — 橋梁FC溶接で許可される最高レベルです。2.0–2.8 kJ/mm入熱での20–40 mm (3/4–1½ in)では、175°F (80°C)予熱が高い水素ポテンシャルを補います。この継手にH8またはH4溶接材料に切り替えると必要な予熱が低下します。

H16 2.0–2.8 kJ/mm · 20–40 mm (3/4–1½ in)における他の橋梁鋼材

H16 2.0–2.8 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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