예열 M270M Gr.345 — H16, Low HI, ≤ 20 mm: 150°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.50의 FC 예열 이해

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 150°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.345 / M270 Gr.50이 사용되는 곳

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.50의 H16 수소 제어

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 mm (3/4 in)에서 예열이 중요한 이유

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)에서의 M270M Gr.345 / M270 Gr.50

Gr.345 (50) under 20 mm covers web stiffeners, bearing stiffener clips, and cross-frame gusset plates — the highest-volume weld details in girder fabrication. These thin plates are fillet-welded to girder webs using semi-automatic FCAW with E71T-1 wire at 2–4 kg/hr deposition. Preheat is quick to achieve with a rosebud torch and verifiable with a temperature-indicating crayon. Joint fit-up at this thickness is critical because thin plate distortion from uncontrolled heat input causes cumulative girder sweep.

H16 지정 시 높은 예열

H16 용접재료는 100g당 최대 16 mL의 확산성 수소를 허용합니다 — FC 교량 용접에서 허용되는 가장 높은 수준입니다. ≤ 20 mm (3/4 in)에서 1.2–2.0 kJ/mm 입열량 시 150°F (70°C) 예열은 높은 수소 잠재력을 보상합니다.

H16 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)에서의 다른 교량 강재

H16 1.2–2.0 kJ/mm에서의 M270M Gr.345 / M270 Gr.50

다양한 조합 시도

D1.5 교량 예열 계산기를 사용하여 AASHTO M270 강재, 수소 수준 및 입열량 조합을 조회하세요. D1.1 예열 계산기도 참조하세요.

관련 가이드