예열 M270M Gr.345 — H4, High HI, > 60 mm: 250°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 H4 hydrogen designation and this heat input band requires 250°F minimum preheat at > 60 mm (> 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.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 H4 수소 제어

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.

> 60 mm (> 2½ in)에서 예열이 중요한 이유

Material over 65 mm (2-1/2 in) includes the heaviest bridge girder flanges and box-section walls. Table 6.3 requires 110°C (225°F) for both groups at this thickness. Extended preheat soak time is necessary to achieve uniform through-thickness temperature. FC preheat for the heaviest sections reaches 180–200°C (350–400°F) at the H16 hydrogen level.

> 60 mm (> 2½ in)에서의 M270M Gr.345 / M270 Gr.50

Gr.345 (50) above 65 mm represents the heaviest plate girder flanges on long-span bridges. At 75–100 mm flange thickness, each CJP splice requires 80+ weld passes with continuous interpass monitoring. Preheat soak-through needs heating mats or induction coils because torch heating alone cannot maintain uniform temperature through 3+ inches of plate. Production rates drop to 1–2 splices per shift at this thickness, making preheat efficiency a major scheduling factor.

FC 교량 용접용 H4 인증 용접재료

H4 보조 지정은 용접재료가 용착 금속 100g당 최대 4 mL의 확산성 수소를 방출함을 인증합니다. 파괴 임계 M270M Gr.345 / M270 Gr.50에서 > 60 mm (> 2½ in) 두께, > 2.8 kJ/mm 입열량 시 H4 용접재료는 FC 표에서 가장 낮은 예열 250°F (120°C)를 달성합니다.

H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)에서의 다른 교량 강재

H4 > 2.8 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.

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