예열 M270M Gr.345S — H16, Mid HI, > 60 mm: 325°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.50S의 FC 예열 이해

Shape-grade 345 MPa (50 ksi) steel for rolled bridge members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 325°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.345S / M270 Gr.50S이 사용되는 곳

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.50S의 H16 수소 제어

Gr.345S (50S) at H16 applies primarily to field-erected cross-frame connections using self-shielded FCAW. The higher preheat requirement at H16 can be challenging to maintain on thin shape flanges that lose heat rapidly to the surrounding air — electric resistance heating pads help maintain uniform temperature.

> 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.345S / M270 Gr.50S

Gr.345S (50S) above 65 mm flange thickness is limited to the heaviest jumbo W-shapes (W14×730 or similar) used in critical transfer structures. These sections have significant residual stress from the rolling process that compounds with welding stresses. Full 225°F preheat plus controlled cooling is essential — some fabricators specify post-weld hydrogen release holds at 400°F for 2 hours on jumbo section connections.

H16 지정 시 높은 예열

H16 용접재료는 100g당 최대 16 mL의 확산성 수소를 허용합니다 — FC 교량 용접에서 허용되는 가장 높은 수준입니다. > 60 mm (> 2½ in)에서 2.0–2.8 kJ/mm 입열량 시 325°F (160°C) 예열은 높은 수소 잠재력을 보상합니다.

H16 2.0–2.8 kJ/mm · > 60 mm (> 2½ in)에서의 다른 교량 강재

H16 2.0–2.8 kJ/mm에서의 M270M Gr.345S / M270 Gr.50S

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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