Préchauffage 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.

Comprendre le Préchauffage FC pour M270M Gr.345S / M270 Gr.50S

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.

Où M270M Gr.345S / M270 Gr.50S est Utilisé

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.

Contrôle d'Hydrogène H16 pour M270M Gr.345S / M270 Gr.50S

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.

Pourquoi le Préchauffage est Important à > 60 mm (> 2½ in)

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.

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

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.

Préchauffage Plus Élevé avec Désignation H16

Les consommables H16 permettent jusqu'à 16 mL d'hydrogène diffusible par 100g — le niveau le plus élevé autorisé pour le soudage FC de ponts. À > 60 mm (> 2½ in) avec apport de chaleur 2.0–2.8 kJ/mm, le préchauffage de 325°F (160°C) compense le potentiel d'hydrogène plus élevé.

Autres Aciers de Pont à H16 2.0–2.8 kJ/mm · > 60 mm (> 2½ in)

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

Essayez Différentes Combinaisons

Utilisez le Calculateur de Préchauffage D1.5 pour Ponts pour consulter tout acier AASHTO M270, niveau d'hydrogène et combinaison d'apport de chaleur. Voir aussi le Calculateur de Préchauffage D1.1 pour l'acier de construction.

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