Vorwärmung 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.

Die FC-Vorwärmung für M270M Gr.345 / M270 Gr.50 Verstehen

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.

Wo M270M Gr.345 / M270 Gr.50 Eingesetzt Wird

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.

Wasserstoffkontrolle H4 für M270M Gr.345 / M270 Gr.50

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.

Warum Vorwärmung bei > 60 mm (> 2½ in) Wichtig ist

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

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.

H4-Zertifizierte Zusatzwerkstoffe für FC-Brückenschweißen

Die Zusatzbezeichnung H4 zertifiziert, dass der Zusatzwerkstoff höchstens 4 mL diffusiblen Wasserstoff pro 100g abgeschiedenes Schweißgut abgibt. Für bruchkritischen M270M Gr.345 / M270 Gr.50 bei > 60 mm (> 2½ in) Dicke mit > 2.8 kJ/mm Wärmeeinbringung erreichen H4-Zusatzwerkstoffe die niedrigste Vorwärmung von 250°F (120°C) in den FC-Tabellen.

Andere Brückenstähle bei H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)

M270M Gr.345 / M270 Gr.50 bei H4 > 2.8 kJ/mm

Verschiedene Kombinationen Ausprobieren

Verwenden Sie den D1.5 Brücken-Vorwärmrechner für jeden AASHTO M270 Stahl, Wasserstoffniveau und Wärmeeinbringungskombination. Siehe auch den D1.1 Vorwärmrechner für Baustahl.

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