Preriscaldo M270M Gr.345W — H4, Low HI, 40–60 mm: 300°F

M270M Gr.345W / M270 Gr.50W

AASHTO M270M Gr.345W (M270 Gr.50W) is a weathering bridge steel with 345 MPa (50 ksi) yield that forms a protective oxide patina for unpainted bridge service. The copper-chromium-nickel alloying provides atmospheric corrosion resistance, eliminating lifetime repainting costs estimated at $15–25 per square foot per cycle. Weld filler must match the weathering composition (E8018-W2 or equivalent) for exposed joints. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7 which carry higher preheat than the non-weathering grades.

Comprendere il Preriscaldo FC per M270M Gr.345W / M270 Gr.50W

Weathering 345 MPa (50 ksi) bridge steel for unpainted service. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 300°F minimum preheat at 40–60 mm (1½–2½ 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.

Dove Viene Usato M270M Gr.345W / M270 Gr.50W

Deployed in unpainted bridge plate girders across humid, coastal, and high-maintenance-cost environments. The weathering patina eliminates lifetime repainting cycles estimated at $15–25/sq ft per cycle. Weld filler must match the weathering composition (E8018-W2 or ER80S-G-W) for exposed joints to ensure the weld face develops the same protective oxide as the base metal. Conventional Gr.345W is being replaced by HPS345W in new designs due to superior weldability.

Controllo Idrogeno H4 per M270M Gr.345W / M270 Gr.50W

Weathering Gr.345W (50W) with H4 benefits from reduced preheat on field splice joints where maintaining temperature in wind-exposed bridge erection conditions is challenging. The E8018-W2 low-hydrogen electrode commonly used for weathering steel field work typically carries H4 or H8 designation.

Perché il Preriscaldo è Importante a 40–60 mm (1½–2½ in)

Material from 40 to 65 mm (1-1/2 to 2-1/2 in) covers heavy girder flanges, thick splice plates, and main member plate. This is the critical thickness range for bridge fabrication — preheat reaches 65°C (150°F) for Group 1 and 80°C (175°F) for Group 2. FC preheat at this thickness can exceed 200°C (400°F) depending on hydrogen level and heat input.

M270M Gr.345W / M270 Gr.50W a 40–60 mm (1½–2½ in)

Gr.345W (50W) at 40–65 mm covers girder flanges on medium-span unpainted bridges where the lifecycle cost of eliminating repainting outweighs the modest material premium. The higher-alloy chemistry for weathering resistance increases the carbon equivalent compared to plain Gr.345, which is why D1.5 assigns weathering grades to Tables 12.6/12.7 rather than 12.4/12.5 for FC preheat — a separate set of tables with generally higher preheat requirements reflecting the increased cracking susceptibility of the Cu-Cr-Ni alloying elements. Flange splice procedures must account for the weathering composition by matching filler metals to ensure consistent patina development across the weld face.

Consumabili Certificati H4 per Saldatura FC di Ponti

Il designatore supplementare H4 certifica che il consumabile deposita non più di 4 mL di idrogeno diffusibile per 100g di metallo depositato. Per frattura critica M270M Gr.345W / M270 Gr.50W a spessore 40–60 mm (1½–2½ in) con apporto termico 1.2–2.0 kJ/mm, i consumabili H4 raggiungono il preriscaldo più basso di 300°F (150°C) nelle tabelle FC.

Altri Acciai da Ponte a H4 1.2–2.0 kJ/mm · 40–60 mm (1½–2½ in)

M270M Gr.345W / M270 Gr.50W a H4 1.2–2.0 kJ/mm

Prova Diverse Combinazioni

Usa il Calcolatore Preriscaldo D1.5 per Ponti per consultare qualsiasi acciaio AASHTO M270, livello di idrogeno e combinazione di apporto termico. Vedi anche il Calcolatore Preriscaldo D1.1 per acciaio strutturale.

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