Preriscaldo M270M Gr.345W — H4, Low HI, ≤ 20 mm: 100°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 100°F minimum preheat at ≤ 20 mm (3/4 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 ≤ 20 mm (3/4 in)

Material up to 20 mm (3/4 in) covers most cross-frame angles, stiffener clips, lateral bracing members, and light bridge plate. At this thickness, hydrogen diffusion is efficient and preheat requirements are the lowest in Table 6.3 — 10°C (50°F) for both groups. In FC service, this thickness tier also carries the lowest preheat in Tables 12.4–12.7, starting at 40°C (100°F) for H4 consumables.

M270M Gr.345W / M270 Gr.50W a ≤ 20 mm (3/4 in)

Gr.345W (50W) weathering steel at thin plate thickness appears in unpainted bridge bearing stiffeners and web attachment plates exposed to the atmosphere. Filler metal must match the weathering composition — E8018-W2 for SMAW or ER80S-G-W for GMAW. The patina development on thin plate is rapid (6–18 months) but requires proper drainage detailing to prevent pack rust between closely spaced plates.

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 ≤ 20 mm (3/4 in) con apporto termico 1.2–2.0 kJ/mm, i consumabili H4 raggiungono il preriscaldo più basso di 100°F (40°C) nelle tabelle FC.

Altri Acciai da Ponte a H4 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 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.

Guide Correlate