Ön Isıtma M270M Gr.345W — H4, High HI, > 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.

M270M Gr.345W / M270 Gr.50W için FC Ön Isıtmayı Anlama

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 > 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.345W / M270 Gr.50W Nerede Kullanılır

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.

M270M Gr.345W / M270 Gr.50W için H4 Hidrojen Kontrolü

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.

> 60 mm (> 2½ in)'de Ön Isıtma Neden Önemlidir

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)'de M270M Gr.345W / M270 Gr.50W

Gr.345W (50W) above 65 mm is increasingly rare as HPS345W replaces it in new designs. The conventional weathering composition at this thickness has elevated lamellar tearing risk from sulfide inclusion elongation — the problem that drove development of the HPS grades with calcium-treated, inclusion-shape-controlled steel. Existing bridges with thick 345W flanges require careful Z-direction tension checks during rehabilitation welding.

FC Köprü Kaynağı için H4 Sertifikalı Sarf Malzemeleri

H4 ek tanımlaması, sarf malzemenin 100g yığılan metal başına en fazla 4 mL difüze edilebilir hidrojen bıraktığını sertifikalandırır. Kırılma kritik M270M Gr.345W / M270 Gr.50W için > 60 mm (> 2½ in) kalınlıkta > 2.8 kJ/mm ısı girdisi ile H4 sarf malzemeleri FC tablolarında en düşük ön ısıtma olan 300°F (150°C)'yi sağlar.

H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)'de Diğer Köprü Çelikleri

H4 > 2.8 kJ/mm'de M270M Gr.345W / M270 Gr.50W

Farklı Kombinasyonları Dene

Herhangi bir AASHTO M270 çelik, hidrojen seviyesi ve ısı girdisi kombinasyonunu aramak için D1.5 Köprü Ön Isıtma Hesap Makinesini kullanın. Yapısal çelik için D1.1 Ön Isıtma Hesap Makinesine de bakın.

İlgili Kılavuzlar