Ön Isıtma M270M HPS345W — H16, Low HI, 40–60 mm: 350°F

M270M HPS345W / M270 HPS50W

AASHTO M270M HPS345W (M270 HPS50W) is a high-performance weathering bridge steel with enhanced weldability through controlled chemistry — 0.11% max carbon, 0.006% max sulfur with calcium treatment for inclusion shape control. Developed under FHWA-funded research to eliminate the lamellar tearing and inconsistent toughness problems of earlier weathering steel bridge designs. The lower carbon equivalent compared to conventional Gr.345W reduces cracking sensitivity at flange splices. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7.

M270M HPS345W / M270 HPS50W için FC Ön Isıtmayı Anlama

High-performance weathering 345 MPa steel with enhanced weldability. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 350°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.

M270M HPS345W / M270 HPS50W Nerede Kullanılır

Preferred over conventional Gr.345W for new unpainted bridge construction. The HPS designation indicates FHWA-developed chemistry with 0.11% max carbon and controlled sulfur for enhanced weldability and lamellar tearing resistance. Flange splice CJP welds benefit from the lower carbon equivalent, reducing reject rates during cold-weather bridge fabrication. Material cost premium over standard Gr.345W is typically 15–25% per ton but eliminates weldability-related rework.

M270M HPS345W / M270 HPS50W için H16 Hidrojen Kontrolü

HPS345W (HPS50W) at H16 partially offsets the weldability advantage of HPS chemistry by allowing high hydrogen levels. The FC preheat requirement approaches that of conventional 345W at H8, reducing the cost advantage of the HPS specification. For this reason, most HPS345W fabrication targets H4 or H8 to capture the full preheat benefit.

40–60 mm (1½–2½ in)'de Ön Isıtma Neden Önemlidir

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.

40–60 mm (1½–2½ in)'de M270M HPS345W / M270 HPS50W

HPS345W (HPS50W) at 40–65 mm covers main flange plates on new unpainted highway bridges. The controlled chemistry gives better CVN toughness transition behavior than conventional 345W — 20–30 J higher at -29°C (−20°F) — which improves the fracture resistance of thick flange splices in cold-climate service. Fabricators report 30–40% fewer repair rates on HPS flange splice welds compared to conventional 345W at the same thickness.

H16 Tanımlamasında Daha Yüksek Ön Isıtma

H16 sarf malzemeleri 100g başına 16 mL'ye kadar difüze edilebilir hidrojene izin verir — FC köprü kaynağında izin verilen en yüksek seviye. 40–60 mm (1½–2½ in)'de 1.2–2.0 kJ/mm ısı girdisi ile 350°F (180°C) ön ısıtma, daha yüksek hidrojen potansiyelini telafi eder.

H16 1.2–2.0 kJ/mm · 40–60 mm (1½–2½ in)'de Diğer Köprü Çelikleri

H16 1.2–2.0 kJ/mm'de M270M HPS345W / M270 HPS50W

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.

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