M270M HPS345W予熱 — H8、Low HI、> 60 mm: 375°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のFC予熱を理解する

High-performance weathering 345 MPa steel with enhanced weldability. Under D1.5 fracture-critical requirements (Clause 12), the combination of H8 hydrogen designation and this heat input band requires 375°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 HPS345W / M270 HPS50Wの使用箇所

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におけるH8水素管理

HPS345W (HPS50W) with H8 is common practice where the HPS weldability advantage partially compensates for the higher hydrogen level. The controlled chemistry means HPS345W at H8 often has lower total cracking susceptibility than conventional 345W at H4 — illustrating how base metal chemistry and hydrogen control interact.

> 60 mm (> 2½ in)で予熱が重要な理由

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)でのM270M HPS345W / M270 HPS50W

HPS345W (HPS50W) above 65 mm is the preferred material for heavy unpainted bridge flanges replacing conventional 345W. The sulfur control (0.006% max) and calcium treatment ensure clean steel with minimal through-thickness anisotropy. At this thickness, the weldability advantage is most pronounced — conventional 345W at 65+ mm required expensive preheat and post-weld hydrogen bake-out procedures that HPS chemistry largely eliminates.

H8 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)における他の橋梁鋼材

H8 1.2–2.0 kJ/mmでのM270M HPS345W / M270 HPS50W

別の組み合わせを試す

D1.5橋梁予熱計算機を使用して、AASHTO M270鋼材の水素レベルと入熱の任意の組み合わせを検索できます。構造用鋼にはD1.1予熱計算機もご覧ください。

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