Vorwärmung M270M HPS345W — H16, Low HI, > 60 mm: 400°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.

Die FC-Vorwärmung für M270M HPS345W / M270 HPS50W Verstehen

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 400°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.

Wo M270M HPS345W / M270 HPS50W Eingesetzt Wird

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.

Wasserstoffkontrolle H16 für M270M HPS345W / M270 HPS50W

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.

Warum Vorwärmung bei > 60 mm (> 2½ in) Wichtig ist

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.

M270M HPS345W / M270 HPS50W bei > 60 mm (> 2½ in)

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.

Höhere Vorwärmung bei H16-Bezeichnung

H16-Zusatzwerkstoffe erlauben bis zu 16 mL diffusiblen Wasserstoff pro 100g — das höchste zulässige Niveau für FC-Brückenschweißen. Bei > 60 mm (> 2½ in) mit 1.2–2.0 kJ/mm Wärmeeinbringung kompensiert die Vorwärmung von 400°F (200°C) das höhere Wasserstoffpotential.

Andere Brückenstähle bei H16 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)

M270M HPS345W / M270 HPS50W bei H16 1.2–2.0 kJ/mm

Verschiedene Kombinationen Ausprobieren

Verwenden Sie den D1.5 Brücken-Vorwärmrechner für jeden AASHTO M270 Stahl, Wasserstoffniveau und Wärmeeinbringungskombination. Siehe auch den D1.1 Vorwärmrechner für Baustahl.

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