التسخين المسبق M270M HPS345W — H16، Low HI، ≤ 20 mm: 150°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.

فهم التسخين المسبق FC لـ M270M HPS345W / M270 HPS50W

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 150°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.

أين يُستخدم M270M HPS345W / M270 HPS50W

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.

التحكم في الهيدروجين H16 لـ 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.

لماذا يهم التسخين المسبق عند ≤ 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 HPS345W / M270 HPS50W عند ≤ 20 mm (3/4 in)

HPS345W (HPS50W) at thin thickness is specified for stiffener attachments and connection details where the improved weldability and lamellar tearing resistance justify the 15–25% material cost premium over conventional 345W. The 0.11% max carbon provides significantly lower carbon equivalent than conventional weathering steel, reducing preheat sensitivity and reject rates during production welding.

تسخين مسبق أعلى بتصنيف H16

المواد المستهلكة H16 تسمح بحد أقصى 16 مل من الهيدروجين القابل للانتشار لكل 100 غ — أعلى مستوى مسموح به للحام FC للجسور. عند ≤ 20 mm (3/4 in) بمدخل حراري 1.2–2.0 kJ/mm، التسخين المسبق 150°F (70°C) يعوض عن إمكانية الهيدروجين الأعلى.

فولاذ جسور أخرى عند H16 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)

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

جرّب تركيبات مختلفة

استخدم حاسبة التسخين المسبق D1.5 للجسور للبحث عن أي فولاذ AASHTO M270 ومستوى هيدروجين وتركيبة مدخل حراري. انظر أيضاً حاسبة التسخين المسبق D1.1 للفولاذ الإنشائي.

أدلة ذات صلة