M270M HPS345W पूर्वतापन — 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.

M270M HPS345W / M270 HPS50W के लिए FC पूर्वतापन को समझना

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.

M270M HPS345W / M270 HPS50W कहाँ उपयोग होता है

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 के लिए H16 हाइड्रोजन नियंत्रण

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.

≤ 20 mm (3/4 in) पर पूर्वतापन क्यों महत्वपूर्ण है

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.

≤ 20 mm (3/4 in) पर M270M HPS345W / M270 HPS50W

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.

H16 पदनाम पर अधिक पूर्वतापन

H16 उपभोज्य प्रति 100g में 16 mL तक विसरणशील हाइड्रोजन की अनुमति देते हैं — FC पुल वेल्डिंग के लिए अनुमत उच्चतम स्तर। 1.2–2.0 kJ/mm ऊष्मा इनपुट के साथ ≤ 20 mm (3/4 in) पर, 150°F (70°C) पूर्वतापन उच्च हाइड्रोजन क्षमता की भरपाई करता है। H8 या H4 उपभोज्य पर स्विच करने से इस जोड़ के लिए आवश्यक पूर्वतापन कम होगा।

H16 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in) पर अन्य पुल स्टील

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

विभिन्न संयोजन आज़माएँ

किसी भी AASHTO M270 स्टील, हाइड्रोजन स्तर, और ऊष्मा इनपुट संयोजन को देखने के लिए D1.5 ब्रिज पूर्वतापन कैलकुलेटर का उपयोग करें। स्ट्रक्चरल स्टील के लिए D1.1 पूर्वतापन कैलकुलेटर भी देखें।

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