M270M Gr.345S पूर्वतापन — H4, High HI, ≤ 20 mm: 100°F

M270M Gr.345S / M270 Gr.50S

AASHTO M270M Gr.345S (M270 Gr.50S) is the structural shape variant of Gr.345, intended for rolled W-shapes and channels used in bridge framing. The "S" suffix indicates the shape-specific chemistry and mechanical property requirements. Used in cross-frame angles, diaphragm members, and built-up sections where rolled shapes are specified rather than plate. Preheat requirements match Gr.345 — Table 6.3 Group 1 for NFC, Tables 12.4/12.5 for FC applications.

M270M Gr.345S / M270 Gr.50S के लिए FC पूर्वतापन को समझना

Shape-grade 345 MPa (50 ksi) steel for rolled bridge members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 100°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 Gr.345S / M270 Gr.50S कहाँ उपयोग होता है

Used as rolled W-shapes and channels in bridge cross-frames, diaphragm members, and built-up sections. The "S" shape designation indicates procurement under AASHTO M270 with shape-specific chemistry and mandatory CVN testing. Common applications include WT sections for cross-frame members, MC channels for diaphragms, and W-shapes for floor beams on shorter spans. Weld details are primarily fillet welds at gusset connections and clip angles.

M270M Gr.345S / M270 Gr.50S के लिए H4 हाइड्रोजन नियंत्रण

Shape-grade Gr.345S (50S) benefits from H4 at gusset-to-shape connections where access for torch preheat is limited by flanges and stiffeners. The lower preheat achievable with H4 reduces the thermal management complexity in tight spaces typical of cross-frame subassemblies.

≤ 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 Gr.345S / M270 Gr.50S

Gr.345S (50S) shapes under 20 mm flange thickness include WT sections for K-frame cross-frames and MC channels for diaphragms. The rolled section geometry concentrates stress at the flange-to-web fillet, making proper preheat at gusset connections critical for fatigue performance. SMAW E7018 is the typical process for shape-to-plate connections in bridge subassemblies because of limited access around shape flanges.

FC पुल वेल्डिंग के लिए H4-प्रमाणित उपभोज्य

H4 पूरक पदनाम प्रमाणित करता है कि उपभोज्य प्रति 100g जमा वेल्ड धातु में 4 mL से अधिक विसरणशील हाइड्रोजन जमा नहीं करता। फ्रैक्चर-क्रिटिकल M270M Gr.345S / M270 Gr.50S के लिए ≤ 20 mm (3/4 in) मोटाई पर > 2.8 kJ/mm ऊष्मा इनपुट के साथ, H4 उपभोज्य FC तालिकाओं में 100°F (40°C) का सबसे कम पूर्वतापन प्राप्त करते हैं। यह पसंदीदा हाइड्रोजन स्तर है जब पूर्वतापन कमी प्राथमिकता हो।

H4 > 2.8 kJ/mm · ≤ 20 mm (3/4 in) पर अन्य पुल स्टील

H4 > 2.8 kJ/mm पर M270M Gr.345S / M270 Gr.50S

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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