M270M Gr.345 पूर्वतापन — H4, Low HI, > 60 mm: 300°F

M270M Gr.345 / M270 Gr.50

AASHTO M270M Gr.345 (M270 Gr.50) is the standard bridge plate and shape grade with 345 MPa (50 ksi) minimum yield, corresponding to ASTM A709 Gr.50. It is the baseline strength for modern highway bridge design per AASHTO LRFD. Used for plate girder flanges, webs, floor beams, cross-frames, and splice plates. Flanges on large plate girders routinely reach 50–75 mm (2–3 in) thick, making preheat compliance at upper thickness tiers a significant production consideration. NFC preheat per Table 6.3 Group 1; FC per Tables 12.4/12.5.

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

Standard 345 MPa (50 ksi) bridge plate for girders and floor beams. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 300°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 Gr.345 / M270 Gr.50 कहाँ उपयोग होता है

Standard for highway bridge plate girder flanges, box girder webs, cross-frame angles, bearing sole plates, and splice plates in bolted-welded connections. Gr.345 (50) is the baseline strength for modern AASHTO LRFD bridge design. Flange butt splices, web-to-flange continuous fillet welds, and bearing stiffener clips are the dominant weld types in girder fabrication. Girder flanges typically range from 20 to 75 mm (3/4 to 3 in) thick with widths from 300 to 750 mm (12 to 30 in), requiring extended preheat soak times on thicker flange splices.

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

Gr.345 (50) with H4 consumables achieves the lowest FC preheat requirements available for the workhorse bridge grade. On girder fabrication lines producing 50–100 meters of flange-to-web fillet weld per shift, the reduced preheat from H4 translates directly to faster welding speed and lower fuel costs for preheat maintenance.

> 60 mm (> 2½ in) पर पूर्वतापन क्यों महत्वपूर्ण है

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) पर M270M Gr.345 / M270 Gr.50

Gr.345 (50) above 65 mm represents the heaviest plate girder flanges on long-span bridges. At 75–100 mm flange thickness, each CJP splice requires 80+ weld passes with continuous interpass monitoring. Preheat soak-through needs heating mats or induction coils because torch heating alone cannot maintain uniform temperature through 3+ inches of plate. Production rates drop to 1–2 splices per shift at this thickness, making preheat efficiency a major scheduling factor.

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.345 / M270 Gr.50 के लिए > 60 mm (> 2½ in) मोटाई पर 1.2–2.0 kJ/mm ऊष्मा इनपुट के साथ, H4 उपभोज्य FC तालिकाओं में 300°F (150°C) का सबसे कम पूर्वतापन प्राप्त करते हैं। यह पसंदीदा हाइड्रोजन स्तर है जब पूर्वतापन कमी प्राथमिकता हो।

H4 1.2–2.0 kJ/mm · > 60 mm (> 2½ in) पर अन्य पुल स्टील

H4 1.2–2.0 kJ/mm पर M270M Gr.345 / M270 Gr.50

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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