M270M Gr.250 पूर्वतापन — H16, Low HI, 40–60 mm: 250°F

M270M Gr.250 / M270 Gr.36

AASHTO M270M Gr.250 (M270 Gr.36) is the metric/US customary designation for the basic structural bridge steel with 250 MPa (36 ksi) minimum yield. It is the direct bridge equivalent of ASTM A709 Gr.36, procured under AASHTO M270 with mandatory Charpy V-notch testing per temperature zone. Used for secondary bridge members — lateral bracing, diaphragm plates, floor beam stiffeners, and bearing components where Gr.345 strength is not needed. Non-fracture-critical preheat follows Table 6.3 Group 1; fracture-critical follows Tables 12.4/12.5 with hydrogen and heat input as additional variables.

M270M Gr.250 / M270 Gr.36 के लिए FC पूर्वतापन को समझना

Basic 250 MPa (36 ksi) bridge steel for secondary members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 250°F minimum preheat at 40–60 mm (1½–2½ 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.250 / M270 Gr.36 कहाँ उपयोग होता है

Specified for secondary bridge members under AASHTO LRFD — lateral bracing angles, diaphragm plates, floor beam stiffeners, bearing seat components, and railing posts. Gr.250 (36) requires CVN testing per AASHTO temperature zone, distinguishing it from plain ASTM A36 by guaranteeing fracture resistance at the bridge design service temperature. Transverse stiffener fillet welds and floor beam web-to-flange joints are high-frequency fabrication details. Temperature zones (1 through 3) determine CVN test temperature: Zone 1 at 21°C (70°F) for moderate climates, Zone 2 at 4°C (40°F) for cold, Zone 3 at -12°C (10°F) for severe cold.

M270M Gr.250 / M270 Gr.36 के लिए H16 हाइड्रोजन नियंत्रण

H16 designation (16 mL/100g max) on Gr.250 (36) is the highest hydrogen level permitted for FC bridge welding. For Gr.250 secondary members, H16 is sometimes specified when using self-shielded FCAW (E71T-8) for field connections where gas shielding is impractical — the resulting higher preheat is accepted as the cost of field weldability.

40–60 mm (1½–2½ in) पर पूर्वतापन क्यों महत्वपूर्ण है

Material from 40 to 65 mm (1-1/2 to 2-1/2 in) covers heavy girder flanges, thick splice plates, and main member plate. This is the critical thickness range for bridge fabrication — preheat reaches 65°C (150°F) for Group 1 and 80°C (175°F) for Group 2. FC preheat at this thickness can exceed 200°C (400°F) depending on hydrogen level and heat input.

40–60 mm (1½–2½ in) पर M270M Gr.250 / M270 Gr.36

Gr.250 (36) at 40–65 mm is uncommon in modern designs because Gr.345 handles the same loads at lighter weight. When specified, it appears in bearing seats and massive foundation assemblies where material cost is secondary to simplicity. At this thickness the HAZ cooling rate is significantly slower, and the 150°F preheat reflects the need to keep cooling rates below the critical rate for hydrogen-induced cracking in the coarse-grained HAZ.

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 40–60 mm (1½–2½ in) पर, 250°F (120°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 · 40–60 mm (1½–2½ in) पर अन्य पुल स्टील

H16 1.2–2.0 kJ/mm पर M270M Gr.250 / M270 Gr.36

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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