Ön Isıtma M270M Gr.250 — H16, Low HI, ≤ 20 mm: 150°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 için FC Ön Isıtmayı Anlama

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 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 Gr.250 / M270 Gr.36 Nerede Kullanılır

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 için H16 Hidrojen Kontrolü

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.

≤ 20 mm (3/4 in)'de Ön Isıtma Neden Önemlidir

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)'de M270M Gr.250 / M270 Gr.36

Gr.250 (36) at up to 20 mm is the lightest bridge fabrication scenario — cross-frame angles, stiffener clips, and lateral bracing gussets. Hydrogen diffusion through this thin section is rapid, so preheat has the least influence on cracking resistance. Most fabricators use E7018 SMAW for short fillet welds at this thickness because the joint lengths are too short for mechanized FCAW setup to be economical. Interpass monitoring is minimal at this tier because heat builds slowly in thin plate.

H16 Tanımlamasında Daha Yüksek Ön Isıtma

H16 sarf malzemeleri 100g başına 16 mL'ye kadar difüze edilebilir hidrojene izin verir — FC köprü kaynağında izin verilen en yüksek seviye. ≤ 20 mm (3/4 in)'de 1.2–2.0 kJ/mm ısı girdisi ile 150°F (70°C) ön ısıtma, daha yüksek hidrojen potansiyelini telafi eder.

H16 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)'de Diğer Köprü Çelikleri

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

Farklı Kombinasyonları Dene

Herhangi bir AASHTO M270 çelik, hidrojen seviyesi ve ısı girdisi kombinasyonunu aramak için D1.5 Köprü Ön Isıtma Hesap Makinesini kullanın. Yapısal çelik için D1.1 Ön Isıtma Hesap Makinesine de bakın.

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