M270M Gr.250予熱 — H16、Low HI、> 60 mm: 350°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のFC予熱を理解する

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 350°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.250 / M270 Gr.36の使用箇所

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におけるH16水素管理

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.

> 60 mm (> 2½ in)で予熱が重要な理由

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)でのM270M Gr.250 / M270 Gr.36

Gr.250 (36) above 65 mm is rare — typically only in large bearing assemblies or rehabilitation projects repairing older bridges where original plate was overspecified. Preheat soak-through at 225°F requires flame heating on both sides for 15–20 minutes on plate this thick. The cost of preheat compliance at this thickness often triggers a design review to consider switching to Gr.345 which achieves the same capacity with thinner, lighter sections.

H16指定での高い予熱

H16溶接材料は100gあたり最大16mLの拡散性水素を許容します — 橋梁FC溶接で許可される最高レベルです。1.2–2.0 kJ/mm入熱での> 60 mm (> 2½ in)では、350°F (180°C)予熱が高い水素ポテンシャルを補います。この継手にH8またはH4溶接材料に切り替えると必要な予熱が低下します。

H16 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)における他の橋梁鋼材

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

別の組み合わせを試す

D1.5橋梁予熱計算機を使用して、AASHTO M270鋼材の水素レベルと入熱の任意の組み合わせを検索できます。構造用鋼にはD1.1予熱計算機もご覧ください。

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