예열 M270M Gr.250 — H16, Low HI, 20–40 mm: 200°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.36의 FC 예열 이해

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 200°F minimum preheat at 20–40 mm (3/4–1½ 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.36이 사용되는 곳

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.36의 H16 수소 제어

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.

20–40 mm (3/4–1½ in)에서 예열이 중요한 이유

Material from 20 to 40 mm (3/4 to 1-1/2 in) includes many girder web plates, splice plates, and bearing stiffener plates. Preheat increases to 20°C (70°F) for Group 1 and 50°C (125°F) for Group 2 under Table 6.3. The thicker section slows hydrogen diffusion, requiring higher preheat to maintain safe cooling rates.

20–40 mm (3/4–1½ in)에서의 M270M Gr.250 / M270 Gr.36

At 20–40 mm, Gr.250 (36) appears in floor beam stiffener plates and diaphragm gussets where loads transfer between main girder and secondary members. Weld details are typically partial-penetration groove welds or large fillet welds at connection brackets. The thicker section slows hydrogen escape, making preheat compliance more important than at thin plate. Fabricators often tack-weld stiffener clips without preheat and then apply full preheat for final welding — D1.5 requires preheat for ALL passes including tacks.

H16 지정 시 높은 예열

H16 용접재료는 100g당 최대 16 mL의 확산성 수소를 허용합니다 — FC 교량 용접에서 허용되는 가장 높은 수준입니다. 20–40 mm (3/4–1½ in)에서 1.2–2.0 kJ/mm 입열량 시 200°F (100°C) 예열은 높은 수소 잠재력을 보상합니다.

H16 1.2–2.0 kJ/mm · 20–40 mm (3/4–1½ in)에서의 다른 교량 강재

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

다양한 조합 시도

D1.5 교량 예열 계산기를 사용하여 AASHTO M270 강재, 수소 수준 및 입열량 조합을 조회하세요. D1.1 예열 계산기도 참조하세요.

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