A709 HPS70W FCAW 예열 — over 2-1/2"

FCAW (Flux Cored Arc Welding)

FCAW uses tubular flux-cored wire, available gas-shielded (E71T-1) or self-shielded (E71T-8) for field work. Category B in Table 5.11.

High-strength FCAW wires such as E81T1-K2 and E91T1-K2 provide tensile matching for Category C steels. The flux system in these wires is formulated for low diffusible hydrogen, often meeting H8 supplementary limits when tested per AWS A4.3. Wire storage requires climate-controlled conditions similar to SMAW electrodes to prevent moisture absorption.

FCAW Tips for High-Strength and TMCP Steels

For A709 HPS70W weathering bridge steel (70 ksi yield, Q&T plate, Category C), FCAW requires higher-strength weathering-compatible wire — E81T1-W2 or similar for both tensile matching and corrosion resistance on exposed joints. Category C minimum preheat: 50°F up to 3/4", stepping to 300°F above 2-1/2". Note: Table 5.11 also sets maximum interpass (400°F up to 1-1/2", 450°F above) to protect.

Typical values for reference — always verify against your approved WPS and electrode manufacturer data.

Filler Metal for FCAW

Gas-shielded: E71T-1C (AWS A5.20, requires 100% CO2) or E71T-1M (requires 75/25 Ar/CO2 mixed gas) — the C/M suffix designates the required shielding gas. Self-shielded: E71T-8 (no external gas, field-ready). Diameter: 0.045" standard, 1/16" for high-deposition. Stick-out: 3/4" to 1-1/4" (longer than GMAW due to resistive heating of flux core).

Typical values for reference — always verify against your approved WPS and electrode manufacturer data.

A709 HPS70W

ASTM A709 HPS70W is the highest-strength weathering bridge steel with 70 ksi minimum yield and 85-110 ksi tensile range, used in long-span bridges and heavily loaded members where weight reduction is critical. Produced as quenched-and-tempered plate in thicknesses up to 4", its high strength places it in Category C of Table 5.11 with correspondingly higher preheat requirements. Table 5.11 footnote (b) sets a maximum preheat/interpass of 400°F for thickness up to 1-1/2” and 450°F for thicker material — this upper limit is unusual in D1.1 and exists because the Q&T microstructure can be degraded by excessive heat. The chemistry includes copper (0.25-0.40%), nickel (0.65-1.00%), and chromium (0.40-0.65%) for atmospheric corrosion resistance, with 0.19% max carbon keeping the CE-IIW in the 0.46-0.52 range.

FCAW를 사용한 A709 HPS70W의 이 예열 이유

Highest-strength 70 ksi weathering bridge steel for long-span applications. The higher strength level of this steel places it in Category C of Table 5.11, which carries elevated preheat requirements compared to Category B grades. At 300°F minimum with FCAW, flux-cored wire in FCAW provides a combination of deoxidizers and low-moisture flux formulations that control hydrogen, but the preheat must still ensure the cooling rate stays slow enough to prevent hydrogen-induced cracking in this higher-hardenability material.

A709 HPS70W의 일반적인 용도

Reserved for long-span bridge main girder flanges, cable-stayed bridge edge girders, arch rib plates, high-load interchange ramp girders, and situations where reducing member depth saves clearance or reduces dead load. HPS70W enables weight savings of 20-30% versus conventional Gr.50 designs, allowing shallower girder sections that reduce embankment costs on grade-separation bridges. Flange thickness often exceeds 2”, making preheat and interpass control critical at every CJP splice and web-to-flange joint. Note that Table 5.11 footnote (b) sets maximum preheat and interpass limits of 400°F for thicknesses up to 1-1/2" and 450°F above. This upper limit is unusual in D1.1 and requires monitoring both minimum and maximum interpass throughout the welding sequence. Fabricators must use dual-readout temperature monitoring to ensure the joint stays within the qualified band. Filler metals must match the 70 ksi minimum tensile while providing weathering-compatible chemistry for exposed joints.

over 2-1/2"에서 예열이 중요한 이유

The heaviest sections demand the highest preheat in Table 5.11. Multi-pass sequences require maintaining interpass temperature throughout.

A709 HPS70W의 범주 C 예열

표 5.11의 범주 C는 경화성과 잔류 응력의 조합이 높은 예열을 요구하는 고강도 강재에 적용됩니다. over 2-1/2"에서 A709 HPS70W의 최소 예열 300°F는 열영향부에서 균열 감수성 마르텐사이트 형성을 방지하기 위해 용접 냉각 속도를 늦춥니다.

over 2-1/2"에서 FCAW를 사용하는 다른 강재

A709 HPS70W, FCAW

다양한 조합 시도

인터랙티브 예열 계산기를 사용하여 D1.1:2025 표 5.11의 모든 강재, 공정, 두께 조합을 조회하세요.

A709 HPS70W 용접 가이드