Ön Isıtma M270M HPS345W — H4, High HI, > 60 mm: 300°F

M270M HPS345W / M270 HPS50W

AASHTO M270M HPS345W (M270 HPS50W) is a high-performance weathering bridge steel with enhanced weldability through controlled chemistry — 0.11% max carbon, 0.006% max sulfur with calcium treatment for inclusion shape control. Developed under FHWA-funded research to eliminate the lamellar tearing and inconsistent toughness problems of earlier weathering steel bridge designs. The lower carbon equivalent compared to conventional Gr.345W reduces cracking sensitivity at flange splices. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7.

M270M HPS345W / M270 HPS50W için FC Ön Isıtmayı Anlama

High-performance weathering 345 MPa steel with enhanced weldability. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 300°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 HPS345W / M270 HPS50W Nerede Kullanılır

Preferred over conventional Gr.345W for new unpainted bridge construction. The HPS designation indicates FHWA-developed chemistry with 0.11% max carbon and controlled sulfur for enhanced weldability and lamellar tearing resistance. Flange splice CJP welds benefit from the lower carbon equivalent, reducing reject rates during cold-weather bridge fabrication. Material cost premium over standard Gr.345W is typically 15–25% per ton but eliminates weldability-related rework.

M270M HPS345W / M270 HPS50W için H4 Hidrojen Kontrolü

HPS345W (HPS50W) already has inherently low carbon equivalent due to HPS chemistry control. Combined with H4 consumables, the preheat requirement drops to the lowest tier in Tables 12.6/12.7 — frequently 20–30°F lower than conventional 345W, compounding the weldability advantage of HPS chemistry with optimized hydrogen control.

> 60 mm (> 2½ in)'de Ön Isıtma Neden Önemlidir

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)'de M270M HPS345W / M270 HPS50W

HPS345W (HPS50W) above 65 mm is the preferred material for heavy unpainted bridge flanges replacing conventional 345W. The sulfur control (0.006% max) and calcium treatment ensure clean steel with minimal through-thickness anisotropy. At this thickness, the weldability advantage is most pronounced — conventional 345W at 65+ mm required expensive preheat and post-weld hydrogen bake-out procedures that HPS chemistry largely eliminates.

FC Köprü Kaynağı için H4 Sertifikalı Sarf Malzemeleri

H4 ek tanımlaması, sarf malzemenin 100g yığılan metal başına en fazla 4 mL difüze edilebilir hidrojen bıraktığını sertifikalandırır. Kırılma kritik M270M HPS345W / M270 HPS50W için > 60 mm (> 2½ in) kalınlıkta > 2.8 kJ/mm ısı girdisi ile H4 sarf malzemeleri FC tablolarında en düşük ön ısıtma olan 300°F (150°C)'yi sağlar.

H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)'de Diğer Köprü Çelikleri

H4 > 2.8 kJ/mm'de M270M HPS345W / M270 HPS50W

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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