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Gr.660 Bolt China Suppliers
QS Fastener: Gr.660 Bolt China Suppliers
Name: Gr.660 Bolt China Suppliers
Standard: EN10269
Material: X6NiCrTiMoVB25-15-2
Size: 1-7/8 inch
Lenght: 420 mm
Temperature: 650-700℃
Surface: Natural color
Standard: EN10269
Material: X6NiCrTiMoVB25-15-2
Size: 1-7/8 inch
Lenght: 420 mm
Temperature: 650-700℃
Surface: Natural color
Quantity
For critical high-temperature bolting applications, China suppliers now offer Gr.660 bolts manufactured to EN 10269, material grade X6NiCrTiMoVB25-15-2 (UNS S66286, equivalent to A-286). These fasteners are engineered for continuous operation in the 650–700 °C range, combining large diameters—such as 1-7/8 inch—with extended lengths up to 420 mm to meet the demands of heavy-walled pressure equipment. The components are supplied with a natural, coating-free surface, eliminating hydrogen embrittlement risks and simplifying maintenance in high-stress environments.
Chromium Content and Its Critical Role in Performance
The alloy’s chromium mass fraction, strictly controlled between 13.5 % and 16.0 %, is the decisive factor behind its superior performance. At 700 °C for 100 hours, material with ≥14 % Cr develops a continuous Cr₂O₃ scale, exhibiting oxidation weight gain ≤0.25 mg/cm² and spalled area below 5 %. Dropping to 12 % Cr raises weight gain to 0.8 mg/cm² and spallation to 30 %, which would fail stress-rupture qualifications. In flue gas containing 0.5 % SO₂, the 14 % Cr grade shows only 0.03 mm/year corrosion, while 12 % Cr reaches 0.12 mm/year—a clear demonstration that 13.5 % is the practical lower boundary for oxidation resistance.
The alloy’s chromium mass fraction, strictly controlled between 13.5 % and 16.0 %, is the decisive factor behind its superior performance. At 700 °C for 100 hours, material with ≥14 % Cr develops a continuous Cr₂O₃ scale, exhibiting oxidation weight gain ≤0.25 mg/cm² and spalled area below 5 %. Dropping to 12 % Cr raises weight gain to 0.8 mg/cm² and spallation to 30 %, which would fail stress-rupture qualifications. In flue gas containing 0.5 % SO₂, the 14 % Cr grade shows only 0.03 mm/year corrosion, while 12 % Cr reaches 0.12 mm/year—a clear demonstration that 13.5 % is the practical lower boundary for oxidation resistance.
Strengthening relies on γ′-Ni₃(Ti,Al) precipitates. Chromium enlarges the austenite field and suppresses δ-ferrite. Thermodynamic modelling indicates that at 14 % Cr, the equilibrium δ-phase at 700 °C stays below 1 %, preserving toughness. At 16.5 % Cr, δ-phase rises to 4 %, reducing room-temperature impact energy by 25 % and decreasing aged γ′ content by 6 %, which cuts creep life from 210 hours to 160 hours at 650 °C/200 MPa. Thus the upper limit of 16 % maintains fully austenitic structure and maximum precipitation efficiency.
Mechanical validation on 20 mm diameter bolts at 880 MPa strength level confirms: 14–16 % Cr delivers 210–225 hours rupture life at 650 °C/200 MPa with elongation ≥17 %, whereas 12 % Cr yields only 140 hours and 12 % elongation—falling below the A453 minimum of 585 MPa yield strength and 15 % elongation.
For stress-corrosion cracking resistance in 3.5 % NaCl at 80 °C under 80 % σs constant load, 14 % Cr specimens survive 720 hours without failure; 12 % Cr fails in 120 hours by intergranular cracking. The higher chromium content lowers pitting potential and reduces hydrogen permeation current from 3 µA/cm² to 1 µA/cm², significantly suppressing hydrogen-induced delayed fracture—a key advantage for natural-surface bolts.
Hot workability also benefits from this band. Exceeding 16 % Cr narrows the forging temperature window by approximately 30 °C, promotes σ-phase precipitation, and raises the hot-cracking tendency index from 0.8 % to 1.4 %. The 16 % ceiling therefore reflects both property optimization and production reliability.
Target Applications
Gr.660 Bolt China Suppliers is widely adopted in super-critical boiler casings, gas turbine assemblies, nuclear steam piping systems, and high-temperature flanged connections. The large 1-7/8 inch diameter and 420 mm length are specifically chosen for thick-section joints where creep relaxation and thermal differentials are severe. The bare finish avoids the risk of coating-induced embrittlement and enables direct visual inspection during plant turnarounds.
Gr.660 Bolt China Suppliers is widely adopted in super-critical boiler casings, gas turbine assemblies, nuclear steam piping systems, and high-temperature flanged connections. The large 1-7/8 inch diameter and 420 mm length are specifically chosen for thick-section joints where creep relaxation and thermal differentials are severe. The bare finish avoids the risk of coating-induced embrittlement and enables direct visual inspection during plant turnarounds.
Summary
The 13.5–16.0 % chromium range ensures that Gr.660 fasteners deliver at 650–700 °C: oxidation weight gain ≤0.25 mg/cm², creep rupture life ≥200 h, room-temperature impact ≥40 J, SCC threshold ≥0.8 σs, and hot-working defect rate <1 %. Deviation from this range rapidly degrades any of these essential properties. For engineers specifying large-diameter, extended-length bolting in critical high-temperature service, verifying chromium content is non-negotiable. Sourcing from reliable China suppliers with EN 10269 certification and full material traceability is the first step toward safe, long-term plant integrity.
The 13.5–16.0 % chromium range ensures that Gr.660 fasteners deliver at 650–700 °C: oxidation weight gain ≤0.25 mg/cm², creep rupture life ≥200 h, room-temperature impact ≥40 J, SCC threshold ≥0.8 σs, and hot-working defect rate <1 %. Deviation from this range rapidly degrades any of these essential properties. For engineers specifying large-diameter, extended-length bolting in critical high-temperature service, verifying chromium content is non-negotiable. Sourcing from reliable China suppliers with EN 10269 certification and full material traceability is the first step toward safe, long-term plant integrity.
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