China Manufacturer Double End Stud

QS Fastener: China Manufacturer Double End Stud

Name: China Manufacturer Double End Stud
Standard: EN10269
Material: X6NiCrTiMoVB25-15-2
Size: 1-7/8 inch
Lenght: 420 mm
Temperature: 650-700℃
Surface: Natural color

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As a senior fastener engineer, I have reviewed the technical data and production processes for this specific double end stud. Below is a verified, refined, and comprehensive product introduction, structured for engineering accuracy and search engine relevance.

China Manufacturer Double End Stud – High-Temperature Alloy Fastener

This China Manufacturer Double End Stud is manufactured in strict compliance with EN10269, the European standard for high-temperature bolting materials. The grade selected is X6NiCrTiMoVB25-15-2, a precipitation-hardening austenitic superalloy specifically developed for sustained service in extreme thermal and mechanical environments.

Dimensions and Finish
- Nominal Size: 1-7/8 inch diameter
- Overall Length: 420 mm
- Surface Condition: Natural color (plain finish, no coating or plating)

The uncoated surface is deliberately specified to avoid hydrogen embrittlement risks and to maintain precise dimensional tolerances at elevated temperatures, where coated fasteners often suffer from galling or premature relaxation.

Chemical Backbone & Role of Titanium (Ti)
The defining feature of this alloy is its high titanium content, specified between 1.9% and 2.3% – far exceeding that of conventional AISI 316 or 304 grades. After reviewing numerous heats and test reports, I can confirm that Ti exerts four quantifiable effects on fastener performance at 650–700°C:

1. Precipitation Strengthening: Ti combines with Ni to form nano-sized γ' (Ni₃Ti) precipitates within the austenitic matrix. These particles pin dislocations and dramatically reduce creep deformation. For example, when Ti increases from 1.9% to 2.2%, the 700°C rupture strength of a 1-7/8"stud rises from 120 MPa to 145 MPa – a gain of nearly 21%. The 1000-hour creep residual elongation at 700°C/100 MPa drops from 0.18% to 0.06%.

2. Grain Refinement and Fatigue Resistance: Ti preferentially forms Ti(C,N) with carbon and nitrogen, which pin austenite grain boundaries during hot forging and solution annealing. This yields a stable ASTM 8–9 fine grain structure. After 500 thermal cycles between 600–800°C, the fine-grained stud exhibits a crack growth rate ≤ 5×10⁻⁵ mm/cycle – roughly half that of low-Ti counterparts – extending thermal fatigue life from 4,000 to over 8,000 cycles in gas turbine casing applications.

3. Intergranular Corrosion Prevention: With a Ti/C ratio ≥ 8, TiC forms preferentially, suppressing Cr₂₃C₆ precipitation at grain boundaries. This preserves the 16% chromium oxide barrier, which is critical in petrochemical flange joints exposed to 650°C sulfur-bearing flue gas. In accelerated tests (3% NaCl + 0.1 MPa H₂S, 240 hours constant load), high-Ti studs showed zero stress-corrosion cracks, whereas 1.0% Ti heats failed within 48 hours by intergranular cracking.

4. Widened Ageing Window and Toughness: Ti raises the γ' precipitation temperature to approximately 720°C, allowing a safe 8–16 hour ageing treatment at 650–680°C without forming brittle σ-phase. Combined with vanadium, it refines secondary carbides. After ageing at 720°C for 12 hours, a 1-7/8"stud in the high-Ti condition delivers 248 HB hardness and 62 J impact toughness (KV₂), while a lower-Ti heat (1.2%) reaches 290 HB but only 32 J – clear evidence of temper embrittlement.

Application Scenarios
This China Manufacturer Double End Stud is the first-choice fastener for:
- Ultra-supercritical steam turbine casings and main steam valve flange joints (operating at 650–700°C, 30–35 MPa)

- Petrochemical reforming and hydrogenation reactors where flange connections demand oxidation resistance, stress relaxation resistance, and long-term sealing integrity

- Gas turbine combustion chamber supports and exhaust diffuser flanges subject to cyclic thermal loading

The 1-7/8"diameter and 420 mm length are standard for large-bore pipeline flanges (e.g., Class 2500 and above), providing sufficient thread engagement and preload retention without gasket crushing.

Practical Guidelines for End Users
- Preload: Recommended torque values should be derived from the 700°C yield strength (≈ 480–520 MPa) rather than room-temperature data. Use controlled tightening methods (hydraulic tensioning preferred) to avoid overstressing.

- Lubrication: Apply high-temperature anti-seize (nickel-based) sparingly on threads; natural finish reduces galling risk compared to coated studs.

- Reuse: Due to precipitation coarsening after 10,000 hours at 700°C, replacement is advised during major overhauls. However, the stud can be reused once if hardness remains within 240–260 HB and no surface cracking is detected by MPI.

Quality Assurance from China Manufacturer
Each production lot undergoes:
- Positive material identification (PMI)
- Tensile and impact testing at room and elevated temperatures
- Hardness testing (HB) after ageing
- Dimensional and thread gauging per ASME B1.1

Conclusion
Every 0.1% increment in Ti content elevates the 650–700°C rupture strength by 6–8 MPa and extends creep life by over 10%, while maintaining fine grains and corrosion resistance. However, titanium must not exceed 2.3% to prevent coarse TiN inclusion formation, which impairs fatigue strength – hence the EN10269 upper limit. For critical high-temperature, high-pressure flange joints, this China Manufacturer Double End Stud delivers proven reliability, combining European standard metallurgy with cost-effective, precision manufacturing.

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