S32750 Hex Head Bolt

QS: S32750 Hex Head Bolt

Name: S32750 Hex Head Bolt
Standard: UNS
Material: S32750
Size: 3/8 to 1 inch
Length: 30 to 1000 mm
Grade: A
Class: 12.9
Application: Used for Chemical Processing, Petrochemicals and Subsea Equipment.

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S32750 Hex Head Bolt, manufactured from high-strength UNS S32750 super duplex stainless steel, covers sizes from 3/8 to 1 inch with lengths ranging from 30-1000 mm, and complies with Class 12.9 performance standards. It exhibits exceptional chloride corrosion resistance, stress cracking resistance, and high mechanical strength, making it specifically designed for demanding environments such as chemical plants, petrochemical facilities, and subsea equipment, ensuring long-term reliability and safety.

In extreme low-temperature environments (-50°C), the S32750 Hex Head Bolt stands out due to its superior cryogenic toughness, making it the fastener of choice for deep-sea, polar, and liquefied natural gas (LNG) applications. Below is a detailed analysis of its low-temperature adaptability from three perspectives: material science, testing standards, and practical applications.

1. Material Science Fundamentals: Core Advantages of Duplex Structure
The cryogenic performance of the S32750 Hex Head Bolt stems from the synergistic effect of its austenitic-ferritic duplex microstructure (approximately 50% austenite + 50% ferrite):
- Austenite Phase (γ): Provides low-temperature toughness to the S32750 Hex Head Bolt, effectively inhibiting crack propagation.
- Ferrite Phase (α): Enhances strength and improves low-temperature stability through nitrogen alloying (0.24-0.32%).

Key Process Controls:
- Solution Treatment (Water quenching at 1050-1120°C): Ensures a balanced duplex ratio in the S32750 Hex Head Bolt, preventing brittle σ-phase precipitation.

- Cold Working Limit (Deformation rate <20%): Prevents excessive hardening of ferrite, which could lead to low-temperature brittleness.

2. Low-Temperature Performance Test Data (ASTM A320/A320M Standard)
Charpy V-notch impact tests validate the cryogenic performance of the S32750 Hex Head Bolt:

Temperature (°C)	Impact Energy (J)	Fracture Morphology
+20	≥100	Ductile Fracture
-50	≥80	Mixed Ductile-Brittle
-196	≤40	Brittle Fracture

Conclusions:
- The S32750 Hex Head Bolt maintains an impact energy exceeding 80J at -50°C, far surpassing common carbon steels (e.g., ASTM A307 bolts with <20J) and meeting the ISO 898-1 Class 12.9 high-strength standard.

- Recommended Lower Limit: -50°C (For lower temperatures, Inconel 718 is required).

3. Practical Applications
(1) Deep-Sea Oil & Gas Equipment (-40°C to -50°C)
- Applications: Subsea Christmas trees, pipe connectors.
- Advantages of S32750 Hex Head Bolt:
- Nitrogen content inhibits hydrogen embrittlement, while the duplex structure delays crack propagation.

(2) Polar Vessels & LNG Storage Tanks
- Comparison Data: 316L bolts exhibit only 30-50J impact energy at -50°C, whereas the S32750 Hex Head Bolt achieves over 80J, making it ideal for LNG carrier cargo holds and polar icebreaker decks.

(3) Cryogenic Chemical Piping
- After prolonged exposure to liquid ammonia/chlorine, the S32750 Hex Head Bolt retains an elongation rate ≥25% (per ASTM A193).

4. Comparison with Competing Materials

Material	Minimum Temp. (°C)	Impact Energy at -50°C (J)	Cost
S32750	-50	≥80	Medium-High
2205 Duplex	-40	50-70	Medium
316L	-30	30-50	Low
Inconel 718	-196	≥100	Very High

Selection Guidelines:
- For -50°C to +200°C: The S32750 Hex Head Bolt offers the best cost-performance ratio.
- Below -50°C: Nickel-based alloys are required.

Conclusion
Through optimized duplex microstructure and stringent process controls, the S32750 Hex Head Bolt achieves an ideal balance of high strength (≥550MPa) and toughness (≥80J) at -50°C, establishing itself as the benchmark fastening solution for deep-water and polar engineering projects.

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