Bulk Alloy 27-7Mo UNS S31277: Properties and Applications

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# Bulk Alloy 27-7Mo UNS S31277: Properties and Applications

## Introduction to Bulk Alloy 27-7Mo UNS S31277

Bulk Alloy 27-7Mo, also known as UNS S31277, is a high-performance austenitic stainless steel designed for extreme environments. This alloy is part of the 6% Mo super austenitic stainless steel family, offering exceptional resistance to corrosion, high strength, and excellent fabricability.

## Chemical Composition

The unique properties of Alloy 27-7Mo stem from its carefully balanced chemical composition:

• Nickel (Ni): 26-28%

• Chromium (Cr): 20-22%

• Molybdenum (Mo): 6.5-8.0%

• Nitrogen (N): 0.30-0.40%

• Iron (Fe): Balance

• Other elements: Small amounts of copper, manganese, and silicon

## Key Properties of Alloy 27-7Mo

### Corrosion Resistance

Alloy 27-7Mo exhibits outstanding resistance to:

• Pitting and crevice corrosion

• Stress corrosion cracking

• General corrosion in acidic environments

• Chloride-induced corrosion

### Mechanical Properties

• High tensile strength: 690 MPa (100 ksi) minimum

• Yield strength: 310 MPa (45 ksi) minimum

• Elongation: 35% minimum

• Excellent toughness at cryogenic temperatures

### Physical Properties

• Density: 8.0 g/cm³

• Melting range: 1320-1390°C (2410-2530°F)

• Thermal expansion coefficient: 15.9 μm/m·°C (20-100°C)

• Thermal conductivity: 12.5 W/m·K

## Applications of Alloy 27-7Mo UNS S31277

### Chemical Processing Industry

The alloy is widely used in:

• Reactors and pressure vessels

• Heat exchangers

• Piping systems

• Valves and pumps handling corrosive media

### Oil and Gas Industry

• Offshore platform components

• Subsea equipment

• Downhole tools

• Seawater handling systems

### Other Applications

• Pharmaceutical equipment

• Pulp and paper processing

• Flue gas desulfurization systems

• Marine applications

## Fabrication and Welding

Alloy 27-7Mo can be readily fabricated using standard techniques:

• Hot working: 1150-900°C (2100-1650°F)

• Cold working: Excellent ductility allows for severe forming operations

• Machining: Similar to other austenitic stainless steels but requires more power

• Welding: Best performed using matching filler metals (ERNiCrMo-3 or similar)

## Comparison with Other Alloys

Compared to standard 316L stainless steel, Alloy 27-7Mo offers:

• Superior corrosion resistance, especially in chloride environments

• Higher strength at both ambient and elevated temperatures

• Better resistance to stress corrosion cracking

• More stable aust