Introduction

CF8M stainless steel is a premium cast austenitic stainless steel defined by authoritative standards including ASTM A351, ASTM A743 and ASTM A744, serving as the cast equivalent of wrought AISI 316 stainless steel.

Its core advantage lies in the addition of molybdenum, which endows it with superior pitting and crevice corrosion resistance compared to molybdenum-free cast stainless steels (e.g., CF8).

1. Classification & Core Definition of CF8M Stainless Steel

Standard Classification & Grade Attribution

CF8M is categorized as a corrosion-resistant cast austenitic stainless steel for pressure-containing components, with clear standard specifications:

• Primary standards: ASTM A351 (for pressure-containing castings), ASTM A743 (for general corrosion-resistant castings), ASTM A744 (for severe service corrosion-resistant castings)
• Unified Numbering System (UNS): J92900
• International equivalent grades: EN 1.4408 (GX6CrNiMo18-10), Chinese standard 06Cr17Ni12Mo2, Japanese JIS SUS316 cast grade

Core Difference from Wrought AISI 316

CF8M and wrought AISI 316 share the same core alloy system, but differ essentially in manufacturing process, leading to performance distinctions:

• CF8M: Cast via molten metal pouring, suitable for complex-shaped components (valves, pump casings, reactor bodies) with inevitable coarse cast grains and minor casting defects (controllable via process optimization)
• AISI 316: Formed via forging/rolling, with dense and refined grains, higher strength and toughness, but limited to simple-shaped components
• Composition nuances: CF8M allows slightly higher Si (≤1.50 wt.%) and Mn (≤1.50 wt.%) than AISI 316 to improve cast fluidity, with consistent Cr, Ni and Mo core ranges

2. Key Properties of CF8M Stainless Steel

CF8M’s comprehensive properties are the foundation of its wide application, covering mechanical, corrosion, physical and processing properties, all verified by standardized tests and industrial practices.

Mechanical Properties of CF8M Stainless Steel

CF8M exhibits stable mechanical properties at room and elevated temperatures, meeting the minimum requirements of ASTM A351 standard, with performance characteristics matching structural component demands:

• Room-temperature mechanical properties (as-cast + solution treated): Tensile strength ≥485 MPa (70 ksi), Yield strength (0.2% offset) ≥205 MPa (30 ksi), Elongation in 50 mm ≥30%, Reduction of area ≥50%, Brinell hardness ≤217 HB
• High-temperature performance: Maintains 80% of room-temperature strength at 550℃, with excellent structural stability; usable long-term at ≤550℃, short-term at ≤800℃
• Low-temperature performance: No brittle transition temperature, retains good toughness at -196℃, suitable for low-temperature pressure-containing components
• Thermal aging note: Prone to 475℃ embrittlement when exposed to 400–500℃ for long periods, caused by spinodal decomposition of trace delta ferrite, leading to reduced toughness and increased strength

Corrosion Resistance of CF8M Stainless Steel

Corrosion resistance is CF8M’s core advantage, far superior to CF8 (304 cast grade) and comparable to wrought 316, supported by scientific mechanisms and quantitative indicators:

• Core corrosion-resistant mechanism: Chromium forms a dense, self-healing passive film (Cr₂O₃) on the surface; molybdenum enriches in the passive film to enhance its stability in chloride and acidic media
• Quantitative indicator: Pitting Resistance Equivalent Number (PREN) = Cr + 3.3Mo, CF8M’s PREN ranges 22–28, much higher than CF8 (PREN 18–20), indicating excellent pitting corrosion resistance
• Resistant media: Seawater, chloride solutions, dilute sulfuric acid, phosphoric acid, organic acids, salt spray and H₂S-containing oil and gas media
• Limited resistance: Not suitable for concentrated nitric acid, hot concentrated sulfuric acid and strong oxidizing media
• Key corrosion resistance features: Resists stress corrosion cracking (SCC) in chloride environments; avoids intergranular corrosion after standard solution treatment; has low uniform corrosion rate (≤0.005 mm/year in seawater)

Physical Properties of CF8M Stainless Steel

CF8M’s physical properties are stable and predictable, providing a basis for structural design and thermal processing:

• Density: 8.0 g/cm³ at 20℃
• Thermal conductivity: 16.2 W/(m·K) at 20℃; increases to 21.5 W/(m·K) at 500℃
• Coefficient of thermal expansion: 17.2 μm/(m·K) (20–100℃); 19.5 μm/(m·K) (20–500℃)
• Elastic modulus: 200 GPa at 20℃
• Magnetic property: Non-magnetic (austenitic structure), no magnetic response under conventional conditions, suitable for magnetic-sensitive equipment

Processing Properties of CF8M Stainless Steel

CF8M has excellent processing adaptability, with process parameters standardized to ensure product quality:

• Castability: Excellent fluidity and shrinkage compensation, suitable for casting complex-shaped components (valves, pump bodies, elbows) with wall thickness ranging from 5 mm to 300 mm
• Weldability: Good weldability, compatible with TIG, MIG and arc welding; matching filler metal (E316L) recommended to avoid intergranular corrosion; no preheating required for welding
• Machinability: Moderate machinability, higher cutting resistance than carbon steel; sharp tools and proper cooling required to avoid work hardening
• Heat treatment: Mandatory solution treatment per ASTM A351, process parameters: heat to 1040–1150℃, hold for 1–3 h (3 h for thick components), water quenching; forms single austenitic structure, eliminates cast stress and improves corrosion resistance

3. Industrial Applications of CF8M Stainless Steel

CF8M’s combination of corrosion resistance, mechanical strength and castability makes it widely used in harsh industrial environments, with targeted applications matching its performance advantages:

Chemical & Petrochemical Industry

CF8M is the preferred material for corrosive pressure-containing components in this industry, accounting for 40% of its total application:

• Key applications: Reaction vessels, heat exchangers, valves, pipes, pump casings and flanges
• Adaptable media: Dilute sulfuric acid, phosphoric acid, acetic acid, chloride-containing solvents and alkaline solutions
• Core advantage: Resists pitting corrosion and SCC in high-temperature, high-pressure and corrosive media, meeting NACE MR0175 standards for H₂S-containing environments

Pharmaceutical & Food Industry

CF8M complies with food and pharmaceutical hygiene standards, suitable for high-purity and corrosion-sensitive processes:

• Key applications: Purified water tanks, drug reaction kettles, juice mixers, dairy conveying pipelines and sanitary valves
• Core advantage: Non-toxic, easy to clean, resistant to organic acid corrosion; no metal ion precipitation, ensuring product purity

Marine Engineering & Offshore Industry

CF8M is ideal for marine environments with high chloride concentrations, solving the core problem of seawater corrosion:

• Key applications: Seawater desalination equipment, ship pipeline systems, offshore platform valves, tidal energy generator components and submarine oil and gas pipelines
• Core advantage: Excellent resistance to seawater corrosion and salt spray erosion, service life 3–5 times longer than carbon steel in marine environments

Power Industry

CF8M is used in critical components of thermal and nuclear power plants, with strict performance requirements:

• Key applications: Nuclear power primary coolant pipelines, elbow fittings, pump casings, thermal power steam valves and heat exchanger tubes
• Core advantage: Stable structure at high temperature, good radiation resistance and corrosion resistance to coolant media; meets nuclear power equipment safety standards

General Industrial Applications

CF8M is also applied in various general industrial scenarios with medium corrosion requirements:

• Water treatment: Sewage treatment equipment, reverse osmosis system components, resistant to chloride and sulfate corrosion
• Mechanical equipment: High-pressure valve bodies, hydraulic system components, balancing castability and strength requirements
• Architectural hardware: Corrosion-resistant handrails, decorative components in coastal areas, combining durability and aesthetics

4. Conclusion

CF8M stainless steel, as a standardized cast austenitic stainless steel, relies on its optimized chemical composition (especially 2–3% molybdenum) and stable austenitic structure to achieve excellent corrosion resistance, mechanical properties and processing adaptability.

It outperforms conventional cast stainless steels in chloride and acidic environments, and its castability makes it irreplaceable for complex-shaped pressure-containing components.

From chemical and petrochemical to marine and nuclear power industries, CF8M provides reliable material support for harsh working conditions.

With the development of high-purity smelting and precision casting technologies, CF8M will further realize low ferrite content (≤1%) and high uniformity, expanding its application in more high-end, high-reliability scenarios.

For engineering practitioners, mastering CF8M’s properties and processing rules is the key to maximizing its performance and ensuring component service life.