304 Stainless Steel Castings (equivalent to ASTM A743 / A351 Grade CF8, UNS J92600, and EN 10283 1.4308) are manufactured using the silica sol investment casting process (lost wax casting). This process produces near-net-shape components featuring tight dimensional control, thin-wall structural integrity, and smooth surface finishes directly from the mold.
Classified as an austenitic chromium-nickel stainless steel, 304/CF8 provides an optimal economic balance between atmospheric corrosion resistance, oxidation performance up to 870°C (1600°F), and mechanical ductility.
Core Capability Boundaries
• Unit Weight Range: 0.02 kg to 45 kg (0.04 lbs to 100 lbs)
• As-Cast Dimensional Tolerance: ISO 8062-3 CT4 – CT6 (VDG P690 Grade D1/D2)
• As-Cast Surface Roughness: Ra 3.2 µm to Ra 6.3 µm (125–250 µin RMS)
• Minimum Cast Wall Thickness: 1.5 mm (0.060 in) over small localized spans
• Annual Capacity: 3,600 Metric Tons of stainless steel investment castings
Manufacturing Process
Our facility uses the Medium-Temperature Wax Silica Sol Shell Process, which eliminates the surface pitting, carbon contamination, and rough finishes typical of sodium silicate (water glass) casting methods.
Process Flow
• Aluminum Tooling Fabrication
• Wax Pattern Injection
• Tree Assembly & Gating
• Multi-Layer Shell Drying & Silica Sol Dip / Stucco Coating
• Dewaxing (Autoclave)
• Shell Firing (1000°C–1150°C)
• Medium-Frequency Induction Melt & Pouring
• Knockout & Cut-Off Gating
• Solution Anneal (1040°C–1120°C)
• Shot Blasting & CNC Machining
• Final Inspection & CMM Verification
Key Manufacturing Steps
• Tooling & Wax Injection: CNC-machined aluminum dies injected with medium-temperature wax under hydraulic pressure control to ensure dimensional stability and minimal shrinkage variance.
• Silica Sol Shell Building: 5 to 7 layers of zircon slurry and fused silica stucco dipping. Controlled temperature (22°C ± 2°C) and humidity (55% ± 5%) in automated drying rooms ensure shell strength and prevent cracking.
• Dewaxing & Firing: Steam autoclave dewaxing followed by high-temperature shell burnout at 1050°C to eliminate organic residues, increase thermal shock resistance, and prevent gas porosity during pour.
• Induction Melting & Pouring: Melted in medium-frequency induction furnaces. Deoxidation and spectrographic chemistry verification occur prior to gravity pouring into preheated ceramic molds.
• Solution Heat Treatment (Mandatory for CF8): Castings are water-quenched from 1040°C–1120°C (1900°F–2050°F) to dissolve chromium carbides back into the austenitic matrix, eliminating intergranular corrosion risks.
Materials and Technical Specifications
Chemical Composition Comparison (%)
|
Element |
ASTM A351 Grade CF8 (Cast) |
ASTM A743 Grade CF8 (Cast) |
EN 10283 1.4308 (Cast) |
AISI 304 (Wrought Ref.) |
|
Carbon (C) |
<= 0.08 |
<= 0.08 |
<= 0.07 |
<= 0.08 |
|
Chromium (Cr) |
18.00 – 21.00 |
18.00 – 21.00 |
18.00 – 20.00 |
18.00 – 20.00 |
|
Nickel (Ni) |
8.00 – 11.00 |
8.00 – 11.00 |
8.00 – 11.00 |
8.00 – 10.50 |
|
Silicon (Si) |
<= 2.00 |
<= 2.00 |
<= 1.50 |
<= 0.75 |
|
Manganese (Mn) |
<= 1.50 |
<= 1.50 |
<= 1.50 |
<= 2.00 |
|
Phosphorus (P) |
<= 0.040 |
<= 0.040 |
<= 0.040 |
<= 0.045 |
|
Sulfur (S) |
<= 0.040 |
<= 0.040 |
<= 0.030 |
<= 0.030 |
Note: CF8 chemistry specifies higher allowable silicon levels (up to 2.00%) than wrought 304 to optimize fluidity during molten metal flow in thin-section investment molds.
Mechanical Properties (Post Solution Heat Treatment)
|
Property |
ASTM A351 / A743 CF8 Standard |
Typical Production Values |
Test Method |
|
Tensile Strength |
>= 485 MPa (70 ksi) |
530 – 620 MPa |
ASTM A370 |
|
Yield Strength (0.2% Offset) |
>= 205 MPa (30 ksi) |
240 – 290 MPa |
ASTM A370 |
|
Elongation in 2 in. (50mm) |
>= 35.0 % |
42.0 – 55.0 % |
ASTM A370 |
|
Reduction of Area |
Not Specified |
45.0 – 60.0 % |
ASTM A370 |
|
Hardness |
<= 183 HBW (typical) |
140 – 170 HBW |
ASTM E10 |
|
Charpy V-Notch Impact (-196°C) |
N/A (Optional testing) |
> 60 J |
ASTM E23 |
Standard As-Cast Tolerances (ISO 8062-3 CT5 Level)
|
Nominal Dimension (mm) |
Tolerance Range (+/- mm) |
Nominal Dimension (mm) |
Tolerance Range (+/- mm) |
|
Up to 10 |
+/- 0.14 |
> 100 to 160 |
+/- 0.52 |
|
> 10 to 18 |
+/- 0.18 |
> 160 to 250 |
+/- 0.66 |
|
> 18 to 30 |
+/- 0.22 |
> 250 to 400 |
+/- 0.86 |
|
> 30 to 50 |
+/- 0.28 |
Straightness / Flatness |
0.2 mm per 100 mm |
|
> 50 to 100 |
+/- 0.38 |
Draft Angle (Internal/External) |
0.5° to 1.0° (0° possible with cores) |
Key Product Features
Core Product Capabilities
• Structural Integration
Consolidates multi-piece welded assemblies into a single component
Accommodates complex internal channels and hollow geometries
• Corrosion Performance
Resists atmospheric oxidation at temperatures up to 870°C
Solution annealed to eliminate chromium carbide precipitation
• Surface Quality
As-cast surface finish of Ra 3.2–6.3 µm
Smooth surface profile suitable for direct electropolishing
• Near-Net Geometry
Minimizes raw material usage and component weight
Provides tight machining stock allowances (0.8 mm – 1.5 mm)
Key Performance Benefits
• Elimination of Weldments: Complex assemblies requiring multi-part welding, stamping, and tube bending can be consolidated into a single investment casting. This eliminates joint leakage risk and assembly labor.
• Corrosion Resistance in Standard Media: Performs reliably in fresh water, organic acids, nitric acid solutions, cold milk/food handling, and industrial atmospheric environments.
• Low Magnetic Permeability: Fully austenitic matrix after solution annealing yields relative magnetic permeability μr < 1.02, critical for medical equipment housings and electronic sensing assemblies.
• Tight Machining Allowances: Near-net shaping leaves only 0.8 mm to 1.5 mm stock on critical functional surfaces, reducing CNC tool wear and cycle times.
Typical Applications
Application Overview
• Fluid Handling Equipment: Valve Bodies, Pump Impellers, Flanges & Tees
• Food Processing Machinery: Mixing Blades, Cutter Heads, Grinder Plates
• Architectural & Structural: Glass Clamps, Pipe Fittings, Hinge Mounts
Industrial Fluid & Process Handling
• Components: Pump casings, open and closed impellers, valve bodies, gland packing nuts, strainer baskets, pipe elbows.
• Operating Conditions: Ambient pressure up to Class 150/300 pressure ratings, fluid temperatures from -196°C to 400°C.
Food, Beverage, and Dairy Processing
• Components: Commercial meat grinder housings, manifold blocks, fluid metering valves, sanitary tri-clamp fittings, homogenizer parts.
• Requirement Compliance: Smooth internal radii (> 3.2 mm) and non-porous surfaces meeting hygienic equipment layout parameters.
Architectural Hardware and Marine Mounts
• Components: Glass curtain-wall spiders, structural cable connectors, marine deck hinges, hawse pipes, door handles.
• Performance: Withstands outdoor weathering without rust staining, accepting mirror or satin mechanical polishes.
Machining and Secondary Operations
While investment casting delivers near-net geometries, tight-tolerance interface features (such as bearing pockets, sealing faces, and tapped threads) require secondary precision machining.
Secondary Finishing Overview
• Precision CNC Machining: Milling, Turning, Boring, Threading (H7 Tolerances)
• Surface Treatment & Finishing: Chemical Passivation, Electropolishing, Mechanical Mirror Polishing
• Post-Processing & Testing: Hydrostatic Testing, Dye Penetrant Inspection, Helium Leak Detection
In-House CNC Capabilities
• Equipment: 3-axis, 4-axis, and 5-axis vertical machining centers (VMCs), CNC turning lathes with live tooling.
• Machining Tolerances: H7 bore diameters, true position down to 0.015 mm, surface finishes to Ra 0.8 µm on turned/milled faces.
• Thread Production: Metric (M), Unified (UNC/UNF), and Pipe (NPT/G/BSPT) internal and external threads cut or thread-milled.
Surface Treatment & Finishing Options
|
Treatment Process |
Technical Parameters |
Operational Purpose |
|
Glass Bead / Sand Blasting |
Media size 100–200 mesh, Ra 3.2–4.5 µm |
Uniform matte finish, scale removal |
|
Chemical Passivation |
ASTM A967 (Citric or Nitric Acid Bath) |
Removes free iron, accelerates oxide layer recovery |
|
Electropolishing |
ASTM B912, micro-smoothing (Ra < 0.4 µm) |
Eliminates microscopic burrs, enhances hygienic performance |
|
Mechanical Mirror Polishing |
Grit finish 240, 400, up to 800 mesh (#8 Mirror) |
Architectural visual appeal, easy-clean food contact |
Quality Control and Inspection
Every production melt is logged, tracked, and verified through a structured Quality Management System certified to ISO 9001:2015.
Quality Inspection Flow
• Melt Chemical Analysis (OES)
• Mechanical Tensile & Hardness Testing
• Dimensional CMM Scanning
• Radiographic / Ultrasonic NDT
• Dye Penetrant (PT) Surface Check
• Hydro/Air Pressure Leak Testing
Chemical and Physical Metallurgical Verification
• Optical Emission Spectroscopy (OES): Chemical analysis performed on every melt prior to pouring; official EN 10204 3.1 material certificate issued for every heat lot.
• Mechanical Testing: Destructive tensile, yield, elongation, and Brinell/Rockwell hardness testing from sample bars cast alongside production molds.
• Microstructure Analysis: Metallographic verification to confirm complete carbide solutioning and absence of detrimental delta-ferrite phases.
Non-Destructive Testing (NDT) & Dimensional Metrology
• Coordinate Measuring Machine (CMM): Hexagon 3D CMM with contact probe and laser line scanner for complex surface profile mapping against CAD models.
• Dye Penetrant Inspection (PT): Performed per ASTM E1417 / ISO 3452 to check for surface cracks, cold shuts, or shrinkage pores.
• Pressure / Hydrostatic Testing: 100% pneumatic testing under water (6 bar/90 psi air) or hydrostatic testing up to 300 bar for pressure-containing castings.
OEM and Custom Manufacturing
We work directly from customer engineering specifications to take parts from early concept through prototype validation and full mass production.
OEM Project Development Timeline
• DFM Analysis & Solidification Gating Simulation (Days 1 - 3)
• Aluminum Tooling Design & Machining (Days 4 - 18)
• Initial Sample Production & Inspection (Days 19 - 25)
• FAI Report & Sample Shipment (Days 26 - 30)
• Serial Production Release (3 - 4 Weeks)
Design for Manufacturability (DFM) Support
Our casting engineers evaluate every submission using solidification modeling software to identify:
• Critical wall thickness transitions that cause shrinkage porosity.
• Ideal gate locations to prevent visual defects on functional surfaces.
• Opportunities to reduce weight while preserving structural rigidity.
Tooling Ownership & Life
• Tooling Construction: P20 steel or high-grade aircraft aluminum injection dies.
• Ownership: Customer retains 100% intellectual property and tooling ownership.
• Maintenance Guarantee: Free routine maintenance, repair, and replacement of dies for the lifetime of the project.
What Buyers Should Provide for an RFQ
To receive an itemized commercial and technical quotation within 24 to 48 hours, please include the following details in your inquiry:
RFQ Checklist
• 3D CAD File: STEP (.stp), IGES (.igs), or SolidWorks (.sldprt) format
• 2D Engineering Drawing: PDF format showing critical dimensions, tolerances, and thread details
• Material Specification: Grade standard (e.g., ASTM A351 CF8, EN 1.4308)
• Quantity & Demand: Annual volume forecast and estimated order batch sizes
• Secondary Machining: Specific surfaces requiring CNC machining and surface finish callouts
• Surface Finish Requirements: As-cast, bead blasted, passivated, or polished
• Inspection & NDT Scope: Required testing (CMM inspection report, Dye Penetrant, Pressure Testing, Radiography)
• Commercial Terms: Target delivery schedule and preferred Incoterms (FOB, CIF, DDP)
Frequently Asked Questions
Q: What is the main difference between cast 304 (CF8) and wrought 304?
A: Cast CF8 (ASTM A351) has a chemistry adjusted for fluid casting, allowing up to 2.0% silicon content compared to 0.75% in wrought 304. CF8 also contains a small, controlled amount of delta-ferrite (typically 5% to 15%) in its austenitic matrix to prevent hot cracking during solidification and improve yield strength.
Q: When should I upgrade from 304 (CF8) to 316 (CF8M)?
A: Select 316 / CF8M when the casting operates in environments exposed to chlorides, marine saltwater, brackish water, or halogenated acids. 316 contains 2.0% to 3.0% molybdenum, which significantly increases pitting corrosion resistance compared to 304. For general industrial, atmospheric, and food contact applications, 304 (CF8) remains the most cost-effective solution.
Q: What is your standard lead time for tooling, samples, and production runs?
A: Rapid Prototypes (3D printed wax/PMMA patterns): 7 to 10 days.
Production Tooling & Initial First Article Samples: 25 to 30 days.
Serial Mass Production Delivery: 30 to 40 days following sample approval.
Q: How do you prevent internal gas porosity and shrinkage in thick sections?
A: We use mold-flow and solidification simulation software prior to cutting tooling dies. This lets us design appropriate gating, runner systems, and insulated risers. Combining this with medium-temperature wax and silica sol shell molds ensures proper feed metal flow into heavy sections as they cool.
